Temperature sensitivity of Ge-B-SiO(2) waveguide Bragg gratings on a crystallized glass substrate

Waveguide Bragg gratings were fabricated by plasma-enhanced chemical-vapor deposition followed by irradiation with KrF excimer laser light through a phase mask. The period of the Bragg grating was 0.53 mum, and the Bragg wavelength was ~1.53 mum . The temperature dependence of the Bragg wavelength was 11 pm/ degrees C for a 10GeO(2) -90SiO(2)(mol.%) core waveguide on a Si substrate, and the Bragg wavelength shift was successfully reduced to 5.0pm/ degrees C by use of a 14GeO(2)-12B(2)O(3)-74SiO(2) (mol.%) core and a crystallized glass substrate with a thermal-expansion coefficient of -2.0x10(-6)(/ degrees C) .     

Phase-shifting mask design for interference exposure of chirp blazed grating

An interference exposure system using a phase-shifting mask was proposed for generating periodic sawtooth optical intensity profile with chirp in period. Multiple space-harmonic waves are launched from the mask by diffraction, and the sawtooth optical intensity is formed by interference based on Fourier synthesis after propagation through an air gap. The design concept merely utilizing positive diffraction-order harmonics with tilt illumination of an exposure light and a design algorithm based on time-reversed configuration for calculating required phase shift amount were proposed and discussed. A phase-shifting mask for a blazed grating of very high chirp rate was designed to demonstrate its potential and feasibility. The grating period changes from 2.2 to 3.1 μm gradually within 0.3 mm length. Sawtooth-like optical intensity profile was confirmed by theoretical simulation as well as preliminary experimental results.     

Multidimensional angle sensing method using guided-mode resonance

Optical Review - A waveguide grating on a transparent substrate can serve as an optical notch filter owing to guided-mode resonance. The filtering wavelength is highly sensitive to an incidence...     

Compact and monolithic coarse wavelength-division multiplexer-demultiplexer fabricated by use of a high-spatial-frequency transmission grating buried in a slab waveguide

A compact and monolithic four-channel demultiplexer with 20-nm spacing was fabricated by use of a high-spatial-frequency transmission grating buried in a silica waveguide. The grating was successfully buried in a silica slab waveguide by overcladding by plasma-enhanced chemical-vapor deposition. The device's size was approximately 5.1 mm x 9.2 mm. The average insertion loss was 13 dB. The average cross talk was -15 dB for adjacent channels and -19 dB for nonadjacent channels. The polarization-dependent loss was estimated to be as low as 0.7 dB.     

Polarization-independent guided-mode resonance filter with cross-integrated waveguide resonators

A cavity-resonator-integrated guided-mode resonance filter (CRIGF) has been proposed and investigated in order to realize high-efficiency narrowband reflection with a small aperture. The CRIGF consists of a grating coupler integrated in a cavity resonator constructed by a pair of distributed Bragg reflectors on a thin-film waveguide. This time, orthogonally crossed integration of two CRIGFs was demonstrated in order to obtain polarization-independent reflection spectrum. An SiO₂-based device with 10?μm aperture was designed and fabricated for around 850?nm wavelength operation, and narrowband polarization-independent reflection was confirmed experimentally.     

Ultrasmall demultiplexer by use of one-dimensional photonic crystal

Silica-based one-dimensional photonic crystal (1D-PC) is fabricated by use of a high-spatial-frequency grating with input and output surfaces tilted with respect to its periodic direction. An incident beam is coupled with the first photonic band in the second Brillouin zone of the 1D-PC. The output beam angle changes 3 degrees with a wavelength change of 1%. A prototype of an ultrasmall demultiplexer is demonstrated by use of a silica slab waveguide with 1D-PC.     

Influence of groove depth and surface profile on fluorescence enhancement by grating-coupled surface plasmon resonance

The fluorescence intensity of a sample placed on a metal grating pattern is enhanced due to excitation by the electric field of the grating-coupled surface plasmon resonance (GC-SPR). The dependence of the enhancement on groove depth and surface profile was studied with the aim of improving the sensitivity of fluorescence detection. The enhancement was found to depend on the groove depth, with intensity most enhanced on grating substrate of about 20 nm depth, which produced an intensity about 30 times greater than that on a flat borosilicate glass substrate. Rigorous coupled wave analysis calculation showed that the shape of the groove influenced GC-SPR, suggesting that controlling not only the depth but also the shape of the grating surface profile can be an important factor in improving the sensitivity of detection by fluorescence microscopy.     

Antireflection microstructures fabricated upon fluorine-doped SiO(2) films

Two-dimensional periodic structures were fabricated upon a fluorine-doped SiO(2) film in which the fluorine content changed gradually in the direction of film thickness. The films were deposited by plasma-enhanced chemical-vapor deposition. The film was periodically patterned into a 1-mum period and an ~1-mum -groove depth by inductive coupled plasma reactive-ion etching followed by chemical etching in a diluted HF solution. A surface reflectance of 0.7% was attained at 1.85-mum wavelength, a value that is one fifth as large as the 3.5% Fresnel reflection of a SiO(2) substrate with a flat surface.     

Mid-infrared wire-grid polarizer with silicides

An infrared (IR) polarizer with tungsten silicide (WSi) wire grid was fabricated by two-beam interference exposure and reactive ion etching. To enhance TM transmittance, silicon monoxide was deposited between the WSi wire grid (400 nm period) and a Si substrate. The transmittance was over 80% in the 4-5 microm wavelength range. The ratio of TM and TE transmittances was over 100 (20 dB) in the 2.5-6 microm wavelength range. The fabricated polarizer has higher durability and better compatibility with microfabrication processes compared with conventional IR polarizers.     

Fabrication of Two-Dimensional Gratings Using Photosensitive Gel Films and Their Characterization

Two-dimensional (2D) surface-relief gratings have been fabricated by the two-beam interference method on photosensitive gel films, which are derived from chemically modified metal-alkoxides, and characterized with respect to surface morphology and antireflection effect. Photosensitive ZrO₂ gel film was deposited on a silica glass substrate using the sol that was prepared from Zr-tetrabutoxide chemically modified with benzoylacetone. The gel film was exposed to two-beam interference fringe (1.0 m period) of He-Cd laser and then rotated by 90° in its own plane, followed by an additional exposure. Leaching of the gel film with ethanol gave lattice or island types of 2D-gratings depending on the dose of laser irradiation. The morphology of the gratings changed with irradiation time of laser, leaching conditions and so on. The formation of 2D-grating of island type on a silica glass substrate substantially reduced the reflection at its surface in a wavelength range of 1.3 to 2.6 m.