In today's security systems, coaxial cables are still commonly used for short-distance video transmission. However, with the rise of IP technology, TCP/IP-based network transmission is becoming increasingly popular. Despite these advancements, neither method fully meets the demands of modern security systems. As a result, optical transceivers have become essential components in the transmission chain, offering superior performance and reliability.
**Classification and Working Principles of Optical Transceivers**
An optical transmission system typically consists of three key components: a light source (optical transmitter), a transmission medium, and a detector (optical receiver). These elements work together to convert electrical signals into optical signals and vice versa. The optical transceiver plays a central role in this process, handling both electro-optical and opto-electrical conversions.
Optical transceivers can be broadly categorized into analog and digital types:
**1. Analog Optical Transceivers**
Analog optical transceivers use Pulse Frequency Modulation (PFM) to transmit real-time video signals. At the transmitting end, the analog video signal undergoes PFM modulation—this could involve frequency, phase, or amplitude modulation—before being converted into an optical signal. Upon reaching the receiver, the optical signal is converted back into an electrical signal, and then demodulated to restore the original video.
These devices can support transmission distances of up to 30 km, with some models capable of reaching 60 km or even hundreds of kilometers. They also offer low distortion, high signal-to-noise ratio, and minimal nonlinear distortion. Additionally, wavelength division multiplexing allows for bidirectional transmission of video and data over a single fiber.
**2. Digital Optical Transceivers**
Digital optical transceivers are gaining traction due to the advantages of digital technology over traditional analog methods. Two main approaches exist: MPEG-II compressed and non-compressed digital transceivers.
MPEG-II-based transceivers compress video signals into N×2 Mbps data streams, which can be transmitted via standard telecom interfaces or directly through optical fibers. This reduces bandwidth usage and allows efficient utilization of existing infrastructure. However, image compression introduces delays of 1-2 seconds, making them unsuitable for real-time applications. They also tend to be more expensive and may introduce minor image distortions.
Non-compressed digital transceivers, on the other hand, perform A/D conversion and multiplex various signals before transmitting them over optical fibers. This approach ensures high-quality, real-time video transmission with excellent signal integrity (SNR > 60 dB, differential phase and gain distortion < 2%). It also supports advanced communication technologies, improving system reliability and reducing costs.
**Application Fields of Optical Transceivers**
Video optical transceivers have been in the Chinese market for over two decades, initially used in sectors with strong financial backing such as government agencies, public services, and industries requiring high transmission efficiency. As domestic technology has matured, their application has expanded significantly.
**Safe City Projects**
The Safe City initiative is a large-scale urban management system that integrates public safety, traffic control, emergency response, and disaster prevention. While video optical transceivers play a smaller role in the overall project, they are critical for linking surveillance systems with alarm, access control, and broadcasting networks. In large-scale projects, the cost of optical transceivers can reach several million yuan.
**Highways**
With long-distance highway projects spanning over 200 km, the demand for video optical transceivers is substantial. Though their share in the total electromechanical budget is small, their impact on the monitoring system is significant. Quality and reliability are key factors, and only well-established brands with strong technical capabilities can succeed in this competitive market.
**Urban Intelligent Transportation**
As cities grow, so do transportation challenges. Many cities, including Beijing, Shanghai, and Shenzhen, have implemented traffic monitoring systems. In the absence of mature IP-based solutions, optical fiber transmission remains the preferred choice. Video optical transceivers are used for traffic counting, signal control, and accident monitoring, ensuring smooth city operations.
**Urban Rail Transit**
With rapid development in rail and highway infrastructure, the need for reliable monitoring equipment has increased. Optical transceivers, thanks to their high bandwidth, long-distance capability, and resistance to interference, are widely adopted. Their growing market demand has led to lower costs and a healthier industry environment.
Currently, Safe City, intelligent transportation, highways, and urban rail transit represent the largest markets for optical transceivers. According to forecasts, China’s urban rail transit investment will reach 415.9 billion yuan between 2010 and 2015, with a compound annual growth rate of 13.8%. The intelligent transportation sector is expected to see around 20 billion yuan in annual investment, with video surveillance accounting for approximately 16%—a significant portion of the market.
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