Surface Roughness Measurement Using Dichromatic Speckle Pattern: An Experimental Study

Surface roughness is studied experimentally by making use of the statistical properties of dichromatic speckle patterns. The rms intensity difference between two speckle patterns produced by two argon laser lines are analyzed in the far field as functions of the object surface roughness and the difference in the two wavenumbers of the illuminating light. By applying previously derived formulas, the rms surface roughness is obtained from rms intensity differences. Glass and metal rough surfaces are used. Other than the scattering arrangement, the experimental setup has a simple spectrometric system and an electronic analyzing circuit

Polarization Characteristics of Double-Clad Elliptical Fibers

A scalar variational analysis based on a Gaussian approximation of the fundamental mode of a double-clad elliptical fiber with a depressed inner cladding is studied. The polarization properties and graphic results are presented; they are given in terms of three parameters: the ratio of the major axis to the minor axis of the core, the ratio of the inner cladding major axis to the core major axis, and the difference between the core index and the inner cladding index. The variations of both the spot size and the field intensity with core ellipticity are examined. It is shown that high birefringence and dispersion-free orthogonal polarization modes can be obtained within the single-mode region and that the field intensity distribution may be more confined to the fiber center than in a single-clad elliptical fiber

Temperature and Strain Sensitivity Measurements of High-Birefringent Polarization-Maintaining Fibers

The strain and temperature sensitivities of three common commercial high-birefringent polarization maintaining fibers (bow-tie, polarization-maintaining and absorption-reducing, and elliptical core fibers) have been measured by using a dynamic polarimetric method. The experimental setup and measuring process are described in detail. Where possible, the measuring data are compared with published data, and good agreement is obtained

Temperature and Strain Sensitivities of High-Birefringence Elliptical Fibers

We have analyzed and calculated the temperature and strain sensitivities of a high-birefringence double-clad elliptical fiber. We propose a method to minimize these sensitivities without increasing the fiber size or weight; this is achieved by selecting suitable fiber parameters—core ellipticity, refractive index difference, and thickness of the inner cladding. In addition, we discuss the design of temperature- or strain-insensitive fibers which may be used in polarimetric strain or temperature sensors. This method may also be used to minimize or enhance other external effects

Full Modeling of Field-Assisted Ion Exchange for Graded Index Buried Channel Optical Waveguides

The numerical modeling of field-assisted ion exchange in glass through a finite aperture is carried out. The effects of unequal ion mobilities and thermal diffusion are included we believe for the first time in the 2-D case. This allows for the modeling of optical channel waveguides with graded index profiles. It is demonstrated that annealing of backdiffused channel guides is far superior to backdiffusion alone in improving their circular symmetry for better coupling to optical fibers

Minimization of Temperature Effects of High-Birefringent Elliptical Fibers for Polarmetric Optical-Fiber Sensors

The temperature dependence of polarization-maintaining fibers is a problem in polarimetric optical-fiber sensors. We report a novel method for making a temperature-insensitive, polarization-maintaining fiber, which may be used for the sensing part in a polarimetric strain sensor. The fiber has a double-clad elliptical core with built-in stresses in the core and cladding regions. To minimize the temperature sensitivity, the built-in stresses are balanced with the refractive-index differences and the core ellipticity properly chosen. The temperature and strain sensitivities of the fiber are calculated. A practical design and some potential applications of such a temperature-insensitive fiber with a high strain sensitivity are presented

Design Optimization of Flattop Interleaver and Its Dispersion Compensation

The objective of this paper is to present a general strategy for design optimization of flattop interleavers, and dispersion compensation for the interleavers, in order to achieve superior optical performance. The interleaver is formed by two multi-cavity Gire-Tournois etalons (MC-GTE) in a Michelson Interferometer (MI). An interleaver that has m cavities in one etalon and n cavities in the other is called an mn-GTE interleaver. Our optimization strategy exploits the general flattop condition and the technique of ripple equalization. Any mn-GTE interleaver may be optimized. The spectral performance can be greatly improved by the optimization process. As an illustration, we present a comprehensive analysis for a 11-GTE and a 21-GTE interleaver. The analytical expressions for flattop conditions, peak and trough positions are derived for optimization. The optimal performance of the interleavers can be controlled by the reflection coefficients and the parameters m and n. To achieve low-dispersion mn-GTE flattop interleavers, we propose to use one additional MC-GTE as a dispersion compensator to compensate for the chromatic dispersion. The analytical expressions of group delays and chromatic dispersions for an MC-GTE interleaver are derived. The optimization strategy of dispersion-ripple equalization is explained. The results show that the dispersion performance can be tailored by changing the reflection coefficients of the MC-GTE, and the dispersion and bandwidth can be enhanced by increasing the number of cavities of the MC-GTE

Fabrication of Tapers and Lenslike Waveguides by a Microcontrolled Dip Coating Procedure

A technique for the fabrication of tapered and lenslike waveguides from solution-deposited thin films is described. Using a microprocessor controlled dipping arm, substrates are withdrawn from a solution with a carefully controlled and varying velocity. In this way optical waveguides with regions of varying thickness are deposited. Following the drying and baking of the films, desired structures are obtained in hard inorganic optical waveguides of good optical quality. With refined profile control, we propose to fabricate other optical waveguide components, for example, thin film lenses with this method

Single-Mode Fiber Microlens with Controllable Spot Size

A novel method for fabricating microlenses on tapered single-mode fibers is shown to be able to control the lens spot size. The fiber cladding is first symmetrically tapered by etching it with an evaporating ammonium bifluoride solution. A hemispheric lens is then melted on the taper tip with a CO2 laser. The lens can reduce the fiber mode radius to 40% of its original value. A theoretical calculation of the focused spot size agrees well with experimental results

Mode Transforming Properties of Tapered Single-Mode Fiber Microlenses

The Gaussian approximation that is typically used to estimate single-mode fiber microlens performance is investigated. It is applied to hemispheric lenses on two types of tapered single-mode fiber. Theoretical and experimental results are compared. The first type of taper, which is fabricated by pulling a fiber while it is melted, has a tapered core and a tapered cladding. The second type of taper, which is fabricated by etching the cladding, has a tapered cladding only. For a tapered-core fiber, coupling to the cladding-guided modes and the finite radius of curvature of the wave front before the lens must be considered to predict the lens spot size accurately, whereas the spot size of a tapered-cladding lens can be predicted from the lens diameter alone. Thus the spot size of a lens on a tapered-cladding fiber is easier to predict and control than that of a lens on a tapered-core fiber. It is also shown that the usual theory used to predict the spot size gives accepted values for tapered-cladding lenses but not for tapered-core lenses