Long-wavelength band (L-band)

Introduction

The L-band, ranging from 1565 nm to 1625 nm, stands for the long-wavelength band (see Figure 1). It is the second primary wavelength band used for optical communication, because attenuation of optical fiber in the L-band is the second lowest after the C-band. In addition, erbium-doped fiber amplifier (EDFA) operating in the L-band is widely available, making the L-band the second choice after the C-band.

Figure 1: O/E/S/C/L-bands

Optical transmission system using C+L band amplification

When employing EDFA in the L-band, however, an extra complexity is added to the system, as one EDFA does not amplify the C- and L-bands simultaneously. Figure 2 shows a typical example of a WDM transmission system using both the C- and L-bands. Signals from N transmitters are multiplexed by wavelength multiplexer and are launched to the fiber. When amplification is needed, the signals are de-multiplexed to the C- and L-bands and amplified by two EDFAs; one for the C-band and the other for the L-band. After amplification, these two bands are multiplexed again and launched to the next fiber section. At the receiver, signals are de-multiplexed to individual channels and detected.

Figure 2: Schematic of WDM system using both C- and L-bands

Introduction of additional amplifier at the amplification site is relatively easy if space and power supply are not critical issues, and L-band amplifiers have been used in terrestrial transmission systems for a long time. In contrast, submarine optical systems used the C-band only for a long time, as both space and power supply are limited under water. It is just recently that submarine optical systems has started using the L band (for example Pacific Light Cable Network).

FiberLabs’ L-band product lineup

FiberLabs offers a wide range of optical instruments operating in the L-band. Please check the following link for details, and feel free to contact us for your specific needs.

• (*) HP stands for “High Power”.
• (*) 4-λ CWDM uses 1531, 1551, 1571, and 1591 nm.
• (*) 8-λ CWDM uses 1471, 1491, 1511, 1531, 1551, 1571, 1591, and 1611 nm.

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