Direct laser writing is a powerful technique for the development of astrophotonic devices, namely by allowing 3D structuring of waveguides and structures. One of the main interests is the possibility to avoid in-plane crossings of waveguides that can induce losses and crosstalk in future multi-telescope beam combiners. We will present our results in 3D three telescope beam combiners in the near infrared, that allow for phase closure studies. Besides, laser writing can be used to inscribe a grating over long distances along the waveguide direction. This can be used as an on-chip diffraction grating or as a way to sample a stationary wave that can be obtained in the waveguide. Thus, integrated optics spectrometers based on the SWIFTS concept (stationary wave integrated Fourier transform spectrometer) have been realized and characterized in the near and mid infrared using commercial chalcogenide glasses. Finally, we will also present our results on laser writing on electro-optic materials, that allow to obtain waveguides and beam combiners that can be phase-modulated using electrodes. We have focused our work on two well-known materials: Lithium Niobate, that allows for TM waveguides and has a high electro-optical coefficient, and BGO, that has a lower coefficient, but presents the advantage of being isotropic, guiding both TE and TM polarizations identically.
In this work, we have demonstrated the use of different technologies to fabricate straight channel waveguides, S-bend waveguides, Y-splitter and Mach-Zehnder (MZ) structures on RbTiOPO4 crystals and its isomorphs. We used reactive ion etching (RIE), inductively coupled plasma-RIE (ICP-RIE), femtosecond pulse laser micro-fabrication and ion diffusion techniques to structure these crystals. Computer simulations have been carried out and compared with the optical characterization of the waveguides which are in agreement with each other.
We report on waveguide lasers at 1064.5 nm in femtosecond laser-written double-cladding waveguides in Nd:GdVO4 crystals. The cladding waveguides guide both transverse electric (TE)- and transverse magnetic (TM)-polarized modes with considerably symmetric single-modal profiles and show good transmission properties (propagation loss as low as 1.0 dB/cm). The detailed structure of the single and double claddings has been imaged by means of μ-Raman analysis, and the observed slight fabrication asymmetries with respect to an ideal circular cladding are in well agreement with the observed differences in TE/TM propagation losses. Importantly, the Raman imaging shows the complete absence of lattice defect at the laser active volume. Under the optical pumping at 808 nm, a maximum output power up to 0.43 W of the continuous wave waveguide laser with a slope efficiency of 52.3% has been achieved in the double-cladding waveguide, which is 21.6% and 23% higher than that from a single-inner cladding waveguide. Furthermore, the maximum output power of the waveguide laser is 72% higher than that of the double-line waveguide due to the double-cladding design.
We report on the development and testing of the building blocks of a possible compact heterodyne setup in the mid-infrared,
which becomes particularly relevant for flight instrumentation. The local oscillator is a Quantum Cascade Laser
(QCL) source at 8.6 μm operable at room temperature. The beam combination of the source signal and the local
oscillator will occur by means of integrated optics for the 10 μm range, which was characterized in the lab. In addition
we investigate the use of superlattice detectors in a heterodyne instrument. This work shows that these different new
components can become valuable tools for a compact heterodyne setup.
Recent results from our work using ultrafast laser writing to fabricate waveguides and on-chip devices inside sulphide chalcogenide glasses are presented in this paper. Low loss single-mode (SM) and multi-mode (MM) waveguide arrays were successfully laser fabricated, for the first time to our knowledge, for operation in the whole near-IR (NIR) to mid- IR (MIR) range (1 to 11 μm wavelengths). These waveguides are demonstrated to have numerical apertures (NA) which can exceed NA=0.2, therefore also allowing for low bend losses as well as direct coupling to QC lasers. We also demonstrate the control over the waveguide mode field diameters (MFDs) (at 1/e2) by changing the waveguide core sizes and index contrasts, achieving typical values of 44 μm at 10.6 μm, down to 6 μm for telecom 1.55 μm light. The optical nonlinear properties of these waveguides have also been preliminarily investigated. Using a femtosecond (fs) optical parametric amplifier system, the optical nonlinearity of bulk gallium lanthanum sulphide (GLS) glass was first measured at 2.5 μm. The upper limits for the nonlinear properties of the laser modified material could be estimated based upon the nonlinear spectral broadening of a 2.5 μm fs pulse train coupled into SM waveguides. Further work includes the demonstration of on-chip three dimensional (3D) beam combiners for the MIR range (10.6 μm in this work), for near future implementation in astronomical observatories for stellar interferometry.
This article reports the advances on the development of mid-infrared integrated optics for stellar interferometry.
The devices are fabricated by laser writing techniques on chalcogenide glasses. Laboratory characterizaton is
reported and analyzed.