Limits of Femtosecond Fiber Amplification by Parabolic Pre-Shaping.

We explore parabolic pre-shaping as a means of generating and amplifying ultrashort pulses. We develop a theoretical framework for modeling the technique and use its conclusions to design a femtosecond fiber amplifier. Starting from 9 ps pulses, we obtain 4.3 µJ, nearly transform-limited pulses 275 fs in duration, simultaneously achieving over 40 dB gain and 33-fold compression. Finally, we show that this amplification scheme is limited by Raman scattering, and outline a method by which the pulse duration and energy may be further improved and tailored for a given application.

Temporal response of surface-relief fiber Bragg gratings to high temperature CO2 laser heating.

The authors use a fiber sensor integrated monitor (FSIM) as a fully functioning system to characterize the temporal response of a surface-relief fiber Bragg grating (SR-FBG) to temperature heating above 1000 degrees C. The SR-FBG is shown to have a rise time of about 77 ms for heating and a fall time of about 143 ms for cooling. The FSIM also provides full spectral scans at high speed that can be used to gain further insights into the temperature dynamics of a given system.

Optical D-fiber-based volatile organic compound sensor.

A fiber-optic sensor used to detect volatile organic compounds is described. The sensor consists of a single-mode D-fiber with a 2.5 microm polydimethylsiloxane layer. The layer is applied to the fiber flat after removal of a section of the fiber's cladding to increase evanescent interaction of the light with the layer. Absorption of volatile organic compounds into the polymer alters the refractive index of the layer, resulting in a birefringent change of the fiber. This change is observed as a shift in polarization of the light carried by the fiber. The sensor has a short length of 3 cm and a response time of around 1 s. The sensor is naturally reversible and gives an exponential response for gas and liquid concentrations of dichloromethane and acetone, respectively.

Volatile organic compound sensing using a surface-relief D-shaped fiber Bragg grating and a polydimethylsiloxane layer.

The authors use a surface-relief fiber Bragg grating with a polydimethylsiloxane (PDMS) layer as a volatile organic compound chemical sensor. A PDMS layer is used because it is compatible with the optical properties of the grating and exhibits good chemical selectivity. As the analyte is absorbed the refractive index of the PDMS changes, causing the Bragg wavelength to shift, and this shift is correlated to chemical type and concentration. The direction and amount of the Bragg wavelength shift is dependent on the absorbed chemical. The authors demonstrate chemical differentiation between dichloromethane and acetone in gaseous states.

Polarization analysis of surface-relief D-fiber Bragg gratings.

Surface-relief fiber Bragg gratings exhibit substantially more polarization dependence than standard fiber Bragg gratings. Using D-fiber with different core orientations, surface-relief gratings are analyzed and fabricated to determine the polarization dependence. We show that the largest Bragg reflection occurs for the polarization state with a dominant TE field component parallel to the flat surface of the fiber. The polarization dependence is adjusted by changing the index of refraction of the surrounding media and by fabricating the surface relief grating using rotated core D-fiber.

Surface-relief fiber Bragg gratings for sensing applications.

We present a new type of fiber Bragg grating (FBG) in which we etch the grating into the flat surface of a D-shaped optical fiber. Instead of being written in the core of the fiber, as are standard FBGs, these surface-relief FBGs are placed in the cladding above the core. These gratings are a viable alternative to standard FBGs for sensing applications. We describe the fabrication process for etching Bragg gratings into the surface of D-fibers and demonstrate their performance as temperature sensors.