JPH01259331A - External synchronization type optical oscillator - Google Patents

Abstract

PURPOSE:To obtain an optical oscillator being excellent in high speed property and non-inductive property by inputting an optical signal which is brought to pulse code modulation, to an optical ring consisting of an optical inverter, an optical amplifier and an optical feedback circuit, and outputting synchronized oscillation light. CONSTITUTION:An optical ring is formed by an optical inverter 1, an optical amplifier 2, an optical coupler 3 and optical waveguides 7-10, and when a prescribed binary light quantity is inputted, inverted output light is obtained. Accordingly, since an output P8 is varied against an input P7, the input P7 is inverted after a propagation delay time of the optical ring, and by its repetition, an optical pulse train is generated. Also, a period of its self-exciting oscillation is determined by a propagation time of light in the optical ring. Accordingly, when an optical signal train which is brought to pulse code modulation is inputted, an optical clock signal which has synchronized with said signal train is outputted, by which an optical oscillator being excellent in a high speed property and a non-inductive property is obtained without using an electric clock reproducing circuit.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is applied to an externally synchronized optical oscillator that reproduces an optical clock signal synchronized with a pulse code modulated optical signal train in the field of optical communication and optical information processing. It is related to.

(Prior Art) In recent years, optical transmission systems have been put into practical use due to advances in optical fiber technology, optical semiconductor technology, and the like. Furthermore, research and development are being conducted on optical switching systems that exchange optical signals transmitted through optical fibers as they are. In order to perform waveform recovery of a pulse code modulated optical signal in these systems or to establish system synchronization, a clock recovery function is required to extract a clock component from the pulse code modulated optical signal.

Conventionally, in order to achieve such a purpose, an optical signal is first converted into an electrical signal by an optical-to-electrical conversion circuit, and then
The clock was regenerated using an electric clock regeneration circuit. Examples of the electric tack regeneration circuit include an LC resonance circuit having a resonance frequency near the signal frequency, or one having a basic structure of a surface acoustic wave filter. However, these clock recovery circuits use electrical signals, so
The inherent advantages of optical signals, such as high speed, wide bandwidth, and non-inductive properties, have not been fully utilized.

(Problems to be Solved by the Invention) In order to take advantage of these inherent advantages of optical signals, it is desirable to realize a circuit that performs optical clock regeneration using optical signals as they are. To realize this, an optical resonant circuit or the like is required, but none has been put to practical use to date.

(Means for Solving the Problems) In the present invention, an optical ring oscillator is configured by an odd number of optical inverters, optical amplifiers, and optical feedback circuits, and automatic oscillation in the optical ring is utilized. An externally synchronized optical system that obtains oscillation output light at a frequency synchronized with the modulation frequency of the pulse code modulated signal by externally injecting a pulse code modulated optical signal into a self-oscillating optical ring and triggering it. Realize an oscillator.

(Function) When an optical ring is constructed by feeding back the output signal of an optical inverter to an input terminal through an optical amplifier, automatic oscillation occurs if the amplification degree of the optical amplifier is greater than a certain value. The frequency of self-oscillation is determined by the propagation time of light within the optical ring.

Further, the optical ring has means for inputting an input optical signal from the outside into the ring, and means for outputting the optical signal within the optical ring to the outside. Here, by setting the self-sustained oscillation frequency near the modulation frequency of the pulse code modulated input optical signal, the frequency of self-sustained oscillation will be synchronized with the modulation frequency of the input optical signal, and the modulation of the input optical signal will occur. An optical clock signal matching the frequency is output.

(Embodiment) FIG. 1 is a block diagram of an embodiment of the present invention, in which 1 is an optical inverter, 2 is an optical amplifier, 3 is an optical coupler, 4 is an optical branching device, 5 is an input terminal, 6 is an output terminal, 7
-10 are optical waveguide furnaces. The optical inverter 1 has a predetermined binary amount of light as input light, and if a high light level is expressed as a logic level of "1°" and a low light level is expressed as a logic level of 0°, then the input light is "0". When the output light is "1", the output light is "1", and when the input light is "1", the output light is "0".

FIG. 2 is a diagram for explaining self-assisted oscillation of the optical ring oscillator in the present invention. Optical inverter 1 in Fig. 1
It shows temporal changes in input light P7 and output light P. At time T, input P7 of optical inverter 1 changes from °“0” to “
1", the output P8 of optical inverter 1 becomes "l" at time T! after the propagation delay time DI of optical inverter l.
to 0''.Due to the change in the output P, the optical waveguide 8
, optical amplifier 2, leading waveguide 9, optical splitter 4, leading waveguide 10
, the input P1 of the optical inverter 1 changes from "1' to "°0" at time T3 after the propagation delay time D2 of the optical coupler 3 and the optical waveguide 7.
become. Propagation delay time D of optical inverter 1 from time T3
At time T4 one day later, the output P8 of the optical inverter 1 changes from "0" to "1". Propagation delay time D of the optical ring from time T4! At a later time T, the input P of the optical inverter l becomes “0”.
The optical pulse train continues to be generated by repeating this process, and the period of automatic oscillation is between time T1 and time T.

The time difference is 2 (DI + Di).

This is equal to twice the delay time required for an optical signal to go around once through the optical inverter 1, optical amplifier 2, optical coupler 3, optical branching device 4, and optical waveguides 7 to 10 connected in series in a ring shape.

FIG. 3 is a perspective view showing an example of the optical inverter 1 according to the present invention. The optical inverter 1 shown in FIG. 1 includes a semiconductor laser 11 that emits output light 12 (CP, L) from a junction surface in the direction of a reflective surface 13 of a Fabry-Bello resonator, and an active region of the semiconductor laser 11. It is composed of a semiconductor laser 14 into which coherent input light 15 (Pi,) is incident. When no input light is input, the semiconductor laser 11 emits output light 12 in the direction in which stimulated emission due to resonance of the Fabry-Perot resonator is maximum. In this state, the coherent input light 15 is transmitted to the semiconductor laser 1.
1, if the frequency of the input light 15 is equal to or very close to the frequency of the output light 12, a quenching effect will occur due to the coupling of the two lights, and the output light 12 will have a reduced power. , and eventually the light emission stops. Third
Regarding the phenomenon of oscillation stop due to injection light of a semiconductor laser in the figure, see References A, A, 5Heronov.

-QUBNCHING BFFECT IN 0PTI
CALLY C0IIPLED GaAsINJECT
ION LASER3”, 5oviet Physi
cs Se++1 conductors Volume 3 No. 3 19
It is described in detail on September 1969, page 314.

FIG. 4 is a third diagram for explaining the operation of the optical inverter.
p in and P in the figure. FIG. 2 is an input/output characteristic diagram showing the relationship between ut. In FIG. 4, when Pln is O, Po is output, and when a light amount Ph greater than the threshold light amount Pth is input to P, . Shikatte p
"1" indicates the state where in is the light amount Ph, "0" indicates the state where P,7 is the light amount O, and "1" indicates the state where Pout is the light amount P0.
”, by making the state in which P out is optical ito correspond to “0”, an inverter with inverted input and output is realized.

FIG. 5 is a diagram showing the operation of the externally synchronized optical oscillator of the present invention. P is a pulse code modulated RZ optical signal train inputted to the optical ring oscillator from the input terminal 5 shown in FIG. 1, and its modulation frequency is near the self-support oscillation frequency of the optical ring oscillator. Here, as an example, the bit string “′1”,
'0'', '''1°゛.

This shows the case of "1". P6 is an optical clock signal train obtained from the output terminal 6 shown in FIG. 1, and as shown in FIG. 5, an output signal train P6 whose frequency is synchronized with the input signal train P is obtained.

(Effects of the Invention) According to the present invention, an optical clock signal synchronized with a pulse code modulated optical signal train can be obtained without using an electric clock recovery circuit.

This makes it possible to create an externally synchronized optical oscillator that takes advantage of the characteristics of light, such as its high speed, broadband properties, and non-inductive properties.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is a diagram for explaining self-assisted oscillation of an optical ring oscillator in the present invention, FIG. 3 is a perspective view showing an example of an optical inverter, and FIG. 4 is an input/output characteristic diagram of an optical inverter, and FIG. 5 is a diagram showing the operation of an externally synchronized optical oscillator. 1... Optical inverter 2... Optical amplifier 3...
Optical coupler 4... Optical splitter 5... Input terminal 6... Output terminals 7 to 10... Optical waveguide
11.14...Semiconductor laser 12 (P, ut)・
... Output light 13 of the semiconductor laser 11 ... Reflection surface 15 (Pi, 1) of the Farpley-Perot resonator ... Input light P of the semiconductor laser 140 ... Optical signal train P incident from the input terminal, ...・Optical clock signal train P obtained from the output terminal
7...Input light P of the optical inverter...Output light Po of the optical inverter...Output level Pth when there is no input light to the optical inverter...Input light threshold Ph at which the output of the optical inverter stops . . . Any input level T3 that exceeds the threshold. T
s...Rise time T2 of human power light P...Output light P,
Falling time T3...Falling time T4 of input light P...Rising time D1 of output light P...Propagation delay time of optical inverter D2...Propagation delay time of optical ring Fig. 3 Fig. 4 1 □t;w;O,'w-.

Claims (1)

[Claims] 1. An optical ring oscillator configured by connecting an odd number of optical inverters, optical amplifiers, and optical feedback circuits in series in a ring shape, an optical input means for inputting an optical signal to the optical ring oscillator, and an optical input means for inputting an optical signal to the optical ring oscillator. 1. An externally synchronized optical oscillator comprising: an optical output means for outputting an optical signal, the output means outputting an optical signal having an oscillation frequency synchronized with the modulation frequency of the optical input signal.