Abstract: A tunable gain flattening filter includes a long-period grating device. The long-period grating device includes: an optical fiber that includes a core having a refractive index and a core guided mode with a first effective index, and a cladding surrounding the core and having a cladding mode with a second effective index that is less than the first effective index; a thermoelectric module, the optical fiber being mounted on the thermoelectric module; a thermoelectric cooler configured to precisely control temperature of the optical fiber; and a thermistor configured as a sensor to provide feedback for the thermoelectric module. A plurality of perturbations in refractive index are defined on the core spaced apart by a periodic distance so as to form a long-period grating with a center wavelength. Diameter of the optical fiber is tapered or etched by HF solution to about 6 to 10 ?m.

Abstract: A label free, reusable and high sensitivity viral fiber sensor is provided in the present invention. The label free, high sensitivity and reusability are the advantages of this sensor. Long Period Microfiber Grating (LPMFG) is used for the sensing device. It allows optically detecting the change in refractive index at the grating surface with an extra high sensitivity. This provides an optical detection method to monitor DNA Hybridization. The single stranded DNA (ssDNA) probe is immobilized onto the LPMFG's surface for hybridizing with a DNA sample in order to identify the viral strain in the sample. This LPMFG-based viral sensor functions by inducing a refractive index change on the grating surface through the bio-molecule binding between the target viral ssDNA and the immobilized probe ssDNA. Regeneration of a surface-immobilized probe without a significant loss of hybridization activity retains at least 10 successive assays without any significant loss of performance (less than 10% decrease).