Few-layer Bismuthene: Sonochemical Exfoliation, Nonlinear Optics and Applications for Ultrafast Photonics with Enhanced Stability

Ferrofluids are suspensions of magnetic nanoparticles that have the attractive feature of being controlled by applied magnetic fields. Ferrofluids have been studied for decades in an ever growing number of applications that take advantage of their response to applied magnetic fields. Here, we provide a summary of recent advances in established and emerging applications of ferrofluids, including applications in optics, sensors, actuators, seals, lubrication, and static/dynamic magnetically driven assembly of structures.

Recent progress in ferrofluids research: novel applications of magnetically controllable and tunable fluids

DOI: 10.1002/adom.201801433 Scientific American selects plasmonic sensing as the top 10 emerging technologies of 2018.[15] Almost every single new plasmonic or photonic structure would be explored to test its sensing ability.[16–29] These works tend to report the sensing performance of their own structure. Some declare that their sensitivity breaks the world record. However, there is still a missing literature on what the world record really is, the gap between the experiments and the theoretical limit, as well as the differences between metal-based plasmonic sensors and dielectric-based photonic sensors. To push plasmonic and photonic sensors into industrial applications, an optical sensing technology map is absolutely necessary. This review aims to cover a wide range of most representative plasmonic and photonic sensors, and place them into a single map. The sensor performances of different structures will be distinctly illustrated. Future researchers could plot the sensing ability of their new sensors into this technology map and gauge their performances in this field. In this review, we focus on optical refractive index (RI) sensors with no fluorescent labeling required. We will utilize two parameters to characterize and compare the performance of optical RI sensors: sensitivity to RI change (denoted by symbol SRI) and figure of merit (in short, FoM). For simplicity, we restrict our discussions to bulk RI change, where the change in RI occurs within the whole sample. There is another case where the RI variation occurs only within a very small volume close to the sensor surface. This surface RI sensitivity is proportional to the bulk RI sensitivity, the ratio of the thickness of the layer within which the surface RI variation occurs, and the penetration depth of the optical mode.[6] The bulk RI sensitivity defines the ratio of the change in sensor output (e.g., resonance angle, intensity, or resonant wavelength) to the bulk RI variations. Here, we limit our discussions to the spectral interrogations and the bulk RI sensitivity SRI is given by[3,5–7,30]

Optical Refractive Index Sensors with Plasmonic and Photonic Structures: Promising and Inconvenient Truth

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.

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A review for optical sensors based on photonic crystal cavities

A new optimized bowl-shaped mono-core surface plasmon resonance based cancer sensor is proposed for the rapid detection of different types of cancer affected cell. By considering the refractive index of each individual cancer contaminated cell with respect to their normal cell, some major optical parameters variation are observed. Moreover, the cancerous cell concentration is considered at 80% in liquid form and the detection method is finite element method with 2 100 390 mesh elements. The variation of spectrum shift is obtained by plasmonic band gap between the silica and cancer cell part which is separated by a thin (35 nm) titanium film coating. The proposed sensor depicts a high birefringence of 0.04 with a maximum coupling length of 66 $\mu$ m. However, the proposed structure provides an optimum wavelength sensitivity level between about 10 000 nm/RIU and 17 500 with a resolution of the sensor between 1.5 × 10−2 and 9.33 × 10−3 RIU. Also, the transmittance variance of the cancerous cell ranges from almost 3300 to 6100 dB/RIU and the amplitude sensitivity ranges nearly between −340 and −420 RIU $^{-1}$ for different cancer cells in major polarization mode with the maximum detection limit of 0.025. Besides, the overall sensitivity performance is measured with respect to their normal cells which can be better than any other prior structures that have already proposed.

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Surface Plasmon Resonance Based Titanium Coated Biosensor for Cancer Cell Detection

A novel and compact magnetic field sensor based on a tapered photonic crystal fiber (PCF) coated with ferrofluid is proposed. It consists of a section of tapered PCF, which is spliced between two single-mode fibers with a waist diameter of $24~\mu $ m. The ferrofluid is filled in the capillary to coat the PCF taper. Experimentally, the refractive index (RI) of the ferrofluid increased under increasing magnetic field intensity ( ${H}$ ) with a sensitivity of $\mathbf {4 \times 10}^{\mathbf {-5}}$ RIU/Gs and the RI sensitivity in the evanescent field is 401 nm/RIU. Therefore, the interference spectrum is shifted as the change of $\boldsymbol {H}$ ranged from 100 to 600 Gs with a sensitivity of 16.04 pm/Gs and resolution of 0.62 Gs. The proposed magnetic field sensor is attractive due to its compact size, low cost, and immunity to electromagnetic interference beyond what conventional magnetic field sensors can offer.

Magnetic Field Sensor Based on Photonic Crystal Fiber Taper Coated With Ferrofluid

A compact optical fiber magnetic field sensor based on the principle of the Sagnac interferometer is proposed. Different from the conventional ones, a ferrofluid-filled high-birefringence photonic crystal fiber (HB-PCF) is inserted into the Sagnac as a magnetic field sensing element. The refractive index of the ferrofluid filled in the cladding air holes of the HB-PCF will change with respect to the applied magnetic field, and subsequently, the birefringence of the HB-PCF will change, which will affect the shifts of the output interference spectrum in Sagnac. Experiments are carried out to verify the simulation model and the results indicate that the interference spectrum exhibits a red shift with the increment in the magnetic field intensity. The sensitivity of the proposed sensor is up to 0.073 nm/mT for a magnetic field intensity ranging from 10 to 40 mT, while the resolution is 0.001 mT. The proposed magnetic field sensor is attractive due to its compact size, low cost, and immunity to electromagnetic interference beyond what conventional magnetic field sensors can offer.

Magnetic Field Measurement Based on the Sagnac Interferometer With a Ferrofluid-Filled High-Birefringence Photonic Crystal Fiber

The tunable refractive index of the magnetic fluid (MF) is a unique optical property, which has attracted a lot of research interest in recent years. In this paper, a method based on the Fresnel reflection at the fiber end face is presented. Experimental measurements are carried out to investigate the magnetic field (intensity and direction) and temperature-dependent refractive index of the MF. For a given concentration, with the increase of the magnetic field intensity, the nMF increases gradually when H//Light, while decreases when H⊥Light. The effect of temperature on nMF is relatively insignificant with the sensitivity of -8 × 10
 -5
/°C. In addition, the mechanism is analyzed from the point of the microstructure by the Monte Carlo method.

Tunable Characteristics and Mechanism Analysis of the Magnetic Fluid Refractive Index With Applied Magnetic Field

A compact and robust refractive index (RI) sensor based on a tapered photonic crystal fiber (PCF) Mach–Zehnder interferometer (MZI) was proposed. It consists of a section of tapered PCF which is spliced between two single-mode fibers (SMF). A strong evanescent field was formed near the tapered region and made it susceptible to external RI variations. The interference was utilized between core modes and cladding modes of the PCF. Experimentally, the sensor exhibits highly RI sensitivity which is found to be 51.902 nm/RIU within a range from 1.3411 to 1.3737. A resolution of 1.93 × 10−5 RIU was achieved since the OSA has a resolution of 1 pm. In addition, a PDMS detection cell is specially designed to increase the stability and robustness of the device. The temperature effect of the sensor is also analyzed. The proposed all-fiber RI sensor based on tapered PCF is attractive due to its compact size, low cost and immunity to electromagnetic interference beyond what conventional refractive index sensors can offer.

PCF taper-based Mach-Zehnder interferometer for refractive index sensing in a PDMS detection cell

Slow light in slotted photonic crystal waveguide is a promising approach for practical applications. Two of the crucial concerns of this technology are the limited bandwidth and the pulse broadening. It was demonstrated that wideband slow light with large group index and low dispersion could be realized by shifting the first and second rows of air holes adjacent to the slot. Keeping the group index at 28, 41, and 105, respectively, the corresponding bandwidths of flat and low dispersion band could reach 17, 6.8, and 1.7 nm around 1550 nm. To further enlarge the bandwidth and group index, the oblique structure was introduced, and the bandwidths over 23.6, 6, and 1.8 nm were achieved with the group index of 30, 45, and 110, respectively. Then the propagation of slow light optical pulse was performed in time domain by the finite-difference time-domain method and a resonant structure was designed for input and output interfaces to improve the coupling efficiency.

Di Wu

Papers

Magnetic Field Sensor Based on Photonic Crystal Fiber Taper Coated With Ferrofluid

Magnetic Field Measurement Based on the Sagnac Interferometer With a Ferrofluid-Filled High-Birefringence Photonic Crystal Fiber

Tunable Characteristics and Mechanism Analysis of the Magnetic Fluid Refractive Index With Applied Magnetic Field

PCF taper-based Mach-Zehnder interferometer for refractive index sensing in a PDMS detection cell

Wideband Slow Light With Large Group Index and Low Dispersion in Slotted Photonic Crystal Waveguide