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We present a reconfigurable ultra-broadband mode converter, which consists of a two-mode fiber (TMF) and pressure-loaded phase-shifted long-period alloyed waveguide grating. We design and fabricate the long-period alloyed waveguide gratings (LPAWG) with SU-8, chromium, and titanium via the photo-lithography and electric beam evaporation technique. With the help of the pressure loaded or released from the LPAWG onto the TMF, the device can realize reconfigurable mode conversion between the LP01 mode and the LP11 mode in the TMF, which is weak sensitive to the state of polarization. The mode conversion efficiency larger than 10 dB can be achieved with operation wavelength range of about 105 nm, which ranges from 1501.9 nm to 1606.7 nm. The proposed device can be further used in the large bandwidth mode division multiplexing (MDM) transmission and optical fiber sensing system based on few-mode fibers.

A compact fiber cascaded structure for simultaneous measurement of curvature and temperature based on Fabry-Perot (FP) interference and anti-resonant (AR) mechanism is designed and experimentally demonstrated. The proposed structure is manufactured by sandwiching a segment of hollow core fiber (HCF) with large inner diameter and suitable length between two segments of single mode fibers (SMFs). Three sample sensors were fabricated with different HCF lengths. With theoretical analysis and experimental verifications, an HCF length of 1197 μm was selected for curvature and temperature experiments. The reflection fringes based on FP interference and transmission envelopes based on AR mechanism can be monitored to measure curvature and temperature variations at the same time. From experimental results, the sensitivities of curvature based on AR mechanism and FP interference are 0.2345 nm/m -1 and -0.1021 nm/m -1 , and those of sensitivities of temperature are 0.0172 nm/℃ and 0.0017 nm/℃, respectively. Therefore, the different responses in curvature and temperature based on two mechanisms enable the proposed structure to simultaneously measure curvature and temperature.

An all-fiber Mach–Zehnder interferometer (MZI) using ring core few-mode fiber (RC-FMF) for curvature sensing is proposed and experimentally demonstrated. The MZI was fabricated by splicing a segment of RC-FMF between two pieces of single-mode fiber (SMF). With the benefit of a RC of the central axis of the RC-FMF, the sensor is more sensitive to curvature compared to other fiber sensors based on ordinary SMF or FMF. Curvature measurement can be achieved by monitoring the wavelength shift of interference dips. Experimental results have shown that the sensitivity of curvature sensing can reach up to − 4.370 n m / m − 1 , within the range of 1.199 − 1.549 m − 1 . Also, the temperature sensing characteristics of the sensor are measured, and the maximum temperature sensitivity is 57.6 pm/°C, ranging from 25°C to 45°C. The proposed MZI sensor has excellent potential for curvature measurement of building structural health monitoring, bridge engineering, and more.

We present a study of all-optical light manipulation arising in a graphene-embedded side-polished fiber (SPF) with a Norland Optical Adhesives (NOA)-coated structure. With the help of the Pauli blocking effect, such an all-fiber device serves to manage the loss of transverse-electric-polarized light when the control light and the signal light are polarized along the direction parallel to the graphene surface. The insertion loss of this device can be effectively reduced with the NOA coating. An enhanced interaction between the graphene and the propagated light can be achieved via the strong evanescent field of the SPF and longer interaction length. This results in effective all-optical manipulation of light with a modulation depth of 10.4 dB (or modulation efficiency of ∼91%) and a modulation slope of ∼1.3, where the required control power is only about 14 dBm. The device has broadband operation wavelength. The insertion loss for both the signal light and the control light are only about 0.6 dB. The experimental results are well-fitting with the simulation study. Such an all-fiber device has the potential for all-optical signal processing.