In recent years, femtosecond-laser writing has recently emerged as one of the most versatile techniques for direct waveguide microfabrication of transparent optical materials. Femtosecond-laser-based fabrication of three-dimensional silicon waveguide enables compact silicon photonics and their integration as large third-order nonlinearity and the high refractive index of silicon allows for tightly confining optical waves to a sub-micron region. The writing process is however challenging because the unique features exhibited by the semiconductor crystal, such as two-photon absorption, free-carrier absorption / dispersion, anisotropic and dispersive third-order nonlinearity, which may drastically influence the writing process at high intensities required for the femtosecond-laser writing. In this work, we provide a detailed description of the underlying physics behind nonlinear optical dynamics in femtosecond laser processing of silicon waveguides, considering the generation of free carriers induced by various absorption mechanisms, plasma formation, refractive index change and their impact on the waveguide microfabrication and performance.
NASA is working with US industry and academia to develop Photonic Integrated Circuits (PICs) for: (1) Sensors (2) Analog RF applications (3) Computing and free space communications. The PICs provide reduced size, weight, and power that is critical for space-based systems. We describe recent breakthrough 3D monolithic integration of photonic structures, particularly high-speed graphene-silicon devices on CMOS electronics to create CMOS-compatible highbandwidth transceivers for ultra-low power Terabit-scale optical communications. An integrated graphene electro-optic modulator has been demonstrated with a bandwidth of 30 GHz. Graphene microring modulators are especially attractive for dense wavelength division multiplexed (DWDM) systems. For space-based optical communication and ranging we have demonstrated generating a variable number of channels from a single laser using breadboard components, using a single-sideband carrier-suppressed (SSBCS) modulator driven by an externally-supplied RF tone (arbitrary RF frequency), a tunable optical bandpass filter, and an optical amplifier which are placed in a loop. We developed a Return--to-Zero (RZ) Differential Phase Shift Keying (DPSK) laser transmitter PIC using an InP technology platform that includes a tunable laser, a Semiconductor Optical Amplifier (SOA), high-speed Mach-Zehnder Modulator (MZM), and an electroabsorption (EAM) modulator. A Silicon Nitride (SiN) platform integrated photonic circuit suitable for a spectrally pure chip-scale tunable opto-electronic RF oscillator (OEO) that can operate as a flywheel in high precision optical clock modules, as well as radio astronomy, spectroscopy, and local oscillator in radar and communications systems is needed. We have demonstrated a low noise optical frequency combs generation from a small OEO prototypes containing very low loss (~1 dB) waveguide couplers of various shapes and sizes integrated with an ultrahigh-Q MgF2 resonators. An innovative miniaturized lab-on-a-chip device is being developed to directly monitor astronaut health during missions using ~3 drops of body fluid sample like blood, urine, and potentially other body fluids like saliva, sweat or tears. The first-generation system comprises a miniaturized biosensor based on PICs (including Vertical Cavity Surface Emitting Laser – VCSEL, photodetector and optical filters and biochemical assay that generates a fluorescent optical signal change in response to the target analyte.
We present the temperature response of a mechanically-induced long-period fiber grating (MLPFG) made in photonic
crystal fiber (PCF) with and without the coating polymer. In both cases, we found a wavelength shift to shorter
wavelengths and a critical decrease of the attenuation peaks. A maximum wavelength shift of 6 nm at 1060 nm was
obtained when the temperature changed from 20 to 80 °C in PCF without the polymer. Whereas, the depth of the
attenuation peaks were dramatically reduced from 12 to almost 2 dB at 1060 nm when the temperature increase from 20
to 100 °C in both experiments. These results are important to consider when MLPFG are applied in a medium with room