一种控制波前传播的衍射光学元件新颖设计方法研究

In recent years more attentions have been paid on such sort of the diffractive optical elements (DOEs) which can control three dimensional wave-front propagation. In this item we proposed a novel method for designing the unconventional DOEs. The method is named adjacent sequence weighting iterative algorithm. It has its physical significance and is consistent with the feature of the light beam propagation. It also has the advantages of the fast convergent speed and obtaining the stationary solution. A diffractive optical element for focusing a diode laser beam into large depth of focus was designed with this new algorithm. The main requirements of this design are that, the diode laser with wavelength l = 780 nm, the diameter of DOE d = 4mm, its focal length f=80 mm, its focal depth Df 3 ±1 mm, and within this focal depth region (2mm ′f50mm) the light energy flowing should be over 80% of the total energy of the beam. The designed element was fabricated by means of photolithography and ion etching techniques and tested by a diode laser beam. The experiment results show the design is successful. Otherwise, two DOEs are designed to convert from a circular-gaussian beam to flat-top square beam and triangular beam respectively with two-dimensional serial weighted iterative algorithm. They realized simultaneity both functions of beam-shape and the uniform distribution of the intensity. The computed results indicated that the energy transformation efficiency of two DOEs is up to 95.3％ and 93.6％ respectively. .We designed the unconventional diffractive optical elements (DOE) for controlling the beam profile in three-dimensional space with the help of the Simulated Annealing algorithm (SA). We obtained some a spatially quantized DOE with 8 phase levels or 16 phase levels. The output intensity distribution along the optical axis is modulated by the designed DOE and the profile in each cross section in the region z=76~84mm fulfills the constraint by the objective profile so that the intensity is focused on the desired region. The hybrid algorithm that combined of both SA and the adjacent sequence weighting iterative algorithm are presented for controlling the three dimensional wave-front propagation. A ring-beam convertor with the vertical and horizontal modulation functions is designed based on the hybrid algorithm. It is a rotation symmetrical DOE with 16 phase levels that is used to convert the input uniform beam to a ring output beam maintaining the same distribution of the intensity in the region z=76~90mm. .A variable phase level method for quantizing is brought forward. This method can overcome the limitation between the fabrication precision and the size of the DOE. An one-dimensional Fresnel zone lens is designed with the method and fabricated by the micro-electronic technology. The diffraction efficiency of the DOE is 90.94% by computing and 86% by testing. he DOE improved the characteristics of the divergent angles of the semiconductor laser evidently.

用衍射光学元件控制三维波前传播是衍射光学领域中一个崭新的研究课题。本项目提出一种新颖串行加权设计方法，它不但具有物理内容、符合光束传播的物理本质，更有收敛速度快可获得稳定解的特点，这是一种普适性强、有特色和创新意义的设计方法。用此新方法优化设计并研制出具有纵深调制功能的衍射相位元件将有广阔的应用前景。