Shao-cheng Yan

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.

Optical electrical current sensor utilizing a graphene-microfiber-integrated coil resonator

A graphene-based electrical current sensor is proposed utilizing a microfiber coil resonator. Monolayer graphene sheet with a large sheet resistance is transferred onto the surface of a glass capillary rod. A microfiber is spirally wrapped around the graphene sheet to form a coil resonator. Heat generated from electrical current shifts the resonant wavelength because of the thermal effect in the microfiber resonator. The sensor exhibits a very good performance with a high sensitivity of 67.297 μm/A2, which is two orders of magnitude higher than that reported earlier. Our results show that microfiber-graphene-integrated devices have great potential for miniature and highly sensitive fiber sensors for monitoring electrical current.

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.

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).

A Fiber Laser Using Graphene-Integrated 3-D Microfiber Coil

We demonstrate a state variable fiber pulse laser based on a graphene-integrated microfiber device. A 3-D microfiber coil integrated with graphene acts as a polarization-sensitive saturable absorber. By adjusting the polarization controllers, stable Q-switched pulses and mode-locked rectangular pulses are observed. To our knowledge, this is the first study conducted to achieve switching between rectangular pulses and Q-switched pulses while keeping the pump power constant. The rectangular pulses have a pulsewidth and repetition rate of ~10 ns and ~940 kHz, respectively, and the Q-switched pulses have a pulsewidth and repetition rate of ~40 μs and ~4.8 kHz, respectively.

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.

Microfluidic flowmeter based on long-period fiber grating coated with few-layer graphene

A microfluidic flowmeter is proposed based on graphene integrated “hot-wire” structure. A long-period fiber grating (LPFG) is written in a single mode fiber by CO2 laser to excite the higher-order mode. Graphene is coated around the grating to absorb the higher-order mode and generate the heat. The fiber is sealed into a home-made tube. When the microfluid flows through the graphene, the heat is taken away and the output spectrum of the fiber grating would shift. The flowmeter is promising for the future microfluidic detection.

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.

A high-sensitivity microfluidic flowmeter based on microfiber coupler

In this paper, we utilize a microfiber coupler (MFC) to realize the measurement of the microfluidic flow rate. A glass capillary is chosen as the microfluidic channel. The capillary is coated with gold film. The MFC is wrapped around the gold film which is to heat the device. One kind of UV adhesive is selected to package the device and isolate it from the ambient. The flow rate of the microfluidics is determined by the wavelength shift of the MFC. The flowmeter shows a very high sensitivity of 0.82 nm/(µl/s) when the microfluidic flow rate is 1 µl/s.

Applications in mechanics of microfiber coupler

In this paper, we demonstrate one kind of fibre-optic device - microfiber coupler (MFC). Spectral response to the micro-force axially is recorded in the experiment. Besides, utilizing the home-made MFC, we propose a high-sensitivity Ampere force based magnetic field meter. We believe more applications in mechanics of the MFC will appear in the near future.