Broadband Operation Research Articles

Numerical modeling of SNSPD absorption utilizing optical conductivity with quantum corrections

Superconducting nanowire single-photon detectors are widely used in various fields of physics and technology, due to their high efficiency and timing precision. Although, in principle, their detection mechanism offers broadband operation, their wavelength range has to be optimized by the optical cavity parameters for a specific task. We present a study of the optical absorption of a superconducting nanowire single photon detector with an optical cavity. The optical properties of the niobium nitride films, measured by spectroscopic ellipsometry, were modeled using the Drude–Lorentz model with quantum corrections. The numerical simulations of the optical response of the detectors show that the wavelength range of the detector is not solely determined by its geometry, but the optical conductivity of the disordered thin metallic films contributes considerably. This contribution can be conveniently expressed by the ratio of imaginary and real parts of the optical conductivity. This knowledge can be utilized in detector design.

A novel cut-out piezoelectric beam with limiters for broadband energy harvesting

In this paper, we proposed a novel cut-out piezoelectric beam with two pairs of motion limiter for broadband operation. By means of the finite element simulation, a superior geometric structure of the corresponding linear model is designed and the model parameters are determined, then the simulation results are verified by experiments. The subsequent experiments mainly investigate the effect of the position of the limiter on the beam and the size of the limiting gap on the amplitude–frequency response of the system. The experimental results show that the frequency bandwidth of the first resonance peak can be significantly expanded from 2.45Hz to 6.28Hz by selecting suitable limiter parameters, which can increase of 256.33% compared with no limiter. Meanwhile, limiters also cause a maximum 171.79% increase in the primary resonance voltage amplitude, and the level of anti-resonance valley can be increased up to 5.35 times. Finally, the influence of external resistance load on the output power of the system is discussed through detailed parametric study, and the maximum power output of 370μW is achieved.

Metasurface-based broadband full Stokes polarimeter with optimized simulation design

A polarimeter, fundamental for characterizing the polarization state of light, is critical for advancing optical measurement techniques by delivering precise polarization information. A compact and portable polarimeter holds particular importance in applications like remote sensing and medical diagnosis. However, existing methods for developing a compact polarimeter are difficult to achieve full Stokes vector detection for broadband operation, and the noise immunity is also very weak. These defects significantly constrain the versatility of polarimeters across diverse application scenarios. Herein, a metadevice with dual-layer subwavelength grating structure for full Stokes vector detection has been proposed, capable of simultaneously achieving broadband detection and noise suppression. The intensity of the four elliptical polarization states of the incident light can be captured by four regions on this metadevice, enabling the computation of the full polarization state information via Mueller matrix inversion. Additionally, a set of optimized retardance at 0.73π and orientation angles at 43°, 80°, 111°, and 146° is provided to effectively suppress the noise. The results indicate that the recovery error remains below 5% across the 450–650 nm spectral range, showcasing a 1.5-fold enhancement in noise suppression capability compared to conventional structures.

Asymmetric bi-level dual-core mode converter for high-efficiency and polarization-insensitive O-band fiber-chip edge coupling: breaking the critical size limitation

Abstract Efficient coupling between optical fibers and on-chip photonic waveguides has long been a crucial issue for photonic chips used in various applications. Edge couplers (ECs) based on an inverse taper have seen widespread utilization due to their intrinsic broadband operation. However, it still remains a big challenge to realize polarization-insensitive low-loss ECs working at the O-band (1,260–1,360 nm), mainly due to the strong polarization dependence of the mode coupling/conversion and the difficulty to fabricate the taper tip with an ultra-small feature size. In this paper, a high-efficiency and polarization-insensitive O-band EC is proposed and demonstrated with great advantages that is fully compatible with the current 130-nm-node fabrication processes. By introducing an asymmetric bi-level dual-core mode converter, the fundamental mode confined in the thick core is evanescently coupled to that in the thin core, which has an expanded mode size matched well with the fiber and works well for both TE/TM-polarizations. Particularly, no bi-level junction in the propagation direction is introduced between the thick and thin waveguide sections, thereby breaking the critical limitation of ultra-small feature sizes. The calculated coupling loss is 0.44–0.56/0.48–0.61 dB across the O-band, while achieving 1-dB bandwidths exceeding 340/230 nm for the TE/TM-polarization modes. For the fabricated ECs, the peak coupling loss is ∼0.82 dB with a polarization dependent loss of ∼0.31 dB at the O-band when coupled to a fiber with a mode field diameter of 4 μm. It is expected that this coupling scheme promisingly provides a general solution even for other material platforms, e.g., lithium niobate, silicon nitride and so on.

Ultra‐Wideband Terahertz Integrated Polarization Multiplexer

AbstractPolarization‐division multiplexing is crucial for increasing channel capacity and spectral efficiency in communications. A key component is the polarization multiplexer, which combines or separates signals with orthogonal polarizations. Existing planar multiplexers lack an ultrawide band for terahertz communications. While microwave‐inspired orthomode transducers (OMTs) provide broadband operation, they suffer from high ohmic loss and bulkiness at terahertz frequencies. Optical integrated polarization beam splitters (PBSs) offer low loss and good integrability but have narrow bandwidths. This work presents a substrateless all‐silicon polarization multiplexer based on tapered directional couplers and air‐silicon effective mediums, integrated monolithically on a compact footprint. The device demonstrates a 37.8% fractional bandwidth, an average insertion loss of 1 dB, and a polarization extinction ratio above 20 dB over 225–330 GHz. This superior performance is enabled by the anisotropy of the effective medium claddings, affecting the two orthogonal guided modes differently. The multiplexer enables simultaneous two‐channel terahertz fiber communications with polarization diversity. It supports aggregated data rates up to 155 and 190 Gbit with bit error rates below hard‐ and soft‐decision forward‐error‐correction limits, respectively. This advancement holds promise for 6G terahertz integrated systems with enhanced channel capacities.

PSF-engineered snapshot full-Stokes polarizing-spectral-imaging via metasurface with reciprocally encoded anisotropic detour phase

A broadband snapshot full-Stokes polarizing-spectral-imaging (PSI) is achieved by reciprocally designing a metal–insulator-metal metasurface with anisotropic detour phase to generate polarizing-spectrally dependent dot-array-shaped point-spread-function (PSF), and the high dimensional information can be retrieved from one snapshot intensity image through the post-computation. It overcomes the restriction on the wavelength selection in principle faced by the propagating phase modulation scheme used in the previous metasurface-based PSI approaches, and brings advantages including compact configuration, fast acquisition and broadband operation. The dependence of the engineered PSF on the polarizing-spectral channel across 100 nm in the visible band is experimentally verified and analyzed, consistent well with the simulation. Reconstruction results for the high dimensional imaging are presented in simulations and experiments based on the established model.

A Broadband MS-Based Circularly Polarized Antenna Array Using Sequential-Phase Feeding Network.

This paper introduces the design of a circularly polarized metasurface-based antenna array for C-band satellite applications that owns broadband operation and high gain characteristics. The single radiating element comprises a Y-shape patch and an above-placed 2 × 2 unit-cell metasurface. Further improvement in operating bandwidth and broadside gain is achieved by arranging four single elements in a 2 × 2 configuration and a sequential-phase feed network. A prototype has been fabricated and measured to validate the feasibility of the proposed antenna array. The measured operating bandwidth is 20% (4.50-5.50 GHz), which is an overlap between a -10 dB impedance bandwidth of 29.8% (4.50-5.99 GHz) and a 3 dB axial ratio bandwidth of 20% (4.50-5.50 GHz). Across this operating band, the peak broadside gain is 10.5 dBi. Compared with the recently published studies, the proposed array is a prominent design for producing a wide operating bandwidth and relatively high gains while maintaining the overall compact dimensions.

Broadband and efficient terahertz helicity inversion by a reconfigurable reflective metasurface based on vanadium dioxide

We experimentally demonstrate the broadband and highly efficient inversion of the rotation direction of the terahertz circular polarization achieved by a dynamic metasurface with vanadium dioxide (VO2). This metasurface converts linear polarization into circular polarization. The rotational direction of the output circular polarization can be reversed based on the VO2 phase transition. The VO2 state can be dynamically switched by injecting direct current into an on-chip circuit. To improve the terahertz-wave utilization efficiency, the metasurface is operated at an incident angle of 45°, thereby eliminating the beam splitter typically used to separate the outgoing wave from the incident wave at normal incidence. To achieve broadband operation, we employ a dispersion-cancelation strategy that cancels the dispersive phase responses between orthogonal linear polarizations. This strategy was previously developed for static metasurfaces; we have applied it to the design of dynamic metasurfaces. At a center frequency of 0.99 THz, the experimental evaluation demonstrated helicity switching with conversion efficiencies of 92% and 87% for the insulating and metallic states of VO2, respectively. Dispersion cancelation is simultaneously achieved for the insulating and metallic states of VO2, resulting in a relative bandwidth of 0.26, which is 3.2 times broader than that of a previously developed efficient dynamic metasurface.

Broadband transparent Huygens' spaceplates

Spaceplates have emerged in the context of nonlocal metasurfaces, enabling the compression of optical systems by minimizing the required empty space between their components. In this work, we design and analyze spaceplates that support resonances with opposite symmetries, operating under the so-called Huygens’ condition. Using the temporal coupled-mode theory, we demonstrate that the spatial compression provided by Huygens’ spaceplates is twice that of conventional single-resonance counterparts. Additionally, they can support broader operational bandwidths and numerical apertures, facilitating the reduction of chromatic aberrations. Moreover, Huygens’ spaceplates maintain nearly full transparency over a wide frequency and angular range, allowing their straightforward cascading for multi-frequency broadband operation. Finally, we propose a physical implementation of a Huygens’ spaceplate for optical frequencies based on a photonic crystal slab geometry.

Four-channel graphene optical receiver

Abstract Silicon photonics with the advantages of low power consumption and low fabrication cost is a crucial technology for facilitating high-capacity optical communications and interconnects. The graphene photodetectors (GPDs) featuring broadband operation, high speed, and low integration cost can be good additions to the SiGe photodetectors, supporting high-speed photodetection in wavelength bands beyond 1.6 μm on silicon. Here we realize a silicon-integrated four-channel wavelength division multiplexing (WDM) optical receiver based on a micro-ring resonator (MRR) array and four p-n homojunction GPDs. These photo-thermoelectric (PTE) GPDs exhibit zero-bias responsivities of ∼1.1 V W−1 and set-up limited 3 dB-bandwidth >67 GHz. The GPDs show good consistence benefiting from the compact active region array (0.006 mm2) covered by a single mechanically exfoliated hBN/graphene/hBN stack. Moreover, the WDM graphene optical receiver realized 4 × 16 Gbps non-return-to-zero optical signal transmission. To the best of our knowledge, it is the first GPD-array-based optical receiver using high-quality mechanically exfoliated graphene and edge graphene-metal contacts with low resistances. Apparently, our design is also compatible with CVD-grown graphene. This work sheds light on the large-scale integration of GPDs with high consistency and uniformity, enabling the application of high-quality mechanically exfoliated graphene, and promoting the development of the graphene photonic integrated circuits.

Monitoring of neoadjuvant chemotherapy through time domain diffuse optics: breast tissue composition changes and collagen discriminative potential.

The purpose of this clinical study is to test a broad spectral range (635-1060 nm) time-domain diffuse optical spectroscopy in monitoring the response of breast cancer patients to neoadjuvant chemotherapy (NAC). The broadband operation allows us to fully analyze tissue composition in terms of hemoglobin, water, lipids and collagen concentration, which has never been systematically studied until now during the course of therapy. Patients are subjected to multiple breast optical imaging sessions, each one performed at different stages of NAC, both on tumor-bearing and contralateral healthy breasts. We correlate the optical results with conventional imaging techniques and pathological response. Preliminary outcomes on 10 patients' data show an average significant reduction in the concentrations of oxy-hemoglobin (-53%, p = 0.0020), collagen (-36%, p = 0.0039) and water (-15%, p = 0.0195), and increase in lipids (+39%, p = 0.0137) from baseline to the end of therapy in the tumor-bearing breast of patients who responded to therapy at least partially. With respect to scattering, the scattering amplitude, a, increases slightly (+15%, p = 0.0039) by the end of the therapy compared to the baseline, while the scattering slope, b, shows no significant change (+4%, p = 0.9219). Some change in the constituents' concentrations was also noticed in the contralateral healthy breast, even though it was significant only for oxy-hemoglobin concentration. We observed that collagen seems to be the only component distinguishing between complete and partial responders by the end of 2-3 weeks from the baseline. In the complete responder group, collagen significantly decreased after 2-3 weeks with respect to baseline (p = 0.0423). While the partial responder group also showed a decrease, it did not reach statistical significance (p = 0.1012). This suggests that collagen could serve as a potential biomarker to measure NAC effectiveness early during treatment. Even though obtained on a small group of patients, these initial results are consistent with those of standard medical modalities and highlight the sensitivity of the technique to changes that occur in breast composition during NAC.

Dynamic control of polarization conversion based on borophene nanostructures in optical communication bands

Polarized light has a number of potential applications in the communication bands, including optical communication, polarization imaging, quantum emission, and quantum communication. Nonetheless, there is a need to enhance the dynamic tunability, broadband operation, and flexibility of polarization control. Here, a borophene structure is proposed to dynamically control the polarization state of reflected light. The coherent excitation of localized surface plasmons (LSPs) empowers the achievement of a perfect linearly-circularly polarization conversion at the commercially important communication wavelength of 1550 nm. The dynamic tunability and switching, as well as the arbitrary polarization conversion, are enabled over a wide spectral range by modulating the carrier concentration of borophene. Moreover, by deforming the borophene array and alternately stimulating the upper and lower layers of the LSPs mode, the polarization rotation direction can be flexibly switched. Finally, the process of near-field coupling between the LSPs and dipole light source positioned at a chosen hotspot is demonstrated. This coupling enables polarization-tunable spontaneous emission enhancement, with a spontaneous emission enhancement exceeding 900. The proposed design contributes to enhancing the speed and efficiency of communication within the domain of quantum communication.

Multi-wavelength and broadband plasmonic switching with V-shaped plasmonic nanostructures on a VO2 coated plasmonic substrate

In this paper, periodic arrays of identical V-shaped gold nanostructures and variable V-shaped gold nanostructures are designed on top of a gold-coated silicon dioxide (SiO2) substrate with a thin spacer layer of vanadium dioxide (VO2) to realize multi-wavelength and broadband plasmonic switches, respectively. The periodic array of identical V-shaped nanostructures (IVNSs) with small inter-particle separation leads to coupled interactions of the elementary plasmons of a V-shaped nanostructure (VNS), resulting in a hybridized plasmon response with two longitudinal plasmonic modes in the reflectance spectra of the proposed switches when the incident light is polarized in the x-direction. The x-direction is oriented along the axis that joins the V-junctions of all VNSs in one unit cell of the periodic array. On exposure to temperature, electric field, or optical stimulus, the VO2 layer transforms from its monoclinic semiconducting state to its rutile metallic state, leading to an overall change in the reflectance spectra obtained from the proposed nanostructures and resulting in an efficient multi-wavelength switching action. Finite difference time domain modelling is employed to demonstrate that an extinction ratio (ER) >12 dB at two wavelengths can be achieved by employing the proposed switches based on periodic arrays of IVNSs. Further, plasmonic switches based on variable V-shaped nanostructures—i.e. multiple VNSs with variable arm lengths in one unit cell of a periodic array—are proposed for broadband switching. In the broadband operation mode, we report an ER >5 dB over an operational wavelength range >1400 nm in the near-IR spectral range spanning over all optical communication bands, i.e. the O, E, S, C, L and U bands. Further, it is also demonstrated that the wavelength of operation for these switches can be tuned by varying the geometrical parameters of the proposed switches. These switches have the potential to be employed in communication networks where ultrasmall and ultrafast switches with multi-wavelength operation or switching over a wide operational bandwidth are inevitably required.

Octave‐Spanning Second‐Harmonic Generation in Dispersion‐Engineered Lithium Niobate‐on‐Insulator Microwaveguide

Broadband lasers, e.g., ultrashort lasers, optical supercontinuum, and frequency combs, are revolutionary coherent light sources, which enable a plethora of state‐of‐the‐art applications ranging from precision spectroscopy to optical clocks. However, the spectral broadening of these coherent light sources mainly relies on the third‐order nonlinearity () and is difficult to extend to the visible or shorter wavelength regime. Second‐order nonlinearity (), which is orders of magnitude larger than , becomes a powerful tool for the frequency translation if its broadband operation is well addressed. Herein, an octave‐spanning second‐harmonic generation scheme is experimentally demonstrated beyond an extremely large frequency range of 135 THz and high conversion efficiency of 1% for sub‐100 pJ for the near‐infrared picosecond supercontinuum in a fiber–waveguide–fiber configuration. The process relies on ultrabroadband birefringence phase matching in the dispersion‐engineered lithium niobate‐on‐insulator ridge microwaveguide. The mode area of microwaveguide well matches with single‐mode lens fiber, reducing coupling loss and ensuring easy packaging. The method provides a new approach to span the wavelength range of coherent light with ‐based wavelength translation for supercontinuum or frequency combs into the visible regime. The result would find applications in spectroscopy, astrophysics, atomic optics, optical synthesis, etc.

A 30-60 GHz Broadband Low LO-Drive Down-Conversion Mixer with Active IF Balun in 65 nm CMOS Technology.

A 30~60 GHz broadband down-conversion mixer driven by low local oscillator (LO) power is presented. The down-conversion mixer utilizes an input signal coupling technique based on the Marchand balun to achieve broadband operation and achieves low LO power drive and low DC power consumption through the use of a weak inversion bias with Gilbert switching devices. The broadband conversion of single-ended to differential signals is achieved using the Marchand balun with compensation lines, and an equivalent circuit analysis is performed. For the intermediate frequency (IF) output, a self-biased IF trans-impedance amplifier with current reusing and an active IF balun structure are used to achieve signal amplification and single-ended signal output. Test results show that the proposed mixer achieves a conversion gain of -1.2 to 6.4 dB in an IF output bandwidth of 0.1 to 5 GHz at radio frequency (RF) input frequencies of 30 to 60 GHz and LO driving power of -10 dBm. The DC power consumption of the core mixing unit of the proposed mixer is 4.8 mW, and the DC power consumption including the IF amplifier is 28.3 mW. The proposed mixer uses a 65 nm CMOS technology with a chip area of 0.26 mm2.

Multilayer-laminated optically transparent 300-GHz-band transmissive beamforming metasurface for wireless communication

A 300-GHz-band transmission-type multilayer metasurface beamformer based on a Jerusalem cross geometry is presented. A metamaterial cell with a continuous 2π phase variation for the radius change was designed and used in the fabrication of a reference device and three types of beamforming devices. The beamforming metasurface devices achieved steering angles of θ = 18°, θ = 30°, and θ = 38°, which were in good agreement with simulated results. A broadband operation in a 40 GHz band, from 280 GHz to 320 GHz was evaluated, showing only minor frequency dependence of the beamforming angles. The design and fabrication methodology can be applied to various types of metasurface devices, such as circular and fan lenses, beamformers, polarization switches, and so on for millimeter-wave frequency bands that are considered to be used in future 6 G wireless network systems.

A broadband Millimeter-Wave rectenna using substrate Integrated Waveguide

In this paper, a circularly polarized rectenna is proposed for microwave energy transmission, which is composed of a broadband Substrate Integrated Waveguide (SIW) antenna and a rectifier circuit. A dielectric resonator is loaded on the SIW antenna, enhancing the impedance bandwidth. Circular polarization is achieved by chamfering the diagonal of the rectangular patch. Two sections of microstrip branches are employed for good impedance matching over the broadband operation. Measured results show that the proposed rectenna has a good impedance performance (|S11| < −10 dB) and high RF-DC conversion efficiency (>50 %) over a relative bandwidth of 22.9 % (29–36.5 GHz). The maximum conversion efficiency of 67.5 % is realized at the input power of 18 dBm.

Subwavelength and broadband on-chip mode splitting with shifted junctions

We design and fabricate a sub-wavelength on-chip mode splitter based on the implementation of a shifted junction between a single-mode waveguide and a multimode waveguide. A proper choice of the device parameters enables to split the input beam into a combination of different guided modes of the multimode waveguide, minimizing radiation and reflection losses that amount to ∼ 0.4 dB in our experiments. Because the splitting mechanism does not rely on phase-matching, we achieve broadband operation that could exceed 200 nm bandwidth (&lt;0.5 dB splitting variation). This approach ensures temporal and phase synchronization among the output modes, with applications spanning from the emergent multimode photonics platform to traditional single-mode photonics operations.

Compact silicon-based Ka-band tunable-phase photonic microwave frequency downconverter.

In this paper, a compact silicon-based photonic microwave frequency downconverter with broadband operation capability and continuous phase shift tunability is proposed and experimentally demonstrated. The photonic converter mainly comprises two micro-ring modulators (MRMs) connected in parallel and a cascaded resonator-based optical bandpass filter (OBPF) whose size is merely 200 × 700 µm2. In the proposed device, a radio frequency (RF) signal and a local oscillator (LO) signal drive the two MRMs for realizing the electro-optic conversion. The OBPF is utilized for selecting the first-order sidebands of both RF and LO signals. By manipulating the phase difference between the RF and LO optical sidebands through thermal-optic effect, the phase of the obtained intermediate frequency (IF) signal from a photodiode can be tuned continuously. Experimental results demonstrate a 137° phase shift while the RF signals of 20 and 40 GHz are downconverted to an IF signal of 0.4 GHz, which indicates the photonic microwave downconverter can be used in the Ka-band phased-array receiver.

On-chip guided wave THz photonic switching with a phase change material on a dielectric waveguide encompassed with a novel micro-fins heater

On-chip photonic components, particularly for switching applications, are becoming more and more in demand to create high-density photonic integrated circuits in the THz regime. The nonvolatile switching can meet the requirement of power saving when the complexity of integrated circuits grows in the near future. Here, we propose and analyse the THz wave switching using a nonvolatile phase change material (PCM) Ge2Sb2Te5 (GST) integrated on a broadband THz dielectric waveguide that is encompassed by a novel micro-fins heater. In the proposed device, a small patch of GST of length 1500μm integrated on top of the HRFZ-Si waveguide provides an acceptable insertion loss and high extinction ratio for its broadband operation in the frequency span of 0.5–1.0 THz. Using a novel micro-fins heater, the phase transformation of the GST is carried out through Joule heating. Short electrical pulses of 11 ms and 4μs are found to be capable of raising the temperature of the GST region above its crystallization and re-amorphization temperature, respectively. The corresponding energy consumption for crystallization and re-amorphization is found to be 61.73 mJ and 19.84 mJ, respectively. The switching speed of our reported device is 100 times better than the previously reported metamaterial-based THz photonic switches using PCMs. Since GST is nonvolatile in nature, no continuous pump power is needed to maintain the particular switching state of the proposed device. The work reported here is a step forward for enabling THz photonic switching, and further THz circuits, in guided wave photonic platform using CMOS-compatible materials.