Ludovic Frein

Non-linear optoelectronic phase-locked loop for stabilization of opto-millimeter waves: towards a narrow linewidth tunable THz source

We propose an optoelectronic phase-locked loop concept which enables to stabilize optical beat notes at high frequencies in the mm-wave domain. It relies on the use of a nonlinear-response Mach-Zehnder modulator. This concept is demonstrated at 100 GHz using a two-axis dual-frequency laser turned into a voltage controlled oscillator by means of an intracavity electrooptic crystal. A relative frequency stability better than 10⁻¹¹ is reported. This approach of optoelectronic down conversion opens the way to the realization of continuously tunable ultra-narrow linewidth THz radiation.

40-GHz Photonic Synthesizer Using a Dual-Polarization Microlaser

An optically-carried microwave synthesis working at 40 GHz is demonstrated by using a two-frequency microchip laser inside a digital phase-locked loop. We report a relative frequency stability better than 2.5!10!11. Different frequency sweeping formats are programmed.

Dual frequency laser with two continuously and widely tunable frequencies for optical referencing of GHz to THz beatnotes

A dual-frequency 1.55 µm laser for CW low noise microwave, millimeter and sub millimeter wave synthesis is demonstrated, where frequency stabilization is possible on each wavelength independently. The solid state Er:Yb laser output power is 7 mW. The amplitude noise is -150 dBc/Hz at 1 MHz offset frequency. In free running regime, the frequency noise is 3.10(5)/f Hz/sqrt(Hz) (800 Hz on a 1µs timescale), better than commercial fibered or semi-conductor sources at this wavelength.

Beat note stabilization of a 10–60 GHz dual-polarization microlaser through optical down conversion

Down-conversion of a high-frequency beat note to an intermediate frequency is realized by a Mach-Zehnder intensity modulator. Optically-carried microwave signals in the 10-60 GHz range are synthesized by using a two-frequency solid-state microchip laser as a voltage-controlled oscillator inside a digital phase-locked loop. We report an in-loop relative frequency stability better than 2.5×10⁻¹¹. The principle is applicable to beat notes in the millimeter-wave range.

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.

Opto-electronic down conversion: A novel approach for optical beat note stabilisation up to the THZ domain

A novel scheme based on opto-electronic down conversion is proposed and demonstrated to obtain an ultra-high spectral purity and tunable optical beat note in the GHz and millimeter wave range. We report an in-loop relative frequency stability better than 10−11. This approach is scalable to the THz domain.

Free-space active polarimetric imager operating at 1.55 μm by orthogonality breaking sensing.

We report the design and optimization of an active polarimetric imaging demonstrator operating at 1.55 μm that is based on the orthogonality breaking technique. It relies on the use of a fibered dual-frequency dual-polarization source raster scanned over the scene. A dedicated opto-electronic detection chain is developed to demodulate the optical signal backscattered at each location of the scene in real time, providing multivariate polarimetric image data in one single scan with limited acquisition time. We experimentally show on a homemade scene that contrast maps can be built to reveal hidden dichroic objects over a depolarizing background, as well as their orientation. Finally, experiments through air turbulence illustrate the benefit of such an imaging architecture over standard polarimetric techniques requiring multiple image acquisitions.

Dual polarization DFB fiber lasers as optical phase-locked microwave sources in the 1-10 GHz range

Fully fibered microwave-optical sources at 1.5 μm are studied experimentally. It is shown that the beat note between two orthogonally polarized modes of a distributed-feedback fiber laser can be efficiently stabilized using an optical phaselocked loop that uses the pump-power induced-birefringence as actuator. Beat notes at 1 GHz and 10 GHz of Erbium doped fiber laser are successfully stabilized to a reference synthesizer, passing from the 3 kHz free-running linewidth to a stabilized sub-Hz linewidth, with a phase noise as low as -75 dBc/Hz at 100 Hz offset from the carrier. An ErbiumYtterbium co-doped fiber laser is also investigated and successfully stabilized. Such dual-frequency stabilized lasers could provide compact integrated components for RF and microwave photonics applications.

Active infrared polarimetric imaging demonstrator by orthogonality breaking sensing

We report the design of a free-space active infrared polarimetric imaging demonstrator operating at 1.55 μm and based on a non-conventional approach: the orthogonality breaking sensing technique. Relying on the illumination of a scene with a specific light source, the imager offers an original tradeoff between image acquisition time (~ 1 s) and polarimetric consistency in comparison to standard polarimetric imagers such as division of time or division of amplitude systems. We will illustrate the capability of such an imager to enhance the visibility of hidden objects on homemade scenes.

Bridging the gap between THz and microwave photonics through optoelectronic generation of interleaved combs Invited paper

Optoelectronic down-conversion and phase locking of mm-wave and THz optical beatnotes using interleaved combs is presented. The generation of the required combs using either nonlinear modulation or four-wave-mixing in highly nonlinear fibers is detailed. These down conversion techniques are then implemented to phase-lock widely tunable mm-wave beatnotes well below the laser linewidth itself. Such achievements are made possible through a thorough trade-off between laser characteristics, optoelectronic arrangement, and electronic-feedback design. These advanced techniques give a new trend for bridging the gap between microwave and THz photonics.