Optical receiving device, optical receiving method, and optical transmission system

Abstract

This optical receiving apparatus comprises a first branching unit which branches an input optical signal into a first optical signal and a second optical signal; a reception amplification unit which amplifies power of the first optical signal; a compensation unit which compensates for a wavelength distortion of the first optical signal for which the power has been amplified; a first detection unit which detects power of the second optical signal; a first control unit which controls the amount of compensation for the wavelength distortion on the basis of the power of the second optical signal; a second branching unit which branches the first optical signal for which the wavelength distortion has been compensated into a third optical signal and a fourth optical signal; a second detection unit which detects power of the third optical signal; and a second control unit which controls, on the basis of the power of the third optical signal, an amplification factor of the power of the first optical signal before the wavelength distortion is compensated.

Description

[Technical Field]

[0001] The present invention relates to an optical receiving device, an optical receiving method, and an optical transmission system. [Background technology]

[0002] Optical transmission systems that batch convert Frequency Division Multiplexing (FDM) signals into Frequency Modulation (FM) signals (hereinafter referred to as "FM batch conversion method") have been introduced into video signal distribution systems (see Non-Patent Document 1).

[0003] In such optical transmission systems, an optical transmitting apparatus (Optical TA) may convert a frequency multiplexed signal (carrier signal) input from a head end (HE) into a wideband frequency modulated signal. The optical transmitting apparatus converts the wideband frequency modulated signal into an optical signal. The optical transmitting apparatus outputs the converted optical signal to a transmission path in a repeater section.

[0004] A video-optical line terminal (V-OLT) outputs an optical signal output to a transmission line in a repeater section to an access section. Here, the video-optical line terminal may compensate for waveform distortion caused by chromatic dispersion in the optical signal in the repeater section.

[0005] The optical signal transmitted through the access section is input to the video optical network unit (Video-Optical Network Unit). The video optical network unit demodulates the input optical signal. By demodulating the optical signal, the video optical network unit generates the original frequency multiplexed signal (carrier signal). Here, since the video optical network units are connected in multiple stages in the relay section, long-distance transmission of optical signals is possible. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] “Transmission equipment for transferring multi-channel television signals over optical access networks by frequency modulation conversion,” ITU-T Rec. J. 185, 2012. Summary of the Invention [Problem to be solved by the invention]

[0007] However, in an optical transmission system, the distance from the video signal optical line termination to the video signal optical line terminal is not constant, and therefore the power of the optical signal input to the video signal optical line terminal is not constant, and the quality of the frequency multiplexed signal (carrier signal) output from the video signal optical line terminal is not constant.

[0008] Generally, the longer the distance from the video signal optical line termination to the video signal optical line terminal, the more the power of the optical signal input to the video signal optical line terminal is attenuated due to loss in the transmission path. As such, there are cases where it is not possible to extend the transmission distance of the optical signal.

[0009] In view of the above circumstances, an object of the present invention is to provide an optical receiving device, an optical receiving method, and an optical transmission system that are capable of extending the transmission distance of an optical signal. [Means for solving the problem]

[0010] One aspect of the present invention is an optical receiving device comprising a first branching unit that branches an input optical signal into a first optical signal and a second optical signal, a receiving amplifier unit that amplifies the power of the first optical signal, a compensation unit that compensates for wavelength distortion of the first optical signal whose power has been amplified, a first detection unit that detects the power of the second optical signal, a first control unit that controls the amount of compensation for the wavelength distortion based on the power of the second optical signal, a second branching unit that branches the first optical signal whose wavelength distortion has been compensated for into a third optical signal and a fourth optical signal, a second detection unit that detects the power of the third optical signal, and a second control unit that controls the amplification factor of the power of the first optical signal before the wavelength distortion is compensated based on the power of the third optical signal.

[0011] One aspect of the present invention is an optical receiving method executed by an optical receiving device, the optical receiving method including the steps of splitting an input optical signal into a first optical signal and a second optical signal, amplifying the power of the first optical signal, compensating for wavelength distortion of the power-amplified first optical signal, detecting the power of the second optical signal, controlling the amount of compensation for the wavelength distortion based on the power of the second optical signal, splitting the first optical signal whose wavelength distortion has been compensated for into a third optical signal and a fourth optical signal, detecting the power of the third optical signal, and controlling the amplification factor of the power of the first optical signal before the wavelength distortion is compensated based on the power of the third optical signal.

[0012] One aspect of the present invention is an optical receiving method executed by an optical transmission system including an optical transmitting device and an optical receiving device, wherein the optical transmitting device generates a frequency-modulated signal and transmits an input optical signal that is intensity-modulated in accordance with the frequency-modulated signal, and the optical receiving device splits the input optical signal into a first optical signal and a second optical signal, amplifies the power of the first optical signal, compensates for wavelength distortion of the power-amplified first optical signal, detects the power of the second optical signal, controls the amount of compensation for the wavelength distortion based on the power of the second optical signal, splits the first optical signal with the wavelength distortion compensated for into a third optical signal and a fourth optical signal, detects the power of the third optical signal, and controls the amplification factor of the power of the first optical signal before the wavelength distortion is compensated based on the power of the third optical signal.

[0013] One aspect of the present invention is an optical transmission system comprising an optical transmitting device and an optical receiving device, wherein the optical transmitting device comprises a frequency modulation unit that generates a frequency-modulated signal and an intensity modulator that transmits an input optical signal that has been intensity-modulated in accordance with the frequency-modulated signal, and the optical receiving device comprises a first branching unit that branches the input optical signal into a first optical signal and a second optical signal, a receiving amplifier unit that amplifies the power of the first optical signal, a compensation unit that compensates for wavelength distortion of the power-amplified first optical signal, a first detection unit that detects the power of the second optical signal, a first control unit that controls the amount of compensation for the wavelength distortion based on the power of the second optical signal, a second branching unit that branches the first optical signal whose wavelength distortion has been compensated for into a third optical signal and a fourth optical signal, a second detection unit that detects the power of the third optical signal, and a second control unit that controls the amplification factor of the power of the first optical signal before the wavelength distortion is compensated for based on the power of the third optical signal. [Effects of the Invention]

[0014] The present invention makes it possible to extend the transmission distance of optical signals. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 illustrates an example of the configuration of an optical transmission system according to an embodiment. [Figure 2] FIG. 1 illustrates an example of the configuration of an optical receiving device according to an embodiment. [Figure 3] FIG. 2 is a sequence diagram illustrating an example of the operation of the optical transmission system according to the embodiment. [Figure 4] FIG. 2 is a diagram illustrating an example of a hardware configuration of an optical receiving device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an example of the configuration of an optical transmission system 1. The optical transmission system 1 is a system (optical transmission network) that transmits optical signals. In the following, as an example, the optical transmission system distributes video signals using optical signals. The video may be a moving image or a still image.

[0017] The optical transmission system 1 includes a head-end device 2, an optical transmitting device 3, a V-OLT 4, a transmission line 5, N (N is an integer equal to or greater than 1) optical receiving devices 6, and a display device 7. The optical transmitting device 3 includes a frequency modulation unit 30 and an intensity modulator 31. The optical receiving device 6 includes a receiving unit 60, a frequency demodulation unit 61, and an amplification unit 62.

[0018] Hereinafter, the section from the optical transmitting device 3 to the V-OLT 4 will be referred to as the "repeater section." Hereinafter, the section from the V-OLT 4 to the optical receiving device 6 will be referred to as the "access section."

[0019] The head-end device 2 (facility of a broadcast distribution company) outputs a frequency multiplexed signal including a video signal to the optical transmitting device 3. The head-end device 2 may also output a frequency multiplexed signal including an audio signal, a data signal, etc., and a video signal to the optical transmitting device 3.

[0020] The optical transmitter 3 is a device (TA) that transmits an optical signal. A frequency multiplexed signal is input to the frequency modulation unit 30 from the head-end device 2. The frequency modulation unit 30 performs optical heterodyne detection processing on the frequency multiplexed signal to generate a frequency modulated signal (FM signal).

[0021] The frequency modulation unit 30 generates a laser beam for transmission. The intensity modulator 31 performs intensity modulation on the laser beam for transmission in accordance with the frequency modulation signal generated by the frequency modulation unit 30. In this way, the intensity modulator 31 generates an intensity-modulated optical signal. The intensity modulator 31 transmits the intensity-modulated optical signal to the V-OLT 4.

[0022] The V-OLT 4 is an optical line termination device for video signals. The V-OLT 4 transmits an optical signal intensity-modulated by an intensity modulator 31 to each optical receiving device 6 via a transmission path 5. The transmission path 5 transmits the optical signal using optical fiber. The transmission path 5 distributes the optical signal to each optical receiving device 6 from optical receiving device 6-1 to optical receiving device 6-N using an optical splitter.

[0023] The optical receiving device 6 (Video - Optical Network Unit) is an optical line terminal for video signals. The receiving unit 60 has a photodiode. The receiving unit 60 converts the optical signal acquired via the transmission path 5 into a frequency-modulated signal (electrical signal). The frequency demodulation unit 61 performs demodulation processing (delay detection) on the frequency-modulated signal to generate a frequency-multiplexed signal including a video signal. The amplification unit 62 amplifies the voltage of the video signal in the frequency-multiplexed signal to a predetermined level.

[0024] The display device 7 is a device that displays video on a screen. The display device 7 acquires a frequency multiplexed signal including a video signal whose voltage has been amplified to a predetermined level from the amplifier unit 62. The display device 7 displays video on a screen in accordance with the video signal in the frequency multiplexed signal.

[0025] Next, an example of the configuration of the optical receiving device 6 will be described. 2 is a diagram showing an example of the configuration of an optical receiving device 6 according to an embodiment. The receiving unit 60 includes a first branching unit 600, a first detecting unit 601, a first control unit 602, a receiving amplifier 603, a compensating unit 604, a second branching unit 605, a second detecting unit 606, a second control unit 607, and a converting unit 608.

[0026] The first branching unit 600 branches the optical signal (input optical signal) input from the V-OLT 4 into a first optical signal and a second optical signal. That is, the first branching unit 600 distributes the first optical signal branched from the input optical signal to the receiving amplifier 603. The first branching unit 600 distributes the second optical signal branched from the input optical signal to the first detector 601.

[0027] The first detector 601 detects the power of the second optical signal “P r1 The first control unit 602 detects the power "P" of the second optical signal. r1 For example, the transmission distance "L" of the access section is calculated from the formula "L=(P out -P r1 -A) / α', where 'P out " represents the power of the optical signal output from the V-OLT4. out " is determined in advance. "A" represents the branch loss (dB) in the access section. "α" represents the loss per unit length (dB / km) in the access section. The first control unit 602 derives the amount of compensation for waveform distortion based on a control signal representing the transmission distance "L" of the access section. The amount of compensation for waveform distortion due to chromatic dispersion is proportional to, for example, the transmission distance "L" of the access section. The first control unit 602 outputs the control signal representing the amount of compensation to the compensation unit 604.

[0028] A control signal indicating an amplification factor is input to the reception amplification unit 603 from the second control unit 607. The reception amplification unit 603 amplifies the power of the first optical signal based on the amplification factor. A control signal indicating a compensation amount is input to the compensation unit 604 (variable dispersion compensation unit) from the first control unit 602. The compensation unit 604 compensates for wavelength distortion of the first optical signal, the power of which has been amplified by the reception amplification unit 603, based on the compensation amount.

[0029] The second branching unit 605 branches the first optical signal, whose wavelength distortion has been compensated, into a third optical signal and a fourth optical signal. That is, the second branching unit 605 distributes the branched third optical signal to the second detecting unit 606. The second branching unit 605 distributes the branched fourth optical signal to the converting unit 608.

[0030] The second detector 606 detects the power of the third optical signal “P r2 The second control unit 607 detects the power "P" of the third optical signal. r2 ", the amplification factor "G" in the receiving amplifier 603 is derived based on the equation "G=P r3-P r2 " where "P r3 " represents the optimum value (dB) of the optical power input to the converter 608. r3 " is determined in advance.

[0031] The converter 608 converts the fourth optical signal into an electrical signal. The frequency demodulator 61 demodulates the frequency multiplexed signal from the electrical signal. The amplifier 62 amplifies the level of the frequency multiplexed signal.

[0032] Next, an example of the operation of the optical transmission system 1 will be described. 3 is a sequence diagram showing an example of operation of the optical transmission system 1 in the embodiment. The optical transmitting device 3 generates a frequency-modulated signal from a frequency-multiplexed signal (carrier signal) input from the head-end device 2 (step S101). The optical transmitting device 3 transmits an input optical signal that has been intensity-modulated according to the frequency-modulated signal to the V-OLT 4 (step S102). The V-OLT 4 relays the input optical signal to each optical receiving device 6 (step S103).

[0033] The optical receiving device 6 splits the input optical signal into a first optical signal and a second optical signal (step S104). The optical receiving device 6 amplifies the power of the first optical signal (step S105). The optical receiving device 6 compensates for waveform distortion of the first optical signal whose power has been amplified (step S106). The optical receiving device 6 detects the power of the second optical signal (step S107). The optical receiving device 6 controls the amount of compensation for waveform distortion of the first optical signal based on the power of the second optical signal (step S108).

[0034] The optical receiving device 6 splits the first optical signal, whose waveform distortion has been compensated, into a third optical signal and a fourth optical signal (step S109). The optical receiving device 6 detects the power of the third optical signal (step S110). The optical receiving device 6 controls the amplification factor of the power of the first optical signal before compensation, based on the power of the third optical signal (step S111).

[0035] The optical receiving device 6 converts the fourth optical signal into an electrical signal (step S112). The optical receiving device 6 generates a frequency multiplexed signal from the electrical signal (step S113). The optical receiving device 6 amplifies the level of the frequency multiplexed signal (step S114).

[0036] As described above, the frequency modulation unit 30 generates a frequency-modulated signal from the frequency-multiplexed signal. The intensity modulator 31 transmits an input optical signal that has been intensity-modulated in accordance with the frequency-modulated signal. The V-OLT 4 relays the intensity-modulated input optical signal.

[0037] The first branching unit 600 branches the input optical signal into a first optical signal and a second optical signal. The receiving amplifier 603 amplifies the power of the first optical signal. The compensation unit 604 compensates for wavelength distortion of the first optical signal whose power has been amplified. The first control unit 602 controls the amount of compensation for wavelength distortion based on the power of the second optical signal.

[0038] In this way, since the receiving amplifier 603 is placed immediately after (at the rear stage of) the first branching unit 600, the power of the optical signal input to the receiving amplifier 603 is stronger than when the receiving amplifier 603 is placed somewhere other than immediately after the first branching unit 600. This improves noise reduction. Furthermore, the optical receiving device 6 dynamically adjusts the amount of chromatic dispersion compensation according to the distance of the access section.

[0039] The second branching unit 605 branches the first optical signal, whose wavelength distortion has been compensated for, into a third optical signal and a fourth optical signal. The second control unit 607 controls the amplification factor of the power of the first optical signal before the wavelength distortion is compensated for by the compensation unit 604, based on the power of the third optical signal. That is, the second control unit 607 controls the amplification factor of the power of the first optical signal in the receiving amplification unit 603.

[0040] In this way, since the second branching unit 605 is arranged immediately after (at the rear stage of) the compensation unit 604, the power of the optical signal (optical power) input to the conversion unit 608 remains constant even if the transmission loss value of the optical signal changes depending on the compensation amount in the compensation unit 604. In other words, the optical receiving device 6 keeps the power of the optical signal input to the conversion unit 608 of the optical receiving device 6 constant regardless of the distance (transmission loss value) of the access section.

[0041] Therefore, the optical receiving device 6 keeps the quality of the frequency multiplexed signal (video signal) it outputs constant regardless of the distance of the access section. This makes it possible to extend the transmission distance of the optical signal. Furthermore, the optical transmission system 1 can be used in a wider area.

[0042] (Example of hardware configuration) 4 is a diagram illustrating an example of a hardware configuration of an optical receiving device 6 according to an embodiment. Some or all of the functional units of the optical receiving device 6 are realized as software by a processor 100, such as a CPU (Central Processing Unit), executing a program stored in a storage device 102 having a non-volatile recording medium (non-transitory recording medium) and a memory 101. The program may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as a flexible disk, a magneto-optical disk, a ROM (Read Only Memory), and a CD-ROM (Compact Disc Read Only Memory), and non-transitory recording media such as a storage device built into a computer system, such as a hard disk. A communication unit 103 executes communication processing.

[0043] Some or all of the functional units of the optical receiving device 6 may be realized using hardware including an electronic circuit (electronic circuit or circuitry) using, for example, an LSI (Large Scale Integrated circuit), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0044] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Industrial Applicability]

[0045] The present invention is applicable to optical transmission systems. [Explanation of symbols]

[0046] 1...optical transmission system, 2...headend device, 3...optical transmitting device, 4...V-OLT, 5...transmission path, 6...optical receiving device, 7...display device, 30...frequency modulation unit, 31...intensity modulator, 60...receiving unit, 61...frequency demodulation unit, 62...amplifying unit, 100...processor, 101...memory, 102...storage device, 103...communication unit, 600...first branching unit, 601...first detection unit, 602...first control unit, 603...receiving amplification unit, 604...compensating unit, 605...second branching unit, 606...second detection unit, 607...second control unit

Claims

1. a first branching unit that branches an input optical signal into a first optical signal and a second optical signal; a receiving amplifier that amplifies the power of the first optical signal; a compensation unit that compensates for wavelength distortion of the first optical signal whose power has been amplified; a first detector that detects the power of the second optical signal; a first control unit that controls the amount of compensation for the wavelength distortion so that the amount is proportional to a transmission distance derived based on the power of the second optical signal; a second branching unit that branches the first optical signal, the wavelength distortion of which has been compensated, into a third optical signal and a fourth optical signal; a second detector that detects the power of the third optical signal; a second control unit that controls an amplification factor of the power of the first optical signal before the wavelength distortion is compensated based on the power of the third optical signal; An optical receiving device comprising:

2. An optical receiving method executed by an optical receiving device, branching an input optical signal into a first optical signal and a second optical signal; amplifying the power of the first optical signal; compensating for wavelength distortion of the power-amplified first optical signal; detecting the power of the second optical signal; controlling the amount of compensation for the wavelength distortion so as to be proportional to a transmission distance derived based on the power of the second optical signal; branching the first optical signal, the wavelength distortion of which has been compensated, into a third optical signal and a fourth optical signal; detecting the power of the third optical signal; controlling an amplification factor of the power of the first optical signal before the wavelength distortion is compensated based on the power of the third optical signal; An optical receiving method comprising:

3. An optical receiving method executed by an optical transmission system including an optical transmitting device and an optical receiving device, The optical transmitter comprises: generating a frequency modulated signal; transmitting an input optical signal intensity-modulated in response to the frequency-modulated signal; The optical receiving device splitting an input optical signal into a first optical signal and a second optical signal; amplifying the power of the first optical signal; Compensating for wavelength distortion of the power-amplified first optical signal; Detecting the power of the second optical signal; controlling the compensation amount for the wavelength distortion so as to be proportional to the transmission distance derived based on the power of the second optical signal; branching the first optical signal whose wavelength distortion has been compensated into a third optical signal and a fourth optical signal; Detecting the power of the third optical signal; controlling an amplification factor of the power of the first optical signal before the wavelength distortion is compensated based on the power of the third optical signal; Optical receiving method.

4. An optical transmission system including an optical transmitter and an optical receiver, The optical transmitter comprises: a frequency modulation unit for generating a frequency modulated signal; an intensity modulator that transmits an input optical signal intensity-modulated in response to the frequency-modulated signal; The optical receiving device a first branching unit that branches an input optical signal into a first optical signal and a second optical signal; a receiving amplifier that amplifies the power of the first optical signal; a compensation unit that compensates for wavelength distortion of the first optical signal whose power has been amplified; a first detector that detects the power of the second optical signal; a first control unit that controls the amount of compensation for the wavelength distortion so that the amount is proportional to a transmission distance derived based on the power of the second optical signal; a second branching unit that branches the first optical signal, the wavelength distortion of which has been compensated, into a third optical signal and a fourth optical signal; a second detector that detects the power of the third optical signal; a second control unit that controls an amplification factor of the power of the first optical signal before the wavelength distortion is compensated based on the power of the third optical signal, Optical transmission system.

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