The field of integrated photonics has expanded since the last century due to the need for even smaller devices, finding numerous applications in areas such as sensing, communications, and information technology. Particularly, the use of optical sensors has increased in recent years due to advantages over classical sensors, including versatility, minimal sample quantities, and label-free quantitative detection of chemical and biological samples. One technique employed for creating integrated photonic structures is ultrashort laser inscription, enabling the fabrication of optical waveguides in transparent materials without the need for masks or chemical processes. This work presents significant advancements in the design, fabrication, and characterization of Mach-Zehnder interferometers (MZIs) based on optical waveguides, utilizing the femtosecond direct laser writing (FDLW) technique. These interferometers have enabled the creation of integrated systems and their application in detecting physical variables such as temperature changes and variations in the refractive index of solutions with varying concentrations, including urea. We manufactured an embedded Mach-Zehnder interferometer in soda-lime glass, exhibiting sensitivity comparable to Silicon-on-Insulator (SOI) devices. A substantial enhancement in sensitivity (~54 pm/°C) was achieved, thanks to the unique three-dimensional (3D) capabilities provided by FDLW, surpassing the typically low thermo-optic coefficient of soda-lime glass. As a proof of concept, we also applied the first FDLW-fabricated MZI for concentration changes detection through evanescent field interaction in fused silica, demonstrating a sensitivity of ~1.22 nm/mM. Such miniaturized structures will significantly impact the development of compact and highly sensitive integrated photonic devices.
An extrinsic fiber Fabry-Perot interferometer (EFFPI) is proposed and implemented for the characterization of waveguides inscribed by the femtosecond-laser direct writing technique. Various waveguides of 7.08 mm in length were inscribed in a soda-lime glass substrate by varying the laser scanning velocity in order to induce different refractive index (RI) changes. The measurement of the RI of the waveguide was carried out by means of an EFFPI formed between the end face of a multicore fiber (MCF) with seven coupled cores and the two polished surfaces of the inscribed waveguide. The end face of the MCF tip provided a broad beam and a wide effective area to ensure a large collection of the reflected light. The optical spectrum obtained by the interference of the multiple reflected beams was transformed to the Fourier domain and visualized in real-time. In the Fourier domain, the waveguides’ optical path length (OPL) was obtained and used to calculate its refractive index since its physical length was fixed and known. To obtain the value of the RI of the medium surrounding the waveguide, the fiber tip was displaced parallel to the polished surface, about 40 μm far from the center of the waveguide. The relative refractive index difference (Δn), which defines the light propagation and the insertion loss in a waveguide, was calculated for each waveguide inscribed at different velocities.
An analysis of the dispersion relation of SiOx submicron optical waveguides in the visible and IR spectral range is
presented. Here is considered that the refractive index (n) of SiOx can be tuned in the range from n=1.457-2 for 2>x>1,
and a film thickness from 50nm to 1000nm. Starting from the dispersion relation and the distribution of the electric field
in the waveguide; cutoff wavelength, cutoff thickness, effective refractive index, effective guide thickness and
confinement factor of a selected mode are calculated.
Design of straight and S-bend optical channel waveguides based on silver ion implantation in SiO2 substrates is
presented. 3D Beam Propagation Method (BPM) calculations are used for the design of the waveguides based on step
index profiles produced from a sequential multiple ion implantation process. An analysis of modal optical confinement
was done by means of the Effective Index Method (EIM) for selecting the right dimensions of the channel waveguides.
Core index values between 1.4623-1.4662 are obtained, depending on the fluence, are considered. Depth and width for
the waveguides were chosen to provide single mode operation. Bending losses are determined as function of bending
radius, refractive index change (Δn), and wavelength.
We report the implantation of Ni and Ti ions in Nd:YAG crystals to generate a modified layer near the surface. The SRIM (Stopping and Range of Ions in Matter) program was used to simulate this damage layer giving ~ 2 microns in depth. From EDS and XPS measurements, a Ni/Ti concentration of ~ 0.05 - 0.15 at.% was calculated. Spectroscopic characterization was realized consisting in absorption, luminescence and decay lifetime. These are preliminary results for the combination of rare earth and transition metal ions to obtain upconversion processes in active materials for the development of integrated light sources in the visible region.
In this work a study of the effects on the optical properties of channel waveguides in Nd:YAG crystals fabricated with
different proton implantations doses is presented. The channel structure was achieved by using an electroformed mask
with openings through which the protons were implanted. The optical properties studied included microphotographs, the
transversal modal distribution at visible wavelengths, the photoluminescence spectra and the laser emission. The laser
performance of the waveguides was obtained in a resonant cavity configuration with mirrors held onto the polished end
faces of the waveguides.
Optical waveguides have been obtained by silver ion implantation on fused silica substrates. First results of a
methodology oriented to design optical waveguides with silver nanoparticles in a dielectric matrix are presented.
Simulation of ion implantation is based on SRIM code and is correlated with a refractive index increase Δn calculated as
a function of the chemical composition. Effective refractive indices of the propagation modes are determined by prismcoupling
technique.
In this work we present the laser performance of channel waveguides which operate at 1064 nm at
room temperature. These channels were made on Nd: YAG crystal by proton implantation with different widths (10, 15
and 20 μm) forming sets of 10 waveguides which are separated by a distance of 215 μm. The results shown are
transversal mode distribution, propagation losses, absorption and luminescence spectra and laser emission characteristics
such as pump power threshold and slope efficiency. The spectroscopic characterization indicates that the optical
properties of the waveguide in comparison with the bulk material are preserved after the implantation process and that
this is a potential technique to develop compact and efficient lasers.
Complex concatenated channel waveguides and multimode interference devices have been fabricated by laser ablation of
silica-on-silicon substrates for the first time to our knowledge. The technique is based on a tightly focused carbon
dioxide laser beam that modifies the refractive index of the area sorrounding the optical waveguide; the process is fast (a
few seconds) without any subsequent mechanical or chemical treatment, and the writing speed is about 500 times faster
than with UV or femtosecond writing. The results are encouraging for prototyping for the development of an optical sixport
device, the equivalent of the widely known microwave technique for amplitude and phase measurements.
In this work, we report continuous laser emission at 1064 nm from channel waveguides fabricated by carbon
implantation on a Nd:YVO4 crystal. A quasi single-mode intensity profile was observed, which was caused by defects in
the cross-sectional geometry of the waveguides. An analysis of the main laser emission parameters is presented using
different output couplers in the laser cavity and the waveguide losses were calculated from these parameters. The laser
output shows high stability operating at room temperature, confirming the excellent optical properties of the yttrium
vanadate host.
Optical waveguides have been formed by proton implantation in Nd:YVO4 crystals using energies from 0.4 to 1 MeV and doses of the order of 1×1016 ions/cm2. Double implants were realized to generate wide optical barriers and a triple implant produced stacked waveguides. Waveguide characterization comprises propagation modes, refractive index profiles, near field imaging and spectroscopic properties. Differences between the waveguides were found in terms of mode confinement which is important for integrated devices.
Optical waveguides have been produced in Nd:YAG and Nd:YVO4 crystals by either proton or carbon implantation. The analysis includes refractive index profiles, spectroscopic properties and particularly laser emission characteristics in the YAG guides. Typical optical barrier profiles were obtained when protons were used. In the case of YVO4, carbon implantation produced a considerable refractive index variation in the guiding region, increasing the ordinary index and reducing the extraordinary index. The spectroscopic studies show that emission bands coming from the 4F3/2 level are not significantly altered by the ion beam process, thus maintaining the crystal quality in the guiding region. The YAG waveguides exhibit good laser emission characteristics at 1 064 nm and high stability in the CW regime.
In this work we report the performance of CW Nd:YAG waveguide lasers operating at 1064 nm at room temperature. The waveguides were fabricated by proton implantation and the main differences in the process of fabrication were the angle of implantation and the total dose implanted. The characterization of the waveguide refractive index profile induced by proton implantation and the main laser characteristics i.e. slope efficiency and threshold are presented. The results indicate that the optical properties of the waveguide in comparison with the bulk material are preserved after the implantation process and that this is a potential technique to develop compact and efficient lasers.
Pulsed laser annealing has been used to modify the surface and refractive index profiles of ion implanted waveguides formed in Nd:YAG and LiNbO3 crystals. Improvements are seen form reduced losses in the niobate guides and by enhanced index confinement in the garnet. In both materials these beneficial changes require optimization, since prolonged laser treatments can introduce surface damage int eh niobate, and/or emphasize the problems of surface instability on the garnet. Overall the improvements in waveguide loss and surface quality are encouraging. New data are discussed for loss and refractive index profiles, and compared with existing data on surface second harmonic generation quality analysis. Optimization of the laser pulse power, and the number of pulses are predicted to improve guide quality in both materials, particularly for guides implanted with more than one energy, which will increase the initial width of the guide boundary.
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