Brant M. Kaylor

Ultrabroadband optical chirp linearization for precision metrology applications

We demonstrate precise linearization of ultrabroadband laser frequency chirps via a fiber-based self-heterodyne technique to enable extremely high-resolution, frequency-modulated cw laser-radar (LADAR) and a wide range of other metrology applications. Our frequency chirps cover bandwidths up to nearly 5 THz with frequency errors as low as 170 kHz, relative to linearity. We show that this performance enables 31-mum transform-limited LADAR range resolution (FWHM) and 86 nm range precisions over a 1.5 m range baseline. Much longer range baselines are possible but are limited by atmospheric turbulence and fiber dispersion.

Accuracy of active chirp linearization for broadband frequency modulated continuous wave ladar

As the bandwidth and linearity of frequency modulated continuous wave chirp ladar increase, the resulting range resolution, precisions, and accuracy are improved correspondingly. An analysis of a very broadband (several THz) and linear (<1 ppm) chirped ladar system based on active chirp linearization is presented. Residual chirp nonlinearity and material dispersion are analyzed as to their effect on the dynamic range, precision, and accuracy of the system. Measurement precision and accuracy approaching the part per billion level is predicted.

MOEMS deformable mirrors for focus control in vital microscopy

Deformable membrane mirrors are promising MOEMS devices for focus control and aberration correction in vital microscopy, offering high speed focus adjustment in an optical system that can be miniaturized for in vivo use. This paper describes mirrors comprising metalized polymer membranes suspended over three concentric circular electrodes for electrostatic actuation. The membranes are 2-μm thick and 3 mm in diameter, made from the fully cross-linked photoset epoxy SU-8 2002. A layer of SU-8 2025 is used to establish a 30-μm thick air gap between the electrodes and the membrane mirror. The membranes are actuated by applying voltage to each electrode individually to achieve displacement as large as 12 μm while minimizing spherical aberration. Surface deflection is studied using phase-shift interferometry under both static and dynamic excitation. Using the deformable MOEMS mirror for focus control in an optical microscope we demonstrate the ability to adjust the location of the focal plane by 85 μm using an N.A. = 0.75 optical system.

Three dimensional digital holographic aperture synthesis

Aperture synthesis techniques are applied to temporally and spatially diverse digital holograms recorded with a fast focal-plane array. Because the technique fully resolves the downrange dimension using wide-bandwidth FMCW linear-chirp waveforms, extremely high resolution three dimensional (3D) images can be obtained even at very long standoff ranges. This allows excellent 3D image formation even when targets have significant structure or discontinuities, which are typically poorly rendered with multi-baseline synthetic aperture ladar or multi-wavelength holographic aperture ladar approaches. The background for the system is described and system performance is demonstrated through both simulation and experiments.

Miniature non-mechanical zoom camera using deformable MOEMS mirrors

We present a miniature non-mechanical zoom camera using deformable MOEMS mirrors. Bridger Photonics, Inc. (Bridger) in collaboration with Montana State University (MSU), has developed electrostatically actuated deformable MEMS mirrors for use in compact focus control and zoom imaging systems. Applications including microscopy, endomicroscopy, robotic surgery and cell-phone cameras. In comparison to conventional systems, our MEMS-based designs require no mechanically moving parts. Both circular and elliptical membranes are now being manufactured at the wafer level and possess excellent optical surface quality (membrane flatness < λ/4). The mirror diameters range from 1 - 4 mm. For membranes with a 25 μm air gap, the membrane stroke is 10 μm. In terms of the optical design, the mirrors are considered variable power optical elements. A device with 2 mm diameter and 10 μm stroke can vary its optical power over 40 diopters or 0.04mm∧(-1). Equivalently, this corresponds to a focal length ranging from infinity to 25 mm. We have designed and demonstrated a zoom system using two MOEMS elements and exclusively commercial off-the-shelf optical components to achieve an optical zoom of 1.9x with a 15° full field of view. The total optical track length of the system is 36 mm. The design is approximately 30 mm x 30 mm x 20 mm including the optomechanical housing and image sensor. With custom optics, we anticipate achieving form factors that are compatible with incorporation into cell phones.

An improved focus control mirror using SU-8 wafer bonding process

We are developing MEMS deformable mirrors for focus control in miniature optical systems, including endoscopic microscopes and small form-factor camera lenses. This paper describes a new process to create mirrors made from the photoset polymer SU-8. The SU-8 also serves as the adhesive layer for wafer bonding, resulting in a simple, low cost fabrication process. The paper describes the process details and the optical properties of the resulting focus control mirrors, which have a diameter of 2 mm, a stroke in excess of 8 μm and very low residual aberration. Multiple actuation electrodes allow control of more than 0.4 μm peak-peak of spherical aberration.

Linearization of ultra-broadband optical chirps for precision length metrology

We demonstrate precise active linearization of ultra-broadband (>5 THz) laser frequency sweeps using a self-heterodyne technique. Frequency errors less than 170 kHz relative to linearity were observed enabling very high resolution ranging over large distances.

Imaging through obscurants with a heterodyne detection-based ladar system

Bridger Photonics has been researching and developing a ladar system based on heterodyne detection for imaging through brownout and other DVEs. There are several advantages that an FMCW ladar system provides compared to direct detect pulsed time-of-flight systems including: 1) Higher average powers, 2) Single photon sensitive while remaining tolerant to strong return signals, 3) Doppler sensitivity for clutter removal, and 4) More flexible system for sensing during various stages of flight. In this paper, we provide a review of our sensor, discuss lessons learned during various DVE tests, and show our latest 3D imagery.

Dynamically Programmable, Dual-Band Computational Imaging System

A dynamically programmable computational imaging system has been demonstrated. The system operates in the visible and near infrared bands. Principal components and random binary measurements were used with the imaging hardware to demonstrate compressive imaging.

Face recognition via a projective compressive sensing system

A projective compressive sensing system for face recognition is presented. The Fisherfaces method was utilized for classification of the face images. The system uses a digital micromirror device to project measurement vectors onto the scene and a single photodetector to collect the backscattered illumination. Experimentally, the system accuracy was 95.5% using only 32 measurements per image; this performance matches the simulation results. The total number of image pixels was 5,736 (84 × 64) resulting in a compression factor of 168 over a conventional imaging system.