JP3035882B2 - Optical receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver for receiving an optical signal transmitted through an optical fiber or the like and discriminating and reproducing the signal into a predetermined electric signal.

[0002]

2. Description of the Related Art In recent years, toward the practical use of a wideband information communication network for performing various services for transmitting information such as data and images in addition to voice, an ultra-large band of several gigabits to several tens gigabits / second has been developed. Studies on capacity optical transmission technology are being actively conducted, and ultra-high speed, miniaturization,
Research for higher reliability is being conducted. This optical receiver performs amplification of a data signal and identification and reproduction of a data signal in a repeater or terminal device in an optical transmission system based on a predetermined clock signal. Examples of a repeater that performs a predetermined process on an input optical signal and outputs the signal as an optical signal include an optical repeater disclosed in Japanese Patent Application Laid-Open No. 62-245751 and a device disclosed in Japanese Patent Application Laid-Open No. 2-52535. All-optical processing repeater.

[0003] Also, the Institute of Electronics, Information and Communication Engineers, the Optical Communication Systems Research Group, and OCS 91-71 disclose an optical receiver that inputs an optical signal, converts the signal into a predetermined electric signal, and outputs the signal. FIG. 5 is a block diagram for explaining the optical receiving apparatus. The converting section 1 mainly converts an optical signal input from the optical fiber 11 into a predetermined electric signal, and the converting section 1 is based on the electric signal obtained by the converting section 1. It comprises a retiming section 2 'for extracting a clock signal contained therein, and a discriminator 3 for discriminating and reproducing an optical signal based on the electric signal from the conversion section 1 and the clock signal from the retiming section 2'. . The conversion unit 1 includes an optical amplifier 12 and a light receiving element 13 ′.
, A preamplifier 14, and a broadband amplifier 14a,
The retiming unit 2 'includes a differentiating circuit 4 and a rectifying circuit 24'.
, A narrow band filter 25, a narrow band amplifier 5, and an electric delay element 26.

The optical receiving apparatus first amplifies an optical signal input through an optical fiber 11 by an optical amplifier 12,
The first light receiving element converts the signal into a predetermined electric signal. When the transmission speed is about 2.4 Gbit / s, an APD (Aval) having an amplification function without passing through the optical amplifier 12 is used.
Anchor Photo Diode) In many cases, the light receiving element 13 ′ is used. However, when the transmission speed is about 10 Gbit / sec, it is difficult to obtain an APD that operates at a high speed. -Pho
The light receiving element 13 ′ composed of to Diode is used.

Next, the electric signal is amplified by a low noise preamplifier 14 and a broadband amplifier 14a. afterwards,
The electric signal is branched, and one of the electric signals is inputted to the discriminator 3, and the other is inputted to the differentiating circuit 4 of the retiming unit 2 '. The output signal from the differentiating circuit 4 is rectified by a rectifying circuit 24 ', and the rectified signal is extracted through a narrow band filter 25 to a clock signal. The extracted clock signal is output to the discriminator 3 and the clock output terminal via the delay element 26.

The input optical signal is RZ (Retu)
If the signal has a clock component such as an rn to Zero signal, the clock component can be extracted by passing the output signal of the wideband amplifier 14a through the narrowband filter 25 as it is. However, the input optical signal is NR
If the signal does not have a clock component such as a Z (Non Return to Zero) signal, it is necessary to extract the clock component using the differentiating circuit 4 and the rectifying circuit 24 '.

The discriminator 3 accurately discriminates and reproduces the input optical signal based on the clock signal extracted in this way and the electric signal obtained from the converter 1. In addition,
When the output level from the narrow band filter 25 does not reach the level required for the operation of the discriminator 3, the signal is amplified using the narrow band amplifier 5. The discriminator 3 uses a delay element 26 with a fixed or variable phase delay so that the phase condition between the electric signal input from the converter 1 and the input clock signal is optimized. Adjust the phase.

[0008]

However, such an optical receiver has the following problems. That is,
In this optical receiver, since the retiming unit for extracting the clock signal from the input optical signal is formed of an electric circuit, it is difficult to electrically extract the clock signal as the transmission speed increases. Become. Also, since the retiming unit is composed of many electric circuits,
In performing high-speed signal processing, the influence of temperature fluctuations is not negligible, and it is extremely difficult to stabilize the phase of the clock signal within the range of the phase margin in the discriminator.

[0009]

SUMMARY OF THE INVENTION The present invention is an optical receiving apparatus for solving such a problem. That is, the optical receiving apparatus according to the present invention includes a conversion unit for obtaining a predetermined electrical signal from an input optical signal, a first optical signal branched from the optical signal, and a predetermined optical signal with respect to the first optical signal. An optical branching means for obtaining a time-delayed second optical signal;
Difference detecting means for obtaining a difference electric signal corresponding to the difference between the optical signal and the second light signal, and rectifying the difference electric signal obtained by the difference detecting means, and converting the difference electric signal into an optical signal based on the rectified signal. A clock extraction unit for extracting a clock signal included therein; and an identification unit for performing identification and reproduction of an optical signal based on the electric signal obtained from the conversion unit and the clock signal obtained from the clock extraction unit. ing.

[0010]

According to the present invention, an input optical signal is split by an optical splitting unit, and one of the first optical signal and the second optical signal delayed by a predetermined time with respect to the first optical signal. The difference electric signal corresponding to the difference is detected by the difference detecting means. Further, the clock extracting means extracts a clock signal included in the optical signal based on the rectified signal of the differential electric signal. That is, the difference detecting means detects a changed portion of the input optical signal, that is, a differential waveform based on the difference between the first optical signal and the second optical signal. As a result, it is possible to obtain information as a source of the clock signal included in the optical signal as it is in the state of the optical signal, and to speed up the signal processing and simplify the electric circuit configuration for extracting the clock signal. Become.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical receiver according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating an optical receiver according to a first embodiment, and FIG. 2 is a signal waveform diagram illustrating an operation of the optical receiver according to the first embodiment. As shown in FIG. 1, the optical receiving apparatus according to the first embodiment mainly includes a conversion unit 1 that converts an optical signal input from an optical fiber 11 into a predetermined electric signal, and a remote unit that extracts a clock signal based on the optical signal. It comprises a timing section 2 and a discriminator 3 for discriminating and reproducing an optical signal based on the electric signal obtained from the conversion section 1 and the clock signal obtained from the retiming section 2.

The conversion unit 1 includes an optical amplifier 12 for amplifying the optical signal input from the optical fiber 11 as it is, a first light receiving element 13 for converting the optical signal into an electric signal, and an output of the first light receiving element 13. And a preamplifier 14 that amplifies the electric signal before transmitting it to the discriminator 3. The preamplifier 14 is not always necessary if the discriminator 3 has sufficient discrimination sensitivity. A first optical splitter 10 is provided on the output side of the optical amplifier 12 and plays a role of sending an optical signal to the retiming unit 2. The retiming unit 2 includes a second optical splitter 20, an optical delay element 21,
A first balanced receiver 23, a first rectifier circuit 24,
It comprises a narrow band filter 25 and an electric delay element 26.

Further, the first balanced receiver 23 has a configuration in which the second light receiving element 23a and the third light receiving element 23b are directly connected. The second light receiving element 23a
A negative bias is applied to the anode of the third light receiving element 23b, and a negative bias is applied to the anode of the third light receiving element 23b.
The output terminal is connected to the cathode 3b.

Next, a signal processing operation in the optical receiver according to the first embodiment will be described. First, an optical signal input from the optical fiber 11 is amplified by the optical amplifier 12 and split into two by the first optical splitter 10. One of them is converted into an electric signal by the first light receiving element 13 and sent to the discriminator 3 via the preamplifier 14. The other optical signal split by the first optical splitter 10 is transmitted to the retiming unit 2.
Is further split into two by the second optical splitter 20, one of which is directed to the second light receiving element 23a constituting the first balanced receiver 23, and the other is directed to the third light receiving element 23b via the optical delay element 21. Is entered.

The other optical signal is given a delay τ1 corresponding to, for example, ビ ッ ト bit to one optical signal by the optical delay element 21. When such two optical signals are input to the first balanced receiver 23, a differential electric signal corresponding to a difference between the respective optical signals is output to an output terminal thereof. The difference electric signal is rectified through the first rectifier circuit 24, and the narrow band filter 25 extracts the clock signal contained therein.

The clock signal is adjusted to a predetermined phase via the electric delay element 26, output to the clock output terminal, and sent to the discriminator 3. Classifier 3
Then, discrimination / reproduction of an optical signal is performed based on the electric signal sent from the conversion unit 1 and the clock signal sent from the retiming unit 2, and the result is output to the data output terminal.

An example of the signal processing operation in the optical receiver of the first embodiment will be described with reference to FIG. For example,
If the input data (S1) is an NRZ code having a predetermined waveform as shown in the figure, the optical delay element 21 shown in FIG.
(S2) is delayed by .tau.1 (for example, equivalent to 1/2 bit) with respect to the input data (S1). When these signals are input to the first balanced receiver 23, the differential electric signal, which is the output (S3a), has a high level at the rising portion of the input data (S1) and a low level at the falling portion. Will appear.

In other words, this signal (S3a) is a differentiated waveform in which the change in the input data (S1) is indicated by a pulse width corresponding to τ1. This differential waveform can be directly obtained by inputting an optical signal to the first balanced receiver 23, and therefore can sufficiently cope with a high transmission speed.

Further, by passing the output (S3a) of the first balanced receiver 23 through the first rectifier circuit 24 shown in FIG. 1, only the high level portion can be extracted (the waveform (S4a) in FIG. 2). reference). The first rectifier circuit 24 may be a simple circuit composed of, for example, one diode. The output (S4a) of the first rectifier circuit 24 is a pulse having a clock component, and by passing this pulse through the narrow band filter 25 shown in FIG. 1, a clock signal included in the optical signal can be extracted. Become like

In the optical receiver according to the first embodiment, the first
The first balanced receiver 23 uses the optical signal branched using the optical splitter 10 and the second optical splitter 20 as it is.
Since the difference is detected and a differential waveform is obtained without passing through a complicated electric circuit, it is possible to sufficiently cope with high-speed signal processing. Further, the electric circuit components in the retiming unit 2 are simplified, the influence on the temperature change can be reduced, and the phase of the clock signal can be easily stabilized within the range of the phase margin in the discriminator 3. .

Next, an optical receiver according to a second embodiment of the present invention will be described. FIG. 3 is a block diagram illustrating an optical receiver according to the second embodiment, and FIG. 4 is a signal waveform diagram illustrating the operation of the second embodiment. As shown in FIG. 3, in the optical receiver according to the second embodiment, the optical fiber 11, the optical amplifier 1
2. The conversion unit 1 including the first light receiving element 13 and the preamplifier 14 and the discriminator 3 are the same as in the first embodiment, but differ in the configuration of the retiming unit 2. In the following,
The description will be made focusing on the different retiming unit 2.

The retiming unit 2 includes a second optical splitter 20,
The optical delay element 21, the third optical divider 30 and the fourth optical divider 40, the first balanced receiver 23 and the second balanced receiver 27, the first rectifier circuit 24 and the second rectifier circuit 28, the adder 29, It comprises a bandpass filter 25 and an electric delay element 26. Further, the second balanced receiver 27 has a configuration in which the fourth light receiving element 27a and the fifth light receiving element 27b are directly connected. A reverse bias of a positive voltage is applied to the cathode of the fourth light receiving element 27a, and a reverse bias of a negative voltage is applied to the anode of the fifth light receiving element 27b. The output terminal is connected to the cathode of the element 27b.

The second balanced receiver 27 receives two optical signals from the third optical splitter 30 and the fourth optical splitter 40, respectively. The output is the second rectifier circuit 2
8, and is added to the rectified signal from the first rectifier circuit 24 by the adder 29.

Next, a signal processing operation in the optical receiver according to the second embodiment will be described. First, an optical signal input from the optical fiber 11 is split by the first optical splitter 10 after passing through the optical amplifier 12, one of which is directed to the first light receiving element 13 side.
The other is sent to the retiming unit 2 side. First light receiving element 1
The signal processing for the light output sent to the third side is the same as in the first embodiment, and the description is omitted here. Retiming unit 2
The optical signal sent to the side is further split into two by the second optical splitter 20, one of which is split into the first balanced receiver 2.
3 is sent to the second light receiving element 23a, and the other is sent to the third light receiving element 23b via the optical delay element 21. From the first balanced receiver 23, a predetermined differential electric signal is output in the same manner as described in the first embodiment.

On the other hand, the two optical signals split by the second optical splitter 20 are split by the third optical splitter 30 and the fourth optical splitter 40, respectively, and are input to the second balanced receiver 27. That is, an optical signal input from the optical fiber 11 is sent to the fifth light receiving element 27b, and an optical signal delayed by τ1 with respect to this optical signal is sent to the fourth light receiving element 27a.
The second balanced receiver 27 composed of the fourth light receiving element 27a and the fifth light receiving element 27b outputs a differential electric signal (hereinafter, referred to as a first differential electric signal) output from the first balanced receiver 23. .) (Hereinafter, referred to as a second differential electric signal).

The adder 29 performs a process of adding a signal obtained by rectifying the first differential electric signal by the first rectifier circuit 24 and a signal obtained by rectifying the second differential electric signal by the second rectifier circuit 28. The result is sent to the narrow band filter 25. The narrow band filter 25 extracts a predetermined clock signal based on the rectified signal sent from the adder 29, and sends it to the clock output terminal and the discriminator 3 via the electric delay element 26. The discriminator 3 discriminates and reproduces the optical signal based on the clock signal sent through the narrow band filter 25 and the electric signal sent from the converter 1, and outputs the result to the data output terminal. .

Next, an example of a signal processing operation in the optical receiver according to the second embodiment will be described with reference to FIG. For example, when the input data (S1) is an NRZ code having a predetermined waveform as shown in FIG. 3, the output (S2) of the optical delay element 21 shown in FIG. (Equivalent to 1/2 bit). Also,
When these signals are input to the second balanced receiver 27, the second differential electric signal, which is the output (S3b), has a low level at the rising edge of the input data (S1) and a high level at the falling edge. Will appear.

The second differential electric signal is converted to the second differential electric signal shown in FIG.
By passing through the rectifier circuit 28, an output (S4b) of the second rectifier circuit as shown in FIG. 4 is obtained. Adder 2 shown in FIG.
9, the output (S4b) of the second rectifier circuit and the output (S4a) of the first rectifier circuit 24 are added, and the output (S5) of the adder shown in FIG. 4 is sent to the narrow band filter 25 shown in FIG. sending. That is, the output (S5) of the adder is a signal corresponding to the pulse width τ1 indicating the rising and falling portions of the input data (S1).

The narrow band filter 25 extracts a clock signal included in the optical signal based on the output (S5) of the adder. That is, in the optical receiving device according to the second embodiment, a waveform having twice the number of pulses can be sent to the narrowband filter 25 as compared with the optical receiving device according to the first embodiment.
This makes it possible to increase the amplitude of the extracted clock signal. That is, the average value Aave of the sine wave output amplitude of the narrow band filter 25 is generally given by equation (1).

[0030]

(Equation 1)

Here, N is the mark ratio (1 / N) of the input waveform of the narrow band filter 25, and Q is a value indicating the characteristic of the narrow band filter 25. For example, Q = 1000, the mark rate of the narrow band filter 25 (see FIG. 1) in the first embodiment is 1/4, and the narrow band filter 25 in the second embodiment is
When the mark ratio of (see FIG. 3) is １ ／, the ratio of the output amplitude of the narrow-band filter between the first embodiment and the second embodiment is as shown in equation (2).

[0032]

(Equation 2)

Therefore, in the optical receiver according to the second embodiment, the amplitude of the clock signal sent from the narrow band filter 25 to the discriminator 3 is about twice as large as that of the first embodiment. This is effective when the insertion loss in the optical splitters 10, 20, 30, 40 and the narrow-band filter 25 is compensated, and it is desired to sufficiently obtain the amplitude of the clock signal to the discriminator 3.

[0034]

As described above, the optical receiving apparatus according to the present invention has the following effects. That is, in the optical receiver of the present invention, the main part of the retiming unit, that is, the part that obtains its differential waveform based on the input optical signal is optically configured, so that it can sufficiently cope with high-speed signal processing. Become. Further, the electric circuit components in the retiming unit are simplified, the influence on the temperature change can be reduced, and the phase of the clock signal can be easily stabilized within the range of the phase margin in the discriminator. These make it possible to provide an optical receiving device that is highly reliable in constructing an optical transmission system that performs high-speed signal processing.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a first embodiment of the present invention.

FIG. 2 is a signal waveform diagram for explaining the operation of the first embodiment.

FIG. 3 is a block diagram illustrating a second embodiment of the present invention.

FIG. 4 is a signal waveform diagram for explaining the operation of the second embodiment.

FIG. 5 is a block diagram illustrating a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 conversion unit 2 retiming unit 3 discriminator 10 first optical splitter 11 optical fiber 13 first light receiving element 20 second optical splitter 21 optical delay element 23 first balanced receiver 24 first rectifier circuit 25 narrow band filter

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H04B 10/26 (72) Inventor Hidenari Maeda 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd. (56 References JP-A-3-6541 (JP, A) JP-A-5-110514 (JP, A) JP-A-2-52535 (JP, A) JP-A-62-257551 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H04B 10/00

Claims (2)

(57) [Claims] A converter for obtaining a predetermined electrical signal from an input optical signal; a first optical signal branched from the optical signal; and a first optical signal delayed by a predetermined time with respect to the first optical signal. Optical branching means for obtaining a second optical signal; difference detecting means for obtaining a differential electric signal corresponding to a difference between the first optical signal and the second optical signal; and the differential detecting means Clock extracting means for rectifying the differential electric signal obtained in the above, and extracting a clock signal included in the optical signal based on the rectified signal; the electric signal obtained from the converting means; and the clock extracting means. And a discriminating means for discriminating and reproducing the optical signal based on the clock signal obtained from the optical receiver. 2. The method according to claim 1, wherein the difference detecting unit includes a first difference electric signal corresponding to a difference between the first light signal and the second light signal, and a first difference electric signal having a polarity opposite to the first difference electric signal. And the clock extracting means rectifies the first differential electric signal and rectifies the second differential electric signal, and generates the clock signal based on the two rectified signals. 2. The optical receiving device according to claim 1, wherein