Modeling and experimental investigation of an integrated optical microheater in silicon-on-insulator.
TL;DR: It has been shown that the performance of a heater improves (in terms of power budget) as the length of a microheater decreases, however, smaller heater size requires higher joule heating to obtain a desired phase shift, which is again found to be dependent on polarization of the guided mode because of thermal stress.
Abstract: A linear piecewise model has been formulated to analyze the performance of a metallic microheater integrated with single-mode waveguides (λ∼1550 nm) in silicon-on-insulator (SOI). The model has been used to evaluate integrated optical microheaters fabricated in a SOI substrate with 2 µm device layer thickness. The Fabry–Perot modulation technique has been used to extract the effective thermo-optic phase shift and response time. The effective thermal power budget of Peff,π∼500 µW (out of actually consumed power Pπ=1.1 mW) for a π phase shift and a switching time of τ∼9 µs, have been recorded for a typical Ti heater stripe of length LH=50 µm, width WH=2 µm, and thickness tH∼150 nm, integrated with a Fabry–Perot waveguide cavity of length ∼20 mm. It has been shown that the performance of a heater improves (in terms of power budget) as the length of a microheater decreases. However, smaller heater size requires higher joule heating to obtain a desired phase shift, which is again found to be dependent on polarization of the guided mode because of thermal stress.
Citations
More filters
TL;DR: A hybrid graphene-silicon-based polarization-insensitive electro-absorption modulator (EAM) with high-modulation efficiency and ultra-broad bandwidth that can be applied in on-chip optical interconnects is proposed.
Abstract: Polarization-insensitive modulation, i.e., overcoming the limit of conventional modulators operating under only a single-polarization state, is desirable for high-capacity on-chip optical interconnects. Here, we propose a hybrid graphene-silicon-based polarization-insensitive electro-absorption modulator (EAM) with high-modulation efficiency and ultra-broad bandwidth. The hybrid graphene-silicon waveguide is formed by leveraging multi-deposited and multi-transferred methods to enable light interaction with graphene layers in its intense field distribution region instead of the commonly used weak cladding region, thus resulting in enhanced light⁻graphene interaction. By optimizing the dimensions of all hybrid graphene-silicon waveguide layers, polarization-insensitive modulation is achieved with a modulation efficiency (ME) of ~1.11 dB/µm for both polarizations (ME discrepancy < 0.006 dB/µm), which outperforms that of previous reports. Based on this excellent modulation performance, we designed a hybrid graphene-silicon-based EAM with a length of only 20 µm. The modulation depth (MD) and insertion loss obtained were higher than 22 dB and lower than 0.23 dB at 1.55 µm, respectively, for both polarizations. Meanwhile, its allowable bandwidth can exceed 300 nm by keeping MD more than 20 dB and MD discrepancy less than 2 dB, simultaneously, and its electrical properties were also analyzed. Therefore, the proposed device can be applied in on-chip optical interconnects.
18 citations
Cites methods from "Modeling and experimental investiga..."
...Moreover, by means of the large thermo-optic coefficient of silicon [13], the thermal modulation method has also been explored for silicon modulators, but the modulation speed was limited and the energy consumption was relatively high....
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TL;DR: In this paper, an integrated optical design of a rectangular-edge filter device in 250-nm silicon-on-insulator platform is proposed and demonstrated experimentally, where the device is designed with a multimode waveguide with asymmetric side-wall grating, which is adiabatically interfaced with input/output single-mode waveguides.
Abstract: An integrated optical design of a rectangular-edge filter device in 250-nm silicon-on-insulator platform is proposed and demonstrated experimentally. The device is designed with a multimode waveguide (supporting at least two modes) with asymmetric side-wall grating, which is adiabatically interfaced with input/output single-mode waveguides. The input/output access waveguides are terminated with grating couplers for optical characterizations. Design parameters are optimized for a sharp-edge or nearly rectangular-edge filter response in optical C-band (1530 nm $\leq \lambda _{\text{edge}} \leq $ 1565 nm). The submicron features and the entire footprint of the devices were defined with a single-step e-beam lithography process by using negative-tone resist and subsequent dry etching of $\sim$ 100 nm by using an inductively coupled reactive ion etching system. All the fabricated devices exhibit a rectangular-edge filter response at $\lambda _{\text{edge}} \sim $ 1560 nm with an edge-extinction of $>$ 40 dB at the rate of 118 dB/nm. The rectangular-edge is followed by a broad pass-band of $\sim $ 40 nm till the first-order Bragg reflected wavelength of $\lambda _B^{00} \sim $ 1600 nm in the transmission characteristics obtained for 1520 nm $\leq \lambda \leq$ 1620 nm. Tunability of a rectangular-edge filter is verified with cladding refractive index change and the observed refractive index sensitivity of the edge is $\sim$ 18 nm/RIU. The limit of detection for 1-dB transmitted power extinction at $\lambda _{\text{edge}}$ of a typical fabricated device is estimated to be 5.3 $\times\, \text{10}^{-4}$ RIU.
13 citations
Cites background from "Modeling and experimental investiga..."
...[21], or a p-i-n/p-n phase-shifter (to avail high-speed plasma dispersion effect) [22]....
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TL;DR: An ultrabroadband add-drop filter/switch circuit is designed and demonstrated by integrating a pair of subwavelength grating waveguides in a Mach-Zehnder interferometer configuration using silicon photonics technology.
Abstract: An ultrabroadband add-drop filter/switch circuit is designed and demonstrated by integrating a pair of subwavelength grating waveguides in a $2\times 2$ Mach–Zehnder interferometer configuration using silicon photonics technology. The subwavelength grating is designed such that its stopband and passband are distinguished by a band-edge wavelength $\lambda _{\text{edge}} \sim$ 1565 nm, separating C and L bands. The stopband ( $\lambda ) is filtered at the drop port of the device, whereas the passband ( $\lambda >\lambda _{\text{edge}}$ ) is extracted either in cross port or in bar port. The device is designed to operate only in TE polarization. Experimental results exhibit a nearly flat-top band exceeding 40 nm for both stopband and passband. The stopband extinction at cross- and bar ports are measured to be $>$ 35 dB with a band-edge roll-off exceeding 70 dB/nm. Wavelength independent directional coupler design and integrated optical microheaters at different locations of the Mach–Zehnder arms for thermo-optic phase detuning are the key for stopband filtering at the drop port and switching of passband between cross- and bar ports with flat top response. Though the insertion loss of fabricated subwavelength grating waveguides are negligibly small, the observed passband insertion loss is $\sim$ 2 dB, which is mainly due to the combined excess loss of two directional couplers. Experimental results also reveal that the passband switching between cross- and bar ports of the device has been possible with an extinction of $>$ 15 dB by an electrical power consumption of $P_\pi \sim$ 54 mW. A switching time of 5 $\mu$ s is estimated by analyzing the transient response of the device. The passband edge could also be detuned thermo-optically at a rate of 22 pm/mW.
12 citations
Cites background or methods from "Modeling and experimental investiga..."
...heater designs are detailed elsewhere [26], [34]; we will focus only on the design of SWG waveguides to be integrated with the MZI arms and thermo-optic tuning in following subsections....
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...5 μm, thickness ∼100 nm) of length LH , directly on the slab and parallel to waveguide axis but at a safe distance so as to avoid unwanted absorption of the guided mode through evanescent field [34]....
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TL;DR: A graphene-based electro-absorption modulator (EAM) with high-modulation efficiency and broad optical bandwidth using a dual-slot hybrid plasmonic waveguide (HPW) and graphene's tunable conductivity is proposed.
Abstract: The hybrid plasmonic effect with lower loss and comparable light confinement than surface plasmon polariton opens new avenues for strengthening light–matter interactions with low loss. Here, we propose and numerically analyze a graphene-based electro-absorption modulator (EAM) with high-modulation efficiency and broad optical bandwidth using a dual-slot hybrid plasmonic waveguide (HPW), which consists of a central dual-slot HPW connected with two taper transitions and two additional dual-slot HPWs for coupling it with the input and output silicon nanowires, where graphene layers are located at the bottom and top side of the whole dual-slot HPW region. By combining the huge light enhancement effect of the dual-slot HPW and graphene’s tunable conductivity, we obtain a high-modulation efficiency (ME) of 1.76 dB/μm for the graphene-based dual-slot HPW (higher ME of 2.19 dB/μm can also be obtained). Based upon this promising result, we further design a graphene-based hybrid plasmonic EAM, achieving a modulation depth (MD) of 15.95 dB and insertion loss of 1.89 dB @1.55 μm, respectively, in a total length of only 10 μm, where its bandwidth can reach over 500 nm for keeping MD>15 dB; MD can also be improved by slightly increasing the device length or shrinking the waveguide thickness, showing strong advantages for applying it into on-chip high-performance silicon modulators.
12 citations
15 Oct 2018
TL;DR: A detailed theoretical and experimental study of metal-microheater integrated silicon waveguide phase-shifters has been carried out in this article, where the effective thermal conductance gw and the effective heat capacitance hw evaluated per unit length of the waveguide are two useful parameters contributing to the overall performance of a thermo-optic phaseshifter.
Abstract: A detailed theoretical and experimental study of metal-microheater integrated silicon waveguide phase-shifters has been carried out. It has been shown that the effective thermal conductance gw and the effective heat capacitance hw evaluated per unit length of the waveguide are two useful parameters contributing to the overall performance of a thermo-optic phase-shifter. Calculated values of temperature sensitivity, SH = 1/gw and thermal response time, τth = hw/gw of the phase-shifter are found to be consistent with the experimental results. Thus, a new parameter ℱH = SH/τth = 1/hw has been introduced to capture the overall figure of merit of a thermo-optic phase-shifter. A folded waveguide phase-shifter design integrated in one of the arms of a balanced MZI switch is shown to be superior to that of a straight waveguide phase-shifter of the same waveguide cross-sectional geometry. The MZI switches were designed to operate in TE-polarization over a broad wavelength range (λ ∼ 1550 nm).
9 citations
References
More filters
TL;DR: The use of free-standing silicon racetrack resonators with undercut structures significantly enhances the tuning efficiency, with one order of magnitude improvement of that for previously demonstrated thermo-optic devices without undercuts.
Abstract: We present thermally tunable silicon racetrack resonators with an ultralow tuning power of 2.4 mW per free spectral range. The use of free-standing silicon racetrack resonators with undercut structures significantly enhances the tuning efficiency, with one order of magnitude improvement of that for previously demonstrated thermo-optic devices without undercuts. The 10%-90% switching time is demonstrated to be ~170 µs. Such low-power tunable micro-resonators are particularly useful as multiplexing devices and wavelength-tunable silicon microcavity modulators.
341 citations
TL;DR: This Letter proposes and demonstrates a high-speed and power-efficient thermo-optic switch using an adiabatic bend with a directly integrated silicon heater to minimize the heat capacity and therein maximize the performance of the thermosensitive switch.
Abstract: In this Letter, we propose and demonstrate a high-speed and power-efficient thermo-optic switch using an adiabatic bend with a directly integrated silicon heater to minimize the heat capacity and therein maximize the performance of the thermo-optic switch. A rapid, τ=2.4 μs thermal time constant and a low electrical power consumption of P(π)=12.7 mW/π-phase shift were demonstrated representing a P(π)τ product of only 30.5 mW·μs in a compact device with a phase shifter of only ~10 μm long.
263 citations
TL;DR: In this paper, a resistive heater optimized for efficient and low-loss optical phase modulation in a silicon-on-insulator (SOI) waveguide was designed and a 61.6 μm long phase shifter was fabricated.
Abstract: We design a resistive heater optimized for efficient and low-loss optical phase modulation in a silicon-on-insulator (SOI) waveguide and characterize the fabricated devices. Modulation is achieved by flowing current perpendicular to a new ridge waveguide geometry. The resistance profile is engineered using different dopant concentrations to obtain localized heat generation and maximize the overlap between the optical mode and the high temperature regions of the structure, while simultaneously minimizing optical loss due to free-carrier absorption. A 61.6 μm long phase shifter was fabricated in a CMOS process with oxide cladding and two metal layers. The device features a phase-shifting efficiency of 24.77 ± 0.43 mW/π and a −3 dB modulation bandwidth of 130.0 ± 5.59 kHz; the insertion loss measured for 21 devices across an 8-inch wafer was only 0.23 ± 0.13 dB. Considering the prospect of densely integrated photonic circuits, we also quantify the separation necessary to isolate thermo-optic devices in the standard 220 nm SOI platform.
201 citations
TL;DR: Both second-order and fifth-order ring resonators are presented, which can find ready application in microwave/radio frequency signal processing.
Abstract: Previously demonstrated high-order silicon ring filters typically have bandwidths larger than 100 GHz. Here we demonstrate 1-2 GHz-bandwidth filters with very high extinction ratios (~50 dB). The silicon waveguides employed to construct these filters have propagation losses of ~0.5 dB/cm. Each ring of a filter is thermally controlled by metal heaters situated on the top of the ring. With a power dissipation of ~72 mW, the ring resonance can be tuned by one free spectral range, resulting in wavelength-tunable optical filters. Both second-order and fifth-order ring resonators are presented, which can find ready application in microwave/radio frequency signal processing.
170 citations
TL;DR: Compact silicon-on-insulator waveguide thermo-optically tunable Fabry-Perot microcavities with silicon/air Bragg mirrors with high-Q cavities enabling fast switching at low drive power (<10 mW) are demonstrated.
Abstract: Compact silicon-on-insulator (SOI) waveguide thermo-optically tunable Fabry-Perot microcavities with silicon/air Bragg mirrors are demonstrated. Quality factors of Q=4,584 are measured with finesse F=82. Tuning is achieved by flowing current directly through the silicon cavity resulting in efficient thermo-optic tuning over 2 nm for less than 50 mW applied electrical power. The high-Q cavities enable fast switching (1.9 μs rise time) at low drive power (<10 mW). By overdriving the device, rise times of 640 ns are obtained. Various device improvements are discussed.
131 citations