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van der Waals heterostructures of two-dimensional (2D) materials have attracted considerable attention due to their flexibility in the design of new functional devices. Despite numerous studies on graphene/2D semiconductor heterostructures, their optoelectronic applications are significantly hindered because of several disadvantages, such as large band gaps and chemical instability. In this work, we demonstrate the fabrication of graphene/S-doped InSe heterostructure photodetectors with excellent photoresponse performance, and this is attributed to the moderate band gap and band gap engineering by element doping of InSe as well as the high carrier mobility of graphene. In particular, the graphene/InSe0.9S0.1 device achieves an ultrahigh photoresponsivity of ∼4.9 × 106 A W−1 at 700 nm and an EQE of 8.7 × 108%, and it exhibits broadband photodetection (visible to near-infrared). More importantly, by virtue of the interaction between n-type graphene arising from the influence of h-BN as a dielectric layer and S-doped InSe with a high work-function, our devices always exhibited positive photocurrent when the polarity of the gate voltage is adjusted, and is different from that the previously reported graphene/2D semiconductor photodetectors. This work not only provides a promising platform for highly efficient broadband photodetectors but also sheds light on tuning the optoelectronic performance through band gap engineering and designing novel heterostructures-based various 2D materials.

The influence of the linear birefringence on magneto-optical property measurement for optical fibers is investigated theoretically and experimentally. The evolution of polarization in fibers is simulated by the Jones matrix. To verify this theoretical model, a magneto-optical system is built to measure the input azimuth, output azimuth and ellipticity. The Faraday rotation of spun fibers with different pitches is measured. The Verdet constant increases, while the linear birefringence decreases as the pitch becomes smaller. For spun fibers with 1 mm pitch, the Verdet constant can be enhanced by about 20.7% at 660 nm, compared with that of the unspun fiber. The results indicate that smaller linear birefringence can provide more accurate Faraday rotation measurement.

Black phosphorus (BP) is an exciting material that possesses excellent electronic properties, such as high mobility, and thickness-dependent, easily tunable band gap, making it a promising candidate for applications in optoelectronics, energy storage and nano-photonics. However, the instability of mechanically exfoliated BP thin films under oxygen and humidity conditions is still a bottleneck in its practical applications. Herein, we choose a facile way to effectively protect BP by selectively adsorbing graphene quantum dots (GQDs) on its surface as a protective layer. This strategy can prevent the degradation of the thin BP layer in the presence of oxygen and humidity. We systematically investigated the impact of GQDs absorption on BP surface via atomic force microscopy, Raman spectroscopy, transmission electron microscopy and electrical measurements. Our results show that GQDs could effectively protects the BP surface from exposure to atmospheric oxidants, resulting in significantly improved stability along with enhanced mobility and on/off ratio of corresponding field-effect transistors (FETs). Importantly, the electrical properties of optimized FETs could be retained for over 24 h even under heating at 100 ℃ in ambient conditions. This work offers a facile approach to efficiently prevent BP and other air-sensitive materials from environmental oxidants for their practical applications.

Fiber-optic magnetic field sensing is an important method of magnetic field monitoring, which is essential for the safety of civil infrastructures, especially for power plant. We theoretically and experimentally demonstrated an optical fiber magnetic field sensor based on a single-mode-multimode-single-mode (SMS) structure immersed into the magnetic fluid (MF). The length of multimode section fiber is determined based on the self-image effect through the simulation. Due to variation characteristics of the refractive index and absorption coefficient of MF under different magnetic fields, an effective method to improve the sensitivity of SMS fiber structure is realized based on the intensity modulation method. This sensor shows a high sensitivity up to 0.097 dB/Oe and a high modulation depth up to 78% in a relatively linear range, for the no-core fiber (NCF) with the diameter of 125 μm and length of 59.8 mm as the multimode section. This optical fiber sensor possesses advantages of low cost, ease of fabrication, high sensitivity, simple structure, and compact size, with great potential applications in measuring the magnetic field.

A europium-doped (Eu-doped) silica optical fiber is fabricated using modified chemical vapor deposition (MCVD) technology. Europium fluoride (EuFsub3/sub) material is introduced into the fiber core with a high temperature vaporizing technique. Its concentration is approximately 0.11 at %. The outer and core diameters of doped fiber are approximately 122 and 9 μm, respectively. Refractive index difference (RID) between core and cladding is approximately 2%. A magneto-optical effect measurement system, which is based on the Stokes polarization parameters method, is set up to analyze its magneto-optical properties. The Verdet constant of the Eu-doped optical fiber is -4.563 rad Tsup-1/supmsup-1/sup, which is approximately double than that of single mode fiber (SMF) at 660 nm.

The Verdet constants of PbS-doped silica optical fiber and single mode fiber (SMF-28e) have been investigated based on a magneto-optical effect measurement system at wavelengths between 660 and 1550 nm. The Verdet constant of PbS-doped fiber is 3.17 rad/Tm, 31.5% larger than that of SMF at 660 nm. The PbS-doped silica optical fiber can become a promising material for Faraday rotator.