Efficient Light Coupling Research Articles

Bonding III-V material to SOI with transparent and conductive ZnO film at low temperature.

A procedure of bonding III-V material to SOI at low temperature using conductive and transparent adhesive ZnO as intermediate layer is demonstrated. Bonding layer thickness of less than 100 nm was achieved in our experiment that guaranteed good light coupling efficiency between III-V and silicon. This bonding method showed good bonding strength with shear stress of 80 N/cm(2). The lowest resistance of the bonded samples was 48.9 Ω and the transmittance of the spin-coated ZnO layer was above 99%. This procedure is applicable for fabricating hybrid III-V/Si lasers.

19.2: Invited Paper: Novel Wide‐Color‐Gamut LED Backlight for 4K LCD Embedded with Mixing Cup Structure for Isotropic Light Source

AbstractWe have developed wide color gamut LED backlight for large size displays embedded with novel mixing cup structure for efficient light coupling from isotropic light source. When isotropic light source is prepared by photo‐excitation of quantum dots, wide color gamut of 150% area size against sRGB(u'v') and 30nm FWHM of Red spectrum in the 55“ 4K resolution large size display prototype of 450nit brightness are achieved.

On-chip cavity optomechanical coupling

On-chip cavity optomechanics, in which strong co-localization of light and mechanical motion is engineered, relies on efficient coupling of light both into and out of the on-chip optical resonator. Here we detail our particular style of tapered and dimpled optical fibers, pioneered by the Painter group at Caltech, which are a versatile and reliable solution to efficient on-chip coupling. First, a brief overview of tapered, single mode fibers is presented, in which the single mode cutoff diameter is highlighted. The apparatus used to create a dimpled tapered fiber is then described, followed by a comprehensive account of the procedure by which a dimpled tapered fiber is produced and mounted in our system. The custom-built optical access vacuum chambers in which our on-chip optomechanical measurements are performed are then discussed. Finally, the process by which our optomechanical devices are fabricated and the method by which we explore their optical and mechanical properties is explained. It is our expectation that this manuscript will enable the novice to develop advanced optomechanical experiments.

Efficient Coupling of Light to Graphene Plasmons by Compressing Surface Polaritons with Tapered Bulk Materials

Graphene plasmons promise exciting nanophotonic and optoelectronic applications. Owing to their extremely short wavelengths, however, the efficient coupling of photons to propagating graphene plasmons-critical for the development of future devices-can be challenging. Here, we propose and numerically demonstrate coupling between infrared photons and graphene plasmons by the compression of surface polaritons on tapered bulk slabs of both polar and doped semiconductor materials. Propagation of surface phonon polaritons (in SiC) and surface plasmon polaritons (in n-GaAs) along the tapered slabs compresses the polariton wavelengths from several micrometers to around 200 nm, which perfectly matches the wavelengths of graphene plasmons. The proposed coupling device allows for a 25% conversion of the incident energy into graphene plasmons and, therefore, could become an efficient route toward graphene plasmon circuitry.

Study of the Light Coupling Efficiency of OLEDs Using a Nanostructured Glass Substrate

We study theoretically the enhancement of the light extraction from an OLED (Organic Light-Emitting Diode) with nanoair-bubbles embedded inside a glass substrate. Due to such a nanostructure inside the substrate, the critical angle which limits the light extraction outside the substrate from the OLED is increased. The theoretical results show that the nanoair bubbles near by the substrate surface can improve the efficiency of the light extraction by 7%. Such a substrate may also be suitable for photovoltaic cells or display screens.

Efficient coupling of hybrid optical waveguide with a sharp bend structure for high integration

A hybrid optical waveguide with a \(90^{\circ }\) sharp bend comprising a dielectric straight waveguide, a tapered dielectric strip waveguide, and a microscale metal gap waveguide is proposed, modeled, fabricated, and characterized with the aim of improving the efficiency of light coupling between the dielectric and plasmonic waveguides. The simulation result using the full-vector finite-difference time domain shows a total transmissivity of about 63 % at a wavelength of 1,550 nm. A set of hybrid optical waveguide with a \(90^{\circ }\) bend is fabricated via the two-step photolithography and a metal lift-off process. From the measured result for the characteristics of the fabricated hybrid optical waveguide, the transmission loss was estimated to be about 17 dB, which is in stark contrast with the simulation value. Nevertheless, such a novel coupling scheme may be of potential use in high-density photonic integration applications.

温度对空间光单模光纤耦合的影响研究

温度对空间光单模光纤耦合的影响研究

Hybrid integrated plasmonic-photonic waveguides for on-chip localized surface plasmon resonance (LSPR) sensing and spectroscopy

We experimentally demonstrate efficient extinction spectroscopy of single plasmonic gold nanorods with exquisite fidelity (SNR > 20dB) and high efficiency light coupling (e. g., 9.7%) to individual plasmonic nanoparticles in an integrated platform. We demonstrate chip-scale integration of lithographically defined plasmonic nanoparticles on silicon nitride (Si3N4) ridge waveguides for on-chip localized surface plasmon resonance (LSPR) sensing. The integration of this hybrid plasmonic-photonic platform with microfluidic sample delivery system is also discussed for on-chip LSPR sensing of D-glucose with a large sensitivity of ∼ 250 nm/RIU. The proposed architecture provides an efficient means of interrogating individual plasmonic nanoparticles with large SNR in an integrated alignment-insensitive platform, suitable for high-density on-chip sensing and spectroscopy applications.

Demonstration of heterogeneous III–V/Si integration with a compact optical vertical interconnect access

Heterogeneous III-V/Si integration with a compact optical vertical interconnect access is fabricated and the light coupling efficiency between the III-V/Si waveguide and the silicon nanophotonic waveguide is characterized. The III-V semiconductor material is directly bonded to the silicon-on-insulator (SOI) substrate and etched to form the III-V/Si waveguide for a higher light confinement in the active region. The compact optical vertical interconnect access is formed through tapering a III-V and an SOI layer in the same direction. The measured III-V/Si waveguide has a light coupling efficiency above ~90% to the silicon photonic layer with the tapering structure. This heterogeneous and light coupling structure can provide an efficient platform for photonic systems on chip, including passive and active devices.

Optically active mechanical modes of tapered optical fibers

Tapered optical fibers with a nanofiber waist are widely used tools for efficient coupling of light to photonic devices or quantum emitters via the nanofiber's evanescent field. In order to ensure well-controlled coupling, the phase and polarization of the nanofiber guided light field have to be stable. Here, we show that in typical tapered optical fibers these quantities exhibit high-frequency thermal fluctuations. They originate from high-Q torsional oscillations that opto-mechanically couple to the nanofiber-guided light. We present a simple ab-initio theoretical model that quantitatively explains the torsional mode spectrum and that can be used to design tapered optical fibers with tailored mechanical properties.

Efficient Active-to-Passive Light Coupling of InGaAsP/InP Laser Using Subwavelength Coupler

We propose a subwavelength coupler for efficient light coupling from an InGaAsP/InP laser to a passive waveguide. The active-to-passive coupling device is designed on the asymmetric twin waveguide (ATG) platform with two InGaAsP layers: one is used as the laser active layer, and the other with a wider band gap is used as the guiding layer of the passive waveguide. By introducing subwavelength trenches in the active InGaAsP layer, the subwavelength coupler is designed to provide a gradual effective index transition region, and it couples the light between the vertically separated active and passive layers. Simulation result shows that coupling efficiency of 86.5% is achieved at a length of only 31 μm.

Masking LED hot spots in a thin direct lit backlight unit using semitransparent and perforated masks

As the demand for thin displays with more features accelerates, the need for backlight systems to become thinner and capable of multiple features increases. Direct lit concepts supporting 2-D dimming provide higher contrast ratios. However masking led hot spots with thinner backlight thicknesses is yet a significant design challenge. Efficient light coupling and recycling mechanisms in combination with relatively high optical efficiencies are key parameters in overall system design. We demonstrate an optimal masking design of the led hot spot for a thin light guide plate in the direct lit architecture. The overall concept system is simulated and prototyped. The resultant performance is discussed.

Optimization of light delivery by a nanowire-based single cell optical endoscope

Here we present a new design and FDTD simulations of light delivery by a nanowire-based intracellular endoscope. Nanowires can be used for minimally invasive and very local light delivery inside cells. One of the main challenges is coupling of light into the nanowire. We propose a new plasmonic coupler interface between cleaved optical fiber and a nanowire, and optimize light coupling efficiency and contrast.

Two-photon excited fluorescence from a pseudoisocyanine-attached gold-coated tip via a thin tapered fiber under a weak continuous wave excitation

A simple tapered fiber based photonic-plasmonic hybrid nanostructure composed of a thin tapered fiber and a pseudoisocyanine (PIC)-attached Au-coated tip was demonstrated. Using this simple hybrid nanostructure, we succeeded in observing two-photon excited fluorescence from the PIC dye molecules under a weak continuous wave excitation condition. From the results of the tip-fiber distance dependence and excitation polarization dependence, we found that using a thin tapered fiber and an Au-coated tip realized efficient coupling of the incident light (~95%) and LSP excitation at the Au-coated tip, suggesting the possibility of efficiently inducing two-photon excited fluorescence from the PIC dye molecules attached on the Au-coated tip. This simple photonic-plasmonic hybrid system is one of the promising tools for single photon sources, highly efficient plasmonic sensors, and integrated nonlinear plasmonic devices.

Highly efficient coupling from an optical fiber to a nanoscale silicon optomechanical cavity

We demonstrate highly efficient coupling of light from an optical fiber to a silicon photonic crystal optomechanical cavity. The fiber-to-cavity coupling utilizes a compact (L ≈ 25 μm) intermediate adiabatic coupler. The optical coupling is lithographically controlled, broadband, relatively insensitive to fiber misalignment and allows for light to be transferred from an optical fiber to, in principle, any photonic chip with refractive index greater than that of the optical fiber. Here we demonstrate single-sided cavity coupling with a total fiber-to-cavity optical power coupling efficiency of 85%.

Coupling and crosstalk characteristics of hybrid silicon plasmonic waveguides

In this paper, the design and analysis of an ultracompact coupler based on a hybrid silicon plasmonic waveguide (HSPW) is proposed and its coupling and crosstalk characteristics have been theoretically investigated for the development of optical interconnects that can be realized using well-established complementary metal-oxide-semiconductor-compatible fabrication techniques. To determine the minimum horizontal separation distance and efficient coupling length for the designed coupler, the symmetric and antisymmetric supermodes are obtained and their characteristics are studied at a wavelength of 1.55 μm. Efficient light coupling is exhibited by the HSPW coupler with 75 % of power transfer between the two HSPWs with ultrashort coupling length of 2.14 μm when the separation distance is 50 nm. Further, it is shown that the crosstalk is significantly reduced with the insertion of metallic strip between the two HSPWs for realizing highly dense integrated plasmonic circuits.

English

The generation of the slow modes in a planar photonic crystal waveguide has been highlighted theoretically and experimentally in the two last decade. However, the exploitation of this phenomenon to control the light propagation in the optical integrated circuits faces several obstacles and technological locks. On the one hand, it is almost impossible to excite this type of modes in the slowing light devices because of the group velocity mismatch and even if we are able to overcome this problem, the frequencies of the slow modes are very close to the band edge which causes the optical signal distortion by high value of group velocity dispersion. On the other hand, the slow modes are characterized by a special spatial distribution of the electromagnetic field which extends beyond the defect which serves as a wave guide, this lead to an intense interaction of a part of the guided light with the holes of photonic crystal and cause the appearance of the different type of losses. Several solutions have been proposed to address these various issues and our contribution is in this perspective, and more specifically, it is trying to find the parameters that enable an optimal coupling of the fast modes of our planar photonic crystal waveguide into his slower one. To achieve this goal, we chose to work in two stages. First, we have sought the structural parameters that will help us to generate a slowly mode with zero-dispersion effect. After, we have worked and demonstrated the efficient static coupling of light into the slow modes photonic crystal waveguide.   Key words: Slab waveguide, photonic crystal, slow modes, efficient coupling.

Temperature-compensated fiber-optic 3D shape sensor based on femtosecond laser direct-written Bragg grating waveguides

Temperature-compensated 3D fiber shape sensing is demonstrated with femtosecond laser direct-written optical and Bragg grating waveguides that were distributed axially and radially inside a single coreless optical fiber. Efficient light coupling between the laser-written optical circuit elements and a standard single-mode fiber (SMF) was obtained for the first time by 3D laser writing of a 1 × 3 directional coupler to meet with the core waveguide in the fusion-spliced SMF. Simultaneous interrogation of nine Bragg gratings, distributed along three laterally offset waveguides, is presented through a single waveguide port at 1 kHz sampling rate to follow the Bragg wavelength shifts in real-time and thereby infer shape and temperature profile unambiguously along the fiber length. This distributed 3D strain and thermal sensor is freestanding, flexible, compact, lightweight and opens new directions for creating fiber cladding photonic devices for a wide range of applications from shape and thermal sensing to guidance of biomedical catheters and tools in minimally invasive surgery.

Enhancement of light extraction of green top-emitting organic light-emitting diodes with refractive index gradually changed coupling layers

By means of refractive index gradually changed coupling layers, a highly efficient green top-emitting OLED (TOLED) with enhanced light coupling efficiency and stable colors over angles has been realized. The refractive index transition of the coupling layers including the doping layer smoothes light extraction from the semitransparent cathode metal to the air, which is the reason for the enhancement of light coupling efficiency. The doping layer in the coupling layers also acts as a microparticle diffuser to eliminate the shift in EL spectra with viewing angles. A universal simulation has also been carried out, and the result suggests that the light coupling efficiency will be enhanced further if the refractive index transition of the coupling layers is continuous.

Bioinspired pit texturing of silicon solar cell surfaces

In order to improve the light-harvesting capability of silicon solar cells, bioinspired texturing of the exposed surface was investigated. The texture has a pit topology, which is the negative of a previously analyzed bioinspired hillock texture. Multifrequency numerical simulations of the light-coupling efficiency were carried out within the framework of the geometrical optics over a large and relevant portion of the solar spectrum. The bioinspired pit texture exhibits an efficiency significantly greater than that of a flat silicon surface, and somewhat outperforms the bioinspired hillock texture.