Purnomo Sidi Priambodo

Fabrication and characterization of high-quality waveguide-mode resonant optical filters

Optical filters containing resonant waveguide gratings are designed and fabricated using low-loss, robust materials. The double-layer filters contain a silicon dioxide diffractive element on a hafnium dioxide waveguide deposited on a fused silica substrate. Noise-pattern formation is minimized by use of an antireflective absorption layer during holographic grating recording in photoresist. Subsequent fabrication steps include metallization, lift-off, and oxygen plasma etch to create a metal etch mask for final CF4 plasma etching of a surface-relief grating. Spectral characterization with a tunable laser shows that the resulting filter exhibits 90% efficiency, 1.2 nm linewidth, and low sidebands.

Photonic devices enabled by waveguide-mode resonance effects in periodically modulated films

The chief properties and possible applications of periodic waveguides and their leaky modes are presented in this paper. After summarizing the basic physics of the guided-mode resonance, computed leaky-mode field patterns are provided to illustrate their structure and the high local focal field enhancement obtainable. An example fabricated bandstop filter is found to exhibit 90% efficiency, 1 nm linewidth, and low sidebands. Computed spectra for a single-layer bandpass filter operating at 1.55 μm wavelength yield low sidebands, extending 100 nm, and an angular aperture of ~1.7°. Resonant vertical-cavity surface-emitting lasers (VCSEL) are presented in which multilayer Bragg-stack mirrors are replaced with leaky-mode resonance layers. The use of guided-mode resonance mirrors provides optical power flow across and laterally along the laser active region. The round-trip gain is thereby increased resulting in high laser efficiency and relaxed mirror reflectivity constraints. As the GMR mirror achieves high reflectivity at resonance, the laser wavelength is locked at the resonance wavelength principally defined by the period. Example resonant VCSEL embodiments are shown along with their computed characteristics. Resonant biosensors are addressed last. The high parametric sensitivity of the guided-mode resonance effect, a potential limitation in filter applications, can be exploited for sensors as illustrated by several examples.

Agarose-Gel Based Guided-Mode Resonance Humidity Sensor

A photonic relative-humidity (RH) sensor employing the guided-mode resonance effect is designed, fabricated, and characterized. An agarose-gel transduction layer is integrated with a periodic silicon-nitride film to form a sensitive optical resonance structure. As the agarose-gel humidifies, the resonance wavelength shifts. Comparison with rigorous diffraction models allows quantification of the gels refractive index and the attendant relative humidity. For the example sensor structure treated, the resonance wavelength shifts by ~9 nm on relative-humidity change from 20% RH to 80% RH

Second-harmonic generation in resonant waveguide gratings incorporating ionic self-assembled monolayer polymer films

Experimental results on resonantly excited second-harmonic generation (SHG) in a periodic ionically self-assembled monolayer (ISAM) film are reported. A double-layer guided-mode resonance filter (GMRF) structure is coated with 40 bilayers of pyrlium-based chi(2) ISAM thin film and excited with the fundamental of a Nd:YAG laser. Enhanced second-harmonic conversion in the ISAM film is achieved because of the local field enhancement associated with the fundamental resonating leaky mode. This method of SHG is particularly promising, as the ISAM films under investigation exhibit anomalous dispersion that may be applied for phase matching to improve nonlinear conversion efficiency.

Characteristics of resonant leaky-mode biosensors

This paper presents key properties and examples of applications of resonant leaky-mode biosensors operating in the subwavelength regime. The main resonance features observed under variation of input wavelength and angle are discussed. The dependence of the resonance lineshape on element design parameters is highlighted. The surface-localized power concentration at resonance is described along with the standing-wave pattern of the leaky modes obtained at normal incidence. An example fabrication process involving holographic patterning, etching, and deposition of high-index material is provided. The fabricated elements resonate well with good agreement between experiment and theory found. As examples of practical applications, experimental results on detection of proteins and bacteria are given. The tag-free resonant sensor technology demonstrated may be feasible for use in fields such as in medical diagnostics, drug development, environmental monitoring, and homeland security.

Resonating periodic waveguides as ultraresolution sensors in biomedicine

Optical sensor technology based on subwavelength periodic waveguides is applied for tag-free, high-resolution biomedical and chemical detection. Measured resonance wavelength shifts of 6.4 nm for chemically attached Bovine Serum Albumin agree well with theory for a sensor tested in air. Reflection peak efficiencies of 90% are measured, and do not degrade upon biolayer attachment. Phase detection methods are investigated to enhance sensor sensitivity and resolution. Direct measurement of the resonant phase response is reported for the first time using ellipsometric measurement techniques.

Simple interferometric fringe stabilization by charge-coupled-device-based feedback control

A method for producing stabilized interference patterns for ultraviolet interference lithography using a CCD camera as the detector element is described. Intensity data obtained from the CCD element are filtered in software to minimize speckle and detector noise effects as well as to determine the relative phase of the interfering beams. A control signal is then issued to correct the fringe drift. The system allows rapid reconfiguration of the lithography setup with minimum realignment of optical components.

Delay bound analysis for hybrid network: IEEE 802.1 lg ERP-OFDM WLAN over fiber

The convergence between WLAN and optical fiber has created a new challenge in network design. In this paper, we propose a comprehensive design simulation of hybrid network concerning the timeout of ACK and CTS, which determine the maximum length of optical fiber. Then, the result of simulation is used to predict the delay bound of inter-devices WLAN.

Cascaded resonant-grating filters: experimental results on lowered sidebands and narrowed lines

Cascaded resonant grating filters are experimentally characterized. The levels to which cascaded resonant filters yield lowered sidebands and narrowed linewidths, as compared with individual filters, are measured. For example, four cascaded filters provide experimental sideband levels at -47 dB over a 50-nm wavelength range, a spectral linewidth of 0.43 nm, with an insertion loss of 3.7 dB.

Optical Spatial Filter to Suppress Beam Wander and Spatial Noise Induced by Atmospheric Turbulence in Free-Space Optical Communications

We propose an optical spatial filter (OSF) method to suppress beam wander and spatial noise effects. Signal from random displacements of the focus spot around the optical axis within the constricted area is collected. This method advantageously suppresses fluctuations in signal intensity. The OSF consists of a pinhole and cone reflector. The pinhole produces Fresnel diffraction on the focus spot. The cone reflector provides directed reflectance onto the pinhole for random focus spot displacements due to beam wander. The calculations of signal power are based on fluctuations of signal intensity that are minimized by the circular aperture function of the pinhole and the cosine of the reflectance angle from the cone reflector. The method is applied to free-space optical communications at a wavelength of 1.55 μm with an atmospheric chamber to provide optical propagation media. Based on calculations, the beam wander angles that can be received by the OSF are from 14.0° to 28.0°. Moreover, based on experiment, the OSF with a pinhole diameter of 20.0 μm and cone reflector diameter of 1.5 mm produces signal power of −15.3 dBm. Both calculations and experiment show that the OSF enhances the received signal power in the presence of turbulence.