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With optical and cable transmission network expansion on the rise toward wider geographical coverage with increasingly broadband content, the 1550nm optical transmitter has grown to be the optimal device technology in metropolitan CATV and long haul CATV network deployment. With well-known low-loss characteristics and suitability for optical amplification in the 1550nm optical transmitter window, these transmitters allow operators to deliver outstanding quality video signal throughout much wider ranges compared with the previously applied 1310nm CATV system. The article focuses on its working principles, typical applications and the product manufacturing aspects in current cable television networks.
Why 1550nm for Long-Distance Transmission?
The 1550 nm optical transmitter uses the 1550 nm wavelength where there is minimal attenuation for the commonly used single-mode fiber (0.2 dB/Km for the 1550 nm compared to 0.35dB/Km for 1310nm). This has the base advantage of extending reach to over 50 Km without regeneration. Even more important, the 1550 nm wavelength band matches well with EDFA, where the optical signal can be gain-shifted somewhere in a chain in an inexpensive manner if all else fails. EDFA technology can produce the required CNR and distortion for analog and digital video distribution and provide extended reach to a typical 1550 CATV transmitter of over 100 Km.
External Modulation Technology
High performance 1550nm optical transmitter solutions are external modulation solutions, as opposed to direct modulation solutions that are used in shorter-range applications. The method is based on a continuous-wave distributed feedback (DFB) laser and an external lithium niobate (LiNbO₃) modulator to modulate the CATV RF signal onto the optical carrier. External modulation provides excellent composite second-order (CSO) and composite triple-beat (CTB) performance, with CNR ≥ 52 dB and CTB ≤ -65 dB. Newer models of the 1550 CATV transmitter feature adjustable stimulated Brillouin scattering (SBS) suppression power from 13dBm to 19dBm, enabling network engineers to tune the performance to match different fiber lengths and launch powers.
Key Applications of 1550nm CATV Transmitters
The 1550nm CATV fiber transmitter is used in various network architectures:
Supertrunking: Connecting headends to distribution hubs over distances up to 80km, and all video sources are brought together into a central transmission backbone.
FTTH Networks: With the 1550nm optical transmitter sending video content in the broadcast band as well as data services, the equipment is able to integrate seamlessly with FTTH equipment at the central office (CO).
Metropolitan Distribution: This is the main video source for city-wide CATV which uses EDFAs to divide the video to reach thousands of customers in various areas throughout the city.
DWDM Integration: The ability of a dense wavelength division multiplexing system to transport several 1550nm video channels using a single fiber in a high capacity backbone transport channel.
Manufacturing Precision for Reliable 1550nm Transmitters
1550nm optical transmitter products require extremely precise production processes to ensure the reliability and continuity of the products. With more than 10 years of experience in the manufacture of CATV fiber transmitter solutions, Shandong Wanshuo Optoelectronic Equipment Co., Ltd. is an experienced manufacturer. It has 12 workshops of high-gradecleanrooms, and adopts the best production lines in the SMT industry, which can realize direct connection rate of 99.8% in PCB assembly with 3D SPI+3D AOI testing. Every 1550 CATV transmitter is fully traceable and end-to-end quality controlled by automated wave soldering, assembly and device production lines. With this intelligent manufacturing process, Shandong Wanshuo can provide long distance optical transmitter solutions which are suitable for the carrier-grade CATV networks around the world with rigorous requirement.
Conclusion
As an important device used in long distance CATV transmission, the 1550nm optical transmitter has excellent signal quality performance over long distances, low fiber attenuation, EDFA compatibility and high external modulation precision. These transmitters can be used in a number of different applications, including supertrunking, FTTH, metropolitan distribution and DWDM, allowing service providers to offer the best video experience. Shandong Wanshuo Optoelectronic Equipment Co., Ltd. remains a reliable supplier of CATV fiber transmitter solutions, equipping products with advanced manufacturing technology and a full range of CATV products.