Photonic Crystal Nanobeam Cavities Research Articles

Design-flexible entanglement of two distant quantum dots bridged by dark whispering gallery modes.

We present a flexible design to realize the entanglement between two distant semiconductor quantum dots (QDs) embedded in separated photonic crystal nanobeam cavities. When bridged by a largely detuned microring cavity, photonic supermodes between two distant nanobeam cavities are formed via whispering gallery modes (WGMs). Due to the large detuning, WGMs in the microring exhibit almost no photonic excitation, showing the "dark WGMs." With the dyadic Green's functions of the nano-structure and the resolvent operators of the Hamiltonian, we numerically investigate the entanglement dynamics of two distant QDs. Furthermore, we prove that the entanglement can be tuned by adjusting the distances between the cavities. Such a scheme paves an efficient way for realizing a scalable quantum network in a solid-state system.

Anti-external interference sensor based on cascaded side-coupled photonic crystal nanobeam cavities for simultaneous sensing of the refractive index and temperature

We present a cascaded side-coupled silicon-on-insulator (SOI) photonic crystal nanobeam cavities (PCNCs) sensor for simultaneous sensing of the refractive index (RI) and temperature. Two types of PCNCs are designed for increasing the demodulation coefficient: the low-index mode cavity exposed to water directly ( c a v 1 ) and the high-index mode cavity covered with SU-8 cladding ( c a v 2 ). Moreover, the cascaded side-coupled system is modeled, and the transmission expression is derived based on temporal coupled-mode theory. Furthermore, the correlations between the structural parameters, the transmission, quality factor are discussed. By using three-dimensional finite-difference time-domain simulations, we further prove the ability to detect RI and temperature simultaneously, obtaining a RI sensitivity of 210 nm/RI unit (RIU) and a temperature sensitivity of 53 pm/K for c a v 1 , whereas there is a RI sensitivity of 0 nm/RIU and a temperature sensitivity of − 90 p m / K for c a v 2 . Moreover, the maximum of external interference ranges of the proposed sensor are 7.5 × 10 − 6 and 0.01 for the RI and temperature, respectively, and the deviation ratios are approximately 0.56% and 3.33% for the RI and temperature, respectively. Therefore, the proposed sensor has strong anti-interference ability and accuracy, which is a promising platform for future applications of dual-parameter sensing.

Reflectionless dual standing-wave microcavity resonator units for photonic integrated circuits

We propose a novel photonic circuit element configuration that emulates the through-port response of a bus coupled traveling-wave resonator using two standing-wave resonant cavities. In this "reflectionless resonator unit", the two constituent cavities, here photonic crystal (PhC) nanobeams, exhibit opposite mode symmetries and may otherwise belong to a single design family. They are coupled evanescently to the bus waveguide without mutual coupling. We show theoretically, and verify using FDTD simulations, that reflection is eliminated when the two cavities are wavelength aligned. This occurs due to symmetry-induced destructive interference at the bus coupling region in the proposed photonic circuit topology. The transmission is equivalent to that of a bus-coupled traveling-wave (e.g. microring) resonator for all coupling conditions. We experimentally demonstrate an implementation fabricated in a new 45 nm silicon-on-insulator complementary metal-oxide semiconductor (SOI CMOS) electronic-photonic process. Both PhC nanobeam cavities have a full-width half-maximum (FWHM) mode length of 4.28 μm and measured intrinsic Q's in excess of 200,000. When the resonances are tuned to degeneracy and coalesce, transmission dips of the over-coupled PhC nanobeam cavities of -16 dB and -17 dB nearly disappear showing a remaining single dip of -4.2 dB, while reflection peaks are simultaneously reduced by 10 dB, demonstrating the quasi-traveling-wave behavior. This photonic circuit topology paves the way for realizing low-energy active devices such as modulators and detectors that can be cascaded to form wavelength-division multiplexed links with smaller power consumption and footprint than traveling wave, ring resonator based implementations.

Controlling the mode profile of photonic crystal nanobeam cavities with mix-and-match unit cells

We report simulations and experimental measurement of a photonic crystal (PhC) designed with different unit cell geometries in a single device. This “mix-and-match” approach enables enhanced mode manipulation by incorporating non-traditional unit cell shapes into a one-dimensional PhC nanobeam cavity. Inclusion of a bowtie-shaped unit cell in the center of a mix-and-match PhC nanobeam cavity comprised elsewhere of either circular or antislot unit cells leads to a 2 order of magnitude reduction in the mode volume of the cavity while maintaining a similar quality factor.

Ultracompact Channel Add-Drop Filter Based on Single Multimode Nanobeam Photonic Crystal Cavity

Ultracompact channel add-drop filter utilizing a single nanobeam photonic crystal cavity is analyzed, designed, and demonstrated. Anti-symmetric multimode periodic waveguide structure is employed to implement mode conversion and thus produce degenerate resonant states in the involved nanobeam cavity. Theoretical analysis results indicate that the inter-modal conversion coefficient and the waveguide-cavity coupling coefficient have significant effects on the lineshape of the filter. By carefully engineering the structure of the multimode nanobeam cavity and its side-coupled configuration, we successfully achieve an ultracompact add-drop filter with device area around 20 μm2. The experimental results on silicon-on-insulator (SOI) platform show that the insertion losses of drop port, the crosstalk of add port of the fabricated filter are -1.1 dB and -14.7 dB, respectively. The modal volume of the involved nanobeam cavity are small as 1.2(λ/n) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , indicating huge potentials in developing low-power consumption tunable devices for future very large scale integration (VLSI) photonic applications.

Ultra-Low Index-Contrast Polymeric Photonic Crystal Nanobeam Electro-Optic Modulator

A novel nanocavity-based polymer-on-insulator (POI) electro-optic modulator (EOM) is proposed. It consists of a polymeric photonic-crystal nanobeam cavity (PCNC) with ultra-low index-contrast ( n $_{\text{cavity}}$ /n $_{bg}$ = 1.17). Based on three-dimensional (3D) finite-difference time-domain (FDTD) method, the PCNC design and optimization are investigated theoretically. A high quality-factor ( Q ) of 3.4 $\,\times\, 10^4$ and small mode-volume of 22.8 ${({\lambda }/n_{SEO}})^{3}$ can be achieved. In order to judge the efficiency of the cavity design for electro-optic (EO) modulation, the optical modes and the electric field distribution are computed using an electromagnetic finite-element solver. Benefiting from the fast and strong EO effect in polymers, the modulator shows an EO modulation efficiency of up to 16 pm/V, which is over an order of magnitude higher than that in lithium niobate (LN) PCNCs. Moreover, the device is only 80 $\mu$ m in length, leading to a voltage-length product $V_{\pi }$ × L = 0.05 V $\cdot$ cm, which is much smaller than those of Mach-Zehnder modulators. To the best of our knowledge, this is the first on-chip POI-based EOM that features both ultra-compact size and high modulation efficiency. Hence, it is potentially an ideal platform for applications in optical communications, electric-field sensing, and tunable photonic circuits.

(Invited) Exciton Dynamics in Air-Suspended Carbon Nanotubes Coupled to Nanobeam Cavities

Air modes in photonic crystal nanobeam cavities offer efficient coupling to air-suspended carbon nanotubes [1,2]. Here we investigate exciton dynamics in the time domain at room temperature. The cavities are fabricated from silicon-on-insulator wafers, and nanotubes are synthesized over the cavities by chemical vapor deposition. Time-resolved photoluminescence measurements are performed on individual nanotubes, and we compare the bright exciton lifetime with and without coupling to the cavity. Purcell enhancement of the exciton recombination is observed [3].Work supported in part by MIC (SCOPE 191503001), RIKEN (Incentive Research Projects), JSPS (KAKENHI JP16H05962), and MEXT (Nanotechnology Platform). H.M. is supported by JSPS Research Fellowship. We thank the Advanced Manufacturing Support Team at RIKEN for technical assistance.[1] R. Miura, S. Imamura, R. Ohta, A. Ishii, X. Liu, T. Shimada, S. Iwamoto, Y. Arakawa, Y. K. Kato, Nat. Commun. 5, 5580 (2014).[2] H. Machiya, T. Uda, A. Ishii, Y. K. Kato, Appl. Phys. Lett. 112, 021101 (2018).[3] H. Machiya, A. Ishii, Y. K. Kato, in preparation.

Active Tuning of Hybridized Modes in a Heterogeneous Photonic Molecule

From fundamental discovery to practical application, advances in the optical and quantum sciences rely upon precise control of light-matter interactions. Systems of coupled optical cavities are ubiquitous in these efforts, yet design and active modification of the hybridized mode properties remains challenging. In this Letter, we demonstrate the ability to thermally control the degree of hybridization in a heterogeneous photonic molecule composed of a ring resonator strongly coupled to a nanobeam photonic crystal cavity. Combining theory and experiment, we show that the composition of the resulting super-modes can be actively tailored and we derive temperature-dependent analytic expressions for the super-mode profiles, frequencies, and volumes. This work illustrates the potential for actively tunable, designer photonic properties using heterogeneous optical cavity devices.

Ultracompact optical switch using a single semisymmetric Fano nanobeam cavity.

We propose and theoretically analyze a generalized four-port waveguide-cavity system with a novel, to the best of our knowledge, semisymmetric Fano structure. By applying the system to a silicon-based photonic crystal nanobeam cavity (PCNC), we experimentally demonstrate an ultracompact crossbar optical switch with high drop port transmission. A low insertion loss of 1.5 dB in the drop port at the cross state is achieved comparing to the 8.5 dB insertion loss in a traditional non-Fano structure. The device is also benefited by the high quality factor and small mode volume for efficient switching and the ultracompact footprint of $ 14\;\unicode{x00B5} {{\rm m}^2} $14µm2 in the core structure. The proposed PCNC switch shows great potential in various optical systems on chip to increase the integration and reduce energy consumption.

Monolithic Silicon-Based Nanobeam Cavities for Integrated Nonlinear and Quantum Photonics

Photonic resonators allowing to confine the electromagnetic field in ultra-small volumes and with long decay times are crucial to a number of applications requiring enhanced nonlinear effects. For applications to integrated photonic devices on chip, compactness and optimized in-plane transmission become relevant figures of merit as well. Here we optimize an encapsulated Si/SiO$_2$ photonic crystal nanobeam cavity at telecom wavelengths by means of a global optimization procedure, where only the first few holes surrounding the cavity are varied to decrease its radiative losses. This strategy allows to achieve close to 10 million intrinsic quality factor, sub-diffraction limited mode volumes, and in-plane transmission above 65\%, in a structure with a record small footprint of around $8~\mu$m$^2$. We address and quantitatively assess the dependence of the main figures of merit on the nanobeam length and fabrication disorder. Finally, we theoretically give a realistic estimate of the single-photon nonlinearity in such a device, which holds promise for prospective experiments in low-power nonlinear and quantum photonics.

Theoretical investigation of integratable photonic crystal nanobeam all-optical switching with ultrafast response and ultralow switching energy

High-performance all-optical switching is of paramount importance to realize integrated photonic circuit. Due to the ultra-sharp resonance mode, it is demonstrated that Fano resonance is far superior to Lorentz resonance for the implementation of all-optical switching. However, it is still a difficulty to realize an integratable all-optical switching with faster response and lower switching energy simultaneously. In this work, we propose double Fano resonances based all-optical switching composed of a silicon-polymer compound photonic crystal nanobeam (PCN) side-coupled with a photonic crystal nanobeam cavity (PCNC). The pump and probe wavelengths locate at the position of two Fano resonant modes. Introducing the excellent Kerr nonlinearity of polymer materials, all-optical switching dynamics are investigated explicitly by numerical pump-probe technique based on the finite-difference time-domain method. Associated with the sharp transmission profile of Fano resonance modes and excellent nonlinear optical property of polymer, sub-picosecond switching time and sub-picojoule switching energy can be realized simultaneously with in-plane pumping scheme. Such PCN-PCNC structures are compact and can be fabricated based on the silicon-on-insulator material, which are compatible with the complementary-metal-oxide-semiconductor technology. Our results eliminate the obstacles for the realization of high-performance optical switching, and unlock the potential for the construction of integrated photonic circuits.

Photonic Crystal Circular Nanobeam Cavity Laser with Type-II GaSb/GaAs Quantum Rings as Gain Material

The optical emission from type-II semiconductor nanostructures is influenced by the long carrier lifetime and can exhibit remarkable thermal stability. In this study, utilizing a high quality photonic crystal circular nanobeam cavity with a high quality factor and a sub-micrometer mode volume, we demonstrated an ultra-compact semiconductor laser with type-II gallium antimonide/gallium arsenide quantum rings (GaSb/GaAs QRs) as the gain medium. The lasing mode localized around the defect region of the nanobeam had a small modal volume and significant coupling with the photons emitted by QRs. It leads the remarkable shortening of carrier lifetime observed from the time-resolved photoluminescence (TRPL) and a high Purcell factor. Furthermore, a high characteristic temperature of 114 K was observed from the device. The lasing performances indicated the type-II QRs laser is suitable for applications of photonic integrated circuit and bio-detection applications.

Design and analysis of refractive index sensors based on slotted photonic crystal nanobeam cavities with sidewall gratings.

We propose and numerically investigate a refractive index sensor based on a one-dimensional slotted photonic crystal nanobeam cavity with sidewall gratings for refractive index sensing in a gaseous environment. By using the three-dimensional finite-difference time-domain method, we demonstrate that our proposed sensor simultaneously possesses a high quality factor of $ 3.71 \times {10^6} $3.71×106 and a high sensitivity of 508 nm/RIU (refractive index unit) at the resonant wavelength near 1583 nm, yielding a detection limit as low as $ 1.97 \times {10^{ - 6}} $1.97×10-6 RIU. Moreover, the mode volume of the cavity's fundamental resonant mode is found to be as small as $ 0.022(\lambda /n)^3 $0.022(λ/n)3, resulting in a very compact effective sensing area. We finally study and assess the effect of fabrication disorder on the performances of our proposed sensor. We believe our proposed sensor will be a promising candidate for applications not only in multiplexed biochemical sensing and multielement mixture detection, but also in optical trapping of single biomolecules or nanoparticles.

Cavity QED based on room temperature atoms interacting with a photonic crystal cavity: a feasibility study

The paradigm of cavity QED is a two-level emitter interacting with a high-quality factor single-mode optical resonator. The hybridization of the emitter and photon wave functions mandates large vacuum Rabi frequencies and long coherence times; features that so far have been successfully realized with trapped cold atoms and ions, and localized solid-state quantum emitters such as superconducting circuits, quantum dots, and color centers Reiserer and Rempe (Rev Modern Phys 87:1379, 2015), Faraon et al. (Phys Rev 81:033838, 2010). Thermal atoms, on the other hand, provide us with a dense emitter ensemble and in comparison to the cold systems are more compatible with integration, hence enabling large-scale quantum systems. However, their thermal motion and large transit-time broadening is a major bottleneck that has to be circumvented. A promising remedy could benefit from the highly controllable and tunable electromagnetic fields of a nano-photonic cavity with strong local electric-field enhancements. Utilizing this feature, here we investigate the interaction between fast moving thermal atoms and a nano-beam photonic crystal cavity (PCC) with large quality factor and small mode volume. Through fully quantum mechanical calculations, including Casimir–Polder potential (i.e. the effect of the surface on radiation properties of an atom), we show, when designed properly, the achievable coupling between the flying atom and the cavity photon would be strong enough to lead to quantum interference effects in spite of short interaction times. In addition, the time-resolved detection of different trajectories can be used to identify single and multiple atom counts. This probabilistic approach will find applications in cavity QED studies in dense atomic media and paves the way towards realizing large-scale, room-temperature macroscopic quantum systems aimed at out of the lab quantum devices.

Photonic Crystal Nanobeam Cavities for Nanoscale Optical Sensing: A Review

The ability to detect nanoscale objects is particular crucial for a wide range of applications, such as environmental protection, early-stage disease diagnosis and drug discovery. Photonic crystal nanobeam cavity (PCNC) sensors have attracted great attention due to high-quality factors and small-mode volumes (Q/V) and good on-chip integrability with optical waveguides/circuits. In this review, we focus on nanoscale optical sensing based on PCNC sensors, including ultrahigh figure of merit (FOM) sensing, single nanoparticle trapping, label-free molecule detection and an integrated sensor array for multiplexed sensing. We believe that the PCNC sensors featuring ultracompact footprint, high monolithic integration capability, fast response and ultrahigh sensitivity sensing ability, etc., will provide a promising platform for further developing lab-on-a-chip devices for biosensing and other functionalities.

Highly Sensitive 1 × 8 Parallel Multiplexing of Ultra-Compact Integrated 1D Photonic Crystal Sensor Array Based on Silicon-on-Insulator Platform

We design a $1\times 8$ highly sensitive ultra-compact on-chip integrated sensor array consisting of a $1\times 8$ power splitter, eight one-dimensional photonic crystal slot nanobeam cavities (1DPC-SNCs) connected by additional 1D photonic crystal tapered nanobeam bandgap filters (1DPC-TNBF), and an $8\times 1$ power combiner. The performance of the device is numerically demonstrated by three-dimensional finite-difference-time-domain (3D-FDTD) method. The whole structure is lying on top of a $2~\mu \text{m}$ buried silicon oxide layer, while remaining high sensitivities (over 400 nm/RIU) of the eight sensors, simultaneously. The proposed 1DPC-SNCs can reach a high-quality factor of $3.6\times 10^{5}$ . On account of the additional band-stop filters and the $8\times 1$ power combiner, eight sensing segments interrogated simultaneously by one input and one output port is realized, with the ultra-compact footprint of $64\times 16\,\,\mu \text{m}^{2}$ ( $26\times 16\,\,\mu \text{m}^{2}$ in sensing region). Therefore, this design is a promising platform for realizing large-scale photonic integrated circuits with high integration density, especially for ultra-compact multiple on-chip sensing.

Photonic crystal nanobeam/micro-ring hybrid-cavities for optical trapping

We propose a new type of hybrid-cavity structure for trapping nanoscale particles. The hybrid cavity is based on a ring waveguide with the incorporation of a photonic crystal nanobeam cavity (PCNC). We design the cavity and investigate the influence of geometric parameters on its performance and optical trapping ability. The numerical results show that high quality factor, low mode volume and strong optical trapping ability can be achieved. The radii of holes are quadratically tapered from the center to two sides with a smaller period in the mirrors of the PCNC and the optical trapping force is proportional to (1−T)Q/V of the cavity. Furthermore, a hybrid cavity with optimal trapping ability is realized with quality factor up to 1.98×106, mode volume as low as 1.90(λ∕nSi)3 and its optical trapping force can be as high as −855 pN/mW, which is 15 times enhanced compared to that of a microring resonator with the same radius.

Simulation study on active control of electromagnetically induced transparency analogue in coupled photonic crystal nanobeam cavity-waveguide systems integrated with graphene.

We proposed and numerically investigated a coupled photonic crystal nanobeam (PCN) cavity-waveguide system which is composed of a bus waveguide and two one-dimensional PCN cavities, acting as bright and dark mode cavities, to achieve a distinct electromagnetically induced transparency analogue (EIT-like) effect by changing the near-field coupling strength between two cavities. By further integrating with graphene on top of the dark mode cavity, the three-dimensional finite-difference time-domain simulation results show that the generated EIT-like transparency window can be actively tuned and a complete on-to-off modulation of the EIT-like effect is realized by electrically tuning the graphene's Fermi level without reoptimizing or refabricating the structure. Theoretical analysis based on the coupled mode theory is then conducted and the results are highly consistent with the numerical results. In addition, we demonstrated that the group delay of the system can also be actively modulated by changing the Fermi level of graphene, achieving a well-controlled slow light effect. Our proposed coupled PCN cavity-waveguide system, combining the merits of PCN cavity and graphene in a single device, may provide a new platform for applications in chip-integrated slow light devices, tunable switches, optical modulators and high-sensitive sensors.

Optimal Photonic Crystal Cavities for Coupling Nanoemitters to Photonic Integrated Circuits

AbstractPhotonic integrated circuits that are manufactured with mature semiconductor technology hold great promise for realizing scalable quantum technology. Efficient interfaces between quantum emitters and nanophotonic devices are crucial building blocks for such implementations on silicon chips. These interfaces can be realized as nanobeam optical cavities with high quality factors and wavelength‐scale mode volumes, thus providing enhanced coupling between nano‐scale quantum emitters and nanophotonic circuits. Realizing such resonant structures is particularly challenging for the visible wavelength range, where many of the currently considered quantum emitters operate, and if compatibility with modern semiconductor nanofabrication processes is desired. Here, it is shown that photonic crystal nanobeam cavities for the visible spectrum can be designed and fabricated directly on‐substrate with high quality factors and small mode volumes. Designs are compared based on deterministic and mode‐matching methods and the latter is found advantageous for on‐substrate realizations. The results pave the way for integrating quantum emitters with nanophotonic circuits for applications in quantum technology.

Tuning the coupling between quantum dot and microdisk with photonic crystal nanobeam cavity.

Strong coupling between solid-state quantum emitters and microcavities paves the way for optical coherent manipulation of quantum state and provides opportunities for quantum information processing. However, it is still a challenge to realize strong coupling due to the spectral and spatial mismatch between quantum emitters and cavity modes. Here, we propose a scheme to tune the coupling between a single QD and a microdisk with 1D photonic crystal nanobeam cavity. Based on Finite-Difference Time-Domain (FDTD) method and Green's function expression for the evolution operator, we demonstrate that QDs with emission wavelengths +1.27 nm and -1.44 nm detuned from the bare microdisk mode can be coupled to the system strongly. Particularly, we observe simultaneous coupling between QD and two cavity supermodes, which enriches the optical coherent control methods of quantum states. By adjusting the distance between the two cavities, we can control the coupling between QD and photons. Furthermore, benefiting from the natural integration of nanobeam cavity to waveguide, such a system provides advantages for implementing quantum internet.