In the non-ablative regime, femtosecond laser pulse duration is known to affect the nature of the modification induced in the microstructure of fused silica. It has been demonstrated than below 200 fs, two different regimes are found, one at low energy, leading to bulk densification while the second one – for higher energy, leading to self-organized structure - nicknamed nanogratings - that induce a net and localized volume expansion of the material. The first regime is particularly interesting for waveguides fabrication, although, so far, the reported refractive index gain remains modest, typically within 10-3 relative net increase that limits the level of compactness for photonics circuits making use of it. Here, we investigate further how shorter pulses, i.e. in the sub-50 fs range, can increase the level of densification and in turn, the net refractive index gain, and possibly lead to an improve process for photonics device fabrication. First results show that indeed, higher level of densification can be obtained, level that we quantify, and that can be further correlated to a net increase of refractive index.
Over the last decade, femtosecond lasers have been used extensively for the fabrication of optical elements via direct
writing and in combination with chemical etching. These processes have been an enabling technology for manufacturing
a variety of devices such as waveguides, fluidic channels, and mechanical components.
Here, we present high quality micro-scale optical components buried inside various glass substrates such as soda-lime
glass or fused silica. These components consist of high-precision, simple patterns with tubular shapes. Typical diameters
range from a few microns to one hundred microns. With the aid of high-bandwidth, high acceleration flexure stages, we
achieve highly symmetric pattern geometries, which are particularly important for achieving homogeneous stress
distribution within the substrate.
We model the optical properties of these structures using beam propagation simulation techniques and experimentally
demonstrate that such components can be used as cost-effective, low-numerical aperture lenses. Additionally, we
investigate their capability for studying the stress-distribution induced by the laser-affected zones and possible related
Fiber optical components such as fiber gratings, fiber interferometers, and in-fiber Fabry-Perot filters are key
components for optical sensing. Fiber optical sensors offer a number of advantages over other optical and electronic
sensors including low manufacturing cost, immunity to electromagnetic fields, long lifetimes, multiplexing, and
environmental ruggedness. Despite the advantages of purely passive optical components described above, fiber sensor
performance and applications have been limited by their total passivity and solid-core/solid cladding structure
configurations. Passive sensors can only gather limited information. Once deployed; set point, sensitivity, trigging time,
responsivity, and dynamic range for each individual fiber sensor cannot be adjusted or reset to adapt to the changing
environment for active sensing. Further, the fiber sensor sensitivity is also limited by the traditional solid core/solid
In this paper, we present a concept of active fiber sensor that can directly powered by in-fiber light. In contrast to a
passive sensor, optical power delivered with sensing signal through the same fiber is used to power in-fiber fiber Bragg
grating sensors. The optical characteristics of grating sensors can then be adjusted using the optical energy. When optical
power is turned off, in-fiber components can serve as traditional passive sensor arrays for temperature and strain
measurements. When optical power is turned on, the fiber sensor networks are capable of measuring a wide array of
stimuli such as gas flow, wall shear stress, vacuum, chemical, and liquid levels in cryogenic, micro-gravity, and other
hostile environments. In this paper, we demonstrate in-fiber light powered dual-function active FBG sensor for
simultaneous vacuum, hydrogen fuel gas, and temperature measurement in a cryogenic environment.