This paper presents a photonic bandgap simulation for real holographic 3D photonic crystals instead of optimal photonic
crystal structures. The holographic photonic crystals are formed through five-beam interference generated by multi-layer
phase mask. The photonic bandgap depends on the relative phase difference among the interfering beams. A maximum
bandgap of 20% of the middle bandgap can exist in these structures which can be formed through single beam, single
phase mask, and single laser exposure process. We also fabricate the multi-layer phase mask by placing a spacer layer
between gratings. Using the multi-layer phase mask, photonic crystal templates are holographically fabricated in a
photosensitive polymer.
In this paper we demonstrate an approach for laser holographic manufacturing of three-dimensional photonic lattice
structures using a single specially designed, diffraction optical element mask. The mask is fabricated by recording
gratings in a photosensitive polymer using a two-beam interference method and has four diffraction gratings in the
sample plane, with a same distance from the opening center and oriented four-fold symmetrically. Four first-order
diffracted beams by the gratings and one non-diffracted central beam overlap and form three-dimensional interference
pattern. The phase of one side beam is delayed by inserting a thin piece of microscope glass slide into the beam. By
rotating the glass slide thus tuning the phase of the side beam, the five beam interference pattern changes from facecenter
tetragonal symmetry into desired diamond-like lattice symmetry. The three-dimensional interference pattern is
recorded in a photosensitive polymer, showing the phase tuning related changes of photonic lattice structures. Combing
an amplitude mask with the phase mask by putting the amplitude mask in the central opening of the diffraction optical
element mask, line defects are produced within the photonic crystal template.
We report an all-fiber hydrogen sensing system for low-temperature operation. The sensor consists of a fiber Bragg
grating written in high-attenuation fiber and coated in Palladium. Heating the sensor with in-fiber light power greatly
enhances sensitivity at low temperatures. A multi-functional infrared light source is used to provide both in-fiber heating
and sensor monitoring. This technology promises a single fiber feedthrough solution for low temperature multipoint
hydrogen leak detection.
We report a new design and fabrication of an integrated two-layer phase mask for five-beam holographic fabrication of
three-dimensional photonic crystal templates. The fabricated phase mask consists of two layers of orthogonally oriented
gratings produced in a polymer. The vertical spatial separation between two layers produces a phase difference among
diffractive laser beams, which has enabled a holographic fabrication of diamond-like photonic crystal templates through
single-beam and single-exposure process. The reported method simplifies the fabrication of photonic crystals and is
amendable for massive production and chip-scale integration of three-dimensional photonic structures.
This paper presents sensitivity enhancement of fiber Bragg grating sensors written in two hole fibers to
external hydrostatic pressure. Finite element analysis was used to optimize the size, diameter, and
configuration of air holes. The fiber core was then fabricated in the region with the maximum birefringence
induced by external pressure. Resonant peak splitting of fiber Bragg gratings were used to gauge the external
hydrostatic pressures. By using 220-μm diameter two hole fibers with 90-μm air holes, the optimized fiber
structure with a fiber core fabricated on the edge of the air hole registered 0.102 pm/psi hydrostatic pressure
response, yielding 6.5 times enhancement than previously reported in two hole fibers. The sensitivity
enhancement of fiber sensors is further demonstrated by controlling the size of air holes.
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