We have fabricated and tested, to the best of our knowledge, the first microfluidic device monolithically integrated with planar chalcogenide glass waveguides on a silicon substrate. High-quality Ge(23)Sb(7)S(70) glass films have been deposited onto oxide coated silicon wafers using thermal evaporation, and high-index-contrast channel waveguides have been defined using SF(6) plasma etching. Microfluidic channel patterning in photocurable resin (SU8) and channel sealing by a polydimethylsiloxane (PDMS) cover completed the device fabrication. The chalcogenide waveguides yield a transmission loss of 2.3 dB/cm at 1550 nm. We show in this letter that using this device, N-methylaniline can be detected using its well-defined absorption fingerprint of the N-H bond near 1496 nm. Our measurements indicate linear response of the sensor to varying N-methylaniline concentrations. From our experiments, a sensitivity of this sensor down to a N-methylaniline concentration 0.7 vol. % is expected. Given the low-cost fabrication process used, and robust device configuration, our integration scheme provides a promising device platform for chemical sensing applications.
High-index-contrast, compact microdisk resonators in thermally evaporated As 2 S 3 and Ge 17 Sb 12 S 71 chalcogenide glass films are designed, fabricated using standard UV lithography and characterized. Our pulley coupler configuration demonstrates coupling of the resonators to monolithically integrated photonic wire waveguides without resorting to demanding fine-line lithography. Microdisk resonators in As 2 S 3 support whisperinggallery-mode with cavity quality factors (Q) exceeding 2 × 10 5 , the highest Q value reported in resonator structures in chalcogenide glasses to the best of our knowledge. We have successfully demonstrated a lab-on-a-chip prototype sensor device with the integration of our resonator with planar microfluidic systems. The sensor shows a refractive index sensitivity of 182 nm/RIU (refractive index unit) and a wavelength resolution of 0.1 pm through resonant peak fit. This corresponds to a refractive index detection limit of 8 × 10 -7 RIU at 1550 nm wavelength, which could be further improved
We demonstrate, for the first time to the best of our knowledge, low-loss, Si-CMOS-compatible fabrication of single-mode chalcogenide strip waveguides. As a novel route of chalcogenide glass film patterning, lift-off allows several benefits: leverage with Si-CMOS process compatibility; ability to fabricate single-mode waveguides with core sizes down to submicron range; and reduced sidewall roughness. High-index-contrast Ge(23)Sb(7)S(70) strip waveguides have been fabricated using lift-off with excellent uniformity of loss propagation and the lowest loss figure of reported to date. We also show that small core Ge(23)Sb(7)S(70) rib waveguides can be fabricated via lift-off as well, with loss figures lower than 0.5 dB/cm. Additionally, we find through waveguide modal analysis that although overall transmission loss is low, the predominant source of this loss comes from scattering at the sidewalls.
In this paper, attributes of chalcogenide glass (ChG) based integrated devices are discussed in detail, including origins of optical loss and processing steps used to reduce their contributions to optical component performance. Specifically, efforts to reduce loss and tailor optical characteristics of planar devices utilizing solution-based glass processing and thermal reflow techniques are presented and their results quantified. Post-fabrication trimming techniques based on the intrinsic photosensitivity of the chalcogenide glass are exploited to compensate for fabrication imperfections of ring resonators. Process parameters and implications on enhancement of device fabrication flexibility are presented.
A thermal reflow technique is applied to high-index-contrast, sub-micron waveguides in As(2)S(3) chalcogenide glass to reduce the sidewall roughness and associated optical scattering loss. We show that the reflow process effectively decreases sidewall roughness of chalcogenide glass waveguides. A kinetic model is presented to quantitatively explain the sidewall roughness evolution during thermal reflow. Further, we develop a technique to calculate waveguide optical loss using the roughness evolution model, and predict the ultimate low loss limit in reflowed high-index-contrast glass waveguides. Up to 50% optical loss reduction after reflow treatment is experimentally observed, and the practical loss limiting factors are discussed.
We have demonstrated the first chalcogenide glass racetrack micro-resonator using a CMOS-compatible lift-off technique with thermally evaporated As 2 S 3 films. The device features a small footprint of 0.012 mm 2 , a cavity Q (quality factor) of 10,000 and an extinction ratio of 32 dB, simultaneously. These resonators exhibit a very high sensitivity to refractive index changes, with a demonstrated detection capability of ∆n As2S3 = (4.5 × 10 -6 ± 10%) RIU (Refractive Index Unit). The resonators were applied to derive photorefractive response of As 2 S 3 to λ = 550 nm light. The resonator devices are a versatile platform for both sensing and glass material property investigation.
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