Gimbal Mirror Research Articles

Ruled surfaces generated by gimbaled mirrors: II. A comparative study of gimbaled mirrors with the dual axis galvanometric scanners for XY scanning.

The theory developed in the first part of this study [J. Opt. Soc. Am. A38, 1884 (2021)JOAOD60740-323210.1364/JOSAA.435621] is extended to an investigation of the ruled surface produced by a gimbaled mirror and its applications to formulate a new criterion that uses the base curve of the ruled surface as a reference scale to divide the scan field into near and far zones and to investigate ruled surfaces produced by the 1D mirror-scanning systems, such as the monogon, the polygon, and the galvanometric scanners as the special cases of that produced by a gimbaled mirror. Results obtained from the two applications described above lead to placing the ruled surface produced by scanners of different architectures on a platform and then bridging them up by the ruled surfaces they produced for a performance comparison. Although all these scanners may have very different scanning geometries and different application areas, there is one thing making them comparable: the key parameters of the ruled surfaces they produced. As an example, we compare the ray deviation power of a gimbaled mirror with that achievable by a dual galvo scanner for XY scanning by way of the key parameters of the ruled surfaces they produced.

Design of a Free Space Optical Communication System for an Unmanned Aerial Vehicle Command and Control Link

An electromagnetic immune Free Space Optical Communication (FSOC) system for an Unmanned Aerial Vehicle (UAV) command and control link is introduced in this paper. The system uses the scheme of omnidirectional receiving and ground scanning transmitting. It has a strong anti-turbulence ability by using a large area detector and short-focus lens. The design of omnidirectional communication improves the ability of anti-vibration and link establishment. Pure static reception has no momentum effect on the platform. The receiver is miniaturized under no use of a gimbal mirror system, beacon camera system, Four-Quadrant Photodetector (QPD) and multi-level lens system. The system can realize omnidirectional reception and the communication probability in 1 s is greater than 99.99%. This design strengthens the ability of the FSOC system, so it can be applied in the UAV command and control, the satellite submarine communication and other occasions where the size of the platform is restricted.

Multisensor Compressive Sensing for High Frame-Rate Imaging System in the THz Band

We present a compressive terahertz (THz) imaging system utilizing a sparse multisensor array to speed up the acquisition process. Spatially modulated object beam is captured with the multipixel array in the $k$ -space. The sparsity of the proposed array sensor is particularly attractive for heterodyne reception. To realize THz spatial light modulation, photoexcitation of a 420- $\mu$ m-thick silicon wafer illuminated by a commercial optical projector is used. To demonstrate multipixel data acquisition and compressive reconstruction, a gimbal mirror is used in conjunction with a single detector. The prototypical system is capable of recording data at two different Fourier points and can reconstruct 64 × 64 pixel image of a metallic aperture object by using 512 mask patterns at 690 GHz. We also demonstrate that the proposed approach is twice as fast as the single-pixel imager, which requires 1024 masks to achieve similar image quality.

Development of Multitarget Acquisition, Pointing, and Tracking System for Airborne Laser Communication

Cluster unmanned aerial vehicles (UAVs) are widely demanded. To achieve high rate and large capacity communication with cluster UAVs, one of the key but still challenge task is to perform multitarget acquisition, pointing, and tracking (APT) under complex airborne environment. To solve this problem, this paper gives one composite axis APT system for multitarget laser communication with cluster UAVs. The APT system consists of a gimbal mirror and piezoelectric fast steering mirrors (FSMs), which can achieve independent and synchronous control of multiple optical axes. The cascade control scheme is designed for the gimbal mirror and the H∞ controller is designed for the FSM. To further improve the control accuracy, the hysteresis compensator based on least square support vector machines (LS-SVM) is proposed. The pruning error minimization method of LS-SVM is applied to reduce the computational cost. The simulation studies validate the control performance of the multitarget APT system. Finally, the experimental prototype is developed. The experimental results further validate the effectiveness of the proposed multitarget APT system.

Transparent conductors for Mid-infrared liquid crystal spatial light modulators

Transparent conductors (TCs) are required for liquid crystal spatial light modulators (LC-SLMs) in order to set up an electric field across the LC layer. In the middle infrared (Mid-IR) range (λ = 2 to 5 μm), LC-SLMs can offer a low-cost, non-mechanical, random-access and compact alternative to the gimbaled mirrors used currently for Mid-IR laser beam-steering. Indium tin oxide (ITO) is the industry standard for applications in the visible spectrum but it performs poorly in the IR, with a transmittance <20% for Mid-IR wavelengths. Little work has been done to develop a comparable material which fulfils the required properties in the Mid-IR: A sheet resistance allowing operation at typical frequencies (≈1 kHz) and, if patterned, with minimal voltage drop along the electrode, a transmittance >50% in the target range, chemical, thermal and mechanical robustness which can endure subsequent processing, and ability to be patterned at low-cost to a resolution comparable to the wavelengths investigated. Ni and Cu ultra thin metallic films (UTMFs), CuxO thin films (TFs), and chemical vapour deposition (CVD) grown mono-layer graphene were investigated. Ni UTMFs and graphene were found to have the best performance with sheet resistance values of 747±86Ω/□ and 360±34Ω/□ respectively for samples having a transmittance of 65% and 97% at λ = 2.3 μm. Both Ni UTMFs and CVD mono-layer graphene were found to be suitably stable with age. An increase of sheet resistance after baking was recorded due to oxidation and desorption of contaminating dopants respectively. Ni UTMFs were found to be patternable down to a 3 μm resolution, limited by the mask, using a standard photo-lithographic lift-off process. Transmissive LC cells with a maximum phase shift of 3π at λ = 2.3 μm were assembled with both Ni UTMFs and mono-layer graphene as TCs on sapphire, with the former having transmittance of 18.7% and contrast ratio of 25.0, and the latter having transmittance of 81.1% and contrast ratio of 50.7.

飛翔鳥の光学的追跡撮影装置の開発

We developed a video recording equipment with the capability of tracking moving objects optically and used it to track flying birds near an airport. In front of the lens of the video camera, a servo-motor-controlled gimbal mirror having 2 degrees of freedom was installed in order to redirect the optical axis of the camera. The images captured by the camera was processed in real time and the mirror direction was updated so that the center of the object stays in the middle of the image frame. We demonstrated this equipment near Haneda Airport. The image of the bird was maintained within approximately ±0.27 degrees from the center of the image frame.

Development of Motorized Slewing Mirror Stage for the UFFO Project

The Ultra-Fast Flash Observatory (UFFO) is a space observatory for optical follow-ups of gamma ray bursts (GRBs), aiming to explore the first 60 seconds of GRBs optical emission. UFFO is utilized to catch early optical emissions from GRBs within few sec after trigger using a Gimbal mirror which redirects the optical path rather than slewing entire spacecraft. We have developed a 15 cm two-axis Gimbal mirror stage for the UFFO-Pathfinder which is going to be on board the Lomonosov satellite which is to be launched in 2013. The stage is designed for fast and accurate motion with given budgets of 3 kg of mass and 3 Watt of power. By employing stepping motors, the slewing mirror can rotate faster than 15 deg/sec so that objects in the UFFO coverage (60 deg × 60 deg) can be targeted in ~1 sec. The obtained targeting resolution is better 2 arcmin using a close-loop control with high precision rotary encoder. In this presentation, we will discuss details of design, manufacturing, space qualification tests, as well as performance tests.

Electrostatically Actuated Two-Dimensional Optical Scanner Having a High Resonant Frequency Ratio of Fast/Slow Axes

Two-dimensional resonant optical scanners actuated by vertical electrostatic combs with a unique electrical isolation structure have been developed. The isolation on the movable frame surrounding 1mm-diameter gimbal mirror is made by trenching the top silicon layer of an SOI wafer with leaving the thick bottom layers. Thanks to the large mass of the frame, the resonant frequencies range in 65.0-89.2Hz for the frame and in 11.9-36.8kHz for the mirror in a 4mm×4mm chip. The resultant frequency ratio of the fast/slow axes reaches over 500 and such a high frequency ratio is utilized to display QVGA image by raster scanning of a laser beam.

Mosaic imaging with spatial light modulator technology

Diffractive wavefront control with spatial light modulator technology has been successfully demonstrated both as a means of steering optical wavefronts and for compensating large optical aberrations. We describe the use of a spatial light modulator operating as a programmable diffractive optic to record extended-field-of-view mosaic images centered about a large off-axis field angle. A gimbaled primary mirror allows the nominal viewing angle to be varied, and diffractive wavefront steering allows images to be acquired at discrete increments in the field angle about the nominal angle. Diffractive wavefront compensation corrects aberrations associated with the primary mirror orientation and changes in field angle introduced by diffractive wavefront steering. A time sequence of images recorded at discrete increments in the field angle is then digitally combined to create a high-pixel-count mosaic image. The effects of diffraction efficiency and wavelength-dependent wavefront errors on image quality are analyzed.

In-orbit measurements of short term attitude and vibrational environment on the Engineering Test Satellite VI using laser communication equipment

Morio ToyoshimaNational Space Development Agency ofJapan2-2-1 SengenTsukuba, Ibaraki 305-8505JapanE-mail: toyoshima.morio@nasda.go.jpKenichi ArakiCommunications Research Laboratory4-2-1 Nukui-KitamachiKoganei, Tokyo 184-8795JapanE-mail: araki@crl.go.jpAbstract. Angular microvibrations of platform jitter on a three-axisattitude-stabilized satellite are measured in space using an onboard la-ser communication terminal. Stable optical tracking control allows themeasurement of relative angular variations from the reference line ofsight of the optical link. The tracking accuracy in this measurement isless than 1 mrad rms. The angular variation and the drift rate on thesatellite are measured at a sampling rate of 500 Hz, and these data aredownlinked to a ground station via a satellite-to-ground optical commu-nication link. The power spectral density of the satellite microvibration iscalculated by a Fourier transform analysis. The frequency spectrum ofthe gimbal mirror’s angular variation is also obtained when the coarsetracking control is operational. The rms value agrees with the residualcoarse tracking error estimated before launch of the satellite. These re-sults will be useful for the future design of a tracking control loop foroptical communication systems.

Matrix Analysis of Gimbaled Mirror and Prism Systems*

This paper shows a general matrix method for analyzing systems of gimbaled mirrors, prisms, and ray projectors. The method shows how to find the gimbal angles which are necessary to ensure that a ray traversing the system obeys some requirement of collimation or orientation. Gimbal angles are considered to be the important measurement parameters, and more meaningful than the usual direction cosines. The methods apply to a large class of optical systems, including those in which gimbals are not specifically used. The gimbal concept will be found very useful in describing the orientation of images in prism systems, such as the peculiar behavior of a penta prism. A gimbal operator is defined and used throughout. The appendix contains a formal development of the mirror as a second-rank tensor together with important properties of prisms as products of mirror matrices.