Side Polishing Research Articles

Modeling and Characterization of an Electrowetting-Based Single-Mode Fiber Variable Optical Attenuator

We report an optofluidics-based variable optical attenuator (VOA) employing a tapered side-polished single-mode optical fiber attached to an electrowetting-on-dielectric (EWOD) platform. The side polishing of the fiber cladding gives access to the evanescent field of the guided mode, while the EWOD platform electrically controls the stepwise translation of a liquid droplet along the variable thickness polished cladding of the fiber. The penetration of the evanescent field into the droplet leads to tunneling of optical power from the fiber core to the droplet, from where it is radiatively lost. As a result of the variable cladding thickness, the position of the droplet along the length of the polished fiber determines the degree of penetration of the evanescent field into the droplet. The droplet position can be electrically changed; thus, controlling the optical power loss from the fiber. This approach has been used to demonstrate an optofluidic continuous-fiber VOA typically providing up to 26 dB of broadband attenuation in the 1550-nm transmission window, with a wavelength dependent loss less than 1.1 dB. In this paper, we present the theoretical modeling and experimental characterization of the system, discussing the influence of the design parameters on the performance of this VOA.

Frequency Bandwidth Adjustment by Precision Post-Processing for a 0.78–0.95 THz Band SIS Mixer

In this study, we demonstrate a method for adjusting the frequency bandwidth of a Superconductor-insulator-superconductor (SIS) mixer device by controlling its thickness after microfabrication. We estimate the relationship between SIS mixer device thickness and frequency bandwidth using electromagnetic (EM) simulation. We propose an optimal method for the precision polishing of the back side of the device. We evaluate the noise temperature and measure the frequency bandwidth of SIS mixer devices with different thicknesses. This study presents the adjustment of the frequency bandwidth of a device through controlling its thickness after microfabrication. This technique may improve the yield of SIS mixer device mass production and support the construction of receivers for ultra-high frequencies such as Atacama Large Millimeter/Submillimeter Array (ALMA) Band 10.

Wet Chemical Polishing for Industrial Type PERC Solar Cells

Industrial PERC cell process flows typically apply the polishing of the rear side after texturing as well as the edge isolation after POCl3 diffusion. In this paper, we present a novel single step polishing process which we apply post double sided texturing and diffusion in order to remove the rear emitter and to reduce the rear surface roughness. One challenge is to minimize the etch back of the front side emitter during rear side polishing due to the reactive gas phase of the polishing process. By optimizing the polishing process, we are able to limit the increase of the emitter sheet resistance below 5Ω/sq. However, the wet cleaning post polishing contributes an additional 20Ω/sq emitter sheet resistance increase which is subject to further optimization. We compensate the emitter sheet resistance increase due to wet cleaning by applying a 45Ω/sq POCl3 diffusion instead of a 60Ω/sq diffusion. The resulting PERC solar cells with polished rear surface post texture and diffusion show conversion efficiencies up to 19.6% which is comparable to the reference PERC cells which apply a rear protection layer instead of a polishing process.

Optical characteristics of a hybrid fiber grating based on a surface long-period grating incorporating a fiber Bragg grating

A hybrid grating based on a surface long-period grating (SLPG) incorporating a fiber Bragg grating (FBG) was proposed, and its optical characteristics were experimentally investigated by changing the external temperature and the ambient refractive index. For the fabrication of the hybrid grating, a FBG was firstly fabricated by using a beam scanning technique with a frequency-doubled Ar+ laser; then, some portion of the cladding region without the FBG was removed by using a side polishing technique. The SLPG was formed on a flat surface of the side-polished fiber (D-shaped fiber) by using a standard contact lithography technique. The transmission spectrum of the hybrid grating was superimposed on those for the SLPG and the FBG. Variations in the external refractive index and the temperature modified the transmission characteristics of the proposed hybrid grating. The ambient index sensitivity of the resonant peak induced by the SLPG was measured to be 810.7 nm/RIU while the resonant peak generated by the FBG was kept constant as the ambient index changed in the index range from 1.30 to 1.45. The temperature sensitivities of two resonant peaks for the SLPG and the FBG were measured to be −0.52 nm/°C and 0.01 nm/°C, respectively. Accordingly, we expect discrimination between two concurrent sensitivities, such as the external refractive index and the temperature sensitivities, to be possible when the hybrid fiber grating is implemented.

Photonic Bandgap Fiber for Infiltration-Free Refractive-Index Sensing

We report a novel photonic bandgap sensor, comprising a D-shaped fiber fabricated via side polishing. It takes advantage of measurand-elicited refractive-index profile changes upon exposure of its side-polished region to an ambient liquid. The bandgap shift can be induced by perturbations in close proximity to the fiber core, such as the change of refractive index in the surrounding. The side-polished all-solid photonic bandgap fiber utilized offers an infiltration-free sensing mechanism, which eliminates difficult air-hole infiltration and evacuation processes experienced by most photonic crystal fiber-based index sensors. Experimental results demonstrated the repeatability and linearity in refractive-index sensing from 1.31 to 1.43 with a sensitivity of 10 -5 refractive-index units (RIUs). Additional study was also conducted to identify the significance of polishing depths in relation to the sensor performance.

Modeling and Analysis of Material Removal Characteristics in Silicon Wafer Double Side Polishing

As advancing technologies increase the demand for yield and planarity in integrated circuits, wafers have become larger and their specifications more stringent. Flatness, thickness variation and nanotopography have emerged as important concerns in the wafering process. Double side polishing has been adopted as a solution to these problems. This paper focuses on the material removal characteristics and wafer profile variation during Si double side polishing. A polishing experiment to investigate Si removal characteristics according to process parameters was carried out in a single head rotary polisher equipped with a monitoring system for friction force. It was found that the material removal rate is related to friction energy rate, and the polishing state was transited and divided into three conditions according to pressure. On the basis of the experimental results, the wafer profile variation in double side polishing was modelled and simulated according to pressure. The friction energy was calculated to find the material removal amount across the wafer. With the conversion of calculated friction energy to the material removal amount, wafer profile variation was simulated. As a result, the wafer profile variation and its range were increased with a pressure increase, and originated from the position near the wafer edge.

Specialty Fiber Coupler: Fabrications and Applications

We review the research on specialty fiber couplers with emphasis placed on the characteristics that make them attractive for biomedical imaging, optical communications, and sensing applications. The fabrication of fiber couplers has been carried out with, in addition to conventional single mode fiber, various specialty fibers such as photonic crystal fiber, double clad fiber, and hole-assisted fiber with a Ge-doped core. For the fiber coupler fabrication, the side polishing and the fused biconical tapered methods have been developed. These specialty fiber couplers have been applied to optical coherence tomography, fluorescence spectroscopy, fiber sensors, and optical communication systems. This review aims to provide a detailed statement on the recent progress and novel applications of specialty fiber couplers.

Second harmonic generation of thermally poled ZnCl 2 or ZnBr 2–B 2O 3–TeO 2 glasses and its mechanism

Second harmonic generation (SHG) was observed from halide, in specific, chlorine or bromine-containing tellurite glasses. The magnitude of SHG increased with increasing halides concentration and poling time. Although the mechanism of SHG is still controversial, it is generally accepted that the idea of the deficiency of cations near the anode side cause SHG. However, in the preset oxyhalide glass system without any singly positive charge cation, the polishing of the anode side showed no effect on SHG. On the other hand, the polishing of the cathode side significantly decreased the magnitude of SHG in the present alkali-free oxyhalide glasses. Therefore, the SHG mechanism in the present oxyhalide glass systems is made evident in which the movement of anions results in an anion-deficient layer near the cathode side.

Loose abrasive slurries for optical glass lapping

Loose abrasive lapping is widely used to prepare optical glass before its final polishing. We carried out a comparison of 20 different slurries from four different vendors. Slurry particle sizes and morphologies were measured. Fused silica samples were lapped with these different slurries on a single side polishing machine and characterized in terms of surface roughness and depth of subsurface damage (SSD). Effects of load, rotation speed, and slurry concentration during lapping on roughness, material removal rate, and SSD were investigated.

Optical Fiber Sensor Based on Air-Gap Long-Period Fiber Gratings

In this work, we propose a novel fiber sensor that is based on an air-gap long-period fiber grating (AG-LPG), which is fabricated by combining fiber side polishing with fiber lithography. Its sensing mechanism is based on the loss-peak wavelength shift of the AG-LPG as the refractive index around the sensing head varies. Experimental results show that the maximum sensitivity is 620 nm/unit index (1.1 nm/%) in the sensing of various sugar solution concentrations. This novel sensing head provides a simple, reliable, repeatable, accurate, and nondestructive approach for detecting various chemical solutions and mixing gases and for biomedical applications.

Surface Roughness and Light Scattering in a Small Effective Area Microstructured Fiber

We report here the combined study of air/silica surface roughness and light scattering in a microstructured optical fiber designed for non-linear operation. Side polishing of the fiber gave access to the surface of the holes, and allowed measurements of their roughness by atomic force microscopy. The observed roughness topography, not reported in such fibers until now, consists of a rather regular arrangement of shallow patterns with lateral size in the micron range and amplitude in the 10 nm range. By comparing measured angle-resolved scattering patterns to coupled-mode calculations, we show that roughness-induced scattering loss can be linked to both the roughness and the overlap of fundamental with radiative modes at the air/silica interfaces. The reduction of surface roughness amplitude down to the thermodynamic limit could permit to strongly decrease the threshold of Raman fiber lasers.

Tm3+ doped cladding pumped silica optic fiber laser

The silica based Tm3+ doped fiber preform with high Ge concentration in preform core area was manufactured by solution doping method. It was made into an optic fiber preform with cross section of a hexagon by side polishing process, and drawn in to cladding pumping Tm3+ doped fiber with inner coverage layer of lower refraction index polymer. The absorption spectrum was measured, and the technical parameters were optimized. The uniform fiber Bragg gratings with reflectivity of 90% and 40% were written in both ends of the fiber by UV light respectively, and the linear optic cavity was constructed. The laser with wavelength of 1947.1031nm and power of 2.05W was emitted by pump laser excited with wavelength of 793nm and power of 5.6W. It shows that the fiber have excellent optical characteristics.

基于侧边抛磨与覆盖材料的光纤光栅温度补偿新方法

基于侧边抛磨与覆盖材料的光纤光栅温度补偿新方法

A kinematic analysis of disk motion in a double sided polisher for chemical mechanical planarization (CMP)

Double sided polishers are commonly used for industrial applications, such as lapping of silicon substrates and chemical mechanical planarization (CMP) of rigid disks. Whereas a kinematic analysis of a single sided polisher, extensively used for IC wafer CMP, is well known, available sources of such an analysis are limited for a double sided polisher, due to its more complicated design. The present work demonstrates a kinematic analysis for obtaining trajectory and relative velocity of a single location on a work piece during double side polishing. Relative velocity is used to calculate travel distance to be compared with the amount removed experimentally obtained. This paper presents mathematical derivation of the analysis and its effectiveness/limitations in conjunction with comparison between the analytical and experimental results.

Applications of Polishing Technology Using Polymer Particles to Silicon Wafers and Quartz Crystal Wafers

This paper deals with a novel polishing technology using polymer particles. It has been proposed and developed by the authors for the purpose of solving the problems associated with polishing pads such as pad deterioration, process inconsistency and poor accuracy. Single side polishing of silicon wafers and double side polishing of quartz crystal square wafers were performed to clarify the basic characteristics of the technology. The results showed that appropriate combination of tool plate with polymer particles could greatly improve polishing characteristics. In particular, the edge profiles can be controlled to have desirable shape as well as amplitudes.

Fabrication and Characteristics of Plastic Optical Fiber Directional Couplers

Directional couplers of gradient-index plastic optical fibers were fabricated and characterized. In particular, we have employed a core-facet technique to make the directional couplers, which require mechanical side polishing and linkage. We have measured insertion loss, excess loss, and coupling ratio of the fabricated couplers as a function of polishing depth and coupling length. We found that polishing depth of <TEX>$\~300{\mu}m$</TEX> and coupling length of <TEX>$\~35mm$</TEX> are optimum conditions for minimizing the insertion and excess losses and for achieving 1: 1 coupling ratio.

Outdiffusion of La and Al from amorphous LaAlO3 in direct contact with Si (001)

We have evaluated the thermal stability of Al2O3/LaAlO3/Si (001) stacks with atomic force microscopy, x-ray diffraction, transmission electron microscopy, and secondary ion mass spectrometry using a back side polishing approach. Crystallization of the amorphous LaAlO3 film was found to occur for rapid thermal anneals (RTA) above 935 °C for 20 s, in flowing N2. Penetration of Al and La into the underlying Si (001) is clearly observed for RTA at or above 950 °C for 20 s in flowing N2.

Continuously tunable fibre attenuator operating in the wavelength range near 1.5 μm

A fibre attenuator is fabricated for the telecommunication wavelength range near 1.5 μm in which a single-mode silica fibre with side polishing is used. The fibre surface is covered by a layer of fluorine-containing polymer with a large thermooptic coefficient. The principle of attenuator operation is based on a change in the conditions of total internal reflection for a guided mode in the polished region due to thermally induced variation in the refractive index of the fluoropolymer layer. The attenuator is insensitive to light polarisation, it has a continuously variable attenuation coefficient in the range 0.2–27 dB, and can be easily incorporated into fibreoptic links.

Tunable photonic crystal fiber coupler based on a side-polishing technique.

A tunable photonic crystal fiber (PCF) coupler, which couples part of the optical power in one PCF with that in another PCF, has been made by side polishing. We fabricated the PCF coupler by mating two side-polished PCFs. We achieved evanescent field coupling between the core modes of the two PCFs by using side polishing to bring the cores close to each other. By adjusting the mating angle between the two side-polished PCFs we obtained as much as 90% tunability in the coupling ratio. The spectrum of the coupling ratio was almost flat, with small ripples, over a 400-nm wavelength range.

Chemical mechanical polishing for decoration and measurement of dislocations on freestanding GaN wafers

The dislocation density in freestanding gallium nitride wafers was measured using atomic force microscope (AFM) imaging of chemical mechanically polished (CMP) samples and with transmission electron microscopy (TEM). Etch pits were introduced after chemical mechanical polishing of the gallium side of the GaN wafer and the pits easily imaged with the AFM. TEM was also utilized to measure the dislocation density. Good agreement was found between the dislocation density measured by TEM and the etch pit density measured by AFM, demonstrating that chemical mechanical polish of the GaN(0001) surface decorates threading dislocations and that the AFM technique provides a reasonably accurate and convenient measure of the dislocation density. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)