Section Of Single-mode Fiber Research Articles

Microfiber Bragg grating for temperature and strain sensing applications

Fiber Bragg grating is inscribed on microfiber with femtosecond laser pulses irradiation. The microfiber is fabricated by stretching a section of single mode fiber over a flame. Periodic grooves are carved on the microfiber by the laser as have been observed experimentally. The microfiber Bragg grating is demonstrated for temperature and strain sensing, and the strain sensitivity is improved with decreased diameters of the microfibers.

Powerful narrow linewidth random fiber laser

In this paper, we demonstrate a narrow linewidth random fiber laser, which employs a tunable pump laser to select the operating wavelength for efficiency optimization, a narrow-band fiber Bragg grating (FBG) and a section of single mode fiber to construct a half-open cavity, and a circulator to separate pump light input and random lasing output. Spectral linewidth down to 42.31 GHz is achieved through filtering by the FBG. When 8.97 W pump light centered at the optimized wavelength 1036.5 nm is launched into the half-open cavity, 1081.4 nm random lasing with the maximum output power of 2.15 W is achieved, which is more powerful than the previous reported results.

Highly Sensitive Airflow Sensor Based on Fabry–Perot Interferometer and Vernier Effect

A novel highly sensitive airflow sensor based on Fabry–Perot interferometer (FPI) and Vernier effect is proposed and demonstrated. The sensor is fabricated by splicing a section of hollow-core fiber (HCF) between a lead-in single mode fiber (SMF) and a section of SMF, which is almost one-fifteenth the length of the HCF. Airflow changes the cavity length of the FPI, which leads to the shift of the reflection spectrum. The reflection beam from the last end of the SMF is utilized to generate the Vernier effect, which enlarges the shift of the spectrum for 9.57 times than that of a single FPI. According to the experimental results, when the airflow ranges from ${\text{0 to 7 m/s}}$ , the spectrum of the sensor shifts as high as 7.9 nm which is almost eight times more than that of the self-heating sensor based on silver-coated FBG. And the highest airflow velocity sensitivity of the sensor can reach ${\text{1.541 nm/(m/s)}}$ in the region of ${\text{3m/s} \sim {7m/s}}$ . Besides, the sensor has a series of advantages such as fast response, low cost, compact size, and reflection measurement.

Fast response Fabry-Perot interferometer microfluidic refractive index fiber sensor based on concave-core photonic crystal fiber.

We report a fast response microfluidic Fabry-Perot (FP) interferometer refractive index (RI) fiber sensor based on a concave-core photonic crystal fiber (CPCF), which is formed by directly splicing a section CPCF with a section of single mode fiber. The CPCF is made by cleaving a section of multimode photonic crystal fiber with an axial tension. The shallow concave-core of CPCF naturally forms the FP cavity with a very short cavity length. The inherent large air holes in the cladding of CPCF are used as the open channels to let liquid sample come in and out of FP cavity. In order to shorten the liquid channel length and eliminate the harmful reflection from the outside end face of the CPCF, the CPCF is cleaved with a tilted tensile force. Due to the very small cavity capacity, the short length and the large sectional area of the microfluidic channels, the proposed sensor provides an easy-in and easy-out structure for liquids, leading to great decrement of the measuring time. The proposed sensor exhibits fast measuring speed, the measuring time is less than 359 and 23 ms for distilled water and pure ethanol, respectively. We also experimentally study and demonstrate the superior performances of the sensor in terms of high RI sensitivity, good linear response, low temperature cross-sensitivity and easy fabrication.

RI Ring Laser Sensor Based on Concatenating CLF and SMF With One Core-Offset Joint

In this letter, a novel all-fiber ring laser refractive index (RI) sensor is proposed and experimentally demonstrated. Such sensor is obtained by inserting a segment of cladding-less fiber between two sections of single-mode fiber with one core-offset joint, which is designed to enlarge the extinction ratio. With the help of ring laser sensing system, a 3-dB bandwidth below 0.2 nm and an optical signal-to-noise ratio near 30 dB can be achieved. Meanwhile, the high output power and the side-mode suppression ratio of the sensor are presented. Experimental results show that the RI sensitivity is 52.3 nm/RIU in the RI range of 1.334–1.370. The sensor also has the advantages of simple structure and low cost, preforming potentials in large-scale productions.

A temperature sensor based on a Brillouin optoelectronic oscillator

ABSTRACTA temperature sensor based on a Brillouin optoelectronic oscillator (BOEO) is presented and demonstrated. In the BOEO loop, a phase modulated light is converted to a microwave signal duo to the asymmetric gain of the Stokes light and the anti‐Stokes light in the stimulated Brillouin scattering to sustain the oscillation. A section of single mode fiber is used as the Brillouin gain medium as well as the sensing element. In this structure, the oscillation frequency of the BOEO varies linearly with the temperature under test. The experimental results show that the temperature sensor features high sensitivity and high stability, thanks to the intrinsic narrow gain spectrum of the stimulated Brillouin scattering. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1952–1955, 2016

Switchable and multi-wavelength linear fiber laser based on Fabry–Perot and Mach–Zehnder interferometers

In this manuscript, switchable and multi-wavelength erbium-doped fiber laser arrangement, based on Fabry–Perot (FPI) and Mach–Zehnder (MZI) interferometers is presented. Here, the FPI is composed by two air-microcavities set into the tip of conventional single mode fiber, this one is used as a partially reflecting mirror and lasing modes generator. And the MZI fabricated by splicing a segment of photonic crystal fiber (PCF) between a single-mode fiber section, was set into an optical fiber loop mirror that acts as full-reflecting and wavelength selective filter. Both interferometers, promotes a cavity oscillation into the fiber laser configuration, besides by curvature applied over the MZI, the fiber laser generates: single, double, triple and quadruple laser emissions with a signal to noise ratio (SNR) of 30dB. These laser emissions can be switching between them from 1525nm to 1534nm by adjusting the curvature radius over the MZI. This laser fiber offers a wavelength and power stability at room temperature, compactness and low implementation cost. Moreover the linear laser proposed can be used in several fields such as spectroscopy, telecommunications and fiber optic sensing systems.

Photonic generation of bipolar direct-sequence UWB signals based on optical spectral shaping and incoherent frequency-to-time conversion

A novel technology to obtain binary phase-coded ultrawideband (UWB) signals for direct-sequence spread-spectrum communication systems is investigated by using a cost-effective incoherent source. The bipolar encoding is performed based on an all-fiber spectrum shaper composed of two FBG arrays to tailor the optical spectrum, and a section of single-mode fiber to achieve incoherent frequency-to-time conversion. We demonstrate a 1.325-Gb/s UWB encoding system by the use of binary spreading codes of 4-chip length via computer simulations. The proposed bipolar UWB encoding technology can be applied to high-speed UWB-over-fiber communication systems.

Comparative study on a core-offset fiber temperature sensor between the faraday rotation mirror structure and the double coupling structure

A temperature sensor based on core-offset single mode fiber (SMF) and a Faraday rotation mirror (FRM) has been proposed and experimentally demonstrated in this paper. This sensor was fabricated by splicing in a section of SMF between two SMFs with a core-offset at two splicing joints. The end of the joint is connected to the FRM, which can double the sensitivity and improve the polarization state stabilization at the sensor output. The variation of the transmission spectrum of the sensor with respect to the surrounding temperature has been experimentally studied. A comparison is made between this design and a laser temperature sensor made of the same core-offset fiber utilizing a double coupling (DC) structure. The results show that, within the range of 1539.42–1553.90nm, the sensitivity of the proposed sensor is 0.89039nm/°C and in the range of 47–63°C. Additionally, the power attenuation is 2.257dB/°C. The temperature sensitivity in the SMF and FRM sensor is increased by an order of magnitude in comparison with the DC sensor. The instability and low sensitivity characteristics of a laser temperature sensor constructed with DC structure can be solved through the use of core-offset SMF and FRM.

One step method to attach gold nanoparticles onto the surface of an optical fiber used for refractive index sensing

Localized surface plasmon resonance (LSPR) has recently emerged as an efficient and powerful tool for bio-photonic applications due to its high sensitivity to refractive index changes. One technique to excite LSP is by the interaction of the evanescent wave of the light guided by an optical fiber with metallic nanoparticles deposited over the surface of the fiber. This paper proposes a novel, simple, and fast method to attach gold nanoparticles to the optical fiber surface, which can be used to construct highly sensitive refractive index sensors based on localized surface plasmon resonance. A hetero-core structured fiber, composed by a small section of single-mode fiber inserted in a multimode fiber, was coated with nanoparticles using the method proposed here. A sensor sensitivity and resolution of 765nm/RIU and ∼1×10−4RIU, respectively, were estimated over a refractive index range of 1.333–1.365. This coating method is appealing to construct optical fiber refractive index sensors since it is very simple and low cost.

Temperature Fiber Sensors Based on Mach–Zehnder Interferometer With Sturdy Structure

This paper presents a highly sensitive and in-line temperature fiber sensor based on Mach-Zehnder interferometer with material overlay. The sensor is constructed using a section of single-mode fiber sandwiched between a no-core fiber and a waist-enlarged taper and immersed in a material with high thermo-optic coefficient. The experimental results indicated that a high temperature sensitivity of 0.825 nm/°C was accomplished for surrounding material with the refractive index of ~1.45. The proposed sensor has numerous merits of in-line applications, high sensitivity, easy fabrication, simple structure, compact size, and furthermore, the structure is sturdy due to its high mechanical strength.

Compressive sensing based high-speed time-stretch optical microscopy for two-dimensional image acquisition.

In this paper, compressive sensing based high-speed time-stretch optical microscopy for two-dimensional (2D) image acquisition is proposed and experimentally demonstrated for the first time. A section of dispersion compensating fiber (DCF) is used to perform wavelength-to-time conversion and then ultrafast spectral shaping of broadband optical pulses can be achieved via high-speed intensity modulation. A 2D spatial disperser comprising a pair of orthogonally oriented dispersers is employed to produce spatially structured illumination for 2D image acquisition and a section of single mode fiber (SMF) is utilized for pulse compression in the optical domain. In our scheme, a 1.2-GHz photodetector and a 50-MHz analog-to-digital converter (ADC) are used to acquire the energy of the compressed pulses. Image reconstructions are demonstrated at a frame rate of 500 kHz and a sixteen-fold image compression is achieved in our proof-of-concept demonstration.

Ultra-high sensitivity Fabry-Perot interferometer gas refractive index fiber sensor based on photonic crystal fiber and Vernier effect.

An ultra-high sensitivity open-cavity Fabry-Perot interferometer (FPI) gas refractive index (RI) sensor based on the photonic crystal fiber (PCF) and Vernier effect is proposed and demonstrated. The sensor is prepared by splicing a section of PCF to a section of fiber tube fused with a section of single mode fiber. The air holes running along the cladding of the PCF enable the gas to enter or leave the cavity freely. The reflection beam from the last end face of the PCF is used to generate the Vernier effect, which significantly improves the sensitivity of the sensor. Experimental results show that the proposed sensor can provide an ultra-high RI sensitivity of 30899 nm/RIU. This sensor has potential applications in fields such as gas concentration analyzing and humidity monitoring.

Lateral force sensing arrangement based on an all fiber Fabry–Perot interferometer

In this work, lateral force sensing detection based on an all fiber intrinsic Fabry–Perot interferometer (IFPI) is presented. The IFPI generates several high-order reflected modes in conventional single-mode fiber (SMF), these modes were affected by lateral force distributed over a short section of SMF. Here, we analyze a fiber optic detection system based on intensity modulation reflection signal. The force is applied from 17 to 89lbsf, over a SMF section and excitation of high-order modes is analyzed. The system presents good sensitivity around 0.1dB/lbf and linear response in forward and backward direction. This system presents good mechanical strength, flexibility, and temperature-phase independent properties.

Curvature and temperature sensor based on bulge-taper structures interferometer with embedded fiber Bragg grating

A sensor head consisting of an all single-mode fiber (SMF) in-line Mach–Zehnder interferometer (MZI) with an embedded fiber Bragg grating (FBG) is proposed and experimentally demonstrated for simultaneous measurement of curvature and temperature. It is fabricated by cascading two bulge-taper fusion structures in a section of SMF including an FBG. The MZI is sensitive to fiber bending and ambient temperature with a sensitivity of −16.59 nm/m−1 in the range of 1.05 to 4.05 m−1 and 58 pm/°C in the range of 30°C to 100°C, respectively. However, the FBG is only sensitive to the latter with a sensitivity of 13 pm/°C. Simultaneous measurement of curvature and temperature is obtained and the cross-sensitivity issue can be solved. The experimental results show that the average relative error of the curvature is 0.38%, which is about 18 times better than that without temperature compensating. The average error of temperature is only 0.21°C.

Mach–Zehnder interferometer formed by a large core-offset splicing fiber for temperature and displacement measurement

A novel, versatile, compact all-fiber Mach–Zehnder interferometer (MZI) for temperature and displacement sensing was proposed and demonstrated in this paper. It was fabricated by splicing a section of single mode fiber (SMF) between two SMFs with a large core-offset at two splicing joints, which were used to excite cladding modes and couple to the fiber core. And then the interference occurred between the cladding and external substances was utilized to measure temperature and displacement. Experimental results showed that the sensitivity of temperature measurement could be up to 25.26pm/°C and the sensitivity of displacement measurement was 96.72nW/mm. In addition, because the measurement of temperature and displacement could be implemented respectively by recording the light wavelength shifts and light intensity variation, temperature and displacement could be measured simultaneously with only one sensor probe. Meanwhile, there were some other advantages of the sensor, such as simple structure, small size, high sensitivity and low cost.

Fabry-Perot cavity based on silica tube for strain sensing at high temperatures.

In this work, a Fabry-Perot cavity based on a new silica tube design is proposed. The tube presents a cladding with a thickness of ~14 μm and a hollow core. The presence of four small rods, of ~20 μm diameter each, placed in diametrically opposite positions ensure the mechanical stability of the tube. The cavity, formed by splicing a section of the silica tube between two sections of single mode fiber, is characterized in strain and temperature (from room temperature to 900 °C). When the sensor is exposed to high temperatures, there is a change in the response to strain. The influence of the thermal annealing is investigated in order to improve the sensing head performance.

Fourier Analysis Applied on MZI Transmission Spectrum for Refractive Index Measurement

An approach for surrounding refractive index (SRI) measurement is proposed and demonstrated using all fiber Mach-Zehnder interferometer (MZI) formed by fusion splicing a short section of thin-core fiber between two sections of single-mode fibers with lateral offsets. The transmission spectrum of the MZI is dominantly formed by the superposition of two cladding modes separately interference with the core mode, which correspond to two frequency components in its fast Fourier transform (FFT) spectrum, respectively. In this letter, the two frequency components are extracted to take the inverse FFT, respectively, thus we can obtain two dual-mode interference (DMI) patterns between the cladding modes and the core mode. As the SRI changes, the shifts of the two DMI patterns with SRI will be observed. Through this way, we can eliminate the influence of multiple interferences and improve the accuracy of the sensor. The approach can also be utilized with other modal interferometric sensors.

A highly sensitive Mach–Zehnder interferometric refractive index sensor based on core-offset single mode fiber

A highly sensitive refractive index (RI) sensor based on all-fiber Mach–Zehnder interferometer (MZI) was simulated and demonstrated. It was fabricated by splicing a section of single mode fiber (SMF) between two SMFs with a slight core offset at two splicing joints, which were used to excite cladding modes and couple the core mode to cladding modes. And then the interference between the core and cladding modes was utilized to measure sounding RI and the sensitivity of the sensor was enhanced by tapering fiber. Experimental results showed that the measured RI sensitivity could be up to 78.7nm/RIU in the range of 1.333–1.374. Meanwhile, the sensor has the advantages of simple structure, small size, high sensitivity and low cost.

All-fiber optical modulator based on no-core fiber and magnetic fluid as cladding**Project supported by the Natural Science Foundation of Tianjin City, China (Grant No. 13JCYBJC16100), the National Natural Science Foundation of China (Grant No. 61107035), the National Key Scientific Instrument and Equipment Development Project of China (Grant No. 2013YQ03091502), and the National Basic Research Program of China (Grant Nos. 2010CB327802

An all-fiber optical modulator, which is composed of a piece of no-core fiber spliced between two sections of single-mode fibers and uses magnetic fluid (MF) as the cladding of the no-core fiber section, is proposed and investigated experimentally. Due to the tunable refractive index and absorption coefficient of MF, the output intensity can be modulated by controlling an applied magnetic field. The dependences of the modulator’s temporal response on the working wavelength, the magnetic field strength (H), and the MF’s concentration are investigated experimentally. The results are explained qualitatively by the dynamic response process of MF under the action of a magnetic field. The findings are helpful for optimizing this kind of modulator.