Asymmetric Waveguide Research Articles

S-Bend Silicon-On-Insulator (SOI) Large Cross-Section Rib Waveguide for Directional Coupler

S-bend contributes the high losses in the silicon-on-insulator (SOI) large cross-section rib waveguide (LCRW). The objective of this work is to investigate S-bend SOI LCRW with two different single-mode dimensions named symmetrical and asymmetrical. The S-bend SOI LCRW has been simulating using beam propagation method in OptiBPM software. The asymmetrical waveguide with two different dimension arc given the best performance if compared to others dimension with 3 µm of waveguide spacing. It achieved 92.24% and 91.10% of normalized output power (NOP) for 1550 nm and 1480 nm wavelength respectively. Moreover, the minimum of S-bend spacing between the two cores is 0.9 µm for both 1550 nm and 1480 nm. Therefore, asymmetrical waveguide with two different dimension arc and 0.9 µm of S-bend spacing are chosen. This analysis is important to determine the right parameter in order to design the SOI passive devices. However, future work should be done to see the performance by designing the coupler and implement in the real system.

Интегрально-оптический преобразователь поляризации излучения на основе асимметричного волновода в стекле

Интегрально-оптический преобразователь поляризации излучения на основе асимметричного волновода в стекле

1.06 μm high-power InGaAs/GaAsP quantum well lasers

The high power and low internal loss 1.06 μm InGaAs/GaAsP quantum well lasers with asymmetric waveguide structure were designed and fabricated. For a 4000 μm cavity length and 100 μm stripe width device, the maximum output power and conversion efficiency of the device are 7.13 W and 56.4%, respectively. The cavity length dependence of the threshold current density and conversion efficiency have been investigated theoretically and experimentally; the laser diode with 4000 μm cavity length shows better characteristics than that with 3000 and 4500 μm cavity length: the threshold current density is 132.5 A/cm2, the slope efficiency of 1.00 W/A and the junction temperature of 15.62 K were achieved.

Dynamically Manipulating the Plasmon-Induced Transparency—Like in Asymmetric Graphene-Based Waveguide Structures

We perform a theoretical and numerical investigation of the process of plasmon-induced transparency (PIT)-like in an asymmetric graphene-based waveguide system with two identical graphene-ribbon resonators. PIT-like phenomenon can be produced by the resonance hybridization between two graphene ribbons with frequency detuning. The hybrid resonance and resonant frequency detuning come from the variation in the phase of propagation waves at resonances and the coupling interaction between ribbons. These variations are induced by shifting the lateral distance between the two ribbons. Moreover, the transparency window can be actively manipulated by adjusting the Fermi energy of graphene without reoptimizing and refabricating the structure. The proposed graphene-based PIT-like structure may result in the development of new compact elements such as tunable sensors, modulators, and switchers.

Compact Si-based asymmetric MZI waveguide on SOI as a thermo-optical switch

A compact low power consuming asymmetric MZI based optical modulator with fast response time has been proposed on SOI platform. The geometrical and performance characteristics were analyzed in depth and optimized using coupled mode analysis and FDTD simulation tools, respectively. It was tested with and without implementation of thermo-optic (TO) effect. The device showed good frequency modulating characteristics when tested without the implementation of the TO effect. The fabricated device showed quality factor, Q ≈ 10,000, and this value is comparable to the Q of the device simulated with 25% transmission loss, showing FSR of 0.195 nm, FWHM ≈ 0.16 nm, and ER of 13 dB. With TO effect, it showed temperature sensitivity of 0.01 nm/°C and FSR of 0.19 nm. With the heater length of 4.18 mm, the device required 0.26 mW per π shift power with a switching voltage of 0.309 V, response time of 10 μ, and figure-of-merit of 2.6 mW μs. All of these characteristics make this device highly attractive for use in integrated Si photonics network as optical switch and wavelength modulator.

Silicon lateral-apodized add-drop filter for on-chip optical interconnection.

A lateral-apodized add-drop filter is demonstrated in a multimode asymmetric waveguide Bragg grating. This design utilizes two individual superposed gratings with the same sidewall corrugation depth. The strong side lobes of the grating filter are efficiently suppressed by mapping the target apodization profile into lateral shifts between the periods of the two gratings. Compared with other apodized technology, this device is easier to be realized. Experimental results show that the side-lobes suppression ratio can reach 18.5dB, and a bandwidth of 9.5nm is achieved by a large corrugation width of 150nm. The insertion loss at the drop port is only 0.8dB, and the extinction ratio is up to 24dB at the through port.

BOUND STATES IN WEAKLY DEFORMED WAVEGUIDES: NUMERICAL VERSUS ANALYTICAL RESULTS

We study bound states in weakly deformed and heterogeneous waveguides, and compare analytical predictions using a recently developed perturbative method with precise numerical results for three different configurations: a homogeneous asymmetric waveguide, a heterogenous asymmetric waveguide and a homogeneous broken strip. We have found excellent agreement between the analytical and numerical results in all the examples; this provides a numerical verification of the analytical approach.

830-nm InGaAs Quantum Well Lasers With Very Low Beam Divergence

We report on our design and fabrication of 830-nm high-power semiconductor lasers with very low beam divergence. Here, we propose a novel approach in which by combining asymmetric waveguide and a feature called “pins” together, we were able to design an optimize epi structure, which not only produces a beam divergence of less than 16°, which is measured at the full width at the half maximum, but also has very good growth tolerance as well. Device test shows the beam divergence is as small as 13°, yet they still retain high slope efficiency of around 1.15 W/A and low threshold current of 400 mA for the devices with cavity length being 2 mm long, and ridge width being 40 μm wide.

Improvement of slope efficiency of GaN-Based blue laser diodes by using asymmetric MQW and InxGa1-xN lower waveguide

Series of GaN-based blue laser diodes (LDs) with different InxGa1-xN quantum barrier (QB) and lower waveguide (LWG) layers are investigated by using the two-dimension simulator LASTIP. It is found that a decrease slope efficiency is resulted when the indium content of InxGa1-xN quantum barrier (QB) layers is higher than about 1%, which is caused by the significantly increase of electron leakage current due to the piezoelectric polarization effect in high indium content InxGa1-xN last QB (LQB) layer. Therefore, an asymmetric MQW with a thin thickness of LQB is designed to lower the piezoelectric polarization effect and to reduce the electron leakage current. Meanwhile, a new LD structure with high InxGa1-xN LWG is also proposed to further reduce the optical loss. The two ways are useful to improve the slope efficiency.

(Invited) Band Gap Engineering and Heterostructures of Low Dimensional Semiconductors

Band gaps are one of the most important parameters of semiconductor materials for their optoelectronic applications since they determine the spectral features of absorptions and emission processes [1,2]. Due to the limited band gaps of natural semiconductors, alloying and heterostructured semiconductors with different band gaps have long been the standard methods of achieving semiconductor structures with new band gaps and functions [3,4]. In this talk, I will report our recent progress on the band gap engineering of 1D semiconductor nanowires and 2D atomically thin layered materials through controlled vapor growth. Using some examples, I will show how to realize composition graded and interface sharped low dimensional semiconductor heterostructures through composition controlled band gap modulation. The achieved band gap engineered nanostructures can give continuously tuned or white light emission, and can be used to realize multi-color nanolasers, wavelength splitter, asymmetric waveguiding and high-performance photodetectors etc [5-7].

Sharp optical magnetic resonances in dielectric waveguide grating structures

We report that a sharp resonance is observed in an asymmetric dielectric waveguide grating structure. This resonance can be characterized by a circulating displacement current in the sub-wavelength unit cell that is associated with a magnetic-dipole mode. It is shown that such a sharp resonance comes from the interaction between two non-degenerate waveguide modes, and can be explained by use of a radiant two-resonator model based on coupled-mode theory. Our analytical model agrees well with the numerical results, and can be used to exploit additional intriguing physical characteristics in the system.

Magnetically-tunable cutoff in asymmetric thin metal film plasmonic waveguide

We theoretically investigated the magnetically tunable cutoff of long-range surface plasmon polariton along thin metal film surrounded by a magneto-optic material on one side and by a nonmagnetic dielectric on the other. The analytically derived cutoff condition predicts that a magnetic field bias can induce a novel degenerate cutoff-state near which the beyond-cutoff radiation on one side can be switched to that on the other by a minor variation of the magnetic field from the bias. The magnetization bias needed for the degeneracy is proportional to the metal film thickness and inversely proportional to the wavelength.

Pseudo-One-Dimensional Magnonic Crystals for High-Frequency Nanoscale Devices

Periodically patterned composite ferromagnetic nanostructures known as magnonic crystals (MCs) are promising for spintronic and other spin-based technologies, as they manipulate spin waves in analogy to photonic crystals' manipulation of light. The authors create an array of asymmetric sawtooth waveguides that presents two different one-dimensional MCs in perpendicular directions, yet not a two-dimensional MC. Its magnonic band structure and gap are tuned by rotating the applied magnetic field, and its edge modes may also be controlled, to yield, say, a GHz-frequency nanoscale filter.

High power, high efficiency continuous-wave 808 nm laser diode arrays

The continuous-wave 100W-class 808nm laser diode arrays with extremely high power conversion efficiency of 68% were reported at the heatsink temperature of 25°C. To the best of our knowledge, this was the highest power conversion efficiency at continuous-wave 106W 808nm laser diode array with 50% fill factor so far. An asymmetric broad waveguide epitaxial structure with very low internal optical loss of 0.5cm−1 was presented. In order to improve the efficiency, various fill factor devices were studied. The 50W laser diode array with 30% fill factoir and 1.0mm cavity length demonstrated power conversion efficiency of 71% at heatsink temperature of 15°C.

Wavefront Matching Method Based on Full-Vector Finite-Element Beam Propagation Method for Polarization Control Devices

We developed a wavefront matching (WFM) method based on the full-vector finite-element beam propagation method (BPM). The WFM method is one of the optimization algorithms based on BPM, and it can deterministically design optimum waveguide structures from desired characteristics. The developed WFM method can be applied to optical waveguides with high refractive-index contrast and polarization control devices, which require full-vector analysis. In this paper, the principle and design procedure of the full-vector WFM method are described. Its validity and effectiveness are demonstrated by designing polarization control devices, such as a polarization converter based on a vertical asymmetric taper waveguide and a polarization splitter-rotator based on taper and Y-branch waveguides.

Characteristics of Asymmetric Nonlinear Waveguide with Graphene Layer: Transverse Electric Mode

The characteristics of a three-layer waveguide is studied. The waveguide structure consists of a thin layer of graphene at the interface between air and a dielectric layer at a distance d from nonlinear media. The dispersion equation of the waveguide is derived from Maxwell's equations and numerically solved using Maple 17. The first two modes of transverse electric fields (TE0 and TE1) are considered. The results show that the surface wave characteristics change as the thickness of dielectric layer and the nonlinearity term change.

Controlling Morphology and Aggregation in Semiconducting Polymers: The Role of Solvents on Lasing Emission in Poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene-vinylene

Systematic experiments were performed to investigate solvent-dependent morphology and aggregation of the semiconducting polymer film poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene] (MEH-PPV), which was span-cast from nonaromatic strong polarity solvents tetrahydrofuran (THF), trichloromethane (TCM) and aromatic weak polarity solvents chlorobenzene (CB), toluene, and p-xylene. The results indicated that the conformation of the spin-cast MEH-PPV films with weak aggregation such as THF and TCM demonstrated excellent lasing emission performances because of inhibiting the fluorescence quenching induced by bi-molecule process. The Atomic Force Microscope (AFM) images confirmed the distinct morphologies of the spin-cast MEH-PPV films. The amplified spontaneous emission (ASE) was investigated in a simple asymmetric slab planar waveguide structure by methods of variable stripe length (VSL) and shifting excitation stripe (SES). The amplified spontaneous emission (ASE) experiments confirmed the distinct polymer chain conformation. The conformation, which preserved from the spin-cast process, indicated the distinct interactions between solvents and MEH-PPV polymer chains. The pure film spectra were performed to confirm the effect of distinct conformation on the material energy level. This work provides insights into the morphology and aggregation effect of the spin-cast polymer films on the performances of lasers.

Tunable Fano Resonance in Asymmetric MIM Waveguide Structure.

A plasmonic waveguide coupled system that uses a metal-insulator-metal (MIM) waveguide with two silver baffles and a coupled ring cavity is proposed in this study. The transmission properties of the plasmonic system were investigated using the finite element method. The simulation results show a Fano profile in the transmission spectrum, which was caused by the interaction of the broadband resonance of the Fabry-Perot (F-P) cavity and the narrow band resonance of the ring cavity. The Fabry-Perot (F-P) cavity in this case was formed by two silver baffles dividing the MIM waveguide. The maximum sensitivity of 718 nm/RIU and the maximum figure of merit of 4354 were achieved. Furthermore, the effects of the structural parameters of the F-P cavity and the ring cavity on the transmission properties of the plasmonic system were analyzed. The results can provide a guide for designing highly sensitive on-chip sensors based on surface plasmon polaritons.

Asymmetric Coplanar Ring Resonator (ACPW) for Microwave Characterization of Silver Composite Conductors

Ring resonators without central ground plane have been used for determining the effective electrical conductivities of composite conductors. Analytical approximations for the conductor, dielectric, and radiation losses of asymmetric coplanar waveguides are applied in our structures. Good agreement between the theoretical approximations, numerical simulation, and measured quality factors ( $Q_{{\mathrm {0}}}$ ) of ring resonators realized with several pure conductors is observed. These analytical formulas are used for extracting the electrical conductivity values from measured quality factors of ring resonators realized by Ag composite conductors (silver–amorphous carbon, silver–tin–indium, and silver–tin).

Negative-index dispersion and accidental mode degeneracy in an asymmetric spoof–insulator–spoof waveguide**Project supported by the National Basic Research Program of China (Grant No. 2013CBA01702) and the National Natural Science Foundation of China (Grant Nos. 61377016, 61575055, 10974039, 61307072, 61308017, and 61405056).

It has been recently demonstrated that negative-index dispersion and mode degeneracy can be achieved by manipulating a spoof–insulator–spoof (SIS) waveguide. In this paper, we propose a new SIS waveguide, which is composed of two spoof surface plasmon polaritons (SSPPs) waveguides drilled with periodic rhomboidal grooves. Both the symmetric and asymmetric cases are investigated. Our simulation results show that the asymmetric SIS waveguides are more significant. By tailoring the tilt of the rhomboidal grooves, the negative-index dispersion can be achieved and the microwave band gap (MBG) can be effectively modulated. At a critical tilt, there appears an accidental mode degeneracy at the edge of the first Brillouin zone. The excitation and propagation of the two coupled modes sustained by the asymmetric SIS waveguides are also demonstrated.