GB2365986A - Signal Power Level Adjustment - Google Patents

Abstract

An optical switch/optical cross-connect incorporates level conditioning within the switching matrix. An analogue control signal is used to control the degree of "openness" of individual switch elements, which determines the insertion loss of the switch/optical cross-connect.

Description

<Desc/Clms Page number 1> SIGNAL POWER LEVEL ADJUSTMENT This proposal relates to signal power level adjustment within an optical switch or optical cross-connect (OXC). The invention reduces switch/OXC interconnections, cost, size, component count and insertion loss by incorporating the level adjustment process within the optical switching fabric.

In a wavelength-division multiplexed (WDM) all-optical network, the wavelengths are routed at major junctions by optical switches or optical cross-connects. Since incident wavelengths can arrive with different power levels and may experience unequal losses through the optical switch/optical cross-connect (OXC), a means of altering the power level of individual wavelengths is essential. This also gives the ability to pre-emphasise the wavelength comb in order to counteract amplifier and filter profiles before lauching into the following transmission segment.

Previous implementations employ a two-stage arrangement, whereby the wavelengths are individually routed and then level-conditioned by optical attenuators before launching into the network (see Figure 1). This approach has a number of disadvantages: 1. The interconnects between the switch matrix and the level -conditioner are numerous if large numbers of wavelengths are to be switched.

2. The background insertion loss of the attenuator is unavoidable.

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3. The extra components and associated electrical interconnections increase the complexity of the architecture and hence the cost.

4. The physical size of the overall switch is increased.

The proposed technique incorporates the level conditioning function within the switching matrix itself, as shown in Figure 2.

Switch matricies are usually operated in a digital manner ie. they are either on or off. If a form of analogue control signal cotA be used to control the switch, the amount that the switch is open will ultimately determine it's insertion loss (in additon to its inherent background loss). By controlling the "openess" of the switch, a variable attenuator functionality can be achieved. This technique can be applied to an nxn switch in a lambda - switch arrangement or in the tuneable filters that are necessary in a broadcast-and-select (B & S) architecture. Figure 3 illustrates the technique for a tuneable filter that is used as a wavelength selector in a B & S architecture.

The analogue control signal will be dependent on the switch technology used. Eg. For thermo-optic polymer-type switches, the control current to the individual thermal elements of the switch will determine the loss of the optical path. If semiconductor optical amplifiers (SOA) are used, the drive current determines the gain of the device and hence the signal power level at the output of the device.

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Although thermo-optic switches and attenuator are available, it is not known of any hybrid device employing the dual functionality outlined above, The secondary signal monitoring function present in all optical switch/OXC designs is situated at the output of the switch. This will provide the necessary feedback to control the switch element control signal hence alleviating the need to calibrate the transfer function of the switching elements.

The present invention offers a simple technique for increasing the functionality of switching elements to obviate the need for an optical power level conditioner at the output of an optical switch/OXC. The result is a reduction in cost, interconnections (complexity), component count, insertion loss and overall physical size,

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Claims (7)

1. CLAIMS 1 An optical device, comprising: a switch matrix, in which the insertion loss of the switch matrix is controlled by one or more analogue control signals.
2. 2. An optical device according to claim 1, comprising a number of optical switch elements in which the degree of openness of the switch elements is controlled to provide a variable attenuation of optical signals passing through the switch matrix.
3. 3. An optical device according to claim 1 or 2, wherein the switch matrix comprises a number of thermo- optic polymer-type switches comprising individual thermal elements, and the analogue control signal is a current supply to each individual thermal element.
4. 4. An optical device according to claim 1 or 2, wherein the switch matrix comprises a number of semiconductor optical amplifiers, and the analogue control signal is a drive current for each amplifier that determines the gain of the amplifier.
5. 5. An optical cross connect for a wavelength division multiplexed communications system comprising an optical device according to any one of the preceding claims.
6. 6. An optical communications system comprising an optical cross connect according to claim 5.
7. 7. An optical device substantially as shown in and/or described with reference to the accompanying drawings.