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Register a new userActive Material, Optical Mode and Cavity Impact on electro-optic Modulation Performance
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In this paper, three different materials Si, ITO and graphene; and three different types of mode structures bulk, slot and hybrid; based on their electrooptical and electro absorptive aspects in performance are analyzed. The study focuses on three major characteristics of electrooptic tuning, i.e. material, modal and cavity dependency. The materials are characterized with established models and the allowed ranges for their key parameter spectra are analyzed with desired tuning in mind; categorizing into n and k dominant regions for plausible electrooptic and electro absorptive applications, respectively. A semi analytic approach, with the aid of FEM simulations for the eigenmode calculations, was used for this work. Electrooptic tuning i.e. resonance shift properties inside Fabry Perot cavities are investigated with modal and scaling concerns in mind. Tuning changes the effective complex refractive index of the mode dictated by the Kramers Kronig relations which subsequently suggest a tradeoff between the resonance shift and increasing losses. The electrical tuning properties of the different modes in the cavity are analyzed, and subsequently a figure of merit, delta-lambda/delta-alpha was chosen with respect to carrier concentration and cavity scaling to find prospective suitable regions for desired tuning effects.
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Electro-optic modulators are utilized ubiquitously ranging from applications in data communication to photonic neural networks. While tremendous progress has been made over the years, efficient phase-shifting modulators are challenged with fundamental tradeoffs, such as voltage-length, index change-losses or energy-bandwidth, and no single solution available checks all boxes. While voltage-driven phase modulators, such as based on lithium niobate, offer low loss and high speed operation, their footprint of 10s of cm-scale is prohibitively large, especially for density-critical applications, for example in photonic neural networks. Ignoring modulators for quantum applications, where loss is critical, here we distinguish between current versus voltage-driven modulators. We focus on the former, since current-based schemes of emerging thin electro-optical materials have shown unity-strong index modulation suitable for heterogeneous integration into foundry waveguides. Here, we provide an in-depth ab-initio analysis of obtainable modulator performance based on heterogeneously integrating low-dimensional materials, i.e. graphene, thin films of indium tin oxide, and transition metal dichalcogenide monolayers into a plurality of optical waveguide designs atop silicon photonics. Using the fundamental modulator tradeoff of energy-bandwidth-product as a design-quality quantifier, we show that a small modal cross section, such as given by plasmonic modes, enables high-performance operation, physically realized by arguments on charge-distribution and low electrical resistance. An in-depth design understanding of phase-modulator performance, beyond doped-junctions in silicon, offers opportunities for micrometer-compact yet energy-bandwidth-ratio constrained modulators with timely opportunities to hardware-accelerate applications beyond data communication towards photonic machine intelligence.
The residual amplitude modulation ($mathrm{RAM}$) is the undesired, non-zero amplitude modulation that usually occurs when a phase modulation based on the electro-optic effect is imprinted on a laser beam. In this work, we show that electro-optic modulators (EOMs) that are used to generate the sidebands on the laser beam also generate a $mathrm{RAM}$ in the optical setup. This result contradicts standard textbooks, which assume the amplitude remains unchanged in the process and should be considered as a fundamental $mathrm{RAM}$ ($mathrm{RAM_{F}}$) for these devices. We present a classical model for the propagation of an infrared laser with frequency $omega_{0}$ in a wedge-shaped crystal and an EOM with an RF modulating signal of frequency $Omega$. Since ${Omega}ll omega_{0}$, we solve Maxwells equations in a time-varying media via a WKB approximation and we write the electromagnetic fields in terms of quasi-plane waves. From the emerging fields of the setup, we compute the associated $mathrm{RAM_{F}}$ and show that it depends on the phase-modulation depth $m$ and the quotient $left(frac{Omega}{omega_{0}}right)$. The $mathrm{RAM_{F}}$ values obtained for the EOMs used in gravitational wave detectors are presented. Finally, the cancellation of $mathrm{RAM_{F}}$ is analyzed.
High performance integrated electro-optic modulators operating at low temperature are critical for optical interconnects in cryogenic applications. Existing integrated modulators, however, suffer from reduced modulation efficiency or bandwidth at low temperatures because they rely on tuning mechanisms that degrade with decreasing temperature. Graphene modulators are a promising alternative, since graphenes intrinsic carrier mobility increases at low temperature. Here we demonstrate an integrated graphene-based electro-optic modulator whose 14.7 GHz bandwidth at 4.9 K exceeds the room-temperature bandwidth of 12.6 GHz. The bandwidth of the modulator is limited only by high contact resistance, and its intrinsic RC-limited bandwidth is 200 GHz at 4.9 K.
We propose a new type of bistable device for silicon photonics, using the self-electro-optic effect within an optical cavity. Since the bistability does not depend on the intrinsic optical nonlinearity of the material, but is instead engineered by means of an optoelectronic feedback, it appears at low optical powers. This bistable device satisfies all the basic criteria required in an optical switch to build a scalable digital optical computing system.
The growth of 3D imaging across a range of sectors has driven a demand for high performance beam steering techniques. Fields as diverse as autonomous vehicles and medical imaging can benefit from a high speed, adaptable method of beam steering. We present a monolithic, sub-microsecond electro-optic switch as a solution satisfying the need for reliability, speed, dynamic addressability and compactness. Here we demonstrate a laboratory-scale, solid-state lidar pointing system, using the electro-optic switch to launch modulated coherent light into free space, and then to collect the reflected signal. We use coherent detection of the reflected light to simultaneously extract the range and axial velocity of targets at each of several electronically addressable output ports.
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