JP3319685B2 - All-optical discrimination reproduction circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an all-optical discriminating / reproducing circuit for discriminating / reproducing signal light whose signal quality has deteriorated without converting it into an electric signal. The signal light transmitted over long distances is
Signal quality is degraded due to increases in loss, waveform distortion, and timing jitter (variation in pulse interval on the time axis). The all-optical discriminating / reproducing circuit has a function of optimizing the pulse amplitude and pulse width of such signal light and removing timing jitter. It should be noted that wavelength conversion may be performed at the time of identification reproduction.

[0002]

2. Description of the Related Art FIG. 3 shows a configuration example of a conventional all-optical discrimination / reproduction circuit. In the figure, 31 is a signal light input terminal, 32 is a clock light generator, 33 is an optical switch, and 34 is a reproduction light output terminal. From the signal light input terminal 31 to the optical switch 33
There are loss, waveform distortion, and timing jitter in the signal light input to. On the other hand, the clock light input from the clock light generator 32 to the optical switch 33 is an undegraded light pulse, and its repetition frequency is set equal to the bit rate of the signal light. The optical switch 33 modulates the intensity of the clock light with the intensity of the signal light and outputs the modulated light to the reproduction light output terminal 34.

As the optical switch 33, there are an optical Kerr shutter, a nonlinear loop mirror, and the like. Here, the operation when a nonlinear loop mirror is used will be described. FIG.
Shows a configuration example of a nonlinear loop mirror. In the figure,
41 is a signal light input port, 42 is a clock light input port, 43 is an optical coupler, 44 is an optical multiplexer, 45 is an optical fiber, and 46 is a reproduction light output port.

[0004] From the clock light input port 42 to the optical coupler 4
The clock light (λ ₂ ) input to 3 is divided into two equal parts, and propagates in opposite directions in the optical fiber 45 forming the loop. On the other hand, the signal light (λ ₁ ) input from the signal light input port 41 to the optical multiplexer 44 propagates through the optical fiber 45 in only one direction. Therefore, clock lights propagating in the optical fiber 45 in opposite directions have different phase shift amounts due to the optical Kerr effect due to the signal light. When the clock light merges again at the optical coupler 43, the balance between the two is lost, and when the phase difference becomes π, the clock light is completely switched and reproduced as reproduction light (λ ₂ ) with respect to the signal light (λ ₁ ). The light is output to the light output port 46.

FIG. 5 shows input / output characteristics of a nonlinear loop mirror. In this input / output characteristic, the transmittance of the clock light from the clock light input port 42 to the reproduction light output port 46 changes according to the signal light intensity. However, when the signal light intensity increases to a certain extent, the transmittance is saturated. I do. Therefore, if the average value of the signal light intensity is set to an appropriate value using an optical amplifier or the like, the fluctuation of the reproduction light intensity can be suppressed with respect to the fluctuation of the signal light intensity.

FIG. 6 shows characteristics of a switching time window of a nonlinear loop mirror. In the nonlinear loop mirror, a rectangular switching window as shown in the figure is formed by a propagation speed difference (walk-off) caused by a wavelength difference between the signal light (λ ₁ ) and the clock light (λ ₂ ). Therefore, even if there is some timing jitter in the signal light, the timing jitter is absorbed by the switching window, and the clock light switched by the signal light and having no timing jitter is output to the reproduction light output port 46 as the reproduction light. You.

[0007] By the above function, the signal light (λ ₁ ) having amplitude fluctuation and timing jitter as shown in FIG.
By switching to a clock light (λ ₂ ) free from amplitude fluctuations and timing jitter, it is possible to obtain a reproduction light (λ ₂ ) that has been identified and reproduced. FIG. 7 shows a state in which “1101” of the RZ signal is identified and reproduced.

[0008]

The input / output characteristics of an all-optical discriminating / reproducing circuit using a non-linear loop mirror have threshold characteristics as shown in FIG. The effect on light intensity cannot be completely eliminated. Furthermore, if the signal light intensity is large and the phase shift given to the clock light exceeds π, the output waveform will be folded, causing waveform distortion.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an all-optical discriminating / reproducing circuit capable of maintaining a constant reproducing light intensity even when the signal light intensity fluctuates at a very high speed and enabling optical discrimination / reproduction without waveform distortion. I do.

[0010]

An all-optical discriminating / reproducing circuit according to the present invention generates an optical amplifying means for amplifying a signal light and an ultra-wide band super continuum light having the same time waveform as the amplified signal light. An optical non-linear medium and a wavelength separation unit that separates and outputs a predetermined wavelength component from the supercontinuum light are provided. The signal light having a predetermined wavelength and light intensity obtained through the optical amplifying means, the optical nonlinear medium, and the wavelength separating means is input to the optical switch together with the clock light.

In the optical non-linear medium, the fluctuation of the light intensity of the input signal light is converted into the spread of the light spectrum. Therefore, even if the light intensity of the input signal light fluctuates greatly, the light intensity of the signal light input to the optical switch can be kept constant, and an optical discrimination / reproduction process without waveform distortion is realized.

[0012]

FIG. 1 shows an embodiment of an all-optical discriminating / reproducing circuit according to the present invention. In the figure, signal light input terminal 3
1. The clock light generator 32, the optical switch 33, and the reproduction light output terminal 34 are the same as those in the conventional configuration shown in FIG. In the present embodiment, an optical splitter 11, an optical amplifier 12 as an optical amplifier, an optical fiber 13 as an optical nonlinear medium, and a bandpass optical filter 14 as a wavelength separator are provided between the signal light input terminal 31 and the optical switch 33. insert.

The signal light input from the signal light input terminal 31 to the optical amplifier 12 via the optical splitter 11 is amplified to a predetermined light intensity and input to the optical fiber 13. At this time,
When the wavelength λs of the input signal light is set near the zero-dispersion wavelength of the optical fiber 13 and the signal light intensity is increased, the supercontinuity in which the signal spectrum spreads to the output of the optical fiber 13 by several tens of times or more is obtained. Am light (hereinafter, referred to as SC light) is generated.

The conditions of the optical fiber 13 for generating the SC light are defined in detail in Japanese Patent Application No. 7-37199 (coherent white light source). According to this, the tertiary nonlinear coefficient of the optical fiber is γ, the energy per pulse of the signal light is E, the peak power of the signal light pulse in the optical fiber is P, the gain of the intensity of the light wave mixing light is G ₀ , the vacuum When the speed of light is c, the length is lnG ₀ / (2 | γ | P) [km] or more in a predetermined wavelength range Δλ including the wavelength λs of the signal light, and the absolute value of the dispersion slope is 16 (| Γ | E) / (Δλ ² InG ₀ ) [ps / nm ² / km] and the absolute value of the dispersion at the wavelength λ ₀ is (16 / πc) · λs ² | γ | P / ( Δλ) ² [ps / nm / km] The following may be used.

Here, the characteristics of the SC light generation phenomenon will be described with reference to FIG. As shown in FIG. 2A, when a signal light having a light intensity equal to or lower than the light intensity at which SC light starts to be generated is input, almost no change in the spectrum of the output light is observed. For example, if the time waveform of the input light is a Gaussian transform-limited waveform, the spectral shape of the output light is also Gaussian. On the other hand, when a signal light having a light intensity equal to or higher than the light intensity at which the SC light starts to be generated is input, the output SC light has a wavelength of interest only because its spectrum is widened as shown in FIGS. 2 (b) and 2 (c). Is constant. That is, the SC light generation phenomenon can be said to be a phenomenon that operates as a light intensity limiter circuit having a threshold for the input signal light intensity. Therefore, if this SC light generation phenomenon is used, waveform distortion and noise components whose light intensity is equal to or less than a certain value are removed, and waveform shaping of signal light can be performed.

When the SC light output from the optical fiber 13 is cut by the band-pass optical filter 14, a signal light pulse having the same time waveform as the input signal light is obtained at the cut wavelength λsc (≠ λs). To return the wavelength of the signal light pulse to the original input signal light wavelength λs, the wavelength of the clock light generated by the clock light generator 32 may be set to λs. The operation of the optical switch 33 is the same as the conventional configuration described with reference to FIGS.

The timing extracting circuit 15 includes the optical splitter 11
A clock signal is extracted from the signal light branched in step (1) and supplied to the clock light generator 31 to generate a clock light synchronized with the signal light and having a repetition frequency equal to the bit rate of the signal light. This clock light and the bandpass optical filter 14
By inputting the signal light having a constant light intensity and the signal light outputted from the optical switch 33 to the optical switch 33, it is possible to obtain the reproduction light (λs) which is identified and reproduced without amplitude fluctuation and timing jitter.

When the optical switch 33 requires a large input light intensity, the optical switch 33 is connected between the band-pass optical filter 14 and the optical switch 33 and between the clock light generator 32 and the optical switch 33, respectively. Amplifiers 16 and 17 may be inserted.

[0019]

As described above, the all-optical discriminating / reproducing circuit of the present invention provides a signal light pulse that is extremely stable and high-speed with respect to a signal light whose waveform is degraded due to fluctuations in light intensity occurring in pulse units. Can be identified and reproduced. Further, since the dynamic range of the identification and reproduction operation is wide and the operating wavelength range can be widened, it is extremely useful as an all-optical identification and reproduction circuit in long-distance and multi-repeater optical transmission and high-speed optical signal processing.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an all-optical discrimination / reproduction circuit of the present invention.

FIG. 2 is a diagram illustrating characteristics of generation of supercontinuum light in an optical fiber.

FIG. 3 is a block diagram showing a configuration example of a conventional all-optical discrimination / reproduction circuit.

FIG. 4 is a diagram showing a configuration example of a nonlinear loop mirror.

FIG. 5 is a diagram showing input / output characteristics of a nonlinear loop mirror.

FIG. 6 is a diagram showing characteristics of a switching time window of a nonlinear loop mirror.

FIG. 7 is a diagram illustrating an optical discrimination / reproduction operation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Optical branching device 12 Optical amplifier 13 Optical fiber 14 Bandpass optical filter 15 Timing extraction circuit 16, 17 Optical amplifier 31 Signal light input terminal 32 Clock light generator 33 Optical switch 34 Reproduction light output terminal 41 Signal light input port 42 Clock light Input port 43 Optical coupler 44 Optical multiplexer 45 Optical fiber 46 Reproduction light output port

Continuation of the front page (56) References JP-A-7-336268 (JP, A) JP-A-6-141002 (JP, A) JP-A-5-284117 (JP, A) JP-A-6-112908 (JP) , A) JP-A-3-278627 (JP, A) JP-A-2-12227 (JP, A) Kentaro Uchiyama et al., Polarization-independent all-optical signal regeneration circuit, IEICE General Conference, 1995 Collection of Lecture Papers Communication 2, March 10, 1995, Vol. 1995, General Part 3, pp. 606 (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/35-1/39 H04B 10/00-10/18 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. A bit rate of a signal light synchronized with the signal light.
A clock light generator that generates a clock light having a repetition frequency equal to the optical signal, and an optical switch that receives the signal light and the clock light, modulates the intensity of the clock light with the intensity of the signal light, and outputs the modulated light as reproduction light. In the all-optical discriminating and reproducing circuit provided, an optical amplifying means for amplifying the signal light, and the signal light amplified by the optical amplifying means are input, and an ultra-wideband supercontinuum light having the same time waveform as the signal light is input. An optical non-linear medium to be generated, and a wavelength separating means for separating and outputting a predetermined wavelength component from the super continuum light, wherein the predetermined wavelength obtained through the optical amplifying means, the optical non-linear medium and the wavelength separating means is provided. An all-optical discrimination / regeneration circuit, wherein signal light having the wavelength and the light intensity is input to the optical switch.