KR-20260063925-A - SIGNAL TRANSMISSION APPARATUS AND METHOD FOR ANALOG RADIO-OVER-FIBER (ROF) TRANSMISSION IN OPTICAL COMMUNICATION SYSTEM

KR20260063925AKR 20260063925 AKR20260063925 AKR 20260063925AKR-20260063925-A

Abstract

A signal transmission method for analog Radio-over-Fiber (RoF) transmission in an optical communication system according to one embodiment of the present disclosure may include the steps of: generating a multi-band optical signal by modulating a multi-band signal generated by a signal generator based on a continuous wave (CW) laser light output by a laser using a Mach-Zehnder Modulator (MZM), wherein the MZM is driven by a single drive method; transmitting the multi-band optical signal through an optical fiber; receiving the multi-band optical signal by an optical detector; deriving an analysis result based on the multi-band optical signal received by the optical detector by a digital signal processor; changing the chirp parameter of the MZM by controlling the bias voltage of the MZM based on the analysis result by a digital signal processor; and outputting an optical signal based on the changed chirp parameter.

Inventors

김종완
허준영
강헌식

Assignees

한국전자통신연구원

Dates

Publication Date: 20260507
Application Date: 20241031

Claims (14)

In a signal transmission method for analog RoF (Radio-over-Fiber) transmission in an optical communication system, A step of generating a multi-band optical signal by modulating a multi-band signal generated by a signal generator based on a continuous wave laser light output by a laser using a Mach-Zehnder Modulator (MZM), wherein the MZM is driven by a single drive method; A step of transmitting the above multi-band optical signal through an optical fiber; A step of receiving the multi-band optical signal by a photodetector; A step of deriving an analysis result based on the multi-band optical signal received by the photodetector by a digital signal processor; A step of changing the chirp parameter of the MZM by controlling the bias voltage of the MZM based on the analysis result by the digital signal processor; and A method comprising the step of outputting an optical signal based on changed chirp parameters.
In Article 1, A method comprising the step of changing the chirp parameter of the above MZM, which compensates for the chromatic dispersion of the optical fiber by adjusting the bias voltage so that the chirp parameter becomes a negative chirp parameter.
In Article 1, A method for deriving an analysis result based on a multi-band optical signal received by a photodetector by the digital signal processor, comprising the steps of analyzing the frequency response of the multi-band optical signal and determining a bias voltage such that the frequency response can be flattened.
In Paragraph 3, The step of analyzing the frequency response of the multi-band optical signal and determining a bias voltage at which the frequency response can be flattened is: A step of analyzing the frequency responses of signals based on various bias voltages; and A method comprising the step of determining a bias voltage corresponding to the frequency response having the flattest graph shape among the above frequency responses.
In Article 1, A method for deriving the analysis result based on the multi-band optical signal received by the photodetector by the digital signal processor, comprising the step of determining the chirp parameter to minimize the chromatic dispersion of the optical fiber.
In Article 1, The step of deriving an analysis result based on the multi-band optical signal received by the photodetector by the digital signal processor is as follows: A step of amplifying the signal received by the above-mentioned photodetector; A step of converting the amplified signal into a digital signal by an analog-to-digital converter; and A method comprising the step of deriving the analysis result based on the digital signal by the digital signal processor.
In Article 1, The step of generating a multi-band optical signal by modulating the multi-band signal generated by the above signal generator with MZM is: A method comprising the step of applying an RF signal to only one of the two arms of the MZM operating as a single drive.
In a signal transmission device for analog RoF (Radio-over-Fiber) transmission in an optical communication system, A laser configured to output CW (continuous wave) laser light; A signal generator configured to generate a multi-band signal, which is an electrical signal; It includes a Mach-Zehnder optical modulator (MZM) configured to generate a multi-band optical signal by modulating the multi-band signal based on the above CW laser light, wherein the Mach-Zehnder optical modulator is driven by a single drive method; A photodetector configured to receive the multi-band optical signal via an optical fiber; and It includes a digital signal processor configured to derive an analysis result based on the multi-band optical signal received by the above-mentioned photodetector, The digital signal processor generates an electrical control signal based on the analysis result, and controls the bias voltage of the Mach-Zehnder optical modulator based on the electrical control signal, A device characterized in that the chirp parameter of the above MZM changes based on the bias voltage.
In Article 8, The device is characterized in that the digital signal processor is further configured to adjust the bias voltage so that the chirp parameter becomes a negative chirp parameter.
In Article 8, The device is characterized in that the digital signal processor analyzes the frequency response of the multi-band optical signal received by the photodetector and determines a bias voltage at which the frequency response can be flattened.
In Article 10, The above digital signal processor is: Analyze the frequency responses of signals based on various bias voltages, and An apparatus characterized by determining a bias voltage corresponding to the frequency response having the flattest graph shape among the above frequency responses.
In Article 8, The device is characterized in that the digital signal processor determines the chirp parameters to minimize the chromatic dispersion of the optical fiber.
In Article 8, The above device is: An amplifier configured to amplify the multi-band optical signal received by the above-mentioned photodetector; and It further includes an analog-to-digital converter that converts the amplified signal into a digital signal, A device characterized in that the digital signal processor is configured to derive the analysis result based on the digital signal.
In Article 8, The above MZM operating as a single drive is configured to include two arms, and A device characterized by applying an RF signal to only one of the two arms.

Description

Signal Transmission Apparatus and Method for Analog Radio-Over-Fiber (ROF) Transmission in Optical Communication System This document relates to a signal transmission device and method for analog Radio-over-Fiber (RoF) transmission in an optical communication system. As data traffic has continuously increased, data transmission speeds have also risen. Consequently, much research is being conducted to utilize higher frequency bands for transmitting high-speed signals. In next-generation wireless communication networks, signal transmission in sub-THz and THz bands, in addition to mmWave, is being considered. High frequency bands are characterized by significant signal loss when penetrating obstacles in the transmission path. In particular, regarding concrete, transmission loss in high frequency bands exceeds 100 dB, making it impossible to use the existing method of transmitting signals from the outside to the inside in the sub-6GHz band. Recently, research has been conducted to compensate for power fading by using two Mach-Zehnder modulators (MZMs) for intensity modulation (IM) and phase modulation (PM), respectively, so that their frequency responses complement each other. In addition, there has been research on improving power fading by adjusting the frequency response curve by controlling the bias in a dual-parallel MZM (DP-MZM). FIGS. 1 and FIGS. 2 are block diagrams illustrating an analog radio-over-fiber (RoF) transmission system according to one embodiment of the present disclosure. Figure 3 is a diagram illustrating the frequency response and frequency dip according to transmission distance. FIG. 4 is a block diagram showing an optical transceiver according to one embodiment of the present disclosure. FIG. 5 is a drawing for explaining a Mach Zehnder optical modulator (MZM) according to one embodiment of the present disclosure. FIGS. 6, 7, and 8 exemplarily show changes in chirp parameters according to the bias voltage of an MZM operating as a dual-drive or single-drive according to one embodiment of the present disclosure. FIGS. 9, 10, and 11 exemplarily show changes in the radio frequency (RF) spectrum according to the bias voltage of an MZM operating as a dual-drive or single-drive according to one embodiment of the present disclosure. FIG. 12 is a flowchart illustrating a signal transmission method for analog RoF (Radio-over-Fiber) transmission in an optical communication system according to one embodiment of the present disclosure. In the following, embodiments of the present disclosure will be described clearly and in detail so that a person skilled in the art can easily practice the present disclosure. Terms such as "unit" and "module" used below, or functional blocks illustrated in the drawings, may be implemented in the form of software configurations, hardware configurations, or combinations thereof. In order to clearly explain the technical concept of the present invention, detailed descriptions of redundant components are omitted below. In this document, each of the phrases such as "A or B", "at least one of A and B", "at least one of A or B", "A, B or C", "at least one of A, B and C", and "at least one of A, B, or C" may include any one of the items listed together with the corresponding phrase, or all possible combinations thereof. FIGS. 1 and FIGS. 2 are block diagrams illustrating an analog radio-over-fiber (RoF) transmission system according to one embodiment of the present disclosure. In FIG. 1, a radio unit (RU) can receive a signal. For example, the received signal may be a radio signal, and the radio signal may be converted into an electrical signal by the RU. The RU can transmit the electrical signal to a main hub unit (MHU). The MHU can convert the received electrical signal into an optical signal, and the optical signal is transmitted to optical couplers (OC 1~N) via a standard single mode fiber (SSMF), and each band signal may be propagated by remote antenna units (RAU 1~N). Referring to Figures 1 and 2, since the directivity of the signal is strong in the high frequency band, a single transmitter is connected to a large number of RAUs via optical fibers to increase the coverage of the frequency band. There may be analog and digital methods for RoF transmission. The analog method is more cost-effective and scalable than the digital method. Referring to Fig. 2, the frequencies assigned to each band ( , ~, ) are different from each other. Therefore, analog RoF transmission systems support a wide range of frequencies and multiple carriers. However, analog RoF transmission systems are characterized by being heavily affected by the channel. Figure 3 is a diagram illustrating the frequency response and frequency dip according to transmission distance. The graph in Figure 3 is plotted exemplarily for a chromatic dispersion (CD) coefficient of 17 ps/nm/km. In one example, for short-distance optical signal transmission, the O-band, which is not affected by chromatic dispersion, can be