Measuring the radius of curvature of spherical surfaces with actively tunable Fizeau and Twyman-Green interferometers.

Accurate and repeatable measurement of the radius of curvature (RoC) of spherical sample surfaces is of great importance in optics. This importance lies in the ubiquitous use of spherical optical elements such as curved mirrors and lenses. Due to a high measurement sensitivity, interferometric techniques are often deployed for accurate characterization of the sample surface RoC.

How good are collimated Gaussian beams produced with engineered diffusers?

Collimating a Gaussian beam from an uncollimated laser source has been achieved via the deployment of engineered diffusers (EDs)-also referred to as light shaping diffusers. When compared to conventional pinhole-based optical collimation systems, this method of beam collimation ensures high optical transmission efficiency at the expense of the introduction of additional speckle and a resulting reduction in spatial coherence. Despite a lower collimation quality, these ED-produced collimated beams are attractive and promising in terms of their deployment in various benchtop or tabletop systems that involve shorter beam propagation distances of up to a few meters while requiring a high optical power throughput.

Towards a more accurate light transport model for non-line-of-sight imaging.

Non-line-of-sight (NLOS) imaging systems involve the measurement of an optical signal at a diffuse surface. A forward model encodes the physics of these measurements mathematically and can be inverted to generate a reconstruction of the hidden scene. Some existing NLOS imaging techniques rely on illuminating the diffuse surface and measuring the photon time of flight (ToF) of multi-bounce light paths.

Low-loss tunable beam collimator and expander assembly with no moving parts using an engineered diffuser and varifocal lenses.

In this paper, we present a novel design for a tunable beam collimator. A variable collimator assists in achieving an adaptive size of an output collimated beam. Alternatively, it can also provide an adjustable output beam divergence angle for a noncollimated beam output.

Simultaneous thickness and phase index measurements with a motion-free actively tunable Twyman-Green interferometer.

In this paper, we present a scheme to simultaneously measure the thickness and refractive index of parallel plate samples, involving no bulk mechanical motion, by deploying an electronically tunable Twyman-Green interferometer configuration. The active electronic control with no bulk mechanical motion is realized via the introduction of a tunable focus lens within the classical motion-based Twyman-Green interferometer configuration. The resulting interferometer is repeatable and delivers accurate estimates of the thickness and refractive index of a sample under test.

Robust, motion-free optical characterization of samples using actively-tunable Twyman-Green interferometry.

Optical interferometry-based techniques are ubiquitous in various measurement, imaging, calibration, metrological, and astronomical applications. Repeatability, simplicity, and reliability of measurements have ensured that interferometry in its various forms remains popular-and in fact continues to grow-in almost every branch of measurement science. In this paper, we propose a novel actively-controlled optical interferometer in the Twyman-Green configuration.

Non-line-of-sight-imaging using dynamic relay surfaces.

The non-line-of-sight (NLOS) imaging problem has attracted a lot of interest in recent years. The objective is to produce images of objects that are hidden around a corner, using the information encoded in the time-of-flight (ToF) of photons that scatter multiple times after incidence at a given relay surface. Most current methods assume a Lambertian, flat and static relay surface, with non-moving targets in the hidden scene.

Phasor field waves: A Huygens-like light transport model for non-line-of-sight imaging applications.

Non-line-of-sight (NLOS) imaging has recently attracted a lot of interest from the scientific community. The goal of this paper is to provide the basis for a comprehensive mathematical framework for NLOS imaging that is directly derived from physical concepts. We introduce the irradiance phasor field (-field) as an abstract quantity for irradiance fluctuations, akin to the complex envelope of the Electrical field (E-field) that is used to describe propagation of electromagnetic energy.

Phasor field waves: experimental demonstrations of wave-like properties.

Time-of-flight (ToF) non-line-of-sight (NLoS) imaging reconstructs images of scenes with light that have undergone diffuse reflections. While, in the past, ToF light propagation and reconstruction methods have been described using their own inverse methods, it has recently been shown that ToF light transport can be described as the propagation of a wave, allowing it to be modeled by the same methods that are applied for direct imaging with electromagnetic or sound waves. This wave of fluctuating optical irradiance is called the phasor field (-field) wave.

Non-line-of-sight imaging using phasor-field virtual wave optics.

Non-line-of-sight imaging allows objects to be observed when partially or fully occluded from direct view, by analysing indirect diffuse reflections off a secondary relay surface. Despite many potential applications, existing methods lack practical usability because of limitations including the assumption of single scattering only, ideal diffuse reflectance and lack of occlusions within the hidden scene. By contrast, line-of-sight imaging systems do not impose any assumptions about the imaged scene, despite relying on the mathematically simple processes of linear diffractive wave propagation.

Low-cost Gaussian beam profiling with circular irises and apertures.

The fundamental Gaussian TEM mode is the most common mode of propagation within various optical devices, modules, and systems. Beam profilers are widely used in accurately ascertaining the cross-sectional irradiance profile of a TEM mode for free-space optical communication systems as well as tracking beam evolution when propagating within optical submodules. We demonstrate beam profiling methods that use low-cost, off-the-shelf, widely available circular apertures such as circular irises and spatial filters.

Improved laser-based triangulation sensor with enhanced range and resolution through adaptive optics-based active beam control.

Various existing target ranging techniques are limited in terms of the dynamic range of operation and measurement resolution. These limitations arise as a result of a particular measurement methodology, the finite processing capability of the hardware components deployed within the sensor module, and the medium through which the target is viewed. Generally, improving the sensor range adversely affects its resolution and vice versa.

Robust motion-free and error-correcting method of estimating the focal length of a lens.

This paper presents a motion-free technique to characterize the focal length of any spherical convex or concave lens. The measurement test-bench uses a Gaussian laser beam, an electronically controlled variable focus lens (ECVFL), a digital micro-mirror device (DMD), and a standard photo-detector (PD). The method requires measuring beam spot sizes for different focal length settings of the ECVFL and using the measurement data to obtain a focal length estimate through an iterative least-squares-based curve-fitting algorithm.

Nonbulk motion system for simultaneously measuring the refractive index and thickness of a sample using tunable optics and spatial signal processing-based Gaussian beam imaging.

This paper presents a novel approach to simultaneously measuring the thickness and refractive index of a sample. The design uses an electronically controlled tunable lens (ECTL) and a microelectromechanical-system-based digital micromirror device (DMD). The method achieves the desired results by using the DMD to characterize the spatial profile of a Gaussian laser beam at different focal length settings of the ECTL.

Toward the design of a motion-free tunable coupling module for varying spatial beam profiles: foundations of optimal coupling of a Gaussian mode into a fiber collimator with a dynamic two-lens system.

In this paper, we present analytical expressions for the coupling of the fundamental Gaussian mode into a fiber collimator (FC) using a two-lens system. For this two-lens system, we also derive the limiting condition imposed on the focal lengths of the two individual lenses and their mutual separation for near-to-perfect mode coupling into the FC. Variations in the spatial mode profile of a Gaussian beam may occur due to various reasons.

Electronically controlled agile lens-based broadband variable photonic delay line for photonic and radio frequency signal processing.

To the best of our knowledge, proposed for the first time is the design of an optically broadband variable photonic delay line (VPDL) using an electronically controlled variable focus lens (ECVFL), mirror motion, and beam-conditioned free-space laser beam propagation. This loss-minimized fiber-coupled VPDL design using micro-optic components has the ability to simultaneously provide optical attenuation controls and analog-mode high-resolution (subpicoseconds) continuous delays over a moderate (e.g.

Smart agile lens remote optical sensor for three-dimensional object shape measurements.

We demonstrate what is, to the best of our knowledge, the first electronically controlled variable focus lens (ECVFL)-based sensor for remote object shape sensing. Using a target illuminating laser, the axial depths of the shape features on a given object are measured by observing the intensity profile of the optical beam falling on the object surface and tuning the ECVFL focal length to form a minimum beam spot. Using a lens focal length control calibration table, the object feature depths are computed.

Noncontact distance sensor using spatial signal processing.

To the best of our knowledge, proposed is the first distance-measurement sensor using direct spatial signal processing. The sensor is implemented using a laser beam engaged in target-dependent spatial beam processing using an electronically controlled variable focus lens (ECVFL). Specifically, the target-reflected beam is observed by an optical detector while electronically scanning the focal length of the ECVFL in the path of the laser beam.

High-dynamic-range hybrid analog-digital control broadband optical spectral processor using micromirror and acousto-optic devices.

For the first time, to the best of our knowledge, the design and demonstration of a programmable spectral filtering processor is presented that simultaneously engages the power of an analog-mode optical device such as an acousto-optic tunable filter and a digital-mode optical device such as the digital micromirror device. The demonstrated processor allows a high 50 dB attenuation dynamic range across the chosen 1530-1565 nm (~C band). The hybrid analog-digital spectral control mechanism enables the processor to operate with greater versatility when compared to analog- or digital-only processor designs.

Smart value-added fiber-optic modules using spatially multiplexed processing.

Intelligent fiber-optic value-added modules (VAMs) are proposed using what we believe to be a novel spatially multiplexed processing technique implemented with both reconfigurable and nonreconfigurable predesigned pixels per impinging beam that enables desired optical power split states needed for realizing a two state reconfigurable VAM. The preferred design uses broadband micromirrors such as ones fabricated via optical microelectromechanical systems technology. The basic VAM design uses two broadband micromirror pixels, where each pixel has its specific location and area and only one of these pixels is electrically driven to adjust its small tilt angle.