L3 Photonic Crystal Nanocavities Research Articles

Hybrid photonic-plasmonic nano-cavity with ultra-high Q/V.

Optical cavities with high figure of merit Q/V is essential to enhance the interaction of light and matter. Here, a hybrid photonic-plasmonic nano-cavity, consisting of an L3 photonic crystal nano-cavity and plasmonic bowtie nano-antennas, is proposed to have an ultrahigh figure of merit Q/V of 8.4×106(λ/n)-3, which is the highest value ever demonstrated for all previous works about L3-type photonic crystal nano-cavities. The value of Q/V is enhanced by more than 25 times compared to that in a bare L3 photonic crystal nano-cavity and is 60 times greater than plasmonic bowtie nano-antennas. As a result, the single-atom cooperativity parameter is improved by 26 times with respect to a bare L3 photonic crystal nano-cavity, and strong coupling between light and a single emitter is achieved. The proposed structure provides a new platform to achieve strong coupling between light and a single emitter, which holds great potential for applications in quantum optics, quantum information, and nonlinear optics.

Quantitative evaluation of enhanced Er luminescence in GaAs-based two-dimensional photonic crystal nanocavities

We evaluate the enhancement of Er luminescence coupled to two-dimensional (2D) photonic crystal (PC) nanocavities by means of photoluminescence measurements and numerical simulations. L3 PC nanocavities are utilized for characterization and evaluation, with GaAs:Er,O grown by low-pressure organometallic vapor phase epitaxy as the active layer. Optical characterization at room temperature demonstrates a 5.8-fold enhancement of Er luminescence due to coupling to the cavity mode of the 2D-PC nanocavities. This enhancement of Er luminescence is supported by a finite-difference time domain simulation where an enhancement of 4.1 times is found, which is in reasonable agreement with the observed experimental results. These results pave the way toward understanding the interaction between cavity modes in PC nanocavities and luminescence from rare-earth elements.

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.

Wideband slow short-pulse propagation in one-thousand slantingly coupled L3 photonic crystal nanocavities

Coupled cavities have been used previously to realize on-chip low-dispersion slow-light waveguides, but the bandwidth was usually narrower than 10 nm and the total length was much shorter than 1 mm. Here we report long (0.05-2.5 mm) slow-light coupled cavity waveguides formed by using 50, 200, and 1,000 L3 photonic crystal nanocavities with an optical volume smaller than (λ/n)3, slanted from Γ-K orientation. We demonstrate experimentally the formation of a single-mode wideband coupled cavity mode with a bandwidth of up to 32nm (4THz) in telecom C-band, generated from the ultra-narrow-band (~300 MHz) fundamental mode of each L3 nanocavity, by controlling the cavity array orientation. Thanks to the ultrahigh-Q nanocavity design, coupled cavity waveguides longer than 1 mm exhibited low loss and allowed time-of-flight dispersion measurement over a bandwidth up to 22 nm by propagating a short pulse over 1,000 coupled L3 nanocavities. The highly-dense slanted array of L3 nanocavity demonstrated unprecedentedly high cavity coupling among the nanocavities. The scheme we describe provides controllable planar dispersion-managed waveguides as an alternative to W1-based waveguides on a photonic crystal chip.

Plasmonic gold nanodiscs fabricated into a photonic-crystal nanocavity

We fabricate and characterise an optical structure consisting of a photonic crystal L3 nanocavity containing two gold nanodisks placed close to a field antinode. We use finite difference time domain (FDTD) modelling to show that the optical properties of the nanocavity are sensitive to the physical separation between the gold nanodisks, and that at reduced separation, the q-factor of a cavity mode polarised parallel to the dimer long-axis is reduced, indicating coupling between the cavity mode and a localised plasmon. Preliminary experimental measurements indeed indicate a damping of the cavity mode in the presence of the dimer; a result consistent with the FDTD modelling. Such a scheme may be used to integrate plasmonic systems into all-optical photonic circuits.

Vectorial near-field imaging of a GaN based photonic crystal cavity

We report a full optical deep sub-wavelength imaging of the vectorial components of the electric local density of states for the confined modes of a modified GaN L3 photonic crystal nanocavity. The mode mapping is obtained with a scanning near-field optical microscope operating in a resonant forward scattering configuration, allowing the vectorial characterization of optical passive samples. The optical modes of the investigated cavity emerge as Fano resonances and can be probed without the need of embedded light emitters or evanescent light coupling into the nanocavity. The experimental maps, independently measured in the two in-plane polarizations, turn out to be in excellent agreement with numerical predictions.

Enhancement of Q-factor in SiN-based planar photonic crystal L3 nanocavity for integrated photonics in the visible-wavelength range

We propose an optimized high-quality (Q)-factor silicon nitride (SiN)-based planar photonic crystal (PhC) cavity on a silicon-on-insulator (SOI) substrate, specially tailored for integrated photonics in the visible-wavelength range. The cavity is in the centre of a SiN planar PhC that consists of a triangular lattice from which three holes are removed, i.e., the three-missing-holes point defect (L3). We detail the optimization of the geometrical parameters of the PhC membrane and show how they can affect the band gap width. Moreover, we investigate the enhancement of the Q-factor by tuning the position and radius of the lateral, upper, and lower boundary holes near the cavity edge. We demonstrate that the calculated Q-factor for the designed cavity increases by a factor of 12 relative to that for a cavity without displaced and reduced air holes, while the calculated mode volume remains almost constant. These high-Q-factor structures would be advantageous in integrated sensing devices.

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.

Asymmetric out-of-plane power distribution in a two-dimensional photonic crystal nanocavity.

Conventional air-bridge two-dimensional photonic crystal (2D-PhC) nanocavities emit light with an equal power distribution for upward and downward out-of-plane directions. Some applications, however, require concentration of the radiation in a preferred direction. In this Letter, we design a 2D-PhC nanocavity that radiates dominantly into one of the out-of-plane directions with a narrow far-field distribution. Our design is based on a conventional air-bridge L3 photonic crystal nanocavity. The asymmetric out-of-plane power distribution is achieved solely by adding periodic shallow holes on the slab surface, which also function as a second-order grating for the directional beaming.

Design of a three-hole defect photonic crystal nanocavity with high-quality and enhanced Purcell factor

An easy to realize L3 photonic crystal nanocavity that exhibits ultrahigh quality factor (Q-factor), ultrasmall mode volume, and a large Q/V mode is proposed. A resonant cavity mode at 910.625 nm wavelength with Q-factor 4.93×10 5 , mode volume 0.802 ( λ/n ) 3 , and Q/V mode6.15×105 ( λ/n )−3 is reported. The proposed design improves Q-factor by a factor of 84 and Q/V mode by a factor of 70 in comparison to unoptimized L3 photonic crystal nanocavity. Such a high-quality nanocavity can be used to realize a strongly interacting quantum dot-nanocavity coupled system.

Study of the organic layer thickness effect in a hybrid photonic crystal L3 nanocavity under optical pumping

We have realized and characterized an optically pumped hybrid photonic crystal (PhC) L3 nanocavity made of an organic material as a gain medium and a Si3N4 two-dimensional PhC. The organic gain medium consists of a guest-host system with tris(8-hydroxyquinolinato) aluminum (Alq3) as the hosting matrix doped with 4-(dicyanomethylene)-2–t-butyl-6(1,1,7,7–tetramethyljulolidyl–9-enyl)-4H-pyran (DCJTB) as a guest. A laser emission at 662 nm with a threshold of 9.3 μJ/cm2 is experimentally observed. The impact of the organic layer thickness on the laser threshold is studied.

Genetically designed L3 photonic crystal nanocavities with measured quality factor exceeding one million

We report on the experimental realization of ultra-high quality factor (Q) designs of the L3-type photonic crystal nanocavity. Based on genetic optimization of the positions of few nearby holes, our design drastically improves the performance of the conventional L3 as experimentally confirmed by direct measurement of Q ≃ 2 × 106 in a silicon-based photonic crystal membrane. Our devices rank among the highest Q/V ratios ever reported in photonic crystal cavities, holding great promise for the realization of integrated photonic platforms based on ultra-high-Q resonators.

Study of modes for two-dimensional L3 photonic crystal nanocavities

This paper mainly investigates the multiple confined modes of GaAs L3 photonic crystal two-dimensional (2-D) structure using single layers of InAs quantum dots as active internal light sources. Theoretical calculations for the wavelength, quality ( Q) factors and polarization of modes are compared to experimental data for L3 photonic crystal nanocavities with end-hole displacements for s = 0 a and s = 0.15 a. It is found that a L3 photonic crystal nanocavity includes five resonant modes and an end-hole displacement not only improves the Q factor of the fundamental mode but also strongly redshifts those modes which have large end-hole-field overlaps, thus reordering the modes. This understanding of the high-order modes should be particularly useful for the selective excitation of emitters that are strongly coupled to the cavity.

Electrical conduction and optical properties of doped silicon-on-insulator photonic crystals

We investigate the electrical properties of silicon-on-insulator (SOI) photonic crystals as a function of both doping level and air filling factor. The resistance trends can be clearly explained by the presence of a depletion region around the sidewalls of the holes that is caused by band pinning at the surface. To understand the trade-off between the carrier transport and the optical losses due to free electrons in the doped SOI, we also measured the resonant modes of L3 photonic crystal nanocavities and found that surprisingly high doping levels, up to 1018/cm3, are acceptable for practical devices with Q factors as high as 4×104.

Refractive index dependence of L3 photonic crystal nano-cavities

We model the optical properties of L3 photonic crystal nano-cavities as a function of the photonic crystal membrane refractive index n using a guided mode expansion method. Band structure calculations revealed that a TE-like full band-gap exists for materials of refractive index as low as 1.6. The Q-factor of such cavities showed a super-linear increase with refractive index. By adjusting the relative position of the cavity side holes, the Q-factor was optimised as a function of the photonic crystal membrane refractive index n over the range 1.6 to 3.4. Q-factors in the range 3000-8000 were predicted from absorption free materials in the visible range with refractive index between 2.45 and 2.8.