Nanjing University; Winner of Changjiang Distinguished Professor and Young Distinguish Scholar Funding; A Fellow of OSA.
Yan-qing Lu,College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, China, received both his BS and Ph.D. degrees from Nanjing University, China, in 1991 and 1996 respectively. He has five-year experiences in US and China telecomm industries. He designed and developed a serial of liquid crystal based fiber-optic devices with his colleagues, which include variable optical attenuators, variable Mux/Demux, DWDM wavelength blocker etc. He is currently a Changjiang distinguished professor at Nanjing University and a Fellow of OSA. His research interests include liquid crystal photonics, fiber optics and nonlinear optics. He is the author or co-author of ~150 peer-reviewed papers in Science, Adv. Mater., Optica, Phys. Rev., Appl. Phys. Lett., Opt. Lett. etc. with ~ 3000 citations. He also holds more than 40 domestic or international patents or pending patents.
Liquid Crystal for Non-display Photonic Applications
Inducing micro-patterns and structures inside a Liquid crystal (LC) cell is an effective way to improve the performance of LC display. However, in addition to display applications, LC also plays an important role in various tunable photonic devices with the advantages of low cost, no moving parts, low power consumption and high reliability. In this talk, I am going to review some of our work in merging LC and various artificial microstructures in different spans. The related photonic applications are discussed.
If the typical size of a LC microstructure is much larger than the light’s wavelength, it would just work like a multi-pixel LC modulator that is very useful in fiber-optic devices to process multi-channel DWDM signals simultaneously. We design and developed a LC based 40 channel 100GHz spacing wavelength blocker that could regulate the light powers of arbitrary channels. This device could play a key role in current ROADM all-optical networks.
If the LC microstructure is in the micrometer span, which is comparable with the light’s wavelength, the diffraction effect thus should be taken into account. As the simplest case of LC diffractive element, LC grating has been widely studied. We developed a serial of LC tunable 1D/2D gratings based on the photo alignment technique with both PA/PA and PA/TN configurations. In addition, ferroelectric LC and blue phase LC gratings are also demonstrated.
To realize arbitrary LC alignment microstructures, we further propose and implement a DMD based dynamic micro-lithography system thus could instantly write complicated patterns in the LC cell. Besides normal phase gratings, more complex patterns such as quasicrystal and chequerboard structures are demonstrated. In comparison with other techniques, our method enables the arbitrary and instant manipulation of LC alignments and light polarization states, facilitating wide applications in display and photonic fields. Among them, a recent attempt is to tailor the light’s wave front for singular optics applications.
As we know, many novel singular optical phenomena have been predicted and demonstrated in both linear and nonlinear optics regimes. Although local optical phase could be controlled directly or through hologram structures in isotropic materials such as glasses, optical anisotropy is still required for manipulating polarization states and wavelengths. The anisotropy could be either intrinsic such as in crystals/LC or the induced birefringence from dielectric or metallic structures. Based on our dynamic micro-lithography system, complex micro-photo-patterning could be generated then further guides the local LC directors. Due to the electro-optically (EO) tunable anisotropy of LC, various reconfigurable complex optical fields such as optical vortices (OVs), multiplexed OVs, OV array, Airy beams and vector beams are obtained. Different LC modes such as homogeneous alignment nematic, hybrid alignment nematic and even blue phase LCs are adopted to optimize the static and dynamic beam characteristics depending on application circumstances.
In a word, we believe the photonic application of LC is a very promising field in both fundamental research and related industry, which deserves more attentions and extensive study.