JP2000013323A - Optical communication system and optical terminal station device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical communication system consisting of an optical terminator that can control a wavelength of an optical signal simply at a low cost and to provide the optical terminal device configuring the optical communication system. SOLUTION: An optical terminal device 10 is provided with a wavelength analysis means 14 that analyzes a wavelength of an optical signal outputted from an optical terminator 20 and with a signal processing means 15 that outputs an optical signal including the analysis result by the wavelength analysis means 14 to the optical terminator 20. The optical terminator 20 is provided with a wavelength adjustment means 26 that changes a wavelength of an outputted optical signal and a signal processing means 25 that receives an optical signal including the analysis result outputted from the optical terminal station device 10 to control the wavelength adjustment means 26.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication system and an optical terminal unit constituting the optical communication system. More particularly, the present invention relates to an optical communication system for controlling the wavelength of an optical signal output from a subscriber optical termination device. The present invention relates to an optical communication system and an optical terminal device that can be centrally and remotely controlled on a terminal device side.

[0002]

2. Description of the Related Art Optical fiber communication has been actively introduced because optical fiber itself has ultra-low loss, ultra-wide band, excellent mechanical characteristics, and excellent electromagnetic characteristics. A PON (Passive Optical Network) that connects an optical terminal equipment on the office side and an optical terminal equipment on the subscriber side via an optical transmission line, and performs two-way communication between them.
k: passive optical network).

[0003] In this optical communication system, in order to transmit signals between optical terminating devices on the subscriber side without collision,
The bandwidth of the transmission burst signal is allocated to the optical terminating device of each subscriber in advance, and the optical terminating device is controlled by the optical terminal device at times other than when information transmission is required in the optical terminating device. There is a time division multiple access system (Time Divesion Multiple Access) that stops transmission from a remote terminal and increases the use time of another optical terminal device.

FIG. 7 shows a conventional subscriber optical communication system. In the figure, an optical terminal equipment OLT installed in a station building is shown.
(Optical Line Terminal) 110 and an optical terminal unit ONU (Optical Network Unit) 120 installed in the subscriber's house.
And ODN (Optical Distribution Network)
k) One optical terminal equipment OL connected at 130
A plurality of optical terminal units ONU120 correspond to T110. The branch coupler 111 in the optical terminal unit OLT 110 has a function of demultiplexing the downstream signal light output from the optical transmission unit E / O 112 and the upstream signal light input to the optical reception unit O / E 113. The signal processing circuit 115 includes an E / O 112
And an input / output electrical signal between the O / E 113. In the optical terminal unit ONU 120, the branch coupler 121 simply performs the demultiplexing of the upstream and downstream signal lights, and the E / O 122
The optical receiving unit O / E 123 performs input / output of signal light, and the signal processing circuit 125 processes upstream and downstream signals.

[0005] In recent years, subscriber optical communication devices have been generally installed outdoors. Optical termination O
When the NU 120 is indoors, the environmental temperature is the same as that of a normal device. However, when the NU 120 is installed outdoors, the same characteristics as those of a hostile (−40 to + 50 ° C.) are required. Further, considering the temperature rise in the apparatus and the self-heating of the laser diode, the ambient temperature of the laser diode must be considered to be -40 to 85 ° C. Although the optical transmission power can be adequately provided by the ability of the laser diode, the wavelength fluctuates depending on the environmental temperature because the wavelength is a physical basic characteristic of the laser diode.

The wavelength of light transmitted from a laser diode is
It changes depending on the ambient temperature and self-heating of the laser diode. In the backbone optical communication system, for example, a 1.55 μm band signal light and an optical direct amplifier are used to make the transmission distance superspan. For example, in this method, since the wavelength range of a main signal applicable to an optical direct amplifier is limited, the wavelength of the laser diode output is strictly controlled.

However, since a low price is required for a subscriber system, a high-performance control circuit and a laser diode for keeping the optical signal wavelength constant cannot be used.

Conventionally, as shown in FIG. 7, a monitor 126 is provided in the optical terminating device 120, the laser light emitted from the laser diode is monitored by the monitor 126, and a temperature control device provided in the laser diode is controlled. The wavelength of laser light has been controlled by controlling the ambient temperature of the laser diode by cooling or heating the laser diode.

[0009]

However, such a conventional method of controlling the wavelength of laser light in an optical termination device requires a circuit for wavelength analysis in the optical termination device. Termination equipment is still relatively expensive. Therefore, there is a need for a lower-cost optical termination device.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an optical communication system including an optical termination device capable of controlling the wavelength of an optical signal easily and at low cost.

It is another object of the present invention to provide an optical terminal device capable of performing bidirectional communication via an optical transmission line with an optical terminating device capable of stabilizing the frequency of an optical signal at a low cost.

[0012]

In order to achieve the above object, an optical communication system according to the first aspect of the present invention provides an optical communication system in which an optical terminal equipment on a station side and an optical terminal equipment on a subscriber side are connected via an optical transmission line. In an optical communication system that performs two-way communication by division multiplexing, the optical terminal device includes a wavelength analysis unit that analyzes a wavelength of an optical signal output from the optical termination device, and an analysis result obtained by the wavelength analysis unit. Signal processing means for outputting an optical signal to the optical terminating device, wherein the optical terminating device includes a wavelength adjusting means for changing a wavelength of the optical signal to be output, and an analysis result output from the optical terminal device. Signal processing means for receiving the optical signal and controlling the wavelength adjusting means.

According to the invention having such a configuration, since the wavelengths of all the optical terminating devices connected on the optical terminal device side can be centrally and remotely controlled, the optical terminating device does not require a wavelength analyzing means. In addition, the optical terminal device can have a simple configuration, and can be made simple and inexpensive.

According to a second aspect of the present invention, there is provided the optical communication system according to the first aspect, wherein the wavelength analyzing means determines whether the wavelength is within a predetermined wavelength range or longer than a predetermined wavelength.
Alternatively, the configuration is such that analysis is performed in one of three states of a shorter wavelength than a predetermined wavelength.

According to the invention having such a configuration, the wavelength is not strictly controlled, but is in one of the three states: longer wavelength, lower wavelength than the predetermined wavelength, or within the predetermined range. As a result, the wavelength control is performed, thereby simplifying the device configuration of the optical terminal device and reducing the electric power consumption.

In an optical communication system according to a third aspect of the present invention, in the optical communication system according to the first or second aspect, the wavelength analyzing means separates the wavelength of the optical signal output from the optical terminating device to a predetermined wavelength or more. Wavelength separating means for separating light into wavelengths equal to or less than a predetermined wavelength, light receiving means for receiving each light separated by the wavelength separating means and converting the light into an electric signal, and output from the light receiving means, respectively. And comparing means for comparing and analyzing the electric signals.

According to the invention having such a configuration, it is possible to easily analyze which of the three states the wavelength of the optical signal from the optical termination device is in.

According to a fourth aspect of the present invention, in the optical communication system according to any one of the first to third aspects, the wavelength adjusting means includes a temperature control circuit for controlling a temperature of a laser diode for generating an optical signal. There is a certain configuration.

According to the invention having such a configuration, by controlling the temperature of the laser diode, the wavelength of the laser beam emitted from the laser diode can be controlled.

According to a fifth aspect of the present invention, there is provided an optical terminal apparatus in an optical communication system which performs two-way communication in a time division multiplex manner with an optical terminal apparatus on a subscriber side via an optical transmission line. A wavelength analyzing means for analyzing the wavelength of the optical signal output from the optical terminating device; and a signal processing means for outputting an optical signal including the analysis result of the wavelength analyzing means to the optical terminating device. is there.

According to the invention having such a configuration, since the wavelengths of all the optical terminal devices connected on the optical terminal device side can be remotely controlled, the optical terminal device does not need the wavelength analyzing means, and The apparatus can have a simple configuration, and can be made simple and inexpensive.

According to a sixth aspect of the present invention, in the optical terminal station device according to the fifth aspect, the wavelength analyzing means separates the wavelength of the optical signal output from the optical terminal device into a predetermined wavelength. Wavelength separating means for separating the light into the above wavelengths and wavelengths equal to or less than a predetermined wavelength, light receiving means for receiving each light separated by the wavelength separating means and converting it into an electric signal, and output from the light receiving means There is provided a configuration having comparison means for comparing and analyzing each electric signal.

According to the invention having such a configuration, the wavelength is not strictly controlled, but is in one of three states: longer or lower wavelength than the predetermined wavelength, or within a predetermined range. As a result, the wavelength control is performed, thereby simplifying the device configuration of the optical terminal device and reducing the electric power consumption.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an optical communication system and an optical terminal device according to the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the optical communication system of the present invention. This optical communication system
In the time-division multiple access system, an optical terminal unit OLT10 installed at the office building side and a plurality of optical terminal units ONU20 installed at the subscriber's house are provided with an optical distributor ODN3.
0, and a plurality of optical terminating devices 20 correspond to one optical terminal device 10.

The optical terminal unit 10 has a branch coupler 11 connected to an optical distributor 30 by an optical fiber. The optical transmitter 12 and the optical receiver 13 are connected by the branch coupler 11 and the optical fiber.
And the wavelength analyzer 14 are connected to each other. Also,
These optical transmitter 12, optical receiver 13, and wavelength analyzer 14
And a signal processing unit 15 electrically connected to each other. The branch coupler 11 has a function of demultiplexing the downstream signal light output from the optical transmission unit 12 and the upstream signal light input to the optical reception unit 13, and further branches the upstream signal light to the wavelength analysis unit 14. It also has functions. This wavelength analyzer 1
The light splitting ratio to 4 is a range that does not affect the minimum light receiving sensitivity in the light receiving unit 13.

The wavelength analyzer 14 has a function of analyzing the upstream signal light from the optical terminal device 20 and detecting whether or not the signal is within the wavelength standard. The signal processing unit 15 includes the optical transmission unit 12
And an input / output of an electric signal between the optical receiving unit 13 and the optical terminating device 2 by analyzing a signal from the wavelength analyzing unit 14.
A signal for controlling the wavelength of 0 is generated. The optical transmission unit 12
The electric signal output from the signal processing unit 15 is converted into an optical signal, and the optical receiving unit 13 converts the signal light from the optical termination device 20 into an electric signal.

On the other hand, the optical terminating device 20 includes a branch coupler 21 connected to the distributor 30 by an optical fiber, an optical transmitter 22 and an optical receiver 23 connected to the branch coupler 21 by an optical fiber, respectively. A signal processing unit 25 electrically connected to the optical transmission unit 22 and the optical reception unit 23;
It has a temperature controller 26 electrically connected to the signal processor 25 and installed in the optical transmitter. Branch coupler 21
Simply performs demultiplexing of upstream and downstream signal lights. Optical transmitter 2
2 converts the electric signal output from the signal processing unit 25 into an optical signal, and the optical receiving unit 23 converts the signal light from the optical terminal device 10 into an electric signal. The signal processing unit 25 includes the optical transmission unit 2
2 has a function of inputting and outputting an electric signal between the optical receiving unit 23 and the optical receiving unit 23, and has a function of extracting wavelength information from a signal received by the optical receiving unit 23 and a function of controlling the temperature control unit 26. . The temperature control unit 26 is controlled according to the wavelength information from the signal processing unit 25 and has a function of heating and cooling the laser diode in the optical transmission unit 22.

The optical distributor 30 has a function of optically distributing a downstream signal from the optical terminal unit 10 to a plurality of optical terminating devices 20 and conversely optically multiplexing an upstream signal from the optical terminal device 20. Have.

FIG. 2 shows a first embodiment of the wavelength analyzer 14. The wavelength analyzer 14a according to the first embodiment includes a prism 41 that disperses incident light, and a shielding plate that shields an intermediate wavelength other than a predetermined long wavelength and a predetermined short wavelength in the light dispersed by the prism 41. 42, a first light receiving element 43 for receiving the long wavelength light split by the prism 41, and a prism 4
2nd light receiving element 44 which receives the short wavelength light split by 1
And a signal which is photoelectrically converted by the first light receiving element 43 and the second light receiving element 44, and a comparator 45 as a comparison means which performs an inversion operation when the light receiving power becomes equal to or higher than a preset threshold value. And Comparator 45
The signal output from is processed by the signal processing unit 15.

In the wavelength analyzer 14a, the optical signal from the optical termination device 20 branched by the branch coupler 11 is
Is refracted by passing through, and the amount of refraction and bending of the course direction depends on the wavelength. The optical signal split by the prism 41 is cut at an intermediate wavelength by a shielding plate 42, and the optical signal of a longer wavelength is received by a first light receiving element 43 and converted into an electric signal. On the other hand, the short-wavelength optical signal is
And is converted into an electric signal. These signals are input to the comparator 45 and output to the signal processing unit 15 when the difference between these electric signals becomes equal to or greater than a predetermined value. For example, a 1.3 μm band signal light is converted to 1.27 to 1.35 μm.
Assuming that m, the shielding plate 42 is selected so as to cut a signal having a wavelength of 1.27 to 1.35 μm.

As described above, in the wavelength analyzer 14a,
It can be analyzed that the signal light from the optical termination device 20 has a long wavelength or a short wavelength.

The signal processing unit 15 processes the signal from the comparator 45 and sends the signal from the optical transmission unit 12 to the optical termination unit 20.
The wavelength control signal (flag) is included in the data of the downstream signal light to be output to the optical head. This flag indicates three types of information: within the wavelength specification, outside the wavelength specification on the long wavelength side, and outside the wavelength specification on the short wavelength side.

FIG. 3 shows an embodiment of the format of the data to be transferred. In order to store the wavelength control signal in the downstream signal, the format of the current ping-pong transmission is slightly changed.

(A) shows the entire format. Data is divided into A to H, and each has a function shown in the figure. At F, since information on each optical terminal device is stored by 5 bytes, a wavelength control signal is stored together with information on delay time. The information on the delay time is obtained by encoding the light emission timing of each optical terminal device in order to prevent the upstream signal light of each optical terminal device from overlapping in the receiving unit.

(B) shows the format in each F, where the first four bytes are used for information relating to the delay time, the second half is used for the wavelength control signal, and if the wavelength is within the wavelength standard, it is shifted to the shorter wavelength side. If there is, the information is divided into three types of flags when it is shifted to the long wavelength side, and information is stored as shown in the figure.

In the optical termination unit 20, the optical receiving unit 23 receives the downstream signal light, and the signal processing unit 25 extracts the wavelength control signal included in the signal, and controls the temperature control circuit 26.

FIG. 4 shows a configuration of one embodiment of the temperature control circuit 26. Laser diode 22 in optical transmitter 22
1, a Peltier element 51 is mounted, and a laser diode 221 can be heated and cooled by flowing a current through the Peltier element 51 in a positive direction or a negative direction. The Peltier element 51 and two power supplies (not shown) are connected via a first transistor 53 and a second transistor 54,
The signal processing unit 25 is connected to respective gate electrodes of the first transistor 53 and the second transistor 54.

For example, when the signal processing unit 25 receives a signal out of the wavelength specification on the long wavelength side, for example, the first transistor 5
3 and the second transistor 54 is turned off.
When a signal out of the wavelength specification on the single wavelength side is received, the first transistor 53 is turned off and the second transistor 54 is turned on, so that a current flows through the Peltier element 51 from the positive electrode to the negative electrode. Conversely, a current flows from the negative pole to the positive pole, thereby heating or cooling the laser diode. If a signal within the wavelength standard is received, the first
Both the transistor 53 and the second transistor 54 are turned off so that no current flows through the Peltier element 51.

The optical terminal device 10 having such a wavelength analyzer 14 and the optical terminal device 20 having a temperature control circuit 26
Since the optical communication system includes a plurality of subscribers, the signals of the plurality of optical terminating devices 20 are time-division multiplexed and input to the optical receiving unit 13 inside the optical terminal device 10, and A part of the light is branched by the coupler 11 to the wavelength analyzer 14. The wavelength analyzer 14 analyzes the wavelength of each optical termination device, performs three types of wavelength analysis, and transmits information to the signal processor 15. The signal processing unit 15 sequentially processes the information from the wavelength analysis unit 14 and transmits one of the three types of wavelength control signals to the corresponding optical terminating device 10 from the optical transmission unit.

In the optical termination unit 20, the wavelength control signal included in the downstream signal is extracted by the signal processing unit 25, and the temperature control circuit 26 cools the laser diode when the wavelength information is long wavelength, If so, the temperature is controlled to heat the laser diode. When the wavelength information is within the wavelength standard, no current is allowed to flow through the Peltier element.

As described above, in the optical communication system of the present embodiment, it can be considered that there is no sudden change in the wavelength in the optical termination device in a normal use state. The idea is that high-speed processing is not required. Therefore, the optical termination device does not analyze the wavelength of the signal light output by itself, but performs the wavelength analysis collectively on the optical terminal device side where the signal light of all the optical termination devices is collected, and the remote The wavelength of the optical termination device is controlled by the operation.

As described above, according to the optical communication system of the present embodiment, the wavelength adjustment means is provided in the optical termination device, so that the optical transmission wavelength is kept within the standard range even if the environmental temperature of the optical termination device is widened. can do. Therefore, restrictions on the installation location of the optical termination device are reduced, and the degree of freedom of the installation location is increased.

Further, the optical terminal equipment has a function of analyzing the wavelength of the signal light.
Since the wavelength analysis function is not required, the configuration of the optical termination device can be simplified, and the price and the size can be reduced.

Furthermore, the control of the ambient temperature of the laser diode in the optical termination device is performed without heating or cooling only when the wavelength deviates from a predetermined wavelength without performing strict temperature control. And wasteful power consumption can be suppressed.

Next, a second embodiment of the optical communication system according to the present invention will be described. In this embodiment, only the wavelength analysis unit of the optical terminal apparatus is different from that of the first embodiment, and the other configuration is the same. Therefore, only the wavelength analysis unit will be described.

FIG. 5 shows a configuration of a wavelength analyzer according to the second embodiment. The wavelength analyzing unit 14b includes the branch coupler 1
In the optical path of the light branched by 1, a first filter 61 that cuts and reflects a wavelength shorter than a predetermined wavelength and transmits an optical signal of a long wavelength, and reflects an optical signal of a wavelength longer than a predetermined wavelength, A second filter 62 that transmits short-wavelength light is disposed, and a first light receiving element 63 that receives an optical signal reflected by the first filter 61 and a second light receiving element 63 that receives an optical signal reflected by the second filter 62. The second light-receiving element 64 compares the signals photoelectrically converted by the first light-receiving element 63 and the second light-receiving element 64, and performs an inversion operation when the light-receiving power becomes equal to or higher than a preset threshold value. And a comparator 65. The signal output from the comparator 65 is processed by the signal processing unit 15.

The first filter and the second filter have wavelength characteristics as shown in FIG. 6, and the first filter 61 has a wavelength λ.
The second filter 62 reflects light having a wavelength shorter than 1
It has the property of reflecting light with a wavelength longer than 2.

The signal light branched by the branch coupler 11 is reflected by the first filter 61, and the signal light having a wavelength shorter than the wavelength λ1 is reflected and input to the first light receiving element 63. The light passes through the filter 61. Next, the first filter 6
The signal light transmitted through 1 is reflected by the second filter 62 as a signal light having a wavelength longer than the wavelength λ2 and is input to the second light receiving element 64. The optical signal having a wavelength shorter than λ2 is transmitted through the second filter 62. The first light receiving element 63 converts the received signal light into an electric signal and outputs it to the comparator 65, and converts the signal light received by the second light receiving element 64 into an electric signal and outputs it to the comparator 65. The comparator 65 outputs a signal to the signal processing unit 15 when the difference between these input signals becomes equal to or greater than a predetermined value.

For example, when the 1.3 μm band signal light is transmitted from 1.27 to
If it is 1.35 μm, the cut wavelength λ1 of the first filter
Is 1.27 μm, and the cut wavelength λ2 of the second filter is 1.27 μm.
35 μm. In this way, the wavelength analyzer 14b can analyze whether the signal light from the optical termination device is in a long wavelength, a short wavelength, or a predetermined wavelength range.

[0051]

As described above, according to the optical communication system of the present invention, it is possible to use a simple and inexpensive optical termination device to keep the wavelength of the signal light output from the optical termination device constant. it can.

Further, according to the optical terminal equipment of the present invention, a simple and inexpensive optical terminal is used to remotely control the signal light collectively so as to keep the wavelength of the signal light output from the optical terminal constant. it can.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an optical communication system of the present invention.

FIG. 2 is a configuration diagram illustrating a wavelength analysis unit according to the first embodiment.

FIGS. 3A and 3B show an embodiment of a format of a downlink signal storing a wavelength control signal. FIG. 3A shows the entire transfer data, and FIG. 3B shows a portion storing the wavelength control signal.

FIG. 4 is a configuration diagram illustrating an embodiment of a temperature control circuit of the optical termination device.

FIG. 5 is a configuration diagram illustrating a wavelength analyzer according to a second embodiment.

FIG. 6 is a graph showing characteristics of the filter of FIG. 5;

FIG. 7 is a configuration diagram showing a conventional optical communication system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Optical terminal unit 11 Branch coupler 12 Optical transmission unit 13 Optical reception unit 14 Wavelength analysis unit 15 Signal processing unit 20 Optical termination device 21 Branch coupler 22 Optical transmission unit 23 Optical reception unit 25 Signal processing unit 26 Temperature control circuit 30 Optical distribution vessel

Claims (6)

[Claims] 1. An optical communication system in which an optical terminal equipment on a station side and an optical terminal equipment on a subscriber side perform two-way communication by time division multiplexing via an optical transmission line, wherein the optical terminal equipment comprises: A wavelength analyzing means for analyzing the wavelength of the optical signal output from the optical terminating device; and a signal processing means for outputting an optical signal including the analysis result of the wavelength analyzing means to the optical terminating device, Comprises a wavelength adjusting means for changing a wavelength of an optical signal to be output, and a signal processing means for receiving the optical signal including the analysis result output from the optical terminal device and controlling the wavelength adjusting means. Optical communication system. 2. The optical communication system according to claim 1, wherein said wavelength analysis means has three states: within a predetermined wavelength range, longer than a predetermined wavelength, and shorter than a predetermined wavelength. An optical communication system characterized in that analysis is performed on any one of them. 3. The optical communication system according to claim 1, wherein the wavelength analyzing unit separates the wavelength of the optical signal output from the optical terminal device and outputs a wavelength of a predetermined wavelength or more and a wavelength of a predetermined wavelength or less. Wavelength separating means for separating light into wavelengths, light receiving means for receiving each light separated by the wavelength separating means and converting the light into an electric signal, and comparing and analyzing each electric signal output from the light receiving means An optical communication system comprising: a comparing unit that performs the following. 4. The optical communication system according to claim 1, wherein said wavelength adjusting means is a temperature control circuit for controlling a temperature of a laser diode for generating an optical signal. system. 5. An optical terminal device on a station side of an optical communication system for performing two-way communication by time division multiplexing with an optical terminal device on a subscriber side via an optical transmission line, wherein the optical terminal device is output from the optical terminal device. An optical terminal device, comprising: a wavelength analyzing means for analyzing the wavelength of the optical signal, and a signal processing means for outputting an optical signal including an analysis result by the wavelength analyzing means to the optical terminal device. 6. The optical terminal device according to claim 5, wherein the wavelength analyzing unit separates the wavelength of the optical signal output from the optical terminal device and outputs a wavelength equal to or greater than a predetermined wavelength and equal to or less than a predetermined wavelength. Wavelength separating means for separating light into wavelengths, light receiving means for receiving each light separated by the wavelength separating means and converting the light into an electric signal, and comparing and analyzing each electric signal output from the light receiving means An optical terminal device, comprising: comparison means for performing the following.