Xuhong Chu

A novel optical readout infrared FPA imaging system with fiber reference channel

A novel fiber reference optical readout method was proposed in the bi-material micro cantilever infrared imaging system, which consists of an infrared imaging channel, an optical readout channel and a fiber reference channel. The fiber reference channel is used to monitor the intensity fluctuation of the light source, and provide a signal to correct the distortion of the infrared images from the optical readout channel. Comparing with the typical optical readout method without any references, the noise equivalent temperature difference (NETD) of such an infrared imaging system with the fiber reference optical readout method can be reduced by about 33% and edges of the IR images become clearer.

Imaging and image restoration of lens-combined modulated wavefront coding

In this paper, it presents a new wavefront coding (WFC) technology that we call lens-combined modulated wavefront coding (LM-WFC). Based on the LM-WFC design method, we establish a large depth of field and large aperture system. Simulation results indicate that the modulation transfer function of the system has a defocus invariant characteristic, which all typical WFC systems have, with a large depth of field. Experimental results for comparing the LM-WFC imaging system and a traditional imaging system are presented. The comparative results demonstrate that the LM-WFC system has an imaging performance invariant over a wide depth of field range.

Sea surface target detection and recognition algorithm based on local and global salient region detection

This paper proposes a new salient region detection algorithm to detect and recognize ship on the sea in a shaky field of view. Based on this situation, the approach this paper adopts to solve the problem is detecting the salient region of each frame separately instead of using tracking algorithm and the salient region detection is based on local and global contrast. The result shows that the interference can be restrained and the shape of target can be detected correctly. It proves that the algorithm in this paper is a highly efficient target detection algorithm for ship detection.

Study on the MWIR imaging ability of optical readout bimaterial microcantilever FPA uncooled infrared imaging system

In this paper, we analyze and experimentally demonstrate the medium-wave infrared (MWIR) imaging ability based on optical readout bimaterial microcantilever focal plane array (FPA) uncooled infrared imaging system. Multiband infrared imaging technology has been a hotspot in the field of infrared imaging. In the infrared band, medium-wave infrared (3~5 μm) has minimal attenuation of atmospheric infrared window, and it also covers many atomic and molecular absorption peak. Imaging study on MWIR radiation source also appears particularly important. First of all, we introduce the bimaterial microcantilever IR sensing principle and the fabrication of the bimaterial microcantilever FPA. Secondly, the paper introduces the theory of the optical-thermal-mechnical reading based on FPA. Finally, the experimental platform was constructed to conduct the MWIR imaging experiment. The medium-wave infrared radiation source consists of a continuous-wave optical parametric oscillator (OPO) that is pumped by a polarization-maintained, single-mode fiber amplifier. The length of the 50mm periodically polarized LiNbO3 crystal (5%MgO) is used as the nonlinear crystal. The stable cavity of the ring is designed, and the output of the 3~4 μm band is realized by the design of the nonlinear crystal polarization period. And the FPA employed in our experiment contains 256×256 pixels fabricated on a glass substrate, whose working bandwidth is covering the three IR atmospheric windows. The experimental results show that the bimaterial microcantilever FPA has a good imaging ability to the MWIR sources.

Analysis of wavefront coding imaging with cubic phase mask decenter and tilt

This paper has examined how the decenter and tilt of a cubic phase mask plate influence the imaging of a wavefront coding system. The calculated phase term of pupil function with mask decenter and tilt indicates that both decenter and tilt change the shape of the system modulation transfer function in a predictable way by changing the phase and defocus parameters. Simulation in an on-axis three-mirror Cassegrain system is presented to confirm the calculated formula result. Experimental results for mask decenter are also presented. The results demonstrate that the decenter of a phase mask has less effect on the point spread function in the z direction than the x and y directions.

Infrared image enhancement based on the edge detection and mathematical morphology

The development of the un-cooled infrared imaging technology from military necessity. At present, It is widely applied in industrial, medicine, scientific and technological research and so on. The infrared radiation temperature distribution of the measured objects surface can be observed visually. The collection of infrared images from our laboratory has following characteristics: Strong spatial correlation, Low contrast , Poor visual effect; Without color or shadows because of gray image , and has low resolution; Low definition compare to the visible light image; Many kinds of noise are brought by the random disturbances of the external environment. Digital image processing are widely applied in many areas, it can now be studied up close and in detail in many research field. It has become one kind of important means of the human visual continuation. Traditional methods for image enhancement cannot capture the geometric information of images and tend to amplify noise. In order to remove noise and improve visual effect. Meanwhile, To overcome the above enhancement issues. The mathematical model of FPA unit was constructed based on matrix transformation theory. According to characteristics of FPA, Image enhancement algorithm which combined with mathematical morphology and edge detection are established. First of all, Image profile is obtained by using the edge detection combine with mathematical morphological operators. And then, through filling the template profile by original image to get the ideal background image, The image noise can be removed on the base of the above method. The experiments show that utilizing the proposed algorithm can enhance image detail and the signal to noise ratio.

Extraction and analysis of the image in the sight field of comparison goniometer to measure IR mirrors assembly

The comparison goniometer is widely used to measure and inspect small angle, angle difference, and parallelism of two surfaces. However, the common manner to read a comparison goniometer is to inspect the ocular of the goniometer by one eye of the operator. To read an old goniometer that just equips with one adjustable ocular is a difficult work. In the fabrication of an IR reflecting mirrors assembly, a common comparison goniometer is used to measure the angle errors between two neighbor assembled mirrors. In this paper, a quick reading technique image-based for the comparison goniometer used to inspect the parallelism of mirrors in a mirrors assembly is proposed. One digital camera, one comparison goniometer and one set of computer are used to construct a reading system, the image of the sight field in the comparison goniometer will be extracted and recognized to get the angle positions of the reflection surfaces to be measured. In order to obtain the interval distance between the scale lines, a particular technique, left peak first method, based on the local peak values of intensity in the true color image is proposed. A program written in VC++6.0 has been developed to perform the color digital image processing.

Holographic illumination to compensate the FPA fabrication errors for FPA IR image system

The FPA Infrared imaging technology is widely used in military and civilian fields, and the optical readout FPA Infrared imaging technology is one of the most important branch. How to get a higher sensitivity IR image is very important since there are many factories that can degrade image quality. In this paper we introduce a method to improve system image quality, which is called the holographic compensate illumination based on the holographic technology. Firstly, we analyze the key influencing factors of the image quality of an optical readout FPA IR imaging system, and the two kinds of manufacturing errors of the FPA are given. Then we point out the principle of the method to compensate the FPA fabrication errors and design the experimental scheme. The result of the experiment shows that we can get a more uniform and higher sensitivity IR image by the method of holographic compensate illumination.

Holographic compensation-based optical readout technique for microcantilever IR image system

The progress of MEMS-based uncooled infrared focal plane arrays (IRFPAs) are one of the most successful examples of integrated MEMS devices. We report on the fabrication and performance of a MEMS IRFPA based on bimaterial microcantilever. The IR images of objects obtained by these FPAs are readout by an optical method. However, it is difficult to avoid unwanted shape distortions in fabrication, which can degrade image quality in many ways. In this paper, the actual manufacturing errors of FPA are widely and deeply analyzed. There are basically two kinds of manufacturing error. The limitations of both kind of error are given. It is alse pointed out that the detecting sensitivity has its special complexity if the shape of the FPA is not ideal flat. To overcome the difficulties in readout process caused by manufacturing errors, a novel holographic compensating illumination technology was given. The possibilities of actualizing this technology are analyzed in many aspects. And a model of computer generated holographic compensation is given as a further development to be actualized in future The experiment shows that it is a feasible way to improve system performance, especially when it is too difficult to perfect the techniques of an FPA fabrication.

Regulation of external harmonic frequency on the route to chaos

We experimentally implement the periodic and quasi-periodic bifurcations routes to chaos based on the semiconductor laser with optical feedback. The effects of the interaction between the relaxation oscillation frequency and external harmonic frequency on the quasi-periodic and period-doubling bifurcations routes to chaos are experimentally analyzed. The results show that the output of the laser evolve into chaos along the period-doubling bifurcations route with the optical feedback strength increasing when the relaxation oscillation frequency is integer multiple of the external harmonic frequency, otherwise, the output of the laser evolve into chaos along the quasi-periodic bifurcations route with the optical feedback strength increasing when the relaxation oscillation frequency is not an exact multiple of the external harmonic frequency. At the same time, the routes of the quasi-periodic and period-doubling bifurcations to chaos are proved theoretically by using the rate equations of the semiconductor laser subject to optical feedback. The results of numerical simulations are consistent very well with our experimental results.