Reconfigurable photonic crystal circuits

We describe progress in the field of tuning, (re)configuration of Photonic crystal (PhC) based devices with a particular emphasis on our recent concepts and techniques that we have developed to tune and/or reconfigure the properties of photonic crystal nanocavities. We show how our hybrid approach based on photosensitive material and tapered silica fiber can tune the (Q, λ) properties of preexisting Photonic crystal cavities. We describe our alternative techniques to create ‘a posteriori’ spatially (re)configurable high‐Q cavities in a PhC platform. We show that optofluidics – the fusion of microfluidics with photonic devices – offers an unquestionable added value to the quest of a truly versatile, (re)configurable photonic crystal based photonic chip.     

Interference grating structures in photonic crystal circuits

Photonic Crystal Circuits have been widely investigated for various optoelectronics device applications. And the gratings in photonics devices are indispensable tool, which is very common for light manipulation. In this study, an interference grating structure formed by Gaussian beam interferences in photonic crystal waveguide such that having Kerr type nonlinearity is proposed and its transmission characteristics are investigated. Finite-Difference Time-Domain method is used to analyze the device characteristics. According to simulation results, the interference grating has shown special transmission characteristics that can bring tunability for photonic crystal devices. This can be an effective method for controlling optical signals in the photonic crystal for all optical switching/routing applications as a part of add/drop multiplexing.     

Intrinsic localized modes in photonic crystal circuits

A discussion of intrinsic localized modes (ILMs) in photonic crystals is given. Emphasis is placed on ILMs in photonic crystal waveguides formed from Kerr nonlinear materials and photonic crystal circuits formed by joining nonlinear photonic crystal waveguides into networks. Work on stationary and propagating ILMs in nonlinear waveguides and waveguide junctions is reviewed. In addition, some discussion is given on the optical bistability of the barrier and junction geometries and on recent results on two-dimensional ILMs in Kerr nonlinear photonic crystals.     

Investigation of ring resonators in photonic crystal circuits

In this paper, we propose the implementation of waveguide-coupled ring resonators in photonic crystal integrated circuits. Using two-dimensional finite difference time domain (2D FDTD) method, we study the spectral characteristics of a waveguide-coupled ring carved in two-dimensional photonic crystal of square lattice (2D SLPC) and based on the results, we suitably modify the structure geometry to establish its performance as a ring resonator. We further investigate the effects of ring dimension and crystal parameters on the resonance properties of the ring resonator.     

Modal selective tuning in a photonic crystal cavity

We present a way to selectively tune the properties of the degenerated modes confined in a single point defect two-dimensional photonic crystal cavity based on a triangular lattice of air holes. We investigate the dependence of the modal properties of the resonator on the position of the first neighbor holes, showing that it is possible to finely tune the resonant frequency of only one of these two modes and to increase the quality factor of the mode that has no frequency shift. This is achieved by controlling the wavevector components inside the cavity. This approach is a viable strategy for the development and the optimization of several innovative devices based on bi-modal cavity arrays, such as arrays of integrated optical filters and optical read-out sections for biosensing applications.     

Scattering matrix approach to large-scale photonic crystal circuits

We propose a scattering matrix approach to the modeling of large-scale photonic crystal circuits and show that the transmission properties of complex circuits can be accurately calculated on the basis of scattering matrices of individual photonic crystal devices and waveguides that connect them. In addition, we show that functional devices such as waveguide bends generally exhibit a discontinuous frequency dependence in the phases associated with their complex reflection and transmission coefficients and emphasize its importance for the adequate modeling of photonic crystal circuits.     

Enhanced all-optical tuning of leaky eigenmodes in photonic crystal waveguides

We demonstrate all-optical switching in an active two-dimensional photonic crystal waveguide, observing as large as 16 nm blueshifts of a leaky eigenmode at 839 nm and switching ratios of almost 70%. These results are larger than those previously observed in similar experiments performed on passive photonic crystal waveguides; the enhancement is due to resonant photogeneration of carriers by In(0.12)Al(0.2)Ga(0.68)As quantum wells in the core of the waveguide. The effective change in the refractive index of the structure is approximately10(-2), with a rise time of approximately1 ps and a decay time of approximately10 ps, potentially allowing high-speed switching and fast modulation rates.     

Analysis and design of efficient coupling in photonic crystal circuits

A rigorous analysis and design of efficient coupling from photonic crystal (PhC) waveguides into conventional dielectric waveguides is reported. Closed-form expressions for the reflection and transmission matrices that completely characterize the scattering that occurs at the interface are derived based on an eigenmode expansion technique and a Bloch basis. Analytic expressions are used to analyze the reflection into PhC waveguides. We obtain that negligible reflection can be achieved by choosing a certain interface within a PhC unit cell. Furthermore, analytic expressions are used to design a novel and compact coupler structure in order to achieve high coupling efficiency when broad dielectric waveguides are considered. Thereby, transmission efficiencies near 100 from the fundamental guided Bloch mode into the fundamental waveguide mode are achieved.     

Defect modes and wavelength tuning of one-dimensional photonic crystal with lithium niobate

The defect state of the one-dimensional photonic crystals consisting of lithium niobate and air is theoretically investigated. By applying an external voltage on the defect layer, remarkable wavelength tuning can be achieved. The relation between the wavelength peak and the external voltage is a straight line and the tuning rate is 1.358 nm/kV. The dependence of the wavelength peak on the angle of incidence was also observed at each applied voltage. This feature can be employed to fabricate tunable filters.     

Broadband waveguide intersections with low cross talk in photonic crystal circuits

We propose a new mechanism for constructing waveguide intersections with broad bandwidth and low cross talk in photonic crystal (PC) circuits. The intersections are created by combination of coupled-cavity wave-guides (CCWs) with conventional line-defect waveguides. This mechanism utilizes the strong dependence of the defect coupling on the field pattern in the defects and the alignment of the defects (i.e., the coupling angle) in CCWs. By properly designing the defect mode, we demonstrate through numerical simulation the establishment of such a waveguide intersection in one of the most useful PCs, which is based on a two-dimensional triangular lattice of air holes made in a dielectric material. The transmission of a 500-fs pulse at ~1.3 microm is simulated by use of the finite-difference time-domain method, showing negligible distortion and low cross talk.     

Tunable photonic crystal circuits: concepts and designs based on single-pore infiltration

We demonstrate that the infiltration of individual pores of certain two-dimensional photonic crystals with liquid crystals and (or) polymers provides an efficient platform for the realization of integrated photonic crystal circuitry. As an illustration of this principle, we present designs for monomode photonic crystal wave-guides and certain functional elements, such as waveguide bends, beam splitters, and waveguide intersections. These devices exhibit very low reflection over broad frequency ranges. In addition, we discuss the inherent tunability of these devices that originates in the tunability of the infiltrated material.     

Temperature tuning of polarization mode dispersion in single-core and two-core photonic liquid crystal fibers

In this paper we present numerical and experimental results of propagation and polarization properties of the photonic liquid crystal fibers (PLCFs) in which only selected micro holes were filled with nematic liquid crystal (LC) guest materials. As a host photonic crystal fiber (PCF) structure, we used a commercially available highly birefringent PCF (Blazephotonics, UK). A tunable laser operated at infrared has powered the PLCFs under investigation infiltrated by the 1550 nematic LC synthesized at the Military University of Technology. Temperature induced changes of the polarization mode dispersion (PMD) as well switching between fundamental and higher order modes and also single-core and two-core propagation were successfully demonstrated.     

Numerical demonstration of slow light tuning in slotted photonic crystal waveguide using microfluidic infiltration

Tuning of the operating wavelength of slow light in the slotted photonic crystal waveguide using microfluidic infiltration has been investigated. Using 2D plane wave expansion method, we numerically demonstrate that the operating wavelength can be shifted from the C to L band, simply by choosing the refractive index of the infiltrated fluid. It is also found that, as the refractive index of the infiltrated fluid changes, the group velocity dispersion has slight variation at different operating wavelength. This design opens the possibility for post-fabrication scheme of tuning the operating wavelength of slow light in slotted photonic crystal waveguide, and allows the device to be optimized for different applications.     

Angular tuning of defect modes spectrum in the one-dimensional photonic crystal with liquid-crystal layer

A one-dimensional ZrO₂/SiO₂ photonic crystal with a 4-n -pentyl-4' -cyanobiphenyl (5CB) nematic defect layer was used to investigate the transmission spectra of light polarized parallel and perpendicular to the liquid-crystal director at different angles of incidence. The spectra of the photonic crystal were shown to split into four polarized components T_ij at oblique incidence. When the incident angle increased, the bandgap edges and the defect modes shifted towards short wavelengths, while the amplitudes of the defect modes increased for the transverse magnetic polarization and decreased for the transverse electric polarization. The observed discrepancy between the defect mode amplitudes in the center and near the edges of the photonic bandgap was found to be related to the radiation losses inside the defect layer of a non-ideal photonic crystal. The simulated transmission spectra obtained using recurrence relations and taking into account the decay of defect modes are in good agreement with the experimental data.     

Polymer-based photonic integrated circuits

A myriad of passive and active guided-wave devices has been successfully demonstrated using the photolime gel polymer. These include high density linear and curved channel waveguide arrays, electro-optic modulator and modulator arrays, highly multiplexed waveguide holograms for wavelength division demultiplexing and optical interconnects, waveguide lens, and rare-earth ion-doped polymer waveguide amplifiers. A single-mode linear channel waveguide array with device packaging density of 1250 channels cm^-1 has been achieved. The first 12-channel wavelength division demultiplexer working at 830, 840, 850, 860, 870, 880, 890, 900, 910, 920, 930 and 940 nm on a GaAs substrate is also described in this paper. A polymer-based electro-optic travelling wave modulator with 40 GHz electrical bandwidth is further delineated. A rare-earth ion-doped polymer waveguide amplifier working at 1.06 μm with 8.5 dB optical gain is also achieved using this polymer matrix. The tunability of the waveguide refractive index of photolime gel polymer allows the formation of a graded index (GRIN) layer. As a result, these active and passive guided wave devices can be realized on any substrate of interest. High quality waveguides (loss<0.1 dB cm^-1) have been made on glass, LiNbO3, fused silica, quartz, PC board, GaAs, Si, Al, Cu, Cr, Au, Kovar, BeO, Al₂O₃ and AIN.     

适用于毫米波带状束行波放大器的光子晶体栅慢波电路研究

提出了一种适用于毫米波及THz波行波放大器的光子晶体栅慢波电路,即横向分布光子晶体栅慢波电路,并提出了分析和设计此类光子晶体栅慢波电路的方法.通过计算光子晶体TE极化的带隙和在带隙内将光子晶体栅慢波电路等效为矩形栅波导慢波电路,从而,光子晶体栅慢波电路的设计得以分为两步独立进行,从而简化了光子晶体栅慢波电路的设计.对横向分布光子晶体栅慢波电路进行了设计和计算,结果表明,与矩形栅波导慢波电路相比,横向分布光子晶体栅慢波电路可以降低工作电压并增加带宽,从而可以降低成本. 关键词： 行波放大器 光子晶体 毫米波 慢波电路     

Mechano-optical wavelength tuning in a photonic crystal microcavity with sub-1 V drive voltage

A micro-bimorph cantilever with self-aligned nanotips is monolithically integrated with a photonic crystal based device using optical and deep UV lithography techniques. Upon electrostatic actuation, the dielectric nanotips perturb the optical field, providing electromechano-optical modulation of light. Static tuning of the optical transmission spectra by more than 600 pm is measured with a sub-1 V drive voltage, resulting in a modulation as high as 21 dB. The observed strong electromechano-optical effect may find application in power efficient devices for optical communication networks, such as wavelength routing elements.     

Thermo-optical sensitivity analysis in photonic crystal circuits based on semiconducting or metallic metamaterial constituents

We introduce a novel analysis technique for predicting thermo-optical sensitivities in photonic crystal (PC) circuits composed of either dielectric-semiconducting or metallic constituents. The proposed numerical analysis is based on a hybrid formalism of the scattering matrix technique combined with the adjoint network method. The proposed computational scheme can, with modest computational resources, predict with high accuracy, the effect of the temperature fluctuations to the light-wave propagation in PCs. Numerical simulations show that PC circuits based on metallic metamaterial platforms are significantly less sensitive to temperature variations than the usual dielectricor semiconducting PCs.     

Remote tuning of NMR probe circuits

There are many circumstances in which the probe tuning adjustments cannot be located near the rf NMR coil. These may occur in high-temperature NMR, low-temperature NMR, and in the use of magnets with small diameter access bores. We address here circuitry for connecting a fixed-tuned probe circuit by a transmission line to a remotely located tuning network. In particular, the bandwidth over which the probe may be remotely tuned while keeping the losses in the transmission line acceptably low is considered. The results show that for all resonant circuit geometries (series, parallel, series-parallel), overcoupling of the line to the tuned circuit is key to obtaining a large tuning bandwidth. At equivalent extents of overcoupling, all resonant circuit geometries have nearly equal remote tuning bandwidths. Particularly for the case of low-loss transmission line, the tuning bandwidth can be many times the tuned circuit's bandwidth, f(o)/Q.     

石墨烯-硅基混合光子集成电路

近年来硅基光子学已经慢慢走向成熟,它被认为是未来取代电子集成电路,实现下一代更高性能的光子集成电路的关键技术.这得益于硅基光子器件与现代的互补金属氧化物半导体工艺相兼容,能够实现廉价的大规模集成.然而,由于受硅材料本身的光电特性所限,在硅基平台上实现高性能的有源器件仍然存在着巨大挑战.石墨烯-硅基混合光子集成电路的发展为解决这一问题提供了可行的方案.这得益于石墨烯作为一种兼具高载流子迁移率、高电光系数和宽带吸收等优点的二维光电材料,能够方便地与现有硅基器件相集成,并充分发挥自身的光电性能优势.本文结合我们课题组在该领域研究的一些最新成果,介绍了国际上在石墨烯-硅基混合光子集成电路上的一些重要研究进展,涵盖了光源、光波导、光调制器和光探测器四个重要组成部分.