Vertical Coupling Structure Research Articles

Computational Study of the Coupling Performances for a Long-Distance Vertical Grating Coupler

We present a high-efficiency silicon grating coupler design based on a left–right mirror-symmetric grating and a metal mirror. The coupler achieves nearly perfect 90-degree vertical coupling. When two SOI chips are placed face to face with a vertical working distance of 50 μm, the chip-to-chip interlayer coupling efficiency reaches as high as 96%. When the vertical working distance ranges from 45 μm to 55 μm, the coupling loss remains below 1 dB. We also verified the effectiveness of our designed vertical coupler through 3D FDTD full-model simulation. The results demonstrate that our proposed vertical coupling structure represents a high-efficiency solution for 3D optical interconnects. The integration of multiple photonic chips in a 3D package with vertical optical and electrical interconnects is also feasible in the foreseeable future.

Bridging the gap between resonance and adiabaticity: a compact and highly tolerant vertical coupling structure

We present a compact, highly tolerant vertical coupling structure, which can be a generic design that bridges the gap between conventional resonant couplers and adiabatic couplers for heterogeneously integrated devices. We show insights on relaxing the coupler alignment tolerance and provide a detailed design methodology. By the use of a multisegmented inverse taper structure, our design allows a certain proportion of the odd supermode to be excited during the coupling process, which simultaneously facilitates high tolerance and compactness. With a total length of 87 μm, our coupler is almost threefold shorter than the state-of-the-art alignment-tolerant adiabatic couplers and outperforms them by demonstrating a more than 94% coupling efficiency (for < 0.3 dB coupling loss) with ± 1 μm misalignment tolerance, which, to our best knowledge, is a new record for III-V-on-silicon vertical couplers. Furthermore, our design has high tolerance to fabrication-induced structural deformation and ultrabroad bandwidth. These features make it particularly suitable for building densely integrated III-V-on-silicon photonic circuits with commercially available microtransfer printing assembly tools. The proposed design can be widely adopted in various integration platforms.

Simulation research of high-efficiency unidirectional vertical coupling grating couplers for optical through-silicon vias in 3D optoelectronic integrated circuits

A unidirectional vertical coupling structure is designed based on optical through-silicon vias (TSVs) and gratings to couple and steer the optical interconnects in 3D optoelectronic integrated circuits. The optical TSVs provide high-speed vertical optical data transmission over short distances. The grating coupler structure achieves efficient coupling between an optical TSV and a planar Si waveguide. Through the action of a mirror that covered the end of the optical TSV cladding and a distributed Bragg reflector(DBR) positioned on the far side away from the waveguide, coupling efficiency of 80% at 1550 nm is obtained in simulations. Our proposed vertical coupling structure represents a high-efficiency solution for 3D optical interconnects and can play an important role in 3D optoelectronic integrated circuits.

Gain spectral narrowing of semiconductor laser based on dual-core vertical coupler structure

Semiconductor FP ridge waveguide lasers based on dual-core vertical coupler structure with different ridge height were fabricated. Their modal gain of these devices around the threshold current were extracted and investigated using the Hakki–Paoli (H–P) method. It is observed that the gain spectrum profile and its 3 dB bandwidth vary with the ridge height. The narrower gain bandwidth of 12 nm was achieved when the ridge height was 4.59 μm, which is smaller than a quarter of that for the laser with the ridge height of 1.6 μm. This phenomenon is attributed to the narrowed gain spectrum induced by wavelength filtering effect of the dual-core vertical coupler (DCVC) structure induced by their co-directional coupling, which further shrinks its amplified spontaneous emission (ASE) spectrum. In addition, further simulation results show that the coupling length also affects the bandwidth of the DCVC structure. Within a single coupling length, the longer the coupling length, the narrower the bandwidth, and the larger the coupling efficiency. Such narrow-spectrum gain characteristic of DCVC structure will enable one to fabricate single longitudinal mode lasers with no need of fabricating gratings.

Vertical Optical Coupling Structure Based on Polymer for Small Size and High-Speed Photodetectors

This letter presents a new collective and passive thin-film 3D vertical optical coupling structure, which is fabricated based on SU-8 polymer. This technology compensates for the alignment errors of the present passive optical coupling solutions. The structure is collectively manufactured on a matrix of small-sized photodiodes on wafer level to vertically couple with a single-mode optical fiber. The proposed structure shows a coupling efficiency between the 10- $\mu \text{m}$ active area diameter photodetector and single-mode fiber of 94% and a 1-dB alignment tolerance of $\pm 9~\mu \text{m}$ at 1550 nm. Its wafer-level mass-production capability and manufacturing process simplicity make this novel coupling approach a potential solution for short- and long-range optical communication applications.

Impact of Madden Julian oscillation (MJO) and other meteorological phenomena on the heavy rainfall event from 19th − 28th December, 2014 over Sri Lanka

This study revealed the influence of Madden Julian oscillation (MJO) and cold surge (CS) on the extreme rainfall events that occurred in Sri Lanka from 19th to 28th December 2014. During this period, the Northeast Monsoon winds over the Bay of Bengal were strengthened by a CS, which intensified convective activity over the Bay of Bengal. Simultaneously, convective phase 3 of the MJO, which was located over the eastern Indian Ocean is associated with a positive rainfall anomaly over Sri Lanka. Westerly wind anomalies associated with MJO phase 3 shifted southward due to the strengthening of northeasterly winds by the CS, forming an incipient vortex to the southeast of Sri Lanka. The low level moisture transport was enhanced by this vortex circulation together with strong cross-equatorial moisture flux transportation. The convectively active phase of MJO provided favourable conditions such as low level convergence, cyclonic relative vorticity, and deep convection for the intensification of vortex into a tropical depression over the southwest Bay of Bengal. Strong upward motion and combination of strong low level convergence with upper-level divergence allowed evacuation of the ascending air mass, aiding the intensification of deep convection. This persistent vertical coupling structure allowed deep convection of moist warm air, which led to heavy rainfall during the period. Combination of a number of factors, such as local terrain effects, CS at low levels, MJO wet phase and a vortex to southeast of Sri Lanka led to an intensification of the tropical depression that caused an extreme rainfall event over the Eastern and Northeastern parts of Sri Lanka.

Highly efficient and perfectly vertical chip-to-fiber dual-layer grating coupler.

A novel high-efficiency silicon-chip-to-fiber grating coupler is investigated here. By introducing a dual layer grating structure with an inter-layer lateral shift to mimic 45° tilted mirror behavior, perfectly vertical coupling is successfully demonstrated. Our numerical results show that a peak silicon-chip-to-fiber coupling efficiency about 70% is possible near 1550 nm. Meanwhile, for the entire telecom C-band, i.e. wavelengths from 1530 nm to 1565 nm, the coupling efficiency is > 50% and the back reflection is less than < 1%. Our proposed high-performance silicon perfectly vertical coupling structure is suitable for interfacing with multi-core fiber platform, which may play an important role in the future CMOS photonic integration technology.

Novel Miniaturized Dual-Band Bandpass Filter with High Suppression Using Low-Temperature Co-Fired Ceramic Technology

A novel low-temperature co-fired ceramic dual-band bandpass filter with a compact size and high selectivity is reported using vertically coupled lines and semi-lumped resonators. Due to the source–load coupling and the characteristics of the resonators, five transmission zeros are introduced to improve the selectivity of the filter. A dual-band filter located at 2.45 and 5.2 GHz has been designed and fabricated in a low-temperature co-fired ceramic substrate to verify the proposed design concept. With the assistance of the vertical coupling structure and low-temperature co-fired ceramic technology, the filter occupies an area of 7.3 × 6.2 mm2.

Phonon engineering in nanostructures: Controlling interfacial thermal resistance in multilayer-graphene/dielectric heterojunctions

Using calculations from first principles and the Landauer approach for phonon transport, we study the Kapitza resistance in selected multilayer graphene/dielectric heterojunctions (hexagonal BN and wurtzite SiC) and demonstrate (i) the resistance variability (∼50−700×10−10 m2K/W) induced by vertical coupling, dimensionality, and atomistic structure of the system and (ii) the ability of understanding the intensity of the thermal transmittance in terms of the phonon distribution at the interface. Our results pave the way to the fundamental understanding of active phonon engineering by microscopic geometry design.

Compact wideband LTCC bandstop filter using vertical coupled‐line units

AbstractA novel compact bandstop filter (BSF) using vertical coupled striplines is presented. Stopband rejection depth and bandwidth can be easily controlled by the coupling factor of the coupled‐line section. A lossless transmission line model analysis is used for filter analysis. To validate the proposed topology, a multilayer BSF centered at 5.8 GHz with bandwidth of 75% is designed and built. Good agreement between measured and simulated results is obtained. With the assistance of vertical coupling structure and LTCC technology, the filter occupies an area of only 4.7 mm × 3.8 mm. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1173–1176, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26787

High Efficient Subwavelength Binary Blazed Grating Beam Splitter via Vertical Coupling

We propose a novel broadband beam splitter (BS) with a single-layer and compact grating vertical coupling structure, which is based on the form birefringence of subwavelength binary blazed grating and effective-medium theory. Rigorous coupled-wave analysis is used to optimize the design of this beam splitter. The simulation and analysis show that the BS for transverse electric (TE) light are designed to split the incident light beam into two beams of equal power (nearly 50% split), which travel in opposite directions in the waveguide. The coupling length is about 9 . The coupling efficiency for the right and the left branches of waveguide are 47% and 52%, respectively. The power difference of two output ports is less than 15% over a 75-nm wavelength bandwidth range.

Cooperative microexcitations in 2+1D chain-bundle dusty plasma liquids

Through direct visualization at the discrete level, the microexcitations in cold 2+1D dusty plasma liquids formed by negatively charged dusts suspended in low pressure gaseous discharges were experimentally investigated, in which the downward ion flow wake field induces strong vertical coupling and chain bundle structure. It is found that the horizontal structure and motion are similar to those of the two-dimensional liquid. Different types of basic cooperative chain excitations: straight vertical chains with small amplitude jittering, chain tilting-restraightening, bundle twisting-restraightening, and chain breaking-reconnection, are observed. The region with good (poor) horizontal structural order prefers the straight (tilted or broken) chains with little (large) titling and tilting rate.

Broadband double‐balanced diode mixer using a Marchand balun with vertical coupling structure

AbstractIn this article, a broadband double‐balanced mixer is presented using a wideband Marchand balun implementation by vertical coupler. Frequency is selected as 1.0–3.7 GHz for radio frequency (RF), 1.14–3.84 GHz for LO, and 140 MHz for IF signals. When LO signal with 7 dBm at 2.64 GHz is injected, a conversion loss of 7.5 dB, and RF to LO isolation of −45 dB are obtained. Also, an average conversion loss of 9 dB, and RF to LO isolation of −25 dB are obtained for frequency band of 1.0–3.7 GHz. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1811–1814, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24488

A broadband microstrip Marchand balun with vertical coupling structure

AbstractIn this paper, a broadband microstrip Marchand balun is presented. It is implemented by new vertical coupled structure, which is suggested to improve the coupling effect in the conventional coupler. Using this vertical coupling structure, the Marchand balun shows broad bandwidth of larger than 115% at the center frequency of 2.3 GHz. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 752–755, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22281

Small sidelobe narrow-passband wavelength filtering in distributed coupling vertical couplers

A narrow passband with a large sidelobe suppression ratio wavelength filter in a vertical coupler structure using a distributed and a slow coupling scheme is proposed and theoretically investigated. 1.4 nm 3 dB passband and 21 dB sidelobe suppression are obtained at the operating wavelength of 1550.7 nm. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 17: 178–181, 1998.

Design and modeling of waveguide-coupled single-mode microring resonators

We discuss a first-order design tool for waveguide-coupled microring resonators based on an approximate solution of the wave propagation in a microring waveguide with micron-size radius of curvature and a large lateral index contrast. The model makes use of the conformal transformation method and a linear approximation of the refractive index profile, and takes into account the effect of waveguide thickness, dispersion, and diffraction. Based on this model, we develop general design rules for the major physical characteristics of a waveguide-coupled microring resonator, including the resonance wavelength, the free spectral range, the coupling ratio, the bending radiation loss and the substrate leakage loss. In addition, the physical model provides leads to alternative coupling designs. We present two examples, one using a phase-matching parallel waveguide with a smaller width than the ring waveguide, and the other using a vertical coupling structure. Both these designs significantly increase the coupling length and reduce or eliminate the dependence on a narrow air gap in a waveguide coupled microring resonator.

Improved vertical directional coupler for optimum edge coupling to an embedded photodetector

An improved vertical coupling structure, consisting of a graded-index planar buried waveguide in glass and a dielectric overlayer, is designed and realized to provide an optimum edge coupling to a modeled GaAs photodetector. Calculations of the attenuation coefficient and coupling efficiency show an optimum absorption behavior. Normal-mode measurements and beam-propagation calculations of the coupling length and power transfer ratio are compared.

Optoelectronic integrated circuit (OEIC) waveguidecoupler for spot size expansion and improved fibrecoupling efficiency

An MOVPE vertical coupler structure is used to provide efficient coupling between InP/InGaAsP optoelectronic integrated circuit (OEIC) waveguides and cleaved monomode fibres. A 2 dB improvement in the coupling efficiency of TE polarised light of wavelength 1.55 µm is demonstrated. The structure does not require any additional growth steps, and is compatible with vertically integrated detector structures.