Hybrid photonic crystal 1.31/1.55 μm wavelength division multiplexer based on coupled line defect channels

The objective of this paper is to investigate the implementation of a hybrid photonic crystal (PhC) 1.31/1.55 μm wavelength division multiplexer (WDM) and wavelength channel interleaver with channel spacing of roughly 0.8 nm between the operating wavelengths of 1.54-1.56 μm. It is based on 1-D photonic crystal (PhC) structure connected with an output 2-D PhC structure. The power transfer efficiency of the hybrid PhC WDM at 1.31 μm and 1.55 μm were computed by eigen-mode expansion (EME) method to be about 88% at both the wavelengths. The extinction ratios obtained for the 1.31 μm and 1.55 μm wavelengths are − 25.8 dB and − 22.9 dB respectively.     

A three-channels WDM based on MMI in photonic crystal

A photonic crystal waveguide coupling structure can be constructed by putting three adjacent photonic crystal waveguides in parallel. Guided mode propagation method is employed to analyze the interference behavior of the approximate solution in such a coupling and the self-image phenomenon in multi-mode waveguides. A three-channel multimode interference wavelength division multiplexing can be obtained. The presented device has a high transmission rate as well as the advantage of multi-wavelength selection, thus it may have a potentially practical application in future photonic integrated circuit.     

Photonic crystals with a chiral basis by holographic lithography

We demonstrate the use of holographic lithography to fabricate chiral photonic crystals. These structures are calculated to exhibit strong optical activity even though they are made from material that is not intrinsically optically active. By control of the polarizations of the interfering plane waves that are used to define the three-dimensional microstructure it is possible to create left- and right-handed and closely related non-chiral structures.     

The position independence of heterostructure coupled waveguides in photonic-crystal switch

Based on studying the propagation states of electromagnetic waves in heterostructure coupled waveguides produced by appropriately modulating the refractive index of rods, the realization of photonic-crystal switch is analyzed and the position effect of the heterostructure coupled waveguides on the switch function is investigated. The simulation results show that the output state is the result of the integral effect of different coupling regions; therefore, the switch function is independent on the distribution of heterostructure coupled waveguides. This property will bring great flexibility to fabricate photonic-crystal switch in practice.     

利用多模干涉效应集成0.98μm/1.55μm波分复用器及掺铒光信号放大器

波分复用器（ＷＤＭ）作为光纤通信中一种重要的元器件，能够在不改变原有通信线路的条件下，有效地增加光纤通信的容量。传统的波分复用器主要基于色散原理，分光比不能准确控制，信号间串音大；而基于平面波导中多模干涉效应研制的波分复用器，具有体积小，损耗低（＜０５ｄＢ），不受光偏振态的影响，易集成等优点；在很宽的工作波长范围内，受环境变化影响小，适合现代通信器件集成化的发展。利用多模干涉效应（ＭＭＩ）集成的０９８μｍ／１５５μｍ波分复用器，波导长度仅几个毫米，分光比例准确，隔离度可达３０－４０ｄＢ，波形失真小，它不仅可用于１５５μｍ光纤激光器和ＥＤＦＡ的集成，也可用于实现１×Ｎ和Ｎ×Ｎ分光，在光纤通信中有广泛的应用前景。     

二维光子晶体的软平板印刷技术制作研究

分析了软平板印刷技术制作二维光子晶体的特点和方法.利用绝缘PDMS模板,采用软平板印刷技术制造了三角晶系结构的二维聚合物光子晶体,采用同样的技术成功制成尺寸为150~500 nm,纵横比达1.25的高密度二维光子晶体.与其他制作技术相比,平板印刷技术具有大尺寸和易于制作的优点.结果表明,制作获得的微结构有很高的保真度.     

A compact wavelength division de-multiplexer based on directional coupling of one-dimensional photonic crystal waveguides

A fundamental dual-channel wavelength division de-multiplexer (WDDM) based on directional coupling of one-dimensional photonic crystal waveguides is presented, and its transmission characteristics of the WDDM are investigated by using finite-difference time-domain method. Calculated results indicate that for this WDDM, without any structural optimization, a high transmittance of more than 95% is observed at output ports. Combining the fundamental dual-channel WDDM with flexible bends of one-dimensional photonic crystal waveguides, we construct a simple and compact four-channel WDDM. Those WDDMs are expected to be applied to highly dense photonic integrated circuits.     

Photonic band gap failure in photonic crystal devices

The photonic crystal is an artificial material with periodic dielectric constant and the key factor to preserve their band features is its periodicity. When the number of periods of photonic crystal is decreased the photonic band gap cannot prevent the light of the corresponding frequencies from propagating in photonic crystal, in another word, photonic band gap will be failure. The minimum periods of photonic crystal device which can keep photonic band gap effective in miniaturization process is analyzed, the transmittance spectrum is calculated by the Finite-difference time-domain algorithm (FDTD) [1], the minimum periods is got in the simulation and the reason which affects the minimum periods is analyzed in this paper.     

Optimization of a 2D photonic crystal add/drop multiplexer based on contra-directional coupling

We present a highly integrated add/drop multiplexer, where the contra-directional coupling is realized by phase matching two photonic crystal waveguides. The device band structure, the corresponding transmission and drop spectra, and the coupling length are carefully analysed. Different device configurations are discussed and by tailoring the coupling factor, we optimize the frequency response of the filter, obtaining a -sized channel selector, characterized by a very high drop efficiency.     

Design of photonic bands for opal-based photonic crystals

To make a device from an opal—or otherwise—the photonic bands and the optical properties derived from them are needed. Knowing the effects of different parameters defining the opal geometry and different possible modifications of its structure are needed, too. An accurate definition of the device will be required to obtain a good performance. With this aim, the optics of light with a wavevector in the vicinity of the L point in the Brillouin zone and its coupling to bare opals band structure are presented. An important aspect is the transition from finite to infinite crystal and the study of size effects on the bands. It is possible to substantially alter the photonic band structure of an opal-based system, while maintaining the lattice structure, simply by growing layers of other materials with an appropriate refractive index. Here, it is shown how, by the growth of accurately controlled thin layers of silicon and germanium, and further processing, one can induce the opening of two complete photonic band gaps (PBGs) in an opal structure. Finally, the possibility to fabricate a simple device consisting in a planar waveguide will be shown. By means of a very simple and inexpensive procedure, engineered planar defects acting as microcavities have been realized. These can be viewed as a particular case of a much more general class of heterostructures that can be grown by combining opal vertical deposition and chemical vapour deposition of oxides. A further step is made by applying electron beam lithography to provide lateral definition and facilitate three-dimensional structuring.     

Realization of tunable optical filter by photonic crystal ring resonators

We have designed a tunable two dimensional (2D) channel drop filter (CDF) based on photonic crystal ring resonators (PCRR). Dropping efficiency and Q factor of single improved ring are 100% and 842, respectively. In this filter the quality factor is significantly improved with respect to other published reports. We investigate parameters which have an effect on resonant wavelength in this CDF, such as dielectric constant of inner, coupling, adjacent and whole rods of the structure and radius of inner rods. The transmission spectrum for our proposed configuration has been investigated using the 2D finite difference time domain (FDTD) method. The area of the proposed structure is about 117 μm².     

A new design of tunable four-port wavelength demultiplexer by photonic crystal ring resonators

A four-channel wavelength demultiplexer based on photonic crystal ring resonators (PCRR), which can be used for photonic integrated circuits, is designed. Dropping efficiency and Q factor of single improved ring are 100% and 842, respectively. In order to achieve the structure of demultiplexer, three improved rings have been used, that every ring has an individual inner rod radius; it means that each ring has a varying resonant wavelength. The results of simulation using finite-difference time-domain (FDTD) method in our proposed structure reveals an average transmitted power higher than 90% for each output port, Channel spacing is about 8 nm and bandwidth for each individual channel is about 2.8 nm. The mean value of the crosstalk between output channels and the area of the proposed structure are about −29 dB and 317 μm², respectively. By changing the radius of inner rods, various wavelengths can be chosen, therefore this device is tunable.     

Modeling and design of 2D photonic crystal based Y type dual band wavelength demultiplexer

In this paper, photonic bandgap (PBG) induced wave guiding application of photonic crystals is exploited to design Dual Band Wavelength Demultiplexer (DBWD) for separating two telecommunication wavelengths, 1.31 and 1.55 μm. Two designs that use silicon rods in air and embedded air holes in silicon are realized for this purpose. Plane wave expansion (PWE) method and two dimension Finite Difference Time Domain (FDTD) methods are used to design and analyze the DBWD in Y type photonic crystal structure. Numerical analysis indicates that these designs enable the separation of two wavelengths with very high optical power extinction ratios. Other filter parameters like transmittance and quality factor are also calculated to confirm superior performance of the proposed design of photonic crystal based DBWD.     

Structure design and performance simulation on monolithic integrated chaotic-optical transmitter with photonic crystal waveguide in external cavity

A novel monolithic integrated chaotic-optical transmitter structure is proposed in this paper. It consists of a distributed feedback laser, a semiconductor optical amplifier, a passive waveguide, and a photonic crystal waveguide. The length of external cavity is shorten to 1.125 mm by the slow light effect in photonic crystal waveguide. The performance of the integrated chaotic-optical transmitter is simulated. A series of dynamic states transiting from steady state, period state, and finally to chaotic laser is obtained. The size and power consumption of the chaotic-optical transmitter are both reduced by introduction of photonic crystal waveguide.     

Enhanced emission of single quantum dot formed by interface fluctuations in photonic-crystal microcavities

We fabricated photonic-crystal (PhC) microcavities tuned to GaAs quantum dots (QDs) formed by interface fluctuation for the first time and observed the spontaneous emission enhancement in a weak coupling regime. A QD is a very thin GaAs quantum well (QW), and its interface steps exhibit quantum dot-like behavior. The emission intensity from the PhC cavity was stronger than that from the area where no PhC pattern was fabricated and the overall shape of the photoluminescence (PL) agreed with the cavity mode calculated with the three-dimensional (3D) finite-difference time domain (FDTD) method. The spontaneous emission enhancement factor was 10.     

Extremely low optical transmittance in the stopbands of photonic crystals

We demonstrate extremely low transmittance characteristics of photonic crystals (PhCs) with a finite thickness in specific photonic bandgaps (PBGs) through numerical simulation, and clarify its origin. Some of the PhCs support decaying Bloch eigenmodes, whose propagation constant (real part of the Bloch wavenumber) as well as their decay constant (imaginary part) changes with frequency inside the bandgap. Such a class of modes can interfere destructively at the exit end of the crystal depending on their round-trip phase change, which creates comb-like valleys in their transmission spectra.     

Extraordinary wavelength dependence of self-collimation effect in photonic crystal with low structural symmetry

We present the optical properties of a new type of photonic crystal (PC) named star-shaped PC (STAR-PC) with anomalous equi-frequency contours. Intentionally introducing low-symmetry in the primitive unit cell gives rise to progressively tilting flat contours, which are observed in the fifth band of the transverse magnetic mode. Due to the intrinsic dispersive feature of the proposed PCs, i.e. tilted self-collimation, the incident signal with different wavelengths can be successfully separated in a spatial domain without introducing any corrugations or complexities inside the structure. We show numerical investigations of wavelength selective characteristic of the proposed PC structure in both time and frequency domains. The STAR-PC approach can be considered a good candidate for the wavelength division applications in the design of compact photonic integrated circuits. For the purpose of wavelength separation implementations, the proposed structure may operate within the wavelength interval of 1484.5–1621.5 nm with a broad bandwidth of 8.82%. The corresponding inter-channel crosstalk value is as low as ?19 dB and the calculated transmission efficiency is above 97%.     

Numerical analysis of high Q-factor photonic-crystal VCSELs with plane-wave admittance method

The paper presents the application of a novel plane-wave admittance method (PWAM) to the three-dimensional and fully vectorial modeling of vertical-cavity surface-emitting lasers with incorporated photonic crystal. The basic mathematical details of the method are given and its convergence is verified for a sample structure. Then the simulations performed with PWAM are used to determine the optimal photonic crystal parameters for low-loss, high-Q-factor regime.     

Design of integrated optical circulator based on photonic crystals

Photonic crystals containing defects produce enhanced Faraday rotation. They have opened up the possibility of fabricating very compact magneto-optics structures. In this work, we have designed a two-dimensional photonic crystal waveguide for use in optical packaging and integrated optical circuits. For design purposes, a temporal coupled mode theory was utilized at the first step. It examined the coupling between cavity and optical ports. After acquiring a general solution, it would be applied to specific problem in hand. Then, optical characteristics of photonic crystal were investigated to design the practical parts such as cavity and waveguides which eventually a triangular crystal lattice of air holes in Bi:YIG (BIG) was considered to be the best candidate. Finally, the results of analytical investigations were evaluated using OptiFDTD software and then were confirmed.     

波分复用光环形网络结构及性能的研究

本文概述了当前波分复用(WDM)光环形网络结构的物理结构和逻辑结构,并对这些网络结构进行简要的分析,同时对实现WDM光环网络结构中的关键问题进行了简要的探讨。最后对我国发展光环形网络给予一些中肯的建议。