ABSTRACT
A lateral shearing interferometric technique combined with an 11.6 µm polydimethylsiloxane (PDMS) transparent thin film is proposed and demonstrated for optical detection of ultrasound. We experimentally report the device change of reflectivity with pressure of 5.1×10-7 Pa-1, 9.5 times more sensitive than the critical-angle-based sensor, 31 times more sensitive than the surface-plasmon-based sensor, and comparable to the Fabry-Perot sensor. The objective-lens-based angle scanning characterization setup inspired from a laser scanning system allows direct comparison between the PDMS sensor and critical-angle-based sensor by adjusting the incident angle with a scanning mirror, thereby eliminating optical and electronics system dependence. The sensing element is easily fabricated through spin coating and the detection element incorporated into an existing optical system with minimum modification.
ABSTRACT
We investigate the performance of surface plasmon and Fabry-Perot modes formed between two closely spaced layers. The motivation for this study is twofold: first, to look for modes that may be excited at lower incident angles compared to the usual Kretschmann configuration with similar or superior refractive index responsivity and, second, to develop a simple and applicable method to study these structures over a wide range of separations without recourse to the construction of ad hoc structures. Using back focal plane observation and appropriate signal processing, we show results for the Otto configuration at visible wavelengths at a range of separations not reported hitherto. Moreover, we investigate a hybrid structure we call the Kretschmann-Otto configuration that gives modes that change continuously from a hybridized surface plasmon mode to a zero-order Fabry-Perot mode. The ability to change the separation to small gap distances enables us to examine the Fabry-Perot modes where we show that it has superior refractive index responsivity, by more than an order of magnitude, compared to the Kretschmann configuration.
ABSTRACT
We demonstrate numerically through rigorous coupled wave analysis (RCWA) that replacing the prism in the Otto configuration with gratings enables us to excite and control different modes and field patterns of surface phonon polaritons (SPhPs) through the incident wavelength and height of the Otto spacing layer. This modified Otto configuration provides us the following multiple modes, namely, SPhP mode, Fabry-Pérot (FP) cavity resonance, dielectric waveguide grating resonance (DWGR) and hybridized between different combinations of the above mentioned modes. We show that this modified grating-coupled Otto configuration has a highly confined field pattern within the structure, making it more sensitive to local refractive index changes on the SiC surface. The hybridized surface phonon polariton modes also provide a stronger field enhancement compared to conventional pure mode excitation.
ABSTRACT
A hybrid III-V/SOI resonant-cavity-enhanced photodetector (RCE-PD) structure comprising a high-contrast grating (HCG) reflector, a hybrid grating (HG) reflector, and an air cavity between them, has been proposed and investigated. In the proposed structure, a light absorbing material is integrated as part of the HG reflector, enabling a very compact vertical cavity. Numerical investigations show that a quantum efficiency close to 100 % and a detection linewidth of about 1 nm can be achieved, which are desirable for wavelength division multiplexing applications. Based on these results, a hybrid RCE-PD sample has been fabricated by heterogeneously integrating an InP-based material onto a silicon-on-insulator wafer and has been characterized, which shows a clear enhancement in photo-current at the designed wavelength. This indicates that the HG reflector provides a field enhancement sufficient for RCE-PD operation. In addition, a capability of feasibly selecting the detection wavelength during fabrication as well as a possibility of realizing silicon-integrated bidirectional transceivers are discussed.
