光学扫描全息术中各向异性边缘增强与螺旋相位滤波

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"Anisotropic edge enhancement in optical scanning holography with spiral phase filtering" 这篇论文探讨了在光学扫描全息术（OSH）中使用螺旋相位板（SPP）实现各向异性边缘增强的方法。光学扫描全息术是一种利用光波干涉原理记录和重建物体三维信息的技术，它具有高分辨率和对物体深度信息的敏感性。SPP是一种特殊的光学元件，能够引入螺旋相位，从而改变通过它的光波的相位分布。在论文中，作者提出将delta函数和SPP作为孔径函数，以实现对物体边缘信息的各向异性增强。delta函数在数学上表示为一个理想的点源，可以聚焦光束到一个非常小的点，而SPP则可以操纵光的传播方向，形成特定的相位分布。这两种孔径的干涉作用用于二维扫描物体，仅记录其边缘信息。他们提出了三种实现方法： 1. 移动SPP：通过改变SPP的位置，可以改变光波的相位分布，进而调整边缘增强的方向和强度。 2. 使用两个偏移的相同电荷SPP：这种配置可以产生更复杂的相位分布，可能允许同时增强多个方向的边缘。 3. 使用两个电荷相反的SPP：这种配置可能会导致相位的互补，从而产生独特的边缘增强效果。计算机模拟结果显示，这种方法有选择性地增强物体特定边缘的能力，这在图像处理和分析中具有重要价值，特别是在需要突出特定结构或特征时。例如，在生物医学成像、材料科学和微结构检测等领域，能够增强特定方向的边缘可以帮助研究人员更清晰地识别和分析目标物体的细节。文章的OCIS代码（Optical Society of America的分类号）为100.2980和090.1995，表明它属于光学的全息技术和成像技术领域。这篇论文的工作为光学扫描全息术提供了一种新的边缘增强技术，可能对未来成像系统的设计和应用产生积极影响。

Anisotropic edge enhancement in optical scanning

holography with spiral phase filtering

Kelly K. Dobson

, Wei Jia (贾伟)

*, and Ting-Chung Poon

Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, VA 24061, USA

Lab of Information Optics and Optoelectronic Technology, Shanghai Institute of Optics and Fine Mechanics,

Chinese Academy of Sciences, Shanghai 201800, China

*Corresponding author: jw81@163.com

Received September 9, 2015; accepted October 27, 2015; posted online December 16, 2015

Anisotropic edge enhancement is simulated using a spiral phase plate (SPP) in optical scanning holography

(OSH). We propose to use a delta function and an SPP as the pupil functions to realize anisotropic edge enhance-

ment. The interference of these two pupils is used to two-dimensionally scan an object to record its edge-only

information. This is done in three ways: first, by shifting the SPP, second, by using two offset SPPs of same

charge, and finally, by using two oppositely charged SPPs. Our computer simulations show the capability of

selectively enhancing the edges of a given object.

OCIS codes: 100.2980, 090.1995, 070.6110.

doi: 10.3788/COL201614.010006.

A common device to generate helical wavefronts or vortex

beams is the spiral phase plate (SPP), which has an

azimuthal structure exp½jnφ, where n is the topological

charge, which is generally a nonzero integer, and 0 ≤ φ <

2π is the azimuthal coordinate

[1,2]

. The simplest SPP

realized with n ¼ 1 has been demonstrated as a spatial

filter in a 4f system to achieve edge enhancement

[3]

and more recently, it was used as a pupil function for iso-

tropic edge extraction in optical scanning holography

(OSH)

[4]

Edge enhancement has found utility in a variety of

image processing applications where detecting the edge or

shape is of interest, such as in industrial inspections

[5,6]

and fingerprint identification

[7,8]

. Generally, the enhance-

ment effect is isotropic or symmetrical such that regardless

of orientation, each edge of the input pattern is enhanced

uniformly. However, in some cases, the feature informa-

tion around certain orientations and edges is of greater

interest and therefore requires anisotropic edge enhance-

ment to emphasize these edges. The methods reported for

selective edge enhancement include changing the integer

power and offset angle of the sine function in the vortex

distribution

[9]

, fractional

[10]

or shifted vortex filters

[11,12]

superposed vortex amplitude filter

[13]

, and the introduction

of astigmatism in the vortex filter

[14]

The use of SPPs for enhancement effects in digital

incoherent holography was first attempted using the

Fresnel incoherent correlation holography technique

[15]

and then by OSH

[4]

. The forme r approach is based on

self-interference and requires the capture of three phase-

shifted recordings sequentially, which could introduce bias

build-up when using complex objects

[16]

. The latter over-

comes this by heterodyne scanning the object such that

the holographic information is carried by the heterodyne

frequency, which can be extracted using electronic filter-

ing. With the scanning property , OSH can be applied in a

variety of fields, ranging from microscopes to remote

sensing

[17,18]

In this Letter, we demonstrate the use of OSH to record

selective edge-only information of an object holographi-

cally. We introduce three methods to do this: (1) shifting

the position of the SPP to position ðr

; φ

Þ in the pupil

plane, (2) using two symmetrically offset vortices of the

same charge, and (3) using two oppositely charged offset

vortices.

OSH is based on a two-pupil optical heterodyne image

processor

[19,20]

that captures the entire holographic infor-

mation of an object with a two-dimensional (2D) scan

while preserving the phase information in the recording

process. The two pupils in the standard OSH system

are such that one pupil is a uniform function or a plane

wave and the other is a delta function or point source.

The interference of these two pupils is used to 2D scan

an object to extract its holographic information.

The two pupil functions, p

ðx; yÞ and p

ðx; yÞ, in the

two-pupil heterodyne scanning image processor presented

in Fig.

1 are lo cated in the front focal plane of lens L

with

focal length f . The pupils are illuminated by collimated

laser beams with temporal frequencies ω

and ω

þ Ω, re-

spectively, where ω

≫ Ω and the frequency shift Ω results

from an acousto-optic modulator. The laser beams are

Fig. 1. Two-pupil heterodyne scanning image processor.

COL 14(1), 010006(2016) CHINESE OPTICS LETTERS January 10, 2016

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