Isaac August

Miniature Compressive Ultra-spectral Imaging System Utilizing a Single Liquid Crystal Phase Retarder

Spectroscopic imaging has been proved to be an effective tool for many applications in a variety of fields, such as biology, medicine, agriculture, remote sensing and industrial process inspection. However, due to the demand for high spectral and spatial resolution it became extremely challenging to design and implement such systems in a miniaturized and cost effective manner. Using a Compressive Sensing (CS) setup based on a single variable Liquid Crystal (LC) retarder and a sensor array, we present an innovative Miniature Ultra-Spectral Imaging (MUSI) system. The LC retarder acts as a compact wide band spectral modulator. Within the framework of CS, a sequence of spectrally modulated images is used to recover ultra-spectral image cubes. Using the presented compressive MUSI system, we demonstrate the reconstruction of gigapixel spatio-spectral image cubes from spectral scanning shots numbering an order of magnitude less than would be required using conventional systems.

Along-track scanning using a liquid crystal compressive hyperspectral imager.

In various applications, such as remote sensing and quality inspection, hyperspectral (HS) imaging is performed by spatially scanning an object. In this work, we present a new compressive hyperspectral imaging method that performs along-track scanning. The method relies on the compressive sensing miniature ultra-spectral imaging (CS-MUSI) system, which uses a single liquid crystal (LC) cell for spectral encoding and provides a more efficient way of HS data acquisition, compared to classical spatial scanning based systems. The experimental results show that a compression ratio of about 1:10 can be reached. Owing to the inherent compression, the captured data is preprepared for efficient storage and transmission.

Compressive sensing resonator spectroscopy

We present a new fast compressive spectroscopic technique based on the resonance spectrometric mechanism. This technique uses an appropriately designed Fabry-Perot resonator and a photo-sensor in order to acquire different multiplexed spectral modulations, from which the original signal is reconstructed using a compressive sensing reconstruction algorithm. We present experimental results that demonstrate the acquisition of hundreds of spectral bands with a compression ratio of about 1:13.

Performance of target detection algorithm in compressive sensing miniature ultraspectral imaging compressed sensing system

Abstract. Compressive sensing theory was proposed to deal with the high quantity of measurements demanded by traditional hyperspectral systems. Recently, a compressive spectral imaging technique dubbed compressive sensing miniature ultraspectral imaging (CS-MUSI) was presented. This system uses a voltage controlled liquid crystal device to create multiplexed hyperspectral cubes. We evaluate the utility of the data captured using the CS-MUSI system for the task of target detection. Specifically, we compare the performance of the matched filter target detection algorithm in traditional hyperspectral systems and in CS-MUSI multiplexed hyperspectral cubes. We found that the target detection algorithm performs similarly in both cases, despite the fact that the CS-MUSI data is up to an order of magnitude less than that in conventional hyperspectral cubes. Moreover, the target detection is approximately an order of magnitude faster in CS-MUSI data.

Compressive spectroscopy by spectral modulation

We review two compressive spectroscopy techniques based on modulation in the spectral domain that we have recently proposed. Both techniques achieve a compression ratio of approximately 10:1, however each with a different sensing mechanism. The first technique uses a liquid crystal cell as a tunable filter to modulate the spectral signal, and the second technique uses a Fabry-Perot etalon as a resonator. We overview the specific properties of each of the techniques.

Optimized depth of field methodology using annular liquid crystal modulator assisted by image processing

An optical-digital tunable depth of field (DOF) methodology is presented. The suggested methodology forms a fused image based on the sharpest similar depth regions from a set of source images taken with different phase masks. Each phase mask contains a different degree of DOF extension and is implemented by using an annular liquid crystal spatial light modulator, which consists of 16-ring electrodes positioned in the pupil plane. A detailed description of the optical setup and characterization of selected pupil phase masks as well as optimization of the binary phase mask for maximal DOF extension is presented. Experimental results are investigated both qualitatively and quantitatively. In addition, the algorithms results are compared with those of some well-known fusion algorithms and proved its supremacy.

Stokes polarimetry, narrowband filtering, and hyperspectral imaging using a small number of liquid crystal devices(Conference Presentation)

The interest in liquid crystal devices for photonic non-display devices has grown recently due to their mature quality and the continuous improvement of their speed combined with the rising nanoscale and optoelectronic technologies. Of particular interest is their application in imaging systems as compact devices to manipulate the wavefront, wavelength, phase or polarization. Recently we have been developing variety of specially designed LC devices integrated into imaging systems for specific spectro-polarimetric imaging applications using small number of LC devices. These included: (i) wide dynamic range tunable filters for hyperspectral imaging and frequency domain optical coherence tomography, (ii) discrete narrowband tunable filter for multispectral imaging, (iii) compact polarization rotator for polarimetric imaging, (v) wideband achromatic waveplate for polarimetric camera, (vii) polarization independent LCFP tunable filter, and lately (vii) single LC retarder for hyperspectral imaging. In this report we shall present the main concepts of these devices and their functionality into spectro-polarimetric imaging systems such as in skin cancer diagnosis, and imaging oximetry [1-4]. Selected Publications: 1. S. Isaacs et.al, Applied Optics 53, H91-H101 (2014). 2. M. AbuLeil et.al., Optics Letter 39, 5487-90 (2014). 3. I. August, et.al., Scientific Reports, communicated 2016. 4. M. AbuLeil et.al., in preparation.

3D reconstructions from spectral light fields

The parametrization of light rays in form of light fields (LF) have become the standard and probably the most common way for the representation, analysis and processing of rays emitted from 3D objects or from 3D displays. Essentially, the LFs are 4D maps representing the spatial and angular distribution of the intensity of the rays. Nowadays, with the increasing availability of spectral imagers, the conventional LF can be augmented with the spectral information, yielding to what we call spectral light fields (SLFs). Spectral light fields refer to a 5D distribution of spatial, angular and spectral ray’s distribution. Thus, the SLF can be viewed as spectral radiance over a 2D manifold, or as 5D parameterization of a plenoptic function. In this paper we show the utility of the SLFs for digital 3D reconstruction. We show that the additional spectral domain provides important information that can be utilized to overcome 3D reconstruction artefacts caused by ambiguities in commonly captured LFs. We demonstrate the utilization of the SLFs for profilomety and refocusing.

Method and algorithm for efficient calibration of compressive hyperspectral imaging system based on a liquid crystal retarder

Recently we presented a Compressive Sensing Miniature Ultra-spectral Imaging System (CS-MUSI)1 . This system consists of a single Liquid Crystal (LC) phase retarder as a spectral modulator and a gray scale sensor array to capture a multiplexed signal of the imaged scene. By designing the LC spectral modulator in compliance with the Compressive Sensing (CS) guidelines and applying appropriate algorithms we demonstrated reconstruction of spectral (hyper/ ultra) datacubes from an order of magnitude fewer samples than taken by conventional sensors. The LC modulator is designed to have an effective width of a few tens of micrometers, therefore it is prone to imperfections and spatial nonuniformity. In this work, we present the study of this nonuniformity and present a mathematical algorithm that allows the inference of the spectral transmission over the entire cell area from only a few calibration measurements.

Target detection with compressive sensing hyperspectral images

During the past years, several compressive spectral imaging techniques were developed. With these techniques, an optically compressed version of the spectral datacube is captured. Consequently, the information about the object and targets is captured in a lower dimensional space. A question that rises is whether the reduction of the captured space affects the target detection performance. The answer to this question depends on the compressive spectral imaging technique employed. In most compressive spectral imaging techniques, the target detection performance is deteriorated. We show that our recently introduced technique, dubbed Compressive Sensing Miniature Ultra-Spectral Imaging (CSMUSI), yields similar target detection and false detection rates to that of conventional hyperspectral cameras.