JPH02291741A - Optical receiver and optical communication network - Google Patents

Abstract

PURPOSE:To detect collision in an optical area by processing an input optical signal by a partial response circuit. CONSTITUTION:In an optical partial response circuit 21, the input optical signal is delayed by one period for a code transmission speed 2f0, and the difference between this signal and the carrier frequency is operated. The discrimination level of a discriminator 26 is set to an about zero level (+ or -DELTA), a clock signal corresponding to the code transmission speed 2f0 extracted by a timing extracting circuit 27 is used to identify both channels. The zero state of the CD channel in the code string consisting of one word and three identification outputs of the just preceding channels at the time of absence of signal collision is generated when two words of signal sequence '01' and '10' are transmitted, and a corresponding CRV pattern is limited. Consequently, this CRV is supervised to detect signal collision.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical receiver that detects collisions of optical signals output from each node in a system in which nodes are connected via an optical transmission line. This relates to optical communication networks.

(Prior Art) FIG. 8 shows the configuration of an optical star network. In this optical star network, an optical star coupler 51 is arranged at a center node, and connections between the optical star coupler 51 and a plurality of communication control adapters 52 are provided. , are connected in a star shape with optical fiber cables.The communication form in this network is packet communication, and CSM A/CD (Carrie
r Sense Multiple Access/Co
Communication is performed using the llision detection) method.

Further, each communication control adapter 52 includes a photoelectric converter transmitter (E/O) 53, a photoelectric converter receiver (0/E) 54,
It includes a transmission/reception control section (TRC) 55 and a plurality of terminal interface sections (TINF) 56.

A plurality of terminal devices 57 are accommodated by each terminal interface 56, and the transmission/reception control unit 55 accommodates each terminal device 57.
The information sent from the packet is received via the terminal interface section 56, and the information sent from the packet is received via the terminal interface section 56. , photoelectric converter transmitter 5
Supply to 3. On the contrary, the transmission/reception control section 55 disassembles the packet addressed to the communication control adapter 52 itself sent from the optical transmission path (optical fiber) via the opto-electric conversion section receiver 54, and sends it to the corresponding terminal. The signal is supplied to the interface unit 56.

Further, the terminal interface section 56 realizes functions such as call setup, call release, and data transmission control with the terminal device 57.

The opto-electric converter receiver 54 detects a chiaria (optical signal) on the optical transmission line under the control of the transmission/reception controller 55.

If this optical transmission line is free, the packet is supplied to the opto-electrical converter transmitter 53, which converts the packet into a Guipulse (Manchester) code and further converts it into an optical signal. Send it to the halo transmission line. On the other hand, the opto-electrical converter receiver 54 converts the packet supplied from the optical transmission line into an electrical signal and then detects the delimiter to realize CSMA/CD type communication.

FIG. 9 shows a conventional opto-electric converter receiver 54 when an intensity modulation (IM) dipulse signal is adopted as a transmission path code.
The configuration is shown below.

In FIG. 9, 61 is an avalanche photodiode (APD), 62 is an APD bias circuit, 63 is an alternating current (AC) amplifier, and 64 is a virtual response (APD).
1, -1) circuit, 65 is the main amplifier, 66 is the waveform shaping circuit, 67 is the comparator, 68.71 is the discriminator, 69
is a coding rule violation (CRV) detection circuit, 70 is a carrier detection circuit, 72 is a timing extraction circuit, and 73 is 1/2
Each frequency dividing circuit is shown.

Optoelectric converter transmitter 53 in other communication control adapter 52
When the optical signal outputted from the optical signal is supplied to the photoelectric converter receiving section 54, it is converted into an electrical signal by the avalanche photodiode 61 to which a bias voltage is applied by the APD bias circuit 62, and the signal is amplified by the AC amplifier 63. After that, the nominal response (1, -1) circuit 6
4.

A highly stable AC amplifier 63 is used to amplify the low level optical reception signal to a distinguishable level. On the other hand, the output signal of the avalanche photodiode 6l supplied to the AC amplifier 63 has a DC component, and level fluctuations in the DC component occur in the output signal of the AC amplifier 63. Therefore, the optimum discrimination level varies depending on the pattern of the input signal, resulting in deterioration of the S/N ratio. In particular, at the rising edge of a human-powered burst signal, it is necessary to wait a certain period of time before data can be correctly identified.

In order to eliminate this DC component level fluctuation, it is sufficient to convert the unipolar signal to AC. In the conventional opto-electrical converter receiver 54 shown in FIG.
is used to suppress DC level fluctuations of the input signal from approximately the rising edge of the input optical burst signal. Also,
In the timing extraction circuit 72 that extracts the clock signal superimposed on the optical signal, a tank circuit with a load Q of 20 to 40 is used to achieve a high-speed rise of the timing signal. With the circuit improvements described above,
The probability of bit synchronization within 10 bits is determined when receiving a burst signal.

First, when a partial response circuit is used, its output signal is converted into a ternary signal, which complicates the configuration of the identification circuit. Many transmission codes are known, but IB2B codes such as Dipulse can simplify the circuit configuration and
I (Bit SequenceIndependent
nce) code.

FIG. 10 shows the sign rule (sign rule in the case of -Δ discrimination) of the signal subjected to the Gwy pulse conversion and the partial response conversion. In the diversity conversion, transmission information D is converted into bD consisting of two signals. Furthermore, partial response (
1, -x)llt 64 delays the input signal by one time slot (period) for the code transmission rate 2fo extracted by the timing extraction circuit 72, and calculates the difference between the signals before and after the delay. Therefore, this operation will affect the following code, and the code rule shown in FIG. 10 takes into consideration the transmission of two consecutive pieces of information (words).

Code of the first half of one word (hereinafter referred to as CD channel)
The signal state is separated into three states: "10", "-", or zero. Also, the second half code (hereinafter referred to as information channel)
The signal state is separated into “+゜゛” or “1”.

In the comparator 67, the discrimination level is set near the zero level (±Δ) (in the example shown in Figure 10, it is set to -Δ).
, symbol transmission rate 2f. for both channels. Identification is made using a clock signal corresponding to . A code string consisting of one word and three identification outputs of the information channel immediately before it can take only the value in the "identification output" column shown in FIG. 10 if there is no signal collision.

Here, a coding rule violation (CRV) is defined as a situation in which an identification error occurs only in the rCD channel, and no identification error occurs in any of the adjacent information channels before or after the rCD channel. That is, the CR pattern is limited to the four patterns shown in FIG. State zero in the CD channel occurs when two words "01" or "10°' are transmitted, and by monitoring the resulting CRV by the CRV detection circuit 69, signal collision can be detected. The information is reproduced by the discriminator 71 from the information channel identification results as shown in FIG.

[Problem to be solved by the invention]

By the way, in the conventional method described above, the optical signal is converted into an electrical signal and then the partial response (1, -1) is
Since the processing was performed by the circuit 64, due to the drive speed limit of this partial response (1, -1) circuit 64,
There has been a problem in that it is difficult to detect collisions of optical packet signals in the optical domain of high-speed (about Gb/s) transmission.

Also, the electric fields of the two colliding packet signals are E1 and E2.
Then, the respective detection currents are E, XF! Do, R2X
E2''(E'' is the conjugate component of E), and if the level difference is large (IEI l >> IE
21) has the problem that it is difficult to detect collisions of optical packet signals with different levels because the shadows of smaller levels are ignored.

The present invention was created in view of these points, and aims to provide an optical receiver and an optical communication network that can easily detect collisions of optical signals with large level differences in the optical domain. The purpose is

[Means to solve the problem]

FIG. 1 is a diagram showing the configuration of an optical receiver and an optical communication network according to the present invention.

1. The optical receiver of claim 1 divides an input optical signal corresponding to a redundant code in which each bit is composed of a multi-level pulse into two parts, gives them different delay times, and then combines them. an optical partial response circuit that outputs a composite optical signal, an optical electrical conversion circuit that converts the composite optical signal into an electrical signal, and a signal identification circuit that identifies transmitted information based on the electrical signal output from the optical electrical conversion circuit. and an optical signal collision detection circuit that monitors the code rule of redundant codes based on the electrical signals output from the optical-to-electrical conversion circuit and detects signal collisions on the transmission path.

j quantity゛12 ■ The optical communication network according to claim 2 comprises the optical receiver according to claim 1, an encoding circuit that converts each bit of transmission information into a redundant code composed of multivalued pulses, and this encoding. It is configured to optically couple a plurality of nodes each having an optical transmitter having an electro-optical conversion circuit that converts the encoded output output from the circuit into an optical signal.

[For production]

In the Nikko partial response circuit of Quantum Engineering 1, an input optical signal corresponding to a redundant code, each bit of which is composed of a multi-level pulse, is divided into two parts, each given a different delay time, and then combined. This combined optical signal is supplied to an optical-to-electrical conversion circuit and converted into an electrical signal, and the converted electrical signal is supplied to a signal identification circuit and an optical signal collision detection circuit. The signal identification circuit identifies transmitted information based on this electrical signal, and the optical signal collision detection circuit monitors redundant code rules based on this electrical signal to detect signal collision.

In the present invention, an input optical signal is processed in the optical domain by a partial response circuit, and in this processing, two optical signals given different delay times are combined and caused to interfere, thereby adjusting the level. Collision detection of signals with a large difference becomes easier.

ii) In the optical communication network according to claim 2, a plurality of nodes are optically coupled, and each node is equipped with the optical receiver and optical transmitter according to claim 1.

This optical transmitter has an encoding circuit and an electrical-to-optical conversion circuit, and the encoding circuit converts each bit of transmission information into a redundant code consisting of multivalued pulses, and converts this conversion output into an electrical signal. An optical conversion circuit converts it into an optical signal and sends it out to an optical transmission line.

In the present invention, when optical signals are simultaneously transmitted from each optically coupled node, the optical receiver of each node receives transmitted information and detects signal collision.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

As the communication network in the embodiment of the present invention, the eighth
Let us consider the optical star network shown in the figure.

FIG. 2 shows the configuration of a photoelectric converter transmitter in an embodiment of the present invention. Photoelectric converter transmitter 1 shown in Figure 2
0 corresponds to the opto-electric converter transmitter 53 in each communication control adapter 52 shown in FIG.

In FIG. 2, 11 represents an encoding circuit, 12 represents a semiconductor laser diode, and 13 represents a laser diode drive circuit.

A CMI code is used as the transmission path code. CM■ code is an I code that converts 1 bit of information signal into 2 bits of transmission path code.
One of the B2B codes, the code transmission speed is 2 times the information transmission speed.
It will be doubled. When an optical fiber with broadband characteristics is selected as the transmission medium, these codes are very effective in ensuring good balance <BSI. FIG. 3 shows the conversion code rules for CMI codes.

Data input to the opto-electric converter transmitter 10 is converted into a CMI code by an encoding circuit 11. The laser diode drive circuit 13 directly performs FM conversion on this CMI code to drive the semiconductor laser diode 12, and an optical signal (FM signal light) is input from the semiconductor laser diode 12 to the optical transmission path.

FIG. 4 shows the spectrum of the optical signal output from the semiconductor laser diode 12. The horizontal axis is the frequency of the optical signal,
The vertical axis indicates the incident light intensity. Assign a transmission line code space (“0”) to the peak on the low frequency side of the spectrum (center frequency f,) and a mark (“1゛”) to the peak on the high frequency side (center frequency rz), and Let the frequency shift be f-(=fz f+).

FIG. 5 shows the configuration of a photoelectric converter receiver in an embodiment of the present invention. Photoelectric converter receiving section 2 shown in FIG.
0 corresponds to the photoelectric converter receiver 54 in each communication control adapter 52 shown in FIG.

In FIG. 5, 21 is an optical partial response circuit, 22 is a light receiving element consisting of a pair of avalanche photodiodes, etc., 23 is an AC amplifier, 24 is a band pass filter, 25 is an amplifier, and 26 is a light receiving element consisting of a pair of avalanche photodiodes. 27 is a timing extraction circuit; 28 is a discriminator for monitoring code conversion rules;
29 is a coding rule error (CRV) detection circuit, 30 is a carrier detection circuit, and 31 is a discriminator for transmission information.

The optical partial response circuit 21 includes two directional couplers and two waveguides connecting them. The optical partial response circuit 21 divides the input optical signal into two parts, one of which is transmitted at a code transmission rate of 2f. 1 against
After being delayed by a period time, the signal is recombined with the other signal and sent to the light receiving element 22.

If the light waves in the two coupled waveguides have the same optical frequency, the output (photocurrent) of the light receiving element 22 will be only a DC component. However, if the two optical frequencies differ by f1, the output of the light receiving element 22 will have the frequency f. There are intermediate frequency (IF) signals. Transmission line code “゜l”′
, “0゛ binary source data converts the IF signal to the center frequency f
It is obtained by passing through the band pass filter 24 (2).

FIG. 6 shows the sign rule for signals subjected to CMI conversion and optical partial response conversion. As described above, the optical partial response circuit 21 delays the optical input signal by one cycle time for the code transmission rate 2fo, and calculates the difference in carrier frequency from that signal. Therefore, this operation will affect the following codes, and the 6th
The coding rule shown in the figure takes into consideration the transmission of two consecutive pieces of information (words).

For the first half code (CD channel) and the second half code (information channel) in one word, bandpass filter 2
The amplitude of the signal extracted by 4 is separated into zero or +'.

The discrimination level in the discriminator 26 is set close to zero level (±Δ)
, and the code transmission rate 2f. is extracted by the timing extraction circuit 27. Both channels are identified using a clock signal corresponding to . A code string consisting of one word and three identification outputs of the information channel immediately before it can take the value of "rIF signal identification output" shown in FIG. 6 if there is no signal collision.

In other words, state zero in the CD channel (when the CD channel of the IF signal identification output is zero) occurs when the signal sequence transmits two words "0vi.""10", and the corresponding CRV pattern is Limited to those shown in Figure 6.

Therefore, by monitoring this CRV, signal collisions can be detected.

Further, the discriminator 31 obtains the original information by inverting the information channel output from the discriminator 26 ("
(See “Playback Output”).

In the embodiment, for example, a preamble pattern ("Ol" pattern) for establishing synchronization is sent at the beginning of the packet. The timing extraction circuit 27 determines the code transmission rate of 2f. based on this preamble pattern. The 1/2 frequency divider circuit 28 further divides the frequency of this clock signal to obtain a clock signal equal to the information transmission level f0. By the way, this 1/2 frequency divider circuit 28
The clock signal output from the clock signal has a phase uncertainty of 180 degrees, and a CRV occurs when the clock signal is out of synchronization. When this CRV is detected by the CRV detection circuit 29, 1
Bit synchronization is established by inverting the phase of the cross signal output from the /2 frequency divider circuit 28 and performing synchronization pull-in.

In the optical star network shown in FIG. 8, optical packet signals are simultaneously sent out from a plurality of communication control adapters 52, and there is a possibility that packet collisions will occur. In this embodiment, self-homodyne detection using the optical partial response circuit 21 causes the detection current to be E+
There are not only components proportional to XE+'' and E2XE2'', but also components proportional to EIXE2'' and E2XE-, and even if the level difference between colliding packets is large, a coding rule error can be easily detected.

Furthermore, in the embodiment, since the partial response conversion is processed in the optical domain by the optical partial response circuit 2l, signal collisions can be detected in the optical domain.

In addition, in the embodiment described above, CMI is used as a redundant code.
Although a code is used, similar processing is also possible with a DMI code whose code rules are shown in FIG.

(Effects of the Invention) As described above, according to the inventions of claims 1 and 2, collision detection in the optical region becomes possible by processing the input optical signal using the partial response circuit.

In addition, in a partial response circuit, two optical signals given different delay times are combined and interfered with, so when two signals collide, the signal with a lower level will affect the one with a higher level. Therefore, collision detection of signals with a large level difference becomes easy.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an optical receiver and optical communication network of the present invention, FIG. 2 is a configuration diagram of a photoelectric converter transmitter according to an embodiment, and FIG.
Figure 4 is an explanatory diagram of the CMI code, Figure 4 is an explanatory diagram of the spectrum of an optical signal, Figure 5 is a configuration diagram of a photoelectric converter receiver according to an embodiment, and Figure 6 is a diagram of the code conversion rule of an embodiment. Explanatory diagram, Fig. 7 is an explanatory diagram of the DMI code, Fig. 8 is a block diagram of an optical star type network, Fig. 9 is a block diagram of a conventional opto-electric converter receiver, and Fig. 10 is a conventional code conversion rule. FIG. In the figure, 10 is a photoelectric converter transmitter, 11 is an encoding circuit, l2 is a semiconductor laser diode, 13 is a laser diode drive circuit, 20 is a photoelectric converter receiver, 21 is an optical partial response circuit, and 22 is a light receiver. 23 is an AC amplifier, 24 is a band pass filter, 25 is an amplifier, 26.31 is a discriminator, 27 is a timing extraction circuit, 28 is a 1/2 frequency divider circuit, 29 is a CRV detection circuit, 30 is a carrier detection circuit It is. Figure Figure ↑ f2 fil clear! 4 pairs figure

Claims (2)

[Claims] (1) An optical partial response circuit that divides an input optical signal corresponding to a redundant code in which each bit is composed of a multilevel pulse into two parts, gives them different delay times, and then combines them to output a combined optical signal; an optical-to-electrical conversion circuit that converts the combined optical signal into an electrical signal; a signal identification circuit that identifies transmission information based on the electrical signal output from the optical-to-electrical conversion circuit; An optical receiver comprising: an optical signal collision detection circuit that monitors redundant code rules based on output electrical signals and detects signal collisions on a transmission path; (2) The optical receiver according to claim 1, an encoding circuit that converts each bit of transmission information into a redundant code composed of multilevel pulses, and converting the encoded output output from this encoding circuit into an optical signal. An optical communication network comprising: an optical transmitter having an electrical-to-optical conversion circuit; and a plurality of nodes having the following optically coupled together.