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Using numerical simulations, we investigate the realization of self-focusing media using two-dimensional graded photonic crystals and their applications for imaging and non-imaging purposes. The two-dimensional graded photonic crystals consist of spatially varying cylindrical holes drilled in a dielectric host. By controlling the gradient of the refractive index and the thickness of the self-focusing medium, it is possible to obtain either a focusing lens with Fourier transforming capabilities or an imaging lens, which produces inverted images. Non-imaging applications include a simple antenna for directive emission obtained from the focusing lens, whereas a directional cloak is obtained by modifying the imaging lens. Graded photonic crystal based devices work well up to the Bragg frequencies. They are compact, made from lossless dielectrics, and compatible with planar lithographic techniques, so they can find applications in a broad frequency range, even at the optical frequencies. [ABSTRACT FROM AUTHOR]

By means of area-transformation method, the material parameters of the invisible cloaks in elliptic-cylindrical and spherical coordinates were obtained. The material parameters of the invisible cloaks are nonsingular and the cloaks can operate in a wide bandwidth due to the area-transformation rather than the point-transformation. The invisible properties of the cloaks are nearly perfect when the original area is small enough compared with its counterpart in the transformed space. Full wave simulations based on finite element method verified the designed cloaks. [ABSTRACT FROM AUTHOR]

Photonic crystal fiber (PCF) modal interferometer is studied for sensing applications. There is a trade-off between high sensitivity and wide sensing range due to the intrinsic two-beam interference. We propose and experimentally demonstrate a three-beam path reflective interferometer by exciting mode conversion at the end surface of a dual-mode PCF. Approximately 5% mode conversion is taken place at the PCF end surface according to our model. In comparison with the normal dual-mode interference in a PCF, the mode conversion induced three-beam interference generates sharper spectrum and expanded sensing range. Gas sensing experiment is implemented with a sensitivity of 3019 nm/RIU. The advantage of expanded sensing range is also experimentally demonstrated. [ABSTRACT FROM AUTHOR]

The acousto-optic (AO) effects of photonic crystals (PCs) were studied. Both the PCs’ periodicity and their index distribution could be modulated instantly by the propagating acoustic wave. As a consequence, the PCs’ band structure becomes tunable. In addition to band gap shift in an ideal PC, AO frequency modulation was observed in a PC with single defect, which is quite different from normal AO tunable filters and gives rise to some interesting applications. Furthermore, in dual-defect situation, synchronized and desynchronized modulations were realized at different acoustic wavelengths. Interesting phenomena such as dual frequency sweeping and dual frequency Q-switching were demonstrated. [ABSTRACT FROM AUTHOR]

Imaging effects in metallic photonic crystals (PCs) are examined theoretically based on the finite difference time-domain method. The analysis shows that, in metallic PC-based systems, far-field images do form at the opposite side of the PC “lens” and more importantly, follow the rule of geometric optics with respect to the changes in the source position as a direct proof of negative refraction. However, the comparison of ideal left-handed media with a metallic PC suggests that the focusing effect in the PC based system is different from that of the ideal left-handed media in many aspects, due to the inhomogeneous nature of the PC. Particularly, strong dependence on the individual geometry as well as the frequency in the PC-based system renders the effective index sensitive to the variations and potentially limits its application as a superlens. [ABSTRACT FROM AUTHOR]

We report the properties of one-dimensional heteroepitaxial all-garnet magneto-optical (MO) photonic crystals (MOPCs) composed of alternating MO-active Bi3Fe5O12 (BIG) and transparent Sm3Ga5O12 (SGG) quarter-wavelength layers grown by rf-magnetron sputtering on Ca,Mg,Zr:Gd3Ga5O12(111) and Gd3Sc2Ga3O12(001) crystals. MOPCs’ spectra, as designed, exhibit a stop band structure and a band gap with the transmittance central peak at 750 nm caused by light localization in the half-wavelength BIG cavity. A series of MOPCs with different numbers of [BIG/SSG]m reflectors (m=4, 5, and 6) has been fabricated to optimize the specific Faraday rotation θF (deg/μm) and MO-quality factor Q(deg)=2|θF|/absorption coefficient. A close BIG-to-SGG lattice match enabled significant improvement of [Bi3Fe5O12/Sm3Ga5O12]m properties compared to previously reported [Bi3Fe5O12/Y3Fe5O12]m [S. Kahl and A. M. Grishin, Appl. Phys. Lett. 84, 1438 (2004)] and [Bi3Fe5O12/Gd3Ga5O12]m [S. I. Khartsev and A. M. Grishin, Appl. Phys. Lett. 87, 122504 (2005)] pulsed laser deposited photonic crystals. At the resonance wavelength λ=750 nm, θF=-20.5 deg/μm and Q=66 deg represent the highest MOPC performance achieved so far. Respectively, these are 470% and 31% enhancements compared to a single layer Bi3Fe5O12 film Faraday rotator with equivalent thickness. [ABSTRACT FROM AUTHOR]

Reactive ion etching (RIE) using a CH4–H2 plasma is investigated for the fabrication of a GaN one-dimensional (1D) photonic crystal (PhC) slab. The dominant control parameter for the etch rate and the sidewall profile is the dc bias. The influence of operating pressure, CH4/H2 ratio, and total gas flow rate on the etching characteristics is also presented. An etch rate as high as 85 nm/min and an overcut angle as low as 5° obtained in this work are among the best values reported for conventional RIE technique. The CH4–H2 process is used to etch 1D PhCs with a lattice parameter ranging from 700 to 350 nm and an air filling factor of 0.30 into a 600-nm-thick GaN/sapphire slab. Sharp peaks corresponding to the resonant modes of the nanopatterned structures are observed in the experimental reflection spectra for all the lattice periods. Furthermore, the good optical quality of the nanostructures is evidenced by a resonantly enhanced second-harmonic generation experiment around 400 nm. A second-harmonic generation enhancement factor as high as 105 is obtained, compared with the unpatterned GaN reference slab. These results demonstrate that the CH4–H2 conventional RIE technique is well adapted to the etching of GaN PhC for the fabrication of next generation photonic devices exploiting nonlinear processes. [ABSTRACT FROM AUTHOR]

We have achieved single-mode laser action in a one-dimensional hybrid photonic crystal (HPC) containing cholesteric liquid crystal (CLC) as a defect and experimentally investigated the polarization characteristics of the laser light. The laser light emitted from the HPC containing the CLC was linearly polarized, which was different from that of the simple CLC, despite the CLC being contained in this structure. We have theoretically calculated the optical propagation to justify the experimental result. The calculated result was in good agreement with the experimental result and showed the difference in optical characteristics between the simple CLC and the HPC containing the CLC. [ABSTRACT FROM AUTHOR]

Five different glass compositions with equal TeO2 molar concentration and various intermediate constituents were prepared to examine the influence of such intermediate species on the tellurite network. A correlation between the glasses’ structural network and optical properties is presented. Peak Raman gain coefficients, on the order of 40 times the gain of SiO2, are reported in this paper. [ABSTRACT FROM AUTHOR]

A two-dimensional square lattice photonic crystal composed of ferroelectric cylinder rods in air background is proposed to realize tunable negative refraction by applying electric field. Based on the Pockels effect, refractive indices of rods can be changed linearly along with applied electric field, and then photonic band structure and equifrequency surface can be modified. The refractive angle could vary from negative to positive depending on intensity of electric field at a certain incident angle. The feasibility of the photonic crystal operating in visible region at the frequency of 476.5 THz was presented, which might have potential applications in photoelectronic devices. [ABSTRACT FROM AUTHOR]

Three deformed and two rotational structures are constructed to study the effect of structural and rotational symmetries on the gap widths of E- and H-polarization bands in photonic crystals. The band structures and field patterns of a triangular lattice of hollow tellurium (Te) rods are calculated using the plane-wave method. The H-polarization band gaps are strongly affected by the interaction between the fields of the rods as the rods are deformed and affected by the reduction in the rotational symmetry as whole rods are rotated. Only the shapes of the rods affect the E-polarization band gaps as the rods are either deformed or rotated. Moreover, H-polarization modes determine the absolute photonic band gap (PBG) width as the rods are rotated, whereas E-polarization modes determine the absolute PBG width as the rods are deformed. [ABSTRACT FROM AUTHOR]

A metallic coating method is used to modify the optical properties of a dielectric photonic lattice and to achieve a near visible photonic band edge. It is experimentally shown that the linear scaling rule of a metallic band edge versus lattice constant holds only for perfect conducting metals. When a metal deviates from a perfect conducting behavior near the plasma wavelength, the metallic photonic band edge is pinned and is nearly independent of lattice constant. For our tungsten photonic lattice, the pinning occurs at λ≈1.5–2 μm. By using a thin copper coating (∼70 nm) to a dielectric photonic lattice, a photonic band edge at λ∼750 nm is observed. This achievement is made possible by the fact that copper is a good conductor at visible wavelengths and the linear scaling rule holds. Finally, this coating method allows for tailoring photonic properties through material engineering at the nanometer scale. [ABSTRACT FROM AUTHOR]

An exact analytical dispersion relation is derived for transverse-magnetic modes with kz=0 in a particular two-dimensional rectangular photonic band gap structure. The dispersion relation is analyzed, and the dispersion characteristics are determined. Analytical results are compared with results from the Massachusetts Institute of Technology Photonic Band Gap Structure Simulator (PBGSS) code. The error tolerance in the PBGSS code is established. Finally, the attenuations of modes with frequencies in global band gaps are computed analytically. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate how sum frequency generation (SFG) and difference frequency generation (DFG) of 150 fs pulses can be enhanced and serve as diagnostics for leaky eigenmodes in a two-dimensional GaAs photonic crystal waveguide. SFG at 795 nm is obtained in reflection from s-polarized 1900 nm and p-polarized 1360 nm pulses, with both input beams coupled to leaky eigenmodes; the SFG is enhanced by >350× compared to that from an untextured GaAs surface. We are able to detect Drude induced subnanometer blueshifts of the SFG, corresponding to refractive index changes of <=10-3. DFG of 1360 nm light obtained in reflection from s-polarized 1900 nm and p-polarized 793 nm pulses displays an enhancement of >500× via three different leaky eigenmodes. As the 793 nm beam polarization is varied from p polarized to right and left circularly polarized, the DFG remains essentially linearly polarized but with a reduced, albeit different, intensity for right and left circularly polarized 795 nm pulses. Futhermore, the plane of polarization also rotates by different amounts for the left and right circularly polarized light, demonstrating interference of the components generated by s- and p-polarized 793 nm pulses. Overall, our results demonstrate how enhanced DFG and SFG from leaky eigenmodes can be used to characterize their properties more precisely than linear optical techniques. [ABSTRACT FROM AUTHOR]

Photonic crystals (PC) based on porous n-Si are fabricated and their structural, optical, and nonlinear optical properties are studied. The n-Si based PC composed of five pairs of layers with alternate porosity reveal a rather broad photonic band gap (PBG) of more than 100 nm and a reflectivity of up to 0.75. An average pore diameter of approximately 90 nm is found in n-Si based PC in contrast to mesoporous p-Si based PC, where pores are approximately 15 nm in diameter. Second-harmonic generation (SHG) spectroscopy reveals the enhancement of the SHG intensity by a factor of 102 at the blue edge of the PBG spectra which is attributed to the fulfillment of the phase matching conditions and the localization of the fundamental optical field in the PC. [ABSTRACT FROM AUTHOR]

An analysis of the optical properties of photonic woodpile structures is presented. We demonstrate large superprism phenomena inside polymeric woodpile structures having a refractive index of less than n=1.6. Due to the low contrast in refractive indices the structures investigated do not possess a complete photonic band gap. Nevertheless, their photonic band structures show strong anisotropy at frequencies slightly above the band gap in the (Γ-X) direction, leading to an extreme sensitivity to the angle and the frequency of the incident light in the propagation direction inside the crystal. Furthermore, if the woodpile structure is arranged in a prism-like shape, the transmitted beam outside the crystal shows a strong sensitivity to the frequency and angle of the incident light. [ABSTRACT FROM AUTHOR]

We recently reported on the realization of ultraviolet photonic crystal laser based on zinc oxide [Appl. Phys. Lett. 85, 3657 (2004)]. Here we present the details of structural design and its optimization. We develop a computational supercell technique that allows a straightforward calculation of the photonic band structure of ZnO photonic crystal slab on sapphire substrate. We find that despite the small index contrast between the substrate and the photonic layer, the low-order eigenmodes have predominantly transverse-electric (TE) or transverse-magnetic polarization. Because emission from ZnO thin film shows a strong TE preference, we are able to limit our consideration to TE bands, spectrum of which can possess a complete photonic band gap with an appropriate choice of structure parameters. We demonstrate that the geometry of the system may be optimized so that a sizable band gap is achieved. [ABSTRACT FROM AUTHOR]

Neodymium-doped GeO2/γ-glycidoxypropyltrimethoxysilane hybrid planar waveguide films were prepared by a low-temperature sol-gel technique from an organic-inorganic hybrid system for photonic applications. Optical properties such as refractive index, thickness, propagation modes, and attenuation coefficient of the hybrid planar waveguides were investigated by using a prism coupling technique. An intense room-temperature yellow-to-violet up-conversion emission at 397 nm (4D3/2→4I13/2) was measured from the hybrid planar waveguide film heated at a low temperature of 100 °C upon excitation with a xenon lamp at the wavelength of 580 nm. In addition to this intense violet emission, a relatively weak ultraviolet emission at 376 nm and a blue emission at 468 nm were also observed. The mechanism of the up-conversion emission is proposed, and they indicate that the excited-state absorption process originating from the long-lived 4F3/2 excited state should be responsible for the up-conversion process. [ABSTRACT FROM AUTHOR]

We modeled the effect of atomic interdiffusion in InGaAsSb/AlGaAsSb quantum well grown on GaSb substrate. The material modification after interdiffusion has been calculated using Fick’s second law of diffusion and the rationalized biquadratic quinary interpolation algorithm. Our results show that both the group-III and group-V atomic interdiffusions lead to blueshifts of ground-state transition energies. For identical diffusion lengths, the group-III interdiffusion produces a larger ground-state blueshift than the group-V interdiffusion. A wavelength blueshift as large as 772 nm is predicted from a 10-nm-wide interdiffused quantum well with an identical diffusion length of 5 nm for both the group-III and group-V sublattices. The large wavelength tuning range indicates that the interdiffusion method can be potentially used to trim the emission wavelengths of InGaAsSb/AlGaAsSb quantum-well structures for various mid-infrared-based photonics devices. Our results will also serve as useful references for a better process control of the epitaxial growth of Sb-based systems. [ABSTRACT FROM AUTHOR]

The focusing properties of a photonic-crystal (PC) slab consisting of a square lattice of rectangular dielectric rods in the air background are studied theoretically. We employ the finite-difference time-domain method to investigate the field patterns of a point source placed in the vicinity of the PC slab and find that an image can form in the opposite side of the slab in a frequency window located slightly below the fundamental band gap. We change the orientation of the rectangular rods and find that when the rods are arranged asymmetrically with respect to the surface normal of the slab, the image spot can show a vertical shift relative to the point source. The influence of the PC slab thickness on the quality of the image is also analyzed. From these simulation results and the equifrequency-surface contour analysis, we find that the dominant physical mechanism that shapes the focusing behavior of these rectangular-rod PC slabs in the ground photonic band is the self-collimation effect instead of the negative refraction effect. [ABSTRACT FROM AUTHOR]

Theoretical investigations are carried out for close-to-lasing two-dimensional finite-sized photonic crystals with active (gain) lattice points. First, laser oscillations with lower thresholds are found to occur near the photonic band edges where optical gain is enormously intensified. For several modes isolated around the band edge, the field-intensity spectra in reciprocal space and the Poynting-vector distributions in real space are investigated in detail in close-to-lasing photonic crystals. By comparing the phenomena that occur in photonic crystals with a symmetric or an asymmetric outward form, this paper clarifies the differences in the feedback mechanisms of these crystals. In a symmetric photonic crystal, laser oscillation occurs through the waves propagating along the straight passages. This feedback is basically the same as that of ordinary one-dimensional lasers, although it exhibits a complicated behavior that light waves propagating in a variety of directions interfere with each other. In an asymmetric photonic crystal, laser oscillation occurs through the waves circulating within the crystal, which could be called recurrent-photon feedback. This feedback, however, can be construed as an extension of the feedback in ordinary one-dimensional distributed-feedback lasers. [ABSTRACT FROM AUTHOR]

Hexagonal photonic crystal microcavities with missing-hole defects were fabricated in suspended InP membranes. Embedded InAs quantum dots were utilized as broadband emitters to characterize the modes of the cavities. Photoluminescence emission consists of two orthogonally polarized peaks corresponding to the two dipole modes of the hexagonal defect cavity of reduced symmetry. The emission wavelength ranges from 745 to 840 meV, depending on the crystal structure, and quality factors are up to 850. Finite-difference time-domain simulations reproduce the cavity mode energies and the quality factor dependence on the crystal structure, but predict quality factors systematically lower. The experimental quality factors and mode splittings are associated with a slight ellipticity of the lattice holes. [ABSTRACT FROM AUTHOR]

We demonstrate electrically switchable third-harmonic generation in low refractive index contrast one-dimensional photonic crystals pumped by a near-infrared laser beam. A dramatic enhancement of the third-harmonic signal is observed on the short wavelength side of the photonic crystal stop band. The enhancement of the third-harmonic generation disappears when an electric field is applied, revealing the electrical switchability of the third-harmonic generation. The observed phenomenon of enhancement is explained theoretically with a coupled-mode model. We also show that up to a modulation frequency of 10 kHz the switching properties are supported in the photonic crystal. [ABSTRACT FROM AUTHOR]

We report on the progress in the growth of highly reflective AlInN–GaN distributed Bragg reflectors deposited by metalorganic vapor phase epitaxy. Al1-xInxN layers with an In content around x∼0.17 are lattice-matched to GaN, thus avoiding strain-related issues in the mirror while keeping a high refractive index contrast of about 7%. Consequently, a reflectivity value as high as 99.4% at 450 nm was achieved with a 40-pair crack-free distributed Bragg reflector. We measured an average absorption coefficient α [cm-1] in the AlInN–GaN Bragg reflectors of 43±14 cm-1 at 450 nm and 75±19 cm-1 at 400 nm. Application to blue optoelectronics is demonstrated through the growth of an InGaN–GaN microcavity light emitting diode including a 12-pair Al0.82In0.18N–GaN distributed Bragg reflector as bottom mirror. The device exhibits clear microcavity effects, improved directionality in the radiation pattern and an optical output power of 1.7 mW together with a 2.6% external quantum efficiency at 20 mA. [ABSTRACT FROM AUTHOR]

A purely optical method to generate and to steer an ultrasonic beam is presented. The generation of the ultrasonic beam in the kilohertz to megahertz regime is achieved by using the optoacoustic effect in a layer attached to the surface of a water tank, which absorbs time-modulated laser pulses. In order to tailor the emitted acoustic wave, diffractive optics concepts are applied to acoustics. To this end, the laser light intensity distribution at the absorbing surface is controlled by sending a computer-calculated pattern to a transmissive high-resolution liquid-crystal display in the beam path. This results in an acoustic analog to the “diffractive optical elements” in laser optics, with the emitted ultrasonic wave emerging in a predetermined way. The proof of principle is demonstrated for examples such as phase gratings and binary Fresnel lenses. The optoacoustic ultrasound generation with holographic diffractive steering is a flexible method with the potential of new applications in ultrasound diagnostics. [ABSTRACT FROM AUTHOR]

We develop a model to study coupled cavity waveguides (CCWs) in photonic crystals, composed of linear chains of coupled cavities. By extending previous work on single mode cavities, we have developed a model applicable to any finite number of quasi-degenerate cavity modes. Our model, which uses a multimode tight-binding approach, allows us to study the interaction between the cavity modes as well as the coupling between the CCW bands. In contrast to previous work the coupling parameters are calculated ab initio from the single cavity field profile. The calculated dispersion relations are shown to be in good agreement with those obtained from the plane wave expansion method. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have investigated the electromagnetic band structure, transmission, and phase time through a one-dimensional structure made of loops pasted together with segments of finite length. In this serial loop structure, the loops and segments are constituted of dielectric monomode materials. Analytic expressions are reported for the band structure for a large number N of loops and for transmission coefficients and phase times for any value of N. Experimental and numerical results show the existence of large gaps in these structures. These gaps originate both from the periodicity of the system and the loop resonant states that create zeroes of transmission. The gap widths depend on the lengths of the finite segment and the loop diameters. Defect modes may occur in these bandgaps by introducing defective segments in the structure. The localized states appear as very narrow peaks both in the transmission spectrum and in the transmission phase time of finite serial loop structures. The localized state behavior is analyzed as a function of the length and of the position of the defect segment. The transmission phase measurements enable us to derive the group velocity as well as the density of states in these structures. The experimental results are obtained using coaxial cables in the frequency range of few hundreds of MHz. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present a procedure for analyzing the properties of multilayer structures with magnetic film. The magneto-optical effect in multilayer-structure magnetic films [e.g., bismuth-substituted yttrium iron garnet (YIG)] and dielectric films (e.g., SiO[sub 2] and Ta[sub 2]O[sub 5]) was investigated theoretically and experimentally to examine the correlation between the magneto-optical properties and the localization effect of light. The film structure of interest, which has symmetric periodicity, is the (Ta[sub 2]O[sub 5]/SiO[sub 2])[sup n]/Bi:YIG/(SiO[sub 2]/Ta[sub 2]O[sub 5])[sup n] structure, where n is the repetition number. We fabricated experimentally a one-dimensional magnetophotonic crystal film of (Ta[sub 2]O[sub 5]/SiO[sub 2])[sup n]/ Bi:YIG/(SiO[sub 2]/Ta[sub 2]O[sub 5])[sup n] (n = 2,6) structures. The theoretical calculation and the measured value for the Faraday rotation were in close agreement. Furthermore, the Faraday rotation of the multilayer structure with n = 6 is 150 times larger than that of a Bi:YIG single-layer film. This is of interest from the point of view of actual magneto-optical device (e.g., optical isolator) fabrication. [ABSTRACT FROM AUTHOR]

We demonstrate coherent all-optical injection and control of a ballistic spin-polarized current in bulk, low-temperature-grown GaAs at room temperature. The spin current is injected by interfering the two-photon absorption of the fundamental (1.55 µm) and the single photon absorption of the second harmonic (0.775 µm) of ∼180 fs pulses that propagate collinearly and have the same circular polarization. Adjusting the relative phase of the two pulses controls the direction of this current. The component of the electrical current transverse to the pulse propagation direction is investigated by monitoring charge collection across a pair of gold electrodes deposited on the GaAs surface. Results are in agreement with recent theoretical predictions. [ABSTRACT FROM AUTHOR]

Recently, theoretical derivation of band structures of electromagnetic waves in two-dimensional microplasma array has been induced by Osamu Sakai et al. [J. Appl. Phys. 101, 073304 (2007)] using a modified plane wave expansion (PWE) method and a frequency-dependent finite difference time-domain (FDTD) method. This report reveals band diagrams with the effects of plasma electron collision frequency, especially focuses on the TE wave by nonmagnetized plasma. Although the band diagrams of TE wave and formulas of calculation look correct at first glance, there are some mistakes in the report which are unfortunately ignored by the authors. The correct formulas of the modified PWE method and FDTD method will be proposed. [ABSTRACT FROM AUTHOR]

We propose a design of phase mask for a single-exposure fabrication of microsphere-type photonic crystals by means of holographic lithography. The photonic crystal could have body-centered tetragonal, body-centered cubic, face-centered cubic, or face-centered tetragonal symmetry. Detailed band-gap calculations elucidate effects of macroscopic and microscopic structural parameters on the formation of photonic full band gaps. [ABSTRACT FROM AUTHOR]

We demonstrate single-mode horizontal and vertical waveguides in a recently proposed photonic crystal having layered square symmetry. The vertical waveguide supports two degenerate polarizations, and thus light can be selectively steered into horizontal waveguides oriented at 90° based on its polarization. We calculate the transmission of 90° bends, both from horizontal waveguide to horizontal waveguide and from horizontal waveguide to vertical waveguide. In the case of the horizontal-horizontal bend, we show a transmission of 83% for a simple (“zero” radius of curvature) bend, and a peak transmission of 100% for a bend which has been optimized by moving one rod from the inner corner to the outer corner of the bend. For the vertical to horizontal bend, we find a transmission of 95% for the allowed polarization, but with a much smaller bandwidth than in the case of the optimized horizontal bend. [ABSTRACT FROM AUTHOR]

Optical properties of a straight 50-row-long photonic crystal waveguide (PCW) are reported. This waveguide is obtained by removing one row of air holes in a triangular lattice two-dimensional photonic crystal etched on a silicon-on-insulator substrate. Transmission measurements are performed on a wide wavelength range (1.15–1.75 μm) with an external white light source. It is found that the experimental data are in very good agreement with both the theoretical transmission calculated by a two-dimensional finite difference time domain method and the theoretical photonic band structure. We show a coupling factor higher than 60% between a monomode ridge waveguide and the PCW. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Polymer has been considered to be an ideal material option for integrated photonics devices. To measure these devices, normally the route of edge coupling is chosen to couple the light into or out of the polymer waveguide, which, however, demands a more difficult alignment procedure compared to the surface coupling. Due to the relatively low refractive indices of polymers, implementing the surface grating coupler for surface coupling in this material system remains a challenge. In this paper, we present a polymer-based surface grating coupler. Rather than through expensive complementary metal-oxide-semiconductor (CMOS) fabrication, the device is fabricated through a simple and fast UV-based soft imprint technique utilizing self-developed low-loss polymer material. The coupling efficiency is enhanced by embedding a thin Si3N4 layer between the waveguide core and under cladding layer. Around -19.8 dB insertion loss from single-mode fiber (SMF) to single-mode fiber is obtained for a straight waveguide with a grating coupler at each end. If the output light is collected with a multimode fiber, the insertion loss can be reduced to around -17.3 dB. Near 12% of the coupling efficiency is achieved between the polymer waveguide and SMF. The 3 dB bandwidth of the transmission is 32 nm and is centered at 1550 nm. The proposed surface grating coupler and its easy fabrication method would be very attractive for practical applications. [ABSTRACT FROM AUTHOR]