Showing papers in "Photonics Research in 2018"
TL;DR: In this paper, surface plasmons supported by two crossed layers of graphene nanoribbons (GNRs) are exploited to achieve dynamically tunable plasmonically induced transparency (PIT) where each GNR operates as both the bright and dark modes simultaneously.
Abstract: Near-field coupled plasmonic systems generally achieve plasmonically induced transparency (PIT) using only one-way bright–dark mode coupling. However, it is challenging to realize such well-designed devices, mainly because they depend significantly on the polarization direction. We exploit surface plasmons supported by two crossed layers of graphene nanoribbons (GNRs) to achieve dynamically tunable PIT, where each GNR operates as both the bright and dark modes simultaneously. The proposed PIT can result from either one-way bright–dark mode interactions or bidirectional bright–bright and bright–dark mode hybridized coupling when the polarization is perpendicular/parallel or at an angle to the GNRs, respectively. Additionally, identical ribbon widths yield polarization-insensitive single-window PIT, whereas different ribbon widths produce polarization-dependent double-window PIT. We examine the proposed technique using plasmon wave functions and the transfer matrix method; analytical and numerical results show excellent agreement. This study can provide physical insight into the PIT coupling mechanisms and advance the applicability and versatility of PIT-based sensing platforms and other active devices.
261 citations
TL;DR: In this article, the tin disulfide (SnS2) was employed as a saturable absorber and its appearance and nonlinear saturable absorption characteristics were also investigated experimentally.
Abstract: In this paper, tin disulfide (SnS2), a two-dimensional (2D) n-type direct bandgap layered metal dichalcogenide with a gap value of 2.24 eV, was employed as a saturable absorber. Its appearance and nonlinear saturable absorption characteristics were also investigated experimentally. SnS2-PVA (polyvinyl alcohol) film was successfully prepared and employed as a mode-locker for achieving a mode-locked Er-doped fiber laser with a pulse width of 623 fs at a pulse repetition rate of 29.33 MHz. The results prove that SnS2 nanosheets will have wide potential ultrafast photonic applications due to their suitable bandgap value and excellent nonlinear saturable absorption characteristics.
218 citations
TL;DR: In this paper, an efficient optical sensor based on a photonic crystal metasurface supporting bound states in the continuum is reported, which exploits a normal-to-the-surface optical launching scheme, with excellent interrogation stability and demonstrates alignment-free performances.
Abstract: The realization of an efficient optical sensor based on a photonic crystal metasurface supporting bound states in the continuum is reported. Liquids with different refractive indices, ranging from 1.4000 to 1.4480, are infiltrated in a microfluidic chamber bonded to the sensing dielectric metasurface. A bulk liquid sensitivity of 178 nm/RIU is achieved, while a Q-factor of about 2000 gives a sensor figure of merit up to 445 in air at both visible and infrared excitations. Furthermore, the detection of ultralow-molecular-weight (186 Da) molecules is demonstrated with a record resonance shift of 6 nm per less than a 1 nm thick single molecular layer. The system exploits a normal-to-the-surface optical launching scheme, with excellent interrogation stability and demonstrates alignment-free performances, overcoming the limits of standard photonic crystals and plasmonic resonant configurations.
190 citations
TL;DR: In this paper, the authors demonstrate significantly improved performance of a microwave true time delay line based on an integrated optical frequency comb source using a broadband micro-comb (over 100nm wide) with a record low free spectral range (FSR) of 49 GHz.
Abstract: We demonstrate significantly improved performance of a microwave true time delay line based on an integrated optical frequency comb source. The broadband micro-comb (over 100 nm wide) features a record low free spectral range (FSR) of 49 GHz, resulting in an unprecedented record high channel number (81 over the C band)—the highest number of channels for an integrated comb source used for microwave signal processing. We theoretically analyze the performance of a phased array antenna and show that this large channel count results in a high angular resolution and wide beam-steering tunable range. This demonstrates the feasibility of our approach as a competitive solution toward implementing integrated photonic true time delays in radar and communications systems.
167 citations
TL;DR: In this paper, a substrate removal technique in a silicon Mach-Zehnder modulator (MZM) is proposed and demonstrated to improve modulation bandwidth based on the novel and optimized traveling wave electrodes, the electrode transmission loss is reduced, and the electro-optical group index and 50 Ω impedance matching are improved simultaneously.
Abstract: In this paper, a substrate removing technique in a silicon Mach–Zehnder modulator (MZM) is proposed and demonstrated to improve modulation bandwidth Based on the novel and optimized traveling wave electrodes, the electrode transmission loss is reduced, and the electro-optical group index and 50 Ω impedance matching are improved, simultaneously A 2 mm long substrate removed silicon MZM with the measured and extrapolated 3 dB electro-optical bandwidth of >50 GHz and 60 GHz at the −8 V bias voltage is designed and fabricated Open optical eye diagrams of up to 90 GBaud/s NRZ and 56 GBaud/s four-level pulse amplitude modulation (PAM-4) are experimentally obtained without additional optical or digital compensations Based on this silicon MZM, the performance in a short-reach transmission system is further investigated Single-lane 112 Gb/s and 128 Gb/s transmissions over different distances of 1 km, 2 km, and 10 km are experimentally achieved based on this high-speed silicon MZM
149 citations
TL;DR: Novel device architectures and improved fabrication techniques have paved a viable way for realizing low-cost, high-density, multi-function integrated devices in the MIR, which is expected to benefit several application domains in the years to come, including communication networks, sensing, and nonlinear systems.
Abstract: Silicon has been the material of choice of the photonics industry over the last decade due to its easy integration with silicon electronics, high index contrast, small footprint, and low cost, as well as its optical transparency in the near-infrared and parts of mid-infrared (MIR) wavelengths (from 1.1 to 8 μm). While considerations of micro- and nano-fabrication-induced device parameter deviations and a higher-than-desirable propagation loss still serve as a bottleneck in many on-chip data communication applications, applications as sensors do not require similar stringent controls. Photonic devices on chips are increasingly being demonstrated for chemical and biological sensing with performance metrics rivaling benchtop instruments and thus promising the potential of portable, handheld, and wearable monitoring of various chemical and biological analytes. In this paper, we review recent advances in MIR silicon photonics research. We discuss the pros and cons of various platforms, the fabrication procedures for building such platforms, and the benchmarks demonstrated so far, together with their applications. Novel device architectures and improved fabrication techniques have paved a viable way for realizing low-cost, high-density, multi-function integrated devices in the MIR. These advances are expected to benefit several application domains in the years to come, including communication networks, sensing, and nonlinear systems.
134 citations
TL;DR: In this article, a new type of heterostructure material with uniformity by employing the magnetron sputtering technique is investigated, which is called MoS2-Sb2Te3-MoS2 heterostructures.
Abstract: Two-dimensional (2D) materials with potential applications in photonic and optoelectronic devices have attracted increasing attention due to their unique structures and captivating properties. However, generation of stable high-energy ultrashort pulses requires further boosting of these materials’ optical properties, such as higher damage threshold and larger modulation depth. Here we investigate a new type of heterostructure material with uniformity by employing the magnetron sputtering technique. Heterostructure materials are synthesized with van der Waals heterostructures consisting of MoS2 and Sb2Te3. The bandgap, carrier mobility, and carrier concentration of the MoS2-Sb2Te3-MoS2 heterostructure materials are calculated theoretically. By using these materials as saturable absorbers (SAs), applications in fiber lasers with Q-switching and mode-locking states are demonstrated experimentally. The modulation depth and damage threshold of SAs are measured to be 64.17% and 14.13 J/cm2, respectively. Both theoretical and experimental results indicate that MoS2-Sb2Te3-MoS2 heterostructure materials have large modulation depth, and can resist high power during the generation of ultrashort pulses. The MoS2-Sb2Te3-MoS2 heterostructure materials have the advantages of low cost, high reliability, and suitability for mass production, and provide a promising solution for the development of 2D-material-based devices with desirable electronic and optoelectronic properties.
131 citations
TL;DR: In this paper, a type of microfiber-based MoTe2 SA fabricated by the magnetron-sputtering deposition (MSD) method was used for high-energy wave-breaking free soliton pulses.
Abstract: The pulse energy in the ultrafast soliton fiber laser oscillators is usually limited by the well-known wave-breaking phenomenon owing to the absence of a desirable real saturable absorber (SA) with high power tolerance and large modulation depth. Here, we report a type of microfiber-based MoTe2 SA fabricated by the magnetron-sputtering deposition (MSD) method. High-energy wave-breaking free soliton pulses were generated with pulse duration/pulse energy/average output power of 229 fs/2.14 nJ/57 mW in the 1.5 μm regime and 1.3 ps/13.8 nJ/212 mW in the 2 μm regime, respectively. To our knowledge, the generated soliton pulses at 1.5 μm had the shortest pulse duration and the highest output power among the reported erbium-doped fiber lasers mode locked by transition metal dichalcogenides. Moreover, this was the first demonstration of a MoTe2-based SA in fiber lasers in the 2 μm regime, and the pulse energy/output power are the highest in the reported thulium-doped fiber lasers mode locked by two-dimensional materials. Our results suggest that a microfiber-based MoTe2 SA could be used as an excellent photonic device for ultrafast pulse generation, and the MSD technique opens a promising route to produce a high-performance SA with high power tolerance and large modulation depth, which are beneficial for high-energy wave-breaking free pulse generation.
118 citations
TL;DR: In this paper, a single phase-type spatial light modulator (SLM) is used to generate tunable vector beams with arbitrarily controllable polarization state, phase, and amplitude.
Abstract: We propose an efficient and robust method to generate tunable vector beams by employing a single phase-type spatial light modulator (SLM). With this method, a linearly polarized Gaussian beam can be converted into a vector beam with arbitrarily controllable polarization state, phase, and amplitude. The energy loss during the conversion is greatly reduced and depends mainly on the reflectivity of the SLM. We experimentally demonstrate that conversion efficiency of about 47% is achieved by using an SLM with reflectivity of 62%. Several typical vector beams, including cylindrical vector beams, vector beams on higher order Poincare spheres, and arbitrary vector beams attached with phases and with tunable amplitude, are generated and verified experimentally. This method is also expected to create high-power vector beams and play important roles in optical fabrication and light trapping.
113 citations
TL;DR: In this paper, a dual-mode waveguide crossing based on subwavelength multimode-interference couplers for a densely integrated on-chip mode-division multiplexing system is proposed and experimentally demonstrated.
Abstract: We propose and experimentally demonstrate a novel ultracompact dual-mode waveguide crossing based on subwavelength multimode-interference couplers for a densely integrated on-chip mode-division multiplexing system. By engineering the lateral-cladding material index and manipulating phase profiles of light at the nanoscale using an improved inverse design method, a subwavelength structure could theoretically realize the identical beat length for both TE0 and TE1, which can reduce the scale of the device greatly. The fabricated device occupied a footprint of only 4.8 μm×4.8 μm. The measured insertion losses and crosstalks were less than 0.6 dB and −24 dB from 1530 nm to 1590 nm for both TE0 and TE1 modes, respectively. Furthermore, our scheme could also be expanded to design waveguide crossings that support more modes.
94 citations
TL;DR: Silicon-rich nitride films are compositionally engineered to create bandgaps that are sufficiently large to eliminate two-photon absorption at telecommunications wavelengths while enabling much larger nonlinear waveguide parameters (5x-500x) than those in stoichiometric silicon nitride.
Abstract: CMOS platforms with a high nonlinear figure of merit are highly sought after for high photonic quantum efficiencies, enabling functionalities not possible from purely linear effects and ease of integration with CMOS electronics. Silicon-based platforms have been prolific amongst the suite of advanced nonlinear optical signal processes demonstrated to date. These include crystalline silicon, amorphous silicon, Hydex glass, and stoichiometric silicon nitride. Residing between stoichiometric silicon nitride and amorphous silicon in composition, silicon-rich nitride films of various formulations have emerged recently as promising nonlinear platforms for high nonlinear figure of merit nonlinear optics. Silicon-rich nitride films are compositionally engineered to create bandgaps that are sufficiently large to eliminate two-photon absorption at telecommunications wavelengths while enabling much larger nonlinear waveguide parameters (5x–500x) than those in stoichiometric silicon nitride. This paper reviews recent developments in the field of nonlinear optics using silicon-rich nitride platforms, as well as the outlook and future opportunities in this burgeoning field.
TL;DR: In this article, a supercontinuum source integrated on-chip spectroscopic sensor is presented, where nonlinear Ge22Sb18Se60 chalcogenide glass waveguides are used as a unified platform for both broadband super-continuum generation and chemical detection.
Abstract: On-chip spectroscopic sensors have attracted increasing attention for portable and field-deployable chemical detection applications. So far, these sensors largely rely on benchtop tunable lasers for spectroscopic interrogation. Large footprint and mechanical fragility of the sources, however, preclude compact sensing system integration. In this paper, we address the challenge through demonstrating, for the first time to our knowledge, a supercontinuum source integrated on-chip spectroscopic sensor, where we leverage nonlinear Ge22Sb18Se60 chalcogenide glass waveguides as a unified platform for both broadband supercontinuum generation and chemical detection. A home-built, palm-sized femtosecond laser centering at 1560 nm wavelength was used as the pumping source. Sensing capability of the system was validated through quantifying the optical absorption of chloroform solutions at 1695 nm. This work represents an important step towards realizing a miniaturized spectroscopic sensing system based on photonic chips.
TL;DR: In this article, the authors investigated the lasing characteristics of a passively mode-locked fiber laser with a finite amount of intracavity birefringence and showed that dual vector solitons can be generated under an anomalous or net normal dispersion regime.
Abstract: Mode-locked fiber lasers that can simultaneously generate two asynchronous ultrashort pulse trains could play an attractive role as the alternative light sources for low-complexity dual-comb metrology applications. Although a few multiplexing schemes to realize such lasers have been proposed and demonstrated, here we investigate the lasing characteristics of a passively mode-locked fiber laser with a finite amount of intracavity birefringence. By introducing a section of polarization-maintaining (PM) fiber into the otherwise-non-PM-single-mode cavity, dual asynchronous pulses with nearly orthogonal states of polarization are generated. With a repetition rate difference of hundreds of hertz, the pulses have well-overlapped spectra and show typical features of polarization-locked vector solitons. It is demonstrated that under an anomalous or net normal dispersion regime, either dual vector solitons or dual dissipative vector solitons can be generated, respectively. Such polarization-multiplexed single single-cavity dual-comb lasers could find further uses in various applications in need of simple dual-comb system solutions.
TL;DR: The mode-locked laser diode has emerged as a promising candidate as a signal source for photonic radar systems, wireless data transmission, and frequency comb spectroscopy.
Abstract: The mode-locked laser diode has emerged as a promising candidate as a signal source for photonic radar systems, wireless data transmission, and frequency comb spectroscopy. They have the advantages of small size, low cost, high reliability, and low power consumption, thanks to semiconductor technology. Mode-locked lasers based on silicon photonics advance these qualities by the use of highly advanced silicon manufacturing technology. This paper will begin by giving an overview of mode-locked laser diode literature, and then focus on mode-locked lasers on silicon. The dependence of mode-locked laser performance on design details is presented.
TL;DR: In this paper, the spin-orbit interaction of light and photonic spin Hall effect on the surface of anisotropic two-dimensional atomic crystals was examined and shown to be sensitive to the orientation of the optical axis, doping concentration, and interband transitions.
Abstract: We examine the spin-orbit interaction of light and photonic spin Hall effect on the surface of anisotropic two-dimensional atomic crystals. As an example, the photonic spin Hall effect on the surface of black phosphorus is investigated. The photonic spin Hall effect manifests itself as the spin-dependent beam shifts in both transverse and in-plane directions. We demonstrate that the spin-dependent shifts are sensitive to the orientation of the optical axis, doping concentration, and interband transitions. These results can be extensively extended to other anisotropic two-dimensional atomic crystals. By incorporating the quantum weak measurement techniques, the photonic spin Hall effect holds great promise for detecting the parameters of anisotropic two-dimensional atomic crystals.
TL;DR: In this article, a parity-time symmetric whispering-gallery mode (WGM) resonator was proposed for single nanoparticle detection using single-antenna sensors. But the authors did not consider the presence of multiple nanoparticles in the mode volume of a WGM sensor.
Abstract: We present a study of single nanoparticle detection using parity-time (PT) symmetric whispering-gallery mode (WGM) resonators. Our theoretical model and numerical simulations show that, with balanced gain and loss, the PT-symmetric WGM nanoparticle sensor, tailored to operate at PT phase transition points (also called exceptional points), exhibits significant enhancement in frequency splitting when compared with a single WGM nanoparticle sensor subject to the same perturbation. The presence of gain in the PT-symmetric system leads to narrower linewidth, which helps to resolve smaller changes in frequency splitting and improve the detection limit of nanoparticle sensing. Furthermore, we also provide a general method for detecting multiple nanoparticles entering the mode volume of a PT-symmetric WGM sensor one by one. Our study shows the feasibility of PT-symmetric WGM resonators for ultrasensitive single nanoparticle and biomolecule sensing.
TL;DR: In this paper, the design, fabrication, and characterization of terahertz spoof surface plasmon polaritons waveguides based on corrugated metal surfaces is described.
Abstract: Surface plasmon polaritons (SPPs) with the features of subwavelength confinement and strong enhancements have sparked enormous interest. However, in the terahertz regime, due to the perfect conductivities of most metals, it is hard to realize the strong confinement of SPPs, even though the propagation loss could be sufficiently low. One main approach to circumvent this problem is to exploit spoof SPPs, which are expected to exhibit useful subwavelength confinement and relative low propagation loss at terahertz frequencies. Here we report the design, fabrication, and characterization of terahertz spoof SPP waveguides based on corrugated metal surfaces. The various waveguide components, including a straight waveguide, an S-bend waveguide, a Y-splitter, and a directional coupler, were experimentally demonstrated using scanning near-field terahertz microscopy. The proposed waveguide indeed enables propagation, bending, splitting, and coupling of terahertz SPPs and thus paves a new way for the development of flexible and compact plasmonic circuits operating at terahertz frequencies.
TL;DR: In this article, the authors proposed a methodology to maximize the absorption bandwidth of a metal-insulator-metal (MIM) based absorber, which is made of a Cr-Al2O3-Cr multilayer design at the initial step, the optimum MIM planar design is fabricated and optically characterized.
Abstract: In this paper, we propose a methodology to maximize the absorption bandwidth of a metal-insulator-metal (MIM) based absorber The proposed structure is made of a Cr-Al2O3-Cr multilayer design At the initial step, the optimum MIM planar design is fabricated and optically characterized The results show absorption above 09 from 400 nm to 850 nm Afterward, the transfer matrix method is used to find the optimal condition for the perfect light absorption in an ultra-broadband frequency range This modeling approach predicts that changing the filling fraction of the top Cr layer can extend light absorption toward longer wavelengths We experimentally proved that the use of proper top Cr thickness and annealing temperature leads to a nearly perfect light absorption from 400 nm to 1150 nm, which is much broader than that of a planar design Therefore, while keeping the overall process lithography-free, the absorption functionality of the design can be significantly improved The results presented here can serve as a beacon for future performance-enhanced multilayer designs where a simple fabrication step can boost the overall device response without changing its overall thickness and fabrication simplicity
TL;DR: In this article, a sensitivityenhanced surface plasmon resonance (SPR) sensor with a metal film modified by an overlayer of tungsten disulfide (WS2) nanosheets is proposed and demonstrated.
Abstract: Tungsten disulfide (WS2), as a representative layered transition metal dichalcogenide (TMDC) material, possesses important potential for applications in highly sensitive sensors. Here, a sensitivity-enhanced surface plasmon resonance (SPR) sensor with a metal film modified by an overlayer of WS2 nanosheets is proposed and demonstrated. The SPR sensitivity is related to the thickness of the WS2 overlayer, which can be tailored by coating a WS2 ethanol suspension with different concentrations or by the number of times of repeated post-coating. Benefitting from its large surface area, high refractive index, and unique optoelectronic properties, the WS2 nanosheet overlayer coated on the gold film significantly improves the sensing sensitivity. The highest sensitivity (up to 2459.3 nm/RIU) in the experiment is achieved by coating the WS2 suspension once. Compared to the case without a WS2 overlayer, this result shows a sensitivity enhancement of 26.6%. The influence of the WS2 nanosheet overlayer on the sensing performance improvement is analyzed and discussed. Moreover, the proposed WS2 SPR sensor has a linear correlation coefficient of 99.76% in refractive index range of 1.333 to 1.360. Besides sensitivity enhancement, the WS2 nanosheet overlayer is able to show additional advantages, such as protection of metal film from oxidation, tunability of the resonance wavelength region, biocompatibility, capability of vapor, and gas sensing.
TL;DR: In this paper, a tunable terahertz meta-lens whose focal length is able to be electrically tuned by ∼4.45λ was demonstrated experimentally, where the lens consists of a metallic metasurface and a monolayer graphene.
Abstract: Metasurfaces have become a new photonic structure for providing potential applications to develop integrated devices with small thickness, because they can introduce an abrupt phase change by arrays of scatterers. To be applied more widely, active metasurface devices are highly desired. Here, a tunable terahertz meta-lens whose focal length is able to be electrically tuned by ∼4.45λ is demonstrated experimentally. The lens consists of a metallic metasurface and a monolayer graphene. Due to the dependence of the abrupt phase change of the metasurface on the graphene chemical potential, which can be modulated using an applied gate voltage, the focal length is changed from 10.46 to 12.24 mm when the gate voltage increases from 0 to 2.0 V. Experimental results are in good agreement with the theoretical hypothesis. This type of electrically controlled meta-lens could widen the application of terahertz technology.
TL;DR: In this article, the properties of spatial solitons in the fractional Schrodinger equation (FSE) with parity-time (PT)-symmetric lattice potential supported by the focusing of Kerr nonlinearity were investigated.
Abstract: We investigate the properties of spatial solitons in the fractional Schrodinger equation (FSE) with parity-time (PT)-symmetric lattice potential supported by the focusing of Kerr nonlinearity. Both one- and two-dimensional solitons can stably propagate in PT-symmetric lattices under noise perturbations. The domains of stability for both one- and two-dimensional solitons strongly depend on the gain/loss strength of the lattice. In the spatial domain, the solitons are rigidly modulated by the lattice potential for the weak diffraction in FSE systems. In the inverse space, due to the periodicity of lattices, the spectra of solitons experience sharp peaks when the values of wavenumbers are even. The transverse power flows induced by the imaginary part of the lattice are also investigated, which can preserve the internal energy balances within the solitons.
TL;DR: In this article, the effect of anti-crossings between the fundamental guided mode and core-wall resonances on the dispersion in hollow-core anti-resonant-reflection photonic crystal fibers was investigated.
Abstract: Spectral anti-crossings between the fundamental guided mode and core-wall resonances alter the dispersion in hollow-core anti-resonant-reflection photonic crystal fibers. Here we study the effect of this dispersion change on the nonlinear propagation and dynamics of ultrashort pulses. We find that it causes emission of narrow spectral peaks through a combination of four-wave mixing and dispersive wave emission. We further investigate the influence of the anti-crossings on nonlinear pulse propagation and show that their impact can be minimized by adjusting the core-wall thickness in such a way that the anti-crossings lie spectrally distant from the pump wavelength.
TL;DR: In this paper, the authors reported a passively Q-switched and mode-locked erbium-doped fiber laser (EDFL) based on PtSe2, a new two-dimensional material, as a saturable absorber (SA).
Abstract: We report a passively Q-switched and mode-locked erbium-doped fiber laser (EDFL) based on PtSe2, a new two-dimensional material, as a saturable absorber (SA). Self-started Q-switching at 1560 nm in the EDFL was achieved at a threshold pump power of 65 mW, and at the maximum pump power of 450 mW, the maximum single Q-switched pulse energy is 143.2 nJ. Due to the polarization-dependent characteristics of the PtSe2-based SA, the laser can be switched from the Q-switched state to the mode-locked state by adjusting the polarization state. A mode-locked pulse train with a repetition rate of 23.3 MHz and a pulse width of 1.02 ps can be generated when the pump power increases to about 80 mW, and the stable mode-locked state is maintained until the pump power reaches its maximum 450 mW. The maximum single mode-locked pulse energy is 0.53 nJ. This is the first time to our knowledge that successful generation of stable Q-switched and mode-locked pulses in an Er-doped fiber laser has been obtained by using PtSe2 as a saturable absorber.
TL;DR: In this paper, transition metal dichalcogenides (TMDs) are successfully applied in fiber lasers for their photoelectric properties, and the modulation depths of WSe2 and MoSe2 SAs with sandwiched structures are effectively increased to 31.25% and 25.69%, respectively.
Abstract: Transition metal dichalcogenides (TMDs) are successfully applied in fiber lasers for their photoelectric properties. However, in previous work, how to improve the modulation depth of TMD-based saturable absorbers (SAs) has been a challenging issue. In this paper, WSe2 and MoSe2 SAs are fabricated with the chemical vapor deposition method. Compared with previous experiments, the modulation depths of WSe2 and MoSe2 SAs with sandwiched structures are effectively increased to 31.25% and 25.69%, respectively. The all-fiber passively Q-switched erbium doped fiber lasers based on WSe2 and MoSe2 SAs are demonstrated. The signal-to-noise ratios of those lasers are measured to be 72 and 57 dB, respectively. Results indicate that the proposed WSe2 and MoSe2 SAs are efficient photonic devices to realize stable fiber lasers.
TL;DR: In this paper, the authors demonstrate several efficient, polarization-independent, all-silicon dielectric metasurfaces in the terahertz regime, which can be easily fabricated using etching technology for semiconductors.
Abstract: Dielectric metasurfaces have achieved great success in realizing high-efficiency wavefront control in the optical and infrared ranges. Here, we experimentally demonstrate several efficient, polarization-independent, all-silicon dielectric metasurfaces in the terahertz regime. The metasurfaces are composed of cylindrical silicon pillars on a silicon substrate, which can be easily fabricated using etching technology for semiconductors. By locally tailoring the diameter of the pillars, full control over abrupt phase changes can be achieved. To show the controlling ability of the metasurfaces, an anomalous deflector, three Bessel beam generators, and three vortex beam generators are fabricated and characterized. We also show that the proposed metasurfaces can be easily combined to form composite devices with extended functionalities. The proposed controlling method has promising applications in developing low-loss, ultra-compact spatial terahertz modulation devices.
TL;DR: In this article, a long-term stable two-dimensional saturable absorption material under ambient conditions was demonstrated for the first time to the best of our knowledge, and the results indicated that multi-layer antimonene is a promising longterm stable SA material that can be applied in the mid-infrared spectral region.
Abstract: We experimentally demonstrate a long-term stable two-dimensional saturable absorption material under ambient conditions—multi-layer antimonene feasible for the mid-infrared spectral region—for the first time to our knowledge. The multi-layer antimonene material prepared using a liquid-phase exfoliation method was coated on a quartz/CaF2 for characterizations and an Au mirror as a reflection-type saturable absorber (SA) device. It has a modulation depth of 10.5%, a saturation peak intensity of 0.26 GW/cm2, and a non-saturation loss of 19.1% measured at 2868.0 nm using the typical power-dependent method. By introducing the SA device into a linear-cavity Ho3+/Pr3+-codoped fluoride fiber laser at 2865.0 nm, stable Q-switched pulses were obtained. It generated a maximum output power of 112.3 mW and pulse energy of 0.72 μJ, while the shortest pulse duration and largest repetition rate were 1.74 μs and 156.2 kHz, respectively. The long-term stability of the SA device was also checked using the same laser setup within 28 days. The results indicate that multi-layer antimonene is a type of promising long-term stable SA material under ambient conditions that can be applied in the mid-infrared spectral region.
TL;DR: In this paper, a multilayer BP flakes coated on microfiber (BCM) was used as a saturable absorber with a modulation depth of 16% and a saturation intensity of 6.8MW/cm2.
Abstract: Black phosphorus (BP), with thickness-dependent direct energy bandgaps (0.3–2 eV), shows an enhanced nonlinear optical response at near- and mid-infrared wavelengths. In this paper, we present experimentally multilayer BP flakes coated on microfiber (BCM) as a saturable absorber with a modulation depth of 16% and a saturable intensity of 6.8 MW/cm2. After inserting BCM into an Er-doped fiber ring laser, a stable dual-wavelength Q-switched state with central wavelengths of 1542.4 nm and 1543.2 nm (with wavelength spacing as small as 0.8 nm) is obtained with the aid of two cascaded fiber Bragg gratings as a coarse wavelength selector. Moreover, single-wavelength Q-switched operation at 1542.4 nm or 1543.2 nm is also realized, which can be switched between the two wavelengths flexibly just by adjusting the intracavity birefringence. These results suggest that BP combined with the cascaded fiber gratings can provide a simple and feasible candidate for a multiwavelength fiber laser. Our fiber laser may have potential applications in terahertz generation, laser radar, and so on.
TL;DR: By attaching vortex gratings onto the facets of a few-mode fiber, an integrated fiber-based OAM (de)multiplexer was demonstrated in this paper, which enabled direct multiplexing of OAM states at one port and the demultiplexing at the other port.
Abstract: The quickly increasing data transfer load requires an urgent revolution in current optical communication. Orbital angular momentum (OAM) multiplexing is a potential candidate with its ability to considerably enhance the capacity of communication. However, the lack of a compact, efficient, and integrated OAM (de)multiplexer prevents it from being widely applied. By attaching vortex gratings onto the facets of a few-mode fiber, we demonstrate an integrated fiber-based OAM (de)multiplexer. A vortex grating fabricated on the fiber facet enables the direct multiplexing of OAM states at one port and the demultiplexing of OAM states at the other port. The measured bit error rate of the carrier signal after propagating through a 5-km few-mode fiber confirms the validity and effectiveness of the proposed approach. The scheme offers advantages in future high-capacity OAM communication based on optical fiber.
TL;DR: In this article, a metasurface composed of a subwavelength metallic slit array embedded in an asymmetric dielectric environment can exhibit either extraordinary optical transmission (EOT) or extraordinary optical diffraction (EOD).
Abstract: We show that a metasurface composed of a subwavelength metallic slit array embedded in an asymmetric dielectric environment can exhibit either extraordinary optical transmission (EOT) or extraordinary optical diffraction (EOD). The cascaded refractive indices of the dielectrics can leverage multiple decaying passages into variant subsections with different diffraction order combinations according to the diffraction order chart in the k-vector space, providing a flexible mean to tailor resonance decaying pathways of the metallic slit cavity mode by changing the wavevector of the incident light. As a result, either the zeroth transmission or −1st reflection efficiencies can be enhanced to near unity by the excitation of the localized slit cavity mode, leading to either EOT or EOD in a single structure, depending on the illumination angle. Based on this appealing feature, a multifunctional metasurface that can switch its functionality between transmission filter, mirror, and off-axis lens is demonstrated. Our findings provide a convenient way to construct multifunctional miniaturized optical components on a single planar device.
TL;DR: In this paper, Bismuth nanosheets (Bi-NSs) were successfully prepared and employed as saturable absorbers to generate a diode-pumped dualwavelength Er3+:SrF2 laser in the mid-infrared region.
Abstract: Bismuth nanosheets (Bi-NSs) were successfully prepared and employed as saturable absorbers to generate a diode-pumped dual-wavelength Er3+:SrF2 laser in the mid-infrared region. Q-switched pulses with a maximum output power of 0.226 W were obtained at an absorbed pump power of 1.97 W. A repetition rate of 56.20 kHz and a minimum pulse duration of 980 ns were achieved. To the best of our knowledge, we present the first application of Bi-NSs in a mid-infrared all-solid-state laser. The results prove that Bi-NSs may be applied as an optical modulator in mid-infrared photonic devices or as a mode-locker and Q-switcher.