JPH09321372A - All optical clocks regenerative circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable mode clocked control by providing a first nonlinear element for generating an optical signal of a third wavelength from optical communication signals of a first and second wavelengths by the four optical wave mixing and second nonlinear element for generating an optical signal of a first wavelength from optical signals of a second and third wavelengths by the four optical wave mixing. SOLUTION: A light of a wavelength λs passed through an optical filter 33 and an optical communication signal of wavelength λp are combined by a multiplexer 35 and fed to a first semiconductor optical amplifier 11 to generate a new optical signal of wavelength λi by the four optical wave mixing. Three output lights from the amplifier 11 are fed to a filter 13 to cut off the light of wavelength λs but only the lights of λp , λi pass through this filter to a second semiconductor optical amplifier 12 to generate a new optical signal of wavelength λs (=2λp -λi ) by the four wave mixing. Among output lights from this amplifier 12 only the light of λs runs on a ring resonator. Thus it is possible to modulate it and enable the mode locked control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an all-optical clock recovery circuit for recovering an optical clock signal from an optical communication signal without converting it into an electric signal.

[0002]

2. Description of the Related Art FIG. 3 shows the configuration of an all-optical clock recovery circuit using a conventional ring resonator laser device. In the figure, an optical amplifier 31, an optical isolator 32, an optical filter 3
3 are connected in a loop through an optical fiber to form a ring resonator laser device having an oscillation wavelength according to the passing wavelength of the optical filter. As an all-optical clock recovery circuit, a coupler 3 is provided between the optical filter 33 and the optical amplifier 31.
4, a multiplexer 35 and a cross phase modulator 36 are inserted.

The optical communication signal is amplified by the optical amplifier 37,
It is input to the ring resonator via the multiplexer 35. In the cross phase modulator 36, the optical communication signal modulates the oscillated light, and mode lock control is applied to the laser device. As a result, the laser device generates an optical pulse synchronized with the frequency of the optical communication signal. This optical pulse is taken out from the coupler 34, and the optical clock signal is regenerated. This operation principle is described in the literature (K. Smith,
et al., "All-optical clock recovery using a mode-lo
cked laser ", IEE Electronics Letters, vol.28, p
p.1814-1816, 1992).

[0004]

By the way, in the conventional all-optical clock recovery circuit shown in FIG. 3, the mutual phase modulator 36 is used.
For example, an optical fiber of about 1 km is used, and its nonlinear effect is used. For this reason, a high output optical amplifier 37 of several W is required, and there is a problem that the entire circuit becomes large. In addition, there is a limit to the clock frequency that can be reproduced due to the dispersion of the optical fiber, and it is currently about 10G.
It was difficult to reproduce ultra-high-speed clock signals above Hz.

An object of the present invention is to provide a small-sized all-optical clock regenerating circuit that enables regenerating a very high speed clock signal.

[0006]

The all-optical clock recovery circuit of the present invention comprises a laser device that constitutes a ring resonator and oscillates light of a first wavelength, and an optical communication signal of a second wavelength in the ring resonator. A multiplexer for inputting and multiplexing with the light of the first wavelength, and a coupler for extracting an optical signal of the first wavelength synchronized with the optical communication signal of the second wavelength from the ring resonator as an optical clock signal, A first nonlinear element for generating an optical signal of a third wavelength by four-wave mixing from light of the first wavelength and an optical communication signal of the second wavelength in the ring resonator; An optical filter that blocks light of a wavelength and a second nonlinear element that generates an optical signal of a first wavelength by four-wave mixing from an optical communication signal of a second wavelength and an optical signal of a third wavelength are inserted.

In this way, two nonlinear elements (semiconductor optical amplifiers) that perform four-wave mixing are arranged in the ring resonator, and an optical filter that blocks light of the oscillation wavelength is inserted between them. This determines whether or not the light of the oscillation wavelength circulates in the ring resonator according to the presence or absence of the optical communication signal.Therefore, the light of the oscillation wavelength is extracted as the optical clock signal synchronized with the optical communication signal. You can

[0008]

FIG. 1 shows an embodiment of an all-optical clock recovery circuit according to the present invention. In the figure, an optical amplifier 31,
The ring resonator laser device including the optical isolator 32 and the optical filter 33 is the same as the conventional one. Let this oscillation wavelength be λs. The all-optical clock recovery circuit includes a coupler 34, a multiplexer 35, and a first semiconductor optical amplifier 1 between an optical filter 33 and an optical amplifier 31 which form a ring resonator.
1, the optical filter 13, and the second semiconductor optical amplifier 12 are inserted. The two semiconductor optical amplifiers 11 and 12 and the optical filter 13 serve as a means (corresponding to the conventional cross phase modulator 36) for modulating the light of the wavelength λs propagating through the ring resonator. Here, the wavelength of the optical communication signal input from the multiplexer 35 to the ring resonator is λp, and the optical filter 13 has a wavelength λ.
It shall block the light of s.

The light having the wavelength λs and the optical communication signal having the wavelength λp, which have passed through the optical filter 33, are combined by the combiner 35 to obtain the first signal.
It is input to the semiconductor optical amplifier 11. In the first semiconductor optical amplifier 11, the wavelength λi (= 2λp−λs) is obtained by mixing four light waves.
A new optical signal of is generated. The wavelength relationship of these three lights is shown in FIG. 3 output from the first semiconductor optical amplifier 11
The two lights are input to the optical filter 13 that blocks the light having the wavelength λs, and only the lights having the wavelengths λp and λi pass and are input to the second semiconductor optical amplifier 12. Second semiconductor optical amplifier 1
In the case of 2, the wavelength λs (= 2λp-
A new optical signal of λi) is generated. Of the light output from the second semiconductor optical amplifier 12, only the light of wavelength λs passes through the optical amplifier 31, the optical isolator 32, the optical filter 33, and the coupler 34 and returns to the multiplexer 35. Thus, when the optical communication signal is input, the optical signal of wavelength λs circulates in the ring resonator.

On the other hand, when no optical communication signal is input to this ring resonator, four-wave mixing does not occur in the first semiconductor optical amplifier 11 and the wavelength λs from the first semiconductor optical amplifier 11 does not occur.
Only the light of is output. However, since the light of wavelength λs is blocked by the optical filter 13, it does not go around the ring resonator. Thus, when the optical communication signal is input, the light propagating in the ring resonator can be modulated, and the mode lock control can be performed. Here, if the gain of the optical amplifier 31 is set to be larger than the loss of the ring resonator, it is possible to completely compensate the loss of the light of the wavelength λs that circulates in the ring resonator due to the gain saturation effect of the optical amplifier 31. It is possible to continue the laser oscillation. Therefore, the optical circuit having this configuration can operate as a laser device that is mode-locked by the optical communication signal and generate an optical pulse synchronized with the optical communication signal. By taking out this optical pulse from the coupler 34, the optical clock signal can be regenerated.

Since the four-wave mixing of the semiconductor optical amplifier is a very high speed phenomenon with a characteristic time of 1 psec or less, the all-optical clock regenerating circuit of the present invention can regenerate an ultrahigh speed clock signal of 100 GHz or more. it can. Further, the semiconductor optical amplifier is an element having a size of about several hundreds of μm and can be integrated with other components constituting the ring resonator laser device, so that it can be easily miniaturized. Similarly, a nonlinear element other than the semiconductor optical amplifier may be used as long as it has a high-speed four-wave mixing phenomenon, is small, and can be integrated with other components.

[0012]

As described above, since the all-optical clock regenerating circuit of the present invention is configured to perform mode-lock control by utilizing a high-speed nonlinear operation called four-wave mixing, it regenerates an ultra-high-speed clock signal. be able to. Further, since a minute non-linear element such as a semiconductor optical amplifier can be used, it can be realized by a small scale circuit.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an all-optical clock recovery circuit according to the present invention.

FIG. 2 is a diagram showing wavelength relationships of four-wave mixing.

FIG. 3 is a block diagram showing a configuration of an all-optical clock recovery circuit using a conventional ring resonator laser device.

[Explanation of symbols]

 11 First Semiconductor Optical Amplifier 12 Second Semiconductor Optical Amplifier 13 Optical Filter 31, 37 Optical Amplifier 32 Optical Isolator 33 Optical Filter 34 Coupler 35 Combiner 36 Mutual Phase Modulator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaki Amamiya 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. A laser device that constitutes a ring resonator and oscillates light of a first wavelength, and an optical communication signal of a second wavelength is input to the ring resonator and multiplexed with the light of the first wavelength. An all-optical clock recovery circuit comprising a multiplexer and a coupler that extracts the optical signal of the first wavelength synchronized with the optical communication signal of the second wavelength from the ring resonator as an optical clock signal, wherein the ring resonance A first nonlinear element for inputting the light of the first wavelength and the optical communication signal of the second wavelength, which are multiplexed by the multiplexer, and generating an optical signal of the third wavelength by mixing four light waves; An optical filter that blocks light of the first wavelength of the output light of the first nonlinear element, and an optical communication signal of the second wavelength and an optical signal of the third wavelength that have passed through the optical filter are input, First by four-wave mixing
An all-optical clock recovery circuit, comprising: a second nonlinear element that generates an optical signal of a wavelength. 2. The all-optical clock recovery circuit according to claim 1, wherein the first nonlinear element and the second nonlinear element are semiconductor optical amplifiers.