This review covers photonic crystal cavities (PCCs) and their applications in optical sensors, with a particular focus on the structures of different PCCs. For each kind of optical sensor, the specific measurement principle, structure of PCC, and the corresponding sensing properties are all presented in detail. The summary of the reported works and the corresponding results demonstrate that it is possible to realize miniature and high-sensitive optical sensors due to the ultra-compact size, excellent resonant properties, and flexibility in structural design of PCCs. Finally, the key problems and new directions of PCCs for sensing applications are discussed.

/pdf/a-review-for-optical-sensors-based-on-photonic-crystal-wcqhfbx0s5.pdf

A review for optical sensors based on photonic crystal cavities

Interrogating an object with a light beam and analyzing the scattered light can reveal kinematic information about the object, which is vital for applications ranging from autonomous vehicles to gesture recognition and virtual reality. We show that by analyzing the change in the orbital angular momentum (OAM) of a tilted light beam eclipsed by a moving object, lateral motion of the object can be detected in an arbitrary direction using a single light beam and without object image reconstruction. We observe OAM spectral asymmetry that corresponds to the lateral motion direction along an arbitrary axis perpendicular to the plane containing the light beam and OAM measurement axes. These findings extend OAM-based remote sensing to detection of non-rotational qualities of objects and may also have extensions to other electromagnetic wave regimes, including radio and sound.

/pdf/detecting-lateral-motion-using-light-s-orbital-angular-5gljakqcb5.pdf

Detecting Lateral Motion using Light's Orbital Angular Momentum.

In this paper, we used the novel defective resonant cavities to design an eight-channel photonic crystal demultiplexer. We showed that by choosing appropriate values for the width of the resonant cavity, the desired wavelengths can be separated. The proposed platform has a square lattice of dielectric rods immersed in air. The value of transmission efficiency for channels was obtained in 94$$-$$-99 % range. In addition, the maximum value of crosstalk and average quality factor for channels were calculated ---11.2 dB and 2200, respectively.

A new proposal for eight-channel optical demultiplexer based on photonic crystal resonant cavities

We theoretically analyze the detection of a cancer cell in the one-dimensional photonic crystal by infiltrating different sample cells in the cavity layer. The defect modes appear in their transmission spectra only if the nanocomposite layers are included on either side of the cavity layer. This analysis is carried out by a dielectric constant and the transmittance peak of the cancer cell is compared with the normal cell. The transmittance peak shifts are analyzed with various filling factors for optimization purposes. Through the shifting spectrum, the sensitivity of cancer cell from the normal cell is obtained from a minimum of 42 nm/RIU to a maximum of 43 nm/RIU.

Enhanced sensitivity of cancer cell using one dimensional nano composite material coated photonic crystal

Photonic crystal (PC) cavities, which possess the advantages of compactness, flexible design, and suitability for integration in a lab-on-a-chip system, are able to distinguish slight variations in refractive index with only a small amount of analyte. Combined with the newly proposed optofluidic technology, PC-cavity devices stimulate an emerging class of miniaturized and label-free biochemical sensors. In this review, an overview of optofluidic PC cavities based biochemical sensors is presented. First, the basic properties of the PC, as well as the sensing principle of the PC cavity, are discussed. Second, the applications of the sensors in detecting gas, liquid, and biomolecule concentrations are reviewed, with a focus on their structures, sensing principles, sensing properties, advantages, and disadvantages. Finally, the current challenges and future development directions of optofluidic PC-cavity-based biochemical sensors are discussed.

Applications and developments of on-chip biochemical sensors based on optofluidic photonic crystal cavities

All-optical switch based on photonic crystal microcavity with multi-resonant modes

We propose and experimentally demonstrate a series of $L_{n}$ slot photonic crystal (PhC) microcavities, which operate as refractive index (RI) gas sensors. The cavities are simply composed of a silicon slab triangular photonic crystal with $n$ holes replaced by a slot, which do not require sophisticated design or high fabrication resolution. With the increase in $n$ 
, the quality factor of the cavity exponentially increases, which is explained by the envelope of electric field approaching a Gaussian profile. An $L_{9}$ slot PhC microcavity with a quality factor exceeding 30 000, sensitivity of 421 nm per RI unit (RIU), and detection limit down to $1\times 10^{-5}$ RIU was experimentally demonstrated. The performance of the device is comparable with other fine-tuned PhC microcavity structures. Due to its simple structure and high fabrication tolerance, it could have wide applications in optical sensors.

$L_{n}$ Slot Photonic Crystal Microcavity for Refractive Index Gas Sensing

We theoretically study the evolution of the resonant modes and the transmission suppression (TS) effect in a perforated ultrathin metallic film (PUMF) with a periodic triangular array of holes. It is found that the properties of different resonances change as the hole radius increases, and the non-monotonic shift of resonant frequency can be interpreted qualitatively from the electric field distribution other than the Fano model. In addition, we analyze the strong mode interaction phenomenon in PUMF. When the diameter of holes approaches to four fifths of the lattice constant, the coupling between dipolar resonance and decapolar resonance can lead to an anticrossing and a large Rabi splitting, which is not available in PUMFs with square lattice; the resulting hybrid modes can be ascribed to the quasi-inphase and quasi-antiphase interferences between dipolar resonance and decapolar resonance. By comparing the TS effect of different resonances under different hole radii, we conclude that although dipolar resonance, short-range surface plasmons, and hybrid modes can all contribute to TS effect; the prominent TS effect in our structure should be mainly caused by the collective dipolar resonance of the structure. These findings might be of interest for the future studies in PUMF-based structures and devices.

Mode Evolution and Transmission Suppression in a Perforated Ultrathin Metallic Film with a Triangular Array of Holes

We present a simple method to design one-dimensional (1D) multichannel filters based on the resonant coupling theory, which can choose not only the peak frequency of each channel but also the quality factors (Q values) independently. This method is described by three samples for the design of two-channel, three-channel, and four-channel filters. An additional defect is introduced symmetrically into both sides of the 1D PhCs—it can generate defect modes that overlap with the channels that require tuning. This defect makes the Q values of these channels reduced but with no frequency shift, while the other channels almost keep invariant. The method is valuable for the design of multichannel filters with each channel and bandwidth adjustable independently.

Design of multichannel filters with each channel wavelength and bandwidth adjustable independently

We present a new approach which allows one to insert a silica nanosphere with a single quantum dot into a high Q photonic crystal slab nanocavity with an asymmetric nanohole in the center. The high Q cavity is optimized by adjusting air holes around the L3-type cavity based on three-dimensional finite-difference time-domain simulation. High Q value of 48 700 in this asymmetric cavity is achieved. The performance of the cavity with an assumed silica sphere containing a single quantum dot in the nanohole is also discussed, in which the Q factor can reach 5×104 and modal volume V is 0.048μm3 (∼0.62(λ0/n)3). It is found that the electric field intensity in the nanohole is much stronger than the maximum electric field in the cavity without a nanohole. This makes it possible to locate the precise position of the quantum dot with respect to the cavity mode electric maximum. This system provides a good candidate for realizing a strong interaction between a quantum dot and cavity for the study of cavity quantum electrodynamics.

Yanjun Song

Papers

All-optical switch based on photonic crystal microcavity with multi-resonant modes

$L_{n}$ Slot Photonic Crystal Microcavity for Refractive Index Gas Sensing

Mode Evolution and Transmission Suppression in a Perforated Ultrathin Metallic Film with a Triangular Array of Holes

Design of multichannel filters with each channel wavelength and bandwidth adjustable independently

High-Q photonic crystal slab nanocavity with an asymmetric nanohole in the center for QED