This paper is focused on the demonstration of an externally modulated analogue fibre-optic link that improves microwave gain with minimal penalty on the output noise. The key device is the optical source composed of parallel wavelength-multiplexed semi-conductor lasers. The microwave gain is proportional to the optical power incident onto the photodetector, while the noise figure is also related to the optical noise parameter ("RIN") of the laser source. The dedicated multi-laser source increases the total optical power well over the maximum values of so-called "power" DFB lasers. Thus it leads to an improved link gain over bandwidths broader than 20 GHz. Simultaneously, this arrangement reduces the equivalent RIN of the multi-laser source (compared to the constituting DFB laser RINs), which keeps the noise figure to a low level. The constituting laser chips are wavelength-multiplexed into a single monomode fibre then into an external modulator. The use of a wavelength multiplexer reduces the insertion losses of each individual DFB laser into the common fibre, in order to increase the total optical power delivered into the link. The wavelength-multiplexing also shifts unwanted heterodyning beatings between optical carriers beyond the photoreceiver bandwidth. We report theoretical and experimental considerations on potential limitations of this device for microwave signal remoting. Experiments show that the modulator efficiency, the signal phase (for each optical carrier) and the microwave distortions have negligible dependency with respect to optical wavelength, while non-linear optical interactions along the fibre are not a stringent penalty. Finally, due to chromatic dispersion limits, we demonstrate the application of broad-bandwidth microwave signal remotings with high gains and low noise figures to a few hundred-metres fibre-link lengths.
We present a new coherent optical Beamformer for the receive mode based on a Dual Frequency Laser and Spatial Light Modulation matrixes. This coherent architecture, described and detailed by different building blocks, allows a full reconfiguration of the beam thanks to the SLM matrixes and a first down conversion due to the conjoint use of a heterodyne source and an external modulator.