Programmable Light Source Research Articles

Fluorescence Excitation-Emission-Matrix Imaging.

We present a 4-dimensional (4D) fluorescence imaging system in which each of the 65,536 pixels in the image array contains an excitation-emission-matrix spectrum with 31 excitation wavelengths and 8 emission wavelengths (x, y, λexc, λem). Hadamard-transform multiplexing of the excitation light from a 31-channel programmable light source allows for an increase in the data acquisition rate so that each 65,536-pixel image can be obtained within 8 s. The system is demonstrated and characterized using, first, a 4D image of 10 capillaries filled with four dye solutions and their binary and ternary mixtures, and, second, using a sequence of about 100 images of layered fluorescent dye solutions and their changing fluorescence as a function of temperature. Multivariate analysis using parallel factor analysis produces images of the spatial distribution of the fluorophores together with their relative intensity as a function of time.

Rapid Fluorescence EEM Spectroscopy Using Super-Cycle Hadamard-Transform Multiplexing.

Hadamard-transform (HT) multiplexing has recently been applied to increasingly complex spectroscopic techniques. It had been shown that the data acquisition time for fluorescence excitation emission matrix (EEM) spectroscopy can be reduced by 1 or 2 orders of magnitude using HT multiplexing of the excitation light using a programmable light source. In these previous studies, the data acquisition rate had been limited by the time it took to record an EEM, that is, to complete one cycle of multiplexed excitation spectra. The extraction of chemical information, such as concentration and chemical identity, is then obtained from parallel factor (PARAFAC) analysis of the sequence of EEMs. In this contribution, we increase the data acquisition rate by another order of magnitude, limited ultimately by the time it takes to record a single excitation spectrum. Our algorithm is entirely based on improved data processing, that is, it can be applied to previously recorded HT multiplexed data sets. The algorithm is based on three previously unexplored approaches: (1) we perform a PARAFAC multivariate analysis on the raw (multiplexed) data set, (2) the time-independent PARAFAC loading vectors are obtained prior to obtaining the time-dependent score vectors, and (3) when loading vectors are difficult to obtain from the EEMs, we instead use a rolling-average approach to considerably increase the stability of the fit. Analysis of experimental data shows that the scores of fluorescence EEMs with seven excitation wavelengths and over 1000 emission wavelengths can be obtained in less than 20 ms.

Autonomous IoT Monitoring Matching Spectral Artificial Light Manipulation for Horticulture.

This paper aims at demonstrating the energy self-sufficiency of a LoRaWAN-based sensor node for monitoring environmental parameters exploiting energy harvesting directly coming from the artificial light used in indoor horticulture. A portable polycrystalline silicon module is used to charge a Li-Po battery, employed as the power reserve of a wireless sensor node able to accurately monitor, with a 1-h period, both the physical quantities most relevant for the application, i.e., humidity, temperature and pressure, and the chemical quantities, i.e., O2 and CO2 concentrations. To this aim, the node also hosts a power-hungry NDIR sensor. Two programmable light sources were used to emulate the actual lighting conditions of greenhouses, and to prove the effectiveness of the designed autonomous system: a LED-based custom designed solar simulator and a commercial LED light especially thought for plant cultivation purposes in greenhouses. Different lighting conditions used in indoor horticulture to enhance different plant growth phases, obtained as combinations of blue, red, far-red and white spectra, were tested by field tests of the sensor node. The energy self-sufficiency of the system was demonstrated by monitoring the charging/discharging trend of the Li-Po battery. Best results are obtained when white artificial light is mixed with the far-red component, closest to the polycrystalline silicon spectral response peak.

Development of Programmable UV-LED Microlithography System for 3D Microfabrication

An advanced UV-LED microlithography system has been introduced for 3D microfabrication. The system comprises an array of UV-LEDs as a programmable light source, a tilt-rotational mask aligner frames to create 3D light traces, and a control computer unit for fully automated operation. A tilt-rotational substrate holder is equipped with high-precision servo motors to create multidirectional UV lights and thereafter fabricating 3D microstructures. The C++-based control software in the main computer provides unique optimal light exposure schemes such as dimming, selective lighting, and synchronizing the stage with the light source that can create complex 3D microstructures. The feature of an adjustable high light intensity up to 472 mW/cm² which used to be more than twice to the conventional systems, has enabled the accessible SU-8 photoresist thickness to a few millimeters. High aspect ratio 2000-μm tall SU-8 pillars and various 3D microstructures including twisted `S' structures, tapered hollow horn structures, open bow-tie structures, and vertical `V' structures have been successfully fabricated to show the great potential the 3D devices in Bio and RF fields. [2021-0153]

HPLC-Detector Based on Hadamard-Transform Fluorescence Excitation-Emission-Matrix Spectroscopy

We present a new rapid-acquisition HPLC detector based on a Hadamard-transform (HT) excitation-emission-matrix (EEM) fluorescence spectrometer allowing the acquisition of two-dimensional spectra at a rate faster than 6 spectra per second (<150 ms per spectrum). The instrument uses discrete ultraviolet light emitting diode (UV LED) light sources which are multiplexed using patterns derived from a Hadamard-matrix and affords faster spectral acquisition compared to conventional sequentially scanning EEM spectrometers. This new programmable light source was combined with a commercial fluorescence spectrometer and integrated as a detector into an HPLC system. We characterize the HT-EEM spectrometer by rapidly separating and detecting a mixture of five different coumarin dyes, with all five analytes eluting in under 2 min. A parallel factor analysis (PARAFAC) algorithm was able to readily separate and identify all coumarin fluorophores without any prior knowledge of the system, even decomposing two coeluting analytes into two distinct PARAFAC components. The HT-EEM spectrometer provides a novel and versatile detection technique suited for rapid online analysis and quantification of analytes in separation methods such as HPLC.

Programmable light source for arbitrary waveform generation in time

Programmable light source is an opto-electronic device, producing modulation of the intensity of light of any, physically permitted, shape. It is composed of an electrically controlled light source connected in a negative feedback to a linear photodetector, and programmable electronic signal generator that drives the light source. Theory of operation, design guidelines, and experimental results are presented.

Development and Evaluation of an Optical Sensing System for Detection of Herbicide Spray Droplets

Real time monitoring of herbicide spray droplet drift is important for crop production management and environmental protection. Existing spray droplet drift detection methods, such as water-sensitive paper and tracers of fluorescence and Rubidium chloride, are time-consuming and laborious, and the accuracies are not high in general. Also, the tracer methods indirectly quantify the spray deposition from the concentration of the tracer and may change the drift characteristics of the sprayed herbicides. In this study, a new optical sensor system was developed to directly detect the spray droplets without the need to add any tracer in the spray liquid. The system was prototyped using a single broadband programmable LED light source and a near infrared sensor containing 6 broadband spectral detectors at 610, 680, 730, 760, 810, and 860 nm to build a detection system for monitoring and analysis of herbicide spray droplet drift. A rotatory structure driven by a stepper motor in the system was created to shift the droplet capture line going under the optical sensor to measure and collect the spectral signals that reflect spray drift droplets along the line. The system prototype was tested for detection of small (Very Fine and Fine), medium (Medium), and large (Coarse) droplets within the droplet classifications of the American Society of Agricultural and Biological Engineers. Laboratory testing results indicated that the system could detect the droplets of different sizes and determine the droplet positions on the droplet capture line with 100% accuracy at the wavelength of 610 nm selected from the 6 bands to detect the droplets.

Touch Sensing for a Projected Screen Using Slope Disparity Gating

This paper introduces a novel touch sensing system for a projected screen with a single camera. To achieve touch sensing with camera image, there are two challenges to overcome. One is to establish robustness against image processing being misled by projected contents. The other is to realize both touch detection and fingertips localization with a single-camera image. In this work, we use Slope Disparity Gating and capture only the region slightly above the projected screen. This selected region is set geometrically so that a part of the finger is captured when touching, and no finger is captured when not touching. A key feature of this study is that the projector can enable this selective imaging capability in the camera while still displaying a normal projected image to the user's eyes. The projector is both a programmable light source for capturing system and an interface display device for the users. We built a prototype system and touch sensing algorithm, evaluated the touch accuracy, demonstrated robustness to a projected content.

Super sub-wavelength interference via high-order correlation of light fields

We propose a scheme to realize super sub-wavelength interference in virtue of high-order spatial correlation with a programmable light source, which can be applied to enhance precision in measurement and control. In this proposal, the light source is produced by modulating the wavefront of a laser beam randomly in time with a phase-only spatial light modulator (SLM). Combing the intensity patterns measured by a CCD camera and the computed intensity patterns using the phase masks loaded on the SLM, the super sub-wavelength interference pattern of an object can be obtained by using high-order spatial correlation measurement. The resolution of the interference pattern can, in principle, be arbitrarily high, and a higher resolution can be obtained as the order of the correlation function increases.

Inverse scattering for reflection intensity phase microscopy.

Reflection phase imaging provides label-free, high-resolution characterization of biological samples, typically using interferometric-based techniques. Here, we investigate reflection phase microscopy from intensity-only measurements under diverse illumination. We evaluate the forward and inverse scattering model based on the first Born approximation for imaging scattering objects above a glass slide. Under this design, the measured field combines linear forward-scattering and height-dependent nonlinear back-scattering from the object that complicates object phase recovery. Using only the forward-scattering, we derive a linear inverse scattering model and evaluate this model's validity range in simulation and experiment using a standard reflection microscope modified with a programmable light source. Our method provides enhanced contrast of thin, weakly scattering samples that complement transmission techniques. This model provides a promising development for creating simplified intensity-based reflection quantitative phase imaging systems easily adoptable for biological research.

Area scanning method for 3D surface profilometry based on an adaptive confocal microscope

Conventional confocal 3D microscopes suffer from a slow measurement speed due to its requirement of scanning in three directions. Although lateral slit scanning has been proven to perform similarly to single point scanning, a direct area confocal scanning microscope is commonly considered impossible as the system is reduced into a wide-field microscope and loses its depth discerning capability. In this article, a direct area scanning method is proposed for 3D surface profilometry based on a tilted focal field. To demonstrate the underlying principle, theoretical analysis is conducted with simulation result, showing that depth discerning capability can be maintained in area scanning when the tilting angle is specifically chosen according to the numerical aperture of the system. An adaptive experimental setup is constructed based on a programmable light source and a programmable array microscope with chromatic axial encoding. Measurement result of a test target using the proposed method is comparable to the result of conventional array scanning. Although the axial uncertainty is increased by a factor of approximately 2.5, the direct area scanning method is more than 300 times faster than the conventional array scanning mode of the same setup.

Light-Controlled Configurable Colorimetric Sensing Array.

Colorimetry is a popular gas-sensing platform, but it is typically limited to one-time use only. Here, we introduce a light-controlled configurable colorimetric sensing array to overcome this limitation. It features a photoactivated reaction between an analyte and a sensing material, such that sensing of an array element can be turned on and off with light. By sequential turning on of each array element, the sensor array can be used multiple times as determined by the number of array elements. This is analogous to a data storage device, which lasts until every storage element is used up. The total number of array elements and the area of each array element are configurable with light. With use of a smartphone screen as a programmable light source, we applied the sensing platform to the detection of oxygen gas and studied the relationship between sensitivity, noise, detection time, and array size. The relationship can be used to configure the array to meet the specifications of different applications.

Cell nuclei detection in multispectral histology images using K-means and expectation-maximisation segmentations

Histology images contain a lot of relevant information which are useful in the diagnostic (cells, cell compartments such as nuclei…). In this topic, the main goal of computer-based image analysis is to identify structures or nuclei in histology images with high accuracy and robustness. Current methods and systems based on colour images give results with a lot of errors. We suggest using multispectral imaging system with a programmable light source (PLS). With the new acquisition system, a 3-band colour image (MS3), a 5-band multispectral image (MS5), a 10-band multispectral image (MS10) and a 25-band multispectral image (MS25) from 450 nm to 700 nm are acquired. After the acquisition, two unsupervised segmentation methods are applied: the expectation-maximisation (EM) and the K-means (KM). Firstly, each band is segmented separately; secondly a fusion of bands is used. A comparison has been drawn between the two segmentation methods. The results show a small superiority of EM segmentation against KM segmentation. It is also noted that the fuse of selected bands from MS5 ensures the best F-measure of cell nuclei detection.

Programmable light source based on an echellogram of a supercontinuum laser.

Illumination systems with tunable spectrums have been receiving an increasing amount of attention due to their wide application and unique capability. This paper proposes a programmable light source in the visible range based on the combination of a prism and an echelle grating. A supercontinuum laser is utilized as the primary source, whose echellogram is projected to a digital mirror device for wavelength selection. A complete calibration procedure is developed to generate any target spectrum of choice. Experiments have shown that spectral peaks with a full width at half-maximum of 1 nm can be easily generated and the wavelength tuning resolution can reach as small as 0.01 nm.

Acquisition of 3D data and spectral color by using RGBD camera and programmable light source : spectral reflectance estimation based on gray color

Acquisition of 3D data and spectral color by using RGBD camera and programmable light source : spectral reflectance estimation based on gray color

Multi‐primary image projector using programmable spectral light source

AbstractThis paper presents a practical prototype of a multi‐primary image projector system in which light source spectra can be programmable for suiting any purpose. Our multi‐primary projection system is mainly configured with a light source component and an image projection component. The programmable light source can reproduce any spectral curve. Spatial images are then generated using a digital mirror device chip that quickly controls the intensity of the light source spectra in 2D image plane. The multi‐primary images in our projection system are reproduced by multiplexing the time‐sequential images with different primary colors. Our multi‐primary image projector realizes not only wide gamut projection but also spectral projection. To achieve this, we also show how light source spectra of four or six primary colors are designed.

An integrated spectral imaging system for producing color images of static and moving objects

AbstractAn integrated spectral imaging system constructed by synchronizing a programmable light source, a high‐speed monochrome camera, and a display device is proposed to produce tristimulus images of static and moving objects effectively in real time onto the display. This system is called the CIE‐XYZ display. Active spectral illuminants, containing both the device characteristics of camera and display, are projected onto object surfaces as time sequence. The images are captured synchronously by the camera and quickly transmitted to the display device in the RGB signal form so that the accurate tristimulus images are displayed. First, we describe the principle of the CIE‐XYZ tristimulus display. The theoretically optimal illuminants contain negative parts in the spectral curves. Second, we design practical illuminants with all positive spectral curves. The color images in our system are composed of the time sequence of RGB component images. Then, the synthesized color images on the display contain color artifacts when objects move fast. An image processing algorithm for correcting the motion color artifact is proposed based on optical flow estimation using a graphics processing unit. The comprehensive performance of the proposed system and algorithms is examined using both static and moving objects. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 329–340, 2015

Spectral imaging by synchronizing capture and illumination

This paper proposes a spectral imaging technology by synchronizing a programmable light source and a high-speed monochrome camera. The light source is capable of emitting arbitrary spectrum in high speed, so that the system has the advantage of capturing spectral images without using filters. The camera and the light source are controlled by a computer in order to capture image sequence synchronously with camera and illuminant control signals. First, we describe a projector for spectrally rendering a real scene as a fundamental usage of the spectral imaging system. Second, we describe the effective applications to (1) spectral reflectance recovery and (2) tristimulus imager. The performances of the proposed algorithms to solve the applied problems are examined in experiments in detail. We demonstrate potential applicability of the proposed spectral imaging technology.

Sensor array-based optical portable instrument for determination of pH

A portable optical instrument is presented that makes it possible to determine pH with a colorimetric sensor array. The use of four membranes containing acid–base indicators makes it possible to cover the full range of pH using the H (hue) coordinate measurements of the HSV colour space. pH sensitive membranes were directly cast onto a plastic support to form a two-dimensional array, located between an OLED display as the programmable light source and a set of digital colour detectors. The resulting microcontroller-based system is immune to optical and electrical interferences. A complete optical and electrical characterization and optimization of the hand-held instrument was carried out. The instrument was used to determine pH using a simple algorithm to select the sensor output that was programmed in the microcontroller. The initial eleven candidate pH membranes were reduced to only four, which permit to obtain reliable pH values. The pH response of the selected four sensing elements was modelled, and calibration curves were applied to a validation set and real samples obtaining positive correlations between the real and predicted data.

Abstract A28: Improving detection through SELF (selective excitation light fluorescence) imaging

Abstract The use of fluorescence imaging and spectroscopy for the detection of early neoplastic epithelial lesions has been well established, with clinically adopted devices in for use in the lung (Onco-LIFE, SAFE-1000, etc), the oral cavity (VELScope and Identaf 3000) and others in development for the cervix and dermatology. Primarily these imaging technologies make use of fluorescence excitation illumination of a single wavelength (predominately in the near UV to blue wavelength ranges) and differentiate between normal and not normal tissue based upon intensity changes and spectral shifts in the emitted tissue autofluorescence (not normal -darker with less green or blue relative the red fluorescence). SELF imaging makes use of a multitude of illumination wavelengths to specifically couple to the action spectra of the fluorophores within the tissue to enhance the differentiation between tissue states, fluorophores and their immediate environment. This methodology makes use of the different absorption spectra (action spectra) of different fluorophores or similar flourophores in different environments. Conventionally this can be done through the sequential illumination with many different excitation wavelengths and sequential image capture, to collect a hyperspectral excitation image data cube followed by some form of spectra unmixing to resolve the individual targets (components) contributing to the image. Each target is identified by a unique weighted sum of pixel intensities across the excitation wavelengths in the data cube. Through the use of a programmable light source such as the OneLight (OneLight Corp.) in which not only the wavelengths of the illumination light, but their individual intensities (alone or in combination) can be selected under computer control it is possible to not only rapidly illuminate with separate excitation wavelengths but to illuminate with a collection of weighted (each wavelength has a different selected intensity) spectra to specifically couple to selected fluorescence targets (specific fluorophores or fluorophores in specific local environments). Thus instead of needing to illuminate with a series of 10 separate excitation wavelengths and collect separate 10 images on can illuminate with a few (2–3) weighted profiles of excitation wavelengths and collect a few (2–3) images, the number of spectra used (images collected) determines the number of targets differentiated. In this fashion it is possible to detect in an image many more specific flourophore types than with conventional fluorescence imaging. SELF imaging in microscopy, wide field macroscopic imaging and ex vivo and in vivo imaging has been demonstrated and will be presented. Citation Information: Cancer Prev Res 2010;3(1 Suppl):A28.