Aramais Zakharian

Carrier Transport in InGaN MQWs of Aquamarine- and Green-Laser Diodes

We studied experimentally and theoretically the substrate-orientation impact on carrier transport and capture in InGaN multiple quantum well (MQW) laser diodes (LDs) with emission in the aquamarine-green spectral range. A new simulation approach was developed to analyze this behavior of LEDs and LDs emitting at these wavelengths. We show that due to deep carrier confinement, the thermal escape from a QW in such devices is negligible. The carrier distribution among QWs is therefore determined by the carrier transport and capture rates. We also show that the ballistic transport mechanism is dominant in this type of MQW active region. In c-plane structures, this mechanism is tunneling-assisted, and therefore, the transport is much slower than in nonpolar and semipolar structures. Because of this, a strong carrier injection nonuniformity observed in c-plane LDs, causes the threshold current increase when number of QWs is >;2. This effect is not observed in semipolar LDs because the carrier transport rate is faster than the capture rate.

Impact of Carrier Transport on Aquamarine-Green Laser Performance

We studied the carrier transport phenomena of the multiple-quantum-well (MQW) active region and their impact on the performance of aquamarine and green laser diodes (LDs) grown on polar and semipolar planes. The ballistic carrier transport mechanism was found to be dominant in the MQW region. For the c-plane, because of the high hole capture probability and slow escape rate, mainly the quantum wells (QWs) positioned close to the p-side are electrically pumped. The optical loss induced by the underpumped QWs further away from the p-side leads to significantly higher laser threshold current density and a longer lasing wavelength with increased number of QWs. These effects are not significant for semipolar LD structures.

Giant optical resonances due to gain-assisted Bloch surface plasmons

We theoretically study Bloch surface plasmon (BSP) resonances in a thin subwavelength-structured metallic film adjacent to a submicron dielectric layer with gain. We show that for a planar gold-silver bimetallic grating resonant excitation of a BSP with the optimum value of gain may result in giant amplification of both transmitted and reflected waves. We explain the effect and illustrate how the electromagnetic near-field structure determines the type of interference (constructive or destructive) between the eigenmodes of the system, which results in either strong enhancement or suppression of the scattered waves.

High performance ion-exchanged integrated waveguides in thin glass for board-level multimode optical interconnects

We fabricated ion-exchanged graded-index optical waveguides in alkali-aluminosilicate glass showing excellent potential for optical backplane and electrical-optical circuit board applications. Motivation and process details are given and experimental results are discussed.

Semi-analytical method for light interaction with 1D-periodic nanoplasmonic structures

We present a detailed description of a computationally efficient, semi-analytical method (SAM) to calculate the electomagnetic field distribution in a 1D-periodic, subwavelength-structured metal film placed between dielectric substrates. The method is roughly three orders of magnitude faster than the finite-element method (FEM). SAM is used to study the resonant transmission of light through nanoplasmonic structures, and to analyze the role of fundamental and higher-order Bloch surface plasmons in transmission enhancement. The method is also suitable for solving the eigenvalue problem and finding modes of the structure. Results obtained with SAM, FEM, and the finite-difference time-domain method show very good agreement for various parameters of the structure.

Quasi-Single-Mode Fiber Transmission for Optical Communications

The transmission of a single fundamental mode in a fiber with cutoff wavelength above the transmission band is studied as a means of allowing a larger fiber effective area and reducing fiber nonlinearity. The reduction of nonlinear impairments is achieved at the expense of a potential new linear impairment in the form of multipath interference (MPI). We use a power-coupled-mode formalism to analyze the growth of MPI, and the effects of fiber and cable attributes on its magnitude and the required complexity of digital signal processing to combat the MPI. Hybrid fiber spans comprised partially of a quasi-single-mode fiber are also analyzed using a modification of the Gaussian noise model of coherent systems to predict optimal configurations, and results from transmission experiments are presented that demonstrate very high spectral efficiencies and performance surpassing that of a purely single-mode fiber system.

Design of universal fiber with demonstration of full system reaches over 100G SR4, 40G sWDM, and 100G CWDM4 transceivers

Universal fiber has an LP01 mode field diameter approximately matched to that of standard single mode fiber, while being a multimode fiber. We analyzed the dependence of the mode field diameter on the core diameter for different core delta values. Guided by the analysis, a universal fiber having a delta of 1.2% was fabricated, showing significantly reduced coupling loss of ~2.3 dB with conventional multimode fiber. We demonstrated that the fiber can transmit with full system reach in both single mode and VCSEL-based multimode transmissions, including 100G SR4, 40G sWDM, and 100G CWDM4 for the first time.

Quasi-single-mode transmission for long-haul and submarine optical communications

Single-mode transmission over few-mode fiber is investigated to enable larger effective area and higher nonlinear tolerance. Multipath interference generated during propagation is modeled. Transmission results illustrate benefits of hybrid spans and multi-subcarrier modulation formats.

Predicting insertion loss in multi-fiber multimode connectors

We develop a comprehensive opto-mechanical model to accurately predict insertion loss (IL) in multi-fiber multimode physical contact connectors and study the effect of various misalignment types and launch conditions. Monte Carlo simulations show good agreement with measured IL.

Grating-based Fiber-to-chip Coupling Efficiency for Small Mode Field Diameter Fibers

We compute the fiber-to-chip coupling efficiency of grating couplers for fiber mode diameters <10μm. Modeling shows that high efficiency (-1.5dB loss) can be achieved with smaller footprint for fibers with half the mode diameter of single-mode-fiber.