基于空间光调制器的 longitudinally polarized subwavelength-sized 光针的偏振 amp...
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光学针的极化和振幅混合调制
极化和振幅混合调制是光学领域中的一个重要技术，用于生成 longitudinally polarized subwavelength-sized optical needle，即纵向极化亚波长尺寸光针。该技术可以应用于各种领域，例如生物成像、纳米加工、激光微加工等。
在这项技术中， researchers 使用了一个 4-f 系统，配备了空间光调制器，来生成实验性的双模交替圆柱矢量光束，这种方法可以增强性能和促进实现。同时，researchers 还使用了模拟退火算法来优化光束聚焦特性，通过_annular aperture 产生振幅调制。
这种技术的原理是基于光束的极化和振幅调制。通过对光束的极化状态进行调制，可以控制光束的极化方向，从而实现光束的纵向极化。同时，通过对光束的振幅进行调制，可以控制光束的强度，从而实现光束的振幅调制。
极化和振幅混合调制技术可以应用于各种领域，例如生物成像、纳米加工、激光微加工等。在生物成像领域中，该技术可以用于生成高分辨率的图像，用于观察生物样本的微细结构。在纳米加工领域中，该技术可以用于生成纳米尺寸的图案，用于制造纳米尺寸的设备。在激光微加工领域中，该技术可以用于生成高精度的激光微加工结果，用于制造微尺寸的零件。
极化和振幅混合调制技术是一个非常有前途的技术，具有广泛的应用前景。该技术可以推动光学领域的发展，促进相关领域的研究和应用。
知识点：
1. 极化和振幅混合调制技术的原理是基于光束的极化和振幅调制。
2. 该技术可以应用于生物成像、纳米加工、激光微加工等领域。
3. 极化和振幅混合调制技术可以生成高分辨率的图像，用于观察生物样本的微细结构。
4. 该技术可以生成纳米尺寸的图案，用于制造纳米尺寸的设备。
5. 极化和振幅混合调制技术可以生成高精度的激光微加工结果，用于制造微尺寸的零件。
6. 该技术可以推动光学领域的发展，促进相关领域的研究和应用。
极化和振幅混合调制技术是一个非常有前途的技术，具有广泛的应用前景。该技术可以推动光学领域的发展，促进相关领域的研究和应用。
COL 11(5), 052601(2013) CHINESE OPTICS LETTERS May 10, 2013
Polarization and amplitude hybrid modulation of
longitudinally polarized subwavelength-sized optical needle
Lijiao Guo (
HHH
www
), Changjun Min (
DDD
ddd
), Shibiao Wei (
¸¸¸
JJJ
), and Xiaocong Yuan (
hhh
)
∗
Institute of Modern Optics Key Laboratory of Optical Information Science and Technology Ministry of Education of China,
Nankai University, Tianjin 300071
§
China
∗
Corresponding author: xcyuan@nankai.edu.cn
Received December 25, 2012; accepted January 28, 2013; posted online April 2, 2013
We present a method of both polarization and amplitude modulations on an incident beam to obtain a
longitudinally polarized subwavelength-sized optical needle. A 4-f system with a spatial light modulator is
used to generate experimentally a two-mode alternate cylindrical vector beam by polarization modulation,
enhancing performance and facilitating implementation. We optimize the beam focusing properties after
passing the beam through an annular aperture to obtain amplitude modulation by the simulated annealing
algorithm. Numerical results indicate that a sharp focal spot (0.417λ) with a long focal depth (8λ) and a
strong longitudinally polarized field can be easily achieved.
OCIS codes: 260.5430, 140.3300.
doi: 10.3788/COL201311.052601.
Focusing an incident beam into a small spot with a long
fo c al depth has received significant research interest in
optical engineering
[1−5]
. The successful generation of ra-
dially polarized beams in recent decades provides a basis
for obtaining a strong longitudinal field co mponent when
it is focused by a high numerical aperture (NA) objec-
tive lens. Possible applications in particle acceleration
[6]
,
fluorescent imaging
[7]
, second-harmonic generation
[8,9]
,
and Raman spectroscopy
[10]
have been reported. Thus,
the generation of a longitudinally polarized beam with a
small transverse s pot and a long depth of focus (DOF)
has drawn considerable interest. For e xample, a small
fo c al spot with a strong longitudinal component is ob-
tained at the focal region by focusing a radially polar-
ized beam with an extremely narrow annular aperture
and a high-NA objective lens
[11,12]
. An amplitude filter
based on Euler transformation can also o bta in a longitu-
dinally polarized b e am with a long DOF of 9λ, whereas
the full-width at half-ma ximum (FWHM) of the focal
sp ot is 0.8λ
[13]
. Radially polarized beams combined with
a binary phase optica l element have efficiently produced
a “pure” longitudinally polarized subwavelength beam
(also ca lled optical needle) with a DOF of 4λ in high-NA
fo c using
[14−16]
. Most previous techniques for manipulat-
ing focal depth and size are based on the amplitude or
phase modulation of radia lly polarized beams.
Cylindrical vector beams other than radially polarized
beams have bee n successfully generated and studied in
recent years, which allows shaping the fo c al spot by po-
larization modulation. In the present study, we propose a
method of both polarization and amplitude modulations
on the incident bea m to obtain an optical needle with
a sharp focal spot and a strong longitudinally polarized
component. We use a 4-f system comprising a spatial
light modulator (SLM) and a common path interferomet-
ric arra ngement
[17,18]
to generate directly a two-mode al-
ternate (TMA) cylindrical vector beam by polarization
modulation. We use an annular aperture to modulate
the amplitude distribution of the TMA beam. A new
optimization approach that combines the simulated a n-
nealing algorithm
[19]
and the TMA beam with an annu-
lar aperture is proposed to enhance the optimization of
beam focusing properties. Optimized results show that
the FWHM of the focal spot for the total e le c tric field is
0.417λ; the DOF can be enhanced to 8λ, and the ratio
of the longitudinal component to the total electric field
for the main-lobe intensity is 0.84.
We firstly investigated the generation of a TMA beam,
as shown in Fig. 1. The TMA beam is a type of cylindri-
cal vector beam, with each point having a polarization
rotated by φ
0
from its radial direction
[20]
. Different from
the radially (φ
0
= 0) and azimuthally (φ
0
= π/2) polar-
ized lights, the beam has two mo des of polarization in
different concentric regions. The beam cross-section is
divided into nconcentric regions (n = 1, 2, 3, · · ·), with
each region corresponding to a focal angle of θ
i
(i =
1, 2, · · · , n). As illustrated in Fig. 1, the transverse beam
profile of the TMA beam comprises five concentric re-
gions, and each region has the polarization state below :
φ
0
=
0, for 0 < θ < θ
1
, θ
2
< θ < θ
3
, θ
4
< θ < α
π, for θ
1
< θ < θ
2
, θ
3
< θ < θ
4
, (1)
where α = arcsin(NA/n
0
) represents the maximum focal
angle determined by the high- NA objective lens; and n
0
is the refractive index of the surrounding medium.
To ge nerate the TMA beam, we use d a 4-f system
comprising a SLM and a common path interferometric
arrangement
[17,18]
, which is conveniently accomplished
by a re designed computer-generated holographic gra t-
ing (HG); the experimenta l setup and HG are shown in
Fig. 2. The SLM used was a reflective liquid-crystal dis-
play containing 1 920 × 1 080 (pixel) that are 8× 8 (µm)
Fig. 1. Focusing layout of a five-region TMA beam. α is the
maximum focal angle determined by the high-NA lens.
1671-7694/2013/052601(4) 052601-1
c
2013 Chinese Optics Letters
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