Dipti Banerjee
The polarization matrix ($2\times2$) obtained from two component eigen-spinors of spherical harmonics help us to evaluate the differential matrix $N$ of the anisotropic optical medium. The geometric phase is realized through {\it helicity} of photon, assuming the transmission of polarized light through the crystal which has been twisted about the normal to its surface over a closed path.
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We demonstrate a photonic analog of twisted bilayer graphene that has ultra-flat photonic bands and exhibits extreme slow light behavior. Our twisted bilayer photonic device, which has an operating wavelength in C-band of the telecom window, uses two crystalline silicon photonic crystal slabs separated by a methyl methacrylate tunneling layer. We numerically determine the magic angle using a finite-element method and the corresponding photonic band structure, which exhibits a flat band over the entire Brillouin zone. This flat band causes the group velocity to approach zero and introduces ligh…
We report trapping and propagation of photonic Dirac mode in a helically twisted hollow core photonic crystal fiber (HC-PCF) where the trapped light in the hollow (air) defect can preserve the orbital angular momentum (OAM). We show that a photonic Dirac point can emerge even in a twisted system for a suitable choice of curvilinear coordinate and the related waveguide defect modes defined in the new basis can preserve the associated OAM during axial translation. The effect of twist rate, defect geometry and crystal dimension on the propagation of OAM carrying trapped Dirac modes is critically …
Large-angle twisted photonic crystal semiconductor nanolasers with ultra-low thresholds operating in the C-band
本文提出大角度扭转光子晶体纳米激光器，通过任意选择扭转角度实现C波段单模激射，具有约25 μm²超紧凑占位面积、0.47 (λ/n)³超小模式体积和约1.25 kW/cm²超低阈值，为高密度集成光子芯片提供高性能纳米相干光源新途径。
We consider light propagation through a twisted nematic liquid crystal. At first, an expression for light transmission is obtained using a rather intuitive approach. Secondly, an accurate solution for light transmission based on Maxwell's equations is derived and compared with the previous one. Both approaches show that when changes in the orientation of the liquid crystal optical axis are small on the scale defined by the optical wavelength (Mauguin limit), the polarization of light approximately follows the optical axis. At the same time, even in this limit, the simple formula for the light …
Twisted bi-layer magnetic photonic crystals
本文提出扭曲磁性双层光子晶体平台，通过调节层间扭曲角实现巨大圆二色性及完美线偏振旋转，为磁性拓扑光子学奠定基础。
Spatial light modulators are widely used to perform modulations of different properties of the electromagnetic field. In this work, a simple optimization method for general double-pass setups was developed. It takes into account the involved polarizing elements and displays, and a numerical simulation based on an exhaustive search routine finds the optimal optical axes orientation of the polarizing elements for the desired modulation. By simultaneously considering both impingements, we are able to take full advantage of the modulation capabilities of the chosen spatial light modulators. In par…
Enhanced Cherenkov radiation in twisted hyperbolic Van der Waals crystals
研究快电子与扭曲双曲范德华晶体相互作用，在平带共振频率实现宽动量范围增强切伦科夫辐射，为定向自由电子辐射提供新途径。
Polaritons - hybrid light-mater excitations - are very appealing for the confinement of light at the nanoscale. Recently, different kinds of polaritons have been observed in thin slabs of van der Waals (vdW) materials, with particular interest focused on phonon polaritons (PhPs) - lattice vibrations coupled to electromagnetic fields in the mid-infrared spectral range with - in biaxial crystals, such as e.g. MoO3. In particular, hyperbolic PhPs - having hyperbola-like shape of their isofrequency curves - in MoO3 can exhibit ultra-high momenta and strongly directional in-plane propagation, promi…
Recently, moiré engineering has been extensively employed for creating and studying novel electronic materials in two dimensions. However, its application in nanophotonic systems has not been widely explored so far. Here, we demonstrate that twisted bilayer photonic crystals provide a new photonic platform with twist-angle-tunable optical dispersion. Compared to twisted two-dimensional materials, twisted bilayer photonic crystals host a rich set of physics and provide a much larger number of degrees of freedom choice of material, lattice symmetry, feature size, twist angle, and interlayer gap,…
We report a series of experimental, analytical and numerical studies demonstrating strong circular dichroism in helically twisted hollow-core single-ring photonic crystal fiber (SR-PCF), formed by spinning the preform during fiber drawing. In the SR-PCFs studied, the hollow core is surrounded by a single ring of non-touching capillaries. Coupling between these capillaries results in the formation of helical Bloch modes carrying orbital angular momentum. In the twisted fiber, strong circular birefringence appears in the ring, so that when a core mode with a certain circular polarization state (…
Frequency conversion of vortex states by chiral forward Brillouin scattering in twisted photonic crystal fibre
本文利用扭曲光子晶体光纤中的手性前向受激布里渊散射激发手性弯曲声子，实现了不同波长下后向传播圆偏振涡旋模式间的频率转换，为经典与量子领域的涡旋态操控提供了新途径。
Polarization vectors of light traveling in a coiled optical fiber rotate around its propagating axis even in the absence of birefringence. This rotation was usually explained due to the Pancharatnam-Berry phase of spin-1 photons. Here, we use a purely geometric method to understand this rotation. We show that similar geometric rotations also exist for twisted light carrying orbital angular momentum (OAM). The corresponding geometric phase can be applied in photonic OAM-state-based quantum computation and quantum sensing.
Twisted heterobilayer photonic crystal based on stacking and selective etching of 2D materials
针对多层扭曲光子晶体纳米加工的挑战，在石墨/Si$_3$N$_4$异质结构中通过干法转移与选择性刻蚀制备了扭曲异质双层光子晶体，实验观察到莫尔位点产生的可见光波段腔光子模式，为光子控制提供了新自由度。
On-Chip Multidimensional Dynamic Control of Twisted Moiré Photonic Crystal for Smart Sensing and Imaging
该研究提出集成MEMS的扭转莫尔光子晶体传感器，可动态调控层间间隙与扭转角，实现电信波段宽范围、全庞加莱球的高精度光谱偏振传感，为多功能平面光子器件提供可扩展方案。
Defect modes are investigated in a band gap of an electrically tunable one-dimensional photonic crystal infiltrated with a twisted-nematic liquid crystal (1D PC/TN). Their frequency shift and interference under applied voltage are studied both experimentally and theoretically. We deal with the case where the defect layer thickness is much larger than the wavelength (Mauguin condition). It is shown theoretically that the defect modes could have a complex structure with the elliptic polarization. Two series of polarized modes interact with each other and exhibit an avoided crossing phenomenon in…
Moire-enabled optical vortex with tunable topological charge in twisted bilayer photonic crystals
本研究利用扭曲双层莫尔光子晶体的层间耦合产生贝塞尔型连续谱准束缚态，实现了拓扑荷可调的光学涡旋阵列，为集成OAM的复用技术提供了新方案。
Removal of guided acoustic wave Brillouin scattering to the quantum-noise limit using symmetric interferometry in twisted photonic crystal fibers
提出扭曲光子晶体光纤(t-PCF)作为首个能完全消除混合扭转径向GAWBS的光纤系统，通过对称干涉仪中的自参考和Stokes检测将GAWBS相位噪声补偿至量子噪声极限。
Twisted light with orbital angular momentum (OAM) has been extensively studied for applications in quantum and classical communications, microscopy, and optical micromanipulation. Ejecting the naturally high angular momentum whispering gallery modes (WGMs) of an optical microresonator through a grating-assisted mechanism, where the generated OAM number ($l$) is the difference of the angular momentum of the WGM and that of the grating, provides a scalable, chip-integrated solution for OAM generation. However, demonstrated OAM microresonators have exhibited a much lower quality factor ($Q$) than…
Weyl points are the degenerate points in three-dimensional momentum space with nontrivial topological phase, which are usually realized in classical system with structure and symmetry designs. Here we proposed a one-dimensional layer-stacked photonic crystal using anisotropic materials to realize ideal type-II Weyl points without structure designs. The topological transition from two Dirac points to four Weyl points can be clearly observed by tuning the twist angle between layers. Besides, on the interface between the photonic type-II Weyl material and air, gappless surface states have also be…
We study the radiation from charged particles crossing a cholesteric plate in the shortwave approximation when the wavelength of photons is much smaller than the pitch of the cholesteric helix whereas the escaping angle of the photon and the anisotropy of the permittivity tensor can be arbitrary. The radiation of photons is treated in the framework of quantum electrodynamics with classical currents. The radiation of the plane-wave photons and the photons with definite projection of the angular momentum (the twisted photons) produced by charged particles crossing the cholesteric plate and movin…
General Framework for Twisted Bilayer Photonic Crystal with Interlayer Coupling and Far-Field Response
本文构建兼顾近场层间耦合与远场响应的扭转双层光子晶体通用理论，解释能带劈裂与散射抑制，并提出可调谐高 Q 平带腔。
Generation of particular polarization states of light, encoding information in polarization degree of freedom, and efficient measurement of unknown polarization are the key tasks in optical metrology, optical communications, polarization-sensitive imaging, and photonic information processing. Liquid crystal devices have proved to be indispensable for these tasks, though their limited precision and the requirement of a custom design impose a limit of practical applicability. Here we report fast preparation and detection of polarization states with unprecedented accuracy using liquid-crystal cel…
Spatially twisted liquid-crystal devices
针对现有液晶器件取向层图案一致的局限，本文提出前后取向层图案不同的非对称空间扭曲液晶结构，制备多q波片并通过偏振表征验证其具备新功能。
A genetic algorithm for the response of twisted nematic liquid crystals to an applied field
针对扭曲向列液晶外场响应数值求解现有方法定制性差、需预设试解的问题，提出一种遗传算法求解方程积分形式，无需试解即可得到与实验高度吻合的快速准确结果。
Topological manipulation of waves is at the heart of the cutting-edge metamaterial researches. Quadrupole topological insulators were recently discovered in two-dimensional (2D) flux-threading lattices which exhibit higher-order topological wave trapping at both the edges and corners. Photonic crystals (PhCs), lying at the boundary between continuous media and discrete lattices, however, are incompatible with the present quadrupole topological theory. Here, we unveil quadrupole topological PhCs triggered by a twisting degree-of-freedom. Using a topologically trivial PhC as the motherboard, we …
Entangled Telecom Photon Generation using Twisted Van der Waals Crystals
该研究利用范德瓦尔工程化的NbOBr₂材料，通过自发参量下转换生成纠缠光子，并通过90度扭曲堆叠实现量子干涉，获得高保真度的偏振纠缠态，展示了高亮度的电信波长量子光源。
Twisted hyperbolic van der Waals crystals for full Stokes mid-infrared polarization detection
本文提出一种基于面内双轴双曲范德华晶体的芯片集成偏振计，通过六个线/圆偏振滤波器实现全斯托克斯中红外偏振探测，消光比超30 dB、透射率超50%，为超紧凑片上偏振探测提供新方案。
We present an experimental study of the quasi-elastic Raman scattering (QES) of plane-wave and twisted light by liquid crystals. Depending on their temperature, these crystals can exhibit isotropic, nematic and chiral nematic phases. The question is addressed of how the phase of a crystal and the state of incident light can affect the quasi-elastic energy spectra of the scattered radiation, whose shape is usually described by the combination of Lorentzian and Gaussian components. Special attention is paid to the \textit{chiral phase}, for which the Raman QES spectrum is dominated by a Lorentzi…
Twisted nonlinear optics in monolayer van der Waals crystals
本研究通过单层范德华晶体中的二次和三次频率混合过程，实现了对涡旋光场波长、轨道角动量和空间分布的独立操控，展示了超紧凑且可扩展的混合纳米技术新途径。
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