JPH0818539A - Optical time division multiplex signal separation system - Google Patents

Abstract

PURPOSE:To obtain the small sized optical DEMUX system capable of high speed operation without polarized wave dependency in the ultrahigh speed optical transmission system employing the optical time division multiplex technology. CONSTITUTION:A signal light subjected to time division multiplex and an output light of a clock light source 100 generating a periodic short pulse are synthesized and inputted to a semiconductor optical amplifier 101 and then an optical interferrometer 102 whose delay time is tau. Cross phase modulation (XPM) is caused in a signal light by a clock light in the semiconductor optical amplifier and the optical interferrometer 102 is used to convert the light into an intensity modulation signal. Since only a high speed phase modulation component is converted into an intensity modulation signal by a delay time tau (<1/Rb), high speed switching not limited by a carrier life is attained and the effect of the fluctuation of the polarized state of the signal light is not caused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical multiplex signal demultiplexing system (DEMUX) used in optical time division multiplexing (OTDM) transmission which is one of ultra high speed optical transmission systems.

[0002]

2. Description of the Related Art The transmission speed of optical fiber transmission has been steadily increasing year by year, and now a 10 Gbit / s optical transmission system is about to be put into practical use. However, it is expected that it will be extremely difficult to cope with the conventional technology in ultra-high speed transmission of 40 Gbit / s due to the limitation of the band of the electric circuit. 2. Description of the Related Art In recent years, studies on a method for realizing a large capacity transmission of 40 to 100 Gbit / s without increasing the speed of an electric circuit by using an optical time division multiplexing (OTDM) technique have been actively studied.
In this method, an optical time division multiplex signal demultiplexing (DEMUX) circuit is used to separate the transmitted ultra high speed optical signal into a low speed optical signal and receive the signal. For example, a high-speed optical switch can be used to cut out every fourth pulse from a 40 Gbit / s optical pulse train to convert it into a 10 Gbit / s optical signal. Since all such separation operations are performed in the light region, the operating speed of the electric circuit is 40-1 even at about 10 Gbit / s.
Large-capacity optical transmission such as 00 Gbit / s is possible.

Optical DEMU used in optical time division multiplexing transmission
As the X circuit, a method utilizing a nonlinear optical effect in a semiconductor optical amplifier or an optical fiber is being studied. Optical DEM
The UX circuit is an optical AND circuit that controls on / off of output of signal light by turning on / off of clock light. Examples of such optical circuits include, for example, Optical Amplifiers and Their Applications Technical Digest, Vol. 14 (1993), 356 to 359, (Optical Amplifiers and Their Applicati
ons Technical Digest, Vol. 14, (Optical Society
of America, Washington DC, 1993.), pp356-359.) shows an example in which an optical AND circuit is realized by an optical loop mirror configuration. FIG. 2 shows the optical DEMUX in the above conventional example.
It is the figure which showed the structure of the circuit.

Signal light and clock light are input to the optical loop mirror 200. The signal light is intensity-modulated light having a transmission rate Rb, and the clock light is a short optical pulse whose repetition period is Rb. Is used. Both lights are optical coupler 201
Is branched into two paths 202 and 203 and input to the semiconductor amplifier 204. The gain and the refractive index in the semiconductor amplifier 204 change according to the waveform of the clock light, and amplitude and phase modulation occur in the signal light incident at the same time. Of these, the phenomenon in which the phase is modulated is called cross phase modulation (XPM). When the clock light is set to be branched only to the path 202, or the intensity of the clock light input to the optical amplifier 204 through the path 202 is set to be higher than when it is passed through the path 203. If so, it is possible to generate XPM only in the signal light traveling counterclockwise in the figure. FIG. 3 shows a state of XPM of the signal light when the signal light is unmodulated light. (1) is the waveform of the clock light, and XPM as shown in (2) occurs in the counterclockwise signal light. This signal light is again combined with the clockwise signal light at the optical coupler 201, so that the loop mirror 20
From 0, signal light output corresponding to XPM can be obtained as shown in FIG. 3 (3) due to light interference. Only the wavelength component of the signal light is extracted by the optical filter 205, and this is extracted by the optical receiver 20.
It is possible to operate as an optical DEMUX by receiving the signal via the optical receiver 6.

[0005]

However, the XPM in the semiconductor optical amplifier has a component having a very fast response time of less than a time constant of several ps and a time constant of 100 ps corresponding to the carrier lifetime in the semiconductor optical amplifier. Components with slow response are mixed. Therefore, the phase change caused by XPM is shown in FIG.
As shown by the dotted line in (2), a slow response component is included. In the conventional optical DEMUX system, optical switching is realized by interfering the light thus phase-modulated with the original signal light, so that the optical switching speed is a nonlinear effect with a slow time constant due to carrier transition. There are problems such as limitation and deterioration of the extinction characteristic of the optical DEMUX. Further, it is very difficult to integrate the loop mirror and the like on a semiconductor substrate.

In addition to this, XPM and Kerr in the optical fiber
An optical DEMUX system using the effect, four-wave mixing, and four-wave mixing in a semiconductor amplifier has been proposed. In these methods, the above-mentioned limitation of the switching speed is relatively insignificant, but there is a problem that the intensity of the output light largely changes depending on the polarization state of the signal light. A method of reducing the polarization dependence by a technology such as polarization diversity has been proposed, but it has problems such as a complicated configuration and difficulty in integration.

An object of the present invention is to solve the above problems, to provide a high-speed switching speed, a high extinction ratio, no polarization dependence, and a simple structure and easy integration.
To provide a method. Another object of the present invention is to provide an optical DEMUX system in which stable operation can be obtained in consideration of phase fluctuation and wavelength fluctuation of signal light, which are problems in constructing an actual system.

[0008]

The above-mentioned problem is caused by a semiconductor optical amplifier to which two lights, that is, a signal light having a transmission rate Rb and a clock light that is a short optical pulse train (repetition frequency: an integer fraction of Rb) are input. After passing the output signal light through the optical interferometer, by receiving with the optical receiver, more specifically, the optical transmittance of the optical interferometer becomes the minimum at the signal light wavelength,
Moreover, the peak intensity of the clock light input to the semiconductor optical amplifier is set to be at least twice the peak intensity of the signal light, and the delay amount τ of the optical interferometer is set to 1 / Rb or less, The signal light output from the semiconductor optical amplifier is preferably passed through an optical interferometer and then received by an optical receiver, particularly preferably by using a Mach-Zehnder type optical interferometer as the optical interferometer.

Furthermore, an optical filter set to transmit the signal light and block the clock light is used to pass the signal light output from the semiconductor optical amplifier through both the optical filter and the optical interferometer. It is possible to achieve this more effectively by receiving the signal light and the clock light into the semiconductor optical amplifier from the directions opposite to each other by receiving them by the optical receiver.

Further, it can be effectively achieved by using the signal light whose phase modulation amount is reduced in advance by using the phase modulation reducing means as the input light of this time division multiplexing signal separation system.

Furthermore, the feedback circuit adjusts the phase difference between the signal light and the clock light so that the optical signal intensity input to the optical receiver becomes maximum, or the optical signal output from the semiconductor optical amplifier. This can be effectively solved by adjusting the phase difference between the signal light and the clock light by the feedback circuit so that the intensity becomes minimum.

Furthermore, the problem can be solved more effectively by adjusting the optical path difference of the optical interferometer by the feedback circuit so that the component of the repetition frequency Rb of the signal light contained in the output light of the optical interferometer becomes maximum. It becomes possible.

[0013]

The signal light output from the semiconductor optical amplifier, to which the signal light of the transmission rate Rb and the clock light of the short optical pulse train (repetition frequency: an integer fraction of Rb) are input, passes through the optical interferometer. By doing so, the phase modulation component generated by XPM can be converted into the intensity modulation component. Since the signal light interferes with itself delayed by the delay amount τ, the output light appears only when the phase change occurs faster than the delay amount τ. If the delay amount is less than a few tens of ps, the carrier lifetime
Almost no output light appears for a phase change with a slow time constant of about several hundred ps. When the semiconductor amplifier is polarization independent, the amount of XPM induced in the signal light does not depend on the polarization state of the signal light, and the polarization independent optical DEMUX can be realized.

Further, light of different wavelengths is used for the clock light and the signal light, and the light transmittance of the optical interferometer becomes minimum when the clock light is not incident and the light of the signal light is interfered when the clock light is incident. Set so that the light transmittance of the meter is maximized. In this way, a positive logic operation in which the output of the optical interferometer for the signal light is turned on / off according to the on / off of the clock light is obtained.

In the optical DEMUX of the present invention, when the intensity of the signal light input to the semiconductor optical amplifier becomes large, a phenomenon called self-phase modulation (SPM) in which the signal light itself undergoes phase modulation due to the intensity change of the signal light itself. Occurs. SPM
Optical DEMUX even when the clock light is off when
Since the signal light is output from the light source, the light becomes crosstalk light, which deteriorates the performance of the optical DEMUX. To prevent this,
It is necessary to make the intensity of SPM smaller than the intensity of XPM (phase modulation caused by clock light) described above. To reduce the amount of crosstalk light below the signal strength, set the SPM strength to XP
Below the reciprocal of the multiplex of the time division signal for the intensity of M,
That is, at least 1/2 or less (in the case of an optical DEMUX that separates two multiplexed optical signals). To do this,
The peak intensity of the clock light input to the semiconductor optical amplifier may be twice or more the peak intensity of the signal light. By setting the intensity of the signal light in this way, the problem of signal distortion depending on the pattern of the signal light and the fluctuation of the mark rate can be reduced.

The output of the optical DEMUX of the present invention is shown in FIG.
As shown in (4), since there are two optical pulses with a time difference of the delay amount τ of the optical delay line 105, the optical switching time has the same width as the delay amount τ. Therefore, by setting the delay amount τ of the optical interferometer to be 1 / Rb or less, the optical switching time is approximately 1 / Rb or less, and the optical DEMUX operation can be realized.

The optical DEMUX of the present invention is shown in FIG.
Since it has the influence of the slow phase modulation component indicated by the dotted line, the time at which the XPM caused by the clock light, that is, the rise time of the clock light (about 1/2 of the clock light pulse width) is the delay amount τ of the optical delay line 105. When the length is longer than that of, the output light intensity of the optical DEMUX decreases. About 3 dB
Assuming that the decrease in the efficiency of 1 is allowed, by setting the pulse width of the clock light to be 4 times or less of the delay amount τ,
It is possible to prevent a decrease in output intensity of the optical DEMUX.

When the signal light and the clock light are incident on the optical receiver at the same time, the clock light acts as noise, which may deteriorate the characteristics of the optical receiver. However, since the clock light and the signal light have different wavelengths, and the interference conditions of the optical interferometer are set to be optimal for the signal light wavelength, the interference conditions are not correct at the wavelength of the clock light. , The clock light is weakened and output. Furthermore, the following method is effective for thoroughly removing the clock light. That is, using an optical filter set to transmit the signal light and block the clock light, the signal light output from the semiconductor optical amplifier is passed through both the optical filter and the optical interferometer, and then the optical receiver. The clock light leaking into the signal light can be removed by receiving at. The same effect can be obtained by disposing the optical filter immediately before the optical interferometer. Moreover, the clock light input to the receiver is removed by inputting the signal light and the clock light into the semiconductor optical amplifier from opposite directions.

Further, in the optical DEMUX system of the present invention, when the input signal light has a phase modulation component faster than the delay amount τ of the optical delay line, the output light may appear even if the clock light is not input. is there. Such a phase modulation component is the frequency chirp that the signal light has from the beginning,
It can be caused by the dispersion of the optical fiber used for transmission. In such a case, a narrow band optical filter,
The optical D of the present invention is obtained by compensating the phase modulation of the signal light in advance by using the phase modulation reducing means using an optical fiber or the like.
The EMUX can operate normally.

Further, even if the input signal has phase fluctuation, the operation of the optical DEMUX can be stabilized by providing the control circuit so that the relative phase difference with the clock light is always constant. For this purpose, the phase difference between the signal light and the clock light is adjusted so that the optical signal strength input to the optical receiver is maximized, or the optical signal strength output from the semiconductor optical amplifier is minimized. A feedback circuit that adjusts the phase difference between the signal light and the clock light so that the phases of the clock light and the signal light can always be in the optimum state.

In addition, even when the input signal has wavelength fluctuation or the wavelength of the signal light cannot be varied, the optical signal included in the output light of the optical interferometer has the maximum optical signal intensity. The operating point of the optical interferometer can always be optimized by adjusting the optical path difference of the interferometer.

[0022]

FIG. 1 is a block diagram showing a first embodiment of the present invention. Two lights, Rb signal light, which is intensity-modulated light modulated with an information signal of transmission rate Rb, and clock light, whose repetition frequency is a fraction of Rb, are incident on the semiconductor optical amplifier 101. The clock light is a control signal for controlling the operation of the optical DEMUX. The output from the semiconductor optical amplifier 101 is supplied to one optical path 104 by the optical delay line 10 having a delay amount τ.
After branching into the two optical paths (103 and 104) having 5 and passing through the optical interferometer 102 which combines again, it is received by the optical receiver 107. In the semiconductor optical amplifier 101, the signal light has a cross phase modulation (XP) proportional to the intensity of the clock light.
M) is induced. When the peak light intensity of the clock light is sufficiently higher than the peak light intensity of the signal light, the gain of the semiconductor optical amplifier 101 and the phase modulation effect by the signal light itself can be ignored because they are small. The signal light that has passed through the semiconductor optical amplifier 101 is input to the optical interferometer 102, and the phase modulation component is converted into intensity modulation.

The operating principle of the present invention will be described with reference to the timing charts of clock light and signal light shown in FIGS. FIG. 4 (1) shows the light intensity of the clock light, and FIG. 4 (2) (3)
Shows the phase of the optical signals in the two optical paths 103 and 104 of the optical interferometer 102. In FIG. 4, the input signal light is considered to be continuous light (CW light) in order to show the operation principle. Since the path 104 includes the optical delay line 105 having the delay time τ, the output light is delayed by τ in time. Optical interferometer 1
02 is set so that the transmittance is minimized by adjusting the wavelength of the signal light when the clock light is not input. That is, at the wavelength of the signal light, the optical paths 103 and 104
The difference in the optical path lengths is exactly (integer + 1/2) times the wavelength. Therefore, when the clock light is input, the output light as shown in FIG. 4 (4) is obtained from the optical interferometer 102.
That is, since the optical signal on which XPM is applied interferes with itself delayed by τ, a large optical output can be obtained in a portion where the phase change is faster than τ, and the pulse width of the output signal is the delay time τ. It is about the same width. Even when there is a slow cross-phase modulation component corresponding to the carrier life shown by the dotted line in FIGS. 4 (2) and (3), the phase modulation component slower than the delay time τ is canceled and the response time of several ps or less Optical switching can be realized. Since the influence of XPM caused by the clock light must not be canceled, the rise / fall time of the clock light pulse needs to be about the same as or shorter than τ.

In the present method, when an amplifier having no gain polarization dependency is used as the semiconductor optical amplifier 101, the amount of XPM induced in the signal light does not depend on the polarization state of the signal light, so that in principle. A polarization-independent optical DEMUX can be realized.

Even when the signal light is an intensity-modulated optical pulse train at the transmission rate Rb, if the pulse width of the clock light is narrower than the pulse width of the signal light, optical switching can be performed according to the same principle as described above. . The embodiment of FIG. 1 was experimentally verified under the following operating conditions. Repeat frequency 10G
Using a clock light with a Hz pulse width of about 10 ps, the delay time of the optical delay line 105 is set to 5 ps and the semiconductor optical amplifier (gain 1
The optical switching operation (switching time 10 ps) was confirmed with the signal light intensity input to 6 dB) at 0.05 mW and the clock light intensity at 0.4 mW.
Further, as the signal light, a signal light of 20 Gbit / s in which an optical pulse having a pulse width of 25 ps is multiplexed is used, and
The DEMUX operation to s was confirmed.

FIG. 5 shows the signal light (1), the clock light (2), and the DEM.
The state of UX output light (3) is shown. Since only the signal light incident at the same time as the clock light is obtained as the DEMUX output light, the repetition frequency is, for example, 10 GHz as the clock light.
By using an optical pulse train with z and a pulse width of about 10 ps, an optical DEMUX that separates a signal of 10 GHz from a signal light of 40 to 100 GHz can be realized.

Pulse width of output light of the optical DEMUX of the present invention
The window width of the optical switch is about the same as the delay time τ of the optical delay line 105. Therefore, in an optical transmission system of 40 to 100 Gbit / s, the delay time of the optical delay line 105 needs to be about 20 to 5 ps, and this length is about 4 to 1 in glass, for example.
mm. Optical interferometer 102 having such a delay amount
Is a size that can be easily realized by using a glass waveguide or a semiconductor optical waveguide. The optical interferometer having the shape of the optical interferometer 102 shown in FIG. 1 is sometimes called a Mach-Zehnder type optical interferometer. It has been reported that the Mach-Zehnder type optical interferometer is manufactured by integrating it with a semiconductor optical amplifier and an optical waveguide. In this respect, the Mach-Zehnder interferometer is one of the most suitable interferometers for the present invention. However, in order to satisfy the function of branching into two optical paths having an optical delay line with a delay amount τ in one optical path and combining them again to cause interference.
The same effect can be obtained by using an optical interferometer called by other names such as Michelson and Fabry-Perot.

Further, by making the peak intensity of the clock light input to the semiconductor optical amplifier 102 sufficiently larger than the peak intensity of the signal light, the semiconductor optical amplifier 1 is also provided.
By making the intensity of the signal light input into the optical signal 02 smaller than the saturated light input intensity of the semiconductor optical amplifier, it is possible to suppress the fluctuation of the output light intensity (pattern effect) due to the fluctuation of the mark rate of the signal light.

If necessary, an optical amplifier such as an optical fiber amplifier can be inserted at an arbitrary position such as in front of the semiconductor optical amplifier 101 or after the optical interferometer 102. Further, the method of the present invention can be applied regardless of whether the signal light modulation method is RZ or NRZ.

FIGS. 6 and 7 show the second and third embodiments of the present invention, and show a method of removing the clock light which becomes the noise of the receiver.

In the second embodiment of FIG. 6, in order to remove the clock light entering the receiver, an optical filter 106 having a characteristic of blocking the clock light wavelength and transmitting the signal light wavelength is provided immediately after the optical interferometer 102. To insert. The optical filter 106
Can be inserted just before the optical interferometer 102 to obtain the same effect.

In the third embodiment of the present invention shown in FIG. 7, since the clock light output from the clock light source 100 is input to the semiconductor optical amplifier 101 from the opposite direction to the signal light, the clock light is incident on the optical receiver. Without using the optical filter, the clock light can be blocked. The embodiment shown in FIG. 6 or 7 can be used in combination with the embodiment described below.

FIG. 8 shows a fourth embodiment of the present invention, which shows a method of compensating for a phase modulation component with respect to a signal light containing a phase modulation component from the beginning. Optical DEMU of the present invention
In the X method, when the input signal light has a phase modulation component that is earlier than the delay amount τ of the optical delay line 105, the output light may appear even if the clock light is not input. Such a phase modulation component may be generated due to the frequency chirp which the signal light originally has or dispersion of the optical fiber used for transmission. Such signal light may be input to the semiconductor optical amplifier after passing through the phase modulation reducing means 108. As the phase modulation reducing means 108, for example, an optical filter having a transmission band narrower than the signal light can be used. It can also be realized by a dispersive medium such as a dispersion compensating fiber, an optical dispersion fiber, a normal dispersion fiber, or an optical grating. It can also be realized by means such as pulse compression using the soliton effect in the optical fiber. In general, any method can be applied as long as it reduces the phase modulation amount of the optical pulse and brings it closer to the transform limit. Furthermore, it is possible to combine and use some of these means. This embodiment can be used in combination with the embodiments described below.

FIG. 9 and FIG. 10 show the fifth and sixth embodiments of the present invention. Even when the input signal has phase fluctuation, the relative phase difference with the clock light is always constant and stable light is obtained. A method of ensuring DEMUX operation is shown.

In the fifth embodiment of FIG. 9, control is performed by utilizing the fact that the output of the optical interferometer 102 becomes maximum when the phase relationship between the signal light and the clock light is optimum. The output from the optical interferometer 102 is branched into two, a first output and a second output,
The first output is received by the optical receiver 107. On the other hand, the second output is detected by the photodetector 109 and is detected by the photodetector 109 by feeding back the detected signal to the phase modulation means 111 through which the clock light 100 passes through the control circuit 110. The phase of the clock light is adjusted so that the signal strength becomes maximum. The photodetector 109 measures the average intensity of light,
The control circuit 110 controls the phase adjusting means 111 so that this value becomes maximum. As a result, even if there is a phase fluctuation of the signal light, a feedback that always provides the optimum phase is applied, and a stable DEMUX operation can be obtained. In this embodiment, the phase adjusting means 111 can be realized by, for example, a variable delay device that changes the length of an optical fiber or the like by using electricity or heat. A well-known phase modulator using a material such as lithium niobate, a GaAs semiconductor, an InP semiconductor, or the like may be used. In addition to this, it can be realized by changing the phase of the signal light or changing the oscillation frequency of the clock light source. It is also possible to perform control so that the frequency component of the repetition frequency Rb included in the signal light in the output of the photodetector 109 becomes maximum.

In the sixth embodiment of FIG. 10, the gain saturation reduction of the semiconductor optical amplifier 102 is utilized, and when the phase relationship between the signal light and the clock light is optimized, the semiconductor optical amplifier 102 is used.
The control is performed based on the fact that the output signal strength of the is minimized. The output from the semiconductor optical amplifier 101 is split into a first output and a second output, and the first output is passed through an optical interferometer 102 and then received by an optical receiver 107. On the other hand, the second output is detected by the photodetector 109, and the detected signal is fed back to the phase modulation means 111, so that the phase of the clock light is minimized so that the signal intensity detected by the photodetector 109 is minimized. Adjust. It is also possible to perform control so that the frequency component of the repetition frequency Rb included in the signal light in the output of the photodetector 109 becomes maximum.
The same phase adjusting means as in the fifth embodiment can be used.

FIG. 11 shows the seventh embodiment of the present invention. In the first to sixth embodiments, the interference condition of the optical interferometer is adjusted by the wavelength of the incident signal light. Interferometer 1
In this example, the wavelength variable of the signal light is made unnecessary by introducing the variable optical delay line 112 that adjusts the interference condition in 02. Further, the present embodiment is effective in that the optical DEMUX can be stably operated even when the wavelength of the incident signal light fluctuates with time. The present invention controls on the basis of the same operating principle as the fifth embodiment shown in FIG. The output of the optical interferometer 102 is split into a first output and a second output, and the first output is received by the optical receiver 107. on the other hand,
The second output is incident on the photodetector 109, and the detected signal is returned to the optical variable delay line 112, whereby the photodetector 10
The delay amount of the optical variable delay line 112 is adjusted so that the frequency component of the repetition frequency Rb included in the signal light detected in 9 becomes the maximum. Due to the function of the variable optical delay line in the optical interferometer 102, the optimum interference condition can be obtained without adjusting the wavelength of the signal light. Further, the operation of the feedback circuit enables stable operation even when the signal light has wavelength fluctuation. In the present example, the control circuit 110 realizes this object by changing the length of the variable optical delay line 112. The maximum delay variation required for the variable optical delay line 112 is about one wavelength. This can be easily achieved by changing the temperature of the optical path of the interferometer, or by injecting current or applying voltage to a medium such as semiconductor or glass. Optical variable delay line 112
The same effect can be achieved even if the phase changing means 111 is changed to that of the fifth embodiment of FIG. It is also possible to perform this control simultaneously with the control shown in the fifth and sixth embodiments.

FIG. 12 shows an eighth embodiment of the present invention, which is an optical signal for separating a multiplexed transmission optical signal formed by multiplexing N optical signals of transmission rate Rb1 into N electrical signals of transmission rate Rb1. DE
It shows the overall configuration of the MUX. When returning the multiplexed transmission optical signal formed by multiplexing N optical signals at the transmission speed Rb1, the incoming signal light is divided into N by using the 1: N optical branch 113, and FIG. Unit optical DEMUX 114 of any one of FIG. 6, FIG. 8, FIG. 8, FIG. 9, FIG. 10, and FIG.
It is possible to separate into N electrical signals of transmission rate Rb1 by using N. The unit light DEMUX 114 in the drawing shows the second embodiment of FIG. 6 as an example. In this embodiment, the phase modulation reducing means 108 can be shared by a plurality of optical DEMUXs. Also, the clock light source 100
In addition to the configuration in which one optical DEMUX is arranged for each optical DEMUX as shown in the figure, a configuration in which a single clock light source 100 is distributed by using a 1: N optical branch and a necessary delay line is added to each is also considered. .

[0039]

INDUSTRIAL APPLICABILITY XPM in a polarization-independent semiconductor optical amplifier
Can be used, an optical DEMUX that does not depend on the polarization state of the signal light can be realized. Also, the delay amount τ of the interferometer
Since it is not affected by the slower phase change, there is an effect that high-speed switching can be realized.

Further, there is an effect that positive logic operation is possible.

Further, the peak intensity of the clock light input to the semiconductor optical amplifier is set to be twice or more the peak intensity of the signal light, so that the signal light itself phase-modulates itself. There is an effect that the effect of modulation can be suppressed and the extinction ratio of output light can be increased. Further, there is an effect that it is possible to reduce the intensity change of the output light and the extinction ratio deterioration which are caused by the pattern of the signal light and the fluctuation of the mark rate.

Further, by setting the delay amount τ of the optical interferometer to 1 / Rb or less, the optical switching time can be suppressed to about 1 / Rb or less, so that the extinction ratio of the output light is increased and crosstalk is reduced. There is.

Further, by using a Mach-Zehnder type optical interferometer as the optical interferometer, the structure of the interferometer is simplified and miniaturized, and the multiple reflection occurring in the interferometer is suppressed and the extinction ratio of the output light is increased. There is an effect that can be.

Further, by using an optical filter set to transmit the signal light and block the clock light, the signal light output from the semiconductor optical amplifier is passed through both the optical filter and the optical interferometer, and then the optical signal is transmitted. By receiving at the receiver,
The leakage of clock light can be effectively suppressed, and it is effective in preventing the characteristic deterioration of the optical receiver.

The same effect can be obtained when the signal light and the clock light are input to the semiconductor optical amplifier from opposite directions.

Further, by further reducing the phase modulation amount of the signal light by using the phase modulation reducing means, the method of the present invention can be applied even when the signal light has a large phase modulation component from the beginning. There is.

Furthermore, by adjusting the phase difference between the signal light and the clock light so that the optical signal strength input to the optical receiver becomes maximum, or the optical signal strength output from the semiconductor optical amplifier is adjusted. By adjusting the phase difference between the signal light and the clock light so that the signal light and the clock light are minimized, a stable optical DEMUX can be provided even when there is phase fluctuation in the signal light.

Further, by adjusting the optical path difference of the optical interferometer so that the intensity of the repetition frequency Rb frequency component contained in the signal light contained in the output light of the optical interferometer is maximized, the wavelength fluctuation of the signal light is adjusted. Stable optical DEM even when there is
UX can provide. This method is also useful in that the wavelength control of the signal light for operating the optical DEMUX becomes unnecessary.

[Brief description of drawings]

FIG. 1 is a first embodiment of the present invention, an optical DEMUX of the present invention.
It is a block diagram which shows.

FIG. 2 is a configuration diagram showing a conventional optical DEMUX.

FIG. 3 is an explanatory diagram of an optical switching operation of a conventional optical DEMUX.

FIG. 4 is an explanatory diagram of an optical switching operation of the optical DEMUX of the present invention.

FIG. 5 is an explanatory diagram of an optical DEMUX operation of the present invention.

FIG. 6 is a configuration diagram of a second embodiment of the present invention, a clock light elimination system using an optical filter.

FIG. 7 is a configuration diagram of a third embodiment of the present invention, which is a clock light removal system by counter incidence of clock light and signal light.

FIG. 8 is a configuration diagram of a system for compensating a phase modulation component of signal light having a phase modulation component in advance according to a fourth embodiment of the present invention.

FIG. 9 is a configuration diagram of a relative phase stabilization system for signal light and clock light by a feedback circuit according to a fifth embodiment of the present invention.

FIG. 10 is a configuration diagram of a relative phase stabilization system for signal light and clock light by a feedback circuit according to a sixth embodiment of the present invention.

FIG. 11 is a configuration diagram of a method for stabilizing the operation of the optical interferometer by the feedback circuit according to the seventh embodiment of the present invention.

FIG. 12 is an overall configuration diagram of an optical DEMAUX according to an eighth embodiment of the present invention.

[Explanation of symbols]

100 ... Clock light, 101 ... Semiconductor optical amplifier, 102 ... Optical interferometer, 103, 104 ... Optical path, 105 ... Optical delay line, 106 ... Optical filter, 107 ... Optical Receiver, 108 ... Phase modulation reducing means, 10
9 ... Photodetector, 110 ... Control circuit, 111 ... Phase changing means,
112 ... Optical variable delay line, 113 ... 1 to N optical branch, 114 ... Unit optical DEMUX, 200 ... Optical loop mirror, 201 ... Optical coupler, 20
2, 203 ... Optical path, 204 ... Semiconductor optical amplifier, 205 ... Optical filter, 206 ... Optical receiver.

Claims (13)

[Claims] 1. At least two lights, a signal light having a transmission rate Rb and a clock light having a repetition frequency that is a fraction of the integer Rb, are incident on a semiconductor optical amplifier, and an output from the semiconductor optical amplifier is generated, An optical time division multiplexed signal characterized by being branched by two optical paths having an optical delay line with a delay amount τ in one optical path, passed through an optical interferometer which combines again, and then received by an optical receiver. Separation method. 2. The wavelength of the signal light that minimizes the light transmittance of the optical interferometer is selected, and the peak intensity of the clock light input to the semiconductor optical amplifier is the peak intensity of the signal light. The delay amount τ of the optical interferometer is set to be approximately twice or more, the reciprocal number of the Rb or less, and the pulse width of the clock light is approximately four times or less of the delay amount τ. The optical time division multiplex signal demultiplexing method according to claim 1, wherein 3. A semiconductor optical amplifier is provided with at least two lights, a signal light having a transmission rate Rb and a clock light having a repetition frequency that is a fraction of Rb that has passed through a phase varying means having a control terminal. After passing the output from the semiconductor optical amplifier through an optical interferometer which branches into two optical paths having an optical delay line with a delay amount τ in one optical path and combines again.
A first output and a second output are branched into two, the first output is received by an optical receiver, the second output is detected by a photodetector, and the detected signal is phase-varied. The optical time division multiplex signal separation system, wherein the phase of the clock light is adjusted so that the signal intensity detected by the photodetector is maximized by returning to the means. 4. The wavelength of the signal light that minimizes the light transmittance of the optical interferometer is selected, and the peak intensity of the clock light input to the semiconductor optical amplifier is the peak intensity of the signal light. The delay amount τ of the optical interferometer is set to be approximately twice or more, the reciprocal number of the Rb or less, and the pulse width of the clock light is approximately four times or less of the delay amount τ. The optical time division multiplexing signal separation system according to claim 3, wherein 5. At least two signals, a signal light having a transmission rate Rb and a clock light having a repetition frequency that is a fraction of Rb and passed through a phase varying means having a control terminal, are incident on a semiconductor optical amplifier. , The output from the semiconductor optical amplifier is branched into two outputs, a first output and a second output,
Output is passed through an optical interferometer that splits into two optical paths having an optical delay line with a delay amount τ in one optical path and is then multiplexed again, and then received by an optical receiver. The phase of the clock light is adjusted so that the signal intensity detected by the photodetector is returned to the phase modulation means, and the signal intensity detected by the photodetector is minimized. Optical time division multiplexing signal separation method. 6. The wavelength of the signal light that minimizes the light transmittance of the optical interferometer is selected, and the peak intensity of the clock light input to the semiconductor optical amplifier is the peak intensity of the signal light. The delay amount τ of the optical interferometer is set to be approximately twice or more, the reciprocal number of the Rb or less, and the pulse width of the clock light is approximately four times or less of the delay amount τ. The optical time division multiplexing signal demultiplexing system according to claim 5, wherein 7. At least two lights, a signal light having a transmission rate Rb and a clock light having a repetition frequency that is a fraction of the integer Rb, are incident on a semiconductor optical amplifier, and an output from the semiconductor optical amplifier is generated. After branching into two optical paths having an optical variable delay line with variable delay amount in one optical path and passing them through an optical interferometer that combines again, it is branched into two of a first output and a second output. Then, the first output is received by the optical receiver, the second output is incident on the photodetector, and the detected signal is fed back to the optical variable delay line to be detected by the photodetector. An optical time division multiplexing signal separation system, wherein the delay amount of the optical variable delay line is adjusted so that the intensity of the repetitive frequency component Rb contained in the signal light becomes maximum. 8. The peak intensity of the clock light input to the semiconductor optical amplifier is approximately twice or more the peak intensity of the signal light, and the delay amount τ of the optical interferometer.
9. The optical time division multiplex signal demultiplexing method according to claim 7, wherein is set to be less than or equal to the reciprocal of Rb, and the pulse width of the clock light is approximately four times or less than the delay amount τ. 9. An optical filter according to claim 1, further comprising an optical filter inserted immediately before or after the optical interferometer, the optical filter transmitting the signal light and blocking the clock light. Time division multiplex signal separation method. 10. The optical time division multiplex signal demultiplexing system according to claim 1, wherein the signal light and the clock light are input to the semiconductor optical amplifier in directions opposite to each other. . 11. The optical time division multiplexing signal demultiplexing system according to claim 1, wherein a signal light which has passed through a phase modulation reducing means in advance is used as the signal light. 12. The optical time division multiplex signal demultiplexing system according to claim 1, wherein a semiconductor optical amplifier whose gain does not depend on an incident optical polarization is used as said semiconductor optical amplifier. 13. When returning a multiplexed transmission optical signal produced by multiplexing N optical signals of a transmission rate Rb1, the multiplexed transmission optical signal is divided into N using a 1: N optical branch. Then, claim 1
N to 12 optical time division multiplexing signal demultiplexing devices using the optical time division multiplexing signal demultiplexing method described in any one of
An optical time division multiplexing signal demultiplexing method characterized by demultiplexing into electrical signals of a book transmission rate Rb1.