JP3462382B2 - Optical switch circuit and optical modulation circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an all-optical type optical switch circuit that uses the optical Kerr effect to switch a signal light pulse train on a time axis by a control light pulse, and a clock light using this optical switch circuit. The present invention relates to an ultrahigh-speed optical modulation circuit that modulates a pulse train on the time axis.

[0002]

2. Description of the Related Art (Optical Switch Circuit) FIG. 9 shows a configuration example of a conventional optical switch circuit utilizing the optical Kerr effect.

In the figure, an input signal light of wavelength λs is combined with control light of wavelength λc (≠ λs) by an optical multiplexer 1, and the combined light is one input port of an optical coupler 2 of 2 × 2. It is led to P ₁ . The branching ratio of the optical coupler 2 depends on the wavelength, and the signal light is split into 1: 1 and output ports P ₂ and P ₂ , respectively.
₃ , the control light is guided to one output port, here the output port P ₂ . The output ports P ₂ and P ₃ of the optical coupler 2 are coupled to both ends of the optical Kerr medium 3 to form a loop. The light that has passed through the loop is extracted to the other input port P ₄ of the optical coupler 2, and the signal light and the control light are separated by the optical demultiplexer 4.

Here, the output ports P ₂ , P of the optical coupler 2
_{Since 3} is connected via the optical Kerr medium 3, the control light input to the optical coupler 2 travels in the optical Kerr medium 3 in the one-way (clockwise direction in the figure) direction, and the signal light is supplied to both left and right sides. Go around. At this time, a phase change Δφ occurs in the clockwise signal light that advances temporally in the same direction as the control light due to the mutual phase modulation. This phase change Δφ is such that the nonlinear constant of the optical Kerr medium 3 is n ₂ , the length of the optical Kerr medium 3 is L, the refractive index of the optical Kerr medium 3 is n, the intensity of the control light is I, and the wavelength of the signal light is λs. Then, Δφ = 2π (n / λs) L · n ₂ · I (1) On the other hand, the counterclockwise signal light traveling counterclockwise with respect to the control light receives an average phase change due to the control light, and the phase change has a small value proportional to the average power of the control light.

Therefore, the phase difference between the signal light components that have been passed through the loop clockwise and counterclockwise and combined again by the optical coupler 2 can be set to π and 0 depending on the presence or absence of the control light pulse. At this time, the signal light is guided to the other input port P ₄ when the phase difference is π due to the interference effect in the optical coupler 2, which is different from the input port P ₄ , and when the phase difference is 0, the input port P ₁ at the input. Return to. That is, as the input signal light, only the pulse temporally overlapping with the control light in the optical Kerr medium 3 is output as the output signal light 1 from the output port of the optical demultiplexer 4.

(Optical Modulation Circuit) Conventionally, as a high-speed optical modulator, a LiNbO ₃ optical modulator mainly utilizing the electro-optic effect and a semiconductor optical modulator utilizing the electroabsorption characteristic have been used. The limit of the modulation speed in such an optical modulator is about several tens Gbit / s.

Therefore, in order to generate a higher-speed signal light, as shown in FIG. 10, a multi-series relatively low-speed signal light (20 Gbit / s or less) is time-division multiplexed to obtain a high-speed signal light (100 Gbit). / s) is known (reference: GEWickens, et al., "20Gbit / s, 205km o
ptical division multiplexed transmission system ", E
lectron. Lett., vol.27, no.11, pp.973-974, 1991).

In FIG. 10, a low-speed optical pulse train (a)
Is branched into N by the optical branching device 11 and the optical modulators 12-1 to 12-12.
-Entered in N. The optical pulse trains (b) input to the optical modulators 12-1 to 12-N are respectively modulated into low-speed optical signal trains (c), which are delayed by the optical delay units 13-1 to 13-N. Is given. Optical delay devices 13-1 to 13
The low-speed optical signal train (d) output from -N is the optical multiplexer 14
Is time-division-multiplexed into a high-speed multiplexed optical signal train (e).

FIG. 11 shows a process of generating a high-speed multiplexed optical signal train (e) from a low-speed optical pulse train (a) when N = 4. When one time slot (time per bit) of the high-speed multiplexed optical signal train (e) is T, the pulse interval of the low-speed optical pulse train (a) is 4T. The data signals for driving the optical modulators 12-1 to 12-N are "101", "111", "101", and "110", respectively, and perform optical intensity modulation or phase modulation on the optical pulse train (b), respectively. To generate an optical signal train (c). Optical delay device 13-1
In 13-N, the optical signal train (c) of each channel is delayed by 0, T, 2T, and 3T to form an optical signal train (d). By time-division multiplexing this optical signal sequence (d),
At the pulse interval T, a high-speed multiplexed optical signal train (e) of "111101011110" is generated.

However, in such an optical time division multiplexer, it is difficult to arrange the positions of the respective optical pulses at equal intervals and to make the optical intensities of the respective optical pulses equal, so that the multiplexed signals to be outputted are output. There is a problem that the pulse interval and the light intensity of the optical signal train vary. As a method of solving this problem, a configuration has been proposed in which the all-optical type optical switch circuit utilizing the above-mentioned optical Kerr effect is used to correct variations in pulse intervals and optical intensities of multiplexed optical signal trains (references). :
JP-A-6-326390 (optical pulse pattern generator)). The structure of this light modulation circuit is shown in FIG.

In FIG. 12, a pulse light source 21 driven by an electric clock has a repetition frequency f at a wavelength λc.
Outputs a ₀ Hz optical pulse train. This optical pulse train is shown in FIG.
Mf the optical time division multiplexing apparatus 22 having the configuration shown in 0 ₀ bit /
It is converted into a multiple optical signal train of s, which has variations in pulse interval and light intensity as described above. Therefore, this multiplexed optical signal sequence is input as control light to the optical multiplexer 1 of the optical switch circuit 23 having the configuration shown in FIG.

On the other hand, the high-speed optical pulse generator 24 driven by the electric clock has the repetition frequency Mf at the wavelength λs.
_{A 0} Hz clock optical pulse train is generated, and this is input to the optical multiplexer 1 of the optical switch circuit 23 having the configuration shown in FIG. 9 as input signal light. Hereinafter, as shown in the description of FIG. 9, the clock light pulse train (input signal light) is switched by the multiplexed light signal train (control light) to become a high-speed light signal train (output signal light). At this time, variations in the pulse interval and light intensity of the multiplexed optical signal train are corrected, and a high-speed optical signal train with small variations in pulse interval and light intensity can be obtained.

The following two characteristics of the optical switch circuit 23 are the reasons why it is possible to correct the variation in the pulse interval and the light intensity of the multiplexed optical signal train input to the optical switch circuit 23 as control light.

First, the relationship between the input light intensity of the multiplexed optical signal train (control light) and the output light intensity of the high-speed optical signal train (output signal light) after switching has the nonlinear characteristic shown in FIG. Is. This is a characteristic obtained by the optical switch circuit 23 using optical interference. Due to this non-linear characteristic, even if the input light intensity of the multiplexed optical signal train (control light) varies in the range A in the figure, the fluctuation of the output light intensity of the high-speed optical signal train (output signal light) after switching becomes small.

Secondly, it has a switching window wider than the pulse width of the switched clock light pulse train (input signal light). In the optical Kerr medium 3 of the optical switch circuit 23, by making a group velocity difference between the multiplexed optical signal train of wavelength λc (control light) and the clock light pulse train of wavelength λs (input signal light), As shown in (1), (2), and (3), a time delay can be generated while the two propagate through the optical Kerr medium 3 (walk-off). In this way, the multiplex optical signal train relatively sweeps the clock light pulse train, thereby functioning as a switching window wider than the pulse width of the clock light pulse train. Here, when the walk-off time is longer than the pulse width of the clock light pulse train, the window shape becomes almost rectangular (FIG. 14).
(Four)). Thus, even if the multiplexed optical signal train has time jitter, both the multiplexed optical signal train and the clock optical pulse train can interact with each other. The high-speed optical signal train (output signal light) after switching has been replaced with the multiplexed optical signal train (control light) to the clock light pulse train (input signal light),
As shown in FIG. 14 (5), time jitter is suppressed (reference: Jinno et al., 1992 IEICE Autumn National Conference B-737).

In the optical switch circuit 23 shown in FIG. 12, by using an optical fiber having an appropriate dispersion value as the optical Kerr medium 3, a multiplexed optical signal train (control light) of wavelength λc and a clock light of wavelength λs are used. A group velocity difference can be provided between the pulse train (input signal light) and a wide switching window can be realized.

[0017]

The phase change Δφ shown in the equation (1) is proportional to the nonlinear constant n ₂ of the optical Kerr medium 3, but the optical fiber which has been mainly used as the optical Kerr medium has been used so far. Since the value of the nonlinear constant n ₂ is small, an optical fiber length of several hundred m to several km was required to change the phase difference by π with a light intensity (˜1 W) equivalent to the semiconductor laser output. Such a long optical fiber is usually wound in a coil shape. Therefore, when force is applied to this optical fiber loop from the outside and rotation occurs along the circumference of the optical fiber loop, there is a difference between the clockwise and counterclockwise optical paths of the signal light propagating in the optical fiber loop due to the Sagnac effect. Will occur.

Here, the Sagnac effect will be described in detail with reference to FIG. The Sagnac effect means that there is a difference between the time taken for the light to make one turn along the rotation direction in the rotating coordinate system and the time taken for the light to make one turn in the opposite direction. FIG. 15 (1) is an example in which the rotation direction of the optical fiber loop is opposite to the light propagation direction, and the optical switch circuit of FIG. 9 corresponds to clockwise signal light. FIG. 15 (2) is an example in which the rotation direction of the optical fiber loop and the light propagation direction are the same, and the optical switch circuit of FIG. 9 corresponds to counterclockwise signal light.

The angular velocity ω with respect to the inertial system of the optical fiber loop and the radius r from the rotation axis of the path through which light passes are ωr << c
If the condition of (c: speed of light) is satisfied, the time difference Δt in these two directions is such that the number of turns of the optical fiber is N, the area surrounded by one path is S (= πr ² ), and If the refractive index is n, then Δt = 4NSω / (c / n) ² (2) (reference: Iwanami Physics and Chemistry).

At this time, the phase difference Δφs in the two directions due to the Sagnac effect is Δφs = (2πc / λs) Δt = (2πc / λs) × 4NSω / (c / n) ² . Here, the optical fiber length L = 2πrN, and S
= Lr / 2N, and therefore v = ωr, Δφs = 4πn ² Lv / cλs (3) For example, when an optical fiber of L = 1 km is used as an optical Kerr medium and a signal light of wavelength λs = 1550 nm is switched, the speed v = 0.05 m / s is set in the optical fiber loop.
When a certain degree of rotation is given, the phase difference Δφs becomes π, and the on / off operation of the optical switch circuit is reversed. Therefore, the conventional optical switch circuit shown in FIG. 9 has a problem that its operation tends to be unstable due to external vibration or the like.

It is an object of the present invention to provide an ultra-high speed all-optical type optical switch circuit which reduces the influence of the Sagnac effect and is stable in operation against external vibration and the like. Another object of the present invention is to provide an ultrahigh speed optical modulation circuit using this optical switch circuit.

[0022]

An optical switch circuit of the present invention comprises a polarization-maintaining optical coupler, a polarization-maintaining optical Kerr medium, a polarization combining means, and a polarization-maintaining optical multiplexer. It is composed of a mirror, a polarization rotation mirror, and an optical demultiplexer. The optical coupler
The linearly polarized input signal light is input to one of the two input ports and split into two output ports in a one-to-one relationship. The polarization combining means inputs the input signal light that has been split in two by the optical coupler, performs polarization combination so that the respective polarized waves match the directions of the two principal axes of the optical Kerr medium that are orthogonal to each other, and forms an optical Kerr medium. Lead. The optical multiplexer inputs the linearly polarized control light and multiplexes it into the input signal light so as to coincide with one main axis of the optical Kerr medium. The polarization rotation mirror rotates the polarizations of the input signal light and the control light that have passed through the optical Kerr medium by 90 degrees and reflects them to re-input them into the optical Kerr medium. The optical demultiplexer separates the control light from the input signal light and the control light reflected by the polarization rotation mirror and reciprocating in the optical Kerr medium.

Here, the input signal light split into two by the optical coupler is polarization-combined by the polarization combining means and reciprocates in the birefringent optical Kerr medium. Each polarization component propagates independently in the optical path that propagates the X axis in the outward path and then propagates in the Y axis in the return path, and the optical path that propagates the Y axis in the outward path and then propagates in the X axis in the return path, and combines the polarized waves. The polarized light is separated by the means, input to the two output ports of the optical coupler, and multiplexed. At this time, the control light is
Since it propagates only in one optical path, it induces a phase change only in the input signal light propagating in that optical path, and does not give a phase change in the input signal light propagating in the other optical path. Therefore, the input signal light that coincides with the control light in time has a phase in two optical paths, and is switched.

Further, the Sagnac effect generated between the two optical paths can be greatly reduced because the Sagnac effects of the X-axis and the Y-axis of the optical Kerr medium cancel each other out, and stable switching is possible. Further, since one optical Kerr medium is used in a reciprocating manner, the required length can be made shorter than in the past, and the cost can be reduced.

The optical modulation circuit of the present invention controls the multiplexed optical signal train of bit rate Nf ₀ [bit / s] by time-division multiplexing the optical signal train of N series of basic bit rates f ₀ [bit / s]. As the repetition frequency Nf ₀ [H
z] clock light pulse train is input as input signal light,
The optical switch circuit according to the present invention is used as an optical switch circuit whose transmittance with respect to the clock light pulse train changes according to the light intensity of the control light.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment of Optical Switch Circuit) FIG. 1 shows a first embodiment of an optical switch circuit of the present invention.

In the figure, an input signal light having a wavelength λs is combined with a control light having a wavelength λc (≠ λs) by a polarization-maintaining optical multiplexer 1, and the combined light is a polarization-maintaining 2 × 2. Optical coupler 2 is guided to _one input port P ₁ . The branching ratio of the optical coupler 2 depends on the wavelength, and the input signal light is split into one to one and guided to the output ports P ₂ and P ₃ , respectively, and the control light is output to one of the output ports, here the output port. You are led to P ₂ .

The input signal light and control light output from the output port P ₂ of the optical coupler 2, the input signal light output from the output port P ₃ of the optical coupler 2, the polarization rotating unit 5 and the polarization It is guided to one port Pa of the polarization-maintaining optical fiber 7 which is a birefringent optical Kerr medium via the polarization combining means constituted by the beam splitter 6. The input signal light and the control light output from the other port Pb of the polarization maintaining optical fiber 7 are reflected by the polarization rotating mirror 8 and are again input to the other port Pb of the polarization maintaining optical fiber 7. The optical demultiplexer 4 is connected to the other input port P ₄ of the optical coupler 2, and the output signal light of wavelength λs and the control light of wavelength λc are separated.

In the optical switch circuit of the present invention, both the input signal light and the control light are linearly polarized waves. Polarization rotation unit 5
Is realized by twisting the polarization maintaining optical fiber by 90 degrees, and rotates the polarization of the input signal light output from the output port P ₃ of the optical coupler 2 by 90 degrees. The input optical signals split into two by the optical coupler 2 are polarization-combined by the polarization beam splitter 8 so that their respective polarizations coincide with the directions of two orthogonal main axes of the polarization-maintaining optical fiber 7. At this time, the polarization of the control light output from the output port P ₂ of the optical coupler 2 is matched to one of the principal axes of the polarization maintaining optical fiber 7. The polarization rotation mirror 8 is configured to rotate the polarized waves of the input signal light and the control light by 90 degrees and reflect the polarized light, which will be described later in detail.

Now, the polarization and propagation paths of the input signal light and the control light in the present optical switch circuit will be described with reference to FIG. The input signal light of linearly polarized wave is generated by the optical coupler 2
The input signal light output from the output port P _{2 of} the optical coupler 2 is A, and the input signal light output from the output port P ₃ of the optical coupler 2 is A. Let B be the optical path through which is transmitted.

In the optical path A, the output port P ₂ of the optical coupler ₂
The input signal light (a) output from the optical fiber passes through the polarization beam splitter 6 with the same polarization and is input to the port Pa of the polarization maintaining optical fiber 7. The input signal light (b) propagates through the polarization-maintaining optical fiber 7 while maintaining the polarization on the X-axis of the two main axes (X, Y) of the polarization-maintaining optical fiber 7 which are orthogonal to each other. The input signal light (c) output from the port Pb of the polarization maintaining optical fiber 7 is reflected by the polarization rotating mirror 8 after rotating the polarization by 90 degrees. The input signal light (d) propagates through the polarization maintaining optical fiber 7 in the reverse direction (Pb → Pa) while maintaining the polarization on the Y axis of the polarization maintaining optical fiber 7. Port P
The input signal light (e) output from a is reflected by the polarization beam splitter 6, the polarization is rotated by 90 degrees by the polarization rotation unit 5, and is input to the output port P ₃ of the optical coupler 2 (f). .

In the optical path B, the output port P ₃ of the optical coupler 2
The input signal light (g) output from the
It is rotated by 90 degrees, reflected by the polarization beam splitter 6, and input to the port Pa of the polarization maintaining optical fiber 7. The input signal light (h) propagates in the polarization maintaining optical fiber 7 while maintaining the polarization on the Y axis of the polarization maintaining optical fiber 7. The input signal light (i) output from the port Pb of the polarization maintaining optical fiber 7 is
The polarization rotation mirror 8 rotates the polarization by 90 degrees and reflects it. The input signal light (j) is polarized in the X-axis of the polarization maintaining optical fiber 7 while being polarized in the opposite direction (Pb
→ Propagate to Pa). The input signal light (k) output from the port Pa passes through the polarization beam splitter 6 and is input to the output port P ₂ of the optical coupler 2 (l).

The linearly polarized control light propagates in the polarization maintaining optical fiber 7 while maintaining the polarization on the X axis of the polarization maintaining optical fiber 7, and the polarization rotating mirror 8 changes the polarization to 90 degrees. It is rotated and reflected, and propagates in the opposite direction (Pb → Pa) through the polarization maintaining optical fiber 7 while maintaining the polarization on the Y axis of the polarization maintaining optical fiber 7.

At this time, the control light is transmitted through the optical path A (from Pa to P
The phase change is induced only in the signal light component propagating in the X-axis in the b direction and the Y-axis in the Pb to Pa direction, and the optical path B
To Pb direction Y axis, and Pb to Pa direction X axis), no phase change is given to the signal light component propagating. Therefore, according to the same principle as that of the conventional optical switch circuit, the signal light that temporally coincides with the control light causes a phase difference in the two optical paths and is switched to the input port P ₄ of the optical coupler 2.

Next, the influence of the Sagnac effect on the present optical switch circuit will be described with reference to FIG. Figure 3
Represents an equivalent route of the optical path A and the optical path B. The part of the optical path A that is affected by the Sagnac effect is the path Xab that propagates the polarization from the port Pa of the polarization-maintaining optical fiber 7 in the Pa direction to the X axis and the path Xab that propagates from the port Pb to the Pa direction. Consists of a path Yba propagating with the Y axis coincident with the Y axis. In the optical path B, a portion affected by the Sagnac effect is a path Yab for propagating polarized light from the port Pa of the polarization-maintaining optical fiber 7 in the direction Pa to Pb in the direction of the Y axis, and a port Ya from the port Pb to the direction of Pa. It is composed of a path Xba that propagates with the polarized wave aligned with the X axis.

When the polarization-maintaining optical fiber 7 rotates in one direction, the time difference Δt between the optical path A and the optical path B caused by the Sagnac effect is t _Xab , t _Yba , which is the time required for propagation of the paths Xab, Yba, Yab, Xba, respectively. , T _Yab , t _Xba , Δt = (t _Xab + t _Yba ) − (t _Yab + t _Xba ) = (t _Xab −t _Xba ) − (t _Yab −t _Yba ) ... (4). That is, it is the difference between the time difference that occurs on the path (Xab and Xba) where the polarized wave propagates on the X axis and the time difference that occurs on the path (Yab and Yba) that propagates the Y axis. In other words, the Sagnac effect between the optical paths A and B is the difference between the Sagnac effect on the X axis and the Sagnac effect on the Y axis.

If the refractive indices of the polarization-maintaining optical fiber 7 with respect to the X axis and the Y axis are n _X and n _Y , respectively, (2), (3), (4)
From the formula, the phase difference ΔΦs between the optical paths A and B is ΔΦs = 4πn _X ² Lv / cλs−4πn _Y ² Lv / cλs (5). Birefringence difference (difference in refractive index with respect to X and Y axes)
Is represented by δn (= n _X −n _Y ), the equation (5) is ΔΦ s = (4πLv / cλs) {n _X ² − (n _X −δn) ² } ≈ (4πn _X ² Lv / cλs) (2δn / n _X ) = ΔΦs _X · (2δn / n _X ) ... (6)

Here, ΔΦs _X is a phase difference due to the Sagnac effect of light propagating along the X axis, and it is assumed that n _X >> δn. This equation (6) shows that the phase difference generated in this optical switch circuit is (2) of the phase difference (≈ΔΦs _X ) of the conventional optical switch circuit.
δn / n _X ) times that. Since δn / n _X of a normal polarization-maintaining optical fiber is about 10 ⁻⁴ , it can be said that the present optical switch circuit can reduce the phase difference due to the Sagnac effect by about 4 digits.

Further, since the present optical switch circuit is configured to reciprocate and use one optical Kerr medium, the length of the optical Kerr medium (polarization maintaining optical fiber 7) can be made shorter than before. There are advantages.

FIG. 4 shows a configuration example of the polarization rotation mirror 8. The polarization rotation mirror shown in FIG. 4 (1) is composed of a polarization beam splitter 31 and a polarization maintaining optical fiber 32 twisted by 90 degrees. The optical Kerr medium (polarization-maintaining optical fiber 7) and the polarization beam splitter 31 are connected so that their principal axes are aligned with each other, and the polarization component perpendicular to the plane of the drawing is reflected upward by the polarization beam splitter 31 to be parallel. The polarized component is transmitted. At this time, the output light from one port is input to the other port after the polarization is rotated by 90 degrees via the polarization maintaining optical fiber 32 twisted by 90 degrees. Therefore, a polarization component perpendicular to the clockwise paper surface passes through the polarization beam splitter 31, and a polarization component parallel to the counterclockwise paper surface is the polarization beam splitter 31.
To reflect. That is, both polarization components are both output to the left, and each polarization is rotated by 90 degrees and input to the optical Kerr medium (polarization maintaining optical fiber 7).

The above operation can be similarly realized by the combination of the quarter-wave plate 33 and the total reflection mirror 34 shown in FIG. 4 (2). That is, the quarter wave plate 33
The linear polarized wave is converted into a circular polarized wave by and is reflected by the total reflection mirror 34, and the polarized wave of the input light is rotated by 90 degrees by converting the circular polarized wave into a linear polarized wave again by the quarter wavelength plate 33. And reflect. Further, it can be also realized by a combination of the Faraday rotator 35 and the total reflection mirror 34 shown in FIG. 4 (3). That is, the Faraday rotator 35 produces a linearly polarized wave of 45
The Faraday rotator 35 rotates the linearly polarized wave by 45 ° again, and then the polarized light of the input light is rotated by 90 ° and reflected.

(Second Embodiment of Optical Switch Circuit) FIG.
Shows a second embodiment of the optical switch circuit of the present invention.
The feature of this embodiment is that the polarization-maintaining optical multiplexer 1 of the first embodiment is arranged between the output port P ₂ of the optical coupler ₂ and the polarization beam splitter 6, and the optical demultiplexer 4 is used. Is arranged between the output port P ₃ of the optical coupler 2 and the polarization rotator 5. The polarization demultiplexer 4 is used as the optical demultiplexer 4. In addition, the optical demultiplexer 4 includes a polarization beam splitter 6
May be disposed between the polarization rotation unit 5 and the polarization rotation unit 5.

In this configuration, the characteristic of the optical coupler 2 is that the branching ratio is 1: 1 with respect to only the input signal light, and the optical coupler 2 with respect to the control light is different from the case of the first embodiment. The condition is unnecessary. That is, since the optical coupler 2 can be a wavelength-independent type, it has a great structural advantage.

(Third Embodiment of Optical Switch Circuit) FIG. 6
Shows a third embodiment of the optical switch circuit of the present invention.
A feature of this embodiment is that the polarization-maintaining optical multiplexer 1 in the first embodiment is arranged between the polarization beam splitter 6 and the port Pa of the polarization-maintaining optical fiber 7.

With this configuration, as in the second embodiment,
The characteristic of the optical coupler 2 may be a branching ratio of 1: 1 only for the input signal light, and the condition of the optical coupler 2 for the control light is unnecessary as compared with the case of the first embodiment, which is structurally different. The advantages of are great. Further, since the optical multiplexer 1 performs both functions of multiplexing and demultiplexing, there is an advantage that the configuration is simple.

(First Embodiment of Optical Modulation Circuit) FIG.
1 shows a first embodiment of an optical modulation circuit of the present invention. The optical modulation circuit of the present embodiment uses the first embodiment of the optical switch circuit of the present invention shown in FIG. 1 in place of the optical switch circuit 23 of the conventional optical modulation circuit shown in FIG. That is, the multiplexed optical signal train output from the optical time division multiplexer 22 is input to the optical multiplexer 1 of the optical switch circuit having the configuration shown in FIG. 1 as control light. Further, the clock light pulse train output from the high-speed light pulse generator 24 is used as the input signal light,
It is input to the optical multiplexer 1 of the optical switch circuit configured as shown in FIG. With such a configuration, the Sagnac effect is reduced, and it is possible to stably obtain a high-speed optical signal train in which variations in pulse interval and light intensity are smaller than those in the conventional configuration.

The optical switch circuit 23 shown in FIG.
The second embodiment shown in FIG. 6 and the third embodiment shown in FIG. 6 can be used similarly. The pulse light source 21 and the high-speed optical pulse generator 24 are driven by an electric clock from two synchronized electric clock signal sources, or driven by an electric clock from one electric clock signal source. Any of

The high-speed optical pulse generator 24 includes a pulse light source for generating an optical pulse train having a repetition frequency f ₀ Hz,
A combination with a means for multiplying the repetition frequency of this optical pulse train by N is general. In addition, a beat obtained by combining light from two semiconductor lasers having different oscillation frequencies is guided to an anomalous dispersion optical fiber to obtain a short optical pulse by adiabatic compression, or CPM (Colliding Pulse Mode-locki
ng) A method using a semiconductor laser is known. However, these methods require feedback control or the like in order to synchronize with the outside, and there is a problem that the configuration becomes complicated.

(Second Embodiment of Optical Modulation Circuit) FIG.
The 2nd Embodiment of the optical modulation circuit of this invention is shown. The feature of this embodiment is that the configuration of the high-speed optical pulse generator 24 is changed. That is, the high-speed optical pulse generator 24 is characterized by using a pulse light source 25 for generating an optical pulse train having a repetition frequency f ₀ Hz and a dispersion imparting means 26 for giving chirping to the optical pulse train.

Focusing on the spectral component of the optical pulse train having the repetition frequency f ₀ given the dispersion by the dispersion providing means 26 at a certain time, two or more different optical frequency components in the optical pulse are included depending on the magnitude of the dispersion. Be done. If the optical frequency difference between the different optical frequency components is M times f ₀ ,
A high-speed optical pulse train having a repetition frequency M · f ₀ can be obtained at the output of the dispersion imparting means 26 (Japanese Patent Application No. 9-1942).
17 (high-speed optical pulse generator)). As a result, a high-speed clock light pulse train synchronized with the outside can be generated very easily.

[0051]

As described above, in the optical switch circuit of the present invention, the phase difference between the two optical paths in the circuit caused by the Sagnac effect is due to the Sagnac effect of the X-axis and the Y-axis of the birefringent optical Kerr medium. Cancel each other out, so it can be greatly reduced. Further, since the configuration is such that one optical Kerr medium is reciprocally used, the required length can be made shorter than in the conventional case. Therefore, the present invention can realize an extremely stable and ultrahigh-speed optical switch circuit and an optical modulation circuit using the same at low cost.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an optical switch circuit of the present invention.

FIG. 2 is a diagram showing polarization and propagation paths of input signal light and control light.

FIG. 3 is a diagram showing equivalent paths of an optical path A and an optical path B.

FIG. 4 is a diagram showing a configuration example of a polarization rotation mirror 8;

FIG. 5 is a configuration diagram showing a second embodiment of an optical switch circuit of the present invention.

FIG. 6 is a configuration diagram showing a third embodiment of an optical switch circuit of the present invention.

FIG. 7 is a configuration diagram showing a first embodiment of an optical modulation circuit of the present invention.

FIG. 8 is a configuration diagram showing a second embodiment of an optical modulation circuit of the present invention.

FIG. 9 is a diagram showing a configuration example of a conventional optical switch circuit.

FIG. 10 is a diagram showing a configuration example of a conventional optical time division multiplexer.

FIG. 11 is a diagram showing an operation example of a conventional optical time division multiplexer.

FIG. 12 is a diagram showing a configuration example of a conventional light modulation circuit.

FIG. 13 is a diagram showing input / output characteristics of an optical switch circuit.

FIG. 14 is a diagram illustrating a switching window by walk-off.

FIG. 15 is a diagram illustrating a Sagnac effect.

[Explanation of symbols]

1 Optical multiplexer 2 Optical coupler 3 optical Kerr medium 4 Optical demultiplexer 5 Polarization rotation part 6 Polarization beam splitter 7 Polarization maintaining optical fiber 8 polarization rotation mirror 11 Optical splitter 12 Optical modulator 13 Optical delay device 14 Optical multiplexer 21 pulse light source 22 Optical Time Division Multiplexer 23 Optical switch circuit 24 High-speed optical pulse light source 31 polarization beam splitter 32 polarization maintaining optical fiber 33 1/4 wave plate 34 Total reflection mirror 35 Faraday rotator

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H04B 10/152 (56) References JP-A-8-262509 (JP, A) JP-A-5-341332 (JP, A) Kaihei 5-188411 (JP, A) T.I. MORIKA. et. al. , ULTRAFAST REFLECTI VE OPTICAL KERR DE MULTIPLEXER USING POLARISATION ROTATION NIROR, ELECTRO NICS LETTERS, March 12, 1992, Vol. 28, No. 6, PP. 521-522 Hidehiko Takara, et al., High-speed optical pulse train generation by chirped optical pulse, Proceedings of the 1997 IEICE Communications Society Conference, August 13, 1997, Vol. 1997, Society B2 , Pp. 425 (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 1/35 H04B 10/04 H04B 10/06 JISST file (JOIS)

Claims (9)

(57) [Claims] 1. A polarization-maintaining optical coupler for inputting linearly polarized input signal light into one of two input ports and splitting it into two output ports in a one-to-one relationship, and a polarization device having an optical Kerr effect. A wave-maintaining optical Kerr medium and an input signal light split in two by the optical coupler are input, and polarization is combined so that respective polarizations coincide with two directions of the principal axes orthogonal to each other in the optical Kerr medium. Polarization-combining means for inputting linearly polarized control light to the optical Kerr medium, and multiplexing the input signal light so as to match one principal axis of the optical Kerr medium. Wave splitter, a polarization rotation mirror that rotates the polarizations of the input signal light and control light that have passed through the optical Kerr medium by 90 degrees and reflects them, and re-inputs them to the optical Kerr medium, and is reflected by the polarization rotation mirror. Light that separates the control light from the input signal light and the control light that have reciprocated through the optical Kerr medium And a filter, the polarization-hand input signal light reciprocating the optical Kerr medium
Input to the stage and let it pass in the opposite direction.
Separated into two linearly polarized waves and input of two separated linearly polarized waves
Signal light is output from each of the two output ports of the optical coupler.
It is input and multiplexed, and when it is mixed with the control light in the input signal light.
Only the input signal light that coincides between the other of the optical coupler
An optical switch circuit characterized in that it is configured to output from an input port . 2. The optical multiplexer is arranged at one input port of the optical coupler, the optical demultiplexer is arranged at the other input port of the optical coupler, and the optical coupler is inputted at one input port of the optical coupler. The optical switch circuit according to claim 1, wherein the control light is output to one of the two output ports. 3. The optical multiplexer is arranged between one output port of the optical coupler and the polarization combiner, and the optical demultiplexer is connected to the polarization combiner and the other output port of the optical combiner. The optical switch circuit according to claim 1, wherein the optical switch circuit is arranged between the two. 4. The optical switch circuit according to claim 1, wherein the optical multiplexer and the optical demultiplexer are arranged between the polarization combining means and the optical Kerr medium by one element. 5. The polarization rotating mirror connects a polarization beam splitter connected according to the principal axis of an optical Kerr medium and a polarization maintaining optical fiber twisted by 90 degrees, and polarizes the input light of the polarization beam splitter. The optical switch circuit according to claim 1, wherein the wave is configured to be rotated by 90 degrees and reflected. 6. The polarization rotating mirror connects a quarter-wave plate and a total reflection mirror, converts linearly polarized light into circularly polarized light by the quarter-wave plate, reflects it by the total reflection mirror, and again. The polarization of the input light is converted by converting the circular polarization into the linear polarization with the quarter-wave plate.
The optical switch circuit according to claim 1, wherein the optical switch circuit is configured to rotate by 90 degrees and reflect. 7. The polarization rotating mirror comprises a Faraday rotator and a total reflection mirror connected to each other, the linear polarization is rotated by 45 degrees by the Faraday rotator, reflected by the total reflection mirror, and again linearly polarized by the Faraday rotator. The optical switch circuit according to claim 1, wherein the polarization of the input light is rotated by 90 degrees and reflected by rotating the wave by 45 degrees. 8. N-series basic bit rate f ₀ [bit / s]
Bit rate Nf ₀ [bit /
[s] is input as a control light, a clock light pulse train having a repetition frequency Nf ₀ [Hz] with an equal pulse interval is input as an input signal light, and the clock light pulse train is generated according to the light intensity of the control light. An optical modulation circuit comprising an optical switch circuit having a changeable transmittance with respect to, wherein the optical switch circuit according to any one of claims 1 to 7 is used as the optical switch circuit. 9. A repetition frequency Nf having an equal pulse interval.
₀ means for generating a clock pulse train of [Hz] is a feature in that it comprises a pulse light source for generating an optical pulse train of repetition frequency f ₀ (Hz), and a dispersion providing means for providing a chirping to the optical pulse train The optical modulation circuit according to claim 8.