Optical linear displacement encoders are frequently used to measure and control the motion of high-precision machine tools and measurement systems. The encoder scales are typically fabricated as diffraction gratings, where the period of the grating is determined by the required resolution and other system design requirements. Coarse gratings - with a period of ~10 um - rely on incoherent sources and Talbot imaging to relay the moving scale pattern to a detector array without using lenses. Higher resolution encoders use finer encoder pitch (<1 um) and laser sources to form grating interferometers which can detect scale displacement to a resolution of better than 10 nm. In all cases, scale motion is detected by measuring interference between wavefronts diffracted by the scale. Although the first-order design of such systems is well understood, the need for high resolution and accuracy demands a detailed understanding of higher order effects resulting from misalignment, aberrations, coherence, and other physical optics effects. In this paper, we show how simulation methods based on wavefront models derived from ray-trace data can provide a detailed and accurate prediction of how system performance depends on a wide variety of design and construction parameters. The resulting simulation is a useful tool for optimizing encoder designs and establishing fabrication and alignment tolerance budgets.

By adopting the basic principle of the reflection (and transmission) of a plane polarized electromagnetic wave incident normal to a stack of films of alternating refractive index, a simple numerical code was written to simulate the maximum reflectivity (transmittivity) of a fiber optic Bragg grating corresponding to various non- uniform strain conditions including photo-elastic effect in certain cases.

We present a new analytical method for solution of 1-D quantum and optical systems, based on the differential transfer matrices. This approach can be used for exact calculation of various functions including reflection and transmission coefficients, band structures as well as bound states. We show the consistency of WKB method with out approach and discuss improvements for even symmetry and infinite periodic structures. Moreover a general variational representation of bound states is introduced. As application examples, we consider several test cases including the reflection and band structure of gratings as well as bounded states of inhomogeneous waveguides. An excellent agreement between the results from our differential transfer matrix method with other methods is observed where possible.

Well-adjusted lighting is one of the most important contributors to good quality and robust measurements in video based inspection systems. The optimal selection of lighting varies from part to part, and system to system. System designers must often select from a significant number of competing illumination sources at varied positions in order to determine how best to illuminate a target edge. In cases where an end user must perform the lighting setup this complexity often results in either a poor measurement or a determination that the inspection cannot be performed. This paper describes a general, simulation based methodology to adjust automatically a set of physical illumination sources (both in magnitude and position) so as to achieve a high quality edge measurement. Specific metrics of edge quality and an approach to search the resulting solution space are also presented.

We present an approach to convert slow running, high fidelity simulations into fast running models via analogy. These high order polynomial models use Data Modeling coupled with multivariate regression. Shown are models for individual data sets, field measured data, simulations like the Navy Experimental Dive Unit rebreather model, simulation driver equations for the Kinetic Impact Debris Distribution model, and a model of a terahertz sensor sensing Bt simulant built from a hardcopy only. These equation-based models are easily embedded into larger system simulations as active model components for enabling system performance and trade analysis. Models are fast running, and in the case of simulation and driver equation modeling, provide results that are significantly shorter in lines of software code.

A number of gases present in the atmosphere play roles of interest to various parties. These are CO₂ for its impact on understanding of global sources and sinks of Carbon, CH₄ and H₂O and their importance for global climate change, HCl and its importance in chemical processes. A space-borne sensor using multiple-wavelength Laser Absorption Spectroscopy (LAS) and mature CW fiber telecom lasers can address the critical questions concerning present and future patterns in these gases. The sensor identified above was designed from the outset using Taguchi Robust design techniques because of the need to adjust to varying science measurement requirements and technology capability as well as achieving optimum performance for optimum cost. The results describe a sensor with a SNR of 150 with a power aperture product of 3.92 watts-m² on the absorption line is sufficient to meet the science requirements of 0.5% accuracy for determining the column density of CO₂.

Imaging LADAR is a hybrid technology that offers the ability to measure basic physical and morphological characteristics (topography, rotational state, and density) of a small body from a single fast flyby, without requiring months in orbit. In addition, the imaging LADAR provides key flight navigation information including range, altitude, hazard/target avoidance, and closed-loop landing/fly-by navigation information. The Near Laser Ranger demonstrated many of these capabilities as part of the NEAR mission. The imaging LADAR scales the concept of a laser ranger into a full 3D imager. Imaging LADAR systems combine laser illumination of the target (which means that imaging is independent of solar illumination and the image SNR is controlled by the observer), with laser ranging and imaging (producing high resolution 3D images in a fraction of the time necessary for a passive imager). The technical concept described below alters the traditional design space (dominated by pulsed LADAR systems) with the introduction of a pseudo-noise (PN) coded continuous wave (CW) laser system which allows for variable range resolution mapping and leverages enormous commercial investments in high power, long-life lasers for telecommunications.

Image sensor sensitivity is critical for machine vision applications where illumination is limited and large depth of field is required. In this paper a method is presented for evaluating image sensor sensitivity by measuring camera signal-to-noise ratio (SNR). The method is simple to implement and produces accurate results. The method measures SNR as a function of target illumination, and relates this to image sensor sensitivity by normalizing with respect to image sensor pixel size. The method can be used to compare cameras with different types and sizes of image sensors, and is particularly useful in comparing the sensitivities of different CMOS sensors, and for comparing CMOS and CCD sensors. We present a new measure of sensitivity: SNR per unit luminous flux-time. The new measure enables the direct comparison of sensor performance.

The increasing use of the next generation focal plane array infrared detectors has resulted in growth in the number and types of Thermoelectric Thermal Reference Sources (TTRS). These TTRSs provide a temperature controllable, radiometrically uniform surface. When viewed by the system detectors, the TTRS allows the system electronics to perform gain and offset calibration as well as DC restoration. This paper describes typical calibration cycles for starring arrays systems. It will include typical calibration temperatures for different ambients and transient times between these calibration points. For several size emitter surfaces, power consumption over the calibration cycle will be shown. Since starring array systems do not have mechanical scanners, other means are required to inject the TTRS image into the optical path. Methods for inserting the TTRS into the optical path will be discussed and examples shown. To aid infrared system design engineers during their design process, TTRS critical paramters for starring array systems will be discussed.

Bechtel Nevada, Los Alamos Operations, has developed a high-speed, nine-frame camera system that records a sequence from a changing or dynamic scene. The system incorporates an electrostatic image tube with custom gating and deflection electrodes. The framing tube is shuttered with high-speed gating electronics, yielding frame rates of up to 5 MHz. Dynamic scenes are lens-coupled to the camera, which contains a single photocathode gated on and off to control each exposure time. Deflection plates and drive electronics move the frames to different locations on the framing tube output. A single charge-coupled device (CCD) camera then records the phosphor image of all nine frames. This paper discusses setup techniques to optimize system performance. It examines two alternate philosophies for system configuration and respective performance results. We also present performance metrics for system evaluation, experimental results, and applications to four-frame cameras.

Optical-microwave interaction has been emphasized in optically reconfigurable antenna arrays (ORA) due to the unique advantage that transparency between the optical control signals and microwave signals makes the antenna less susceptible to jamming. One of the important parts in ORA is an optically controlled microwave switch (OMS) as synaptic elements. A gap-structure OMS has been developed as a low-cost and simple device which operates in all frequencies. However, the OMS is essentially operated in a CW-mode, and adverse effects are observed in the CW-mode operation. Although a CW-mode OMS has been investigated previously, a detailed analysis has not been reported. In this paper, we present an analysis, and the numerical simulations are compared with the previous measurements.

High-resolution measurement of the free spectral range (FSR) for an etalon is becoming more important as greater amounts of information are multiplexed through a single fiber. A method to test the FSR of etalons or etalon based optical components used at telecommunication frequencies is discussed. Slope at a specific point of the etalon response curve is utilized as a means measurement of FSR. The theory that describes how slope, varying as a function of differing etalon signal peaks, can be utilized for the measurement of FSR is developed. This technique has been shown to measure FSR with a resolution of approximately one part in 2000.

A Fabry-Perot fiber optic sensor utilizes a unique interferometric mechanism and signal processing technique. It employs a Fizeau interferometer and a Charge-Coupled Device to locate the position of the maximum interference fringe intensity rather than absolute light intensity, which is most likely affected by external stressors such as irradiation and high pressure/temperature. A Fabry-Perot fiber optic temperature sensor was investigated for potential application in harsh environments expected in nuclear power plants. The sensor design and simulation of its signal processing are fully described in this paper. A methodology was developed based on IEEE-323 and ISA-dS67.06 to evaluate the sensors in normal and abnormal design basis accident environments. The experimental results of radiation and environmental qualification tests are summarized. Two sensors exhibited no failure and acceptable performance when exposed to gamma radiation to doses of 15 kGy and 1.33 MGy, respectively. Three sensors were irradiated to a total neutron fluence of 2.6x10¹⁶ neutrons/cm² and a total gamma dose of 1.09MGy. These demonstrated a temperature shift of about 34°F but responded linearly to temperature, and the offset was reduced by approximately 63% through annealing the sensors.

It has been known for some time that the technology of the uncooled infrared thermal imaging system could provide a low-cost, compact-structure, low-power consumption thermal imaging device. This paper describes the theoretic limitation modal of the uncooled thermal imager's performance; temperature fluctuation noise limit is explored and presented. NETD affected by the detector structure and the noise is calculated theoretically. The theoretical curves of the relation between NETD and detector temperature, background temperature, thermal conductance and the area of the pixel are presented.

We present the design of an hybrid opto-digital joint transform correlator using a Fourier optical processor in combination of an electronic system based in a digital signal processor (DSP) or a field programmable gate arrays (FPGA).

The paper designs a set of system for measuring the responding characteristic of detector of PIN photon diode. The paper introduces the principle and structure of the PIN diode detector, and then describes the researching background and the responding characteristic of the detector. The detailed designing plan is given, and the step of implement is brought out. The system is composed of three subsystems. The first is optical system. The optical system can produce a laser of 1.06μm with a certain frequency and energy, with the aid of light source and CCD camera, the laser beam can focus on the surface of the photon detector of PIN diode. The second is signal-testing system. It can measure the responding characteristic of the photon detector, and the average noise power. The third is temperature control system. The responding characteristic of the photon detector in the high temperature and low temperature can be obtained with the temperature-control device. All the data is recorded and analyzed by the computer. At last, the paper provides the structure of the system and the testing result of the photon detector.

We have applied the single effective index method to reduce the two-dimensional refractive index profile into the one-dimensional refractive index structure and modified the wave equations to obtain the paraxial wave equations. Then, TE and TM polarized fields in the curved single-mode planar waveguides are analyzed by using the scalar beam-propagation method employing the finite-difference method with a slab structure. The bending loss in bent waveguides is analyzed for optical fields obtained from the beam-propagation method and comparisons are made between the loss for the waveguides with various radius of curvature and the refractive index difference. The outward shift of the optical field, which is generated at the connection between a straight and a bent waveguide, is obtained from the results of calculation of location of the maximum optical intensity. The transition loss can be reduced by introducing an optimized inward offset at a straight-to-bend junction.

We have applied the double effective index method to reduce the two-dimensional refractive index profile into the one-dimensional refractive index structure and modified the wave equations to obtain the paraxial wave equations. Then, TE and TM polarized fields in the curved single-mode planar waveguides are analyzed by using the scalar beam-propagation method employing the finite-difference method with a slab structure. The birefringence for TE and TM polarized fields in bent waveguides is calculated from the phase difference of the optical fields. The wavelength shift due to the birefringence of TE and TM polarized fields in bent waveguides is also calculated.

In this article, a new variational approach for extraction of leaky modes in layered waveguides is proposed. To verify the method, results of analysis of a typical test case is compared to the other references, being in agreement with them. The efficiency of the proposed approach is compared to other reported methods.

The design of an ASIC, which is capable of connecting multiple Ethernets by SDH links through complex network topology, is given here. A closed-loop congestion control mechanism over the entire network is put forward, a scheduling algorithm for traffic of four differenct priorities is suggested and the requried buffer size under self-similar traffic is calculated.