WO2024053053A1

WO2024053053A1 - Optical transmission device, optical transmission method, and optical communication system

Info

Publication number: WO2024053053A1
Application number: PCT/JP2022/033739
Authority: WO
Inventors: 遼宮武; 利明下羽; 暁弘田邉; 陽一深田; 真良関口; 智暁吉田
Original assignee: 日本電信電話株式会社
Priority date: 2022-09-08
Filing date: 2022-09-08
Publication date: 2024-03-14
Also published as: WO2024053131A1

Abstract

Provided is an optical transmission device comprising: a plurality of oscillators that generate a plurality of laser beams; a first batch conversion unit that generates a first frequency modulation signal by performing frequency modulation batch conversion on a first narrowband signal by using the plurality of laser beams; a first frequency converter that converts a second narrowband signal into a third narrowband signal; a second batch conversion unit that generates a second frequency modulation signal by performing frequency modulation batch conversion on the third narrowband signal by using the plurality of laser beams; a second frequency converter that changes the frequency of the second frequency modulation signal; an adder that adds the second frequency modulation signal, the frequency of which has been changed, and the first frequency modulation signal, on the frequency axis; and an optical intensity modulator that generates an optical intensity-modulated optical signal by performing optical intensity modulation on the addition result.

Description

Optical transmitting device, optical transmitting method, and optical communication system

The present invention relates to an optical transmission device, an optical transmission method, and an optical communication system.

An optical communication system that collectively converts frequency division multiplexing (FDM) signals into frequency modulation (FM) signals has been introduced into video signal distribution systems (see Non-Patent Document 1). Hereinafter, the batch conversion to a frequency modulated signal will be referred to as "FM batch conversion." The video signal in Non-Patent Document 1 includes a cable television signal (bandwidth: 90 to 770MHz) and a right-handed circularly polarized intermediate frequency signal (BS/CS right-handed IF signal) of a broadcasting satellite and a communication satellite (bandwidth: 1. This is a multi-channel video signal that includes a left-handed circularly polarized intermediate frequency signal (BS/CS left-handed IF signal) (2.2 to 3.2 GHz) of a broadcasting satellite and a communication satellite.

In the optical receiving device of the optical communication system that performs FM batch conversion, the delay detection method is adopted as the demodulation method of the frequency division multiplexed signal, so the bandwidth of the optical signal is set to the current bandwidth (W = 3.2 GHz). It is difficult to expand beyond this. Therefore, for example, when an optical signal (wideband signal) with a bandwidth of 2W, which is twice the bandwidth of 2W, is transmitted, the optical communication system simply connects the two signal systems in parallel. will be prepared for. An optical transmitter of an optical communication system transmits a wavelength multiplexed signal of a frequency modulated signal (FM signal) to an optical receiver for each signal system with a bandwidth of "W".

However, by parallelizing the signal system, the number of oscillators (laser diodes) and the number of optical intensity modulators each double in the optical transmission device of the optical communication system. Furthermore, in the optical receiver of the optical communication system, the number of photodetectors (photodiodes) is doubled. As described above, there is a problem in that it is not possible to transmit and receive broadband signals subjected to FM batch conversion at low cost.

In view of the above circumstances, an object of the present invention is to provide an optical transmission device, an optical transmission method, and an optical communication system that are capable of transmitting and receiving broadband signals subjected to FM batch conversion at low cost.

One aspect of the present invention includes: a first oscillator that generates a first laser beam with a first oscillation frequency; a second oscillator that generates a second laser beam with a second oscillation frequency; a first batch conversion unit that generates a first frequency modulation signal by performing frequency modulation batch conversion on a first narrowband signal having a predetermined narrow bandwidth and a first center frequency using a laser beam; , a first frequency converter that converts the second narrowband signal having the predetermined narrow bandwidth and the second center frequency into a third narrowband signal having the predetermined narrow bandwidth and the first center frequency; a second batch conversion unit that generates a second frequency modulation signal by performing frequency modulation batch conversion on the third narrowband signal using the first laser beam and the second laser beam; a second frequency converter that changes the frequency of the second frequency modulation signal so that the overlap between the first frequency modulation signal and the second frequency modulation signal on the frequency axis is reduced; and the second frequency modulation signal whose frequency has been changed. an adder that adds the two-frequency modulation signal and the first frequency modulation signal on the frequency axis; and an adder that adds the two-frequency modulation signal and the first frequency modulation signal; The present invention is an optical transmission device including an optical intensity modulator that generates an optical signal whose intensity is modulated by performing modulation.

One aspect of the present invention is an optical transmission method performed by an optical transmission device, which includes: generating a first laser beam at a first oscillation frequency; generating a second laser beam at a second oscillation frequency; A first frequency modulated signal is obtained by performing frequency modulation batch conversion on a first narrow band signal having a predetermined narrow bandwidth and a first center frequency using the first laser beam and the second laser beam. converting the second narrowband signal having the predetermined narrow bandwidth and the second center frequency into a third narrowband signal having the predetermined narrow bandwidth and the first center frequency; generating a second frequency modulated signal by performing frequency modulation batch conversion on the third narrowband signal using the first laser beam and the second laser beam; changing the frequency of the second frequency modulation signal so that the overlap between the signal and the second frequency modulation signal on the frequency axis becomes small; 1 frequency modulation signal on the frequency axis, and performing optical intensity modulation on the addition result of the frequency-changed second frequency modulation signal and the first frequency modulation signal. An optical transmission method includes the step of generating an intensity-modulated optical signal.

One aspect of the present invention is an optical communication system including an optical transmitter and an optical receiver, wherein the optical transmitter includes a first oscillator that generates a first laser beam of a first oscillation frequency, and a second oscillator that generates a first laser beam of a first oscillation frequency. a second oscillator that generates a second laser beam with a certain frequency; and a first narrowband signal with a predetermined narrow bandwidth and a first center frequency, using the first laser beam and the second laser beam. A first batch conversion section that generates a first frequency modulation signal by performing modulation batch conversion, and a second narrowband signal having the predetermined narrow bandwidth and the second center frequency, Frequency modulation batch conversion of the third narrowband signal using a first frequency converter that converts the third narrowband signal having the first center frequency, and the first laser beam and the second laser beam. By performing this, the second batch conversion section that generates the second frequency modulation signal, and the second batch conversion section that generates the second frequency modulation signal, reduce the overlap between the first frequency modulation signal and the second frequency modulation signal on the frequency axis. a second frequency converter that changes the frequency of the two-frequency modulation signal; an adder that adds the second frequency modulation signal whose frequency has been changed and the first frequency modulation signal on a frequency axis; a light intensity modulator that generates a light intensity modulated optical signal by performing light intensity modulation on the addition result of the second frequency modulated signal and the first frequency modulated signal; The optical receiver includes a photodetector that converts the light intensity modulated optical signal into the second frequency modulated signal and the first frequency modulated signal whose frequency has been changed, and the second frequency modulated signal whose frequency has been changed. a first bandpass filter that extracts the first frequency modulated signal from the frequency modulated signal and the first frequency modulated signal, and by performing delay detection processing on the extracted first frequency modulated signal, a first delay detector that generates the first narrowband signal; a first low-pass filter that removes high frequency components of the first narrowband signal; a second frequency modulated signal whose frequency has been changed; a second bandpass filter that extracts the second frequency modulated signal whose frequency has been changed from the first frequency modulated signal; a first frequency inverse converter that generates the second frequency modulated signal by making the frequency the same as the frequency, and a first frequency inverse converter that generates the second frequency modulated signal, and a third narrowband signal that a second delay detector that generates the second narrowband signal; a second low-pass filter that removes the high frequency component of the third narrowband signal; and a second low pass filter that removes the high frequency component of the third narrowband signal; and a second frequency inverter that generates a signal.

According to the present invention, it is possible to transmit and receive broadband signals subjected to FM batch conversion at low cost.

1 is a diagram showing a configuration example of an optical communication system in a first embodiment; FIG. 3 is a flowchart illustrating an example of the operation of the optical transmitter in the first embodiment. 7 is a flowchart illustrating an example of the operation of the optical receiver in the first embodiment. FIG. 2 is a diagram illustrating a configuration example of an optical communication system in a comparative example with the first embodiment. FIG. 3 is a diagram illustrating a configuration example of an optical communication system in a second embodiment. 7 is a flowchart illustrating an example of the operation of the optical transmitter in the second embodiment. 7 is a flowchart illustrating an example of the operation of the optical receiver in the second embodiment. FIG. 2 is a diagram illustrating a configuration example of an optical communication system in a comparative example with a second embodiment. FIG. 2 is a diagram showing an example of the hardware configuration of an optical communication device in each embodiment.

Embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram showing a configuration example of an optical communication system 1a in the first embodiment. The optical communication system 1a is a system that communicates using optical signals. The optical communication system 1a includes an optical transmitter 2a, a transmission line 3, and an optical receiver 4a.

The optical transmission device 2a (optical subscriber line terminal device) is, for example, a V-OLT (Video Optical Line Terminal). The optical transmitter 2a includes a band splitter 20, a first oscillator 21, a second oscillator 22, a batch converter 23, a frequency converter 24, a batch converter 25, a frequency converter 26, and an adder. 27 and a light intensity modulator 28. The batch conversion unit 23 includes a phase modulator 231 and a photodetector 232. The batch conversion unit 25 includes a phase modulator 251 and a photodetector 252. Here, the first signal system batch converter 23 shares the first oscillator 21 and the second oscillator 22 with the second signal system batch converter 25. The transmission line 3 is an optical transmission line, and includes, for example, an optical fiber.

The optical receiving device 4a (optical line terminating device) is, for example, a V-ONU (Video Optical Network Unit). The optical receiver 4a includes a photodetector 40, a bandpass filter 41, a delay detector 42, a low-pass filter 43, a multiplexer 44, a bandpass filter 45, and a frequency inverse converter 46. , a delay detector 47, a low-pass filter 48, and a frequency inverse converter 49.

First, details of the optical transmitter 2a will be explained.
A signal with a bandwidth of "2W" (a wideband frequency division multiplexed signal) is input to the band divider 20 from, for example, a head-end device (not shown). The band divider 20 divides a signal with a bandwidth of "2W" into signals (each narrowband signal) with a proportionally divided bandwidth on the frequency axis. For example, the band divider 20 may equally divide a signal with a bandwidth of "2W" on the frequency axis, or may divide a signal with a bandwidth of "2W" unequally at any proportion. In the following, the band divider 20 equally divides a signal with a bandwidth of "2W" into each signal with a bandwidth of "W" on the frequency axis, as an example.

The band divider 20 outputs a narrowband signal (narrowband frequency division multiplexed signal) with a bandwidth “W” and a center frequency “A” (first center frequency) to the phase modulator 231. The band divider 20 outputs a narrowband signal (narrowband frequency division multiplexed signal) having a bandwidth “W” and a center frequency “B” (second center frequency) to the frequency converter 24 .

The first oscillator 21 is a laser oscillator with a first oscillation frequency, and is, for example, a narrow linewidth laser diode. The first oscillator 21 outputs laser light at a first oscillation frequency (first laser light) to the phase modulator 231 and the phase modulator 251.

The second oscillator 22 is a laser oscillator with a second oscillation frequency, and is, for example, a narrow linewidth laser diode. The second oscillator 22 outputs a laser beam with a second oscillation frequency (second laser beam) to the photodetector 232 and the photodetector 252.

In the first signal system, the batch conversion unit 23 is a functional unit that executes FM batch conversion (frequency modulation batch conversion). The batch conversion unit 23 generates the first FM signal “S _FM1 (t)” by performing batch FM conversion on the narrowband signal input from the band divider 20.

The phase modulator 231 generates a phase-modulated optical signal using a narrowband signal (first narrowband signal) with a bandwidth "W" and a center frequency "A" and a laser beam with a first oscillation frequency. do. The photodetector 232 (photodiode) converts the phase-modulated optical signal into a first FM signal "S _FM1 (t)" (electrical signal) using a laser beam of the second oscillation frequency. Photodetector 232 outputs the first FM signal to adder 27 .

In the second signal system, the frequency converter 24 converts a narrowband signal (second narrowband signal) with a bandwidth "W" and a center frequency "B" into a narrowband signal (second narrowband signal) with a bandwidth "W" and a center frequency "A". signal (third narrowband signal). Here, the frequency converter 24 converts the frequency so that the amount of light leakage is below a threshold value or the signal-to-interference signal ratio of the optical signal is below a certain level. The frequency converter 24 outputs a narrowband signal having a bandwidth “W” and a center frequency “A” to the phase modulator 251.

In the second signal system, the batch conversion unit 25 is a functional unit that executes frequency modulation batch conversion (FM batch conversion). The batch conversion unit 25 performs batch FM conversion on the narrowband signal input from the frequency converter 24 to generate a second FM signal “S _FM2 (t)”.

The phase modulator 251 generates a phase-modulated optical signal using a narrowband signal having a bandwidth "W" and a center frequency "B" and a laser beam having a second oscillation frequency. The photodetector 252 (photodiode) converts the phase-modulated optical signal into a second FM signal "S _FM2 (t)" (electrical signal) using a laser beam of the second oscillation frequency. Photodetector 252 outputs the second FM signal to frequency converter 26 .

Note that the center frequency of the first FM signal after FM batch conversion in the first embodiment is the difference (absolute value) between the first oscillation frequency and the second oscillation frequency. Similarly, the center frequency of the second FM signal after FM batch conversion in the first embodiment is the difference (absolute value) between the first oscillation frequency and the second oscillation frequency. Therefore, the center frequency of the first FM signal after FM batch conversion in the first embodiment is equal to the center frequency of the second FM signal after FM batch conversion in the first embodiment.

In the second signal system, _the frequency converter 26 converts the frequency converter ₍ FM The frequency of the second FM signal is changed so that deterioration in communication quality due to interference between signals is sufficiently reduced. For example, the frequency converter 26 changes the center frequency of the second FM signal according to the determined frequency conversion amount. As a result, the frequency converter 26 generates the second FM signal "S _FM2 '(t)" (electrical signal) as the second FM signal whose frequency has been changed.

The method for determining the amount of frequency conversion of the second FM signal is not limited to a specific method. For example, it is considered that the amount of interference decreases as the first FM signal "S _FM1 (t)" and the second FM signal "S _FM2 '(t)" become farther apart on the frequency axis. Therefore, _the frequency converter ₂₆ converts the amount of frequency conversion (first frequency conversion A frequency conversion amount (second frequency conversion amount) that is larger than the frequency conversion amount) may be determined as the frequency conversion amount of the second FM signal. The predetermined amount "α" is determined in advance based on, for example, communication quality specifications. Thereby, the amount of interference can be reliably suppressed according to the amount of frequency conversion optimized based on the communication quality specifications. For example, the frequency converter 26 may uniformly determine a frequency conversion amount predetermined based on communication quality specifications, etc., as the frequency conversion amount of the second FM signal.

The adder 27 adds the first FM signal "S _FM1 (t)" and the second FM signal "S _FM2 '(t)" on the frequency axis. The optical intensity modulator 28 performs optical intensity modulation on the added FM signal (addition result). Thereby, the light intensity modulator 28 generates a light intensity modulated optical signal. The light intensity modulator 28 outputs the light intensity modulated optical signal to the transmission line 3. The transmission line 3 transmits a light intensity modulated optical signal (a broadband signal) to an optical receiver 4a.

Next, details of the optical receiver 4a will be explained.
A light intensity modulated optical signal (broadband signal) is input to the photodetector 40 from the transmission line 3 . That is, an optical signal (wavelength multiplexed signal) including the first FM signal and the second FM signal is input to the photodetector 40 from the transmission line 3 . The photodetector 40 converts the light intensity modulated optical signal into an electrical signal including a first FM signal "S _FM1 (t)" and a second FM signal "S _FM2 '(t)". Photodetector 40 outputs the converted electrical signal to bandpass filter 41 and bandpass filter 45.

In the first signal system, the bandpass filter 41 extracts the first FM signal from the electric signal including the first FM signal and the second FM signal. The delay detector 42 performs delay detection processing (demodulation processing) on the extracted first FM signal. Thereby, the delay detector 42 generates a narrowband signal (first narrowband signal) having a bandwidth "W" and a center frequency "A". The low-pass filter 43 removes high frequency components of the narrowband signal having a bandwidth "W" and a center frequency "A".

The multiplexer 44 multiplexes (adds) a narrowband signal with a bandwidth "W" and a center frequency "A" and a narrowband signal with a bandwidth "W" and a center frequency "B". The multiplexer 44 outputs a frequency division multiplexed signal with a bandwidth of "2W" to a predetermined device (not shown). The predetermined device is, for example, a display device.

In the second signal system, the bandpass filter 45 extracts the second FM signal "S _FM2' (t)" from the electric signal including the first FM signal "S _FM1 (t)" and the second FM signal "S _FM2 '(t)". ” (second narrowband signal). The frequency inverse converter 46 makes the frequency of the second FM signal "S _FM2 '(t)" whose frequency has been changed by the frequency converter 26 the same as the frequency of the first FM signal, thereby converting the second FM signal "S FM2 (t)" into the second FM signal "S _FM2 (t)". t).

In the second signal system, the delay detector 47 performs delay detection processing (demodulation processing) on the second FM signal "S _FM2 (t)". As a result, the delay detector 47 generates a narrowband signal (third narrowband signal) having a bandwidth of "W" and a center frequency of "A". The low pass filter 48 removes high frequency components of the narrowband signal with a bandwidth "W" and a center frequency "A". The frequency inverse converter 49 generates a narrowband signal (second narrowband signal) having a bandwidth "W" and a center frequency "B" based on the narrowband signal having a bandwidth "W" and a center frequency "A". do. That is, the frequency inverse converter 49 converts a narrowband signal with a bandwidth "W" and a center frequency "A" into a narrowband signal with a bandwidth "W" and a center frequency "B". The frequency inverse converter 49 outputs a narrowband signal having a bandwidth “W” and a center frequency “B” to the multiplexer 44 .

Note that each of the frequency converter 24, the frequency converter 26, the frequency inverse converter 46, and the frequency inverse converter 49 may be provided in the first signal system instead of being provided in the second signal system.

Next, an example of the operation of the optical communication system 1a will be explained.
FIG. 2 is a flowchart showing an example of the operation of the optical transmitter 2a in the first embodiment. In the common signal system, the band divider 20 divides a signal with a bandwidth of "2W" into each signal with a bandwidth of "W" on the frequency axis (step S101: band division processing).

In the first signal system, the phase modulator 231 generates a phase-modulated optical signal using a narrowband signal with a bandwidth "W" and a center frequency "A" and a laser beam with a first oscillation frequency. (Step S102: first phase modulation process). The photodetector 232 converts the phase-modulated optical signal into a first FM signal using a laser beam of the second oscillation frequency (step S103: first photodetection process). Each functional unit of the first signal system advances the process to step S108.

In the second signal system, the frequency converter 24 converts a narrowband signal with a bandwidth "W" and a center frequency "B" into a narrowband signal with a bandwidth "W" and a center frequency "A" (step S104 : first frequency conversion process). The phase modulator 251 generates a phase-modulated optical signal using a narrowband signal with a bandwidth "W" and a center frequency "B" and a laser beam with a second oscillation frequency (step S105: the first phase modulation processing). The photodetector 252 converts the phase modulated optical signal into a second FM signal using a laser beam of the second oscillation frequency (step S106: second photodetection process). The frequency converter 26 changes the frequency of the second FM signal so that the overlap between the first FM signal and the second FM signal on the frequency axis becomes smaller (step S107: second frequency conversion process).

In the common signal system, the adder 27 adds the first FM signal and the second FM signal whose frequency has been changed (step S108: addition process). The light intensity modulator 28 performs light intensity modulation on the added FM signal (step S109: light intensity modulation process).

FIG. 3 is a flowchart showing an example of the operation of the optical receiver 4a in the first embodiment. The photodetector 40 converts the light intensity modulated optical signal into an electrical signal including the first FM signal and the second FM signal whose frequency has been changed (step S201: third photodetection process).

In the first signal system, the bandpass filter 41 extracts the first FM signal from the electric signal included in the first FM signal and the second FM signal whose frequency has been changed (step S202: first bandpass filter processing). The delay detector 42 performs delay detection processing on the extracted first FM signal (step S203: first delay detection processing). The low-pass filter 43 removes high-frequency components of the narrowband signal having a bandwidth "W" and a center frequency "A" (step S204: first low-pass processing).

In the second signal system, the bandpass filter 45 extracts the second FM signal whose frequency has been changed from the electrical signal that includes the first FM signal and the second FM signal whose frequency has been changed (step S205: the second bandpass filter process). The frequency inverse transformer 46 makes the center frequency of the second FM signal whose frequency has been changed the same as the center frequency of the first FM signal (step S206: first inverse transform process). The delay detector 47 performs delay detection processing on the second FM signal (step S207: second delay detection processing). The low-pass filter 48 removes high-frequency components of the narrowband signal having a bandwidth "W" and a center frequency "A" (step S208: second low-pass processing). The frequency inverse converter 49 generates a narrowband signal having a bandwidth "W" and a center frequency "B" based on the narrowband signal having a bandwidth "W" and a center frequency "A" (step S209: the second (inverse conversion process).

The multiplexer 44 separates a narrowband signal (narrowband frequency division multiplexed signal) with a bandwidth "W" and a center frequency "A", and a narrowband signal (narrowband frequency division multiplexed signal) with a bandwidth "W" and a center frequency "B". frequency division multiplexed signal) (step S210: multiplexing process).

As described above, in the optical transmission device 2a of the optical communication system 1a, the band splitter 20 separates a first narrowband signal having a predetermined narrowband width "W" and a first center frequency "A", and a predetermined narrowband signal having a predetermined narrowband width "W" and a first center frequency "A". A predetermined wideband signal is divided on the frequency axis into a second narrowband signal having a width "W" and a first center frequency "B". The first oscillator 21 generates a first laser beam having a first oscillation frequency. The second oscillator 22 generates a second laser beam having a second oscillation frequency. The batch conversion unit 23 (first batch conversion unit) converts the first laser beam and the second laser beam into a first narrowband signal having a predetermined narrowband width “W” and a first center frequency “A”. The first FM signal "S _FM1 (t)" is generated by performing FM batch conversion on the signals. The frequency converter 24 (first frequency converter) converts a second narrow band signal having a predetermined narrow bandwidth "W" and a second center frequency "B" into a second narrow band signal having a predetermined narrow bandwidth "W" and a first center frequency. It is converted into a third narrowband signal of "A". The batch conversion unit 25 (second batch conversion unit) converts the second FM signal “S _FM2” by performing FM batch conversion on the third narrowband signal using the first laser beam and the second laser beam. (t)" is generated. The frequency converter 26 (second frequency converter) changes the frequency of the second FM signal so that the overlap between the first FM signal and the second FM signal on the frequency axis becomes smaller. The adder 27 adds the second FM signal "S _FM2 '(t)" whose frequency has been changed and the first FM signal "S _FM1 (t)" on the frequency axis. The light intensity modulator 28 generates a light intensity modulated optical signal by performing light intensity modulation on the addition result of the second FM signal whose frequency has been changed and the first FM signal.

Furthermore, in the optical receiving device 4a of the optical communication system 1a, the photodetector 40 converts the light intensity modulated optical signal into a second FM signal whose frequency has been changed and a first FM signal. The bandpass filter 41 (first bandpass filter) extracts the first FM signal from the second FM signal whose frequency has been changed and the first FM signal. The delay detector 42 (first delay detector) generates a first narrowband signal by performing delay detection processing on the extracted first FM signal. The low-pass filter 43 (first low-pass filter) removes high frequency components of the first narrowband signal. The bandpass filter 45 (second bandpass filter) extracts a second FM signal whose frequency has been changed from the second FM signal whose frequency has been changed and the first FM signal. The frequency inverse converter 46 (first frequency inverse converter) generates a second FM signal by making the frequency of the second FM signal whose frequency has been changed the same as the frequency of the first FM signal. The delay detector 47 (second delay detector) generates a third narrowband signal by performing delay detection processing on the second FM signal. The low-pass filter 48 (second low-pass filter) removes high frequency components of the third narrowband signal. The frequency inverse converter 49 (second frequency inverse converter) generates a second narrowband signal based on the third narrowband signal from which high frequency components have been removed. The multiplexer 44 multiplexes the first narrowband signal from which high frequency components have been removed and the second narrowband signal.

In this way, the optical transmitter 2a divides the broadband signal to be transmitted into each narrowband signal. The optical transmitter 2a performs FM batch conversion on each narrowband signal. The optical transmitter 2a multiplexes each narrowband FM signal on the frequency axis. The optical transmitter 2a performs optical intensity modulation on the multiplexed FM signal. The optical transmitter 2a transmits the optical intensity modulated FM signal to the optical receiver 4a using the transmission path 3. The optical receiver 4a separates the multiplexed FM signal into each narrowband FM signal. The optical receiver 4a performs predetermined demodulation processing on each narrowband FM signal.

Here, the functional units that can be shared are shared. For example, in the optical transmitter 2a, each oscillator (narrow linewidth laser diode) and optical intensity modulator 28 are shared by two signal systems. Furthermore, in the optical receiving device 4a, by simply adding a simple processing unit (for example, an optical demultiplexer, a wavelength division multiplex filter, a multiplexer, etc.), the broadband signal (multiplexed FM signals) can now be received.

As a result, it is possible to transmit and receive broadband signals subjected to FM batch conversion at low cost. Furthermore, it is possible to reduce the size of the optical transmitter 2a and the size of the optical receiver 4a, respectively.

<Comparative example with the first embodiment>
FIG. 4 is a diagram illustrating a configuration example of an optical communication system 100a in a comparative example with the first embodiment. The optical communication system 100a is a comparative example with the optical communication system 1a. The optical communication system 100a includes an optical transmitter 200a, a transmission path 3, and an optical receiver 400a. The optical transmitter 200a is a comparative example with the optical transmitter 2a. The optical receiving device 400a is a comparative example with the optical receiving device 4a.

The optical transmitter 200a includes a band splitter 20, a batch converter 230, a frequency converter 24, a batch converter 250, an optical intensity modulator 28-1, an optical intensity modulator 28-2, and a multiplexer. A container 29 is provided. The batch conversion section 230 includes a phase modulator 231, a photodetector 232, a first oscillator 21-1, and a second oscillator 22. The batch conversion unit 250 includes a phase modulator 251, a photodetector 252, a first oscillator 21-2, and a third oscillator 30. Here, the first signal system batch conversion unit 230 and the second signal system batch conversion unit 250 share the first oscillator 21-1, the first oscillator 21-2, the second oscillator 22, and the third oscillator 30. do not.

The optical receiver 400a includes an optical demultiplexer 50, a wavelength division multiplex filter 51, a wavelength division multiplex filter 52, a photodetector 40-1, a photodetector 40-2, and a delay detector 42. , a low-pass filter 43, a multiplexer 44, a delayed detector 47, a low-pass filter 48, and a frequency inverse converter 49.

Next, details of the optical transmitter 200a will be explained, focusing on the differences from the optical transmitter 2a.
In the first signal system, the batch conversion unit 230 is a functional unit that executes FM batch conversion (frequency modulation batch conversion). The batch conversion unit 230 generates the first FM signal “S _FM1 (t)” by performing batch FM conversion on the narrowband signal input from the band splitter 20.

In the first signal system, the first oscillator 21-1 outputs laser light at a first oscillation frequency to the phase modulator 231. The phase modulator 231 generates a phase-modulated optical signal using a narrowband signal (first narrowband signal) with a bandwidth "W" and a center frequency "A" and a laser beam with a first oscillation frequency. do. The second oscillator 22 outputs laser light at a second oscillation frequency to the photodetector 232. The photodetector 232 converts the phase-modulated optical signal into a first FM signal "S _FM1 (t)" (electrical signal) using a laser beam of the second oscillation frequency. The optical intensity modulator 28-1 performs optical intensity modulation on the first FM signal. The optical intensity modulator 28-1 outputs the optical intensity modulated first FM signal to the multiplexer 29.

In the second signal system, the frequency converter 24 converts a narrowband signal (second narrowband signal) with a bandwidth "W" and a center frequency "B" into a narrowband signal (second narrowband signal) with a bandwidth "W" and a center frequency "A". signal (third narrowband signal). The frequency converter 24 outputs a narrowband signal having a bandwidth “W” and a center frequency “A” to the phase modulator 251.

In the second signal system, the batch conversion unit 250 is a functional unit that executes FM batch conversion (frequency modulation batch conversion). The batch conversion unit 250 generates the second FM signal “S _FM2 (t)” by performing batch FM conversion on the narrowband signal input from the frequency converter 24 .

In the second signal system, the first oscillator 21-2 outputs laser light at the first oscillation frequency to the phase modulator 251. The phase modulator 251 generates a phase-modulated optical signal using a narrowband signal having a bandwidth "W" and a center frequency "B" and a laser beam having a second oscillation frequency. The third oscillator 30 is a laser oscillator with a third oscillation frequency, and is, for example, a narrow linewidth laser diode. The third oscillator 30 outputs laser light at a third oscillation frequency to the photodetector 252. The photodetector 252 (photodiode) converts the phase-modulated optical signal into a second FM signal "S _FM2 (t)" (electrical signal) using a laser beam of the third oscillation frequency. Photodetector 252 outputs the second FM signal to optical intensity modulator 28-2. The optical intensity modulator 28-2 outputs the optical intensity modulated second FM signal to the multiplexer 29.

Note that the center frequency of the first FM signal after FM batch conversion in the comparative example with the first embodiment is the difference between the first oscillation frequency and the second oscillation frequency. Similarly, the center frequency of the second FM signal after FM batch conversion in the comparative example with the first embodiment is the difference between the first oscillation frequency and the third oscillation frequency.

The multiplexer 29 generates a wavelength multiplexed signal by multiplexing the optical intensity modulated first FM signal and the optical intensity modulated second FM signal. The multiplexer 29 uses an optical signal to transmit a wavelength multiplexed signal to the optical receiver 400a.

Next, details of the optical receiving device 400a will be explained, focusing on the differences from the optical receiving device 4a.
An optical signal (wavelength multiplexed signal) including the first FM signal and the second FM signal is input from the transmission line 3 to the optical demultiplexer 50 (optical splitter). The optical demultiplexer 50 outputs an optical signal including the first FM signal and the second FM signal to the wavelength division multiplex filter 51 and the wavelength division multiplex filter 52.

In the first signal system, the wavelength division multiplex filter 51 (wavelength division multiplex filter) outputs a light intensity modulated optical signal (first FM signal) to the photodetector 40-1. A light intensity modulated optical signal (first FM signal) is input from the wavelength division multiplex filter 51 to the photodetector 40-1. The photodetector 40-1 converts the light intensity modulated optical signal into an electrical signal including the first FM signal "S _FM1 (t)". Photodetector 40-1 outputs the converted electrical signal to delay detector 42.

The delay detector 42 performs delay detection processing (demodulation processing) on the electrical signal including the first FM signal. The low-pass filter 43 removes high frequency components of the narrowband signal having a bandwidth "W" and a center frequency "A". The multiplexer 44 adds a narrowband signal with a bandwidth "W" and a center frequency "A" and a narrowband signal with a bandwidth "W" and a center frequency "B".

In the second signal system, the wavelength division multiplex filter 52 (wavelength division multiplex filter) outputs a light intensity modulated optical signal (second FM signal) to the photodetector 40-2. A light intensity modulated optical signal (second FM signal) is input from the wavelength division multiplex filter 52 to the photodetector 40-2. The photodetector 40-2 converts the light intensity modulated optical signal into an electrical signal including the second FM signal "S _FM2 (t)". Photodetector 40-2 outputs the converted electrical signal to delay detector 47.

The delay detector 47 performs delay detection processing (demodulation processing) on the electrical signal including the second FM signal. The low pass filter 48 removes high frequency components of the narrowband signal with a bandwidth "W" and a center frequency "A". The frequency inverse converter 49 returns the center frequency of the second FM signal from which the high frequency component has been removed to "B". The frequency inverse converter 49 outputs a narrowband signal having a bandwidth “W” and a center frequency “B” to the multiplexer 44 .

In this way, in the optical communication system 100a of the comparative example with the first embodiment, two signal systems are simply provided in parallel. Therefore, the optical communication system 100a cannot transmit and receive signals at low cost.

(Second embodiment)
The main difference between the second embodiment and the first embodiment is that each signal (each narrowband signal) with a bandwidth "W" is input to the optical transmitter. In the second embodiment, differences from the first embodiment will be mainly explained.

FIG. 5 is a diagram showing a configuration example of the optical communication system 1b in the second embodiment. The optical communication system 1b is a system that communicates using optical signals. The optical communication system 1b includes an optical transmitter 2b, a transmission line 3, and an optical receiver 4b.

The optical transmitter 2b includes a first oscillator 21, a second oscillator 22, a batch converter 23, a frequency converter 24, a batch converter 25, a frequency converter 26, an adder 27, and a light intensity modulator. A container 28 is provided. The batch conversion unit 23 includes a phase modulator 231 and a photodetector 232. The batch conversion unit 25 includes a phase modulator 251 and a photodetector 252. Here, the first signal system batch converter 23 shares the first oscillator 21 and the second oscillator 22 with the second signal system batch converter 25.

The optical receiver 4b includes a photodetector 40, a bandpass filter 41, a delay detector 42, a low-pass filter 43, a bandpass filter 45, a frequency inverse converter 46, and a delay detector 47. , a low-pass filter 48 and a frequency inverse converter 49.

Next, details of the optical transmitter 2b will be explained, focusing on the differences from the optical transmitter 2a in the first embodiment.
In the first signal system, a narrowband signal (first narrowband signal) having a bandwidth of "W" is inputted to the phase modulator 231 from, for example, a headend device (not shown). The center frequency of this narrowband signal is, for example, "A". The phase modulator 231 generates a phase-modulated optical signal using a narrowband signal with a bandwidth of "W" and a laser beam with a first oscillation frequency.

In the second signal system, a narrowband signal (second narrowband signal) with a bandwidth "W" is inputted to the frequency converter 24 from, for example, a headend device (not shown). The center frequency of this narrowband signal is, for example, a predetermined center frequency different from "A" (eg, frequency "B"). The frequency converter 24 converts a narrowband signal having a bandwidth "W" and a predetermined center frequency into a narrowband signal having a bandwidth "W" and a center frequency "A". The frequency converter 24 outputs a narrowband signal (third narrowband signal) having a bandwidth “W” and a center frequency “A” to the phase modulator 251.

Next, details of the optical receiving device 4b will be explained, focusing on the differences from the optical receiving device 4a in the first embodiment.
The low-pass filter 43 removes high frequency components of the narrowband signal having a bandwidth "W" and a center frequency "A". The low-pass filter 43 outputs a narrowband signal with a bandwidth "W" and a center frequency "A" to a predetermined device (not shown). The predetermined device is, for example, a display device. The frequency inverse converter 49 removes high frequency components of the narrowband signal having a bandwidth "W" and a predetermined center frequency. The low-pass filter 43 outputs a narrowband signal having a bandwidth "W" and a predetermined center frequency (for example, a frequency "B") to a predetermined device (not shown).

Next, an example of the operation of the optical communication system 1b will be explained.
FIG. 6 is a flowchart showing an example of the operation of the optical transmitter 2b in the second embodiment. Each process from step S301 to step S308 is similar to each process from step S102 to step S109 illustrated in FIG.

FIG. 7 is a flowchart showing an example of the operation of the optical receiving device 4b in the second embodiment. Each process from step S401 to step S309 is similar to each process from step S201 to step S209 illustrated in FIG.

As described above, compared to the optical transmitter 2a of the optical communication system 1a of the first embodiment, the optical transmitter 2b of the optical communication system 1b has two frequency division multiplexed signals with a bandwidth of "W". If the signals are input to the optical transmitter 2b in parallel in a system, the band divider 20 is not necessary. Further, compared to the optical receiving device 4a of the optical communication system 1a of the first embodiment, the optical multiplexer 44 is not necessary in the optical receiving device 4b of the optical communication system 1b.

As a result, it is possible to transmit and receive frequency division multiplexed signals (a plurality of narrowband signals corresponding to a wideband signal) with a bandwidth of "W" transmitted in each signal system at low cost.

<Comparative example with the second embodiment>
FIG. 8 is a diagram showing a configuration example of an optical communication system 100b in a comparative example with the second embodiment. Optical communication system 100b is a comparative example with optical communication system 1b. The optical communication system 100b includes an optical transmitter 200b, a transmission line 3, and an optical receiver 400b. The optical transmitter 200b is a comparative example with the optical transmitter 2b. Optical receiving device 400b is a comparative example with optical receiving device 4b.

The optical transmitter 200b includes a batch conversion section 230, a frequency converter 24, a batch conversion section 250, a light intensity modulator 28-1, a light intensity modulator 28-2, and a multiplexer 29. The batch conversion unit 230 includes a phase modulator 231, a photodetector 232, a first oscillator 21-1, and a second oscillator 22. The batch conversion unit 250 includes a phase modulator 251, a photodetector 252, a first oscillator 21-2, and a third oscillator 30. Here, the first signal system batch conversion section 230 and the second signal system batch conversion section 250 share the first oscillator 21-1, the first oscillator 21-2, the second oscillator 22, and the third oscillator 30. do not.

The optical receiver 400b includes an optical demultiplexer 50, a wavelength division multiplex filter 51, a wavelength division multiplex filter 52, a photodetector 40-1, a photodetector 40-2, and a delay detector 42. , a low-pass filter 43, a multiplexer 44, a delayed detector 47, a low-pass filter 48, and a frequency inverse converter 49.

Next, details of the optical transmitter 200b will be explained, focusing on the differences from the optical transmitter 2b in the second embodiment.
In the second signal system, the first oscillator 21-2 outputs laser light at the first oscillation frequency to the phase modulator 251. The phase modulator 251 generates a phase-modulated optical signal using a narrowband signal having a bandwidth "W" and a center frequency "B" and a laser beam having a second oscillation frequency. The third oscillator 30 is a laser oscillator with a third oscillation frequency, and is, for example, a narrow linewidth laser diode. The third oscillator 30 outputs laser light at a third oscillation frequency to the photodetector 252. The photodetector 252 (photodiode) converts the phase-modulated optical signal into a second FM signal "S _FM2 (t)" (electrical signal) using a laser beam of the third oscillation frequency. Photodetector 252 outputs the second FM signal to optical intensity modulator 28-2. The optical intensity modulator 28-2 outputs the optical intensity modulated second FM signal to the multiplexer 29.

Note that the center frequency of the first FM signal after FM batch conversion in the comparative example with the second embodiment is the difference (absolute value) between the first oscillation frequency and the second oscillation frequency. Similarly, the center frequency of the second FM signal after FM batch conversion in the comparative example with the second embodiment is the difference (absolute value) between the first oscillation frequency and the third oscillation frequency.

The multiplexer 29 generates a wavelength multiplexed signal by multiplexing the optical intensity modulated first FM signal and the optical intensity modulated second FM signal. The multiplexer 29 uses an optical signal to transmit a wavelength multiplexed signal to the optical receiver 400b.

Next, details of the optical receiving device 400b will be explained, focusing on the differences from the optical receiving device 4b in the second embodiment.
An optical signal (wavelength multiplexed signal) including the first FM signal and the second FM signal is input from the transmission line 3 to the optical demultiplexer 50 (optical splitter). The optical demultiplexer 50 outputs an optical signal including the first FM signal and the second FM signal to the wavelength division multiplex filter 51 and the wavelength division multiplex filter 52.

As described above, the optical communication system 100b of the comparative example with the second embodiment cannot transmit and receive signals at low cost.

(Hardware configuration example)
FIG. 9 is a diagram showing an example of the hardware configuration of an optical communication device in each embodiment. The hardware configuration example of the optical communication device 101 illustrated in FIG. This corresponds to an example of the hardware configuration of the optical transmitter 2b of the second embodiment and an example of the hardware configuration of the optical receiver 4b of the second embodiment.

Some or all of the functional units of the optical communication device 101 are implemented by a processor 102 such as a CPU (Central Processing Unit), a storage device 104 having a non-volatile recording medium (non-temporary recording medium), and a memory 103. It is realized as software by executing a program stored in . The program may be recorded on a computer-readable recording medium. A computer-readable recording medium is a storage medium such as a flexible disk, a magneto-optical disk, a ROM (Read Only Memory), a CD-ROM (Compact Disc Read Only Memory), or a hard disk built into a computer system. It is a non-temporary recording medium such as a device. The communication unit 105 executes optical communication processing using predetermined optical equipment.

Some or all of the functional units of the optical communication device 101 may be implemented 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). It may be realized using hardware including an electronic circuit or circuitry.

Although the embodiments of the present invention have been described above in detail with reference to the drawings, the specific configuration is not limited to these embodiments, and includes designs within the scope of the gist of the present invention.

The present invention is applicable to systems that communicate using optical signals.

1a, 1b... Optical communication system, 2a, 2b... Optical transmitting device, 3... Transmission line, 4a, 4b... Optical receiving device, 20... Band splitter, 21... First oscillator, 22... Second oscillator, 23... All at once Conversion unit, 24... Frequency converter, 25... Bulk conversion unit, 26... Frequency converter, 27... Adder, 28... Light intensity modulator, 29... Multiplexer, 30... Third oscillator, 40... Photodetector , 41... Bandpass filter, 42... Delayed detector, 43... Low pass filter, 44... Multiplexer, 45... Bandpass filter, 46... Frequency inverse converter, 47... Delayed detector, 48... Low-pass Pass filter, 49... Frequency inverter, 50... Optical demultiplexer, 51... Wavelength division multiplex filter, 52... Wavelength division multiplex filter, 100a, 100b... Optical communication system, 101... Optical communication device, 102... Processor, 103...Memory, 104...Storage device, 105...Communication unit, 200a, 200b...Optical transmitter, 230...Batch conversion unit, 231...Phase modulator, 232...Photodetector, 250...Batch conversion unit, 251... Phase modulator, 252...photodetector, 400a, 400b...optical receiving device

Claims

a first oscillator that generates a first laser beam having a first oscillation frequency;
a second oscillator that generates a second laser beam with a second oscillation frequency;
A first frequency modulated signal is obtained by performing frequency modulation batch conversion on a first narrow band signal having a predetermined narrow bandwidth and a first center frequency using the first laser beam and the second laser beam. a first batch conversion unit that generates
a first frequency converter that converts the second narrowband signal having the predetermined narrow bandwidth and the second center frequency into a third narrowband signal having the predetermined narrow bandwidth and the first center frequency;
a second batch conversion unit that generates a second frequency modulation signal by performing frequency modulation batch conversion on the third narrowband signal using the first laser light and the second laser light;
a second frequency converter that changes the frequency of the second frequency modulation signal so that the overlap between the first frequency modulation signal and the second frequency modulation signal on the frequency axis becomes small;
an adder that adds the second frequency modulated signal whose frequency has been changed and the first frequency modulated signal on a frequency axis;
an optical intensity modulator that generates an optical intensity modulated optical signal by performing optical intensity modulation on the addition result of the second frequency modulated signal whose frequency has been changed and the first frequency modulated signal; An optical transmitting device equipped with.
The optical transmitter according to claim 1, further comprising a band divider that divides a predetermined wideband signal into the first narrowband signal and the second narrowband signal on a frequency axis.
The second frequency converter converts the second frequency converter according to a second frequency conversion amount that is larger than the first frequency conversion amount such that an amount of interference between the first frequency modulation signal and the second frequency modulation signal becomes a predetermined amount. The optical transmitter according to claim 1 or 2, wherein the optical transmitter changes the frequency of a frequency modulated signal.
An optical transmission method performed by an optical transmission device, the method comprising:
generating a first laser beam having a first oscillation frequency;
generating a second laser beam having a second oscillation frequency;
A first frequency modulated signal is obtained by performing frequency modulation batch conversion on a first narrow band signal having a predetermined narrow bandwidth and a first center frequency using the first laser beam and the second laser beam. a step of generating
converting the second narrowband signal having the predetermined narrow bandwidth and the second center frequency into a third narrowband signal having the predetermined narrow bandwidth and the first center frequency;
generating a second frequency modulated signal by performing frequency modulation batch conversion on the third narrowband signal using the first laser beam and the second laser beam;
changing the frequency of the second frequency modulation signal so that the overlap between the first frequency modulation signal and the second frequency modulation signal on the frequency axis becomes small;
adding the second frequency modulated signal whose frequency has been changed and the first frequency modulated signal on a frequency axis;
and generating a light intensity modulated optical signal by performing light intensity modulation on the addition result of the second frequency modulated signal and the first frequency modulated signal, the frequency of which has been changed. Method.
An optical communication system comprising an optical transmitter and an optical receiver,
The optical transmitter includes:
a first oscillator that generates a first laser beam having a first oscillation frequency;
a second oscillator that generates a second laser beam with a second oscillation frequency;
A first frequency modulated signal is obtained by performing frequency modulation batch conversion on a first narrow band signal having a predetermined narrow bandwidth and a first center frequency using the first laser beam and the second laser beam. a first batch conversion unit that generates
a first frequency converter that converts the second narrowband signal having the predetermined narrow bandwidth and the second center frequency into a third narrowband signal having the predetermined narrow bandwidth and the first center frequency;
a second batch conversion unit that generates a second frequency modulation signal by performing frequency modulation batch conversion on the third narrowband signal using the first laser light and the second laser light;
a second frequency converter that changes the frequency of the second frequency modulation signal so that the overlap between the first frequency modulation signal and the second frequency modulation signal on the frequency axis becomes small;
an adder that adds the second frequency modulation signal whose frequency has been changed and the first frequency modulation signal on a frequency axis;
an optical intensity modulator that generates an optical intensity modulated optical signal by performing optical intensity modulation on the addition result of the second frequency modulated signal and the first frequency modulated signal whose frequency has been changed; have,
The optical receiving device includes:
a photodetector that converts the light intensity modulated optical signal into the second frequency modulated signal and the first frequency modulated signal whose frequency has been changed;
a first bandpass filter that extracts the first frequency modulation signal from the second frequency modulation signal whose frequency has been changed and the first frequency modulation signal;
a first delay detector that generates the first narrowband signal by performing delay detection processing on the extracted first frequency modulation signal;
a first low-pass filter that removes high frequency components of the first narrowband signal;
a second bandpass filter that extracts the second frequency modulated signal whose frequency has been changed from the second frequency modulated signal whose frequency has been changed and the first frequency modulated signal;
a first frequency inverse converter that generates the second frequency modulation signal by making the frequency of the second frequency modulation signal whose frequency has been changed the same as the frequency of the first frequency modulation signal;
a second delay detector that generates the third narrowband signal by performing delay detection processing on the second frequency modulation signal;
a second low-pass filter that removes high frequency components of the third narrowband signal;
a second frequency inverse converter that generates the second narrowband signal based on the third narrowband signal from which high frequency components have been removed;
Optical communication system.
The optical transmitter further includes a band divider that divides the predetermined wideband signal into the first narrowband signal and the second narrowband signal on the frequency axis,
6. The optical communication system according to claim 5, wherein the optical receiver further includes a multiplexer that multiplexes the first narrowband signal from which high frequency components have been removed and the second narrowband signal.
The second frequency converter converts the second frequency converter according to a second frequency conversion amount that is larger than the first frequency conversion amount such that an amount of interference between the first frequency modulation signal and the second frequency modulation signal becomes a predetermined amount. The optical communication system according to claim 5 or 6, wherein the frequency of the frequency modulated signal is changed.