Exotic III-V coherent photonic sources: from physics to industry
The aim is to generate and control exotic coherent light states, along spatial, temporal and polarization observables. For this purpose, we develop high power lasers based on III-V nanotechnologies, emitting in the NIR and MIR: GaAs and Sb-based VeCSEL optically pumped by a diode (Equipex EXTRA, LPN RENATECH). These sources address various applications: Gas detection, agro-environment control, security, optical tweezers for biology… Innovative micro-chip lasers (fig.1) emitting a low divergence low noise monochromatic tunable wave, are under industrial development with INNOPTICS startup company (SFO Innovation award 2013, SATT-AXLR Funder, Patent ). These « OPSCAN » devices allow surpassing state-of-the art commercial technologies, thanks to a combination of power-coherence-wavelength tunability performances and integration. Upstream research has led to the demonstration (patent ) of the first VORTEX laser (fig.2) generating a beam carrying controlled Orbital-Angular-Momentum, based on photonic crystals, of great interest for bio-photonics.
 A. Garnache, et al., Patent UM2/CNRS, #EP14305752.9 (2014).
A. Laurain, et al., Optics Express, 18 (2010), 14631. Laser Focus World (August 1010).
 A. Garnache, et al., Patent UM2/CNRS, #EP14307037.3 (2014)
This site presents the research efforts performed at IES (in Montpellier, France) concerning the design, fabrication and physical study of new photonic sources, the so-called VeCSEL (Vertical External-Cavity Surface Emitting Lasers), which are based on innovative semiconductor nanostructures.
These lasers are inherently compact, wavelength flexible (in both the Near Infra-Red and Mid Infra-Red ranges) and widely tunable, allowing high power high coherence TEM00 single-frequency emission, overcoming other technologies performance and features.
This VeCSEL gemoetry demonstrates a particular ability for the generation and the control of new coherent light states : modeless lasers, Vortex lasers, two-frequency lasers, ...
This work is extended by a physical study of the laser coherence and noise, based on a strong background concerning optical instrumentation (free-space and fibred) and custom electronics.
To an Eignestate of Light at High Power
The main objective when designing a single-frequency continuous-wave laser is to reach high coherence concerning the three physical axes on which a light state can be projected :
- High spatial coherence along the |k> axis, in order to permit long length collimation or diffraction limited spot-size at the focus of a lens, thus to spatially concentrate the light. This is typically linked to the ability of the laser to select a single transverse mode, thus relevant to the cavity stability.
- High time coherence along the |z> axis and reach ultimately single-frequency narrow linewith operation of the laser light. This axis is typically linked to the cavity length and to the aibility of the laser to select a single longitudinal mode.
- A well defined polarisation state |E>, for example a strong linear polarization. This property is usually governed by gain dichroïsm or birefringence effect.
For example, for a 1 Watt beam at 1 µm, this is equivalent to confinate 1018 photons per second in a single light state of stimulated emission !
The main purpose of this project is to reach such a high coherence state while overcoming other soruces limitations concerning :
- the Wavelength flexibility : because the VeCSELs gain medium is made of semiconductor, this kind of laser ca be fabricated for emission in a very wide range of wavelengths, from blue light (with intra-cavity doubling) to mid-IR (up to 3µm).
- High power / High Brightness emission : owing to their geometry, VeCSELs can be obtained even at very high power while preserving high beam quality. For examples, VeCSELs are used today as replacement for standard Verdi pump systems for Diode-Pumped Solid-State Lasers.
- High coherence : narrow linewidth, diffraction limited beam and strongly polarized emission are demonstrated, even at high multiwatt power.
- Compactness : thanks to the use of semiconductor technology, laser light control can easily be integrated over very small sizes. For that reason, VeCSELs can be obtained in a very compact set-up when packaged with micro-optics, even while being optically pumped.
- Functionnality : VeCSELs can feature many functionnalities such as broadband tunability for target applications, such as gaz spectroscopy.
Targeted Applications for VeCSELs emitting in the 0.4µm-1.5µm range
The wavelength flexibility, compactness and high coherence emission of the VeCSEL permits to address the requirements of a very wide range of applications, such as :
|RGB laser illuminators for next-generation TV or projectors.||High accuracy gyroscopes for satellites navigation.|
|Radar, Lidar, Telecom.||Metrology, Atomic Clocks, ...|
Targeted Applications for VeCSELs emitting in the Mid-IR 2.3µm-2.7µm
Mid-IR VeCSELs can also address the requirements for various applications, from medical applications to gas analysis or free-space telecommunications.
|Medical Diagnostic & Surgery||Remote Sensing / Environmental Monitoring / Climatology / Atmospheric Physics ...|
|Free Space Communications||Sensing & Security|
Indeed, The 2-3 ?m Mid-IR window is especially well adapted for laser spectroscopy applications as many molecules of interest exhibit strong absorption lines : CH4, NH3, CO, HF near 2.3 ?m for gas analysis/detection applications and H2O, CO2 near 2.7 ?m for isotopic ratio spectroscopy application. This last application is of great interest for atmospheric physics, climatology, environment...
The VeCSEL in the Lasers State of the Art
Because it is a Diode-Pumped Solid-State semiconductor laser, the VeCSEL is at the crossing of two technologies :
|Traditionnal Diode-Pumped Solid-State Lasers (DPSSL), Fiber Laser, OPO, Dye&Gas Lasers||Usual Monolithic Semiconductor Diode Laser (µcavity VCSELs)|
|Bad Wavelength Flexibility (spectral holes), bulky
Applications : Lab, pump, lidar, cutting, metrology, medical, military ...
|Physical Limits, Low Coherence|
Applications : Data storage, Telecom, Pump, Gaz Analysis, Position sensing ...
Wavelength Flexibility and Compactness
We have to overcome the Technical Limits of DPSSLs and the Physical Limits of semiconductor diode lasers, while preserving both the high Coherence, Wavelength Flexibility and Compacity. This can be achieved by means of the VeCSEL technology.
The wavelength is easy to tune/adjust thanks to QW’s (Quantum Well) Ingeneering. Semiconductor lasers - including VeCSELs - are low consumption lasers, exhibiting low threshold. They also benefit in broad homogeneous gain (kT 200 cm-1), leading to widely tunable lasers.
The VeCSELs developed at IES are optimized for high coherence as they rely on a high finesse stable cavity (F 500) with mm-cm length. This leads to diffraction limited beams exhibiting ultra-low spontaneous emission limits (Shallow-Townes Limit < 1Hz), allowing narrow linewidth and low noise operation.
A VeCSEL is composed by a semiconductor nanostructure, called "gain-mirror" or "1/2 VCSEL", combining both the active section and the backside HR mirror. The cavity is usually closed thanks to a concave mirror, leading to a high fiesse optically stable cavity. The 1/2 VCSEL structure can be designed to be pumped optically or electrically.
The VeCSEL works inherently for high coherence light generation, owing to its cm-length stable high-finesse cavity design, while other semiconductor laser technologies such as DFB (Distributed Feedback Laser), µ-cavity VCSELs or ECDLs (Extended-Cavity Diode Laser) are limited because of the high amount of losses inside the laser cavity and the waveguiding principles on which they rely.