JP2011029792A - Optical terminal, and ftth-adopted catv system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an FTTH-adopted CATV system that allows operation of a plurality of communication services without deteriorating a communication quality. <P>SOLUTION: As shown in Fig.2, an optical terminal 11 has an E/O converter 100, a wavelength controller 101, a comparator circuit 102, and an O/E converter 103. The E/O converter 100 is a device for converting an electric signal inputted to the optical terminal 11 into an optical signal by using a variable wavelength laser. The comparator circuit 102 compares and determines frequencies of the electric signals inputted to the optical terminal 11. The wavelength controller 101 is a device that makes control for changing an oscillation wavelength of the variable wavelength laser into two different wavelengths according to the frequency of the electric signal determined by the comparator circuit 102. If the optical terminal 11 is used in an FTTH-adopted CATV system, a plurality of communication services are operated without deteriorating the communication quality. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical terminal that mutually converts an electric signal and an optical signal, and an FTTH CATV system, and is particularly suitable for providing a plurality of communication services.

  In a conventional CATV system using a coaxial cable, when performing different communication services, a dedicated terminal device is installed in each subscriber's home, and a dedicated terminal control device is installed in the center for each communication service. Communication control is often performed by assigning a different frequency to each communication service.

  Patent Document 1 describes an optical transmission method in which a transmission station is provided with an LD capable of controlling the emission wavelength, and a reception station controls communication by controlling the wavelength of an optical signal of the transmission station. It is shown that the communication quality can be improved according to the method. In Patent Document 1, the receiving station notifies the transmitting station of the wavelength used for communication at regular intervals, the transmitting station detects the vacant wavelength from the notification, and the transmitting station controls the LD to control the vacant wavelength. There is also shown an optical transmission method for controlling to emit light.

JP-A-5-308346

  Providing different communication services is also possible in the FTTH CATV system, but it is necessary to assign different wavelengths to optical signals for each communication service so that communication does not collide. Requires a plurality of LDs that emit light of different wavelengths. However, since LD is expensive, there is a problem that the cost of an optical terminal becomes high when a plurality of LDs are used.

  In addition, since the optical transmission method disclosed in Patent Document 1 is different in communication control method from the CATV system, the communication control device and terminal device used in the CATV system cannot be used as they are. Therefore, when shifting from the existing CATV system to the system based on the optical transmission method of Patent Document 1, the communication control device and the terminal device must be renewed, and the existing equipment is wasted, resulting in high cost. End up.

  Therefore, an object of the present invention is to realize an optical terminal and an FTTH system CATV system capable of operating a plurality of communication services at low cost without changing the communication control system currently implemented in the CATV system. It is.

  According to a first aspect of the present invention, there is provided an optical terminal that mutually converts an electric signal and an optical signal, an E / O converter that converts an inputted electric signal into an optical signal using a wavelength tunable laser, and an E / O A wavelength control device that controls a wavelength of an optical signal output from the converter; and a comparison circuit that determines a frequency of the input electric signal. The wavelength control device outputs an optical signal output from the E / O converter. The optical terminal is controlled to be a specific wavelength corresponding to the frequency of the electrical signal determined by the comparison circuit.

  The wavelength tunable laser may use any wavelength tunable means. For example, the following wavelength tunable laser can be used. One is a semiconductor laser in which the oscillation wavelength can be controlled by temperature and driving current value. The other one is a DBR type semiconductor laser in which the wavelength is variable by changing the refractive index of the Bragg reflector according to current or temperature. The other is an external resonator type semiconductor laser in which the wavelength is variable by changing the resonator length by rotating and moving the diffraction grating and the resonator mirror by a piezoelectric element or the like. The other is a semiconductor laser in which a wavelength is made variable by adding a MEMS actuator structure to the element, thereby changing the resonator length. The other is that a wavelength tunable element is configured using an acoustooptic element, a photonic crystal, a nonlinear optical crystal, and the like, and the light of the semiconductor laser is converted by the wavelength tunable element.

  According to a second aspect of the present invention, in the first aspect, the optical terminal further comprises a delay circuit connected between the branch end to the comparison circuit and the electric signal input end of the E / O converter. It is.

  According to a third aspect of the present invention, there are provided a plurality of terminal control devices, a plurality of optical terminals connected to the plurality of terminal control devices via an optical transmission line, and mutually converting an electric signal and an optical signal, and each optical terminal The number of the terminal control devices is the same as the number of the terminal control devices connected to each other through the electric transmission line, the communication control is performed corresponding to each of the plurality of terminal control devices, and the frequency of the electric signal to be output is different for each corresponding terminal control device. The optical terminal includes an E / O converter that converts an input electrical signal into an optical signal using a wavelength tunable laser, and a wavelength of an optical signal output from the E / O converter. And a comparison circuit that determines the frequency of the input electric signal, and the wavelength control device determines the wavelength of the optical signal output from the E / O converter by the comparison circuit. A specific wavelength corresponding to the frequency of the electrical signal To control a CATV system FTTH system, characterized in that.

  In a fourth aspect based on the third aspect, the optical terminal further includes a delay circuit connected between the branch end to the comparison circuit and the electric signal input end of the E / O converter. The FTTH system CATV system.

  According to the present invention, the optical terminal can output optical signals having two or more different wavelengths. Therefore, in the FTTH CATV system, if the optical terminal of the present invention is used when different communication services are operated, it is possible to prevent the uplink communication of each communication service from colliding and to suppress the deterioration of the communication quality. be able to. In addition, the optical terminal of the present invention can be configured at low cost because only one wavelength tunable laser is required. Further, since the FTTH CATV system of the present invention does not change the conventional communication control method, the terminal control device and the terminal device used in the conventional CATV system can be used as they are. Therefore, even when a conventional CATV system using a coaxial cable is shifted to an FTTH CATV system, the system can be transferred at low cost.

  Further, according to the second and fourth inventions, the delay circuit delays the input of the electric signal to the E / O converter, thereby increasing the time required for driving the wavelength tunable laser of the E / O converter. Can be converted into an optical signal having a stable wavelength.

The figure which showed the structure of the FTTH system CATV system. The figure which showed the structure of the optical terminal. The figure which showed the structure of the optical terminal.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings. However, the present invention is not limited to the examples.

  FIG. 1 is a diagram illustrating the configuration of the FTTH CATV system according to the first embodiment. The FTTH CATV system includes CMTSs (cable modem terminal systems) 10A and 10B arranged at a center, a plurality of optical terminals 11 arranged at each subscriber's house, and a plurality of terminals arranged at each subscriber's house. CM (cable modem) 12A, 12B. The CMTSs 10A and 10B correspond to the terminal control device of the present invention, and the CMs 12A and 12B correspond to the terminal device of the present invention. The CMTSs 10 </ b> A and 10 </ b> B are connected to the mixer 14, and the mixer 14 is connected to the optical transceiver 15. The optical transceiver 15 is connected to the optical distributor 16 via the optical fiber cable 13. The optical fiber cable 13 is distributed to the number of subscribers by the optical distributor 16 and connected to the optical terminal 11. The optical terminal 11 is connected to the duplexer 18 via the coaxial cable 17, and the duplexer 18 is connected to the CMs 12 </ b> A and 12 </ b> B via the coaxial cable 17.

  FIG. 2 is a diagram illustrating a configuration of the optical terminal 11. The optical terminal 11 includes an E / O converter 100, a wavelength control device 101, a comparison circuit 102, an O / E converter 103, amplifiers 104 and 105, a duplexer 106, a branching device 107, have. The E / O converter 100 is connected to the upstream communication side core 13 </ b> A of the optical fiber cable 13, and the O / E converter 103 is connected to the downstream side communication core 13 </ b> B of the optical fiber cable 13. The electric signal input side of the E / O converter 100 and the electric signal output side of the O / E converter 103 are connected to the duplexer 106, and the duplexer 106 is connected to the coaxial cable 17. In addition, amplifiers 104 and 105 are inserted between the E / O converter 100 and the duplexer 106 and between the O / E converter 103 and the duplexer 106, respectively. A branching unit 107 is provided between the E / O converter 100 and the amplifier 104. An E / O converter 100 is connected to the main line side, and a comparison circuit 102 is connected to the branching side. The comparison circuit 102 is connected to the wavelength control device 101.

  The E / O converter 100 is a device that converts an electrical signal into an optical signal using a wavelength tunable laser, and the comparison circuit 102 compares and determines the frequency of the electrical signal input to the optical terminal 11. is there. The wavelength control device 101 is a device that performs control to change the oscillation wavelength of the tunable laser to two different wavelengths according to the frequency of the electrical signal determined by the comparison circuit 102.

  As the wavelength tunable laser used in the E / O converter 100, for example, a distributed feedback type (DFB type) semiconductor laser or a distributed Bragg reflector type (DBR type) semiconductor laser can be used. In these semiconductor lasers, since the oscillation wavelength depends on the temperature of the active region, the oscillation wavelength can be controlled by controlling the temperature of the active region using a heating / cooling element such as a Peltier element. These semiconductor lasers can also control the oscillation wavelength by controlling the drive current value. In the DBR type semiconductor laser, the wavelength can be controlled by changing the refractive index of the DBR region by temperature, current, or the like.

  In addition, it is also possible to use an external resonator type semiconductor laser in which the wavelength is variable by changing the resonator length by rotating and moving the diffraction grating and the resonator mirror by a piezoelectric element or the like. In addition, it is also possible to use a semiconductor laser in which a wavelength is made variable by adding a MEMS actuator structure to the element and thereby changing the resonator length. In addition, a wavelength tunable element may be configured using an acousto-optic element, a photonic crystal, a nonlinear optical crystal, or the like, and a semiconductor laser beam converted by a wavelength conversion element may be used.

  Next, an operation during uplink communication in the FTTH CATV system of the first embodiment will be described.

  In the FTTH CATV system of the first embodiment, the CMTS 10A controls the timing of uplink communication from each subscriber's CM 12A, and the CMTS 10B controls the timing of each subscriber's uplink communication from the CM 12B. For this reason, the uplink communication between CMs 12A of each subscriber and the uplink communication between CMs 12B of each subscriber are controlled so as not to collide, thereby suppressing a decrease in communication quality.

  On the other hand, the CMTS 10A does not control the timing of uplink communication from the CM 12B, and the CMTS 10B does not control the timing of uplink communication from the CM 12A. Therefore, uplink communication may collide between CM 12A and CM 12B, and communication quality may deteriorate. This is avoided by the operation of the optical terminal 11 as follows.

  Consider a case where uplink communication from a CM 12A of a certain subscriber and uplink communication from the CM 12B of another subscriber occur simultaneously.

  An electric signal having a frequency f1 output from a CM 12A of a subscriber is input to the optical terminal 11 of the subscriber via the coaxial cable 17. The electric signal input to the optical terminal 11 is amplified by the amplifier 104 and then input to the E / O converter 100. A part of the electric signal is input to the comparison circuit 102 by the branching unit 107. The comparison circuit 102 compares and determines the frequency of the electrical signal, determines that the frequency is f1, and outputs a signal corresponding to the frequency f1 of the electrical signal output from the CM 12A to the wavelength control device 101. The wavelength control device 101 controls the wavelength tunable laser of the E / O converter 100 so as to output an optical signal having a wavelength λ1 corresponding to the frequency f1 based on the signal from the determination circuit 102. As a result, the electric signal having the frequency f1 from the CM 12A input to the E / O converter 100 is converted into an optical signal having the wavelength λ1, and is output to the core 13A on the upstream communication side of the optical fiber cable 13.

  On the other hand, an electrical signal having a frequency f2 (a value different from f1) output from another subscriber CM 12B is input to the optical terminal 11 of the subscriber via the coaxial cable 17. The electric signal input to the optical terminal 11 is amplified by the amplifier 104 and then input to the E / O converter 100, and a part of the electric signal is input to the comparison circuit 102 by the branching device 107. . The comparison circuit 102 determines that the frequency of the electrical signal is f2, and the wavelength control apparatus 101 outputs an optical signal having a wavelength λ2 (a value different from λ1) corresponding to the frequency f2 based on the determination of the determination circuit 102. Thus, the wavelength tunable laser of the E / O converter 100 is controlled. As a result, the electric signal having the frequency f2 from the CM 12B input to the E / O converter 100 is converted into an optical signal having the wavelength λ2, and output to the core 13A on the upstream communication side of the optical fiber cable 13.

  The optical signal having the wavelength λ1 output from the optical terminal 11 of a certain subscriber and the optical signal having the wavelength λ2 output from the optical terminal 11 of another subscriber are mixed in the optical distributor 16. Here, if the wavelengths of the two optical signals are sufficiently different, the communication quality will not deteriorate due to interference. Therefore, even if an uplink communication from a CM 12A of a certain subscriber and an uplink communication from the CM 12B of another subscriber occur simultaneously, a decrease in communication quality is prevented by the operation of the optical terminal 11. Can do.

  When the difference between λ1 and λ2 that does not deteriorate the communication quality is 1500 to 1650 nm, if the wavelength difference is 0.05 nm or more, it is possible to sufficiently prevent the communication quality from being lowered. In addition, electrical signals from the CMs 12A and 12B that may be transmitted simultaneously have different frequencies between the CM 12A that is communication-controlled by the CMTS 10A and the CM 12B that is communication-controlled by the CMTS 10B. Therefore, it is not necessary for the optical transmitter / receiver 15 on the center side to separately receive the optical signal with a wavelength filter used in a general wavelength multiplexing method, and it is not necessary to strictly control the wavelengths of λ1 and λ2.

  The driving speed of the wavelength tunable laser is preferably as fast as possible. The time required for driving the laser is desirably 1.5 μs or less.

  When an electrical signal is simultaneously output from the CM 12A and CM 12B in a certain subscriber, the electrical signal of the frequency f1 output from the CM 12A and the electrical signal of the frequency f2 output from the CM 12B are demultiplexer 17. Are mixed and input to the optical terminal 11, and the mixed electric signal is converted into an optical signal having the wavelength λ1 or λ2 and output. At this time, since the CMTSs 10A and 10B are controlled so that the communication timings of the CMs 12A and 12B do not collide, no electrical signal is output from the CM 12A or CM 12B of other subscribers. Only one optical signal is input, and quality degradation due to communication collision does not occur.

  As described above, according to the FTTH-system CATV system of the first embodiment, the two communication services of the communication service between the CMTS 10A and the CM 12A and the communication service between the CMTS 10B and the CM 12B are collided with each other. It is possible to provide a service with excellent communication quality. Further, the optical terminal 11 only needs to have one wavelength tunable laser, and can be manufactured at low cost.

  The FTTH CATV system of the second embodiment is obtained by replacing the optical terminal 11 of the first embodiment with an optical terminal 21 shown in FIG. The optical terminal 21 is obtained by inserting a delay circuit 200 between the main line side output end of the branching device 107 and the electric signal input end of the E / O converter 100 in the optical terminal 11. Is the same as that of the optical terminal 11. According to the optical terminal 21, the delay circuit 200 can delay the input of an electric signal to the E / O converter 100, so that the drive of the wavelength tunable laser in the E / O converter 100 can be stabilized. Can take the time it takes. That is, after the wavelength is converted and the oscillation wavelength of the laser is stabilized, the output of the laser can be modulated using data based on electrical signals. Therefore, even a tunable laser having a relatively low driving speed can be employed.

  In the first and second embodiments, two controllers are used to operate two services. However, if the wavelength of the wavelength tunable laser of the optical terminal is variable to three or more different wavelengths, three or more are used. It is also possible to operate other communication services.

  In the first and second embodiments, a case where two-fiber optical fiber cables are used for two-way communication is shown. However, a single-fiber optical cable can be obtained by using a duplex system using a wavelength multiplexing device. It is also possible to use it.

  The present invention is suitable when two or more communication services are operated in an FTTH CATV system.

10A, 10B: CMTS
11: Optical terminal 12A, 12B: CM
13: Optical fiber cable 14: Mixer 15: Optical transceiver 16: Optical distributor 17: Coaxial cable 18: Demultiplexer 100: E / O converter 101: Wavelength controller 102: Comparison circuit 103: O / E converter 200: delay circuit

Claims (4)

In an optical terminal that converts electrical signals and optical signals to each other,
An E / O converter that converts an input electrical signal into an optical signal using a wavelength tunable laser;
A wavelength control device for controlling the wavelength of an optical signal output from the E / O converter;
A comparison circuit for determining the frequency of the input electric signal;
Have
The wavelength control device controls the wavelength of the optical signal output from the E / O converter to be a specific wavelength corresponding to the frequency of the electrical signal determined by the comparison circuit;
An optical terminal characterized by that.   The optical terminal according to claim 1, further comprising a delay circuit connected between a branch end to the comparison circuit and the electric signal input end of the E / O converter. A plurality of terminal control devices;
A plurality of optical terminals connected to the plurality of terminal control devices via an optical transmission line, and mutually converting electrical signals and optical signals;
Each optical terminal is connected via an electrical transmission line, is controlled to communicate with each of the plurality of terminal control devices, and the frequency of the electrical signal to be output is different for each corresponding terminal control device, The same number of terminal devices as the number of terminal control devices;
Have
The optical terminal is
An E / O converter that converts an input electrical signal into an optical signal using a wavelength tunable laser;
A wavelength control device for controlling the wavelength of an optical signal output from the E / O converter;
A comparison circuit for determining the frequency of the input electric signal;
Have
The wavelength control device controls the wavelength of the optical signal output from the E / O converter to be a specific wavelength corresponding to the frequency of the electrical signal determined by the comparison circuit;
FTTH CATV system characterized by this.   The optical terminal according to claim 3, further comprising a delay circuit connected between a branch end to the comparison circuit and the electric signal input end of the E / O converter. FTTH system CATV system.

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