Two-dimensional mapping of electro-optic phase retardation in lithium niobate crystals by digital holography

We demonstrate accurate two-dimensional mapping of the phase retardation induced by the electro-optic effect in lithium niobate crystals. Off-axis digital holography is used to investigate congruent z-cut crystals. The spatially resolved optical path difference is interferometrically measured while a linearly rising voltage ramp is applied to the crystal. This procedure provides information on the uniformity of crystals' electro-optic properties and offers the ability to detect the presence of defects that is of fundamental importance for reliable processing of photonic devices.     

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.     

铁电液晶缺陷光子晶体调谐滤波器的设计

将铁电液晶作为缺陷层引入一维光子晶体中,用电场改变液晶分子的取向,形成光子晶体快速可调谐滤波器.用传输矩阵法研究了铁电液晶缺陷光子晶体的可调谐滤波特性,计算了电压和液晶材料参量对滤波器透射谱的影响.结果表明:改变电压能容易改变光子晶体滤波器透射峰的位置、强度、个数和带宽,实现良好的调谐滤波功能.     

Electro-optic polarization converter with programmable spectral output in lithium niobate

An electro-optic polarization converter with programmable spectral output produced on lithium niobate at the 1530 nm wavelength regime is reported. Programmability is achieved by applying spatially periodic weighted voltages on interdigital electrode sets to independently adjust the coupling coefficients, and is controlled electronically via a personal computer interface. The operation of a device with 16 electrode sets as a programmable tunable wavelength filter is demonstrated. The number of selectable channels depends on the number of electrode sets. A 3-dB bandwidth ∼1 nm and a tuning range of 10 nm are measured. Nearest side lobes ?18 dB below the main peak are realized with apodization.     

The superprism effect using large area 2D-periodic photonic crystal slabs

The “superprism effect” is an effect observed in photonic crystal structures whereby the direction of light propagation is extremely sensitive to the wavelength and angle of incidence. To realize the superprism effect, new structures are presented which rely on the sensitivity of the phase velocity in a two-dimensional (2D) photonic crystal slab to observe angular magnification outside the photonic crystal medium. Constant frequency contour calculations for a photonic crystal slab of finite thickness are used to predict the phase velocity superprism effect. Further analysis using 2D finite-difference time-domain simulations indicate that a large area photonic crystal and wide excitation beam are necessary for clear observation of the superprism effect. A fabrication technique is demonstrated to achieve the structure's required nanometer-sized features over centimeter-scale areas.     

基于对称广义Fibonacci光子晶体结构的电光可调谐滤波器

本文构建了含有电光材料LiNbO3的一维对称广义Fibonacci光子晶体结构,提出并设计了一种基于该结构的可调谐滤波器,并利用传输矩阵法对设计的滤波器的可调谐滤波特性进行了理论研究.数据模拟结果表明:保持对称广义Fibonacci光子晶体的几何结构不变,通过改变电极所在处施加在电光介质(LiNbO3)层上的外加电场,...     

Electro-optically tunable microring resonators on lithium niobate

Electro-optical tuning of a microring resonator fabricated on lithium niobate (LiNbO3) is presented. The device structure, including microring resonator and couplers, is designed in detail and is produced by titanium diffusion on the wet-etched LiNbO3 ridge surface. The resonance wavelengths for TM and TE polarizations can be tuned by electro-optic effect. The output characteristics of through port and drop port in the microring resonators are measured, and the effect of applied voltage on the shift of resonant wavelength is discussed. The presented microring resonators have the features of fast tuning speed, high material stability, bidirection wavelength shift, and no heating interference. Realization of such a microring resonator on LiNbO3 makes the utilization of electro-optic tuning and nonlinear effects in the versatile photonic applications of microring resonators achievable.     

基于对称广义Fibonacci光子晶体结构的电光可调谐滤波器

本文构建了含有电光材料LiNbO₃的一维对称广义Fibonacci光子晶体结构,提出并设计了一种基于该结构的可调谐滤波器,并利用传输矩阵法对设计的滤波器的可调谐滤波特性进行了理论研究.数据模拟结果表明:保持对称广义Fibonacci光子晶体的几何结构不变,通过改变电极所在处施加在电光介质(LiNbO₃)层上的外加电场,即可实现滤波器的滤波通道波长的调节,滤波通道波长的改变与外加电压呈线性关系,随着外加电压的增加,滤波通道波长向短波长方向移动.此外,电压一定时,通道波长随光的入射角的增加向短波长方向移动;光的入射角一定时,外加正电压下,通道波长随电压增加发生蓝移,而外加负电压下,通道波长随反向电压的增加发生红移.最后,讨论了双电场作用下的多通道波长滤波器的结构极其特性.以上结果对于新型光子晶体器件的设计具有重要的参考价值.     

对称双缺陷光子晶体的可调谐滤波特性分析

基于光子晶体的光子局域特性,并利用光子晶体的介观压光效应,提出了一种新型的双通道可调滤波器结构.采用传输矩阵法对该滤波器的光学传输特性进行了理论推导,建立了透射谱与光子晶体结构参数的关系,讨论了介观压光效应对双缺陷光子晶体透射谱的影响,并对所设计的光子晶体结构进行了数值模拟.结果表明:随着入射角度的增大,缺陷峰发生蓝移.随着各介质层折射率或几何厚度的增加,缺陷峰发生红移.当光子晶体发生轴向拉伸应变时,缺陷峰的位置向长波长移动,但缺陷峰的峰值大体不变,从而验证了此滤波器的可调节性.该光子晶体滤波器结构紧凑,可调谐性好,为光子晶体激光器及传感器的设计提供了一定的理论参考.     

Tunable multilayer narrowband filter containing an ultrathin metallic film and a lithium niobate defect

By using lithium niobate (LiNbO₃) as a defect layer, a tunable multilayer narrowband reflection-and-transmission filter containing an ultrathin metallic film is proposed. Due to the voltage dependence of the refractive index for LiNbO₃, tunable optical filtering properties have been theoretically investigated based on the calculated wavelength-dependent reflectance and transmittance. The dependences of peak wavelength on the applied voltage and the angle of incidence are numerically illustrated. The results reveal that in addition to working as a tunable filter, it can also be expected to act as a refractometric optical sensor.     

Electro-optic Solc-type wavelength filter in periodically poled lithium niobate

We demonstrate an electro-optic Solc-type wavelength filter in periodically poled lithium niobate (PPLN). A Solc-type transmission spectrum is observed experimentally in PPLN with four periods from 20.2 to 20.8 microm. Modulation of the transmission power of the filter is realized by application of electric fields along the Y axis of the PPLN. It is observed that the wavelength can also be tuned by temperature.     

Figure of merit for near-velocity-matched traveling-wave modulators

We derive a relationship between the bandwidth and active length and a figure of merit for velocity- and near-velocity-matched lithium niobate traveling-wave electro-optic modulators. The figure of merit is given by the bandwidth per unit drive voltage squared and is independent of the length of the device. Alternatively, this figure of merit can be described by its inverse, which is proportional to the device's switching energy.     

Electro-optic Solc-type flat-top bandpass filter based on periodically poled lithium niobate

Based on the spectrum waveform similarity (SWS) rule we discovered in periodically poled lithium niobate (PPLN), a compact tunable flat-top bandpass filter is proposed theoretically, from which the bandwidth of the flat-top waveform can be obtained. For practical application, tunable flat-top filter can be easily achieved by selecting appropriate electric field along the transverse direction of PPLN. The tolerance analysis for this kind of tunable flat-top bandpass filter is also presented.     

Superprism properties in 2D polymer photonic crystals at high normal frequencies

The superprism effects of higher bands, i.e., for normal frequencies of higher than one, in two-dimensional (2D) polymer photonic crystals (PCs) are investigated. It is shown that in a polymer PC of triangular symmetry with filling factor of about 31%, the gradual transition of the hexagonal into triangular equi-frequency dispersion contours leads to a strong superprism in the 6th band at a normal frequency of 1.2. This dispersion is more prominent than those observed in the lower bands in 2D PCs. Also, this requires a lattice constant longer than the concerned wavelength. Furthermore, in a 2D polymer PC with a filling factor of about 83% a strong discontinuous superprism effect occurs at normal frequencies higher than one, which is due to an abrupt transition between two modes with the refraction angles of opposite signs. The effect can be exploited for switching applications as demonstrated in the paper.     

基于一维耦合腔光子晶体的声光可调谐平顶滤波器的研究

本文利用一维耦合腔光子晶体,提出了一种声光可调谐平顶滤波器.该滤波器利用声光效应,通过改变超声波频率使一维耦合腔光子晶体透射谱的平顶滤波器的中心波长产生漂移,从而实现可调谐的滤波功能.基于传输矩阵法和声光效应理论,建立了这种平顶滤波器的理论模型;利用COMSOL软件,对平顶滤波器的矩形度、通带带宽、插入损耗、可调谐特性、加工精度进行仿真研究.研究结果表明,通过施加频率为6-11 MHz的超声波,可实现通带带宽为5-6 nm及中心波长在1514-1562 nm范围内可调谐的平顶滤波器;在可调谐范围内通带带宽内插入损耗不超过2.23 dB,最低仅为0.78 dB,矩形度最低可达1.4;加工误差在±10 nm内平顶滤波器的中心波长、矩形度、插入损耗、通带带宽出现的偏差很小.该平顶滤波器具有易于设计和集成、通带平坦、可调谐范围宽、通带带宽稳定、插入损耗低、品质因素高的特点,在光开关、可调谐光纤激光器、光纤传感等光通信领域有重要应用.     

Fibre-Format Photonic Source Based on Efficient Frequency Doubling of Continuous-Wave Erbium-Fibre Laser Amplifier

We demonstrate a compact photonic device based on efficient and wavelength-tunable doubling of an all fibreformat source. Quasi-phase-matched second-harmonic generation in periodically poled lithium niobate is used to generate 90.6 m W at 775.9 nm with a single-pass conversion efficiency of 14.7%. A t uning bandwidth of 2.1 nm and a tuning temperature range of 150.6 ± 1.7℃ can be achieved. The Er-doped seed fibre source is amplified by a clad-pumped Er^3＋/Yb^3＋-codoped fibre laser with a high output power up to 2.18 W over a tunable wavelength range from 1535nm to 1570nm.     

A Bragg grating embedded in a slab waveguide fabricated by the implantation of high-energy light ions in KLTN substrate

Electro-optically tunable transmission grating was imprinted in potassium lithium tantalate niobate by irreversible spatial patterning of the dielectric constant. While embedded into waveguided architecture, it provides a reliable and versatile building block for opto-electronic circuitry, capable of both active switching and multiplexing. Realization of such a block is critical for the fabrication of integrated photonic circuits in electro-optic substrates by means of Refractive Index Engineering by fast ion implantation.     

Tunable polarization-independent Šolc-type wavelength filter based on periodically poled lithium niobate

We demonstrated a compact structure to implement the tunable ?olc-type wavelength filter based on periodically poled lithium niobate device. The theoretical analysis and experimental results show that the wavelength filter exhibits polarization independent. By comparing the polarization-independent and single-pass ?olc-type filters, same wavelength spectrum response was observed, while the improvement on the transmission power was obviously achieved and the polarization dependent loss was eliminated efficiently using polarization diversity and multiplexing.     

Ultra-fast optical switches using 1D polymeric photonic crystals

We report fabrication of ultra-fast optical switches operated at a wavelength of 1064 nm using spin-coated one-dimensional polymeric photonic crystals doped with nonlinear-optical dyes. The optical switches are controlled either by an applied electric-field voltage or by a pump light by use of two different optical-configurations. The response time of the electro-optic switch and the all-optical switch are limited by the applied voltage and the laser used, respectively. The polymeric photonic crystals can be easily fabricated with low cost.     

Photonics Devices Based on Hybrid Approach Combining Liquid Crystals and Sol-Gel Waveguides

In this article, the analysis of both an integrated electro-optic switch and a continuously tunable filter based on a Bragg grating in planar waveguide with a liquid crystal overlayer is reported. The fast and bistable switching of smectic C* in the surface-stabilized liquid crystal structure has been utilized in order to investigate the possibility of realizing an integrated electro-optical switch, whereas the soft-mode of smectic A* liquid crystals, allowing a continuous modulation of extraordinary refractive index, have been utilized in order to design an integrated wavelength filter in the wavelength range of interest for optical communication. Moreover, the performance of an electro-optical router, working at the wavelength of 1.55 μm and based on the multimode interference effects together with the electro-optic effect of smectic A* liquid crystal, is theoretically and numerically discussed.