JP3635556B2 - Optical signal processor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical signal processing apparatus that inputs an ultrahigh-speed optical signal exceeding 100 Gbit / s obtained by time-division multiplexing optical signals of a plurality of channels in an optical domain and separates the optical signals of each channel into optical signals. The present invention also relates to an optical signal processing apparatus that passes, branches, or inserts time-separated optical signals for each channel.
[0002]
[Prior art]
Conventionally, processing of ultra-high-speed optical signals exceeding 100 Gbit / s exceeds the limit of electrical signal processing speed, so time-division separation into low-speed optical signals capable of electrical signal processing using a method utilizing optical nonlinearity The method of processing is taken. For example, for an ultrahigh-speed optical signal of 10 Gbit / s optical signal per channel that is time-division multiplexed 10 channels into 100 Gbit / s, a 10 GHz timing clock synchronized with the ultrahigh-speed optical signal is extracted. A 10 Gbit / s, 10 channel optical signal is time-division separated using a timing clock. For this purpose, a circuit for extracting a timing clock synchronized with an ultrafast optical signal and an optical pulse time division separation circuit are used.
[0003]
An example of a timing clock extraction circuit synchronized with an ultrahigh-speed optical signal is disclosed in Japanese Patent Application Laid-Open No. 7-287264 (optical correlation detection circuit and optical clock phase locked loop circuit). This discloses a circuit configuration for extracting a timing clock having a frequency of an integer of the bit rate in synchronization with the optical signal from an ultrafast optical signal time-division multiplexed in the optical domain.
[0004]
An optical pulse time-division separation circuit that time-separates an optical signal of an arbitrary channel from an ultrahigh-speed optical signal has a configuration that uses an optical nonlinear phenomenon due to the interaction between an optical signal and a clock optical pulse synchronized with the channel. Are known. In this configuration, a light source that generates a clock light pulse having a predetermined delay amount for each channel to be selected using a phase shifter, an optical delay line, etc., an optical nonlinear processing unit, and an optical nonlinear processing unit generate an optical nonlinear phenomenon. There is a need for a high-power optical amplifier to obtain sufficient optical power.
[0005]
[Problems to be solved by the invention]
In the conventional configuration described above, the number of clock light pulses increases as the number of time-division-separated channels increases, and the configuration of the clock light pulse light source becomes complicated and the operation becomes unstable. That is, even if a predetermined delay amount is set for each of the plurality of clock light pulses, it is difficult to stably operate the plurality of optical nonlinear processing units thereafter, causing a problem of loss of synchronization. Therefore, it is not easy to input an ultrahigh-speed optical signal exceeding 100 Gbit / s and time-separate the optical signal of each channel using the optical nonlinear phenomenon.
[0006]
The present invention is not time-division-separated using an optical nonlinear phenomenon of an ultrafast optical signal and a clock optical pulse, but uses an optical modulator that can operate at a clock frequency less than half the bit rate of the ultrafast optical signal, An object of the present invention is to provide an optical signal processing apparatus capable of stably time-separating an ultrahigh-speed optical signal exceeding 100 Gbit / s into optical signals of respective channels. It is another object of the present invention to provide an optical signal processing apparatus that passes, branches, or inserts an optical signal time-division-separated by this configuration for each channel.
[0007]
[Means for Solving the Problems]
The optical signal processing apparatus according to the present invention includes an optical branching device, a timing extraction circuit, a clock generation unit, and an optical modulator corresponding to each channel. The timing extraction circuit inputs an ultrahigh-speed optical signal having a bit rate f obtained by time-division multiplexing optical signals of N channels (N is an integer of 2 or more) having a predetermined bit rate for each channel. A timing clock having a frequency f / k (k is a natural number) synchronized with the high-speed optical signal is output. The clock generation means distributes the timing clock of the frequency f / k given from the clock tracking means , multiplies each according to the bit rate of each channel, and the timing clock and the timing for phase adjustment in accordance with the phase of each channel Generate a clock. Each optical modulator is driven by a timing clock in accordance with the phase of each channel, and outputs the optical signal of each channel by time-division separation from the ultrahigh-speed optical signal distributed by the optical splitter.
[0008]
Also, the optical signal time-separated by an optical modulator driven by a timing clock output for phase adjustment from the clock generation means is converted into an electrical signal, and the frequency f output from the electrical signal and the timing extraction circuit A clock tracking unit is provided that compares the phase with the timing clock of / k and controls the phase of the timing clock so that they coincide with each other and supplies the phase to the clock generation unit .
[0009]
In addition to the above configuration, the optical signal processing device that passes, branches, or inserts the time-division-separated optical signal for each channel, in addition to the above-described configuration, A channel selection circuit that inputs an optical signal newly inserted for each channel, selects and outputs one of each channel, and gives a predetermined delay to the optical signal of each channel selected by the channel selection circuit , An optical delay control unit for exchanging time slots, a clock light source for outputting a clock optical pulse of frequency f synchronized with a timing clock of frequency f / k, and each channel output from the clock optical pulse and the optical delay control unit And a time-division multiplexing unit for outputting an ultrafast optical signal with a bit rate f that is time-division multiplexed.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 shows a first embodiment of the optical signal processing apparatus of the present invention. In this embodiment, it is assumed that a 40 Gbit / s optical signal is two-channel and a 20 Gbit / s optical signal is time-division multiplexed into two channels, and an ultrahigh-speed optical signal having a bit rate of 120 Gbit / s is input.
[0011]
In the figure, an ultrafast optical signal with a bit rate f (= 120 Gbit / s) is distributed by the optical branching device 11 to the timing extraction circuit 12 and the optical modulators 13-0 to 13-4. The timing extraction circuit 12 outputs a timing clock having a frequency f / k (k is a natural number, here k = 6, f / k = 20 GHz) synchronized with the ultrafast optical signal. This timing clock becomes a drive signal for each of the optical modulators 13-0 to 13-4 via the phase controller 14, the clock distributor 15, and the optical modulator drive circuit 16. In addition, a clock tracking unit is configured by the photodetector 17, the phase comparator 18, and the phase controller 14 that convert the output optical signal of the optical modulator 13-0 into an electrical signal.
[0012]
The phase controller 14 controls the phase of the timing clock according to the error signal output from the phase comparator 18. The clock distributor 15 distributes five phase-controlled timing clocks. The optical modulator driving circuit 16 multiplies each of the five distributed timing clocks according to the bit rate of each channel that is time-division multiplexed, and gives a predetermined delay so as to be synchronized with the phase of each channel. Further, the optical modulator is electrically amplified to a driveable level, a predetermined bias voltage is added, and the result is input to the optical modulators 13-0 to 13-4.
[0013]
Here, as shown in FIG. 2, the drive clocks of the optical modulators 13-0 to 13-4 are 20 GHz, 40 GHz, 40 GHz, 20 GHz, and 20 GHz, respectively, and further matched to the phase of the channel corresponding to each bit rate. Thus, the optical signals of each channel are time-division separated.
[0014]
The clock tracking means is provided as necessary for stable time division separation operation. The optical signal time-division-separated by the optical modulator 13-0 is converted into an electrical signal by the photodetector 17, and the phase of the electrical signal and the timing clock output from the timing extraction circuit 12 is compared by the phase comparator 18. The phase controller 14 controls the timing clock phase to the clock distributor 15 so that they match. That is, the clock tracking means compensates for the delay fluctuation that is received when the timing clock extracted by the timing extraction circuit 12 is distributed to each optical modulator. As a result, a stable optical modulator output can be obtained even if a delay fluctuation occurs in the distributed timing clock due to a change in the temperature inside the apparatus.
[0015]
In the above configuration, the optical modulators 13-1 to 13-4 are set by equalizing the optical signal delays from the input of the optical branching device 11 to the timing extraction circuit 12 and the optical modulators 13-0 to 13-4. Thus, the optical signal of each channel can be time-separated and separated. Furthermore, since the timing clock extracted by the timing extraction circuit 12 can compensate for the delay fluctuation that is received when the timing clock is distributed to each optical modulator 13 due to a change in the temperature in the apparatus, the optical modulator can be driven stably. it can. As a result, an ultrafast optical signal exceeding 100 Gbit / s can be time-division-separated into optical signals for each channel.
[0016]
(Second embodiment)
FIG. 3 shows a second embodiment of the optical signal processing apparatus of the present invention. In this embodiment, it is assumed that an optical signal of 20 Gbit / s is time-division multiplexed in 5 channels and an ultrahigh-speed optical signal having a bit rate of 100 Gbit / s is input.
[0017]
In the figure, an ultrafast optical signal with a bit rate f (= 100 Gbit / s) is distributed by the optical branching device 11 to the timing extraction circuit 12 and the optical modulators 13-0 to 13-5. The timing extraction circuit 12 outputs a timing clock having a frequency f / k (k is a natural number, here k = 5, f / k = 20 GHz) synchronized with the ultrafast optical signal. This timing clock becomes a drive signal for each of the optical modulators 13-0 to 13-4 via the phase controller 14, the clock distributor 15, and the optical modulator drive circuit 16. In addition, a clock tracking unit is configured by the photodetector 17, the phase comparator 18, and the phase controller 14 that convert the output optical signal of the optical modulator 13-0 into an electrical signal. The clock tracking means is the same as that in the first embodiment.
[0018]
The phase controller 14 controls the phase of the timing clock according to the error signal output from the phase comparator 18. The clock distributor 15 distributes seven phase-controlled timing clocks. The optical modulator driving circuit 16 gives a predetermined delay so as to be synchronized with the phase of each channel time-division multiplexed with respect to each timing clock, and further electrically amplifies the optical modulator to a level at which the optical modulator can be driven. A bias voltage is added and input to the optical modulators 13-0 to 13-5.
[0019]
The optical signals output from the optical modulators 13-1 to 13-5 are converted into electric signals of 20 Gbit / s by the photodetectors 17-1 to 17-5, respectively. That is, a 100 Gbit / s ultra high-speed optical signal is time-division-separated into 5 channels of 20 Gbit / s electrical signals. The 20 Gbit / s electrical signal of each channel is input to a time division separation circuit 19 driven by a timing clock output from the clock distributor 15 and further time-division-separated into 8 channels for each channel, for a total of 40 It is converted to a 2.5 Gbit / s electrical signal of the channel.
[0020]
(Third embodiment)
FIG. 4 shows a third embodiment of the optical signal processing apparatus of the present invention.
The feature of this embodiment is that a configuration for branching / inserting the optical signal of each channel that is time-division-separated by the optical modulators 13-1 to 13-4 is added to the configuration of the first embodiment. .
[0021]
The optical signals of the respective channels time-separated by the optical modulators 13-1 to 13-4 are input to the channel selection circuit 21 and pass as they are or branch to the branch port to replace the inserted signal input from the insertion port. Output as a signal. The passage signal or insertion signal of each channel output from the channel selection circuit 21 is input to the time division multiplexing unit 23 after the time slots between the channels are switched by the optical delay control unit 22. The time division multiplexing unit 23 is configured by an optical AND circuit (for example, a four-wave mixing circuit), and takes the AND of the clock light pulse output from the clock light source 24 and the passing signal or insertion signal of each channel, and the optical signal of each channel is obtained. Time division multiplexed output.
[0022]
The insertion signal of each channel input to the channel selection circuit 21 is synchronized with the timing clock output from the timing extraction circuit 12 by the delay control unit 25. The optical delay control unit 22 and the clock light source 24 also operate in synchronization with the same timing clock.
[0023]
The optical modulator 13-0, the photodetector 17, the phase comparator 18, and the phase controller 14 constituting the clock tracking means are the same as those in the first embodiment, and are provided as necessary.
[0024]
By the way, the values of the number of channels and the bit rate in each of the embodiments described above are examples, and the same applies even if other values are set. Further, as the optical modulator, an electroabsorption optical modulator having a high transmission optical signal characteristic with respect to a driving clock is suitable, but a known optical modulator such as an interference optical switch is also used. be able to. Moreover, as the optical branching device 11, an optical fiber coupler or a quartz optical waveguide can be used. The phase comparator 18 may be configured to compare the phases after converting each signal into a low-frequency signal by various known techniques.
[0025]
(Fourth embodiment)
FIG. 5 shows a fourth embodiment of the optical signal processing apparatus of the present invention.
The feature of this embodiment is that the optical modulator used in the timing extraction circuit 12 in the third embodiment and the optical modulator that time-separates the optical signal of each channel are shared. Also, the bit rate of the input ultrahigh-speed optical signal is 100 Gbit / s, and the optical signal of 10 Gbit / s is branched / inserted. In addition, it is assumed that the passing channel and the channel to be branched / inserted are different.
[0026]
The timing extraction circuit 12 includes a 40 GHz optical modulator 31, a photodetector 32, a mixer 33, a phase comparator 34, a 10 GHz VCO 35, and a multiplier (× 4) 36. The output signal of the 10 GHz VCO 35 is multiplied by 4 by the multiplier 36 to become a 40 GHz signal, and the 40 GHz optical modulator 31 is driven. An ultrahigh-speed optical signal with a bit rate of 100 Gbit / s is modulated by a 40 GHz optical modulator 31, and a 20 GHz component included in the output light (the optical modulation sideband beat component around the basic repetitive component) is detected by the photodetector 32. Is done. The 20 GHz signal output from the optical detector 32 is converted into a 10 GHz signal by the mixer 33, and the phase is compared with the output signal of the 10 GHz VCO 35 as a reference signal by the phase comparator 34. The phase comparator 34 feeds back the error signal to the 10 GHz VCO 35. With such a PLL configuration, a 10 GHz timing clock synchronized with the ultrafast optical signal can be obtained from the 10 GHz VCO 35.
[0027]
The 20 Gbit / s optical signal output from the 40 GHz optical modulator 31 is further input to the 10 GHz optical modulator 37 to obtain a 10 Gbit / s optical signal. As described above, the 40 GHz optical modulator 31 is used for time division separation of a 10 Gbit / s optical signal together with extraction of the timing clock.
[0028]
The 100 GHz clock light source 40 driven by the timing clock extracted by the channel selection circuit 38, the time division multiplexing unit 39, and the timing extraction circuit 12 is added to the channel selection circuit 21, the time division multiplexing unit 23, and the clock light source 24 in FIG. Correspond. Note that the optical delay control unit 22 in FIG. 4 is omitted. Further, the 10 Gbit / s insertion signal source 41 driven by the timing clock outputs an insertion signal synchronized with the timing clock in the same manner as the delay control unit 25 in FIG.
[0029]
【The invention's effect】
As described above, the optical signal processing device of the present invention includes a timing extraction circuit that outputs a timing clock whose frequency is an integral fraction of the bit rate in synchronization with an ultrafast optical signal, and a bit of the ultrafast optical signal. By using an optical modulator that can operate at a clock frequency less than half the rate, an ultrahigh-speed optical signal exceeding 100 Gbit / s can be stably time-separated into optical signals of each channel with a simple configuration. Further, the time-division-separated optical signal can be passed or branched / inserted for each channel, and the time slot can be switched between the channels.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of an optical signal processing device of the present invention.
FIG. 2 is a diagram showing a timing clock for driving each optical modulator in the first embodiment.
FIG. 3 is a block diagram showing a second embodiment of the optical signal processing device of the present invention.
FIG. 4 is a block diagram showing a third embodiment of the optical signal processing device of the present invention.
FIG. 5 is a block diagram showing a fourth embodiment of the optical signal processing apparatus of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Optical branching device 12 Timing extraction circuit 13 Optical modulator 14 Phase controller 15 Clock distributor 16 Optical modulator drive circuit 17 Photo detector 18 Phase comparator 19 Time division separation circuit 21 Channel selection circuit 22 Optical delay control unit 23 Division multiplexing unit 24 Clock light source 31 40 GHz optical modulator 32 Photo detector 33 Mixer 34 Phase comparator 35 10 GHz VCO (voltage controlled oscillator)
36 multiplier (× 4)
37 10 GHz optical modulator 38 Channel selection circuit 39 Time division multiplexing unit 40 100 GHz clock light source 41 10 Gbit / s insertion signal source

Claims (4)

An optical branching unit that inputs and distributes an ultrahigh-speed optical signal having a bit rate f by time-division multiplexing optical signals of N channels (N is an integer of 2 or more) having a predetermined bit rate for each channel;
A timing extraction circuit that inputs an ultrahigh-speed optical signal having a bit rate f distributed by the optical splitter and outputs a timing clock having a frequency f / k (k is a natural number) synchronized with the ultrahigh-speed optical signal;
A timing clock having a phase-controlled frequency f / k supplied from the clock tracking means is distributed, multiplied according to the bit rate of each channel, and a timing clock and a timing clock for phase adjustment in accordance with the phase of each channel Clock generating means for generating
An optical modulator driven by the timing clock for phase adjustment time-division-separates an optical signal of a predetermined channel from an ultrahigh-speed optical signal, converts the optical signal into an electrical signal, and the electrical signal and the timing extraction circuit is the phase compared with the timing clock of a frequency f / k output from said clock tracking means for controlling the phase of the timing clock so they match given to the clock generating means,
Corresponding to each channel, which is driven by a timing clock that matches the phase of each channel output from the clock generation means, and outputs the optical signal of each channel by time-division separation from the ultrafast optical signal distributed by the optical splitter With an optical modulator,
The optical signal processing apparatus, wherein the optical modulator is an electroabsorption optical modulator.   2. The optical signal processing apparatus according to claim 1, wherein each optical signal delay amount distributed from the optical splitter to the timing extraction circuit and each optical modulator is set equal.   2. The optical signal processing apparatus according to claim 1, wherein the bit rate f of the ultrahigh-speed optical signal is 100 Gbit / s or more and is at least twice the timing clock frequency for driving the optical modulator. In addition to the configuration of the optical signal processing device according to claim 1,
A channel selection circuit that inputs an optical signal of each channel that is time-division-separated by each optical modulator and an optical signal that is newly inserted for each channel, and selects and outputs one of each channel;
An optical delay control unit that gives a predetermined delay to the optical signal of each channel selected by the channel selection circuit, and performs switching of time slots;
A clock light source that outputs a clock light pulse of frequency f synchronized with the timing clock of frequency f / k;
A time-division multiplexing unit that ANDs the optical signal of each channel output from the optical pulse and the optical delay control unit and outputs an ultrahigh-speed optical signal with a bit rate f that is time-division multiplexed. An optical signal processing device.

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