Multiple defect characterization in finite-size waveguiding photonic bandgap structures

A powerful and efficient model recently proposed by the authors based on the leaky mode propagation method is used to characterize photonic bandgap structures incorporating multiple defects, having arbitrary shape and geometrical parameter values. The importance of the defect-mode characterization in photonic bandgap materials is due to the intensive use of defects for light localization to design very promising optical devices. This paper provides a new, efficient method to model defects in waveguiding, finite-size photonic bandgap devices and analytical and closed-form expressions for the reflection and transmission coefficients and out-of-plane losses,which is very useful and easily implemented under any operating conditions. Moreover, the method has been applied to examine the capabilities of waveguiding photonic bandgap devices in dense wavelength division multiplexing filtering applications. Therefore, the design of two optical filters for such applications has been carried out and optimal design rules have been drawn using the new model.     

Tunable bandpass microwave filters based on defect commandable photonic bandgap waveguides

A new type of tunable filter based on a commandable defect in the bandgap of a periodic CPW structure is proposed. The defect level is tuned either mechanically by adding a covering slab over the device or electrically by polarising diodes located at the defect. The validity of this concept is experimentally demonstrated at 4 GHz. This kind of filter is well suited for applications in the 10 to 60 GHz frequency range.     

Characteristics of a photonic crystal defect waveguide-coupled quantum-dot photodiode

We have investigated the characteristics of an In/sub 0.4/Ga/sub 0.6/As self-organized quantum-dot (QD) resonant-cavity photodiode. The QD epitaxy and the design of the two-dimensional photonic crystal cavity are tailored for 1.3-/spl mu/m wavelength operation. The input excitation to the photodiode is provided with an in-plane defect waveguide designed with the same photonic crystal. The measured spectral photocurrent characteristics reflect mode coupling between the waveguide and detector and the resonant cavity effect due to total internal reflection and photonic bandgap confinement. The photocurrent response is explained with a model involving the circulating fields in the cavity. The characteristics are also dependent of cavity size. Enhancement and narrowing (/spl sim/ 10 nm) of the photoresponse at /spl lambda//spl sim/1.3 /spl mu/m are observed. A spectral dip, of /spl sim/ 10-nm width, also observed at 1.3 /spl mu/m is possibly due to the anticrossing mechanism, uniquely present in photonic crystal waveguides.     

Nanofabrication of 1-D photonic bandgap structures along a photonic wire

A strongly-guided one-dimensional (1-D) waveguide called a photonic wire has high spontaneous emission coupling efficiency, enabling one to realize low-threshold lasers. Combined with the use of 1-D photonic bandgap structures consisting of arrays of holes etched within the photonic wire, novel microcavity lasers can be realized. We report the nanofabrication of a photonic bandgap structure for 1.5 /spl mu/m wavelength along a InGaAsP photonic wire, and discuss numerical simulations for its electrodynamics.     

Two-dimensional Kagome photonic bandgap waveguide

The transverse-magnetic photonic-bandgap-guidance properties are investigated for a planar two-dimensional (2-D) Kagome waveguide configuration using a full-vectorial plane-wave-expansion method. Single-moded well-localized low-index guided modes are found. The localization of the optical modes is investigated with respect to the width of the 2D Kagome waveguide, and the number of modes existing for specific frequencies and waveguide widths is mapped out     

四方格子全固光子带隙光纤带隙特性研究

基于平面波展开法,对四方格子全固光子带隙光纤带隙随结构的变化特性进行了数值模拟,并与具有相同结构参数三角格子全固光子带隙光纤进行了比较,数值结果表明带隙的位置由高折射率棒的结构参数决定,而与高折射率棒的排列方式和棒之间的间距无关,这一结果与反谐振效应非常吻合。最后对理想和实际拉制出的四方格子的全固态光子带隙光纤的带隙进行了比较,得出了在设计光纤时,应利用较低的带隙的结论。     

Block copolymers as photonic bandgap materials

Block copolymers self-assemble into one-, two-, and three-dimensional periodic equilibrium structures, which can exhibit photonic bandgaps. This paper outlines a methodology for producing photonic crystals at optical length scales from block copolymers. Techniques for enhancing the intrinsic dielectric contrast between the block copolymer domains, as well as increasing the characteristic microdomain distances, and controlling defects are presented. To demonstrate the applicability of this methodology, a self-assembled one-dimensional periodic structure has been fabricated that reflects visible light. The wealth of structures into which block copolymers can assemble and the multiple degrees of freedom that can be built into these materials on the molecular level offer a large parameter space for tailoring new types of photonic crystals at optical length scales     

Meander microstrip photonic bandgap filter using a Kaiser taperingwindow

Compact photonic bandgap structures in microstrip technology with reasonable physical sizes have recently been proposed as efficient frequency-band reflectors. Here, it is shown how the application of a Kaiser tapering window to the periodic pattern etched in the ground plane of the structure provides appreciable performance improvement, reducing both passband ripple and stopband attenuation and increasing bandwidth     

Honeycomb photonic bandgap fiber with a modified core design

Air-silica honeycomb fiber with a modified core design is introduced. The core has a concentrated high-index region. Such core design helps defect core mode stay in the cladding's photonic bandgap for a longer wavelength range (>1000 nm) as compared to conventional design. We further point out the importance of our core design in reducing the number of defect modes supported by the fiber structure.     

新型复式矩形光子晶体完全带隙分析

文章提出一种复式矩形光子晶体结构,首先利用平面波展开法(PWM)计算这种光子晶体的能带结构,然后对结构参数值进行优化,得到较大的光子带隙.分析结果表明, 当采用单晶硅作为介质柱材料时,长方晶格的晶格常数比值为0.35～0.45,正方介质柱边长与长方晶格长轴比值为0.45～0.50,得到的完全带隙可达到0.50～0.58,完全带隙率达到近39%,这对于研制性能优良的光子晶体器件具有重要意义.     

Air guiding with honeycomb photonic bandgap fiber

We notice that honeycomb cladding was overlooked for air-guiding photonic bandgap fiber design. Air-silica honeycomb cladding is shown in this letter to be able to guide light in a slightly large-sized hollow core, with a reasonably wide bandwidth (/spl sim/200 nm). Noncircular air-hole shape is also explored for air-guiding honeycomb fiber design.     

Confinement losses in air-guiding photonic bandgap fibers

The wavelength dependence and the structural dependence of confinement losses in air-guiding photonic bandgap fibers (PBGFs) are, for the first time, investigated by using a full-vector finite element method. It is confirmed from computed results that one of the main causes of transmission losses in air-guiding PBGFs is the confinement loss and that, even if using large air holes of diameter to pitch ratio of 0.9, at least twenty rings of air hole arrays are required in the cladding region to reduce the confinement loss to a level of 0.01 dB/km.     

Dielectric waveguides in two-dimensional photonic bandgap materials

We investigate the performance and guiding properties of waveguides fabricated in a finite two-dimensional (2-D) photonic bandgap (PBG) structure. Confinement in the direction perpendicular to the plane of periodicity is achieved by fabricating the 2-D PBG structure in a high dielectric layer enclosed by two lower dielectric layers. Simulations using the finite-difference time-domain (FDTD) method are performed to investigate the energy transport in such waveguides. Good qualitative agreement is found with the experimental observations     

Channel drop filter using a single defect in a 2-D photonic crystal slab waveguide

This paper describes a theoretical and experimental analysis of the channel drop filter using a single defect formed near the two-dimensional (2-D) photonic crystal slab waveguide. First, we calculate the transmission spectrum of a 2-D photonic crystal waveguide and show that high transmittance for a wide wavelength range (/spl sim/60 nm) is obtained in the 1.55-/spl mu/m region. We also show that a defect state having a wavelength within the high transmission wavelength range can be formed in the photonic bandgap by introducing a single defect of appropriate radius. Next, we fabricate several devices and show that the emission wavelength from each defect can be tuned by changing the defect radius. The measured tuning characteristics coincide well with the calculated results. From the near-field pattern of the device, we estimate the emission efficiency of the present device at almost a few tens percent. We clarify the structural condition in order to obtain the maximum output efficiency and show that tuning of emission wavelength while maintaining high output efficiency is possible by selecting appropriate defect radius and position. Based on these results, we propose an ultrasmall channel drop filter for a wavelength-division-multiplex optical communication system.     

Guided properties and applications of photonic bandgap fibers

The authors have reviewed some of their recent studies on photonic bandgap fibers (PBGFs). PBGFs that confine light in the core by the photonic bandgap effect of cladding have potential applications in various photonic devices. In this paper, the guided properties and tuned mechanics of anti-resonant PBGFs are theoretically illustrated. The special coupling properties in multi-core PBGFs, such as decoupling and resonant coupling effect,are then introduced. Finally, fiber Bragg grating inscribed in all-solid PBGFs is theoretically and experimentally studied, and special resonant characteristics are also observed.     

Modeling of fully etched waveguiding photonic bandgap structures

Modeling of a 1-D finite-height, finite-length fully etched waveguiding photonic bandgap structures, based on the leaky mode propagation method, is proposed for the first time. So far only infinitely long gratings have been modeled by this approach. Finite extension structures having deep grooves, high refractive index contrast, and an arbitrary profile of the etched region can be modeled in very short computer time, starting from the infinitely-long photonic bandgap structure. Useful analytical and closed-form expressions for the reflection and transmission coefficients and out-of-plane losses are derived, which are valid for any operating conditions. One of the most important applications of the model relevant to 1-D photonic bandgap devices is to determine the losses occurring also in 2-D devices. Comparisons of results in terms of transmittance, losses, bandgap position and complex propagation constant with those obtained by the bi-directional mode expansion and propagation method and an exact vectorial method show an excellent agreement together with a strongly reduced CPU time for our method. Full investigations of three different etching profiles (i.e., rectangular, triangular and saw-tooth) are carried out. Particular attention is paid to the physical behavior around the first and second Bragg interaction regions. We demonstrate that the rectangular shape exhibits the highest losses and the widest bandgap, while the saw-tooth grating exhibits the lowest losses and the narrowest bandgap. Quick and accurate determination of the out-of-plane losses in a large variety of photonic bandgap devices is also demonstrated     

Amplification properties of erbium-doped solid-core photonic bandgap fibers

A novel erbium-doped photonic bandgap fiber (PBGF) with honeycomb cladding and down-doped solid-core is proposed in this letter. This fiber is more practicable than reported erbium-doped air-core PBGF due to its Gaussian-like field distribution and low confinement loss. Theoretical analysis shows that it can largely improve pump efficiency (gain-to-pump-power ratio) for small pump power and reduce the optimum fiber length by 20%-50% for a wide range of pump powers, compared with erbium-doped step-index fiber.     

Extending transmission bandwidth of air-core photonic bandgap fibers

Air-core photonic bandgap fibers offer many unique properties and are critical to many emerging applications. A notable property is the high nonlinear threshold which provides a foundation for applications at high peak powers. The strong interaction of light and air is also essential for a number of emerging applications, especially those based on nonlinear interactions and spectroscopy. For many of those applications, much wider transmission bandwidths are desired to accommodate a wider tuning range or the large number of optical wavelengths involved. Presently, air-core photonic bandgap fibers have a cladding of hexagonal lattice. The densely packed geometry of hexagonal stacking does not allow large nodes in the cladding, which would provide a further increase of photonic bandgaps. On the other hand, a photonic cladding with a square lattice can potentially provide much larger nodes and consequently wider bandgap. In this work, the potentials of much wider bandgap with square lattice cladding is theoretically studied and experimentally demonstrated.