Fiber-Optic Point-Based Sensor Using Specklegram Measurement.

Here, we report a fiber-optic point-based sensor to measure temperature and weight based on correlated specklegrams induced by spatial multimode interference. The device is realized simply by splicing a multimode fiber (MMF) to a single-mode fiber (SMF) with a core offset. A series of experiments demonstrates the approximately linear relation between the correlation coefficient and variation. Furthermore, we show the potential applications of the refractive index sensing of our device by disconnecting the splicing point of MMF and SMF. A modification of the algorithm in order to improve the sensitivity of the sensor is also discussed at the end of the paper.

Versatile hybrid plasmonic microfiber knot resonator.

A planar, all-optical fiber polarizer-based device based on a hybrid plasmonic microfiber knot resonator (HPMKR) is demonstrated in this Letter. A microfiber knot resonator (MKR) can be flexibly attached to the gold film, which forms the hybrid plasmonic mode with high propagation loss. Therefore, the device can be used not only as a broadband polarizer, but also as a high-quality resonator by tuning the geometry of the MKR. The polarizer has an extinction ratio of more than 15 dB ranging from 1200 to 1600 nm, and the Q-factor is more than 52,000 for one polarization state. For a chosen polarization, the resonator has an extinction ratio of nearly 15 dB, even though the diameter of the microfiber is more than 5 µm, which is unattainable for a normal MKR. By further optimizing and packaging, the device can be utilized as a weight sensor, with a sensitivity of 18.28 pm/g (51.2 pm/kPa) for the cavity resonant wavelength. Further, a vibration sensor on a HPMKR structure for detecting vibration from tens of hertz to several kilohertz is demonstrated.

Orbital angular momentum (OAM) conversion and multicasting using N-core supermode fiber.

We propose and numerically demonstrate a conversion and multicasting scheme of orbital angular momentum (OAM) states by using N-core supermode fiber (NCSF), where the topological charges of converted OAM states mainly depend on the injected OAM state and the number of fiber cores. The conversion efficiency (CE) of the converted OAM states could be optimized by properly designing the fiber structure. Take N = 6 as an example, ~37% CE could be achieved at telecom bands. Moreover, even for a fabricated NCSF, the CE could be dynamically changed by stretching the fiber or by adjusting the refractive index of the fiber cores through external control of the environmental conditions. Meanwhile, OAM multicasting could also be realized in the designed NCSF. The crosstalk between the multicasted OAM channels and their neighboring ones are assessed to be less than -30 dB. The proposed fiber-based OAM conversion and multicasting system is compatible with the existing optical fiber communication systems, showing potential applications in the future.

"Hot-wire" microfluidic flowmeter based on a microfiber coupler.

Using an optical microfiber coupler (MC), we present a microfluidic platform for strong direct or indirect light-liquid interaction by wrapping a MC around a functionalized capillary. The light propagating in the MC and the liquid flowing in the capillary can be combined and divorced smoothly, keeping a long-distance interaction without the conflict of input and output coupling. Using this approach, we experimentally demonstrate a "hot-wire" microfluidic flowmeter based on a gold-integrated helical MC device. The microfluid inside the glass channel takes away the heat, then cools the MC and shifts the resonant wavelength. Due to the long-distance interaction and high temperature sensitivity, the proposed microfluidic flowmeter shows an ultrahigh flow rate sensitivity of 2.183 nm/(µl/s) at a flow rate of 1 µl/s. The minimum detectable change of the flow rate is around 9 nl/s at 1 µl/s.

Microfiber-coupler-assisted control of wavelength tuning for Q-switched fiber laser with few-layer molybdenum disulfide nanoplates.

Based on the liquid exfoliated method, we obtained the few-layer molybdenum disulfide (MoS2) nanoplates solution. By thermal evaporation method, we directly deposited MoS2 thin film onto the facet of a fiber patch cord. The modulation depth of the film is as high as 29%, and a Q-switched fiber laser was achieved. We also provided a new method to continuously tune the output laser with a tuning sensitivity of ∼5.5 nm/(1% strain) by controlling the cavity loss with a strained microfiber coupler (MFC).

Differential twin receiving fiber-optic magnetic field and electric current sensor utilizing a microfiber coupler.

A magnetic field and electric current meter is proposed based on a differential twin receiving microfiber coupler (MC) sensor. The sensor is fabricated by bonding a MC and an aluminium (Al) wire together. With the small diameter of several micrometers, the output power at each port of the coupler shows high sensitivity to the distortion of Al wire from the Lorentz force induced by the magnetic field or the thermal expansion caused by the electric current. The ratio of the difference to the sum of the output signals from the two output ports can be used to eliminate the variation in the sensitivity. Using our proposed sensor, we measured a magnetic field sensitivity of ~0.0496 mT(-1), current sensitivity of ~1.0899 A(-1) without any magnetic field, and good repeatability are also shown in this paper.

A miniature reflective micro-force sensor based on a microfiber coupler.

A compact highly sensitive microfiber coupler based reflective micro-force sensor is presented. The device is fabricated by fusing two twisted optical fibers and then connecting two of the pigtails to form a Sagnac loop. The sensor has a high force sensitivity of ~3754 nm/N which is three orders of magnitude larger than traditional optical fiber force sensors, and a low detection limit of ~1.6 µN. The good repeatability is also shown in this paper.