JPH02183236A - Light timing extracting circuit - Google Patents

Abstract

PURPOSE:To making the power of extracted light timing light sufficiently large and not dependent upon the power of input signal light by providing a progressive waveform semiconductor laser amplifier in a Fabry-Perot type resonator. CONSTITUTION:A single mode fiber 6a, a dielectric multilayered film 7a, a SELFOC lens 5a, a semiconductor laser amplifier 4, a SELFOC lens 5b, a dielectric multilayered film 7b, and a single mode fiber 6b are arranged in the course of input signal light 8 in order. Here, when ASK-modulated signal light 8 is inputted to the light timing extracting circuit, the semiconductor laser amplifier 4 causes implantation synchronization and a mode lock phenomenon and the Fabry-Perot resonator consisting of the dielectric multilayered films 7a - 7b functions as a resonator providing amplifying operation internally, so that the timing light 9 is extracted and outputted. Consequently, the output power of the timing light 9 is intense and does not depend upon the intensity of the input signal light 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical timing extraction circuit that extracts an optical clock component without converting an optical signal into electricity.

``Prior Art'' Conventionally, when extracting a clock component of input signal light, Fabry-Per, not shown in FIG.

A shaped resonator 1 was used. This Pabry -
The inner surface of the Perot-type resonator l is mirror-polished, and input signal light incident from the outside is repeatedly reflected by these mirror surfaces, thereby causing a resonance phenomenon within the resonator i. Here, the input signal light 2 is RZ (Re
(turn to zero) code. And Fabry-Perot type resonator l
The resonator length is determined according to the modulation frequency of the input signal light 2. When input signal light 2 is input to this P ary -Perot resonator 1 , its clock component is extracted and output as timing light 3 .

``Problems to be Solved by the Invention'' By the way, the Fabry-Perot type resonator described above uses the power of the extracted timing light to operate an optical identification circuit or an optical/electrical converter connected afterwards. There is a problem that the timing light 3 is not sufficient to control the input signal light 2 depending on the level fluctuation of the input signal light 2.
m1 and the input signal light 2 fluctuate from the level of
There is a problem in that when "0" (low level) continues in , the level of the timing light 3 decreases.

This invention was made in view of the above circumstances,
Even when there are level fluctuations in the input signal light,
Another object of the present invention is to provide an optical timing extraction circuit that can extract timing light at a stable level.

"Means for Solving the Problems" In order to solve the above problems, the present invention is based on the ASK (
A mpuliLude Shift K eyin
g) An optical timing extraction circuit that extracts an optical clock component from modulated input signal light, comprising: a Fabry-Perot type resonator having a resonant frequency that matches the modulation frequency of the ASK-modulated input signal light; and the resonator. It is characterized by comprising a traveling wave semiconductor laser amplifier with an end face anti-reflection coating disposed inside.

"Operation" According to the above configuration, a mode-locking phenomenon and a synchronous pull-in phenomenon occur in the traveling wave semiconductor laser amplifier interposed inside the Fabry-Pero L-type resonator.

Therefore, the Pabry-Perot type resonator functions as a resonator that has an amplification effect inside, and the clock component of the light input to the resonator is extracted and output.

"Example" Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a previous timing extraction circuit according to an embodiment of the present invention. In the figure, 4 is a traveling wave semiconductor laser amplifier (SLA), 5a and 5b are Selfoc lenses, 6a and 6b are single mode fibers, and 7
a and 7b are dielectric multilayer films that increase reflectance. These elements are arranged on the path of the input signal light 8 from the single mode fiber 6a to the dielectric multilayer film 7a to the Selfoc lens 5a to the semiconductor laser amplifier 4 to the Selfoc lens 5.
b → dielectric multilayer film 7b → single mode fiber 61)
They are arranged in the following order. Then, the dielectric multilayer film 7
The space between a and 7b constitutes a Fabry-Perot resonator. Here, the resonance frequency is determined by the distance between the dielectric multilayer films 7a and 7b, and in this embodiment, the distance between the modulation frequency fm of the input signal light and the modulation frequency fm is I+n=C/L (C
The dielectric multilayer films 7a and 7b are arranged so that the relationship of the speed of light (2,99× 10 I1 m/s) holds true.

In this configuration, when a current is injected into the semiconductor laser amplifier 4, the semiconductor laser amplifier 4 enters the oscillation state and CW
(Continuous Wave; Continuous Wave) Output shift of light. In this case, the spectrum shown in FIG. 2 is obtained as the output spectrum of the semiconductor laser amplifier 4.

As shown in the figure, the mode spacing of the oscillation longitudinal mode is approximately f
It becomes n+GH2. However, due to refractive index dispersion based on the injected carrier density, the mode spacing is not equal. Furthermore, the phase relationship between longitudinal modes is also random.

Now, when the ASK-modulated signal light 8 is input to this optical timing extraction circuit, a mode-locking phenomenon occurs in the semiconductor laser amplifier 4. This phenomenon will be explained below.

First, the optical field (J(r, t)) of the signal light ASK-modulated at the frequency fmGHz follows the following equation (1).

% formula %))])] where A(r) is the amplitude of the optical field, a is the modulation degree, φ is the phase, ω. =2π"m. Looking at the above equation (1), it can be seen that a sideband wave is generated with respect to the carrier angular frequency ωm of light. This situation is shown in FIG.

Input signal light 8 having two sidebands is incident on semiconductor laser 4 through single-mode fiber 6a, dielectric multilayer film 7a, and SELFOC lens 5a. In this case, the frequency r0 of the optical field is the oscillation longitudinal mode I' of the semiconductor laser 4.
An important condition is that the values almost match j (j=i −3, i −2, . . . ). When this condition is satisfied, an injection locking phenomenon occurs in the semiconductor laser amplifier 4, and fj is pulled into fo. The injection locking width in this case is described in detail in, for example, "Semiconductor Lasers and Integrated Circuits" by Yasuharu Suesue. A similar injection locking phenomenon also occurs for sideband frequencies r0±fa+. That is, a chain reaction occurs in which the sideband component is amplified, and a sideband is further generated in the adjacent mode and amplified. The synchronization phenomenon thus generated leads to aligning the phases between the longitudinal modes and keeping the frequency intervals constant.

The power of the signal light 9 outputted after being mode-locked in this way becomes independent of the level of the input signal light 8 as the injection current increases. Figure 4 shows the literature “S, Kobayas
hi and T, kimura, IEEE J, Qu
antum Electron, QE-17,5,P
This is data showing the relationship between output power and injection current in a semiconductor laser, quoted from ``P., 681-689 (1981)''. In this figure, the horizontal axis is the injection current normalized to the oscillation threshold, and the vertical axis is the injection current normalized to the oscillation threshold. indicates the output power normalized by the free-running oscillation power of the optical timing extraction circuit.
In this figure, the theoretical values determined using the input power as a parameter are drawn with solid lines and broken lines. Looking at this diagram,
It can be seen that as the injected current increases, the output power approaches the free-running oscillation power. This free-running oscillation power is several IIIW
It becomes the power of

In this way, the mode-locking phenomenon occurs in the semiconductor laser amplifier 4 with the injection amount □ period, so the dielectric multilayer films 7a to 7b
The Fabry-Perot# shaker is composed of
It functions as a resonator with an internal amplification effect.

Therefore, as shown in FIG. 5, when a signal light ASK-modulated with an RZ code with a speed fmGbit/s is input to this optical timing extraction circuit as an input signal light 8, the timing light with a frequency rI11 shown in FIG. 9 will be extracted and output. Here, the output power of this timing light 9 is as strong as several IIW and does not depend on the intensity of the input signal light 8.

In the above embodiment, the case where the input signal light is ASK modulated has been explained, but it is also possible to inject a sinusoidally modulated signal light as the input signal light and set the injection current of the semiconductor laser below the oscillation threshold. Then, Fabry-Per
The ot# and longitudinal modes are model-locked over the entire wide gain distribution of the semiconductor laser, that is, about 6 Tυz (50 nm). Therefore, it is also possible to generate extremely short pulses (sub-picosecond pulses).

"Effects of the Invention" As explained above, according to the present invention, there is provided a Pabry-Perot type resonator having a resonant frequency that matches the modulation frequency of the ASK-modulated input signal light; Since the traveling wave semiconductor laser amplifier with the end face anti-reflection coating is provided, the power of the extracted optical timing light is sufficiently strong and there is an advantage that it does not depend on the input signal light power. Further, according to the present invention, since extremely short pulses can be generated, it can also be used as an extremely short pulse generation circuit.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an optical timing extraction circuit according to an embodiment of the present invention, FIG. 2 is a diagram showing an emission spectrum from the optical timing extraction circuit in the same embodiment, and FIG. 3 is an ASK diagram in the same embodiment. FIG. 4 is a diagram showing the optical spectrum of the modulated input signal light, FIG. 4 is a diagram explaining the relationship between the output optical power and the input signal optical power in the semiconductor laser, and FIG. 5 is the diagram showing the optical spectrum of the modulated input signal light. Figure 6 shows the input signal light, Figure 6 shows the timing light extracted by the optical timing extraction circuit, Figure 7 shows the Fabry-Perot
This is a conventional optical timing extraction circuit using a resonator. 4... Traveling wave semiconductor laser amplifier 5a,
5 b...Selfie medium ivy lens 6 a, 6
b...Single mode fiber 'la, 7b
・・・・・・High reflectance dielectric multilayer film Figure 3 Figure 4 Figure I Brain '12 T! Enter @ Hikari r/1 City Funeral 5 Figure 6 i-i, - Figure 7 =, =

Claims (1)

[Scope of Claims] In an optical timing extraction circuit that extracts an optical clock component from an ASK-modulated input signal light, a Fabry-Perot type resonator having a resonant frequency matching the modulation frequency of the ASK-modulated input signal light is provided. and a traveling wave semiconductor laser amplifier with an end face anti-reflection coating disposed inside the resonator.