Polarisation insensitive planar dielectric slab waveguide extended hemi-elliptical lens

The authors present the performance of a patch fed planar dielectric slab waveguide extended hemi- elliptical lens antenna. The lens is constructed using polystyrene and weighs only 90 g. The maximum lens dimensions are 11 lambda times 13 lambda in the lens plane and it is 0.6 lambda thick. From 18 to 30 GHz the lens can handle both TM₀ and TE₀ signals simultaneously and at 22 GHz it can be made to generate a 1.5 dB axial ratio circularly polarised signal when fed by a linearly polarised patch antenna orientated to 38deg with respect to the horizontal. The measured gain and half-power beamwidth for TM₀ and TE₀ excitation at 28.5 GHz are 18.5 dB (aperture efficiency of 85%), 4.1deg and 18.7 dB, 4.4deg, respectively, both with a -10 dB return loss bandwidth of about 10%.     

24 GHz automotive radar planar Luneburg lens

A planar Luneburg lens whose permittivity distribution is modified by two types of hole density control in the central region and by dielectric thickness control in the edge region is reported. The lens was designed to operate at 24 GHz in Transverse Electromagnetic (TEM) mode. Experimental radiation patterns show good agreement with the simulation. The measured 3 dB beamwidth of the vertical polarised H-plane pattern is 5deg with 14 dB gain at 24 GHz for a 12.2lambda, 15.24 cm diameter lens, cross polar levels were below -30 dB. Its small size and lightweight, 53% of material is removed, and better than 20% bandwidth makes it useful for vehicular use in the 24 GHz unlicensed Industrial, Scientific, Medical (ISM) equipment band and for 24 GHz short range radar applications     

Light propagation in a planar dielectric waveguide with a gyrotropic layer

The nature of the magneto-optic Kerr effect in a planar dielectric waveguide geometry has been investigated by calculation of the Jones matrix for a planar waveguide structure with a gyrotropic magnetic material as one wall. The intensity of the component of the field that is in the polarization state orthogonal to the input was calculated as a function of length of the gyrotropic material and input polarization state. The degree of polarization rotation depends on the relative orientation of the magnetization in the magnetic material and the direction of propagation. It is found that there exists an optimal waveguide length and input polarization at which the output signal is maximized and that a significant enhancement in polarization rotation is available with respect to free-space reflection. These results indicate that a magnetic-film-bounded planar waveguide can be used for device applications such as magnetic field sensors or magneto-optic modulators.     

Improvements of the ray trace through the generalized Luneburg lens

An analytical expression for the gradient of the generalized Luneburg lens is found and applied to the computation of the profile and the gradient of the refractive index.     

Broadband microwave Luneburg lens made of gradient index metamaterials

Luneburg lenses are able to form perfect focus that is free of aberration. Because of the varying refractive index throughout the lens, incoming electromagnetic waves can travel in a curved path and be guided to focus at the back of the lens. The implementation of Luneburg lenses is often difficult due to the challenges in creating a medium with varying refractive index using normal materials. This problem can be overcome with the use of gradient index metamaterials. We report a two dimensional Luneburg lens made of gradient index metamaterials. It consists of 17 concentric shells with etched patterns on a printed circuit board working in microwave X band frequency. The broad properties of the Luneburg lens are then discussed.     

Determination of light beam curvature in a rotating Luneburg lens

We have determined the curvature of a beam of coherent electromagnetic radiation and its angular and linear deviation in a rotating microsatellite representing a Luneburg lens in the optical segment of accuracy augmentation for new-generation global navigation satellite systems.     

Analysis of mode scattering from an abruptly ended dielectric slab waveguide by an accelerated iteration technique

A new modification of the integral equation method using an iteration technique with "accelerating" parameters is presented to solve the problem of guided-mode scattering from an abruptly ended asymmetrical slab waveguide. The optimal choice of the parameters is shown to be closely connected with the variational principle. The electric-field distribution at the terminal plane, the reflection coefficient of the guided mode, and the far-field radiation pattern are computed. Numerical results are presented for several cases of abruptly ended waveguides, including the systems with constant and variable profiles of the refractive indices. The phenomenon of the radiation pattern rotation is examined in detail.     

Optical planar waveguide for cell counting

Low cost counting of cells has medical applications in screening, military medicine, disaster medicine, and rural healthcare. In this report, we present a shallow, buried, planar waveguide fabricated by potassium ion exchange in glass that enables low-cost and rapid counting of metal-tagged objects that lie in the evanescent field of the waveguide. Laser light transmitted through the waveguide was attenuated proportionately to the presence of metal-coated microstructures fabricated from photoresist. This technology enables the low-cost enumeration of cells from blood, urine, or other biofluids.     

A slab optical waveguide with negative effective thickness

Two new asymmetric slab optical waveguides with a left-handed media (LHM) cover or substrate are studied. The effective thickness is derived by using normalized waveguide parameters. An analytical method is then proposed to calculate the universal effective thickness. We show that negative effective thickness exists in the waveguide with a LHM substrate, unlike in conventional waveguide or other LHM waveguides studied previously. However, for the waveguide with a LHM substrate, the shape of high-order mode behaves like that of a traditional slab waveguide, and neither the fundamental mode nor the other higher order modes have the novel phenomena of negative effective thickness. Both TE and TM modes are discussed.     

硅基平面波导材料的制作

采用火争水解法（ＦＨＤ）在Ｓｉ基上淀ＳｉＯ２预制材料,然后在真空中／空气气氛中高温处理（１３８０℃）,制得玻璃化的ＳｉＯ２膜材料;该材料膜厚适中（１０－３０μｍ）、平整度好、光滑透明,适合制作单模、多模列阵平面波导光栅。并利用ＸＲＤ、ＳＥＭ、台阶仪等仪器对ＳｉＯ２膜进行了测试分析。     

Single-arm double-mode double-order planar waveguide interferometric sensor

A sensor is described for which interference measurements of the phase delay between two propagating modes of different orders in a slab thin-film waveguide are used as the sensing technique. The basic building block of the sensor is a polymer film doped with an indicator dye such as Bromocresol Purple. The modes of two orders such as TM(0) and TM(1) are simultaneously excited in the light-guiding film with a focusing optics and a prism coupler. The modes are decoupled from the film and recombined to produce an interference pattern in the face of an output optical fiber. The sensitivity of the sensor to the ambient temperature change is 1.5 degrees C, and the sensitivity to NH(3) is 200 parts in 10(6) for one full oscillation of the signal.     

Single-mode fiber-linearly tapered planar waveguide tunable coupler

We developed a simple system of tunable fiber-film coupler using a linearly tapered thin-film planar waveguide (PWG) evanescently coupled by a single-mode distributed fiber half-coupler. We investigate the characteristics of the coupler theoretically and experimentally taking into consideration the refractive index (n(f)) of nonuniform films, the magnitude of nonuniformity (m) of the films, and the source wavelength (lambda). The thickness variation of the nonuniform film is along the direction of propagation of optical power. Tapered and plano-concave thin films of a mix of oils as well as a plano-concave poly(methyl methacrylate) film were fabricated to serve as nonuniform PWG's. Similar to single-mode fiber with a uniform thickness PWG coupler, such a coupler also provides light modulation with a change of n(f). However, position shifting of a half-coupler in a tapered PWG structure along the direction of propagation exhibits the variation of fiber throughput power. This action serves as a simple system for a tunable fiber-film coupler. Wavelength-dependent throughput fiber power for such a coupler also behaves as a filter. The center wavelength can be controlled by shifting the position of the half-coupler. A coupling fiber as a half-coupler can be used for efficient coupling. We performed a theoretical analysis of the structure using Marcuse's model and observed good agreement with the experimental results.     

Mode coupling in tilted planar waveguide gratings

Three different grating tilting formulas for predicting the optimum grating tilt angle for strong mode coupling in planar waveguide gratings are derived. The optimum tilt angles obtained by the ray-optics approach deviate ~1 degrees for transmissive mode coupling and ~1.5 degrees for reflective mode coupling from those computed by the coupled-mode approach. The coupled-mode analysis and ray-optics analysis of the tilted planar waveguide gratings show that the transmissive planar waveguide gratings should be tilted more than 84 degrees for strong TE(0)-to-TE(mu) mode coupling near 1550 nm.     

Polarization properties of a four-layer dielectric waveguide

A new integrated-optics polarizer system is analyzed. Calculations are made and experiments carried out to demonstrate the performance of this system. Pis’ma Zh. Tekh. Fiz. 24, 35–39 (March 26, 1998)     

Embossable grating couplers for planar waveguide optical sensors

Planar optical waveguides are an attractive tool for use in analytical chemistry and spectroscopy. Although similar to fiber optics, planar waveguides have been slow to be commercially accepted due to the difficulty of coupling light into the guide. Generally, prism coupling is the method of choice in the laboratory, as efficiencies approaching 80% can be reached. However, prisms are impractical for routine use for several reasons: expensive positioning equipment is required, coupled power is sensitive to environmental fluctuations, and prism coupling prohibits the fabrication of a truly planar device. The use of thin gratings on the surface of the waveguide allows for a two-dimensional structure to be maintained, while providing enough efficiency to be useful as a sensor. Our research efforts focus on developing a technique to make inexpensive, reproducible gratings that are easy to fabricate. By chemically modifying the surface of a commercial grating with a suitable release agent, it is possible to emboss replica gratings onto a variety of waveguide types. The fabrication of embossed gratings will be described, and their performance on glass, ion-diffused, polymer, and semiconductor waveguides will be presented.     

Sol-gel-based, planar waveguide sensor for water vapor

A water vapor sensor based on a combination of sol-gel processing and planar optical waveguide technologies has been developed. The indicator erythrosin B was entrapped in a thin sol-gel film (thickness ～100 nm) prepared from methyltriethoxysilane, dimethyldiethoxysilane, and tetraethoxysilane. This dye exhibits an increase in absorbance in the presence of liquid or gaseous water. The sol-gel layer containing the dye was deposited onto a sol-gel-derived, single-mode planar waveguide. Outcoupled light intensity measurements (at 514.5 nm) over a range of water vapor concentrations (in a nitrogen gas stream) yielded a response over a wide range of relative humidity (<1-～70%) at room temperature. Response and reversal times were less than 1 min, which may make this sensor attractive for real-time monitoring applications.     

Sol-gel-based, planar waveguide sensor for gaseous iodine

A novel sensor for gaseous iodine has been developed using a combination of sol-gel processing and planar integrated optical waveguiding technologies. The sensing principle is based on the detection of a charge transfer complex formed between iodine and phenyl groups that have been incorporated into a porous, methylated glass film. The glass film was prepared from siloxane precursors by the sol-gel method. Sensors were fabricated by coating the film over a single-mode planar waveguide. Light was coupled into and out of the laminate structure using integral grating couplers, and formation of the charge transfer complex was monitored as attenuated total reflection of the guided wave. The sensor exhibits a linear response to I(2) in the range of 100 ppb to 15 ppm with response and recovery times less than 15 s. The response is selective to 4 ppm iodine in the presence of 10 ppm chlorine and is stable for at least 3 months.