基于H-PDLC光栅的电控光闸：新型高效集成方案

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本文主要探讨了一种基于可切换全息聚合物分散液晶（Holographic Polymer Dispersed Liquid Crystal, H-PDLC）光栅的电控光学斩波器的设计与实现。这种新型光学器件通过编程、可调和周期性的外部驱动源实现了对光的精确控制，相较于传统的机械式光学斩波器，具有显著的技术优势。首先，H-PDLC光学斩波器的一大亮点是其快速响应时间。由于H-PDLC材料的电致相变特性，能够在短时间内改变液晶分子的排列，从而改变光的传播路径或透射状态，这使得其在需要快速切换光通量的应用中表现得更为高效，如光通信系统中的信号调制或者光探测中的脉冲处理。其次，与机械式斩波器可能存在由于部件运动引起的机械磨损和变形不同，H-PDLC斩波器的响应更少受到这类问题的影响。其结构的非机械性设计降低了磨损的可能性，确保了信号的稳定传输，尤其在需要长时间运行且对信号质量要求高的环境中，这显得尤为重要。再者，H-PDLC光栅的集成性和控制性得到了显著提高。由于H-PDLC材料的自组装性质，可以方便地与其他光学元件集成在一起，形成微型化、紧凑型的光学系统。此外，电控操作使得控制信号的传输更加灵活，可以通过简单的电信号调整来实现光强的精细调节，这在自动化程度较高的现代科技应用中具有明显优势。此外，该研究还涉及到占空比的精确控制，即在开和关状态之间切换的时间比例，这是衡量光学斩波器性能的重要指标。通过调整驱动源参数，研究人员能够精确控制H-PDLC光栅的占空比，这对于实现不同类型的光信号处理，如频率混频、脉冲宽度调制等任务至关重要。文章中提到的实验数据，如“230.2090”、“090.2890”、“050.1950”、“230.3720”，可能是实验测量或特定性能参数的结果，但没有具体的上下文，难以确定其具体含义。这些数值可能是关于响应速度、开关时间、占空比误差或其他性能参数的测试结果。总结来说，H-PDLC光栅为基础的电控光学斩波器凭借其快速响应、低变形、易集成和高精度控制等特点，展现了巨大的技术潜力，特别是在高性能光学系统中，如激光雷达、光纤通信和光子计算等领域，将有广泛的应用前景。未来的研究可能会进一步优化材料性能，提升器件的稳定性和可靠性，以满足不断发展的光电子技术需求。

Decemb er 10, 2010 / Vol. 8, No. 12 / CHINESE OPTICS LETTERS 1167

Electrically controlled optical choppers based on

holographic polymer dispersed liquid crystal gratings

Jihong Zheng (郑郑郑继继继红红红)

1∗

, Guoqiang Sun (孙孙孙国国国强强强)

, Ken Wen (温温温垦垦垦)

, Tingting Wang (王王王艇艇艇艇艇艇)

Songlin Zhuang (庄庄庄松松松林林林)

, Yanjun Liu

, and Stuart Yin

College of Optics and Electron Information Engineering, University of Shanghai for Science and Technology,

Shanghai 200093, China

Department of Engineering Science and Mechanics, Pennsylvania State University, PA 16802, USA

Department of Electrical Engineering, Pennsylvania State University, PA 16802, USA

∗

E-mail: jihongzheng2002@yaho o.com.cn

Received May 5, 2010

An electrically controlled optical chopp er based on switchable holographic polymer dispersed liquid crystal

(H-PDLC) gratings is demonstrated through a programmable, adjustable, and periodic external driving

source. Compared with traditional mechanical optical chopp ers, the H-PDLC chopper exhibits many

advantages, including faster response time, less waveform deformation, as well as easier integration, control,

and fabrication, to name a few. Its excellent performance makes the device potentially useful in frequency

mo dulation optical systems, such as frequency division multiplexed microscopy system.

OCIS codes: 230.2090, 090.2890, 050.1950, 230.3720.

doi: 10.3788/COL20100812.1167.

Holographic polymer dispersed liquid crystal (H-PDLC)

has been receiving intensive attention in photonics since

Sutherland et al. first reported about it in 1993

[1]

. H-

PDLC-based gratings are tunable and switchable

[2−5]

be-

cause the refractive index matching between the polymer

bonder and the liquid crystal droplets can be adjusted

by a suitable external driving voltage. Thus, many H-

PDLC-based devices have been demonstrated, such as

lenses

[6−8]

, optical switches

[3,4]

, optical attenuators

[9,10]

and dynamic gain equalizers

[11]

. H-PDLC-based de-

vices have high diffraction efficiency and fast response

time, and are easy to fabricate. Therefore, these devices

have been extended to other applications, including in-

formation storage

[12]

, sensing

[13]

, lasing

[14−16]

, photonic

crystals

[17−19]

, and other optical devices

[20−23]

Majority of the H-PDLC-based opto-electronic devices

that have been conceived and implemented only take

advantage of the basic characteristics of H-PDLC Bragg

gratings, such as excellent wavelength or angle selectiv-

ity, to realize the intensity modulation or wavelength

division. H-PDLC grating can modulate the input light

to the “ON” or “OFF” state, as allowing it to act as

an optical chopper through the application of a periodic

driving source to replace the conventional mechanical

optical choppers.

Generally speaking, a conventional optical chopper

consists of a slotted rotating disc, which modulates the

light beam. A conventional chopper design has slow re-

sponse time and is prone to mechanical deformation. Me-

chanical choppers, especially those with multiple beams

modulation, cannot easily achieve real-time, small-scale,

and integrated design. H-PDLC choppers, on the other

hand, can overcome these limitations and exhibit sev-

eral advantages, such as faster response time (less than

1 ms), easier fabrication and integration, etc. In this

letter, we conceive and demonstrate experimentally an

electrically controlled chopper based on H-PDLC. The

proposed chopp er not only has the potential to replace

mechanical chopper in several conventional applications,

such as beam modulation, it is also suitable for a number

of emerging applications, such as in frequency division

multiplexed confocal microscopes

[24]

H-PDLC grating works as an electrically controlled

switch. At the “OFF” state, the H-PDLC phase grating

formed by the mismatch of the refractive index between

the liquid crystal droplet and polymer bonder diffracts

the incoming linearly polarized light. However, when a

suitable electric field is applied, the polarization direc-

tions of all liquid crystal (LC) molecular directors are

reoriented along the electric field direction. In partic-

ular, the Bragg grating disappears when the ordinary

refractive index of the LC matches the refractive index

of the surrounding polymer. In this case, the incident

laser beam transmits the cell directly without diffraction,

corresponding to the “ON” state. Therefore, by applying

a proper electric field, H-PDLC grating can be switched

between the “ON” and “OFF” states. Furthermore,

given that such kind of switching can be realized with

nearly 100% efficiency at fast speed

[2−4]

without the risk

of scattering loss

[25]

, the H-PDLC-based switch can be

used as a fast speed chopper.

The fabrication of H-PDLC grating with high

diffraction efficiency and fast switch time is an impor-

tant step in realizing the H-PDLC-based optical chopper.

In our experiment, H-PDLC gratings were fabricated

from a formulation of 39.9 wt.-% LC, TEB300 (Tsing-

Hua Yawang), 39.9 wt.-% monomer, EB8301(UCB), 8

wt.-% crosslinking monomer, N-vinylpyrrollidone (NVP)

(Sigma-Aldrich), 0.07 wt.-% photoinitiator, rose Ben-

gal (RB) (Sigma-Aldrich), 0.13 wt.-% coinitiator, N-

phenylglycine (NPG) (Sigma-Aldrich), and 12 wt.-%

surfactant, S-271 (ChemService). The LC TEB300 has

an ordinary refractive index of n

= 1.511 and a bire-

fringence of ∆n = 0.168 at 589 nm. All the materials

were mechanically blended according to the appropriate

weight ratios; these were stirred in an ultrasonic cleaner

1671-7694/2010/121167-04

° 2010 Chinese Optics Letters

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