Many applications rely on the ultra-precise timing of optical signals through fiber, such as fiber interferometers, large telescope arrays, in phase arrayed antennae, optical metrology, and precision navigation and tracking. Environmental changes, specifically those caused by temperature fluctuations, lead to variations in the propagation delay of optical signals and thereby decrease the accuracy of the system’s timing. The cause of these variations in delay is the change in the glass properties of the optical fiber with temperature. Both the refractive index of the glass and the length of the fiber are dependent on the ambient temperature. Traditional optical fiber suffers from a delay sensitivity of 39 ps/km/K. We are reducing the temperature sensitivity of the fiber delay through the application of a novel design of optical fiber, Anti-Resonant Hollow Core Fiber. The major improvement in the thermal sensitivity of this fiber comes from the fact that the light is guided in an air core, with very little overlap into the glass structure. This drastically reduces the impact that the thermally sensitive glass properties have on the propagation time of the optical signal. Additionally, hollow core fiber is inherently radiation insensitive, due to the light guidance in air, making it suitable for space applications.
Many applications rely on the ultra-precise timing of optical signals through fiber, such as fiber interferometers, large telescope arrays, in phase arrayed antennae, optical metrology, and precision navigation and tracking. Environmental changes, specifically those caused by temperature fluctuations, lead to variations in the propagation delay of optical signals and thereby decrease the accuracy of the system’s timing.
The cause of these variations in delay is the change in the glass properties of the optical fiber with temperature. Both the refractive index of the glass and the length of the fiber are dependent on the ambient temperature. Traditional optical fiber suffers from a delay sensitivity of 39 ps/km/K. We are reducing the temperature sensitivity of the fiber delay through the application of a novel design of optical fiber, Anti-Resonant Hollow Core Fiber. The major improvement in the thermal sensitivity of this fiber comes from the fact that the light is guided in an air core, with very little overlap into the glass structure. This drastically reduces the impact that the thermally sensitive glass properties have on the propagation time of the optical signal. Additionally, hollow core fiber is inherently radiation insensitive, due to the light guidance in air, making it suitable for space applications.
Inspired by biological multicontrollability, we have devised the concept of multicontrollable metasurfaces. Comprising electrically small elements called MetaAtoms, a metasurface could be either homogeneous or graded on the wavelength scale for operation in the terahertz regime. The MetaAtoms would comprise diverse pixels each of which is made of magnetically controlled, thermally controlled, electrically controlled, or optically controlled material. Stacks of parallel multicontrollable metasurfaces would function as multicontrollable metamaterials.
KEYWORDS: Receivers, Wavelength division multiplexing, Clocks, Modulation, Local area networks, Signal attenuation, Multiplexing, Transmitters, Data processing, Optical amplifiers
This work introduces the concept of a digital Wavelength Division Multiplexed (WDM) network for small avionic and space platforms. For packaging and heat transfer efficiency, all optical wavelength sources occupy a common location. Addressable wavelengths are allocated to each receiver, which may be reached by selection or tuning of a transmitter wavelength. Individual delays may be applied to assure synchronization at each receiver. The output of each individual source wavelength is pre-modulated with a clock signal. Signal modulation is applied by passing or rejecting the clock signals. Due to the simplicity of the modulation, the control plane functions can be merged with the data plane functions. Although the concept is based on a single data rate, the digital WDM LAN concept can possibly be extended to process packet and analog payloads.
In this paper, we report laboratory test results of an LPG that can maintain a constant resonant peak depth over an
enhanced tuning range when it is coated with an ITO electrode that has optimized thickness and refractive index.
Without the ITO layer, LPG tuning ranges as large as 50 nm have been achieved when the ambient index is
increased from 1.00 (air) to ~1.444 (index of the silica cladding), but the peak depth cannot be maintained. When a
properly designed, high-index ITO overlay is coated onto the silica cladding, mode transition effects coincide with
the LPG's intrinsic sensitivity to changes in the ambient index, resulting in a stable peak depth over an enhanced
tuning range. The authors have experimentally demonstrated an LPG coated with ITO that can be tuned in excess of
150 nm with an ambient refractive index change of less than 0.01. To the best of the authors' knowledge, this is the
highest sensitivity reported for an LPG to date. In addition to the tuning performance, the resonant peak remains
within 1 dB of its maximum depth for at least 100 nm of the tuning range, which allows the tunable LPG to be used
in real applications.
A unique all-fiber tunable filter is based on the combination of a single resonant band long period grating (LPG) and an electro-optic polymer second cladding layer. The single resonant band LPG is fabricated by etching the cladding of a 125 μm thick fiber and using ultraviolet (UV) illumination to write the grating. Once a single resonant band has been achieved, an ITO electrode is sputtered onto the thin silica cladding and then a polymer second cladding layer is applied. The refractive index of the polymer determines the resonant wavelength of the filter. After a second electrode is coated onto the second cladding, the polymer index is tuned by applying an external electric field. Recent modeling and experimentation has shown that a high index ITO inner electrode can increase the tuning range of the filter up to 10 times by inducing cladding mode transitions.
In this paper, we will present our preliminary results on our development of infrared and terahertz generation by ultrafast laser pulses. The objective of this project is to develop (i) portable and cost effective spatially coherent broadband Infrared (IR) and Terahertz (THz) illuminating light sources. To effectively generate spatially coherent broadband IR and THz sources, we use a novel nonlinear optical technical approach by harnessing the huge nonlinear effect of the specially designed and fabricated photonic crystal fibers (PCF). The major merits of these unique light sources are: (1) broad band (covering a wide range of spectroscopic signatures), (2) spatially coherent (so that beams can be delivered to the far distance like laser beams), (3) compact, portable and small footprint (all fiber design), (4) cost effective (traditional approaches such as cascaded laser systems are complicated and expensive for covering broadband).
In this work, an investigation of the tuning characteristics of electrically tunable long-period gratings (LPGs) is
presented. A precise four-layer model is used to quantitatively analyze the tuning potential of the gratings and
experimental data is provided to support the analysis. The four-layer model includes a silica core layer with an inscribed
LPG, a thin silica cladding layer (~40 μm), an ultra-thin (~ 50 nm) high refractive index indium-tin dioxide (ITO) inner
electrode layer, and a tunable electro-optic polymer layer. It has been found that the inner electrode layer, made of high
refractive index ITO, can be modeled as a high index overlay and causes the forward propagating modes in the thin silica
cladding to reorganize as the ambient refractive index changes. This reorganization effect can lead to a significant
increase (10 plus fold) in the tuning range of LPG tunable filters. Moreover, the required specifications of the tunable
polymer layer are quantitatively analyzed. Finally, the required characteristics of the electro-optic polymer are realized
by using a nano-composite of zinc sulfide and ferroelectric relaxor poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer.
A unique all-fiber tunable filter is based on the combination of a single resonant band long period grating (LPG) and an electro-optic polymer second cladding layer. The single resonant band LPG is fabricated by etching the cladding of a standard 125 μm thick fiber and using either ultraviolet (UV) illumination or electric arc discharge to write the grating. Once a single resonant band has been achieved, a polymer second cladding layer is applied to the LPG. The refractive index of the polymer cladding determines the resonant wavelength of the filter and is tuned by applying an external electric field. The grating fabrication method and type of polymer used for the second cladding affect filter performance, and both must be considered when designing an application specific all-fiber filter.
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