Photonic crystals (PhCs) have recently been the focus for the developing micro- and nano-optical sensors, due to its
capability to control and manipulate light on planar devices. This paper presents a novel design of micro-optical pressure
sensor based on 2-dimensional PhC slab suspended on Si substrate. A line defect was introduced to the PhC slab to guide
and reflect light with frequency in the photonic bandgap in the plane of the slab. The structure, with certain surface
treatment, can be used in miro-scale pressure catheters in heart ablation surgeries and other biomedical applications. The
working principle of the device is to modify light reflection in the PhC line defect waveguide by moving a substrate
vertically in the evanescent field of the PhC waveguide. Evanescent field coupling is the critical step that affects light
transmission and reflection. High resolution electron-beam lithography and isotropic wet etching have been used to
realize the device on the top layer of a Si-On-Insulator (SOI) wafer. The PhC slab is released by isotropic wet etch of the
berried oxide layer. The output reflection spectrum of the device under different pressure conditions is simulated using
3-dimensional finite difference time domain (FDTD) method. The result showed that when the PhC slab is close enough
to the substrate (less than 400 nm), the reflected light intensity decreases sharply when the substrate moves towards the
PhC slab. Mechanical response of the sensor is also studied.
Photonic crystals (PhCs) exhibiting negative refraction have attracted much attention in recent years, with a vast majority of this research focusing on subwavelength imaging. Although the possibility of an open cavity using such a PhC is mentioned in Notomi's pioneering work, fewer researchers have addressed this issue except one study of an open cavity using three 60-degree PhC wedges of the hexagonal lattice. This paper reports our study of several different open cavity configurations in hexagonal and square lattices. To form an open cavity using PhC with negative refraction, there are many parameters to optimize, such as the lattice type, lattice period, the diameter of the hole or rod, materials, and the geometrical configurations. We first propose several configurations for open cavities in general, including two square slabs, two or more prism slabs, and one slab with two reflectors; Then we demonstrate some results obtained from photonic crystals with square and hexagonal lattices, simulated by the use of the finite-difference time-domain (FDTD) method. It is shown that resonance can occur at the first band and higher bands. The Q-factor obtained is about 280 to 400, which can be improved by optimizing the surface terminations of the photonic crystal prisms.
Light can interact with periodic microstructures, also known as photonic crystals, in many ways. In this talk we will consider the use of photonic crystals to modify the wavefront and wavevector direction of waves propagating in photonic crystal slab waveguides and will compare these effects with those at arise from modification of the Poynting vector. We will discuss the underlying principles and will consider applications of these devices, in particular for wavelength demultiplexing. We will illustrate our investigation by considering the design of 1-D and 2-D photonic crystal superprism demultiplexers, and show that compact (<4 mm chip size) and high resolution (100 GHz) multichannel devices can be obtained.
An aspheric collimating slab waveguide lens is designed using a diverging planar 1-D photonic crystal. An approximation method for analysis of such structures has been developed. A lens design procedure (which minimizes area) is also introduced. For illustration purposes, we use Silicon on insulator technology with the minimum feature size of 100 nm. We show that fast lens with 130 μm focal length, f/# = 1.3 is achievable with an etching area of only 658 μm2.
Here we report a new type of dispersive structure for wavelength multiplexing/demultiplexing, based on a planar 1-D photonic crystal prism. We introduce a computationally efficient technique for simulating this structure. Simulations are carried out to determine the angular dispersion as a function of period, slant angle in the prism area and prism apex angle. The design has been optimized for good performance in a moderate refractive index contrast system (silica and silicon nitride) and promises reduced scattering losses when compared with existing 2-D superprism designs.
An analytical approximate method is introduced for obtaining wave vector diagrams for planar 1-D photonic crystal. Based on the best separable wave solution, a variational formula provides the best estimate to the propagation constant. The wave vector diagram and the wave profile are obtained for a typical PCVD technology. Due to the iterative nature of the method, any wave amplitude nonlinearity can also be modeled easily.
An optical processing technique is introduced. This technique can improve the resolution of any scanning imaging system, that extract information by using the electronic behavior of materials. In this optical processing technique proper transparency, and adjusting the scanning light intensity are used. This technique can improve the performance of digital image enhancer. We implement our idea on a familiar millimeter image converter.
A moving spot illuminated semiconductor panel is used to convert millimeter wave images to visible displays. The response of semiconductors to moving spot illumination is important in this method. In this paper the response of a semiconductor panel to a moving Gaussian (laser) spot is considered in detail. Initially, the profile of excess carrier in the bulk of the semiconductor panel for Gaussian illumination vs. position, scanning velocity, width of the semiconductor panel, etc., are studied. Using the expression for excess carrier, the single path attenuation of a millimeter wave through moving Gaussian spot illuminated semiconductor panel vs. standard deviation of Gaussian spot and scanning velocity is studied.
Performance parameters of tapered distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers are compared with earlier configurations, such as uniform grating DFB, (lambda) /4 phase-shifted DFB and uniform grating DBR lasers. Parameters such as oscillation conditions (above and below threshold), mode pattern along the laser length, output power, effects of nonzero end reflections on oscillation conditions, yield of the gain, linewidth an differential quantum efficiency are obtained for tapered DFB and DBR lasers. To find oscillation conditions a nonlinear model is used, which considers gain saturation due to longitudinal field intensity variation along the laser. Grating shape is of rectangular type. For tapering profile, a class of polynomial curves of hyperbolic form with a degree of freedom is used. For the analysis F-matrix approach is applied. For purpose of comparison, a constant effective coupling coefficient for all structures is defined. Some new important results have been obtained which show that, tapered DFB lasers are superior to phase shifted DFB lasers. Improvement of tapered DBR over uniform DBR depends on the type of performance parameter.
Radiation coupled mode theory with first order perturbation is used to investigate the optimum shape and depth in trapezoidal gratings (which includes rectangular and triangular cases) for radiative and nonradiative applications. Optimum trapezoidal grating shape for nonradiative purposes is obtained for both DFB and DBR lasers. For radiative purposes Optimum triangular grating are obtained for DBR lasers.
A method of conversion of millimeter wave images to visual displays is the use of semiconductor panel under scanning light spot. In this method of conversion, the behavior of semiconductor panel under moving spot of light is important. Performance of this system has been under investigation for last three decades. In this paper excess millimeter wave attenuation through semiconductor panel, due to moving rectangular illuminated spot, with arbitrary intensity profile across the length of the spot is formulated. Numerical calculation is done, for uniform and linearly graded cases. Effects of scanning velocity and spot dimensions on the excess millimeter wave attenuation are considered. It is shown that, with proper choice of parameters, higher system resolution is attainable with linearly graded intensity.
The gain coupled gratings are analyzed by the extension of a well-known coupled mode theory, first developed by Streifer et al. in 1977. We present a new matrix method that takes into account the polarization nature of the non-dominant modes, that has been ignored in the previous theories. Our method can analyze any grating irrespective of its shape, its order and its type. It is based on slicing the grating layer such that in each layer, the equivalent waveguide refractive index and excitation can be considered as constants. We obtain different coupled wave equations, as we applied this method to pure gain coupled DFB lasers. It is worth noting that our theory is presented in the under threshold regime.
The superiority of gain or loss-coupled DFB lasers over the index coupled ones are evident in many respects. However the fabrication of first order gain or loss coupled gratings involves many difficulties. Therefore we are practically restricted to employing higher order gain or loss-coupled gratings. One of the main disadvantages of higher order gratings is radiation losses. To take into account both the effects of higher order modes on coupling and losses in linear regime, we apply a well-known coupled wave analysis due to Striefer et al. In 1977 to loss coupled DFB lasers. This theory using the first order perturbation analysis is suitable for analyzing shallow gratings. It leads to a pair of coupled wave equations, where coefficients indicate all the possible coupling losses.
A new coupled mode theory is formally developed for analyzing the grating-assisted codirectional couplers. We show its superiority and inferiority with respect to existing theories. It belongs to the orthogonal category of coupled mode theories.
Dielectric corrugated waveguides are used in DFB and DBR lasers. Coupled mode theory is used to study the effect of variations in grating shape on the performance of DFB and DBR lasers. The purpose of this paper is to find the optimum geometry for different applications.
In DFB and OBR lasers, phase of corrucation at the reflective end and possible change of reflectivity at the facets, may alter the conditions of oscillation. These result the variation on the output power amplitude and the wavelength. The purpose of tapering at the grating is to reduce these effects. In addition, with dissimilar tapering, we can increase mode selectivity of such lasers. In this paper, we consider reflection coefficient of tapered DBR as a function of end facet reflection coefficient, and deviation from the Bragg's condition. It is shown that tapering improves the operation of DFB and DBR lasers.
In this paper formulation and graphical representation for excess semiconductor panel due to moving laser light source as a function of city position the laser beamwidth and the panel width are studied. semiconductor panel can be used as a laser sensor and millimeter wave
Scanning laser beam semiconductor panel can be used for conversion of millimeter
waves to visual displays. For this easy and direct method of conversion, the behavior
of semiconductor panel under scanning laser beam is required. Formulas for excess
carriers due to moving spot of light have beam obtained. Using these formulas single
path total field attenuation through semiconductor panel for scanning laser light spot
excitation as a function of scanning velocity, position and laser beam width are studied.
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