ABSTRACT
Black arsenic-phosphorus (b-AsP), an alloy containing black phosphorus and arsenic in the form of b-AsxP1-x, has a broadly tunable band gap changing with the chemical ratios of As and P. Although mid-infrared photodetectors and mode-locked or Q-switched pulse lasers based on b-AsP (mostly b-As0.83P0.17) are investigated, the potential of this family of materials for near-infrared photonic and optoelectronic applications at telecommunication bands is not fully explored. Here, we have verified a multifunctional fiber device based on b-As0.4P0.6 nanosheets for highly responsive photodetection and dual-wavelength ultrafast pulse generation at around 1550 nm. The fiber laser with a saturable absorber (SA) based on b-As0.4P0.6 nanosheets can output dual-wavelength mode-locking pulses with a larger bandwidth and spectral separation than those based on other two-dimensional (2D) materials. Remarkably, it is found that the b-As0.4P0.6-based photodetector can achieve a high responsivity of 10,200 A/W at 1550 nm and a peak responsivity of 2.29 × 105 A/W at 980 nm. Our work suggests that b-As0.4P0.6 shows great potential in ultrafast photonics, dual-comb spectroscopy, and infrared signal detection.
ABSTRACT
An all-fiber integrated photodetector is proposed and demonstrated by assembling a graphene/palladium diselenide (PdSe2) Van der Waals heterostructure onto the endface of a standard optical fiber. A gold film is covered on the heterostructure working as an electrode and a mirror, which reflects back the unabsorbed residual light for further reusage. Owing to the low bandgap of PdSe2, the all-fiber photodetector shows a broadband photoresponse from 650 to 1550â nm with a high photoresponsivity of 6.68×104 AW-1, enabling a low light detection of 42.5 pW. And the fastest temporal response is about 660 µs. Taking advantage of heterostructures, the photodetector can work in self-powered mode with the on/off ratio about 82. These findings provide new strategies for integrating two-dimensional materials into optical fibers to realize integrated all-fiber devices with multi-function applications.
ABSTRACT
Carbon-based nanomaterials such as carbon nanotubes (CNTs) and graphene have great potential for high-performance all-carbon photodetectors due to their unique optical and electronic properties. Here, we assemble a hybrid CNT/graphene film prepared by depositing CNTs on a single layer graphene with a side-polished optical fiber to achieve a novel all-fiber integrated photodetector. Because CNTs strongly enhanced the interaction between graphene and the fiber mode, the photodetector shows an extra-high photoresponsivity over the visible and infrared region. Especially at 1550 nm, the photoresponsivity is found to be â¼1.48 × 105 A W-1, which is 6.5 times larger than those of photodetectors without CNTs. These findings provide a highly versatile, reproducible, and low-cost platform to integrate novel zero-, one-, and two-dimensional materials into optical fibers and deliver more sophisticated functionalities.
ABSTRACT
The coupling of the optical and mechanical degrees of freedom using optical force in nano-devices offers a novel mechanism to implement all-optical signal processing. However, the ultra-weak optical force requires a high pump optical power to realize all-optical processing. For such devices, it is still challenging to lower the pump power and simultaneously broaden the bandwidth of the signal light under processing. In this work, a simple and cost-effective optomechanical scheme was demonstrated that was capable of achieving a broadband (208 nm) and micro-Watt (â¼624.13 µW) light-control-light effect driven by a relatively weak optical force (â¼3 pN). In the scheme, a tapered nanofiber (TNF) was evanescently coupled with a substrate, allowing the pump light guided in the TNF to generate a strong transverse optical force for the light-control-light effect. Additionally, thanks to the low stiffness (5.44 fN nm-1) of the TNF, the light-control-light scheme also provided a simple method to measure the static weak optical force with a minimum detectable optical force down to 380.8 fN. The results establish TNF as a cost-effective scheme to break the limitation of the modulation wavelength bandwidth (MWB) at a low pump power and show that the TNF-optic optomechanical system can be well described as a harmonic oscillator.
ABSTRACT
Upon reflection, a light beam embedded with m-order orbital angular momentum (OAM) will undergo the Imbert-Fedorov (IF) shift, which induces OAM sidebands. The energies of the neighboring {-m-1} and {-m+1} sideband modes of the reflected beam are always equal. Controllable OAM sidebands are theoretically achieved by introducing a monolayer graphene in a three-layer structure composed of air, hexagonal boron nitride, and metal. By modulating the Fermi energy of graphene, the OAM-dependent IF shift can be tuned from positive to negative values, and the OAM sideband modes can be suppressed or enhanced, since the reflectivity for perpendicular and parallel polarizations vary with the Fermi energy. These findings provide an alternative method for the control of optical OAM in the terahertz region.
ABSTRACT
The spin Hall effect (SHE) of light beams reflected from an air-chiral interface are investigated systematically. Due to the intrinsic chiral asymmetry of the medium, a horizontally polarized incident Gaussian beam will undergo asymmetric spin splitting, i.e., both the displacements and energies of two spin components of the reflected beam are different. One spin component can undergo large displacement near points of |rpp| = |rsp| (rpp and rsp are the Fresnel reflection coefficients), where the reflected beams are almost in circular polarization states. Moreover, for an incident beam carrying orbital angular momentum (OAM), the two spin components acquire additional OAM dependent shifts, which attribute to the asymmetric spin splitting. Thus, the asymmetric spin splitting of the reflected beam will vary with the incident OAM. These findings provide a deeper insight into the SHE of light, and they may have potential application in precision metrology.
ABSTRACT
The angular Goos-Hänchen shift of vortex beam is investigated theoretically when a Laguerre-Gaussian (LG) beam is reflected by an air-metamaterial interface. The upper limit of the angular GH shift is found to be half of the divergence angle of the incident beam, i.e., |Θup| = (|â| + 1)1/2/k0w0, with â, k0, and w0 being the vortex charge, wavenumber in vacuum, and beam waist, respectively. Interestingly, the upper limited angular GH shift is accompanied by the upper-limited spatial IF shift. A parameter F is introduced to compare the total beam shift with the beam size. F varies with the vortex charge â and the propagation distance zr. The values of F at zr = ∞ plane can approach 0.5, which are always larger than those at zr = 0 plane. These findings provide a deeper insight into optical beam shifts, and they may have potential application in precision metrology.
ABSTRACT
The spin splitting of light beams carrying orbital angular momentum (OAM) is investigated theoretically in attenuated internal reflection in the Kretschmann configuration. The excitation of the surface plasmon resonance (SPR) can significantly enhance the OAM-induced Imbert-Fedorov (IF) shift and the OAM-dependent spin splitting. The cooperation effect of these two shifts will result in an asymmetric spin splitting, which varies with the incident angle and polarization state. Specially, at the SPR angle, the OAM-induced IF shift vanishes, and the OAM-dependent spin splitting will cause a symmetric spin splitting. However, when the incident beam is horizontally polarized, the OAM-induced IF shift predominates. Thus the two spin components of the reflected will not be split; instead, they will be shifted together. This flexible control of the optical spin splitting can find applications in quantum information and precision metrology.
