What Is a Pump-LD (Excitation Laser)?
Overview
A pump-LD (Laser Diode) is a light source for a fiber amplifier used in optical communication networks.
Types of pump-LDs include a simple structure FP-LD (Fabry-Perot Laser Diode) and an FBG-LD. An FBG-LD outputs light with high wavelength stability and narrow spectral width by connecting an FBG, in which a diffraction grating is formed on a polarization maintaining fiber, to an FP-LD. Spectral examples of each are indicated below.
FBG module schematic
Example FP-LD spectrum
Example FBG-LD spectrum
FP-LDs are mainly used for EDFAs (Erbium Doped Fiber Amplifiers), and output light matching the pumping wavelength of the EDFA, particularly the 1.48 μm band wavelength with good pumping efficiency. In recent years, FP-LDs have also started to be used for forward pumping in FRAs (Fiber Raman Amplifiers).
FBG-LDs are mainly used for FRAs, and the center wavelength can be selected according to the required wavelength specifications of the FRA.
Anritsu provides both 1.48 μm LD modules suitable for EDFAs and 1.4 μm FBG-LD modules suitable for FRAs.
1.48 μm LD modules provide optical output power from 120 to 650 mW and a center wavelength of 1,475±15 nm, according to the characteristics of the EDFA.
1.4 μm FBG-LD modules can output up to 500mW at a center wavelength can be determined according to the required specifications of the FRA.
We can also provide 1.3 μm band FBG-LD modules which can be used for higher order FRAs and S-band FRAs.
Anritsu LD modules comply with Telcordia GR-468-CORE for extremely high reliability, as well as the RoHS directive. The module has an industry-standard 14-pin butterfly shape and includes a TEC (Thermo-Electric Cooler) for temperature control and PD for optical output monitor.
Features
FP-LD module
Suitable as a pumping light source for EDFA. Some models are also applicable for forward pumping for Fiber Raman Amplifiers.
- Optical output: 120 to 650 mW (in 10 mW increments)
- Wavelength range: 1,475±15 nm
- Fiber: Single Mode Fiber (SMF) or Polarization Maintaining Fiber (PMF)
- Optical connector: Supports various optical connectors
- 14-pin butterfly package
- Includes optical isolator, monitor photo diode, and cooler
FBG-LD FBG LD module
A Pumping light source for Fiber Raman Amplifiers, also available in 1.3μm band.
- Optical output and wavelength range: 410 to 500 mW/1,420 to 1,485 nm, 500 to 650 mW/1,420 to 1,470 nm
- Fiber: Polarization maintaining fiber (φ0.25 mm, UV coated)
- Optical connector: Supports various optical connectors
- 14-pin butterfly package
- Internal monitor PD and TEC
Applications
Optical Fiber Amplifiers (EDFA/FRA)
Optical fiber amplification technology enables optical signal to be amplified without the need to convert it into electricity at a relay station, in order to compensate for transmission loss in optical fibers. The main types of optical fiber amplifiers are EDFA and FRA.
EDFA uses an optical fiber core doped with the rare earth element erbium (Er, atomic number 68) as the gain medium to amplify optical signal in the 1.55 um band via optical excitation. This EDFA that was invented in the late 1990s enables batch amplification of WDM (Wavelength Division Multiplexing) and is an important element of long hole networks such as undersea optical cables and high-capacity communication systems such as access networks.
EDFA schematic
An excitation light source for EDFA uses a 0.98 um band or 1.48 um band wavelength. Excitation light in the 0.98 um band has low quantum-conversion efficiency and a low noise figure (NF). On the other hand, excitation light in the 1.48 um band has high quantum-conversion efficiency.
Anritsu has been providing 1.48 um LD modules as excitation light sources since EDFAs started to be used as optical amplifiers for communication.
An FRA differs from an EDFA in that it is an optical amplifier that uses the optical fiber in the transmission route itself as the gain medium. It utilizes the nonlinear optical effect in the optical fiber called Stimulated Raman Scattering to have a gain band in the approximately 100 nm long wavelength region of the excitation light for optical signal in the 1.55 um band. Therefore, it can change the excitation light wavelength to amplify a signal light in a specific wavelength region.
Stimulated Raman Scattering Spectrum of Optical Fiber
In order to obtain a more accurate excitation light wavelength, an FBG-LD is used as the excitation light source for FRA. This FBG-LD contains fiber (FBG) with a diffraction grating inside the output fiber of the LD module. This FBG enables LD optical output with high wavelength stability and wavelength selectivity. Anritsu provides FBG modules for a wide range of wavelength in the 1.4 um band.
FRA schematic
