Molly R. Krogstad

Nonlinear characterization of Ge 28 Sb 12 Se 60 bulk and waveguide devices

Single-mode Ge₂₈Sb₁₂Se₆₀ strip waveguides, fabricated with thermal evaporation and lift-off, were demonstrated at 1.03 µm. The linear and nonlinear optical properties of these waveguides were shown to be similar to bulk samples, with differences attributed to small variations in composition of ~4 atomic % or less. From z-scan measurements at 1.03 µm using circularly polarized, ~200 fs pulses at 374 kHz, Ge₂₈Sb₁₂Se₆₀ was found to have a nonlinear refractive index ~130 x fused silica and a two-photon absorption coefficient of 3.5 cm/GW. Given the large two-photon absorption coefficient, this material shows promise for optical limiting applications at 1 µm.

Optical Characterization of Chalcogenide Ge–Sb–Se Waveguides at Telecom Wavelengths

Nonlinear single-mode Ge 28 Sb 12 Se 60 strip waveguides were demonstrated at 1.53-1.55 μm. The waveguides were fabricated by photo-or e-beam lithography, followed by thermal evaporation and lift-off. The linear propagation loss, ranging from 4.0 to 6.1 dB/cm, is compared for waveguides under various fabrication conditions. Using measurements of the power-dependent transmission and spectral broadening, the nonlinear loss β and nonlinear refractive index n 2 of the waveguides fabricated with e-beam lithography are determined to be 0.014±0.003 cm/GW and 5±2×10 -19 m 2 /W, respectively, at 1.55 μm. Given the large measured figure of merit, n 2 /(βλ) = 2.3±0.9, this platform holds promise for nonlinear applications at telecom wavelengths.

Linear and nonlinear optical properties of Ge-Sb-Se waveguides at telecom wavelengths

Sub-micron Ge-Sb-Se waveguides, fabricated by e-beam lithography, thermal evaporation, and lift-off, were characterized at 1.53-1.55 μm. Linear loss is compared under various fabrication conditions, and spectral broadening measurements reveal a large nonlinearity.

Design and fabrication of high-Q chalcogenide glass micro-disk resonators (Conference Presentation)

Chalcogenide glass (ChG) which contain one or more chalcogen elements is one of the most interesting material for infrared (IR) photonics owing to its unique optical properties, such as high refractive index, strong optical nonlinearity, and wide infrared transparency. In this paper, we experimentally demonstrate high-quality ChG micro-disk resonators on oxidized silicon wafers fabricated by the standard UV photolithography and lift-off. Quality factor of micro-disk resonators are often limited by optical scattering loss induced by lithographically defined edge roughness. Thermal reflow of chalcogenide itself may significantly reduce edge roughness, but thermal shrinkage and deformation of the material during the reflow make it hard to precisely control the overall size and shape of the fabricated device. Instead, we reduce the sidewall roughness using thermal reflow of photoresist and modified bi-layer lift-off process. Typically, the thermal reflow of resist destroys the undercut or vertical sidewall profile of developed resist layer, making it extremely difficult or impossible to subsequently use lift-off or etching for patterning. We address this issue by first wet etching the silica substrate to undercut the reflowed photoresist, creating an overhang required for lift-off. ChG film is then deposited to produce a micro-disk resonator with much improved edge roughness. To finally create a micro-disk resonator on a silica pillar, we adopt vapor etching of the silica substrate. With optimized conditions of reflow and undercut, we obtained high quality ChG disk-resonators with extremely smooth edge profile, operating in the infrared region. Complete characterization results will be presented at the conference. The new method is compatible with traditional CMOS process and thus expected to have great potentials for fabricating high quality photonic integrated devices.

High quality chalcogenide-silica hybrid wedge resonator

Chalcogenide glasses, with high nonlinearity and low loss, have captured research interest as an integrated device platform for near- and mid-infrared nonlinear optical devices. Compared to silicon-based microfabrication technologies, chalcogenide fabrication processes are less mature and a major challenge is obtaining high quality devices. In this paper, we report a hybrid resonator design leveraging a high quality silica resonator to achieve high Q factors with chalcogenide. The device is composed of a thin chalcogenide layer deposited on a silica wedge resonator. The hybrid resonators exhibit loaded Q factors up to 1.5 x 105 in the near-infrared region. We also measured the effective thermo-optic coefficient of the device to be 5.5x10-5/K, which agreed well with the bulk value. Thermal drift of the device can be significantly reduced by introducing a titanium dioxide cladding layer with a negative thermo-optic coefficient.

Corrections to “Optical Characterization of Chalcogenide Ge–Sb–Se Waveguides at Telecom Wavelengths”

Nonlinear single-mode Ge₂₈Sb₁₂Se₆₀ strip waveguides were demonstrated at 1.53-1.55 μm. The waveguides were fabricated by photo-or e-beam lithography, followed by thermal evaporation and lift-off. The linear propagation loss, ranging from 4.0 to 6.1 dB/cm, is compared for waveguides under various fabrication conditions. Using measurements of the power-dependent transmission and spectral broadening, the nonlinear loss β and nonlinear refractive index n₂ of the waveguides fabricated with e-beam lithography are determined to be 0.014±0.003 cm/GW and 5±2×10^-19 m²/W, respectively, at 1.55 μm. Given the large measured figure of merit, n₂/(βλ) = 2.3±0.9, this platform holds promise for nonlinear applications at telecom wavelengths.

Third-Order Nonlinearities of Ge28Sb12Se60 for Waveguide Devices

The optical nonlinearities of the chalcogenide Ge₂₈Sb₁₂Se₆₀ are studied using the z-scan technique with femtosecond and picosecond laser pulses at 1.0 μm. Results indicate this glass shows promise for nonlinear optical waveguide devices.