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Photonic switches have attractive application prospects in optical communication data networks that require dynamic reconfiguration. Integrating optical switching devices with optical fiber, the most widely deployed photonic technology platform, can realize signal transmission and processing in practical applications. Here, we demonstrate the multilevel optical switching using the phase-change material Ge2Sb2Te5 (GST) integrated on a graded-index multimode fiber. This switching process works by exploiting the significant difference in extinction coefficient between the crystalline state and the amorphous state of the GST. Using GST to achieve the switch function, no external energy source is needed to maintain the existing state of the switch, and the device is nonvolatile. This multi-level optical switch is an all-fiber integrated device. We apply GST to the end facets of the graded-index multimode fiber by magnetron sputtering, which is a reflective structure. A pulsing scheme is used to control the optical propagation state of the optical modulation signal to realize the switching function. It can store up to 11 non-volatile reliable and repeatable levels encoded by the pump source laser with a wavelength of 1550 nm. At the same time, the switching process between states is on the order of hundreds of nanoseconds. The present experimental results demonstrate the feasibility of 11 multilevel states in the field of optical fibers commonly used in communications. It can be well coupled with the all-fiber terminal device. It also shows that the device is still applicable in the 1525 nm∼1610 nm broadband range, promising for designing future multilevel photonic switches and memory devices.

The multicore fiber beam shaping devices based on surface plasmon polaritons (SPPs) have been proposed and demonstrated. The gold film is covered on the end face of the optical fiber. An air slit is perforated in the center of each core and the gratings with a fixed period are designed on the gold film on one side of the slit to obtain a deflected beam. Multiple deflected beams based on the multicore fiber interfere and form a periodic field, where the period of the interference field is determined by the deflection angle of the beams and the spacing between the cores. The interference field of the multiple deflected beams can be used to trap the nanosphere. The Maxwell stress tensor method is used to calculate the transverse and longitudinal trapping forces on a nanosphere. The nanosphere can be stably trapped at 45 μm away from the end face of the fiber. Such an all-fiber trapping system is compact and flexible integration, and is promising for long-working-distance and multiple-particle trapping.

A proposal toward the enhancement in the sensitivity of a fiber-based surface plasma resonance (SPR) refractive index (RI) sensor is explored experimentally using a Bessel-like beam as the input source. We splice a section of single-mode fiber and a section of multimode fiber to construct the Bessel-like beam, which contains a series of concentric rings for the consistency of the resonance angle configuration to improve the performance of the SPR sensor. We fabricate a dual-truncated-cone (DTC) structure of the fiber to excite and receive the SPR signals. The larger the number of concentric rings, the higher the sensitivity. The number of concentric ring is determined by the length of the multimode fiber. When the grinding angle of the DTC-sensing probe is 15° and the length of the multimode fiber is 500 µm, the maximum testing average sensitivity is 6908.3 nm/RIU, which is more sensitive than the previous SPR sensor introduced by the Gaussian beam as the input source in multimode fibers.

Gradient metasurfaces have attracted much attention due to intriguing wavefront and polarization manipulation. Here, a bilayer gradient metasurface is constructed by use of a rectangular nanorod layer and its complementary nanoaperture. It reveals asymmetric anomalous reflection and symmetric anomalous transmission for two counter-propagating directions. The dependence of the anomalous reflection and transmission phenomena on nanostructure thickness are numerically studied in optical frequencies. The increasing metallic layer thickness of the gradient metasurface greatly enhances anomalous reflection of the left-handed circularly polarized wave (LCP) for the nanorod side and suppresses anomalous reflection for the other side. Both resonant frequencies of anomalous reflection and transmission linearly shift with the refractive index. The bilayer gradient metasurface is important for realizing wavefront modulation and optical sensing.

A novel demodulation method is presented to expand the measurement dynamic range for fiber optic strain sensors using PDH technology. The new control algorithm uses two integrators to form a 2nd order control, and the FFPI strain sensor can have a dynamic range of 20 dB/octave larger than the PID control method when the input signal frequency decreases a magnitude. A strain resolution of 4.7 pɛ Hz−1/2@10Hz, a 118 dB@10Hz dynamic range without consecution, and 158 dB with consecution is obtained. The experiment results show that the new control method can improve the sensing system’s dynamic range with the corner frequency unchanged and without the system noise level degradation.

We propose and demonstrate a novel approach to transport a strongly absorbing particle in an X-typed trajectory reciprocally in pure liquid glycerol based on a dual-beam optical fiber trap. We perform the X-typed light field by integrating a glass microsphere on the tip of a two-core fiber. The motion of the absorbing particle in pure liquid glycerol is dominated by the Δα-type photophoretic forces (FΔα). The incident laser power determines the direction of FΔα. Therefore, we may perform the reciprocating transport of the absorbing particle by changing and controlling the laser power. It is simple to manufacture the fiber probe and convenient to operate the transport of the microparticle. Our research expands the applications of absorbing particles in targeted drug delivery, biological sampling, and optically mediated particle clearing.

The spider dragline silk (SDS) has a supercontraction characteristic, which may cause the axial length of the SDS to shrink up to 50% when the SDS is wet or the relative humidity is higher than 58% RH. In this manuscript, we employ the supercontraction characteristic of the SDS to measure relative humidity. We connect two sections of a single-mode fiber (SMF) and a section of multimode fiber (MMF) with a sandwich structure to fabricate a single-mode-multimode-single-mode (SMS) interferometer. Then we fix the SDS on two SMFs to configure a bow-shaped sensing unit. The increase of environmental humidity will cause the supercontraction of the SDS, which will cause the change of the SDS length. The excellent mechanical properties of the SDS will generate a strong pulling force and change the bending of the arch, whose interference spectrum will shift correspondingly. In this way, we may perform relative humidity sensing. In the relative humidity range of 58% RH to 100% RH, the average sensitivity is as high as 6.213 nm/% RH, higher than most fiber-based humidity sensors. Compared with the traditional sensing structure with humidity-sensitive materials, the proposed sensor improves the sensitivity with environmental friendliness. The results suggest that the SDS can be used for high-sensitivity humidity sensors, and its degradability and biocompatibility also have a vast development space in biochemical sensors.

We present a high-resolution polarization crosstalk measurement method for polarization maintaining fiber (PMF) with considerable dispersion. The birefringence dispersion of the PMF severely degrades the spatial resolution of the distributed polarization crosstalk measurement. Conventional dispersion compensation methods are effective for modest birefringence dispersion coefficients (for instance, of 0.0014 ps/nm/km). We present an iterative matched filter (IMF) method to cope with the case of considerable birefringence dispersion. We measured the distributed polarization crosstalk of a PMF coil with a birefringence dispersion coefficient of 0.235 ps/nm/km. By applying the IMF method, we obtained a spatial resolution of 0.09 m at any position of the PMF (a maximum of 12.36 m without dispersion compensation).

By using a seven-core fiber (SCF), we propose and demonstrate a novel segmented detection SPR sensor, which solves two bottlenecks about the fiber SPR sensor of low sensitivity and the difficulty in the multichannel detection. The proposed sensor has ultra high sensitivity and wide detection range because of employing the segmented detection technology. Besides that, the proposed sensor employs reflection-type time division multiplexing (TDM) technology in fiber multichannel detection for the first time. We couple light into and out of the six circularly symmetric distributed cores of the seven-core fiber to realize the three channel SPR sensing and testing. This three-channel SPR sensor has the advantages of detecting biochemical or multi analytes reactions and eliminating the distractions due to temperature fluctuations or sample composition variations and adsorption of non-target molecules to the sensor surface. This SPR sensor also has the advantages of online monitoring by inserting into the blood vessel because of its small size. Furthermore, this paper has deeply researched the relationship between the refractive index of the solution to be measured, the grinding angle of the sensing channel, the sensitivity and the detection range. In this paper, we propose a novel segmented detection method which realizes the wide detection range with the wider refractive index range of 1.333~1.395 and the narrower working bandwidth of 250nm compared with the common SPR sensor, the average sensitivity and the maximum sensitivity of the sensor reach 7387.1nm/RIU and 8502.5nm/RIU respectively.

We demonstrate a novel integrated optical fiber interferometer for in-fiber optofluidic detection. It is composed of a specially designed hollow optical fiber with a micro-channel and two cores. One core on the inner surface of the micro-channel is served as sensing arm and the other core in the annular cladding is served as reference arm. Fusion-and-tapering method is employed to couple light from a single mode fiber to the hollow optical fiber in this device. Sampling is realized by side opening a microhole on the surface of the hollow optical fiber. Under differential pressure between the end of the hollow fiber and the microhole, the liquids can form steady microflows in the micro-channel. Simultaneously, the interference spectrum of the interferometer device shifts with the variation of the concentration of the microfluid in the channel. The optofluidic in-fiber interferometer has a sensitivity of refractive index around 2508 nm/RIU for NaCl. For medicine concentration detection, its sensitivity is 0.076 nm/mmolL−1 for ascorbic acid. Significantly, this work presents a compact microfluidic in-fiber interferometer with a micro-channel which can be integrated with chip devices without spatial optical coupling and without complex manufacturing procedure of the waveguide on the chips.

Biological microfibers are remarkable materials with diversity in their chemistry, structure and functions that provide a range of solutions for photonic structures. Here we proposed and demonstrated a humidity detection technique for spectral tuning of whispering gallery modes (WGMs) in a cylindrical microresonator formed by a piece of spider egg sac silk (SpEss) from Araneus Ventricosus. We launched a supercontinuum laser into the SpEss via a tapered single-mode fiber to excite WGMs. When the ambient humidity changed, the profile diameter and effective refractive index of the SpEss changed, which caused the WGM resonant dips to shift. The experimental results showed that when the relative humidity (RH) changed from 20% to 75% RH, the average testing sensitivity of the proposed sensor was 389.1 pm/%RH and the maximum testing sensitivity was 606.7 pm/%RH in the range of 60% to 75% RH. Also, the proposed SpEss-based humidity sensor showed a fast response time of 494 ms and good repeatability with fluctuations less than 8% compared with the initial test values. The SpEss-based sensor expanded the application of spider silk as a biodegradable and biocompatible material in biochemical sensing.

Although optical tweezers function well for the majority of transparent particles, the absorbing particles experience a considerably high absorption force that can destroy the stable optical traps. Photophoretic force is an alternative mechanism that can be used to trap the absorbing particles. The major difficulty that is associated with the utilization of photophoretic forces for trapping strongly absorbing particles in liquids is the presence of considerable absorption on the illuminated side; a positive photophoretic force is usually induced, thereby pushing away the absorbing particles from the high-intensity region of the laser source. Here, we demonstrate a novel principle for the optical trapping and manipulation of strongly absorbing particles by harnessing strong Δα-type photophoretic forces while suppressing their stochastic nature in pure liquid glycerol using a normal divergent Gaussian beam and a Bessel-like beam. Further, our approach expands the optical manipulation of strong absorbing particles to liquid media and provides position control over the trapped particles, including the optical transportation and pinpoint positioning of the 3-μm objects over a distance of a millimeter.

This paper presents a method to improve the dynamic range of white light interferometer (WLI) based polarization mode coupling (PMC) measurement system beyond 100 dB. The limitation of interference beat noise is overcame by analyzing in detail the inherent noises that have impacts on the detection sensitivity. An improved PMC measurement system and method are proposed for testing ultra-high polarization extinction ratio (PER) of polarization-related devices. The method can improve dynamic range dramatically through eliminating interference beat noise and enhancing the tested interference intensity simultaneously, which are verified theoretically and experimentally. In addition, a Y-junction with ~80 dB PER of LiNbO3 chip corresponding to a weak signal is tested as an application example. The results demonstrate that the high PER interferogram can be identified clearly and steadily with standard deviation 0.9 dB (3σ) @ ~80 dB. This proposed method is highly beneficial in fabrication and evaluation for polarization devices with ultra-high PER.

Efficient and controllable launching function of an optical tweezers is a challenging task. We present and demonstrate a novel single fiber optical tweezers which can trap and launch (clean) a target polystyrene (PS) microsphere (diameter~10μm) with independent control by using two wavelengths beams: 980nm and 1480nm. We employ 980nm laser beam to trap the target PS microsphere by molding the fiber tip into a special tapered-shape; and we employ 1480nm laser beam to launch the trapped PS microsphere with a certain velocity by using the thermophoresis force generated from the thermal effect due to the high absorption of the 1480nm laser beams in water. When the launching force is smaller than the trapping force, the PS microsphere will be trapped near the fiber tip, and the launching force will blow away other PS microspheres in the workspace realizing the cleaning function; When the launching force is larger than the trapping force, the trapped PS microsphere will be launched away from the fiber tip with a certain velocity and towards a certain direction, realizing the launching function. The launching velocity, acceleration and the distance can be measured by detecting the interference signals generated from the PS microsphere surface and the fiber tip end-face. This PS microsphere launching and cleaning functions expanded new features of single fiber optical tweezers, providing for the possibility of more practical applications in the micro manipulation research fields.

A white light temporal interferometric technique for measurement of the quasi-distributed birefringence dispersion (BD) in a polarization maintain (PM) device with high accuracy based on weighted least square (WLS) method is presented. It is verified theoretically and experimentally that the accuracy of WLS method and the conventional ordinary least square (OLS) method both are proportional to the signal-to-noise ratio (SNR) of interferogram, whereas the WLS method holds a higher scaling factor because it is more suitable for heteroscedastic model that has unequal error variance. The experiment results show a repeatability of ~4.6 × 10(-5) ps/nm @ 1550 nm with WLS method for 100 sets of data, and ~4.3 × 10(-4) ps/nm with OLS method, for an interferogram with SNR of 30 dB. Besides, WLS method without iterative operation is carried out by using power spectrum of interferogram as weight value. The feasibility of this technique is demonstrated by distinguishing the quasi-distributed BD of every part for a packaged Y-waveguide with two 1m-long PM pigtails.

We present an abruptly tapered twin-core fiber optical tweezers, which is fabricated by fusing and drawing the twin-core fiber. In the twin-core fiber, the two beams are guided by the tapered fiber. At the end of the fiber tip, a larger converge angle between the two beams are made due to the abrupt tapered shape, which is formed a fast divergent optical field. The microscopic particle trapping performance of this special designed tapered twin-core fiber tip is investigated. The functionality of the proposed novel twin-core fiber optical tweezers is extended since an in-fiber integrated Mach-Zehnder interferometer has been used to control orientation of the trapped particle. The distribution of the optical field emerging from the tapered fiber tip is simulated based on the beam propagation method (BPM). By using this two-beam combination technique, a strong enough gradient forces well is obtained for microscopic particles trapping in three dimensions. The abruptly tapered twin-core fiber optical tweezers is rigid and easy to handle, especially useful for building up a multi-tweezers system for trapping and manipulating micro-scale particles.