A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

Supercontinuum generation, photonic crystal fiber

Flexibility in engineering holey structures and controlling the wave guiding properties in photonic crystal fibers (PCFs) has enabled a wide variety of PCF-based plasmonic structures and devices with attractive application potential. Metal thin films, nanowires, and nanoparticles are embedded for achieving surface plasmon resonance (SPR) or localized SPR within PCF structures. This paper begins with an outline of plasmonic sensing principles. This is followed by an overview of fabrication and experimental investigation of plasmonic PCFs. Reported plasmonic PCF designs are categorized based on their target application areas, including optical/biochemical sensors, polarization splitters, and couplers. Finally, design and fabrication considerations, as well as limitations due to the structural features of PCFs, are discussed.

Recent advances in plasmonic photonic crystal fibers: design, fabrication and applications

In this work, an octagonal Penrose-type photonic quasi-crystal fiber (PQF) with dual-cladding is proposed. By optimizing three geometric degrees of freedom, the PQF exhibits ultra-flattened near-zero dispersion of 0.014±0.293  ps/nm/km, ultra-low order confinement loss of 10−4  dB/km, and large effective mode area of over 16.2  μm2 in a broadband of wavelength from 1.27 to 1.67 μm, covering almost all optical communication bands. At the common communication wavelength 1.55 μm, completely opposite trends of the dispersion and the confinement loss varying with the air-filling factor in the inner cladding are demonstrated. In addition, the robustness of optical properties including dispersion, confinement loss, and effective mode area in this PQF is discussed, assuming a deviation ±3% of all air holes.

Broadband ultra-flattened dispersion, ultra-low confinement loss and large effective mode area in an octagonal photonic quasi-crystal fiber.

HER2 breast cancer biomarker detection using a sandwich optical fiber assay

https://onlinelibrary.wiley.com/doi/pdf/10.1002/lpor.202000588

Optical Vernier Effect: Recent Advances and Developments

The survey focuses on the most significant contributions in the field of fiber optic plasmonic sensors (FOPS) in recent years. FOPSs are plasmonic sensor-based fiber optic probes that use an optical field to measure the biological agents. Owing to their high sensitivity, high resolution, and low cost, FOPS turn out to be potential alternatives to conventional biological fiber optic sensors. FOPS use optical transduction mechanisms to enhance sensitivity and resolution. The optical transduction mechanisms of FOPS with different geometrical structures and the photonic properties of the geometries are discussed in detail. The studies of optical properties with a combination of suitable materials for testing the biosamples allow for diagnosing diseases in the medical field.

https://www.mdpi.com/2076-3417/9/5/949/pdf

Recent advances in plasmonic sensor-based fiber optic probes for biological applications

A novel fiber Michelson interferometer (FMI) based on parallel dual polarization maintaining fiber Sagnac interferometers (PMF-SIs) is proposed and experimentally demonstrated for temperature sensing. The free spectral range (FSR) difference of dual PMF-SIs determines the FSR of envelope and sensitivity of the sensor. The temperature sensitivity of parallel dual PMF-SIs is greatly enhanced by the Vernier effect. Experimental results show that the temperature sensitivity of the proposed sensor is improved from -1.646 nm/°C (single PMF-SI) to 78.984 nm/°C (parallel dual PMF-SIs), with a magnification factor of 47.99, and the temperature resolution is improved from ±0.03037°C to ±0.00063°C by optimizing the FSR difference between the two PMF-SIs. Our proposed ultrasensitive temperature sensor is with easy fabrication, low cost and simple configuration which can be implemented for various real applications that need high precision temperature measurement.

Ultrasensitive temperature sensor with Vernier-effect improved fiber Michelson interferometer

Using finite-element method, we propose a photonic quasi-crystal fiber-based refractive index biosensor (PQF-RIBS), which works based on the surface plasmon polariton. We determine the loss spectra for two different variations of the refractive index of analyte, $n_{a}$ . From the detailed numerical analysis, we find that the PQF-RIBS exhibits a maximum refractive index sensitivity of 6000 nm/RIU and a resolution of $1.6\,\, \times \,\,10^{-6}$ RIU when $n_{a}$ is increased from 1.45 to 1.46. Besides, this sensor does exhibit the negative refractive index sensitivity of −4000 nm/RIU and a resolution of $2.5\,\, \times \,\,10^{-6}$ RIU for a sensing range from 1.52 to 1.53. Furthermore, we carry out selective filling of liquid in the selective holes of the proposed biosensor for a sensing wavelength range from 900 to 1200 nm. Finally, we also study the influence of the structural parameters, namely, diameter of the core and diameter of the air holes in the cladding over the loss spectra of a fundamental mode for a particular $n_{a}$ of 1.47.

Designing a Biosensor Using a Photonic Quasi-Crystal Fiber

We propose a simple geometric, highly responsive and miniaturized surface plasmon polariton microbiosensor using a photonic quasicrystal fiber. Here, we consider gold as plasmonic material as the external coating for exciting the surface plasmon to detect the refractive index of the external analyte sensing to facilitate the practical realization. Further, we carry out detailed characteristics evaluations such as wavelength and amplitude sensitivities, resolution, full-width at half maximum, the figure of merit, signal to noise ratio and detection limit for both 6-fold and 8-fold plasmonic sensors. The proposed 6 and 8-fold sensors show a maximum sensitivity of 28,000 nm/RIU for an analyte range of 1.41–1.42 and 27,000 nm/RIU for an analyte range of 1.4–1.41, respectively. While the figure-of-merit of the 6-fold sensor is 491, for the 8-fold sensor, it is 231. Besides, the structural parameters and the arrangements of the air-holes in cladding region add to the sensing performance. The proposed sensing systems operate for a wide range of wavelengths from 600 to 1300 nm. Thus, the proposed sensors might turn out to be promising candidates for the refractive index-based biological and chemical detections.

M. S. Aruna Gandhi

Papers

Recent advances in plasmonic sensor-based fiber optic probes for biological applications

Ultrasensitive temperature sensor with Vernier-effect improved fiber Michelson interferometer

Designing a Biosensor Using a Photonic Quasi-Crystal Fiber

Visible to near infrared highly sensitive microbiosensor based on surface plasmon polariton with external sensing approach

High sensitivity photonic crystal fiber-based refractive index microbiosensor