Open Access
Designing a terahertz optical sensor based on helically twisted photonic crystal fiber for toxic gas sensing
(Springer Nature, 2025-01-17) Sharif, Vahid; Saberi, Hana; Pakarzadeh, Hassan; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza
A novel helically twisted photonic crystal fiber (PCF) is designed and proposed for sensing toxic gases with refractive indices ranging from 1.00 to 1.08. The PCF consists of twelve hollow pipes arranged circularly around the hollow core to support THz radiation propagation. Low-loss polymer Topas is used as the background material of cladding. The fiber is twisted 360 degrees over 50 cm to enhance anti-resonance in the THz region. The fundamental LP01 mode is analyzed using the finite-difference eigenmode (FDE) method. The sensor operates across four frequency bands (0.2 to 3.0 THz) with minimal transmission loss (similar to 10(-4) 1/cm). Key parameters such as refractive index sensitivity, relative sensitivity, resolution, and figure of merit (FOM) are evaluated. The average refractive index sensitivities are 1450, 2250, 3000, and 2550 for Bands 1 to 4, respectively, with 100% relative sensitivity across all bands. The sensor detects refractive index changes as small as 10(-4). The FOM, defined as the inverse of the full width at half maximum, exceeds 30 1/RIU, reaching up to 250 1/RIU due to sharp resonance peaks. Compared to other THz sensors, this design offers enhanced performance in sensing gases like SOx, NOx, and CO, while maintaining a simple structure.
Open Access
Rayleigh signature interrogation in time-domain DAS sensors using the short-frequency Fourier transform
(SPIE, 2025-05-22) Sharif, Vahid; Sagüés García, Mikel; Loayssa Lara, Alayn; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
We present a general method to determine the dependence of Rayleigh backreflection in an optical fiber on position and optical frequency. It is based on applying the so-called short-frequency Fourier transform to signals obtained from coherent optical time-domain reflectometry (COTDR) measurements. The proposed method enables the implementation of distributed acoustic sensors (DAS) with high linearity, spatial resolution, and measurement frequency, while being immune to signal fading. Additionally, the technique is compatible with both conventional COTDR setups and those employing pulse compression, including phase-coded compression waveforms. We experimentally demonstrate the technique with DAS measurements of a 50-km sensing fiber, achieving a 2-m spatial resolution and a sensitivity of 137 p epsilon/root Hz using a pulse-compression COTDR with a P4 phase-coded compression waveform.
Open Access
General method for Rayleigh signature interrogation in distributed acoustic sensors based on optical time-domain reflectometry
(IEEE, 2025-07-15) Sharif, Vahid; Sagüés García, Mikel; Loayssa Lara, Alayn; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
We introduce a method to measure the Rayleigh signature of an optical fiber, which is defined as the frequency dependence of the backscattering from each position along its length. The method uses the Short-Frequency Fourier transform to extract frequency-dependent time-resolved information from the spectrum of the detected pulse response in an optical time-domain reflectometry (OTDR) setup. The Rayleigh signature obtained can be used to implement broadband high-sensitivity high-linearity distributed acoustic sensors (DAS) that are immune to signal fading problems commonly affecting other OTDR-based systems. Rayleigh signature interrogation has been widely applied in optical frequency-domain reflectometry sensors and some specialized OTDR configurations. However, to our knowledge, this is the first technique that enables its general use in conventional single-pulse coherent OTDR setups, as well as in other time-domain systems that measure the impulse response of a fiber, such as those that utilize pulse compression. We experimentally demonstrate the method in a conventional heterodyne-detection OTDR DAS and also in a enhanced-performance pulse compression setup employing phasecoded waveforms. Measurements in a 50 km fiber with spatial resolution 2 m and a sensitivity of 113 p/√Hz demonstrate the capabilities of the technique.
Open Access
Urban water leakage detection system based on distributed acoustic sensing over dark fiber networks
(Optica Publishing Group, 2025) Sharif, Vahid; Sagüés García, Mikel; Loayssa Lara, Alayn; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
A novel system for automatically detecting leaks in urban water supply networks is proposed and experimentally demonstrated in a real-world scenario. It leverages the extensive fiber optic access network infrastructure already available.

Sharif, Vahid

Email Address

person.page.identifierURI

Birth Date

Job Title

Last Name

First Name

person.page.departamento

person.page.instituteName

ORCID

person.page.observainves

person.page.upna

Name

Filters

Author

Subject

Date

Has files

Item Type

Type

Settings

Sort By

Results per page

Search Results