Chunchen Lin

Fabrication and characterization of three-dimensional silicon tapers

We present the fabrication of 3D adiabatically tapered structures, for efficient coupling from an optical fiber, or free-space, to a chip. These structures are fabricated integrally with optical waveguides in a silicon-on-insulator wafer. Fabrication involves writing a single grayscale mask in HEBS glass with a high-energy electron beam, ultra-violet grayscale lithography, and inductively coupled plasma etching. We also present the experimentally determined coupling efficiencies of the fabricated tapers using end-fire coupling. The design parameters of the tapered structures are based on electromagnetic simulations and are discussed in this paper.

Wavelength scale terahertz two-dimensional photonic crystal waveguides

A terahertz-scale two-dimensional photonic-crystal waveguide based on a silicon-on-insulator was fabricated, and the optical transmission spectrum was measured. Terahertz beam propagation characteristics were observed using a thermal imaging camera, with incident light in the 10.1-10.7 microm range. The measured transmission spectrum was in good agreement with a three-dimensional finite-difference time-domain calculation.

Negative refraction imaging in a hybrid photonic-crystal device at near-infrared frequencies

We present the experimental demonstration of imaging of a point source by negative refraction at near-infrared frequencies using a hybrid photonic crystal device. The photonic crystal device, fabricated by patterning holes in 260nm silicon-on-insulator, integrates a triangular-lattice photonic crystal with a large photonic bandgap and square-lattice photonic crystal with negative refraction. Experimental results show that the output of a line-defect photonic bandgap waveguide provides a nearly ideal point source and then is imaged through the photonic crystal by negative refraction.

Experimentally demonstrated filters based on guided resonance of photonic-crystal films

We demonstrate a guided resonance filter based on photonic crystals (PhCs), which are fabricated in a high-permittivity material. The resulting spectra from a three-dimensional analysis of the structure and experimental measurement results show sharp dips and flattop transmissions. These provide promising properties in constructing sensitive and compact wavelength-selective devices, such as wavelength-division multiplexers.

Efficient terahertz coupling lens based on planar photonic crystals on silicon on insulator.

We present a promising coupling device, namely, a terahertz (THz) planar photonic crystal (PhC) lens based on the effective refractive-index contrast between the PhC and the surrounding unpatterned area. Three-dimensional finite-difference time-domain calculations show a 90% power transfer from a 100-microm silicon waveguide to a 10-microm waveguide, and 45% coupling efficiency is confirmed experimentally. These results demonstrate the utility of the PhC lens as an effective approach to coupling into PhC THz circuits.

Fabrication of terahertz two-dimensional photonic crystal lens on silicon-on-insulator

Using the special dispersion properties of photonic crystals (PhCs), we present a promising novel coupling device, the terahertz (THz) planar photonic crystal (PhC) lens. Three-dimensional finite-difference time-domain (3D-FDTD) calculations show a 90% power transfer from a 100 mm waveguide to a 10 mm waveguide, and experimental results confirm its high efficiency. Furthermore, the PhC lens couples the wave into a PhC line-defect waveguide is also reported. These achievements manifest the usefulness of the PhC lens as an effective approach to couple the wave into future THz circuits.

Fiber-to-waveguide evanescent coupler for planar integration of silicon optoelectronic devices

We present a method for coupling from a single mode fiber, or fiber ribbon, into an SOI waveguide for integration with silicon opto-electronic circuits. The coupler incorporates the advantages of the tapered waveguides and prism couplers, yet offers the flexibility of planar integration. The coupler can be fabricated on a double polished silicon wafer using direct polishing or grayscale photolithography. Tapered waveguides or J-couplers are then used as lateral mode converters. An experimental setup with a rotational stage and a pneumatic plunger has been built for adjusting the incident angle and tunnel layer thickness, which are key factors in determining the coupling efficiency. When optimal coupling is achieved on the setup, the coupler can be packaged using epoxy bonding. Thus, a fiber-waveguide parallel coupler or connector can be easily constructed. Electromagnetic calculation predicts a coupling efficiency of 77%(-1.14dB insertion loss) for a silicon-to-silicon coupler with a uniform tunnel layer. The coupling efficiency is experimentally achieved to be 46%(-3.4dB insertion loss) excluding the loss in silicon and the reflections from the input surface and output facet.

Photonic crystal planar lens working at low frequencies

In this paper, we demonstrate the design and fabrication of a planar lens based on the dispersion property of a photonic crystal. When a photonic crystal is illuminated with a low frequency within its dispersion diagram it behaves very similar to an isotropic material, whose resultant index is kept a constant, and is determined by the ratio of high index material and low index material. To validate our design, we performed the experiment in millimeter regime, where the photonic crystal lens was fabricated using a CNC micro-milling machine, and a millimeter wave imaging system was built based on a vector network analyzer. For the lens, we have observed its ability to collimate an incident point source both in the amplitude and phase.

A correlator sensor chip based on the integration of meta-materials and photonic crystals

In this paper, we utilize advanced artificial materials, namely, photonic crystals (PhCs) and meta-materials, to construct a sensing head with miniaturized antennas as detecting devices and embedded signal channelization for preprocessing. We experimentally demonstrated miniaturized antennas based on meta-materials, as well as, hybrid lattice PhCs and Schottky diodes for RF channelization. To further decrease the size of the system, we also present our initial design and simulation results for a PhC slow wave delay line, which also functions as a waveguide to the channelized signals.

AlGaAsSb/InGaAsSb photovoltaic transistors and high-efficiency solar cell with nano-antenna structures

We present a new design of high sensitivity, multi-spectral capability AlGaAsSb/InGaAsSb phototransistors for infrared sensing and solar energy conversion applications. These devices are grown by molecular beam epitaxy (MBE), which exhibit high responsivity at room-temperature. The 50% cutoff wavelength of spectral photoresponse is 2.2 μm. Similar structures are also investigated for solar cell applications. The possibility of increasing the solar energy conversion is explored by incorporating nano-antenna array into the solar cell. The broad-band nano-antenna is designed using Ansoft HFSS. The results indicate high solar energy conversion can be achieved for highly efficiency, flexible, lightweight solar power generations for the applications such as aircraft, airbase and special operations.