JPH0795756B2 - Optical R-R-R code conversion circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical NRZ-RZ code conversion circuit for converting an optical signal of NRZ code into an optical signal of RZ code.

(Prior art and its problems) The application of optical technology to the field of communication or information processing is currently based on the advantages that the application of optical fiber to the transmission line does not suffer from broadband characteristics, low loss, and induced noise of the optical fiber. It is taking place. In the future, optical memory,
It is expected that an optical signal processing device, such as an optical switch or an optical computer, will be used for communication processing or information processing of an optical signal as it is by using an optical logic circuit or the like. When such an optical signal processing device is realized, the output optical signal of the optical signal processing device may be an NRZ code. For example, the output optical signal of the optical switch described in Japanese Patent Application No. 57-216708 is an NRZ code. When the output optical signal of such an NRZ code is transmitted through the optical fiber transmission line, there arises a problem that it becomes difficult to perform timing reproduction by the light receiving device at the transmission destination.
Therefore, it is necessary to convert the output optical signal of the NRZ code into the optical signal of the RZ code and send it out to the transmission line. In conventional optical fiber transmission, by generating an electrical signal of RZ code on the transmission side and converting this electrical signal into an optical signal,
It is common to obtain an optical signal of RZ code and make it incident on an optical fiber. Therefore, when the optical signal of the NRZ code is output from the optical signal processing device, the optical signal is first converted into an electrical signal, and then NRZ / RZ conversion is performed, and the electrical signal of the RZ code is converted into an optical signal again. The optical signal of RZ code can be transmitted through the optical fiber by converting and entering the optical fiber. However, this method has a drawback in that two conversion circuits for optical signals → electrical signals and electric signals → optical signals are indispensable, and the configuration is complicated, although the conversion is performed between optical signals.

(Object of the Invention) An object of the present invention is to provide an optical NRZ-RZ code conversion circuit for converting an optical signal of NRZ code into an optical signal of RZ code.

(Structure of the Invention) In order to achieve the above-mentioned object, the present invention provides an optical signal composed of a semiconductor laser having a differential gain or a bistable characteristic, in which an optical signal of an NRZ code is interrupted by a sub-clock electrical signal synchronized with a main clock signal. It is configured by a gate.

Further, in order to achieve the above object, the present invention provides an optical gate comprising a semiconductor laser having a saturable absorption portion in a resonator, which interrupts an optical signal of NRZ code with a sub clock optical signal synchronized with a main clock signal. It is configured by.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a first embodiment of the present invention. First
According to the drawings, the first embodiment of the present invention shows a clock signal source.
An optical signal processing device 101 that performs optical signal processing in synchronization with a main clock signal of an optical signal or an electric signal supplied from 103 through a conductor or an optical waveguide 102, and one of the optical signal processing device 101 at the emitting end. The optical waveguide 104 that touches the end face, the incident end touches the other end face of the optical waveguide 104, and the clock signal source 1
Optical gate 105 supplied with a sub clock electrical signal synchronized with the main clock signal from conductor 03 via conductor 107, and optical gate 1
And an optical transmission line 106 whose one end face is in contact with the emission end of 05.

FIG. 2 is a diagram showing a time chart for explaining the operation of the first embodiment of the present invention shown in FIG. In FIG. 2, 201 is emitted from the optical signal processing device 101, and is guided by the optical waveguide 104.
Numeral 202 represents an optical signal of the NRZ code which is incident on the optical gate 105 via optical path, 202 represents a sub-clock electrical signal supplied from the clock signal source 103 to the optical gate 105 through the conductor 107, and 203 represents an optical signal from the optical gate 105. It represents an optical signal emitted to the transmission path 106. The optical signal processing device 101 operates in synchronization with a main clock signal of an electric signal or an optical signal supplied from a clock signal source 103 through a conductor or an optical waveguide 102, and the main clock signal and the sub-clock electric signal 202 are synchronized. Therefore, the output optical signal 201 of the NRZ code and the sub clock electrical signal 202 are synchronized. Further t _c from each of the time t _b of the period T from the time t _a of each shown in FIG. 2 to the next t _a
The voltage value of the sub-clock electrical signal 202 is V _H during the period τ
And other periods are V _L. The optical gate 105 opens the gate when the voltage value of the sub-clock electrical signal 202 is V _{H and} the light amount P _h1
When the incident light signal of is output, the light signal of the light amount P _h2 is emitted, and when the light amount of the incident light signal is 0 and the voltage value of the sub clock electrical signal 202 is V _L , the light amount of the emitted light signal is It is 0. Therefore, if the output optical signal 201 of the NRZ code is the light intensity P _h1 during the period T from the time t _a to the next t _a , the optical signal 203 is the light intensity during the period τ from the time t _b to t _c within the period T. It becomes P _h2 , and the light intensity becomes 0 otherwise. On the other hand, the light quantity between the light signal 203 during the period T as long as the light amount is 0 in the optical signal 201 during the period T from time t _a to the next t _a is zero. In this way, the NRZ code optical signal 201 can be converted into the RZ code optical signal 203. The duty ratio τ / T of the RZ code is usually set to 50% in many cases.

The optical gate 105 shown in FIG. 1 inputs an input optical signal to a semiconductor laser having a differential gain or a bistable characteristic and changes an injection current by the gate electric input signal to change the logic of the input optical signal and the gate electric input signal. It can be realized by an optoelectronic logic element that performs a product operation or an electronic optical switch that turns on / off an input optical signal by a gate electric input signal. An optoelectronic logic element for performing a logical product operation is described in detail in Japanese Patent Application No. 58-163449.
Further, the electronic optical switch is described in detail, for example, in Technical Report OQE81-79, pages 35 to 40, "1.3 μm LiNbO ₃ 4 × 4 switch with single mode optical fiber array", in Technical Report OQE81-79.

FIG. 3 is a diagram showing a second embodiment of the present invention. According to FIG. 3, the second embodiment of the invention is a clock signal source 303.
An optical signal processing device 301 for performing optical signal processing in synchronization with a main clock signal of an electric signal or an optical signal supplied from a conductor or an optical waveguide 302, and an optical signal processing device 3
An optical waveguide 304 whose one end face is in contact with the output end of 01 and a clock signal source 303 whose other end face is in contact with the incident end
An optical gate 305 supplied with a sub-clock optical signal synchronized with the main clock signal from the optical waveguide 307, and an optical gate 3
And an optical transmission line 306 whose one end face is in contact with the emission end of 05.

FIG. 4 is a diagram showing a time chart for explaining the operation of the first embodiment of the present invention shown in FIG. In Figure 4
Reference numeral 401 represents an NRZ code optical signal emitted from the optical signal processing device 301, passed through the optical waveguide 304 and incident on the optical gate 305, and 402 is a gate signal from the clock signal source 303 to the optical gate 305 through the optical waveguide 307. The sub clock optical signal is supplied, and 403 is an optical signal emitted from the optical gate 305 to the optical waveguide 306. The optical signal processing device 301 operates in synchronization with a main clock signal of an electric signal or an optical signal supplied from a clock signal source 303 through a conductor or an optical waveguide 302, and operates as a main clock signal and a sub clock optical signal 402.
Are synchronized, the output optical signal 401 of the NRZ code and the sub clock optical signal 402 are synchronized. Furthermore between each of the time t _b duration τ until t _c of the period T from each of the time t _a as shown in FIG. 4 to the next t _a, the light amount of the sub-optical clock signal 404 P
_{It is h3} , and is 0 in other periods. The optical gate 305 opens the gate when the light quantity of the sub clock optical signal 402 is P _h3 , and at this time, if the incident light signal of the light quantity P _h1 is added, it emits the light signal of the light quantity P _h2 and the incident light signal 401 When the light quantity is 0 and when the light quantity of the sub clock optical signal 402 is 0, the light quantity of the outgoing light signal 403 is 0. Therefore, if the output optical signal 401 of the NRZ code is the light amount P _h1 during the period T from the time t _a to the next t _a , the optical signal 403 is in the period T and during the period τ from the time t _b to t _c. Light intensity P
It becomes _h2 , and the light intensity becomes 0 otherwise. On the other hand, if the light intensity of the optical signal 401 is 0 during the period T from the time t _a to the next t _a , the light intensity of the optical signal 403 is 0 during the period T. In this way N
The optical signal 401 of the RZ code is converted into the optical signal 403 of the RZ code.
The duty ratio τ / T of the RZ code is usually set to 50% in many cases.

The optical gate 305 in FIG. 3 can be realized by an optical logical product element that performs a logical product operation of an input optical signal and a gate optical input signal.

FIG. 5 shows a specific example of an optical AND element that can be used as the optical gate 305. In FIG. 5, the optical AND element is realized by a semiconductor laser 51 having a saturable absorption portion in the resonator, and output light output from the active layer.
52 is the output, and the input light is externally injected into the active layer 53
And the input light 54 is the input. A semiconductor with a saturable absorber in the resonator can be used to set the operating point
The total light intensity P _in and the light intensity P _{out of the} output light
A differential gain characteristic can be provided in the characteristics between and. Details of the semiconductor laser having such a differential gain characteristic are described in the Technical Report of the Institute of Electronics and Communication Engineers ED81-10, page 7.

FIG. 6 is a diagram for explaining the operation of a semiconductor laser having a differential gain characteristic used for the optical AND element, and is _obtained by adding the light _amounts P _in3 and P _in4 of the input lights 53 and 54 in FIG. The relationship between the light amount P _in = P _in3 + P _in4 and the light amount P _{out of the} output light is shown. That is, when the total light intensity P _in of the input light is increased from 0, the light intensity P _out of the output light at P _in = P _th rapidly increases from almost 0 to the value of P _out = P ₁ , and then the total light intensity of the input light is increased. _Is greater than P _in = P _th
Out takes a constant value of P _out = P ₁ and shows a differential gain characteristic near P _th . Quantity P _in3 of the input light 53 and 54 at this time, P _in4 input logic level "L" in the _{P in3} = P in3L, a _{P in4} = P in4L, input logic level "H" in the _{P in3} = P in3H, P _in4 = P _in4H
Suppose Further, at the output logic level “L” of the output light 52, the light quantity P _{out of the} output light is P _out = 0, and at the output logic level “H”, the light quantity of the output light P _out = P ₁ . And 0 <P _in3L , _Set P _in3L , P _in3H , P _in4H , and P _in5L so that P _in4H <P _th . By doing so, the total input light intensity P _in = P _in3 + P _in4 > P _th and the output light intensity is only when the input light levels 53 and 54 are all P _in3H and P _in4H at the input logic level "H". When the light intensity P _out = P ₁ , the output logic level becomes “H” and the operation of the optical AND operation is realized.

(Effect of the Invention) As described above, according to the present invention, an optical signal of NRZ code is converted into RZ
It is possible to obtain an optical NRZ-RZ code conversion circuit that converts a coded optical signal.

[Brief description of drawings]

FIG. 1 shows a first embodiment of the present invention, and FIG. 2 shows a first embodiment.
FIG. 3 is a diagram showing a time chart for explaining the operation of the first embodiment of the present invention, FIG. 3 is a diagram showing a second embodiment of the present invention, and FIG. 4 is a diagram showing the present invention of FIG. FIG. 5 is a diagram showing a time chart for explaining the operation of the second embodiment, FIG. 5 is a diagram showing a structure of an optical AND element which is a specific example of the optical gate 305 in FIG. 3, and FIG. 6 is an optical logic. It is a figure for demonstrating operation | movement of a product element. In the figure, 101 and 301 are optical signal processing devices, 103 and 303 are clock signal sources, 105 and 305 are optical gates, and 51 is a semiconductor laser having a saturable absorption portion.

Claims (2)

[Claims] 1. An optical NRZ, comprising an optical gate made of a semiconductor laser having a differential gain or a bistable characteristic, in which an optical signal of an NRZ code is interrupted by an auxiliary clock electric signal synchronized with a main clock signal. -RZ code conversion circuit. 2. An optical gate composed of a semiconductor laser having a saturable absorption portion in a resonator, wherein an optical signal of NRZ code is interrupted by a sub-clock optical signal synchronized with a main clock signal. Optical NRZ-RZ code conversion circuit.