Publications by authors named "Yukitoshi Otani"

26 Publications

  • Page 1 of 1

Minimizing scattering-induced phase errors in differential interference contrast microscopy.

J Biomed Opt 2020 12;25(12)

Utsunomiya University, Department of Optical Engineering, Tochigi, Japan.

Significance: Differential interference contrast (DIC) microscopes allow noninvasive in vivo observation of transparent microstructures in tissue without the use of fluorescent dyes or genetic modification. We show how to modify a DIC microscope to measure the sample phase distribution accurately and in real-time even deep inside sample tissue.

Aim: Our aim is to improve the DIC microscope's phase measurement to remove the phase bias that occurs in the presence of strong scattering.

Approach: A quarter-wave plate was added in front of the polarization camera, allowing a modified phase calculation to incorporate all four polarization orientation angles (0 deg, 45 deg, 90 deg, and 135 deg) captured simultaneously by the polarization camera, followed by deconvolution.

Results: We confirm that the proposed method reduces phase measurement error in the presence of scattering and demonstrate the method using in vivo imaging of a beating heart inside a medaka egg and the whole-body blood circulation in a young medaka fish.

Conclusions: Modifying a polarization-camera DIC microscope with a quarter-wave plate allows users to image deep inside samples without phase bias due to scattering effects.
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http://dx.doi.org/10.1117/1.JBO.25.12.123703DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7734411PMC
December 2020

Dynamic calibration for enhancing the stability of a channeled spectropolarimeter.

Appl Opt 2020 Oct;59(30):9424-9433

Channeled spectropolarimeters are optical instruments that measure the spectral dependence of the polarization of light without any mechanically moving parts. An important factor in achieving stable and accurate measurements is the calibration process, especially in dynamic environments where temperature fluctuations or other factors affect the retardance of the components in the polarimeter. In previous research, a self-calibration algorithm that accounts for these variations was developed, without any additional reference measurements. In this paper, we identify an ambiguity in the self-calibration phase, which limits the allowed temperature changes to surprisingly small ranges. We show how to adaptively estimate and correct for the phase ambiguity using a polynomial curve-fitting algorithm, extending the temperature range to virtually all practical scenarios. Lastly, we demonstrate the ability of the modified self-calibration algorithm to provide stable reconstruction of the Stokes vector for a temperature range >40, using an experimental channeled spectropolarimeter.
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http://dx.doi.org/10.1364/AO.409054DOI Listing
October 2020

Dynamic parallel phase-shifting electronic speckle pattern interferometer.

Appl Opt 2020 Sep;59(27):8160-8166

Methods for measuring variations in diffuse surfaces using electronic speckle pattern interferometry (ESPI) are widely used and well known. In this research, we present an out-of-plane ESPI system coupled to a Michelson configuration to generate simultaneous parallel interferograms with different phase shifts. The system uses circular polarization states to generate parallel phase shifted interferograms. Due to the polarization states, the fringes do not experience a contrast reduction, thus avoiding measurement errors that affect spatial or temporal phase-shifting in interferometry. The basic operating principle of polarization modulation is described, and results that represent the temporal evolution of an aluminum plate are presented. The generation of two simultaneous patterns allows one to track the dynamic performance of the plate.
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http://dx.doi.org/10.1364/AO.401309DOI Listing
September 2020

Phase stepping through polarizing modulation in electronic speckle pattern interferometry.

Appl Opt 2020 Jul;59(20):6005-6011

We have demonstrated a speckle out-of-plane interferometer that employs phase-stepping procedures by means of polarization modulation. The system generates circular polarization states with opposite signs at each arm of the system, which overlap at the output of the interferometer, to generate phase shifts operating a conventional linear polarizer; the emerging polarization states have been analyzed to obtain the shifts needed to process the optical phase. The phase-stepping technique is demonstrated with a two-step algorithm to measure out-of-plane displacement on a flat metal plate.
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http://dx.doi.org/10.1364/AO.397137DOI Listing
July 2020

Compensating for nonlinear dispersion in channeled spectropolarimetry.

Appl Opt 2020 Jun;59(16):5032-5040

All common waveplate materials exhibit nonlinear dispersion of retardance, producing an unwanted chirp in the interference fringes that channeled spectropolarimeters use for heterodyning polarization data. After showing how to quantify this nonlinearity, we survey the common waveplate materials and find that MgF has significantly lower nonlinearity than any other available material. We also quantify the degree of crosstalk caused by dispersion nonlinearity and show that, unlike in linear dispersion, the degree of crosstalk depends on the sequence of how the phase calibration is implemented. Regardless of how the calibrated phases have been obtained, shifting each channel to baseband prior to windowing minimizes crosstalk error.
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http://dx.doi.org/10.1364/AO.388473DOI Listing
June 2020

Simultaneous balancing of geometric transformation and linear polarizations using six-fold-mirror geometry over the visible region.

Opt Lett 2020 May;45(9):2510-2513

The presence of optical rotation due to the Berry phase and coating-induced linear polarizations across a set of rays deteriorate the form of a point spread function. In this Letter, we model an optical system with six aluminum coated fold mirrors, and we show how to balance geometric transformation, linear retardance, and linear diattenuation simultaneously. We minimize the linear polarizations by arranging the six fold mirrors in three pairs of crossed-fold-mirror geometry. In the same optical model, we also show that geometric transformation induced by the first set of three mirrors is canceled out by the second set of three mirrors by rotating the eigen-polarizations in opposite direction with the same amount. We perform experimental verification using a spectroscopic Mueller matrix polarimeter over the visible spectral range.
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http://dx.doi.org/10.1364/OL.390026DOI Listing
May 2020

Single shot 3D profilometry by polarization pattern projection.

Appl Opt 2020 Feb;59(6):1654-1659

We demonstrate a uniaxial 3D profilometry system illuminating the sample with a linear polarization pattern and measuring a polarization camera. The linear polarization pattern is generated by a spatial light modulator and a quarter-wave plate in the optical system. The system can measure four different fringe patterns with a phase difference of 90 deg simultaneously in the polarization camera. Therefore, we can measure three-dimensional shapes in a single shot. We present the measurement principles of the system and show the results of a real-time 3D profilometry experiment.
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http://dx.doi.org/10.1364/AO.382690DOI Listing
February 2020

Alignment precision of polarization components.

Appl Opt 2019 Dec;58(36):9750-9756

Recent research publications in the polarization literature have discussed methods of correcting for azimuthal alignment errors of optical elements in postprocessing. However, we show that high angular precision is not difficult to achieve during system alignment, so that postprocessing correction should be unnecessary. We estimate the alignment precision achievable for linear polarizers and waveplates in polarization systems. This shows that using an optical signal model for alignment allows a precision limited by the quality of the optics and detectors rather than the quality of the mechanics, rendering millidegree alignment precision possible with ordinary rotational mounts.
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http://dx.doi.org/10.1364/AO.58.009750DOI Listing
December 2019

Angularly selective microstructured surface for tuning seasonal sunlight interaction.

Opt Express 2019 Dec;27(25):36426-36437

In the temperate latitudes, high-reflectivity exterior surfaces save energy spent on ventilation and cooling during summer, but cost energy on heating in winter. Angularly selective surfaces that adjust their reflectivities by sun position allow beneficial effects in both seasons - high reflectivity in summer and high absorption in winter. Here we show how a planar microstructured surface can produce such an angularly selective behavior and estimate its energy efficiency under direct solar irradiance at 35° N. Results show that such an ideal angularly selective surface has the potential to improve efficiency by up to 43.2% compared to a conventional concrete surface. Numerical results for an aluminum one-dimensional periodic structure indicate that it achieves a 25.7% improvement of efficiency. Finally, we validate the designed structure by measuring the reflectivity of the fabricated surface at a series of angles.
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http://dx.doi.org/10.1364/OE.27.036426DOI Listing
December 2019

Speckle-field digital polarization holographic microscopy.

Opt Lett 2019 Dec;44(23):5711-5714

We present a new polarization holographic microscopy technique based on speckle-field illumination with enhanced spatial resolution and controlled coherent noise reduction. The proposed technique employs a spatial light modulator for the generation of a sequential speckle pattern for the illumination of the sample. The developed microscope is capable of simultaneous extraction of orthogonal polarization components of the field emanating from the sample. We demonstrate the potential features of the technique by presenting spatially resolved images of the known samples and the inhomogeneous anisotropic samples. The technique has substantial significance in biomedical imaging with digital auto-focusing and complex field imaging.
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http://dx.doi.org/10.1364/OL.44.005711DOI Listing
December 2019

Compact and high-speed Stokes polarimeter using three-way polarization-preserving beam splitters.

Appl Opt 2019 Jul;58(21):5644-5649

We present a new real-time Stokes parameter measurement technique using three polarized beam splitters without mechanical motion or electrical tuning. This system can analyze the polarization state of light at 30 kHz, limited only by the speed of the detector analog to digital converters. The optical system is also compact (52×30×25  mm) because it consists only of small volume optical devices. We show that the system can measure arbitrary polarization states with an accuracy of better than 0.006 in the normalized Stokes parameters. We also demonstrate the ability to measure fast dynamic polarization states by analyzing the state produced by a fast rotating quarter-wave plate and the time-dependent stress induced in a PMMA block by hitting the block with a hammer.
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http://dx.doi.org/10.1364/AO.58.005644DOI Listing
July 2019

Quantitative discrimination of biological tissues by micro-elastographic measurement using an epi-illumination Mueller matrix microscope.

Biomed Opt Express 2019 Aug 9;10(8):3847-3859. Epub 2019 Jul 9.

Graduate School of Engineering, Utsunomiya University, Utsunomiya, Tochigi, 321-8585, Japan.

We propose a method for estimating the stiffness of bio-specimens by measuring their linear retardance properties under applied stress. For this purpose, we employ an epi-illumination Mueller matrix microscope and show the procedures for its calibration. We provide experimental results demonstrating how to apply Mueller matrix data to elastography, using chicken liver and chicken heart as biological samples. Finally, we show how the histograms of linear retardance images can be used to distinguish between specimens and quantify the discrimination accuracy.
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http://dx.doi.org/10.1364/BOE.10.003847DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6701520PMC
August 2019

Erratum: Video-rate quantitative phase analysis by a DIC microscope using a polarization camera: errata.

Biomed Opt Express 2019 06 23;10(6):2967-2968. Epub 2019 May 23.

Department of Optical Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya, Tochigi, Japan.

[This corrects the article on p. 1273 in vol. 10, PMID: 30891345.].
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http://dx.doi.org/10.1364/BOE.10.002967DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6583344PMC
June 2019

Video-rate quantitative phase analysis by a DIC microscope using a polarization camera.

Biomed Opt Express 2019 Mar 19;10(3):1273-1281. Epub 2019 Feb 19.

Department of Optical Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya, Tochigi, Japan.

This paper describes how to take advantage of the replacement of an intensity camera with a polarization camera in a standard differential interference contrast (DIC) microscope. Using a polarization camera enables snapshot quantitative phase analysis so that real-time imaging of living transparent tissues become possible. Using our method, we quantify the phase measurement accuracy using a phantom consisting of glass beads embedded in lacquer. In order to demonstrate these advantages, we image the pumping heart and blood flow in a living egg.
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http://dx.doi.org/10.1364/BOE.10.001273DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6420286PMC
March 2019

Robust full Stokes imaging polarimeter with dynamic calibration.

Opt Lett 2019 Feb;44(4):891-894

We present a full Stokes imaging polarimeter using a rotating retarder in combination with a polarization camera-a detector array on which a pixelated polarizer array is attached. By itself, a polarization camera cannot capture the full Stokes parameters, but we add a rotating retarder in front and show how it can be used to provide full Stokes images. In addition, we demonstrate the advantage that it can be recalibrated dynamically while taking measurements, allowing accurate measurements even in environments where the retardance in changing.
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http://dx.doi.org/10.1364/OL.44.000891DOI Listing
February 2019

Retinal imaging with optical coherence tomography and low-loss adaptive optics using a 2.8-mm beam size.

J Biophotonics 2019 06 11;12(6):e201800192. Epub 2019 Mar 11.

Optical+Biomedical Engineering Laboratory, Department of Electrical, Electronic and Computer Engineering, University of Western Australia, Crawley, Western Australia, Australia.

As data acquisition for retinal imaging with optical coherence tomography (OCT) becomes faster, efficient collection of photons becomes more important to maintain image quality. One approach is to use a larger aperture at the eye's pupil to collect more photons that have been reflected from the retina. A 2.8-mm beam diameter system with only seven reflecting surfaces was developed for low-loss retinal imaging. The larger beam size requires defocus and astigmatism correction, which was done in a closed loop adaptive optics method using a Shack-Hartmann wavefront sensor and a deformable mirror (DM) with 140 actuators and a ±2.75 μm stroke. This DM facilitates defocus correction ranging from approximately -3 D to +3 D. Comparing the new system with a standard 1.2-mm system on a model eye, a signal-to-noise gain of 4.5 dB and a 2.3 times smaller speckle size were measured. Measurements on the retinas of five subjects showed even better results, with increases in dynamic range up to 13 dB. Note that the new sample arm only occupies 30 cm × 60 cm, which makes it highly suitable for imaging in a clinical environment. Figure: B-scan images obtained over a width of 8 deg from the right eye of a 31-year-old Caucasian male. While the left side was imaged with a standard 1.2-mm OCT system, the right side was imaged with the 2.8-mm system. Both images were collected with the same integration time and incident power, after correction of aberrations. Using the dynamic range within the images, which is determined by comparing the highest pixel value to the noise floor, a difference in dynamic range of 10.8 dB was measured between the two systems.
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http://dx.doi.org/10.1002/jbio.201800192DOI Listing
June 2019

Stokes polarimeter performance: general noise model and analysis: erratum.

Appl Opt 2018 08;57(24):6998

We correct two errors in Appl. Opt.57, 4283 (2018)APOPAI0003-693510.1364/AO.57.004283.
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http://dx.doi.org/10.1364/AO.57.006998DOI Listing
August 2018

Multiwavelength wavefront detection based on a lateral shear interferometer and polarization phase-shifting techniques.

Appl Opt 2018 Aug;57(24):6860-6865

We present a multiwavelength analysis of a wavefront detected by a color camera and a lateral shear interferometer. The system employs polarization phase-shifting techniques by rotating a linear polarizer at the output and detecting the phase information through a frequency demodulation algorithm. By considering the phase modulation obtained by rotating the analyzer, a frequency filter centered on the desired peak carries the phase and amplitude information of the detected wavefront. Theoretical approach, the consideration of Jones matrices of each element, and experimental results show the feasibility of the implementation.
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http://dx.doi.org/10.1364/AO.57.006860DOI Listing
August 2018

Demonstration of a terahertz pure vector beam by tailoring geometric phase.

Sci Rep 2018 Jun 6;8(1):8690. Epub 2018 Jun 6.

Center for Optical Research & Education (CORE), Utsunomiya University, 7-1-2, Yoto, Utsunomiya, Tochigi, 321-8585, Japan.

We demonstrate the creation of a vector beam by tailoring geometric phase of left- and right- circularly polarized beams. Such a vector beam with a uniform phase has not been demonstrated before because a vortex phase remains in the beam. We focus on vortex phase cancellation to generate vector beams in terahertz regions, and measure the geometric phase of the beam and its spatial distribution of polarization. We conduct proof-of-principle experiments for producing a vector beam with radial polarization and uniform phase at 0.36 THz. We determine the vortex phase of the vector beam to be below 4%, thus highlighting the extendibility and availability of the proposed concept to the super broadband spectral region from ultraviolet to terahertz. The extended range of our proposed techniques could lead to breakthroughs in the fields of microscopy, chiral nano-materials, and quantum information science.
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http://dx.doi.org/10.1038/s41598-018-26964-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5989212PMC
June 2018

Stokes polarimeter performance: general noise model and analysis.

Appl Opt 2018 May;57(15):4283-4296

We calculate the photometric Stokes parameter covariance matrices and SNRs estimated by polarimeters exposed to general noise distributions, such as mixed Poisson-Gaussian (PG) noise. The measurement model includes the effects of optical losses and detector quantum efficiency, enabling quantitative comparison of instruments that have different photometric efficiencies. We demonstrate this capability by comparing the performance of many common polarimeter configurations, including diattenuator-based systems, such as Azzam's four-detector polarimeter [Opt. Lett.10, 309 (1985)OPLEDP0146-959210.1364/OL.10.000309] and Kudenov's stacked photovoltaic polarimeter [Opt. Express24, 14737 (2016)OPEXFF1094-408710.1364/OE.24.014737]. Working with the full covariance matrix under mixed PG noise, we also show that instruments optimized under assumptions of Gaussian noise simultaneously exhibit optimal behavior under Poisson noise.
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http://dx.doi.org/10.1364/AO.57.004283DOI Listing
May 2018

Mueller-matrix modeling and characterization of a dual-crystal electro-optic modulator.

Opt Express 2016 Oct;24(21):24213-24224

A general mathematical model based on Mueller-matrix calculation is presented to describe the optical behavior of a dual-crystal electro-optic modulator. The two crystals inside the modulator are oriented at ± 45° with respect to the horizontal, thereby cancelling natural birefringence and temperature-induced birefringence. We describe the behavior of the modulator as a function of the ellipticity of the crystals, the rotation angles of the crystals and the applied voltage. By fitting the measured data with a Mueller-matrix model that uses values for the ellipticity and orientation angles of the crystals, the simulated data and the experimental measurements could be matched. This Mueller-matrix includes physical properties of the thermally compensated electro optic modulator, and the matrix can be used in simulations where these device-specific properties are important, for instance in the modeling of a polarization-sensitive optical coherence tomography system.
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http://dx.doi.org/10.1364/OE.24.024213DOI Listing
October 2016

Determination of the polarization states of an arbitrary polarized terahertz beam: vectorial vortex analysis.

Sci Rep 2015 Mar 24;5:9416. Epub 2015 Mar 24.

Center for Optical Research &Education (CORE), Utsunomiya University, Yoto 7-1-2, Utsunomiya, Tochigi 321-8585, Japan.

Vectorial vortex analysis is used to determine the polarization states of an arbitrarily polarized terahertz (0.1-1.6 THz) beam using THz achromatic axially symmetric wave (TAS) plates, which have a phase retardance of Δ = 163° and are made of polytetrafluorethylene. Polarized THz beams are converted into THz vectorial vortex beams with no spatial or wavelength dispersion, and the unknown polarization states of the incident THz beams are reconstructed. The polarization determination is also demonstrated at frequencies of 0.16 and 0.36 THz. The results obtained by solving the inverse source problem agree with the values used in the experiments. This vectorial vortex analysis enables a determination of the polarization states of the incident THz beam from the THz image. The polarization states of the beams are estimated after they pass through the TAS plates. The results validate this new approach to polarization detection for intense THz sources. It could find application in such cutting edge areas of physics as nonlinear THz photonics and plasmon excitation, because TAS plates not only instantaneously elucidate the polarization of an enclosed THz beam but can also passively control THz vectorial vortex beams.
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http://dx.doi.org/10.1038/srep09416DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4371186PMC
March 2015

Developmental and morphological studies in Japanese medaka with ultra-high resolution optical coherence tomography.

Biomed Opt Express 2015 Feb 6;6(2):297-308. Epub 2015 Jan 6.

Center for Optical Research and Education (CORE), Utsunomiya University, Japan.

We propose ultra-high resolution optical coherence tomography to study the morphological development of internal organs in medaka fish in the post-embryonic stages at micrometer resolution. Different stages of Japanese medaka were imaged after hatching in vivo with an axial resolution of 2.8 µm in tissue. Various morphological structures and organs identified in the OCT images were then compared with the histology. Due to the medaka's close resemblance to vertebrates, including humans, these morphological features play an important role in morphogenesis and can be used to study diseases that also occur in humans.
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http://dx.doi.org/10.1364/BOE.6.000297DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4354602PMC
February 2015

Generation of achromatic, uniform-phase, radially polarized beams.

Opt Express 2014 Feb;22(3):3306-15

Axially symmetric half-wave plates have been used to generate radially polarized beams that have constant phase in the plane transverse to propagation. However, since the retardance introduced by these waveplates depends on the wavelength, it is difficult to generate radially polarized beams achromatically. This paper describes a technique suitable for the generation of achromatic, radially polarized beams with uniform phase. The generation system contains, among other optical components, an achromatic, axially symmetric quarter-wave plate based on total internal reflection. For an incident beam with a constant phase distribution, the system generates a beam with an extra geometrical phase term. To generate a beam with the correct phase distribution, it is therefore necessary to have an incident optical vortex with an azimuthally varying phase distribution of the form exp( + iθ). We show theoretically that the phase component of radially polarized beam is canceled out by the phase component of the incident optical vortex, resulting in a radially polarized beam with uniform phase. Additionally, we present an experimental setup able to generate the achromatic, uniform-phase, radially polarized beam and experimental results that confirm that the generated beam has the correct phase distribution.
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http://dx.doi.org/10.1364/OE.22.003306DOI Listing
February 2014

Achromatic axially symmetric wave plate.

Opt Express 2012 Dec;20(28):29260-5

School of Biomedical Engineering, Saitama Medical University, 1397-1 Yamane, Hidaka, Saitama, 350-1241, Japan.

An achromatic axially symmetric wave plate (AAS-WP) is proposed that is based on Fresnel reflections. The wave plate does not introduce spatial dispersion. It provides retardation in the wavelength domain with an axially symmetric azimuthal angle. The optical configuration, a numerical simulation, and the optical properties of the AAS-WP are described. It is composed of PMMA. A pair of them is manufactured on a lathe. In the numerical simulation, the achromatic angle is estimated and is used to design the devices. They generate an axially symmetric polarized beam. The birefringence distribution is measured in order to evaluate the AAS-WPs.
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http://dx.doi.org/10.1364/OE.20.029260DOI Listing
December 2012

Common-path achromatic interferometer-coronagraph: nulling of polychromatic light.

Opt Lett 2005 Sep;30(17):2224-6

Tokyo University of Agriculture and Technology, 2-24-16, Nakamachi, Koganei-shi, Tokyo, Japan.

A three-dimensional common-path interferometer is proposed, which can achromatically null out an on-axis source while it maintains the detectability of an off-axis source. A geometric phase in the three-dimensional interferometer introduces an achromatic pi-phase shift to the light from the on-axis source, such that destructive interference nulls out the axial light at one of the ports of the interferometer. Light from the off-axis source, which is exempt from the pi-phase shift, comes out from both ports with equal intensity. The common-path scheme makes the system highly immune to environmental disturbances.
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http://dx.doi.org/10.1364/ol.30.002224DOI Listing
September 2005