• Journal of the Optical Society of Korea
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• v.20 no.4
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• pp.481-487
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• 2016

This study presents a new optical system for a combiner-type head-up display (HUD) with a cylindrical lens as an asymmetrical aberration corrector, instead of a freeform mirror. In the initial design process based on off-axial aberration analysis, we obtain an off-axis two-mirror system corrected for linear astigmatism and spherical aberration by adding a conic secondary mirror to an off-axis paraboloidal mirror. Thus, since the starting optical system for an HUD is corrected for dominant aberrations, it enables us to balance the residual asymmetrical aberrations with a simple optical surface such as a cylinder, not a complex freeform surface. From this design process, an optical system for an HUD having good performance is finally obtained. The size of the virtual image is 10 inches at 2 meters away from a combiner, and the area of the eye box is 130×50 mm².

• Journal of the Optical Society of Korea
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• v.16 no.3
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• pp.270-276
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• 2012

An off-axis integral floating system using a concave mirror is analyzed to resolve the image distortion incurred by the off-axis optical arrangement. The concave mirror can be adopted as the floating device to improve the optical efficiency. The image distortion due to the tilting axis of the concave mirror needs to be analyzed precisely to generate the pre-distortion image. In this paper, we calculate the image deformation in the off-axis structure of the concave mirror using the geometrical optics. Using the calculation results, the compensated elemental image can be generated for the pre-distortion integrated image, which can be projected to the floating 3D image without image distortion. The basic experiments of the off-axis integral floating are presented to prove and verify the proposal.

• Current Optics and Photonics
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• v.3 no.5
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• pp.374-381
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• 2019

This study examined a method for designing the optical cavity of a non-dispersive infrared gas detector. The infrared gas detector requires an optical cavity design to lengthen the ray path. However, the optical cavity with multiple reflecting surfaces has off-axis aberration due to the characteristics of the reflecting optical system. The rays were parallelized by using the off-axis parabolic mirror to easily increase the ray path and eliminate off-axis aberration so that the rays are admitted to the effective area of the infrared detector uniformly. A prototype of an infrared gas detector was produced with the designed optical cavity to confirm the performance.

• Current Optics and Photonics
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• v.1 no.4
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• pp.364-371
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• 2017

Compared to one made of glass, an aluminum mirror features light weight, compact design, low cost, and quick manufacturing. Reflective mirrors and supporting structures can be made from the same material, to improve the athermal performance of the system. With the rapid development of ultraprecise machining technologies, the field of applications for aluminum mirrors has been developed rapidly. However, most of them are rotationally symmetric in shape, and are used for infrared applications. In this paper, the design and manufacture of an off-axis aluminum mirror used for a three-mirror-anastigmat (TMA) optical system at visible wavelengths is presented. An optimized, lightweight design provides a weight reduction of more than 40%, while the surface deformation caused by earth's gravity can meet the required tolerance. The two pieces of an off-axis mirror can be diamond-turned simultaneously in one setup. The centrifugal deformation of the off-axis mirror during single-point diamond turning (SPDT) is simulated through the finite-element method (FEM). The techniques used to overcome centrifugal deformation are thoroughly described in this paper, and the surface error is reduced to about 1% of the original value. After post-polishing, the form error is $1/30{\lambda}$ RMS and the surface roughness is better than 5 nm Ra, which can meet the requirements for visible-light imaging.

• Current Optics and Photonics
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• v.5 no.6
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• pp.660-671
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• 2021

We present a novel optical system for an augmented reality head-up display (AR HUD) with two virtual images at different conjugates by employing a confocal off-axis two-mirror and introducing the horopter circle. For a far virtual image with large asymmetrical aberrations, we initially obtain an off-axis two-mirror system corrected for these aberrations and compensated for the down angle by configuring its parameters to satisfy the confocal and Scheimpflug conditions, respectively. In addition, this system is designed to reduce the biocular parallax by matching Petzval surface into the longitudinal horopter circle in a near virtual image. This design approach enables us to easily balance the residual aberrations and biocular parallax when configuring the optical system with two different conjugates, which results in an AR HUD available for near and far virtual images together.

• Korean Journal of Optics and Photonics
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• v.28 no.6
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• pp.263-272
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• 2017

To design a wide-field optical system, the inverted telephoto configuration, which has a negative front group and a positive rear group, is popular. For a two-mirror system, the inverse Cassegrain system has the inverted telephoto configuration, but the inverse Cassegrain system with the conventional, axially symmetric configuration shows severe field screening and ray obstruction. To avoid these problems, we put the aperture stop on the secondary mirror of an inverse Cassegrain system to increase field of view, and designed a wide-field off-axis two-mirror system which only uses the off-axis field, without ray obstruction.

• Journal of the Optical Society of Korea
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• v.19 no.6
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• pp.604-613
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• 2015

An unobstructed off-axis two-mirror system is presented in this paper. First a suitable initial configuration is established based on third-order aberration theory. In order to achieve a wide field of view (FOV) with high image quality , the diffractive mirror is adopted in the two-mirror system to increase the optimization freedom and the aberration relationship between diffractive phase coefficients and Zernike coefficients is derived. Furthermore, a complete comparison design example with a focal length of 1200 mm, F-number of 12, and FOV of 40° × 2° is given to verify the aberration correction ability of the diffractive mirror. The system average wavefront error is 0.007 λ (λ=0.6328 μm) developed from 0.061 λ when the system didn’t adopt the diffractive mirror. In this system the phase modulation function of the diffractive mirror is established as an even function of x, so we could obtain a symmetrical imaging quality about the tangential plane, and the symmetric aberration performance also brings considerable convenience to alignment and testing for the system.

• Journal of Astronomy and Space Sciences
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• v.29 no.2
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• pp.233-244
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• 2012

The Korea Astronomy and Space Science Institute and the Department of Astronomy at the University of Texas at Austin are developing a near infrared wide-band high resolution spectrograph, immersion grating infrared spectrometer (IGRINS). The compact white-pupil design of the instrument optics uses seven cryogenic mirrors, including three aspherical off-axis collimators and four flat fold mirrors. In this study, we introduce the optomechanical mount designs of three off-axis collimating mirrors and one flat slit-viewer fold mirror. Two of the off-axis collimators are serving as H and K-band pupil transfer mirrors, and are designed as system alignment compensators in combination with the H2RG focal plane array detectors in each channel. For this reason, the mount designs include tip-tilt and parallel translation adjustment mechanisms to properly perform the precision alignment function. This means that the off-axis mirrors' optomechanical mount designs are among the most sensitive tasks in all IGRINS system hardware. The other flat fold mirror is designed within its very limitedly allowed work space. This slit-viewer fold mirror is mounted with its own version of the six-point kinematic optics mount. The design work consists of a computer-aided 3D modeling and finite element analysis (FEA) technique to optimize the structural stability and the thermal behavior of the mount models. From the structural and thermal FEA studies, we conclude that the four IGRINS mirror mounts are well designed to meet all optical stability tolerances and system thermal requirements.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.2
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• pp.13-19
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• 2012

Ultra Precision Machining Techniques, such as manufacturing Micro Lens Array(MLA), off-axis mirror, $F-{\theta}$ lens for laser printer, are achieved, based on technologies in consequence of development of modern high-precision machining mechanism. Above all, FTS(Fast Tool Servo) and STS(Slow Tool Servo) are more innovative technologies for reducing time and development costs. In this paper, it is described that MLA machining technique by FTS, off-axis mirror machining technique by STS, optics for observing space, and development of infrared aspheric lens for a thermal imaging microscope.

• Journal of The Korean Astronomical Society
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• v.43 no.5
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• pp.169-181
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• 2010

We develop a proto-model of an off-axis reflective telescope for infrared wide-field observations based on the design of Schwarzschild-Chang type telescope. With only two mirrors, this design achieves an entrance pupil diameter of 50 mm and an effective focal length of 100 mm. We can apply this design to a mid-infrared telescope with a field of view of $8^{\circ}{\times}8^{\circ}$. In spite of the substantial advantages of off-axis telescopes in the infrared compared to refractive or on-axis reflective telescopes, it is known to be difficult to align the mirrors in off-axis systems because of their asymmetric structures. Off-axis mirrors of our telescope are manufactured at the Korea Basic Science Institute (KBSI). We analyze the fabricated mirror surfaces by fitting polynomial functions to the measured data. We accomplish alignment of this two-mirror off-axis system using a ray tracing method. A simple imaging test is performed to compare a pinhole image with a simulated prediction.