Partially coherent twisted vector vortex beam enabling manipulation of high-dimensional classical entanglement.

In this paper, we present a novel form of a partially coherent beam characterized by classical entanglement in higher dimensions. We coin the term "twisted vector vortex (TVV) beam" to describe this phenomenon. Similar to multi-partite quantum entangled states in higher dimensions, the partially coherent twisted vector vortex beam possesses distinct properties such as non-uniform polarization, vortex phase, and twist phase. Through experiments, we offer empirical evidence for these three degrees-of-freedom in the light field. The results demonstrate that the state of the light is inseparable in terms of polarization and orbital angular momentum (OAM) modes. Additionally, the twist phase introduces an additional dimension in controlling the vector vortex beam. This research reveals the possibility of new controlling dimensions in classical entanglement through the chirality of coherence within partially coherent light. Consequently, this opens up new avenues for the utilization of partially coherent light in both classical and quantum domains.

Generating a hollow twisted correlated beam using correlated perturbations.

In this study, a twisted correlated optical beam with a dark hollow center in its average intensity is synthesized by correlated correlation perturbation and incoherent mode superposition. This new hollow beam has a topological charge (TC) mode with a zero value compared with a coherence vortex that has a TC mode with a nonzero value. We transform the twisted correlated beam from solid centered to dark hollow centered by constructing a correlation between the twist factor and the spot structure parameter. Theoretical and experimental results show that twist correlation makes the random optical beam an asymmetric orbital angular momentum spectral distribution and a tunable intensity center. Controlling the correlation parameters can make the focal spot of the twisted beam a dark core when the dominant mode of the TC is still zero. The new nontrivial beams and their proposed generation method provide important technical preparations for the optical particle manipulation with low coherence environment.

Control of orbital angular momentum of optical vortex beams with complex wandering perturbations.

This work investigates how independent perturbations and cross-correlation perturbations affect optical vortex beams. Theoretical and experimental results show that both perturbations cause the intensity, average orbital angular momentum (OAM), and the OAM spectrum of the vortex beam to vary periodically with the perturbation direction, but with different periods. When the beam is subjected to independent perturbations, the average OAM changes periodically with θ in every π/2; when the beam is subjected to cross-correlation perturbations, the average OAM varies with θ in every π. The results of this work provide a method to control the OAM and regulate low-coherence vortex beams in turbulent environments.

Ultra-high sensitivity strain sensor based on biconical fiber with a bulge air-bubble.

An ultra-high sensitivity Fabry-Perot interferometer (FPI) strain sensor is proposed and experimentally demonstrated. It is composed of a biconical fiber with a bulge air-bubble at its waist. Because of the good stress concentration capability of the tapered fiber, the bulge air-bubble is easily deformed when it is stressed, resulting in an ultra-high strain sensitivity of 101.7 pm/µÉ›, which is the highest strain sensitivity among the direct wavelength interrogation-based strain sensors reported so far, to the best of our knowledge. Moreover, the proposed sensor has a low temperature sensitivity of ∼1pm/∘C; thus an extreme low temperature cross sensitivity of less than 10 nɛ/°C can be achieved.

Vernier effect of two cascaded in-fiber Mach-Zehnder interferometers based on a spherical-shaped structure.

The Vernier effect of two cascaded in-fiber Mach-Zehnder interferometers (MZIs) based on a spherical-shaped structure has been investigated. The envelope based on the Vernier effect is actually formed by a frequency component of the superimposed spectrum, and the frequency value is determined by the subtraction between the optical path differences of two cascaded MZIs. A method based on band-pass filtering is put forward to extract the envelope efficiently; strain and curvature measurements are carried out to verify the validity of the method. The results show that the strain and curvature sensitivities are enhanced to -8.47 pm/µÎµ and -33.70 nm/m-1 with magnification factors of 5.4 and -5.4, respectively. The detection limit of the sensors with the Vernier effect is also discussed.

Saturable absorber based on a single mode fiber - graded index fiber - single mode fiber structure with inner micro-cavity.

An Er-doped mode-locked fiber laser with a saturable absorber based on single mode - graded index multimode - single mode fiber (SMF-GIMF-SMF) with inner micro-cavity is demonstrated. The modulation depth of the saturable absorber was measured to be 1.9% when the SMF-GIMF-SMF structure is bent to a certain state. Such a simple saturable absorber enables the mode-locking operation in a ring Er-doped fiber laser and ultrafast pulses with pulse energy of 0.026 nJ and pulse width of 528 fs at the fundamental repetition rate of 14.34 MHz can be generated. In addition, the harmonic mode-locking operation can also be achieved.

Stretched graded-index multimode optical fiber as a saturable absorber for erbium-doped fiber laser mode locking.

A novel mode-locking method based on the nonlinear multimode interference in the stretched graded-index multimode optical fiber (GIMF) is proposed in this Letter. The simple device geometry, where the light is coupled in and out of the stretched GIMF via single-mode fibers, is demonstrated to exhibit the temporal intensity discrimination required for mode locking. The nonlinear saturable absorber (SA) characteristics of the device are controllable by simply adjusting the strength of the stretching applied. The modulation depth of the device, which consists of ∼23.5 cm GIMF, is tuned from 10.37% to 22.27%. Such a simple SA enables the wavelength-switchable mode-locking operation in a ring Er-doped fiber laser, and ultrafast pulses with a pulse width of 506 fs at 1572.5 nm and 416 fs at 1591.4 nm were generated. The versatility and simplicity of the SA device, together with the possibility of scaling the pulse energy, make it highly attractive in ultrafast photonics.

PDMS-coated fiber volatile organic compounds sensors.

The functionality of poly(dimethylsiloxane) (PDMS)-based interferometric fiber sensors for volatile organic compounds (VOCs) detection is investigated and experimentally demonstrated. Two interferometric configurations are considered in this work, namely Fabry-Perot (FP) and Sagnac interferometers (SI). Both sensors are functionalized with a thin layer of VOC-sensitive polymer: PDMS, whose degree of swelling varies as a function of VOC concentrations. This swelling effect will result in an optical path length and birefringence modulation for FP and SI sensors, respectively. In this paper, the two common VOCs, ethanol and 2-propanol, were detected by the proposed sensor and the inverse matrix method was used to differentiate the VOC in gas mixture.

FOXD3 suppresses tumor growth and angiogenesis in non-small cell lung cancer.

The transcription factor forkhead box D3 (FOXD3), widely studied as a transcriptional repressor in embryogenesis, participates in the carcinogenesis of many cancers. However, the expression pattern and role of FOXD3 in non-small cell lung cancer (NSCLC) have not been well characterized. We report that FOXD3 is significantly downregulated in NSCLC cell lines and clinical tissues. FOXD3 overexpression significantly inhibits cell growth and results in G1 cell cycle arrest in NSCLC A549 and H1299 cells. In a xenograft tumor model, FOXD3 overexpression inhibits tumor growth and angiogenesis. Remarkably, expression of vascular endothelial growth factor (VEGF) was reduced in FOXD3 overexpression models both in vitro and in vivo. These findings suggest that FOXD3 plays a potential tumor suppressor role in NSCLC progression and represents a promising clinical prognostic marker and therapeutic target for this disease.

Preparation and SERS Study of Silver Microstructures with Dendritic Shape.

In the surface ehanced Raman scattering (SERS) technology, not only to improve the making process of SERS substrates, to be fast and easily, but also to enhance the SERS enhance factor, an easy replacement reaction between zinc and silver nitrate solution has been adopted to prepare silver micro-structures SERS-active substrate. The silver micro-substrates have many advantages. These substrates have good stability, well preservation, an easy making method and a fast making process. The surface profile of the silver microparticles is investigated by scanning electron microscope (SEM). The silver microstructures are dendritic shape in a symmetrical fashion with symmetrical distribution. When the time of the replace reaction is 40, 50 and 60 s, respectively, the average lengths of "trunks" in the silver dendritic microsubstractes are about 3, 5 and 10 µm, and the lengths of the "branches" are about 700 nm, 2 µm and 3 µm, respectively. The result shows that the longer time the replacement reaction takes, the longer lengths of the "trunks" and "branches" in the silver dendritic microsubstractes become. With the time of replace reaction increasing, the "trunk" and "branch" in the silver dendritic microsubstractes grow longer and a large amount of nano-level "leaves" grow out from the "branches" of the silver dendritic microsubstractes, so the silver micro size dendrates have nano level structure on surface. In order to investigate the SERS-active substrates application in SERS, a Fourier transform Raman spectrograph with a 1 064 nm laser wavelength is used to measure the SERS spectra. And good SERS spectra have been obtained by using dendritic silver microsubstrates on the silicon chip as a SERS substract, and Rhodamine 6G (R6G) as a molecule probe. It is found that the silver micro-substrates have good Raman characteristics. And comparing these SERS spectra, it gets the conclution that the spectra with best SERS enhance effect are obtained when R6G is obsorbed on the silver dendritic micro-substractes whose preparing time is 40s, and at that time, the analytical enhancement factor for SERS signals is approximately 10(3). And when the silicon ships are dealed with surfactants Polyvinylpyrrolidone (PVP) and keeping the other conditions the same as before, the SERS enhance effect of the spectra becomes better, and the enhancement factor turn to be approximately 10(4). What's more, the silver microstructures can be preserved several monthes under deionized water and the repeatment of the expriment result is well in general.

Reflective long-period fiber grating-based sensor with Sagnac fiber loop mirror for simultaneous measurement of refractive index and temperature.

In this paper, we propose a reflective long-period grating-based sensor with a Sagnac fiber loop mirror (SFLM) for simultaneous measurement of refractive index (RI) and temperature. By cascading the SFLM to the end of a long-period fiber grating (LPFG), the LPFG works as a reflection operation, which is convenient in some applications. Further, the SFLM and the LPFG have different sensitivities to RI and temperature. As a result, RI and temperature measurement can be simultaneously achieved by monitoring the wavelength shifts of the LPFG and the SFLM's dips in the reflection spectrum. Experimental results show that the temperature sensitivity can reach 1.533 nm/°C, and the RI sensitivity is from 16.864 nm/RIU (refractive index unit) to 113.142 nm/RIU when the RI range is from 1.333 to 1.430. The application for 40 km long-distance RI and temperature measurement shows that the sensor has potential application in long-distance sensing.

Compact micro-displacement sensor with high sensitivity based on a long-period fiber grating with an air-cavity.

We proposed and experimentally demonstrated a compact micro-displacement sensor with high sensitivity based on a long-period fiber grating (LPG) with an air-cavity. The sensor head is obtained by composing an air-cavity with the ends of a LPG and a single mode fiber (SMF). The wavelength shift of the LPG has a linear relationship with the length of the air gap which agrees well with the theoretical analysis. The experimental results show that the sensitivity is ~0.22 nm/µm within the micro-displacement range of 0 to 140 µm.

Phenomenon in an alcohol not full-filled temperature sensor based on an optical fiber Sagnac interferometer.

An alcohol not full-filled high-birefringence photonic crystal fiber (HiBi-PCF) temperature sensor based on an optical fiber Sagnac interferometer (OFSI) is demonstrated and investigated in detail. A new phenomenon that the resonant dip wavelengths of the temperature sensor blueshift with temperature increasing is observed, which is contrary to that of the previously reported alcohol filled HiBi-PCF OFSI temperature sensor. By considering the influences of the group birefringence and the thermo expansion of alcohol, this phenomenon is explained very well. The temperature sensitivity of the proposed sensor is about -1.17 nm/°C and is only one-sixth of that of the alcohol full-filled HiBi-PCF OSFI.

Partially liquid-filled hollow-core photonic crystal fiber polarizer.

A compact fiber polarizer is demonstrated by the filling of selected air holes of a hollow-core photonic crystal fiber (PCF) with a liquid. The liquid-filling results in an asymmetric waveguide structure, leading to a large polarization dependent loss. A 6 mm long ethanol-filled PCF exhibits a polarization extinction ratio of ∼18 dB over a wavelength range from 1480 nm to 1600 nm.

High-sensitivity temperature sensor based on an alcohol-filled photonic crystal fiber loop mirror.

A compact temperature sensor based on a fiber loop mirror (FLM) combined with an alcohol-filled high-birefringence photonic crystal fiber (PCF) is proposed and experimentally demonstrated. The output of the FLM is an interference spectrum with many resonant dips, of which the wavelengths are quite sensitive to the change of the refractive index of the filled alcohol for the interference of the FLM. Simulation analysis predicts a high temperature sensitivity, and experimental results show it reaches up to 6.6 nm/°C for the 6.1-cm-long PCF used in the FLM.

[Measurement of refractive index with a PM-LPG based Sagnac loop sensor].

By inscribing a long-period fiber grating (LPG) on a polarization-maintaining fiber (PMF), a fiber Sagnac loop sensor for simultaneous measurement of refractive index and temperature has been proposed and demonstrated. The LPG was fabricated on the PMF by using a CO2 laser, and then inserted into a fiber loop formed by using a normal single-mode fiber coupler. One of the transmission minimum of the Sagnac loop sensor was measured, whose wavelength varied with temperature and the intensity changed with refractive index. Temperature sensitivity of -0.654 nm x degrees C(-1) and refractive sensitivity of 49.9 dB x RIU(-1) have been achieved. The sensor system shows advantages of small size and low cost, and owns a good application prospect.

Modeling of PCF with multiple reciprocity boundary element method.

The multiple reciprocity boundary element method (MRBEM) is applied to the modeling of Photonic Crystal Fiber (PCF). With the MRBEM, the Helmholtz equation is converted into an integral equation using a series of higher order fundamental solutions of the Laplace equation. It is a much more efficient method to analyze the dispersion, birefringence and nonlinearity properties of PCFs compared with the conventional direct boundary element method (BEM).

Multipoint relative humidity measurement by polyvinyl alcohol-coated Fresnel reflection-based optical fiber sensors with an array-waveguide grating.

A simple multipoint humidity measurement by polyvinyl alcohol (PVA)-coated Fresnel reflection-based optical fiber sensors with an Array-Waveguide Grating (AWG) is proposed and demonstrated. Every channel end of the AWG is split as a vertical planar surface, and then is coated with a layer of a PVA whose refractive index is sensitive to moisture. The reflection intensity for each channel will change with its surrounding humidity, since the optical fiber interface's Fresnel reflection is affected strongly by the refractive index difference of the interface two sides. Multiplexing is achieved by the AWG with 16 channels, in which 15 channels can be used as sensing heads when they are coated with a layer of PVA and the left one is used as a reference channel. The experimental setup is simple and easy to handle. Experimental results show that the proposed Fresnel reflection-based optical fiber sensor for multipoint humidity measurement works well and the average sensitivity is 0.135 dB∕% relative humidity (RH) within the measurement range of 30%-80% RH.

Simultaneous measurement of refractive index and temperature based on intensity demodulation using matching grating method.

A solution refractive index (SRI) and temperature simultaneous measurement sensor with intensity-demodulation system based on matching grating method were demonstrated. Long period grating written in a photonic crystal fiber (LPG-PCF), provides temperature stable and wavelength dependent optical intensity transmission. The reflective peaks of two fiber Bragg gratings (FBGs), one of which is etched then sensitive to both SRI and temperature, another (FBG2) is only sensitive to temperature, were located in the same linear range of the LPG-PCF's transmission spectrum. An identical FBG with FBG2 was chosen as a matching FBG. When environments (SRI and temperature) change, the wavelength shifts of the FBGs are translated effectively to the reflection intensity changes. By monitoring output lights of unmatching and matching paths, the SRI and temperature were deduced by a signal processing unit. Experimental results show that the simultaneous refractive index and temperature measurement system work well. The proposed sensor system is compact and suitable for in situ applications at lower cost.

Multiplex and simultaneous measurement of displacement and temperature using tapered fiber and fiber Bragg grating.

A simple method to work out the multiplexing of tapered fiber based sensors is proposed and demonstrated. By cascading a tapered fiber with a fiber Bragg grating (FBG), the sensor head is provided with a wavelength identification, different FBGs provide the sensor heads with different reflective peaks and they can be distinguished in optical spectrum. By compositing several such sensor heads with a multi-channel beam splitter, a star-style topological structure sensor for multipoint sensing is achieved. At the same time, the output intensity at the peak wavelength is sensitive to one external physical parameter applied on the related FBG-cascaded tapered fiber and the central wavelength of the peak is only sensitive to temperature, so that that parameter and temperature can be measured simultaneously. A sensor for dual-point measurement of the displacement and temperature simultaneously is experimentally demonstrated by using a 2 × 2 coupler in this paper. Experiment results show that the sensor works well and the largest sensitivities reach to 0.11 dB/µm for displacement in the range of 0-400 µm, and ∼0.0097 nm/°C for temperature between 20 °C and 70 °C.