Objective: To develop a polarisation maintaining low-noise pre-amplifier with flattened gain-curve within the spectral amplification range of Ytterbium doped fibres.Targeted Improvements: Low-noise pre-amplifier for 1064 nm are not used in the terrestrial fibretelecom market and are not produced with good noise performance. Description: Wavelength Division Multiplexing is a technique commonly used in terrestrial high-capacity optical transport networks to increase the amount of traffic conveyed by one individual optical fibre. Laser sources with slightly different (but very stable) wavelengths, each of them carrying a certain amount of data, are multiplexed by means of passive photonic components into a single mode fibre. Because the lowest attenuation in standard single mode fibres used for terrestrial telecom applications is at the so-called third window (around 1550nm), manufacturers have focused the effort in developing passive and active optical components fulfilling the standardized wavelength grid at 1550nm (according to the ITUrecommendation "ITU G.694.1, Spectral grids for WDM applications: DWDM frequency grid"). For free space optical communications, 1064nm was selected for EDRS because of an improved link budget caused by higher antenna gains (compared to 1550nm) and the availability ofhighly sensitive receivers based on homodyne detection and BPSK modulation. In addition the electrical to optical conversion (wall-plug) efficiency is higher and the radiation sensitivity lower at 1064 mm compared to 1550nm. Ytterbium doped optical fibre amplifiers operating around 1064 nm have a broad amplification spectrum (1025nm - 1075nm), which is well suited for wavelength division multiplexing (WDM). However, the supplier base is limited because wavelength around 1064nm cannot be used in terrestrial fibre applications. This activity will therefore develop an Ytterbium doped low-noise optical fibre pre-amplifier with a flattened gain-curve to support WDM at 1064nm in free-space optical communications. The aspect of low-noise performance (close to a theoretical noise figure of 3 dB) is an important aspect of the development as well as the use of space compliant components.

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