Yasuhisa Tamagawa

Multilens system design with an athermal chart

We have introduced an athermal chart that plots chromatic dispersive power and thermal dispersive power on a Cartesian coordinate, and we give the design method of a multilens system in contact that satisfies achromatism and athermalization. The advantages of this chart are (1) that the condition of achromatism and athermalization is clear and (2) that the approximate power of the lenses that compose the multilens system is easily found on the chart. Design indices are given through a few design examples with an athermal chart.

Configuration of an off-axis three-mirror system focused on compactness and brightness

We propose a configuration of an off-axis three-mirror system for maximum compactness and brightness. The chief ray is arranged to cross three times inside the system, and the system has a round configuration for compactness. We introduced into the design a ray triangle formed by the reflection points of the chief rays at the mirrors. The ray triangle indicates the size and the brightness of the system. Based on the proposed configuration, a design example of a 4 degrees x 4 degrees field of view is shown. The F-number of the system is 2.2, in close agreement with the estimation from the ray triangle.

3D imaging LADAR with linear array devices: laser, detector and ROIC

This paper introduces the recent development of 3D imaging LADAR (LAser Detection And Ranging) in Mitsubishi Electric Corporation. The system consists of in-house-made key devices which are linear array: the laser, the detector and the ROIC (Read-Out Integrated Circuit). The laser transmitter is the high power and compact planar waveguide array laser at the wavelength of 1.5 micron. The detector array consists of the low excess noise Avalanche Photo Diode (APD) using the InAlAs multiplication layer. The analog ROIC array, which is fabricated in the SiGe- BiCMOS process, includes the Trans-Impedance Amplifiers (TIA), the peak intensity detectors, the Time-Of-Flight (TOF) detectors, and the multiplexers for read-out. This device has the feature in its detection ability for the small signal by optimizing the peak intensity detection circuit. By combining these devices with the one dimensional fast scanner, the real-time 3D range image can be obtained. After the explanations about the key devices, some 3D imaging results are demonstrated using the single element key devices. The imaging using the developed array devices is planned in the near future.

Dual-band optical systems with a projective athermal chart: design

We introduce a projective athermal chart that is produced as a view plane of the perspective projection of a three-dimensional space consisting of two chromatic dispersive powers and the mean thermal dispersive power. In addition, we show a design method for dual-band optical systems with this chart and a design example of a three-lens optical system operating in the 3-5- and 8-12-mum wavelength bands.

New design method for athermalized optical systems

This paper describes a new design method for athermalized optical systems. It can be accomplished by combining optical materials and by selecting suitable lens powers. However, there are difficulties in determining material and power of each lens, because achromatism is simultaneously required. To determine the condition of eliminate thermal focus shift and longitudinal chromatic aberration easily by simple drawing, an athermal chart is proposed which is constructed by plotting chromatic dispersive power and thermal dispersive power on a cartesian coordinate system.

Multiband optical system using spectral filters with diffractive optical elements

For multiband sensor applications we propose an optical system that forms different spectral images with a constant magnification and distortion over all spectral bands. Spectral filter devices are introduced for three major purposes; for determining spectral range of the bands, for correcting chromatic aberrations, and for a constant magnification and distortion. The spectral filter device has an interference band pass filter on one plane surface and a refractive-diffractive hybrid element on the other surface. The diffractive element is designed to compensate chromatic aberration in each spectral band and the aspheric refractive element has a function of setting focal length of each band to a constant value. We have designed and fabricated an optical system for two bands. The diffraction orders of the diffractive element are designed to optimize the diffraction efficiencies. Experimental results show that the difference in magnification between two bands is smaller than one pixel over full field of view. Measured MTF and images indicate that aberrations including chromatic aberration of the optical system are well compensated.

Demonstration on range imaging of 256×256 pixels and 30 frames per second using short wavelength infrared pulsed time-of-flight laser sensor with linear array receiver

Abstract. We demonstrated the range imaging with high resolution of 256×256  pixels and high frame rate of 30 frames per second (fps) using a short wavelength infrared pulsed time-of-flight laser sensor, which is suitable for long range imaging. We additionally demonstrated the long range imaging of more than 1 km and wide field of view imaging of 12  deg× 4  deg, 768×256  pixels, and 10 fps. For these demonstrations, we developed the linear array devices of the aluminum indium arsenide avalanche photodiode array and silicon germanium bipolar complementary metal oxide semiconductor read-out integrated circuit array. We also deployed the flattop beam illumination optics with the beam division and recombination method and realized efficient line shape illumination.

Development of Wide-Angle Three-Mirror System with Spiral Optical Axis

A design method of wide-angle three-mirror system with spiral optical axis is proposed. Asymmetric optical systems have more degrees of freedom than co-axial systems. The increased degrees of freedom can be applied for removal of ray obscuration by mirrors to achieve wide-angle and low F-number system design. The asymmetric system design requires three-dimensional comprehension of system structure and correction of asymmetric aberrations. In order to simplify the structure comprehension, a base sphere is introduced. The system structure can be changed into the two-dimensional structure of mirror interferences by the base sphere. The dominant asymmetric aberrations are spherical-like and astigmatism-like aberrations. The spherical-like aberration is eliminated by each mirror inidividualy and the astigmatism-like aberration is reduced by counterbalance of whole mirrors. An example of F/2 system with as wide angle as 30x24 degrees FOV is designed. The example system is fabricated by precision machining process for an infrared camera.

Air-grid polarization splitter for infrared imaging systems

Polarimetric sensing is adequate for detection of man-made targets, which generally have artificial smooth surfaces. In this paper, we propose an infrared polarization imaging system for detection of man-made targets in natural backgrounds. In order to obtain the polarization properties, images in different polarization states are required. Sequential capturing of polarization images is not suitable for practical systems because the movements of targets and backgrounds cause errors in polarization estimation. The proposed system is capable of capturing simultaneous polarization images. A Brewster angle polarization splitter (BAPS) is used for the polarization imaging system to separate the polarization components of the incident light. We introduce a new type of BAPS structure, called air-grid structure. The air-grid structure is composed of a series of parallel cavity lines on a single plane and shows structural birefringence. As a result, the refractive indices of the air-grid structure satisfy the Brewster angle condition and the total reflection for orthogonal polarization components at the same incident angle. This new structure enhances the field of vie of the BAPS and is ideal for imaging systems.

Physically based reflectance model utilizing polarization measurement

A surface bidirectional reflectance distribution function (BRDF) depends on both the optical properties of the material and the microstructure of the surface and appears as combination of these factors. We propose a method for modeling the BRDF based on a separate optical-property (refractive-index) estimation by polarization measurement. Because the BRDF and the refractive index for precisely the same place can be determined, errors cased by individual difference or spatial dependence can be eliminated. Our BRDF model treats the surface as an aggregation of microfacets, and the diffractive effect is negligible because of randomness. An example model of a painted aluminum plate is presented.