The analog optical transceiver uses PFM modulation technology to transmit image signals in real time. The transmitting end performs PFM modulation on the analog video signal, and then performs electrical-optical conversion. After the optical signal is transmitted to the receiving end, it performs photoelectric conversion, and then performs PFM demodulation to recover the video signal. Digital optical transceiver is a machine that controls optical signals through digital circuits and uses codes similar to 0 and 1 to realize optical communication. It is widely used in optical fiber communication and other fields. Next, we will introduce the difference between analog optical transceiver and digital optical transceiver in detail!
1. The signal transmission method on the optical fiber is different
. The optical signal emitted by the optical head on the analog optical transceiver is an analog optical modulation signal, which is respectively called the amplitude, frequency, and phase changes caused by the amplitude, frequency, and phase changes of the input analog carrier signal. It is amplitude modulation, frequency modulation and phase modulation optical transceiver. The optical signal emitted by the optical head on the digital optical transceiver is a digital signal, that is, 0 or 1 corresponds to two states of optical signal strong and weak, and different combinations of 0 and 1 represent video, audio, and data signals of different amplitudes.
2. The analog signal transmission input and output processing methods are different.
Regardless of analog or digital optical transceivers, the input baseband video, audio, and data signals must be processed. For analog AM optical transceivers, the processing method is to modulate the amplitude of video, audio, and data to a high-frequency carrier signal, so that the amplitude of the high-frequency carrier signal changes with the amplitude of the video, audio, and data; while the digital optical transceiver modulates the input The baseband video, audio, and data are converted into high-resolution analog to digital. For example, the amplitude signal of the 1Vp-p amplitude range is represented by a 12bits digital signal. 1V is equally divided into 4096, so the maximum voltage amplitude caused by the analog-to-digital conversion The error is 1/4096V (about 2.5mV), this error voltage is called the quantization error voltage, the voltage values of various amplitudes from 0V, 1/4096V, 2/4096V...the maximum 1V corresponds to the digital code respectively 000000000000000000000001, 000000000010 ...111111111111. The digital code signal directly controls the strong and weak states of the optical signal emitted by the optical head (corresponding to 0 or 1), and the receiving optical transceiver performs digital-to-analog conversion on the digital code to restore the original baseband video, audio, and data signals.
3.
Distortion, distortion, and interference of video, audio, and data signals caused by different processing methods. Because analog optical transceivers need to perform amplitude modulation, frequency modulation, and phase modulation, the amplitude of the analog signal changes and the amplitude of the carrier signal due to modulation, Whether the change of frequency and phase is a linear relationship of one-to-one correspondence becomes the key to the quality of the pseudo-optical transceiver. It is difficult to achieve true linear modulation, and the non-linear shape will inevitably cause signal distortion; at the same time, the modulated carrier signal must also modulate the optical signal. The non-linearity of the signal is also a very important factor. As we all know, the non-linearity of the optical device has a great influence on the environmental temperature change, the stability of the working voltage, and the optical emission power. Therefore, the optical device needs 7-10 days in production. Process screening, aging, and testing of thermal cycle aging, etc. can only control this transformation within a certain range; long-distance transmission of optical signals in optical fibers will cause optical signal power attenuation, transmission frequency drift, and phase distortion The optical signal dispersion effect can also cause optical signal distortion; when the optical signal reaches the receiving end, the receiving optical device still causes nonlinear distortion. The analog signal after photoelectric conversion enters demodulation, and demodulation and modulation will produce nonlinear distortion like modulation. . Therefore, comprehensive analog optical transceivers, from input signal modulation electrical-optical conversion-optical output-photoelectric conversion-demodulation, will cause non-linear distortion, and these signal distortions are inherent, so they must not be eliminated, so analog It is difficult for optical transceivers to transmit video images, audio quality, and data to very satisfactory results.
4. Intermodulation distortion caused by simultaneous interpretation of multiple signals
In field monitoring applications, users may have many kinds of signals, such as video images, audio, data, Ethernet, telephone or other user-defined signals, each of which is separate To use a pair of optical transceivers for transmission is inevitably expensive. Therefore, in order to improve the utilization efficiency of optical fibers and reduce costs, all necessary signals are multiplexed in the optical transceivers for transmission on a pair or one optical fiber. For frequency modulation, amplitude modulation, and phase modulation optical transceivers, it is difficult to transmit high-speed signals such as 10/100M Ethernet signals or multiple telephones. Mix multiple channels of video or audio signals with frequency modulation, amplitude modulation, and phase modulation on a certain carrier. It will inevitably cause various mirror images and intermodulation interference. Therefore, there are many famous foreign brands in the market that frequently interfere with each other when multi-channel video, audio, and data simultaneous transmission of FM, AM, and phase modulation optical transceivers of famous foreign brands. These unstable phenomena are inherent and difficult for analog modulation technology for a long time. Solved problems and shortcomings. Therefore, the transmission signal capacity of analog optical transceivers is limited, and generally does not exceed 4 channels of simultaneous signal transmission.
V. Different stability
Because the analog modulated optical transceiver adopts the carrier modulation method, the carrier and the optical head are easily affected by the environmental temperature. There is a shortcoming that the transmission quality changes with environmental changes. Because of this shortcoming, the maintenance of analog optical transceivers has become a headache for some large and important projects, which has also caused great dissatisfaction to many engineering contractors or owners. Therefore, it is a wise choice to choose a digital optical transceiver for some important projects.
6. The price is different.
Due to the different system structure , the price of analog optical transceiver and digital optical transceiver is slightly different. Generally speaking, the price of single-channel video, audio, and data digital optical transceiver is slightly higher than that of single-channel analog optical transceiver. On the contrary, data digital optical transceivers are much cheaper than analog optical transceivers, and the video effect after transmission is much higher than that of analog products. Therefore, the price/performance ratio of digital optical transceivers is higher than that of analog video optical transceivers.
Well, the above content is the detailed explanation of the difference between the analog optical transceiver and the digital optical transceiver by Feichang Technology, I hope it can be helpful to everyone! Feichang Technology, a professional manufacturer of optical transceivers, optical fiber transceivers, industrial switches, and protocol converters, independently researches and develops brands, welcome to come to understand and communicate.