Qingfeng Cui

Design of multilayer diffractive optical elements with polychromatic integral diffraction efficiency

What we believe to be a new method for designing multilayer diffractive optical elements (MLDOEs) for wideband with consideration of polychromatic integral diffraction efficiency (PIDE) is presented. The benefit of this method is that the maximum PIDE over the entire waveband for MLDOEs can be obtained. The design process and simulation of the MLDOEs with regard to an example for visible waveband are described, and the comparison of diffraction efficiencies of the MLDOEs for different choices of design wavelengths with different methods is given.

Diffraction efficiency change of multilayer diffractive optics with environmental temperature

In this paper, the effect of an environmental temperature change on multilayer diffractive optical elements (MLDOEs) is studied in terms of the diffraction efficiency and the polychromatic integral diffraction efficiency (PIDE). The relation between the diffraction efficiency of MLDOEs and environmental temperature is analyzed theoretically, and examples of different MLDOEs are discussed in the visible and infrared wavebands. The result shows that the diffraction efficiency reduction is no more than 5% and the PIDE reduction is less than 1.5% for optical plastic MLDOEs in the visible waveband when the environmental temperature ranges from −62 to 71 °C, and that the decrease of both the diffraction efficiency and PIDE for MLDOEs is more significant in the mid-wave infrared than in the long-wave infrared. The analysis result can be considered during optical engineering design with MLDOEs.

Optimal design of a multilayer diffractive optical element for dual wavebands.

A method for optimal design of a multilayer diffractive optical element (MLDOE) for dual-wide-waveband optical systems is presented with consideration of polychromatic integral diffraction efficiency (PIDE) and the weight factors of PIDE for each waveband. The design process and simulation of a MLDOE in mid-wave and long-wave IR are described, and the comparison of diffraction efficiency of the MLDOEs for different design wavelength pairs determined by different methods is given. This method can make the design process more rational and more reasonable and can give a better design result than that with the conventional design method.

Effects of manufacturing errors on diffraction efficiency for multilayer diffractive optical elements

The effect of manufacturing errors on diffraction efficiency for multilayer diffractive optical elements (MLDOEs) used in imaging optical systems is discussed in this paper. The relationship of diffraction efficiency and depth-scaling errors are analyzed for two different cases: the two relative depth-scaling errors change in the same sign and in the opposite sign. For the first condition, the corresponding diffraction efficiency decreases more slowly. The effect of periodic width errors on diffraction efficiency is also evaluated. When the two major manufacturing errors coexist, the magnitude of the decrease of diffraction efficiency is analyzed for MLDOEs. The result can be used for analyzing the effects of the manufacturing errors on diffraction efficiency for MLDOEs.

High diffraction efficiency of three-layer diffractive optics designed for wide temperature range and large incident angle.

A mathematical model of diffraction efficiency and polychromatic integral diffraction efficiency affected by environment temperature change and incident angle for three-layer diffractive optics with different dispersion materials is put forward, and its effects are analyzed. Taking optical materials N-FK5 and N-SF1 as the substrates of multilayer diffractive optics, the effect on diffraction efficiency and polychromatic integral diffraction efficiency with intermediate materials POLYCARB is analyzed with environment temperature change as well as incident angle. Therefore, three-layer diffractive optics can be applied in more wide environmental temperature ranges and larger incident angles for refractive-diffractive hybrid optical systems, which can obtain better image quality. Analysis results can be used to guide the hybrid imaging optical system design for optical engineers.

Achromatic negative index lens with diffractive optics

In this paper, achromatization of a negative index lens is achieved by introducing the diffractive optical elements (DOEs) into the negative index lens. The diffraction efficiency of the negative index material (NIM) DOEs is deduced based on the special propagating laws and imaging properties of negative index lenses, and the expression for microstructure height is given. As an example, an achromatic refractive–diffractive negative index lens with 150 mm focal length and 15 mm entrance pupil diameter is discussed from wavelength 0.848 μm through wavelength 0.912 μm to wavelength 1.114 μm. According to the deduced expression for the NIM DOEs, the diffraction efficiency is calculated, and the diffraction efficiency curve is fitted by interpolation.

Tolerance analysis of multilayer diffractive optics based on polychromatic integral diffraction efficiency.

Multilayer diffractive optical elements (MLDOEs) can achieve high diffraction efficiency for broadband wavelength. Polychromatic integral diffraction efficiency (PIDE) is the key concern for evaluating diffraction efficiency over the waveband. The modulation transfer function of a hybrid refractive-diffractive optical system is directly affected by the PIDE. The relationship between PIDE and continuous manufacturing errors for microstructure heights and periodic widths of MLDOEs is studied theoretically in this paper, and an example of MLDOEs is discussed in the visible waveband. The analysis results can be used for manufacturing error control in microstructure heights and periodic widths.

Optimal design method on diffractive optical elements with antireflection coatings

The effect of antireflection coatings on diffraction efficiency of diffractive optical elements (DOEs) was studied and the mathematical model of diffraction efficiency affected by antireflection coatings for DOEs is presented. We found antireflection coatings can cause a significant reduction on diffraction efficiency at the designed, or the central wavelength. In order to solve this problem, we proposed a method to keep 100% diffraction efficiency at the designed wavelength by ensuring the 2π phase induced by DOEs and the antireflection coatings. Diffraction efficiency affected by antireflection coatings for DOEs with consideration of antireflection coatings are simulated. Analysis results can be utilized for refractive-diffractive hybrid imaging optical system optimal design and image quality evaluation.

Aberration and boresight error correction for conformal aircraft windows using the inner window surface and tilted fixed correctors

A static solution to aberrations and boresight error for tilted conformal aircraft windows at different look angles is reported. The solution uses the inner window surface to correct the window aberrations at a 0° look angle and uses fixed correctors behind the window to correct the residual window aberrations at other look angles. Then, the boresight error for the window at different look angles is corrected by tilting the fixed correctors. The principle of the solution is discussed, and a design example shows that the solution is effective in correcting the aberrations and boresight error for a tilted conformal aircraft window at different look angles.

Design of a dual-band MWIR/LWIR circular unobscured three-mirror optical system with Zernike polynomial surfaces

This paper discusses the optical design of an uncooled dual-band MWIR/LWIR optical system using a circular unobscured three-mirror system which is particularly suitable for wide spectral range , large aperture and small volume imaging systems. The system is designed at focal length 310mm, F-number 1.55 with field of view 1.77°×1.33°. A coaxial three-mirror system is calculated by the paraxial matrix as a starting point. With the condition that the focal point of each conic mirror is placed to coincide successively, elements in the system are tilted and decentered properly to make the system unobscured and the mirrors are arranged to form a round configuration for compactness. The optical path is folded inside the region surrounded by the mirrors. Zernike polynomial surfaces which are limited to be symmetric about tangential plane are used to correct aberrations and to improve the image quality. The modulation transfer function of this system is above 0.65 in MWIR band and above 0.5 in LWIR band all over the field of view at the Nyquist frequency of 20 line pairs per millimeter. The result shows that the space can be utilized efficiently, the system is compact and image quality is favorable.