Pawel Kniazewski

Investigation of limitations of optical diffraction tomography

Optical diffraction tomography (ODT) applied to measurement of optical microelements is limited by low dynamic range, i.e., only objects with small deviations of refractive-index distribution can be measured. Therefore in this paper the limitations and errors of ODT are investigated throughout extensive numerical experiments. It is shown that these errors can be reduced by introduction of additional numerical focusing in the tomographic reconstruction algorithm. Additionally, new tomographic reconstruction algorithm using back propagation in reference medium for optical microelements measurement with known design is proposed. This hybrid reconstruction algorithm allows significant extension of ODT applicability in measurement of elements having large deviations of refractive-index distribution.

Microinterferometric tomography of photonics phase elements

Microinterferometric tomography method for determination of 3D refractive index distribution in phase elements is described. Applications of this method to measurement of gradient index fibers, fiber splices and single mode fiber are presented. Initial results of holey fiber testing are given and future trends in development of this method (applications to photonic structures) are discussed.

Application of microinterferometric tomography as an evaluation tool for phase micro-objects

Microinterferometric tomography allows for determination of three-dimensional refractive index distributions in phase isotropic microelements. In this paper we present the measurement of the refractive index profile of the optical fibers exposed to the gamma radiation. Nuclear radiation is known to affect the guiding properties of optical fibers and it is therefore essential to characterize these effects to assess the applicability of fiber-optic technology for communication and sensing in nuclear industry. It is already well known that radiation affects the absorption of the fiber. Here, we investigated whether we could quantify the effect of radiation on the refractive index of core and cladding of an optical fiber.

Characterization of Refractive Index Distribution in Spherical Microlenses Fabricated by Deep Proton Writing

In this letter, we present the results of the refractive index measurements on deep proton writing microlenses. The measurement method used is interferometric tomography. It is a nondestructive method for the determination of the 3-D internal refractive index distributions. The influence of the different fabrication steps on the refractive index distribution is discussed.

Improved microinterferometric tomography method for reconstruction of refractive index

In this paper we present the improved interferometric tomography method for determination of 3D refractive index distribution. The improvement relies on numerical correction of experimental results obtained for strongly refractive objects based on the a priori, approximate knowledge about the refractive index distribution in the object under test. The complete correction methodology is presented and discussed. The applicability of the method is shown through the numerical simulations of the reconstruction process and the experiments including reconstruction of refractive index distribution in a grin lens.

Application of photoelastic tomography to measurement of refractive indices in optical anisotropic microelements

In the paper we present method for three-dimensional measurement of birefringence distribution in anisotropic objects. The tool, which we used is combination of classic polariscopy with tomographic reconstruction method. Tomographic reconstruction is performed using the filtered backpojection algorithm. The results of measurement of glass capillary infilled with licquid crystal are presented together with the results of numerical simulation of measurement process. Simulations include polarized light propagation performed by means of finite difference time domain method combined with Jones calculus. The numerical simulations are performed for various birefringence values and allow for determination of relative errors of birefringence distribution. Additionally the absolute refractive indices are determined experimentally through the measurement of capillary with polarization sensitive microinterferometric tomography.

Photoelastic tomography for birefringence determination in optical microelements

In the paper we have analyzed the optical system for 3D measurement of birefringence of micro-optical elements. For small objects, where the fine birefringence sampling in the measurement is necessary, the diffraction of light can not be neglected. Thus the standard tomographic reconstruction algorithm gives considerable errors. In the paper we have analyzed such errors through simulation of reconstruction of object having variable stepindex and continuous distribution of birefringence.

Three-dimensional reconstruction of refractive index distribution in optical phase elements by interferometric and photoelastic tomography

The paper gives a review of interferometric and photoelastic tomography with focus on their necessary modification when applied to 3D refractive index determination in micro-objects. Specifically the influence of diffraction phenomenon and radial run-out occurring during measurement are analyzed. The analysis are confirmed by results of measurements of 3D refractive index distribution in a multimode and single mode fibres.

Application of the microinterferometric tomography setup to the reliability tests of the fiber sensors exposed to cumulated gamma radiation

In this paper we report on the measurement of the refractive index profile of optical fibers exposed to the gamma radiation. The tool we used for determining the refractive index distribution is microinterferometric tomography. Nuclear radiation is known to affect the guiding properties of optical fibers and it is therefore essential to characterize these effects to assess the applicability of fiber-optic technology for communication and sensing in space applications and in nuclear industry. We show that the fibres exhibit a slight refractive index increase which confirms results reported earlier.

Studies of photoelastic tomography process for 3D birefringence determination in phase microobjects

In the paper we present the method for 3D measurement of birefringence in photonics components by means of automated photoelasticity combined with tomography. The enhanced measurement procedure is described and the experimental results obtained for an exotic phase object, namely glass capillary infilled with liquid crystals are presented. The sources of errors are discussed for the cases of different object models and the numerical experiments aiming in determination of limitations of the experimental procedures are performed. Finally the possibility of reduction of these errors by an introduction of additional numerical focusing priori the tomographic reconstruction algorithmis shown and its applicability is proven by numerical simulations.