Baojun Zuo

Wavefront coding technique for controlling thermal defocus aberration in an infrared imaging system.

We use a wavefront coding approach to control thermal defocus aberration in an IR imaging system. The design method of athermalized system using a wavefront coding technique is discussed. An athermalized long wave IR optical system, which works at temperatures ranging from -40 °C to 60 °C, is designed by employing a cubic phase mask. Computer simulations and the first experimental demonstration are executed to verify the performance of this wavefront coded athermalized system and to clarify the issues related to its implementation.

Design of fixed correctors used in conformal optical system based on diffractive optical elements.

A conformal dome was designed and the aberration characteristics of the dome were analyzed using Zernike aberration theory. By deriving the equation used to correct Zernike aberrations, the phase coefficients and the phase orders of diffractive optical elements (DOEs) used to correct primary Zernike aberrations were obtained. DOEs were simulated to correct the aberrations of the conformal dome by using optical design software, and the aberrations of the conformal dome decreased dramatically. Finally, a complete cooled conformal optical system was designed. The results show that the number of the fixed correctors elements decreases by using DOEs, and the optical system has better imaging quality.

Focusing properties of two-dimensional photonic quasicrystal flat lens at different object distances

We report the object-distance effect on the focusing properties of a two-dimensional (2-D), photonic quasicrystal (PQC) flat lens by numerical simulation. For the image power and image quality, the half-thickness of the flat lens is no longer the optimal object distance. The object-image distance is not always double the flat lens thickness, which is apparently different from a 2-D, periodic photonic crystal (PPC) flat lens and left-handed material (LHM) flat lens. With the point-light source located near half-thickness of the lens object distance, a 2-D PQC flat lens can achieve a perfect image in a certain range. With an appropriate object distance, a 2-D PQC flat lens is much better than a 2-D PPC flat lens in the aspect of imaging resolution. The results are beneficial to understand the focusing and imaging of a 2-D PQC flat lens.

Joint influences of aerodynamic flow field and aerodynamic heating of the dome on imaging quality degradation of airborne optical systems.

We investigated the joint influences exerted by the nonuniform aerodynamic flow field surrounding the optical dome and the aerodynamic heating of the dome on imaging quality degradation of an airborne optical system. The Spalart-Allmaras model provided by FLUENT was used for flow computations. The fourth-order Runge-Kutta algorithm based ray tracing program was used to simulate optical transmission through the aerodynamic flow field and the dome. Four kinds of imaging quality evaluation parameters were presented: wave aberration of the exit pupil, point spread function, encircled energy, and modulation transfer function. The results show that the aero-optical disturbance of the aerodynamic flow field and the aerodynamic heating of the dome significantly affect the imaging quality of an airborne optical system.

Multitarget compounding technique based on dimpled mirror

Abstract. The multitarget compounding technique is key in an infrared hardware-in-the-loop simulation system. In this study, the beam-broadening theory and carefully designed experiments are presented to analyze a multitarget compounding system based on a dimpled mirror. By paraxial approximation of geometrical optics, the expression of broadened beamwidth of a dimpled-mirror two-mirror three-reflection concentric system was obtained as the function of system parameters. A multitarget compounding setup was designed and experiments were performed. Excellent matching results were achieved between the beamwidth theory and the experiments. Experimental results demonstrated that the beam-broadening theory is creditable and suitable to design the multitarget compounding system. The theory and experiments are beneficial to the future development and implementation of multitarget compounding technique.

Support mechanism design of large aperture reflective mirror for large temperature variations

A cold-background multi-target compounding system provides infrared targets for a hardware-in-the-loop simulation system, in which large aperture reflective mirrors are employed. In this paper, we propose a combined belt-back structure and design the flexible connection to solve the support mechanism of large aperture mirrors for 100 K temperature variations. By Finite Element Method analysis, the root mean square of the optimized mirror was better than λ/40 under self-gravity and 100 K temperature variations. By Zernike polynomial fitting, the modulate transmission function of the multi-target compounding system was over 0.5 and the root mean square spot diameter was less than 0.05 mrad. Results demonstrate that the proposed support mechanism was effective, providing analytical data for a 1 m level mirror for large environment temperature variations.

Off-axis aberration effect on beamwidth in multitarget compounding system

Multitarget compounding system is a decisive subsystem of the infrared hardware-in-the-loop simulation system and the concentric structure with dimpled mirror is a potential multitarget compounding system. By inducting the off-axis aberration, the effect of off-axis aberration on broadening beamwidth was investigated for the practical multitarget compounding system. A critical abaxial distance was found when the axial spherical aberration was equal to the focal length of small mirrors. Outgoing beamwidth was increasing with abaxial distances when abaxial distance was over the critical distance. A laboratory multitarget compounding system was designed to demonstrate the effect.