As the name implies, optical transceivers are terminal devices for optical signal transmission. In the long-distance optical fiber transmission, the optical cable has little effect on the signal transmission. The transmission quality of the optical fiber transmission system mainly depends on the quality of the optical transceiver. Because the optical transceiver is responsible for the photoelectric conversion and the optical transmission and the optical reception, its advantages and disadvantages directly affect the entire system. Many new users or interested users are required to understand the performance and application of optical transceivers in order to better configure and purchase.
Optical transceiver application classification
According to the application field, the current optical transceiver equipment has the following types:
1. Monitoring optical transceiver: used to transmit video signals (such as ordinary video camera output is a video signal), and can simultaneously support the transmission of audio, control data, digital signals and Ethernet signals, mainly used in highways, urban transport, community Security and all areas that need to be monitored;
2. Optical transceivers for radio and television: used to transmit RF signals, and its end-to-end transmission is not point-to-point. It branches directly in the optical path and can be used by a transmitter to multiple receivers. It is mainly used in the optical transmission field of cable TV;
3. Telecom Optical Transceivers: Each basic channel of its terminal is 2M, which is also commonly referred to as 2M. Each 2M channel can transmit 30 telephones or transmit 2M bandwidth network signals. It is only a fixed-bandwidth channel, and its use depends mainly on The supporting equipment connected to the optical transceiver is G.703 protocol, which is mainly used in the field of fixed bandwidth telecommunication optical communications.
Based on the different applications of these fields, the optical transceivers used by radio and television and telecommunications are relatively fixed and have fewer varieties. This is not detailed here. This chapter mainly introduces the configuration of optical transceivers used in the surveillance field.
The configuration of the optical transceiver is mainly determined according to the design and actual needs of the project. The signals transmitted by the optical transceiver are mainly video, audio, and control signals. Therefore, the configuration is also based on these aspects.
Video index
The main technical indicators of the video are: input/output level, impedance, signal-to-noise ratio, bandwidth, differential gain, differential phase, and so on. Input/output levels, impedance, and bandwidth are all standard in the monitoring area. Video input and output: 1VP-P, impedance: 75Ω, bandwidth: 10Hz-10MHz (except special application requirements). The main indicators that affect the performance of the optical transceiver in the video part are:
· Signal to Noise Ratio (S/N): The ratio of signal to noise. The higher the value, the better. Intuitionally, the image has snowflake and fluttering interference patterns, and regular fine twill patterns are all low in signal to noise. , In the signal to noise ratio digital optical transceiver can generally reach 67dB, while the analog optical transceiver generally does not exceed 60dB;
Differential gain (DG): The index mainly affects the saturation of the color signal. The DG distortion of the video signal means that the gain characteristic of the system changes with the level of the input signal. In general, since the luminance blanking level changes to the white level, a change occurs in the amplitude of the chroma signal at the output end of the video channel, so that in the bright part and the dark part, the color saturation, hue (especially saturation Degrees) have different changes. The digital optical transceiver DG ≤ 1%, and the analog optical transceiver DG ≤ 3%;
Differential phase (DP): its index mainly affects the hue of the color signal. The DP distortion of the video signal means that the phase shift characteristic of the system changes with the input video signal. The amount of phase shift on the transmission line varies with different luminance levels, and the phase shift between the color burst and the color subcarriers changes, so that the hue of the bright part and the dark part of the picture differ. The digital optical transmitter DP≤0.70, and the analog optical transmitter DP≤30;
The number of coded bits (only in the digital optical transceiver): Generally 8/10/12bit, the higher the number of bits, the greater the sample size, the better the image quality, but the data traffic will also increase significantly. Transmission media bandwidth requirements are more stringent.
Selecting the optical transceiver from the video side mainly evaluates the quality of the optical transceiver according to these indicators, and then selects according to the number of ways, such as: 1, 2, 4, 8, 16, 32, etc.
Audio indicator
The indicators that affect the performance of the optical transceiver in the audio part include bandwidth, impedance, input and output levels, maximum output power, signal-to-noise ratio, and nonlinear distortion. However, due to the relatively inconsistent application of audio, such as: probes (pickers) arranged at monitoring points, background music in parks, or intercoms between the two places, their requirements for audio transmission are all different. Should be considered as appropriate according to the actual situation.
In addition to the number of channels, the audio selection also divides one-way audio and two-way audio according to actual needs. Where one-way audio is applied, such as transmitting the signal of the pickup in the monitoring alarm, it only transmits the audio signal from the front end to the control center and applies bi-directional audio. Places such as audio toll stations and other places.
The selection of control data parameters for control of data transmission shall take into account the use of the data, ie, communication equipment at both ends of the system, such as a matrix, hard disk recorder or other control host and front end terminal equipment. The parameters of the data are:
Data interface: RS232, RS422, RS485 and TTL;
Data format: Manchester, Bi-phase, two-phase system;
Data rate: 1200/2400/4800/9600/11520;
Work mode: single, half duplex or full duplex.
According to these parameters, select or customize the type and quantity of optical transceiver data interfaces.
According to the above, and combined with the actual situation, determine the number of various signals, consider whether to reuse, you can come to each information point to use which or what kind of models of optical transceivers, the number of optical transceivers, optical transceivers accounted for The number of fiber cores makes the system configuration more reasonable and cost-effective.
Optical transceiver application classification
According to the application field, the current optical transceiver equipment has the following types:
1. Monitoring optical transceiver: used to transmit video signals (such as ordinary video camera output is a video signal), and can simultaneously support the transmission of audio, control data, digital signals and Ethernet signals, mainly used in highways, urban transport, community Security and all areas that need to be monitored;
2. Optical transceivers for radio and television: used to transmit RF signals, and its end-to-end transmission is not point-to-point. It branches directly in the optical path and can be used by a transmitter to multiple receivers. It is mainly used in the optical transmission field of cable TV;
3. Telecom Optical Transceivers: Each basic channel of its terminal is 2M, which is also commonly referred to as 2M. Each 2M channel can transmit 30 telephones or transmit 2M bandwidth network signals. It is only a fixed-bandwidth channel, and its use depends mainly on The supporting equipment connected to the optical transceiver is G.703 protocol, which is mainly used in the field of fixed bandwidth telecommunication optical communications.
Based on the different applications of these fields, the optical transceivers used by radio and television and telecommunications are relatively fixed and have fewer varieties. This is not detailed here. This chapter mainly introduces the configuration of optical transceivers used in the surveillance field.
The configuration of the optical transceiver is mainly determined according to the design and actual needs of the project. The signals transmitted by the optical transceiver are mainly video, audio, and control signals. Therefore, the configuration is also based on these aspects.
Video index
The main technical indicators of the video are: input/output level, impedance, signal-to-noise ratio, bandwidth, differential gain, differential phase, and so on. Input/output levels, impedance, and bandwidth are all standard in the monitoring area. Video input and output: 1VP-P, impedance: 75Ω, bandwidth: 10Hz-10MHz (except special application requirements). The main indicators that affect the performance of the optical transceiver in the video part are:
· Signal to Noise Ratio (S/N): The ratio of signal to noise. The higher the value, the better. Intuitionally, the image has snowflake and fluttering interference patterns, and regular fine twill patterns are all low in signal to noise. , In the signal to noise ratio digital optical transceiver can generally reach 67dB, while the analog optical transceiver generally does not exceed 60dB;
Differential gain (DG): The index mainly affects the saturation of the color signal. The DG distortion of the video signal means that the gain characteristic of the system changes with the level of the input signal. In general, since the luminance blanking level changes to the white level, a change occurs in the amplitude of the chroma signal at the output end of the video channel, so that in the bright part and the dark part, the color saturation, hue (especially saturation Degrees) have different changes. The digital optical transceiver DG ≤ 1%, and the analog optical transceiver DG ≤ 3%;
Differential phase (DP): its index mainly affects the hue of the color signal. The DP distortion of the video signal means that the phase shift characteristic of the system changes with the input video signal. The amount of phase shift on the transmission line varies with different luminance levels, and the phase shift between the color burst and the color subcarriers changes, so that the hue of the bright part and the dark part of the picture differ. The digital optical transmitter DP≤0.70, and the analog optical transmitter DP≤30;
The number of coded bits (only in the digital optical transceiver): Generally 8/10/12bit, the higher the number of bits, the greater the sample size, the better the image quality, but the data traffic will also increase significantly. Transmission media bandwidth requirements are more stringent.
Selecting the optical transceiver from the video side mainly evaluates the quality of the optical transceiver according to these indicators, and then selects according to the number of ways, such as: 1, 2, 4, 8, 16, 32, etc.
Audio indicator
The indicators that affect the performance of the optical transceiver in the audio part include bandwidth, impedance, input and output levels, maximum output power, signal-to-noise ratio, and nonlinear distortion. However, due to the relatively inconsistent application of audio, such as: probes (pickers) arranged at monitoring points, background music in parks, or intercoms between the two places, their requirements for audio transmission are all different. Should be considered as appropriate according to the actual situation.
In addition to the number of channels, the audio selection also divides one-way audio and two-way audio according to actual needs. Where one-way audio is applied, such as transmitting the signal of the pickup in the monitoring alarm, it only transmits the audio signal from the front end to the control center and applies bi-directional audio. Places such as audio toll stations and other places.
The selection of control data parameters for control of data transmission shall take into account the use of the data, ie, communication equipment at both ends of the system, such as a matrix, hard disk recorder or other control host and front end terminal equipment. The parameters of the data are:
Data interface: RS232, RS422, RS485 and TTL;
Data format: Manchester, Bi-phase, two-phase system;
Data rate: 1200/2400/4800/9600/11520;
Work mode: single, half duplex or full duplex.
According to these parameters, select or customize the type and quantity of optical transceiver data interfaces.
According to the above, and combined with the actual situation, determine the number of various signals, consider whether to reuse, you can come to each information point to use which or what kind of models of optical transceivers, the number of optical transceivers, optical transceivers accounted for The number of fiber cores makes the system configuration more reasonable and cost-effective.