Exploring the Role of Wavelengths in Optical Networks

Optical networks utilize specific wavelengths of light to transmit data efficiently over fiber-optic cables. The choice of wavelength is crucial, as it directly influences the network’s performance, including factors like attenuation, dispersion, and overall data-carrying capacity. In this article, we will explore the roles and common uses of commonly used wavelengths.

850 nm and 1300 nm

850nm and 1300 nm wavelengths are primarily used in multimode fiber systems for short-distance communication, such as within a building or on a campus local area network (LAN). Multimode fiber has a large core diameter, 62.5 microns for OM1 and 50 microns for OM2 to OM5, which is much larger than the wavelength of the light carried in it. Due to this feature, it has a high light-carrying capacity, essentially multiple light propagation modes.

In practical applications, the larger core size of multimode fibers simplifies the connection process. It also permits the use of more affordable electronic components, like light-emitting diodes (LEDs) and vertical-cavity surface-emitting lasers (VCSELs), which function efficiently at 850 nm and 1300 nm wavelengths.

 

1310 nm and 1490 nm

The 1310 nm and 1490 nm wavelengths are used in single-mode fiber systems for medium-distance communication with minimal dispersion. They are suitable for Gigabit Ethernet and 10 Gigabit Ethernet over distances up to 20 km.

In Passive Optical Networks (PONs), the 1310 nm and 1490 nm wavelengths are fundamental to facilitating bidirectional communication between the Optical Line Terminal (OLT) at the service provider’s central office and the Optical Network Terminals (ONTs) at the customer’s premises. The 1490 nm wavelength is designated for downstream transmissions, carrying data and voice signals from the OLT to multiple ONTs. Conversely, the 1310 nm wavelength is reserved for upstream communications, enabling ONTs to send data back to the OLT. This separation of upstream and downstream traffic via distinct wavelengths allows for simultaneous two-way communication over a single optical fiber without interference.

1270 nm and 1577 nm

In XGS-PON (10 Gigabit Symmetric Passive Optical Network) systems, the 1577 nm wavelength is designated for downstream data transmission, delivering high-speed internet, voice, and video services from the Optical Line Terminal (OLT) to multiple Optical Network Terminals (ONTs). Conversely, the 1270 nm wavelength is allocated for upstream data transmission, allowing ONTs to send data back to the OLT. This separation of upstream and downstream wavelengths facilitates simultaneous bidirectional communication over a single optical fiber, enhancing network efficiency and performance. The use of these specific wavelengths in XGS-PON supports symmetrical 10 Gbps data rates, catering to the increasing demand for high-bandwidth applications and services.

 

1550 nm

In optical communication systems, the 1550 nm wavelength is extensively utilized due to its low attenuation properties, allowing for efficient long-distance data transmission. This wavelength falls within the third transmission window of optical fibers, where signal loss is minimal, making it ideal for high-capacity, long-haul networks.

Additionally, the 1550 nm region is compatible with Erbium-Doped Fiber Amplifiers (EDFAs), which can amplify optical signals without electrical conversion, further extending transmission distances. This capability is particularly beneficial in Dense Wavelength Division Multiplexing (DWDM) systems, where multiple data channels are transmitted simultaneously over a single fiber, each assigned a specific wavelength within the 1550 nm range.

 

1625 nm and 1650 nm

The 1625 nm and 1650 nm wavelengths are primarily reserved for fiber testing and maintenance purposes. These wavelengths are situated beyond the standard communication bands, allowing technicians to perform in-service testing without disrupting active data traffic. Optical Time-Domain Reflectometers (OTDRs) operating at 1625 nm or 1650 nm can detect faults, measure attenuation, and assess the overall integrity of optical fibers. The use of these wavelengths ensures that maintenance activities do not interfere with operational wavelengths, maintaining network reliability and performance.

 

CWDM and DWDM Networks

In optical networking, Coarse Wavelength Division Multiplexing (CWDM) and Dense Wavelength Division Multiplexing (DWDM) are two prevalent technologies that enable the transmission of multiple data channels over a single optical fiber by assigning each channel a unique wavelength. CWDM typically operates over a wavelength range from 1270 nm to 1610 nm, with channel spacing of 20 nm, allowing for up to 18 channels.

In contrast, DWDM utilizes a narrower channel spacing, often 0.8 nm or less, enabling a higher number of channels within the 1528.77 nm to 1563.86 nm range, primarily within the C-band. This dense channel allocation allows DWDM systems to support a significantly greater number of data channels, making them suitable for long-haul transmissions and high-capacity networks.

結論

Understanding the specific roles and applications of these wavelengths enables the design of efficient and reliable optical networks tailored to various communication needs. Multiple systems can use the same fiber using a multiplexer, such as a GPON and XGSPON on the same network. However, the use of the same wavelength, or even adjacent wavelengths can cause interference. As there are overlapping functions of commonly used wavelengths, network designers must have a clear understanding of current and future applications.