JP2008263300A - Subscriber-side terminating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a subscriber-side terminating device using a Fabri Perot type laser diode capable of extending the transmission distance of an optical fiber inexpensively with a simple configuration. <P>SOLUTION: The subscriber-side terminating device has a heating unit 15 which heats a single-fiber bidirectional optical module 5 having a laser diode 6 as the Fabri Perot type laser diode having a light emission wavelength of a 1.31 μm, a temperature sensor 11 detects ambient temperature of the single-fiber bidirectional optical module 5, and a temperature compensating circuit 12 controls the heating unit 15 based upon the detected temperature of the temperature sensor 11 to hold the ambient temperature of the single-fiber bidirectional optical module 5 above set temperature. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is a communication carrier for constructing an optical subscriber system such as FTTB (Fiber to The Building) or a passive optical network system (PON system) such as FTTH (Fiber To The Home). And an optical network unit (ONU) that constitutes an optical subscriber access network applied to a private network.

  Conventionally, there is a one-to-one relationship in an optical subscriber system between an optical line terminal (OLT) that is a central station that can communicate with a higher-order backbone network and an optical line terminal. In the passive optical subscriber system, the optical fiber and the optical branching device are used to connect in a one-to-many relationship. Uplink communication, which is the communication path from the subscriber-side termination device to the station-side termination device, and downlink communication, which is the communication path from the station-side termination device to the subscriber-side termination device, are defined as the uplink communication wavelength and the downlink communication wavelength. Instead, a method of wavelength multiplexing within a single optical fiber is used. In this single-core bidirectional optical communication, a laser diode having a light emission wavelength of 1.31 μm band is used for upstream communication, and a laser diode of 1.49 μm band, 1.55 μm band or 1.65 μm band is used for downstream communication. An optical fiber made of quartz is usually used for communication between the terminal equipment on the station side and the terminal equipment on the subscriber side, and this optical fiber made of quartz is a single mode optical fiber whose chromatic dispersion is zero at about 1.31 μm. (SMF).

  In recent years, the transmission rate of main signal data has increased from about 100 Mbps to about 1000 Mbps, and it is predicted that the data transmission rate will continue to increase in the future. Therefore, further ensuring of transmission quality is required. The amount of degradation in transmission quality is determined by the transmission distance, that is, the length of the optical fiber, the amount of chromatic dispersion of the optical fiber, the spectrum line width of the laser diode, and the transmission speed of the main signal data, and is closely related to the amount of chromatic dispersion.

  In a subscriber-side termination device that is strongly demanded to reduce the price, an inexpensive Fabry-Perot laser diode (FP-LD: Fabry-Perot Laser Diode, multimode oscillation) is used. Fabry-Perot laser diodes are inexpensive but have poor transmission characteristics, and the emission center wavelength fluctuates greatly with respect to ambient temperature fluctuations. In order to suppress fluctuations in the emission center wavelength due to temperature fluctuations in the laser diode, a Peltier element and a thermistor are provided around the laser diode, and a temperature compensation circuit that cools or heats the Peltier element by passing a current is used. A method of controlling is known. However, since the Peltier element is expensive and requires a temperature compensation circuit having cooling and heating functions, a subscriber-side termination device using the Peltier element is not common.

  In addition, the laser diode used in the station side termination device is used in a wavelength band in which the emission wavelength is 1.49 μm band, 1.55 μm band or 1.65 μm band, and the chromatic dispersion of the optical fiber is large. For this reason, distributed feedback laser diodes (DFB-LD: Single Mode Oscillation) with good transmission characteristics and small fluctuations in emission center wavelength with respect to ambient temperature fluctuations are often used. More expensive than type laser diodes.

  As these measures, Patent Document 1 uses a Fabry-Perot laser diode whose emission wavelength is 1.31 μm band for both the upstream signal of the subscriber-side termination device and the downstream signal of the station-side termination device, and reduces the transmission speed of the downstream signal. An optical transceiver is disclosed that is set at a higher speed than an upstream signal and that encodes the downstream signal in an encoding format in which there is a free spectrum in a low frequency region. As described above, the optical transceiver of Patent Document 1 adopts an encoding method that changes the frequency spectrum between upstream and downstream, so that substantially the same wavelength can be obtained even when information transmission amount that is substantially symmetrical between upstream and downstream is generated. It enables high-speed transmission service while using it.

JP 2003-198487 A

  However, in the technique disclosed in Patent Document 1 described above, since the subscriber-side termination device is configured using a Fabry-Perot laser diode, the amount of transmission quality deterioration between the station-side termination device and the subscriber-side termination device. In order to maintain a certain level, the length of the optical fiber, which is the transmission distance, or the chromatic dispersion amount of the optical fiber must be limited. When extending the transmission distance, light is emitted in a region where the chromatic dispersion amount is small. It is necessary to select a Fabry-Perot laser diode to be used. However, when a Fabry-Perot laser diode with a large manufacturing error of the emission center wavelength is selected, there is a problem that the cost becomes high in a manufacturing lot with a low yield. Further, when the transmission distance is further extended, there is a problem that it is necessary to use a distributed feedback laser diode which has good transmission characteristics but is expensive.

  The present invention has been made to solve the above-described problems. Even in a subscriber-side terminating device using a Fabry-Perot laser diode whose emission wavelength is in the 1.31 μm band, transmission is performed with an inexpensive and simple circuit. The purpose is to extend the distance.

  A subscriber-side terminating device according to the present invention is a subscriber-side terminating device that transmits and receives optical signals and electrical signals between a station device and a subscriber device, the station-side interface unit on the station device side, and the subscriber device Side subscriber side interface unit, an optical / electrical conversion unit that receives an optical signal input from the station side interface unit and converts it into an electrical signal, and an electrical signal input from the subscriber side interface unit A bidirectional optical module having an electrical / optical conversion unit that converts it into an optical signal, a heating unit that heats the bidirectional optical module, a temperature sensor that detects a temperature of the bidirectional optical module, and the temperature sensor Temperature compensation means for controlling the heating unit based on the output of the above.

  According to the present invention, since the heating unit for heating the bidirectional optical module and the temperature compensation means for controlling the heating unit are provided in the subscriber-side terminating device, the temperature of the bidirectional optical module is set to the set temperature or higher. Therefore, it is possible to obtain a subscriber-side terminating device capable of extending the transmission distance with an inexpensive and simple configuration.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a subscriber-side terminal device according to Embodiment 1 of the present invention.
A subscriber-side terminating device 1 according to Embodiment 1 includes a level conversion unit 2, a frame control unit 3, an LD driver unit 4, a single-core bidirectional optical module (bidirectional optical module) 5, a limiting unit 10, and a temperature sensor 11. The temperature compensation circuit (temperature compensation means) 12 and the heating unit 15 are configured. The single-core bidirectional optical module 5 includes a laser diode (electric / optical conversion unit) 6, a wavelength multiplexing / demultiplexing unit 7, a photodetector (optical / electrical conversion unit) 8, and a transimpedance amplifier 9. It has an interface with the fiber. The temperature compensation circuit 12 includes a temperature setting circuit 13 and a temperature control circuit 14. The subscriber-side terminating device 1 includes a subscriber-side LAN cable 16 through which a LAN main signal output to the station side and a LAN main signal output to the subscriber side are conducted, and an optical main signal output to the station side. A station-side optical fiber 17 that conducts the optical main signal output to the subscriber side but is conducted is connected.

  As for the communication direction of the main signal, the direction transmitted from the subscriber-side LAN cable 16 to the station-side optical fiber 17 after passing through the subscriber-side terminating device 1 is defined as upstream, and from the station-side optical fiber 17 to the subscriber-side The direction transmitted to the subscriber LAN cable 16 after passing through the terminating device 1 is defined as downlink. The main signal is a signal transmitted / received in the main communication of the transmission system.

  The level converter 2 converts the electrical level of the input signal. The upstream LAN main signal input from the subscriber-side LAN cable 16 is converted into an upstream electrical main signal and output to the frame control unit 3, and the downstream electrical main signal input from the frame control unit 3 is converted to a downstream LAN main signal. The data is converted and output to the subscriber side LAN cable 16. The frame control unit 3 controls the output timing of the upstream electrical main signal input from the level conversion unit 2 and outputs it to the LD driver unit 4 and also controls the wavelength of the downstream electrical main signal input from the limiting unit 10. A filtering process is performed and output to the level converter 2. The LD driver unit 4 is a driving unit that drives the laser diode 6. The LD driver unit 4 converts the upstream electrical main signal input from the frame control unit 3 into an upstream current main signal that is a driving signal for the laser diode 6. To supply.

  The laser diode 6 is a Fabry-Perot laser diode whose emission wavelength is a 1.31 μm band, is driven by receiving an upstream current main signal that is a drive signal from the LD driver unit 4, and is an upstream light main that is a laser signal light. A signal is emitted. The Fabry-Perot laser diode used for the laser diode 6 is provided with a mirror having a high reflectivity facing each other, and only light of a specific frequency that hits the mirror surface perpendicularly is strengthened by continuous reflection until an oscillation mode is formed. Amplified. On the other hand, a distributed feedback laser diode known as a semiconductor laser as well as a Fabry-Perot laser diode has a diffraction grating whose refractive index changes periodically inside the resonator, and only for light of a specific wavelength. By providing feedback, wavelength selectivity is provided. Although there is an advantage that the oscillation wavelength can be adjusted by adjusting the period of the diffraction grating, there is a disadvantage that it is more expensive than a Fabry-Perot laser diode.

  The wavelength multiplexing / demultiplexing unit 7 has a wavelength multiplexing / demultiplexing function, combines the upstream optical main signal input from the laser diode 6 with the downstream optical main signal transmitted from the station side device, and the station side optical fiber 17. And the downstream optical main signal input from the station side optical fiber 17 is demultiplexed and output to the photodetector 8. The photodetector 8 converts the downstream optical main signal input from the wavelength multiplexing / demultiplexing unit 7 into a downstream current main signal, and the transimpedance amplifier 9 converts the downstream current main signal input from the photodetector 8 into an electrical main signal. And output to the limiting unit 10. The limiting unit 10 has a 2R reproduction function, performs waveform shaping (Reshaping) and identification reproduction (Regeneration) on the electric main signal input from the transimpedance amplifier 9 with a specific identification threshold value, and outputs it to the frame control unit 3.

  The temperature sensor 11 is a sensor that outputs a different value corresponding to a change in ambient temperature. For example, a chip thermistor, which is an element whose resistance value changes depending on the temperature, may be used. Further, the temperature sensor 11 outputs the detected temperature information to the temperature compensation circuit 12. The temperature compensation circuit 12 determines whether or not the temperature information input from the temperature setting circuit 13 is higher than the set temperature of the temperature setting circuit 13 and the temperature setting circuit 13 that stores the target temperature of the observation part as the set temperature. When the temperature falls below the set temperature, the temperature control circuit 14 is configured to send a heating signal to the heating unit 15. The temperature control circuit 14 is configured by a circuit such as a transistor that controls output power to the heating unit 15 when, for example, it is determined that the temperature information falls below a set temperature.

  The heating unit 15 includes an element that generates heat in response to a heating signal input from the temperature control circuit 14 of the temperature compensation circuit 12, and includes a heating element such as a winding resistor. By the temperature compensation operation (ATC: Auto Temperature Control) by the temperature sensor 11, the temperature compensation circuit 12, and the heating unit 15, the temperature of the laser diode 6 in the single-core bidirectional optical module 5 can always be kept at a set temperature or higher.

  In general, the emission center wavelength of a laser diode has a property of shifting to a longer wavelength side as the temperature rises. It is said that the wavelength shift amount due to the temperature of the emission center wavelength of the Fabry-Perot laser diode is 0.5 nm / ° C., and the shift amount of the emission center wavelength of the distributed feedback laser diode is 0.1 nm / ° C. Thus, the wavelength shift amount due to the temperature of the emission center wavelength of the Fabry-Perot laser diode is about five times larger than that of the distributed feedback laser diode. Further, it is known that the manufacturing error of the emission center wavelength of the Fabry-Perot laser diode is larger than that of the distributed feedback laser diode.

  For example, when the wavelength fluctuation width due to temperature change of a Fabry-Perot laser diode with an emission wavelength of 1.31 μm band and the manufacturing error are combined, the distribution of emission center wavelengths has a width of 1.26 μm to 1.36 μm, which is 0.1 μm On the other hand, the distribution of the emission center wavelength of the distributed feedback laser diode having the emission wavelength of 1.31 μm band is 1.29 μm to 1.33 μm and 0.04 μm wide, and the emission center wavelength of the Fabry-Perot laser diode is Is much larger than the distribution of the center wavelength of the distributed feedback laser diode.

  Transmission quality degradation (Transmitter and dispersion) in IEEE802.3ah 1000BASE-PX10-U (subscriber-side terminating device, transmission distance 10 km, transmission speed 1.25 Gbps, single mode optical fiber), which is a standard for optical subscriber access networks The specified value of penalty) is specified as 2.8 dB at maximum. The smaller the transmission quality deterioration amount is, the lower the transmission quality after transmission is.

  In the first embodiment in which a Fabry-Perot type laser diode is used as the laser diode 6, assuming that the RMS (root mean square) spectrum line width is 3.0 nm, the transmission quality deterioration amount described above is obtained. The allowable emission center wavelength satisfying a certain 2.8 dB is 1.28 μm to 1.35 μm. When the operating environment temperature of the laser diode 6 becomes the lowest temperature, the emission center wavelength of the laser diode 6 becomes the shortest wave. For example, assuming that the lower limit of the operating environment temperature of the subscriber-side terminating device 1 is 0 ° C. In the subscriber-side terminating device 1 on which the laser diode 6 having an emission center wavelength of 1.28 μm is mounted, the maximum transmission distance is 10 km.

  However, in the first embodiment, since the temperature sensor 11, the temperature compensation circuit 12, and the heating unit 15 are provided, the ambient temperature of the single-core bidirectional optical module 5 can be kept at a set temperature or higher. In addition, the temperature of the laser diode 6 inside the single-core bidirectional optical module 5 can be kept at a set temperature or higher. For example, when the temperature of the laser diode 6 can be maintained at 20 ° C. or more, the emission center wavelength of the laser diode 6 is shifted to the longer wavelength side, 1.29 μm (1.28 μm + 0.5 nm / ° C. × (20 ° C. −0 ° C.)). Further, the maximum transmission distance can be set to 10 km or more of the maximum transmission distance when the lower limit of the operating environment temperature is assumed to be 0 ° C.

  As described above, the temperature sensor 11, the temperature compensation circuit 12, and the heating unit 15 are provided, and by keeping the laser diode 6 inside the single-core bidirectional optical module 5 at or above the set temperature, the emission center wavelength is shifted to the longer wavelength side. A light emission center wavelength close to 1.31 μm at which the chromatic dispersion of the optical fiber becomes zero can be obtained. Therefore, the amount of chromatic dispersion of the optical fiber is suppressed, transmission quality deterioration can be suppressed, and the maximum transmission distance can be extended.

  As described above, according to the first embodiment, the heating unit configured by the heating element such as the resistor and the temperature compensation circuit that controls only the heating of the heating unit are provided. The ambient temperature of the optical module can be kept above the set temperature, and the laser diode in the single-core bidirectional optical module can also be kept above the set temperature. In addition, the wavelength dispersion amount of the optical fiber can be suppressed with an inexpensive and easy configuration, and the transmission distance of the subscriber-side terminating device can be extended.

Embodiment 2. FIG.
FIG. 2 is a block diagram showing the configuration of the subscriber-side termination device according to Embodiment 2 of the present invention.
This subscriber-side terminator is configured by incorporating the temperature sensor and heating unit of the subscriber-side terminator according to Embodiment 1 shown in FIG. 1 into the single-core bidirectional optical module. In the following, the same or corresponding parts as the constituent elements of the subscriber terminal apparatus according to the first embodiment are denoted by the same reference numerals as those used in the first embodiment, and the description thereof is omitted or simplified.

  The subscriber-side terminating device 1 according to Embodiment 2 includes a temperature sensor 11 and a heating unit 15 inside the single-core bidirectional optical module 5. Therefore, the temperature sensor 11 and the heating unit 15 can be provided in the vicinity of the laser diode 6, the observation point of the temperature sensor 11 approaches the laser diode 6, and the temperature of the laser diode 6 can be measured more accurately. Further, even when the temperature measured by the temperature sensor 11 is lower than the set temperature of the temperature compensation circuit 12 and heating by the heating unit 15 is required, the temperature of the laser diode 6 can be increased efficiently.

  As described above, according to the second embodiment, since the temperature sensor and the heating unit are incorporated in the single-core bidirectional optical module, the accurate temperature of the laser diode can be measured. It is possible to increase the temperature of the heat efficiently.

Embodiment 3 FIG.
FIG. 3 is a block diagram showing the configuration of the subscriber-side terminating device according to Embodiment 3 of the present invention.
This subscriber-side termination device is configured without providing the temperature sensor, temperature compensation circuit, and heating unit of the subscriber-side termination device according to the first embodiment shown in FIG. In the following, the same or corresponding parts as the constituent elements of the subscriber terminal apparatus according to the first embodiment are denoted by the same reference numerals as those used in the first embodiment, and the description thereof is omitted or simplified.

  A subscriber-side terminating device 1 according to Embodiment 3 includes a level conversion unit 2, a frame control unit 3, a single-core bidirectional optical module 5, and a limiting unit 10. The single-core bidirectional optical module 5 includes an LD driver unit 4, a laser diode 6, a wavelength multiplexing / demultiplexing unit 7, a photodetector 8, and a transimpedance amplifier 9 in the same package. Further, the subscriber-side terminating device 1 includes a subscriber-side LAN cable 16 through which a LAN main signal output to the station side and a LAN main signal output to the subscriber side are conducted, and an optical main output to the station side. A station-side optical fiber 17 through which the signal and the optical main signal output to the subscriber side are connected is connected.

  The level converter 2 converts the upstream LAN main signal input from the subscriber-side LAN cable 16 into an electrical main signal and outputs it to the frame controller 3. The frame control unit 3 controls the output timing of the upstream electrical main signal input from the level conversion unit 2 and outputs it to the LD driver unit 4. The LD driver unit 4 is a driving unit that drives the laser diode 6. The LD driver unit 4 converts the upstream electrical main signal input from the frame control unit 3 into an upstream current main signal that is a driving signal for the laser diode 6. To supply. The laser diode 6 is a Fabry-Perot laser diode whose emission wavelength is a 1.31 μm band, is driven by receiving an upstream current main signal that is a drive signal from the LD driver unit 4, and is an upstream light main that is a laser signal light. A signal is emitted. The wavelength multiplexing / demultiplexing unit 7 has a wavelength multiplexing / demultiplexing function, combines the upstream optical main signal input from the laser diode 6 with the downstream optical main signal transmitted from the station side device, and the station side optical fiber 17. Output to.

  In general, the LD driver is a heating element, and when the LD driver unit 4 is provided in the single-core bidirectional optical module 5, the temperature in the single-core bidirectional optical module 5 is increased by the self-heating of the LD driver unit 4. The temperature of the laser diode 6 mounted in the single-core bidirectional optical module 5 can also be increased. Furthermore, the heat generated from the LD driver unit 4 can be used efficiently by providing a casing to seal the single-core bidirectional optical module 5 or by providing the LD driver unit 4 in the vicinity of the laser diode 6. . By increasing the temperature of the laser diode 6 in this manner, the emission center wavelength of the laser diode 6 is shifted to the longer wavelength side, and the chromatic dispersion of the optical fiber becomes zero, as in the first embodiment. An emission center wavelength close to 31 μm can be obtained. Therefore, the amount of chromatic dispersion of the optical fiber is suppressed, transmission quality deterioration can be suppressed, and the maximum transmission distance can be extended.

  As described above, according to the third embodiment, since the LD driver unit is provided inside the single fiber bidirectional optical module, the LD driver can be used even when the ambient temperature of the single fiber bidirectional optical module is low. The temperature of the laser diode formed inside the single-fiber bidirectional optical module can be kept higher than the ambient temperature by the self-heating of the part. Further, the temperature of the laser diode can be maintained without providing the temperature sensor, the temperature compensation circuit, and the heating unit, the number of parts can be reduced, and the subscriber-side termination device can be configured at a low cost.

  Further, according to the third embodiment, since the casing for sealing the single-core bidirectional optical module is provided, or the LD driver part is provided in the vicinity of the laser diode, the heat generated from the LD driver part is reduced. It can be used efficiently.

It is a block diagram which shows the structure of the subscriber side termination | terminus apparatus which concerns on Embodiment 1 of this invention. It is a block diagram which shows the structure of the subscriber side termination | terminus apparatus which concerns on Embodiment 2 of this invention. It is a block diagram which shows the structure of the subscriber side termination | terminus apparatus which concerns on Embodiment 3 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Subscriber side termination device, 2 level conversion part, 3 frame control part, 4 LD driver part, 1 core bidirectional | two-way optical module, 6 laser diode, 7 wavelength multiplexing / demultiplexing part, 8 photodetector, 9 transimpedance amplifier, 10 Limiting unit, 11 temperature sensor, 12 temperature compensation circuit, 13 temperature setting circuit, 14 temperature control circuit, 15 heating unit, 16 subscriber side LAN cable, 17 station side optical fiber.

Claims (3)

In a subscriber-side terminating device that transmits and receives optical signals and electrical signals between a station device and a subscriber device,
A station-side interface unit on the station device side;
A subscriber-side interface unit on the subscriber device side;
An optical / electrical converter that receives an optical signal input from the station side interface unit and converts it into an electrical signal, and an electrical / electrical unit that receives an electrical signal input from the subscriber side interface unit and converts it into an optical signal. A bidirectional optical module having an optical conversion unit;
A heating unit for heating the bidirectional optical module;
A temperature sensor for detecting the temperature of the bidirectional optical module;
A subscriber-side termination device comprising temperature compensation means for controlling the heating unit based on an output of the temperature sensor.   The subscriber-side terminating device according to claim 1, wherein the heating unit and the temperature sensor are mounted in the bidirectional optical module. In a subscriber-side terminating device that transmits and receives optical signals and electrical signals between a station device and a subscriber device,
A station-side interface unit on the station device side;
A subscriber-side interface unit on the subscriber-side terminating device side;
An optical / electrical converter that receives an optical signal input from the station side interface unit and converts it into an electrical signal, and an electrical / electrical unit that receives an electrical signal input from the subscriber side interface unit and converts it into an optical signal. A bidirectional optical module having an optical conversion unit and an LD driver unit for driving the electrical / optical conversion unit;
A subscriber-side terminating device, wherein the LD driver circuit maintains the temperature in the bidirectional optical module by self-heating.

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