Optical Coupling Efficiency Research Articles

Development of silicon photonic devices for optical interconnects

Silicon photonic devices based on complementary-metal-oxide-semiconductor (CMOS) compatible technologies have shown attractive performances on very-large-scale monolithic optoelectronic integration, high speed modulation and switching, and efficient off-chip optical coupling. This paper presents the recent progress on fast silicon optical modulation, wavelength-insensitive optical switching and efficient optical coupling techniques in our group. Several CMOS-compatible silicon optical couplers with different structures have been developed, showing the highest coupling efficiency of 65%. Broadband silicon-based optical switches with sub-nanosecond switching on-off time are experimentally realized. Silicon modulators with novel PN junctions are demonstrated with the speed up to 50 Gb s−1.

The progress of silicon-based grating couplers

Silicon-based photonic integrated chips recently have attracted great attention and actively intervened in many applications such as optical communications, optical interconnects, and optical sensing for relevant research institutions. Photonic integrated circuits are the key block to build information infrastructures. Among of them, grating couplers play an important role in silicon photonics, due to high efficient optical coupling on/off photonic chips. Also, they have many advantages in high density photonic packaging and on-wafer testing, such as large alignment tolerances and no requirements for wafer scribing or chip polishing. This review focuses on the principles and performances of grating couplers on silicon-on-insulator substrates. In this article, we also discuss the state-of-art and the trends in the near future, with a summary of our achievements over the last few years.

Single package directly modulated laser bidirectional optical subassembly using a modified mini-dual-in-line package for 10 Gbps passive optical networks

A bidirectional optical subassembly comprised of a 2.5 Gbps distributed feedback (DFB) laser diode (LD) directly modulated laser transmitter and a 10 Gbps positive intrinsic negative photodiode receiver was developed for an optical network unit of a 10 Gbps passive optical network. Here, a low-cost mini-dual-in-line package was modified to contain whole components of a transmitter and receiver in a single space while satisfying the requirements of 10 Gbps micro-device package standards. The transmitter was fabricated to achieve high optical output power by placing a micro aspheric lens very close to the DFB LD and reducing the thermal resistance between an LD chip and heat sink to bring down the DFB LD chip temperature. As a result, the transmitter output power was 3.5 dB higher than a conventional transistor outline can BOSA due to a high optical coupling efficiency of more than 70% and a low thermal resistance for heat dissipation. The receiver sensitivity was −21 dBm at a bit error rate of 10−3 and the sensitivity penalty of the receiver due to signal crosstalk was less than 0.3 dB.

Organized Plasmonic Clusters with High Coordination Number and Extraordinary Enhancement in Surface‐Enhanced Raman Scattering (SERS)

Organized Plasmonic Clusters with High Coordination Number and Extraordinary Enhancement in Surface‐Enhanced Raman Scattering (SERS)

Organized Plasmonic Clusters with High Coordination Number and Extraordinary Enhancement in Surface‐Enhanced Raman Scattering (SERS)

Noble metal nanoparticles exhibit optical excitations known as surface plasmons that produce large enhancement of the local light intensity under external illumination, particularly when the nanoparticles are arranged in closely spaced configurations.1 The interparticle gap distance2 plays a critical role in the generation of hotspots with high electromagnetic fields, and thus such assembled nanoparticles find application to ultrasensitive detection, for example through surface-enhanced Raman scattering3 (SERS) and nonlinear optics, among other feats.4 Controlled assembly using colloidal chemistry is an emerging and promising field for high-yield production of metal nanoparticle clusters with small interparticle gaps.5 However, most of the reported methods rely on the use of nucleic acids or other organic molecules as linking elements,6 which yield long separation distances and thus weak plasmon coupling. Additionally, only simple clusters, such as dimers and trimers, have been efficiently synthesized. Herein, we report the controlled assembly of gold nanospheres into well-defined nanoparticle clusters with large coordination numbers (up to 7) and high symmetry. We further demonstrate ultrasensitive direct and indirect SERS sensing, thus corroborating the outstanding optical performance of these clusters with robust enhancement factors that are over three orders of magnitude higher than those of single particles.

Light induced fluidic waveguide coupling

We report on the development of an opto-fluidic waveguide coupling mechanism for planar solar concentration. This mechanism is self-adaptive and light-responsive to efficiently maintain waveguide coupling and concentration independent of incoming light's direction. Vapor bubbles are generated inside a planar, liquid waveguide using infrared light on an infrared absorbing glass. Visible light focused onto the bubble is then reflected by total internal reflection (TIR) at the liquid-gas interface and coupled into the waveguide. Vapor bubbles inside the liquid are trapped by a thermal effect and are shown to self-track the location of the infrared focus. Experimentally we show an optical to optical waveguide coupling efficiency of 40% using laser light through a single commercial lens. Optical simulations indicate that coupling efficiency > 90% is possible with custom optics.

Simple coupling method for enhancing Brillouin scattering signal in polymer optical fibres

A simple, efficient, and cost-effective method to enhance a Brillouin scattering signal in perfluorinated graded-index (GI-) polymer optical fibres (POFs) is proposed and demonstrated. In this method, instead of the conventional butt-coupling of a POF to a silica singlemode fibre (SMF), a multimode fibre (MMF) with a proper mode-field diameter of the fundamental mode is additionally inserted between the two fibres to improve the optical coupling efficiency from the POF to the SMF. After theoretical analysis, it is experimentally shown that the Brillouin signal in the POF is clearly enhanced simply by inserting standard MMFs, which are commercially available at affordable cost.

Reflective self-organizing lightwave network using a phosphor

Self-organization of optical waveguides that connect two optical devices automatically through a reflective self-organized lightwave network (R-SOLNET) using a phosphor was simulated by the finite difference time domain method. The simulation showed that a R-SOLNET is constructed between a waveguide with a core width of 1.2 μm and a phosphor target, which is located a distance of 6.4 μm from the waveguide edge and guides the probe beam to the phosphor target. The optical coupling efficiency was 95% when the waveguide and phosphor target were fully aligned. Even when the misalignment was 800 nm, a coupling efficiency of 60% was obtained. The coupling efficiency for the SOLNET without the phosphor target was 16%. In addition, experiments to confirm the principle of a R-SOLNET using a phosphor were performed with an optical fiber and tris(8-hydroxyquinolinato) aluminum (Alq 3 ) phosphor target. The experiments revealed that the write beam is propagated toward the Alq 3 target, and consequently, a R-SOLNET connecting the fiber edge and Alq 3 target is formed to guide probe beams to the target. The R-SOLNET expanded from the diameter of the fiber core to the width of the Alq 3 target.

Fiber coupling efficiency on focal plane spot extension caused by turbulence

Fiber optic components have been used in high speed free space optical communication systems. The received laser beam in such a system must be coupled into a single-mode fiber at the input of the receiver module. However, laser propagation through atmospheric turbulence medium degrades pattern matching and limits the fiber coupling efficiency. According to the theory of optical system resolution fiber coupling efficiency on focal plane spot extension caused by turbulence is researched. Results show that coupling efficiency of short spot extension is little different than the long spot extension. The efficiency achieves maximum when the relationship has been met between relative aperture, wavelength of incident light, radius of receiving fiber and atmosphere coherence length in turbulence medium. When turbulence environment is deteriorated coupling efficiency can be maintained at maximum by adjusting coupling system focus.

Cost-effective 10 Gb/s polymer-based chip-to-chip optical interconnect

Board-level optical links are an attractive alternative to their electrical counterparts as they provide higher bandwidth and lower power consumption at high data rates. However, on-board optical technology has to be cost-effective to be commercially deployed. This study presents a chip-to-chip optical interconnect formed on an optoelectronic printed circuit board that uses a simple optical coupling scheme, cost-effective materials and is compatible with well-established manufacturing processes common to the electronics industry. Details of the link architecture, modelling studies of the link's frequency response, characterisation of optical coupling efficiencies and dynamic performance studies of this proof-of-concept chip-to-chip optical interconnect are reported. The fully assembled link exhibits a −3 dBe bandwidth of 9 GHz and −3 dBo tolerances to transverse component misalignments of ±25 and ±37 µm at the input and output waveguide interfaces, respectively. The link has a total insertion loss of 6 dBo and achieves error-free transmission at a 10 Gb/s data rate with a power margin of 11.6 dBo for a bit-error-rate of 10−12. The proposed architecture demonstrates an integration approach for high-speed board-level chip-to-chip optical links that emphasises component simplicity and manufacturability crucial to the migration of such technology into real-world commercial systems.

The metal grating coupling of long-wavelength quantum well infrared photodetectors: surface plasmon effect

The distribution of electromagnetic field of 2D metal grating in the Long-Wavelength Quantum Well Infrared Photodetectors(LW-QWIPs) was studied by Finite Time Domain Method(FDTD).The result shows that making good use of the surface plasmons can remarkably improve the optical coupling efficiency in the LW-QWIPs.It also shows that using a metal grating with the ratio of the hole diameter to the grating period ranged from 0.8 to 0.9,optimal optical coupling can be achieved.

Semiellipsoid microlens fabrication method using UV proximity printing

We present a new semiellipsoid microlens fabrication method that controls the printing gap in the UV lithography process without thermal reflow. The UV proximity printing method can precisely control the curvature radius ratio of the semiellipsoid microlens in the fabrication process. The proposed fabrication method facilitates mass production to achieve a high-yield and high-coupling semiellipsoid microlens that is suitable to be used in commercial fiber transmission systems. A semiellipsoid microlens can be tipped on a single-mode fiber end to improve power coupling efficiency from laser diodes. The semiellipsoid microlens allows increasing the fiber spot size and numerical aperture. It is very important to control the geometric parameters in the assembly procedure to increase the optical coupling efficiency between the laser diode and single-mode fiber. Wide misalignment tolerance, low loss, and low manufacturing cost could be achieved by the proposed fabrication method. The theoretical model is first developed to predict the optical coupling efficiency for various microstructure geometries of semiellipsoid microlens and assembly parameters in this study. Then, the Taguchi method is applied to obtain the optimal geometric parameters setting. The results show that optical coupling efficiency could be significantly improved by using the optimal geometric parameters setting.

Escaped and Trapped Emission of Organic Light-Emitting Diodes

By locating the emitters around the first and second antinode of the metal electrode, the escaped and trapped emission of small molecule based bottom emission organic light-emitting diodes is investigated by using an integrating sphere, a fiber spectrometer and a glass hemisphere. It is found that the external coupling ratio by locating the emitters at the second antinode (at a distance of 220 nm from the cathode) is 70%, which is higher than that of an emitter at the first antinode (60 nm from the cathode) in theory and experiment. Extending the “half-space" dipole model by taking the dipole radiation pattern into account, we also calculate the optical coupling efficiency for the emitter at both the first and second antinode. Our experimental and theoretical results will benefit the optimization of device structures for the higher out-coupling efficiency.

Spectral Response and Noise Temperature of a 2.5 THz Spiral Antenna Coupled NbN HEB Mixer

Abstract We report on a 2.5 THz spiral antenna coupled NbN hot electron bolometer (HEB) mixers, fabricated with in-situ process. The receiver noise temperature with lowest value of 1180 K is in good agreement with calculated quantum efficiency factor as a function of bias voltage. In addition, the measured spectral response of the spiral antenna coupled NbN HEB mixer shows broad frequency coverage of 0.8-3 THz, and corrected response for optical losses, FTS, and coupling efficiency between antenna and bolometer falls with frequency due to diffraction-limited beam of lens/antenna combination.

10-Gbps electroabsorptive modulated laser bidirectional optical subassembly using novel two-window flat package for passive optical network

A novel 10-Gbps bidirectional optical subassembly (BOSA) comprised of a 1577 nm electroabsorptive modulated laser (EML) transmitter optical subassembly (TOSA) and 1270 nm avalanche photodiode (APD) receiver optical subassembly (ROSA) was developed. Here, a 10-Gbps microdevice compatible two-window flat package was proposed to simplify the EML BOSA structure, considering both the mechanical reliability and cooling performance. As a result, an optical output power of 8 dBm was obtained due to a high optical coupling efficiency of 60%, an extinction ratio of 7 dB, and a dispersion penalty at 20 km transmission of less than 1.5 dB for the EML TOSA. The APD ROSA sensitivity was -21.5 dBm at a bit error rate (BER) of 10−12 and -27 dBm at a BER of 10−3 without forward error correction. In addition, the sensitivity penalty of the APD ROSA due to signal crosstalk was less than 1.2 dB.

Surface Plasmon-Enhanced Nanopillar Photodetectors

We demonstrate nanopillar-(NP) based plasmon-enhanced photodetectors (NP-PEPDs) operating in the near-infrared spectral regime. A novel fabrication technique produces subwavelength elongated nanoholes in a metal surface self-aligned to patterned NP arrays that acts as a 2D plasmonic crystal. Surface plasmon Polariton Bloch waves (SPP-BWs) are excited by the metal nanohole array resulting in electric field intensity "hot spots" in the NP. The NP periodicity determines the peak responsivity wavelength while the nanohole asymmetry produces polarization-dependent coupling of the SPP-BW modes. Resulting photodetectors have 0.28 A/W responsivity peaked at 1100 nm at a reverse bias of -5 V. Designs for further increasing the optical coupling efficiency into the nanopillar are explored. This technology has potential applications for plasmonically enhanced focal plane arrays and plasmonic photovoltaics.

All-fiber optic acoustic sensor based on multimode-single mode-multimode structure

A simple and low cost optical fiber acoustic sensor based on multimode-single mode-multimode (MSM) fiber structure is presented. The optical coupling efficiency between hetero-core fibers spliced structure is modulated by acoustic pressure through a thin metal foil. Acoustic wave is detected by measuring the intensity change of transmission light. Experiments are carried on to testify the performance of MSM fiber acoustic sensor and the experimental results show that the acoustic wave can be sensitively detected within 11kHz frequency range.

Characterization of Coupling Efficiency and Absorption Coefficient for Fiber-Coupled SNSPD With an Optical Cavity

We report the characterization of optical coupling efficiency and the absorption coefficient of fiber-coupled superconducting nanowire single photon detector with an optical cavity, which limit the system detection efficiency. The small lenses were applied to compact fiber-coupled package and the efficient optical coupling higher than 95% were confirmed experimentally. The absorption coefficient was also verified and reached to ~ 60% at 1550 nm wavelength and optimum polarized condition. The system detection efficiencies at 1550, 1310 and 810 nm were 28, 40 and 3%, respectively, which are related to the absorptance dependencies on wavelengths.

Grating-Based Optical Fiber Interfaces for Silicon-on-Insulator Photonic Integrated Circuits

In this paper, we review our work on efficient interfaces between a silicon-on-insulator photonic IC and a single-mode optical fiber based on grating structures. Several device configurations are presented that provide high efficiency, polarization insensitive, and broadband optical coupling on a small footprint. The high alignment tolerance and the fact that the optical fiber interface is out-of-plane provide opportunities for easy packaging and wafer-scale testing of the photonic IC. Finally, an optical probe based on a grating structure defined on the fiber facet is described.

Quality-factor enhancement of supermodes in coupled microdisks

We investigate the optical modes in a coupled pair of semiconductor microdisks in symmetric and asymmetric configurations both experimentally and theoretically. While the quality factors of coupled first- and second-order whispering gallery modes (WGMs) show a conventional crossing, the quality factors of the same-order WGMs reveal an interesting splitting behavior, leading to the formation of high- and low-quality supermodes. Our results are reproduced by numerical simulations, and an explanation based on optical interference is suggested. Quality-factor splitting is a subtle phenomenon that might help to design microarchitectures for efficient optical coupling in cavity quantum electrodynamic experiments.