Wide Operating Wavelength Research Articles

Cascaded dual-channel broadband SPR fiber optic sensor based on Ag and Ag/ZnO/PDMS film structure.

In order to broaden the sensing bandwidth of surface plasmon resonance (SPR) sensors, we propose and demonstrate a dual-channel SPR fiber optic sensor with wide bandwidth. The sensor is fabricated using no-core fiber (NCF), in which the film consists of a silver film and a ZnO film. The sensing characteristics are investigated by simulation and experiment. The resonance wavelength range of the SPR sensor can be significantly tuned by varying the thickness of the ZnO film. In the experiments, a dual-channel SPR sensor that can be used for simultaneous detection of temperature and refractive index was realized by cascading ZnO/Ag film with Ag film. The experimental results show that the two sensing channels are independent without crosstalk. The sensitivity of this sensor is 3512 nm/RIU in the range of 1.333 ∼ 1.385 and 4.6 nm/°C in the range of 0 ∼ 60 °C, which is better than most of the current dual-channel SPR sensors. In addition, the experimental results show that this sensor has good stability in use. The sensor proposed in this work has the advantages of a wide operating wavelength range, simple and compact structure, and high sensitivity. It has a broad application prospect in the simultaneous measurement of refractive index and temperature of liquids.

Thermally tunable GeSi electro-absorption modulator with a wide effective operating wavelength range

We demonstrate a GeSi electro-absorption modulator with on-chip thermal tuning for the first time, to the best of our knowledge. Theoretical simulation proves that the device temperature can be tuned and the effective operating wavelength range can be broadened. When the heater power is 4.63 mW, the temperature of the waveguide increases by about 27 K and the theoretical operating wavelength range is broadened by 23.7 nm. The experimental results show that the optical transmission line shifted to the longer wavelength by 4.8 nm by every 1 mW heater power. The effective static operating wavelength range of the device is increased from 34.4 nm to 60.1 nm, which means it is broadened by 25.7 nm. The band edge shift coefficient of 0.76 nm/K is obtained by temperature simulation and linear fitting of the measured data. The device has a 3 dB EO bandwidth of 89 GHz at 3 V reverse bias, and the eye diagram measurement shows a data rate of 80 Gbit/s for non-return-to-zero on–off keying modulation and 100 Gbit/s for 4 pulse amplitude modulation in the 1526.8 nm to 1613.2 nm wavelength range as the heater power increases from 0 mW to 10.1 mW.

Recent Progress on Plasmonic and Dielectric Chiral Metasurfaces: Fundamentals, Design Strategies, and Implementation

AbstractOver the years, researchers have been exploring ways to artificially design chiral structures and materials, namely metamaterials and metasurfaces. They exhibit unique optical properties that can be used for various applications. However, metasurfaces comprise symmetry‐breaking structures that provide a more convenient solution for planar chiral optics regardless of whether they are plasmonic or dielectric. In general, plasmonic chiral metasurfaces are more suitable for applications requiring a high confinement level and substantial optical near‐field enhancement. In contrast, dielectric chiral metasurfaces are ideal for wide operating wavelength ranges and low losses. This review summarizes the recent progress on plasmonic and dielectric chiral metasurfaces. It includes the fundamental concepts, design strategies, and their implementation for applications in holographic displays, imaging and sensing, and detection. Moreover, an overview of chiral metasurfaces to generate the nonlinear effects, hosting bound states in the continuum, and the significant role of machine‐learning‐based design approaches are also discussed. Finally, some future developments are highlighted where chiral metasurfaces are expected to play a vital role.

Recent Progress in III–V Photodetectors Grown on Silicon

An efficient photodetector (PD) is a key component in silicon-based photonic integrated circuits (PICs). III–V PDs with low dark current density, large bandwidth, and wide operation wavelength range have become increasingly important for Si photonics in various applications. Monolithic integration of III–V PDs on Si by direct heteroepitaxy exhibits the lowest cost, the largest integration density, and the highest throughput. As the research of integrating III–V lasers on Si flourishes in the last decade, various types of III–V PDs on Si with different device structures and absorption materials have also been developed. While the integration of III–V lasers on Si using various technologies has been systematically reviewed, there are few reviews of integrating III–V PDs on Si. In this article, we review the most recent advances in III–V PDs directly grown on Si using two different epitaxial techniques: blanket heteroepitaxy and selective heteroepitaxy.

A waveguide-integrated self-powered van der Waals heterostructure photodetector with high performance at the telecom wavelength.

Two-dimensional (2D) materials are attractive candidates for high-performance photodetectors due to their wide operating wavelength and potential to integrate with silicon photonics. However, due to their limited atomic thickness and short carrier lifetime, they suffer from high driving source-drain voltages, weak light-matter interactions and low carrier collection efficiency. Here, we present a high-performance van der Waals (vdWs) heterostructure-based photodetector integrated on a silicon nitride photonic platform combining p-type black phosphorus (BP) and n-type molybdenum disulfide (MoS2). Owing to the efficient carrier separation process and dark current suppression at the junction interface of the vdWs heterostructure, high photodetectivity and a fast response speed can be achieved. A fast response time (∼2.08/3.54 μs), high responsivity (11.26 mA W-1), and a high light on/off ratio (104) operating in the near-infrared telecom band are obtained at zero bias. Our research highlights the great potential of the high-efficiency waveguide-integrated vdWs heterojunction photodetector for integrated optoelectronic systems, such as high-data-rate interconnects operated at standardized telecom wavelengths.

Optical angular transparency and broadband absorption based on photonic topological transition in black phosphorus/aluminum oxide hyperbolic metamaterial

Based on the photonic topological transition (PTT), the transmission properties of a black phosphorus/aluminum oxide multilayered hyperbolic metamaterial (HMM) are theoretically investigated in the mid-infrared region. The results demonstrate that an angular transparency window appears near the transition point of PTT, which is achieved by tailoring the topology of the HMM’s equi-frequency surface. The angular full width at half maximum of the transparency window is 2.34°, and the transmittance is higher than 99.8% at normal incidence. In addition, the operating wavelength can be flexibly tuned by adjusting the concentration of electrons. Besides, a layered cascade structure with a wide operating wavelength (1 µm) and an enhanced angular selectivity performance is proposed, which resolves the shortcoming of a single working wavelength. In addition, the spectral-selective behavior of absorption is also explained based on the PTT. These attractive properties make the black phosphorus-based HMM hold promise for potential applications in angularly selective systems and energy harvesting.

Harnessing Dynamical Encircling of an Exceptional Point in Anti-PT-Symmetric Integrated Photonic Systems.

Dynamically encircling an exceptional point in a non-Hermitian system can lead to chiral behaviors, but this process is difficult for on-chip PT-symmetric devices which require accurate control of gain and loss rates. Here, we experimentally demonstrated encircling an exceptional point with a fixed loss rate in a compact anti-PT-symmetric integrated photonic system, where chiral mode switching was achieved within a length that is an order of magnitude shorter than that of a PT-symmetric system. Based on the experimental demonstration, we proposed a topologically protected mode (de)multiplexer that is robust against fabrication errors with a wide operating wavelength range. With the advantages of simplified fabrication and characterization processes, the demonstrated system can be used for studying higher-order exceptional points and for exotic light manipulation.

Directional control of propagating graphene plasmons by strain engineering

Control of propagating surface plasmon on a scale beyond the diffraction limit is important for the development of integrated nanophotonic circuits and optical information technology. In this paper, a strain-based modulation mechanism for directional control of propagating graphene plasmons was proposed. We demonstrated numerically that the GPs can be directionally controlled by the implementation of strain on graphene. The topologies of GPs excited by a z-polarized optical emitter in unstrained and strained graphene were illustrated both in real space and momentum space. When imposing strain engineering to graphene in different directions with a different modulus, multi-dimensional control of GPs in any direction can be realized. The simulated propagation length ratio η of the GPs can reach 3.5 when the strain with a modulus of 0.20 is applied along or perpendicular to the zigzag direction of graphene. Besides, the effect of PDMS on GPs was investigated finally for the experiments to be carried out and we show that the PDMS does not affect the generation of directional GPs under strain engineering. Our proposed directional control of GPs not only has the advantages of wide operating wavelength but does not require additional coupling mechanisms, which is beneficial to the design of integrated photonic devices.

Broadband GaSb saturable absorber for pulse generation from C-band to mid-infrared

Material with nonlinear response to light intensity, i.e., the saturable absorber, is an important mean to realize pulsed lasers which have wide applications in many fields. In this paper, we report a broadband optical-intensity modulator, magnetron-sputtered GaSb thin film, for pulse generation from C-band to mid-infrared regions. By the virtue of GaSb thin film, soliton pulses with 308 fs/585 fs pulse width and 17.82 mW/64.69 mW output power were obtained at 1559 nm/1902 nm in an Er-doped fiber laser (EDFL) and a Tm-doped fiber laser (TDFL) respectively. Furthermore, GaSb thin film coated on a gold mirror was successfully used to achieve 2783 nm Q-switching operation of a Er3+:ZBLAN fiber laser with a maximum output power of 420 mW. With such a wide operation wavelength range, GaSb thin film is of great potential for many nonlinear optical applications.

Broadband high-efficiency near-infrared graphene phase modulators enabled by metal–nanoribbon integrated hybrid plasmonic waveguides

Abstract The phase modulator is a key component in optical communications for its phase modulation functions. In this paper, we numerically demonstrate a variety of ultra-compact high-efficiency graphene phase modulators (GPMs) based on metal–nanoribbon integrated hybrid plasmonic waveguides in the near-infrared region. Benefiting from the good in-plane mode polarization matching and strong hybrid surface plasmon polariton and graphene interaction, the 20 μm-length GPM can achieve excellent phase modulation performance with a good phase and amplitude decoupling effect, a low insertion loss around 0.3 dB/μm, a high modulation efficiency with V π L π of 118.67 V μm at 1.55 μm, which is 1–3 orders improvement compared to the state-of-the-art graphene modulators. Furthermore, it has a wide modulation bandwidth of 67.96 GHz, a low energy consumption of 157.49 fJ/bit, and a wide operating wavelength ranging from 1.3 to 1.8 μm. By reducing the overlap width of the graphene–Al2O3–graphene capacitor, the modulation bandwidth and energy consumption of the modulator can be further improved to 370.36 GHz and 30.22 fJ/bit, respectively. These compact and energy-efficient GPMs may hold a key to various high-speed telecommunications, interconnects, and other graphene-based integrated photonics applications.

Highly efficient mode-locked and Q-switched Er3+-doped fiber lasers using a gold nanorod saturable absorber

Mode-locked and Q-switched pulsed fiber laser sources with wavelengths of 1.55 μm are widely used in various fields. Gold nanorods (GNRs) have been applied in biomedicine and optics owing to their biocompatibility, easy fabrication, and unique optical properties. This paper presents the analysis of a saturable absorber based on a colloidal gold nanorod (GNR) thin film for dual-function passively mode-locked and Q-switched 1.55-μm fiber lasers. The colloidal GNR thin film possesses superior properties such as a wide operating wavelength range, large nonlinear absorption coefficient, and a picosecond-order recovery time. Its modulation depth and saturation intensity at 1.55 μm are 7.8% and 6.55 MW/cm2, respectively. Passive mode-locked or Q-switched laser operation is achieved by changing the number of GNR thin-film layers. The advantages of these high-quality GNRs in mode-locked and Q-switched fiber lasers with record-high slope efficiency are verified by conducting comprehensive material and laser dynamic analyses. The self-starting mode-locked fiber laser with an efficiency as high as 24.91% and passively Q-switched fiber laser with the maximum energy of 0.403 μJ are successfully demonstrated. This paper presents the novel demonstration of reconfigurable mode-locked and Q-switched all-fiber lasers by incorporating colloidal GNR thin films.

Fractional Fourier single-pixel imaging.

Single-pixel imaging technology has a number of advantages over conventional imaging approaches, such as wide operation wavelength region, compressive sampling, low light radiation dose and insensitivity to distortion. Here, we report on a novel single-pixel imaging based on fractional Fourier transform (FRFT), which captures images by acquiring the fractional-domain information of targets. With the use of structured illumination of two-dimensional FRFT base patterns, FRFT coefficients of the object could be measured by single-pixel detection. Then, the object image is achieved by performing inverse FRFT on the measurements. Furthermore, the proposed method can reconstruct the object image from sub-Nyquist measurements because of the sparsity of image data in fractional domain. In comparison with traditional single-pixel imaging, it provides a new degree of freedom, namely fractional order, and therefore has more flexibility and new features for practical applications. In experiments, the proposed method has been applied for edge detection of object, with an adjustable parameter as a new degree of freedom.

Asymmetric-ration optical power couplers based on nano-pixel structure

An optical power coupler is one of the most well-used components in integrated photonics. Although couplers with an output power ratio 1:1 have been widely studied in the past, constructing asymmetric-ration optical power couplers is still an issue that is difficult to be addressed by using traditional Y-branch waveguides. Artificial intelligence (AI) assisted design is an effective technique for realizing complex optical structures. In this work, we have designed asymmetric-ration optical power couplers by using AI assisted design. Two couplers with the targeted splitting power ratio as 1:9 and 1:99 have been designed, respectively. In the AI assisted design, the coupler area was divided into discrete nano-pixels in the shape of circular holes with the same dimension. The AI controlled each pixel to be occupied by waveguide or air and trialed the occupation of each pixel one by one. In a 3.4 × 3.2 µm2 area, it took 1452 trials to obtain one optimized coupler. As a result, a splitting power ratio of 1:9.007 and 1:99.004 for the two couplers has been confirmed by using the finite-difference time-domain method. In addition, the waveguide configuration was further modified as the excess loss of the AI-designed coupler was a bit high, more than 3.50 dB. The way to reduce the loss is as follows: 1) positioning optimization of the output waveguide to avoid light scattering at the boundary between the coupler and the output waveguide, and 2) widening the output waveguide width to avoid insufficient light coupling. As a result, a scattering loss reduction of 1.7 dB by position optimization, and a coupling loss reduction of 1.6 dB by width widening were confirmed. The achieved design also exhibited a wide operation wavelength ranging from 1500–1600 nm in addition to sufficient fabrication tolerance of ±10 nm (± 11%).

Wide-band silicon photonic MOEMS spectrometer requiring a single photodetector.

We propose a novel integrated micro-opto-mechanical-system spectrometer design in a monochromator setup. It consists of a concave grating fabricated in a planar waveguide that is connected to a rotational electrostatic actuator, which enables angular tuning of the grating. The spectrometer covers a wide operational wavelength range (>100 nm), covering partially the E-band and fully covering the S, C, and L-bands (1416.6 nm - 1696.6 nm), and requires a single photodetector to acquire the spectrum. The spectrometer is designed to exhibit low optical losses throughout the range of motion. The spectrum can be acquired at a frequency of 1.76 kHz. The simulated acquired spectrum features an average insertion loss of -1.8 dB and a crosstalk better than -70 dB with a resolution as low as 1.62 nm. The entire device covers an area of 4 mm x 4 mm and is based on a thick silicon-on-insulator platform.

Liquid-crystal splitter for generating and separating autofocusing and autodefocusing circular Airy beams.

A unique splitter is proposed and demonstrated to realize the generation and separation of autofocusing and autodefocusing circular Airy beams (CABs). The design of the splitter is derived from the Fourier transform of a CAB associated with the Pancharatnam-Berry phase, and the fabrication is carried out via a liquid-crystal photo-patterning technique. Autofocusing and autodefocusing CABs of orthogonal circular polarization states are spatially diffracted under the modulation of the splitter, and the energy distribution between these two CABs can be controlled by the incident polarization. A focal length of 40 cm is obtained, which can be customized as required. The propagation dynamics of the generated autofocusing and autodefocusing CABs are investigated, and the experimental results are in good accordance with the corresponding simulations. The additional merits of the splitter, such as reconfigurability, tunability, high efficiency, and wide operating wavelength range, may motivate novel applications of CABs in the areas of laser optics, biomedicine, and modern displays.

Design of silicon waveguide polarization beam splitter based on reversed Δβ directional coupler

We report a directional coupler type polarization beam splitter using silicon waveguides designed for 1550–1600 nm wavelengths. The device uses the coupling strength difference between the TE and TM modes. We use a reversed Δβ structure to achieve a wide operational wavelength range. The gap between the waveguides needs to be wide enough to attain a sufficient extinction ratio for the TE mode. Simulation results show that an over 100 nm operational 20 dB extinction ratio wavelength range can be attained at 1520–1620 nm wavelengths by this simple structure. The fabrication width tolerance exceeds 10 nm which is enough for foundry processes.

Hybrid ultrathin-silicon/graphene waveguide photodetector with a loop mirror reflector.

Graphene has emerged as a promising solution for on-chip ultrafast photodetection for its advantages of easy integration, high mobility, adjustable chemical potential, and wide operation wavelength range. In order to realize high-performance photodetectors, it is very important to achieve efficient light absorption in the active region. In this work, a compact and high-speed hybrid silicon/graphene photodetector is proposed and demonstrated by utilizing an ultra-thin silicon photonic waveguide integrated with a loop mirror. With this design, the graphene absorption rate for the fundamental mode of TE polarization is improved by ∼5 times compared to that in the conventional hybrid silicon/graphene waveguide with hco=220 nm. One can achieve 80% light absorption ratio within the active-region length of only 20 µm for the present silicon/graphene waveguide photodetector at 1550 nm. For the fabricated device, the responsivity is about 25 mA/W under 0.3V bias voltage and the 3-dB bandwidth is about 17 GHz. It is expected to achieve very high bandwidth by introducing high-quality Al2O3 insulator layers and reducing the graphene channel length in the future.

High performance temperature and refractive index dual-purpose sensor based on the ethanol-sealed metal-dielectric-metal waveguide

In order to enhance the working performance of existing temperature sensor and refractive index sensor of sub-wavelength waveguide, the design of ring regular octagon surface plasmon resonance sensor with sharp transmission peak, high sensitivity and high integration was proposed in this paper based on surface plasmon polaritons. The feasibility of using ethanol as a thermosensitive filler to establish a linear conversion relationship between temperature and effective refractive index was analyzed theoretically. The reason why the real part of effective refractive index changes abruptly with the change of waveguide width is also explained. The multimode interference coupled mode theory (MICMT) was used to fit and analyze the transmission peak of the sensor, and then the finite element methods (FEM) is used for simulation analysis. Results obtained by the theory of the MICMT are consistent very well with those from simulation. In order to obtain the optimal parameter setting of the ring regular octagon surface plasmon resonance sensor, various parameters of the sensor are simulated by FEM. It is found that increasing <i>L</i> and decreasing <i>H</i> will improve the sensitivity of the sensor, while decreasing parameter <i>w</i> can not only improve the amplitude of transmission peak, but also keep the sensitivity unchanged. This characteristic of parameter <i>w</i> greatly improves the robustness of the sensor. All kinds of physical phenomena in this paper are analyzed in detail. Firstly, the phenomenon of transmission peak displacement caused by parameter changes is explained through the analysis of magnetic field distribution, and then the phenomenon of inconsistent sensitivity of different transmission peaks is explained through photon energy formula. Compared with the previous structural design, the dual-purpose sensor has many advantages such as wide operating wavelength range, narrow full width at half maximum and easy to integrate. As a temperature sensor and refractive index sensor, its sensitivity was as high as 0.9 nm/℃ and 2400 nm/RIU. The study of this structure broke through the limitations of some traditional cavities, in order to provide a high- performance cavity selection for the micro-nano photon temperature and refractive index dual-purpose sensor based on the design of surface plasmon polaritons in the future.

Broadband graphene modulator based on a plus-shaped plasmonic slot waveguide.

A novel broadband graphene modulator based on a plus-shaped plasmonic slot waveguide (PSPSW) has been demonstrated. The designed modulator includes four square silver nanowires and a graphene-${{\rm Al}_2}{{\rm O}_3}$Al2O3-graphene layer. Four silver nanowires are separated from each other by an ${{\rm SiO}_2}$SiO2 gap layer, forming a plus-shaped slot waveguide. This modulator overcomes the challenge of polarization mismatch between the electric field of the plasmonic mode and the graphene plane. The highly confined plasmonic mode can strongly interact with the graphene sheets. The properties of three eigenmodes and the effect of the geometric parameters have been studied. By geometric optimization, this modulator could offer a high modulation depth of 1.13 dB/µm, a wide operation wavelength ranging from 1200 to 1600 nm, and a large modulation bandwidth of 95 GHz. This design may promote the development of graphene-based nanophotonic devices.

Optical bistable switch based on the nonlinear Kerr effect of chalcogenide glass in a rectangular defect of a photonic crystal

An optical bistable switch based on a photonic crystal resonator using the nonlinear effect of a chalcogenide glass in a rectangular defect cavity is proposed and investigated numerically. The influences of the designed cavity and refractive index of the Kerr nonlinear medium on the transmission of the resonator are analyzed precisely through finite-difference time-domain simulation. The simulation results show that our compact structure possesses excellent switching characteristics by tuning the incident electric intensity. The properties of the optical bistability are investigated at the resonance wavelength with three different detuning parameters. In addition, the results show that this switch has a wide operating wavelength regime and fast operation speed of 90 Gb/s. Considering numerous characteristics, such a high-speed switch can find application for all-optical devices.