Spherical aberration of gradient-index rod lenses

Spherical aberration was measured and, by carrying out the computer simulation for ray tracing with the approximate solution of ray equation, the refractive-index distribution parameters of a gradient-index rod lens were determined to most fit the observed data.     

Birefringence measurements in gradient-index rod lenses

Stress birefringence can be found in gradient-index (GRIN) materials because they contain a variation in composition. GRIN glass fabricated by ion exchange may contain stress from two different processes. These include a size difference between the exchange and the diffusing ions and a variation in the thermal-expansion coefficient across the gradient region. The optical properties of the stressed material are polarization dependent, and therefore image quality is directly affected. We examine birefringence in GRIN rod lenses that have lengths more than ten times greater than their diameters. The effects are more easily observed in long rod lenses because of the large optical path lengths.     

Light scattering with single-mode fiber collimators

The recent development and availability of fiber-optic components including graded-index (GRIN) microlenses and the unique optical properties of single-mode optical fibers make it possible to build ideal detector systems for light-scattering measurements. We show that the simple coupling of a 0.25-pitch GRIN lens and a single-mode optical fiber to form a collimator makes a nonimaging detector system with properties that are superior to conventional setups based on pinholes and that approaches the theoretical limit of a perfectly coherent detector.     

Alignment tolerances for plane-wave to single-mode fiber coupling and their mitigation by use of pigtailed collimators

We discuss the efficiency with which coherent plane waves can be coupled to single-mode fibers in the presence of deterministic or stochastic misalignments of the fiber relative to the focal point of a lens. We point out how the alignment demands can be relaxed by means of graded-index-lens fiber-pigtailed collimators.     

Homogenous concept for the coupling of active and passive single-mode devices by utilizing planar gradient-index lenses and silicon-V grooves

A new concept for a common interface between passive and active single-mode devices is proposed. The submicrometer alignment accuracy necessary for efficient coupling of single-mode devices is extended to the range of some 10 mum by beam expansion with planar gradient-index microlenses; the increased angular sensitivity is satisfied by the use of planar surfaces. The imaging system is used off axis, resulting in a suppression of backreflections in the range >60 dB. Of many possible variations of components (fibers, waveguides, optoelectronic integrated circuits, edge-emitting lasers, vertical-cavity surface-emitting lasers, photodiodes), the coupling of fibers and waveguides is examined in detail. Expected coupling efficiency and sensitivity to lateral misalignment are calculated by use of a modified beam-propagation method. In this way, the overall performance of the connector can be compared with existing connector concepts, and the feasibility of the concept is proven. Experimental results for the fiber-fiber connector are given.     

Birefringence in gradient-index rod lenses: a direct measurement method and interferometric polarization effects

Gradient-index (GRIN) media can contain stress birefringence resulting from the variation in material composition. Anisotropy in a GRIN rod lens affects ray propagation and can degrade image quality. A technique, believed to be new, for measuring birefringence in GRIN rod lenses has been developed. The change in optical path difference (OPD) for orthogonal polarizations is measured directly. With this method, effects on OPD from standard imaging aberrations are excluded. Birefringence measurements for various GRIN rod samples are presented. The data are compared with results obtained previously by use of a Twyman-Green measurement method. Also, the polarization effects on tilt fringes observed with the direct measurement method and the Twyman-Green method are presented and modeled theoretically. Tilt fringes for large birefringence test cases are also modeled.     

Single-mode fiber coupling efficiency with graded-index rod lenses

Losses are calculated for the single-mode graded-index- (GRIN-) lens coupler. The main advantage of this coupling system is large separation between fibers with small power loss. The excess loss of the GRIN-lens coupler is due primarily to the misalignments of the GRIN lenses and is most sensitive to angular tilt rather than lateral offset or end separation. The excess loss is calculated from the overlap of two differently sized or misaligned Gaussian beams. Experimental results show that this method is adequate for predicting losses that are due to misalignments of the GRIN lenses.     

Interferometric chromatic dispersion measurements of long, gradient-index rod lenses in the visible and the near infrared

A new procedure is presented for testing long, radial-gradient-index rod lenses in a phase-stepping Twyman-Green interferometer. In addition, a method for converting the measured optical phase data to the rod's index of refraction profile is reviewed. This procedure was used to measure refractive-index profile dispersions over the wavelength range of 441 to 1064 nm. These measurements provide the first data for refractive-index profiles of rod lenses in the infrared and show the existence of positive dispersion, negative dispersion, and near-infrared dispersion reversal in some samples. The dispersion results suggest the need for modifications to the current glass model.     

Chromatic aberrations of radial gradient-index lenses. II. Selfoc lenses

Simple equations used for analyzing chromatic aberrations of Selfoc lenses were derived in terms of Buchdahl chromatic coordinates and Buchdahl dispersion constants. The equations that employ gradient-index chromatic constants Ψ(1) and Ψ(2) are used for selecting suitable ion-exchange pairs to design an achromatic Selfoc lens.     

Colorless gradient-index cylindrical lenses with high numerical apertures produced by silver-ion exchange

Colorless gradient-index cylindrical lenses with high numerical apertures in slabs 200-1000 μm thick have been fabricated by silver-sodium ion exchange in a specially developed glass. The lenses with numerical apertures of 0.6 are characterized by index profiles and by spherical and chromatic aberration. On-axis focusing properties and the application to the collimation of high-power laser diode bars are discussed.     

Fabrication method of ultra-small gradient-index fiber probe

Fabrication method and device of ultra-small gradient-index(GRIN) fiber probe were investigated in order to explore the development of ultra-small probes for optical coherence tomography(OCT) imaging.The beamexpanding effect of no-core fiber(NCF) and the focusing properties of the GRIN fiber lens were analyzed based on the model of GRIN fiber probe consisting of single-mode fiber(SMF),NCF and GRIN fiber lens.A stereo microscope based system was developed to fabricate the GRIN fiber probe.A fiber fusion splicer and an ultrasonic cleaver were used to weld and cut the fiber respectively.A confocal microscopy was used to measure the dimensions of probe components.The results show that the sizes of probe components developed are at the level of millimeter.Therefore,the proposed experimental system meets the fabrication requirements of an ultra-small self-focusing GRIN fiber probe.This shows that this fabrication device and method can be employed in the fabrication of ultrasmall self-focusing GRIN fiber probe and applied in the study of miniaturized optical probes and OCT systems.     

Hybrid microdiffractive-microrefractive lens with a continuous relief fabricated by use of focused-ion-beam milling for single-mode fiber coupling

The design, microfabrication, and testing of a hybrid microdiffractive-microrefractive lens with a continuous relief that is used with a laser diode for monomode fiber coupling is discussed. The hybrid microlens with a diameter as small as 65 mum and a numerical aperture of 0.25 is fabricated directly onto a spherical surface by use of focused-ion-beam milling technology. A focused Ga(+) ion beam is used to mill the continuous relief microstructure at an acceleration voltage of 50 kV. From the test results a coupling efficiency of 71% (-1.49 dB) was achieved at room temperature. A diffraction efficiency of the main diffractive order, -1, was measured to as high as 90.5% at a wavelength of 635 nm. This indicates that the hybrid microlens was suitably designed within the application requirements and satisfactorily manufactured with focused-ion-beam milling.     

Conoscopic evaluation of the birefringence of gradient-index lenses: infidelity sources

Gradient-index lenses are samples whose special characteristics must be taken into account to design the optical polariscopes that can be applied in the evaluation of their birefringence. We discuss the main infidelity sources that modify the conoscopic patterns when a traditional polariscopic setup is used.     

Optical shifter for a three-dimensional image by use of a gradient-index lens array

We propose a new function of the two-dimensional lens array that is composed of many gradient-index lenses. The array forms three-dimensional (3D) images. The characteristics of the 3D images depend on the length of the gradient-index lens. Especially, if the length of the lens is an odd-integer multiple of the half period of the optical path, 3D images are pseudoscopic with a reversed depth. The two lens arrays are positioned at a suitable distance, so that orthoscopic 3D images with the correct depth are formed in front of the lens array.     

Mode-field diameter of single-mode optical fiber by far-field scanning

I use the direct far-field method to measure the mode-field diameter of a single-mode fiber with an expanded uncertainty of 30 nm, with a coverage factor of 2. For a step-index fiber with a mode-field diameter of approximately 9 mum, the major sources of uncertainty are nonlinearity in the electronics, angular errors and scattered light in the apparatus, and the polarization and noncircularity of the mode of the fiber. The paper concludes by showing an inconsistency in the derivation of the far-field expression for mode-field diameter.     

可吸收壳聚糖纤维增强壳聚糖棒材

在采用原位沉析法制备壳聚糖棒材的同时,加入壳聚糖纤维作为增强材料,制成了壳聚糖纤维增强的壳聚糖棒材复合材料。研究了壳聚糖纤维的长度及添加量对壳聚糖棒材力学性能的影响,通过扫描电镜观察分析了材料的断面形貌。结果表明,壳聚糖纤维能显著提高壳聚糖棒材的力学性能,壳聚糖棒材的弯曲强度随壳聚糖纤维添加量的增加先增加而后下降,随着壳聚糖纤维长度的增加而增加。当壳聚糖纤维(17 mm)质量分数为5%时,壳聚糖棒材的弯曲强度达到134 MPa,与未增强的壳聚糖棒材相比,弯曲强度提高了55.7%。这种纯天然的复合材料在可吸收内固定材料方面将具有广阔的用途。