JP-7856611-B2 - Optical transmitting device and optical receiving device

JP7856611B2JP 7856611 B2JP7856611 B2JP 7856611B2JP-7856611-B2

Inventors

田中和樹

Assignees

ＫＤＤＩ株式会社

Dates

Publication Date: 20260511
Application Date: 20230920

Claims (9)

An optical transmitting device connected to an optical receiving device via an optical transmission path, A means for generating carrier light, A control means for controlling the frequency of the carrier light according to the time variation pattern of the frequency, A generating means that generates signal light to be transmitted to the optical receiving device by modulating the carrier light generated by the generating means based on an electrical signal, Equipped with, An optical transmitting device in which, in the aforementioned time-varying pattern, the difference in frequencies separated by a predetermined period is greater than the bandwidth of the signal light.
The optical transmitting apparatus according to claim 1, wherein the predetermined period is a period based on the propagation delay difference between the direct light, which is the signal light that reaches the optical receiving device without reflection in the optical transmission path, and the first reflected light among one or more reflected lights, which are the signal light that reaches the optical receiving device after being reflected an even number of times in the optical transmission path.
The optical transmitting device according to claim 2, wherein the first reflected light is the reflected light among the one or more reflected lights that has the smallest propagation delay difference with the direct light.
The optical transmitting apparatus according to claim 2, wherein the first reflected light is the reflected light with the largest propagation delay difference from the direct light among the reflected light whose level in the optical receiving device is greater than the threshold.
The optical transmitting device according to claim 2, wherein the first reflected light is the reflected light that has the largest propagation delay difference from the direct light among the reflected light that has been reflected only twice in the optical transmission path and reached the optical receiving device.
The optical transmitting device communicates with the optical receiving device using time-division duplexing. The optical transmitting device according to claim 1, wherein the control means controls the frequency of the carrier light such that, during the period in which the optical transmitting device transmits the signal light to the optical receiving device, the difference in the frequencies of the carrier light separated by a predetermined period is greater than the bandwidth of the signal light.
The optical transmitting device communicates with a plurality of optical receiving devices via the optical transmission path and has at least the same number of generating means as the number of optical receiving devices, as described in claim 1.
An optical transmitting device according to any one of claims 1 to 7 and an optical receiving device connected via the optical transmission path, A variable optical filter into which the received light from the optical transmission path is input, A control means for controlling the passband of the optically tunable filter according to the aforementioned time-varying pattern, A conversion means for converting the received light that has passed through the optically tunable filter into photoelectric energy, An optical receiving device equipped with the following features.
An optical transmitting device according to any one of claims 1 to 7 and an optical receiving device connected via the optical transmission path, A local light generation means that generates local light whose frequency changes according to the aforementioned time-varying pattern, A demodulation means for demodulating the received light from the optical transmission path based on the local light to generate the electrical signal, An optical receiving device equipped with the following features.

Description

This disclosure relates to a technology for suppressing the effects of reflected light in optical communication systems. Optical transmission lines have multiple connection points for connecting optical fibers. These optical fibers are connected using optical connectors or fusion splicing. At these connection points, a portion of the signal light transmitted from the optical transmitter to the optical receiver is reflected back towards the optical transmitter. A portion of the signal light reflected back towards the optical transmitter may be further reflected back towards the optical receiver at another connection point. The optical transmitter has isolators to block light propagating in the opposite direction to the transmitted signal light, so there is no problem even if reflected signal light reaches the optical transmitter. On the other hand, the optical receiver receives received light that includes signal light that reached the receiver without reflection in the optical transmission line (hereinafter referred to as direct light) and signal light that reached the receiver after being reflected an even number of times in the optical transmission line (hereinafter referred to as reflected light). Because the propagation delays of direct light and reflected light are different, the reflected light becomes interference light with the direct light, affecting the demodulation of the direct light. Patent Document 1 and Non-Patent Document 1 disclose configurations for performing dithering to suppress the effects of reflected light. Specifically, Non-Patent Document 1 discloses a configuration in which dithering light is generated using a phase modulator dedicated to dithering. Furthermore, Patent Document 1 discloses a configuration in which transmitted light, including signal light and dithering light, is generated by driving a light source with both an information-carrying signal and a dithering signal. Japanese Patent Publication No. 2010-232764 Byung Gon Kim, et. al. , "Reflection-Tolerant RoF-Based Mobile Fronthaul Network for 5G Wireless Systems", JOURNAL OF TECHNOLOGY, VOL. 37, NO. 24, December 15, 2019 Configuration diagrams of optical communication systems according to several embodiments.Configuration diagrams of an optical transmission device according to several embodiments.A diagram showing the time variation patterns of the carrier light frequency in several embodiments.Diagrams illustrating the configuration of the light source according to several embodiments.A diagram showing the received light received by an optical receiver according to several embodiments.Configuration diagrams of optical receiving devices according to several embodiments.Configuration diagrams of optical communication systems according to several embodiments.A diagram showing the time evolution patterns of the frequencies of multiple carrier lights generated by multiple light sources according to several embodiments.Figure 8 is a diagram illustrating the use of multiple carrier light sources.Configuration diagrams of an optical transmission device according to several embodiments.Configuration diagrams of an optical transmission device according to several embodiments. The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more features from the multiple features described in the embodiments may be combined arbitrarily. Furthermore, identical or similar configurations will be given the same reference numeral, and redundant descriptions will be omitted. <First Embodiment> Figure 1 is a configuration diagram of an optical communication system according to this embodiment. The optical transmitter 1 transmits signal light to the optical receiver 2 via the optical transmission path 3. The signal light is obtained by modulating carrier light with an electrical signal that carries information. In addition, another optical receiver 2 may be located in the same building where the optical transmitter 1 is located, and another optical transmitter 1 may be located in the same building where the optical receiver 2 is located. The other optical transmitter 1 transmits signal light to the other optical receiver 2 via another optical transmission path 3. The optical transmitter 1 and the other optical receiver 2 can be implemented as a single optical communication device. Similarly, the other optical transmitter 1 and the optical receiver 2 can be implemented as a single optical communication device. The optical transmission path 3 has multiple connection points (reflection points) 31, 32, and 33. Although Figure 1 shows three reflection points, the number of reflection points can be any number of two or more. The signal light transmitted by the optical transmitter 1 to the optical transmission path 3 can be re