Optimal design of a gravitational wave telescope system for the suppression of stray light.

For gravitational wave detection, the telescope is required to have an ultra-low wavefront error and ultra-high signal-to-noise ratio, where the power of the stray light should be controlled on the order of less than 10-10. In this work, we propose an alternative stray light suppression method for the optical design of an off-axis telescope with four mirrors by carefully considering the optimal optical paths. The method includes three steps. First, in the period of the optical design, the stray light caused by the tertiary mirror and the quaternary mirror is suppressed by increasing the angle formed by the optical axes of the tertiary mirror and the quaternary mirror and reducing the radius of curvature of the quaternary mirror as much as possible to make sure the optical system provides a beam quality with a wavefront error less than λ/80. Next, the stray light could satisfy the requirement of the order of 10-10 when the level of roughness reaches 0.2 nm, and the pollution of mirrors is controlled at the level of CL100. Finally, traditional stray light suppression methods should also be applied to mechanics, including the use of the optical barrier, baffle tube, and black paint. It can be seen that the field stop can efficiently reduce stray light caused by the secondary mirror by more than 55% in the full field of view. The baffle tube mounted on the position of the exit pupil can reduce the overall stray light energy by 5%, and the difference between the ideal absorber (absorption coefficient is 100%) and the actual black paint (absorption coefficient is 90%) is 3.2%. These simulation results are confirmed by the Monte Carlo method for a stray light analysis. Based on the above results, one can conclude that the geometry structure of the optical design, the quality of mirrors, and the light barrier can greatly improve the stray light suppression ability of the optical system, which is vital when developing a gravitational wave telescope with ultra-low stray light energy.

Advanced Biomimetic Multispectral Curved Compound Eye Camera for Aerial Multispectral Imaging in a Large Field of View.

In this work, we demonstrated a new type of biomimetic multispectral curved compound eye camera (BM3C) inspired by insect compound eyes for aerial multispectral imaging in a large field of view. The proposed system exhibits a maximum field of view (FOV) of 120 degrees and seven-waveband multispectral images ranging from visible to near-infrared wavelengths. Pinhole imaging theory and the image registration method from feature detection are used to reconstruct the multispectral 3D data cube. An airborne imaging experiment is performed by assembling the BM3C on an unmanned aerial vehicle (UAV). As a result, radiation intensity curves of several objects are successfully obtained, and a land type classification is performed using the K-means method based on the aerial image as well. The developed BM3C is proven to have the capability for large FOV aerial multispectral imaging and shows great potential applications for distant detecting based on aerial imaging.

Long-working-distance 3D measurement with a bionic curved compound-eye camera.

The bionic curved compound-eye camera is a bionic-inspired multi-aperture camera, which can be designed to have an overlap on the field of view (FOV) in between adjacent ommatidia so that 3D measurement is possible. In this work, we demonstrate the 3D measurement with a working distance of up to 3.2 m by a curved compound-eye camera. In that there are hundreds of ommatidia in the compound-eye camera, traditional calibration boards with a fixed-pitch pattern arrays are not applicable. A batch calibration method based on the CALTag calibration board for the compound-eye camera was designed. Next, the 3D measurement principle was described and a 3D measurement algorithm for the compound-eye camera was developed. Finally, the 3D measurement experiment on objects placed at different distances and directions from the compound-eye camera was performed. The experimental results show that the working range for 3D measurement can cover the whole FOV of 98° and the working distance can be as long as 3.2 m. Moreover, a complete depth map was reconstructed from a raw image captured by the compound-eye camera and demonstrated as well. The 3D measurement capability of the compound-eye camera at long working distance in a large FOV demonstrated in this work has great potential applications in areas such as unmanned aerial vehicle (UAV) obstacle avoidance and robot navigation.

Biomimetic multispectral curved compound eye camera for real-time multispectral imaging in an ultra-large field of view.

In this work, we demonstrate a prototype of a biomimetic multispectral curved compound eye camera (BMCCEC). In comparison with traditional multispectral imaging systems, the BMCCEC developed in this work has the distinct features of multi-spectral imaging on multiple targets in real time in an ultra-large field of view (FOV), which can be attributed to its biomimetic curved compound eye structure as well as the multispectral cluster network. Specifically, the BMCCEC has a total of 104 multispectral ommatidia and a FOV of 98°×98°, which is able to realize 7-band multispectral imaging with center wavelengths of 500 nm, 560 nm, 600 nm, 650 nm, 700 nm, 750 nm and 800 nm and a spectral resolution of 10 nm. A prototype of BMCCEC was then manufactured and multispectral imaging experiments were performed based on it. As a result, the red edge feature of the spectrum of green plants has been successfully obtained and retrieved with a good accuracy.

Biomimetic curved compound-eye camera with a high resolution for the detection of distant moving objects.

In this Letter, we demonstrate the design and fabrication of a biomimetic curved compound-eye camera (BCCEC) with a high resolution for detecting distant moving objects purpose. In contrast to previously reported compound-eye cameras, our BCCEC has two distinct features. One is that the ommatidia of the compound eye are deployed on a curved surface which makes a large field of view (FOV) possible. The other is that each ommatidium has a relatively large optical entrance and long focal length so that a distant object can be imaged. To overcome the mismatch between the curved focal plane formed by the curved compound eye and the planar focal plane of the CMOS image sensor (CIS), an optical relay subsystem is introduced between the compound eye and the CIS. As a result, a BCCEC with 127 ommatidia in the compound eye is designed and fabricated to achieve a large FOV of up to 98∘×98∘. The experimental results show that objects with a size of 100 mm can be clearly resolved at a distance of 25 m. The capture of the motion trajectories of a moving object is also demonstrated, which makes it possible to detect and track the moving targets in a huge FOV for security surveillance purposes.

Multispectral curved compound eye camera.

In this work, we propose a new type of multispectral imaging system, named multispectral curved compound eye camera (MCCEC). The so called MCCEC consists of three subsystems, a curved micro-lens array integrated with selected narrow-band optical filters, an optical transformation subsystem, and the data processing unit with an image sensor. The novel MCCEC system can achieve multi-spectral imaging at an ultra-large field of view (FOV), and obtain information of multiple spectrum segments at real time. Moreover, the system has the advantages of small size, light weight, and high sensitivity in comparison with conventional multispectral cameras. In current work, we mainly focus on the optical design of the MCCEC based on the overlap of FOV between the neighboring clusters of ommatidia to achieve the multispectral imaging at an ultra-large FOV. The optical layout of the curved micro-lens array, narrow-band filter array and the optical relay system for image plane transformation are carefully designed and optimized. The whole size of the optical system is 93 mm × 42 mm × 42 mm. The simulation results show that a maximum FOV of about 120° can be achieved for seven-waveband multispectral imaging with center wavelengths of 480 nm, 550 nm, 591 nm, 676 nm, 704 nm, 740 nm, and 767 nm. The new designed MCCEC has a great potential as an airborne or satellite-born payload for real time remote sensing and thus paves a new way for the design of compact and light-weight spectral-imaging cameras with an ultra large FOV.

Feasibility of hyperspectral analysis for discrimination of rabbit liver VX2 tumor.

BACKGROUND: Hepatocellular carcinoma is one of the most common malignant tumors worldwide. Currently, the most accurate diagnosis imaging modality for hepatocellular carcinoma is enhanced magnetic resonance imaging. However, it is still difficult to distinguish cirrhosis lesions, and novel diagnosis modalities are still needed. AIM: To investigate the feasibility of hyperspectral analysis for discrimination of rabbit liver VX2 tumor. METHODS: In this study, a rabbit liver VX2 tumor model was established. After laparotomy, under direct view, VX2 tumor tissue and normal liver tissue were subjected to hyperspectral analysis. RESULTS: The spectral signature of the liver tumor was clearly distinguishable from that of the normal tissue, simply from the original spectral curves. Specifically, two absorption peaks at 600-900 nm wavelength in normal tissue disappeared but a new reflection peak appeared in the tumor. The average optical reflection at the whole waveband of 400-1800 nm in liver tumor was higher than that of the normal tissue. CONCLUSION: Hyperspectral analysis can differentiate rabbit VX2 tumors. Further research will continue to perform hyperspectral imaging to obtain more information for differentiation of liver cancer from normal tissue.