JP7723334B2 - Optical transmitting device, optical transmitting method, and optical communication system - Google Patents

Description

The present invention relates to an optical transmitting device, an optical transmitting method, and an optical communication system.
This application claims priority based on international application PCT/JP2022/033739 filed on September 8, 2022, the contents of which are incorporated herein by reference.

Optical communication systems that batch convert Frequency Division Multiplexing (FDM) signals into Frequency Modulation (FM) signals have been introduced into video signal distribution systems (see Non-Patent Document 1). Hereinafter, batch conversion to Frequency Modulation signals will be referred to as "FM batch conversion." The video signals in Non-Patent Document 1 are multi-channel video signals that include cable television signals (bandwidth: 90-770 MHz), right-handed circularly polarized intermediate frequency signals from broadcasting and communication satellites (BS/CS right-handed IF signals) (bandwidth: 1.0-2.1 GHz), and left-handed circularly polarized intermediate frequency signals from broadcasting and communication satellites (BS/CS left-handed IF signals) (2.2-3.2 GHz).

R.Miyatake, T.Shitaba, A.Tanabe, Y.Fukada, T.Yoshida, “Optical transmission experiment on FM conversion method with wideband phase modulation,” IEICE Communications Express, Vol.1, 1-6, 2021.

In optical receiving devices in optical communication systems that perform FM batch conversion, delay detection is used as the demodulation method for frequency-division multiplexed signals, making it difficult to expand the bandwidth of the optical signal beyond the current bandwidth (W = 3.2 GHz). For this reason, for example, when transmitting an optical signal (broadband signal) with a bandwidth of "2W," which is twice the bandwidth "W," the optical communication system simply has two signal systems in parallel. The optical transmitting device in the optical communication system transmits a wavelength-multiplexed signal of a frequency-modulated signal (FM signal) to the optical receiving device for each signal system with bandwidth "W."

However, parallelization of signal systems doubles the number of oscillators (laser diodes) and optical intensity modulators in optical transmitting devices in optical communication systems. Furthermore, doubles the number of photodetectors (photodiodes) in optical receiving devices in optical communication systems. As a result, there is a problem in that FM batch-converted wideband signals cannot be transmitted and received at low cost.

In view of the above circumstances, the present invention aims to provide an optical transmitting device, an optical transmitting method, and an optical communication system that are capable of transmitting and receiving FM batch-converted wideband signals at low cost.

One aspect of the present invention is a system including a first batch conversion unit that generates a first frequency-modulated signal by performing frequency modulation batch conversion on a first narrowband signal having a predetermined narrow bandwidth and a first center frequency using a first laser beam having a first oscillation frequency and a second laser beam having a second oscillation frequency; a first frequency converter that converts the second narrowband signal having the predetermined narrow bandwidth and a second center frequency into a third narrowband signal having the predetermined narrow bandwidth and the first center frequency; and a second frequency converter that converts the third narrowband signal by performing frequency modulation batch conversion on the third narrowband signal using the first laser beam and the second laser beam or a third laser beam having a third oscillation frequency. an adder that adds the second frequency-modulated signal and the first frequency-modulated signal on a frequency axis; and an optical intensity modulator that generates an optical intensity-modulated optical signal by performing optical intensity modulation on the sum of the frequency-changed second frequency-modulated signal and the first frequency-modulated signal, wherein the center frequency of the first frequency-modulated signal is equal to the absolute value of the difference between the first oscillation frequency and the second oscillation frequency, and the center frequency of the second frequency-modulated signal is equal to the absolute value of the difference between the first oscillation frequency and the second oscillation frequency or the third oscillation frequency.

One aspect of the present invention is an optical transmission method executed by an optical transmitting device, which includes the steps of: generating a first frequency-modulated signal by performing frequency modulation batch conversion on a first narrowband signal having a predetermined narrow bandwidth and a first center frequency using a first laser beam having a first oscillation frequency and a second laser beam having a second oscillation frequency; converting the second narrowband signal having the predetermined narrow bandwidth and a second center frequency into a third narrowband signal having the predetermined narrow bandwidth and the first center frequency; and performing frequency modulation batch conversion on the third narrowband signal using the first laser beam and either the second laser beam or a third laser beam having a third oscillation frequency. a step of generating a second frequency-modulated signal by adding the second frequency-modulated signal and the first frequency-modulated signal on a frequency axis; and a step of generating an optical intensity-modulated optical signal by performing optical intensity modulation on the sum of the frequency-changed second frequency-modulated signal and the first frequency-modulated signal, wherein a center frequency of the first frequency-modulated signal is equal to the absolute value of the difference between the first oscillation frequency and the second oscillation frequency, and a center frequency of the second frequency-modulated signal is equal to the absolute value of the difference between the first oscillation frequency and the second oscillation frequency or the third oscillation frequency.

One aspect of the present invention is an optical communication system comprising an optical transmitting device and an optical receiving device, wherein the optical transmitting device comprises a first batch conversion unit that generates a first frequency-modulated signal by performing frequency modulation batch conversion on a first narrowband signal having a predetermined narrow bandwidth and a first center frequency using a first laser beam having a first oscillation frequency and a second laser beam having a second oscillation frequency; a first frequency converter that converts the second narrowband signal having the predetermined narrow bandwidth and a second center frequency into a third narrowband signal having the predetermined narrow bandwidth and the first center frequency; and a third frequency converter that converts the second narrowband signal having the predetermined narrow bandwidth and the first center frequency into a third narrowband signal having the predetermined narrow bandwidth and the first center frequency using the first laser beam and the second laser beam or the third laser beam having a third oscillation frequency. a second batch conversion unit that generates a second frequency-modulated signal by performing frequency modulation batch conversion on a third narrowband signal; an adder that adds the second frequency-modulated signal and the first frequency-modulated signal on a frequency axis; and an optical intensity modulator that generates an optical intensity-modulated optical signal by performing optical intensity modulation on the result of adding the frequency-changed second frequency-modulated signal and the first frequency-modulated signal, and the optical receiving device includes a photodetector that converts the optical intensity-modulated optical signal into the frequency-changed second frequency-modulated signal and the first frequency-modulated signal, and an adder that converts the frequency-changed second frequency-modulated signal and the a first bandpass filter that extracts the first frequency-modulated signal from a first frequency-modulated signal; a first differential detector that generates the first narrowband signal by performing differential detection processing on the extracted first frequency-modulated signal; a first low-pass filter that removes high-frequency components of the first narrowband signal; a second bandpass filter that extracts the frequency-shifted second frequency-modulated signal from the frequency-shifted second frequency-modulated signal and the first frequency-modulated signal; and a first low-pass filter that generates the second frequency-modulated signal by making the frequency of the frequency-shifted second frequency-modulated signal the same as the frequency of the first frequency-modulated signal. an optical communication system comprising: a frequency inverter; a second differential detector that generates the third narrowband signal by performing differential detection processing on the second frequency-modulated signal; a second low-pass filter that removes high-frequency components from the third narrowband signal; and a second frequency inverter that generates the second narrowband signal based on the third narrowband signal from which the high-frequency components have been removed; wherein the center frequency of the first frequency-modulated signal is equal to the absolute value of the difference between the first oscillation frequency and the second oscillation frequency, and the center frequency of the second frequency-modulated signal is equal to the absolute value of the difference between the first oscillation frequency and the second oscillation frequency or the third oscillation frequency.

This invention makes it possible to transmit and receive FM batch converted wideband signals at low cost.

FIG. 1 is a diagram illustrating an example of the configuration of an optical communication system according to a first embodiment. 4 is a flowchart illustrating an example of the operation of the optical transmitting device in the first embodiment. 4 is a flowchart illustrating an example of the operation of the optical receiving device in the first embodiment. FIG. 10 is a diagram illustrating an example of the configuration of an optical communication system in a comparative example to the first embodiment. FIG. 10 is a diagram illustrating a configuration example of an optical communication system according to a second embodiment. 10 is a flowchart illustrating an example of the operation of the optical transmitting device in the second embodiment. 10 is a flowchart illustrating an example of the operation of the optical receiving device according to the second embodiment. FIG. 10 is a diagram illustrating an example of the configuration of an optical communication system in a comparative example to the second embodiment. FIG. 10 is a diagram illustrating an example of the configuration of an optical communication system according to a third embodiment. FIG. 2 is a diagram illustrating an example of a hardware configuration of an optical communication device in each embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the accompanying drawings.
(First embodiment)
1 is a diagram showing an example of the configuration of an optical communication system 1a according to a 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 transmitting device 2a (optical line termination) is, for example, a V-OLT (Video-Optical Line Terminal). The optical transmitting device 2a comprises a band splitter 20, a first oscillator 21, a second oscillator 22, a batch conversion unit 23, a frequency converter 24, a batch conversion unit 25, a frequency converter 26, an adder 27, and an optical intensity modulator 28. The batch conversion unit 23 comprises a phase modulator 231 and a photodetector 232. The batch conversion unit 25 comprises a phase modulator 251 and a photodetector 252. Here, the batch conversion unit 23 of the first signal system shares the first oscillator 21 and second oscillator 22 with the batch conversion unit 25 of the second signal system. The transmission path 3 is an optical transmission path, and includes, for example, an optical fiber.

The optical receiving device 4a (optical line terminal) is, for example, a V-ONU (Video-Optical Network Unit). The optical receiving device 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, a frequency inverse converter 46, a delay detector 47, a low-pass filter 48, and a frequency inverse converter 49.

First, the optical transmitter 2a will be described in detail.
A signal with a bandwidth of "2W" (wideband frequency division multiplexed signal) is input to the band splitter 20 from, for example, a headend device (not shown). The band splitter 20 divides the signal with bandwidth "2W" on the frequency axis into signals (narrowband signals) with bandwidths pro rata-divided at any ratio. For example, the band splitter 20 may divide the signal with bandwidth "2W" equally on the frequency axis, or may divide the signal with bandwidth "2W" unequally at any ratio. In the following, the band splitter 20 will, as an example, equally divide the signal with bandwidth "2W" on the frequency axis into signals with bandwidth "W".

The band splitter 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 splitter 20 outputs a narrowband signal (narrowband frequency division multiplexed signal) with 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, for example, a narrow linewidth laser diode. The first oscillator 21 outputs laser light with the 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, for example, a narrow linewidth laser diode. The second oscillator 22 outputs laser light with the second oscillation frequency (second laser light) to the photodetector 232 and the photodetector 252.

In the first signal system, the batch conversion unit 23 is a functional unit that performs FM batch conversion (frequency modulation batch conversion). The batch conversion unit 23 performs FM batch conversion on the narrowband signal input from the band splitter 20 to generate a first FM signal “S _FM1 (t).”

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 laser light of a first oscillation frequency. The photodetector 232 (photodiode) converts the phase-modulated optical signal into a first FM signal "S _FM1 (t)" (electrical signal) using laser light of a second oscillation frequency. The photodetector 232 outputs the first FM signal to the 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 (third narrowband signal) with a bandwidth "W" and a center frequency "A". Here, the frequency converter 24 converts the frequency so that the amount of optical leakage is below a threshold or so that the signal-to-interference signal ratio of the optical signal is below a certain level. The frequency converter 24 outputs the narrowband signal with a bandwidth "W" and a center frequency "A" to the phase modulator 251.

In the second signal system, the batch converter 25 is a functional unit that performs frequency modulation batch conversion (FM batch conversion). The batch converter 25 performs FM batch 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 with 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 the laser beam having the second oscillation frequency. The photodetector 252 outputs the second FM signal to the 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 changes the frequency of the second FM signal so that the overlap between the first FM signal "S _FM1 (t)" and the second FM signal "S _FM2 '(t)" on the frequency axis is sufficiently small (so that the degradation of communication quality due to interference between the FM signals is sufficiently small). 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 with the changed frequency.

The method for determining the frequency conversion amount of the second FM signal is not limited to a specific method. For example, it is considered that the greater the distance between the first FM signal "S _FM1 (t)" and the second FM signal "S _{FM2 '} (t)" on the frequency axis, the smaller the amount of interference. Therefore, the frequency converter 26 may determine, as the amount of frequency conversion of the second FM signal, a frequency conversion amount (second _frequency conversion amount) that is greater than the frequency conversion amount (first frequency conversion amount) that results in a predetermined amount "α" of interference between the first FM signal "S FM1 (t)" and the second FM signal "S FM2 '(t)." The predetermined amount "α" is determined in advance based on, for example, the specifications of communication quality. This allows the amount of interference to be reliably suppressed in accordance with the frequency conversion amount optimized based on the specifications of communication quality. Alternatively, for example, the frequency converter 26 may uniformly determine, as the amount of frequency conversion of the second FM signal, a frequency conversion amount that is predetermined based on, for example, the specifications of communication quality.

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). As a result, the optical intensity modulator 28 generates an optical intensity modulated optical signal. The optical intensity modulator 28 outputs the optical intensity modulated optical signal to the transmission path 3. The transmission path 3 transmits the optical intensity modulated optical signal (broadband signal) to the optical receiving device 4a.

Next, the optical receiving device 4a will be described in detail.
An optical intensity modulated optical signal (broadband signal) is input to the photodetector 40 from the transmission path 3. That is, an optical signal (wavelength multiplexed signal) including a first FM signal and a second FM signal is input to the photodetector 40 from the transmission path 3. The photodetector 40 converts the optical intensity modulated optical signal into an electrical signal including the first FM signal "S _FM1 (t)" and the second FM signal "S _FM2 '(t)." The photodetector 40 outputs the converted electrical signal to the bandpass filter 41 and the bandpass filter 45.

In the first signal system, the bandpass filter 41 extracts the first FM signal from an electrical signal containing the first FM signal and the second FM signal. The differential detector 42 performs differential detection processing (demodulation processing) on the extracted first FM signal. As a result, the differential detector 42 generates a narrowband signal (first narrowband signal) with a bandwidth "W" and a center frequency "A". The low-pass filter 43 removes high-frequency components from the narrowband signal with a bandwidth "W" and a center frequency "A".

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

In the second signal system, the bandpass filter 45 extracts the second FM signal "S _FM2 '(t)" (second narrowband signal) from the electrical signal including the first FM signal "S _FM1 (t)" and the second FM signal "S _FM2 '(t)." The frequency inverter 46 generates the second FM signal "S _FM2 (t)" by making 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.

In the second signal system, the differential detector 47 performs differential detection processing (demodulation processing) on the second FM signal "S _FM2 (t)." As a result, the differential detector 47 generates a narrowband signal (third narrowband signal) having a bandwidth "W" and a center frequency "A." The low-pass filter 48 removes high-frequency components from the narrowband signal having a bandwidth "W" and a center frequency "A." The frequency inverter 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." In other words, the frequency inverter 49 converts the narrowband signal having a bandwidth "W" and a center frequency "A" into a narrowband signal having a bandwidth "W" and a center frequency "B." The frequency inverter 49 outputs the narrowband signal having a bandwidth "W" and a center frequency "B" to the combiner 44.

In addition, the frequency converter 24, the frequency converter 26, the frequency inverter 46, and the frequency inverter 49 may each be provided in the first signal system instead of the second signal system.

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

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 laser light of 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 laser light of a second oscillation frequency (step S103: first optical detection process). Each functional unit of the first signal system proceeds to step S108.

In the second signal system, the frequency converter 24 converts a narrowband signal with a bandwidth of "W" and a center frequency of "B" into a narrowband signal with a bandwidth of "W" and a center frequency of "A" (step S104: first frequency conversion process). The phase modulator 251 generates a phase-modulated optical signal using the narrowband signal with a bandwidth of "W" and a center frequency of "B" and laser light of a second oscillation frequency (step S105: first phase modulation process). The photodetector 252 converts the phase-modulated optical signal into a second FM signal using laser light of the second oscillation frequency (step S106: second optical detection 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 is reduced (step S107: second frequency conversion process).

In the common signal system, the adder 27 adds the first FM signal and the frequency-shifted second FM signal (step S108: addition process). The optical intensity modulator 28 performs optical intensity modulation on the added FM signal (step S109: optical intensity modulation process).

Figure 3 is a flowchart showing an example of the operation of the optical receiving device 4a in the first embodiment. The optical detector 40 converts the optical 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 optical detection process).

In the first signal system, the bandpass filter 41 extracts the first FM signal from an electrical signal containing the first FM signal and the frequency-shifted second FM signal (step S202: first bandpass filter processing). The differential detector 42 performs differential detection processing on the extracted first FM signal (step S203: first differential detection processing). The low-pass filter 43 removes high-frequency components from the narrowband signal with bandwidth "W" and center frequency "A" (step S204: first low-pass processing).

In the second signal system, the bandpass filter 45 extracts the frequency-shifted second FM signal from an electrical signal containing the first FM signal and the frequency-shifted second FM signal (step S205: second bandpass filter processing). The frequency inverse converter 46 sets the center frequency of the frequency-shifted second FM signal to the same as the center frequency of the first FM signal (step S206: first inverse conversion processing). The differential detector 47 performs differential detection processing on the second FM signal (step S207: second differential detection processing). The low-pass filter 48 removes high-frequency components from the narrowband signal with bandwidth "W" and center frequency "A" (step S208: second low-pass processing). The frequency inverse converter 49 generates a narrowband signal with bandwidth "W" and center frequency "B" based on the narrowband signal with bandwidth "W" and center frequency "A" (step S209: second inverse conversion processing).

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

As described above, in the optical transmission device 2a of the optical communication system 1a, the band divider 20 divides a predetermined wideband signal on the frequency axis into a first narrowband signal having a predetermined narrow bandwidth "W" and a first center frequency "A" and a second narrowband signal having a predetermined narrow bandwidth "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 converter 23 (first batch converter) uses the first laser beam and the second laser beam to perform FM batch conversion on the first narrowband signal having the predetermined narrow bandwidth "W" and the first center frequency "A," thereby generating a first FM signal "S _FM1 (t)." The frequency converter 24 (first frequency converter) converts the second narrowband signal having the predetermined narrow bandwidth "W" and the second center frequency "B" into a third narrowband signal having the predetermined narrow bandwidth "W" and the first center frequency "A." The batch conversion unit 25 (second batch conversion unit) performs FM batch conversion on the third narrowband signal using the first laser light and the second laser light, thereby generating a second FM signal "S _FM2 (t)." 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 is reduced. The adder 27 adds the frequency-changed second FM signal "S _FM2 '(t)" and the first FM signal "S _FM1 (t)" on the frequency axis. The optical intensity modulator 28 performs optical intensity modulation on the result of adding the frequency-changed second FM signal and the first FM signal, thereby generating an optical intensity-modulated optical signal.

In the optical receiving device 4a of the optical communication system 1a, the photodetector 40 converts the optical intensity-modulated optical signal into a frequency-shifted second FM signal and a first FM signal. The bandpass filter 41 (first bandpass filter) extracts the first FM signal from the frequency-shifted second FM signal and the first FM signal. The differential detector 42 (first differential detector) generates a first narrowband signal by performing differential detection processing on the extracted first FM signal. The low-pass filter 43 (first low-pass filter) removes high-frequency components from the first narrowband signal. The bandpass filter 45 (second bandpass filter) extracts the frequency-shifted second FM signal from the frequency-shifted second FM signal and the first FM signal. The frequency inverse converter 46 (first frequency inverse converter) generates the second FM signal by matching the frequency of the frequency-shifted second FM signal to the frequency of the first FM signal. The differential detector 47 (second differential detector) generates a third narrowband signal by performing differential detection processing on the second FM signal. The low-pass filter 48 (second low-pass filter) removes high-frequency components from the third narrowband signal. The frequency inverter 49 (second frequency inverter) generates a second narrowband signal based on the third narrowband signal from which the high-frequency components have been removed. The combiner 44 combines the first narrowband signal from which the high-frequency components have been removed and the second narrowband signal.

In this way, the optical transmitting device 2a divides the wideband signal to be transmitted into each narrowband signal. The optical transmitting device 2a performs FM batch conversion on each narrowband signal. The optical transmitting device 2a combines each narrowband FM signal on the frequency axis. The optical transmitting device 2a performs optical intensity modulation on the combined FM signal. The optical transmitting device 2a transmits the optical intensity modulated FM signal to the optical receiving device 4a using the transmission path 3. The optical receiving device 4a separates the combined FM signal into each narrowband FM signal. The optical receiving device 4a performs a predetermined demodulation process on each narrowband FM signal.

Here, sharable functional units are shared. For example, in the optical transmitting device 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, simply by adding simple processing units (e.g., an optical demultiplexer, wavelength division multiplexing filter, and multiplexer, etc.), it becomes possible to receive FM batch-converted wideband signals (multiplexed FM signals).

This makes it possible to transmit and receive FM batch-converted wideband signals at low cost. It also makes it possible to reduce the size of the optical transmitting device 2a and the optical receiving device 4a.

Comparative Example with First Embodiment
4 is a diagram showing an example of the configuration of an optical communication system 100a in comparison 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 transmitting device 200a, a transmission line 3, and an optical receiving device 400a. The optical transmitting device 200a is a comparative example with the optical transmitting device 2a. The optical receiving device 400a is a comparative example with the optical receiving device 4a.

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

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

Next, the optical transmitter 200a will be described in detail, focusing on the differences from the optical transmitter 2a.
In the first signal system, the batch conversion unit 230 is a functional unit that performs FM batch conversion (frequency modulation batch conversion). The batch conversion unit 230 performs FM batch conversion on the narrowband signal input from the band splitter 20 to generate a first FM signal “S _FM1 (t).”

In the first signal system, the first oscillator 21-1 outputs laser light of 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) having a bandwidth "W" and a center frequency "A" and the laser light of the first oscillation frequency. The second oscillator 22 outputs laser light of 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 the laser light 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) having a bandwidth "W" and a center frequency "B" into a narrowband signal (third narrowband signal) having a bandwidth "W" and a center frequency "A". The frequency converter 24 outputs the 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 performs FM batch conversion (frequency modulation batch conversion). The batch conversion unit 250 performs FM batch conversion on the narrowband signal input from the frequency converter 24 to generate a second FM signal “S _FM2 (t).”

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

Note that the center frequency of the first FM signal after FM batch conversion in the comparative example to 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 to 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 transmits the wavelength-multiplexed signal to the optical receiving device 400a using the optical signal.

Next, the optical receiving device 400a will be described in detail, focusing on the differences from the optical receiving device 4a.
An optical signal (wavelength multiplexed signal) including a first FM signal and a second FM signal is input to the optical demultiplexer 50 (optical splitter) from the transmission path 3. The optical demultiplexer 50 outputs the optical signal including the first FM signal and the second FM signal to the wavelength division multiplexing filter 51 and the wavelength division multiplexing filter 52.

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

The differential detector 42 performs differential detection processing (demodulation processing) on the electrical signal containing the first FM signal. The low-pass filter 43 removes high-frequency components from the narrowband signal with bandwidth "W" and center frequency "A". The combiner 44 adds the narrowband signal with bandwidth "W" and center frequency "A" and the narrowband signal with bandwidth "W" and center frequency "B".

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

The differential detector 47 performs differential detection processing (demodulation processing) on the electrical signal containing the second FM signal. The low-pass filter 48 removes the high-frequency components of the narrowband signal with bandwidth "W" and center frequency "A". The frequency inverse converter 49 returns the center frequency of the second FM signal from which the high-frequency components have been removed to "B". The frequency inverse converter 49 outputs the narrowband signal with bandwidth "W" and center frequency "B" to the combiner 44.

As such, in the optical communication system 100a, which is a comparative example to the first embodiment, two signal systems are simply provided in parallel. As a result, the optical communication system 100a cannot transmit and receive signals at low cost.

Second Embodiment
The second embodiment is different from the first embodiment in that each signal (narrowband signal) of bandwidth "W" is input to the optical transmitter. The second embodiment will be described focusing on the differences from the first embodiment.

Figure 5 is a diagram showing an example configuration of an 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 transmitting device 2b, a transmission path 3, and an optical receiving device 4b.

The optical transmitting device 2b includes a first oscillator 21, a second oscillator 22, a batch conversion unit 23, a frequency converter 24, a batch conversion unit 25, a frequency converter 26, an adder 27, and an optical 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 batch conversion unit 23 of the first signal system shares the first oscillator 21 and second oscillator 22 with the batch conversion unit 25 of the second signal system.

The optical receiving device 4b comprises 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, a delay detector 47, a low-pass filter 48, and a frequency inverse converter 49.

Next, the optical transmitter 2b will be described in detail, 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, for example, "W" is input 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 the narrowband signal having a bandwidth of "W" and laser light having a first oscillation frequency.

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

Next, the optical receiving device 4b will be described in detail, focusing on the differences from the optical receiving device 4a in the first embodiment.
The low-pass filter 43 removes high-frequency components from the narrow-band signal having a bandwidth "W" and a center frequency "A". The low-pass filter 43 outputs the narrow-band signal having 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 inverter 49 removes high-frequency components from the narrow-band signal having a bandwidth "W" and a predetermined center frequency. The low-pass filter 43 outputs the narrow-band signal having a bandwidth "W" and a predetermined center frequency (for example, frequency "B") to a predetermined device (not shown).

Next, an example of the operation of the optical communication system 1b will be described.
6 is a flowchart showing an example of the operation of the optical transmitter 2b in the second embodiment. The processes from step S301 to step S308 are the same as the processes from step S102 to step S109 shown in FIG.

Figure 7 is a flowchart showing an example of the operation of the optical receiving device 4b in the second embodiment. The processes from step S401 to step S309 are the same as the processes from step S201 to step S209 illustrated in Figure 3.

As described above, in comparison with the optical transmitting device 2a of the optical communication system 1a of the first embodiment, in the optical transmitting device 2b of the optical communication system 1b, when a frequency division multiplexed signal of bandwidth "W" is input to the optical transmitting device 2b in parallel via two signal systems, the band splitter 20 is not required. Also, in comparison with the optical receiving device 4a of the optical communication system 1a of the first embodiment, in the optical receiving device 4b of the optical communication system 1b, the multiplexer 44 is not required.

This makes it possible to transmit and receive frequency division multiplexed signals (multiple narrowband signals equivalent to wideband signals) of bandwidth "W" transmitted by each signal system at low cost.

Comparative Example with Second Embodiment
8 is a diagram showing an example of the configuration of an optical communication system 100b as a comparative example to the second embodiment. The optical communication system 100b is a comparative example to the optical communication system 1b. The optical communication system 100b includes an optical transmitting device 200b, a transmission line 3, and an optical receiving device 400b. The optical transmitting device 200b is a comparative example to the optical transmitting device 2b. The optical receiving device 400b is a comparative example to the optical receiving device 4b.

The optical transmitting device 200b includes a batch conversion unit 230, a frequency converter 24, a batch conversion unit 250, an optical intensity modulator 28-1, an optical 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 batch conversion unit 230 for the first signal system and the batch conversion unit 250 for the second signal system do not share the first oscillator 21-1, the first oscillator 21-2, the second oscillator 22, and the third oscillator 30.

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

Next, the optical transmitter 200b will be described in detail, 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 of a first oscillation frequency to a phase modulator 251. The phase modulator 251 generates a phase-modulated optical signal using a narrowband signal with a bandwidth "W" and a center frequency "B" and laser light of a second oscillation frequency. The third oscillator 30 is a laser oscillator of the third oscillation frequency, such as a narrow-linewidth laser diode. The third oscillator 30 outputs the laser light of the third oscillation frequency to a photodetector 252. The photodetector 252 (photodiode) converts the phase-modulated optical signal into a second FM signal "S _FM2 (t)" (electrical signal) using the laser light of the third oscillation frequency. The photodetector 252 outputs the second FM signal to an optical intensity modulator 28-2. The optical intensity modulator 28-2 outputs the optical intensity-modulated second FM signal to a multiplexer 29.

Note that the center frequency of the first FM signal after FM batch conversion in the comparative example to 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 to 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 transmits the wavelength-multiplexed signal to the optical receiving device 400b using the optical signal.

Next, the optical receiving device 400b will be described in detail, focusing on the differences from the optical receiving device 4b in the second embodiment.
An optical signal (wavelength multiplexed signal) including a first FM signal and a second FM signal is input to the optical demultiplexer 50 (optical splitter) from the transmission path 3. The optical demultiplexer 50 outputs the optical signal including the first FM signal and the second FM signal to the wavelength division multiplexing filter 51 and the wavelength division multiplexing filter 52.

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

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

As such, the optical communication system 100b, which is a comparative example to the second embodiment, cannot transmit and receive signals at low cost.

(Third embodiment)
The third embodiment is different from the first and second embodiments mainly in that the optical transmitter includes an odd number of oscillators (for example, three) and that the optical transmitter does not include a frequency converter. The third embodiment will be described focusing on the differences from the first and second embodiments.

In the first and second embodiments, if even one of the two oscillators provided in the optical transmitting device fails, there is a problem in that both the first FM signal "S _FM1 (t)" and the second FM signal "S _FM2 '(t)" cannot be transmitted. If redundancy were simply implemented by doubling the number of oscillators to four, costs would increase. Therefore, in the third embodiment, tolerance to failures is improved while suppressing increases in costs.

Figure 9 is a diagram showing an example configuration of an optical communication system 1c in the third embodiment. The optical communication system 1c is a system that communicates using optical signals. The optical communication system 1c includes an optical transmitting device 2c, a transmission path 3, and an optical receiving device 4c.

The optical transmitting device 2c is, for example, a V-OLT. The optical transmitting device 2c includes a band splitter 20, a first oscillator 21, a second oscillator 22, a batch conversion unit 23, a frequency converter 24, a batch conversion unit 25, an adder 27, an optical intensity modulator 28, and a third oscillator 30. 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.

As such, the optical transmitting device 2c of the third embodiment has one less frequency converter and one more oscillator than the optical transmitting device 2a of the first embodiment. Therefore, the number of required elements and cost are not increased in the optical transmitting device 2c of the third embodiment compared to the optical transmitting device 2a of the first embodiment.

Here, the batch conversion unit 23 of the first signal system shares the first oscillator 21 of the first oscillator 21, second oscillator 22, and third oscillator 30 with the batch conversion unit 25 of the second signal system. The batch conversion unit 23 of the first signal system does not share the second oscillator 22 with the batch conversion unit 25 of the second signal system. The batch conversion unit 25 of the second signal system does not share the third oscillator 30 with the batch conversion unit 23 of the first signal system. In this way, since neither the second oscillator 22 nor the third oscillator 30 is shared, even if one of the second oscillator 22 or the third oscillator 30 fails, the FM signal is transmitted using the other oscillator.

The optical receiving device 4c (optical line terminal) is, for example, a V-ONU. The optical receiving device 4c includes a photodetector 40, a bandpass filter 41, a delay detector 42, a low-pass filter 43, a multiplexer 44, a bandpass filter 45, a frequency inverter 46, a delay detector 47, a low-pass filter 48, and a frequency inverter 49.

Next, we will explain the details of the optical transmitting device 2c, focusing on the differences from the optical transmitting device 2c in the first embodiment.

The first oscillator 21 is a laser oscillator with a first oscillation frequency “f _LD1 ”, and is, for example, a narrow linewidth laser diode. The first oscillator 21 outputs laser light with the 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 “f _LD2 ”, and is, for example, a narrow linewidth laser diode. The second oscillator 22 outputs laser light with the second oscillation frequency (second laser light) to the photodetector 232.

The third oscillator 30 is a laser oscillator with a second oscillation frequency “f _LD3 ”, and is, for example, a narrow linewidth laser diode. The third oscillator 30 outputs laser light with a third oscillation frequency (third laser light) to the photodetector 252.

In FM batch conversion, an FM signal is generated using a heterodyne detection method. The center frequency of the FM signal generated by the heterodyne detection method is the difference (absolute value) between the operating frequencies of the two oscillators used. Therefore, the center frequency of the first FM signal "S _FM1 (t)" after FM batch conversion is equal to the difference (absolute value) between the first oscillation frequency and the second oscillation frequency, "|f _LD1 - f _LD2 |". Similarly, in the third embodiment, the center frequency of the second FM signal "S _FM2 '(t)" after FM batch conversion is equal to the difference (absolute value) between the first oscillation frequency and the third oscillation frequency, "|f _LD1 - f _LD3 |".

The photodetector 232 (photodiode) converts the phase-modulated optical signal into a first FM signal “S _FM1 (t)” (electrical signal) using the laser light of the second oscillation frequency. The photodetector 232 outputs the first FM signal to the adder 27.

The photodetector 252 (photodiode) converts the phase-modulated optical signal into a second FM signal "S _FM2 '(t)" (electrical signal) using the laser light of the third oscillation frequency. The photodetector 252 outputs the second FM signal "S _FM2 '(t)" to the adder 27.

As described above, the optical transmitting device 2c includes the third oscillator 30 that generates laser light of the third oscillation frequency. The optical transmitting device 2c does not need to include the frequency converter 26. The photodetector 232 converts the phase-modulated optical signal into the first FM signal "S _FM1 (t)" using the laser light of the second oscillation frequency. The third oscillator 30 generates the laser light of the third oscillation frequency. The photodetector 252 converts the phase-modulated optical signal into the second FM signal "S _FM2 '(t)" using the laser light of the third oscillation frequency. Here, the center frequency of the first FM signal is equal to the difference (absolute value) between the first oscillation frequency and the second oscillation frequency. The center frequency of the second FM signal is equal to the difference (absolute value) between the first oscillation frequency and the third oscillation frequency.

This makes it possible to transmit and receive FM batch converted wideband signals at low cost while improving the reliability of optical communication systems.

In each embodiment, the frequency converter 24 inputs a narrowband signal to the batch conversion unit 25, so that it is possible to prevent the sidebands of the second FM signal "S _FM2 '(t)" from becoming wideband.

In each embodiment, the optical communication system may include three or more signal systems. In the optical transmitting device, different signal systems among the three or more signal systems may share at least one or more functional units (e.g., oscillators).

In each embodiment, the optical transmitting device is provided with a multiplexer (coupler) (not shown) in front of the photodetector. The input to the photodetector passes through the multiplexer provided in front of the photodetector. For example, the optical signal (phase-modulated optical signal) generated by the phase modulator 231 and the second laser light output from the second oscillator 22 are multiplexed by the multiplexer in front of the photodetector 232 and input to the photodetector 232.

(Example of hardware configuration)
9 is a diagram illustrating an example of a hardware configuration of an optical communication device in each embodiment. The example of the hardware configuration of the optical communication device 101 illustrated in Fig. 9 corresponds to the example of the hardware configuration of the optical transmitting device 2a in the first embodiment, the example of the hardware configuration of the optical receiving device 4a in the first embodiment, the example of the hardware configuration of the optical transmitting device 2b in the second embodiment, the example of the hardware configuration of the optical receiving device 4b in the second embodiment, the example of the hardware configuration of the optical transmitting device 2c in the third embodiment, and the example of the hardware configuration of the optical receiving device 4c in the third embodiment.

Some or all of the functional units of the optical communication device 101 are realized as software by a processor 102, such as a CPU (Central Processing Unit), executing programs stored in a storage device 104, which has a non-volatile recording medium (non-transitory recording medium), and in memory 103. The programs may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as flexible disks, magneto-optical disks, ROMs (Read Only Memory), and CD-ROMs (Compact Disc Read Only Memory), as well as non-transitory recording media such as hard disks and other storage devices built into computer systems. The communication unit 105 performs optical communication processing using specified optical equipment.

Some or all of the functional units of the optical communication device 101 may be realized using hardware including electronic circuits (electronic circuits 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).

(Appendix 1)
One aspect of the present invention includes a first oscillator that generates a first laser beam having a first oscillation frequency, a second oscillator that generates a second laser beam having a second oscillation frequency, a first batch conversion unit that generates a first frequency-modulated signal by performing frequency modulation batch conversion on a first narrowband signal having a predetermined narrow bandwidth and a first center frequency using the first laser beam and the second laser beam, a first frequency converter that converts the second narrowband signal having the predetermined narrow bandwidth and a second center frequency into a third narrowband signal having the predetermined narrow bandwidth and the first center frequency, and a frequency converter that converts the third narrowband signal using the first laser beam and the second laser beam. a second batch conversion unit that generates a second frequency-modulated signal by performing frequency modulation batch conversion on the first frequency-modulated signal; a second frequency converter that changes the frequency of the second frequency-modulated signal so that overlap between the first frequency-modulated signal and the second frequency-modulated signal on the frequency axis is reduced; an adder that adds the frequency-modulated second frequency-modulated signal and the first frequency-modulated 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 of the frequency-modulated second frequency-modulated signal and the first frequency-modulated signal.

(Appendix 2)
an optical transmission method executed by an optical transmitting device, the optical transmission method including the steps of: generating a first laser beam having a first oscillation frequency; generating a second laser beam having a second oscillation frequency; generating a first frequency-modulated signal by performing frequency modulation batch conversion on a first narrowband 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 a 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-modulated signal so that overlap between the first frequency-modulated signal and the second frequency-modulated signal on a frequency axis is reduced; adding the frequency-modulated second frequency-modulated signal and the first frequency-modulated signal on the frequency axis; and generating an optical-intensity-modulated optical signal by performing optical intensity modulation on the addition result of the frequency-modulated second frequency-modulated signal and the first frequency-modulated signal.

(Appendix 3)
One aspect of the present invention is an optical communication system including an optical transmitting device and an optical receiving device, wherein the optical transmitting device includes a first oscillator that generates a first laser beam having a first oscillation frequency, a second oscillator that generates a second laser beam having a second oscillation frequency, a first batch conversion unit that generates a first frequency-modulated signal by performing frequency modulation batch conversion on a first narrowband signal having a predetermined narrow bandwidth and a first center frequency using the first laser beam and the second laser beam, a first frequency converter that converts the second narrowband signal having the predetermined narrow bandwidth and a second center frequency into a third narrowband signal having the predetermined narrow bandwidth and the first center frequency, and a second batch conversion unit that generates a second frequency-modulated signal by performing frequency modulation batch conversion on the third narrowband signal using a first laser beam and the second laser beam; a second frequency converter that changes the frequency of the second frequency-modulated signal so that overlap between the first frequency-modulated signal and the second frequency-modulated signal on a 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 the frequency axis; and an optical intensity modulated signal that is generated 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. and an optical intensity modulator that generates an optical signal, and the optical receiving device includes a photodetector that converts the optical 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-modulated signal from the second frequency-modulated signal and the first frequency-modulated signal whose frequency has been changed, a first differential detector that generates the first narrowband signal by performing differential detection processing on the extracted first frequency-modulated signal, a first low-pass filter that removes high-frequency components from the first narrowband signal, and a first bandpass filter that extracts the second frequency-modulated signal and the first frequency-modulated signal whose frequency has been changed. a first frequency inverse converter that generates the second frequency-modulated signal by making the frequency of the frequency-modulated second signal the same as the frequency of the first frequency-modulated signal; a second differential detector that generates the third narrowband signal by performing differential detection processing on the second frequency-modulated signal; a second low-pass filter that removes high-frequency components from the third narrowband signal; and a second frequency inverse converter that generates the second narrowband signal based on the third narrowband signal from which the high-frequency components have been removed.

The above describes in detail an embodiment of the present invention with reference to the drawings, but the specific configuration is not limited to this embodiment and also includes designs that do not deviate from 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 path, 4a, 4b...optical receiving device, 20...band splitter, 21...first oscillator, 22...second oscillator, 23...batch conversion unit, 24...frequency converter, 25...batch conversion unit, 26...frequency converter, 27...adder, 28...optical intensity modulator, 29...combiner, 30...third oscillator, 40...photodetector, 41...bandpass filter, 42...delay detector, 43...low-pass filter, 44...combiner, 45...bandpass filter, 46...frequency inverse converter, 47...delay Detector, 48... low-pass filter, 49... frequency inverse converter, 50... optical demultiplexer, 51... wavelength division multiplexing filter, 52... wavelength division multiplexing filter, 100a, 100b... optical communication system, 101... optical communication device, 102... processor, 103... memory, 104... storage device, 105... communication unit, 200a, 200b... optical transmitting device, 230... batch conversion unit, 231... phase modulator, 232... photodetector, 250... batch conversion unit, 251... phase modulator, 252... photodetector, 400a, 400b... optical receiving device

Claims (7)

a first batch conversion unit that generates a first frequency-modulated signal by performing frequency modulation batch conversion on a first narrowband signal having a predetermined narrow bandwidth and a first center frequency using a first laser light having a first oscillation frequency and a second laser light having a second oscillation frequency;
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-modulated signal by performing frequency modulation batch conversion on the third narrowband signal using the first laser light and the second laser light or a third laser light having a third oscillation frequency;
an adder that adds the second frequency-modulated signal 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 a result of adding the second frequency-modulated signal and the first frequency-modulated signal, the frequency of which has been changed;
a center frequency of the first frequency modulated signal is equal to the absolute value of the difference between the first oscillation frequency and the second oscillation frequency;
a center frequency of the second frequency-modulated signal is equal to the absolute value of the difference between the first oscillation frequency and the second oscillation frequency or the third oscillation frequency;
Optical transmitter. An optical transmitting device as described in claim 1, further comprising a band splitter that splits a predetermined wideband signal into the first narrowband signal and the second narrowband signal on the frequency axis. a second frequency converter that changes the frequency of the second frequency-modulated signal so that overlap between the first frequency-modulated signal and the second frequency-modulated signal on a frequency axis is reduced when the frequency modulation batch conversion is performed on the third narrowband signal using the second laser light;
the second frequency converter changes the frequency of the second frequency-modulated signal in accordance with a second frequency conversion amount that is greater than a first frequency conversion amount at which an amount of interference between the first frequency-modulated signal and the second frequency-modulated signal becomes a predetermined amount;
3. The optical transmitter according to claim 1, wherein the adder adds the second frequency-modulated signal whose frequency has been changed and the first frequency-modulated signal on the frequency axis. An optical transmission method executed by an optical transmitting device,
generating a first frequency-modulated signal by performing frequency modulation batch conversion on a first narrowband signal having a predetermined narrow bandwidth and a first center frequency using a first laser light having a first oscillation frequency and a second laser light having a second oscillation frequency;
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 light and the second laser light or a third laser light having a third oscillation frequency;
adding the second frequency modulated signal and the first frequency modulated signal on a frequency axis;
generating an intensity-modulated optical signal by performing optical intensity modulation on a result of adding the frequency-shifted second frequency-modulated signal and the first frequency-modulated signal;
a center frequency of the first frequency modulated signal is equal to the absolute value of the difference between the first oscillation frequency and the second oscillation frequency;
a center frequency of the second frequency-modulated signal is equal to the absolute value of the difference between the first oscillation frequency and the second oscillation frequency or the third oscillation frequency;
Optical transmission method. An optical communication system including an optical transmitting device and an optical receiving device,
The optical transmitter comprises:
a first batch conversion unit that generates a first frequency-modulated signal by performing frequency modulation batch conversion on a first narrowband signal having a predetermined narrow bandwidth and a first center frequency using a first laser light having a first oscillation frequency and a second laser light having a second oscillation frequency;
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-modulated signal by performing frequency modulation batch conversion on the third narrowband signal using the first laser light and the second laser light or a third laser light having a third oscillation frequency;
an adder that adds the second frequency-modulated signal 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 a result of adding the second frequency-modulated signal and the first frequency-modulated signal, the frequency of which has been changed;
The optical receiving device
a photodetector for converting the intensity-modulated optical signal into the second frequency-modulated signal and the first frequency-modulated signal, the frequency of which has been changed;
a first bandpass filter for extracting the first frequency modulated signal from the second frequency modulated signal whose frequency has been changed and the first frequency modulated signal;
a first differential detector that generates the first narrowband signal by performing differential detection processing on the extracted first frequency-modulated signal;
a first low-pass filter that removes high frequency components of the first narrowband signal;
a second bandpass filter for extracting the frequency-shifted second frequency-modulated signal from the frequency-shifted second frequency-modulated signal and the first frequency-modulated signal;
a first frequency inverter that generates the second frequency modulated signal by making the frequency of the frequency-shifted second frequency modulated signal the same as the frequency of the first frequency modulated signal;
a second differential detector that performs differential detection processing on the second frequency-modulated signal to generate the third narrowband signal;
a second low-pass filter for removing high frequency components of the third narrowband signal;
a second frequency inverter that generates the second narrowband signal based on the third narrowband signal from which high frequency components have been removed,
a center frequency of the first frequency modulated signal is equal to the absolute value of the difference between the first oscillation frequency and the second oscillation frequency;
a center frequency of the second frequency-modulated signal is equal to the absolute value of the difference between the first oscillation frequency and the second oscillation frequency or the third oscillation frequency;
Optical communication system. the optical transmission device further includes a band divider that divides a predetermined wideband signal into the first narrowband signal and the second narrowband signal on a frequency axis;
6. The optical communication system according to claim 5, wherein the optical receiving device further comprises a multiplexer that multiplexes the first narrowband signal from which high frequency components have been removed and the second narrowband signal. a second frequency converter that changes the frequency of the second frequency-modulated signal so that overlap between the first frequency-modulated signal and the second frequency-modulated signal on a frequency axis is reduced when the frequency modulation batch conversion is performed on the third narrowband signal using the second laser light;
the second frequency converter changes the frequency of the second frequency-modulated signal in accordance with a second frequency conversion amount that is greater than a first frequency conversion amount at which an amount of interference between the first frequency-modulated signal and the second frequency-modulated signal becomes a predetermined amount;
7. The optical communication system according to claim 5, wherein the adder adds the second frequency-modulated signal whose frequency has been changed and the first frequency-modulated signal on the frequency axis.