We report on the development and characterization of a compact visible Brillouin fiber laser. The laser is designed in a short cavity configuration and demonstrates an output power of 30 mW. Detailed analysis reveals an intrinsic linewidth of 6 Hz, indicating exceptional spectral purity. Comprehensive gain characterization was performed as a function of pump power, providing critical insight into the laser's performance and limitations. These findings contribute to the advancement of compact, highly stable visible fiber lasers for quantum technologies and microwave photonics.

Mid-infrared spectral imaging is becoming increasingly attractive in various fields, from polymer analysis to vegetation monitoring. While conventional architectures such as push -broom systems are now commercially available, applications demanding high spectral resolution or tunability increasingly rely on laser-based illumination. However, coherent sources introduce metrological challenges, including speckle artifacts, intensity instabilities, and beam pointing fluctuations. This work presents correction strategies addressing these effects in a tunable laser imaging system with 10 nm spectral resolution, enabling accurate and reliable data acquisition.

Outdoor measurement of chlorophyll fluorescence at the leaf scale as a reliable and fast probe of plant photosynthetic activity is a challenge in agronomy. A better understanding of the stationary and transient heterogeneity of photosynthetic activity within the canopy will require concomitant leaf scale measurements targeting different strata, since irradiance varies depending on leaf orientation and position within the canopy. As a contribution to the emergence of such tools, this communication presents the development and preliminary measurements of chlorophyll fluorescence LiDAR, with an measurement range of 60 cm and a footprint of 30 cm(2). It was performed indoors on maize.

We propose a theoretical description and experimental validation of a frequency self-stabilized photonic oscillator. This photonic oscillator which relies on a solid-state laser and a nonreciprocal Brillouin fiber resonator (BFR) arranged in an optical phase-locked loop (OPLL) was recently shown to provide very narrow linewidth in the Hz range. Special attention is given to end up with analytical expressions relying on coupled-mode formalism, of the BFR dynamics in which the non-resonant configuration for the pump has to be addressed. Furthermore, the transfer function of the full system is derived from the response of each component within the OPLL leading to two interleaved loops, relative to the phase and to the amplitude fluctuations of the optical field. An experimental setup including a solid-state Er:Yb laser is detailed and used to test the model predictions, both for phase noise level and response time. This model opens the way to the optimization of this new type of photonic oscillator which can be adapted to any kind of pump laser.

In this paper, the design of integrated photonics components for blue/near-ultraviolet wavelength range is presented. Optical properties of the silicon oxynitride (SiON) in this spectral range are exploited to develop a complete library of photonic integrated components for operation in blue/near-UV spectral range

The development of precision laser spectroscopy around 420 nm for gas sensing, atomic clocks and laser cooling is slowed down by the lack of compact narrow linewidth laser sources allowing lab-to-market technology transfer. In the infrared (IR) part of the spectrum, the laser diode technology is mature to address those kind of specifications but for shorter wavelengths there are still technological issues. Commercial blue laser diodes have a wide multimode optical spectrum. To improve the frequency noise performances, the use of an external cavity has been proven to favor single mode behavior. Nevertheless, opto-mechanical instabilities of the external cavity limit the laser linewidth to a few MHz. To overcome this issue, we propose a compact and low-cost all-fiber-based locking setup for frequency noise suppression of a 420 nm external-cavity diode laser. This versatile and compact optical reference allows to reduce the laser frequency noise up to 40 dB associated with a linewidth reduction from 850 kHz to 20 kHz. To our knowledge this is the first demonstration of such a stabilization scheme in this wavelength range. The originality of our work is to point out that actual performances of fiber based photonic components around 420 nm, limit the noise reduction efficiency of such optoelectronic feedback loop scheme. This simple locking scheme might be implemented for a large range of wavelengths and can be integrated on a small footprint for embedded applications requiring narrow linewidth blue laser diodes.

Recently, we proposed an active mid-infrared (MIR) hyperspectral imaging system for early detection of plant water stress. A quantum cascade tunable laser powered this stand-off detection system, in which “speckle” in images due to coherent nature of laser radiation. The speckle affects the spatial resolution of the images. In this article, we evaluate several speckle suppression methods suitable for the mid-infrared region. To quantify the reduction of speckle, we compare their spatial contrast. We combined optical techniques and showed their ability to reduce the speckle contrast from its initial value 0.413 down to 0.11, representing a 73% reduction

The increase of spectral purity for a laser (fibers, microsphere, integrated optics, etc.) is of major interest for various optical functions (sources, sensors, filters, optical clocks, etc.) and for different fields of application (optical communication, spectroscopy, defense, metrology, environment, health, etc.) as the system’s margin could be considerably improved. One of the most promising approach to generate compact and narrow linewidth lasers is based on the stimulated Brillouin scattering (SBS) optical nonlinearity. The establishment of SBS in an optical cavity gives rise to the emission of a Stokes wave, which is more coherent than the optical pump used in the linear process. Impressive noise performances have been reported in such Brillouin lasers. They are measured in terms of frequency noise and reduction factor higher than 40 dB may be reached when the noise level of Stokes wave is compared to that of the pump. Frequency noise analysis consists in studying the fluctuations of a laser optical frequency. (A derivative links phase noise and frequency noise). Measurements of the laser power spectral density in the electrical domain (DC-MHz) using an electrical spectrum analyzer give all the properties of the laser line (centered on its optical frequency). The wavelength-tunability could be a very attractive property for many applications. We realize such a tunable C-Band laser with excellent performances for the whole wavelength range. Its intrinsic laser linewidth is a few ten’s of mHz. Its integrated linewidth is in the kHz (or sub-kHz) range and it could be potentially improved by locking the laser signal to a better stable reference. The frequency noise reduction is above 60 dB. . Its integrated linewidth is in the kHz (or sub-kHz) range and it could be potentially improved by locking the laser signal to a better stable reference. The nice point of our approach is that different commercial tunable C-band sources may be used, for which we simply improved the spectral properties. The method can be generalized to other wavelength ranges.

We demonstrate a compact and low-cost all-fiber-based locking setup for frequency-noise suppression of a 420 nm external-cavity diode laser. Frequency noise reduction in the 100 Hz to 800 kHz range is demonstrated up to 40 dB associated with a linewidth narrowing from 850 kHz to 20 kHz for 10 ms integration time. This simple locking scheme might be implemented for a large range of wavelengths and can be integrated on a small footprint for embedded applications requiring narrow linewidth blue laser diodes.

Narrow linewidth laser diodes (LDs) emitting in the near-UV (NUV) are gaining attention for applications ranging from spectroscopy to atom cooling and interferometry or other applications requiring high spectral purity. InGaN edge-emitting LDs can exhibit a power of hundreds of mW in an unstable multimode regime detrimental to aforementioned uses. In this paper we report on a compact and robust design based on a low-cost blue LD, a beam shaping optical system and a fiber Bragg grating (FBG) acting as a wavelength selective reflector. One longitudinal mode of the non-antireflection coated laser diode is selected by a close to 30 pm bandwidth FBG allowing a few mW output power around 400 nm and a sidemode- suppression-ratio approaching 50 dB exceeding our last published results. Our previous studies showed that a single-frequency regime with a sub-MHz integrated linewidth and an estimated intrinsic linewidth of 16 kHz was possible by a carefully engineered external cavity. We will study the influence of the cavity length with different fiber types (SM or PM). Assessment will focus on the linewidth and a detailed intensity and frequency noise analysis of the emission. We will also investigate for the first-time the stability of several types of UV-FBG submitted to tens of mW of 400 nm light guided into the fiber core. This work demonstrates state-of-the-art performances by connecting low-cost components and opens the way to the fabrication of highly coherent laser sources that could meet the markets for the NUV applications.

In this paper, we study the intensity noise performance of frequency-doubled lasers. In particular, we investigate how the relative intensity noise (RIN) of multimode fiber lasers is affected by the second harmonic generation process. We first develop an analytical approach and show that, in contrast with a single-mode laser, the low frequency RIN (or excess noise) of a two-mode laser can increase of more than 6 dB after the frequency-doubling operation. This occurs when the intensities of both modes are different and this is explained by a nonlinear coupling between noise and intensity of modes. To deal with more commonly-used multimode fiber lasers, we have extended our study to any number of modes. For this purpose, we have developed a model to numerically simulate the dynamics of a multimode fiber laser. This model includes noise sources and mode competition dynamics due to spatial hole burning. It gives access to the complex amplitude of the electric field of the laser. Using this model, we have confirmed that the excess noise of frequency-doubled multimode fiber lasers can be more than 6 dB higher than the excess noise of the laser before frequency-doubling.

Thermal imaging and the recent availability of widely tunable infrared QCL lasers (Quantum Cascade Laser) allow us to propose an active hyperspectral imaging system operating in mid-infrared (MIR) band to obtain simultaneously large amounts of spatial and spectral information on the samples. In order to evaluate more precisely the capacities of the active hyperspectral imaging, we propose a system composed of four powerful QCL tunable lasers (in order to cover 3 - 5 μm and 7 - 11 μm wavelengths) and three cameras: a visible and near-infrared (NIR) range, a bolometer for 7 - 13 μm range and an InSb cooled camera for 3 - 5 μm range. We present the algorithm for image acquisition, image and data processing. Finally, we present and discuss some preliminary results using this system to characterize plant leaves under controlled growing conditions.

We realize a fiber Bragg grating InGaN-based laser diode emitting at 400 nm and demonstrate its high coherency. Thanks to the fabrication of a narrowband fiber Bragg grating in the near-UV, we can reach single-mode and single-frequency regimes for the self-injection locked diode. The device exhibits 44 dB side-mode suppression ratio and mW output power. Detailed frequency noise analysis reveals sub-MHz integrated linewidth and 16 kHz intrinsic linewidth. Such a narrow linewidth laser diode in the near-UV domain with a compact and low-cost design could find applications whenever coherency and interferometric resolutions are needed.

The first InGaN-based LDs were reported in 1996 by Nakamura and co-workers and commercialized from 1999 by the Nichia Corporation. Since then, huge efforts have been devoted to the optimization of the epitaxial layers (doping, defect concentration, shortening of the radiative lifetime, etc.). Nowadays, blue laser diodes emitting hundreds of mW are commercially available but they often exhibit multimode behaviors for both transverse and longitudinal directions. The InGaN-based laser diode technology is still in its infancy, compared to its long wavelength counterparts and only recently the first electrically pumped single mode blue laser diodes have been demonstrated with a resolution limited linewidth of 11.7 GHz. At telecom wavelengths, a mature approach to force the laser diode in a single frequency regime consists in using an external feedback by means of Fiber Bragg Grating. Nevertheless, to our knowledge, such a compact design has not been proposed for blue laser diodes yet.