Guided waves (GWs) are very popular for the damage detection of thin-walled structures. They propagate large distances and relatively few may be used for damage localization. The problem with their use for complex structures is the signal processing. Due to the presence of multiple modes, and mode conversion and reflections from the structure boundaries and discontinuities the signal processing is indeed challenging. In order to reduce the complexity, lower frequencies are used to limit the excitation only to the fundamental modes. Even then the signal processing may be challenging. So efforts are focussed on the ability of some sensors to detect only a particular wave. This paper aims at investigating the suitability of the polarization maintaining FBG (PM-FBG) for this purpose.
We experimentally demonstrate efficient reduction of heralded telecom single-photon spectral bandwidth by a factor exceeding 220, from 130 GHz to below 550 MHz. The transformation is achieved in an all-fiber setup using dispersive stretching and complex electro-optic phase modulation. The approach is deterministic and results in a 27-fold increase in photon detection probability at the target wavelength. Combined with system transmission of 40% the interface enables increasing the single-photon flux into a spectrally narrowband absorber by a factor of 11. Our approach may enable efficient interfacing matter-based quantum systems with high-rate quantum communication channels and pulsed entangled photon pair sources.
Guided waves (GW) allow fast inspection of a large area and hence have received great interest from the structural health monitoring (SHM) community. Fiber Bragg grating (FBG) sensors offer several advantages but their use has been limited for the GW sensing due to their limited sensitivity. FBG sensors in the edge-filtering configuration have overcome the issue with sensitivity and there is a renewed interest in their use. The FBG sensors have directional sensitivity and are passive in nature. This makes it difficult to apply the existing signal processing and damage detection techniques such as tomography, phased array approach etc. As a result, there is a need to develop novel damage detection techniques which take into consideration the specific limitations of the use of FBG sensors. This paper applies the ellipse and hyperbola based techniques for a FBG sensor based network. The paper identifies the specific challenges and applies solutions to overcome those challenges. A comparative assessment of the two methods is presented with the help of experimental data.
We experimentally demonstrate spectral manipulation of heralded single photons by electro-optic temporal phase modulation employing complex, Fresnel-like wide-band electronic waveforms. We show spectral compression of classical telecom light enhancing its maximal intensity by over 80, by compressing its full-width at half maximum (FWHM) bandwidth from 0.856 nm down to 3.1 pm (383 MHz), thus achieving a compression factor of over 270. We show a compression gain by increasing the aperture of a Fresnel time lens (temporal waveform duration). We demonstrate a similar compression on a single-photon level from ~1.5 nm (~190 GHz) down to the sub-2GHz regime. Our findings should significantly improve the performance of future quantum information processors based on hybrid quantum networks.
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