The concept of surface plasmon resonance can be used to build the most-sensitive instruments for refractive index sensing with dielectric and metal layers which are sub-wavelength in thickness. This is demonstrated with the electric field calculations on plasmonic gratings, of both rectangular and sinusoidal profiles, on polymer layer. The finite element method is also used to find the optimal thickness of the layers and to calculate the reflection, transmission, and absorption spectra of the plasmonic gratings, to identify the wavelength range most appropriate to the application.
Photonic crystal (PhC) structures with appropriate characteristics are necessary to control spontaneous emission from fluorophores while designing miniaturized lasers. We report the fabrication and detailed studies on the emission features of two different spectrally engineered PhC heterostructures made from dye-doped opal and one-dimensional (1-D) multilayer stack. Our results demonstrate notable enhancements of emission from PhC heterostructure enabled by the stopband overlap of three-dimensional (3-D) opals and 1-D multilayers. In the presence of the 1-D multilayer, the distributed feedback from opals further enhances the emission from the dye. We emphasize the role of the interplay of the spectral overlap of stopbands and the band edges in the dye-doped PhC heterostructures to control their emission features. The emission results obtained from our heterostructures are very much dependent on the relative spectral position of the stopbands of the constituent 1-D and 3-D photonic crystals. Input pump energy-dependent emission results indicate that such heterostructures are potential candidates for designing colloidal PhC-based lasers.
Broadband, all-angle negative refraction (AANR) effects and imaging with subwavelength resolution have been analyzed in a honeycomb lattice of silicon rods in air background, as well as in the inverse structure of air holes in a silicon wafer. In the rod lattice, it was possible to obtain AANR effects for transverse-magnetic (TM) polarization in the second band (TM2) with a bandwidth as large as ∼23% after optimizing the ratio of feature size to the lattice constant as 0.44 and a super-lensing effect with a binary coherent source resolution of 0.68λ. On the other hand, the hole lattice shows AANR for both TM2 (bandwidth of 14%) and TE2 (bandwidth of 15.3%) bands with an additional advantage of polarization-independent AANR of 5% bandwidth. The hole lattice also shows a super-lensing behavior, which helps in imaging with a subwavelength resolution of 0.19λ for a single-point source and 0.80λ with a binary source for TM polarization while it is 0.48λ and 0.97λ, respectively, for transverse-electric (TE) polarization. The conditions for perfect imaging have been studied, and the phenomenon of dual negative refraction for both TE and TM polarization is also discussed.
An enhancement in photonic band-edge-induced absorption and emission from rhodamine-B dye doped polystyrene pseudo gap photonic crystals is studied. The band-edge-induced enhancement in absorption is achieved by selecting the incident angle of the excitation beam so that the absorption spectrum of the emitter overlaps the photonic band edge. The band-edge-induced enhancement in emission, on the other hand, is possible with and without an enhancement in band-edge-induced absorption, depending on the collection angle of emission. Through a simple set of measurements with suitably chosen angles for excitation and emission, we achieve a maximum enhancement of 70% in emission intensity with band-edge-induced effects over and above the intrinsic emission in the case of self-assembled opals. This is a comprehensive effort to interpret tunable lasing in opals as well as to predict the wavelength of lasing arising as a result of band-edge-induced distributed feedback effects.
Over the past decade, scientists have learned how to manipulate the interaction of radiation with structured materials to an unprecedented level. For decades, our world was limited to materials with primarily positive permittivities and permeabilities, with a few exceptions such as plasmas, for example, whose permittivities can be negative. The research in metamaterials coupled with the rapid advancements in micro- and nanofabrication technologies has removed this limitation and has opened the door to almost arbitrary material properties with some extraordinary consequences across the electromagnetic spectrum, ranging from radio frequencies to optical frequencies. These developments have been strongly complemented by the developments in periodic dielectric photonic crystals where band-gap effects lead to mind-blowing dispersion characteristics and consequent effects. Almost simultaneously, the optics of metals has been brought to center-stage where the plasmonic excitations enable the electromagnetic radiation to interact resonantly with the structured material at very small sub-wavelength scales. These interactions prove to be the key to manipulating the optical near-field, and surprising effects such as sub-wavelength scale imaging by so-called super-lenses made of negative refractive index or plasmonic materials have been discovered.
In this paper we propose and demonstrate a novel technique to suppress pump in four-wave mixing experiments. The residual pump powers at the fiber output are reflected by fiber-Bragg gratings (FBGs), amplified by an EDFA to compensate for pump losses in feedback path, and fed back to the fiber. With the increase in total input power to the fiber, the ratio of signal and idler to pump increases. Additional optical filters can then be used for further pump suppression. In our experiments, two pump waves of wavelengths 1549.70nm and 1549.85nm are combined using a 3dB coupler and fed to a highly-nonlinear fiber (HNLF) of length 1km, nonlinear coefficient of 12.4/W-km, and zero dispersion wavelength (ZDW) of 1513nm. Without feedback, we obtained the signal and idler to pump ratios of -21dB and -20.6dB respectively. After filtering by FBGs of 95% reflectivity and unity gain feedback, the ratio becomes - 14.1dB and -12.2dB respectively. When the residual pumps are amplified and fed back to the HNLF, the ratio improves to -7.5dB and -8.6dB indicating the potential of our method.
Spectral distribution of emission was measured in a large angular range (8 deg to 180 deg) around a self-assembled photonic crystal synthesized from colloids of Rhodamine-B dye-doped polystyrene. Its comparison with the emission from the same dye-doped colloids in a liquid suspension provides a better understanding of the anisotropic propagation of light within the structure due to its pseudo-gap properties. The spontaneous emission is suppressed by 40% in the presence of the stop band over a large bandwidth (∼50%) of the first-order bandgap in the ΓL direction, due to the appropriate choice of the colloidal diameter. Spectral shifts in the spontaneous emission spectrum occur with the variation in the detection angle. The inevitable disorder in the self-assembled crystals and the resultant effect on emission was modeled by comparing the experimentally obtained reflection spectrum with the band structure calculated using the Korringa-Kohn-Rostoker method to exclude finite-size effects. Reflection and transmission are complementary because of the absence of strong absorptive effects. The extent of redistribution in the emission from a photonic crystalline environment with respect to a homogeneous emitter is significant in the spectral and spatial domains.
Waveguide (WG) structures are patterned on polymeric thin films and on three-dimensional colloidal photonic crystals
(PhC). Different techniques such as direct laser writing, electron beam lithography (EBL), optical lithography and femto-second
laser writing are used to pattern the WG structures on PPR, polymethyl methacrylate (PMMA) and SU-8
photoresists. All these techniques are found to be successful in writing the WG structures on thin films. Air channel WGs
are formed by EBL and direct laser writing techniques on PMMA and PPR, respectively. The air channel is further
infiltrated with a higher index zinc oxide by sol-gel chemistry for guidance of light by total internal reflection. The
structure written on SU-8 by optical lithography and on PMMA thin film by femto second laser writing resulted in the
ridged WG structures where the guidance is possible by total internal reflection. The WG writing is also successfully
carried out by electron beam lithography and femto second laser writing on PhCs fabricated from PMMA and
polystyrene colloidal particles using inward growing self-assembly method. Unlike the earlier WG structures, the light
guidance is possible due to photonic band gap effect in PhC WG, only for the wavelengths that lie within the stop band of
the PhC. The quality of the written structures is characterized using images from scanning electron microscope, atomic
force microscope and optical microscope. For optical characterization, a diode laser beam is successfully guided through
the WG structure fabricated on PMMA PhC by EBL and on SU-8 thin film by optical lithography method.
Three-dimensionally ordered photonic crystals were grown using self-assembly technique from Rhodamine-B dye doped polystyrene micro-spheres resulting in a stop band at 611 nm overlapping the emission spectrum of the dye. When excited at a wavelength away from the stop band, using a frequency-doubled Nd:YAG laser, the crystal showed angle-dependent suppression of spontaneous emission of the dye in the wavelength range of the photonic stop band and enhancement at the band edge, in reflection and transmission geometries. Spectral narrowing, a sharp threshold and a highly directional emission, all indicative of stimulated emission, were observed from the active photonic crystal matrix.
A simple technique to obtain a tunable laser using an erbium doped fiber in a ring cavity is proposed and demonstrated. The design does not include intra cavity filters to achieve tunable action; instead, it relies on the influence of intra cavity loss on the lasing wavelength. The dependence of tunability on factors such as the doping concentration of the fiber, reflectivity of the coupler, length of the doped fiber and pump power is discussed comprehensively using an analytical model and demonstrated experimentally. The effect of pump power on the lasing wavelength as seen in the experiment, which is not a direct consequence of the analytical model of fiber lasers, is discussed qualitatively. The key to enhance tunability is to increase the inversion levels in the fiber, which is possible with the use of shorter lengths of fiber with higher dopant concentration and larger pump powers, with maximum reflection into the cavity.
We present a systematic analysis of three dimensionally ordered photonic crystals made of dyed-polystyrene spheres fabricated using the newly reported inward growing self assembling method. The SEM and AFM images show good ordering of the spheres with (111) plane parallel to the substrate. The photonic stop band is tuned by varying the angle of incidence of light and made to coincide with the emission wavelength of the dyes. The multiple Bragg diffraction effects observed at high angles of incidence are interpreted. The high reflectance values obtained along with the observation of the higher order bands, and the photonic stop band splitting at high angles of incidence show the superior quality of the photonic crystals fabricated using these dyed polystyrene spheres in less than three hours.
We have performed calculations using the Transfer Matrix method to study the photonic band gap properties of bare opals of different diameters, different thicknesses, sintered opals with the filling fractions varying between 0.74 and 1.00, partial and complete coating with semiconducting GaN and lastly, inverted opals. Two prominent directions [100] and [111] have been analyzed. Sintering improves the gap and shifts the energy range of its occurrence, while partial coating gives a better bandgap than complete coating. Inverted opals with semiconductor background shows a gap with transmission decreasing to much lower values, as expected due to an improvement in dielectric contrast.
We have investigated a Fabry-Perot filter and a nonlinear fiber loop mirror (NFLM) for their suitability as photonic switching devices. In the light of new information available on chalcogenide glasses with respect to their nonlinear optical coefficients and attenuation levels, we have found from our analysis that fibers made of these doped glasses hold a lot of promise. The advantage is seen to be more in the case of FP filters than in NFLM, which is rather due to the fact that some of these glass compositions have very high losses at (Lambda) equals 1.55 micrometers . We have made a comparison between the use of Silica glass and Chalcogenide glass as the switching medium. We have also studied the effect of reducing the losses in Chalcogenide glass fibers.
This paper presents the analysis of Erbium Doped Fiber Amplifier (EDFA) operated in the saturation regime for high output signal power. Results indicate that Er3+ doped silica fibers with higher numerical aperture and erbium ion concentration can be used as efficient, high gain power amplifiers in the 1.55micrometers region. It is also observed that the optimum fiber length in high power EDFA does not change appreciably with increasing pump power or signal power.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.