A laser scanning optical system using four isolated semiconductor lasers has been newly developed for a high- speed, high-resolution digital copier and printer. This system can synchronously scan four beams, so that it can form an electrostatic latent image on a photoconductive drum four times faster than a single beam optical system.

The fundamental considerations involved in the design of a print engine, or of a printer component such as a laser printhead, arise from visual acuity characteristics of the human visual system and from the physics of interaction of light with scattering/absorbing media. For production of gray-scale images, the visual system imposes strict limitations on unintended luminance variations, both in contrast magnitude and in spatial distribution. Unintended variations in size, spacing, and lightness of the picture elements composing the image are a major source of image degradation. Further, the scattering of light in a medium such as paper leads to the Yule-Nielsen Effect in which the surface luminance of paper between picture elements is altered in a non-linear way as pixel-to-pixel spacing or pixel size changes.

Presented herein is a model for a laser diode exhibiting not only electrical and radiant characteristics, but also the thermal characteristics of droop and crosstalk. Also presented is the model's implementation in SPICE simulation. A behavioral level laser diode model is developed using the SPICE ideal diode, a resistive/capacitive network, and SPICE's ability to accept mathematical relationships to describe simulation schematic components. Modeled were various electrical and thermal dynamic effects that occur during DC and transient operation. The resistive/capacitive network models the thermal resistance and capacitance within the laser diode. The instantaneous input power devoted to heating is separate from the power converted to radiant energy with a relational feedback loop. Equations are used to derive a `droop' current that arises from the heating. The effect of droop then is implemented by the subtraction of the `droop' current from the input driving current to yield an `effective' driving current into the modeled laser diode. The model's parameters are adjusted to achieve a performance match to electrical and radiant energy empirical data. The radiant energy is expressed accurately in magnitude and in units of mA rather than mW. Two parallel laser diode intensity control systems, each containing a laser diode model, are simulated. The two laser diodes were also connected in such a fashion as to model crosstalk between the two lasers. The model provided expected results over a wide range of bias and transient excitations from a step current to low and high duty cycle input pulses representing gray levels.

In this paper, a rigorous vector analysis is performed to investigate the asymmetry of dual beam scanning field produced by a rotating polygon. Some basic equations of dual beam scan are derived, such as, the position vector for the incident point, the scalar expression for reflected ray, scan pattern on observation plane etc. Based on these equations, the asymmetry of scan angle and velocity are discussed, and it is shown that the reduction of the incident angle (theta) _y, (theta) _y and the x₀/R_F, the increase of the number of polygon facets will decrease the asymmetry of scan angle. The small values of (theta) _y, x₀/R_F, P/R_F in a range of 1.3 approximately 1.6, and small scanning angle in near-field help to reduce the asymmetry of scan velocity.

A line scanning device for laser based High Definition Television applications is being developed at IOF. High speed scanning is achieved by a rotating polygonal mirror supported from two hemispherical aerodynamic bearings. For an operation of around 80 000 rotations per minute (rpm), balancing of the rotor to a high precision is necessary. We derive the balancing requirements from elementary considerations and describe in detail how balancing is performed. The method of balancing and the measurement equipment are presented. From the experimental results it is seen, that sufficient balancing for operation at target speed can be obtained within the Rigid Rotor Approximation. However, stability is not satisfactory without additional efforts. Therefore, an `elastic' balancing concept is presented, where mirror related unbalances are compensated on the part itself. Preliminary results within this approach show that stability of the system is improved. This opens up the possibility to significantly increase long term stability and confirms the basic design concept.

A new application of synchronously working micromachined silicon mirrors for a laser beam projection technique producing images on the whole circumference of a cylindrical shaped screen will be discussed within this contribution. The mechanically active mirror area of 12 square millimeters has been divided into 49 single mirrors in order to achieve both fast steering and light power distribution. Diffraction of the laser beam due to the regularly arranged mirrors and its influence to the contrast has been experimentally determined on a small sized projection system. Analytically calculated thermal effects on the mirror shape caused by light power dissipation and heat transfer correspond to the measurements by thermographic imaging and topographic metrology. Investigations concerning phase lag and amplitude difference between the mirrors lead to a design of specially shaped hinges with reduced sensitivity to the main fabrication tolerances.

The Risley optical scanning system consists of two sequential wedge prisms, which have wedge angles A₁ and A₂, that are capable of rotating about the optical scan axis at angular speeds (omega) ₁ and (omega) ₂. When a focused laser beam is directed along the optical scan axis and through the prisms, the emergent beam is deviated in a direction according to the relative orientation of the prisms with respect to each other. When the individual prisms are rotated clockwise or counterclockwise, the combined deviation angle and the orientation phase change with time, such that the image spot traces out a vector pattern. This paper presents an interesting set of generated scan patterns that include regular polygons by selecting particular values for the ratios of A₂/A₁ and (omega) ₂/(omega) ₁.

Two-axis scanning is generally accomplished using two separate single-axis scanners. In order to improve the functionality of a dual-axis scanning system and eliminate aperture transfer problems, MedCam, Inc. has developed a two-axis single deflector scanner using MEMS and micromachining techniques. Various configurations of the MedCam microscanner have demonstrated large scan angles at high scan rates with aperture diameters ranging from 1 mm to 10 mm. The scanner is extremely compact and may be used in small, portable applications.

Most laser projectors for LADAR systems are limited to small scan angles as they utilize acousto-optic devices, spatial light modulators, or fine-steering mirrors for beam steering. Additionally, the projected beam is usually circular and Gaussian. In order to improve the functionality of such systems, MEMS-based mirrors and diffractive optics may be used. This paper describes Digital Optics Corporation's work in developing and demonstrating a novel LADAR scanning system that incorporates a MEMS scanning mirror coupled with diffractive optical elements in a compact breadboard system. The MedCam MEMS mirror has been demonstrated with a 2D scan mode across large scan angles. The MEMS mirror system is experimentally compared to a Liquid Crystal Spatial Light Modulator based system. The diffractive elements generate spot arrays or other patterns that are more conductive to target detection schemes that an ordinary gaussian beam shape.

Currently VLSI foundries are pushing for small feature size and higher operating voltages. These ongoing developments in integrated circuit fabrication processes result in devices exhibiting excellent electrical performance, but poor optical quality. Increased reflectivity and planarization are necessary to produce high efficiency beam steering devices. Steps taken to improve optical performance of silicon backplanes will also be discussed.

We describe a design for an agile, electronically- configurable, optical beam steering array to be used in directional free-space transmission of optical signals. The proposed device employs a 1D array of tunable resonant transmissive modulators constructed from customized multi- layered stacks of dielectric materials. Each modulator may be individually configured to transmit an optical signal with a known amount of phase and group velocity modulation. Proper configuration of each individual modulator results in diffractive interactions between multiple modulator outputs, providing a method for directional optical signal transmission. Of particular focus within this paper is the design of the individual modulator. We generate custom transmission functions by varying the parameters describing the modulator's specific construction, such as number of layers within the multi-layer stack, refractive indices of stack materials, layer thickness, and combinations of periodic versus non-periodic layer repetitions. A computational optimization of the variables describing the stack's construction strives to maximize the amount of optical signal modulation obtainable within defined limits. Our optimization is based largely on maximizing transmitted phase delay. We discuss trade-offs between methods of increasing device performance versus practical limitations of fabrication technologies.

Phase Array Antennas provided angular scanning (beam steering) from fixed antenna structures. Photonics can accomplish the beam steering with improvements in size and weight along with the remoting benefits utilizing fiber optics. Photonic advantages include True Time Delay beam steering eliminating the beam squint imposed by phase shifted signals produced in an electronic implementation. Another benefit of beam steering is the ability to position nulls in the spacial pattern to reduce the interference signals. Hybrid circuits utilizing both photonic and electronic components take advantages of the best aspects of each technology. Various types of photonic implementations are included.

The banana mirror system is an alternative approach for the design of telecentric laser scanners with a large scan format instead of using an f-(theta) scan lens. We developed an analytical model describing the ideal banana scanner configuration, that consists of a converging beam which is deflected as a pure cone (generating a primary scan circle) and a combination of a hyperbolic and a parabolic cylindrical mirror. this model is called the Ideal Scanner Model (ISM). We will introduce the concept of conical deflection and present the basic features of the ISM theory.

Electrically-controlled diffractive gratings are developed on the basis of cholesteric liquid crystal confined between two transparent non-patterned electrodes. The electrodes are coated with alignment layers providing either planar or homeotropic anchoring. For planar alignment the applied electric field causes reorientation of initial (zero field) planar state and creates 1D modulated structures in the plane of the cell. The modulations occur via two distinct scenarios: (1) nucleation and expansion of `stripes' and (2) undulation of quasinematic layers in the plane normal to the cell's plates. the process (2) is faster since it does not require overcoming an energy barrier. In cells with homeotropic surface alignment modulated structures exist without applied voltage. Magnetic field is used to provide uniform orientation of these structures. Confocal microscope studies and 2D computer simulations are carried out to reveal the fine structure of the diffractive gratings.

This paper will introduce the benefits, operating ranges and recent advances in galvanometer technology for scanning applications. Several different actuator and position detector technologies and designs will be presented. This will include moving iron, moving coil and moving magnet actuators along with several capacitive and optical position detector designs that offer positioning speed as fast as 150 micro-seconds and positioning repeatability/resolution to a single microradian. The performance and system design trade- offs that one should consider during the selection of the appropriate galvanometer technology and the optical systems design will be discussed along with a performance comparison of the galvanometer to other optical scanning technologies.

This paper outlines the benefits and limitations of oscillating device methodologies, including tuning fork, taut band, and torsion rod designs. Issues relating to drive electronics, such as locking a resonant device to an external clock are also addressed. Design applications are exemplified and discussed.

This paper discusses the design considerations in the development of a high duty cycle sawtooth scanning system based on galvanometric scanner technology. The system is suitable for high definition television, data recording systems, imaging systems, and other important raster scanning applications. Test results show that the developed galvanometric scanner system can achieve a duty cycle above 80 percent while operating at 96 Hz with a mirror aperture of 32 mm and useable scan angle of 28 degrees.

Fast-steering mirrors, called FSMs, for short, and sometimes referred to as fine-steering or tip-tilt mirrors, are primarily two-axis devices originally developed for a variety of demanding air and space applications for line-of- sight pointing and beam stabilization. Ball Aerospace has been engaged in the design and development of fast-steering mirrors since 1983. In 1994, Ball began employing lessons learned from these one-of-a-kind custom units to develop a commercial line of low cost (< $DLR50 K), high- performance mirrors to serve the general optics community. This paper first provides a brief overview of our overall FSM development history and some successful applications. Next, our commercial FSMs are described along with performance specifications and test results. Parameters of interest discussed include bandwidth, acceleration, accuracy, reliability, and types of mirror substrates. Test results on two models of commercial 3-in mirrors demonstrating accuracies of < 1 (mu) rad, life and reliability > 10⁸ cycles, and the ability to endure high-level random vibration are presented.

Electro-optic (EO) scanners can be used as fine tracking actuators to improve the servo bandwidth in future high density/high data-rate optical disk drives. In this paper we report on the use of an EO scanner in a new optical tracking system. Track following has been accomplished with a servo bandwidth of 200 kHz and we have demonstrated track switching between nine tracks using only an EO scanner. A fine tracking experiment using an EO scanner has been demonstrated in parallel with a voice-coil actuated lens to expand the fine tracking range. Significant improvement in track switching speed and track following are demonstrated with the scanner/lens actuators as compared to tracking with the lens actuator alone.

Optical encoders are the most common means for measuring linear or rotary position. A photodetector senses the occlusion, reflection, or diffraction of light by a structure that moves linearly or rotates relative to a fixed light source. Counting the switching between `on' and `off' gives a measure of position, and velocity is determined through numerical differentiation. This paper proposes the use of an electrooptic beam scanner to improve the accuracy of the detection of both position and velocity, by scanning the light source across the moving structure and comparing the phase of the photodetector signal to the phase of the scan. The Doppler effect between the forward and backward scan can provide velocity information without numerical differentiation. A simple experiment for detecting the position of a razor edge demonstrates the concept for position.

Light beam deflection and modulation unit (LDMU) is an inherent part of any laser projection system. The acousto- optic devices are known as the most flexible and convenient ones among such units. As amount of information to be displayed in the projection system screen is one of the most important characteristics of LDMU, it is necessary to assign this characteristic to acousto-optic deflector-modulator and to estimate if for different versions of the devices. The way of information transmission through the acousto-optic modulation and deflection system has been observed in the present paper. The specific information characteristics of acousto-optic LDMU such as information transmission capability and information capacity, has been defined. Their dependence on such physical and technical parameters as resolving power, dynamic range, diffraction efficiency, and frequency bandwidth, has been established and studied. The experimental studies of 2D acousto-optic LDMU based on tellurium dioxide single crystals have shown that even broadcasting TV mode can be provided by a projection which using such kind of LDMU. It has also been shown that the maximum screen size depends only on the power of lasers, and is practically independent on the acousto-optic LDMU parameters.

The performance of modern infrared sensors is more likely to be limited by residual non-uniformity artifacts in the imagery, than by the performance of individual elements in the focal plane array. A highly effective method of achieving passive scene based non-uniformity correction in scanning forward-looking infrared sensors is described. A single optical element located in the afocal provides gain, offset and clamping functions on a continuous basis. It offers many advantages over current active and passive non- uniformity correction mechanisms. Several devices have been built and demonstrated.

In this paper we describe an approach and present results from a recently developed system that produces video-rate, 3D maps of the image space using a scanning laser configuration and a patented micro-channel plate intensified detector. The scene is viewed from a separate location to provide depth information via triangulation. The detector provides an estimate of position of the apparent landing spot of the laser beam for each scan angle from which a depth estimate is calculated. The system is designed to scan an approximate 15 X 15 degree field-of-view at distances from 1.5 to 2.5 meters with a resolution of 1.5 cm at rates of 10 - 30 full images per second, and can accommodate range gating to reduce scattered light interference.

A method of conversion of millimeter wave images to visual displays is the use of semiconductor panel under scanning light spot. In this method of conversion, the behavior of semiconductor panel under moving spot of light is important. Performance of this system has been under investigation for last three decades. In this paper excess millimeter wave attenuation through semiconductor panel, due to moving rectangular illuminated spot, with arbitrary intensity profile across the length of the spot is formulated. Numerical calculation is done, for uniform and linearly graded cases. Effects of scanning velocity and spot dimensions on the excess millimeter wave attenuation are considered. It is shown that, with proper choice of parameters, higher system resolution is attainable with linearly graded intensity.

A reduction in the distortion of a single facet mirror, rotating at high speeds, was sought using finite element methods of analysis (FEA). Improvements in geometry were constrained by the need to preserve the original single facet shape, prescribed principal diameters and method of spindle mounting. The aim was to reduce the out-of-balance forces/moments and to simplify the method of balancing. The approach was to model the effects of the removal of surplus mass, in a simple manner to suit machine manufacturing, whilst maintaining the desired mirror inclination and aperture. Attention was paid to assessing the accuracy of the FEA method by employing purely analytical methods where possible. To this end, analytical solutions were derived and mathematical routines were written in MATLAB to provide the appropriate checks. In particular, the calculation of the moments of inertia about the principal axes and the modeling of the high stress regions at the location of the balance weights, were examined in detail. The given geometry was assembled from three parts, namely, a mirror cylinder, a balance ring and a clamping lock-nut. In order to take account of the relative compliance between these parts, it was necessary to model the system as an assembly of contacting surfaces with appropriate interference forces. It was found that the calculated distortions were excessively high and that satisfactory performance could only be met by fabricating the mirror from a single piece of material. Analysis of a single part mirror indicated that, with judicious removal of material, it was possible to balance the mirror in a single plane. This decreased the localized stress levels caused by the balancing weights and greatly reduced the distortion across the mirror surface.

Low (up to 40 Hz) and high frequency (approximately 2.0 kHz) piezoelectric choppers of the IR radiation are considered. The methods and results of calculation of the amplitude- frequency characteristics, mechanical stress-strains state and temperature heating of PZ flextensional actuators are given. The obtained voltage and frequencies valuations realize the maximum of electromechanical coupling and minimum heating at resonant oscillations with equal amplitude of strains.

In Tri-level xerography, the control of the modulated levels creates a new set of problems, which did not plague the usual binary levels in normal xerography. One of the many concerns is controlling overshoot of the mid-level exposure so that the signal does not invade into the high-level exposure. Another concern is to maintain adequate signal width, which correlates well with the desired output pattern.