JPH0843865A - All light reproducing repeater - Google Patents

Abstract

PURPOSE:To realize an all light reproducing repeater which is not required to have a function to adjust an optical path length. CONSTITUTION:This all light reproducing repeater has a second ring 12 which is coupled to a first ring 11 via a coupler 7 to couple the light signal to be reproduced polarized to a first plane of polarization in one direction and to branch and couple the light signal polarized to a second plane of polarization orthogonal with the first plane of polarization to two directions and is forwed with the polarization maintaining optical wave guide and amplifiers 4, 5 which amplify the light signal propagating therein to one direction. The overall length L of the first and second rings is set at L=mcT (m is a positive integer, c is a light velocity and T is the period of the pulse signals coming at a light input terminal). The two rings are so set as to form a mode synchronized laser for the light signals of the period T by the light signals alternately propagating these two rings. The repeater is provided with an orthogonal polarization wave generator 8 which converts the energy of a part of the light clock signals which are the outputs of the amplifiers to the energy of second plane of polarization and a nonlinear optical element 6 on the light input terminal 1 side by a distance DELTAL from the point M equidistant from the coupler. The light signals generated by interference of the output light thereof and the light signal to be reproduced in the coupler are branched to the output terminal by a polarization beam splitter 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for pulse regenerative repeating of an optical transmission line. The present invention relates to a regenerative repeater for amplifying, retiming and outputting a blunted optical pulse that arrives via a transmission line.

[0002]

2. Description of the Related Art When an intensity-modulated optical signal is transmitted through an optical fiber transmission line, the waveform and S / N ratio of the optical signal deteriorate due to dispersion and loss of the optical fiber. Therefore, after converting the optical signal to an electrical signal using the optical repeater and identifying the electrical signal by the clock obtained by the timing extraction circuit,
It is converted into an optical signal again and regenerated and relayed. However, in this method, the transmission speed of the optical signal is limited by the operation speed of the optical / electrical, electric / optical conversion circuit, timing extraction circuit or identification circuit.

Therefore, in order to break the operating speed limit of the electric circuit, an attempt to realize a regenerative repeater function of an ultrahigh-speed optical signal in the optical region, that is, an all-optical regenerative repeater has been proposed.
(M.Jinno et al, "Nonlinear operations of 1.55mm wav
elength multielectrode distributed-feedback laser
diodes and their applications for optical signal pr
ocessing ", IEEE J. Lightwave Technol, 10, pp.448-457 (1
992), JKLucek et al, "All-optical signal regenera
tor ", Nonlinear guided-wave phenomena, TuD3 (1993)).
This conventional example will be described with reference to FIG. FIG. 5 is a block diagram of a conventional device. The optical pulse signal is divided into two, one of them is input to the optical clock generator 20, and the other is guided to the optical switch circuit 30 (optical AND circuit). The optical clock generator 20 has a self-oscillating DFB (Distributed feedbac).
k) -LD (Laser diode) and mode-locked fiber ring laser are used. Injection of one of the two divided optical signals into these pulse-operated lasers causes injection locking, and the generated optical pulse is synchronized with the average repetition cycle of the incident optical signal, and the optical clock signal is converted from the optical signal. Can be extracted. The extracted optical clock signal is modulated by the optical switch circuit 30 controlled by the other divided optical pulse signal. As such an optical switch circuit, a bistable DFB-LD or a nonlinear loop mirror is used. By using such an all-optical regenerative repeater, it is possible to regenerate an optical signal whose waveform has been deteriorated due to dispersion of an optical fiber and reduce jitter included in the optical signal.

[0004]

However, in order to properly operate these all-optical regenerative repeaters, an optical delay device or other optical path adjusters are used for the timing of the optical signal and the optical clock signal before entering the optical switch. Need to be adjusted with high accuracy. Assuming a transmission speed of about 100 Gb / s, the optical path length must be adjusted with a precision of a fraction of 2 mm (corresponding to one time slot). Furthermore, since the optical path length easily changes due to temperature or mechanical vibration, the optical path length adjuster requires highly accurate automatic control, which is a drawback of all-optical regenerative repeaters proposed so far. .

The present invention has been made against such a background, and an object thereof is to provide an all-optical regenerative repeater which does not require an optical path length adjusting function.

[0006]

In the conventionally proposed all-optical regenerative repeater, an optical clock signal and an optical signal are independently supplied to an optical switch. Therefore, the timings of both are controlled by an optical path length adjuster. It had to be adjusted with high precision. The present invention proposes a method of constructing an all-optical regenerative repeater in which an optical clock generator and an optical switch are integrated, thereby eliminating the optical path length adjusting function and solving the drawbacks of the conventional all-optical regenerative repeater. It is characterized by

The present invention is an all-optical regenerative repeater, which is characterized by an optical input terminal (1) to which a reproduced optical signal polarized on the first polarization plane is input, and the first polarization plane. A first ring (11) formed by a polarization-maintaining optical waveguide to which a to-be-reproduced optical signal that is polarized is coupled, and a to-be-reproduced light that is polarized in the first plane of polarization by this first ring. Formed by a polarization-maintaining optical waveguide in which signals are coupled in one direction and optical signals polarized in a second polarization plane orthogonal to the first polarization plane are coupled through a coupler (7) that branches and couples in two directions. The second ring (12) and an amplifier (4, 5) provided in the second ring and amplifying an optical signal propagating in the second ring in one direction. The total length L of the ring (11) and the second ring (12) is L = mcT (where m is Positive integer, c is the speed of light, T is the period of the pulse signals arriving to the optical input terminal), the two rings by an optical signal propagating through the two rings are alternately period T
Is set to be a mode-locked laser for the optical signal of, and a part of the energy of the optical clock signal as the output optical signal of the amplifier provided in the second ring is converted into the energy of the second polarization plane. Orthogonal polarization generator (8)
And a nonlinear optical element (6) provided in the first ring (11) on the optical input terminal side by a distance ΔL from a point equidistant from the coupler (7), the nonlinear optical element A polarization beam splitter for branching the optical signal generated by the interference of the output light of (6) and the optical signal input from the optical input terminal in the coupler (7) from the second ring to the output terminal (10). This is where (3) is provided.

Instead of the first ring and the combiner, a Mach-Zehnder interferometer is coupled to the second ring, a non-linear optical element is inserted in two loop paths of the Mach-Zehnder interferometer, and one end of the Mach-Zehnder interferometer is inserted. Can also be configured as an optical input terminal.

Alternatively, the MQW semiconductor crystal may be inserted into one loop path of the Mach-Zehnder interferometer.

[0010]

Operation: The reproduced optical signal polarized in the first polarization plane is input from the optical input terminal. The first ring is formed by a polarization-maintaining optical waveguide to which the reproduced optical signal polarized in the first polarization plane is coupled, and the first ring is polarized in the first polarization plane. The reproduction optical signal is coupled in one direction, and the optical signal polarized in the second polarization plane orthogonal to this first polarization plane is formed by the polarization maintaining optical waveguide through a coupler that splits and couples in two directions. Combined with the second ring. The amplifier in this second ring amplifies the optical signal in one direction. The total length L of the first ring and the second ring is L = mcT (where m is a positive integer, c is the speed of light, and T is the period of the pulse signal arriving at the optical input terminal). These two rings have a period T due to an optical signal propagating alternately in
The orthogonal polarization generator, which is set up to be a mode-locked laser for the optical signal in the second ring and is provided in the second ring, outputs a part of the energy of the optical clock signal as the output optical signal of the amplifier to the second polarization. Convert to wavefront energy. The nonlinear optical element in the first ring is provided on the optical input terminal side by a distance ΔL from the point of equidistant from the coupler, and the output light of the nonlinear optical element and the optical signal input from the optical input terminal are coupled. And generate an optical signal. This optical signal is branched from the second ring to the output terminal by the polarization beam splitter.

Instead of the first ring and the combiner, a Mach-Zehnder interferometer is coupled to the second ring, a non-linear optical element is inserted in two loop paths of the Mach-Zehnder interferometer, and one end of the Mach-Zehnder interferometer is inserted. Can also be an optical input terminal.

An MQW semiconductor crystal may be inserted in one loop path of this Mach-Zehnder interferometer.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram of the first embodiment of the present invention.

The present invention is an all-optical regenerative repeater, which is characterized by an optical input terminal into which a regenerated optical signal polarized in the TE polarization (horizontal polarization) which is the first polarization plane is input. 1
And a ring 11 formed by a polarization maintaining optical waveguide to which the reproduced optical signal polarized in the TE polarization plane is coupled,
The reproduced optical signal polarized in the TE polarization plane is coupled to the ring 11 in one direction and is polarized in the TM polarization (vertical polarization) which is the second polarization plane orthogonal to the TE polarization plane. A ring 12 formed by a polarization-maintaining optical waveguide that is coupled via a coupler 7 that branches and couples in two directions, and the ring 12
An optical isolator 4 and an optical amplifier 5 as an amplifier for amplifying an optical signal propagating in the ring 12 in one direction, and the total length L of the ring 11 and the ring 12 is L = mcT (however, m is a positive integer, c is the speed of light, T is the period of the pulse signal arriving at the optical input terminal), these two rings 1
The two rings 11 and 12 are set so as to be mode-locked lasers for the optical signal of the period T by the optical signals propagating alternately in 1 and 12, and are provided in the ring 12 as output optical signals of the optical amplifier 5. The orthogonal polarization generator 8 for converting a part of the energy of the optical clock signal into the energy of the TM polarization plane is provided in the ring 11 on the optical input terminal 1 side by a distance ΔL from the point equidistant from the coupler 7. The optical signal generated by the interference between the output light of the nonlinear optical element 6 and the optical signal input from the optical input terminal 1 in the coupler 7 is branched from the ring 12 to the optical output terminal 10. It is provided with a wave beam splitter 3.

First, the principle of the present invention will be described with reference to FIG. FIG. 2 is a diagram for explaining the principle of the present invention.
Polarizations perpendicular and horizontal to the paper are TM and TE respectively.
Defined as polarized wave. Further, this optical system is composed of a polarization maintaining fiber (a PANDA fiber is assumed here). The configuration and operation of the present invention will be described below. The branching ratio of the coupler 7, which is the polarization maintaining optical fiber coupler at the point B in FIG. 2, is such that for TE polarization, almost 100% of the optical signal is coupled to ports 4 to 1 and ports 3 to 2,
The light from the port a is coupled to the port c and the port d in almost one-to-one relation to the M polarization, and the ports a and b of the coupler 7 and the ports c and d are coupled by the polarization maintaining fiber. , Two rings 11 and 12 are configured, and the optical filter 2, the polarization beam splitter 3 (PBS), the optical isolator 4, and the optical amplifier 5 are inserted in the ring 11. The polarization plane of the polarization beam splitter 3 is adjusted so that the TM polarization becomes the ring 12.
Further, a cross polarization generator 8 in which the main axes of the polarization maintaining fibers are tilted and connected is provided at one location A of the ring 12 so as to be taken out. In addition, in the ring 11,
A nonlinear optical element 6 whose refractive index changes depending on the light intensity is inserted at a position displaced from the center M by ΔL. In addition, the total optical path length L of the two rings 11 and 12 with respect to the TE polarization is mcT with respect to the average repetition period T of the optical signal.
Adjust so that However, m is a positive integer and c is the speed of light in the polarization maintaining fiber.

When such an optical system is constructed, the present optical system operates as a mode-locked laser synchronized with the input optical pulse signal for the TE polarized wave, but for the TM polarized wave, as shown in FIG. The part surrounded by a square operates as an optical switch that opens and closes with an input optical pulse signal. The detailed operation will be described below.

First, attention will be paid to the TE polarization. The TE polarization is determined by setting the split ratio of the coupler 7 to the two ring 1
Propagate 1 and 12 in the shape of figure 8. Therefore, these two rings 11 and 12 act as an optical resonator for the TE polarized light. The TE-polarized optical pulse signal externally input to the nonlinear optical element 6 in the ring 11 induces a nonlinear refractive index change in the nonlinear optical element. Therefore, the light propagating through the two rings 11 and 12 as TE polarized waves undergoes phase modulation. Moreover, since the length L of the optical resonator and the average repetition period T of the optical signal have a relationship of L = mcT,
FM mode synchronization synchronized with the repetition cycle of the optical pulse signal is applied, and an optical pulse with a repetition cycle T is generated as TE polarized light, which propagates as two optical clock signals in the two rings 11 and 12 in a figure eight shape. become. Further, the center wavelength of the optical clock signal is adjusted by the optical filter 2 so as to be substantially equal to that of the optical pulse signal.
The above mode-locked oscillation for the TE polarized wave can also be realized by coupling the branching ratio of the coupler 7 to the TE polarized waves at almost 100% from the ports a to c and from the ports d to b.

The TE-polarized optical clock signal generated in this manner is partially converted into TM-polarized light by the orthogonal polarization generator 8 at the point A of the ring 12, and is surrounded by a square in FIG. Incident on the ring 11. As described above, according to the set value of the branching ratio of the coupler 7, the loop surrounded by the square has a TOAD (Terahertz Optical Asy
mmetric Demultiplexer) (JPSokoloff et al, "A terah
ertz optical asymmetric demultiplexer (TOAD) ", IEEE
It operates as an optical switch called Photon.Technol.Lett, 5, pp, 787-790 (1993)).

The operation of TOAD will be described below. The TM polarization component of the optical clock signal that has entered the loop of TOAD from the port a of the coupler 7 is equally divided into right and left and propagates through the ring 11. Here, the counterclockwise optical clock signal is synchronized with the optical pulse signal and enters the nonlinear optical element 6 (TW-LDA) at the same time as the optical pulse signal. This counterclockwise optical clock signal receives a change in the refractive index due to the optical nonlinear effect of the nonlinear optical element 6 induced in proportion to the rise time of the optical pulse signal (the fastest rise time is up to ps),
This counterclockwise optical clock signal (TM polarized wave) undergoes a phase change. On the other hand, the optical clock signal propagating clockwise in the ring 11 is 2ΔL /
Since it passes through the non-linear optical element 6 in time earlier by c,
It is not subject to refractive index changes due to optical nonlinear effects caused by optical pulse signals. For this reason, a phase difference occurs between the two-direction optical clock signals, and if the peak power of the optical pulse signal is adjusted so that this phase difference becomes 180 degrees, the optical clock signal in the portion that temporally overlaps with the optical pulse signal becomes The light is interfered by the coupler 7 and is emitted from the port b on the side opposite to the port a on which the optical clock signal is incident.

By the way, since the change in the refractive index induced by the optical pulse signal is proportional to the change in the carrier density in the nonlinear optical element 6, this change in the refractive index is determined by the carrier lifetime even after the fall of the optical pulse signal ( Τc as a typical value
= 100 to 300 ps), it is necessary to set the repetition period of the optical pulse signal to be larger than τc. Both bidirectional optical clock signals that are incident on the nonlinear optical element 6 after the optical pulse signal undergo a transient refractive index change determined by τc, but the bidirectional time difference 2Δ
If L / c is sufficiently smaller than τc, the changes in the refractive index in both directions are almost the same. Therefore, the optical clock signal is emitted from the port a on which the optical clock signal is incident. Needless to say, the two-way optical clock signal that has entered the nonlinear optical element 6 before the optical pulse signal in time does not undergo a change in the refractive index due to the nonlinear effect in the nonlinear optical element 6, so the optical clock signal is incident. The light is emitted from the port a. Therefore, only the optical clock signal existing within the time determined by 2ΔL / c after the optical pulse signal is incident on the nonlinear optical element 6 is emitted from the port b on the side opposite to the port a on which the optical clock signal is incident. Becomes Therefore, the TOAD operates as an optical switch having a gate width of 2ΔL / c controlled by the optical pulse signal. The intensity of the optical clock signal is sufficiently smaller than that of the optical pulse signal, and the change in the refractive index of the nonlinear optical element due to the optical clock signal is negligible.

As described above, the T of the optical clock signal is
The M polarization component is modulated by TOAD controlled by an optical pulse signal, and then taken out of the ring 12 via the polarization beam splitter 3. That is, the polarization beam splitter 3 outputs an optical clock signal corresponding to the optical pulse signal. That is, an optical pulse signal from which the jitter of the optical pulse signal is removed can be obtained.

The first embodiment of the present invention shown in FIG. 1 is realized by directly using the principle diagram shown in FIG. 2 as an embodiment. However, a traveling wave type semiconductor laser amplifier (TW-LDA) is used as the nonlinear optical element 6, and the optical amplifier 5
As a polarization maintaining rare earth doped fiber 51 and a multiplexer 5
2. The excitation light source 53 was used. Moreover, it is also possible to use TW-LDA instead of the optical amplifier 5. further,
If MQW (Multiple Quantum Well) semiconductor crystal is used instead of TW-LDA, τc is improved and an ultrafast optical pulse signal can be reproduced.

Although the TOAD is used as the optical switch in the first embodiment of the present invention, the TW-LD which is a non-linear optical element is used.
A so-called NOLM in which A is replaced with a polarization maintaining optical fiber
(Nonlinear Loop Mirror) (K.Uchiyama et al, "100Gb / s
all-optical demultiplexing using nonlinear optica
l loop mirror with gating-width control ", Electron.
Lett, 29, pp, 1870-1871 (1993)) can also be used. In the NOLM, the change in the refractive index due to the optical nonlinear effect of the polarization maintaining optical fiber induced by the optical pulse signal propagating in the NOLM in one direction gives a phase difference to the bidirectional CW light. Optical switch operation is realized. By using an optical fiber for the non-linear optical element, τc is improved and an ultrafast optical pulse signal can be reproduced.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a block diagram of the second embodiment of the present invention. The second embodiment of the present invention uses traveling wave type semiconductor laser amplifiers 61 and 62 (TW-LDA) as nonlinear optical elements, and the couplers 43 and 44 are polarization maintaining optical fiber couplers. The ring 12 is similar to that of the first embodiment of the present invention.
Also, in this optical system, the part surrounded by a square is a part that operates as an optical switch (K. Tajima et al, "Experimenta
l verification of novel symmetric-Mach-Zehnder typ
e all-optical switch ", International workshop on fe
mtosecond technology, pp.49-50 (1994)), this switch is composed of a Mach-Zehnder interferometer. Traveling wave type semiconductor laser amplifiers 61 and 6 are provided in each arm of the interferometer.
As two, two TW-LDAs are arranged with a shift of ΔL (= L1, L2).

The branching ratio of the coupler 43 is set so that 100% optical signals are coupled to the ports a to b and the ports d to c for the TE polarized wave and operate as a 3 dB coupler for the TM polarized wave. To do. Similarly, with respect to the branching ratio of the coupler 44, almost 100% of the optical signals are coupled to the ports a ′ to b ′ and the ports d ′ to c ′ for the TE polarization, and as a 3 dB coupler for the TM polarization. Set it to work. The TE polarization component of the optical pulse signal enters the interferometer including the traveling wave type semiconductor laser amplifier 61 via the port d ′ of the coupler 44 and the port c ′. The optical pulse signal propagates in both the arm in which the traveling wave type semiconductor laser amplifier 61 is inserted and the arm in which the traveling wave type semiconductor laser amplifier 62 is inserted due to the branching ratio of the coupler 44, and the traveling wave type semiconductor laser amplifier is transmitted. A nonlinear refractive index change is induced in 61 and 62. The TE polarization propagating clockwise in the ring 12 passes only through the traveling wave type semiconductor laser amplifier 62 in the interferometer. Therefore, the TE polarized wave propagating clockwise in the ring 12 is subjected to phase modulation by the traveling wave type semiconductor laser amplifier 62 by the optical pulse signal. Moreover, when the relationship between the optical resonator length L and the average repetition period T of the optical signal is set to L = mcT, F synchronized with the repetition period of the optical pulse signal is obtained.
The M-mode synchronization is applied, and the optical clock signal synchronized with the repetition period of the optical pulse signal propagates clockwise in the ring 12. Further, the center wavelength of the optical clock signal is adjusted by the optical filter 2 so as to be substantially equal to that of the optical pulse signal.

The optical clock signal generated in this way is partially converted into TM polarized light by the orthogonal polarization generator 8 provided at the point A in the ring 12, and is surrounded by a square in FIG. Incident on the interferometer. From the branching ratio of the couplers 43 and 44, the optical system surrounded by a square in FIG. 3 operates as a Mach-Zehnder interferometer for the TM polarization component of the optical clock signal, and becomes an optical switch controlled by the optical pulse signal. .

The operation will be described below. The optical pulse signal which is the TE polarized wave is output from the coupler 4 by the branching ratio of the coupler 44.
It is divided into two by 4 and enters the ring 12 and the interferometer including the traveling wave type semiconductor laser amplifier 61. Since the optical clock signal (TE component) propagating clockwise in the ring 12 is synchronized with the optical pulse signal, it enters the traveling wave type semiconductor laser amplifier 62 at the same time as the optical pulse signal, so that the optical pulse signal rises. Proportional to time (fastest rise time is ~ ps)
The induced refractive index change of the traveling wave type semiconductor laser amplifier 62 is caused by the optical nonlinear effect. On the other hand, with respect to the optical clock signal incident on the traveling wave type semiconductor laser amplifier 61, the traveling wave type semiconductor laser amplifier is temporally preceded by ΔL / c with respect to the optical pulse incident on the traveling wave type semiconductor laser amplifier 62. Since it passes through 61, it does not undergo a refractive index change due to the optical nonlinear effect caused by the optical pulse signal. For this reason, a phase difference occurs between the two optical pulses, and if the peak power of the TM polarization component of the optical pulse signal is adjusted so that this phase difference becomes 180 degrees, the light in the portion that temporally overlaps the optical pulse signal The clock signal interferes with the coupler 44 and exits from the port b '.

By the way, since the change in the refractive index induced by the optical pulse signal is proportional to the change in the carrier density in the traveling wave type semiconductor laser amplifiers 61 and 62, this change in the refractive index occurs even after the optical pulse signal falls. Since it lasts for a time determined by the life (typically τc = 100 to 300 ps), it is necessary to set the repetition period of the optical pulse signal larger than τc. Both optical clock signals that have entered the traveling-wave type semiconductor laser amplifiers 61 and 62 temporally after the optical pulse signal undergo a transient refractive index change determined by τc, but the time difference ΔL / c is greater than τc. If it is sufficiently small, the changes in the refractive index of both optical clock signals are almost the same. Therefore, after interference at the coupler 44, the optical clock signal is emitted from the port d '. Needless to say,
Since the optical clock signal that has entered the traveling wave type semiconductor laser amplifiers 61 and 62 temporally earlier than the optical pulse signal does not undergo the refractive index change due to the optical nonlinear effect in the traveling wave type semiconductor laser amplifiers 61 and 62, Emit from d '.
Therefore, only the optical clock signal existing within the time determined by ΔL / c after the optical pulse signal is incident on the traveling wave type semiconductor laser amplifier 62 is emitted from the port b ′. Therefore, this switch operates as an optical switch having a gate width ΔL / c controlled by the optical pulse signal. Therefore, the optical clock signal emitted from the port b'becomes an optical pulse signal corresponding to the optical pulse signal. Since the optical clock signal is a mode-locked optical pulse train, it means that the optical pulse signal is reproduced as an optical pulse signal without jitter.

Therefore, by arranging the polarization beam splitter 3 as described in the first embodiment of the present invention, the reproduced light pulse signal can be obtained as the TM polarization. However, in the embodiment of the present invention, as the optical amplifier 5, an optical fiber amplifier in which the polarization maintaining rare earth-doped fiber 51 is pumped by the pumping light source 53 via the multiplexer 52 is used. Instead of the optical fiber amplifier 5, it is possible to use a traveling wave type semiconductor laser amplifier. Further, the traveling wave type semiconductor laser amplifier 6
If an MQW semiconductor crystal is used instead of 1, 62, τc
Can be improved and an ultra-high speed optical signal can be reproduced.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 4 is a block diagram of the third embodiment of the present invention. The third embodiment of the present invention is characterized in that the MQW semiconductor crystal 71 is used for one loop path of the Mach-Zehnder interferometer. Others are the same as the second embodiment of the present invention.

The TE polarization component of the optical pulse signal is coupled to the coupler 4
From the branching ratio of 4, the light is split into two by the coupler 44 and is incident on the interferometer including the MQW semiconductor crystal 71 and the ring 12. The TM polarized wave generated by the orthogonal polarized wave generator 8 is split into two when it is incident on the coupler 43. Since the optical clock signal propagating clockwise in the ring 12 is synchronized with the optical pulse signal, it is incident on the MQW semiconductor crystal 71 at the same time as the optical pulse signal, so that it is proportional to the rise time of the optical pulse signal (the fastest rise time). The time is up to ps), and the refractive index changes due to the induced optical nonlinear effect of the MQW semiconductor crystal 71.
Since this change in the refractive index lasts for a time (typically τc to 10 ps) determined by the carrier life even after the optical pulse signal falls, it is necessary to set the repetition period of the optical pulse signal larger than τc. On the other hand, the optical clock signal that has entered the other arm is not affected by the change in the refractive index due to the optical nonlinear effect caused by the optical pulse signal, so that a phase difference occurs between both optical clock signals, and this phase difference is 180 If the peak power of the TM polarization component of the optical pulse signal is adjusted so that the optical pulse signal becomes equal to the frequency, the optical clock signal of the portion that temporally overlaps with the optical pulse signal interferes with the coupler 44 and is emitted from the port b ′. Becomes Needless to say, when the optical pulse signal does not enter the MQW semiconductor crystal 71, the optical pulse does not undergo a refractive index change due to the optical nonlinear effect in the MQW semiconductor crystal 71, and therefore the optical pulse is emitted from the port d ′. Therefore, this switch operates as an optical switch controlled by the optical pulse signal.

Therefore, by arranging the polarization beam splitter as described in the first embodiment of the present invention, the reproduced optical pulse signal can be obtained as the TM polarization. However, in the third embodiment of the present invention, an optical fiber amplifier in which a polarization-maintaining rare earth-doped fiber 51 is pumped by a pumping light source 53 via a multiplexer 52 is used as the optical amplifier 5. Instead of the optical fiber amplifier, a traveling wave type semiconductor laser amplifier can be used.

[0033]

As described above, according to the present invention,
By integrating the optical clock generator and the optical switch, it is possible to configure an all-optical regenerative repeater that does not require an optical path length adjusting function.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the principle of the present invention.

FIG. 3 is a block diagram of a second embodiment of the present invention.

FIG. 4 is a block diagram of the third embodiment of the present invention.

FIG. 5 is a block diagram of a conventional device.

[Explanation of symbols]

 1 Optical Input Terminal 2 Optical Filter 3 Polarization Beam Splitter 4 Optical Isolator 5 Optical Amplifier 6 Nonlinear Optical Element 7, 43, 44 Coupler 8 Orthogonal Polarization Generator 10 Optical Output Terminal 11, 12 Ring 20 Optical Clock Generator 30 Optical Switch circuit 51 Polarization-maintaining rare earth-doped fiber 52 Combiner 53 Excitation light source 61, 62 Traveling wave type semiconductor laser amplifier 71 MQW semiconductor crystal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masatoshi Saruwatari 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. An optical input terminal (1) to which a reproduced optical signal polarized in a first polarization plane is input, and a polarization maintaining in which the reproduced optical signal polarized in the first polarization plane is coupled. A first ring (11) formed by an optical waveguide, and a reproduced optical signal polarized in the first polarization plane are coupled in one direction to the first ring, and the first ring (11) is orthogonal to the first polarization plane. A second ring (12) formed by a polarization maintaining optical waveguide in which optical signals polarized in two polarization planes are coupled via a coupler (7) that branches and couples in two directions, and this second ring. An amplifier (4, 5) provided in the first ring for amplifying an optical signal propagating in the second ring in one direction, the first ring (11) and the second ring (1).
The total length L of 2) is as follows: L = mcT (where m is a positive integer, c is the speed of light, T is the period of the pulse signal arriving at the optical input terminal), and the optical signal that alternately propagates through these two rings is used. These two rings have a period T
Orthogonally polarized wave generator which is set so as to be a mode-locked laser for the optical signal of and is provided in the second ring to convert a part of the energy of the optical signal output from the amplifier into the energy of the second polarization plane. (8) and the first ring (11)
A non-linear optical element (6) provided on the optical input terminal side by a distance ΔL from a point equidistant from the coupler (7) therein, and the output light of the non-linear optical element (6) and the optical input. An optical signal generated by interference between the optical signal input from the terminal and the coupler (7) is output from the second ring to the output terminal (10).
An all-optical regenerative repeater comprising a polarization beam splitter (3) for branching into. 2. A Mach-Zehnder interferometer is coupled to the second ring in place of the first ring and the coupler, and a nonlinear optical element is inserted in two loop paths of the Mach-Zehnder interferometer, and the Mach-Zehnder interferometer is inserted. An all-optical regenerative repeater, characterized in that one end of is a light input terminal. 3. The all-optical regenerative repeater according to claim 2, wherein an MQW semiconductor crystal is inserted in one loop path of the Mach-Zehnder interferometer.