JPH02126244A - External synchronism type optical oscillator - Google Patents

Abstract

PURPOSE:To facilitate self-oscillation by feeding output light from the 1st input/ output terminal of an optical inverter circuit back, applying a light signal after pulse code modulation to a 2nd input terminal, and triggering and obtaining oscillation output light from a 2nd output terminal. CONSTITUTION:The output light from the 1st input/output terminal of the optical inverter circuit 11 is fed back to a mirror 12, a light trigger signal 14 is inputted to the 2nd input input/output terminal, and the oscillation output light is frequency synchronized with the modulation frequency of the signal after pulse code modulation appears at the 2nd input/output terminal as the output 13 of an external period type optical oscillator. In this constitution, the output from the 1st input/output terminal of the optical inverter circuit 11 can be fed back without being lowered in level by branching and confluence and the self-oscillation is facilitated; and an optical path for feeding the output light back can be made linear, the size is reduced, and the constitution is simplified.

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. Research and development is also underway on optical switching systems that exchange optical signals transmitted through optical fibers in their original form. In these systems, a clock recovery function is required to extract a clock component from a pulse code modulated optical signal in order to perform waveform recovery of the pulse code modulated optical signal or to establish system synchronization.

Conventionally, in order to achieve this purpose, an optical signal was once converted into an electrical signal by an optical-to-electrical conversion circuit, and then a clock was regenerated by an electrical lock regeneration circuit. Examples of the electric lock regeneration circuit include an LC resonant circuit having a resonant frequency near the signal frequency, and a circuit having a basic structure of a surface acoustic wave filter. However, since these clock recovery circuits use electrical circuits, the inherent advantages of optical signals, such as high speed, wide band, and non-inductive properties, are not fully utilized.

Therefore, an externally synchronized optical oscillator has been proposed in which a ring-type optical self-excited oscillator using an optical inverter circuit is triggered by externally injecting a pulse code modulated optical signal (Sasayama, Habara, Japanese Patent Application No. 63-087363). ).

FIG. 2 is a configuration diagram of an example of a ring-type externally synchronized optical oscillator, in which 21 is an optical inverter circuit, 22, 25, and 27 are optical waveguides, 23 is an optical splitter, 24 is an externally synchronized optical oscillator output, 26 is a light combiner, and 28 is a light trigger.

A part of the output of the optical inverter circuit 21 is output by an optical branching device 23 as an externally synchronized optical oscillator output 24, and the rest is fed back to the input of the optical inverter circuit 21 via an optical waveguide 25 and an optical combiner 26. Ru. By injecting an optical trigger 28, which is a pulse code modulated optical signal, into this ring type optical self-sustained oscillator via an optical combiner 26,
It is possible to obtain an externally synchronized optical oscillator output 24 that is synchronized with the optical trigger.

(Problems to be Solved by the Invention) An externally synchronized optical oscillator using a ring-type optical self-help oscillator using an optical inverter circuit has been proposed, but the output light of the optical inverter circuit is used as the output light of the externally synchronized optical oscillator. Due to the branching for extraction, the merging of the optical trigger injected from the outside and the returned optical inverter circuit output light, the returned optical inverter circuit output light decreases, making self-oscillation difficult.

In addition, it is necessary to provide a loop-shaped optical path for returning the output light of the optical inverter circuit, which increases the size.
The configuration will also be complicated.

(Means for Solving the Problems) The present invention relates to an externally synchronized optical oscillator using a semiconductor laser optical inverter circuit as an optical inverter circuit. In a semiconductor laser, two parallel arm openings usually constitute a resonator, and light is input and output through the arm openings. That is, the semiconductor laser optical inverter circuit is capable of inputting and outputting from two directions corresponding to the opening of the arm. Therefore, the input terminal and output terminal corresponding to the first arm opening surface are called the first input/output terminal, and the input terminal and output terminal corresponding to the second arm opening surface are called the second input terminal and the second output terminal, respectively. We will call it the output terminal. These input/output terminals, input terminals, and output terminals are all utilized as described below to construct a small externally synchronized optical oscillator that can easily self-oscillate.

First, an optical self-excited oscillator is constructed by feeding back the output light from the first input/output terminal of the optical inverter circuit to the first input terminal using a feedback circuit.

An external device that outputs oscillation output light at a frequency synchronized with the modulation frequency of the pulse code modulated signal by injecting a pulse code modulated optical signal into the second input terminal of the optical inverter circuit from the outside and triggering it. Realize a synchronous optical oscillator. The oscillation output light of the externally synchronized optical oscillator is taken out from the second output terminal of the optical inverter circuit, so that the output light from the first input/output terminal of the optical inverter circuit is not reduced by branching or merging. , can be fed back to the optical inverter circuit, facilitating automatic oscillation. In addition, the optical path for returning the output light of the optical inverter circuit is
It can be made straight, its dimensions are small, and its construction is simple.

(Function) When the output light of the optical inverter circuit is fed back, automatic oscillation occurs if the intensity of the returned output light is greater than a certain value. The frequency of automatic oscillation is determined by the propagation time of light until the output light of the optical inverter circuit returns and the response time of the components constituting the optical self-help oscillator.

The externally synchronized optical oscillator of the present invention has means for inputting an input optical signal from the outside into the optical self-exciting oscillator, and means for outputting the optical signal to the outside within the optical self-exciting oscillator. By setting the automatic oscillation frequency near the modulation frequency of the pulse code modulated input optical signal, the automatic oscillation frequency is
The optical clock signal is synchronized with the modulation frequency of the input optical signal and outputs an optical clock signal that matches the modulation frequency of the input optical signal.

FIG. 3 is a diagram illustrating the synchronization pull-in operation of an externally synchronized optical oscillator. The intensity of the optical trigger takes two values: a high level (11) and a low level (L). These H and L correspond to the logic level "1/0". As shown in Figure 3 (a-1), when the optical trigger intensity is always L, the externally synchronized optical oscillator has a self-sustained oscillation frequency f0 as shown in Figure 3 (a-2). Automatically oscillates, as shown in Figure 3 (b-1),
In the case of an RZ multiplied signal optical trigger that is pulse code modulated with a clock frequency f near f0, the output of the externally synchronized optical oscillator is generated by the optical trigger as shown in Figure 3 (b-2). synchronously pulled in.

(Embodiment) FIG. 1 is a block diagram of a linear externally synchronized optical oscillator which is an embodiment of the present invention, in which 11 is an optical inverter circuit;
12 is a mirror, 13 is an externally synchronized optical oscillator output, and 14 is an optical trigger.

The output light of the optical inverter circuit 11 is output in two directions, and the output light from the first input/output terminal is fed back to the optical inverter circuit 11 by the mirror 12, thereby forming an optical self-excited oscillator.

The output light from the second output terminal is taken out as an externally synchronized optical oscillator output 13.

The optical trigger 14 is input to the second input terminal of the optical inverter circuit 11. Although FIG. 1 shows a configuration in which light is emitted into free space, it is also possible to adopt a configuration in which light is passed through a waveguide.

FIG. 4 is a diagram illustrating the operation of a polarization conversion type optical inverter circuit, which is an example of a semiconductor laser optical inverter circuit, which inputs 7M polarized light to a semiconductor laser and outputs a TE polarized component of the output light from the semiconductor laser. .

FIG. 4(a) shows a case where the input light intensity of the 7M polarized light (7M light) is small, and in this case, the amplification factor of the TE polarized light (TE light) of the semiconductor laser 41 is lower than that of the 7M light. Since the gain is larger than the amplification factor, the semiconductor laser 41 oscillates with TE light. Figure 4(b) shows the case where the input light intensity of 7M polarized light (7M light) is large. In this case, the amplification factor of 7M light becomes large, so the amplification factor of TE light becomes small, and the output The intensity of the TE polarized component of the light (TIE output light) 42 decreases. In addition, 43 in the figure is input light of 7M polarization, 44
indicates an analyzer. In FIG. 4, unlike the input light, the output light is taken out from the output-side arm opening of the semiconductor laser 41, but the output light can also be taken out from the same arm opening. Therefore, an output that is inverted in intensity from the input light can be obtained. However, in the configuration shown in FIG. 4, one arm opening is used only as an input terminal and the other arm opening is used only as an output terminal, but this optical impark circuit is used as an externally synchronized optical In order to apply it to an oscillator, it is necessary to have a configuration in which both open surfaces of the arms can be used as both input and output terminals.

FIG. 5 is a configuration diagram of an example of an optical inverter circuit applied to the externally synchronized optical oscillator of the present invention, in which 51 is a Fabry-Bello semiconductor laser, 52 is a Faraday rotator, and 53.5
5 is an analyzer, 54 is a beam splitter, 56 is a mirror,
57 is an optical trigger, 58 is an externally synchronized optical oscillator output, 59
is the first arm opening, 510 is the second arm opening, and 511 is the first arm opening.
, 512 is the second output terminal, 513 is the second
shows the input terminal of The area surrounded by the dotted line is the optical impark circuit. The TE polarized light component of the output light from the first arm opening 59 of the Fabry-Bello semiconductor laser 51 passes through the Faraday rotator 52 and the analyzer 53, and then passes through the analyzer 53 and the Faraday rotator 52 again by the mirror 56. The light becomes 7M polarized light and is returned to the Fabry-Perot semiconductor radar 51. By adding an anti-reflection film to the first arm opening 59 and reducing the reflectance, the output light intensity from the first arm opening 59 is increased, and the light intensity returning to the fiber bellow semiconductor laser is increased. You can also do that. The externally synchronized optical oscillator output 58 is a Fabry-Perot semiconductor laser 51.
It is obtained by extracting the TE polarized light component or the TM polarized light component of the output light from the second arm opening surface 510 using the analyzer 55. Although 7M polarized light is input as the optical trigger 57, it is also possible to use TE polarized light instead.

The TIE polarization component of the output light from the first arm opening 59 of the Fabry-Perot semiconductor laser 51 is transmitted by the Faraday rotator 52.
The polarization direction is rotated so that the light is converted into 7M polarized light. For this purpose, it is necessary to adjust the rotation angle of the polarization direction of the Faraday rotator 52 to (45+90x(N-1) 1 degree (N is a natural number). TE of output light from surface 59
This is because the polarized light component passes through the Faraday rotator 52 twice before returning to the Fabry-Perot semiconductor laser 51.

The TM polarization component (TM specific output) of the output light from the first arm opening 59 of the Fabry-Perot semiconductor laser 51 can also be fed back in the same way as the TE output light. In this case, the 7M output light is The feedback gain of the 7M light and the TE light can be adjusted by the analyzer 53. In the configuration without the analyzer 53,
The feedback gains of the 7M light and the TE light are approximately 1:1. If this analyzer 53 is not available, a λ/4 plate can be used in place of the Faraday rotator 52.

FIG. 6 is a block diagram of an example of an optical inverter circuit using a λ/4 plate instead of a Faraday rotator.

The range surrounded by the dotted line is the optical inverter circuit, and 61
is a Fabry Bellow semiconductor laser, 62 is a λ/4 plate, 63
is a beam splitter, 64 is an analyzer, 65 is a mirror 66
67 is an optical trigger, 67 is an externally synchronized optical oscillator output, 68 is a first arm opening surface, 69 is a second arm opening surface, 610 is a first input/output terminal, 611 is a second output terminal, 612 is a A second input terminal is shown.

(Effects of the Invention) According to the present invention, an optical clock signal synchronized with a Hals code modulated optical signal train can be obtained using a small circuit that can easily self-oscillate. Furthermore, since no electrical circuit is used, it is possible to realize an externally synchronized optical oscillator that takes advantage of the characteristics of light, such as high speed, broadband, and non-inductive properties.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a linear externally synchronized optical oscillator which is an embodiment of the present invention, Fig. 2 is a block diagram of an example of a ring externally synchronized optical oscillator, and Fig. 3 (a-1), ( a-2), (b-1)
, (b-2) is a diagram explaining the synchronization pull-in operation of an externally synchronized optical oscillator, FIGS. 4(a) and (b) are diagrams explaining the operation of a polarization conversion type optical inverter circuit, and FIG. FIG. 6 is a block diagram of an example of an optical inverter circuit using a λ/4 plate instead of a Faraday rotator. 11... Optical inverter circuit 12... Mirror 13.
... Externally synchronized optical oscillator output 14... Optical trigger 21... Optical inverter circuit 22... Optical waveguide 23... Optical splitter 24... Externally synchronized optical oscillator output 25... Optical waveguide 26... Light combiner 27
... Optical waveguide 28 ... Optical trigger 41 ...
- Semiconductor laser 42... TE polarization component of output light 43... 7M polarized input light 44... Analyzer 51
... Fabry-Perot semiconductor laser 52 ... Faraday rotator 53 ... analyzer 54 ... beam splitter 55 ... analyzer 56 ... mirror
57... Optical trigger 58... Externally synchronized optical oscillator output 59... First arm opening 510... Second arm opening 511... First input/output terminal 512... Second output terminal 513...Second input terminal 61...Fabry Bellow half, four body laser 62...
λ/4 plate 63...beam splitter 64
...Analyzer 65...Mirror 66...
Optical trigger 67...Externally synchronized optical oscillator output 68...First arm opening 69...Second arm opening 610...First input/output terminal...Second output terminal ...Second input terminal Patent applicant Nippon Telegraph and Telephone Corporation Figure 1 Figure 2 Figure 25 Time opening Figure 3 Time open qr, Time Time Figure 5 Figure 6

Claims (1)

[Claims] 1. An optical self-exciting oscillator comprising an optical inverter circuit using a semiconductor laser, a means for feeding back the output of the optical inverter circuit to the optical inverter circuit, and an optical input for inputting an optical signal to the optical self-exciting oscillator. and an optical output means for outputting an optical signal from the optical self-excited oscillator, the optical output means outputting an optical signal having an oscillation frequency synchronized with the modulation frequency of the optical signal from the optical input means. An externally synchronized optical oscillator featuring: