arXiv subjects

Hamed Dalir

Publications and source records attributed to Hamed Dalir.

45 records · Page 3Linked to original sources

arXiv2018

0.52 V-mm ITO-based Mach-Zehnder Modulator in Silicon Photonics

Electro-optic modulators transform electronic signals into the optical domain and are critical components in modern telecommunication networks, RF photonics, and emerging applications in quantum photonics and beam steering. All these applications require integrated and voltage-efficient modulator solutions with compact formfactors that are seamlessly integratable with Silicon photonics platforms and feature near-CMOS material processing synergies. However, existing integrated modulators are challenged to meet these requirements. Conversely, emerging electro-optic materials heterogeneously integrated with Si photonics open a new avenue for device engineering. Indium tin oxide (ITO) is one such compelling material for heterogeneous integration in Si exhibiting formidable electro-optic effect characterized by unity order index at telecommunication frequencies. Here we overcome these limitations and demonstrate a monolithically integrated ITO electro- optic modulator based on a Mach Zehnder interferometer (MZI) featuring a high-performance half-wave voltage and active device length product, VpL = 0.52 V-mm. We show, how that the unity-strong index change enables a 30 micrometer-short pi-phase shifter operating ITO in the index-dominated region away from the epsilon-bear-zero ENZ point. This device experimentally confirms electrical phase shifting in ITO enabling its use in multifaceted applications including dense on-chip communication networks, nonlinearity for activation functions in photonic neural networks, and phased array applications for LiDAR.

physics.app-ph↗

arXiv2018

Microring Resonators Coupling Tunability by Heterogeneous 2D Material Integration

Atomically thin 2D materials provide a wide range of basic building blocks with unique properties, making them ideal for heterogeneous integration with a mature chip platform. An understanding the role of excitons in transition metal dichalcogenides in Silicon photonic platform is a prerequisite for advances in optical communication technology, signal processing, and possibly computing. Here we demonstrate passive tunable coupling by integrating few layers of MoTe2 on a micro-ring resonator. We find a TMD-to-rings circumference coverage length ratio to place the ring into critical coupling to be about 10% as determined from the variation of spectral resonance visibility and loss as a function of TMD coverage. Using this TMD ring heterostructure, we further demonstrate a semi-empirical method to determine the index of an unknown TMD material (nMoTe2 of 4.36+.011i) near for telecommunication-relevant wavelength.

physics.optics↗

arXiv2018

Selective Near Perfect Light Absorbtion by Graphene Monolayer Using Aperiodic Multilayer Microstructures

We investigate 1D aperiodic multilayer microstructures in order to achieve near total absorption in preselected wavelengths in a graphene monolayer. Our structures are designed by a genetic optimization algorithm coupled to a transfer matrix code. Coupled mode theory (CMT) analysis, in accordance with transfer matrix method (TMM) results, indicates the existence of a critical coupling in a graphene monolayer for perfect absorptions. Our findings show that the near-total-absorption peaks are highly tunable and can be controlled simultaneously or independently in wide range of wavelengths in the near-infrared and visible. Our proposed approach is metal free and does not require surface texturing or patterning, and can be applied for other two dimensional (2D) materials.

physics.optics↗

arXiv2018

Attojoule-Efficient Graphene Optical Modulators

Electro-optic modulation is a technology-relevant function for signal keying, beam steering, or neuromorphic computing through providing the nonlinear activation function of a perceptron. With silicon-based modulators being bulky and inefficient, we here discuss graphene-based devices heterogeneously integrated. This study provides a critical and encompassing discussing of the physics and performance of graphene modulators rather than collecting relevant published work. We provide a holistic analysis of the underlying physics of modulators including the graphenes index tunability, the underlying optical mode, and discuss resulting performance vectors of this novel class of hybrid modulators. Our results show that the reducing the modal area, and reducing the effective broadening of the active material are key to improving device performance defined by the ratio of energy-bandwidth and footprint. We further show how the waveguides polarization must be in-plane with graphene such as given by plasmonic-slot structures. A high device performance can be obtained by introducing multi- or bi-layer graphene modulator designs. Lastly, we present recent results of a graphene-based hybrid-photon-plasmon modulator on a silicon platform, requiring near Boltzmann approximation (100mV) low drive voltages. Being physically compact this 100 aJ/bit modulator opens the path towards a new class of attojoule opto-electronics.

physics.app-ph↗

arXiv2017

Hybrid Photonic-Plasmonic Non-blocking Broadband 5x5 Router for Optical Networks

Photonic data routing in optical networks overcomes the limitations of electronic routers with respect to data rate, latency, and energy consumption while suffering from dynamic power consumption, non-simultaneous usage of multiple wavelength channels, and large footprints. Here we show the first hybrid photonic-plasmonic, non-blocking, broadband 5x5 router. The compact footprint (<250 μm2) enables high operation speed (480 GHz) requiring only 82 fJ/bit (1.9 dB) of averaged energy consumption (routing loss). The router supports multi-wavelength up to 206 nm in the telecom band. Having a data-capacity of >70 Tbps, thus demonstrating key features required by future high data-throughput optical networks.

physics.app-ph↗

arXiv2017

Low-loss Tunable 1-D ITO-slot Photonic Crystal Nanobeam Cavity

Tunable optical material properties enable novel applications in both versatile metamaterials and photonic components including optical sources and modulators. Transparent conductive oxides (TCOs) are able to highly tune their optical properties with applied bias via altering their free carrier concentration and hence plasma dispersion. The TCO material indium tin oxide (ITO) exhibits unity-strong index changes, and epsilon-near-zero behavior. However, with such tuning the corresponding high optical losses, originating from the fundamental Kramers-Kronig relations, result in low cavity finesse. However, achieving efficient tuning in ITO-cavities without using light matter interaction enhancement techniques such as polaritonic modes, which are inherently lossy, is a challenge. Here we discuss a novel one-dimensional photonic crystal nanobeam cavity to deliver a cavity system offering a wide range of resonance tuning range, while preserving physical compact footprints. We show that a vertical Silicon-slot waveguide incorporating an actively gated-ITO layer delivers ~3.4 nm of tuning. By deploying distributed feedback, we are able to keep the Q-factor moderately high with tuning. Combining this with the sub-diffraction limited mode volume (0.1 (λ/2n)3) from the photonic (non-plasmonic) slot waveguide, facilitates a high Purcell factor exceeding one thousand. This strong light-matter-interaction shows that reducing the mode volume of a cavity outweighs reducing the losses in diffraction limited modal cavities such as those from bulk Si3N4. These tunable cavities enable future modulators and optical sources such as tunable lasers.

physics.optics↗

arXiv2017

MODetector (MOD): A Dual-Functional Optical Modulator-Detector for On-Chip Communication

Physical challenges at the device and interconnect level limit both network and computing energy efficiency. While photonics is being considered to address interconnect bottlenecks, optical routing is still limited by electronic circuitry, requiring substantial overhead for optical-electrical-optical conversion. Here we show a novel design of an integrated broadband photonic-plasmonic hybrid device termed MODetector featuring dual light modulation and detection function to act as an optical transceiver in the photonic network-on-chip. With over 10 dB extinction ratio and 0.8 dB insertion loss at the modulation state, this MODetector provides 0.7 W/A responsivity in the detection state with 36 ps response time. This multi-functional device: (i) eliminates OEO conversion, (ii) reduces optical losses from photodetectors when not needed, and (iii) enables cognitive routing strategies for network-on-chips.

physics.app-ph↗

arXiv2017

Roadmap on Atto-Joule per Bit Modulators

Electrooptic modulation performs the conversion between the electrical and optical domain with applications in data communication for optical interconnects, but also for novel optical compute algorithms such as providing nonlinearity at the output stage of optical perceptrons in neuromorphic analogue optical computing. Since the clock frequency for photonics on chip has a power overhead sweet slot around 10s of GHz, ultrafast modulation may only be required in long distance communication, but not for short onchip links. Here we show a roadmap towards atto Joule per bit efficient modulators on chip as well as some experimental demonstrations of novel plasmon modulators with sub 1fJ per bit efficiencies. We then discuss the first experimental demonstration of a photon plasmon-hybrid Graphene-based electroabsorption modulator on silicon. The device shows a sub 1V steep switching enabled by near ideal electrostatics delivering a high 0.05dB per V um performance requiring only 110 aJ per bit. Improving on this design, we discuss a plasmonic slot based Graphene modulator design, where the polarization of the plasmonic mode matches with Graphenes inplane dimension. Here a push pull dual gating scheme enables 2dB per V um efficient modulation allowing the device to be just 770 nm short for 3dB small signal modulation. This in turn allows for a device-enabled two orders of magnitude improvement of electrical optical co integrated network on chips over electronic only architectures. The latter opens technological opportunities in in cognitive computing, dynamic data-driven applications system, and optical analogue compute engines to include neuromorphic photonic computing.

physics.app-ph↗

arXiv2017

Plasmonic Optical Modulator based on Adiabatic Coupled Waveguides

In atomic multi-level systems, adiabatic elimination is a method used to minimize complicity of the system by eliminating irrelevant and strongly coupled levels by detuning them from one-another. Such a three-level system, for instance, can be mapped onto physical in form of a three-waveguide system. Actively detuning the coupling strength between the respective waveguide modes allows modulating light propagating through the device, as proposed here. The outer waveguides act as an effective two- photonic-mode system similar to ground- and excited states of a three-level atomic system, whilst the center waveguide is partially plasmonic. In adiabatic elimination regime, the amplitude of the middle waveguide oscillates much faster in comparison to the outer waveguides leading to a vanishing field build up. As a result, the middle waveguide becomes a dark state and hence a low insertion-loss of 8 decibel is expected to keep when achieving the modulation depth as high as 70 decibel despite the involvement of a plasmonic waveguide in the design presented here. The modulation mechanism relies on switching this waveguide system from a critical coupling regime to adiabatic elimination condition via electrostatically tuning the free-carrier concentration and hence the optical index of a thin ITO layer residing in the plasmonic center waveguide. This alters the effective coupling length and the phase mismatching condition thus modulation in each of outer waveguides. Our results show a modulator energy efficiency as low as 40 atto-joule per bit and an extinction ratio of 50 decibel. Given the minuscule footprint of the modulator, the resulting lumped-element limited RC delay is expected to exceed 200 giga hertz. This type of modulator paves the way for next-generation both energy-and speed conscience optical short-reach interconnects.

physics.optics↗