Optical access network system

Abstract

An optical access network system capable of transmitting and receiving high-speed signals and which allows the number of subscribers to be increased without increasing the number of wavelengths used is provided. An optical line terminal and an optical network unit are joined via an optical fiber transmitting line, a star coupler, and a plurality of branching optical fiber transmitting lines. The optical line terminal and optical network unit are constituted comprising an optical processing section and an electrical processing section. The optical processing section comprises a light-emitting element and a light-receiving element. The electrical processing section comprises a transmitting signal processing section that generates an encoded transmitting signal in the form of an electrical signal by encoding a transmitting signal and a receiving signal processing section that obtains a receiving signal by decoding a code-division-multiplexed signal that has been converted from optical-signal form to electrical-signal form by the light-receiving element. The optical access network system is characterized in that the decoding processing circuit that the receiving signal processing section comprises is constituted comprising an analog matched filter and a decision circuit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the present invention will be better understood from the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic block constitutional view of an optical access network system;

FIG. 2 serves to describe the process whereby a transmitting signal is encoded;

FIG. 3 serves to describe the process whereby a receiving signal is decoded;

FIG. 4 serves to describe an aspect in which reflected light from an optical connector is incorporated in a receiving signal processing section; FIG. 5 shows the relationship between the receiving signal and the peak position of an auto-correlation waveform in a case where a signal resulting from the mixing of the reflected transmitting signal is decoded, in the optical access network system of the first invention;

FIG. 6 is a schematic block constitutional view of an analog matched filter;

FIG. 7 is a schematic block constitutional view of a decision circuit which serves to describe the operating principles of the decision circuit;

FIG. 8 is a schematic block constitutional view of an optical network unit of an embodiment A of the optical access network system of a second invention;

FIG. 9 is a schematic block constitutional view of an optical network unit of an embodiment B of the optical access network system of the second invention;

FIG. 10 shows the relationship between the receiving signal and the peak position of an auto-correlation waveform in a case where a signal resulting from the mixing of the reflected transmitting signal is decoded, in the optical access network system of the second invention; and

FIG. 11 is a schematic block constitutional view of a multiple wavelength optical access network system.

Claims

1. An optical access network system in which a star coupler is provided at one end of an optical fiber transmitting line and which performs bidirectional optical communication by means of code division multiplexing, by allocating mutually different codes to each of a plurality of optical network units that are each joined to a plurality of branching optical fiber transmitting lines formed split by said star coupler, between an optical line terminal that is joined to the other end of said optical fiber transmitting line and said plurality of optical network units, wherein each of said plurality of optical network units and said optical line terminal comprises: a transmitting signal processing section for generating an encoded transmitting signal by encoding a transmitting signal and outputting said encoded transmitting signal; and a receiving signal processing section for receiving a code-division-multiplexed signal that is transmitted after being code-division-multiplexed and for obtaining a receiving signal by decoding said code-division-multiplexed signal, and said receiving signal processing section comprises a decoding processing circuit that decodes said code-division-multiplexed signal and said decoding processing circuit comprises an analog matched filter and a decision circuit,said analog matched filter comprising an analog shift register, a positive signal adder, a negative signal adder, an analog adder that adds output signals from each of said positive signal adder and said negative signal adder, and a lowpass filter.

2. The optical access network system according to claim 1, wherein said transmitting signal processing section comprises a code assignment circuit that encodes said transmitting signal and a delay circuit that is connected downstream of said code assignment circuit and which outputs said encoded transmitting signal after adjusting a phase of said encoded transmitting signal.

3. The optical access network system according to claim 1, wherein said analog shift register is an analog shift register that is formed by a charge coupled device.

4. The optical access network system according to claim 2, wherein said analog shift register is an analog shift register that is formed by a charge coupled device.

5. The optical access network system according to claim 1, wherein said decision circuit comprises a threshold value processing circuit that processes a signal that is output after being decoded by said analog matched filter and converts the signal into a decoded signal in digital form, and a latch circuit that generates the receiving signal from said decoded signal in digital form and outputs said receiving signal.

6. The optical access network system according to claim 2, wherein said decision circuit comprises a threshold value processing circuit that processes a signal that is output after being decoded by said analog matched filter and converts the signal into a decoded signal in digital form, and a latch circuit that generates the receiving signal from said decoded signal in digital form and outputs said receiving signal.

7. The optical access network system according to claim 1, wherein said code assignment circuit which said encoding processing circuit of said transmitting signal processing section comprises and which generates an encoded transmitting signal by encoding a transmitting signal is an EXNOR (Exclusive NOR), which is a gate circuit obtained by connecting an inverter to the output of an EXOR (Exclusive OR) gate.

8. The optical access network system according to claim 2, wherein said code assignment circuit which said encoding processing circuit of said transmitting signal processing section comprises and which generates an encoded transmitting signal by encoding a transmitting signal is an EXNOR (Exclusive NOR), which is a gate circuit obtained by connecting an inverter to the output of an EXOR (Exclusive OR) gate.

9. An optical access network system in which a star coupler is provided at one end of an optical fiber transmitting line, comprising an optical line terminal that is joined to the other end of said optical fiber transmitting line, and optical network units that are joined to each of N branching optical fiber transmitting lines (N is a natural number of two or more) formed with N branches by said star coupler, and in which first to Nth channels are allocated sequentially to said N optical network units and bidirectional communication using code-division-multiplexing is performed between said optical line terminal and said N optical network units, wherein each of said N optical network units and said optical line terminal comprises a transmitting signal processing section that generates an encoded transmitting signal by encoding a transmitting signal and outputs said encoded transmitting signal, and a receiving signal processing section that receives an encoded receiving signal that is transmitted after being encoded and decodes said encoded receiving signal to extract and output a receiving signal, andcode that is set for said transmitting signal processing section that an optical network unit of a kth channel (k is a natural number from 1 to N) comprises which encodes and outputs an uplink signal which is a signal for transmitting from said optical network unit of said kth channel to said optical line terminal, and code that is set for said transmitting signal processing section that said optical line terminal comprises which encodes and outputs a downlink signal which is a signal for transmitting from said optical line terminal to said optical network unit of said kth channel are mutually different.

10. The optical access network system according to claim 9, wherein code that is set for said transmitting signal processing section that an optical network unit of a pth channel (p is a natural number from 1 to N) comprises which encodes and outputs an uplink signal which is a signal for transmitting from said optical network unit of said pth channel to said optical line terminal, and code that is set for said transmitting signal processing section that said optical line terminal comprises which encodes and outputs a downlink signal which is a signal for transmitting from said optical line terminal to an optical network unit of a qth channel (q is a natural number of 1 to N) are equal to one another, and sets (p, q) of the natural numbers p and q are limited to N sets which are (1, 2), (2, 3), (3, 4), . . . (p, p+1), . . . (N−1, N) and (N, 1).