Mirror Rotation Research Articles

Calibration and Validation of the TEMPEST-D CubeSat Radiometer

Temporal Experiment for Storms and Tropical Systems-Demonstration (TEMPEST-D) is a 6U CubeSat satellite with a cross-track scanning millimeter-wave radiometer measuring at five frequencies from 87 to 181 GHz. It employs a direct-detection architecture with InP HEMT monolithic microwave integrated circuit (MMIC) low-noise amplifiers and related new technologies. An end-to-end two-point external calibration is performed every 2-s rotation of the scanning mirror, based on observations of the cosmic microwave background and an internal blackbody calibration target, with three thermistors to monitor the target physical temperature. Corrections for antenna pattern effects and cross-scan biases based on prelaunch measured values were updated using data from an on-orbit calibration pitch maneuver. Validation of the observed brightness temperatures ( T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) is performed by comparing to coincident nonprecipitating ocean observations from five well-calibrated on-orbit instruments, including Global Precipitation Measurement (GPM) mission Microwave Imager (GMI) and four Microwave Humidity Sounder (MHS) sensors on board NOAA-19, MetOp-A, MetOp-B, and MetOp-C satellites. Absolute calibration accuracy is within 1 K for all channels, well within the 4-K requirement. Calibration precision, or stability over time, is within 0.6 K for all channels, also well within the 2-K requirement. The intrinsic noise of TEMPEST-D is lower than MHS, resulting in similar on-orbit noise equivalent differential temperatures (NEDTs), even though TEMPEST-D has a much shorter integration time of 5 ms as compared to 18 ms for MHS. As a result, although the TEMPEST-D radiometer is substantially smaller, lower power, and lower cost than similar current operational radiometers, it has comparable or better performance in terms of instrument noise, calibration accuracy, and calibration stability or precision.

Multi-particle finite-volume effects for hexagon tessellations

Correlation functions of gauge-invariant composite operators in mathcal{N} = 4 super Yang-Mills theory can be computed by integrability using triangulations. The elementary tile in this process is the hexagon, which should be glued by appropriately inserting resolutions of the identity involving virtual (“mirror”) magnons. We consider this problem for five-point functions of protected operators. At one-loop in the ’t Hooft coupling, it is necessary to glue three adjacent tiles which involves two virtual magnons scattering among each other. We show that the result can be simplified by using an adapted mirror rotation and employing appropriate summation techniques. The mirror-particle contributions then yield hyperlogarithms of weight two. Finally, we use these results to investigate braiding prescriptions introduced in earlier work on the problem.

Excess Relative-Intensity-Noise Reduction in a Fiber Optic Gyroscope Using a Faraday Rotator Mirror

The fiber optic gyroscope (FOG) suffers from the excess relative intensity noise (RIN) caused by the broadband light source, which significantly impacts the angular random walk (ARW) of the FOG. The existing suppression methods for the excess RIN usually require complex configuration or devices with big volume, and thus are not suitable for practical applications especially in small-sized FOGs. What is more, as the key parameters or components, that determine the practical suppression effects of the excess RIN, and the corresponding impacting mechanisms are not clarified, there is no efficient way in evaluating or optimizing the excess-RIN reduction configuration in practice. In this work, we propose a simple but effective method to achieve the reduction of the excess RIN at the demodulation frequency, in which a Faraday rotator mirror is inserted to the dead arm of the source coupler to realize the delay line filter for the excess RIN. Experimental results show that the ARW is improved from 1.70 mdeg/h <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> to 0.58 mdeg/h <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> for a navigation-grade FOG. More importantly, this work provides a comprehensive understanding on how the main defects in the excess-RIN reduction scheme impact the practical excess-RIN suppression effects both theoretically and experimentally, which demonstrates the inherent robustness of the proposed scheme against internal and external influencing factors. This method is especially suitable for realizing the excess-RIN reduction in small-sized FOGs and upgrading the existing FOG products with minimal modifications, and is also potentially referable in evaluating and optimizing other similar excess-RIN reduction schemes.

Mueller matrix ellipsometer using dual continuously rotating anisotropic mirrors

We demonstrate calibration and operation of a single wavelength (660 nm) Mueller matrix ellipsometer in normal transmission configuration using dual continuously rotating anisotropic mirrors. The mirrors contain highly spatially coherent nanostructure slanted columnar titanium thin films deposited onto optically thick gold layers on glass substrates. Upon rotation around the mirror normal axis, sufficient modulation of the Stokes parameters of light reflected at oblique angle of incidence is achieved. Thereby, the mirrors can be used as a polarization state generator and polarization state analyzer in a generalized ellipsometry instrument. A Fourier expansion approach is found sufficient to render and calibrate the effects of the mirror rotations onto the polarized light train within the ellipsometer. The Mueller matrix elements of a set of anisotropic samples consisting of a linear polarizer and a linear retarder are measured and compared with model data, and very good agreement is observed.

Rotationally Symmetric Lacunary Functions and Products of Centered Polygonal Lacunary Functions

This work builds upon previous studies of centered polygonal lacunary functions by presenting proofs of theorems showing how rotational and dihedral mirror symmetry manifest in these lacunary functions at the modulus level. These theorems then provide a general framework for constructing other lacunary functions that exhibit the same symmetries. These investigations enable one to better explore the effects of the gap behavior on the qualitative features of the associated lacunary functions. Further, two renormalized products of centered polygonal lacunary functions are defined and a connection to Ramanunjan’s triangular lacunary series is made via several theorems.

High thermal-stability Er-doped superfluorescent fiber source with a vertical cleaved fiber tail

Abstract Mean wavelength stability, a key indicator for evaluating the dynamic performance of Er-doped superfluorescent fiber source (ED-SFS) and high-precision fiber optic gyroscope (FOG), shows high sensitivity to environmental temperature fluctuations. In this paper, a thermally-stable ED-SFS in a one-stage backward configuration is proposed by incorporating a vertical cleaved fiber tail which acts as a Fresnel reflector. Our proposed method demonstrates a mean wavelength stability of 150 ppm and a scale factor error of 702 ppm. Comparing with alternative techniques such as Faraday rotator mirror (FRM) or fiber mirror (FM) over a 100 °C range (−40 °C to +60 °C), the wavelength stability and scale factor error are 105~120 ppm and 230~400 ppm less, respectively. The proposed ED-SFS has a spectral width (FWHM) of 37.682 nm and 10.42 mW output power, which satisfies the requirements of high-precision FOG.

Trace Hydrogen Sulphide Gas Sensor Based on Cu/rGO Membrane-Coated Photonic Crystal Fibre Michelson Interferometer

Abstract A novel Michelson interferometric hydrogen sulphide sensor coated with copper/reduced graphene oxide (Cu/rGO) composite membrane is proposed and fabricated. A section of endlessly photonic crystal fibre (EPCF) was sandwiched in two single-mode fibres (SMFs). One SMF was spliced and tapered with EPCF; the other SMF was connected with the Faraday rotator mirror to construct the Michelson structure. The cladding of the EPCF was coated by the Cu/rGO-sensing membrane, which was prepared by the dip-coating method. The obtained Cu/rGO-sensing film has a length of 25.0 mm. The fabricated sensing membrane is characterised by the scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and so on. Experimental results demonstrated that the Cu/rGO-sensing film has a 24.56-nm thickness with a compact and uniform appearance. The XPS and Raman spectra indicate that there are three elements (C, O, and Cu), which are consistent with the expected compositions of the Cu/rGO membrane. With the increase of concentration of hydrogen sulphide, the interference spectra appear red-shifted. The linearity of 0.97662 and the sensitivity of 13.23 pm/ppm are achieved. In addition, the dynamic response and recovery time of the sensor are approximately 70 and 88 s, respectively. The surface adsorption energies of the film are calculated by the density functional theory. The theoretical results are in good agreement with the experimental findings. This sensor has some key advantages of small size, simple structure, easy fabrication, and great applicability for detecting the trace hydrogen sulphide.

Holographic display having a wide viewing zone using a MEMS SLM without pixel pitch reduction.

A one-micron pixel pitch is believed to be required for spatial light modulators (SLMs) to realize holographic displays possessing a wide viewing zone. This study proposes the use of a microelectromechanical systems (MEMS) SLM for not only displaying holographic patterns but also scanning laser beam. During the rotation of MEMS mirrors in the MEMS SLM, the timing of laser pulses illuminating the MEMS SLM is controlled to change the reflection direction of light modulated by the MEMS SLM in order to enlarge the viewing zone. In this technique, the width of the viewing zone depends on the rotation angle of MEMS mirrors, and not on the pitch of pixels (MEMS mirrors). We experimentally demonstrated the enlargement of the viewing zone angle to ∼40° using the MEMS SLM with a pixel pitch of 13.68 µm.

Michelson Interferometric Hydrogen Sulfide Gas Sensor Based on NH2-rGO Sensitive Film

Abstract A highly sensitive hydrogen sulfide gas sensor based on NH2-rGO-coated thin-core-fibre (TCF) Michelson interferometer (MI) is proposed and evaluated. Two sections of TCFs are alternately sandwiched between three single-mode-fibres (SMFs). A Faraday rotator mirror (FRM) is fixed to the end of the last SMF to reflect the light signal and enhance the interference. Then the structure SMF-TCF-SMF-TCF-SMF-FRM (STSTS-F) is successfully constructed. NH2-rGO, as sensing film, is coated on two TCFs and is used to detect traces of hydrogen sulfide gas. Raman spectra and XPS analysis show that NH2-rGO has been successfully synthesised. The thickness of the NH2-rGO film coated on the TCF surface is about 500 nm. By introducing 0–60 ppm hydrogen sulfide gas into the chamber, with the increase in concentration of the gas, the monitoring trough exhibits a blue shift. Our experimental results show that the sensor has good linearity (R 2 = 0.98096) and selectivity for hydrogen sulfide gas. The sensitivity is 21.3 pm/ppm, and the response and recovery times are about 72 and 90 s, respectively. The sensor has the advantages of high sensitivity, high selectivity, and small size, enabling the detection of trace hydrogen sulfide in toxic gas environments.

Simultaneous measurement of strain and temperature based on a long-period fiber grating written on high birefringence photonic crystal fiber concatenated with a Faraday rotator mirror

Here we report simultaneous measurement of strain and temperature, carried out by incorporating a long-period fiber grating (LPFG) written on high birefringence photonic crystal fiber (HBPCF), referred to as an HBPC-LPFG, and a Faraday rotator mirror (FRM) concatenated in series with the LPFG. The HBPC-LPFG used as a sensor head was fabricated by irradiating CO2 laser pulses to unjacketed HBPCF with line-by-line technique. The HBPC-LPFG connected in series with the FRM exhibits a polarization-independent wavelength-dependent loss spectrum in its reflection spectrum, which has two resonance dips (RDs) with different cladding-mode orders, designated as RDs 1 and 2. As the two RDs in the fabricated HBPC-LPFG ended with the FRM have dissimilar cladding-mode orders, their strain sensitivities and their temperature sensitivities are different from each other. For the two RDs with resonance wavelengths of λ1 = ∼1470.5 nm and λ2 = ∼1495.1 nm, strain and temperature responses were investigated in an applied strain range from 0 to 1790 μe (step: 179 μe) and an ambient temperature range from 30°C to 95°C (step: 5°C), respectively. The strain sensitivities of the RDs 1 and 2 were measured to be approximately −0.77 and −1.07 pm / μe at room temperature, and the temperature sensitivities of the RDs 1 and 2 were measured as ∼10.44 and ∼8.56 pm / ° C without applied strain, respectively. Owing to their linear and independent responses to strain and temperature, strain and temperature changes applied to the HBPC-LPFG can be simultaneously estimated from the measured wavelength shifts of the RDs 1 and 2 using their predetermined strain and temperature sensitivities.

Dimensionality Reduction Method for 3D-Handwritten Characters Based on Oriented Bounding Boxes

Dimensionality reduction of 3D-handwritten characters can be problematic because of random mirror rotations and angle rotations which appear after using the traditional algorithms. In order to overcome the above drawbacks of the traditional methods, this study proposes a new algorithm for dimensionality reduction of 3D-handwritten characters based on oriented bounding boxes. First, we get a 3D discrete point set T and generate a 3D trajectory. Then, we apply an oriented bounding box model and determine the projection surface. Next, we perform three coordinate transformations, including (1) pre-transforming the 3D discrete point set T into the projection point set T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , (2) converting T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> to a two-dimensional point set T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> which has solved the problem of mirror rotation, and (3) converting T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> to a dimensionally reduced point set T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> which has solved the problem of angle rotation. Finally, we obtain a dimensionally reduced image without mirror and angle rotations. The experimental results confirm that the proposed method can not only obtain a better visual dimensionally reduced image, but also has a higher recognition rate than the conventional ones.

A Terahertz Imaging System with Rotation Mirror

In this article, a THz imaging system with rotation mirror is built. The system considers both imaging speed and cost of hardware. The transmission-mode design realizes miniaturization of the system. With the system, we are able to acquire image size of 60 × 80 mm2 in 60 seconds, while a raster-scan THz imaging system with the same hardware conditions needs more than 30 minutes. Moreover, internal information of object could be got with the THz imaging system reported in this article.

Absorbers with spin-selection based on metasurface

In recent years, due to their features nonexistent in natural matirials, the perfect absorbers based on metasurfaces have become a hot research point. Although great progress has been made, the absorbers with spin-selection are rarely reported. However, the absorbers with spin-selection have more widespread applications in chiral sensors and satellite communication. Therefore, a spin-selection absorber based on the metasurface with modified square split-ring structure is proposed. Firstly, the theoretical conditions for generating the spin-selection absorption are analyzed theoretically, and then the qualified metasurface unit cell is designed under the guidance of the theory. We design an asymmetric modified square split-ring resonator to break both the &lt;i&gt;n&lt;/i&gt;-fold (&lt;i&gt;n&lt;/i&gt;&gt;2) rotational symmetry and mirror symmetry. The unit cell is composed of three layers, i.e. the top layer, which is a modified square split-ring, the middle layer, which is an FR4 dielectric plate with a thickness of 4 mm, and the bottom layer, which is an all-metal plate acting as the reflecting incident wave. In order to obtain the optimal performance, the designed meta-atom is optimized by CST Microwave Studio, a well-known commercial full wave simulation software.The numerical simulation results show that the unit cell can selectively absorb the right-handed circularly polarized waves and reflect left-handed circularly polarized waves at 7.2 GHz. A maximum absorption rate for the absorption of right-handed circularly polarized (RCP) waves reaches a value higher than 90%, while the absorption rate of the other spin state is kept lower than 19%. In addition, to meet the need of practical applications, the absorption performance is also further investigated under different oblique incident angles, with the wave vectors confined in the &lt;i&gt;x-z&lt;/i&gt; plane and &lt;i&gt;y-z&lt;/i&gt; plane, respectively. Finally, to further understand the mechanism of spin-selection absorber, the surface current distributions are also simulated for LCP and RCP wave, respectively. The different surface current distributions are obtained for incident LCP and RCP wave, which is a solid evidence for spin-selection absorption. This paper offers a reference for the generation of spin-selection absorber. The proposed method not only is suitable for microwave region, but also can be extended to higher frequencies, and hopefully it can be widely used in the field of communication.

柱面镜旋转对整形光束远场焦斑的影响

柱面镜旋转对整形光束远场焦斑的影响

Residual stress birefringence of highly reflective mirrors with different numbers of layers.

Residual stress birefringence of highly reflective mirrors is a challenging problem due to its dubious origin and intricate nature. In this paper, the birefringences of highly reflective mirrors manufactured under the same deposition parameters but structured with different numbers of high- and low-refractive-index (HL) layer pairs are measured with the cavity ring-down technique by the mirror rotation method together with a differential loss approximation model. Experimental results show that birefringence retardation increases with the increasing number of HL layer pairs. Further measurements across the mirror surface indicate a non-uniform birefringence distribution, while curvature analysis of the stress-deformed surface provides more clues to the origins of birefringence.

Polarization influence and its mitigation on laser frequency noise measurement by a short-delayed self-homodyne interference method.

This paper investigated how a polarization state influences frequency noise measurement accuracy of the short-delayed self-homodyne interference method. An autopolarization control method was demonstrated to mitigate polarization-induced fading (PIF) in a 120-deg phase difference Mach-Zehnder Interferometer (MZI). This method used a feedback adjustment with simulated annealing algorithm, which had the advantages of a short control period, high accuracy, and easy implementation. Frequency fluctuations' power spectral density and linewidth results measured by the improved MZI were consistent with the results of the Michelson interferometer, which used the Faraday rotator mirrors (FRMs) to overcome PIF. The novel MZI structure is unrestricted to FRMs and can extend the capability of the short-delayed self-homodyne interference technique for many special bands' laser frequency noise measurements such as visible bands.

Refractive index measurement using OTDR-based ring-down technique with S fiber taper

We proposed and demonstrated a fiber loop ring-down (FLRD) sensor based on S fiber taper (SFT) cascaded with a Faraday rotator mirror (FRM) for refractive index (RI) measurement. The FLRD cavity is established conveniently by an optical time domain reflectometry (OTDR). The net loss of the cavity is modulated by the RI-sensitive SFT. The surrounding refractive index (SRI) measurement can be realized by monitoring the slope of the ring-down pulses envelope. Owing to the compensation provided by the erbium-doped fiber amplifier (EDFA), the ring-down pulses signal of the OTDR-based FLRD cavity is improved effectively. Within the measurement range of 1.3330∼1.3518, the proposed sensor has a linear response to the SRI with a sensitivity of 2646.307 dB/(kmRIU) at the interrogating wavelength of 1550 nm. Compared with the conventional FLRD sensors, the proposed OTDR-based RI sensor has the advantages of simple design and reflective sensing structure, which is easily implementable and cost-effective.

Passive harmonic mode-locked ytterbium-doped fiber laser with chirped pulse amplification

A passive harmonic mode-locked ytterbium-doped fiber laser with all-normal dispersion has been demonstrated. The mode-locking mechanism of the laser is based on the interaction between semiconductor saturable absorber mirror and nonlinear polarization rotation. The repetition rate of the laser is adjustable from 7.91 MHz to 31.65 MHz. Via the chirped pulse amplification, the 1 ps mode-locked pulse at the fundamental repetition rate of 7.91 MHz is compressed to 720 fs with single pulse energy of 12.6 nJ.

Modeling and characterization of a dual-wavelength SOA-based single longitudinal mode random fiber laser with tunable separation

In this work, a novel Single longitudinal mode (SLM) dual-wavelength random fiber laser (DW-RFL) with narrow line-width and tunable separation between the two modes in the range 1.5 – 25 nm (187 GHz – 3.12 THz) is presented. The laser is based on Rayleigh backscattering in a standard single mode fiber of 2 km length acting as distributed mirrors and a semiconductor optical amplifier (SOA) acting as the optical amplifier. Two optical band pass filters are used for the wavelength selection, and two Faraday Rotator mirrors are used to sustain the stability of the two lasing wavelengths against fiber random birefringence. The measured line-width of each mode of the laser varies from 3 to 11.5 kHz with lasing wavelengths and SOA pump currents. The power and the wavelength stabilities at the peak power of each mode were also investigated.

Wideband polarizers, switches and waveguide for overmoded corrugated transmission lines

Overmoded corrugated waveguide is efficient at transmitting power over a large frequency bandwidth. This operational flexibility becomes important in multi-frequency systems. For 50-mm diameter aluminum corrugated waveguide nominally designed for the ITER 170 GHz ECH system, the theoretical ohmic loss of the HE11mode is around 0.3e-3 dB/m. In a possible dual-frequency system at ITER, the theoretical loss in the same waveguide increases to a manageable 0.8e-3 dB/m at 104 GHz. As examples of other wideband components, General Atomics has built several pairs of 63.5-mm diameter waveguide polarizers for the TCV tokamak’s ECH transmission line that are designed to operate for 1 MW at frequencies ranging from 82.6 to 118 GHz. In addition, polarizers have been designed for ITER’s 50-mm diameter transmission line. A computer code that calculates both the required mirror rotation angles and the ohmic losses predicts that these polarizers will function effectively at both 170 GHz and 104 GHz. A new class of wideband waveguide switches with rotary actuators have been supplied for the 82.6–126 GHz transmission lines at TCV, further emphasizing the broadband capabilities of corrugated waveguide components.