Silicon and porous silicon mid-infrared photonic crystals

A 3D silicon micromachining method based on proton beam writing combined with electrochemical anodization of p-type silicon enables fabrication of mid-infrared photonic crystals made of silicon and porous silicon. Here, example structures of silicon 1D and 2D photonic crystals are demonstrated. Progress and problems of fabricating 3D photonic crystals made of silicon are discussed. The strategy of fabricating photonic crystals purely made of porous silicon, and the characterization method of all these mid-infrared structures, are discussed. Due to the flexibility of this fabrication method, photonic devices and integrated photonic circuits may be built on a single chip, for which two 2D silicon photonic crystals with one on top of the other are demonstrated.     

Giant third-harmonic in porous silicon photonic crystals and microcavities

A giant enhancement (no less than by 10³) of the optical third-harmonic generation in one-dimensional porous silicon microcavities and photonic crystals was observed experimentally. The enhancement is due to the resonant enhancement of the fundamental field in the cavity mode and the fulfillment of the phase matching condition at the photonic band gap edges of the photonic crystal and in the vicinity of the microcavity mode.     

Simulation and fabrication study of porous silicon photonic crystal

The present work reports design and fabrication of porous silicon based one-dimensional (1D) photonic crystal. Distributed Bragg reflector (DBR) is a 1D photonic crystal composed of multilayer stack of high and low refractive index layers. Design of porous silicon DBR is a complex one and requires appropriate control in optical parameters of its constituent layers. In order to design DBR, two porous silicon single layer samples were fabricated using current density of 10 and 50 mA/cm². Optical characterization of single layer samples showed series of interference fringes. Reflective interferometric Fourier transform spectroscopy (RIFTS) method was employed to determine optical constants of porous silicon single layers. DBR simulation was carried out based on transfer matrix method. DBR was then fabricated using optical parameters obtained from RIFTS method. Reflection bandwidth of prepared DBR was found to be 216 nm, which is comparable to the simulated value of 203 nm.     

一维多孔硅光子晶体反射特性及制作的理论研究

在一维光子晶体光学传输特性理论的基础上,运用传输矩阵法推导了一维多孔硅光子晶体的反射特性,并对其反射特性与结构参数的关系进行了分析。给出了采用脉冲电化学阳极腐蚀法制备一维多孔硅光子晶体的制作模型。利用计算机数值模拟的方法给出了各种一维多孔硅光子晶体的典型反射谱。为多孔硅光子晶体的实际应用奠定了理论基础。     

Physics and applications of photonic crystals

In this article, we investigate how the photonic band gaps and the variety of band dispersions of photonic crystals can be utilized for various applications and how they further give rise to completely novel optical phenomena. The enhancement of spontaneous emission through coupled cavity waveguides in a one-dimensional silicon nitride photonic microcrystal is investigated. We then present the highly directive radiation from sources embedded in two-dimensional photonic crystals. The manifestation of novel and intriguing optical properties of photonic crystals are exemplified experimentally by the negative refraction and the focusing of electromagnetic waves through a photonic crystal slab with subwavelength resolution.     

Modeling of the optical properties of porous silicon photonic crystals in the visible spectral range

Optical devices based on photonic crystals are of great interest because they can be efficiently used in laser physics and biosensing. Photonic crystals allow one to control the propagation of electromagnetic waves and to change the emission characteristics of luminophores embedded into photonic structures. One of the most interesting materials for developing one-dimensional photonic crystals is porous silicon. However, an important problem in application of this material is the control of the refractive index of layers by changing their porosity, as well as the refractive index dispersion. In addition, it is important to have the possibility of modeling the optical properties of structures to choose precisely select the fabrication parameters and produce one-dimensional photonic crystals with prescribed properties. In order to solve these problems, we used a mathematical model based on the transfer matrix method, using the Bruggeman model, and on the dispersion of silicon refractive index. We fabricated microcavities by electrochemical etching of silicon, with parameters determined by the proposed model, and measured their reflection spectra. The calculated results showed good agreement with experimental data. The model proposed allowed us to achieve a microcavity Q-factor of 160 in the visible region.     

Novel optical modulator using silicon photonic crystals

We propose a novel compact and integrated optical modulator, which consists of p–i–n silicon photonic crystals with triangular lattice and a line defect waveguide. The device operation is based on a dynamic shift of the photonic band gap (PBG), which induced change in the silicon refractive index by the free carrier injection. We have numerically analyzed and investigated its light modulation performance by using plane wave expansion (PWE) method and finite-difference time-domain method. With small size, rapid response time and high extinct ratio, the designed optical modulator can be used in photonic integrated circuits.     

Thermal emission of macroporous silicon chirped photonic crystals

In this Letter we report on the thermal properties of macroporous silicon photonic crystals with the unit cell gradually varied along the pore axis. We show experimentally that arbitrarily large omnidirectional total-reflectance bands can be produced with such structures. We also demonstrate that those bands can be effectively used to reduce thermal radiation in large spectral bands.     

Preparation of one-dimensional porous silicon photonic quantum-well structures

One-dimensional porous silicon (PSi) photonic quantum-well structures have been electrochemically fabricated and spectroscopically characterized. The photonic well in the structure is a photonic crystal (PC) consisting of alternately stacked high- and low-refractive-index PSi layers. Discrete states are observed in both reflectance and transmission spectra. It is found that the number of confined states appearing in the photonic bandgap of the photonic barrier depends on the number of periods adopted in the well PC. Thus, increased confined photonic states can be created simply by increasing the number of periods of the well PC in the structures. Received: 26 February 2002 / Accepted: 17 May 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-21/6510-4949, E-mail: xyhou@fudan.edu.cn     

Spherical silicon optical resonators: Possible applications to biosensing

We observed whispering gallery modes in the 90^° elastic light scattering and 0^° transmission spectra of a 500 μm silicon microsphere in the near-infrared telecommunication wavelengths. The whispering gallery modes have quality factors on the order of 10⁵. An autocorrelation function analysis of the 90^° elastic light scattering and 0^° transmission spectra is performed. The differential autocorrelation of the 90^° elastic light scattering and 0^° transmission spectra reveal a spectral mode spacing 0.23 nm of the whispering gallery modes, which can be used for spectral calibration as well as the calibration of the microsphere size. The spectral shift of the whispering gallery modes can be measured for biosensing applications. An estimation analysis is performed for the adsorption of 30 DNA base pairs on the microsphere results in a wavelength shift of 0.57 nm, which is approximately 40 times the linewidth of the whispering gallery modes. This high sensitivity heralds silicon microspheres as possible candidates for biosensing applications.     

可实现偏振无关单向传输的二维硅基环形孔光子晶体

基于光子晶体来构筑偏振无关光二极管在光电集成领域具有重大的应用价值.首先提出了一种环形孔光子晶体,能带结构显示其对横电及横磁模式同时展现出显著的方向带隙.以此构建了三角形状的环形孔光子晶体,利用时域有限差分法计算其透过谱及场分布图,发现该结构能实现偏振无关单向传输特性,然而正向透过率太低(约20%).进一步引入尺寸较小的三角形状的环形孔光子晶体构成光子晶体异质结结构,有效地提高了偏振无关单向传输性能,正向透过率增大了一倍.通过界面结构的调整,正向透过率进一步增大,优化后的环形孔光子晶体异质结结构能同时对类横电及类横磁模式入射光实现单向传输,且正向透过率达到了44%.     

Low dimensional silicon structures for photonic and sensor applications

We review here our work on the photonic and sensor applications of nanostructured silicon. As we change the dimensionality of silicon very fascinating and new optical properties of the material appear. Light sources, modulators, waveguides, logical gates are a few examples of the various photonic devices which have been developed based on silicon nanocrystals. Needless to say, all these devices rely on quantum confinement and on the interplay between bulk and surface properties. Size effects and surface reconstructions are two critical issues which one has to master to employ silicon nanocrystals. Finally the use of silicon nanocrystals to develop innovative sensing mechanisms to reveal biomolecules or poisoning gasses will be discussed.     

Slow-light-enhanced upconversion for photovoltaic applications in one-dimensional photonic crystals

We present an approach to realizing enhanced upconversion efficiency in erbium (Er)-doped photonic crystals. Slow-light-mode pumping of the first Er excited state transition can result in enhanced emission from higher-energy levels that may lead to finite subbandgap external quantum efficiency in crystalline silicon solar cells. Using a straightforward electromagnetic model, we calculate potential field enhancements of more than 18× within he slow-light mode of a one-dimensional photonic crystal and discuss design trade-offs and considerations for photovoltaics.     

Design and optimization of one-dimensional photonic crystals for thermophotovoltaic applications

We explore the optical characteristics and fundamental limitations of one-dimensional (1D) photonic crystal (PhC) structures as means for improving the efficiency and power density of thermophotovoltaic (TPV) and microthermophotovoltaic (MTPV) devices. We analyze the optical performance of 1D PhCs with respect to photovoltaic diode efficiency and power density. Furthermore, we present an optimized dielectric stack design that exhibits a significantly wider stop band and yields better TPV system efficiency than a simple quarter-wave stack. The analysis is done for both TPV and MTPV devices by use of a unified modeling framework.     

Investigation on LaF3/porous silicon system for photonic application

<正>We present the investigation on LaF_3/porous silicon(PS) system that has properties of both the materials to be applied in photonics.Epilayers of LaF_3 are grown on PS under different anodization conditions using electron-beam evaporation(EBE).The characteristics of the LaF_3/PS system are analyzed by X-ray diffraction(XRD),scanning electron microscope(SEM),energy dispersive X-ray spectroscopy(EDX),and photoluminescence(PL).XRD confirms the polycrystalline nature of the LaF_3 film.Nearly stoichiometric growth of LaF_3 on PS is established by EDX.Such a thin LaF_3 layer grown on PS leads to a good enhancement of PL yield of PS.But with the increasing thickness of LaF_3 layer,PL intensity of PS is found to decrease along with a small blue-shift.     

Optimization of porous silicon preparation technology for SERS applications

A series of porous silicon samples prepared at different etching parameters, namely etchant composition, etching time and current density, was investigated as substrates for surface-enhanced Raman scattering (SERS). Silver nanostructures were deposited on porous silicon by immersion plating method and Rhodamine 6G was used as analyte. The relation between the etching parameters, morphology of porous silicon surface and its SERS efficiency after silver deposition is examined. We show that a high HF content in the etchant allows the formation of a film with close-packed silver nanocrystals, which possess strong surface enhancement properties.     

Numerical analysis of a photonic crystal fiber based on two polarized modes for biosensing applications

This paper presents a theoretical study on a photonic crystal fiber plasmonic refractive index biosensor. The proposed photonic crystal fiber sensor introduces the concept of simultaneous detection with the linearly polarized and radially polarized modes because the sensing performance of the sensor based on both modes is relatively high, which will be useful for selecting the modes to make the detection accurately. The sharp single resonant peaks of the linearly polarized mode and radially polarized mode, are stronger and more sensitive to the variation of analyte refractive index than that of any other polarized mode in this kind of photonic crystal fiber. For linearly polarized mode and radially polarized mode, the maximum sensitivities of 10448.5nm per refractive index unit and 8230.7nm per refractive index unit can be obtained, as well as 949.8 and 791.4 for figure of merits in the sensing range of 1.33-1.45, respectively. Compared with the conventional Au-metalized surface plasmon resonance sensors, our device is better and can be applied as a biosensor.     

Anisotropic photonic crystals and microcavities based on mesoporous silicon

A technique to prepare one-dimensional anisotropic photonic crystals and microcavities based on anisotropic porous silicon exhibiting optical birefringence has been developed. Reflectance spectra demonstrate the existence of a photonic band gap and of an allowed microcavity mode at the photonic band gap center. The spectral position of these bands changes under rotation of the sample about its normal and/or under rotation of the plane of polarization of the incident radiation. The dependence of the shift of the spectral position of the photonic band gap edges and of the microcavity mode on the orientation of the polarization vector of incident electromagnetic wave with respect to the optical axis of the photonic crystals and microcavities was studied.     

Surface wave photonic device based on porous silicon multilayers

Porous silicon is widely studied in the field of photonics due to its interesting optical properties. In this work, we present theoretical and first experimental studies of a new kind of porous silicon photonic device based on optical surface wave. A theoretical analysis of the device is presented using plane-wave approximation. The porous silicon multilayered structures are realized using electrochemical etching of p⁺-type silicon. Morphological and optical characterizations of the realized structures are reported.     

Optimal tunability of waveguides based on silicon photonic crystals infiltrated with liquid crystals

In this work we study the optimization of the tunability range in waveguides based on two-dimensional silicon photonic crystal infiltrated with liquid crystal. The analyzed structure consists of a two-dimensional silicon photonic crystal with a triangular lattice of circular holes where a line of scatterers in the direction Γ–K has been replaced by a line of circular holes with different radius infiltrated by E7 liquid crystal. To this end, we use the plane-wave expansion method considering anisotropy and modelling supercells to account for the lattice defects that define the waveguide. Finally we study the field distributions of the guided modes in order to analyze their symmetries and confinement.