Femtosecond Laser Written Research Articles

Integrated All-In-Silica Optofluidic Platform Based on Microbubble Resonator and Femtosecond Laser Written Surface Waveguide

Integrated All-In-Silica Optofluidic Platform Based on Microbubble Resonator and Femtosecond Laser Written Surface Waveguide

Temperature Compensated Differential Pressure Sensor Based on a Glass Membrane With Femtosecond Laser Written Bragg Gratings

Temperature Compensated Differential Pressure Sensor Based on a Glass Membrane With Femtosecond Laser Written Bragg Gratings

Impact of Glass Free Volume on Femtosecond Laser-Written Nanograting Formation in Silica Glass.

In this study, we investigate the effects of densification through high pressure and temperature (up to 5 GPa, 1000 °C) in the making of nanogratings in pure silica glass, inscribed with femtosecond laser. The latter were monitored through retardance measurements using polarized optical microscopy, and their internal structure was observed under scanning electron microscopy. We reveal the difficulty in making nanogratings in densified silica glasses. Based on this observation, we propose that free volume may be a key precursor to initiate nanograting formation.

Femtosecond Laser Written Depressed-Cladding Waveguide 2 × 2, 1 × 2 and 3 × 3 Directional Couplers in Tm3+:YAG Crystal.

Ion-doped crystal-based compact devices capable of beam splitting and coupling are enthralling for a broad range of classical and quantum integrated photonics applications. In this work, we report on the fabrication of depressed-cladding waveguide 2D 2 × 2, 1 × 2 and 3D 3 × 3 directional couplers in Tm:YAG crystal by femtosecond laser writing. The performances of the couplers are characterized at 810 nm, showing single-mode guidance, polarization independence, finely matched splitting ratios. These results open up new opportunities in the beneficial fabrication of 3D circuits and devices in crystals.

Addressing the Fabrication Difficulties of Femtosecond Laser Written Surface Waveguides for Enhanced Evanescent Coupling

In this work, the fabrication of optical waveguides embedded in fused silica (Suprasil1) and boro-aluminosilicate glass (Eagle2000) is demonstrated with femtosecond laser direct writing, as well as their suitability to be brought to the surface, through wet etching, for enhanced evanescent coupling with the external dielectric medium. Fused silica demonstrated to be inappropriate in this particular application, as the guiding region is at the bottom of the induced modification, creating a barrier between the guided mode and the substrate’s boundary. Furthermore, the existence of nanogratings meant that, upon contact of the top of the induced modification with the substrate’s boundary, the waveguide is quickly etched. Eagle2000 demonstrated to be superior to fused silica due to its characteristic modification cross-section and absence of nanogratings, which allowed the placement of the guiding region as close to the substrate’s surface as required. However, surface roughness arising from the creation of insoluble products in the HF solution was found. The addition of HCl to dissolve these products was implemented.

Reconfigurable Photonics on a Glass Chip

Reconfigurability of integrated photonic chips plays a key role in current experiments in the area of linear-optical quantum computing. We demonstrate a reconfigurable multiport interferometer implemented as a femtosecond laser-written integrated photonic device. The device includes a femtosecond laser-written $4\times 4$ multiport interferometer equipped with 12 thermooptical phase shifters, making it a universal programmable linear-optical circuit. We achieve a record fast switching time for a single nested Mach-Zender interferometer of $\sim10$ ms and quantitatively analyse the reconfigurability of the optical circuit. We believe, that our results will improve the current state of quantum optical experiments utilizing femtosecond laser-written photonic circuits.

Optimization of Broadband Y-Junction Splitters in Fused Silica by Femtosecond Laser Writing

Optical Y-junction power splitters owe their inherent broadband spectral behavior to their design. However, depending on the fabrication technique employed, asymmetries in the junction might arise, perturbing its performance; this is the case in femtosecond laser written Y-junctions where one arm is typically written over the top of the other. In this letter, the spectral behavior of Y-junctions fabricated in fused silica by the femtosecond laser direct writing technique was analyzed and optimized for the first time, to the best of our knowledge. The junction arms output power balance as well as the corresponding spectral flatness between 1300 and 1600 nm is substantially increased by the implementation of an initial separation between the arms at the junction diverging point, enabling the manufacturing of balanced broadband Y-junctions.

Directly laser-written integrated photonics devices including diffractive optical elements

Femtosecond laser-written integrated devices involving Fresnel Zone Plates (FZPs) and waveguide arrays are demonstrated as built-in optical couplers. These structures were fabricated in borosilicate glass using a direct laser writing technique. The optical properties of these integrated photonic structures were investigated using CW lasers and high-resolution CCDs. For a single FZP coupled to a single waveguide, the overall coupling efficiency was 9%. A multiplexed optical coupler composed of three FZP layers was demonstrated to couple three waveguides simultaneously in a waveguide array. Structures of this type can be used as platforms for multichannel waveguide coupling elements or as microfluidic sensors that require higher light collecting efficiency.

Temperature and Strain Sensing With Femtosecond Laser Written Bragg Gratings in Defect and Nondefect Suspended-Silica-Core Fibers

The spectral behavior in the C-band of fiber Bragg gratings (FBGs) was analyzed as a function of temperature and strain. The FBGs were fabricated in pure silica four-leaf-clover-shaped suspended-core fibers by (DUV) femtosecond laser exposure (3.6 W at 800 nm, 130 fs, 1 kHz frequency tripled to 350 fs, 650 mW at 267 nm). A defect fiber (with a hollow hole in the core) and nondefect fiber were compared both yielding ≈1 pm/μe sensitivity to strain but different sensitivity to temperature (from 3.0 pm/°C to 8.4 pm/°C for the defect fiber and 10 pm/°C for the nondefect fiber). The 16% to 70% relative difference between the thermal coefficients of the two fibers, together with their similar strain sensitivity enables the simultaneous measurement of strain and temperature.

New Characterization Technique for Femtosecond Laser Written Waveguides in Yb/Er-Codoped Glass

We have developed a procedure for the complete characterization of femtosecond-laser written Er/Yb-codoped glass waveguides. The procedure is based on precise measurements of both pump and 1.5 ?m -band output powers when the waveguide is diode-laser pumped at 980 nm. The dependence of these optical powers on the input pump power is fitted to the results derived from a detailed numerical model of the propagation of the optical powers inside the waveguide. As a result of the fitting procedure the 980-nm absorption cross-section of the Yb3+ ion and the coefficients for both Yb3+ ? Er3+ non-radiative energy-transfer and Er3+ ion upconversion are obtained. Moreover, the transmission losses for both pump and signal wavelengths and the coupling losses at each waveguide end are also determined. The model takes into account that the fs-laser writing process may induce transmission losses with a spectral dependence (?(?)) departing from the Rayleigh scattering scaling law ( ?-4) and is valid both for single mode and multimode propagation. It has been tested in fs-laser written waveguides produced under non-optimal conditions in order to test the robustness of the method, providing excellent results.

Spectral Loss Characterization of Femtosecond Laser Written Waveguides in Glass With Application to Demultiplexing of 1300 and 1550 nm Wavelengths

Femtosecond laser written waveguides in glass were characterized across the full telecom spectrum to gain insight into waveguide loss mechanisms, and to aid in the design of a low-loss 1300/1550 nm wavelength demultiplexer. A lambda-4 wavelength scaling of propagation loss confirms Rayleigh scattering as a principal loss mechanism. Laser exposure was optimized for generating low-loss directional couplers with high isolation between the 1300 and 1550 nm bands. Dispersive coupling in the straight and curved wavelength regions was balanced with a 1.5-fold difference in 1300 and 1550 nm beat lengths, leading to the first demonstration of 1300/1550 nm demultiplexer written with a laser. A minimum interaction length of 3.2 mm, ~2 dB insertion loss and channel isolations of 16.7 and 18.8 dB are reported.