Yuankun Lin

Phase tunable holographic fabrication for three-dimensional photonic crystal templates by using a single optical element

This paper demonstrates a phase tunable holographic fabrication of three-dimensional photonic lattice structures using a single optical element. A top-cut four-side prism is employed to generate five-beam three-dimensional interference patterns. A silica glass slide is inserted into the optical path to adjust the phase of one interfering beam relative to other four beams. The phase control of the interfering laser beam renders the lattice of the interference pattern from a face-center tetragonal symmetry into a high contrast, interconnecting diamondlike symmetry. This method provides a flexible approach to fabricating three-dimensional photonic lattices with improved photonic band structures.

Fabrication of two-layer integrated phase mask for single-beam and single-exposure fabrication of three-dimensional photonic crystal.

In this paper, 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 phase mask consists of two layers of orthogonally oriented gratings produced in a polymer. The vertical spatial separation between two layers produces a phase shift among diffractive laser beams, which enables the holographic fabrication of inter-connected three-dimensional photonic structures. A three-dimensional photonic crystal template was fabricated using the two-layer phase mask and was consistent with simulations based on the five beam interference. The reported method simplifies the fabrication of photonic crystals and is amendable for massive production and chip-scale integration of three-dimensional photonic structures.

Five beam holographic lithography for simultaneous fabrication of three dimensional photonic crystal templates and line defects using phase tunable diffractive optical element

This paper demonstrates an approach for laser holographic patterning of three-dimensional photonic lattice structures using a single diffractive optical element. The diffractive optical element is fabricated by recording gratings in a photosensitive polymer using a two-beam interference method and has four diffraction gratings oriented with four-fold symmetry around a central opening. Four first-order diffracted beams from the gratings and one non-diffracted central beam overlap and form a 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 face-center tetragonal symmetry into diamond-like lattice symmetry with an optimal bandgap. Three-dimensional photonic crystal templates are produced in a photoresist and show the phase tuning effect for bandgap optimization. Furthermore, by integrating an amplitude mask in the central opening, line defects are produced within the photonic crystal template. This paper presents the first experimental demonstration on the holographic fabrication approach of three-dimensional photonic crystal templates with functional defects by a single laser exposure using a single optical element.

Holographically formed three-dimensional Penrose-type photonic quasicrystal through a lab-made single diffractive optical element

Large-area three-dimensional Penrose-type photonic quasicrystals are fabricated through a holographic lithography method using a lab-made diffractive optical element and a single laser exposure. The diffractive optical element consists of five polymer gratings symmetrically orientated around a central opening. The fabricated Penrose-type photonic quasicrystal shows ten-fold rotational symmetry. The Laue diffraction pattern from the photonic quasi-crystal is observed to be similar to that of the traditional alloy quasi-crystal. A golden ratio of 1.618 is also observed for the radii of diffraction rings, which has not been observed before in artificial photonic quasicrystals.

Effect of structural variation on the photonic band gap in woodpile photonic crystal with body-centered-cubic symmetry

A woodpile photonic crystal template with body-centered-cubic symmetry can be fabricated by exposing the photoresist to a four-beam interference pattern or a pattern generated through a diffractive optical element. We present detailed photonic band-gap calculations for photonic structures obtained under various possible fabrication conditions. The woodpile photonic crystal has a full photonic band gap up to 19% of the gap center frequency when the photoresist template is converted into silicon. The tolerance of the band gap to deviations of the structural parameters from their optimum values indicates great flexibility of the holographic fabrication process.

Photonic crystals with defect structures fabricated through a combination of holographic lithography and two-photon lithography

This paper presents the capability of direct laser writing of complex defect structures in holographically formed three-dimensional photonic crystals in dipentaerythritol penta/hexaacrylate (DPHPA) monomers mixed with photoinitiators. The three-dimensional photonic crystal template was fabricated through prism-based holographic lithography. Defect structures are fabricated through the two-photon polymerization excited by a femtosecond laser. The strengths of two optical lithographic techniques are combined with holographic lithography providing a rapid and large area microfabrication and two-photon lithography providing flexibility in fabrication of defect structures. The optical fabrication process is simplified in the negative tone DPHPA without prebake and postexposure bake as is required of SU-8 while maintaining a capability for constructing photonic structures with small features.

Holographic fabrication of photonic crystals using multidimensional phase masks

This paper reports the experimental approaches to the fabrication of two-layer integrated phase masks and the fabrication of photonic crystal templates using the phase mask based on holographic lithography technique. The photonic crystal template is formed by exposing photoresist mixtures to five-beam interference patterns generated through the phase mask. The fabricated phase mask consists of two layers of orthogonally oriented gratings produced in a liquid crystal and photoresist mixture. A polymerization-induced phase separation preserves the grating structure during the exposure. The vertical spatial separation between two layers of gratings produces a phase difference among diffracted laser beams, which enables the holographic fabrication of diamondlike photonic crystal structures. The fabricated photonic crystal structure is consistent with simulations based on the five-beam interference. The two-layer phase mask opens up an opportunity of direct printing photonic structures.

Maximum and overlapped photonic band gaps in both transverse electric and transverse magnetic polarizations in two-dimensional photonic crystals with low symmetry

In this paper, photonic band gaps have been systematically calculated for two-dimensional photonic crystals in centered rectangular lattices with elliptical patterns for both transverse electric and transverse magnetic polarizations. Two-dimensional centered rectangular lattices can be considered to be a stretched or compressed form of the hexagonal lattice with lower symmetry. For infinitely thick two-dimensional photonic crystals, the maximum overlapped photonic band gaps for both transverse electric and transverse magnetic polarizations occur in the well-studied hexagonal lattice. However, the maximum overlapped band gap happens in centered rectangular lattices with elliptical patterns for two-dimensional photonic crystal slabs, supporting other studies that reducing symmetry can open overlapped photonic band gaps.

In-fiber colloidal photonic crystals and the formed stop band in fiber longitudinal direction

We report a microfluid-guided growth of colloidal photonic crystals inside a twin-hole optical fiber. The microfluid is pumped by the vapor pressure and capillary force of the solvent sealed in a vial. A face-centered-cubic lattice-type structure has been achieved for colloidal photonic crystals grown inside the twin-hole optical fiber. The colloidal crystal growths at air-colloid interfaces, fiber microchannel-colloid interfaces, and crystal-colloid boundaries are studied with scanning electronic microscope. Optical reflection measurement reveals a stop band along the fiber longitudinal direction due to the Bragg diffraction of in-fiber colloidal photonic crystals. The in-fiber photonic crystal adds an optical function to the microstructure optical fiber by incorporating spectral control through a structural resonance in the cladding region of the optical fiber.

Negative refraction behaviors in two-dimensional elliptical-rod photonic crystals in a centered rectangular lattice

It is shown that negative refractions exist in two-dimensional photonic crystals consisting of centered rectangular lattices of elliptical dielectric rods in air. These lattices can be considered as deviated structures from well-studied, strict hexagonal lattices. There is a tolerance of negative refractions to deviations of structural parameters from the hexagonal lattice, indicating certain flexibilities for fabrication process for these photonic crystals including the hexagonal one.