Near infrared spectro-interferometer using femtosecond laser written GLS embedded waveguides and nano-scatterers.

Guided optics spectrometers can be essentially classified into two main families: based on Fourier transform or dispersion. In the first case, an interferogram generated inside an optical waveguide and containing the spectral information is sampled using spatially distributed nanodetectors. These scatter quasi-non-perturbingly light into the detector that is in contact with the waveguide, helping to reconstruct the stationary wave. A dedicated FFT processing is needed in order to recover the spectrum with high resolution but limited spectral range. Another way is to directly disperse the different wavelengths to different pixels, either introducing differential optical path in the same propagation plane (multiple Mach-Zehnder interferometers or Arrayed Waveguides Gratings), or using a periodic structure to perpendicularly extract the optical signal confined in a waveguide (photonic crystals or surface gratings), and by means of a relay optics, generate the spectrum on the Fourier plane of the lens, where the detector is placed. Following this second approach, we present a laser-fabricated high-resolution compact dispersive spectro-interferometer (R>2500, 30nm spectral range at λ = 1560nm), using four parallel waveguides that can provide up to three non-redundant interferometric combinations. The device is based on guided optics technology embedded in bulk optical glass. Ultrafast laser photoinscription with 3D laser index engineering in bulk chalcogenide Gallium Lanthanium Sulfide glass is utilized to fabricate large mode area waveguides in an evanescently-coupled hexagonal multicore array configuration, followed by subsequent realization of nanoscaled scattering centers via one dimensional nanovoids across the waveguide, written in a non-diffractive Bessel configuration. A simple relay optics, with limited optical aberrations, reimages the diffracted signal on the focal plane array, leading to a robust, easy to align instrument.

Large-mode-area infrared guiding in ultrafast laser written waveguides in sulfur-based chalcogenide glasses.

Current demands in astrophotonics impose advancing optical functions in infrared domains within embedded refractive index designs. We demonstrate concepts for large-mode-area guiding in ultrafast laser photowritten waveguides in bulk Sulfur-based chalcogenide glasses. If positive index contrasts are weak in As2S3, Ge doping increases the matrix rigidity and allows for high contrast (10(-3)) positive refractive index changes. Guiding with variable mode diameter and large-mode-area light transport is demonstrated up to 10 µm spectral domain using transverse slit-shaped and evanescently-coupled multicore traces.

Midinfrared frequency combs from coherent supercontinuum in chalcogenide and optical parametric oscillation.

We observe the coherence of the supercontinuum generated in a nanospike chalcogenide-silica hybrid waveguide pumped at 2 µm. The supercontinuum is shown to be coherent with the pump by interfering it with a doubly resonant optical parametric oscillator (OPO) that is itself coherent with the shared pump laser. This enables coherent locking of the OPO to the optically referenced pump frequency comb, resulting in a composite frequency comb with wavelengths from 1 to 6 µm.

Mid-infrared supercontinuum generation in As2S3-silica "nano-spike" step-index waveguide.

Efficient generation of a broad-band mid-infrared supercontinuum spectrum is reported in an arsenic trisulphide waveguide embedded in silica. A chalcogenide "nano-spike", designed to transform the incident light adiabatically into the fundamental mode of a 2-mm-long uniform section 1 µm in diameter, is used to achieve high launch efficiencies. The nano-spike is fully encapsulated in a fused silica cladding, protecting it from the environment. Nano-spikes provide a convenient means of launching light into sub-wavelength scale waveguides. Ultrashort (65 fs, repetition rate 100 MHz) pulses at wavelength 2 µm, delivered from a Tm-doped fiber laser, are launched with an efficiency ~12% into the sub-wavelength chalcogenide waveguide. Soliton fission and dispersive wave generation along the uniform section result in spectral broadening out to almost 4 µm for launched energies of only 18 pJ. The spectrum generated will have immediate uses in metrology and infrared spectroscopy.

Fourth-order cascaded Raman shift in AsSe chalcogenide suspended-core fiber pumped at 2 µm.

Cascaded Raman wavelength shifting up to the fourth order ranging from 2092 to 2450 nm is demonstrated using a nanosecond pump at 1995 nm in a low-loss As(38)Se(62) suspended-core microstructured fiber. These four Stokes shifts are obtained with a low peak power of 11 W, and only 3 W are required to obtain three shifts. The Raman gain coefficient for the fiber is estimated to (1.6±0.5)×10(-11) m/W at 1995 nm. The positions and the amplitudes of the Raman peaks are well reproduced by the numerical simulations of the nonlinear propagation.

Low loss microstructured chalcogenide fibers for large non linear effects at 1995 nm.

Microstructured optical fibers (MOFs) are traditionally prepared using the stack and draw technique. In order to avoid the interfaces problems observed in chalcogenide glasses, we have developed a new casting method to prepare the chalcogenide preform. This method allows to reach optical losses around 0.4 dB/m at 1.55 µm and less than 0.05 dB/m in the mid IR. Various As(38)Se(62) chalcogenide microstructured fibers have been prepared in order to combine large non linear index of these glasses with the mode control offered by MOF structures. Small core fibers have been drawn to enhance the non linearities. In one of these, three Stokes order have been generated by Raman scattering in a suspended core MOF pumped at 1995 nm.

Microstructured chalcogenide optical fibers from As(2)S(3) glass: towards new IR broadband sources.

The aim of this paper is to present an overview of the recent achievements of our group in the fabrication and optical characterizations of As(2)S(3) microstructured optical fibers (MOFs). Firstly, we study the synthesis of high purity arsenic sulfide glasses. Then we describe the use of a versatile process using mechanical drilling for the preparation of preforms and then the drawing of MOFs including suspended core fibers. Low losses MOFs are obtained by this way, with background level of losses reaching less than 0.5 dB/m. Optical characterizations of these fibers are then reported, especially dispersion measurements. The feasibility of all-optical regeneration based on a Mamyshev regenerator is investigated, and the generation of a broadband spectrum between 1 µm and 2.6 µm by femto second pumping around 1.5 µm is presented.

Strong infrared spectral broadening in low-loss As-S chalcogenide suspended core microstructured optical fibers.

We report the fabrication and characterization of the first guiding chalcogenide As(2)S(3) microstructured optical fibers (MOFs) with a suspended core. At 1.55 microm, the measured losses are approximately 0.7 dB/m or 0.35 dB/m according to the MOF core size. The fibers have been designed to present a zero dispersion wavelength (ZDW) around 2 microm. By pumping the fibers at 1.55 microm, strong spectral broadenings are obtained in both 1.8 and 45-m-long fibers by using a picosecond fiber laser.

Experimental investigation of Brillouin and Raman scattering in a 2SG sulfide glass microstructured chalcogenide fiber.

In this work, we investigate the Brillouin and Raman scattering properties of a Ge15Sb20S65 chalcogenide glass microstructured single mode fiber around 1.55 microm. Through a fair comparison between a 2-m long chalcogenide fiber and a 7.9-km long classical single mode silica fiber, we have found a Brillouin and Raman gain coefficients 100 and 180 larger than fused silica, respectively.

Second-harmonic generation of thermally poled chalcogenide glass.

Second harmonic generation (SHG) has been obtained in a sample of Ga5Ge20Sb10S65 glass submitted to a thermal poling treatment. An original characterization method is used for the determination of the induced second-order nonlinear profile. A reproducible chi(2) susceptibility of 4.4 +/- 0.4 pm/Volt was achieved for specific poling conditions.