Seminar by Dr. Fabien Bretenaker on "Low-noise lasers and amplifiers for microwave photonics and metrology applications"

Microwave photonics links will play an important role in future microwave systems. They allow for example to carry analog signals or radar local oscillators on an optical carrier over long distances. They also carry out a number of functions such as phase shifts, the introduction of delays on ultra-broad bandwidths, reconfigurable filtering of signals, or even more complex functions such as spectral analysis or correlation of microwave signals.

One of the key elements of such microwave photonics links is the laser source. In order for example to optically distribute a microwave local oscillator, one can use a single-frequency laser and modulate it with an external modulator. In this case, one needs a laser with an extremely low intensity noise. An alternative strategy consists in forcing the laser to oscillate on two orthogonal polarization modes. The beat note between these two modes then lies in the desired microwave range, and naturally exhibits a 100% modulation index. Moreover, the fact that these two frequencies originate from the same cavity allows them to exhibit a low noise. We have obtained such a dual-frequency oscillation from Vertical External Cavity Surface Emitting Lasers (VECSELs) [1,2], and deeply analyzed their noises and the amplitude and phase noise correlations between the two modes [3]. Moreover, we have recently applied these techniques to the realization of low-noise lasers for compact atomic clocks [4].

Another key element to future microwave photonics links is low noise optical amplifiers. However, conventional amplifiers, based for example on erbium-doped fibers, semiconductors, or Raman effect in fibers, degrade the signal-to-noise ratio. Indeed, quantum mechanics tells us that the noise figure of such phase independent amplifiers, that is to say that amplify similarly all quadratures of the field, cannot be less than 3 dB for a large gain. We have thus recently started to build so-called phase sensitive amplifiers based on parametric conversion in highly nonlinear fibers, and shown that such amplifiers are interesting for microwave photonics applications [5].

Event Date: 
Tuesday, December 11, 2018 - 10:30Wednesday, December 12, 2018 - 11:30

Speaker:  Dr. Fabien Bretenaker              

                 Laboratoire Aimé Cotton, Orsay, France & Raman Research Institute, Bangalore

Tuesday 11, Dec 2018 - Wednesday 12, Dec 2018
10:30 AM - 11:30 AM