Zhilin Xu

Simultaneous measurement of refractive index and temperature using multimode microfiber-based dual Mach–Zehnder interferometer

A multimode microfiber (MMMF)-based dual Mach-Zehnder interferometer (MZI) is proposed and demonstrated for simultaneous measurement of refractive index (RI) and temperature. By inserting a section of MMMF supporting a few modes in the sensing arm of the MZI setup, an inline interference between the fundamental mode and the high-order mode of MMMF, as well as the interference between the high-order mode of MMMF and the reference arm, i.e., the dual MZI, is realized. Due to different interference mechanisms, the former interferometer achieves RI sensitivity of 2576.584  nm/RIU and temperature sensitivity of -0.193  nm/°C, while the latter one achieves RI sensitivity of 1001.864  nm/RIU and temperature sensitivity of 0.239  nm/°C, demonstrating the ability to attain highly accurate multiparameter measurements.

Experimental demonstration of large capacity WSDM optical access network with multicore fibers and advanced modulation formats

Towards the next generation optical access network supporting large capacity data transmission to enormous number of users covering a wider area, we proposed a hybrid wavelength-space division multiplexing (WSDM) optical access network architecture utilizing multicore fibers with advanced modulation formats. As a proof of concept, we experimentally demonstrated a WSDM optical access network with duplex transmission using our developed and fabricated multicore (7-core) fibers with 58.7km distance. As a cost-effective modulation scheme for access network, the optical OFDM-QPSK signal has been intensity modulated on the downstream transmission in the optical line terminal (OLT) and it was directly detected in the optical network unit (ONU) after MCF transmission. 10 wavelengths with 25GHz channel spacing from an optical comb generator are employed and each wavelength is loaded with 5Gb/s OFDM-QPSK signal. After amplification, power splitting, and fan-in multiplexer, 10-wavelength downstream signal was injected into six outer layer cores simultaneously and the aggregation downstream capacity reaches 300 Gb/s. -16 dBm sensitivity has been achieved for 3.8 × 10-3 bit error ratio (BER) with 7% Forward Error Correction (FEC) limit for all wavelengths in every core. Upstream signal from ONU side has also been generated and the bidirectional transmission in the same core causes negligible performance degradation to the downstream signal. As a universal platform for wired/wireless data access, our proposed architecture provides additional dimension for high speed mobile signal transmission and we hence demonstrated an upstream delivery of 20Gb/s per wavelength with QPSK modulation formats using the inner core of MCF emulating a mobile backhaul service. The IQ modulated data was coherently detected in the OLT side. -19 dBm sensitivity has been achieved under the FEC limit and more than 18 dB power budget is guaranteed.

Microfiber-Based Inline Mach–Zehnder Interferometer for Dual-Parameter Measurement

An approach to realizing simultaneous measurement of refractive index (RI) and temperature based on a microfiber-based dual inline Mach-Zehnder interferometer (MZI) is proposed and demonstrated. Due to different interference mechanisms, as one interference between the core mode and the lower order cladding mode in the sensing single-mode fiber and the other interference between the fundamental mode and the high-order mode in the multimode microfiber, the former interferometer achieves RI sensitivity of -23.67 nm/RIU and temperature sensitivity of 81.2 pm/°C, whereas those of the latter are 3820.23 nm/RIU, and -465.7 pm/°C, respectively. The large sensitivity differences can provide a more accurate demodulation of RI and temperature. The sensor is featured with multiparameters measurement, compact structure, high sensitivity, low cost, and easy fabrication.

Investigation of temperature sensing characteristics in selectively infiltrated photonic crystal fiber.

In this paper, we investigate and experimentally demonstrate the influences of distance between the silica core and the glycerin core of a selectively glycerin-infiltrated photonic crystal fiber (PCF) on the mode characteristics, as well as the temperature sensitivity. By comparing the simulation and experiment results of three single-void glycerin-infiltrated PCFs with the glycerin core being one period, two periods and three periods away from the silica core respectively, it reveals that the smaller distance between the silica core and the glycerin core does not affect the modes indices, but increases the intensities of modes in the glycerin core and thus enhances the temperature sensitivity. Consequently, the temperature sensitivity can be controlled and tuned by appropriately designing the structure parameters of glycerin-infiltrated PCF. Besides, the highest temperature sensitivity up to -3.06nm/°C is obtained in the experiment as the glycerin core is nearest to the silica core. This work provides insights into the design and optimization of the liquid-infiltrated PCF for sensing applications.

Graphene-Assisted Microfiber for Optical-Power-Based Temperature Sensor

Combined the large evanescent field of microfiber with the high thermal conductivity of graphene, a sensitive all-fiber temperature sensor based on graphene-assisted micro-fiber is proposed and experimentally demonstrated. Microfiber can be easily attached with graphene due to the electrostatic force, resulting in an effective interaction between graphene and the evanescent field of microfiber. The change of the ambient temperature has a great influence on the conductivity of graphene, leading to the variation of the effective refractive index of microfiber. Consequently, the optical power transmission will be changed. The temperature sensitivity of 0.1018 dB/°C in the heating process and 0.1052 dB/°C in the cooling process as well as a high resolution of 0.0098 °C is obtained in the experiment. The scheme may have great potential in sensing fields owing to the advantages of high sensitivity, compact size, and low cost.

Optical chaos and hybrid WDM/TDM based large capacity quasi-distributed sensing network with real-time fiber fault monitoring.

Optical chaos and hybrid WDM/TDM based large capacity quasi-distributed sensing network with real-time fiber fault monitoring is proposed and proof-of-concept demonstrated. The multiplexing capacity can promisingly reach to 512.

Wideband Microfiber Fabry–Pérot Filter and Its Application to Multiwavelength Fiber Ring Laser

A microfiber Fabry-Pérot (MFP) filter consisting of two microfiber Sagnac loop mirrors as the reflectors and a section of microfiber as the cavity is proposed and fabricated. Owing to the high coupling efficiency induced by the large evanescent field of the microfiber, a broadband comb spectrum with high extinction ratio and flat amplitude can be obtained. The MFP with the extinction ratio of 15 dB as well as the free spectrum range of 0.18 nm is fabricated by bending and twisting a microfiber tapered from a single mode fiber. Consequently, the MFP is applied to an erbium-doped fiber ring laser as the wavelength filter. Assisted by a section of highly nonlinear fiber to suppress the mode competition, 42-wavelength lasing oscillations are achieved at room temperature.

Highly sensitive temperature sensor based on D-shaped microfiber with high birefringence

A high sensitive temperature sensor based on D-shaped microfiber with high birefringence is proposed and demonstrated. In order to obtain D-shaped microfiber, we polish a single mode fiber (SMF) and then taper down the polished region into micrometer size. By utilizing Sagnac loop interferometer, we achieve high refractive index (RI) sensitivity of 9951nm/RIU. Further, we realize temperature detection assisted by sucrose solution with high thermo-optic coefficient. Experimental results demonstrate high temperature sensitivity up to -0.98921nm/°C within the range of 22°C-60°C. The sensor is featured with high sensitivity, compact structure and easy fabrication.

Volume Strain Sensor Based on Spectra Analysis of In-Fiber Modal Interferometer

An optical in-fiber modal interferometer-based volume strain sensor for earthquake prediction is proposed and experimentally demonstrated. The sensing element is formed by wrapping a multimode-singlemode-multimode fiber structure onto a polyurethane hollow column. Due to the modal interference between the excited guided modes in the fiber, strong interference pattern could be observed in the transmission spectrum. Theoretical analysis verifies that the resonant wavelength shifts as a result of the volume strain variation caused by the column deformation with square root relationship. Sensitivity > 3.93 p, / με within the volume strain ranging from 0 to 1300 με is also experimentally demonstrated. By taking the response of bidirectional change of volume strain and the sluggish character of the employed sensing material into consideration, the sensing system presents good repeatability and stability.

Highly sensitive strain sensor based on helical structure combined with Mach-Zehnder interferometer in multicore fiber

Optical fiber sensors for strain measurement have been playing important roles in structural health monitoring for buildings, tunnels, pipelines, aircrafts, and so on. A highly sensitive strain sensor based on helical structures (HSs) assisted Mach-Zehnder interference in an all-solid heterogeneous multicore fiber (MCF) is proposed and experimentally demonstrated. Due to the HSs, a maximum strain sensitivity as high as −61.8 pm/με was experimentally achieved. This is the highest sensitivity among interferometer-based strain sensors reported so far, to the best of our knowledge. Moreover, the proposed sensor has the ability to discriminate axial strain and temperature, and offers several advantages such as repeatability of fabrication, robust structure and compact size, which further benefits its practical sensing applications.