Optical waveguides using a visible transparent nitride were developed to perform fluorescence measurement on a chip. Through finite difference time domain (FDTD) design, the exciting green light was guided by the micron-scale ridge waveguide, while its evanescent wave was expanded outside the waveguide surface and capable to efficiently excite the fluorescent molecules that were approaching the waveguide facets. Since the waveguide was centimeters long, it has a longer fluorescence excitation path comparing to traditional samples prepared for microscopy measurements. As result, the waveguide device can excite stronger fluorescent signals. In addition, the nitride waveguide was prepared by the complementary metal–oxide–semiconductor (CMOS) process thus enabling high volume manufacturing and reducing the cost of the device fabrication.
The AlN waveguide was then integrated with a microfluidic devices to experimentally demonstrate real-time fluorescence detection. Solution samples with different dye concentrations were sequentially injected into the microfluidic chamber. By recording the emission signals, we showed that the fluorescent signals were consistently amplified as the dye concentrations increased. In addition, real-time fluorescence detection with a response time less than seconds was achieved. The developed waveguide based fluorescence measurement provides a new miniaturized platform for low cost and highly accurate point-of-care application.
Tunable photonic circuits were demonstrated by using ferroelectrics that had large electro-optic effect. The photonic circuits were fabricated by complementary metal–oxide–semiconductor (CMOS) technology thus enabling their integration with the present microelectronics for high speed signal modulation. From the scanning electron microscopy and energy-dispersive X-ray spectroscopy, we showed the photonic devices, including the optical waveguides, had sharp waveguide edges and interfaces. A sharp fundamental waveguide mode was observed over a broad spectral range. Tunability using Pockels effect were experimental results. Our device paves the way for ultra broadband integrated photonics critical for optical computing.
In-situ gas analysis was demonstrated using a mid-infrared (mid-IR) microcavity. Optical apertures were made of ultrathin silicate membranes using the complementary metal-oxide-semiconductor (CMOS) process. Fourier transform infrared spectroscopy (FTIR) shows that the silicate membrane is transparent in the range 2.5 - 6.0 μm, overlapping with gas absorption lines and therefore enables gas detection applications. CH4, CO2, and N2O were selected as analytes due to their strong absorption bands corresponding to functional group stretching: C-H, C-O, and O-N, respectively. A short response time of subsecond and high accuracy of gas identification were achieved. The chip-scale mid-IR sensor is a new platform for an in-situ, remote, and embedded gas monitoring system.
Chip-scale chemical sensors were demonstrated using flexible mid-Infrared (mid-IR) photonic circuits consisting of aluminum nitride (AlN) waveguides on ultrathin substrates. The AlN waveguide structure was fabricated by the complementary metal–oxide–semiconductor (CMOS) process. The waveguide sensor is highly bendable because the thin device thickness, which effectively reduces the surface strain. Through spectrum scanning over the characteristic -OH absorption, the waveguide sensor can differentiate methanol, ethanol, and water, and accurately determine the chemical compositions of the water/ethanol mixtures. Real-time chemical monitoring was accomplished by measuring the waveguide mode attenuation at λ = 2.65 μm. Due to the high mechanical flexibility and mid-IR transparency, the AlN chemical sensor enables integrated photonics for biomedical wearables and remote environmental monitoring.
Novel optical materials capable of advanced functionality in the infrared will enable optical designs that can offer lightweight or small footprint solutions in both planar and bulk optical systems. UCF’s Glass Processing and Characterization Laboratory (GPCL) with our collaborators have been evaluating compositional design and processing protocols for both bulk and film strategies employing multi-component chalcogenide glasses (ChGs). These materials can be processed with broad compositional flexibility that allows tailoring of their transmission window, physical and optical properties, which allows them to be engineered for compatibility with other homogeneous amorphous or crystalline optical components. This paper reviews progress in forming ChG-based GRIN materials from diverse processing methodologies, including solution-derived ChG layers, poled ChGs with gradient compositional and surface reactivity behavior, nanocomposite bulk ChGs and glass ceramics, and meta-lens structures realized through multiphoton lithography (MPL).
The mid-Infrared wavelength range (2-20 µm), so-called fingerprint region, contains the very sharp vibrational and rotational resonances of many chemical and biological substances. Thereby, on-chip absorption-spectrometry-based sensors operating in the mid-Infrared (mid-IR) have the potential to perform high-precision, label-free, real-time detection of multiple target molecules within a single sensor, which makes them an ideal technology for the implementation of lab-on-a-chip devices.
Benefiting from the great development realized in the telecom field, silicon photonics is poised to deliver ultra-compact efficient and cost-effective devices fabricated at mass scale. In addition, Si is transparent up to 8 µm wavelength, making it an ideal material for the implementation of high-performance mid-IR photonic circuits. The silicon-on-insulator (SOI) technology, typically used in telecom applications, relies on silicon dioxide as bottom insulator. Unfortunately, silicon dioxide absorbs light beyond 3.6 µm, limiting the usability range of the SOI platform for the mid-IR. Silicon-on-sapphire (SOS) has been proposed as an alternative solution that extends the operability region up to 6 µm (sapphire absorption), while providing a high-index contrast. In this context, surface grating couplers have been proved as an efficient means of injecting and extracting light from mid-IR SOS circuits that obviate the need of cleaving sapphire. However, grating couplers typically have a reduced bandwidth, compared with facet coupling solutions such as inverse or sub-wavelength tapers. This feature limits their feasibility for absorption spectroscopy applications that may require monitoring wide wavelength ranges. Interestingly, sub-wavelength engineering can be used to substantially improve grating coupler bandwidth, as demonstrated in devices operating at telecom wavelengths.
Here, we report on the development of fiber-to-chip interconnects to ZrF4 optical fibers and integrated SOS circuits with 500 nm thick Si, operating around 3.8 µm wavelength. Results on facet coupling and sub-wavelength engineered grating coupler solutions in the mid-IR regime will be compared.
A chip-scale biochemical sensor was developed using mid-Infrared (mid-IR) transparent silicon nitride (SiN) optical waveguides. The label free detection was conducted at λ = 2.70 - 2.81 μm because these spectral regions overlap with the characteristic glucose absorption associated with O-H stretches. Strong intensity attenuation at λ > 2.73 μm was found for the SiN waveguide covered by glucose and a detection limit less than 0.5 ng was experimentally demonstrated. The observed high sensitivity is attributed to a long mid-IR - glucose interaction length owning to the waveguide geometry and an increased sensing surface from the pedestal structure.