Simple Optical Arrangement Research Articles

Spectrally multiplexed Hong-Ou-Mandel interference with weak coherent states.

We explore the suitability of a virtually imaged phased array as a spectral-to-spatial mode-mapper (SSMM) for applications in quantum communication such as a quantum repeater. To this end, we demonstrate spectrally resolved Hong-Ou-Mandel (HOM) interference with weak coherent states (WCSs). Spectral sidebands are generated on a common optical carrier, and WCSs are prepared in each spectral mode and sent to a beam splitter followed by two SSMMs and two single-photon detectors, allowing us to measure spectrally resolved HOM interference. We show that the so-called HOM dip can be observed in the coincidence detection pattern of matching spectral modes with visibilities as high as 45% (maximum 50% for WCSs). For unmatched modes, the visibility drops significantly, as expected. Due to the similarity between HOM interference and a linear-optics Bell-state measurement (BSM), this simple optical arrangement figures as a candidate for the implementation of a spectrally resolved BSM. Finally, we simulate the secret key generation rate using current and state-of-the-art parameters in a measurement-device-independent quantum key distribution scenario and explore the trade-off between rate and complexity of a spectrally multiplexed quantum communication link.

Engraving Depth‐Controlled Nanohole Arrays on Fused Silica by Direct Short‐Pulse Laser Ablation

AbstractPeriodic nanohole arrangements constitute an important building block of advanced photonic devices. Aside from standard nanofabrication tools, a direct laser‐based approach is introduced here, that enables single‐step and point‐by‐point machining of arrays of holes with subwavelength diameters and depths reaching several micrometers at the surface of fused silica. The method relies on a simple optical arrangement including an axicon combined with an amplitude mask to shape the laser intensity in appropriately truncated micro‐Bessel beams of adjustable length. The suitability and limitations of the technique are investigated to fabricate arrays of cylindrical nanoholes with tunable depths. In particular, the challenge of avoiding crosstalk effects during the laser‐writing process of high‐density arrays is explored. The achievability of square arrays of nanoholes at the surface of fused silica, with diameters down to 200 nm and variable depths from 3 to 20 µm at a spatial density defined by a pitch of 1.5 µm is demonstrated. The performance level shows the potential of the direct‐laser‐processing method towards the realization of integrated devices, offering a highly flexible and cost‐effective alternative technique to current nanofabrication methods.

Spatially multiplexed femtosecond/picosecond coherent anti-Stokes Raman scattering for multipoint array measurements.

A novel, to the best of our knowledge, method for multipoint hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering measurements is presented. The pump/Stokes and probe beams are each split into 16 discrete points with 90 and 24 µJ/pulse, respectively, using simple diffractive optical elements, which are used in combination with a focusing lens and narrowband spectral amplifier for 1 kHz excitation along a linear array of probe volumes. Single-shot and averaged temperature and O2/N2 profile measurements are demonstrated along a line with 1 mm spacing in room temperature and heated N2 flows. This enables measurements over varying spatial extents for 1D profiles and potentially 2D grids in a simple and compact optical arrangement.

Three-dimensional imaging of biological cells using surface plasmon coupled emission.

.SignificanceBiological cell imaging has become one of the most crucial research interests because of its applications in biomedical and microbiology studies. However, three-dimensional (3D) imaging of biological cells is critically challenging and often involves prohibitively expensive and complex equipment. Therefore, a low-cost imaging technique with a simpler optical arrangement is immensely needed.AimThe proposed approach will provide an accurate cell image at a low cost without needing any microscope or extensive processing of the collected data, often used in conventional imaging techniques.ApproachWe propose that patterns of surface plasmon coupled emission (SPCE) features from a fluorescently labeled biological cell can be used to image the cell. An imaging methodology has been developed and theoretically demonstrated to create 3D images of cells from the detected SPCE patterns. The 3D images created from the different SPCE properties at the far-field closely match the actual cell structures.ResultsThe developed technique has been applied to different regular and irregular cell shapes. In each case, the calculated root-mean-square error (RMSE) of the created images from the cell structures remains within a few percentages. Our work recreates the base of a circular-shaped cell with an RMSE of . In addition, the images of irregular-shaped cell bases have an RMSE of . Finally, we obtained a 3D image with an RMSE of for a random cellular structure.ConclusionsDespite being in its initial stage of development, the proposed technique shows promising results considering its simplicity and the nominal cost it would require.

Phase Diversity-Based Fourier Ptychography for Varying Aberration Correction

Fourier ptychography (FP) is geared toward high-resolution imaging with a large field of view efficiently. In the original illumination-based FP scheme, the aberrations in optical systems can be well reconstructed, which plays a prominent role in simple and compact optical arrangements. Unfortunately, the reconstruction strategy for recovering an optical system’s pupil function fails to carefully consider the nature of the field-dependent pupil function in the aperture-scanning FP scheme, which affects the quality of the reconstructed image to a certain extent. Based on this observation, we report a phase diversity-based FP (PDFP) scheme for varying aberration correction. We image USAF resolution target with the proposed PDFP scheme and demonstrate our ability to correct varying aberration and improve image quality. The reported approach allows aperture-scanning FP technology to use simpler optical systems for imaging and may facilitate the further development of FP in practical applications such as industrial inspection and long-distance imaging.

High-precision surface parallelism measurement using digital image correlation method

An improved touch-trigger probe method for surface parallelism measurement is proposed, which enables conventional mechanical probe-based detection techniques to evaluate the surface parallelism degree with higher accuracy. The distance detection of the sensing probe is equipped with a simple optical arrangement associated with the digital image correlation method to perform submicron accuracy measurements. The optical arrangement consists only of an inexpensive USB digital microscope. A feasibility study of the measurement method was carried out by measuring three gauge blocks with known parallelism deviations. The experimental setup for the measurement of parallelism error of gauge blocks is described in detail. The experimental results using the proposed method are in good agreement with those certified by the supplier. It has been confirmed that the final accuracy of the developed system could be able to reach the submicron level and meet the requirement of the metrology. In addition, this system is simple to manufacture, low in cost, and easy to operate.

Full-field Fourier ptychography (FFP): Spatially varying pupil modeling and its application for rapid field-dependent aberration metrology

Digital aberration measurement and removal play a prominent role in computational imaging platforms aimed at achieving simple and compact optical arrangements. A recent important class of such platforms is Fourier ptychography (FP), which is geared toward efficiently creating gigapixel images with high resolution and large field of view (FOV). In current FP implementations, pupil aberration is often recovered at each small segment of the entire FOV. This reconstruction strategy fails to consider the field-dependent nature of the optical pupil. Given the power series expansion of the wavefront aberration, the spatially varying pupil can be fully characterized by tens of coefficients over the entire FOV. With this observation, we report a Full-field Fourier Ptychography (FFP) scheme for rapid and robust aberration metrology. The meaning of “full-field” in FFP is referred to the recovery of the “full-field” coefficients that govern the field-dependent pupil over the entire FOV. The optimization degrees of freedom are at least two orders of magnitude lower than the previous implementations. We show that the image acquisition process of FFP can be completed in ∼1 s and the spatially varying aberration of the entire FOV can be recovered in ∼35 s using a central processing unit. The reported approach may facilitate the further development of FP. Since no moving part or calibration target is needed in this approach, it may find important applications in aberration metrology. The derivation of the full-field coefficients and its extension for Zernike modes also provide a general tool for analyzing spatially varying aberrations in computational imaging systems.

Design of a Smartphone Platform Compact Optical System Operational Both in Visible and Near Infrared Spectral Regime

We report here the design of a low-cost and field portable smartphone-based compact optical system, which is suitable for applications in the visible (VIS)-near infrared (NIR) spectroscopic region. Using the universal serial bus-on the go protocol, the battery of the smartphone is used to power an external light-emitting diode, and its ambient light sensor (ALS) is used as a photo-detector. Using simple optical arrangements, a collimated light beam of a specific wavelength is allowed to pass through the sample solution, and the transmitted modulated light signal from the sample is received by the ALS of the smartphone. A custom built application “PhotoSense” has been developed, which configures the smartphone to measure intensity variation of the modulated signal into a readable form from the ALS sensor. Further using the same application, the field sensing data can be saved as a text file in the phone memory, and by using the communication facility, it can be shared anywhere in the world. The performance of the designed optical device has been evaluated for the VIS-NIR wavelength region of the incident light by measuring iron(II) and phosphate concentrations in water medium. The sensitivity of the device in measuring iron(II) and phosphate concentrations is found to be in terms of absorbance unit (AU) as 0.189 and 0.274 AU/(mg.L−1), respectively. The limit of detection of the proposed device is found to be 0.053 and 0.069 mg.L−1 for both the analytes.

Optical Method for Estimating the Chlorophyll Contents in Plant Leaves.

This work introduces a new vision-based approach for estimating chlorophyll contents in a plant leaf using reflectance and transmittance as base parameters. Images of the top and underside of the leaf are captured. To estimate the base parameters (reflectance/transmittance), a novel optical arrangement is proposed. The chlorophyll content is then estimated by using linear regression where the inputs are the reflectance and transmittance of the leaf. Performance of the proposed method for chlorophyll content estimation was compared with a spectrophotometer and a Soil Plant Analysis Development (SPAD) meter. Chlorophyll content estimation was realized for Lactuca sativa L., Azadirachta indica, Canavalia ensiforme, and Lycopersicon esculentum. Experimental results showed that—in terms of accuracy and processing speed—the proposed algorithm outperformed many of the previous vision-based approach methods that have used SPAD as a reference device. On the other hand, the accuracy reached is 91% for crops such as Azadirachta indica, where the chlorophyll value was obtained using the spectrophotometer. Additionally, it was possible to achieve an estimation of the chlorophyll content in the leaf every 200 ms with a low-cost camera and a simple optical arrangement. This non-destructive method increased accuracy in the chlorophyll content estimation by using an optical arrangement that yielded both the reflectance and transmittance information, while the required hardware is cheap.

Balanced-path homodyne I/Q-interferometer scheme with very simple optical arrangement using a polarizing beam displacer.

A new balanced-path homodyne I/Q-interferometer scheme using a specially designed polarizing beam displacer (PBD) is described. The PBD is designed for splitting the s- and p-polarization components of the input beam into two parallel output beams which can be used as two beams of a balanced-path interferometer. The interferometer has a very simple optical arrangement because all of seven optical components used for interfacing two arms of the interferometer into the I/Q-demodulator in the previous schemes are replaced by the single PBD. A simple optical arrangement makes the interferometer less susceptible to environmental perturbations. It will be shown that the RMS fluctuations during a long-term phase noise measurement for 24 hours is ~7 × 10-5 rad. in an open lab environment. In addition, the separation between two arms of the interferometer is adjustable which makes the interferometer very flexible for many sensor applications. Potential use of our new interferometer as an interferometric sensor will be demonstrated by employing a displacement sensor arrangement.

Plasma airflow jets diagnosis by means of time-resolved tomography

A simple optical arrangement combining a single high-speed CCD camera and a set of mirrors has been setup to record simultaneously light intensity of atmospheric air plasma jet issued from multiple directions. The adopted approach is presented and its potential benefit to examine plasma emission in 3D is outlined. Rebuild local emission distributions are briefly analyzed for two typical jet exhibiting different flow structures.

Complete snapshot Stokes polarimeter based on a single biaxial crystal.

We propose a new complete snapshot Stokes polarimeter based on a single biaxial crystal. It presents different strengths (snapshot, complete polarimetric measurements, large data redundancy, and high sensitivity) in a simple and compact optical arrangement. The polarimeter is experimentally implemented and analyzed in terms of accuracy and repeatability.

In situ measurement of the effective nonlinear absorption order in multiphoton photoresists

AbstractKnowledge of the order of the effective nonlinear absorption in multiphoton photoresists is a key element in the development of improved materials for multiphoton absorption polymerization (MAP). The direct measurement of this nonlinearity has proven challenging. A new technique called 2‐beam initiation threshold (2‐BIT) is presented that allows for the unambiguous, in situ measurement of the order of the effective nonlinear absorption using a simple optical arrangement that can be employed with virtually any MAP setup. This technique is benchmarked using three common commercial photoinitiators that have been used previously in MAP and one common dye that acts as a photoinitiator. The linear absorption spectrum is demonstrated to be a poor predictor of the effective order of nonlinear absorption at a given wavelength. Surprisingly, for two of these initiators the effective nonlinear absorption process is dominated by 3‐photon absorption in the 800 nm wavelength range, suggesting that 2‐BIT is a valuable means of identifying initiators that can improve the resolution of MAP. image

Versatile and widely tunable mid-infrared erbium doped ZBLAN fiber laser.

We report on a long wavelength emitting rare earth doped fiber laser with the emission centered at 3.5 μm and tunable across 450 nm. The longest wavelength emission was 3.78 μm which is the longest emission from a fiber laser operating at room temperature. In a simple optical arrangement employing dielectric mirrors for feedback, the laser was capable of emitting 1.45 W of near diffraction limited output power at 3.47 μm. These emission characteristics complement the emissions from quantum cascade lasers and demonstrate how all infrared dual wavelength pumping can be used to access high lying rare earth ion transitions that have previously relied on visible wavelength pumping.

An Investigation into the Effect of Hydrodynamic Cavitation on Diesel using Optical Extinction

A conventional diesel and paraffinic-rich model diesel fuel were subjected to sustained cavitation in a custom-built high-pressure recirculation flow rig. Changes to the spectral extinction coefficient at 405 nm were measured using a simple optical arrangement. The spectral extinction coefficient at 405 nm for the conventional diesel sample was observed to increase to a maximum value and then asymptotically decrease to a steady-state value, while that for the paraffinic-rich model diesel was observed to progressively decrease. It is suggested that this is caused by the sonochemical pyrolysis of mono-aromatics to form primary soot-like carbonaceous particles, which then coagulate to form larger particles, which are then trapped by the filter, leading to a steady-state spectral absorbance.

Simultaneous Measurement of In-Plane and Out-of-Plane Deformations Using Dual-Beam Spatial-Carrier Digital Speckle Pattern Interferometry

Digital speckle pattern interferometry (DSPI) is an advanced technique for both in-plane and out-of-plane deformation measurements of diffuse surfaces in nanoscale. It has been widely used in aerospace engineering and other high-tech industries due to the advantages of non-contact, high-accuracy and full-field measurement. Traditionally, DSPI uses temporal phase shifting method to achieve precise deformation measurement, but it is only suitable for quasi-static deformation. Spatial-carrier method is another effective phase retrieval method used in DSPI and its validity has been verified in some DSPI setups. DSPI with spatial-carrier method enjoys the advantages of simple optical arrangement, easy operation, and above all, high-speed measurement of deformation. This paper introduces a dual-beam spatial-carrier digital speckle pattern interferometry system, with which in-plane and out-of-plane deformations can be measured simultaneously as well as quickly. In the optical setup, two lasers are employed to illuminate the measured object with different illumination angles, and two single-mode fibers server as carriers to transmit the reference beams. In-plane and out-of-plane deformations can be obtained by combining the phase maps of both channels. Theoretical discussion and experimental analysis are both presented.

One-step Jones matrix polarization holography for extraction of spatially resolved Jones matrix of polarization-sensitive materials.

We propose, for the first time to our knowledge, a method for realizing one-step measurement of two-dimensional Jones matrix parameters of polarization-sensitive materials. This method could be called one-step Jones matrix polarization holography (JMPH). Our theoretical analysis and the experimental results demonstrate that a double-source polarization interferometer combined with angular multiplexing holography make it possible to realize one-step holographic measurements of four spatially resolved Jones matrix parameters. Compared with the existing methods, our one-step JMPH has a simpler optical arrangement and easier measuring procedure. We believe that it will provide a new approach for development of an integrated system suitable for measuring, in real-time, a Jones matrix or transmittance matrix, as well as dynamic polarization imaging.

An experimental investigation into the effect of hydrodynamic cavitation on diesel

Samples of commercial diesel were subjected to 40 h of intense cavitation flow across a diesel injector in a specially designed high-pressure recirculation flow rig. Changes to the optical absorption and scattering properties of the diesel over time were identified by the continuous measurement of spectral extinction coefficients at 405 nm by means of a simple optical arrangement. Identical diesel samples were maintained at 70 °C for 40 h in a heated water bath, in order to distinguish the effects of hydrodynamic cavitation and temperature on the cavitated diesel samples. The commercial diesel samples subjected to high-pressure cavitation flow and water bath heating revealed a response to the flow and temperature history that was identified by an increase in the optical extinction coefficients of the cavitated and heated samples. The contribution of cavitation flow and temperature to the variation in spectral extinction coefficient was identified. It was concluded that the increases observed in the spectral extinction coefficients of the cavitated commercial diesels were caused by the cavitation affecting the aromatics in the commercial diesel samples.

Particle Size Measurements Using a New Signal Processing Method

Transmission fluctuation spectrometry (TFS) is a new method for particle analysis based on the statistical fluctuations of a transmission signal. With simple optical arrangement and easy operation, the method can be applied to real-time, online measurements. The transmission signal with fluctuations are analyzed by using 1st order band-pass filters, and the experimental data in the frequency domain are obtained. The particle size distribution (PSD) and particle concentration are extracted from the experimental data with the modifed Chahine interations. It is found that the measurements using band-pass filters are of better resolution in the PSD than those with low-pass filters.

Development of thin-film tunable band-pass filters based hyper-spectral imaging system applied for both surface enhanced Raman scattering and plasmon resonance Rayleigh scattering

We describe the development of a hyper-spectral imaging (HSI) system composed of thin-film tunable band-pass filters (TF-TBPFs) and its application to inhomogeneous sample surfaces. Compared with existing HSI systems, the system has a simpler optical arrangement and has an optical transmittance of up to 80% owing to polarization independence. The HSI system exhibits a constant spectral resolution over a spectral window of 80 nm (530 to 610 nm) and tunable spectral resolution from 1.5 to 3.0 nm, and requires only 5.4 s per measurement. Plasmon resonance and surface enhanced Raman scattering (SERS) from inhomogeneous surfaces dispersed with Ag nanoparticles (NP) have been measured with the HSI system. The measurement of multiple Ag NPs is consistent with conventional isolated NP measurements as explained by the electromagnetic mechanism of SERS, demonstrating the validity of the HSI system.