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.     

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 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.     

General formula for coupling-loss characterization of single-mode fiber collimators by use of gradient-index rod lenses

A general formula for determining the coupling loss between two single-mode fiber collimators with the simultaneous existence of separation, lateral offset and angular tilt misalignments, and spot-size mismatch is theoretically derived by use of the Gaussian field approximation. Based on this general formula, the formulas for coupling losses that are due to the misalignment of insert separation, lateral offset, and angular tilt are given. The formula for the coupling loss that is due to Gaussian spot-size mismatch of two single-mode collimators is also given. Good agreement between these formulas and experimental results is demonstrated with gradient-index rod lens-based fiber collimators operating in the 1300-nm band.     

Interferometric measurement of the refractive-index gradient distribution in gradient-index optical blanks

Anew interferometric method for measuring the refractive-index distribution in a plane-parallel section cut from a gradient-index lens blank is described. A standard double-pass interferometric scheme modified to provide a single pass of the beam through the investigated gradient-index sample is used. The two-dimensional variation of the refractive index in dimensions transverse to the sample surface is measured with an accuracy of better than 1 × 10(-4).     

Broad-band superachromatic retarders and circular polarizers for the UV,visible and near infrared

Abstract

We present designs for two combinations of conventional achromatic retarders that can be used, over the wavelength range from 300 to 1100 nm, to obtain retardations of a quarter-wave and a half-wave, respectively, as well as a combination that can be used as a circular polarizer over this range of wavelengths.     

Refractive index of air: new equations for the visible and near infrared

The precision of modern length interferometry and geodetic surveying far exceeds the accuracy, which is ultimately limited by the inadequacy of currently used equations for the refractive index of the atmosphere. I have critically reviewed recent research at the National Physical Laboratory, the International Bureau of Weights and Measures, and elsewhere that has led to revised formulas and data for the dispersion and density of the major components of the atmosphere. I have combined selected formulas from these sources to yield a set of equations that match recently reported measurements to within the experimental error, and that are expected to be reliable over very wide ranges of atmospheric parameters and wavelength.     

Scattering of visible and near infrared radiation by NaCl ice and glacier ice

Measurements are presented for the phase functions of glacier ice, columnar NaCl ice, and grease ice. Results for glacier ice show a shoulder at 80° characteristic of scattering from vapor bubbles. The NaCl ice types show similar forward scattering but significantly stronger backscattering. The scattering is predominantly due to the brine inclusions, and in the visible region the phase functions are independent of wavelength. For columnar NaCl ice samples, the phase functions depend on sample orientation as well as deflection angle; however, this effect can be ignored for many applications. Orientation-averaged values are presented for general use, and the empirical results are fitted to bimodal Henyey-Greenstein functions.     

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.     

Traceable laser power measurements of diode laser radiation in the near infrared

We report a new calibration setup for laser radiometry at the Physikalisch-Technische Bundesanstalt, the German National Metrology Institute. Measurements of laser diode power of free beam diode lasers in the near infrared spectral range at a wavelength of 808 nm for powers up to 250 W and at wavelengths of 915 nm, 940 nm, and 980 nm for laser powers up to 25 W have been established. The calibration setup, the standard detector, the uncertainty budget and first calibration results will be presented and discussed. The standard uncertainty of the HLR302 standard detector is 0.2%. This uncertainty might be the main contribution to the overall uncertainty in customer calibrations, depending on the quality of the transfer detectors.     

On-line simultaneous monitoring of polarization mode dispersion and chromatic dispersion

We have developed new expressions for power fading and average power fading owing to polarization mode dispersion (PMD) and chromatic dispersion in terms of the angle of precession of the output state of polarization about the PMD vector. Based on these expressions, a simple and novel pilot-tone-based technique for simultaneous monitoring of chromatic dispersion and PMD is proposed. Experimental results demonstrate the effectiveness of the proposed technique; these results agree well with the theoretical analysis.     

Retrieval of aerosol profile variations in the visible and near infrared: theory and application of the single-scattering approach

A linear relationship between the variations in radiance measured in the visible and near infrared by satellites and variations of aerosol-extinction profile has been derived, hence reducing the problem to that of solving a Fredholm integral equation of the first kind. The retrieved profiles, by the linear constrained-inversion method, have proved to be accurate in the lower atmosphere, even if simultaneous changes are taking place in the stratosphere. Variations in the stratosphere, however, are retrieved with a lesser degree of accuracy and only as long as no variations occur in the tropospheric haze.