Abstract
We demonstrated a reflective-type liquid crystal (LC) intensity modulator in 1550 nm telecomm band. An effective way to compensate the residual phase of a LC cell is proposed. With the adjustment of a true zero-order quarter wave plate and enhanced by total internal reflection induced birefringence, over 53 dB dynamic range was achieved, which is much desired for some high-end optical communication, infrared scene projection applications. In addition, the driving voltages were decreased and adjustable. Mechanical and spectral tolerance measurements show that our LC modulator is quite stable. Further applications of our experimental setup were discussed including bio-sensors and high speed modulators.
Highlights
Background and motivationIn addition to the well-known flat panel displays and projectors, liquid crystal (LC) has been widely used in many tunable photonic devices, such as spatial light modulators, tunable lenses, optical phase arrays, variable optical attenuators (VOAs), and optical switches. [1,2,3,4,5,6]
A polarization beam displacer (PBD) and a homogeneously-aligned, 45°-rubbed LC cell are sandwiched between an input fiber collimator and a silica retro-reflector
A quartz true zero-order quarter wave plate (QWP) is placed between the PBD and LC cell
Summary
In addition to the well-known flat panel displays and projectors, liquid crystal (LC) has been widely used in many tunable photonic devices, such as spatial light modulators, tunable lenses, optical phase arrays, variable optical attenuators (VOAs), and optical switches. [1,2,3,4,5,6]. For MEMS technology, light is mechanically deflected high contrast ratio is relatively easy to achieve; while with regard to a LC device, which is normally based on polarization manipulation. Both the polarizer quality and accurate polarization control should be satisfied simultaneously. Even the VA cell still has slight initial phase retardation due to the LC pretilt angle To solve this problem, some companies use oblique dielectric birefringent coatings to compensate the residual phase. We demonstrated that an over 53 dB dynamic range may be achieved with wide spectral tolerance range Another merit is that the driving voltage becomes adjustable at any given attenuation state. We found that our setup and compensation technique are very suitable for some other applications like biosensoring and high speed electro-optic modulating
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