Showing papers by "Jianquan Yao published in 2022"

Dynamic phase assembled terahertz metalens for reversible conversion between linear polarization and arbitrary circular polarization

Abstract: If a metalens integrates the circular polarization (CP) conversion function, the focusing lens together with circular-polarizing lens (CPL) in traditional cameras may be replaced by a metalens. However, in terahertz (THz) band, the reported metalenses still do not obtain the perfect and strict single-handed CP, because they were constructed via Pancharatnam-Berry phase so that CP conversion contained both left-handed CP (LCP) and right-handed CP (RCP) components. In this paper, a silicon based THz metalens is constructed using dynamic phase to obtain single-handed CP conversion. Also, we can rotate the whole metalens at a certain angle to control the conversion of multi-polarization states, which can simply manipulate the focusing for incident linear polarization (LP) THz wave in three polarization conversion states, including LP without conversion, LCP and RCP. Moreover, the polarization conversion behavior is reversible, that is, the THz metalens can convert not only the LP into arbitrary single-handed CP, but also the LCP and RCP into two perpendicular LP, respectively. The metalens is expected to be used in advanced THz camera, as a great candidate for traditional CPL and focusing lens group, and also shows potential application in polarization imaging with discriminating LCP and RCP.

Terahertz metasurface zone plates with arbitrary polarizations to a fixed polarization conversion

Abstract: Metasurfaces that can realize the polarization manipulation of electromagnetic waves on the sub-wavelength scale have become an emerging research field. Here, a novel strategy of combining the metasurface and Fresnel zone plate to form a metasurface zone plate is proposed to realize the conversion from nearly arbitrary polarizations to a fixed polarization. Specifically, when one polarized wave is incident on adjacent ring zones constructed by different types of meta-atoms, the transmitted waves generated by odd-numbered and even-numbered ring zones converge at the same focus and su-perimpose to generate a fixed polarized wave. As function demonstrations, we have designed two types of metasurface zone plates: one is a focused linear polarizer, and the other can convert nearly arbitrary polarized waves into focused circularly polarized waves. The simulated and measured results are consistent with theoretical expectations, suggesting that the proposed concept is flexible and feasible. Our work provides an alternative platform for polarization manipulation and may vigorously promote the development of polarization photonic devices. Terahertz metasurface zone plates with arbitrary polarizations to a fixed polarization conversion. Opto-Electron Sci 1 , 210014 (2022).

All‐Dielectric Trifunctional Metasurface Capable of Independent Amplitude and Phase Modulation

Abstract: It is essential to independently control the amplitude, phase, and polarization of electromagnetic waves, and there is an urgent need to integrate multiple functions independently on a single device. Here, an all‐silicon multifunctional metasurface platform that can arbitrarily and independently encode three pairs of amplitude and phase profiles into a single‐layer device is proposed. Three complex amplitude functions can be presented independently by switching the polarization states of the incident and transmitted waves. As a proof of the feasibility and flexibility of the platform, three examples are designed here: the first can generate multipair foci of equal intensity, the second can generate multipair axial bifocals of equal intensity, and the third can generate multipair foci of arbitrary intensity ratios. The experimental results are in good agreement with the simulations. The proposed multifunctional metasurface platform is powerful in manipulating the amplitude, phase, and polarization of electromagnetic waves, which can find applications in particle manipulation, biology, imaging, and other fields.

Creating Longitudinally Varying Vector Vortex Beams with an All‐Dielectric Metasurface

Abstract: Vector vortex beams have attracted considerable research attention owing to their unique optical properties, and have been explored in vortex filtering, photon entanglement, and the photonic spin hall effect. In this work, a universal all‐dielectric metasurface platform is proposed that can generate longitudinally varying vector vortex beams in the terahertz band. As a proof‐of‐concept demonstration, a series of metasurface examples generating evolution of topological charges and vector polarization states of generated vector vortex beams are characterized. The experimental results agree well with the simulations, fully verifying the feasibility of the proposed scheme. The proposed metasurface strategy may find applications ranging from optical traps to polarization optics.

Dual-band giant spin-selective full-dimensional manipulation of graphene-based chiral meta-mirrors for terahertz waves.

Abstract: The ability to simultaneous achieve circular dichroism (CD) and wavefront manipulation is extremely important for many practical applications, especially for detecting and imaging. However, many of the previously observed weakness chiral features are limited to nanostructures with complex three-dimensional building configurations, single narrow-band response, and no active tunability, which are getting farther and away from the goal of integration and miniaturization. Here, a platform of bi-layer all-graphene meta-mirrors with spin-selective full-dimensional manipulation is proposed to simultaneously achieve giant dual-band CD response and wavefront shaping, based on the principle of the hybridization coupling. By simply controlling the structural variables of the meta-mirror and the characteristic parameters of graphene, that is, the combination of passive and active regulation, the proposed design can selectively manipulate the polarization, amplitude, phase, and working frequency of the incident circularly polarized wave near-independently. As a proof of concept, we used the meta-mirror to design two metasurface arrays with spin-selective properties for dynamic terahertz (THz) wavefront shaping and near-field digital imaging, both of which show a high-performance dynamic tunability. This method could provide additional options for the next-generation intelligent THz communication systems.

Diatomic terahertz metasurfaces for arbitrary-to-circular polarization conversion.

Abstract: Polarization control is crucial for tailoring light-matter interactions. Direct manipulation of arbitrarily incident polarized waves could provide more degrees of freedom in the design of integrated and miniaturized terahertz (THz) devices. Metasurfaces with unprecedented wave manipulation capabilities could serve as candidates for fulfilling this requirement. Here, a kind of all-silicon metasurface is demonstrated to realize the conversion of arbitrary incident polarization states to circular polarization states in the THz band through the mutual interference of monolayer achiral meta-atoms. Also, we confirmed that the conversion intensities are controllable using the evolution behavior of arbitrary polarization states defined on the Poincaré sphere. Meta-platforms with circularly polarized incidence experience spin-selective destructive or constructive interference, exhibiting broadband circular dichroism (BCD) in the target frequency range. Based on the versatility of the proposed design, the feasibility of the theoretical derivation has been verified in the experiment process. By introducing the geometric phase principle, the proposed design is demonstrated to be an attractive alternative to achieve chiral wavefront manipulation. This work may provide a promising avenue to replace the cumbersome cascaded optical building blocks with an ultrathin meta-platform, which can be used in chiral spectroscopy, imaging, optical communication, and so on.

Optically Tunable Terahertz Metasurface Absorber

Abstract: Tunable absorbers are promising for reconfigurable metasurface applications. Here a tunable terahertz (THz) perfect absorber is proposed which consists of high resistance silicon (undoped silicon) and can realize the switch between perfect reflection and perfect absorption (optical pumping, 1064 nm continuous wave). The proposed THz absorber exhibits perfect absorption around 0.74 THz and a 90% absorption bandwidth of 0.5 THz. Additionally, the working frequency range of the device can be easily designed by adjusting the side length and height of the square silicon pillars. Effective medium theory, mode analysis, and impedance matching theory are used to design and explain the proposed THz absorber. The experimental results agree well with the simulations. The proposed scheme allows for more flexible design of THz absorbers, and the device is easier to be fabricated. The proposed tunable THz absorber can find applications in THz sensing, modulator, and optic-electro switches.

Ultra-narrowband terahertz circular dichroism driven by planar metasurface supporting chiral quasi bound states in continuum

Abstract: Terahertz (THz) chirality pursues customizable manipulation from narrowband to broadband. While conventional THz chirality is restricted by non-negligible linewidth and unable to handle narrowband well. Recently, the concept “quasi bound states in continuum” (quasi-BIC) is introduced to optics resonance system whose the quality factor can be extremely high with the ultra-low radiative loss, thus providing a conceptual feasibility for wave control with ultra-narrow linewidth. Herein, we construct quasi-BIC in a planar all-silicon THz metasurface with in-plane C2 and mirror symmetries breaking. Such system not only exposes the symmetry-protected BIC, but also exposes the parameter-tuned BIC assigned to single resonance type. An extremely narrow linewidth with high quality factor is obtained at quasi-BIC frequency, which achieves the ultra-narrowband THz chirality.

Time-Modulated Transmissive Programmable Metasurface for Low Sidelobe Beam Scanning

Abstract: Programmable metasurfaces have great potential for the implementation of low-complexity and low-cost phased arrays. Due to the difficulty of multiple-bit phase control, conventional programmable metasurfaces suffer a relatively high sidelobe level (SLL). In this manuscript, a time modulation strategy is introduced in the 1-bit transmissive programmable metasurface for reducing the SLLs of the generated patterns. After the periodic time modulation, harmonics are generated in each reconfigurable unit and the phase of the first-order harmonic can be dynamically controlled by applying different modulation sequences onto the corresponding unit. Through the high-speed modulation of the real-time periodic coding sequences on the metasurface by the programmable bias circuit, the equivalent phase shift accuracy to each metasurface unit can be improved to 6-bit and thus the SLLs of the metasurface could be reduced remarkably. The proposed time-modulated strategy is verified both numerically and experimentally with a transmissive programmable metasurface, which obtains an aperture efficiency over 34% and reduced SLLs of about −20 dB. The proposed design could offer a novel approach of a programmable metasurface framework for radar detection and secure communication applications.

Intracavity spherical aberration for selective generation of single-transverse-mode Laguerre-Gaussian output with order up to 95

Abstract: Abstract We investigate the generation of single-transverse-mode Laguerre-Gaussian (LG) emission from a diode-end-pumped Nd:YVO 4 , 1064 nm laser using mode selection via intracavity spherical aberration (SA). We present both theoretical and experimental investigations, examining the limits of the order (both radial and angular indices) of the LG modes which can be produced, along with the resultant output power. We found that in order to generate single-mode emission of low-order LG modes which have relatively small beam diameters, lenses with shorter focal-length were required (to better differentiate neighboring LG modes via SA). The converse was true of LG modes with high-order. Through appropriate choice of the focal length of the intracavity lens, we were able to generate single-mode, LG 0,± m laser output with angular indices m selectable from 1 to 95, as well as those with non-zero radial indices p of up to 4.

Large-range alignment-free distributed-cavity laser based on an improved multi-lens retroreflector

Abstract: Junjie Liu (刘俊杰), Aihua Wang (王爱华), Quan Sheng (盛 泉), Yue Qi (齐 岳), Sijia Wang (王思佳), Meng Wang (王 盟), Degang Xu (徐德刚), Shijie Fu (付士杰), Wei Shi (史 伟), and Jianquan Yao (姚建铨) 1 Institute of Laser and Optoelectronics, School of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin 300072, China 2 Key Laboratory of Optoelectronic Information Science and Technology (Ministry of Education), Tianjin University, Tianjin 300072, China 3 Tianjin Jinhang Institute of Technical Physics, Tianjin 300308, China 4 Tianjin Suowei Electronic Technology Co., Ltd., Tianjin 300384, China 5 Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China

Single-frequency Tm-doped fiber laser with 215 mW at 2.05 µm based on a Tm/Ho-codoped fiber saturable absorber.

Abstract: We demonstrate an efficient single-frequency Tm-doped fiber laser at 2050 nm. A ring cavity scheme is employed to boost the net gain at the wavelength. A piece of Tm/Ho-codoped fiber with an absorption coefficient at 2050 nm higher than that of a Tm-doped fiber is used to establish the dynamic Bragg grating for enhancing the frequency selection capability. A single-frequency output of 215 mW is obtained under 2 W of 1570-nm pump power, with the slope efficiency being 22%. To the best of our knowledge, this is the highest single-frequency all-fiber laser oscillator output power above 2 µm.

Structured Vector Field Manipulation of Terahertz Wave along the Propagation Direction Based on Dielectric Metasurfaces

Abstract: The generation and manipulation of vector light fields are of great significance for both fundamental research and industrial applications of polarized optics. In recent years, the spatial domain control of structured vector fields has gradually expanded from two‐ to three‐dimensional, including traditional optics and meta‐optics. Here, a new method to generate and manipulate structured vector light fields along the propagation direction is proposed, and the functionality in terahertz band using all‐silicon metasurfaces is demonstrated. The coherent superposition of orthogonal circularly polarized terahertz waves through long focal depth and multifocal metalens is completed, and varying phase differences between them in the propagation direction via path accumulation or initial phase design are introduced, thereby continuous variation or independently designed vector polarization distributions in multiple planes are obtained. It is worth mentioning that the proposed scheme is not only for the design of transverse electric field components, but also shows a strong ability for manipulation of the longitudinal component. This scheme realizes the polarization distribution designs of three‐dimensional vector fields in three‐dimensional space, and provides a new inspiration for the generation and manipulation of vector beams based on meta‐optics.

Inhibition of buried cavities and defects in metal halide perovskite photodetectors via two-step spin-coating method

Abstract: The performance of perovskite photodetector (PPD) is sensitive to the quality of perovskite films. Solution-processed perovskite films suffer from the excess lead halide and irregular nanocavities located the buried interface,...

Intracavity spherical aberration for selective generation of single-transverse-mode Laguerre-Gaussian output with order up to 95

Abstract: Abstract We investigate the generation of single-transverse-mode Laguerre-Gaussian (LG) emission from a diode-end-pumped Nd:YVO 4 , 1064 nm laser using mode selection via intracavity spherical aberration (SA). We present both theoretical and experimental investigations, examining the limits of the order (both radial and angular indices) of the LG modes which can be produced, along with the resultant output power. We found that in order to generate single-mode emission of low-order LG modes which have relatively small beam diameters, lenses with shorter focal-length were required (to better differentiate neighboring LG modes via SA). The converse was true of LG modes with high-order. Through appropriate choice of the focal length of the intracavity lens, we were able to generate single-mode, LG 0,± m laser output with angular indices m selectable from 1 to 95, as well as those with non-zero radial indices p of up to 4.

In-Situ Growth of 2D Assisted Passivation layer Enable High-performance and Stable 2D/3D Stacked Perovskite Photodetectors for Visible Light Communication Applications

Abstract: Two-dimensional (2D) perovskites have shown more considerable advantages in terms of stability than their three-dimensional (3D) counterparts. However, the intrinsic poor light absorption and charge transport capacity impede the improvement...

Enhancing the field of view of a distributed-cavity laser incorporating cat-eye optics by compensating the field-curvature

Abstract: The influence of field curvature (FC) on a distributed-cavity laser incorporating cat-eye optics was theoretically and experimentally investigated. We found that the FC can defocus the cat-eye and seriously limit its field of view (FoV), since the cavity stability region becomes very narrow at long working distances of several meters. Three improved cat-eye designs are demonstrated, in which the FC-induced defocusing was compensated by choosing off-the-shelf components with appropriate parameters or by using a customized aspheric lens. With these new designs, a distributed-cavity diode-end-pumped Nd:YVO4 laser was capable of operating efficiently within a large receiver FoV of ±20°, which was an order of magnitude larger than that achieved prior to optimization (using a traditional cat-eye design), at a long working distance of 5 m. The effectiveness and robustness of these new designs pave the way for alignment-free lasers with long-distributed-cavities, which are essential for resonant laser charging applications.

All‐Silicon Diatomic Terahertz Metasurface with Tailorable Linear Polarization States

Abstract: Polarization plays a key role in fundamental science, and the improvement in miniaturization and practicability of polarization conversion devices could provide more degrees of freedom for light–matter interactions. Metasurfaces that can manipulate arbitrary polarization states at subwavelength scales can significantly reduce the complexity of meta‐optical systems. Here, a general design of an all‐silicon diatomic metasurface operating in the terahertz band that can generate a tailorable linear polarization state by the superposition of two meta‐atoms with individual geometric parameters is experimentally demonstrated. By periodically arranging polarization‐converting and polarization‐maintaining meta‐atoms, the existence of interference effects enables the proposed diatomic meta‐platform to act as an optimal linear polarization operator. The gradient arrangement of the meta‐molecules under the profile of the propagation phase is deduced by using the advanced Jones matrix, so that the polarization filtering and wavefront manipulation can be realized simultaneously, including the generation of tightly converged vortex and bifocal focusing beams. This demonstration of generating tailorable linear polarization states located on the Poincaré sphere directly from arbitrarily polarized waves can significantly facilitate the development of functional polarization meta‐devices.

Gigahertz femtosecond laser-by a novel asymmetric one-dimensional photonic crystal saturable absorber device with defect layer

Abstract: Abstract High repetition frequency (HRF) ultrashort pulse fiber laser has been widely used in laser cold processing. The technical solutions such as short cavity length fiber laser have been proposed to achieve HRF ultrashort pulse output recently. However, the application of material-based saturable absorbers in this field has been astricted due to the low modulation depth, low damage resistance threshold, and high saturation fluence. Here, we designed a one-dimensional asymmetric photonic crystal with defect layer (1D-APCDL) as a novel saturable absorber, where the defect layer is Bi1.6Sb0.4Te3 with high modulation depth. The harmonic pulse with 3.82 GHz repetition frequency is achieved at the wavelength of 1562 nm, which is the highest repetition frequency of the topological insulator-based ring fiber laser so far to the best of our knowledge. The research provides a new saturable absorber solution, and provides a new idea for the application of material-based nonlinear optical chip in high-repetition frequency ultrashort pulse fiber lasers.

Three-stimulus control ultrasensitive Dirac point modulator using an electromagnetically induced transparency-like terahertz metasurface with graphene.

Abstract: This letter presents a fabricated Dirac point modulator of a graphene-based terahertz electromagnetically induced transparency (EIT)-like metasurface (GrE & MS). Dynamic modulation is realized by applying three stimulus modes of optical pump, bias voltage, and optical pump-bias voltage combination. With increasing luminous flux or bias voltage, the transmission amplitude undergoes two stages: increasing and decreasing, because the graphene Fermi level shifts between the valence band, Dirac point, and conduction band. Thus, an approximate position of the Dirac point can be evaluated by the transmission spectrum fluctuation. The maximum modulation depth is measured to be 182% under 1 V. These findings provide a method for designing ultrasensitive terahertz modulation devices.

Versatile Polarization Conversion and Wavefront Shaping Based on Fully Phase‐Modulated Metasurface with Complex Amplitude Modulation

Abstract: The fully phase‐modulated metasurfaces, implementing independent wavefront control of output cross‐ and co‐polarized components under circularly polarized (CP) incidence, can effectively break the shackles that the Pancharatnam–Berry phases and spin‐decoupled metasurfaces can only manipulate the cross‐polarization component. With this, the scheme of complex amplitude modulation is introduced as a new degree of freedom, which can further modulate the intensity and phase of the output cross‐polarized (co‐polarized) component, and thus become an alternative approach for designing multi‐functional polarization manipulation metasurfaces. Three representative metasurfaces are verified with particular polarization conversion and wavefront shaping, demonstrating the flexibility and practicability of the design scheme. Such a concept opens up a new platform for multifarious integrated optics through harnessing the new degree of freedom and may further accelerate the development of metasurface polarization optics.

Niobium carbide MXene-optics fiber-sensor for high sensitivity humidity detection

Abstract: Niobium carbide (Nb2CTX) MXene is an emerging two-dimensional material and exhibits promising potential in relative humidity (RH) measurement because of its superior photoelectronic and structural properties. Here, Nb2CTX nanosheets were integrated with microfibers via an optical deposition method, and a fiber-optic-based RH sensing strategy was experimentally demonstrated. The ambient H2O molecules could be absorbed and intercalated into the Nb2CTX sheets, thereby modulating the transmission spectra of the microfiber interferometer. The RH sensing experiments showed that the transmission spectra initially blue-shifted as the RH levels increased from 18.5% to 72.4% RH, and the sensitivity was −86 pm/% RH because the effective refractive index of Nb2CTX changes, whereas the transmission spectra exhibited a red shift in the RH range of 72.4%–95.4% RH with a high sensitivity of 585 pm/% RH because of the structure of Nb2CTX variations. The combination of Nb2CTX MXene and fiber optics exhibits great prospects in the RH sensing field and brings innovative ideas for gas-sensing applications.

Ultra-broadband optical detection from the visible to the terahertz range using a miniature quartz tuning fork.

Abstract: We report and experimentally demonstrate a novel, to the best of our knowledge, sensitive and wideband optical detection strategy based on the light-induced thermoelastic effect in a miniature quartz tuning fork (mQTF) with low stiffness prongs. Compared with a traditional QTF, the soft prongs of the mQTF result in improved sensitivity. Experimental results demonstrate that the mQTF exhibits ∼54-fold superior sensitivity compared to a QTF, and the mQTF sensor has an ultra-broadband optical response, ranging from visible light to terahertz wavelengths. Its response time reaches 11.7 ms, and the minimum noise equivalent power (NEP) is measured to be 2.2 × 10-9 W Hz-1/2 at room temperature. The mQTF exhibits advantages in its cost-effectiveness, sensitivity, and ultra-broadband response, and provides a promising approach for the detection of low-dose optical and terahertz-wave radiation.

Low-concentration antibiotic detection in water based on enhanced photothermal effect

Abstract: Streptomycin sulfate (STS) is a broad-spectrum antibiotic widely present in water as a source of pollution. STS produces ototoxicity and nephrotoxicity if ingested in excess. Here, we propose a photothermal sensor to detect contaminated water based on a Nb2CTx MXene integrated few-mode fiber coupler (FMFC) and the photothermal effect of STS. Nb2CTx MXene exhibits strong absorption ability for biomolecules, which can enhance the interaction between STS and light by depositing it on the surface of the FMFC, thereby improving the detection performance of the proposed sensor. Under irradiation of a 405 nm laser, the photon energy is absorbed by STS and converted into heat energy, changing the transmission characteristics of the few-mode fiber. The results show that the sensitivity reaches 210.66 nm/(mg/ml) in the linear range of 0.02–0.1 mg/ml, with a detection limit of 94.93 ng/ml. In practical applications, the photothermal effect is stimulated by natural light to improve the suitability of the device application. Furthermore, this photothermal sensor eliminates complicated sample processing, making it potentially applicable for real-time food safety, environmental pollutant detection, and disease diagnosis.

High-efficiency Thulium-doped fiber laser at 1.7 μm

Abstract: An efficient Tm-doped fiber laser was demonstrated at the wavelength region of 1.7 μm, which wavelength was ever considered as an obstacle for efficient laser generation with Tm-doped fiber due to the serious re-absorption effect. In this work, bi-directional pump at 1570 nm was employed for sufficient pump absorption, and gain fiber length was optimized to decrease re-absorption loss of signal light and suppress amplified spontaneous emission in the 1.8–2 μm region. A maximum output power of 5.92 W at 1720 nm was achieved in experiment, corresponding to a slope efficiency with respect to the launched pump power of 64%. Numerical simulation was also implemented to investigate the further output power optimization. This work shows that a high 1.7 μm laser efficiency, which is comparable with that achieved with the special homemade Tm-doped fiber, can be realized by using the commercial silica Tm-doped fiber.