CN1273755A - Wavelength-selective optial switching apparatus optical communication apparatus using it and using method in optical communication apparatus - Google Patents

Abstract

An optical switching apparatus is designed to implement a serial switching architecture for wavelength division multiplexed optical communication systems. The design allows for add/drop switching of a selected wavelength channel without switching a non-selected wavelength channel, thereby avoiding potential data loss on the non-selected channel during the add/drop switching interval. Exemplary implementations utilize fiber-optics and free-optics based approaches. The serial architecture readily accommodates new wavelength plans and/or the addition of new wavelength channels.

Description

Wavelength selective optical switching device, optical communication device using it, and method of use in optical communication device

Cross-references with related applications

This application claims the benefit of US Patent Application Serial No. 60/059,214, filed September 18, 1997, which is incorporated herein by reference. Background of the invention

The present invention relates to wavelength division multiplexing (WDM) optical communication systems. In particular, the present invention relates to a novel wavelength selective switching scheme for these systems, which is based on a simple series configuration, and an optical switching device designed to realize this configuration. In a preferred form, the device is configured as a wavelength selective add/drop switch. The invention also relates to optical communication devices and methods of utilizing structures thereof.

In WDM optical communication systems, the optical transmission spectrum is divided into multiple wavelength bands or channels for communication. Multiple optical signals can be sent simultaneously over a common path (usually an optical fiber), each on a different wavelength channel. This allows different groups of end users or devices to communicate on different channels simultaneously.

A typical WDM optical communication system is constructed as a network of nodes interconnected by optical fiber links. End users and devices connect to the network at respective nodes. To optimize network usage, node designs often include signal add/drop functionality whereby signals on one wavelength channel or any combination of wavelength channels can be dropped and/or added at the node. For this purpose, the nodes may be constructed as (or include) Wavelength Add/Drop Multiplexers (WADMs). The parts forming a node should add as little loss to the system as possible, they should be very reliable, and they should provide effective switchability to WADM, so that signals on the respective channels can be switched on and off at the node as the communication requirements dictate. pass, split or join.

Most WADM-capable node designs rely on parallel configurations to provide signal add/drop functionality. For example, one proposed design uses a switch structure in parallel between the multiplexer and demultiplexer to enable switching of individual channels. Another proposed design uses a pair of star couplers interconnected by a wave-selective parallel switching structure.

FIG. 1 a shows a WADM 10 of the first-mentioned design. WADM 10 includes a demultiplexer (DEMUX) 12 that includes a connection to an input line 14 (eg, an optical fiber or planar optical path) to receive multiplexed optical signals at wavelengths λ ₁ -λ _n . DEMUX 12 demultiplexes the optical signals, and it outputs these signals respectively to corresponding 2x2 optical switches S ₁ -S _n connected to its output side. As shown in FIG. 1a, the switches S ₁ -S _n are connected to the input side of a multiplexer (MUX) 16 which combines the signals from the switches for transmission on output line 20 .

Each of the switches S ₁ -S _n can be assumed to be in a "bar" state or a "cross" state under electronic control. In the through state, the signal entering the switch from DEMUX 12 passes through the switch to MUX 16 so that it remains transmitted on output line 20 . A channel carrying such a signal is said to be in the "through" state. The switches for the wavelength channels λ ₁ and λ _n are shown in the through state. In the bypass state (shown by the switch for channel _λi ), the signal entering the switch is directed to the corresponding drop line 18 (such as for transmission to an end user) without passing through it to the output line 20. Alternatively, another signal of the same wavelength λ _i can be input to the system by means of a corresponding joining line 19 for transmission on output line 20 . The channel for wavelength λ _i is then said to be in an "add/drop" state.

The WADM shown in Figure 1a is complex, expensive and based on an inflexible design. More specifically, the design cannot be extended to add new wavelength channels to the communication network. This means that the initial node design must include excess capacity to allow possible addition of wavelength channels in the future, or special components and an additional WADM structure must be added to accommodate new channels in the future. The former option is not economical in terms of cost, since funds must be allocated for equipment to handle more channels than initially required. The latter option may entail substantial future expense and may be problematic due to additional system wear and tear.

Parallel configurations based on star couplers are also problematic. For example, the star coupling method is inherently lossy, and the loss increases with the number of channels (loss increases by ⁿ² , where n is the number of add/drop channels required at a node). Furthermore, star coupler based designs, like the design in Figure 1a, are complex, expensive, and not easily scalable to accommodate additional wavelength channels beyond the original design capacity.

Figure 1b shows a known signal add/drop block 30 based on a serial configuration. As shown, such a component can be fabricated by placing a Bragg grating device 33 tuned to the desired wavelength λ _i between two optical circulators 32 , 36 . Bragg grating devices can be implemented in various forms including fiber optic and planar devices. Each circulator 32 , 36 includes respective ports 1 , 2 and 3 .

Component 30 receives a mixed set of signals of different wavelengths λ ₁ -λ _n at port 1 of optical circulator 32 on input line 14 (eg, a fiber or planar optical path). The signal propagates to the Bragg grating 33 via port 2 of the circulator 32 . The Bragg grating passes all signals through and through ports 2 and 3 of the circulator 36 to the output line 20 except for the signal of wavelength λ _i . The signal of wavelength λ _i , which is the signal to be dropped, is reflected by the Bragg grating and propagates to the drop line 38 via ports 2 and 3 of the circulator 32 . The signal of the wavelength λ _i to be added can be input at port 1 of the circulator 36 via the addition line 39 and combined on the output line 20 with the rest of the transmission signal.

Part 30 has the advantage of a relatively simple design, but it is not switchable. Thus, the signal on the channel reflected by the Bragg grating 33 must be split. The component can be designed to drop/add signals of multiple wavelengths by including additional gratings between the circulators. However, all wavelengths reflected by the grating must still be separated. Therefore, component 30 cannot provide the optional add/drop functionality required for efficient WDM network usage.

Figure 1c shows a proposed WADM design 30' based on a switchable cascade configuration. This design includes a plurality of series-connected 2×2 optical switches S ₁ -S _n+1 (n is the number of channels) arranged between a pair of optical circulators 32, 36, as described in connection with FIG. 1b, each A circulator has three ports. Optical circulators 32, 36 are connected to input line 14 and output line 20, respectively. Adjacent switches in the series are coupled to each other by wavelength selective Bragg gratings 33 _i (i=1 to n) tuned to the respective wavelengths of the system and additional bypass lines 35 . Drop line 38 and drop line 39 are connected to optical circulators 32, 36, respectively.

In operation of WADM 30', the switches _S1 - _Sn are constructed (using the bypass and bypass states) such that the incoming WDM signal is passed to the grating corresponding to the signal to be dropped. The grating reflects the corresponding signal back to optical circulator 32 where it is to be dropped via drop line 38 . The remaining signal (thru channel) passes through the grating to circulator 36 and to output line 20 . The dropped signal may be replaced by a new signal input to circulator 36 via join line 39 .

The WADM 30' can be expanded as needed to accommodate additional wavelengths. This is done by adding new switches to the existing series structure and tuning the Bragg gratings appropriately. Therefore, WADM30' can be made, which can meet the initial channel capacity of the network without providing excessive capacity, and can be expanded later as needed.

While the switchable serial configuration of WADM 30' provides good flexibility for expansion, WADN 30' has a significant risk of data loss. This is because the signals of all wavelength channels (including the through channel) are switched. For example, when a signal of wavelength λ _i is to be dropped, the corresponding switch S ₁ is switched to a bypass state, so that all channels are transmitted to the grating 33 ₁ . As a result, signal data on the through channel can be lost during handover.

Summary of the invention

The present invention provides an improved switchable tandem configuration for WDM network applications. As will be seen below, the present invention provides the simplicity and ease of expansion associated with cascaded configurations while avoiding the potential for lost data associated with designs that require switching through channels (see discussion above for Figure 1c ).

According to a main aspect of the present invention, the present invention provides a switching device for WDM optical communication, the device includes a wavelength selective optical switching assembly, which includes an input port for receiving a plurality of optical wavelength channels, an output port, a wavelength selection Filters and Optical Switching Devices. A wavelength selective filter is constructed and arranged to direct signals on a plurality of received propagation wavelength channels to an output port and to direct signals on another received wavelength channel to an optical switching device. Optical switching means is provided which enables other wavelength channels to be switched between a diameter state and a drop or add/drop state without switching multiple wavelength channels.

In a preferred form, the optical switching assembly includes first and second optical circulators, each optical circulator having at least first, second and third ports. The first port of the first circulator constitutes the input port, and the third port of the second circulator constitutes the output port. The wavelength selective filter includes a reflective grating connected between the two second ends of the first and second circulators. The optical switching device is connected between the third port of the first circulator and the first port of the second circulator.

In another preferred form, the optical switching assembly includes first and second optical couplers, each optical coupler having at least first, second and third ports. The first port of the first coupler constitutes the input port, and the second port of the second coupler constitutes the output port. The wavelength selective filter includes a reflective grating coupled between the second port of the first coupler and the first port of the second coupler. The optical switching device is connected between the two third ports of the first and second couplers.

In yet another preferred form, the wavelength selective filter comprises a four port filter device having a thin film notch filter coupled to first through fourth ports. The first port and the fourth port constitute an input port and an output port respectively. Signals on multiple channels received at the first port are reflected from the thin film filter to a fourth port, while signals on another received channel pass through the filter to a second port. An optical switching device is connected between the second and third ports.

Yet another preferred mode uses a wavelength selective Mach-Zehnder filter arrangement. The Mach-Zehnder device may include first and second 2x2 optocouplers, each 2x2 optocoupler having first, second, third, and fourth ports. The first port of the first coupler constitutes the input port. The third and fourth ports of the first coupler are respectively connected to the first and second ports of the second coupler by the first and second phase-shifting optical paths. Reflective grating sections are disposed in the first and second phase-shifting optical paths. The optical switching device is connected between the second port of the first coupler and the third port of the second coupler, and the fourth port of the second coupler constitutes an output port.

Yet another preferred mode uses a wavelength-selective thin-film filter that is reflective for a plurality of received wavelength channels and transmissive for another received wavelength channel, and is positioned between In one signal path propagated from the input port. The switching device has a part switchable between a first position and a second position. In the first position, the switchable member blocks the signal transmitted through the thin film filter so that the signal propagates to the output port. In the second position, the switchable member allows the transmitted signal to be dropped through the filter.

In yet another preferred form, all optical elements of the wavelength selective filter and the optical switching device are elements of free-optics (not waveguide elements). A structure based on active optics is advantageous from the standpoint of reducing the number of components and thus the overall cost of the device.

According to another main aspect of the present invention, a switching device for WDM optical communication may comprise an input port (which is configured to receive a plurality of multiplexed optical signals each on a different wavelength channel), an output port , the first optical path from the input port to the output port and the second optical path from the input port to the output port. The second optical path includes an optical switching device, and the first optical path includes a wavelength selective filter configured such that at least one selected signal propagates to the switching device and the remaining signals propagate via an optical path including the first optical path to output port. The switching device has a first state and a second state, the first state causes at least one selected signal propagating from the wavelength selective filter to propagate to the output terminal through the second optical path, and in the second state, the secondary wavelength At least one selected signal propagated by the selective filter so as not to propagate to the output port.

Preferred modes also include implementations based on elements using optical circulators, optical couplers, notch filter arrangements or active optics.

According to still another main aspect of the present invention, the present invention provides a signal add/drop device for a WDM optical communication system, the device comprising a plurality of wavelength selective add/drop switches coupled in series, wherein each switch is configured to The corresponding wavelength channel is switched between the direct state and the add/drop state without switching another wavelength channel present in the switch.

As will be seen hereinafter, yet another aspect of the present invention relates to the design of a wavelength selective add/drop switching arrangement with redundant add/drop switching capability, and to apparatus and methods that would benefit from such a design.

The above and other aspects of the present invention, as well as its features and advantages, will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings.

Figure overview

Figure 1a is a schematic diagram of a WADM design based on a parallel configuration.

Figure 1b is a schematic diagram of a signal add/drop component based on a serial configuration.

Figure 1c is a schematic diagram of a WADM design based on a switchable series configuration.

Figure 2 schematically illustrates the series connection of a plurality of switch assemblies according to the invention.

Figure 3 is a schematic diagram of a wavelength selective add/drop switch in accordance with the present invention.

Figures 4a and 4b show the "through" state and the "add/drop" state of a 4-port optical switch, respectively.

Figure 5 schematically shows the series connection of two Bragg gratings.

Figures 6 and 7 are 4-port fiber optic switches that can be used in the wavelength selective add/drop switch of the present invention.

Figure 8 is a schematic diagram of another embodiment of a wavelength selective add/drop switch using fiber optic couplers.

Figure 9 is a schematic diagram of another embodiment of a wavelength selective add/drop switch using a Mach-Zehnder filter.

Figure 10 is a schematic diagram of another embodiment of a wavelength selective add/drop switch using a 4-port thin film notch filter.

Figure 11 shows the output spectra of the wavelength selective add/drop switch in the add/drop state and the through state.

Fig. 12 shows the transmission spectrum of the drop port of the wavelength selective add/drop switch in the add/drop state and the through state.

Figure 13 schematically depicts another embodiment of the present invention based on active optics design.

FIG. 14 shows a modification of the embodiment of FIG. 13 .

Figure 15 schematically depicts another embodiment based on active optics design.

FIG. 16 shows a modification of the embodiment of FIG. 15 .

Figure 17 schematically illustrates the application of the present invention to two-way communication.

FIG. 18 schematically shows a wavelength selective add/drop arrangement for the embodiment of FIG. 17. FIG.

19 and 20 show variations of the device of FIG. 18 .

Description of the preferred embodiment

Figure 2 shows a WADM system based on a switchable tandem configuration according to the present invention. The basic building block of the system is the wavelength selective add/drop switch (WSA/D switch). In the form shown, the system comprises a series connection of WSA/D switch assemblies, one switch assembly being provided for each wavelength channel λ ₁ -λ _n present in the system. Depending on system requirements, switch assemblies configured to switch more than one wavelength channel may be used. The component nature of the system allows for easy reconfiguration and expansion to accommodate new channel plans and to add new channels. Reconfiguration is accomplished by simply reinstalling individual components within the system. Expansion is simply the addition of new switch assemblies, which are configured to switch new channels to be added to the system.

For the system shown in Figure 2, a preferred WSA/D switch design will be substantially transparent to all channels except the one or some channels under consideration. It will also allow efficient switching of the channel under consideration between the direct state and the add/drop state (or drop state if no signal is added), without switching other channels. Therefore, switching of the considered channel does not disrupt the transmission of other channels.

Figure 3 is a schematic diagram of such a WSA/D switch design. The WSA/D switch 40 shown in FIG. 3 comprises an optical switching device (here a 2×2 switch S _i and a wavelength selective filter assembly 45 connected thereto) comprising two optical circulators 42 and 46 and a single fiber Bragg grating 43 tuned to the selected wavelength _λi . The port 1 of the circulator 42 and the port 3 of the circulator 46 form the input port and the output port of the WSA/D switch respectively. Switch _Si , preferably wavelength insensitive (not wavelength selective), is connected via line 44 to module 45 at port 3 of circulator 42 and port 1 of circulator 46 . The WSA/D switch can assume one of two states (through state or add/drop state) with respect to a channel of wavelength λ _i , depending on the state of the 4-port switch S _i . The corresponding states of the switches S _i are diagrammatically shown in FIGS. 4a and 4b.

Input signals for channel wavelengths λ ₁ -λ _n are provided via input line 14 to the WSA/D switch input port. All input signals propagate through a circulator 42 to a grating 43 tuned to a selected wavelength λ _i . The through-channel signals (signals at all wavelengths except λ _i ) propagate to output line 20 through grating 43 and circulator 46 .

The signal of the channel λ _i selected by the grating 43 is reflected back through the circulator 42 and transmitted from port 3 of the circulator to the switch S _i . When switch S _i is in the through state ( FIGS. 3 and 4 a ), the selected signal propagates through port 4 of the switch to port 1 of circulator 46 and from port 3 of the circulator to output line 20 . When the switch S _i is in the add/drop state (FIG. 4b), the selected signal propagates to the drop line 48 via port 3 of the switch. In this state, signals of wavelength λ _i can be added at port 2 of switch S _i via join line 49 . Ports 2 and 3 of switch S _i then constitute the add and drop ports of WSA/D switch 40, respectively.

As will be understood from the foregoing description, the structure of FIG. 3 provides two paths from the input port to the output port of WSA/D switch 40 . In more detail, the signal on the through channel propagates to the output port via a first path comprising circulator 42 , grating 43 and circulator 46 . The signal on the selected channel of wavelength λ _i propagates to the output port via a second path comprising the assembly of circulator 42 , line 44 and switch S _i and circulator 46 . Since the through-channel signals propagate only through the circulators 42, 46 and the grating 43, their propagation is not disrupted during the switching of the switch _Si .

Arranging the switch S _i in the second path then allows switching the selected channel between the through state and the add/drop state without causing the through channel to be switched. This avoids the risk of losing data that accompanies switching through channels. Other attributes of the WSA/D switch 40 include its low loss, assembly and less complexity, i.e. the switch can be constructed with only two discrete components (filter assembly 45 and 4-port switch S _i ) .

The WSA/D switch 40 can be changed to add or drop multiple signals by providing a grating for each signal wavelength. For example, signals at wavelengths _λ1 and _λ2 can be dropped and added from the WSA/D switch by replacing grating 43 with the series connection of gratings 66 and 67 shown in FIG.

Various types of optical switches can be used as the 4-port switch S _i . Figure 6 shows an overclad fiber optic switch 50, the principle of operation of which is disclosed in US Patent Nos. 4,763,977 and 5,353,363 (both of which are incorporated herein by reference). The switch 50 includes a WDM fiber coupler 51 with two optical fibers. Ends 52 a and 52 b of one optical fiber protrude from opposite ends of the coupler 51 , and ends 53 a and 53 b of the other optical fiber protrude from opposite ends of the coupler 51 . The coupler 51 is fixed at one end by suitable fixing means, while the other end of the coupler can be switchably bent by means of bending means 56 . Electromagnetic, piezoelectric, bimetallic, and other types of devices can provide the small controlled movements needed to bend the coupler. The function of the switch 50 is to couple the optical signal applied to the fiber end 52a to another fiber and appear at the fiber end 53b when the coupler is not bent. Similarly, when the coupler is unbent, a signal applied to fiber end 53a is coupled to another fiber and emerges at fiber end 52b. When the fiber is bent, the optical signal applied to the fiber remains uncoupled and emerges at the fiber end 52b. 4,204,744; 4,303,302; 4,318,587 and 4,337,995 (all of which are incorporated herein by reference), coupler 51 may be deflected into a bent state. The rotary motion of the switch disclosed in US Pat. No. 5,146,519 (which is hereby incorporated by reference) is also well suited for diverter switch 50; the linear motion of the switch actuator can simply be converted to a twisting motion.

The 4-port switch S _i can also be designed according to FIG. 7 . In the structure of Fig. 7, the switchable optical fiber (it is connected to the input port 1) can be switched between the drop port 3 and the output port 4 as shown by the double arrow a, similarly, the switchable optical fiber 58 (it is connected to the input port Port 2) can be switched to or from port 4, as indicated by the double arrow b.

In the unswitched state, the switchable fibers 58 and 59 are in the positions represented by the solid lines, so that the signal channel is connected from port 1 to port 4 . In the switched state, the switchable fibers 58 and 59 are in the positions represented by dashed lines 58' and 59'. Therefore, the signal channel is connected from port 1 to port 3, and port 2 is connected to port 4. Switching between the two illustrated states can be accomplished by means such as those disclosed in US Patents Re 31,579; 4,204,744; 4,303,302;

FIG. 8 shows a WSA/D switch 70 in which the circulator of FIG. 3 is replaced by optocouplers 72 , 76 . As shown in FIG. 8 , the filter assembly 75 includes two 3dB couplers 72 and 76 (each with respective ports 1-3 ) and a fiber Bragg grating 43 . Channel signals of wavelengths λ ₁ -λ _n are received on input line 14 of switch 70 and coupled to grating 43 by through ports 1 and 2 of coupler 72 . The received signal propagates to port 1 of coupler 76 and from port 2 thereof to output line 20, except for the signal at wavelength _λ1 . The signal at wavelength λ _i is reflected back to port 2 of coupler 72 and from port 3 to port 4 of its port switch S _i , where it may or may not be dropped depending on the state of switch S _i . When switch S _i is in the through state, the signal at wavelength λ _i propagates to port 3 of coupler 76 where it is coupled to port 2 and placed on output line 20 . The signal propagates to the drop line 48 when the switch S _i is in the add/drop state. Depending on the system in which WSA/D switch 70 is used, it may be desirable to put an isolator into line 14.

Obviously, similar to the arrangement of FIG. 3, WSA/D switch 70 provides two optical paths from its input port to its output port, with the attendant advantages described above.

Figure 9 shows another WSA/D switch 80 according to the present invention. Where the two optical circulators and a fiber Bragg grating of FIG. 3 are replaced with a Mach-Zehnder (MZ) wavelength selective filter assembly 85, various MZ filter assembly 85 .

Simply put, the MZ filter assembly works as follows. An input channel signal having a plurality of wavelengths is provided by the input line 14 and enters the filter assembly 85 through port 1 of the first coupler 82 . After passing through coupler 82, the wavelengths are separated and the signals in each arm are phase shifted by π/2. Wavelengths not in resonance with the Bragg grating 83 in the phase shifting path are sent to the coupler 86 . There, due to the additional π/2 phase shift, all light is again interferometrically coupled to port 4 of coupler 86 and output from the MZ-WSA/D switch to output line 20 . The wavelength _λi is reflected by the Bragg grating and suffers a second π/2 phase shift on propagation back to the coupler 82, whereupon it exits the filter assembly at port 2 of the coupler and propagates to the 4-port switch S _i . Any signal at _λi propagating from the 4-port switch to coupler 86 will be reflected by the Bragg grating and sent from port 3 of coupler 86 to its port 4, which is the same as the input signal at _λi from port 1 of coupler 82 Send to port 2 the same way.

The 4-port switch operates in the manner described in connection with FIG. 3 . Thus, when the 4-port switch is in the through state, the signal selected by the MZ filter assembly 85 is reflected around the path containing the switch S _i and transmitted by ports 3 and 4 of the coupler 86 out of the MZ-WSA/D switch 80. When the switch S _i is in the add/drop state, the signal selected by the MZ filter assembly 85 is dropped at port 3 of the switch S _i , and a new signal of the same wavelength can be added at port 4 of the switch (see Fig. 4b).

Figure 4 shows yet another WSA/D switch 90 in accordance with the present invention. This switch uses a 4-port thin film notch filter assembly 95 instead of a Bragg grating. Notch filter assembly 95 may be constructed, for example, as taught in Thin Film Filters by H.A. Macleod, American Elsevier Press, 1969, which is hereby incorporated by reference.

The working principle of the switch 90 is as follows. Input channel signals of different wavelengths λ ₁ -λ _n are provided by means of input line 14 and enter WSA/D switch 90 through input port 1 of filter assembly 95 . All input channel signals except the λ _i channel signal are reflected from the surface 92a of the thin film notch filter 92 and output to the output line 20 at the output port 4 of the filter assembly. The λ _i channel signal propagates through the notch filter 92 and from its surface 92b to port 2 of the filter assembly where it is coupled by means of one of the two lines 44 to a 4-port switch S _i . When the 4-port switch is in the through state, the λ _i channel signal propagates around the path containing line 44 and switch S _i and is delivered to port 3 of the filter assembly, from which the signal propagates back through the notch filter Optical device 92, will output from port 4. Ports 1-4 are also optically coupled to thin film filter 92, as respective GRIN lenses (gradient index lenses - not shown) are attached to those ports. When the switch S _i is in the add/drop state, the λ _i channel signal from port 2 is transferred to the drop line 48, while by means of the add line 49 a new signal can be added on the same channel. The added signal propagates from switch S _i to port 3 , from which it propagates through notch filter 92 to port 4 and output line 20 .

The operation of a dual channel wavelength selective add/drop switch of the type disclosed in connection with Figs. 3 and 5 has been described. The switch was made using two commercially available optical circulators and a multi-clad meander coupler of the type shown in Figure 6. Two fiber Bragg gratings connected in series were fabricated to operate at wavelengths of 1554.8 nm and 1555.8 nm. Furthermore, a single-channel switch operating at a wavelength of 1557 nm has been demonstrated. Single-channel switches perform similarly to dual-channel switches.

Figure 11 shows the output port transmission spectra of the dual-channel device when the 4-port switch is in the add/drop state and the pass-through state. In the through state, the insertion loss is 3.7 dB and 1.9 dB for the selected channel and the adjacent channel, respectively (curves 98 and 99). The directivity is 36dB (curves 100 and 101), which is limited by the meander coupler switch.

The reflection spectrum at the drop port is shown in FIG. 12 . The insertion loss of the switch in the add/drop state is 1.8dB (curves 102 and 103), and the directivity is 34dB (curves 104 and 105). Adjacent channel rejection is limited by the sidebands of the fiber Bragg gratings used. The insertion loss of the switch is limited by the loss of the circulator and the loss of the fusion splice between the high delta fiber used for the Bragg grating and the standard single-mode fiber used for the circulator (the insertion loss of the bent switch is only 0.15dB) .

By reducing the splice loss to a negligible level, the insertion loss can be reduced to 1.75dB and 0.8dB for the selected and adjacent channels, respectively. Assuming these low losses, it can be estimated that 32 single-channel switches can be cascaded before accumulating a total insertion loss of 30dB. In fact, by using the Mach-Zehnder filter type switches described in connection with FIG. 9, the total insertion loss can be as low as 18 dB for 32 switches.

Experimental results indicate that a WSA/D switch according to the present invention can be fabricated with low insertion loss and high directivity.

13-16 illustrate additional WSA/D switches according to the invention. Wavelength selective thin film filters are used in the designs of Figures 13, 16, but unlike the embodiment of Figure 10, they are based on the use of active optics (not waveguide elements) to obtain the wavelength selection and channel switching functions. This allows combining the thin film filter and channel switching section into a single device. The number of parts of the overall switch design as well as the number of fiber optic splices can then be reduced, thereby reducing production costs.

FIG. 13 shows a WSA/D switch 100 . The switch has four optical ports including input port 1 connected to input line 14 , output port 4 connected to output line 20 , add port 2 connected to add line 109 and drop port 3 connected to drop line 108 . The input ports are coupled to other ports by means of respective GRIN lenses 102 ₁ - 102 ₄ and a wavelength selective switch assembly 105 comprising a thin-film wave filter 103 and a switchable element consisting here of a movable mirror part M _i . Of course, if signal adding capabilities are not required, the adding ports and associated GRIN lenses can be omitted.

The thin film filter 103 is transmissive to the light of the selected channel wavelength λ _i and reflective to the light of the remaining channel wavelengths. Filters are suitably arranged to reflect light of the remaining channel wavelengths for propagation to the output port by means of the GRIN lens ₁₀₂₄ . Light of the selected wavelength is transmitted by the filter towards the drop port GRIN lens ₁₀₂₃ , which is substantially optically aligned with the input port GRIN lens ₁₀₂₁ across the thin film filter.

The switchable member _Mi has first and second mirrors 104, 106 mounted on a common support 107 and can be moved between two positions, one of which corresponds to the through state of the channel of wavelength _λi (Fig. 13 The position shown by the solid line), and the other position corresponds to the add/drop status of the channel (the position shown by the dotted line). In the straight-through position, the first mirror 104 is arranged to intersect the light rays of wavelength λ _i transmitted by the thin film filter 103 . The light is then reflected to the second mirror 106 which in turn reflects the light back through a thin film filter to the output port GRIN lens 102 ₄ to place the light on the output line 20 . In the add/drop position of the switchable member _Mi , the first and second mirrors 104, 106 are connected from the respective optical paths between the input and drop GRIN lenses 102 ₁ , 102 ₃ and between the output and add GRIN lenses 102 ₄ , 102 The light path between ₂ is removed. Then, the light of the wavelength λ _i transmitted by the thin film filter propagates to the branch port 3 by means of the GRIN lens 102 ₃ . Alternatively, the drop signal can be replaced by a signal of the same wavelength which is introduced at the add port 2 by means of the line 109 . The new signal propagates from the join port to the output port 4 through the GRIN lens 102 ₂ , the thin film filter 103 and the output port GRIN lens 102 ₄ .

Power can be easily supplied to the movable member M _i by various mechanisms. For example, it is possible to attach a permanent magnet to the mirror support and place two electromagnets at respective detent positions corresponding to the through state and add/drop state positions of the movable member.

It should be understood that, as in the above-described embodiments, the light of the through channel (the channel not switched by the optical switching device) and the light of the selected channel wavelength λ _i are along the different distance from the input port to the output port of the WSA/D switch 100. path, and only the optical path of the selected channel wavelength is switched. In more detail, the through channel follows a path that includes the input port GRIN lens 102 ₁ , the entrance face of the thin film filter 103 and the output port GRIN lens 102 ₄ . The light of selected wavelength λ _i passes along a line including the input port GRIN lens 102 ₁ , passes through the film filter 103 for the first time, first and second reflective surfaces 104 and 106 of the movable member M _i , and passes through the film for the second time. Filter 103 and output port GRIN lens 102 ₄ . Thus, as in the previous embodiment, the selected channel of wavelength _λi can be switched between the through and add/drop states without switching the through channel.

Although this need not be the case in practice, arranging the first and second mirrors 104, 106 on a common movable support is advantageous because it facilitates accurate and stable alignment of the mirrors. As a variant, the switchable element can be made of a prism, and the mirror surface is formed by a reflective end face on the prism. Alignment of the GRIN lenses 102 ₁ - 102 ₄ can be done simply by "following the light path" when constructed, starting at the input port and going to the output port, add port and drop port (in the latter two case, the mirror moves out of the route). The output port and join port GRIN lenses 102 ₄ , 102 ₂ are generally optically aligned across the thin film filter 103 as are the input port and drop port GRIN lenses 102 ₁ , 102 ₃ .

Another advantage of the active optics design is that it allows permanent attachment of all optical fibers associated with the WSA/D switch 100 so that they are stationary. In contrast, opto-mechanical switches, such as those discussed in connection with previous examples, allow movement of optical fibers within the switch.

The optical properties of the WSA/D switch are optimized for through channels, for which insertion loss is expected to be only about 0.5 dB. Switchable channels will experience the most loss in the straight-through state, but even in this case insertion loss less than 1.5dB is expected. Because the switching occurs on the backside of the filter 103, the through channel is not affected during the switching. Crosstalk is also limited to the out-of-band crosstalk that can be picked up by the filter elements. Furthermore, since the thin-film filter will only allow light of the selected wavelength λi to pass through it, it prevents the bundle of optical signals from having unapproved wavelengths. Any out-of-band wavelengths of the device entering the add port will be reflected by the thin film filter into the drop port and out of the output port. This is advantageous for security purposes. In addition, since the second reflective surface 106 is disposed at the straight-through position of the switch in the path from the join port to the output port, even the light of the selected wavelength cannot be absorbed by the join port unless in the join/disconnect state of the switch. introduce.

FIG. 14 shows an embodiment that provides additional channel add/drop capabilities in a variation of the FIG. 13 design. In FIG. 14, a WSA/D switch 100' comprises two series-coupled wavelength-selective switching assemblies 105, 105', each with a thin-film filter tuned to a different wavelength, disposed (optically) at the input port 1 and output port 4, additional add and drop ports 2', 3' and associated GRIN lenses 102' ₂ and 102' ₃ are provided to accommodate add/drop functionality for additional wavelengths.

In the embodiment of FIG. 14 , the through-channel signal follows a first optical path comprising an input port GRIN lens 102 ₁ , a first thin film filter 103 , a second thin film filter 103 ′ and an output port GRIN lens 102 ₄ . The channel signal switched by the first filter length selective switching component 105 follows (in the through state) a path from the input port to the output port, which path includes the straight-through channel just described, plus the switchable M _i ' part. To be more specific, the path along which the light ray follows includes the input port GRIN lens 102 ₁ , the first path through the thin film filter 103, the first and second mirrors of the switchable element _Mi , the first path through the thin film filter 103 The second channel and the incident surface of the second thin film filter 103 ′, the light is reflected from the incident surface of the second thin film filter 103 ′ to the output port GRIN lens 102 ₄ . The channel signal switched by the second optical switching component 105' follows (in the straight-through state) a similar path, except that its light is reflected by the first thin film filter 103 and transmitted by the second thin film filter 103' , and then guided to the output port GRIN lens 102 ₄ by the second switchable member M _I ′.

As will be appreciated from Fig. 4, the basic active optics design of Fig. 13 can be advantageously expanded by simply inserting additional wavelength selective switching devices and corresponding add and drop GRIN lenses, without having to go back to fiber.

Occasionally, the structures shown in Figures 13 and 14 may not provide suitable optical performance for some applications due to polarization-related losses caused by the large angles of incidence on the filter. However, the active optics approach can be easily implemented with smaller reflection angles. Figure 15 shows such an embodiment.

In the embodiment of FIG. 15, the WSA/D switch 300 includes a plurality of waveguide-selective thin-film filters 303a-303c tuned to a selected wavelength _λi and mounted on a set of parallel mounting rails 350 for Determine the zig-zag portion of the optical path that couples output port 1 and output port 4. The through-channel signal received at port 1 via input line 14 propagates from the GRIN lens ₃₀₂₁ to the first filter 303a. Filter 303a (which is reflective for the through channel filter length) reflects the signal to filter 303b, from which the signal is reflected to filter 303c and then to GRIN lens ₃₀₂₄ for transmission on output line 20 on spread.

The switchable member M _i ′ includes a pair of mirrors 304 , 306 mounted on a common movable support platform 307 . As indicated by the double-headed arrow, platform 307 is moveable between a first position (solid line) corresponding to the straight-through position for wavelength _λi and a second position (filter line) corresponding to the add/drop state . To simplify the drawing, alternate positions of the mirrors 304, 306 are not shown in FIG. 15 .

In the first position of the platform 307, the mirror 304 is arranged between the drop port GRIN lens ₃₀₂₃ and the first thin film filter 303a, while the mirror 306 is arranged between the join port GRIN lens ₃₀₂₂ and the third thin film filter 303c between. The light of the selected channel wavelength _λi entering the switch is initially transmitted by the first optical filter 303a to propagate towards the drop port GRIN lens ₃₀₂₃ . However, the transmitted light is blocked by mirror 304 , which reflects the light to mirror 306 . Mirror 306 reflects the light back into the through channel path by means of filter 303c. The light then travels to GRIN lens 302 ₄ and output port 4 . In this state, the positioning of the mirror 306 will also prevent the introduction of extraneous signals by the join port.

In the add/drop position, the movable support 307 is arranged so that the mirrors 304, 306 do not block between the drop port GRIN lens ₃₀₂₃ and the first membrane 303a and between the add port GRIN lens ₃₀₂₂ and the third membrane filter. The respective optical paths between optical devices. Therefore, light entering the switch at the selected channel wavelength λ _i passes through the first thin film filter and then propagates through the GRIN lens 302 ₃ to the drop port 3 . An add signal at channel wavelength λ _i can be added via add port 3 , and the add signal will propagate from port 2 through 302 ₂ , third thin film filter 303 c and GRIN lens 302 ₄ to output port 4 .

In a modification of the configuration shown in Fig. 15, the second thin film filter 303b can be replaced by a mirror. However, it is best to use the filters shown. In particular, the filter will transmit (and thus remove) the remaining light of wavelength λ _i that was not removed at filter 303a, thus allowing the use of filters that are less transmissive for wavelength λ _i .

As in the previous embodiments, the WSA/D switch shown in Figure 15 provides two optical paths from the input port to the output port. For the through channel, the optical path includes an input port GRIN lens 302 ₁ , first to third filter units 303a-303c, and an output port GRIN lens 302 ₄ . On the other hand, the switchable channel follows a path comprising input port GRIN lens 302 ₁ , pass filter 303 a , mirror 304 , mirror 306 and pass filter 303 c to output port GRIN lens 302 ₄ . In this design, the add/drop channel switching also occurs outside of a thin film filter that is transparent to that channel rather than the through channel, so that the switching operation does not disrupt the through channel propagation.

The structure of Figure 15 is easily expandable by providing additional suitably tuned thin film filters on mounting rail 350 to extend the tortuous path, as well as providing additional add and drop ports, movable mirrors and GRIN lenses , and its arrangement is similar to the corresponding structure in Figure 15. Of course, the output port is relocated corresponding to the end of the extended tortuous path.

Figure 16 shows an embodiment in which the arrangement of Figure 15 is extended to provide selective add/drop functionality for a second channel at wavelength _λi . Additional components corresponding to those of the first channel controlling the wavelength λ _i are indicated in FIG. 16 by corresponding primed reference numerals. In this instance, the signal light of wavelength λ _i passing through the optical filter 303c from the mirror 306 (straight-through state) or from the GRIN lens ₃₀₂₂ (add/drop state) propagates from the optical filter 303c to the output along the tortuous optical path portion Port GRIN lens 302 ₄ due to thin film filters 303a'-303c' tuned to λ _j . Channels of wavelength _λi are switchable between a straight-through state and a add/drop state, as described in connection with FIG. 15 . With correspondingly added components and in the same way, the channels of wavelength λ _j are switchable.

Figure 17 shows how the basic serial configuration of the present invention can be used to provide a node configuration supporting redundant communications (eg, as in a bidirectional ring network). Simply put, a bidirectional ring network uses multiple nodes interconnected with one or more pairs of fiber optic transmission lines to form a ring. The two fiber optic lines can be installed along different routes and carry information in opposite directions to each other with respect to the ring. This increases the survivability of the network in the event of multiple failures, such as fiber cuts and/or node component failures. For a more detailed description of bidirectional networks see "Optical Networks, A Practical Perspective" by R. Ramaswami et al., Morgan Kaufmann Press, 1998, which is hereby incorporated by reference.

In the structure of Fig. 17, a network node N includes a plurality of bidirectional wavelength selective add/drop devices AD ₁ -AD _n . These means comprise respective signal processing means SPD ₁ -SPD _n each configured to receive and transmit a respective one of the wavelengths λ ₁ -λ _n . For example, the signal processing means may be a Synchronous Optical Network (SONET) Add/Drop Multiplex Terminal, a SONET Line Termination Equipment or an Internet Protocol (IP) router. Of course, different types of signal processing devices can be used for different wavelength channels according to the design requirements of the node. The signal processing means electronically processes the received data and the data to be transmitted as optical signals via the WDM optical communication network.

Each signal processing device is connected to respective add and drop ports of a pair of wavelength selective add/drop (WSA/D) switches for a corresponding optical wavelength channel. Each WSA/D switch belongs to one of two series structures (they are used to switch the eastbound and two-row signals respectively).

Each WSA/D switch is constructed in accordance with the principles of the invention as previously described. For example, any one of the structures in Figs. 3, 8-10 and 13 may be used, or a combination of a plurality of them may be used. Arrangements such as those shown in Figures 14 and 16 could of course also be used to provide add/drop switching for multiple signal processing means, unless separate switch components are preferred for the individual wavelengths.

It will be appreciated that the structure shown in Figure 17 can be easily modified and/or expanded to accommodate changing system requirements. In order to change the structure, the add/drop devices AD ₁ -AD _n can be arranged in a different series order. Alternatively, one (or several) of these devices may be replaced by an identical device operating at the new wavelength (or respective new wavelengths). Another modification may include replacing or augmenting the WSA/D switch pair of one or more devices, and setting the associated signal processing devices to operate at the respective wavelengths to which their new WSA/D switch pair is tuned. Expansion is accomplished by adding one or more add/drop devices, each device operating on its own new wavelength, which can be added at the end or in the middle of the tandem structure.

FIG. 18 is a more detailed diagram showing an exemplary structure of the bidirectional wavelength selective add/drop device AD _i of FIG. 17 . The device includes a signal processing device SPD _i , an eastbound (shown in the upper part of the figure) WSA/D switch and a westbound (shown in the lower part of the figure) WSA/D switch. In the shown configuration, each WSA/D switch includes a wavelength-selective filter assembly tuned to wavelength λ _i and an optical switching device S _i consisting of 2x2 fiber optic switches. Thus, for example, such a specific structure may be described in conjunction with any of FIGS. 3 and 8-10. The signal processing means SPD _i are connected by add line 49 and drop line 48 to respective 2x2 switches S _i of the eastbound and westbound WSA/D switches.

In the through state of the eastbound WSA/D switch, signals at wavelength _λi received on eastbound input fiber 14 will propagate to eastbound output fiber 20 for transmission with the eastbound through channel signal. In the add/drop state of the eastbound 2×2 switch, the received signal of the channel wavelength λ _i is dropped to the signal processing device SPD _i through the west drop line. The signal processing unit may also introduce new signals via the east join line on the same channel for propagation on the eastbound output fiber 20 with the through channel. Switching of the westbound 2x2 switch provides the same add/drop functionality for westbound propagation of channel wavelength λi.

The signal processing means SPD _i and the optical switches are controlled by a common network management and control system (not shown). The specific control operations of the network management and control system will depend on the type of network involved and its failure prevention procedures. For example, in so-called Unidirectional Path Switched Ring (UPSR) networks, signal traffic is transmitted in both eastbound and westbound directions. In this case the signal processing means will process the signal received from one of the drop lines 48 and output any new signal on the selected wavelength channel via the add line 49 in both directions. In the event of a co-occurrence failure (such as fiber cut or 2×2 switch failure on one side of the selected drop line), the signal processing device will switch to the "protection" mode according to the failure mode to receive data through other drop lines and pass through a Or two joining lines continue to send new signals. For a more detailed discussion of UPSR and other ring networks, see the aforementioned Ramaswami et al.

Figures 19 and 20 show an alternative embodiment using an optical switching device S _i ' comprising a plurality of interconnected switches (preferably insensitive to wavelength) to collectively provide the above-mentioned 2x2 switch. Join/drop function.

Referring to FIG. 19 , each switching device includes two interconnected 1×2 optical switches S1 _i , S2 _i . Preferably the four 1x2 switches are independently powered so that a power failure to one switch will not disable any other switches.

Each switch S1 _i has an input end connected to an optical fiber 44 (the optical fiber 44 leads from a corresponding wavelength selective filter assembly) to receive a selected signal of wavelength λ _i ; an output port; and a second output port connected to the corresponding input port of the switch _S2i . The input port of each switch S1 _i is switchable between its two output ports so that the signal on the output port can propagate to the corresponding switch S2 _i or signal processing device SPD _i .

Each switch _S2i has a second input port connected to a corresponding join line 49 and an output port connected to an optical fiber 44 (the optical fiber 44 leads back to the corresponding filter assembly). The output port of each switch S2 _i is switchable between two input ports so that a signal on one input port can propagate to a corresponding filter assembly for transmission on a corresponding output fiber.

In FIG. 19, the add/drop status of each optical switching device S _i ' is indicated by the solid line status of the associated switch pair S1 _i , S2 _i . The pass-through state is represented by a dotted line state.

Compared to the configuration in FIG. 18, the configuration shown in FIG. 19 increases the node's ability to withstand a second failure. For example, if the eastbound 2x2 switch in Figure 18 fails (either mechanically or due to loss of power to the switch), the add/drop device AD _i can still transmit and receive via the westbound 2x2 switch. However, if a second failure occurs on the westbound side, such as a westbound fiber being cut or a westbound 2x2 switch failing, the add/drop device AD _i is isolated from the network (cannot send and/or receive).

In the add/drop arrangement AD _i ' of Figure 19, a single switch failure on the eastbound (or westbound) side will only prevent eastbound (or westbound) reception or transmission, but not both. The remaining switches on that side can still be used. For example, if two drop switches fail, the east join switch can still be used for eastbound transmission. Thus, the only additional fault on the westbound side that can isolate the add/drop device from the network is a fault that prevents westbound reception, such as a cut on the input fiber 14' or a failure of the east drop switch. Additional failures that disrupt westbound transmission (such as a cut on the output fiber 20' or a failure of the west add switch) will not isolate the add/drop device because the device is still able to operate on the output fiber 20 by means of the east add switch. Eastbound dispatch.

Figure 20 shows an add/drop arrangement AD _i '' having the same switching structure as that of Figure 19. This arrangement differs from that of Figure 19 in that the west add and drop switches share the power supply and the east add and drop The switch shares another power supply. The fault tolerance of the device of Fig. 20 is similar to that of the device of Fig. 19 for mechanical switch failure. However, the tolerance of the power fault of the switch is reduced relative to the device of Fig. 19, which Because of the shared power supply, the overall reliability is still higher than that of the device in Fig. 18 .

Those skilled in the art will understand that the embodiments shown and described herein are illustrative only and that various changes and modifications may be made while maintaining the basic principles and scope of the invention.

Claims (66)

1. A switching device for wavelength division multiplexing optical communications, characterized in that the device comprises: A wavelength selective optical switching assembly comprising an input port configured to receive a plurality of optical wavelength channels, an output port, a wavelength selective filter, and an optical switching device; said wavelength selective filter is constructed and arranged to direct signals on a plurality of received wavelength channels to propagate to said output port and to direct signals on another received wavelength channel to said optical switching means ; Said optical switching means is arranged and operated to switch said other wavelength channel between a pass-through state and a drop or add/drop state without switching said plurality of wavelength channels. 2. The apparatus of claim 1, wherein the optical switching means comprises a 4-port non-wavelength-selective optical switch. 3. The apparatus of claim 2, wherein the wavelength selective filter comprises at least one wavelength selective grating. 4. The apparatus of claim 1, wherein all optical components of the wavelength selective filter and the optical switching device are active optical components. 5. The device of claim 1, wherein the wavelength selective filter comprises a thin film filter that is transmissive to the other wavelength channel and reflective to the plurality of wavelength channels, the thin film filter an optical device is disposed in the path of a signal propagating from the input port, the switching portion has a switchable member between a first position and a second position, the switchable member blocks the said signal on said another channel transmitted by said thin film filter such that the signal propagates back through said thin film filter to said output port, said switchable member being in said second position This signal is allowed to be dropped. 6. A switching device for wavelength division multiplexing optical communication, characterized in that the device comprises: a wavelength selective optical switching assembly comprising an input port configured to receive a plurality of optical wavelength channels, an output port, a first optical circulator, a second optical circulator, a wavelength selective filter, and an optical switching device; Each of the first and second circulators has first, second and third ports, the first port of the first circulator constitutes the input port, and the third port of the second circulator constitutes the the above output port; The wavelength selective filter includes a reflective grating connected between the second ports of the first and second circulators, the grating configured to direct signals on a plurality of received wavelength channels through the first a second circulator propagates to the output port and directs a signal on another received wavelength channel to the optical switching device; The optical switching device is connected between the third port of the first circulator and the first port of the second circulator, and switches the other one wavelength channel without switching the plurality of wavelength channels. 7. The apparatus of claim 6, wherein the optical switching means comprises a 4-port non-wavelength-selective optical switch. 8. A switching device for wavelength division multiplexing optical communication, characterized in that the device comprises: a wavelength selective optical switching assembly comprising an input port configured to receive a plurality of optical wavelength channels, an output port, a first optical coupler, a second optical coupler, a wavelength selective filter, and an optical switching device; Each of the first and second couplers has first, second and third ports, the first port of the first coupler making up the input port, the second port of the second coupler making up the the above output port; The wavelength-selective filter includes a reflective grating connected between the second port of the first coupler and the first port of the second coupler, the grating configured to guide wavelengths received at a plurality of the signal on the channel propagates through the second coupler to the output port and directs the signal on the other received wavelength channel to the optical switching device; The optical switching device is connected between the third ports of the first and second couplers, and switches the other wavelength channel between the through state and the drop or add/drop state without switching the multiple wavelength channels. 9. The apparatus of claim 8, wherein the first and second couplers are fiber optic couplers. 10. The apparatus of claim 8, wherein the optical switching means comprises a 4-port non-wavelength-selective optical switch. 11. A switching device for wavelength division multiplexing optical communication, characterized in that the device comprises: A wavelength selective optical switching assembly comprising an input port configured to receive a plurality of optical wavelength channels, an output port, a wavelength selective filter, and an optical switching device; The wavelength selective filter comprises a 4-port notch filter arrangement having a thin film notch filter coupled to a first port, a second port, a third port and a fourth port, the first port and the fourth port constitute the input port and the output port respectively; The notch filter is configured to reflect signals on a plurality of received wavelength channels for propagation to the fourth output port and transmit signals on another received wavelength channel for transmission via the second port propagates to the optical switching device; The optical switching device is connected between the second port and the third port, and switches the other wavelength channel between the through state and the drop or add/drop state without switching the multiple wavelength channels. 12. The apparatus of claim 11, wherein the optical switching means comprises a 4-port non-wavelength-selective optical switch. 13. A switching device for wavelength division multiplexing optical communication, characterized in that the device comprises: A wavelength selective optical switching assembly comprising an input port configured to receive a plurality of optical wavelength channels, an output port, a wavelength selective Mach-Zehnder filter arrangement, and an optical switching arrangement; The Mach-Zehnder filter arrangement is constructed and arranged to direct signals on a plurality of received wavelength channels to the output port and to direct signals on another received wavelength channel to the optical switching device; The optical switching means is provided and switches the other wavelength channel between a straight-through state and a drop or add/drop state without switching the plurality of wavelength channels. 14. The apparatus of claim 13, wherein the optical switching means comprises a 4-port non-wavelength-selective optical switch. 15. The apparatus of claim 13, wherein said Mach-Zehnder filter arrangement comprises first and second 2×2 optical couplers, each said optical coupler having a first port, a second port, Two ports, a third port and a fourth port, the first port of the first coupler constitutes the input port, the third and fourth ports of the first coupler are composed of the first and second phase-shifting optical paths respectively Connected to the port of the second coupler, a reflective grating part is set in the first and second phase shifting optical paths, and the optical switching device is connected to the second port of the first coupler and the first between the third ports of the two couplers, and the fourth port of the second coupler constitutes the output port. 16. The apparatus according to claim 15, wherein the reflective grating portion comprises first and second reflective gratings disposed in the first and second phase-shifting optical paths, respectively, the first and second Two reflective gratings are tuned to the other channel. 17. A switching device for wavelength division multiplexing optical communication, characterized in that the device comprises: an input port configured to receive a plurality of multiplexed optical signals each on a different wavelength channel; output port; a first optical path from the input port to the output port; and a second optical path from the input port to the output port; The second optical path includes an optical switching device and the first optical path includes a wavelength selective filter configured such that at least a selected signal propagates to said switching means and causes the rest of said signals to propagate to said output port; The switching device has a first state and a second state in which the switching device causes the at least one selected A signal propagates to the output port, and in the second state, the at least one selected signal propagating from the wavelength selective filter is dropped so as not to propagate to the output port. 18. The apparatus of claim 17, wherein the switching means comprises a 4-port non-wavelength selective optical switch. 19. The device of claim 18, wherein the 4-port switch has first and fourth ports respectively coupled to the input port and the output port in the first state, and in the first state In the second state, the second port coupled to the output port via the fourth port and the third port coupled to the input port via the first port, the second and fourth ports respectively constitute Join and drop ports. 20. The device of claim 17, wherein the device comprises a first optical circulator and a second optical circulator, each of the optical circulators having first, second and third ports, the The first port of the first circulator constitutes the input port, the third port of the second circulator constitutes the output port, and the wavelength selective filter includes The reflective grating between the second port of the circulator, and the switching device is connected between the third port of the first circulator and the first port of the second circulator. 21. The device of claim 17, wherein the device comprises a first optocoupler and a second optocoupler, each of the optocouplers having first, second and third ports, the The first port of the first coupler constitutes the input port, the second port of the second coupler constitutes the output port, and the wavelength selective filter includes the first port connected to the first coupler a reflective grating between the second port and the first port of the second coupler, and the switching device is connected between the third port of the first and second coupler. 22. The apparatus of claim 17, wherein said apparatus comprises a four-port filter arrangement having a thin-film notch filter constituting said wavelength-selective filter, said thin-film notch filter The optical device is coupled to the first port, the second port, the third port and the fourth port, the first port and the fourth port constitute the input port and the output port respectively, and the switching device is connected to the first port Between the second port and the third port, and the thin film notch filter is configured to reflect the remaining part of the signal to propagate to the fourth port and transmit the at least one The selected signal is transmitted to the optical switching device through the second port. 23. The apparatus of claim 17, wherein the apparatus comprises a Mach-Zehnder filter assembly incorporating the wavelength selective filter, the Mach-Zehnder filter assembly comprising: first and second 2×2 optocouplers each having first, second, third and fourth ports; The first port of the first coupler constitutes the input port, and the third and fourth ports of the first coupler are respectively connected to the first port of the second coupler by the first and second phase-shifting optical paths. and a second port, and the fourth port of the second coupler constitutes the output port; and reflective grating portions disposed in said first and second phase-shifting optical paths; The switching device is connected between the second port of the first coupler and the third port of the second coupler. 24. The apparatus of claim 23, wherein said reflective grating portion comprises first and second reflective gratings in said first and second phase-shifting optical paths, respectively, said first and second A reflective grating is tuned to the channel of the selected signal. 25. The apparatus of claim 17, wherein said wavelength selective filter is a thin film filter that transmits said one signal and reflects said remaining signal, and said switching means comprises a switchable member between a first position and a second position in which the switchable member blocks the one signal so that the signal propagates back through the thin film filter to the output port , the switchable member allows the signal to be dropped in the second position. 26. A switching device for wavelength division multiplexing optical communication, characterized in that the device comprises: input port; a first wavelength selective optical switching component; and an output port and a drop port optically coupled to the input port via the optical switching assembly; The optical switching assembly includes a thin film filter and a switching device; The thin film filter transmits the light of the first communication wavelength and reflects the light of the second communication wavelength, and the thin film filter is arranged in an optical path propagating from the input port for reflecting the light of the second wavelength , to propagate to the output port and transmit light of the first wavelength; The switching device has a switchable member between a first position and a second position in which the switchable member blocks light of the first wavelength transmitted by the thin film filter to This light is caused to propagate to the output port, the switchable member in the second position allowing light of the first wavelength transmitted by the thin film filter to propagate to the drop port. 27. The device of claim 26, wherein the switchable member has a first reflective surface that blocks light of the first wavelength transmitted by the thin film filter in the first position . 28. The apparatus of claim 27, wherein said switching means has a second reflective surface, and said first reflective surface reflects blocked light to said second reflective surface for propagation to said output port. 29. The device of claim 28, wherein the second reflective surface reflects the blocked light back through the thin film filter. 30. The apparatus of claim 28, wherein said first and second reflective surfaces are fixedly disposed on a common movable support. 31. The apparatus of claim 30, wherein the support is a prism. 32. The device of claim 26, further comprising a drive mechanism for moving the switchable member between the first and second positions. 33. The device of claim 26, further comprising: second branch port; a second wavelength-selective optical switching assembly comprising a second thin film filter and a second switching device; The second thin-film filter transmits light of the second wavelength and reflects light of the first wavelength, the thin-film filter disposed on the In the optical path, used to reflect the light of the first wavelength to propagate to the output port, and transmit the light of the second wavelength; The second switching means includes a switchable member between a first position and a second position, the switchable member blocking the second light transmitted by the second thin film filter at the first position. wavelength of light to cause the light to propagate to the output port, the switchable member in the second position allows light of the second wavelength transmitted by the second thin film filter to propagate to the The second branch port. 34. The device of claim 26, further comprising: a join port coupled to the output port via the first optical switching component; Wherein, the thin film filter is arranged in the light path propagating from the adding port, and when the switchable member is in the first position, the thin film filter blocks the light path, and when the When the switchable member is at the second position, the film filter does not block the light path. 35. The device of claim 26, wherein the input port is coupled to the first optical switching component via a first lens, and the dropout port is coupled to the first optical switching assembly via a second lens. Switching assembly, the second lens is substantially optically aligned with the first lens across the thin film filter. 36. The device of claim 26, further comprising: an input port coupled to the output port via the first optical switching component, the adding port is coupled to the first optical switching component via a first lens, and the output port is coupled to the first optical switching component via a second lens An optical switching assembly, the second lens is substantially optically aligned with the first lens across the thin film filter. 37. The device according to claim 26, wherein the first optical switching component further comprises a plurality of reflectors, and the set of reflectors together with the thin-film optical filter determine a line coupled to the input port and the meandering optical path of the output port, the thin film filter is arranged at the apex of the meandering optical path. 38. The apparatus of claim 37, wherein at least one of said reflectors is an applied thin film filter that transmits light at said first wavelength and reflects light at said second wavelength , and the switchable member in the first position allows the blocked light of the first wavelength to propagate through the additional thin film filter and enter the meandering optical path. 39. The apparatus of claim 38, wherein the second thin film filter is coupled to an adding port for adding a signal to be transmitted to the output port via a portion of the meandering optical path. 40. The arrangement of series-connected switching devices of claim 26, wherein the first wavelengths associated with respective thin film filters are different. 41. A switching device for wavelength division multiplexing optical communication, characterized in that the device comprises: an input port configured to receive a plurality of wavelength channels; wavelength selective optical switching components; and an output port coupled to the input port via the switching component; said switching assembly is configured to switch a selected wavelength channel between a direct state and a drop or add/drop state without switching another wavelength channel present in said switching assembly, wherein said switching All optics of the assembly are active optics. 42. The device of claim 41, wherein the active optics include a thin film filter that transmits light at a first communication wavelength and reflects a second communication wavelength and a switchable member. wavelength of light, the thin film filter being disposed in the optical path propagating from said input port for reflecting light of said second wavelength to propagate at said output port and transmitting light of said first wavelength, The switchable member is switchable between a first position and a second position, when the switchable member is in the first position, the thin film filter blocks the light transmitted by the thin film filter light of a first wavelength, thereby causing the light to propagate to the output port, and allowing light of the first wavelength transmitted by the thin film filter to propagate when the switchable member is in the second position to the breakout port. 43. The apparatus of claim 42, wherein said active optics include respective lenses coupling said input, output and drop ports to said thin film filter. 44. The apparatus of claim 43, wherein a lens for the input port is substantially optically aligned with a lens for the dropout port across the pellicle filter. 45. The apparatus of claim 43, wherein the lens is a GRIN lens. 46. A signal adding/dropping device for a wavelength division multiplexing optical communication system, characterized in that the device includes: A plurality of wavelength selective add/drop switches coupled in series, each of said switches configured to switch a corresponding wavelength channel between a through state and a add/drop state without switching another one present in the switch wavelength channel. 47. The apparatus of claim 46, wherein each said switch is configured to switch only a corresponding wavelength channel. 48. The device of claim 46, wherein at least one of said switches comprises: A wavelength selective optical switching assembly comprising an input port configured to receive a plurality of optical wavelength channels, an output port, a wavelength selective filter, and an optical switching device; providing said wavelength selective filter which directs signals on a plurality of received wavelength channels for propagation to said output port and directs signals on another received wavelength channel to said optical switch device; Said optical switching means is arranged to switch said other wavelength channel between a straight-through state and a drop or add/drop state without switching said plurality of wavelength channels. 49. The device of claim 46, wherein at least one of said switches comprises: an input port configured to receive a plurality of multiplexed optical signals, each said signal being on a different wavelength channel; output port; a first optical path from the input port to the output port; a second optical path from the input port to the output port; The second optical path includes optical switching means, and the first optical path includes a wavelength selective filter configured to cause at least one selected one of the signals to pass through a path that includes the first optical path. propagating to the switching means and causing the remainder of the signal to propagate to the output port; The switching means has a first state and a second state in which the at least one selected signal propagating from the wavelength selective filter is caused to propagate through the second optical path to the said output port, and in said second state, said at least one selected signal propagating from said wavelength selective filter is dropped so as not to propagate to said output port. 50. The device of claim 46, wherein at least one of said switches comprises: input port; a first wavelength selective optical switching component; and an output port and a drop port coupled to the input port via the optical switching assembly; The optical switching component includes a thin film filter and a switching device; the thin film filter transmits light of the first communication wavelength and reflects light of the second communication wavelength, and the optical filter is arranged on the optical path propagating from the input port wherein, for reflecting the light of the second wavelength to propagate to the output port, and transmitting the light of the first wavelength; the switching device has a switchable member between a first position and a second position in which the switchable member blocks light of the first wavelength transmitted by the thin film filter, and This light is caused to propagate to the output port, while in the second position light of the first wavelength transmitted by the thin film filter is allowed to propagate to the drop port. 51. The device of claim 46, wherein at least one of said switches comprises: an input port configured to receive a plurality of wavelength channels; wavelength selective optical switching components; and an output port coupled to the input port via the switching component; said switching assembly is configured to switch a selected wavelength channel between a direct state and a drop or add/drop state without switching another wavelength channel present in said switching assembly, wherein said switching All optics of the assembly are active optics. 52. The apparatus of claim 46, wherein each switch is an assembly having an input port, an output port, a drop port, and a join port, and the input and output ports of the respective switches are connected such that the components. 53. The device of claim 46, wherein at least one of said switches comprises: a wavelength selective optical switching assembly comprising an input port configured to receive a plurality of optical wavelength channels, an output port, a first optical circulator, a second optical circulator, a wavelength selective filter, and an optical switching device; Each of said first and second optical circulators has first, second and third ports, the first port of said first circulator constitutes said input port, and the third port of said second circulator constitutes said output port; The wavelength selective filter includes a reflective grating connected between the second ports of the first and second circulators and configured to direct signals on a plurality of received wavelength channels to pass through the a second circulator propagates to the output port and directs a signal on another received wavelength channel to the optical switching device; The optical switching device is connected between the third port of the first circulator and the first port of the second circulator, and it switches the other one wavelength channel without switching the plurality of wavelength channels. 54. The device of claim 46, wherein at least one of said switches comprises: a wavelength selective optical switching assembly comprising an input port configured to receive a plurality of optical wavelength channels, an output port, a first optical coupler, a second optical coupler, a wavelength selective filter, and an optical switching device; Each of the first and second couplers has first, second and third ports, the first port of the first coupler making up the input port, the second port of the second coupler making up the the above output port; The wavelength selective filter includes a reflective grating connected between the second port of the first coupler and the first port of the second coupler, which is configured to guide light on a plurality of received wavelength channels a signal to propagate to the output port via the second coupler and direct a signal on another received wavelength channel to the optical switching device; The optical switching device is connected between the third ports of the first and second couplers, and it switches the other wavelength channel between the through state and the drop or add/drop state without switching all multiple wavelength channels. 55. The device of claim 46, wherein at least one of said switches comprises: A wavelength selective optical switching assembly comprising an input port configured to receive a plurality of optical wavelength channels, an output port, a wavelength selective filter, and an optical switching device; The wavelength selective filter comprises a 4-port notch filter arrangement having a thin film notch filter coupled to a first port, a second port, a third port and a fourth port ports, the first port and the fourth port constitute the input port and the output port respectively; said notch filter is configured to reflect signals of a plurality of received wavelength channels for propagation to said fourth output port and transmit signals on another received wavelength channel for transmission via said a second port propagates to the optical switching device; The optical switching device is connected between the second port and the third port, and it switches the other wavelength channel between the through state and the drop or add/drop state without switching the multiple wavelength channels. 56. The device of claim 46, wherein at least one of said switches comprises: A wavelength selective optical switching assembly comprising an input port configured to receive a plurality of optical wavelength channels, an output port, a wavelength selective Mach-Zehnder filter arrangement, and an optical switching arrangement; The Mach-Zehnder filter arrangement is constructed and arranged to direct signals on a plurality of received wavelength channels to the output port and to direct signals on another received wavelength channel to the optical switching device; Said optical switching means is arranged to switch said another wavelength channel between a straight-through state and a drop or add/drop state without switching said plurality of wavelength channels. 57. The device of claim 56, wherein at least one of said switches comprises: said Mach-Zehnder optical filter arrangement, which includes first and second 2×2 optical couplers, each said optical coupler having a first port, a second port, a third port and a fourth port, said The first port of the first coupler forms the input port, and the third and fourth ports of the first coupler are respectively connected to the ports of the second coupler by the first and second phase-shifting optical paths, in the A reflective grating part is set in the first and second phase-shifting optical paths, and the optical switching device is connected between the second port of the first coupler and the third port of the second coupler, and the The fourth port of the second coupler constitutes the output port. 58. The apparatus of any one of claims 1, 6, 8, 11, 13, and 17, wherein the optical switching means comprises a plurality of interconnected optical switches that cooperate to operate in the through state Toggle between and join/drop status. 59. The device of claim 58, wherein the plurality of optical switches comprises two 1x2 optical switches. 60. A wavelength selective add/drop switching device with redundant add/drop switching capability, characterized in that the device comprises: a signal processing device configured to receive and transmit optical signals; and a pair of wavelength selective add/drop switches, each of said switches is arranged to input and output signals on a plurality of optical wavelength channels on different optical transmission lines, and has connected add ports for receiving signals from said The processing means receives the optical signal on a selected one of the wavelength channels, and the connected drop port is used to drop the optical signal on the selected wavelength channel to the signal processing means, and is also configured Each add/drop switch switches a selected wavelength channel between a straight-through state and a add/drop state without switching another wavelength channel present in the switch. 61. The device according to claim 60, wherein at least one switch of the wavelength selective add/drop switch constitutes an item's device. 62. An optical communication device, characterized in that said device comprises a plurality of wavelength selective add/drop switch means according to claim 60, wherein the first add/drop switch of the relevant pair is at the first interconnected in series, and the second add/drop switches of the relevant pair are interconnected in a second series. 63. A method for providing at least one new wavelength channel and/or a new wavelength scheme in a wavelength division multiplexing optical communication network, characterized in that the method comprises: providing a network node comprising an optical communication device as claimed in claim 62; and Altering said optical communications equipment by one or more of the following: a) replace at least one add/drop switching device with each identical device operating on the relevant new wavelength channel; b) rearrange the sequence order of the add/drop switching device; c) replacing the switch pair of at least one add/drop switching device with a switch pair tuned to a different wavelength channel to operate the add/drop switching device on a different wavelength channel; d) provide another said add/drop switching device working on a new wavelength channel, and connect the first add/drop switch and the second/drop switch of said another switch device to said the first sequence and the second sequence. 64. A signal adding/dropping device for a wavelength division multiplexing optical communication system, characterized in that the device comprises: A plurality of wavelength selective add/drop switching assemblies coupled in series, each of said assemblies being configured to switch a corresponding wavelength channel between a pass-through state and a add/drop state without switching another channel present in the assembly a wavelength channel. 65. The device of claim 64, wherein said switching assembly defines a tortuous light path through said sequence. 66. The device of claim 42, wherein the switchable member in the first position causes blocked light to propagate back through the thin film filter.

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