Currently in the highway, transportation, electronics, surveillance, security, industrial automation, power, customs, water conservancy, banking and Other fields video image, audio, data, Ethernet, telephone and other optical transceivers began to use a large number of applications. The initial analog FM, AM, PM optical transceivers occupy a considerable proportion in the market. The transmission method is to modulate the baseband video, audio, data and other signals on a carrier frequency, transmit the optical transceiver through the transmitter, and then pass the other end. The receiving optical transceiver demodulates and restores the corresponding baseband video, audio, and data signals. The digital optical transceivers, which have been widely used in domestic and foreign projects, digitize the high-resolution digital baseband video, audio, and data to form a high-speed digital stream, and multiplex the multiplexed digital streams to transmit the optical transceiver. It is transmitted, and then it is received, demultiplexed, and restored by the receiving optical transceiver at the other end, and then restored to analog video, audio, and data by digital analog conversion. Judging from the current market situation, analog optical transceivers have gradually withdrawn from the market, and digital optical transceivers have mushroomed in the market, and digital is replacing analog. This is also a significant historical development trend of optical fiber communication technology. Due to the high transmission signal quality of digital optical transceivers, there are no shortcomings such as analog frequency modulation, phase modulation, amplitude modulation interference caused by multiple signals in the amplitude modulation terminal, low transmission quality due to environmental interference, and poor long-term operation stability. Digital optical transceivers have been widely used in the project. What is the difference between analog video optical transceivers and digital optical transceivers? This is also a question that many users are concerned about. This article discusses the following aspects:
1, the signal transmitted on the optical fiber is not the same
As the name suggests, the optical signal emitted by the analog optical transceiver is an analog optical modulation signal. It changes amplitude, frequency, and phase of the optical signal with the amplitude, frequency, and phase of the input analog carrier signal, which are called amplitude modulation, frequency modulation and phase modulation optical transceiver respectively. . The optical signal transmitted by the optical head of the digital optical transceiver is a digital signal, that is, 0 or 1 corresponds to the strong or weak state of the optical signal. Different combinations of 0 and 1 represent video, audio, and data signals of different amplitudes.
2, analog signal transmission input and output processing is not the same
Regardless of analog, digital optical transceivers, the input baseband video, audio, and data signals must all be processed. For the analog AM optical transceiver, 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 varies with the amplitude of the video, audio and data; for the analog FM optical transceiver, processing The method is to modulate the amplitude of video, audio and data to a high-frequency carrier signal so that the frequency of the high-frequency carrier signal varies with the amplitude of the video, audio and data; for the analog phase-modulating optical transceiver, the processing method is to video, The amplitude of audio and data modulates a high-frequency carrier signal such that the phase of the high-frequency carrier signal varies with the amplitude of video, audio, and data. The digital optical transceiver performs high-resolution analog-to-digital conversion on the input baseband video, audio, and data. For example, a 1Vp-p amplitude range amplitude signal is represented by a 12-bit digital signal, and 1V is equally divided into 4096, so the modulus The maximum voltage amplitude error caused by the conversion is 1/4096V (about 2.5mV). This error voltage is called the quantization error voltage. The voltage values ​​of various amplitudes correspond to 0V, 1/4096V, 2/4096V, and 1V maximum. The numbers are encoded as 000000000000, 000000000001, 000000000010...111111111111. The digitally encoded signal directly controls the strong and weak states of the optical signal emitted by the optical head (corresponding to 0 or 1). The receiving optical unit then performs digital-to-analog conversion of the digital coding and restores the original baseband video, audio, and data signals.
3, different processing methods, caused by the video, audio, data signal distortion, distortion, different interference
Since the analog optical transceiver needs to perform amplitude modulation, frequency modulation, and phase modulation, whether the amplitude of the analog signal and the change of amplitude, frequency, or phase of the carrier signal due to modulation are one-to-one linear relationship becomes the key to the quality of the optical transceiver. So far, it is difficult to achieve true linear modulation, non-linear shape will inevitably cause signal distortion; At the same time, the modulated carrier signal signal must also modulate the optical signal, the nonlinearity of the optical signal is also a very important factor, as we all know, the optical device Non-linearity and environmental temperature changes, operating voltage stability, light emission power have a great influence, so the optical device needs 7-10 days of thermal cycle aging in production process screening, aging, testing can only be The conversion is controlled within a certain range; the optical signal is transmitted over a long distance in the optical fiber, which causes the power of the optical signal to be attenuated, the transmission frequency shifts, and the phase distortion. The dispersion effect of the optical signal also causes distortion of the optical signal; the optical signal arrives at the reception At the end, the receiving optical device still needs to cause nonlinear distortion, and the photoelectrically converted analog signal enters Demodulation, demodulation and modulation will produce nonlinear distortion. Therefore, the synthetic analog optical transceiver, from the input signal modulation - electro-optical conversion - optical transmission - photoelectric conversion - demodulation of the five processes, will cause non-linear distortion, and these signal distortion distortion is inherent, so it can not be eliminated, so the analog optical transmission The effects of video images, audio quality, and data are difficult to achieve satisfactory results. The digital optical transceiver only has quantization error of analog-to-digital conversion (such as 2.5mv for a 1V video signal at 12bits), which is not enough to cause signal distortion.
4. Intermodulation distortion caused by simultaneous transmission of multiple signals
In field monitoring applications, users may have a variety of signals, such as video images, audio, data, Ethernet, telephone or other user-defined signals. Each signal is transmitted by a pair of optical transceivers, which is necessarily expensive. In order to increase the utilization efficiency of the optical fiber and reduce the cost, necessary signals are multiplexed in the optical transceiver for transmission on one pair or one optical fiber. For FM, AM and PM optical transceivers, it is difficult to transmit high-speed signals such as 10/100M Ethernet signals or multi-channel telephones. Multiple-channel video or audio signals are mixed in frequency modulation, amplitude modulation, and phase modulation on a single carrier. Inevitably will cause all kinds of mirroring, intermodulation interference. Therefore, at present, there are many phenomena of mutual interference between FM, AM, and phase-shifting optical multi-channel video, audio, and data transmission of well-known foreign brands. These unstable phenomena have always been inherent in analog modulation technology. Disadvantages. Therefore, the analog optical transceiver has a limited capacity for transmitting signals and generally does not exceed the simultaneous transmission of four signals. The digital optical transceivers transmit digital signals, which are easy to use for large-capacity multiplexing and do not interfere with each other. For example, all-digital optical transceivers from Beijing Feiboite Technology Co., Ltd. can achieve up to 128 channels of video, audio, data, Ethernet, and telephone transmissions on the same fiber without any crosstalk interference.
5, different stability
Since the analog-modulated optical transceiver adopts the carrier modulation method, the carrier and the optical head are easily affected by the ambient temperature. There are disadvantages of the transmission quality changing with the environment. Because of this shortcoming, the maintenance of analog optical transceivers has become a headache for large-scale and important projects, which has also caused great dissatisfaction for many engineering contractors or owners. Therefore, choosing digital optical transceivers for some important projects is a wise choice.
6, the price is different
Due to different architectures, the prices of analog optical transceivers and digital optical transceivers are slightly different. In general, single-channel video, audio, and data digital optical transceivers are slightly more expensive than single-channel analog optical transceivers, and four-channel video, audio, and data digital optical transceivers have the opposite It is much cheaper than analog optical transceivers. Therefore, the cost performance of digital optical transceivers is higher than that of analog optical transceivers.
1, the signal transmitted on the optical fiber is not the same
As the name suggests, the optical signal emitted by the analog optical transceiver is an analog optical modulation signal. It changes amplitude, frequency, and phase of the optical signal with the amplitude, frequency, and phase of the input analog carrier signal, which are called amplitude modulation, frequency modulation and phase modulation optical transceiver respectively. . The optical signal transmitted by the optical head of the digital optical transceiver is a digital signal, that is, 0 or 1 corresponds to the strong or weak state of the optical signal. Different combinations of 0 and 1 represent video, audio, and data signals of different amplitudes.
2, analog signal transmission input and output processing is not the same
Regardless of analog, digital optical transceivers, the input baseband video, audio, and data signals must all be processed. For the analog AM optical transceiver, 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 varies with the amplitude of the video, audio and data; for the analog FM optical transceiver, processing The method is to modulate the amplitude of video, audio and data to a high-frequency carrier signal so that the frequency of the high-frequency carrier signal varies with the amplitude of the video, audio and data; for the analog phase-modulating optical transceiver, the processing method is to video, The amplitude of audio and data modulates a high-frequency carrier signal such that the phase of the high-frequency carrier signal varies with the amplitude of video, audio, and data. The digital optical transceiver performs high-resolution analog-to-digital conversion on the input baseband video, audio, and data. For example, a 1Vp-p amplitude range amplitude signal is represented by a 12-bit digital signal, and 1V is equally divided into 4096, so the modulus The maximum voltage amplitude error caused by the conversion is 1/4096V (about 2.5mV). This error voltage is called the quantization error voltage. The voltage values ​​of various amplitudes correspond to 0V, 1/4096V, 2/4096V, and 1V maximum. The numbers are encoded as 000000000000, 000000000001, 000000000010...111111111111. The digitally encoded signal directly controls the strong and weak states of the optical signal emitted by the optical head (corresponding to 0 or 1). The receiving optical unit then performs digital-to-analog conversion of the digital coding and restores the original baseband video, audio, and data signals.
3, different processing methods, caused by the video, audio, data signal distortion, distortion, different interference
Since the analog optical transceiver needs to perform amplitude modulation, frequency modulation, and phase modulation, whether the amplitude of the analog signal and the change of amplitude, frequency, or phase of the carrier signal due to modulation are one-to-one linear relationship becomes the key to the quality of the optical transceiver. So far, it is difficult to achieve true linear modulation, non-linear shape will inevitably cause signal distortion; At the same time, the modulated carrier signal signal must also modulate the optical signal, the nonlinearity of the optical signal is also a very important factor, as we all know, the optical device Non-linearity and environmental temperature changes, operating voltage stability, light emission power have a great influence, so the optical device needs 7-10 days of thermal cycle aging in production process screening, aging, testing can only be The conversion is controlled within a certain range; the optical signal is transmitted over a long distance in the optical fiber, which causes the power of the optical signal to be attenuated, the transmission frequency shifts, and the phase distortion. The dispersion effect of the optical signal also causes distortion of the optical signal; the optical signal arrives at the reception At the end, the receiving optical device still needs to cause nonlinear distortion, and the photoelectrically converted analog signal enters Demodulation, demodulation and modulation will produce nonlinear distortion. Therefore, the synthetic analog optical transceiver, from the input signal modulation - electro-optical conversion - optical transmission - photoelectric conversion - demodulation of the five processes, will cause non-linear distortion, and these signal distortion distortion is inherent, so it can not be eliminated, so the analog optical transmission The effects of video images, audio quality, and data are difficult to achieve satisfactory results. The digital optical transceiver only has quantization error of analog-to-digital conversion (such as 2.5mv for a 1V video signal at 12bits), which is not enough to cause signal distortion.
4. Intermodulation distortion caused by simultaneous transmission of multiple signals
In field monitoring applications, users may have a variety of signals, such as video images, audio, data, Ethernet, telephone or other user-defined signals. Each signal is transmitted by a pair of optical transceivers, which is necessarily expensive. In order to increase the utilization efficiency of the optical fiber and reduce the cost, necessary signals are multiplexed in the optical transceiver for transmission on one pair or one optical fiber. For FM, AM and PM optical transceivers, it is difficult to transmit high-speed signals such as 10/100M Ethernet signals or multi-channel telephones. Multiple-channel video or audio signals are mixed in frequency modulation, amplitude modulation, and phase modulation on a single carrier. Inevitably will cause all kinds of mirroring, intermodulation interference. Therefore, at present, there are many phenomena of mutual interference between FM, AM, and phase-shifting optical multi-channel video, audio, and data transmission of well-known foreign brands. These unstable phenomena have always been inherent in analog modulation technology. Disadvantages. Therefore, the analog optical transceiver has a limited capacity for transmitting signals and generally does not exceed the simultaneous transmission of four signals. The digital optical transceivers transmit digital signals, which are easy to use for large-capacity multiplexing and do not interfere with each other. For example, all-digital optical transceivers from Beijing Feiboite Technology Co., Ltd. can achieve up to 128 channels of video, audio, data, Ethernet, and telephone transmissions on the same fiber without any crosstalk interference.
5, different stability
Since the analog-modulated optical transceiver adopts the carrier modulation method, the carrier and the optical head are easily affected by the ambient temperature. There are disadvantages of the transmission quality changing with the environment. Because of this shortcoming, the maintenance of analog optical transceivers has become a headache for large-scale and important projects, which has also caused great dissatisfaction for many engineering contractors or owners. Therefore, choosing digital optical transceivers for some important projects is a wise choice.
6, the price is different
Due to different architectures, the prices of analog optical transceivers and digital optical transceivers are slightly different. In general, single-channel video, audio, and data digital optical transceivers are slightly more expensive than single-channel analog optical transceivers, and four-channel video, audio, and data digital optical transceivers have the opposite It is much cheaper than analog optical transceivers. Therefore, the cost performance of digital optical transceivers is higher than that of analog optical transceivers.
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