Silicon Photonic Crystal Nanocavities Research Articles

Detection of ionized air using a photonic-crystal nanocavity excited by broadband light from a superluminescent diode.

It has been shown that silicon photonic crystal nanocavities excited by spectrally narrow light can be used to detect ionized air. Here, to increase the range of possible applications of nanocavity-based sensing, the use of broadband light is considered. We find that the use of a superluminescent diode (SLD) as an excitation source enables a more reproducible detection of ionized air. When our photonic-crystal nanocavity is exposed to ionized air, carriers are transferred to the cavity and the light emission from the cavity decreases due to free carrier absorption. Owing to the broadband light source, the resonance wavelength shifts caused by the carriers in this system (for example, due to temperature fluctuations) do not influence the emission intensity. SLD-excited cavities could be useful to determine the density of ions in air quantitatively.

Giant Enhancement of Nonlinear Harmonic Generation in a Silicon Topological Photonic Crystal Nanocavity Chain

AbstractStrongly enhanced third‐harmonic generation (THG) by the topological localization of an edge mode in a Su‐Schrieffer‐Heeger (SSH) chain of silicon photonic crystal nanocavities is demonstrated. The edge mode of the nanocavity chain not only naturally inherits resonant properties of the single nanocavity, but also exhibits the topological feature with mode robustness extending well beyond individual nanocavity. By engineering the SSH nanocavities with alternating strong and weak coupling strengths on a silicon slab, the edge mode formation that entails a strong THG signal similar to that obtained from a single nanocavity is observed, which both show three orders of magnitude enhancement compared with that in a trivial SSH structure. The results indicate that the photonic crystal nanocavity chain can provide a promising on‐chip platform for topology‐driven nonlinear photonics.

Dynamic modulation in graphene-integrated silicon photonic crystal nanocavity* *Project supported by the National Natural Science Foundation of China (Grant No. 11674273) and the Science and Technology Plan Projects of Colleges and Universities of Shandong Province, China (Grant No. J15LJ52).

Silicon-based electro-optic modulators are the key devices in integrated optoelectronics. Integration of the graphene layer and the photonic crystal (PC) cavity is a promising way of achieving compact modulators with high efficiency. In this paper, a high-quality (Q) acceptor-type PC nanocavity is employed to integrate with a single-layer graphene for realizing strong modulation. Through tuning the chemical potential of graphene, a large wavelength shift of 2.62 nm and a Q factor modulation of larger than 5 are achieved. A modulation depth (12.8 dB) of the reflection spectrum is also obtained. Moreover, the optimized PC nanocavity has a large free spectral range of 131.59 nm, which can effectively enhance the flexibility of the modulator. It shows that the proposed graphene-based PC nanocavity is a potential candidate for compact, high-contrast, and low-power absorptive modulators in integrated silicon chips.

Giant enhancement of the effective Raman susceptibility in metasurfaces made of silicon photonic crystal nanocavities.

We demonstrate that stimulated Raman amplification can be enhanced by more than four orders of magnitude in a silicon metasurface consisting of a periodic distribution of specially engineered photonic crystal (PhC) cavities in a silicon PhC slab waveguide. In particular, by designing the PhC cavities so as they possess two optical modes separated by the Raman frequency of silicon, one can achieve large optical field enhancement at both the pump and Stokes frequencies. As a consequence, the effective Raman susceptibility of the nonlinear metasurface, calculated using a novel homogenization technique, is significantly larger than the intrinsic Raman susceptibility of silicon. Implications to technological applications of our theoretical study are discussed, too.

Photolithographically fabricated silicon photonic crystal nanocavity photoreceiver with laterally integrated p-i-n diode

We fabricated a SiO2-clad all-silicon high-Q integration of p-i-n diode with photonic crystal nanocavity to demonstrate channel selective photoreceiver operation at a speed of 0.1 Gbs-1 for telecom wavelength light. This SiO2-clad device is photolithographically fabricated with a fabrication method compatible with that used for a complementary metal-oxide semiconductor, and the structure allows future mass production. The dark current is as small as 37.6 pA, which is possible because of the all-silicon structure clad with SiO2. As a result of the low noise, the minimum detectable optical power is −20 dBm, while the footprint of this integrated device is a very small 50 μm2. The characteristics of this device may allow us to use it as a compact monitoring device for optical networks.

One-volt silicon photonic crystal nanocavity modulator with indium oxide gate.

The ever-increasing global network traffic requires a high level of seamless integration between optical interconnect systems and complementary metal-oxide-semiconductor (CMOS) circuits. Therefore, it brings stringent requirements for future electro-optic (E-O) modulators, which should be ultracompact, energy efficient, high bandwidth, and in the meanwhile, able to be directly driven by the state-of-the-art CMOS circuits. In this Letter, we report a low-voltage silicon photonic crystal nanocavity modulator using an optimized metal-oxide-semiconductor (MOS) capacitor consisting of an In2O3/HfO2/p-Si stacked nanostructure. The strong light-matter interaction from the accumulated free carriers with the nanocavity resonant mode results in holistic improvement in device performance, including a high tuning efficiency of 250pm/V and an average modulation strength of 4dB/V with a moderate Q factor of ∼3700 and insertion loss of ∼6 dB using an ultrashort electrode length of only 350nm. With 1V driving voltage over a capacitive loading of only 13fF, the silicon photonic nanocavity modulator can achieve more than 3dB extinction ratio with energy consumption of only 3fJ/bit. Such a low-voltage, low-capacitance silicon nanocavity modulator provides the feasibility to be directly driven by a CMOS logic gate for single-chip integration.

Enhanced Raman scattering of graphene using double resonance in silicon photonic crystal nanocavities

We demonstrate enhancements of Raman scattering from graphene on two-dimensional photonic crystals using double resonances, which originate from simultaneous enhancements by a localized guided mode and a cavity mode. By adjusting the photonic crystal cavity parameters, the double resonance can be tuned to the G′ Raman scattering. Excitation wavelength dependence measurements show a large Raman peak enhancement when the excitation and emission wavelengths meet the double resonance condition. Furthermore, spatial imaging measurements are performed to confirm that the enhancement is localized at the cavity, and we find that the enhanced Raman intensity is 60 times larger compared to the on-substrate Raman signal. The observed cavity enhancement of Raman scattering opens up new possibilities for the development of graphene-based light sources for silicon photonics.

1305 nm Few‐Layer MoTe2‐on‐Silicon Laser‐Like Emission

AbstractThe missing piece in the jigsaw of silicon photonics is a light source that can be easily incorporated into the standard silicon fabrication process. Here, silicon laser‐like emission is reported that employs few‐layer semiconducting transition metal dichalogenides of molybdenum ditelluride (MoTe2) as a gain material in a silicon photonic crystal L3 nanocavity. An optically pumped MoTe2‐on‐silicon laser‐like emission at 1305 nm, i.e. in the center of the “O‐band” of optical communications, is demonstrated at room temperature and with a threshold power density of 1.5 kW/cm2. The surprising insight is that, contrary to common understanding, a monolayer MoTe2 is not required to achieve higher efficiency laser‐like operation. Instead, few‐layer MoTe2 offers a higher overlap between the two dimensional (2D) gain material and the optical mode for sufficient gain. The ability to use few‐layer material opens new opportunities for deploying manufacturing methods such as chemical vapor deposition and thereby brings 2D‐on‐silicon devices a step closer to becoming a scalable technology.

Ultracompact Silicon-Conductive Oxide Nanocavity Modulator with 0.02 Lambda-Cubic Active Volume.

Silicon photonic modulators rely on the plasma dispersion effect by free-carrier injection or depletion, which can only induce moderate refractive index perturbation. Therefore, the size and energy efficiency of silicon photonic modulators are ultimately limited as they are also subject to the diffraction limit. Here we report an ultracompact electro-optic modulator with total device footprint of 0.6 × 8 μm2 by integrating voltage-switched transparent conductive oxide with one-dimensional silicon photonic crystal nanocavity. The active modulation volume is only 0.06 um3, which is less than 2% of the lambda-cubic volume. The device operates in the dual mode of cavity resonance and optical absorption by exploiting the refractive index modulation from both the conductive oxide and the silicon waveguide induced by the applied gate voltage. Such a metal-free, hybrid silicon-conductive oxide nanocavity modulator also demonstrates only 0.5 dB extra optical loss, moderate Q-factor above 1000, and high energy efficiency of 46 fJ/bit. The combined results achieved through the holistic design opened a new route for the development of next generation electro-optic modulators that can be used for future on-chip optical interconnects.

Ultrafast on‐Chip Remotely‐Triggered All‐Optical Switching Based on Epsilon‐Near‐Zero Nanocomposites

On-chip-triggered all-optical switching is a key component of ultrahigh-speed and ultrawide-band information processing chips.[1-4] This switching technique, the operating states of which are triggered by a remote control light, paves the way for the realization of cascaded and complicated logic processing circuits and quantum solid chips. Here, a strategy is reported to realize on-chip remotely-triggered, ultralow-power, ultrafast, and nanoscale all-optical switching with high switching efficiency in integrated photonic circuits. It is based on control-light induced dynamic modulation of the coupling properties of two remotely-coupled silicon photonic crystal nanocavities, and extremely large optical nonlinearity enhancement associated with epsilon-near-zero multi-component nanocomposite achieved through dispersion engineering. Compared with previous reports of on-chip direct-triggered all-optical switching, the threshold control intensity, 560 kW/cm2, is reduced by four orders of magnitude, while maintaining ultrafast switching time of 15 ps. This not only provides a strategy to construct photonic materials with ultrafast and large third-order nonlinearity, but also offers an on-chip platform for the fundamental study of nonlinear optics.

Enhanced radiative recombination rate for electron-hole droplets in a silicon photonic crystal nanocavity

Enhanced radiative recombination rate for electron-hole droplets in a silicon photonic crystal nanocavity

Photonic crystal nanocavity assisted rejection ratio tunable notch microwave photonic filter

Driven by the increasing demand on handing microwave signals with compact device, low power consumption, high efficiency and high reliability, it is highly desired to generate, distribute, and process microwave signals using photonic integrated circuits. Silicon photonics offers a promising platform facilitating ultracompact microwave photonic signal processing assisted by silicon nanophotonic devices. In this paper, we propose, theoretically analyze and experimentally demonstrate a simple scheme to realize ultracompact rejection ratio tunable notch microwave photonic filter (MPF) based on a silicon photonic crystal (PhC) nanocavity with fixed extinction ratio. Using a conventional modulation scheme with only a single phase modulator (PM), the rejection ratio of the presented MPF can be tuned from about 10 dB to beyond 60 dB. Moreover, the central frequency tunable operation in the high rejection ratio region is also demonstrated in the experiment.

Purcell enhancement of fast-dephasing spontaneous emission from electron-hole droplets in high-Qsilicon photonic crystal nanocavities

We have observed electron-hole droplet emission enhanced by silicon photonic crystal nanocavities with different $Q$ values and simulated their Purcell effect using a semiclassical theory considering the temporal dephasing of the emission. When the photon loss rate of the nanocavities is smaller than the dephasing rate of the emission, the cavity-enhanced integrated photoluminescence (PL) intensity is unchanged by the cavity $Q$ value. This is because the Purcell enhancement of the spontaneous emission rate is saturated in a high-$Q$ region. In contrast, the peak intensity of the cavity-enhanced PL is proportional to the cavity $Q$ value without saturation. These results suggest that a high-$Q$ nanocavity is suitable for fabricating bright narrowband light emitting devices that concentrate the broadband emission energy of fast-dephasing emitters in a narrowband cavity resonance.

On-Chip Multiple Electromagnetically Induced Transparencies in Photon–Plasmon Composite Nanocavities

Chip-integrated multiple electromagnetically induced transparencies are realized using a photon–plasmon composite nanocavity (composed of a single photonic crystal nanocavity coupled with a single plasmonic nanocavity), i.e., comprehensively utilizing the superiorities of photonics as well as plasmonics. The destructively interferential coupling of one broad-band plasmonic nanocavity mode with two narrow-band silicon photonic crystal nanocavity modes generates two electromagnetically induced transparency windows. The two transparency windows simultaneously have a narrow line width of 15 nm, a high transmission contrast of 70%, and a strong slow light effect. A large group refractive index of more than 400 is obtained at the transparency window center, indicating a 10-fold increase in comparison with earlier results. The photon–plasmon composite nanocavity has a feature size of only 2 μm. The transparency window shifts 30 nm for the photon–plasmon composite nanocavity covered with a monolayer of graphene e...

Enhanced electron-hole droplet emission from surface-oxidized silicon photonic crystal nanocavities.

We have observed electron-hole droplet (EHD) emission enhanced by silicon photonic crystal (Si PhC) nanocavities with a surface oxide. The EHD is employed as a massive emitter that remains inside the nanocavity to achieve efficient cavity-emitter coupling. Time-resolved emission measurements demonstrate that the surface oxide greatly reduces the nonradiative annihilation of the EHDs and maintains them in the PhC nanocavities. It is found that the surface-oxidized Si PhC nanocavity enhances EHD emission in addition to the Purcell enhancement of the resonant cavity, which will contribute to works on Si light emission and the cavity quantum electrodynamics of electron-hole condensates.

Single germanium quantum dot embedded in photonic crystal nanocavity for light emitter on silicon chip.

A silicon light emitter in telecom-band based on a single germanium quantum dot precisely embedded in a silicon photonic crystal nanocavity is fabricated by a scalable method. A sharp resonant luminescence peak is observed at 1498.8 nm, which is enhanced by more than three orders of magnitude. The Purcell factor for the fundamental resonant mode is estimated from enhancement factor and increased collection efficiency. The cavity modes coupled to the ground state and excited state emission of germanium quantum dot are identified in the luminescence spectrum. Our devices provide a CMOS-compatible way of developing silicon-based low-power consuming light emitters, and are promising for realizing on-chip single photon sources.

Chip-scale optical interconnects and optical data processing using silicon photonic devices

Recent advances in the density and complexity of photonic integrated circuits have facilitated possible implementation of chip-scale optical communication systems. Chip-scale optical interconnects and optical data processing are two important functions to transmit and process signal in the optical domain. Silicon photonics offers a promising platform to enable chip-scale optical interconnects and optical data processing using silicon photonic devices. In this paper, we review our recent progress in the design, modeling, and fabrication of silicon photonic devices and their applications in chip-scale optical interconnects and optical data processing with advanced modulation formats. For chip-scale optical interconnects, we experimentally demonstrate digital signal transmissions in silicon microring and silicon vertical slot waveguide. Terabit chip-scale optical interconnect is demonstrated in the experiment. Also, we experimentally demonstrate analog signal transmissions in silicon microring and silicon photonic crystal nanocavity. For chip-scale optical data processing, we experimentally demonstrate all-optical wavelength conversion using a silicon waveguide, simultaneous polarization and wavelength demultiplexing using 2D grating coupler connected with microrings, two-mode (de)multiplexing using a tapered asymmetrical grating-assisted contra-directional coupler, and two-/three-mode (de)multiplexing using asymmetrical directional converter. In addition, we propose and simulate chip-scale optical data exchange, chip-scale high-base optical computing, and chip-scale optical coding/decoding by using nonlinear interactions in a silicon-organic hybrid slot waveguide. The obtained theoretical and experimental results of chip-scale optical interconnects and optical data processing indicate possible integration of optical communication functions on a monolithic chip.

Operation bandwidth optimization of photonic differentiators.

We theoretically investigate the operation bandwidth limitation of the photonic differentiator including the upper limitation, which is restrained by the device operation bandwidth and the lower limitation, which is restrained by the energy efficiency (EE) and detecting noise level. Taking the silicon photonic crystal L3 nano-cavity (PCN) as an example, for the first time, we experimentally demonstrate that the lower limitation of the operation bandwidth does exist and differentiators with different bandwidths have significantly different acceptable pulse width range of input signals, which are consistent to the theoretical prediction. Furthermore, we put forward a novel photonic differentiator scheme employing cascaded PCNs with different Q factors, which is likely to expand the operation bandwidth range of photonic differentiator dramatically.

High-speed electro-optic modulator integrated with graphene-boron nitride heterostructure and photonic crystal nanocavity.

Nanoscale and power-efficient electro-optic (EO) modulators are essential components for optical interconnects that are beginning to replace electrical wiring for intra- and interchip communications.1-4 Silicon-based EO modulators show sufficient figures of merits regarding device footprint, speed, power consumption, and modulation depth.5-11 However, the weak electro-optic effect of silicon still sets a technical bottleneck for these devices, motivating the development of modulators based on new materials. Graphene, a two-dimensional carbon allotrope, has emerged as an alternative active material for optoelectronic applications owing to its exceptional optical and electronic properties.12-14 Here, we demonstrate a high-speed graphene electro-optic modulator based on a graphene-boron nitride (BN) heterostructure integrated with a silicon photonic crystal nanocavity. Strongly enhanced light-matter interaction of graphene in a submicron cavity enables efficient electrical tuning of the cavity reflection. We observe a modulation depth of 3.2 dB and a cutoff frequency of 1.2 GHz.

25-channel all-optical gate switches realized by integrating silicon photonic crystal nanocavities.

Silicon-based photonic crystal nanocavities with different lattice pitches were monolithically integrated with a total length of only 200 μm, and were operated as a multi-channel all-optical switch with a large processing density of 42 Tb/s/mm2. A pump light and a signal light were assigned to two cavity modes in each cavity, and in this way all-optical gate switching was achieved in a 25 channel resonant dip with an energy cost in the femtojoule regime. We also demonstrated a wavelength-division multiplexing operation by selecting three neighboring channels, and thus achieved gate switching without inter-channel optical crosstalk. As far as we know, this was the first demonstration of a many-channel all-optical switch that can handle an optical signal with bit-by-bit Gb/s repetition in an integrated photonic crystal chip.