We experimentally demonstrate an on-chip polycrystalline PbTe photoconductive detector integrated with a chalcogenide glass waveguide. The device is monolithically fabricated on silicon, operates at room-temperature, and exhibits a responsivity of 1.0 A/W at wavelengths between 2.1 and 2.5 μm.
Solution-based electrospray film deposition, which is compatible with continuous, roll-to-roll processing, is applied to chalcogenide glasses. Two chalcogenide compositions are demonstrated: Ge 23 Sb 7 S 70 and As 40 S 60 , which have both been studied extensively for planar mid-infrared (mid-IR) microphotonic devices. In this approach, uniform thickness films are fabricated through the use of computer numerical controlled (CNC) motion. Chalcogenide glass (ChG) is written over the substrate by a single nozzle along a serpentine path. Films were subjected to a series of heat treatments between 100 °C and 200 °C under vacuum to drive off residual solvent and densify the films. Based on transmission Fourier transform infrared (FTIR) spectroscopy and surface roughness measurements, both compositions were found to be suitable for the fabrication of planar devices operating in the mid-IR region. Residual solvent removal was found to be much quicker for the As 40 S 60 film as compared to Ge 23 Sb 7 S 70 . Based on the advantages of electrospray, direct printing of a gradient refractive index (GRIN) mid-IR transparent coating is envisioned, given the difference in refractive index of the two compositions in this study.
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Multiphoton absorption coefficients and nonlinear refractive indices of germanium in the near and mid-infrared (2–5 μm) are reported. The nonlinear coefficients are measured by open and closed aperture Z-scan with 150 fs pulses at a repetition rate of 1 kHz. The nonlinear refractive index of Ge has a peak value of 9.1×10−5cm2/GW at a wavelength of 3 μm. The effect of free electrons generated by multiphoton absorption is discussed by investigating the variation of multiphoton absorption coefficients at different input powers. Kramers-Kronig relations are also discussed with regard to the relationship between nonlinear refractive index and two photon absorption coefficient.
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