Slotted Photonic Crystal Cavity Research Articles

High-Sensitivity and Wide Detection-Range Refractive-Index Sensor Based on Amplitude Change in Slotted Photonic Crystal Nanobeam Cavity

High Q-factor is essential for the realization of high sensitivity photonic crystal-based sensors. The Q-factor is usually optimized for a specific refractive-index (RI) value of the ambient background. However, a small change in the RI reduces the Q value, and therefore limits the performance of the sensor to a narrow RI range. Here, we report a high-sensitivity RI sensor with a wide detection-range based on amplitude change of the fundamental mode in slotted photonic crystal nanobeam cavity. Both wavelength and amplitude sensitivity of 333 nm/RIU and 188/RIU are realized in the RI range from 1.3 to 1.6, respectively. To the best of our knowledge, this represents the widest sensing range ever reported in photonic crystal cavities. Owing to the wide sensing range and the insignificance of the Q value, this approach would find applications in various research areas in integrated lab-on-chip systems for optofluidic- and bio-sensing applications.

Ultrafast all-optical switching in a silicon-polymer compound slotted photonic crystal nanobeam cavity

Ultrafast all-optical switching in a silicon-polymer compound slotted photonic crystal nanobeam cavity

On-chip trapping and sorting of nanoparticles using a single slotted photonic crystal nanobeam cavity

In this work, we propose a slotted photonic crystal nanobeam cavity (PCNC) to trap and sort the 120 nm and 30 nm nanoparticles. The simulation shows that the maximum optical trapping force of the 120 nm particle is 38.7 pN/mW, and that of the 30 nm particle is 10.8pN/mW. It is calculated that the trapping threshold power of the 120 nm particle is 35.3µW, and that of the 30 nm particle is 41.6 µW. Because the width of the slot is 100 nm, when the input power is between 35.3 µW and 41.6 µW, only the 120 nm particle can be trapped in the upper cladding of the slotted-PCNC. When the input power is greater than 41.6 µW, the 120nm particle is still trapped in the upper cladding of the slotted-PCNC, while the 30 nm particle is trapped inside the slot of the slotted-PCNC. By properly controlling the input power and the direction of flow in the microfluidic channel, the sorting of particles can be achieved. In addition, trapping of the particles causes different redshifts of peak wavelengths. Thus, the proposed slotted-PCNC can detect particle trapping and sorting by monitoring the resonant wavelength shifts. What is the most important, compared with previous reported single particle trapping work, is that the proposed work can realize both trapping and sorting. Therefore, provided with the ultra-compact footprint and excellent performance, the proposed slotted-PCNC shows great potential for a multifunctional lab-on-a-chip system.

Analysis on slotted photonic crystal cavity and waveguide combination in silicon-on-insulator platform

In this work, we report the numerical and simulation studies on the coupling behaviors of silicon-on-insulator (SOI) slotted photonic crystal cavity (SPhCC) and slotted photonic crystal waveguide (SPhCW). Coupled mode theory (CMT) based numerical calculations for a coupled structure consisting of SOI SPhCC and SPhCW have shown that the structure reaches a strong coupling when the Qc≥2Qi in which Qi and Qc are the quality factors of the cavity alone and of the cavity when coupled with waveguide, respectively, then the transmission of the output signal is less than 0.25, and the build-up factor is of nanosecond. In the simulation scheme with Plane wave expansion (PWE) and Finite-difference time-domain (FDTD) methods, the slot confined PhC cavity mode, which lies deep below in the band-gap, has been excited properly from the side coupling SPhCW with the obtained transmission of around 0.22. Our study sheds light on the SOI SPhCC-SPhCW coupled structure, knowledge of which may enable its applications in integrated circuits, hybrid silicon platform and sensing.

Silicon slotted photonic crystal cavities fabricated by deep-ultraviolet lithography

Slotted photonic crystal (SPC) cavities provide strong evanescent fields, high quality factors, and small mode volumes. Hence, SPC cavities have been identified as promising candidates for the implementation of high-performance sensors and the development of hybrid devices combining silicon with other active materials. Nevertheless, most state-of-the-art demonstrations rely on electron beam lithography and operate in the telecommunications band near the 1550 nm wavelength. Here, we report the experimental demonstration of SPC cavities operating in the datacom O-band, near 1340 nm wavelength, fabricated using deep-ultraviolet (DUV) lithography. The O-band provides very interesting properties for sensing, communications, and hybrid integration: namely, lower optical absorption of water, lower dispersion in standard optical fibers, and the emission of active materials like carbon nanotubes. On the other hand, DUV fabrication opens interesting opportunities for large volume production. The proposed cavities exhibit a high quality factor exceeding 20,000 and a small mode volume of 0.023 ( λ / n ) 3 . These results open interesting perspectives to exploit enhanced light–matter interaction in SPC cavities harnessing industrial-like fabrication processes.

High sensitivity and anti-external interference dual-parameter sensor based on a multimode slotted photonic crystal nanobeam cavity

We put forward a multimode slotted nanobeam cavity (MM-SPCNC) supporting both air and dielectric modes through a specific design of band properties. Dual-parameter detection is realized by jointly measuring the resonance wavelength shifts of both air and dielectric modes. The proposed sensor is robust against external interference and shows higher sensitivity compared with other dual-parameter sensors. The maximum external interference ranges of the proposed sensor are 4.82×10−6 and 0.05 for refractive index (RI) and temperature (T), respectively, which indicates that the sensor can effectively resist against external interference. The RI and T sensitivities of the fundamental air mode are 421 nm/RIU and 58 pm/K respectively, whereas those of the fundamental dielectric mode are 706 nm/RIU and 46 pm/K respectively. The proposed sensor thus represents a promising candidate for future multifunctional and lab-on-chip sensing applications.

NOEMS Based Slotted Photonic Crystal Cavity for the Sensing of Force

In the paper, a two dimensional slotted photonic crystal cavity (2D-SPCC) has been designed and optimized for the application of sensing. The optimized 2D-SPCC has been incorporated in a silicon cantilever to form a nano-opto-electro-mechanical system (NOEMS) for sensing the physical parameters like - force, displacement and strain. An applied force at the cantilever-tip generates strain which results in deformation of the SPCC parameters like slot-width. This structural change in the 2D-SPCC changes the optical behavior of the device, which can be sensed, and thus operate as a physical sensor. Resonant wavelengths of the SPCC are determined for different length and breadth of the cantilever. The results show a linear dependence of the resonant wavelength with the change in the physical parameters. The 2D-SPCC has a high quality factor and sensitivity of $\sim\!9 \, \times\, 10^6$ and 4.2 nm $\mu$ N respectively, due to which the minimum detectable force, displacement and strain for the proposed design are found as 0.0202 $\mu$ N, 0.090 707 $\mu$ m and 0.019 979 respectively for a cantilever of length 40 $\mu$ m and breadth 20 $\mu$ m. Hence, the proposed NOEMS sensor is expected to be highly relevant for different industrial applications.

Design of dielectric-mode and air-mode slotted photonic crystal nanofiber cavities for refractive index sensing

We propose two different designs of slotted photonic crystal nanofiber cavities (SPCNCs), dielectric-mode (DM) SPCNC and air-mode (AM) SPCNC, and numerically investigate their refractive index sensing performances when they are immersed in an aqueous environment. By using the three-dimensional finite-difference time-domain method, we demonstrate that the DM-SPCNC (AM-SPCNC) simultaneously possesses a high quality factor of 1.49 × 107 (7.96 × 106) and a high sensitivity of 598 nm/refractive index unit (RIU) (423 nm/RIU) at the resonant wavelength of 1525.94 nm (1585.06 nm), yielding a figure of merit as high as 5.8 × 106 RIU−1 (2.1 × 106 RIU−1). Moreover, the mode volume of the DM-SPCNC’s (AM-SPCNC’s) fundamental resonant mode is found to be as small as 0.12 (λ/n)3 (0.24 (λ/n)3), resulting in a very compact effective sensing area. With these distinct features, we believe our proposed cavities are potentially ideal platforms for applications in multiplexed biochemical sensing, multielement mixture detection, and optical trapping of single biomolecules or nanoparticles.

Suspended slotted photonic crystal cavities for high-sensitivity refractive index sensing.

We present the design, fabrication, and characterization of a suspended slotted photonic crystal (SSPhC) cavity sensor based on the silicon-on-insulator platform. The sensing performance can be dramatically enhanced by the optimized SSPhC cavity as most of the light energy can be distributed in the low index region (∼57%). By measuring the spectrum response of the cavity sensor immersed in NaCl solutions with different mass concentrations, an ultra-high sensitivity around 656 nm/RIU has been experimentally demonstrated. Furthermore, the whole size of the cavity sensor (including the grating couplers) is 320 × 40 µm2, making the high-sensitivity device attractive for the realization of large-scale multi-channel on-chip sensors.

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.

A Slotted Photonic Crystal Nanobeam Cavity for Simultaneous Attainment of Ultra-High Q-Factor and Sensitivity

An optical refractive index (RI) sensor is proposed based on a slotted photonic crystal nanobeam cavity. Three rows of parabolic-tapered air-holes are used to design the cavity and an embedded narrow slot is used to obtain a highly localized optical field in a low refractive index region in order to produce a strong light matter interaction. The number and the radii of the air holes, the width of the slot, and the number of rows are optimized to address the most challenging issue of RI sensor design, i.e. to obtain a high Q-factor and sensitivity, simultaneously. The plane wave expansion method has been used to facilitate the design procedure and a 3-D finite difference time domain method has been used to obtain the simulation outcome. The outcomes for the optimized cavity show an ultra-high Q-factor $\sim 4.3\times 10^{7}$ along with a sensitivity ~975 nm/RIU at a wavelength 1534 nm, for which the figure-of-merit is calculated as $2.73\times 10^{7}$ . However, the slot-width can be varied to obtain a Q-factor of $8\times 10^{7}$ and sensitivity of 1100 nm/RIU individually. The device also has an ultra-small mode volume of the order of 0.0253 $(\lambda /n)^{3}$ . Hence, all together, the sensor is expected to be a promising candidate for the lab-on-chip sensor application.

Simultaneously high-Q and high-sensitivity slotted photonic crystal nanofiber cavity for complex refractive index sensing

We proposed and theoretically investigated a one-dimensional slotted photonic crystal nanofiber cavity (SPCNC) for complex refractive index sensing in a gaseous environment. Three-dimensional finite-difference time-domain simulations show that a high quality factor (Q) of 1.45×106 and a high sensitivity of 756 nm/refractive index unit (RIU) can be simultaneously achieved for the detection of the real part of the refractive index (RI) of the surrounding gas. In addition, we demonstrated that the SPCNC possesses the capability of detecting the change of the imaginary part of the RI. A high sensitivity of 1525 nm/RIU is obtained, and Q is found to decrease with increasing absorption strength but still remains as high as 1.1×104 for strong absorption. We believe our proposed SPCNC with excellent sensing performances, ultra-small mode volume, and compact footprint may offer the potential to develop multiplexed sensing techniques for applications in multielement mixture detection.

Surface-sensitive diamond photonic crystals for high-performance gas detection.

Diamond slotted photonic crystal (PhC) cavities were fabricated and used for gas detection. They exhibit wavelength sensitivity reaching a 350 nm per unit change of the refractive index of the gaseous environment of the PhC. With a simple oxidized surface termination, diamond PhCs display an ultrahigh sensitivity to the surface adsorption of polar molecules. Gaseous concentrations as low as 80 parts per million (ppm) of hexanol vapor in nitrogen are probed, and a detection limit in the ppm range is inferred, demonstrating a high interest of such devices for trace sensing.

Strong optomechanical coupling in a slotted photonic crystal nanobeam cavity with an ultrahigh quality factor-to-mode volume ratio.

We describe the design, fabrication, and characterization of a one-dimensional silicon photonic crystal cavity in which a central slot is used to enhance the overlap between highly localized optical and mechanical modes. The optical mode has an extremely small mode volume of 0.017(λvac / n)3, and an optomechanical vacuum coupling rate of 310 kHz is measured for a mechanical mode at 2.69 GHz. With optical quality factors up to 1.2 × 105, fabricated devices are in the resolved-sideband regime. The electric field has its maximum at the slot wall and couples to the in-plane breathing motion of the slot. The optomechanical coupling is thus dominated by the moving-boundary effect, which we simulate to be six times greater than the photoelastic effect, in contrast to most structures, where the photoelastic effect is often the primary coupling mechanism.

Design of an ultra-compact slotted photonic crystal nanobeam cavity for biosensing

Here, we elucidate a novel biosensor in aqueous environments based on a slotted photonic crystal nanobeam cavity. A slot is introduced in the center of the photonic crystal nanobeam cavity, which reduces the mode volume by an order of 10 without sacrificing the quality factor and sensitivity. This sensor is characteristic of an ultra-small mode volume of 0.076(λ/n)3 and shows a prominent advantage in regards to single nanoparticle detection, where the minimum detectable nanoparticle radius is around 1 nm. Additionally, its quality factor is as high as 6.08×106 and its sensitivity is around 460 nm/RIU, which is promising for refractive index sensing. This sensor can also be integrated into a high-density array of sensor networks because of the unparalleled fabrication advantages.

Slotted photonic crystal nanobeam cavity with an ultrahigh quality factor-to-mode volume ratio

We describe the design, fabrication, and characterization of a 1-dimensional silicon photonic crystal cavity with a quality factor-to-mode volume ratio greater than 10(7), which exceeds the highest previous values by an order of magnitude. The maximum of the electric field is outside the silicon in a void formed by a central slot. An extremely small calculated mode volume of 0.0096 (λvac/n)(3) is achieved through the abrupt change of the electric field in the slot, despite which a high quality factor of 8.2 × 10(5) is predicted by simulation. Quality factors up to 1.4 × 10(5) are measured in actual devices. The observation of pronounced thermo-optic bistability is consistent with the strong confinement of light in these cavities.

High-Q silicon-on-insulator slot photonic crystal cavity infiltrated by a liquid

We report the experimental realization of a high-Q slot photonic crystal cavity in Silicon-On-Insulator (SOI) configuration infiltrated by a liquid. Loaded Q-factor of 23 000 is measured at telecom wavelength. The intrinsic quality factor inferred from the transmission spectrum is higher than 200 000, which represents a record value for slot photonic crystal cavities on SOI, whereas the maximum of intensity of the cavity is roughly equal to 20% of the light transmitted in the waveguide. This result makes filled slot photonic crystal cavities very promising for silicon-based light emission and ultrafast nonlinear optics.

Slotted photonic crystal nanobeam cavity with parabolic modulated width stack for refractive index sensing

We present the design, fabrication, and the characterization of high-Q slotted 1D photonic crystal (PhC) cavities with parabolic-width stack. Their peculiar geometry enables the location of the resonating mode close to the air-band. The majority of optical field distributes in the slotted low-index area and the light matter interaction with the analytes has been enhanced. Cavities with measured Q-factors ~10(4) have been demonstrated. The refractive index sensing measurement for NaCl solutions with different concentrations shows a sensitivity around 410. Both the achieved Q-factor and the sensitivity are higher than the one reported recently by using 2D slotted PhC cavities. The total size for the sensing part of the present device is reduced to 16.8 × 2.5 μm(2).

Horizontally slotted photonic crystal nanobeam cavity with embedded active nanopillars for ultrafast direct modulation

A horizontally slotted photonic crystal nanobeam cavity with an embedded active nanopillar structure is proposed for ultrafast direct modulation. By designing the thicknesses of both the nanobeam and the horizontal slot layer, the quality factor (Q factor) and the mode volume (Vn) of the proposed cavity can be engineered independently. As a result, the spontaneous emission (SpE) rate is enhanced with a small Vn of 2.4 while the SpE rate and the cavity photon lifetime have an optimal Q factor of ∼ 1000. In our simulation, the modulation bandwidth could be enhanced up to 170 GHz with different emission linewidths of the active nanopillar.

A superhigh-frequency optoelectromechanical system based on a slotted photonic crystal cavity

We develop an all-integrated optoelectromechanical system that operates in the superhigh frequency band. This system is based on an ultrahigh-Q slotted photonic crystal (PhC) nanocavity formed by two PhC membranes, one of which is patterned with electrode and capacitively driven. The strong simultaneous electromechanical and optomechanical interactions yield efficient electrical excitation and sensitive optical transduction of the bulk acoustic modes of the PhC membrane. These modes are identified up to a frequency of 4.20 GHz, with their mechanical Q factors ranging from 240 to 1730. Directly linking signals in microwave and optical domains, such optoelectromechanical systems will find applications in microwave photonics in addition to those that utilize the electromechanical and optomechanical interactions separately.