Hollow-Core Fiber-Based Biosensor: A Platform for Lab-in-Fiber Optical Biosensors for DNA Detection

In this paper, a novel platform for lab-in-fiber-based biosensors is studied. Hollow-core tube lattice fibers (HC-TLFs) are proposed as a label-free biosensor for the detection of DNA molecules. The particular light-guiding mechanism makes them a highly sensitive tool. Their transmission spectrum is featured by alternations of high and low transmittance at wavelength regions whose values depend on the thickness of the microstructured web composing the cladding around the hollow core. In order to achieve DNA detection by using these fibers, an internal chemical functionalization process of the fiber has been performed in five steps in order to link specific peptide nucleic acid (PNA) probes, then the functionalized fiber was used for a three-step assay. When a solution containing a particular DNA sequence is made to flow through the HC of the TLF in an ‘optofluidic’ format, a bio-layer is formed on the cladding surfaces causing a red-shift of the fiber transmission spectrum. By comparing the fiber transmission spectra before and after the flowing it is possible to identify the eventual formation of the layer and, therefore, the presence or not of a particular DNA sequence in the solution

Analysis of a silicon subwavelength grating ring resonator as a refractometric sensor

Silicon sub-wavelength grating ring resonators (SGRRs), based on the combination of gratings and ring resonators, enable to engineer the light guidance in a finer manner. These structures can be used as the building blocks in integrated optics and sensing platforms. In this work, we consider a SGRR operating at a wavelength of 1550 nm made with a Si core layer, with index 3.47, positioned on a SiO2 substrate with index 1.46. For the application as refractometric sensor, the air top cladding of the structure is replaced with aqueous solutions with refractive index values in the range 1.332-1.350. The described devices have been numerically studied using an axis-symmetric model, employing the eigenfrequency analysis of the COMSOL Multiphysics software. The refractive index (RI) sensitivity is calculated by taking into account the wavelength shift of four guided modes in the mentioned range of RI values. Results have demonstrated that the highest sensitivity of 12920 nm/RIU is found for the third mode of the device with an initial effective index of 1.7707. This demonstrates the excellent potential of the proposed SGRR in the early detection of the small amount of bio/chemical analytes in medicine, biology, and chemical applications

Toward the development of direct emission yellow fiber lasers for biomedical applications

The paper presents the design and preliminary experimental validation of a fiber laser with direct emission in the yellow. The active material is a Dy-doped custom-made phosphate fiber, which is pumped by high-power blue diode lasers emitting at 450 nm. A suitable model has been developed to optimize the laser behavior and validated with a low-power version of the laser cavity with femtosecond written Bragg grating mirrors