Wavefront sensing using a liquid-filled photonic crystal fiber

Photonic lantern tip/tilt detector for adaptive optics systems

In this work, we demonstrate a four-core multicore fiber photonic lantern tip/tilt wavefront sensor. To diagnose the low-order Zernike aberrations, we exploit the ability of the photonic lantern to encode the characteristics of a complex incoming beam at the multimode facet of the sensor to intensity distributions at the multicore fiber output. Here, we provide a comprehensive numerical analysis capable of predicting the performance of fabricated devices and experimentally demonstrate the concept. Two receiver architectures are implemented to discern tip/tilt information by (i) imaging the four-core fiber facet on a 2D detector and (ii) direct power measurement of the single mode outputs using a multicore fiber multiplexer and photodetectors. For both receiver schemes, an angular detection window of ∼0.4^∘ at 1064 nm can be achieved. Our results are expected to further facilitate the development of intensity-based fiber wavefront sensors for adaptive optics systems.

Wavefront sensing based on fiber coupling in adaptive fiber optics collimator array

A new method of wavefront sensing based on fiber coupling in the adaptive fiber optics collimator (AFOC) array has been proposed. The scheme and the recovery process of this sensor are introduced. An experiment of recovering static aberrations utilizing such method with a 7-element AFOC array with filled factor of 0.875 is presented. Experimental results reveal that the wavefront recovery residual error RMS is less than 0.116 μm, under the conditions where the original aberration is with RMS of 0.674 μm and mainly includes Zernike modes of low orders. This method aims at providing abilities for active wavefront sensing and efficiently correcting outside aberrations to the future laser transmission systems based on fiber collimator arrays.

Exploring adaptive optics on focus-scan for nonlinear materials characterization

Z-scan is a well-established technique used to measure the nonlinear refractive index and absorption coefficient of thin and transparent materials. The method requires the displacement of the sample along the focus of a laser beam. Therefore, the Z-scan is not suitable for experiments where the sample cannot be axially translated. Here, we explore a deformable mirror to create controllable defocus aberrations, translating the focus of the beam through the sample, alternatively to the sample displacement. The technique is based on time behavior analysis of the light beam transmitted by the nonlinear sample, at different defocus configurations. The method is validated by measuring reference samples (CS₂ and SiO₂) and comparing them with the conventional Z-scan technique.

Hartmann-Shack wavefront sensing without a lenslet array using a digital micromirror device

The common Hartmann-Shack wavefront sensor makes use of a lenslet array to sample in-parallel optical wavefronts. Here, we introduce a Hartmann-Shack wavefront sensor that employs a digital micromirror device in combination with a single lens for serial sampling by scanning. Sensing is analyzed numerically and validated experimentally using a deformable mirror operated in closed-loop adaptive optics with a conventional Hartmann-Shack wavefront sensor, as well as with a set of ophthalmic trial lenses, to generate controllable amounts of monochromatic aberrations. The new sensor is free of crosstalk and can potentially operate at kilohertz speed. It offers a reconfigurable aperture that can exclude unwanted parts of the wavefront.

Retina-simulating phantom produced by photolithography

Cone photoreceptors have a narrow acceptance angle that is well matched to the size of the eye pupil and dampens the visual impact of aberrations and scattering. However, the structure of the human retina is not replicated in existing eye models used to test refractive designs or retinal implants that restore partial vision to the blind. Here, we report on an artificial waveguide-based retinal phantom manufactured by photolithography in photoresist film with dimensions and refractive index contrast similar to the retinal receptor layer. The optical performance of the waveguide array is analyzed in terms of angular coupling efficiency, and it is experimentally verified that the structure leads to improved resolution and contrast of optical images transmitted through the layer when defocus is present.

Versatile dispersion characteristics of water solution of glycerine in selective filling of holes in photonic crystal fibers

Using a glycerine-water solution with various concentrations, we investigate the dispersion characteristics of photonic crystal fibers by selective filling of holes. Our analysis is based on a simple but accurate semi-vectorial solution of Helmholtz's equation by the finite difference method devised with a mode-field convergence technique and crosschecked by results with those from a deeply involved multipole method. Significantly, a better ultra-flatness but near-zero group velocity dispersion is revealed with a 20% glycerine-water solution that is superior to pure water of a very recent case when the holes of the first ring of the fiber are filled. This versatile effect in management of holes of identical diameter with liquid is expected to play a guiding role in studies of supercontinuum generation.