JPH05346599A - Optical discriminating and reproducing device - Google Patents

Abstract

PURPOSE:To obtain a fully optical type optical regenerating repeater which can operate at an extremely high speed without the speed limitation of electric circuitry. CONSTITUTION:This optical discriminating and reproducing device has a means which amplifies input light signal pulses, a multiplexing means 2 which multiplexes the input light signal pulses 1 and light clock pulses 3 synchronized with them, an optical nonlinear means 4 which is coupled with its output and has tertiary nonlinear effect, and a demultiplexing means 5 which demultiplexes a light signal generated as a result of 4-photon mixture by the nonlinear means from the input light signal pulses and light clock pulses 3; and the time relation between the both is so adjusted that the input light signal pulses are different in propagation speed from the light clock pulses in the optical nonlinear means and meet the light clock pulses almost in the center of the nonlinear means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication device and an optical signal processing device. In particular, the present invention relates to an all-optical type optical discriminating / reproducing apparatus for retiming and discriminating / reproducing in a light region for a weak binary digital signal propagated through a transmission line.

[0002]

2. Description of the Related Art In a current optical communication device, an optical signal actually flows only in a portion of a transmission line, and in a repeater, the optical signal is once converted into an electric signal,
The electronic circuit performs equalization amplification, retiming, and identification / reproduction processing, and then returns to an optical signal for transmission. Not only is the device complicated by photoelectric conversion, but the operating speed is limited by electronic circuits. The complication of the device due to the interposition of such electrical processing,
In order to solve the problem of processing speed limitation, an optical repeater that processes an optical signal at high speed without converting the optical signal into an electric signal is required.

As such an all-optical type optical repeater, an optical linear amplifier utilizing stimulated emission in a semiconductor laser or an erbium-doped fiber has been conventionally used.

[0004]

However, the above-mentioned optical linear amplifier has a problem in that it accumulates noise and jitter during long-distance multi-stage relay.
It has a drawback that waveform deterioration occurs due to dispersion.
In order to solve these problems, an optical regenerator that performs equalization amplification, retiming, and identification regeneration in the optical region is indispensable. The present invention has been made in view of the above problems, and an object of the present invention is to provide an all-optical type optical identification / regenerator capable of operating at an ultrahigh speed without being subject to electronic circuit speed limitation.

[0005]

The features of the present invention are that a means for amplifying an input optical signal pulse, a combining means for combining the input optical signal pulse and an optical clock pulse synchronized therewith, and an output thereof. An optical non-linear means having a third-order nonlinear effect for coupling, and a demultiplexing means for demultiplexing an optical signal generated as a result of four-photon mixing by the optical non-linear means from an input optical signal pulse and an optical clock pulse, The optical signal pulse has a different propagation speed from the optical clock pulse in the optical nonlinear means,
In the optical discriminator / regenerator, the time relationship between the optical nonlinear means and the optical clock pulse is adjusted so that the optical clock pulse and the optical clock pulse are adjusted at almost the center of the optical nonlinear means.

[0006]

The optical intensity modulated binary digital optical signal pulse propagates through the optical transmission line while receiving the attenuation of the optical intensity, the fluctuation of the time position, the waveform distortion and the accumulation of noise, and the optical discriminator of the present invention is used. Input to the optical regenerator including. This optical signal pulse is amplified by an optical amplifier and input to an optical fiber together with an optical clock pulse generated by an optical timing extractor not included in the present invention. Optical clock pulse
It is synchronized with the input signal but does not contain jitter and the pulse interval is constant. Further, it has a pulse width similar to that of the input optical signal pulse.

The optical discrimination regenerator of the present invention is based on the four-photon mixing in the optical fiber described below. Four-photon mixing is a phenomenon in which light of a fourth wavelength satisfying the phase matching condition is generated from light of two or three waves having different wavelengths due to the third-order nonlinear effect in the optical fiber. Now, the optical signal pulse train (angular frequency: ω ₁ ) and the optical clock pulse train (angular frequency: ω 1
_{It is considered that 3} ) is incident on the optical fiber and only light having an angular frequency ω ₄ (= 2ω ₁ −ω ₃ ) generated by four-photon mixing is extracted as output light. Here, four-photon mixing occurs only when the optical signal pulse and the optical clock pulse are simultaneously incident, and the generated light is a logical product of the two, and therefore inherits the data of the optical signal pulse train.

Since the wavelengths of the optical signal pulse and the optical clock pulse are different, they propagate in the optical fiber at different speeds due to chromatic dispersion. Since the input optical signal pulse has jitter, the time position has a certain distribution, but the signal pulse having the average time position adjusts the average time position of both to meet the optical clock pulse at the exact center of the optical fiber. .. In this way, even if the time position of the input optical signal pulse varies, if the deviation from the average position is shorter than half of the propagation time of the optical fiber, the input optical signal pulse will have an optical clock pulse somewhere in the optical fiber. It is possible to generate light with an angular frequency ω ₄ (= 2ω ₁ −ω ₃ ) by mixing four photons. This light is synchronized with the input signal but does not include jitter, and because it is the result of amplification of a clock pulse whose pulse interval is constant, it inherits the data of the input optical signal but does not include jitter. The above is the principle by which the optical identification and regenerator of the present invention can suppress jitter.

Further, due to four-photon mixing, the angular frequency ω ₄
Since the light intensity of (= 2ω ₁ −ω ₃ ) exponentially increases with respect to the input optical signal pulse intensity, a component having a small peak light intensity is suppressed. That is, it is possible to suppress the unnecessary light pulse in the space and the spontaneous emission light noise generated by the optical amplifier.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings by showing embodiments. FIG. 1 is a diagram showing a configuration of an embodiment of the present invention, in which 1 is an input optical signal pulse, 2 is an optical amplifier, 3 is an optical clock pulse synchronized with the input optical signal pulse train 1, and 4 is an input optical signal. An optical multiplexer for multiplexing the signal pulse and the optical clock pulse, 5 for an optical fiber, 6 for an optical demultiplexer for demultiplexing the optical reproduction signal 7 generated by four-photon mixing from the input optical signal pulse and the optical clock pulse. is there. FIG. 2 is a diagram showing the arrangement of the input optical signal pulse, the optical clock pulse, and the optical reproduction signal.

The optical intensity modulated binary digital optical signal pulse 1 has the following characteristics: attenuation of optical intensity, fluctuation of time position, waveform distortion,
While receiving the accumulation of noise, it propagates through the optical transmission line and is input to the optical regenerator including the optical discriminator of the present invention. The optical signal pulse is amplified by the optical amplifier 2 and input to the optical fiber 5 via the optical multiplexer 4 together with the optical clock pulse 3 produced by the optical timing extractor not included in the present invention. The optical clock pulse is synchronized with the input signal but does not include jitter, and the pulse interval is constant. Further, it has a pulse width similar to that of the input optical signal pulse. Four
Angular frequency generated by photon mixing ω ₄ (= 2ω ₁ −ω
The optical power P ₄ of ₃ ) is proportional to the optical power P ₃ of the optical clock pulse 2, and can be expressed as follows using the optical power P ₁ of the optical signal pulse 1.

[0012]

[Equation 1]

Here, γ is an index representing the magnitude of the nonlinear effect, and γ = 2πn ₂ / λA using the nonlinear constant n ₂ , the signal light pulse wavelength 1, and the effective core area A _eff of the fiber.
given by _eff . D is the dispersion in the signal light pulse wavelength, Δλ is the wavelength difference between the signal light pulse and the clock light pulse, c is the speed of light, and L is the length of the fiber. FIG. 3 is a diagram showing P ₄ / P ₃ with D [ps / nm, km] (Δλ) ² [nm ² ] on the horizontal axis. At this time, λ = 1.55 μm, n ₂ =
3.2 × 10 ⁻²⁰ m ^{2 /} W and L = ^2.5 km were used. From the figure, it can be seen that there is a gain peak in the dispersion region as long as the dispersion is negative, and the wavelength difference at which the gain becomes maximum (phase matching occurs) Δλ increases as the signal light pulse power increases. For example, P ₁ = 0.5 W, D = -1 ps / n
A gain of about 20 dB is obtained when m, km and Δλ = 2 nm.
Since the four-photon mixing occurs only when the optical signal pulse and the optical clock pulse are incident at the same time, the generated light is a logical product of the two and therefore inherits the data of the optical signal pulse train. This state is shown in FIG. Figure 4 (a)
Shows an input optical signal pulse train having "1011" data as an example, and 8 and 9 show time positions of the input end and the output end of the optical fiber with reference to the optical clock pulse (b). Even if there is jitter in the input optical signal pulse train, fluctuations occur due to the walk-off of the input optical signal pulse and the optical clock pulse. The walk-off time (optical fiber length / propagation) of the input optical signal pulse and the optical clock pulse in the optical fiber. If it is shorter than the speed difference), the input optical signal pulse and the optical clock pulse overlap somewhere in the optical fiber, and due to the four-photon mixing, the reproduced signal output 10 modulated by the optical signal pulse is obtained.

Since the horizontal axis of FIG. 3 is D (Δλ) ² , D
If (the signal light pulse wavelength is made closer to the zero-dispersion wavelength from the long wavelength side), the wavelength difference Δλ between the signal light pulse and the clock light pulse is increased while maintaining the gain. It is possible to increase the group velocity difference of the clock light pulse and propagate it in the optical fiber at different velocities. Since the input optical signal pulse has jitter, the time position has a certain distribution, but the signal pulse having the average time position adjusts the average time position of both to meet the optical clock pulse at the exact center of the optical fiber. .. By doing this, even if the time position of the input optical signal pulse varies,
If the deviation from the average position is shorter than half the propagation time of the optical fiber, the input optical signal pulse encounters an optical clock pulse somewhere in the optical fiber, and the angular frequency ω due to four-photon mixing
It is possible to generate light of ₄ (= 2ω ₁ −ω ₃ ). This light is synchronized with the input signal but does not include jitter, and because it is generated as a result of amplification of a clock pulse whose pulse interval is constant, it inherits the data of the input optical signal but does not include jitter. The above is the principle by which the optical identification and regenerator of the present invention can suppress jitter.

Further, the intensity of light having an angular frequency ω ₄ (= 2ω ₁ −ω ₃ ) generated by four-photon mixing exponentially increases with respect to the intensity of the input optical signal pulse, so that the peak light intensity is small. The component is suppressed. That is, it is possible to suppress the unnecessary light pulse in the space and the spontaneous emission light noise generated by the optical amplifier.

When the optical power of the reproduction signal light pulse generated by the four-photon mixing is less than the power required for the transmission of the next stage, it can be amplified by using an optical amplifier. Although the wavelengths of optical signals in the transmission lines in the subsequent stages are different from those in the transmission lines in the previous stage, this can be dealt with by appropriately designing the optical repeater.

[0017]

As described above, by using the optical discriminator / reproducer of the present invention, a very high speed input optical signal pulse train containing jitter, optical intensity fluctuation, spontaneous emission optical noise, and other optical signals not containing them can be used. It becomes possible to reproduce the signal pulse train.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 2 is a diagram showing an arrangement of input optical signal pulses, optical clock pulses, and optical reproduction signals in the present invention.

FIG. 3 is a diagram showing a ratio P ₄ / P ₃ of optical power P ₄ generated by four-photon mixing and optical power P ₃ of an optical clock pulse.

FIG. 4 is an explanatory diagram of the operation of the present invention.

[Explanation of symbols]

 1 input optical signal pulse train 2 optical amplifier 3 optical clock pulse train 4 optical multiplexer 5 optical fiber 6 optical demultiplexer 7 regenerated optical signal pulse train

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04B 10/06

Claims (1)

[Claims] 1. A means for amplifying an input optical signal pulse, a combining means for combining the input optical signal pulse and an optical clock pulse synchronized therewith, and a light having a third-order nonlinear effect coupled to its output. And a demultiplexing unit for demultiplexing an optical signal generated as a result of four-photon mixing by the optical nonlinear unit from an input optical signal pulse and an optical clock pulse. An optical discrimination regenerator characterized in that the optical clock pulse has a propagation speed different from that of the optical clock pulse, and the time relationship between the two is adjusted so as to meet the optical clock pulse at approximately the center of the optical nonlinear means.