JP4034798B2 - Optical ADM apparatus, system, and method - Google Patents

Description

  The present invention relates to an optical ADM (Add-Drop-Multiplexing) apparatus, system, and method in an optical fiber transmission system using wavelength division multiplexing transmission technology, and more particularly to extracting and inserting a desired channel signal in a transmission line. The present invention relates to an optical ADM apparatus, system, and method.

  Optical ADM technology that transmits wavelength multiplexed signals through optical fibers and extracts / inserts desired channel signals at each node at a plurality of nodes connected by optical fibers provides a large-scale and flexible optical network. Expected as a thing.

  In general, an optical ADM apparatus provided at each node is used for branching / merging optical signals with optical filter elements such as an optical multiplexer / demultiplexer and an optical bandpass filter, and an optical switch that realizes extraction / insertion of a desired channel. It is composed of an optical coupler. Therefore, in an optical ADM apparatus, each channel signal suffers a considerable amount of insertion loss in optical devices such as optical filter elements, optical switches, and optical couplers. In addition, transmission loss due to the optical fiber connecting the nodes is also incurred.

  In order to compensate for these losses, it is necessary to connect an optical amplifier to the output of the optical ADM device to increase the level of the optical signal. An optical amplifier that is currently in widespread use is an optical fiber amplifier in which an optical fiber in which an optical fiber is doped with a rare earth is pumped by a high-power semiconductor laser.

  By the way, each node in the optical network often needs a function of switching channel signals to be extracted and inserted as necessary. When the channel to be extracted / inserted is switched, the average input light intensity to the optical fiber amplifier placed between the nodes changes instantaneously, and the average of other channel signals (node passing signals) not involved in extraction / insertion There is a problem that the strength is affected and the transmission characteristics are deteriorated. Further, the number of channel signals extracted at each node does not necessarily match the number of channel signals inserted at the node. As a result of simultaneous channel switching for many channel signals, if the number of channels of wavelength multiplexed signals decreases instantaneously, the gain of the optical fiber amplifier to the node passing signal increases more than necessary, and the optical fiber The signal waveform of the node passing signal is instantaneously deteriorated due to the nonlinear effect.

  In order to cope with such a problem, for example, there is a method of installing a dummy light source whose wavelength does not overlap with the wavelength multiplexed signal in the optical ADM device (see, for example, Patent Document 1). When switching the extraction / insertion channel at the node, the dummy light source is instantaneously emitted and wavelength-multiplexed and then guided to the optical fiber amplifier, or the total number of extraction channels exceeds the insertion channel number and passes through the total number of channels. When the number decreases, the dummy light source emits light so as to compensate for the light intensity corresponding to the decrease in the number of channels, and after wavelength multiplexing, the light is guided to the optical fiber amplifier. By this method, the intensity of the input light to the optical fiber amplifier is kept almost constant, so that it is possible to suppress the deterioration of the transmission characteristics of the node passing signal.

As another coping method, for example, there is a method of controlling the gain of the optical fiber amplifier when the extraction / insertion channel is switched or when the number of channels changes due to passage through a node (for example, see Patent Document 2). Specifically, the output intensity of the pump laser of the optical fiber amplifier is controlled based on the information signal of channel switching and channel number fluctuation, and the fluctuation of the gain of the optical fiber amplifier to the node passing signal is suppressed.
JP 2004-266251 A JP 2000-353841 A

  However, in the first prior art described above, a dummy light source that does not participate in signal transmission is required for each optical ADM device, which is not economical. If there are many fluctuations in the number of channels after passing through the node, either a plurality of dummy light sources or a dummy light source with high output intensity and high dynamic range must be prepared. The oscillation wavelength of the dummy light source must be set within the practical band of the optical fiber amplifier while avoiding the wavelength of the wavelength multiplexed signal. Therefore, when a plurality of dummy light sources are prepared, there is a problem that the maximum number of channels of the wavelength multiplexed signal is restricted by the wavelength range of the dummy light source.

  Further, since the low-frequency cutoff frequency (time constant) of the optical fiber amplifier is on the order of kHz (milliseconds), the gain fluctuation of the optical fiber amplifier accompanying the change in the total number of channels in the optical ADM apparatus substantially follows this time constant. Therefore, in the second prior art, even if a technique is used in which the output light intensity of the optical fiber amplifier is monitored and feedback control is performed to the pump laser of the optical fiber amplifier, the gain fluctuation due to the change in the total number of channels that occurs instantaneously is avoided. Cannot follow.

  Furthermore, the control to the pump laser must be sent immediately before the number of channels changes (changes), and control signal data corresponding to the amount of change in the number of channels must be provided in the optical fiber amplifier in advance. There was a problem that the control process was complicated.

  The present invention has been made to solve the above-described problems, and does not require a dummy light source for generating a wavelength signal not involved in signal transmission in the optical ADM apparatus, and performs complex control of the pumping light source of the optical fiber amplifier. It is an object of the present invention to provide an optical ADM apparatus, system, and method that are not necessary and in which the transmission characteristics of a node passing signal are little changed due to channel switching of an extraction signal and insertion signal in the optical ADM apparatus and a change in the total number of channels.

In order to solve the above-described problems, an optical ADM apparatus according to the present invention is an optical ADM (Add-Drop-Multiplexing) apparatus connected to an amplifier, and a wavelength obtained by wavelength multiplexing a plurality of inverted RZ optical signals having different wavelengths. A Mach-Zehnder interferometer that inputs a multiplexed signal from a first amplifier and outputs an RZ optical signal and a band-suppressed inverted RZ optical signal is provided, and the Mach-Zehnder interferometer converts the band-suppressed inverted RZ optical signal to a second amplifier. output to the channel frequency interval before Symbol wavelength multiplexed signal, said integer multiples or a half integer multiple of the free spectral range of the Mach-Zehnder interferometer, the occupied bandwidth of the RZ optical signal, the band suppression inverted RZ optical signal characterized in that it is twice the occupied band.

The optical ADM apparatus according to the present invention is an optical ADM (Add-Drop-Multiplexing) apparatus connected to an amplifier, and a first wavelength-multiplexed signal obtained by wavelength-multiplexing a plurality of inverted RZ optical signals having different wavelengths . input from the amplifier, comprising a Mach-Zehnder interferometer and outputs the RZ optical signal and band suppression inverted RZ optical signal, the Mach-Zehnder interferometer, and outputs the band suppression inverted RZ optical signal to the second amplifier, pre Symbol The channel frequency interval of the wavelength multiplexed signal is an integral multiple of the free spectrum range of the Mach-Zehnder interferometer, and the optical pulse amplitude ratio between the RZ optical signal and the band suppression inverted RZ optical signal is 1. To do.

In the optical ADM system of the present invention, the number of all-optical ADM devices is plural.
An optical ADM (Add-Drop-Multiplexing) device connected to an amplifier, a wavelength multiplexed signal obtained by wavelength multiplexing a plurality of inverted RZ optical signals having different wavelengths is input from a first amplifier, and an RZ optical signal and a band comprising a Mach-Zehnder interferometer and outputs the suppression inverted RZ optical signal, the Mach-Zehnder interferometer, and outputs the band suppression inverted RZ optical signal to the second amplifier, the channel frequency interval before Symbol wavelength multiplexed signal, said an integer multiple or half-integer multiple of the free spectral range of the Mach-Zehnder interferometer, the occupied bandwidth of the RZ optical signal, characterized in that it is twice the occupied band of the band suppression inverted RZ optical signal, 0 or more An optical ADM device,
An optical ADM (Add-Drop-Multiplexing) device connected to an amplifier, a wavelength multiplexed signal obtained by wavelength multiplexing a plurality of inverted RZ optical signals having different wavelengths is input from a first amplifier, and an RZ optical signal and a band comprising a Mach-Zehnder interferometer and outputs the suppression inverted RZ optical signal, the Mach-Zehnder interferometer, and outputs the band suppression inverted RZ optical signal to the second amplifier, the channel frequency interval before Symbol wavelength multiplexed signal, said Zero or more optical ADM devices, which are integer multiples of a free spectrum range of a Mach-Zehnder interferometer, and an optical pulse amplitude ratio between the RZ optical signal and the band-suppressed inverted RZ optical signal is 1. It is characterized by comprising.

Optical ADM method of the present invention is an optical ADM method for use in an optical ADM (Add-Drop-Multiplexing) device connected to the amplifier, an integral multiple of the previous SL wavelength multiplexed signal channel frequency spacing free spectrum range Alternatively, a Mach-Zehnder interferometer that is a half-integer multiple is prepared, and a wavelength multiplexed signal obtained by wavelength-multiplexing a plurality of inverted RZ optical signals having different wavelengths is input from the first amplifier to the Mach-Zehnder interferometer. An RZ optical signal and a band suppression inverted RZ optical signal are output, the band suppression inverted RZ optical signal is output from the Mach-Zehnder interferometer to a second amplifier, and the occupied band of the RZ optical signal is the band suppression inverted It is characterized by being twice the occupied band of the RZ optical signal.

Also, an optical ADM method of the present invention is an optical ADM method for use in an optical ADM (Add-Drop-Multiplexing) device connected to the amplifier, the channel frequency interval before Symbol wavelength multiplexed signal is free spectral range A Mach-Zehnder interferometer that is an integral multiple is prepared, and a wavelength-multiplexed signal obtained by wavelength-multiplexing a plurality of inverted RZ optical signals having different wavelengths is input from the first amplifier to the Mach-Zehnder interferometer. Signal and a band suppression inverted RZ optical signal, and the Mach-Zehnder interferometer outputs the band suppression inverted RZ optical signal to a second amplifier. The optical signals of the RZ optical signal and the band suppressed inverted RZ optical signal are output. The pulse amplitude ratio is 1.

  According to the optical ADM apparatus, system, and method of the present invention, a dummy light source that generates a wavelength signal that is not involved in signal transmission is not required in the optical ADM apparatus, and it is necessary to perform complex control on the pumping light source of the optical fiber amplifier. In addition, it is possible to reduce fluctuations in transmission characteristics of the node passing signal due to channel switching of the extraction signal / insertion signal in the optical ADM device and a change in the total number of channels.

Hereinafter, an optical ADM apparatus, system, and method according to embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
First, an optical signal generation apparatus 100 that generates an inverted RZ optical signal input by the optical ADM apparatus of this embodiment will be described with reference to FIG.
As shown in FIG. 1A, the optical signal generation apparatus 100 includes LPFs 101 and 104, amplifiers 102 and 105, a single mode laser 103, and a push-pull MZ modulator 106. The optical signal generation device 100 is a device for obtaining an inverted RZ optical signal. The inverted RZ optical signal is a signal in which the relationship between the logic of the data code and the intensity of the optical signal is inverted.
The LPFs 101 and 104 each input an NRZI signal (non-return-to-zero inverted signal). These signals form a differential NRZI signal pair. The LPFs 101 and 104 have a predetermined cut-off frequency, and pass only signals having a cut-off frequency or less among the input NRZI signals.

  The amplifiers 102 and 105 amplify the output signals of the LPFs 101 and 104, respectively, and output the amplified signals to the push-pull-Mach-Zehnder optical intensity modulator 106. The single mode laser 103 generates a laser having a single frequency and inputs this laser to the push-pull-Mach-Zehnder optical intensity modulator 106.

The push-pull-Mach-Zehnder optical intensity modulator 106 includes optical phase modulators 107 and 108 and a phase corrector 109.
Optical phase modulation sections 107 and 108 receive the output signals of amplifiers 102 and 105, respectively, and modulate the phase of the single mode laser based on these signals. The phase corrector 109 corrects the phase of the single mode laser output from the optical phase modulator 107. In general, since the distances from the respective output ends of the optical phase modulators 107 and 108 to the position where the single mode laser is synthesized are different, the phase corrector 109 corrects the difference between the two distances.
The push-pull MZ modulator 106 combines the single mode laser output from the phase corrector 109 and the single mode laser output from the optical phase modulator 108, and outputs an inverted RZ optical signal that is a combined light. .

Next, the state of signals in the optical signal generation device 100 will be described with reference to FIG. In FIG. 1B, the horizontal axis indicates time, and the vertical axis indicates amplitude.
The top two signal histories in FIG. 1B indicate inputs. The next third signal history (Optical phase at MZ arm # 1) shows the history of the output signal of the optical phase modulation unit 107. The fourth signal history (Optical phase at MZ arm # 2) indicates the history of the output signal of the optical phase modulator 108. The fifth history is a signal history obtained by taking a difference between the output signal of the optical phase modulation unit 107 and the output signal of the optical phase modulation unit 108. The last sixth signal history is a history of the inverted RZ optical signal output from the optical signal generation device 100.
“1” shown above and below in FIG. 1B indicates a mark bit. As can be seen from FIG. 1B, the optical phase of the inverted RZ optical signal is inverted for each mark bit.

  Then, a plurality of optical signal generation apparatuses 100 are prepared, and these optical signal generation apparatuses 100 are set to generate inverted RZ optical signals having different wavelengths. The inverted RZ optical signal generated by each optical signal generation device 100 is optically multiplexed by an optical multiplexer (not shown), and is output from the optical multiplexer as a wavelength multiplexed signal. The wavelength multiplexed signal is transmitted through an optical fiber. Fiber transmission.

Next, how the wavelength division multiplexed signal output from the optical multiplexer is input to the optical ADM apparatus according to the present embodiment of the present invention will be described with reference to FIG. FIG. 2 shows an optical ADM system in which a plurality of optical ADM devices are connected via optical fibers.
The optical ADM system of this embodiment includes optical fibers 201, 205, and 209, optical fiber amplifiers 202, 204, 206, 208, and 210, and optical ADM devices 203, 207, and 211.
The optical fibers 201, 205, and 209 are for transmitting the above-described wavelength multiplexed signal. The optical fiber amplifiers 202, 204, 206, 208, and 210 amplify the wavelength multiplexed signal transmitted through the optical fiber. The optical ADM devices 203, 207, and 211 extract only the optical signal of the desired wavelength channel, and other channel signals pass through the nodes. In some cases, an optical signal having the same wavelength as that of the extracted wavelength channel is newly inserted. When a new signal is inserted, the residual component of the extracted signal is sufficiently suppressed to avoid crosstalk with the extracted signal of the same channel.

Next, the optical ADM apparatus of this embodiment will be described with reference to FIG.
As shown in FIG. 3C, the optical ADM apparatus of the present embodiment includes a Mach-Zehnder interferometer 303 and an optical demultiplexer 304. The optical ADM apparatus shown in FIG. 3C is a case where the optical ADM apparatus extracts a desired channel but does not insert a new signal.

  The Mach-Zehnder interferometer 303 includes two optical coupler units 301 and 302 and two optical paths (optical path 1 and optical path 2). Each of the optical coupler units 301 and 302 is, for example, a 3 dB optical coupler. The Mach-Zehnder interferometer 303 is a two-input two-output optical passive component.

  When there is a difference between the lengths of the two optical paths, the transmittance-wavelength curve of the Mach-Zehnder interferometer 303 is sinusoidal, and the period is a value obtained by dividing the speed of light by the difference between the lengths of the two optical paths (2 (The reciprocal of the delay time difference of the optical signal propagating in the optical path). In general, this value is called a free spectrum range (hereinafter abbreviated as FSR).

  When the inverse of the propagation time difference (FSR) between the two optical paths in the Mach-Zehnder interferometer 303 is twice or more the bit rate frequency of the inverted RZ optical signal, the inverted RZ optical signal is coupled to one input port of the Mach-Zehnder interferometer. As shown in FIG. 3B, the RZ optical signal and the band-suppressed inverted RZ optical signal are generated from the two output ports (two outputs shown in FIGS. 6B and 6C). . At this time, the channel frequency interval of the wavelength multiplexed signal matches the value of FSR × n (n: natural number, n = 1, 2,...) (Integer multiple of FSR) or FSR × n / 2 (half integer multiple of FSR). Let me. In order to obtain an output with higher accuracy, the FSR is preferably 1.8 to 2.5 times the bit rate frequency of the inverted RZ optical signal. This corresponds to setting the FSR so that the occupied band of the optical signal is substantially preserved even when the optical signal passes through the Mach-Zehnder interferometer 303.

  The optical demultiplexer 304 is connected to one output port of the Mach-Zehnder interferometer 303, and a wavelength-separated Drop signal is generated from the optical demultiplexer 304.

As shown in FIG. 3B, an RZ optical signal and a band-suppressed inverted RZ optical signal are generated from the output port of the Mach-Zehnder interferometer 303, but the band-suppressed inverted RZ optical signal is more average light intensity. Enhanced. When the Mach-Zehnder interferometer 303 of FSR 100 GHz receives, for example, an inverted RZ optical signal with a bit rate of 40 Gbit / s, the ratio of the average optical intensity of the output band-suppressed inverted RZ optical signal to the RZ optical signal is approximately 8: 2. The band suppression inverted RZ optical signal is about four times higher in average light intensity.
Therefore, the RZ optical signal from the Mach-Zehnder interferometer is used as the Drop optical signal output from the optical demultiplexer 304, and the band-suppressed inverted RZ optical signal is directly guided to the fiber transmission line to be input to the optical fiber amplifier 204. The light intensity can be increased and the deterioration of the light S / N can be suppressed.

  Even if a plurality of optical ADM devices 203 having the configuration shown in FIG. 3C are installed in the fiber transmission line, the band-suppressed inverted RZ optical signal output from the Mach-Zehnder interferometer 303 of each optical ADM device passes through each node. By using the RZ optical signal output from the other port of the Mach-Zehnder interferometer as an extraction signal in each optical ADM device, it is used as a signal, and the occupied optical band of the passing channel signal due to passing through a plurality of stages of the Mach-Zehnder interferometer It is possible to sufficiently suppress the eye opening degree deterioration accompanying the decrease, and the extinction ratio deterioration is small for the RZ optical signal used as the extraction signal.

Next, a case will be described with reference to FIG. 4 where a wavelength division multiplexed signal based on a band suppression inverted RZ optical signal is transmitted and a new signal is to be inserted at a desired channel wavelength at the next node.
In this case, as shown in FIG. 4, an optical demultiplexer 405, an optical multiplexer 406, an optical transmitter 407, an optical switch 408, an optical receiver that inputs the band suppression inverted RZ optical signal output from the optical ADM device 203. A device (or terminator) 409 is provided.

  The optical demultiplexer 405 separates the wavelength of the input wavelength multiplexed signal one by one. The optical demultiplexer 405 outputs a band suppression inverted RZ optical signal having a wavelength corresponding to the unnecessary band suppression inverted RZ optical signal to the optical switch 408. Other unnecessary band suppression inverted RZ optical signals are output to the optical multiplexer 406 as they are.

When terminating an unnecessary band suppression inverted RZ optical signal, the optical switch 408 connects the terminal B and the terminal C shown in FIG. At the same time, the optical switch 408 connects the terminal A and the terminal D, and introduces a new optical signal from the optical transmitter 407 via the terminal A instead of the terminated band suppression inverted RZ optical signal. Then, the optical switch 408 outputs this new optical signal to the optical multiplexer 406.
On the other hand, when the band suppression inverted RZ optical signal is allowed to pass without terminating the band suppression inverted RZ optical signal, the optical switch 408 connects the terminals B and D and the terminals A and C shown in FIG. To do.

  The optical multiplexer 406 receives the wavelength-separated band-suppressed inverted RZ optical signal input from the optical demultiplexer 405, inputs the signal from the terminal D of the optical switch 408, combines these signals, and combines the wavelength. Multiplexed and wavelength-multiplexed band suppression inverted RZ optical signal is output.

  As described above, since the fluctuation of the input light intensity to the optical fiber amplifier 410 is automatically suppressed regardless of whether a new signal is inserted or not, the gain fluctuation of the optical fiber amplifier when the optical switch 408 is switched. Can be sufficiently reduced.

Next, a case where the optical coupler 501 is used instead of the Mach-Zehnder interferometer 303 instead of using the Mach-Zehnder interferometer 303 as shown in FIG. 3C will be described with reference to FIG.
Even if the Mach-Zehnder interferometer 303 is not used as shown in FIG. 3C and the optical coupler 501 is used instead as shown in FIG. Variations can be suppressed.

  However, when the optical coupler 501 is used, the pulse amplitude of the optical signal decreases according to the branching ratio of the coupler. On the other hand, in the Mach-Zehnder interferometer 303, the pulse amplitudes of the band-suppressed inverted RZ optical signal and the RZ optical signal output from the Mach-Zehnder interferometer 303 can be made substantially equal to the pulse amplitude of the inverted RZ optical signal that is the input signal. That is, even if the average light intensity decreases compared to the original signal, the intensity amplitude value of the optical signal hardly changes (the input in FIG. 6A and the two outputs in FIGS. 6B and 6C). And compare). For this reason, the use of the Mach-Zehnder interferometer 303 is superior to the use of the optical coupler 501 in terms of received signal quality.

  Further, when the band of the optical receiver 409 is smaller than the bit rate frequency, if the inverted RZ optical signal is received as it is, the inverted pulse width is widened, the apparent extinction ratio is deteriorated, and the received light sensitivity is lowered. However, the RZ optical signal generated by the Mach-Zehnder interferometer 303 and the band-suppressed inverted RZ optical signal are characterized by alleviating such a problem.

  The configuration shown in FIG. 3C is also effective when the FSR of the Mach-Zehnder interferometer 303 is about the bit rate frequency of the inverted RZ optical signal. That is, in this case, when the inverted RZ optical signal is coupled to one input port of the Mach-Zehnder interferometer, an RZ optical signal and an NRZ optical signal are generated from the two output ports (FIGS. 6E and 6). (D)). The NRZ optical signal is obtained by band-suppressing the inverted RZ optical signal, and the sign of the optical signal is opposite to that of the RZ optical signal. In this case, the average optical intensity of each optical signal is substantially equal, and the amplitude of the optical pulse is theoretically equivalent to the inverted RZ optical signal that is the input signal. Therefore, in the configuration of FIG. 3C, even if a Mach-Zehnder interferometer having approximately half the FSR is used, it is effective for suppressing the gain fluctuation of the optical fiber amplifier. At this time, the channel frequency interval of the wavelength multiplexed signal is made to coincide with the value of FSR × n. In order to obtain an output with higher accuracy, the FSR is preferably 0.9 to 1.3 times the bit rate frequency of the inverted RZ optical signal. This corresponds to setting the FSR so that the optical pulse amplitude ratio between the two output ports of the Mach-Zehnder interferometer 303 is approximately 1 when the optical signal passes through the Mach-Zehnder interferometer 303.

  According to the first embodiment described above, the RZ optical signal from the Mach-Zehnder interferometer is used as the Drop optical signal output from the optical demultiplexer 304, and the band-suppressed inverted RZ optical signal is directly guided to the fiber transmission line. Thus, the input light intensity to the optical fiber amplifier 204 can be increased, and the deterioration of the optical S / N can be suppressed. In addition, since fluctuations in the input light intensity to the optical fiber amplifier 106 are automatically suppressed regardless of whether a new signal is inserted or not, fluctuations in the gain of the optical fiber amplifier when the optical switch 104 is switched are sufficiently reduced. be able to.

  The number of extraction channels fluctuated by converting the inverted RZ optical signal into a band-suppressed inverted RZ signal and an RZ optical signal by a Mach-Zehnder optical interferometer, and wavelength multiplexing with other passing channels without extracting one of them. Therefore, the fluctuation of the average optical intensity of the wavelength multiplexed signal can be suppressed, and the waveform deterioration of the optical signal due to the optical gain fluctuation accompanying the fluctuation of the input optical intensity to the optical fiber amplifier connected to each ADM unit can be reduced.

  In the optical ADM output, the band suppression inverted RZ signal or RZ optical signal output from the Mach-Zehnder interferometer is wavelength-multiplexed together with other node passing channels when no new signal is inserted, and the same channel is extracted when a new signal is inserted. Since the optical signal to be received is terminated and received by the optical ADM unit, the average input light to the optical fiber amplifier connected to the output of the optical ADM unit is selected even if the insertion or non-insertion of a new signal is selected by the optical switch. Since the change in the intensity is small, it is possible to suppress the waveform deterioration of the optical signal due to the gain fluctuation of the optical fiber amplifier accompanying the switching of the optical switch.

(Second Embodiment)
The optical ADM apparatus of this embodiment will be described with reference to FIG.
As shown in FIG. 7, the optical ADM apparatus of this embodiment includes a Mach-Zehnder interferometer 303, an optical switch 408, an optical demultiplexer 405, an optical multiplexer 406, an optical transmitter 407, and an optical receiver 409. . In the following, the same parts as those already described are designated by the same reference numerals and the description thereof is omitted.

  In the present embodiment, the 2 × 2 optical switch 408 selects whether to pass a specific wavelength channel signal or to extract a Drop signal (RZ optical signal) and leave the band-suppression inverted RZ optical signal as a dummy signal. be able to. That is, when a specific wavelength channel signal is allowed to pass, the optical switch 408 connects the terminal B and the terminal D shown in FIG. 7 and further connects the terminal A and the terminal C. In this case, the wavelength channel signal passing through the terminal A and the terminal C does not pass through the optical ADM device 203 but is output to the optical multiplexer 406 as the signal input to the optical demultiplexer 405. On the other hand, when leaving the band suppression inverted RZ optical signal as a dummy signal while extracting the Drop signal (RZ optical signal), the optical switch 408 connects the terminal B and the terminal C shown in FIG. A and terminal D are connected. In this case, the signal output from the Mach-Zehnder interferometer 303 becomes a band suppression inverted RZ optical signal, and this band suppression inverted RZ optical signal is output to the optical multiplexer 406.

  Since the change in the average light intensity that occurs when the optical switch 408 is switched is about 12.5%, the maximum value of the change in the average light intensity of the wavelength multiplexed signal combined with the other channel signal by the optical multiplexer 406 is 12.2. 5% divided by the number of channels. For example, even in the case of 2-channel transmission, the ratio is sufficiently small as 6.25%. Therefore, if this embodiment is adopted, it is possible to suppress the gain fluctuation of the optical fiber amplifier 204 connected to the output of the optical ADM apparatus.

  As a matter of course, this embodiment may be prepared for all channels. That is, the optical switch 408 and the Mach-Zehnder interferometer 303 are provided for all wavelength channel signals. In this case, the maximum fluctuation value of the average light intensity of the input signal to the optical fiber amplifier is 12.5%.

Further, a modification of the optical ADM apparatus shown in FIG. 7 will be described with reference to FIG.
Instead of the 2 × 2 optical switch 408, a 3 × 2 optical switch 802 is used. Of the three inputs of the 3 × 2 optical switch 802, two inputs are the same as the two inputs of the optical switch 408, and one new input is the output of the optical transmitter 801. The optical transmitter 801 performs optical transmission similar to that of the optical transmitter 407.

  The optical ADM apparatus shown in FIG. 8 can efficiently extract a desired channel signal and insert a new signal. That is, when a new signal is inserted, terminal A and terminal D shown in FIG. 8 are connected, and terminal E and terminal C are further connected. In this case, the signal output from the Mach-Zehnder interferometer 303 becomes a band-suppression inverted RZ optical signal, and a new signal can be guided to the optical multiplexer 406, and the Drop (old) signal outputs the optical demultiplexer output to the Mach-Zehnder interferometer. The optical signal is received after being guided and converted into an RZ optical signal, and the band suppression inverted RZ optical signal of the old signal can be terminated in the optical switch. The other two cases are the same as the switch switching shown in FIG.

  According to the second embodiment described above, fluctuations in transmission characteristics of node passing signals can be reduced. Further, the maximum value of the change in the average light intensity of the wavelength multiplexed signal combined with the other channel signal by the optical multiplexer 406 is a sufficiently small ratio of 6.25% even in the case of 2-channel transmission. Therefore, if this embodiment is adopted, it is possible to suppress the gain fluctuation of the optical fiber amplifier 204 connected to the output of the optical ADM apparatus. Moreover, the optical switch can efficiently extract a desired channel signal and insert a new signal.

  A desired channel signal is exchanged, extracted, and a new signal is inserted between a plurality of wavelength division multiplexed signals via an optical switch unit, and two optical signal components output from the Mach-Zehnder interferometer are used for a channel to which a new signal is not inserted. One of them is wavelength-multiplexed with other channel signals to suppress fluctuations in the average optical intensity of newly generated wavelength-multiplexed signals due to changes in the connection state in the optical switch section, and to reduce the light caused by gain fluctuations in the optical fiber amplifier. Reduces signal waveform degradation.

(Third embodiment)
The optical ADM apparatus of this embodiment will be described with reference to FIG.
As shown in FIG. 9, the optical ADM apparatus according to this embodiment includes optical demultiplexers 903, 904, 907, and 908, an optical switch unit 909, optical multiplexers 910, 911, 912, and 913, a fixed attenuator 914, and the like. 918, Mach-Zehnder interferometers 915 and 919, and couplers 916 and 920 are provided. Except for the optical switch unit 909, the other device portions are the same as those described above. Four sets of a pair of optical demultiplexers and optical multiplexers are prepared, and they are connected via an optical switch unit 909.

  In the present embodiment, the optical signal is exchanged for the desired channel between the wavelength multiplexed signal 1 and the wavelength multiplexed signal 2 to generate new wavelength multiplexed signal 3 and wavelength multiplexed signal 4. In the switching example of the optical switch unit 909 shown in FIG. 9, the λ1 and λ2 channel optical signals of the wavelength multiplexed signal 1 are sent to the wavelength multiplexed signal 3, and the channel signals of λ3 and λ6 of the wavelength multiplexed signal 1 are output ports. Are sent to an optical multiplexer 911 to which a Mach-Zehnder interferometer 915 is connected, and a Drop signal 1 is output from the Mach-Zehnder interferometer.

  In this embodiment, it is not necessary to transfer λ3 and λ6 of the wavelength multiplexed signal 1 to the wavelength multiplexed signal 3, but in order to suppress the gain fluctuation of the optical fiber amplifier 917, the wavelengths λ3 and λ6 output from the Mach-Zehnder interferometer 915 are suppressed. The signal is wavelength-multiplexed with other channel wavelength signals. The connection state of the optical switch unit 909 is determined so that the λ4 channel signal of the wavelength multiplexed signal 1 is transferred to the wavelength multiplexed signal 4. On the other hand, the λ5 channel signal of the wavelength multiplexed signal 1 is terminated in the optical switch unit, and a new λ5 channel signal is input to the optical demultiplexer 904 and transferred to the wavelength multiplexed signal 3 through the optical switch unit 909. In the following, each channel signal of the wavelength multiplexed signal 2 is also transferred to the wavelength multiplexed signal 3, the wavelength multiplexed signal 4, termination, Drop reception, new signal by switching the path by the optical switch unit 909 as shown in FIG. The insertion is done.

  In the example of FIG. 9, the total number of channels to the optical fiber amplifiers 917 and 921 used to amplify the wavelength multiplexed signals 3 and 4 does not change regardless of the Add / Drop, termination, and channel switching of the optical signal. ing. By performing wavelength multiplexing transmission of a channel signal component (one of the Mach-Zehnder interferometer outputs) that is not received by the subsequent optical node unit installed in the fiber transmission line, it is possible to suppress the gain fluctuation of the optical fiber amplifier.

  The fixed attenuators 914 and 918 arranged in the optical ADM apparatus according to the present embodiment match the light intensity per channel with the light intensity per channel of the dummy optical signal output from the Mach-Zehnder interferometers 915 and 919. It is used to make it. Actually, there is an excess optical loss inside the Mach-Zehnder interferometers 915 and 919. Therefore, the light intensity attenuation amounts of the fixed attenuators 914 and 918 can be adjusted in consideration of the internal losses of the Mach-Zehnder interferometers 915 and 919, respectively. preferable.

  In addition, the embodiment of FIG. 9 relates to channel signal replacement, extraction, and insertion between two wavelength division multiplexed signals. However, this embodiment is extended to the channel signal between a number of wavelength division multiplexed signals. The scale may be expanded for replacement, extraction, and insertion. In this case, it goes without saying that the gain fluctuation of the optical fiber amplifier used for optical amplification of each wavelength division multiplexed signal is suppressed.

  According to the above third embodiment, the gain fluctuation of the optical fiber amplifier can be suppressed by wavelength-multiplexing the channel signal component that is not received by the subsequent optical node unit laid in the fiber transmission line. .

(Fourth embodiment)
The optical ADM apparatus of this embodiment will be described with reference to FIG.
As shown in FIG. 10, the optical ADM apparatus of this embodiment includes a Mach-Zehnder interferometer 1001, optical demultiplexers 1002, 1003, 1006, optical multiplexers 1004, 1007, and a 2 × 1 optical switch group 1005. .

  In the present embodiment, the wavelength interval of the wavelength multiplexed signal (same as the frequency interval) is approximately half of the FSR of the Mach-Zehnder interferometer 1001. In FIG. 10, for example, it is assumed that the channel frequency interval of a plurality of 40 Gbit / s inverted RZ optical signals is 50 GHz, and the FSR of the Mach-Zehnder interferometer 1001 is 100 GHz.

  From one port of the Mach-Zehnder interferometer 1001, an odd channel signal is converted to RZ, and a wavelength multiplexed output in which the even channel signal is band-suppressed is obtained. Further, from the other port of the Mach-Zehnder interferometer 1001, the band of the odd channel signal is suppressed, and a wavelength multiplexed output in which the even channel signal is converted to RZ is obtained. The two outputs of the Mach-Zehnder interferometer 1001 are wavelength-separated by optical demultiplexers 1002 and 1003 at intervals of 50 GHz. The RZ-converted optical signal is treated as an extraction signal, and the band-suppressed inverted RZ optical signal component is as follows. This is sent to the 2 × 1 optical switch group 1005. A signal source of an insertion (Add) channel is connected to the 2 × 1 optical switch group 1005. By switching each 2 × 1 switch, whether a new Add signal is inserted or an original signal is passed (Through). You can choose. An optical multiplexer 1007 is connected to the output of the 2 × 1 optical switch group 1005 and performs transmission as a new wavelength multiplexed signal. With such a configuration, fluctuations in the input light intensity of the optical fiber amplifier 1008 connected to the output of the optical multiplexer 1007 can be reduced, and gain fluctuations in the optical fiber amplifier 1008 associated with channel switching can be suppressed.

(First modification)
A first modification of the fourth embodiment will be described with reference to FIG.
The optical ADM apparatus according to the present modification includes a Mach-Zehnder interferometer 1101, optical demultiplexers 1102 and 1006, an optical multiplexer 1007, and a 2 × 1 optical switch group 1005. The 2 × 1 optical switch group 1005, the insertion (Add) signal source, and the optical multiplexer 1007 are the same as those in the configuration example of FIG.

  In this modification, the FSR of the Mach-Zehnder interferometer 1101 is the same (50 GHz) as the frequency interval of the wavelength multiplexed signal. When a 40 Gbit / s inverted RZ optical signal is input to the Mach-Zehnder interferometer 1101 of FSR 50 GHz, an NRZ optical signal is generated from one port of the Mach-Zehnder interferometer, and an RZ optical signal is generated from the other port (FIG. 6E). FIG. 6 (D)). Therefore, the RZ optical signal is used as an extraction signal at the optical node, and the NRZ optical signal is used as a passing signal or a dummy signal.

  A plurality of wavelength-multiplexed NRZ optical signals from the Mach-Zehnder interferometer 1101 are wavelength-separated by an optical demultiplexer, and then each 2 × 1 switch selects whether to pass or replace with a new inverted RZ optical signal. When the NRZ optical signal and the RZ optical signal are generated from the Mach-Zehnder interferometer 1101, the average optical intensity is divided into about 50:50 in the NRZ and RZ optical signals as compared with the original inverted RZ optical signal. Therefore, also by this modification, the fluctuation | variation of the input light intensity to the optical fiber amplifier 1008 connected to the output of the optical multiplexer 1007 can be reduced.

(Second modification)
A second modification of the fourth embodiment will be described with reference to FIG.
The optical ADM apparatus according to this modification includes a Mach-Zehnder interferometer 1001 and a three-terminal optical circulator 1201.

  In this modification, the two output ports C and D of the Mach-Zehnder interferometer 1001 of FSR 100 GHz are connected by an optical fiber 1202. At this time, when an inverted RZ optical signal of 40 Gbit / s is input to the port A of the Mach-Zehnder interferometer 1001, the inverted RZ optical signal is input to the port B and the 3-terminal optical circulator 1201 in the same manner as when the inverted RZ optical signal is input to the Mach-Zehnder interferometer 1001 of FSR 50 GHz. An optical signal converted into an RZ optical signal and an NRZ optical signal can be output from the output E. Therefore, even if the configuration of the optical signal conversion unit of FIG. 12 is introduced into the configuration of FIG. 11, the same effect can be obtained.

(Third Modification)
A third modification of the fourth embodiment will be described with reference to FIG.
The optical ADM apparatus according to this embodiment includes three-terminal optical circulators 1301, 1304, 1305, a Mach-Zehnder interferometer 1001, optical interleavers 1302, 1303, and an optical coupler 1306.

  The difference from the example of FIG. 10 is that an even / odd channel RZ optical signal and a band-suppressed inverted RZ optical signal obtained by inputting a plurality of inverted RZ optical signals at intervals of 50 GHz to a Mach-Zehnder interferometer of FSR 100 GHz are optical interleavers. The wavelength separation is performed for each even / odd channel by 1302, and a plurality of band suppression inverted RZ optical signals are extracted for each even / odd channel via the optical circulator 1301, and are multiplexed via the optical coupler 1306. The even / odd channel RZ optical signal components are input again to the Mach-Zehnder interferometer 1001, and NRZ-type optical signals are extracted from two ports of the Mach-Zehnder interferometer 1001, one of which is output via the optical circulator. Switching between the new signal and the passing signal can be achieved by using a new signal source, an optical switch group 1005, and an optical multiplexer 1007 as shown in FIG.

(Fourth modification)
A fourth modification of the fourth embodiment will be described with reference to FIG.
The optical ADM apparatus of this embodiment includes a Mach-Zehnder interferometer 1001, optical demultiplexers 1002, 1003, and 1006, an optical multiplexer 1007, a 2 × 1 optical switch group 1005, and a 3 dB coupler group 1401.

  The difference from the example of FIG. 10 is that a 3 dB coupler group 1401 is provided between the two optical demultiplexers 1002 and 1003 to which the output of the Mach-Zehnder interferometer 1001 of FSR 100 GHz is connected. The port of the 3 dB coupler is determined so that the optical signal output from the 3 dB coupler group 1401 and guided to the 2 × 1 optical switch group 1005 becomes a band suppression inverted RZ optical signal having a high average optical intensity. An optical signal that passes through the 3 dB coupler group 1401 and is re-input to the Mach-Zehnder interferometer 1001 via the optical demultiplexers 1003 and 1002 is converted into an RZ optical signal or an NRZ optical signal, and is therefore used as an extraction channel signal. Good. Selection of a new insertion signal and a band-suppressed RZ optical signal is performed by a 2 × 1 optical switch group 1005.

  With such a configuration, a new wavelength multiplexed signal is generated at the output of the optical multiplexer 1007, and fluctuations in the average input light intensity to the optical fiber amplifier 1008 connected to the output of the optical multiplexer 1007 can be reduced. Gain fluctuations occurring in the amplifier 1008 can be reduced.

  According to the fourth embodiment described above, fluctuations in the input light intensity of the optical fiber amplifier 1008 connected to the output of the optical multiplexer 1007 are reduced, and fluctuations in the gain of the optical fiber amplifier 1008 associated with channel switching are suppressed. be able to.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

(A) is a block diagram of an optical signal generation device that generates an optical modulation signal input by the optical ADM device according to the embodiment of the present invention, and (B) is a diagram showing a signal history related to the optical signal generation device. The figure which shows the optical ADM system with which the optical ADM apparatus which concerns on embodiment of this invention is connected via the optical fiber. (A), (B) is a block diagram of a Mach-Zehnder interferometer, (C) is a block diagram of an optical ADM device according to the first embodiment of the present invention. The block diagram in the case of transmitting the wavelength division multiplexing signal by a band suppression inversion RZ optical signal, and inserting a new signal in a desired channel wavelength in the following node. FIG. 3C is a block diagram when an optical coupler is used instead of the Mach-Zehnder interferometer. (A) shows the waveform of an optical signal which is an input signal of the optical ADM apparatus according to the first embodiment of the present invention, and (B), (C), (D) and (E) are the first of the present invention. 2 shows a waveform of an optical signal that is an output signal of the optical ADM device according to the embodiment. The block diagram of the optical ADM apparatus which concerns on the 2nd Embodiment of this invention. The block diagram which shows the modification of FIG. The block diagram of the optical ADM apparatus which concerns on the 3rd Embodiment of this invention. The block diagram of the optical ADM apparatus which concerns on the 4th Embodiment of this invention. The block diagram of the 1st modification of FIG. The block diagram of the 2nd modification of FIG. The block diagram of the 3rd modification of FIG. The block diagram of the 4th modification of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Optical signal production | generation apparatus, 101, 104 ... Low pass filter, 102, 105 ... Amplifier, 103 ... Single mode laser, 106 ... Push pull-Mach-Zehnder type optical intensity modulator, 107, 108 ... Optical phase modulation part, 109 ... Phase corrector 201, 205, 209 ... optical fiber, 202, 204, 206, 208, 210, 410, 917, 921, 1008 ... optical fiber amplifier, 203, 207, 211 ... optical ADM device, 301, 302 ... light Couplers 303, 915, 919, 1001, 1101 ... Mach-Zehnder interferometers, 304, 405, 903, 904, 907, 908, 1002, 1003, 1006, 1102 ... optical demultiplexers, 406, 910, 911, 912 913, 1004, 1007 ... optical multiplexer, 407, 801 ... optical transmitter, 4 8 ... 2x2 optical switch, 409 ... optical receiver, 501 ... 3dB optical coupler, 802 ... 3x2 optical switch, 909 ... optical switch unit, 914, 918 ... fixed attenuator, 916,920 ... coupler, 1005 ... 2 × 1 optical switch group, 1201, 1301, 1304, 1305... Three-terminal optical circulator, 1202... Optical fiber, 1302, 1303, optical interleaver, 1306, optical coupler, 1401, 3 dB coupler group.

Claims (11)

An optical ADM (Add-Drop-Multiplexing) device connected to an amplifier,
A Mach-Zehnder interferometer for inputting a wavelength multiplexed signal obtained by wavelength multiplexing a plurality of inverted RZ optical signals having different wavelengths from the first amplifier, and outputting the RZ optical signal and the band-suppressed inverted RZ optical signal;
The Mach-Zehnder interferometer outputs the band suppression inverted RZ optical signal to a second amplifier,
Channel frequency interval before Symbol wavelength multiplexed signal, said integer multiples or a half integer multiple of the free spectral range of the Mach-Zehnder interferometer, the occupied bandwidth of the RZ optical signal, a second band occupied by the band suppression inverted RZ optical signal An optical ADM apparatus characterized by being doubled. The Mach-Zehnder interferometer has two output ports. The first optical demultiplexer connected to one output port for wavelength separation and the signal connected to the other output port for wavelength separation. A second optical demultiplexer; and
Two channel signals having the same wavelength in each first channel signal wavelength-separated by the first optical demultiplexer and each second channel signal wavelength-separated by the second optical demultiplexer 2. The optical ADM apparatus according to claim 1, wherein when one of them is extracted, the other is passed without being extracted.   The optical ADM apparatus according to claim 2, further comprising a switch for replacing the channel signal to be passed with the new channel signal when a new channel signal is inserted. An optical ADM (Add-Drop-Multiplexing) device connected to an amplifier,
A Mach-Zehnder interferometer for inputting a wavelength multiplexed signal obtained by wavelength multiplexing a plurality of inverted RZ optical signals having different wavelengths from the first amplifier, and outputting the RZ optical signal and the band-suppressed inverted RZ optical signal;
The Mach-Zehnder interferometer outputs the band suppression inverted RZ optical signal to a second amplifier,
The channel frequency interval before Symbol wavelength multiplexed signal, said integer multiples of the free spectral range of the Mach-Zehnder interferometer, the amplitude ratio of the optical pulses of the RZ optical signal and the band suppression inverted RZ optical signal is 1 A characteristic optical ADM apparatus.   When extracting a channel signal of a certain wavelength of the wavelength multiplexed signal, it further comprises switch means for selecting whether or not to insert a new signal having the same wavelength as that of the extracted channel signal. The optical ADM apparatus according to claim 1 or 4.   5. The optical ADM apparatus according to claim 1, further comprising an optical demultiplexer that inputs the RZ optical signal and outputs a Drop signal obtained by wavelength-separating the signal. An optical ADM (Add-Drop-Multiplexing) device connected to an amplifier,
An optical demultiplexer for wavelength-separating the wavelength multiplexed signal input from the first amplifier ;
A Mach-Zehnder interferometer in which the enter with a certain signal to the extracted channel signal ones of wavelength separated signal, and outputs the RZ optical signal and band suppression inverted RZ optical signal,
Comprising said band suppression inverted RZ signals, and a multiplexer for outputting the non-extracted channel signal multiplexed by multiplexing the signal to a second amplifier of said wavelength separated signal,
The channel frequency interval of the wavelength multiplexed signal is an integer multiple or a half integer multiple of the free spectrum range of the Mach-Zehnder interferometer, and the occupied band of the RZ optical signal is twice the occupied band of the band suppression inverted RZ optical signal. optical ADM device you wherein a is. An optical ADM (Add-Drop-Multiplexing) device connected to an amplifier,
An optical demultiplexer for wavelength-separating the wavelength multiplexed signal input from the first amplifier;
A Mach-Zehnder interferometer that inputs a certain signal of the wavelength-separated signals as an extraction channel signal and outputs an RZ optical signal and a band-suppressed inverted RZ optical signal;
A combiner that combines the band-suppressed inverted RZ signal and the non-extracted channel signal of the wavelength-separated signal and combines them to a second amplifier; and
The channel frequency interval of the wavelength multiplexed signal is an integral multiple of the free spectrum range of the Mach-Zehnder interferometer, and the optical pulse amplitude ratio between the RZ optical signal and the band-suppressed inverted RZ optical signal is 1. An optical ADM device.   It comprises zero or more optical ADM devices according to claim 1 and zero or more optical ADM devices according to claim 4 so that the number of all-optical ADM devices is plural. An optical ADM system. An optical ADM method used in an optical ADM (Add-Drop-Multiplexing) device connected to an amplifier,
Channel frequency interval before Symbol wavelength multiplexed signal prepared Mach-Zehnder interferometer is an integral multiple or half-integer multiples of the free spectral range,
A wavelength multiplexed signal obtained by wavelength multiplexing a plurality of inverted RZ optical signals having different wavelengths is input from the first amplifier to the Mach-Zehnder interferometer,
From the Mach-Zehnder interferometer, an RZ optical signal and a band suppression inverted RZ optical signal are output,
From the Mach-Zehnder interferometer, the band suppression inverted RZ optical signal is output to a second amplifier,
2. The optical ADM method according to claim 1, wherein an occupied band of the RZ optical signal is twice an occupied band of the band suppression inverted RZ optical signal. An optical ADM method used in an optical ADM (Add-Drop-Multiplexing) device connected to an amplifier,
Channel frequency interval before Symbol wavelength-multiplexed signal is provided Zehnder interferometer is an integral multiple of the free spectral range,
A wavelength multiplexed signal obtained by wavelength multiplexing a plurality of inverted RZ optical signals having different wavelengths is input from the first amplifier to the Mach-Zehnder interferometer,
From the Mach-Zehnder interferometer, an RZ optical signal and a band suppression inverted RZ optical signal are output,
From the Mach-Zehnder interferometer, the band suppression inverted RZ optical signal is output to a second amplifier,
An optical ADM method, wherein an optical pulse amplitude ratio between the RZ optical signal and the band suppression inverted RZ optical signal is 1.

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