Dichroic Beam Splitter Research Articles

NIR to LWIR Dichroic Beamsplitter Designed and Manufactured for Space Optical Remote Sensor

The infrared dichroic beamsplitter plays an important role in infrared multi-band imaging systems, especially for infrared remote sensing. This paper presents the design and preparation of a dichroic beamsplitter that is capable of reflecting near infrared (NIR) and shortwave infrared (SWIR), and transmitting medium wave infrared (MWIR) as well as longwave infrared (LWIR). A single crystal germanium (Ge) sheet is used as the substrate of the dichroic beamsplitter, while Ge, zinc sulfide (ZnS) and ytterbium trifluoride (YbF3) are selected as coating materials. The average reflectance of the dichroic beamsplitter is more than 95% in bands 1.28 to 1.38 μm, 1.58 to 1.83 μm, and 1.95 to 2.32 μm, and the average transmittance is more than 92% in bands 3.7 to 6.2 μm and 7.5 to 12.5 μm at an incident angle of 45°. The dichroic beamsplitter has been successfully applied in the optical system of infrared remote sensing. It provides a technical approach for other optical systems to separate the optical spectrum from NIR to LWIR.

Scattering characteristics of various nodular defects in a dichroic beam splitter.

Dichroic beam splitters are widely used in multi wavelength laser systems, and their scattering loss affects the signal-to-noise ratio and performance of the system. In this study, we investigate forward and backward scattering induced by nodular defects in a dichroic beam splitter. The seed size, seed position, and geometric constants of nodules exhibited distinct effects on the scattering characteristics. The modeling and simulation provide valuable insights into the relationship between the structural parameters of nodules and their scattering characteristics, offering practical guidance for various high-performance optical multilayer coatings and systems.

Miniaturized thin-film filters to connect multiple self-written waveguides

Self-written waveguides (SWWs) have been well investigated within the last decades. In most cases, they are used as low-loss coupling structures, i.e., to connect buried optical structures in photonic integrated circuits. In this work, we extend the field of possible applications for SWWs by embedding a novel thin-film filter to split the beam and connect multiple output ports simultaneously. The multilayer design of the dielectric filter can be customized to enable its application as a dichroic beamsplitter for photonic networks. The embedded thin-film filter was characterized in detail and used to connect an additional optical sensing element, which is also based on SWWs, to demonstrate its usability for measurement of physical quantities.

A flexible and versatile system for multi-color fiber photometry and optogenetic manipulation

Here, we present simultaneous fiber photometry recordings and optogenetic stimulation based on a multimode fused fiber coupler for both light delivery and collection without the need for dichroic beam splitters. In combination with a multi-color light source and appropriate optical filters, our approach offers remarkable flexibility in experimental design and facilitates the exploration of new molecular tools invivo at minimal cost. We demonstrate straightforward re-configuration of the setup to operate with green, red, and near-infrared calcium indicators with or without simultaneous optogenetic stimulation and further explore the multi-color photometry capabilities of the system. The ease of assembly, operation, characterization, and customization of this platform holds the potential to foster the development of experimental strategies for multi-color fused fiber photometry combined with optogenetics far beyond its current state.

A Dichroic Beamsplitter for the Laser Protection of Infrared Detectors

The design and fabrication approach of a dichroic beamsplitter to meet the protection requirements of infrared detectors for blinding laser weapons is presented. The dichroic beamsplitter must protect against 1064 and 532 nm lasers and have high transmittance in the detection beam band of 3.6–4.7 µm. In order to realize the protection and antireflection (AR) functions of the dichroic beamsplitter, Ta2O5, which has a wide band gap and high thermodynamic stability, was selected as the high-refractive-index material. A multilayer stack was deposited on a silicon substrate by ion-assisted electron beam evaporation. The manufactured dichroic beamsplitter features a high laser-induced damage threshold (LIDT), excellent spectral characteristics in the requested spectral region, and good environmental stability.

Dichroic beam splitter for visible, short-wave infrared, and mid-wave infrared

Multispectral electro-optical/infrared payloads are being developed for a variety of defence and commercial system applications. Many applications depend on their ability to detect and recognize low-contrast and distant targets in a complex environment. The development of such systems necessitates the use of specialized optical filters capable of separating different spectral bands. To separate the bands from visible to mid-wave infrared (MWIR), a dichroic beam splitter is used. We have designed and simulated these two beam splitters with a 45-deg angle of incidence that will be used to separate the bands from visible to MWIR. The beam splitter in such an optical system must separate visible, short-wave infrared (SWIR), and MWIR. We present the thin-film coating design and simulation of these two beam splitters. The first beam splitter separates MWIR from visible and SWIR. The second beam splitter separates the remaining two bands: visible and SWIR.

The spectrally modulated self-coherent camera (SM-SCC): Increasing throughput for focal-plane wavefront sensing

Context. The detection and characterization of Earth-like exoplanets is one of the major science drivers for the next generation of telescopes. Direct imaging of the planets will play a major role in observations. Current direct imaging instruments are limited by evolving non-common path aberrations (NCPAs). The NCPAs have to be compensated for by using the science focal-plane image. A promising sensor is the self-coherent camera (SCC). An SCC adds a pinhole to the Lyot stop in the coronagraph to introduce a probe electric field. The pinhole has to be separated by at least 1.5 times the pupil size to separate the NCPA speckles from the probe electric field. However, such a distance lets through very little light, which makes it difficult to use an SCC at high speed or on faint targets. Aims. A spectrally modulated self-coherent camera (SM-SCC) is proposed as a solution to the throughput problem. The SM-SCC uses a pinhole with a spectral filter and a dichroic beam splitter, which creates images with and without the probe electric field. This allows the pinhole to be placed closer to the pupil edge and increases the throughput. Combining the SM-SCC with an integral field unit (IFU) can be used to apply more complex modulation patterns to the pinhole and the Lyot stop. A modulation scheme with at least three spectral channels can be used to change the pinhole to an arbitrary aperture with higher throughput. This adds an additional degree of freedom in the design of the SM-SCC. Methods. The performance of the SM-SCC is investigated analytically and through numerical simulations. Results. Numerical simulations show that the SM-SCC increases the pinhole throughput by a factor of 32, which increases the wavefront sensor sensitivity by a factor of 5.7. The reconstruction quality of the sensor is tested by varying the central wavelength of the spectral channels. A smaller separation between the wavelength channels leads to better results. The SM-SCC reaches a contrast of 1 × 10−9 for bright targets in closed-loop control with the presence of photon noise, phase errors, and amplitude errors. The contrast floor on fainter targets is photon-noise-limited and reaches 1 × 10−7. The SM-SCC with an IFU can handle randomly generated reference field apertures. For bright targets, the SM-SCC-IFU reaches a contrast of 3 × 10−9 in closed-loop control with photon noise, amplitude errors, and phase errors. Conclusions. The SM-SCC is a promising focal-plane wavefront sensor for systems that use multiband observations, either through integral field spectroscopy or dual-band imaging.

Design and fabrication of multilayer dichroic beam splitter

Beam splitters are primarily used for applications like avionic displays, optical storage, fluorescence applications, optical interferometry, semiconductor instrumentation where some of the information needs to be reflected as well as transmitted. They operate on the principle of light being reflected and transmitted by various interfaces where it is split by percentage of overall intensity or wavelength. In this study, design and fabrication of a dichroic optical beam splitter for filtering of red and green light from a white light source has been presented. Here, a symmetric dielectric multilayer stack with 15 alternating layers of alumina and silica are deposited on BK-7 glass using e-beam evaporation technique. High and low refractive indices of 1.63 and 1.46 respectively are used with quarter-wave optical thicknesses of layers. The beam splitter is designed for 45 ̊ angle of incidence using FilmstarTM design software. Transmission spectrum obtained from UV-Vis-NIR double beam spectrophotometer shows reflectance of ~54% at 660 nm (red wavelength region) and transmittance of ~88% at 550 nm (green wavelength region). The coated sample is further subjected to adhesion and hardness test according to MIL standard and no peel off or scratch is observed indicating excellent durability of the coating. The modelled and measured results closely agree with one another over visible spectral regions. Copyright © 2017 VBRI Press.

Onboard dynamic image exposure control for the Star–Planet Activity Research CubeSat (SPARCS)

ABSTRACT The Star–Planet Activity Research CubeSat (SPARCS) is a 6U CubeSat under development to monitor the flaring and chromospheric activity of M dwarfs at near-ultraviolet (NUV) and far-ultraviolet (FUV) wavelengths. The spacecraft hosts two UV-optimized delta-doped charge-coupled devices fed by a 9-cm telescope and a dichroic beam splitter. A dedicated science payload processor performs near-real-time onboard science image processing to dynamically change detector integration times and gains to reduce the occurrence of pixel saturation during strong M dwarf flaring events and provide adequate flare light-curve structure resolution while enabling the detection of low-amplitude rotational modulation. The processor independently controls the NUV and FUV detectors. For each detector, it derives control updates from the most recent completed exposure and applies them to the next exposure. The detection of a flare event in the NUV channel resets the exposure in the FUV channel with new exposure parameters. Implementation testing of the control algorithm using simulated light curves and full-frame images demonstrates a robust response to the quiescent and flaring levels expected for the stars to be monitored by the mission. The SPARCS onboard autonomous exposure control algorithm is adaptable for operation in future point source-targeting space-based and ground-based observatories geared towards the monitoring of extreme transient astrophysics phenomena.

Time‐resolved photometry of the high‐energy radiation of M dwarfs with the Star‐Planet Activity Research Cubesat

AbstractKnow thy star, know thy planet, … especially in the ultraviolet (UV). Over the past decade, that motto has grown from mere wish to necessity in the M dwarf regime, given that the intense and highly variable UV radiation from these stars is suspected of strongly impacting their planets' habitability and atmospheric loss. This has led to the development of the Star‐Planet Activity Research CubeSat (SPARCS), a NASA‐funded 6U CubeSat observatory fully devoted to the photometric monitoring of the UV flaring of M dwarfs hosting potentially habitable planets. The SPARCS science imaging system uses a 9‐cm telescope that feeds two delta‐doped UV‐optimized CCDs through a dichroic beam splitter, enabling simultaneous monitoring of a target field in the near‐UV and far‐UV. A dedicated onboard payload processor manages science observations and performs near‐real‐time image processing to sustain an autonomous dynamic exposure control algorithm needed to mitigate pixel saturation during flaring events. The mission is currently halfway into its development phase. We present an overview of the mission's science drivers and its expected contribution to our understanding of star‐planet interactions. We also present the expected performance of the autonomous dynamic exposure control algorithm, a first‐of‐its‐kind onboard a space‐based stellar astrophysics observatory.

Simple but effective: strong efficiency boost for a linear variable filter-based spectrometer

A method to drastically enhance detection efficiency of a linear variable filter (LVF) sensor across an extended and continuous wavelength range is presented. The efficiency is increased by a wavelength preselection concept, where the incoming light is divided into partial spectra to reduce otherwise unavoidable reflection losses of filter-based spectrometers. The simple but effective setup uses selected and successively arranged dichroic beamsplitters, which ensures an optimized compromise between efficiency enhancement and minimum increasing complexity. When connected to a two-dimensional camera and combined with a tilted LVF, this compact optical system allows the continuous recording of the full wavelength range between 450 and 850 nm with a resolution of ∼19 nm at 508.6 nm. An efficiency enhancement factor of up to 5.7 is achieved in comparison to a conventional LVF setup. The working principle was verified by measuring the reflection spectra of different natural and artificial green leaves. The proposed approach for increasing the efficiency can be miniaturized and applied to a broad range of other filter-based sensors.

HiPERCAM: a quintuple-beam, high-speed optical imager on the 10.4-m Gran Telescopio Canarias

ABSTRACT HiPERCAM is a portable, quintuple-beam optical imager that saw first light on the 10.4-m Gran Telescopio Canarias (GTC) in 2018. The instrument uses re-imaging optics and four dichroic beamsplitters to record $u_{\rm s}\, g_{\rm s}\, r_{\rm s}\, i_{\rm s}\, z_{\rm s}$ (320–1060 nm) images simultaneously on its five CCD cameras, each of 3.1-arcmin (diagonal) field of view. The detectors in HiPERCAM are frame-transfer devices cooled thermo-electrically to 183 K, thereby allowing both long-exposure, deep imaging of faint targets, as well as high-speed (over 1000 windowed frames per second) imaging of rapidly varying targets. A comparison-star pick-off system in the telescope focal plane increases the effective field of view to 6.7 arcmin for differential photometry. Combining HiPERCAM with the world’s largest optical telescope enables the detection of astronomical sources to gs ∼ 23 in 1 s and gs ∼ 28 in 1 h. In this paper, we describe the scientific motivation behind HiPERCAM, present its design, report on its measured performance, and outline some planned enhancements.

Design and Testing of Augmented Reality-Based Fluorescence Imaging Goggle for Intraoperative Imaging-Guided Surgery.

The different pathways between the position of a near-infrared camera and the user’s eye limit the use of existing near-infrared fluorescence imaging systems for tumor margin assessments. By utilizing an optical system that precisely matches the near-infrared fluorescence image and the optical path of visible light, we developed an augmented reality (AR)-based fluorescence imaging system that provides users with a fluorescence image that matches the real-field, without requiring any additional algorithms. Commercial smart glasses, dichroic beam splitters, mirrors, and custom near-infrared cameras were employed to develop the proposed system, and each mount was designed and utilized. After its performance was assessed in the laboratory, preclinical experiments involving tumor detection and lung lobectomy in mice and rabbits by using indocyanine green (ICG) were conducted. The results showed that the proposed system provided a stable image of fluorescence that matched the actual site. In addition, preclinical experiments confirmed that the proposed system could be used to detect tumors using ICG and evaluate lung lobectomies. The AR-based intraoperative smart goggle system could detect fluorescence images for tumor margin assessments in animal models, without disrupting the surgical workflow in an operating room. Additionally, it was confirmed that, even when the system itself was distorted when worn, the fluorescence image consistently matched the actual site.

Atomic Faraday beam splitter for light generated from pump-degenerate four-wave mixing in a hollow-core photonic crystal fiber

We demonstrate an atomic Faraday dichroic beam splitter suitable for spatially separating signal and idler fields from pump degenerate four-wave mixing in an atomic source. By rotating the plane of polarization of one mode ${90}^{\ensuremath{\circ}}$ with respect to the other, a subsequent polarizing beam splitter separates the two frequencies, which differ by only 13.6 GHz, and achieves a suppression of $(\ensuremath{-}26.3\ifmmode\pm\else\textpm\fi{}0.1)$ and $(\ensuremath{-}21.2\ifmmode\pm\else\textpm\fi{}0.1)$ dB in the two outputs, with a corresponding transmission of 97% and 99%, respectively. This technique avoids the necessity of using spatial separation of four-wave mixing modes and thus opens the door for enhancing the process efficiency in waveguide experiments. As a proof of principle, we generate light via four-wave mixing in $^{87}\mathrm{Rb}$ loaded into a hollow-core photonic crystal fiber and interface it with the atomic Faraday dichroic beam splitter.

Copper Sulfate Pentahydrate Target Behavior During Pulsed Laser Deposition to Produce Dichroic Coatings for Beam Splitters

Copper sulfate pentahydrate (CuSO4·5H2O) used as target in the pulsed laser deposition (PLD) process led to producing thin films with dichroic properties. The coatings were applied on glass slab and hemp fabrics. Investigation of CuSO4·5H2O transformation during ablation and deposition based on FTIR analysis showed that the thin film chemical composition is a mixture of different products resulted from CuSO4·5H2O dehydration and decomposition, followed by melting and vaporization of the CuO and recombination of the different species in the plasma of ablation. Simulation in COMSOL of the CuSO4·5H2O laser heating anticipates the processes and phenomena to be expected during PLD. Optical properties of the thin films are investigated in UV-Vis as reflecting properties and by laser induced fluorescence (LIF). Applications are considered for dichroic plate beamsplitters, as well as others. Dichroic beamsplitters have a large range of applications among which they are useful for combining / splitting laser beams of different color. When the chemical composition provides also electrical conductivity specific properties, the coating may bring more value to the new device or material. In order to ascertain whether a dichroic system can be produced one way or the other achieving at the same time specific characteristics, it is important to understand the physico – chemical processes behind that. With this study, we determine the method to produce dichroic coatings on glass and on hemp fabric, looking at the same time into the mechanism that leads to the result.

4-dB Quadrature Squeezing With Fiber-Coupled PPLN Ridge Waveguide Module

We have developed an optical parametric amplification module for quadrature squeezing with input and output ports coupled with optical fibers for both fundamental and second harmonic. The module consists of a periodically poled LiNbO${}_{3}$ ridge waveguide fabricated with dry etching, dichroic beamsplitters, lenses and four optical fiber pigtales. The high durability of the waveguide and the good separation of squeezed light from a pump beam by the dichroic beamsplitter enable us to inject intense continuous-wave pump light with the power of over 300 mW. We perform $-$4.0${\pm}$0.1 dB of noise reduction for a vacuum state at 1553.3 nm by using a fiber-optics-based measurement setup, which consists of a fiber-optic beamsplitter and a homemade fiber-receptacle balanced detector. The intrinsic loss of the squeezed vacuum in the module is estimated to be 25%. Excluding the extrinsic loss of the measuremental system, the squeezing level in the output fiber of the module is estimated to be $-$5.7${\pm}$0.1 dB. A modularized alignment-free fiber-coupled quadrature squeezer could help to realize quantum information processing with fiber optics.

Optical design of the multi-wavelength imaging coronagraph Metis for the solar orbiter mission

This paper describes the innovative optical design of the Metis coronagraph for the Solar Orbiter ESA-NASA mission. Metis is a multi-wavelength, externally occulted telescope for the imaging of the solar corona in both the visible and ultraviolet wavelength ranges. Metis adopts a novel occultation scheme for the solar disk, that we named “inverse external occulter”, for reducing the extremely high thermal load on the instrument at the spacecraft perihelion. The core of the Metis optical design is an aplanatic Gregorian telescope common to both the visible and ultraviolet channels. A suitable dichroic beam-splitter, optimized for transmitting a narrow-band in the ultraviolet (121.6 nm, HI Lyman-α) and reflecting a broadband in the visible (580–640 nm) spectral range, is used to separate the two optical paths. Along the visible light optical path, a liquid crystal electro-optical modulator, used for the first time in space, allows making polarimetric measurements.

Scanning polarization lidar LOSA-M3: opportunity for research of crystalline particle orientation in the ice clouds

Abstract. The article describes a scanning polarization lidar, LOSA-M3, developed at the V. E. Zuev Institute of Atmospheric Optics, the Siberian Branch of the Russian Academy of Sciences (IAO SB RAS), as part of the common use center “Atmosphere”. The first results of studying the crystalline particle orientation by means of this lidar are presented herein. The main features of the LOSA-M3 lidar are the following: (1) an automatic scanning device, which allows changing the sensing direction in the upper hemisphere at the speed up to 1.5∘ s−1 with the accuracy of the angle measurement setting of at least 1 arcmin, (2) separation of the polarization components of the received radiation that is carried out directly behind the receiving telescope without installing the elements distorting polarization, such as dichroic mirrors and beam splitters, and (3) continuous alternation of the initial polarization state (linear–circular) from pulse to pulse that makes it possible to evaluate some elements of the scattering matrix. For testing lidar performance several series of measurements of the ice cloud structure in the zenith scan mode were carried out in Tomsk in April–June 2018. The results show that the degree of horizontal orientation of particles can vary significantly in different parts of the cloud. The dependence of signal intensity on the tilt angle reflects the distribution of particle deflection relative to the horizontal plane and is well described by the exponential dependence. The values of the cross-polarized component in most cases show a weak decline of intensity with the angle. However, these variations are smaller than the measurement errors. We can conclude that they are practically independent of the tilt angle. In most cases the scattering intensity at the wavelength of 532 nm has a wider distribution than at 1064 nm.

Ratiometric widefield imaging with spectrally balanced detection.

Ratiometric imaging is an invaluable tool for quantitative microscopy, allowing for robust detection of FRET, anisotropy, and spectral shifts of nano-scale optical probes in response to local physical and chemical variations such as local pH, ion composition, and electric potential. In this paper, we propose and demonstrate a scheme for widefield ratiometric imaging that allows for continuous tuning of the cutoff wavelength between its two spectral channels. This scheme is based on angle-tuning the image splitting dichroic beamsplitter, similar to previous works on tunable interference filters. This configuration allows for ratiometric imaging of spectrally heterogeneous samples, which require spectral tunability of the detection path in order to achieve good spectrally balanced ratiometric detection.

Polarization modeling and predictions for Daniel K. Inouye Solar Telescope part 5: impacts of enhanced mirror and dichroic coatings on system polarization calibration

The Daniel K. Inouye Solar Telescope (DKIST) is designed to deliver accurate spectropolarimetric calibrations across a wide wavelength range and large field of view for solar disk, limb, and coronal observations. DKIST instruments deliver spectral resolving powers of up to 300,000 in multiple cameras of multiple instruments sampling nanometer scale bandpasses. We require detailed knowledge of optical coatings on all optics to ensure that we can predict and calibrate the polarization behavior of the system. Optical coatings can be metals protected by many dielectric layers or several-micron-thick dichroics. Strong spectral gradients up to 60 deg retardance per nanometer wavelength and several percent diattenuation per nanometer wavelength are observed in such coatings. Often, optical coatings are not specified with spectral gradient targets for polarimetry in combination with both average- and spectral threshold-type specifications. DKIST has a suite of interchangeable dichroic beam splitters using up to 96 layers. We apply the Berreman formalism in open-source Python scripts to derive coating polarization behavior. We present high spectral resolution examples on dichroics where transmission can drop 10% with associated polarization changes over a 1-nm spectral bandpass in both mirrors and dichroics. We worked with a vendor to design dichroic coatings with relatively benign polarization properties that pass spectral gradient requirements and polarization requirements in addition to reflectivity. We now have the ability to fit multilayer coating designs which allow us to predict system-level polarization properties of mirrors, antireflection coatings, and dichroics at arbitrary incidence angles, high spectral resolving power, and on curved surfaces through optical modeling software packages. Performance predictions for polarization at large astronomical telescopes require significant metrology efforts on individual optical components combined with system-level modeling efforts. We show our custom-built laboratory spectropolarimeter and metrology efforts on protected metal mirrors, antireflection coatings, and dichroic mirror samples.