Coaxial Optical System Research Articles

Robotically steerable intraluminal imaging probe with side-viewing 3D photoacoustic computed tomography

This Letter presents, for the first time to our knowledge, a continuum robotic-steered endoluminal volumetric photoacoustic tomography probe. With regard to the design of the probe, a coaxial optical and acoustic imaging system has been developed that employs a custom designed piezoelectric micromachined ultrasonic transducer (PMUT). The dimensions of the system are constrained within a cylindrical housing with a diameter of 12 mm and a length of 30 mm. In regard to the robot design, the motion capabilities of the continuum robot have been successfully modeled and characterized. Based on the proposed system, the potential for early detection and screening of gastrointestinal cancers through phantoms has been validated. The experimental results demonstrate that the robotic-assisted photoacoustic system performs well in localizing unknown lesions and characterizing deep-seated abnormalities, exhibiting promising clinical applications.

Effects of aperture shapes on imaging spatial quality from end-to-end perspective

With the continuous advancement of optical imaging technology and the increasing requirement for remote sensing applications, high-resolution spatial imaging technology has been extensively researched. Subject to the diffraction limitation, the optical aperture is continuously increasing to obtain more target details, which leads to larger satellite platforms and higher manufacturing costs. In order to balance the cost of satellite platforms and the imaging quality of space cameras, this paper focuses on the optical aperture, which affects both of the above by conducting an end-to-end analysis of the space imaging process to examine its effects on overall imaging spatial quality. This paper formulates the optical aperture optimization problem by establishing the evaluation functions for deployment cost and imaging quality. Two types of optical systems commonly used in space imaging, the coaxial reflective optical system with annular aperture and the topologically compact optical system with square aperture are studied based on the proposed optimization model. Their imaging characteristics and design principles are summarized. The optimization model proposed can be applied to the optical aperture design of any manufacturable optical system to guide the design of the entire space camera and even the satellite platforms.

Compact Coaxial Four-Mirror Optical System Based on Multi-Surface Integration

Compact Coaxial Four-Mirror Optical System Based on Multi-Surface Integration

Off-axis four-mirror telescope with a wide field of view and a long focal length using double integrated mirrors.

An off-axis four-mirror optical system has the advantages of a wide field of view (FOV) and a small telephoto ratio. However, it will bring difficulties in assembly and detection. Here we report an off-axis four-mirror free-form telescope with a long focal length and a wide field of view based on two integration mirrors. The initial structure of a coaxial four-mirror optical system is established based on the Seidel aberration theory. A Zernike Fringe free-form surface is introduced to correct aberrations. By gradually increasing the entrance pupil diameter and the FOV, we finally obtain an off-axis four-mirror telescope with a FOV of 0.4∘×20∘, an F-number of 11.5, a long focal length of 2000mm, and a volume of 360×400×600m m 3. In addition, four mirrors remain coaxially aligned, remarkably facilitating detection and adjustment. The proposed off-axis four-mirror telescope, with double integration mirrors, holds great potential for application in aerospace remote sensing observations.

Si Photonics FMCW LiDAR Chip with Solid-State Beam Steering by Interleaved Coaxial Optical Phased Array.

LiDAR has attracted increasing attention because of its strong anti-interference ability and high resolution. Traditional LiDAR systems rely on discrete components and face the challenges of high cost, large volume, and complex construction. Photonic integration technology can solve these problems and achieve high integration, compact dimension, and low-cost on-chip LiDAR solutions. A solid-state frequency-modulated continuous-wave LiDAR based on a silicon photonic chip is proposed and demonstrated. Two sets of optical phased array antennas are integrated on an optical chip to form a transmitter-receiver interleaved coaxial all-solid-state coherent optical system which provides high power efficiency, in principle, compared with a coaxial optical system using a 2 × 2 beam splitter. The solid-state scanning on the chip is realized by optical phased array without a mechanical structure. A 32-channel transmitter-receiver interleaved coaxial all-solid-state FMCW LiDAR chip design is demonstrated. The measured beam width is 0.4° × 0.8°, and the grating lobe suppression ratio is 6 dB. Preliminary FMCW ranging of multiple targets scanned by OPA was performed. The photonic integrated chip is fabricated on a CMOS-compatible silicon photonics platform, providing a steady path to the commercialization of low-cost on-chip solid-state FMCW LiDAR.

Optical design and precision analysis of a single-line-array pendulum sweep high-resolution mapping camera.

With the improvement of the satellite resolution, it is urgent to develop the single-line-array mapping camera. However, the camera accuracy is influenced by the satellite attitude's rapid maneuvering during the imaging process. In our study, a coaxial four-mirror optical system with a field bias with a focal length of 7050mm, F-number of 10.8, field of view of 1.2°, and spectral range of 450-800nm is designed. By combining mathematical modeling and ray tracing, the offset of the camera interior orientation elements caused by the misalignment of the secondary mirror is derived. The simulation results show that the maximum relative error does not exceed 2.119%. Besides, a desensitization design method based on the magnification parameter control method is proposed, and the results show that the sensitivity of camera interior orientation elements to the secondary mirror is reduced, indicating the effectiveness of the system desensitization design, which is of great significance for the improvement of camera accuracy.

Optical design and implementation of a compact and long focal length imaging system

In this paper, we demonstrate a compact and long focal length imaging system for building detection. This system is an all-spherical system. In order to avoid the use of aspheres, the system relies on two groups of correction elements to correct aberrations. This allows for short manufacturing cycles and simplified adjustments. The system works in the visible band from 460 nm to 750 nm. The focal length is 900 mm, and the optical length is only 280 mm. The designed modulation transfer function (MTF) is consistent with the diffraction limit. The MTF curve is 0.63 at the Nyquist frequency of 78 lp/mm. The optomechanical structure is developed based on the analysis consequence of tolerance and stray light, and a device is fabricated. We also propose a simplified method for measuring the space between the primary mirror and the secondary mirror in a compact coaxial optical system. According to the experimentation, the device is proven to meet the application requirement. Detailed descriptions of the design and implementation are provided.

Design and Control of a Novel 3-D Piezoelectric Scanning Coaxial Optical Microscope System

This paper presents a novel three-dimensional (3D) optical measurement system combining an optical microscope (OM) and a z-axis piezoelectric scanner. The proposed system includes an advanced controller for the piezoelectric scanner and an algorithm to process OM imaging data. The z-axis piezoelectric scanner uses a back-propagation neural network (BPNN) to control the upward movement of the sample in a step-wise manner. At the point where each step induces a small steady-state error, the OM captures an image in that position. Each 2D OM image undergoes denoising via connected-component labeling (CCL) before being converted into 3D data via image processing. The layered images are then stacked in a 3D arrangement to construct an accurate 3D image of the sample.

An ADB Headlight Module with Coaxial Optical System for Lighting and Sensing

An ADB Headlight Module with Coaxial Optical System for Lighting and Sensing

Design of high-density coaxial four-mirror optical system with field-bias and multi-light-channel coupled

Design of high-density coaxial four-mirror optical system with field-bias and multi-light-channel coupled

Precise positioning of the test surface and screen in a coaxial software configurable optical test system

The coaxial software configurable optical test system (SCOTS) is an aspheric and freeform surface metrology method with high accuracy. The positioning accuracy of the test surface and screen seriously affects the measurement accuracy. In this paper, a novel method, PDCMC (positioning with differential computation, calibration board assisted, 3D measurement and component displacement), is proposed for the precise positioning in the coaxial SCOTS. In the proposed method, a flat crystal is used as the initial test mirror. In the initial system, the positioning of the screen is carried out using the differential computation method. Then, the positioning of a calibration board is carried out based on the feature points on the calibration board. The relative position and attitude among the flat crystal, the calibration board and the actual test surface are provided by a 3D coordinate measuring machine. Finally, through coordinate transformation and data processing, the precise positioning of the test surface and screen can be completed in the actual coaxial SCOTS. The proposed method is highly versatile and suitable for almost all kinds of test surfaces. Simulation and experiments demonstrate the feasibility and accuracy of the proposed method. Compared with the existing universal positioning method, the proposed method has the advantages of fewer required components and higher precision.

Horizontal alignment technology of coaxial three-mirror optical system

Horizontal alignment technology of coaxial three-mirror optical system

Research on Light-Small Lens Structure Design and Weight Reduction Optimization Based on Neural Network

In order to meet the design requirements of low weight and high specific stiffness for a small space camera lens assembly, based on the compact coaxial four-mirror optical system, a dynamic optimization design concept is proposed firstly, and then the initial lightweight design of lens structure is realized in an integrated assembly form. And then the BP neural network & genetic algorithm is used to dynamically optimize the lens structure parameters, which reduces the weight of the whole lens while ensuring the high specific stiffness of the lens, and realizes the goal of lens lightening design.

Initial configuration design of off-axis reflective optical system based on vector aberration theory

The traditional method of designing the initial configuration of off-axis reflective optical system is to first obtain the initial configuration of coaxial reflective optical system, and then achieve the unobscured design with an offset aperture stop or a biased input field, or both. Because the aberration distribution of coaxial reflective optical system is not applicable to the off-axis reflective optical system, the obtained unobscured off-axis reflective optical system has large aberration, and the unobscured design process is complicated. In this paper we present a method of designing an initial configuration of off-axis reflective optical system based on vector aberration theory. With this design method, a good unobscured initial configuration of off-axis reflective optical system can be directly obtained by using an offset aperture stop or a biased input field, or both. Based on the vector aberration theory and gaussian brackets, the third-order aberration coefficient is derived for off-axis reflective optical system. Initial configuration performance is important for optical design, especially for the complicated optical system design. The selection of initial configuration highly affects the final system imaging performance, fabrication difficulty and alignment difficulty. An error function is established to evaluate the performance of off-axis reflective optical system, and it consists of aberration coefficients and other constraints. The genetic algorithm is a highly parallel, random and adaptive global optimization algorithm. To obtain a good initial configuration for the off-axis reflective optical system, the genetic algorithm is used to search for the initial configuration with minimum residual aberration. This method can obtain a good initial configuration of off-axis reflective optical system for further optimization. The benefit of this design method is demonstrated by designing an off-axis three-mirror optical system. For the focal plane array, a long-wave infrared off-axis three-mirror optical system is designed. A good initial configuration is obtained with the proposed method, which achieves the unobscured design by using an offset aperture stop and a biased input field. To improve the performance of initial configuration, the obtained initial configuration is optimized with the optical design software. The designed optical system has good imaging quality. As the mirrors are free from the tilts and decenters, the designed optical system is aligned easily.

Noise reduction in modulation measurement profilometry based on the wavelet transform method

Modulation measurement profilometry can achieve the reconstruction of a tested object with complex or step-like surface. The technology applying coaxial and coimage plane optical systems in which the projection axis coincides with the observation axis can effectively avoid the defects of shadow, shade, and phase discontinuity. All of these weaknesses are largely present in optical three-dimensional sensing based on trigonometric measurement principle. However, in the practical application, the captured fringe patterns are always inevitably influenced by noise, which will directly affect the measurement accuracy. As a well-known and remarkable time-frequency analysis tool, the wavelet transform (WT) method has a strong noise immunity and is suitable to analyze nonstationary signals. Comparisons between the WT method and the Fourier transform method are made not only by computer simulations appearing robust within various types of noise but also the practical experiment. It shows that the WT method is helpful in the enhancement of measurement accuracy. Additionally, experiment further verifies its strong antinoise ability.

Elimination of nonlinearity in modulation measurement profilometry by Wavelet Transform

Modulation measurement profilometry applies coaxial and coimage plane optical systems to reconstruct the surface shape of the measured object, in which, the direction of the grating projection is the same as that of CCD to capture the images. This technology completes the reconstruction by the extraction of modulation values instead of phase information. It can effectively avoid the shadows, shutoff and calculation of phase unwrapping and accomplish the shape measurement for object with complex surface. However, in the practical application, the measurement precision is usually affected by the nonlinearity of CCD’s photoelectric response. In order to avoid the influence of high-order harmonics on fundamental spectrum, Wavelet Transform is introduced into fringe analysis and modulation extraction. With the merits of local analysis and multi-resolution, this method can obtain higher measurement precision by comparing with the Fourier transform method. Both computer simulation and practical experiment testified the validity of the proposed method.

同轴偏视场共孔径面阵成像光学系统设计

同轴偏视场共孔径面阵成像光学系统设计

Calculation of the overlap factor for scanning LiDAR based on the tridimensional ray-tracing method.

The overlap factor is used to evaluate the LiDAR light collection ability. Ranging LiDAR is mainly determined by the optical configuration. However, scanning LiDAR, equipped with a scanning mechanism to acquire a 3D coordinate points cloud for a specified target, is essential in considering the scanning effect at the same time. Otherwise, scanning LiDAR will reduce the light collection ability and even cannot receive any echo. From this point of view, we propose a scanning LiDAR overlap factor calculation method based on the tridimensional ray-tracing method, which can be applied to scanning LiDAR with any special laser intensity distribution, any type of telescope (reflector, refractor, or mixed), and any shape obstruction (i.e., the reflector of a coaxial optical system). A case study for our LiDAR with a scanning mirror is carried out, and a MATLAB program is written to analyze the laser emission and reception process. Sensitivity analysis is carried out as a function of scanning mirror rotation speed and detector position, and the results guide how to optimize the overlap factor for our LiDAR. The results of this research will have a guiding significance in scanning LiDAR design and assembly.

Automatic low-order aberration correction based on geometrical optics for slab lasers.

In this paper, we present a method based on geometry optics to simultaneously correct low-order aberrations and reshape the beams of slab lasers. A coaxial optical system with three lenses is adapted. The positions of the three lenses are directly calculated based on the beam parameters detected by wavefront sensors. The initial sizes of the input beams are 1.8 mm×11 mm, and peak-to-valley (PV) values of the wavefront range up to several tens of microns. After automatic correction, the dimensions may reach nearly 22 mm×22 mm as expected, and PV values of the wavefront are less than 2 μm. The effectiveness and precision of this method are verified with experiments.

A Coaxial and Off-axial Integrated Three-mirror Optical System with High Resolution and Large Field of View

A novel optical design for high resolution, large field of view (FOV) and multispectral remote sensing is presented. An f/7.3 Korsch and two f/17.9 Cook three-mirror optical systems are integrated by sharing the primary and secondary mirrors, bias of the FOV, decentering of the apertures and reasonable structure arrangement. The aperture stop of the Korsch system is located on the primary mirror, while those of the Cook systems are on the exit pupils. High resolution image with spectral coverage from visible to near-infrared (NIR) can be acquired through the Korsch system with a focal length of 14 m, while wide-field imaging is accomplished by the two Cook systems whose focal lengths are both 13.24 m. The full FOV is 4°×0.13°, a coverage width of 34.9 km at the altitude of 500 km can then be acquired by push-broom imaging. To facilitate controlling the stray light, the intermediate images and the real exit pupils are spatially available. After optimization, a near diffraction-limited performance and a compact optical package are achieved. The sharing of the on-axis primary and secondary mirrors reduces the cost of fabrication, test, and manufacture effectively. Besides, the two tertiary mirrors of the Cook systems possess the same parameters, further cutting down the cost.