JP3199286B2 - Optical packet signal phase synchronization circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for time division multiplex transmission using an optical packet signal. In particular, the present invention relates to an optical packet signal phase synchronization circuit for keeping a time interval between optical packet signals constant.

[0002]

2. Description of the Related Art In a high-speed optical packet communication, when an optical packet signal is to be time-division multiplexed due to a long-term change in optical path length due to a temperature change or the like, for example, a change in the length of an optical fiber. Phase synchronization may not be achieved. In such a case, conventionally, the optical signal is once converted into an electric signal, the frame phase is synchronized, and then the optical signal is converted again into an optical signal. Such an example is shown in FIG.

FIG. 3 shows a conventional 4-input optical packet signal phase synchronization circuit. In this conventional example, four series of optical packet signals having a phase shift are respectively converted into photoelectric converters 31 to 34.
, The electric signal is input to the elastic store memory 35 to synchronize the frames with each other, and the electric signal is combined by the coupler 36 and then converted into the optical signal by the electro-optical converter 37. .

[0004]

However, in this conventional example, since an optical signal is once converted into an electric signal, the transmission band of a signal to be handled is limited, and an optical packet signal having a signal speed of several tens Gbit / s or more is used. It was very difficult to process.

An object of the present invention is to provide an optical packet signal phase-locked circuit that solves such a problem and synchronizes the phase of the optical packet signal as it is.

[0006]

SUMMARY OF THE INVENTION An optical packet signal phase synchronization circuit according to the present invention comprises a plurality of optical pulse trains having a fixed period for each channel and an optical packet signal synchronized with the optical pulse train being multiplexed and inputted. An optical delay line, an optical coupler that multiplexes the output lights of the plurality of optical delay lines, and a plurality of optical delays that monitors the output light of the optical coupler and matches the timing of the optical pulse train for each channel. Monitoring control means for controlling a relative delay amount of the line.

When the number of channels is two, it is preferable to control the delay amount of one of the two optical delay lines. If the number of channels exceeds two, it is preferable to synchronize the phases of the optical packet signals in every two channels and synchronize the phases again two by two.

The wavelength of the optical pulse train of each channel is λ
Is ₂ and the wavelength lambda ₁ of the optical packet signal is set to different values, as the monitoring control unit, and a wavelength filter which transmits light of the wavelength lambda _2, the peak value of the light intensity transmitted through the wavelength filter is pre An optical threshold detector for electrically detecting whether or not a predetermined threshold is exceeded; and an optical delay amount of at least one of a plurality of optical delay lines based on an output of the optical threshold detector And an electric control circuit that electrically controls the control signal.

It is preferable that the optical coupler has a two-output configuration, one output of which is supplied to the monitoring control means, and the other output being output to the optical transmission line as an optical packet multiplexed signal.

[0010]

An optical pulse train synchronized with the optical packet signal, in particular, an optical pulse train which is desired to be temporally synchronized with the head pulse of the optical packet signal is generated and multiplexed with the optical packet signal. This corresponds to superimposing a timing signal based on an optical pulse train on the optical packet signal. When such optical packet signals are combined with each other, the optical pulse trains overlap each other when their phases are synchronized. Therefore, it is monitored whether or not the light intensity of the light pulse train exceeds a threshold. Specifically, the wavelength λ ₂ of the optical pulse train is set to a value different from the wavelength λ ₁ of the optical packet signal, and the wavelength λ ₂ is separated by a wavelength filter, and the light intensity is electrically measured. If the measured peak value of the light intensity exceeds the threshold value, it can be determined that the optical pulse trains overlap each other and that the phase is synchronized. If the measured peak value of the light intensity does not exceed the threshold value, it is determined that the phase synchronization has been lost, and the phase of the optical packet signal is controlled by adjusting the optical delay line. This makes it possible to compensate for a phase shift of about the pulse width of the light pulse.

[0011]

FIG. 1 is a block diagram showing an optical packet signal phase synchronization circuit according to a first embodiment of the present invention. Here, a configuration is shown in which the phases of optical packet signals input from two channels (hereinafter referred to as “channel 1” and “channel 2”) are synchronized and multiplexed.

In this embodiment, an optical pulse train having a constant period for each channel and an optical packet signal synchronized with the optical pulse train are multiplexed and input as a plurality of optical delay lines, and the optical variable delay lines 3-1 and 3-1 are used as optical delay lines. 3-2, a 2 × 2 optical coupler 4 for multiplexing the output lights of the plurality of optical variable delay lines 3-1 and 3-2, and monitoring the output light of the optical coupler 4 A wavelength filter 5, an optical threshold detector 6, and an electric control circuit 7 are provided as monitoring and control means for controlling the relative delay amounts of the plurality of optical delay lines so that the timing of each optical pulse train coincides.

An optical packet signal having a wavelength λ ₁ is input to the channel 1, and a short optical pulse train having a constant cycle at a wavelength λ ₂ is output from the laser diode 1-1 in synchronization with the optical packet signal. This is, for example, the laser diode 1-
1 and an electro-optical converter, which is a source of the optical packet signal, are operated by the same synchronization signal. The optical packet signal of the channel 1 and the short optical pulse train from the laser diode 1-1 are combined by the 2 × 1 optical coupler 2-1 so that the leading pulse and the short optical pulse of the optical packet signal overlap. This combined light is input to the optical variable delay line 3-1.

Similarly, for the channel 2, an optical packet signal of the wavelength λ ₁ and a short optical pulse train of the wavelength λ ₂ output from the laser diode 1-2 at a constant period are also converted by the 2 × 1 optical coupler 2-2. The signals are combined and input to the optical variable delay line 3-2.

The outputs of the optical variable delay lines 3-1 and 3-2 are 2 ×
The two light couplers 4 combine the light. The 2 × 2 optical coupler 4 is
An optical packet signal is multiplexed and output to one of the two output ports, and monitor light is output to the other. Here, since the optical packet signal exists only in the packet slot having a fixed period, the optical variable delay lines 3-1 and 3-2 are initialized so that the short optical pulses of both channels temporally overlap. .

The monitor light output from the 2 × 2 optical coupler 4 is
The light having a wavelength λ ₂ , that is, a short light pulse component passes through a wavelength filter 5 and enters a light threshold detector 6.
In the state where the optical variable delay lines 3-1 and 3-2 are initially set,
The optical packet signals output from the respective devices are phase-synchronized, and the timings of the short optical pulses incident on the optical threshold detector 6 from the respective optical packets also match. But,
When the optical path length changes due to a temperature change or a temporal change, the timing shifts. The light threshold detector 6 detects whether the peak value of the light intensity transmitted through the wavelength filter 5 exceeds a predetermined threshold value, that is, the state where the short light pulses overlap, or the light intensity peak value. It is detected whether the value does not exceed the threshold value, that is, whether the timing of the short light pulse is shifted. If the timing of the short optical pulse is shifted, the phase of the optical packet signal is also shifted.
At least one of 1 and 3-2 (3-1 in the illustrated example)
Is electrically controlled.

Since the short optical pulse train is used as the timing signal in this manner, the optical packet signal can be phase-synchronized with a synchronization accuracy of about the pulse width of the short optical pulse.
In this case, the response speed of the optical threshold detector becomes a problem. However, if an optical bistable element is used, a response speed of about the pulse width of a short optical pulse can be obtained.

FIG. 2 is a block diagram showing a second embodiment of the present invention, and shows an n-channel input configuration in which a plurality of optical packet signal phase synchronization circuits shown in FIG. 1 are connected in a tree form.

The first-stage circuit synchronizes the phases of channel 1 and channel 2, channel 3 and channel 4,..., Channel n-1 and channel n, and multiplexes the optical packet signals of the two channels.

The second-stage circuit synchronizes and multiplexes the optical packet multiplexed signal obtained in the first-stage circuit by two sequences. The channel 1 to channel 4 will be described. A signal in which channel 1 and channel 2 are multiplexed is input to an optical variable delay line 8, and a signal in which channel 3 and channel 4 are multiplexed is input to optical variable delay line 9. And the 2 × 2 optical coupler 10
To join. The variable optical delay lines 8 and 9 are initialized as in the first embodiment. The 2 × 2 optical coupler 10 outputs an optical packet multiplexed signal for channel 1 to channel 4 to one of the two output ports, and outputs monitor light to the other output port. From the monitor light, a short light pulse component is extracted by the wavelength filter 11 and the light intensity detector 12 measures the peak value of the light intensity. When this peak value does not exceed the threshold,
That is, if the short optical pulses from both paths do not overlap, it is determined that the phase synchronization has been lost, and the electric control circuit 13 sends at least one of the optical variable delay lines 8 and 9, in this example, the optical variable delay line. 8 is adjusted.

In the same manner, n × 1 optical packet signals can be time-division multiplexed and their phases can be synchronized.

[0022]

As described above, the optical packet signal phase-locked loop according to the present invention adjusts the phase with an accuracy of about the pulse width of the optical pulse against the phase shift due to a long-term change in the optical path length. The optical packet signal that has been compensated and whose phase has been compensated can be time-division multiplexed.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a second embodiment of the present invention.

FIG. 3 is a block diagram showing a conventional optical packet signal phase synchronization circuit.

[Explanation of symbols]

 1-1, 1-2 Laser diode 2-1, 2-2 2 × 1 optical coupler 3-1, 3-2, 8, 9 Optical variable delay line 4, 10 2 × 2 optical coupler 5, 11 Wavelength Filter 6,12 Optical threshold detector 7,13 Electric control circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-229938 (JP, A) JP-A-53-20706 (JP, A) JP-A-5-102930 (JP, A) JP-A 63-209 9246 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04J 14/00-14/08 H04B 10/00-10/28 H04J 3/00

Claims (3)

(57) [Claims] 1. An optical pulse train having a constant period for each channel and an optical packet signal synchronized with the optical pulse train are multiplexed and input to a plurality of optical delay lines, respectively. An optical coupler for multiplexing, monitoring control means for monitoring the output light of the optical coupler, and controlling the relative delay amount of the plurality of optical delay lines so that the timing of the optical pulse train for each channel matches. An optical packet signal phase synchronization circuit comprising: 2. The wavelength of the optical pulse train is all λ ₂ and is set to a value different from the wavelength λ ₁ of the optical packet signal. The monitoring control means is a wavelength filter that transmits light of the wavelength λ _2. An optical threshold detector for electrically detecting whether the peak value of the light intensity transmitted through the wavelength filter exceeds a predetermined threshold, and an output of the optical threshold detector 2. An optical packet signal phase-locked loop according to claim 1, further comprising: an electric control circuit for electrically controlling at least one optical delay amount of said plurality of optical delay lines based on the following. 3. The optical coupler according to claim 1, wherein the optical coupler has a two-output configuration, one output of which is supplied to the monitoring control means, and the other output is output to the optical transmission line as an optical packet multiplexed signal. 3. The optical packet signal phase synchronization circuit according to 2.