JPH09236832A - Optically controlled light switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce cross talk and facilitate switching superior in SN ratio by giving light pulses of appropriate power also to the pulses not supjected to separation by a control pulse pattern generating circuit. SOLUTION: The control pulses which are emitted form a control pulse light source 7 with a repeat frequency corresponding to N channels and have wavelengths different from that of the signal light are branched into N branches by a 1×N branch circuit 9 to be made incident on each light delay line 10. The relative time delay corresponding to the channel interval exists between the light delay lines 10 and the control pulse passing through the jth pass becomes the control pulse for the jth channel. The light on each pass is set at an appropriate peak power by each variable attenuator 11, merged by a N×1 coupler 12, and then inputted to an optical loop 3 through a wave synthesizer 4. When the first channel pulse is extracted, the control pulse for the channel adjusts the variable attenuator 11 so that the two bi-directional light in the optical loop 3 generates a phase difference of π.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical control type optical switch, and particularly to a high speed optical switch, an optical communication device, an optical computer, etc., which uses 100 Gbit / s class ultra high speed optical communication and optical signal processing. The present invention relates to an optical signal train switch and a demultiplexing circuit.

FIG. 1 shows the configuration of an optical control type optical switch proposed so far, and FIG. 2 shows a schematic diagram for explaining the operation principle thereof. The operation principle of the conventional light control type optical switch will be described below with reference to FIGS. Here, a case where an optical pulse signal time-divided into N channels from the input signal line 1 is input will be described as an example.

The input signal (a) is 2 by 2 × 2 optical coupler 2.
The branched and branched clockwise and counterclockwise optical signals propagate in the optical loop 3. Now, if the branching ratio of the 2 × 2 optical coupler 2 is 1: 1 and the polarization directions of both lights propagating through the optical loop 3 are the same, both lights will interfere 100% at the 2 × 2 optical coupler 2,
Neglecting the loss of 2 × 2 optical coupler 2 and optical loop 3,
The total input power is output from the input signal line in the direction opposite to the input direction. This occurs because the optical path length between both lights is equal and the phase difference between both lights is zero.

Now, let us consider a case where the first channel in the N-channel time-division multiplexed signal train shown in FIG. 2A is used as the separation target pulse. An optical pulse having a wavelength different from that of the signal light emitted from the control pulse light source is input as a control pulse (b ′) via the multiplexer 4 on the optical loop 3. At that time, it is input at a timing to be superimposed on the separation target pulse.
Now, by inputting the control pulse (b ′) to the optical loop 3, nonlinear polarization occurs in the waveguide medium (for example, glass in the case of an optical fiber) forming the optical loop according to its intensity, and its refractive index changes.

As a result, the counterclockwise light of the separation target pulse has an optical path length difference due to the peak power of the control pulse (b '), and the non-separation target pulse has no optical path length difference. Further, since the clockwise light passes each control pulse for a moment, the optical path length change corresponding to the average power of the control pulse (b ′) occurs. Here, the phase difference between the two lights of the separation target pulse is π
By inputting the control pulse (b ′), the separation target pulse is output from the output signal line 5 of the 2 × 2 optical coupler 2. Here, by providing the wavelength filter 6 that cuts the wavelength of the control pulse (b ′), switching (gating) becomes possible.

Next, the above operation will be described quantitatively by using mathematical expressions. The input signal (a ') is input from port # 1. The transmittance T of the signal branched by the 2 × 2 optical coupler 2 having the branching ratio k at the port # 2 is represented by T = 1-4k (1-k) cos ² (Δφ / 2) (1). Here, Δφ is the phase difference between the clockwise light and the counterclockwise light. When Δφ is 0 when k = 0.5, T
Is a 100% mirror.

Now, when the control light (b ') is temporally superposed on the pulse to be separated via the WDM coupler and inputted in the clockwise direction, the cross phase modulation by the control light causes Δφ.
When T = π, T in the equation (1) becomes maximum. If the transmittance when the control light is off is the static transmittance To, To = 1-4k (1-k) (2). When k ≠ 0.5, the balance of interference is lost and the port # Crosstalk that leaks into 2 occurs. The output pulse at this time is shown in FIG.

Here, the phase difference π with respect to the separation target pulse
Consider the case of giving. The number of multiplexes is N. Here, the rate at which channels (2 to N) that are not to be separated leak into the output port is defined as channel crosstalk (CT). Now, assuming that the control light waveform is Gaussian, the phase change occurring in the clockwise component of the separation target channel can be expressed by the following equation.

[Equation 1] However,

[Equation 2] Where P is the peak power of the control light, tc is the full width at half maximum of the control light, l is the loop length, τ is the walk-off, λ is the wavelength of the signal light, n ₂ and Aeff are the nonlinear refractive index and the effective index of each loop fiber, respectively. It represents the core cross-sectional area.

On the other hand, the counterclockwise component of the separation target channel also causes a phase change due to the control light propagating in the opposite direction, as represented by the following equation.

(Equation 3)

In the clockwise component of the non-separation target channel, the pulses do not overlap with each other, so that no phase change occurs. However, the counterclockwise component of the non-separation target channel causes the phase change of the following equation, similarly to the separation target channel. Δφ _ccw = Δφ ' _ccw (5)

Here, when Δφ _{cw −Δφ ccw} = π, the separation target channel is output from port # 2. At the same time, the non-separated channels that _cause a phase shift of Δφ _ccw also partially leak power from port # 2 as channel crosstalk. This channel crosstalk can be expressed by the following equation.

(Equation 4) However,

(Equation 5) It is.

This is generally called a non-linear loop mirror type optical switch (Nonlinear Optical Loop Mirror: NOLM), and ultra-high speed switching is possible by using an optical non-linear effect which is a high speed phenomenon of picosecond or less. (Paper "100 Gb using a non-linear loop mirror
Study of it / s demultiplexing circuit "IEICE Technical Report OCS-95-
40).

[0013]

By the way, the above-mentioned conventional optical control type optical switch is capable of picosecond-class ultra-high speed switching, and both lights in the loop pass through the same path, which causes disturbance. There is an advantage that the influence of the phase fluctuation is canceled out and stable switching is possible, but since the pulse which is not the separation target is also slightly affected by the control light, the input signal line in the 2 × 2 optical coupler is slightly affected. However, there is a problem that 100% is not output and channel crosstalk shown by the equation (6) occurs and the final SN ratio is deteriorated.

In view of the above-mentioned circumstances, an object of the present invention is to provide an optical control type optical switch which has a small crosstalk and can perform switching with a good SN ratio.

[0015]

In order to achieve the above object, the present invention provides an optical control type optical switch for extracting a 1-channel signal from an optical signal train in which N-channel optical pulse signals are time-division multiplexed. The input signal line to which the optical pulse signal is input, the 2 × 2 optical coupler that splits the optical power of this input line into two, the optical loop configured by connecting the two outputs of this 2 × 2 optical coupler, and the optical pulse signal A control pulse light source for generating a control light pulse for switching, a 1 × N branch device for branching the control light pulse emitted from this control pulse light source into N, and each output provided on each output of this 1 × N branch device N optical delay lines that provide a relative time delay between them, N variable attenuators that adjust the power of the optical pulses on the N optical delay lines, and the outputs of these variable attenuators are combined into one. N x 1
A control pulse pattern generation circuit including a coupler, a multiplexer provided on the optical loop for inputting the output of the control pulse pattern generation circuit, a port other than the input line on the input side of the 2 × 2 optical coupler And an output signal line connected to the output signal line, and a wavelength filter provided on the output signal line for removing the wavelength of the control signal.

According to the present invention as described above, the control pulse pattern generation circuit cancels the phase change between the two lights by giving an optical pulse of appropriate power to the non-separation target pulse. Crosstalk is reduced and good SN switching is possible.

[0017]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 3 is a diagram showing an embodiment of the present invention. In the figure, 1 is an input signal line, 2 is a 2 × 2 optical coupler,
3 is an optical loop, 4 is a multiplexer, 5 is an output signal line, 6 is a wavelength filter, 7 is a control pulse light source, 8 is a control pulse pattern generation circuit, 9 is a 1 × N branching device, and 10 is N lights. Delay line,
Reference numeral 11 is an N variable attenuator, and 12 is an N × 1 combiner. FIG.
FIG. 4 is a diagram schematically showing a pulse in this embodiment.

Here, as shown in FIG. 4, an example will be described in which the pulse of the first channel is extracted from the input signal pulse train (a) in which the N-channel signals are time-division multiplexed. A control pulse having a wavelength different from that of the signal light, which is emitted from the control pulse light source 7 at a repetition period of N channels.
(b) is N-branched by the 1 × N branching device 9 and enters each optical delay line 10. There is a relative time delay corresponding to the channel interval of the N-channel multiplexed input signal between the optical delay lines 10, and the control pulse passing through the jth path is the control pulse for the jth channel (b). become.

The light on each path is set to an appropriate peak power by the variable attenuator 11, merged by the N × 1 coupler 12, and input to the optical loop 3 via the multiplexer 4. Where 1
The control pulse for the second channel adjusts the variable attenuator so that the phase difference between the two-direction light in the optical loop 3 becomes π. Further, the other control pulses (b) are adjusted so that each variable attenuator has power enough to cause a phase change equal to the phase change generated in the clockwise light.

Next, the above operation will be described quantitatively by using mathematical expressions. It is assumed that all the attenuation rates of the variable attenuators 11 other than those for the first channel used for each path in the control pulse pattern generation circuit 8 are R. Here, assuming that the control light is Gaussian, the phase change occurring in the clockwise component of the separation target channel can be expressed by equation (3). On the other hand, the counterclockwise component of the separation target channel is represented by the following equation.

(Equation 6)

The phase change occurring in the clockwise component of the non-separation target channel can be expressed by the following equation.

(Equation 7)

The phase change that occurs in the counterclockwise component of the non-separation target channel can be expressed by equation (7). Here, since Δφ _{cw −Δφ ccw} = π, the channel crosstalk can be expressed by the following equation.

(Equation 8) However,

[Equation 9] It is.

This means that the phase change occurring in the counterclockwise component can be canceled by adjusting R appropriately. As an example, regarding the channel crosstalk when the static transmittance is 30 dB, the multiplexing numbers are 8, 16, and 6.
In the case of 4, R is -9.5 dB and -12.2 d, respectively.
The phase shift amount can be canceled at B and -17.8 dB. This is shown in the output pulse (c) of FIG. It can be seen that the magnitude of channel crosstalk is smaller than that in (c ′) of FIG.

As an alternative example, an optical gate switch can be used as the variable attenuator 11 in the control pulse pattern generation circuit 8 described above. In this case, by adjusting the injection bias current to the optical gate switch, it is possible to perform the same operation as in the above-mentioned embodiment, and also to control the optical gate switch from the outside in synchronization with the input signal to Any signal from 1 to channel N can be dynamically selected. The above circuit is
It can be applied to an optical switch drive circuit in an optical ATM switch (see Japanese Patent Application No. 7-20764).

[0025]

As described above, in the light control type optical switch according to the present invention, the phase generated between the two lights is generated by applying the light pulse of the appropriate power to the non-separation target pulse by the control pulse pattern generation circuit. It offsets the changes, thus reducing crosstalk and allowing SN for better switching.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a conventional light control type optical switch.

FIG. 2 is a schematic diagram for explaining the operation principle of FIG.

FIG. 3 is a diagram showing a configuration of an optical control type optical switch of the present invention.

FIG. 4 is a schematic diagram for explaining the operation principle of FIG.

[Explanation of symbols]

 1 Input signal line 2 2 × 2 Optical coupler 3 Optical loop 4 Multiplexer 5 Output signal line 6 Wavelength filter 7 Control pulse light source 8 Control pulse pattern generation circuit 9 1 × N brancher 10 N optical delay lines 11 N Variable attenuator 12 N × 1 combiner (a) Input signal pulse train (b) Control pulse (c) Output pulse

Claims (1)

[Claims] 1. An optical control type optical switch for extracting a 1-channel signal from an optical signal train in which N-channel optical pulse signals are time-division multiplexed, an input signal line to which the optical pulse signal is input, and an optical power of the input line. 2 × 2 optical coupler for branching into two, an optical loop configured by connecting two outputs of the 2 × 2 optical coupler, a control pulse light source for generating a control optical pulse for switching an optical pulse signal, and the control A 1 × N branching device for N-branching a control light pulse emitted from a pulse light source, and N optical delay lines provided on each output of the 1 × N branching device to give a relative time delay between the outputs. A control pulse pattern generation circuit comprising N variable attenuators for adjusting the power of the optical pulses on the N optical delay lines and an N × 1 combiner for combining the outputs of the variable attenuators into one; The control pulse provided on the optical loop A multiplexer for inputting the output of the turn generation circuit, an output signal line connected to a port other than the input line on the input side of the 2 × 2 optical coupler, and a wavelength of a control signal provided on the output signal line An optical control type optical switch comprising a wavelength filter for removal.