JPH04163532A - Light clock extraction circuit - Google Patents

Abstract

PURPOSE:To make high speed operation performable and a high frequency light clock extractably by utilizing the injection synchronous phenomenon of a semiconductor laser and extracting a light clock with two semiconductor lasers, a light branch circuit and a light wave circuit. CONSTITUTION:Input light 6 injected into both first and second semiconductor lasers 8, 9 via a light bran circuit 7 draws output light of the first semiconductor laser 8 in its carrier frequency f1 by means of each injection synchronous phe nomenon of these semiconductor lasers 8, 9, and also it draws output light of the first semiconductor laser 8 in the side band frequency of the input light 6, namely, frequency distant as far as clock frequency Df from the carrier frequency f1. These two output light waves are joined together by a light wave circuit 10, but at this time, they interfere with each other, and a difference in the frequencies, that is, a light signal, where light power alternately varies in synchronization with the clock frequency f of the input light 6, namely, a light clock is outputted. With this constitution, high speed operation is made performable, thus the high frequency light clock is extractable.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical clock extraction circuit that extracts an optical clock from an optical signal.

(Prior Art) Fig. 2 shows an example of a conventional circuit of this type, in which 1 is an input light, 2 is an optical-to-electric conversion element, 3 is a clock extraction circuit, and 4 is an electric-to-optical conversion element. Element 5 is output light. Input light 1 is received by an optical-to-electrical conversion element 2 consisting of a pin photodiode or the like, and converted into an electrical signal. The clock extraction circuit 3 consists of an electrical tank circuit or a phase-locked loop, and extracts the clock period from the electrical signal,
Generates an electrical lock signal. Electrical-optical conversion element 4
consists of only a semiconductor laser or a semiconductor laser and an external optical modulator such as LiNbOs that modulates its output light, and can be used by directly modulating the semiconductor laser with the clock signal or by using an external optical modulator driven by the clock signal. By modulating the output light of the semiconductor laser with an optical modulator, an optical clock including a clock component, that is, output light 5 is output.

(Problem to be Solved by the Invention) However, in the above circuit, the operating speed is limited by the usable frequency band of each element and electric circuit, and the frequency of the optical clock that can be extracted cannot be made very high (usually about 1 to 10 GHz). There was a problem.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, it is an object of the present invention to provide an optical clock extraction circuit capable of high-speed operation and capable of extracting a high-frequency optical clock.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an optical system that extracts an optical clock from an input light whose carrier frequency is fl, whose clock frequency is Δf, and whose information is represented by the intensity of optical power. The clock extraction circuit includes a first semiconductor laser that oscillates at a frequency approximately equal to the carrier frequency f1, a second semiconductor laser that oscillates at a frequency approximately equal to a frequency separated by a clock frequency Δf from the carrier frequency f1, and first and second semiconductor lasers that oscillate at a frequency approximately equal to a clock frequency Δf apart from the carrier frequency f1. We propose an optical clock extraction circuit that includes an optical branching circuit that branches and injects human-powered light into a second semiconductor laser, and an optical multiplexing circuit that multiplexes the output lights of the first and second semiconductor lasers.

(Function) According to the present invention, the input light injected into the first and second semiconductor lasers via the optical branching circuit transfers the output light of the first semiconductor laser to the input light due to the injection locking phenomenon of the semiconductor lasers. The output light of the second semiconductor laser is pulled into the sideband frequency of the input light, that is, a frequency separated by a clock frequency Δf from the carrier frequency f1. These two output lights are combined by an optical multiplexing circuit, but at this time, they interfere with each other, and the difference in their frequencies is an optical signal whose optical power alternately fluctuates in synchronization with the clock frequency Δf of the input light. Optical clock is pressured.

(Embodiment) FIG. 1 shows an embodiment of the optical clock extraction circuit of the present invention, in which 6 is an input light, 7 is an optical branching circuit, 8 and 9 are semiconductor lasers, and 10 is an optical multiplexing circuit. , 11 is the output light, 12
．． 13, 14, and 15 are lenses.

The input light 6 has a carrier frequency fl, a clock frequency Δf, and the information is expressed by the intensity of the optical power (light intensity), as shown in FIG. 3(a). It has a spectrum having a peak at a frequency f1 and a frequency (sideband frequency) separated by a frequency Δf from the frequency f1.

The optical branching circuit 7 branches the input light 6 and outputs the semiconductor lasers 8 and 9.
It is intended for injection.

The semiconductor lasers 8 and 9 have a DFB structure or a DBR structure that oscillates at a single frequency. The injected DC current and operating temperature are adjusted in advance so that the carrier frequency in the absence of light is either (f1 + Δf) or (fl - Δf), here approximately equal to (fl - Δf). shall be taken as a thing.

The optical multiplexing circuit 10 is for multiplexing the output lights of the semiconductor lasers 8 and 9 to produce an output light 11.

In addition, lenses 12.13 and 14.15 are semiconductor lasers 8
, 9 and the optical branching circuit 7 and optical multiplexing circuit 10.

As the optical branching circuit 7 and the optical multiplexing circuit 10, it is possible to use a 3 dB optical coupler using an optical fiber, a half mirror, a directional coupler using a glass or semiconductor waveguide, or a Y branch circuit.

Next, the operation will be explained.

The input light 6 is branched by an optical branching circuit 7, and is split into lenses 12 and 1.
3 into semiconductor lasers 8 and 9. At this time, due to the well-known injection locking phenomenon, the oscillation frequencies of the semiconductor lasers 8 and 9 are pulled to whichever is closer to the carrier frequency of the input light 6 or the two sideband frequencies. Specifically, the oscillation frequency of the semiconductor laser 8 is pulled in by the carrier frequency f1 of the input light 6, and the oscillation frequency of the semiconductor laser 9 is pulled in by the sideband frequency (fl-Δf) of the input light 6.
be drawn into. FIGS. 3(b) and 3(e) show the spectra of the output light from the semiconductor lasers 8 and 9, respectively. Also, at this time, the carrier frequency and phase of the output light of the semiconductor laser 8 match the carrier frequency f1 of the input light 6, and the carrier frequency and phase of the output light of the semiconductor laser 9 match the sideband frequency ( fl−Δf
) matches.

The output lights of the semiconductor lasers 8 and 9 are combined by an optical multiplexing circuit 10, but at this time, they interfere with each other, and the optical powers alternate in synchronization with the difference in their carrier frequencies, that is, the clock frequency Δf of the input light 6. An optical signal, ie, an output light (optical clock) 11, which fluctuates as shown in FIG. Also, here, the optical power of the input light 6 at each clock timing may be high or low depending on the information as shown in FIG. 4(a), but each semiconductor laser 8, 9 Since it oscillates continuously, the optical power of the output light 11 is at the same level at all timings, as shown in FIG. 4(b).

In the above embodiment, it is easy to set the oscillation wavelengths of the semiconductor lasers 8 and 9 to 1.30 μm and 1.31 μm, and in this case, the frequency difference Δf is 1.76×
The frequency is 1012Hz, which enables extremely high-speed operation.

FIG. 5 shows another embodiment of the present invention, in which an example constructed using an optical integrated circuit is shown. That is, in the figure, 21
is a semiconductor substrate, 22 is a waveguide type optical branch circuit, 23.24
2 is a semiconductor laser, and 25 is a waveguide type optical multiplexing circuit. According to this embodiment, lens 12 in the embodiment of FIG.
.about.15 is no longer necessary, and the configuration becomes simpler. Note that the other configurations and operations are the same as those of the embodiment shown in FIG.

(Effects of the Invention) As explained above, according to the present invention, input light is converted into an electrical signal by using two semiconductor lasers, an optical branching circuit, and an optical multiplexing circuit, and utilizing the injection locking phenomenon of semiconductor lasers. Since the optical clock can be extracted without any interference, there is no need for conventional optical-to-electrical conversion elements, electric-to-optical conversion elements, electric circuits, etc., which enables high-speed operation and allows high-frequency optical clocks to be extracted. It has the advantage that it can be extracted, integrated on a semiconductor substrate, and realized with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the optical clock extraction circuit of the present invention, FIG. 2 is a block diagram showing an example of a conventional optical clock extraction circuit, and FIG. An explanatory diagram showing the spectrum of the input light and each laser output light in the circuit of Fig. 1, and Fig. 4 (a) and (b) are explanatory diagrams showing temporal changes in the light intensity of the input light and output light in the circuit of Fig. 1. 5 are block diagrams showing other embodiments of the optical clock extraction circuit of the present invention. 6... Input light, 7... Optical branching circuit, 8.9.23°24... Semiconductor laser, 10... Optical multiplexing circuit, 11
... Output light, 12.13, 14.15... Lens,
21... Semiconductor substrate, 22... Waveguide type optical branching circuit, 25... Waveguide type optical multiplexing circuit. Patent Applicant Nippon Telegraph and Telephone Co., Ltd. Agent Patent Attorney Yoshi 1) Takashi Takashi Figure 1 shows an embodiment of the optical clock extraction circuit of the present invention Figure 2 shows an example of a conventional optical clock extraction circuit Figure 2'f+ Figure 4 shows the frequency input source and the overlap tram of each laser beam Figure 4 shows the temporal change in the light intensity of the input light and output light

Claims (1)

[Claims] In an optical clock extraction circuit that extracts an optical clock from an input light whose carrier frequency is f1 and whose clock frequency is Δf, and whose information is represented by the intensity of optical power, The first oscillating
a second semiconductor laser that oscillates at a frequency substantially equal to a frequency separated by a clock frequency Δf from the carrier frequency f1; and an optical branching circuit that branches and injects input light into the first and second semiconductor lasers. An optical clock extraction circuit comprising: an optical multiplexing circuit that multiplexes the output lights of the first and second semiconductor lasers.