JP5212411B2 - Optical signal reproducing apparatus and optical signal reproducing method - Google Patents

Description

  The present invention performs 3R reproduction by amplifying (Re-amplification) and shaping (Re-shaping) an optical pulse signal in which waveform distortion or phase variation occurs, and correcting (Re-timing) phase variation. The present invention relates to an optical signal reproducing device and an optical signal reproducing method.

  The rapid increase in communication capacity is expected to realize an optical transmission system exceeding 100Gbps. If the transmission speed exceeds 100 Gbps, transmission performance degradation due to optical fiber chromatic dispersion, polarization mode dispersion, nonlinear optical effect, SNR (Singnal to Noise Ratio) degradation, etc. will become more prominent. It becomes difficult to maintain the same transmission performance as a / 40Gbps class system.

  Non-Patent Document 1 as a related technology related to this has improved transmission quality of 160Gbps optical signals by introducing a non-linear optical loop mirror (NOLM) that uses the nonlinear effect of optical fiber An all-optical 3R regenerative repeater technique is disclosed.

Murai et al., “Field Demonstration Experiment of 160Gb / s All-Optical 3R Regenerative Repeater Transmission”, IEICE Technical Technique OCS2008-122, 2009-1

  The optical 3R regeneration method disclosed in Non-Patent Document 1 is a regenerative repeater technique that can also be applied to ultra-high-speed optical transmission exceeding 100 Gbps, but it is not as long as an EDFA (Erbium-doped Fiber Amplifier) or highly nonlinear fiber. Since many parts having a long waveguide are used, a timing shift (fluctuation) occurs between the optical pulse signal as input data and the clock signal extracted from the same optical pulse signal, and the reproduction operation becomes unstable. There is a problem. In particular, in order to realize 160 Gbps class ultra-high-speed optical transmission, it is necessary to adjust the timing with an accuracy of at least ± 1 ps, and even a slight timing fluctuation greatly affects the reproduction performance.

  The present invention has been made in order to solve the above-mentioned problems, and the same optical pulse as the optical pulse signal used as input data when 3R reproduction is performed on an optical pulse signal in which waveform distortion or phase variation occurs. It is an object of the present invention to reduce the influence of a timing shift with respect to a clock signal extracted from a signal.

In order to solve the above problems, the present invention generates a reproduced optical pulse signal by shaping and amplifying an input optical pulse signal in which waveform distortion or phase variation has occurred, and correcting the phase variation. An optical signal regeneration device or an optical signal regeneration method, comprising: control signal generation means for generating an optical control signal indicating ON / OFF of the input optical pulse signal; and an optical signal for generating an optical recovery clock signal having a predetermined pulse waveform A regenerative clock signal generating means; and an optical logic gate unit that inputs the optical control signal and the optical regenerated clock signal, generates and outputs the regenerated optical pulse signal that is a logical product of both , clock signal generating means is inputted to the optical logic gate inputs only optical control signal passed through the optical logic gate, the optical reproduction to the input optical control signal And wherein the synchronizing the lock signal.

  According to the present invention, when 3R reproduction is performed on an optical pulse signal in which waveform distortion or phase variation occurs, the timing between the optical pulse signal serving as input data and the clock signal extracted from the same optical pulse signal is changed. The influence of deviation can be reduced. Thereby, it is possible to improve the reproduction performance of the ultra-high speed optical transmission.

It is a schematic block diagram of the optical signal reproducing | regenerating apparatus based on this invention. It is explanatory drawing regarding operation | movement of the optical logic gate device based on this invention. It is explanatory drawing about the operation principle of the optical signal reproduction | regeneration method based on this invention. It is a schematic block diagram of the conventional optical signal reproduction | regeneration apparatus. It is explanatory drawing about the principle of operation of the conventional optical signal reproduction | regeneration method.

  DESCRIPTION OF EMBODIMENTS Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an example of an optical signal reproducing apparatus to which an optical signal reproducing method according to the present invention is applied. In the present embodiment, the optical signal regenerator 1 shown in FIG. 1 has an input signal (reproduced signal) having an optical pulse signal of RZ-OOK (Return to Zero-On Off Keying) with a wavelength of λs and a transmission rate of 160 Gbps. It is assumed that the signal) S1 is reproduced and the same 3R reproduction signal S4 as the original wavelength λs is output.

  As shown in FIG. 1, an optical signal reproducing apparatus 1 includes a wavelength converter 11 that shapes a pulse waveform of an input signal (reproduced signal) S1 and converts a wavelength to λc, and a nonlinear loop that operates as an optical logic gate unit. The main component includes a mirror (hereinafter, “NOLM”) 20 and an optical clock generation unit 21 that outputs a 160 GHz optical reproduction clock signal S3 for the reproduction signal S4 to the NOLM 20.

  On the other hand, the conventional optical signal regenerator 2 shown in FIG. 4 represents the schematic configuration of the all-optical 3R regenerative repeater disclosed in Non-Patent Document 1 using the same components as in FIG. Is. As can be seen by comparing FIG. 1 and FIG. 4, the greatest difference between the two is that the optical clock generators 21 and 22 that generate the 160 GHz optical recovery clock signal take in the signal that is the clock recovery source. That is, in the conventional optical signal regeneration device 2 (FIG. 4), the control signal S2 input to the NOLM 20 is branched and captured immediately before the optical coupler 18a, whereas the optical signal regeneration device 1 of the present embodiment. In FIG. 1, the output signal from the NOLM 20 output from the optical coupler 18b is taken in, and the component of the control signal S2 superimposed thereon is extracted. The difference between the two operations will be described later.

Here, first, the structure of the NOLM 20 common to both and the principle of operation as an optical logic gate unit will be described. The NOLM 20 is a two-input × two-output optical coupler 18b (first optical coupler) that is a polarization maintaining 3 dB coupler, and a long non-linear structure with both ends connected to the two output ports in a loop shape. An optical fiber 19 (for example, a highly nonlinear polarization-maintaining fiber having a length of 300 m, dispersion of 1.2 ps / nm / km, γ to 15 W ⁻¹ km ⁻¹ , propagation loss of 1.9 dB / km formed in a coil shape) This is a circuit of an all-optical system composed of a 2-input × 1-output optical coupler 18a (second optical coupler) which is another polarization maintaining coupler disposed in the middle of the loop.

The 160 GHz optical regenerative clock signal S3 having the same wavelength λs as that of the input signal S1 and having the same waveform as the regenerative signal S4 is incident on the input port P1 of the optical coupler 18b. The clock signal S3R and the counterclockwise clock signal S3L are divided into two (50:50) and propagate in the optical fiber 19 in opposite directions. When the two clock signals S3R and S3L arrive at the coupler 18b again and are combined, the component of the clock signal S3 is not normally emitted to the input port P2 due to interference between the two signals. Even when the phase of the counterclockwise clock signal S3L that becomes the coupled light of the optical coupler 18b is shifted by π / 2 with respect to the incident light, the light passes through the optical coupler 18b twice before reaching the input port P2. Thus, the influence of the phase change at the coupling portion is canceled out.

  On the other hand, when the control signal S2 having a large signal intensity having a wavelength λc different from the wavelength λs of the optical clock signal is incident from the other optical coupler 18a, the optical fiber 19 is refracted due to the high nonlinearity. A cross phase modulation (XPM) action in which the rate changes is induced, and the phase of the clock signal S3R propagating in the same direction as the control signal S2 changes. Using this property, the fiber length and signal strength are adjusted so that the phase of the clock signal S3R is shifted by exactly π when the control signal S2 is turned on. Thereby, there is no interference between the signals when the clockwise clock signal S3RS and the counterclockwise clock signal S3L resulting from the phase shift by π by the control signal S2 reach the coupler 18b again and are combined. Therefore, the optically regenerated clock signal resulting from the combination of both is emitted from the input port P2 of the optical coupler 18b.

  FIG. 2 is a schematic signal waveform diagram for explaining the switching operation of the optically regenerated clock signal S3 by the NOLM 20. In the figure, the broken line is the waveform of two clock signals that have propagated in opposite directions in the optical fiber 19 and arrived at the optical coupler 18b, and the solid line is the waveform of the signal emitted from the input port P2 of the optical coupler 18b. . The left part of FIG. 2 shows the state in which the clockwise clock signal S3R and the counterclockwise clock signal S3L are in phase and cancel each other out when the control signal S2 is OFF. It is represented by an anti-phase waveform imitating a vibration phenomenon (in-phase signals propagating in opposite directions are drawn on the upper and lower sides). Similarly, in the right part of FIG. 2, when the control signal S2 is ON, the clockwise clock signal S3RS whose phase is shifted by π and the counterclockwise clock signal S3L are in opposite phases. In this way, the signals are intensified with each other in the same phase waveform (the opposite phase signals are drawn overlapping each other).

  In this way, the NOLM 20 transmits the optical regenerative clock signal S3 incident on the input port P1 through the input port P2 and outputs it only when the control signal S2 is ON. That is, the NOLM 20 functions as an ultra-high speed optical AND gate that outputs a logical product value of the control signal S2 and the optical reproduction clock signal S3.

  The input signal S1 is, for example, a 160 Gbps RZ-OOK optical pulse signal having a wavelength λs of 1550 nm. The wavelength converter 11 is, for example, a Mamyshev type wavelength converter in which the basic configuration of an EDFA, a highly nonlinear dispersion flattening fiber, and a signal extraction wavelength filter is cascade-connected in two stages, and shaping the pulse waveform of the input signal S1 ( Re-shaping> and wavelength conversion to a wavelength λc (for example, 1541 nm) as a control signal S2 different from the wavelength λs, and the wavelength-converted signal is amplified by an optical amplifier 12a such as an EDFA. In addition, for example, only the wavelength components before and after λc are transmitted by the optical filter 13a which is an optical bandpass filter having a transmission band of 3.5 nm, and enters the NOLM 20 as the control signal S2 through the optical coupler 18a.

  This control signal S2 propagates clockwise in the optical fiber 19, and its signal component is emitted to the input port P1 of the optical coupler 18b. After being branched to the optical filter 13c side by the optical circulator 17, for example, the transmission band Only the wavelength component in the vicinity of the wavelength λc that has passed through the optical filter 13c, which is an optical bandpass filter with a wavelength of 3.5 nm, is extracted and input to the clock recovery circuit 14.

The clock recovery circuit 14 receives a 40 Gbps control signal from a 160 Gbps control signal by a synchronization circuit.
Are extracted and output to the mode-locked laser 15. The mode-locked laser 15 generates a reference optical pulse signal having a predetermined width (for example, 2 ps) modulated with the wavelength λs in synchronization with the input 40 GHz electric clock signal, and is amplified by the optical amplifier 12b. The signal is input to the time division multiplexing circuit 16.

  The time division multiplexing circuit 16 generates and outputs a 160 GHz optical pulse signal by bit multiplexing the input 40 GHz reference optical pulse signal (repeat the reference optical pulse signal four times at equal time intervals within the same period). The signal amplified by the optical amplifier 12c is incident on the NOLM 20 as the optical reproduction clock signal S3 via the optical circulator 17 and the optical coupler 18b.

  As described above, the output of the optical regenerative clock signal S3 incident on the input port P1 of the optical coupler 18b is ON / OFF controlled by the control signal S2 in which the same data as the input signal S1 is modulated. Thereafter, for example, only the wavelength component in the vicinity of the wavelength λs is extracted by the optical filter 13b which is an optical bandpass filter having a transmission band of 3.5 nm, and is output as the reproduction signal S4.

  FIG. 3 is an explanatory diagram of the operation principle of the optical signal reproduction method according to the present invention. In FIG. 3, (a) shows a control signal Us (t) in consideration of a relative time position change (Tw: walk-off time) with respect to the optical clock signal. This relative change in time position is caused by the propagation speeds of the control signal and the optical clock signal being different due to dispersion of the optical fiber, and Tw = D · Δλ · L. Here, D is the dispersion value of the optical fiber, Δλ is the wavelength detuning, and L is the optical fiber length. FIG. 3B shows a phase change profile (square integration of control signal) by XPM, and the phase change Δφ (maximum value: π) is a relative time position change: Tw and a pulse of the control signal Us (t). Determined by shape. FIG. 3C shows an optical clock signal in the same propagation direction as the control signal, and the phase change superimposed on the optical clock signal is proportional to the pulse energy of the control signal Us (t). Normally, the input timing of the control signal Us (t) to the optical fiber is adjusted so that the time position at the output of the optical fiber is symmetric with respect to the time center of the clock signal Uc (t) propagating in the same direction. For example, consider a case where the time for the control signal Us (t) to pass through the optical fiber is 3 ps later than the optical clock signal Uc (t), that is, Tw = 3 ps. At this time, if the control signal Us (t) is input by 1.5 ps (Tw / 2) before the optical clock signal Uc (t) at the input end of the optical fiber, the control signal Us is output at the optical fiber output end. (T) is output with a delay of 1.5 ps (Tw / 2) with respect to the optical clock signal Uc (t), and the relative time position relationship of FIGS. 3A and 3C is realized. In such a relationship, as shown in FIGS. 3B and 3C, the time center of the phase change profile induced by XPM using the control signal Us (t) as the pump light is the optical clock. It perfectly coincides with the time center of Uc (t), and ideal phase modulation is superimposed on the optical clock Uc (t). FIG. 3D shows a reproduction signal and is reproduced when the control signal Us (t) is on, that is, when the phase of the optical clock signal Uc (t) in FIG. 3C is shifted by π. The

  As shown in FIG. 1, the control signal S2 representing the data to be reproduced and the optical clock signal S3R have different incident paths. For this reason, in the control signal S2, the propagation time from the entrance of the NOLM 20 to the exit through the optical coupler 18a and the optical fiber 19 due to the influence of pressure change due to external temperature change, vibration, wind pressure, etc. Fluctuations, so-called timing fluctuations, occur. However, in the optical signal regeneration method according to the present embodiment, the signal that is the source of the optical regeneration clock that enters the NOLM 20 is captured from the control signal that has exited the NOLM 20, so that the timing fluctuation information of the control signal S2 is used as the optical regeneration clock. Provide feedback. As a result, a shift in relative time position between the optical reproduction clock S3R and the control signal S2 used for the switching operation can be reduced, and the reproduction performance can be improved.

  On the other hand, the operation principle of the conventional optical signal reproduction method will be described with reference to FIG. If there is a similar timing fluctuation in the control signal Us (t) from the entrance of the NOLM 20 to the exit via the optical coupler 18a and the optical fiber 19, in the conventional optical signal regeneration method, the NOLM 20 Since the signal that is the source of the optical regenerative clock incident on the signal is taken in from the entrance side before passing through the waveguide (NOLM 20), the timing fluctuation information is not fed back to the optical regenerative clock S3R. For this reason, as shown in FIGS. 5A and 5C, a timing shift occurs between the generated optical regenerated clock S3R and the control signal Us (t) used for the switching operation. The phase change profile by XPM is also shifted by ΔT from the optimum timing as shown in FIG. Due to this influence, the phase change superimposed on the optical reproduction clock S3R becomes smaller than π, and the probability that the signal intensity of the reproduction signal Uc (t) decreases and a signal reproduction error occurs as shown in FIG. Becomes larger.

  Therefore, according to the optical signal regeneration method according to the present invention, since the optical regeneration clock is extracted from the control signal propagated through the highly nonlinear fiber, the input signal passes through the optical coupler 18a and the optical fiber 19 from the entrance of the NOLM 20, similar to the input signal. Thus, it is possible to absorb the influence of the timing fluctuation caused by the external environment change or the like that occurs until the exit is reached. As a result, it is possible to reduce the timing shift between the control signal and the optical reproduction clock.

  The embodiments of the present invention are not limited to these, and various modifications can be made without departing from the spirit of the present invention. For example, in this embodiment, the NOLM is used as the optical logic gate unit, but other optical gate elements such as a polarization separation switch including a polarization beam splitter may be used.

1, 2 Optical signal regeneration device 11 Wavelength converter (control signal generating means)
12a, 12b, 12c Optical amplifiers 13a, 13b, 13c Optical filter 14 Clock recovery circuit (clock extraction means)
15 Mode-locked laser (reference light pulse signal generating means)
16 Time division multiplexing circuit (time division multiplexing means)
17 Optical circulator 18a Optical coupler (second optical coupler)
18b Optical coupler (first optical coupler)
19 Optical fiber (nonlinear optical fiber)
20 Nonlinear Loop Mirror (NOLM) (Optical Logic Gate)
21 and 22 Optical clock generator (optical regenerative clock signal generator)
P1, P2 input port S1 input signal (input optical pulse signal)
S2 Control signal (light control signal)
S3 optical reproduction clock signal S3R, S3L clock signal S4 reproduction signal

Claims (10)

An optical signal reproduction device that generates a reproduction optical pulse signal by shaping and amplifying an input optical pulse signal in which waveform distortion or phase variation has occurred, and correcting the phase variation,
Control signal generating means for generating an optical control signal indicating ON / OFF of the input optical pulse signal;
Optical regenerative clock signal generating means for generating an optical regenerated clock signal having a predetermined pulse waveform ;
An optical logic gate unit that inputs the optical control signal and the optical regenerative clock signal, generates and outputs the regenerative optical pulse signal that is a logical product of both , and
The optical reproduced clock signal generating means is inputted to the optical logic gate inputs only optical control signal passed through the optical logic gate, the optical reproduced clock signal to the input optical control signal An optical signal reproducing device that is synchronized. 2. The regenerated optical pulse signal is a signal generated by cross-phase modulation between the optical regenerated clock signal generated by the optical regenerated clock signal generation means and the passed optical control signal. 2. An optical signal reproducing device according to 1. The optical logic gate unit is:
The optical regenerative clock signal incident on the first input end is branched and emitted to the two output ends with equal intensity, and the regenerated optical pulse signal is output to the second input end. A first optical coupler with two outputs;
A nonlinear optical fiber having both ends connected in a loop to the two output ends of the first optical coupler;
The nonlinear loop mirror provided with the 2nd optical coupler which is installed in the middle of the nonlinear optical fiber, and multiplexes and enters the optical control signal. Optical signal reproducing device. The wavelength of the optical regenerative clock signal is the same as the wavelength of the input optical pulse signal,
The wavelength of the optical control signal is a wavelength separated from the optical regenerated clock signal by an optical bandpass filter,
4. The optical signal regeneration apparatus according to claim 3, wherein the optical regeneration clock signal is generated based on at least a signal incident by the second optical coupler. The optical regenerative clock signal generation means further extracts a clock signal having a frequency of 1 / N of the clock frequency from the optical control signal;
Reference optical pulse signal generation means for generating a reference optical pulse signal having the 1 / N frequency from the 1 / N frequency clock signal;
The time division multiplexing means for generating the optical regenerative pulse signal having the clock frequency by repeating the reference optical pulse signal N times at equal time intervals within the same period. Item 4. The optical signal regeneration device according to any one of Items 3 to 3. An optical signal reproduction method for generating a reproduction optical pulse signal by shaping and amplifying an input optical pulse signal in which waveform distortion or phase variation has occurred, and correcting the phase variation,
A control signal generation step of generating an optical control signal indicating ON / OFF of the input optical pulse signal;
An optical regenerated clock signal generating step for generating an optical regenerated clock signal having a predetermined pulse waveform ;
A reproduction optical pulse signal generation step of inputting the optical control signal and the optical reproduction clock signal, and generating and outputting the reproduction optical pulse signal, which is a logical product of the two , by an optical logic gate unit;
In the optical reproduced clock signal generation step, it is input to the optical logic gate inputs only optical control signals transmitted through the optical logic gate, the optical reproduced clock signal to the input optical control signal A method for reproducing an optical signal, comprising synchronizing the signals. 7. The reproduction optical pulse signal is a signal generated by cross-phase modulation between the optical reproduction clock signal generated by the optical reproduction clock signal generation unit and the optical control signal. Optical signal regeneration method. The optical logic gate unit is:
The optical regenerative clock signal incident on the first input end is branched and emitted to the two output ends with equal intensity, and the regenerated optical pulse signal is output to the second input end. A first optical coupler with two outputs;
A nonlinear optical fiber having both ends connected in a loop to the two output ends of the first optical coupler;
8. The optical signal regeneration method according to claim 6, wherein the optical signal regeneration method is a nonlinear loop mirror including a second optical coupler that multiplexes and enters the optical control signal into the nonlinear optical fiber. The wavelength of the optical regenerative clock signal is the same as the wavelength of the input optical pulse signal,
The wavelength of the optical control signal is a wavelength separated from the optical regenerated clock signal by an optical bandpass filter,
9. The optical signal reproduction method according to claim 8, wherein the optical reproduction clock signal is generated based on at least a signal incident by the second optical coupler. The optical reproduction clock signal generation step further includes a clock extraction step of extracting a clock signal having a frequency of 1 / N of the clock frequency from the optical control signal;
A reference optical pulse signal generation step for generating a reference optical pulse signal having the 1 / N frequency from the 1 / N frequency clock signal;
7. A time division multiplexing step of generating the optical regenerative pulse signal having the clock frequency by repeating the reference optical pulse signal N times at equal time intervals within the same period. Item 10. The optical signal regeneration method according to any one of Items 9 to 9.

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