The establishment of data centers and the expansion of mobile networks require higher capacity and longer distance transmission. IEEE is promoting the commercialization of 100 GbE, as well as research into 400 GbE and investigation into 800 GbE. ITU-T is promoting the commercialization of coherent transceivers that use phase modulation, such as DP-QPSK, for long-distance transmission, as well as research into methods for modulating a greater number of values (16 QAM and 32 QAM) in order to increase the transmission capacity without increasing the symbol rate.
Increasing the modulation method and symbol rate requires extra investment because the transmission equipment needs to be replaced. However, since fiber amplifiers can amplify an optical signal, the fiber amplifier equipment can be reused even if the modulation method and symbol rate are changed. Broadly speaking, there are 2 types of fiber amplifiers; EDFA (Erbium Doped Fiber Amplifier) and FRA (Fiber Raman Amplifier). 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 enables batch amplification of WDM (Wavelength-Division Multiplexing) and is an important element of long haul networks such as undersea optical cables and high-capacity communication systems such as access networks. FRA differs from 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 100 nm long wavelength region of the excitation light. Therefore, it can shift the excitation light wavelength to amplify an optical signal in a specific wavelength region.
Anritsu provides pump LDs, SOAs, and gain chips for optical communication.
Pump LDs are LD modules for fiber amplifier, and we provide a 1.48 um FP-LD module suitable for EDFA and an FP-LD with 1.4 um FBG suitable for FRA. The FP-LD with FBG connects fiber with FBG (Fiber Bragg Grating) formed on the FP-LD and provides high wavelength stability and narrow linewidth by selecting the wavelength.
An SOA is an optical semiconductor that directly amplifies an input signal and is generally embedded as a receiver amplifier in a CFP or CFP2 module in order to amplify the WDM wavelength of 100GBASE-ER4/ZR4 on the reception side.
A gain chip is a light source for external cavity type tunable lasers and is optimal for coherent transceivers and external cavity type tunable lasers for ITLA because it has a wide gain bandwidth and large gain.
Some examples of the optimal applications for each light source are indicated below.
- Optimal light source for EDFA and FRA: Pump LD
- Optimal optical device as receiver amplifier of ER4 and ZR4 transceiver: SOA
- Optimal light source for coherent transceiver and ITLA: Gain chip