Hesam Moradinejad

Compact, 15 Gb/s electro-optic modulator through carrier accumulation in a hybrid Si/SiO(2)/Si microdisk.

High-speed electro-optic modulators are among the key elements in any optical interconnect system. In this work we design and demonstrate an electro-optic modulator based on carrier accumulation on a multilayer integrated photonic platform comprising a stack of high quality Si, SiO(2), and Si layers. The device consists of a 3-μm radius microdisk with an embedded capacitor. Characterization results reveal an operation bandwidth of exceeding 10 GHz. The device is capable of transmitting 15 Gb/s with the on/off keying format in a single polarization. The proposed structure can be self-trimmed by up to 1 nm in wavelength by applying a dc bias voltage without any power consumption. This feature eliminates the need for power-hungry thermal-based compensation methods to address the resonance wavelength mismatch due to fabrication imperfections.

Double-Layer Crystalline Silicon on Insulator Material Platform for Integrated Photonic Applications

We report a high optical-quality double-layer silicon (Si) material platform with a thin interface oxide using a low-temperature wafer bonding technique. To assess the quality of the platform, resonators with different radii are fabricated, and their quality factors (Q) are measured. Qs of 25 k and 350 k are demonstrated in 2-μm- and 20-μm-radius microring resonators, respectively. The former is the most compact high-Q resonator demonstrated in any type of double-layer Si platform, and the latter is the highest Q demonstrated in a double-layer Si platform to date. This material platform enables a new set of integrated optical devices for a wide range of applications, including high-speed modulators, tunable filters, and low-power switches.

Field-programmable optical devices based on resonance elimination

Optical switches are among the essential building blocks in optical networks due to their unique role in routing data. In this Letter, for the first time to our knowledge, we have exploited a high-quality factor (Q) optical microresonator combined with the well-known irreversible dielectric breakdown phenomenon to introduce a simple field-programmable on/off optical switch. This simple unit can be thought of as a building block for more complex optical systems with different functionalities. By using this simple unit we have demonstrated an optical field-programmable 2×2 switch. After the device is programmed by the user, no external electrical signal is needed to maintain the state of the device. The same approach can readily be adopted to design a field-programmable arbitrary N×N optical switch.

Strain relaxation via formation of cracks in compositionally modulated two-dimensional semiconductor alloys

Composition modulation of two-dimensional transition-metal dichalcogenides (TMDs) has introduced an enticing prospect for the synthesis of Van der Waals alloys and lateral heterostructures with tunable optoelectronic properties. Phenomenologically, the optoelectronic properties of alloys are entangled to a strain that is intrinsic to synthesis processes. Here, we report an unprecedented biaxial strain that stems from the composition modulation of monolayer TMD alloys (e.g., MoS2xSe2(1 - x)) and inflicts fracture on the crystals. We find that the starting crystal (MoSe2) fails to adjust its lattice constant as the atoms of the host crystal (selenium) are replaced by foreign atoms (sulfur) during the alloying process. Thus, the resulting alloy forms a stretched lattice and experiences a large biaxial tensile strain. Our experiments show that the biaxial strain relaxes via formation of cracks in interior crystal domains or through less constraint bounds at the edge of the monolayer alloys. Griffith’s criterion suggests that defects combined with a sulfur-rich environment have the potential to significantly reduce the critical strain at which cracking occurs. Our calculations demonstrate a substantial reduction in fracture-inducing critical strain from 11% (in standard TMD crystals) to a range below 4% in as-synthesized alloys.2D alloys: intrinsic strain in MoS 2x Se 2(1-x) ternary crystalsComposition modulation synthesis of ternary alloys of atomically thin transition metal dichalcogenides gives rise to intrinsic biaxial strain. A team led by Ali Adibi at Georgia Institute of Technology reported the onset of a substantial biaxial strain in monolayer MoS2xSe2(1-x) that is intrinsically linked to the two-step composition modulation synthesis used to grow the ternary alloy. As the S atoms replace the Se atoms of the starting MoSe2 host crystal, the resulting alloy forms a stretched lattice and develops a large biaxial tensile strain. Morphological and spectroscopic characterisations suggest that such strain results in the onset of fracture in the crystal, and further relaxes via formation of cracks within the crystal domains. Theoretical modelling indicates that pre-existing cracks give a substantial contribution in weakening the strength of the synthesized van der Waals alloy.

High-Q integrated photonic microresonators on 3C-SiC-on-insulator (SiCOI) platform

We report a high-quality 3C-silicon carbide (SiC)-on-insulator (SiCOI) integrated photonic material platform formed by wafer bonding of crystalline 3C-SiC to a silicon oxide (SiO2)-on-silicon (Si) substrate. This material platform enables to develop integrated photonic devices in SiC without the need for undercutting the Si substrate, in contrast to the structures formed on conventional 3C-SiC-on-Si platforms. In addition, we show a unique process in the SiCOI platform for minimizing the effect of lattice mismatch during the growth of SiC on Si through polishing after bonding. This results in a high-quality SiCOI platform that enables record high Qs of 142,000 in 40 µm radius SiC microring resonators. The resulting SiCOI platform has a great potential for a wide range of applications in integrated optics, including nonlinear optical devices, quantum optical devices, and high-power optical devices.

Polarization cross-coupling between microring and bus waveguide in double-layer SOI

We investigate polarization cross-coupling between modes of microring resonators and waveguides due to structural asymmetries. We experimentally demonstrate the coupling between a double-layer SOI waveguide fundamental TM mode and microring higher-order radial TE modes.

Lab-on-chip silicon nitride microring sensor at visiblewavelength using glycoprotein receptors

A full biosensor system based on referenced and spectrally multiplexed arrays of silicon nitride microrings with glycoprotein receptors is demonstrated. Underlying system design guidelines and fundamental noise limits of the device are discussed.

High-Q resonators on Bi-layer Si platform using wafer bonding

We report the development of a high quality bi-layer silicon material platform using wafer bonding. We have experimentally demonstrated high quality-factor resonators (>200,000) in this material platform for both TE and TM polarizations.

Multi-Layer Material Platforms for Reconfigurable Nanophotonic Structures

We present a hybrid material platform based on vertical integration of multiple silicon and/or silicon-nitride layers. Using these materials, we demonstrate compact, low-loss, and low-power reconfigurable resonance-based photonic devices with high power handling and fast reconfiguration.