Bruno Bourliaguet

Microstructured fiber splicing

We present experimental results on Microstructured Optical Fiber (MOF) splicing with a simple method relying on conventional electric-arc splicers. The results are presented in terms of fusion losses and tensile strength. An electric-arc splicing system is used to demonstrate its effectiveness in splicing MOFs together as well as splicing MOF with a single mode fiber.

Deep periodic domain inversions in x-cut LiNbO3 and its use for second harmonic generation near 1.5μm

In this letter, we report the fabrication of deep x-cut periodically poled lithium niobate (PPLN) crystal. The technique relies on ridges performed by wet etching to improve poling field penetration into the substrate and, hence, to provide more depth to inverted domains. Based on this approach, domain inversions as deep as 6.5μm were achieved. As an application, reverse proton exchanged waveguides were fabricated on top of the PPLN to demonstrate efficient second harmonic generation in the near infrared. A conversion efficiency as high as 46%W−1cm−2 was measured near 1.5μm.

Low-voltage tunable second-harmonic generation in an x-cut periodically poled lithium niobate waveguide

We report a new method of tuning the second-harmonic signal generated in a periodically poled lithium niobate (PPLN) waveguide. This technique relies on the recent progress in the fabrication of PPLNs on x-cut substrates along with periodical coplanar electrodes to reduce the tuning voltage while preserving the conversion efficiency. Our scheme exploits a type I interaction implemented in a titanium waveguide to impede cancellation of the electro-optical coefficients and to minimize the group-velocity mismatch between the first- and second-harmonic modes. The tuning range covers 58 nm with an applied voltage of +/-150 V.

Latest developments in active remote sensing at INO

Remote sensing or stand-off detection using controlled light sources is a well known and often used technique for atmospheric and surface spatial mapping. Today, ground based, vehicle-borne and airborne systems are able to cover large areas with high accuracy and good reliability. This kind of detection based on LiDAR (Light Detection and Ranging) or active Differential Optical Absorption Spectroscopy (DOAS) technologies, measures optical responses from controlled illumination of targets. Properties that can be recorded include volume back-scattering, surface reflectivity, molecular absorption, induced fluorescence and Raman scattering. The various elastic and inelastic backscattering responses allow the identification or characterization of content of the target volumes or surfaces. INO has developed instrumentations to measure distance to solid targets and monitor particles suspended in the air or in water in real time. Our full waveform LiDAR system is designed for use in numerous applications in environmental or process monitoring such as dust detection systems, aerosol (pesticide) drift monitoring, liquid level sensing or underwater bathymetric LiDARs. Our gated imaging developments are used as aids in visibility enhancement or in remote sensing spectroscopy. Furthermore, when coupled with a spectrograph having a large number of channels, the technique becomes active multispectral/hyperspectral detection or imaging allowing measurement of ultra-violet laser induced fluorescence (UV LIF), time resolved fluorescence (in the ns to ms range) as well as gated Raman spectroscopy. These latter techniques make possible the stand-off detection of bio-aerosols, drugs, explosives as well as the identification of mineral content for geological survey. This paper reviews the latest technology developments in active remote sensing at INO and presents on-going projects conducted to address future applications in environmental monitoring.

Deep x-cut PPLN for efficient frequency conversion

A new technique is presented for the fabrication of deep x-cut PPLN. The method takes advantage of a ridge structure to improve the field penetration into the crystal. PPLN deeper than 6.5 microns is obtained.

Low-loss splicing of microstructured fibers with conventional electric-arc splicers

We present experimental results demonstrating the possibility of obtaining low-loss splices of microstructured optical fibers (MOFs) by using conventional electric-arc splicers. We show evidence of the effectiveness of the method by splicing two MOFs together as well as a MOF with a standard single mode fiber (SSMF). The results are presented in terms of fusion losses and tensile strength. Theoretical calculations of the losses attributable to mode mismatch between the MOF and the SMF suggest that the splicing losses could be further reduced by optimizing the MOF design parameters. For the case of a MOF-MOF splicing, the loss that could be due to a possible rotational misalignment that comes with the non-cylindrical symmetry of the modal distribution is also evaluated.

Broadband spectroscopic lidar for SWIR/MWIR detection of gaseous pollutants in air

A broadband SWIR/MWIR spectroscopic lidar for detection of gaseous pollutants in air is presented for doing differential optical absorption spectroscopy (DOAS). One of the distinctive parts of the lidar is the use of a picosecond PPMgO:LN OPG (optical parametric generator) capable of generating broadband (10 to <100 nm FWHM) and tunable (1.5 to 3.9 μm) SWIR/MWIR light. The optical source layout and properties are presented, along with a description of the lidar breadboard. Results from indoor simulated typical operation of the lidar will be discussed, the operation consisting in emitting the broadband coherent light along a line of sight (LOS) and measuring the back-scattering returns from of a topographic feature or aerosols. A second distinctive part is the gated MCT-APD focal plane array used in the output plane of the grating spectrograph of the lidar system. The whole of the returned spectra is measured, within a very short time gate, at every pulse and at a resolution of a few tenths to a few nm. Light is collected by a telescope with variable focus for maximum coupling of the return to the spectrograph. Since all wavelengths are emitted and received simultaneously, the atmosphere is “frozen” during the path integrated measurement and hopefully reduces the baseline drift problem encountered in many broadband scanning approaches. The resulting path integrated gas concentrations are retrieved by fitting the molecular absorption features present in the measured spectra. The use of broadband pulses of light and of DOAS fitting procedures make it also possible to measure more than one gas at a time, including interferents. The OPG approach enables the generation of moderate FWHM continua with high spectral energy density and tunable to absorption features of a great number of molecules. Proposed follow-on work and applications will also be presented.

Proposal for a standoff bio-agent detection SWIR/MWIR differential scattering lidar

A SWIR/MWIR spectroscopic lidar is proposed for standoff bio-agent cloud detection using simultaneous broadband differential scattering (DISC). Measurements and/or modeling of DISC spectra of simulants are revisited and the rational of the SWIR/MWIR DISC approach is explained, especially in light of the LWIR DISC experiments and conclusions done elsewhere. Preliminary results on the construction of a low power non-linear broadband source in the SWIR/MWIR are presented. Light from a 1064-nm pump laser is passed through a period and temperature tunable PPMgO:LN Optical Parametric Generator (OPG) to generate broadband light with a full width at half maximum (FWHM) of 10 to >100 nm in the SWIR/MWIR between 1.5 and 3.9 μm. Broadband coherent light from this source is to be emitted towards a cloud that generates back-scattering. This source is being used in a short-range chemical remote detection breadboard, showing the possible dual use of the setup. Light collected by the receiver telescope is coupled to a grating spectrometer and the return signal (DISC in the proposed setup) is detected using a gated MCT-APD array in much the same way clouds are interrogated using UV-LIF. A programmable volume of space along the laser beam path is imaged at the entrance of the spectrometer and 320 spectral channels can be measured simultaneously, attenuating the effects of atmospheric instabilities on DISC measurements. Proposed follow-on work will be presented.

Hyperspectral fluorescence lifetime lidar for geological exploration

We have developed a small, relatively lightweight and efficient lidar instrument for remotely detecting and classifying minerals. The system is based on a pulsed, eye-safe, diode pumped Nd:YAG laser, tripled (355nm) or quadrupled (266nm), for UV excitation of minerals, which then fluoresce with a typical spectrum and lifetime. Fluorescence is detected through a telescope / filter / fiber bundle / spectrograph / multi-channel detector system capable of photon counting. Transmission and detection efficiency have been optimized to reduce the need for high optical excitation energy. Detection electronics are based on gated charge integration using a multi-anode photomultiplier tube. Spectra shown are measured in the 420 to 720 nm visible range with 355 nm laser excitation. Results show that it is relatively easy to distinguish between vegetation and non-vegetation spectra using lifetime data. Lifetime of vegetation is relatively short when compared to the mineral samples investigated. Although results shown are measured in a controlled environment on the ground, the system is being developed for eventual use in a low altitude airborne application. System parameters are presented and upgrade paths are discussed.

Widely tunable SHG in a PPLN using a low voltage

We report a new technique based on domain inversions in x-cut LiNbO3 to tune the quasi-phasematching condition of a SHG process. The tuning range covers 58 nm with an applied voltage of plusmn150 V.