Jean-Pierre Coulon

High spectral purity microwave and terahertz oscillator

We report on the design of an ultra stable microwave/THz oscillator and on the realization and the characterization of its laser source. The tunable oscillator is expected to show below -150 dB rad2/Hz phase instability at an offset frequency of 10 kHz for a 30 GHz carrier frequency, as well as 18 GHz, 100 GHz, 400 GHz and 1 THz carrier frequencies.

Experimental evidence of a fundamental noise floor at the tens of millihertz level in laser locking onto unbalanced fibre-based Michelson interferometer

Large arm length imbalance fibre-based interferometers have shown great potential for laser frequency stabilization and control, with frequency noise power spectral density close to the 10−1 Hz/Hz1/2 level [1]. In order to understand the performance of such frequency stabilization systems, it is important to distinguish the intrinsic noise of the frequency reference, which is ultimately limited by fibre thermal noise, and the locking noise, which is limited by the detection noise but can also be affected by residual amplitude modulation fluctuations in phase modulator or other less well known causes. It is often difficult to measure the out-of-loop locking noise when one laser is locked to a frequency reference. However, the fibre length noise practically cancels when two lasers are locked onto the same interferometer with a small frequency difference, which allows to measure the out-of-loop locking noise to a very low level [2].

Note: Efficient diode laser line narrowing using dual, feed-forward + feed-back laser frequency control

We have achieved distributed feedback laser diode line narrowing by simultaneously acting on the diode current via a feed-back loop and on an external electrooptic phase modulator in feed-forward actuator. This configuration turns out to be very efficient in reaching large bandwidth in the phase correction: up to 15 MHz with commercial laser control units. About 98% of the laser power undergoes narrowing. The full width at half maximum of the narrowed optical spectrum is of less than 4 kHz. This configuration appears to be very convenient as the delay in the feed-forward control electronics is easily compensated for by a 20 m optical fiber roll.

DUAL, FEED-FORWARD + FEED-BACK LASER FREQUENCY CONTROL FOR EFFICIENT AND CONVENIENT DIODE LASER LINE NARROWING

Distributed feedback (DFB) diode lasers are convenient, small footprint and robust single mode laser sources. DFB lasers have an emission linewidth in the MHz to several MHz range, which may be too large for some applications, such as cold atom physics, optical clocks, laser ranging, lidar or gas sensing... Control of the diode forward current allows for the control the frequency of the emitted laser beam.