Gradient Index Microlenses Research Articles

Laser scanning gradient index optics microscope: submicrometre scale spectroscopy and imaging at cryogenic temperatures.

A laser scanning far-field optical microscope for low-temperature imaging and spectroscopy based on gradient index optics is presented. A rod-shaped gradient index microlens is used as a zero-working-distance solid immersion objective lens. The obtained lateral resolution is 310 nm of the FWHM at a wavelength of 545 nm. A laser scanning mechanism located outside an optical cryostat enables one to achieve large scanning ranges independent of temperature. The use of the microscope for submicrometre-scale spectroscopy and low-temperature photochemistry performed on molecular J aggregates in thin polymer films is presented.

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.

Refractive-index measurement of gradient-index microlenses by diffraction tomography

Diffraction tomography is applied to reconstruction of the gradient-index distribution of planar gradient-index microlenses, fabricated by thermal ion exchange. Measurements of the single-phase projections are performed by phase-shifting interferometry For reconstruction, the Rytov approximation for smooth inhomogeneities is applied. Results are compared with measurement results from other methods and simulation results.

Gradient-index microlenses: numerical investigation of different spherical index profiles with the wave propagation method

Ion-exchange microlenses are available with different gradient-index profiles. We investigate the dependence of the imaging properties on the steepness of the index profiles. Therefore we model the index distribution by the Fermi function as radial distribution with spherical symmetry. The results are compared to index profiles according to the Doremus model.

Optical sensor array in an artificial compound eye

Optical systems of compound eyes are of great interest in the study of micro-optics. We propose an artificial visual sensor in a model of the apposition eye of an insect. As a key component unit of the visual sensor, a sensor array consisting of 16 x 16 individual optical sensors each with a small view field is fabricated and examined. To achieve both the practical assembly and the compact size of the sensor array, a photodiode array, a glass substrate with a pinhole array, and a group of rod-type gradient-index microlenses are stacked. The optical thickness of the sensor array is 2.9 mm. Because of the low intensity of light received by the photodiode the photocurrent is amplified 10⁷ times in current-to-voltage conversion efficiency. The fabricated sensor array produces a mosaic image with 16 x 16 pixels and eight shades of gray scale. By arranging several of these sensor arrays along a circumference, a wide-field-angle visual sensor similar to a compound eye could be realized.

Gradient-index microlens formed by ion-beam sputtering

This paper describes the fabrication and characteristics of a gradient-index microlens by using a low-stress, high-transmittance film that is deposited by ion-beam sputtering. The key techniques in forming this film are sputtering with N(2) gas, performing ion-beam irradiation during deposition, and stabilizing the deposition acceleration current. An integrated device consisting of the microlens and a laser diode is demonstrated. The focusing spot size is 2 microm x 3 microm at a distance of 11 microm from the lens facet.