JP2008042550A - Optical communication system - Google Patents

Abstract

A linear relay distance is limited by nonlinearity of a transmission line optical fiber.
An optical amplifier that collectively amplifies wavelength multiplexed signal light, a wavelength selective demultiplexer installed on the output side of the optical amplifier, and a plurality of transmissions installed on the output side of the wavelength selective demultiplexer A path optical fiber, a wavelength selective multiplexer installed on the output side of the transmission path optical fiber, and an optical amplifier for amplifying the wavelength multiplexed signal light installed on the output side of the wavelength selective multiplexer Prepare.
[Selection] Figure 2

Description

  The present invention relates to an optical communication system that transmits an optical signal using an optical fiber laid in a city as a transmission path.

  FIG. 1 shows a configuration example of a conventional transmission system used in a wavelength division multiplexing optical communication system (see, for example, Non-Patent Document 1). FIG. 1 shows an optical fiber multiplex (or spatial multiplex) linear repeater system using an optical amplifier. Each of the transmission line optical fibers F11, F12, F21, and F22 includes an nth and an (n + 1) th transmission line fiber section ( n is a natural number) and optical amplifiers A30, A31, A40, A41, A50, and A51 as linear repeaters before and after each of the transmission line optical fibers F11, F12, F21, and F22. Here, for simplicity, the case where the number of multiplexed optical fibers is two is shown.

  In this optical communication system, wavelength division multiplexing (WDM) signal light wavelengths transmitted through the transmission line optical fibers F11, F12, F21, and F22 are mainly bands of optical amplifiers A30, A31, A40, A41, A50, and A51. Alternatively, it is determined by the types of transmission line optical fibers F11, F12, F21, and F22. For example, in an L-band transmission system using a dispersion-shifted fiber, the wavelengths are 100 GHz intervals in the L band. Accordingly, each of the transmission line optical fibers F11, F12 and F21, F22 has a wavelength multiplexed wavelength that is basically defined by the same wavelength range and wavelength interval.

H. Masuda, S .; Kawai and KI. Suzuki, “Optical SNR enhanced amplification in long distance recurrence-loop WDM transmission experimenting using 1580 nm band hybrid amplifier I ELV. 35 No. 5, pp 411-412

  In such a conventional optical fiber communication system, the linear repeater distance, which is the distance between the transmitter and the receiver, which are electrical stage termination devices, is the light per channel of signal light due to the nonlinearity of the transmission line optical fiber. Limited by the fiber input power (Psin) limit.

  That is, if there is no optical fiber nonlinearity, the linear relay distance can be extended by increasing Psin, but in reality, Psin is reduced by optical fiber nonlinearity such as four-wave mixing (FWM) or cross-phase modulation (XPM). Limited and linear relay distance is limited. Therefore, it is necessary to overcome the linear relay distance limitation.

  An object of the present invention is to provide an optical communication system that can solve the disadvantage that the linear relay distance is limited by the above-described factors. To do.

  The present invention is an optical communication system, and the feature of the present invention is that it is installed in a transmitter that outputs wavelength multiplexed signal light or a linear repeater that linearly relays wavelength multiplexed signal light. An optical amplifier that collectively amplifies the wavelength-multiplexed signal light, a wavelength selective demultiplexer installed on the output side of the optical amplifier, and a plurality of transmission line optical fibers installed on the output side of the wavelength selective demultiplexer And a wavelength selective multiplexer installed on the output side of the transmission line optical fiber, and a receiver for inputting wavelength multiplexed signal light installed on the output side of the wavelength selective multiplexer, or wavelength multiplexing And an optical amplifier that collectively amplifies the wavelength-multiplexed signal light installed in a linear repeater that linearly relays the signal light.

  In this way, by demultiplexing the output light of the optical amplifier and transmitting it through a plurality of transmission line optical fibers, a transmission line optical fiber that minimizes the influence of nonlinearity on each demultiplexed wavelength is obtained. Since the restriction of the optical fiber input power due to the nonlinearity of the transmission line optical fiber can be relaxed, the output of the optical amplifier can be increased, the number of optical amplifiers can be reduced, and the linear repeater can be used. The distance can be increased.

  For example, the wavelength selective demultiplexer is an interleaver, demultiplexes wavelength channels arranged at equal intervals of the input signal light into odd and even channels, and the wavelength selective multiplexer is an interleaver, The wavelength channels demultiplexed into the odd-numbered and even-numbered channels of the signal light are multiplexed so as to be arranged at equal intervals.

  Alternatively, the wavelength selective demultiplexer is an arbitrary wavelength selective device, demultiplexes wavelength channels arranged at equal intervals of the input signal light into a plurality of unequal intervals, and the wavelength selective multiplexer It is an arbitrary wavelength selection device, and multiplexes a plurality of wavelength channels of input signal light arranged at unequal intervals into an equal interval.

  Alternatively, the wavelength selective demultiplexer is a wavelength division filter, demultiplexes the input signal light into short wavelength and long wavelength channels, and the wavelength selective multiplexer is a wavelength division filter, and the input short wavelength And the signal light of the long wavelength channel is multiplexed. At this time, for example, the transmission line optical fiber that transmits the short wavelength channel is a fiber having a zero dispersion wavelength in addition to the short wavelength channel band, and the transmission line optical fiber that transmits the long wavelength channel is the long channel. It is a fiber having a zero dispersion wavelength in addition to the wavelength channel band.

  Alternatively, it comprises a multiplexer that multiplexes the signal light and the distributed Raman amplification excitation light installed between the transmission line optical fiber and the wavelength selective multiplexer, and an excitation light source that outputs the excitation light. You can also. In this case, for example, among the plurality of transmission line optical fibers, a distributed Raman amplification excitation light source having a Raman gain peak at the wavelength of the signal light propagating in the first transmission line optical fiber, and the plurality of transmission line lights A distributed Raman amplification pumping light source having a Raman gain peak at the wavelength of signal light propagating in the second transmission line optical fiber among the fibers is provided, and the multiplexer is a wavelength division filter.

  When the present invention is viewed from the viewpoint of an optical transmitter, the present invention is applied to the optical communication system of the present invention, and is installed on the output side of the optical amplifier that collectively amplifies the wavelength multiplexed signal light that is output. An optical transmitter including a wavelength selective demultiplexer.

  When the present invention is viewed from the viewpoint of a linear repeater, the present invention is applied to the optical communication system of the present invention, and is installed on the output side of the optical amplifier that collectively amplifies the wavelength multiplexed signal light to be relayed. This is a linear repeater including a wavelength selective duplexer and a wavelength selective multiplexer installed on the input side of the optical amplifier.

  When the present invention is viewed from the viewpoint of an optical receiver, the present invention is applied to the optical communication system of the present invention, and is installed on the input side of the optical amplifier that collectively amplifies the received wavelength multiplexed signal light. An optical receiver including a wavelength selective multiplexer.

  According to the present invention, the disadvantage that the linear relay distance, which has been a problem in the prior art, is limited can be solved. As a result, the number of optical amplifiers can be reduced as compared with the prior art.

  Embodiments of the present invention will be described below with reference to the drawings.

(First Example)
The configuration of the optical communication system of the first embodiment is shown in FIG. In this embodiment, interleaver demultiplexers D1 and D2 are installed on the output side of optical amplifiers A1 to A3 having inputs and outputs of a single-core optical fiber, and two-core is disposed downstream of the demultiplexers D1 and D2. Transmission line optical fibers-1 and -2 are connected. Interleaver multiplexers M1 and M2 are installed on the signal light output side of the two-core transmission line optical fibers-1 and -2.

  The interleaver demultiplexers D1 and D2 and the multiplexers M1 and M2 have a configuration in which directional couplers of two input ports and two output ports are connected in multiple stages in cascade. Further, the interleaver demultiplexers D1 and D2 and the multiplexers M1 and M2 respectively demultiplex and multiplex the signal light channel (wavelength channel) at equal intervals. For example, the demultiplexers D1 and D2 include a WDM channel (λ1, λ2, λ3,..., In FIG. 2) and an odd channel (λ1, λ3, λ5,. Demultiplexed into channels (λ2, λ4, λ6,... In FIG. 2).

  As an example of the signal light band, when the optical amplifiers A1 to A3 are C-band erbium-doped fiber amplifiers (EDFAs), and the transmission line optical fibers -1 and -2 are dispersion shifted fibers (DSFs), they are about 1530 nm to about 1560 nm. is there. At this time, the frequency interval of 100 GHz is about 0.8 nm in terms of wavelength interval. As a comparison with the prior art, in this embodiment, interleaver demultiplexers D1 and D2 and multiplexers M1 and M2 and two transmission line optical fibers -1 and -2 are used. Then, instead of the interleaver demultiplexers D1 and D2 and the multiplexers M1 and M2 and the two transmission line optical fibers -1 and -2, one transmission line optical fibers F11, F12, F21, and F22 are used. ing.

  At this time, in the prior art, Psin is limited to about −10 dBm per channel due to FWM and XPM in the transmission line optical fiber. On the other hand, in this embodiment, Psin can be set to about -4 dBm per channel. However, these Psin are powers at which the deterioration of the signal light time waveform starts to become noticeable due to the nonlinear effect in the transmission line optical fiber. Therefore, ignoring the insertion loss of the interleaver demultiplexers D1 and D2 and the multiplexers M1 and M2, Psin is improved by about 6 dB, so that the optical signal-to-noise ratio (optical SNR) of the optical amplifier output in the nth section is improved. Can be obtained.

  For example, when the loss in the nth section is the same, an optical SNR improvement of about 6 dB can be obtained. This optical SNR improvement can be used for linear relay distance extension. For example, a linear relay distance extension of about 3 times can be achieved. If a constant optical SNR is assumed, the loss in the nth section can be increased by about 6 dB.

  On the other hand, when the insertion loss of the interleaver demultiplexers D1 and D2 and the multiplexers M1 and M2 is considered, the following is obtained. First, typical insertion loss of the interleaver demultiplexers D1 and D2 and the multiplexers M1 and M2 is about 1 dB. Regarding securing Psin, it is sufficient to increase the output of the optical amplifiers A1 to A3 by about 1 dB, which is the insertion loss of the interleaver demultiplexers D1 and D2, and this is easy.

  Further, due to the insertion loss of the interleaver multiplexers M1 and M2, the noise figure as a linear repeater is degraded by about 1 dB, and the optical SNR is degraded by about 1 dB. Therefore, the total optical SNR improvement is about 5 dB. That is, Psin is improved by about 6 dB, the optical SNR is improved by about 5 dB, and the loss in the n-th section is improved by about 5 dB. Also, a linear relay distance extension of about 2.5 times can be achieved.

  FIG. 11 shows the input signal light power (Psin) spectrum in the above embodiment and the prior art, where the horizontal axis represents wavelength and the vertical axis represents signal light power. FIG. 12 shows optical SNR spectra in the above-described embodiments and the prior art, where the horizontal axis represents wavelength and the vertical axis represents optical SNR. These figures show how Psin and optical SNR are improved. In the above comparison, Psin is improved by about 6 dB and optical SNR is improved by about 5 dB.

  The above is the superiority of the present embodiment over the prior art when compared with the same number of optical amplifiers. Further, in the prior art of FIG. 1, the following configuration is required to obtain a linear relay distance substantially the same as that of the present embodiment.

  That is, the channel arrangement of the WDM system-1 shown in FIG. 1 is the odd-numbered channel or even-numbered channel having the 200 GHz interval, and the channel arrangement of the WDM system-2 is the odd-numbered channel or even-numbered channel having the 200-GHz interval. Therefore, the number of fibers required to transmit the same number of channels to the same linear repeater distance is the same between the conventional technique and this embodiment. Similarly, the number of necessary optical amplifiers is twice as large in the prior art as in the present embodiment.

  Therefore, this embodiment has a significant advantage over the prior art in terms of system cost, linear repeater installation space, and power consumption.

  The above example is an example when the optical amplifiers A1 to A3 are C-band EDFAs and the transmission line optical fibers -1 and -2 are DSFs, but the optical amplifiers are L-band EDFAs and the transmission line optical fibers are DSFs. Sometimes it has the same effect. The optical amplifier may be a C-band or L-band EDFA, and the transmission line optical fiber may be a non-zero DSF (NZDSF). For example, FIG. 3 shows an example in which the optical amplifiers are Raman amplifiers R1 to R3, and the transmission line optical fibers -1 and -2 are NZDSFs. That is, this embodiment generally does not limit the types of optical amplifiers and transmission line optical fibers.

(Second embodiment)
The configurations of the first and second optical communication systems of the second embodiment are shown in FIGS. 4 and 5, respectively. In the first and second optical communication systems of the present embodiment, two and three transmission line optical fibers -1 to -3 are used for one optical amplifier A1 to A3, respectively. The following points are mainly different between the first embodiment and the present embodiment.

  That is, in the first embodiment, an interleaver is used for the signal channel demultiplexers D1 and D2 and the multiplexers M1 and M2, and the signal channels are demultiplexed and multiplexed at equal intervals. On the other hand, in the first part of the present embodiment, arbitrary wavelength selection devices (WSS) are used for the demultiplexers D10-1 and D11-1 and the multiplexers M10-1 and M11-1 of the signal channel. The WSS is, for example, a MEMS type or a combination of a circulator and a plurality of fiber gratings.

  Equally spaced signal channels propagating through the optical amplifiers A1 to A3 are divided into non-uniformly spaced (unequally spaced -1) in the transmission line optical fiber-1 by the WSS demultiplexers D10-1 and D11-1. The optical fiber-2 is demultiplexed to the remainder of the unequal interval-1. Unequal interval -1 is an arrangement that suppresses signal quality degradation in FWM, and the remaining unequal interval -2 is inferior to unequal interval -1 in the FWM suppression effect, but is superior to the equal interval arrangement. . In the unequal interval-1, the wavelength position of the noise light generated by the FWM is different from the wavelength position of the signal light channel in the unequal interval-1.

  Therefore, FWM can be suppressed and Psin can be improved by the wavelength arrangement (unequally spaced -1 and -2). Examples of the signal light band and the transmission line optical fiber are the C band and the DSF.

  In Part 2 of the present embodiment, WSS demultiplexers D10-2 and D11-2 with one input port and three output ports, and WSS multiplexers M10-2 and M11-2 with three input ports and one output port are provided. Used. First, unequal interval-1 is allocated to the transmission line optical fiber-1, and the remaining signal channels are divided into two at unequal interval-2 and unequal interval-3 so that signal quality degradation due to FWM is minimized. Are allocated to transmission line optical fibers -2 and -3, respectively. The unequal interval-2 and the unequal interval-3 are made as close to the unequal interval-1 as possible to minimize signal quality degradation due to FWM. Compared with the first unequal interval-2 of the present embodiment, the second unequal interval-2 and -3 of the present embodiment have a higher FWM suppression effect, so the second of the present embodiment is more , There is a feature that a large improvement in Psin can be obtained.

(Third embodiment)
The configuration of the optical communication system of the third embodiment is shown in FIG. The following points are mainly different from the first embodiment. That is, in the first embodiment, the transmission line optical fibers-1 and -2 are the same kind of fibers, but this embodiment is different. That is, in the system of the present embodiment, 1.3 micron zero dispersion fiber (SMF) and DSF can be used in each transmission line section, and the optical amplifiers A10 to A12 collectively amplify the C-band and L-band signal lights. It can be an EDFA or a Raman amplifier.

  In the operation of this embodiment, the signal light emitted from the optical amplifiers A10 and A11 is divided into two by the wavelength division filter (WDM) demultiplexers D20 and D21 into the C band and the L band. Thereafter, the C-band signal light is guided to the SMF, and the L-band signal light is transmitted to the DSF. At this time, since the zero dispersion wavelength of SMF is 1.3 μm, it is outside the C band, and since the zero dispersion wavelength of DSF is 1.55 μm, it is outside the L band.

  Therefore, since the zero dispersion wavelength is out of the band in each signal light band, signal quality degradation in the FWM can be suppressed. The C-band and L-band signal lights after transmission are multiplexed by the WDM multiplexers M20 and M21 and guided to the optical amplifiers A11 and A12 at the subsequent stage. At this time, since signal quality deterioration due to FWM is small in both the C-band and L-band signal lights, high Psin can be ensured.

(Fourth embodiment)
The configuration of the optical communication system of the fourth embodiment is shown in FIG. The following points are mainly different from the first embodiment. That is, in this embodiment, the optical amplifiers A20 to A22 are C-band EDFAs, the transmission line optical fibers usable in the nth section are DSFs, and the transmission line optical fibers usable in the (n + 1) th section are SMFs. Therefore, in the nth section, unequal intervals −1 and −2 are used for the two transmission line optical fibers, and in the n + 1 section, the equally spaced wavelength arrangement is used for one transmission line optical fiber. Yes. Regarding the (n + 1) th section, in the first embodiment, two transmission line optical fibers are used, but in this embodiment, there is a difference that one transmission line optical fiber is used. Therefore, this embodiment has an advantage that the number of transmission line optical fibers to be used is small.

(Fifth embodiment)
The configuration of the optical communication system of the fifth embodiment is shown in FIG. The following points are mainly different from the first embodiment. That is, distributed Raman amplification in the transmission line optical fiber is used using the Raman excitation light sources L1 and L2. By this distributed Raman amplification, the equivalent noise figure of the linear repeater is reduced, and the influence of the noise figure due to the insertion loss of the interleaver multiplexer M1 can be reduced.

(Sixth embodiment)
The configuration of the optical communication system of the sixth embodiment is shown in FIG. The fifth embodiment and this embodiment are mainly different in the following points. That is, in this embodiment, the optical amplifiers A10 and A11 are C + L band EDFAs or Raman amplifiers, the transmission line optical fiber is NZDSF, the signal light wavelength for the transmission line optical fiber-1 is C band, and the signal for the transmission line optical fiber-2 The light wavelength is in the L band.

  The distributed Raman excitation light source L10 for the transmission line optical fiber-1 is for the C band, and the distributed Raman excitation light source L11 for the transmission line optical fiber-2 is for the L band. On the other hand, in the method of the fifth embodiment, the distributed Raman excitation light sources L1 and L2 for the transmission line optical fibers -1 and -2 are the same, that is, for the C + L band.

  In this embodiment, the distributed Raman amplification band can be reduced to about half that in the case of the fifth embodiment (C + L band), and is high when the distributed Raman pumping light power of the transmission line optical fiber input is limited. There is an advantage that Raman gain can be obtained. For example, the minimum value of the Raman gain in the signal band in the fifth embodiment is 8 dB, but the minimum value of the Raman gain in the signal band in the present embodiment is 14 dB. Therefore, a remarkable Raman gain improvement and an optical SNR improvement were obtained.

(Seventh embodiment)
The configuration of the optical communication system of the seventh embodiment is shown in FIG. The following points are mainly different from the first embodiment. That is, the present embodiment is applied to the repeaterless transmission section. The signal light output from the optical amplifier A1 installed in the transmitter TX is transmitted through this repeaterless transmission section and input to the optical amplifier A2 in the receiver RX. Compared with the case where a single-core transmission line optical fiber is used for the repeaterless transmission section, this embodiment can secure a higher Psin and can extend the repeaterless transmission distance.

  According to the present invention, since the output light of the optical amplifier is transmitted through a plurality of transmission line optical fibers, the restriction on the optical fiber input power due to the nonlinearity of the optical fiber is relaxed, so that the output of the optical amplifier is increased. The number of optical amplifiers can be reduced, and the linear relay distance can be increased.

The block diagram of the optical communication system of a prior art. The block diagram of the optical communication system of a 1st Example. The block diagram of the optical communication system using NZDSF of a 1st Example. The block diagram of the optical communication system of a 2nd Example (the 1). The block diagram of the optical communication system of 2nd Example (the 2). The block diagram of the optical communication system of a 3rd Example. The block diagram of the optical communication system of 4th Example. The block diagram of the optical communication system of 5th Example. The block diagram of the optical communication system of 6th Example. The block diagram of the optical communication system of 7th Example. The figure which shows the input signal optical power (Psin) spectrum in a 1st Example and a prior art. The figure which shows the optical SNR spectrum in a 1st Example and a prior art.

Explanation of symbols

A1-A3, A10-A12, A20-A22, A30, A31, A40, A41, A50, A51 Optical amplifiers D1, D2, D10-1, D10-2, D11-1, D11-2, D20, D21 demultiplexing F11, F12, F21, F22 Transmission path optical fibers L1, L2, L10, L11 Raman excitation light sources M1, M2, M10-1, M10-2, M11-1, M11-2, M20, M21 multiplexer R1 R3 Raman amplifier TX Transmitter RX Receiver

Claims (10)

An optical amplifier that collectively amplifies the wavelength-multiplexed signal light installed in a transmitter that outputs wavelength-multiplexed signal light or a linear repeater that linearly relays wavelength-multiplexed signal light;
A wavelength selective demultiplexer installed on the output side of the optical amplifier;
A plurality of transmission line optical fibers installed on the output side of the wavelength selective demultiplexer;
A wavelength selective multiplexer installed on the output side of this transmission line optical fiber;
The wavelength-multiplexed signal light installed in the receiver that inputs wavelength-multiplexed signal light installed on the output side of this wavelength selective multiplexer or in the linear repeater that linearly relays wavelength-multiplexed signal light An optical communication system, comprising: an optical amplifier that performs collective amplification. The wavelength selective demultiplexer is an interleaver, and demultiplexes wavelength channels arranged at equal intervals of input signal light into odd and even channels,
The optical communication system according to claim 1, wherein the wavelength selective multiplexer is an interleaver, and multiplexes the wavelength channels of the input signal light that are demultiplexed into odd-numbered and even-numbered channels so that the wavelength channels are equally spaced. The wavelength selective demultiplexer is an arbitrary wavelength selection device, demultiplexes wavelength channels arranged at equal intervals of input signal light into a plurality of unequal intervals,
The optical communication system according to claim 1, wherein the wavelength selective multiplexer is an arbitrary wavelength selective device, and multiplexes wavelength channels arranged at a plurality of unequal intervals of input signal light into an equal interval arrangement. The wavelength selective demultiplexer is a wavelength division filter, demultiplexes the input signal light into short wavelength and long wavelength channels,
The optical communication system according to claim 1, wherein the wavelength selective multiplexer is a wavelength division filter and multiplexes the input short wavelength and long wavelength channel signal lights. The transmission line optical fiber for transmitting the short wavelength channel is a fiber having a zero dispersion wavelength other than the short wavelength channel band,
The optical communication system according to claim 4, wherein the transmission line optical fiber for transmitting the long wavelength channel is a fiber having a zero dispersion wavelength in addition to the long wavelength channel band. A multiplexer for multiplexing the signal light and the distributed Raman amplification pumping light installed between the transmission line optical fiber and the wavelength selective multiplexer;
The optical communication system according to claim 1, further comprising: an excitation light source that outputs the excitation light. Among the plurality of transmission line optical fibers, a pumping light source for distributed Raman amplification having a Raman gain peak at the signal light wavelength propagating in the first transmission line optical fiber;
A distributed Raman amplification excitation light source having a Raman gain peak at a signal light wavelength propagating in the second transmission line optical fiber among the plurality of transmission line optical fibers, and
The optical communication system according to claim 6, wherein the multiplexer is a wavelength division filter. Applied to the optical communication system according to any one of claims 1 to 7,
An optical amplifier that collectively amplifies the output wavelength multiplexed signal light;
An optical transmitter comprising: a wavelength selective demultiplexer installed on the output side of the optical amplifier. Applied to the optical communication system according to any one of claims 1 to 7,
An optical amplifier that collectively amplifies the wavelength multiplexed signal light to be relayed;
A wavelength selective demultiplexer installed on the output side of the optical amplifier;
A linear repeater comprising a wavelength selective multiplexer installed on the input side of the optical amplifier. Applied to the optical communication system according to any one of claims 1 to 7,
An optical amplifier that collectively amplifies the received wavelength multiplexed signal light;
An optical receiver comprising a wavelength selective multiplexer installed on the input side of the optical amplifier.

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