We develop a continuous wave terehertz (THz) imaging system operating at 288 GHz. This imaging system simply consitutes three parts including the source, two optical lenses, and the detector. The entire size is smaller than the tranditional pulsed THz imaging system. In this developed system, the THz wave is generated by a horn attenna which concentrates the wave in an azimuth angle of 3° ~ 5°. The source originates from a singnal generator, and then the frequency increases to 288 GHz after passing through an 8X multiplier. Next, THz wave is focused by a THz lens on the test sample. By controling the sample position in the x-z plane, we can scan it pixel-by-pixel in which each step along the x- or z- axes is 0.1 mm. After penetrating the test sample, another lens collects the transmitted THz wave and focuses them into the thermal detector. This detector can disply the collected THz power. Finally, by drawing the detected power of each pixel, a transmitted-intensity figure for all pixels is obtained. The resolution of this THz imaging system is about 1~2 mm at present. We have measured human molar tooth and obtained its transmitted figures. Besides, we also develop a technology to adjust the positions of the source and detector by a system containing one laser, one beamsplitter, and two mirrors. The relative positions between the source and detector is very important. The input of the source and the output of the detector are small so that they have to aim at each other very accurately in order to collect maximum transmitted power in the detector.
Multilayer titanium photonic crystals are fabricated with the mature integrated circuit (IC) technology, which is similar
to the Damascene interconnect process. The photonic crystals that we created have the face-centered-tetragonal lattice
symmetry. In each layer, the feature size, height and the spacing of the titanium rods is 100 nm, 200 nm and 300 nm,
respectively. To our knowledge, this is at the first time that the three-dimensional titanium photonic crystals are realized
successfully with 100-nm line width. The reflectance spectra of
three- and four-layer titanium photonic crystals are
measured with the Fourier-transform infrared spectroscopy and simulated with the three-dimensional finite different time
domain method. Through both the experimental observation and the calculation verification, the characterization of the
photonic band gap is demonstrated at near-infrared wavelengths and the optical behavior of titanium photonic crystals is
discussed for incident light waves of s- and p-polarization. Moreover, the absorption spectra are derived from the
reflectance and transmittance spectra due to the law of conservation of energy. It is found that absorption near the
photonic band edge is modified and enhanced in a narrow bandwidth because of the well-known recycling-energy
mechanism. The large band gap can suppress black body radiation in the mid-infrared range and recycle energy into the
near infrared. According to Kirchoff's law, the absorptance of a body equals its emissivity. Thus, the multilayer titanium
photonic crystals would be applied as an efficient near-infrared light source with a narrow bandwidth, and produced on a
mass scale with the standard IC technology.
In this presentation, a simple patchwork to the classical mode matching method (MMM) is proposed to analyze rib ARROWs. MMM gives the modal effective index and the lateral part of modal power loss, and the total modal loss is obtained by including the vertical part which is estimated by a simple yet physical method described here. The simplified MMM (SMMM) is also presented to analyze the effect of TE-TM couplings. Simulation results of selected rib ARROW structures are discussed and compared with those obtained by the Effective Index Method (EIM).
An ARROW-B (antiresonant reflecting optical waveguide, type B) surface plasmon resonance (SPR) sensor operating in aqueous environment is proposed. The characteristics, design, and optimization of the Au-coated ARROW-B SPR sensor are discussed. The operating range of the sensor can be shifted by adding a dielectric overlay. The detectable changes of the refractive index down to the order of 10-5 can be achieved. The design of an ARROW SPR sensor on Si substrates for detecting hydrogen molecules with palladium as the metal film will also be discussed.
The Benes network has two major advantages: one is that it has the lowest system insertion loss and the other is that it needs the fewest switches and drivers. However, lower signal- to-noise ratio (SNR) is its major disadvantage. The generally modified dilated Benes (GMDB) network has been proposed to obtain a higher SNR, but this network needs much more drivers. In this presentation, the modified Benes network is proposed to obtain a higher SNR with the same number of drivers as Benes network.
Volume-type holographic optical elements perform polarization-dependent characteristics, and highly polarization-selective holographic elements can be achieved with suitable designs. In addition, wavelength-selective characteristics can also be designed with volume-type holographic optical elements. These polarization-selective and wavelength-selective components have been designed and fabricated in various structures. In this presentation, we first review the basic structures of our holographic polarization-selective and wavelength-selective elements. Normally incident and output coupling of our compact and light-weight components provide better flexibility and easier alignment for system applications. Based on these holographic optical elements, we will introduce the compact structures for various optical interconnect applications.
Two hybrid optical elements re presented for dual-focus pickup in the digital versatile disk (DVD) system. One is a hybrid dual-focus lens and the other is a holographic regional mirror. The optical head consisting of these two hybrid optical elements can read the information recorded on two layers of DVD simultaneously. Its specifications are described. The fabrication parameters of these two hybrid optical elements are derived.
A novel low-loss bending structure in dielectric waveguides is proposed. In the proposed structure, an antiresonant Fabry-Perot cavity parallel to the original waveguide is added at the outer side of the bend in order to reduce the bending loss. Based on a simple design rule for the antiresonant cavity, the materials can be flexibly chosen to be adapted to fabrication methods. The beam propagation method is used to verify this low-loss design. The double- bend and curved structures using the same principle for further loss improvement are also presented.
Highly polarization-selective holographic elements can be achieved with suitable designs. The presented holographic polarization-selective elements are compact and light- weight, and the feature of normally incident and output coupling provide better flexibility and easier alignment for system applications. With suitable designs and arrangements, these elements can be combined to implement star couplers to distribute equal optical power from each input channel to all output channels. In addition, based on our holographic polarization-selective elements with electro-optic halfwave plates, holographic polarization-dependent and polarization- independent optical switches are introduced. The structures to use these switches in various compact 3D multistage interconnection networks for reconfigurable interconnections and in self-healing rings for network service restoration are presented.
The rectangular crossbar network is commonly used in switching networks due to its many advantages, such as easy connection-path rebuilding, wide-sense nonblocking network, and no crossover in its interconnection lines. However, this network has the major disadvantage of non-zero differential loss. In this presentation the cyclic crossbar network is presented to reduce this differential loss to zero and still maintain the original advantages. In addition, using holographic optical switches to implement this new network with no interconnection lines is discussed in detail.
Holographic optical switches are presented to implement Multistage Type 1 interconnection networks. These switches have unique features of compactness, lightweight and flexibility, which are suitable for system applications. The procedure to implement Multistage Type 1 network with our holographic optical switches has been discussed in detail. After optimum design, the unique features of compactness and flexibility of holographic optical switches efficiently eliminate all interconnection lines between switches. Not only the number of required components are reduced, but also the space of the system is significantly saved.
A novel coupling structure between antiresonant reflecting optical waveguides (ARROW's) is proposed. In this structure, the separation thickness between dual ARROW's is chosen for destructive interference in the decoupling section, and changed to an efficiently coupling value in the coupling section. The coupling length is about 710 micrometers for InP/InGaAsP materials, which is very promising for practical applications.
A substrate-mode holographic structure for wavelength-division-demultiplexing application is introduced. This type of substrate-mode hologram diffracts normally incident beams into a dielectric substrate with total internal reflection condition. The diffracted beams then propagate through the substrate and are separated for different wavelengths. Normally incident coupling and output on-axis imaging with this structure provide easier alignment with optical fibers.
Broad-bandwidth substrate-mode holograms for optical interconnect applications are investigated. These devices use total internal reflection to translate optical beams, and holographic elements to couple light in and out of the guiding substrate. Transmission and reflection-types of substrate-mode holograms are compared, and the reflection-type of devices give a broader angular bandwidth. The fabrication technique of reflection substrate-mode holograms are discussed and experimental results are given.
A novel substrate-mode grating pair structure for wavelength-division-demultiplexing (DEMUX) application is presented. An input grating coupler diffracts normally incident beams at an angle beyond the critical angle in the dielectric substrate. The diffracted beams then propagate through the substrate with total internal reflection to the output coupling grating and are separated for different wavelengths. Normally incident coupling and output on- axis imaging with this structure provide easier alignment with optical fibers. Three types of substrate-mode grating pairs providing the property of polarization-insensitive high-efficiency are investigated.
An optical fiber and on-chip waveguide interconnect system is presented. The method of mode propagation by Fourier expansion for our simulation and design to efficiently couple optical signals from single-mode optical fibers to on-chip waveguides is discussed. Simulation and experimental results will be given and the feasibility of this interconnect structure will be investigated.
In this paper, we examine board-to-board two-way communications with holographic optical elements. For this application, substrate-mode holograms with a high efficiency (> 90%) and broad angular bandwidth (Full Width at Half Maximum > 8 degree(s)) are fabricated. The experimental results for two-way communications between two circuit boards with these elements are given.
In this presentation the requirements of a free-space optical bus for connecting electronic processors at the multichip module and board levels of interconnection are discussed. Experimental results for holographic elements suitable for beam division polarization switching and guided propagation are also described. The talk will conclude with an overview of CAD methods needed to incorporate these components into a bus system.
In this paper the characteristics and methods of forming substrate-mode holographic optical elements are described. These components use total internal reflection to translate an optical beam, and holographic elements to couple light in and out of the guiding substrate. These gratings also have several useful polarization properties which are then discussed and demonstrated. The paper concludes with a description of the application of polarization-sensitive substrate-mode holographic elements to an optical bus system.
Methods for designing substrate-mode holographic (SMH) optical elements are discussed in detail. These
include techniques which account for the thickness change of a volume material during processing, and construction
and reconstruction at different wavelengths. A method to reduce the angular sensitivity of these elements is also
presented. Experimental results for components formed in dichromated gelatin with diffraction efficiency exceeding
95% and a FWHM (full angular width of the efficiency at half maximum) of more than 5° are given. Results for
cascaded grating pairs are also discussed.