Corner Cube Reflector Research Articles

Remote Motion Control of Micro Vehicles by Two-Way Laser Communication Technology

A novel remote-control method for micro vehicles based on two-way laser communication is proposed. The vehicle receives operational commands in the frequency changes of a pulsed-laser. The laser also plays a role in tracking the vehicle by following the position of a corner-cube reflector equipped on the vehicle. At the same time, the vehicle returns information by means of a MEMS mirror equipped on the vehicle; the mirror transmits information as frequency changes in the light-path vibrations of the reflected laser-beam. The advantage of this system is that the all of these communication functions are achieved by a single laser beam; and the proposed method will contribute to simplify the mechanism and reduce the weight of micro vehicles. An experiment with a small wheeled-vehicle was conducted, and the results show that the concept exhibits a sufficiently accurate performance to control micro vehicles.

Effect of face separation in corner-cube reflectors

We explore the effect of separation between the faces of a corner-cube reflector on its performance. This is important because, in several retroreflector applications, one (or more) face of the module is some type of modulator. The fabrication and assembly of these modules invariably results in, or requires, gaps between the faces. A two-dimensional aperture optical model is developed to analyze the effect of this separation on performance. A geometric optics approach is used to evaluate the consequence of the separation on the effective retroreflection area. Diffraction effects are then included to provide a complete model of the corner cube retroreflector (CCR). The results show that the separation-to-face length ratio (δ/L) is an important parameter in maximizing performance of the retroreflector module. We show that an increasing δ/L results in a rapid reduction in the retroreflected power. A CCR illuminated along the body-center direction, which yields the highest effective area, sees a 58% reduction in retroreflected power when δ/L=0.2. Consequently, the field of view of the retroreflector reduces significantly. On the basis of this work, we propose that an effective triface retromodulator could be a GaAs-on-Si modulator grown on a silicon precision corner-cube array, thus filling the entire surface with active material.

The Typical Flight Performance of Blowflies: Measuring the Normal Performance Envelope of Calliphora vicina Using a Novel Corner-Cube Arena

Despite a wealth of evidence demonstrating extraordinary maximal performance, little is known about the routine flight performance of insects. We present a set of techniques for benchmarking performance characteristics of insects in free flight, demonstrated using a model species, and comment on the significance of the performance observed. Free-flying blowflies (Calliphora vicina) were filmed inside a novel mirrored arena comprising a large (1.6 m1.6 m1.6 m) corner-cube reflector using a single high-speed digital video camera (250 or 500 fps). This arrangement permitted accurate reconstruction of the flies' 3-dimensional trajectories without the need for synchronisation hardware, by virtue of the multiple reflections of a subject within the arena. Image sequences were analysed using custom-written automated tracking software, and processed using a self-calibrating bundle adjustment procedure to determine the subject's instantaneous 3-dimensional position. We illustrate our method by using these trajectory data to benchmark the routine flight performance envelope of our flies. Flight speeds were most commonly observed between 1.2 ms−1 and 2.3 ms−1, with a maximum of 2.5 ms−1. Our flies tended to dive faster than they climbed, with a maximum descent rate (−2.4 ms−1) almost double the maximum climb rate (1.2 ms−1). Modal turn rate was around 240°s−1, with maximal rates in excess of 1700°s−1. We used the maximal flight performance we observed during normal flight to construct notional physical limits on the blowfly flight envelope, and used the distribution of observations within that notional envelope to postulate behavioural preferences or physiological and anatomical constraints. The flight trajectories we recorded were never steady: rather they were constantly accelerating or decelerating, with maximum tangential accelerations and maximum centripetal accelerations on the order of 3 g.

Spectral behavior of a terahertz quantum-cascade laser

In this paper, the spectral behavior of two terahertz (THz) quantum cascade lasers (QCLs) operating both pulsed and cw is characterized using a heterodyne technique. Both lasers emitting around 2.5 THz are combined onto a whisker contact Schottky diode mixer mounted in a corner cube reflector. The resulting difference frequency beatnote is recorded in both the time and frequency domain. From the frequency domain data, we measure the effective laser linewidth and the tuning rates as a function of both temperature and injection current and show that the current tuning behavior cannot be explained by temperature tuning mechanisms alone. From the time domain data, we characterize the intrapulse frequency tuning behavior, which limits the effective linewidth to approximately 5 MHz.

22 Years of AJISAI spin period determination from standard SLR and kHz SLR data

Satellite Laser Ranging (SLR) is a powerful and efficient technique to measure spin parameters of satellites equipped with corner cube reflectors. We obtained spin period determination of the satellite AJISAI from SLR data only: 17246 pass-by-pass estimates from standard 1–15 Hz SLR data (14/Aug/1986–30/Dec/2008) and 1444 pass-by-pass estimates (9/Oct/2003–30/Dec/2008) from data of the first 2 kHz SLR system from Graz, Austria. A continuous history of the slowing down of AJISAI spin is derived from frequency analysis, and corrected for the apparent effects. The apparent corrections, elaborated here, allowed very accurate determination of AJISAI initial spin period: 1.4855 ± 0.0007 [s]. The paper identifies also non-gravitational effects as a source of the periodical changes in the rate of slowing down of the satellite.

Imaging quality of a retroreflective screen in head-mounted projection displays

A retroreflective screen composed of miniature corner cube reflectors (CCRs) or microbeads redirects an incident ray in the reverse direction. Recently the retroreflective screen was utilized as a key element in head-mounted projection displays (HMPDs). Most prior efforts in developing the HMPD technology have been focused on optimizing the optical design of the projection optics, neglecting the imaging artifacts caused by the screen. Few efforts have been attempted to analyze and evaluate the overall image quality of the HMPD system with the presence of a retroreflective screen. This paper first applies a ray-tracing method to examine the imaging properties of a single CCR. Through the combination of both the geometrical imaging effect and the diffraction effect, the imaging properties of a CCR-based retroreflective screen are analyzed and characterized. Based on these analytical results, the paper further evaluates how the imaging artifacts of a retroreflective screen degrade the spatial resolution of an HMPD system and limit the tolerance range of the distance from an HMPD user to the screen. Finally, a discussion is employed to illustrate potential techniques in minimizing the image quality degradation through the optimization of the corner cube size in a retroreflective screen.

10 Years of LAGEOS-1 and 15 years of LAGEOS-2 spin period determination from SLR data

Satellite Laser Ranging (SLR) stations measure distance to the satellites equipped with Corner Cube Reflectors (CCRs). These range measurements contain information about spin parameters of the spacecraft. In this paper we present results of spin period determination of two passive satellites from SLR data only: 10 years of LAGEOS-1 (10426 values), and 15 years of LAGEOS-2 (15580 values). The measurements have been made by standard 10 Hz SLR systems and the first 2 kHz SLR system from Graz (Austria). The obtained data allowed calculation of the initial spin period of the satellites: 0.61 s for LAGEOS-1 and 0.906 s for LAGEOS-2. Long time series of the spin period values show that the satellite’s slowing down rate is not constant but is oscillating with a period of 846 days for LAGEOS-1 and 578 days for LAGEOS-2. The results presented here definitely prove that the SLR is a very efficient technique able to measure spin period of the geodetic satellites.

Assembly of Micro-3-D Components on SOI Wafers Using Novel SU-8 Locking Mechanisms and Vertical One-Push Operation

A novel out-of-plane assembly technique of 3-D microstructures is proposed and demonstrated by using simple vertical one-push operations. This one-push method has large probe positioning tolerance in both vertical and lateral directions to reduce the overall complexity of the assembly process. Micromirrors and corner cube reflectors are fabricated on silicon-on-insulator wafers using SU-8 photoresist as a second structure layer in a low-temperature process. Batch assembly of multiple mirrors assembled simultaneously is demonstrated.

Application of a corner-cube reflector in nanosecond radar tomography

Experimental results are presented on the nanosecond radar application for test site tomography with radar calibration by a corner-cube reflector. It is demonstrated that the presence of the corner-cube reflector leads to the occurrence of false targets that can be used for detection of weakly reflecting targets.

Characterization of ICESat/GLAS waveforms over terrestrial ecosystems: Implications for vegetation mapping

ICESat/GLAS laser altimetry data have become increasingly utilized for vegetation mapping and canopy characterization. Waveform shapes are dependent upon complex relationships between several factors on the illuminated surface including topography, brightness, clouds, satellite pointing, laser energy, footprint size, shape and orientation, and vegetation height and position within the footprint. However, the understanding of these factors is presently unclear. We first examine the simple case introduced into the GLAS waveform by laser retro‐reflectors placed at White Sands, New Mexico, as a proxy for vegetation height detection. We observed that the 1/e2 energy distribution was only an approximation and that strong reflectors contribute to the returned energy beyond the estimated parameters. The precise position of the corner cube reflector within each footprint coupled with laser pointing angle is an important factor on the estimated vegetation height. Next we examine the implications of vegetation structure and surface topography on the waveform shape and derived elevations, compared with data from an airborne lidar system at Freeman Ranch, Texas, which has been targeted by ICESat since 2005. Small‐footprint waveforms were combined to synthesize the energy distribution within a GLAS footprint, and they compared well (>90% correlation) to the GLAS waveforms. The GLAS‐estimated canopy heights compared well (μ = 0.21 m) to the airborne lidar estimates during leaf‐on conditions. However, GLAS‐estimated ground elevations are biased by ∼1 m compared to airborne lidar in vegetated regions. In this landscape, the GLAS‐energy ratio (canopy‐to‐ground energy) was a good indicator (R2 = 0.74) of the amount of woody cover within the footprint.

Prospects in the orbital and rotational dynamics of the Moon with the advent of sub-centimeter lunar laser ranging

Lunar laser ranging (LLR) measurements are crucial for advanced exploration of the laws of fundamental gravitational physics and geophysics as well as for future human and robotic missions to the Moon. The corner-cube reflectors (CCR) currently on the Moon require no power and still work perfectly since their installation during the project Apollo era. Current LLR technology allows us to measure distances to the Moon with a precision approaching 1 mm. As NASA pursues the vision of taking humans back to the Moon, new, more precise laser ranging applications will be demanded, including continuous tracking from more sites on Earth, placing new CCR arrays on the Moon, and possibly installing other devices such as transponders, etc. for multiple scientific and technical purposes. Since this effort involves humans in space, then in all situations the accuracy, fidelity, and robustness of the measurements, their adequate interpretation, and any products based on them, are of utmost importance. Successful achievement of this goal strongly demands further significant improvement of the theoretical model of the orbital and rotational dynamics of the Earth–Moon system. This model should inevitably be based on the theory of general relativity, fully incorporate the relevant geophysical processes, lunar librations, tides, and should rely upon the most recent standards and recommendations of the IAU for data analysis. This paper discusses methods and problems in developing such a mathematical model. The model will take into account all the classical and relativistic effects in the orbital and rotational motion of the Moon and Earth at the sub-centimeter level. The model is supposed to be implemented as a part of the computer code underlying NASA Goddard’s orbital analysis and geophysical parameter estimation package GEODYN and the ephemeris package PMOE 2003 of the Purple Mountain Observatory. The new model will allow us to navigate a spacecraft precisely to a location on the Moon. It will also greatly improve our understanding of the structure of the lunar interior and the nature of the physical interaction at the core–mantle interface layer. The new theory and upcoming millimeter LLR will give us the means to perform one of the most precise fundamental tests of general relativity in the solar system.

Manufacturing of molds for replication of micro cube corner retroreflectors

Retroreflectors composed of micron-sized cube corner elements are widely used as reflectors on clothes for safety reasons or for measuring applications. Due to the small size of the individual reflector elements structured films can be flexed widely without affecting the geometry of each element too much so that it can still fulfill its function. However, the efficiency of triangle cube corner reflectors widely used today is limited. It could be improved by applying structures with a hexagonal shape resulting in a significantly better performance of the reflector. Up to now these structures are not machinable at micron size (50–500 μm) in sufficient quality. This paper introduces a new machining process, diamond micro chiselling, which is capable of generating these micro retroreflectors and other microoptic structure geometries not machinable so far.

基于可调谐半导体激光吸收光谱的开放光路气体传感器方法研究

Tunable diode laser absorption spectroscopy (TDLAS) is a new method to detect trace-gas qualitatively or quantificationally based on the scan characteristic of the diode laser to obtain the absorption spectroscopy in the characteristic absorption region. A time-sharing scanning open-path TDLAS system using two near infrared distributed feedback (DFB) tunable diode lasers is designed to detect CH4 and H2S in leakage of natural gas. A low-cost Fresnel lens is used in this system as receiving optics which receives the laser beam reflected by a solid corner cube reflector with a distance of up to about 60 m. High sensitivity is achieved by means of wavelength-modulation spectroscopy with second-harmonic detection. The minimum detection limits of 1.1 ppm·m for CH4 and 15 ppm·m for H2S are demonstrated with a total optical path of 120 m. The simulation monitoring experiment of nature gas leakage was carried out with this system. According to the receiving light efficiency of optical system and detectable minimum light intensity of detection, the detectable optical path of the system can achieve 1-2 km. The sensor is suitable for natural gas leakage monitoring application.

The SPQR experiment: detecting damage to orbiting spacecraft with ground-based telescopes

The objective of the Specular Point-like Quick Reference (SPQR) experiment was to evaluate the possibility of improving the resolution of ground-based telescopic imaging of manned spacecraft in orbit. The concept was to reduce image distortions due to atmospheric turbulence by evaluating the Point Spread Function (PSF) of a point-like light reference and processing the spacecraft image accordingly. The target spacecraft was the International Space Station (ISS) and the point-like reference was provided by a laser beam emitted by the ground station and reflected back to the telescope by a Cube Corner Reflector (CCR) mounted on an ISS window. The ultimate objective of the experiment was to demonstrate that it is possible to image spacecraft in Low Earth Orbit (LEO) with a resolution of 20 cm, which would have probably been sufficient to detect the damage which caused the Columbia disaster. The experiment was successfully performed from March to May 2005. The paper provides an overview of the SPQR experiment.

Output polarization states of a corner cube reflector irradiated at non-normal incidence

A method has been developed for determining the polarization state of the retro-reflected beam from a corner cube irradiated with an input beam of arbitrary polarization state and of arbitrary tilt angle to the cube. Experimentally, the output beam consists of six distinct beamlets of different polarization states that are focused into six non-overlapping regions in the active area of the detector. The overall polarization state of the beam as measured by the photodetector can thus be represented by the incoherent superposition of the polarization states of the six beamlets. Experiments have been performed that verify the theory for a linearly polarized input beam irradiating the corner cube.

Optically-Interrogated Zero-Power MEMS Magnetometer

A magnetic-field-sensing system that consists of a miniature zero-power magnetometer, an integrated micromachined corner-cube reflector (CCR), a commercially available diode laser, and a photodetector array, has been designed, fabricated, assembled, and tested. The zero-power-magnetometer design is based on a ferromagnetic MEMS magnetometer, which consists of a permanent magnet that is torsionally suspended to allow rotation about a single axis. A single mirror of the CCR is attached to the magnetometer torsion beam. When the magnet rotates in response to a change in magnetic field, the torsion beam will twist and cause the mirror to become misaligned. The non-ideality of the CCR can be interrogated with a laser and a photosensor array can be used to measure the reflected signal. This method of magnetic sensing completely eliminates sensor-node power consumed at the remote location. The sensor node developed for this paper occupies a volume of only 1.5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and can detect a magnetic field between 820 A/m to 6 kA/m with an uncertainty of 90 A/m at a 1-m optical-interrogation range. The primary application of this technology is in wireless sensing systems that must operate continuously without providing or maintaining the sensor-node energy (e.g., replacing batteries or scavenging energy) or in extremely harsh environments where power supplies and integrated circuits (IC) are not an option

Dynamic Response Modeling of MEMS Micromirror Corner Cube Reflectors With Angular Vertical Combdrives

A model for the dynamic response of microelectromechanical-systems micromirrors with angular vertical combdrive electrostatic actuators has been proposed based on a numerical solution of the nonlinear dynamic equations for torsional oscillation. The torque generated by the electrostatic drive is assumed to depend at least on the second order of the turn angle, and the model shows a shift in the resonant frequency with drive voltage, in agreement with the experimental results obtained from components fabricated by self-assembly of bonded silicon parts. The dynamic response of a corner cube reflector (CCR) based on a pair of scanning mirrors and a fixed mirror is predicted using the model, and the theoretical response agrees well with the experimental results. From the model, a small initial misalignment of the CCR mirrors can be determined

A novel plane mirror interferometer without using corner cube reflectors

The conception and properties will be introduced of an interferometer that exclusively uses plane mirrors as reflectors; thus, these interferometers correspond well to the original Michelson interferometer. First, the relationship between the interference conditions and the detection with photodiodes will be discussed using the example of known interferometers as well as reasons given for primarily using corner cube reflectors in these devices. Next, the conceptual design of the plane mirror interferometer will be presented. This type of interferometer possesses new properties which are significant for metrological and technical applications. Only one measuring beam exists between the polarizing beam splitter and the measuring mirror and this beam alone represents the Abbe axis. This property allows the significant reduction of the Abbe error. The interferometer is able to tolerate tilting on the order of about 1′. This ensures the orthogonality between the measuring beam and the measuring mirror during the measurement. This property can be used in three-dimensional measurements to erect the three measuring beams as a x–y–z Cartesian coordinate system on the basis of three orthogonal mirrors. The plane-mirror interferometer also allows non-contact measurements of planar and curved surfaces, e.g. silicon wafers.

Method for calibrating system parameters of a multidirectional interferometers system

A multidirectional interferometer system has been proposed and developed to measure the position and orientation of a positioning stage. In this method the system parameters, such as positions of the corner-cube reflectors and directions of the rays in the interferometers, must be determined beforehand. However, it is difficult to find ways to determine the system parameters for each different system with necessary accuracy. This paper proposes a systematic method for calibrating the system parameters when the number of the interferometers is larger than the degrees of freedom of the stage. The method is verified for a two-dimensional stage by both simulation and experiment.

Retroreflecting optical modulator using an MEMS deformable micromirror array

A modulating corner-cube reflector with one microelectromechanical-system (MEMS) mirror that deforms from a flat into a hexagonal array of concave reflective microlenses to disperse the retroreflected wavefront is demonstrated. It is shown that such retromodulators can operate under a wide range of wavelength and angle illumination using Huygens-Fresnel propagation analysis, and this analysis is verified using devices fabricated by surface micromachining. A gold-coated silicon-nitride membrane suspended over 1-mm-diameter circular cavities had a resonant frequency of 160 kHz and 0.55-/spl mu/m maximum deformation with 79 V applied. While this deflection was only 2/3 of the design value of 0.8 /spl mu/m, we measured an up to 7:1 modulation contrast ratio from a prototype retromodulator, which achieved 100-kHz modulation over a 100-nm optical bandwidth, a 35/spl deg/ range of incident angles, and temperatures ranging from 20 to 100/spl deg/C.