Effect of fabrication errors in channel waveguide Bragg gratings

The spectral performances of nonideal rectangular Bragg gratings, integrated in a rib waveguide, are analyzed by a multilayer approach based on the effective-index method. The effects of errors on the photolithographic definition of the grating, that is, period and shape, and of errors on the control of etching depth are investigated. Also the influence of the stitching error, which is unavoidable when the grating is realized by means of electron-beam photolithography, is addressed. A novel analytical approach that extends coupled-mode theory to the analysis of real gratings is also presented.     

Design and fabrication of tapered microfiber waveguide with good optical and mechanical performance

In this paper, the inherent dependence of optical and mechanical characteristics of tapered microfiber waveguide on its contour profile is studied. Both theoretical analysis and experimental investigation are given. In theory, the optimal profile parameters of the tapered microfiber are proposed to improve the microfiber performance, where it is better to make the tapered microfiber keep two longer than 5-mm-long transition regions which have a decaying exponential profile. And the uniform waist diameter of the tapered microfiber should be more than 600?nm and less than 1?μm. In this case, the microfiber indicates several favorable advantages, such as low loss, strong evanescent field and relatively shorter transition region. In experiment, according to the profile parameters we proposed, we successfully fabricated a tapered microfiber with a low loss of 0.05?dB in air and 0.8?dB on a MgF₂ substrate at the wavelength of 1550?nm, and it has low surface roughness.     

Widely tunable optical bandpass filter by use of polymer long-period waveguide gratings

We report the design and fabrication of a widely tunable optical bandpass filter based on using two identical long-period gratings formed along a polymer channel waveguide with a section of the waveguide core removed. The peak transmission of the passband of the fabricated filter is approximately 60% and the bandwidth of the passband is approximately 6 nm. The filter is thermally tunable over the C + L band (1520-1610 nm) for both TE and TM polarizations with a temperature control of approximately 30 degrees C.     

Optical waveguide biosensors constructed with subwavelength gratings

The reflection resonance spectrum of a subwavelength diffraction-grating-coupled waveguide is used to analyze biomolecular interactions in real time. By detecting this resonance wavelength shift, the optical waveguide biosensor provides the ability to identify the kinetics of the biomolecular interaction on an on-line basis without the need for extrinsic labeling of the biomolecules. A theoretical analysis of the subwavelength optical waveguide biosensor is performed. A biosensor with a narrow reflection resonance spectrum, and hence an enhanced detection resolution, is then designed and fabricated. Currently, the detection limit of the optical waveguide sensor is approximately 10(-5) refractive-index units. The biosensor is successfully applied to study of the dynamic response of an antibody interaction with protein G adsorbed on the sensing surface.     

Design and fabrication of binary slanted surface-relief gratings for a planar optical interconnection

We propose the use of binary slanted surface-relief gratings with parallel-groove walls as input and output couplers in a planar optical interconnect. Parametric optimization of cascaded output couplers is employed to design an interconnect consisting of N output couplers producing a uniform intensity distribution with a high efficiency that may be realized in one lithographic etching step. The sensitivity of a N = 4 interconnect to various fabrication errors is analyzed. We demonstrate the operation of a slanted surface-relief grating manufactured with electron-beam lithography and reactive-ion etching for an operating wavelength of lambda = 0.633 mum.     

Analysis of antiresonant reflecting optical waveguide gratings by use of the method of lines

The modal spectral response of an antiresonant reflecting optical waveguide (ARROW) with periodic corrugations or grating is calculated for both shallow and deep gratings with the Method of Lines. The effect of the ARROW layer thickness and the grating depth on the spectral response is studied. It is found that when the ARROW-layer thickness is close to resonance, the ripples in the reflection spectra become smooth and the peak reflectivity drops. This is attributed to the large increase in the leakage loss of the ARROW waveguide near resonance. The ARROW grating is characterized by modal reflectivity spectra, which exhibit a strong polarization discrimination property, in favor of the TE polarization.     

硅基底平面波导光通讯集成器件的模拟、设计及工艺

随着平面波导制作工艺的日益成熟 ,制造精度的不断提高 ,成本的持续下降 ,平面波导光集成器件尤其是 Si基底上 Si O2 平面波导集成器件在光通信系统中的应用更加重要和广泛 .Y分支分束器、MMI耦合器、阵列波导光栅 (AWG)和蚀刻衍射光栅 (EDG)等平面波导集成器件正扮演着越来越重要的作用 ,BPM等数值计算方法在这些器件的设计和模拟中也起了重要作用 .本文就此作了一些探讨 .     

Large polarization response of planarized optical waveguide functionalized with 2D material overlays

ABSTRACT

We propose a planarized optical waveguide structure functionalized with 2D materials that exhibits strong polarization dependent light interaction. Numerical study on both TE – and TM-polarized lights propagation in the 2D material coated optical waveguide is carried out. The effective index, n_eff of optical waveguide increases with the increase of refractive index of the 2D material overlay but decreases when its extinction coefficient is increased. On the other hand, the effective extinction coefficient, k_eff of 2D material coated waveguide increases with the increase of both the real and imaginary parts of 2D material refractive index. It is found that TE-mode has a stronger interaction with 2D material overlay compared to TM-mode, giving rise to potential application like waveguide polarizer. By optimizing the coating thickness, TM-pass waveguide polarizer with high polarization extinction ratio of 78.5 and 97.7?dB can be produced using black phosphorus and graphene oxide, respectively, with a coating length of only 1?mm.     

Wavelength response of waveguide volume grating couplers for optical interconnects

The wavelength response of a waveguide volume grating coupler (WVGC) is analyzed for coupling light from a slab waveguide into the superstrate. A leaky-mode approach is used in conjunction with rigorous coupled-wave analysis. A quantitative theoretical study of the effect of index modulation, waveguide index, and grating thickness on the wavelength bandpass of a WVGC is also presented. The FWHM wavelength bandpasses found for high-efficiency couplers range from 173 to 525 nm. The various Bragg conditions that can be used in designing a WVGC are also presented and compared. The use of the propagation constant of the mode being outcoupled as the incident wave vector in the Bragg condition is shown to produce the highest coupling efficiency.     

Crossed phase gratings with diffractive optical elements

Orienting two identical or complementary diffractive gratings with a small angle between the grating grooves allows a new crossed-grating device to be constructed. This device has an effective profile that varies locally. For understanding the effects of this variation and the diffraction efficiency of the gratings, the local profiles were correlated with the moiré period of the crossed-grating system by use of various techniques. Asymmetric intensity behavior in the first order of the crossed gratings was seen. Effectively, the diffraction efficiency of the crossed gratings yielded a response equivalent to that of a grating with variable blaze that could be useful in optical computing as a passive optical switching device. One of several models is described that creates greater asymmetric behavior.     

Deposition and characterization of silica-based films by helicon-activated reactive evaporation applied to optical waveguide fabrication

Planar silicon dioxide optical waveguides were deposited by use of a plasma-activated reactive evaporation system, at a low deposition temperature and with reduced hydrogen contamination, on thermally oxidized silicon wafers. The deposited films show a refractive-index inhomogeneity of less than 0.1%, a thickness nonuniformity of less than 5%, and a material birefringence of approximately 5 x 10(-4). Rib-type channel waveguides were formed on the deposited films by means of hydrofluoric acid etching. The transmission loss of the rib waveguides is determined to be as low as 0.3 dB/cm at a wavelength of 1310 nm for TE polarization, after subtraction of the calculated leakage and scattering losses. Owing to the presence of the OH vibrational overtone band, an additional loss peak of 1 dB/cm is found near the 1385-nm wavelength. The experimental results of transmission loss at wavelengths of 1310 and 1550 nm are compared with analytic expressions for interface scattering and leakage loss.     

Interferometric fabrication of modulated submicrometer gratings in photoresist

Interferometric recording is applied to the fabrication of modulated submicrometer gratings in photoresist.High diffraction efficiency requires optimized recording conditions, which are obtained by the use of an on-axis continuous surface-relief grating for the generation of the object beam. The optimized phase function is copied into the resist layer by means of a self-aligned two-step recording process with an intermediate copy in a volume photopolymer hologram. As a result, we demonstrate high carrier frequency surface-relief off-axis fan-out gratings for illumination in transmission with visible light.     

Detailed study of silver metallic film diffusion in a soda-lime glass substrate for optical waveguide fabrication

We present the study of multimode glass waveguides fabricated by a silver-ion electromigration process followed by a diffusion process. The study is concerned mainly with the diffusion process, which occurs by variation of the diffusion time. The obtained guides are analyzed by the prism-coupling technique, which determines their effective refractive indices that are treated by the inverse WKB method,assumed to be proportional to the silver ions' concentration profiles, for which a Gaussian model is attributed. Diffusion coefficients then are determined from these Gaussian profiles experimentally by both methods. These diffusion coefficients show a concentration dependence related to the variation of the diffusion time. A mathematical model representing the best fit to this dependence is also presented. Finally, our results are compared with other research results, with which we find good agreement.     

Photolytic fabrication of phase gratings on silver halide crystals

Diffraction phase gratings are formed on samples of crystalline silver halide by exposing them through a mask to 353-nm laser light followed by chemical processing. The exposure and photographic development processes generate metallic silver strips on the sample surface. The fixing process removes the silver strips, leaving grooves on the surface as deep as 1.1 microm. Gratings of 100-microm period are thus formed. The groove depth is determined by optical methods and is confirmed by atomic force microscopy. This method can be used to form diffractive optical elements on IR transmitting fibers and waveguides as well as on crystals.     

Oblique incidence of gaussian beams on waveguide gratings with the four-wave coupled-mode theory

Diffraction of obliquely incident Gaussian beams on waveguide gratings with infinitely long grooves is described. The analysis is based on the angular spectrum of the beam and on the grating response derived from the four-wave coupled-mode theory, which simultaneously considers all four (approximately) synchronous waves. Results concerning the shapes of the emerging beams and their directions, the power content, and the possibility of beam splitting could differ significantly from those obtained by means of two-wave coupling. The analysis method is general and can be performed on many kinds of realistic beam shapes and applications.     

Analysis of photonic crystal waveguide gratings with coupled-mode theory and a finite-element method

Both rod and air-hole types of photonic crystal waveguide gratings are proposed and their coupling coefficients and transmission characteristics are effectively investigated by using a simple coupled-mode theory combined with a finite-element method. The results obtained are compared with the results obtained by using a full numerical simulation method. A new definition for unperturbed waveguides is introduced to obtain accurate coupling coefficients. It is shown that, by using a pi-phase-shifted waveguide structure in the case of an air-hole type of photonic crystal waveguide grating, the coupling coefficient is strongly enhanced. The accuracy of the method is discussed through numerical examples of high-index-contrast waveguide gratings.     

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.     

Superresolution optical system with two fixed generalized Damman gratings

We present a system that exceeds the Rayleigh limit of resolution, by placing two fixed gratings in predetermined positions. Lukosz suggested a setup that managed to exceed the Rayleigh limit of resolution [J. Opt. Soc. Am. 56, 1463 (1966); 57, 932 (1967)]. However, Lukosz's technique had some drawbacks that the new suggested system attempts to resolve. Similar to Lukosz's technique, the proposed system works without any moving elements and with no time- or wavelength-restricting conditions. It is suitable for coherent or incoherent two-dimensional imaging. However, the new system contains some important modifications. Although the system uses only two gratings, it is capable of producing superresolution without using an additional imaging lens at the output plane. The generalized Damman gratings allow for obtaining undistorted spectral restoration of information. To achieve superresolution, the input object is duplicated. The trade-off for higher resolution is a smaller field of view. Experimental results validate the theoretical analysis.