Resonant Feedback Research Articles

Silicon Photonics High-Order Distributed Feedback Resonators Filters

High-order distributed feedback resonators realized in silicon-on-insulator technology for the implementation of high-performance integrated optical filters are reported. This approach combines design simplicity and flexibility in a compact footprint with filter transfer functions featuring a flat-top response, large out-of-band rejection of more than 40 dB, ultra-steep roll-off up to 1000 dB/nm, and unprecedented stopband-to-passband ratios up to 600 for high-index-contrast technology. Active control of the coupled cavities through local micro heaters is employed for optimizing the filter response and passband tuning. Exemplary implementations of a box-like transfer function filter with a bandwidth of 25 GHz and of a narrow linewidth 2 GHz filter realized with 6 th - and 3 rd -order filter designs, respectively, are presented.

Solution-processed nanographene distributed feedback lasers

The chemical synthesis of nanographene molecules constitutes the bottom-up approach toward graphene, simultaneously providing rational chemical design, structure-property control and exploitation of their semiconducting and luminescence properties. Here, we report nanographene-based lasers from three zigzag-edged polycyclic aromatics. The devices consist of a passive polymer film hosting the nanographenes and a top-layer polymeric distributed feedback resonator. Both the active material and the laser resonator are processed from solution, key for the purpose of obtaining low-cost devices with mechanical flexibility. The prepared lasers show narrow linewidth ( < 0.13 nm) emission at different spectral regions covering a large segment of the visible spectrum, and up to the vicinity of the near-infrared. They show outstandingly long operational lifetimes (above 105 pump pulses) and very low thresholds. These results represent a significant step forward in the field of graphene and broaden its versatility in low-cost devices implying light emission, such as lasers.

Analysis and design aspects of delayed resonator absorber with position, velocity or acceleration feedback

A thorough analysis of six delayed resonator configurations is performed. Considering either lumped or distributed delays, feedback is taken from acceleration, velocity or position measurements. Next to presenting stability maps derived by the Cluster Treatment of Characteristic Roots, the robustness in the vibration suppression is analyzed. It is shown that the deterioration of vibration suppression caused by mismatch between the design and true excitation frequencies can be decreased by a proper selection of the delayed resonator configuration and the frequency operable range. Besides, the force and energy demands from the resonator feedback are studied with respect to the absorber physical parameters. All the results are derived for a dimensionless model form and as such they are universally valid. Thus, with respect to the important design specifications, the analysis is complete and can be used as guidelines for parametrization of the given delayed resonator set, with respect to the operable conditions.

Low-Threshold Organic Lasers Based on Single-Crystalline Microribbons of Aggregation-Induced Emission Luminogens.

Solid-state lasers (SSLs) play an important role in developing optoelectronic devices, optical communication, and modern medicine fields. As compared with inorganic SSLs, the electrically pumped organic SSLs (OSSLs) still remain unrealized because of the high lasing threshold and low carrier mobility. Herein, we first demonstrate the laser action at ∼520 nm based on the self-assembled single-crystalline organic microribbons of the aggregation-induced emission (AIE) molecules of 1,4-bis(( E)-4-(1,2,2-triphenylvinyl)styryl)-2,5-dimethoxybenzene (TPDSB). Moreover, these as-prepared organic microribbons exhibit an effective optical waveguide with a low optical loss of 0.012 dB μm-1, indicating good light confinement for laser resonator feedback. Impressively, the multiple mode and the single mode lasing are both achieved from individual organic microribbons, whose lasing threshold is as low as 653 nJ cm-2. These "bottom-up" synthesized organic microribbons based on AIE-active molecules offer a new strategy for the realization of the ultralow threshold OSSLs, which would eventually contribute to the realization of electrically pumped OSSLs.

Resonant feedback for axion and hidden sector dark matter searches

Resonant feedback circuits are proposed as an alternative to normal modes of conducting wall cavities or lumped circuits in searches for hidden sector particles. The proposed method offers several potential advantages over the most sensitive axion searches to date, including coverage of a wider range of axion masses, the ability to probe many axion masses simultaneously, and the elimination of experimentally troublesome mechanical tuning rod mechanisms. After an outline of the proposed method, we present a noise budget for a straw-man experiment configuration. We show that the proposed experiment has the potential to probe the axion mass range 2–40μeV with 38 days of integration time. Other existing and proposed resonant searches for hidden sector particles may also benefit from this approach to detection.

Optimized design of robust resonator with distributed time-delay

An extension of the well-known delayed resonator concept is proposed with the objective to enhance its robustness in vibration suppression under guaranteeing stability of the overall set up. The novel resonator feedback is based on an acceleration measurements passing through a delay of polynomial distribution. The feedback design is formulated as an optimization problem over the parameter set formed by the polynomial coefficients and the gain of the delay free part. The first objective is to minimize the sensitivity of the resonator performance with respect to variations of the excitation frequency, i.e. to widen its frequency stop-band centered at the nominal excitation frequency. The second, equally significant objective is to guarantee that this does not lead to instability of the overall mechanical system coupled with the absorber and to ensure sufficient stability margin. The arising non-convex and non-smooth optimization problem is widely discussed and a penalty method is developed, where the unconstrained problem in every iteration step is solved using available software tools for optimization and spectral design of time delay systems. The proposed design technique is validated by simulations for two case study examples.

A highly accurate measurement of resonator Q-factor and resonance frequency.

The microwave cavity perturbation method is often used to determine material parameters (electric permittivity and magnetic permeability) at high frequencies, and it relies on the measurement of the resonator parameters. We present a method to determine the Q-factor and resonance frequency of microwave resonators which is conceptually simple but provides a sensitivity for these parameters which overcomes those of existing methods by an order of magnitude. The microwave resonator is placed in a feedback resonator setup, where the output of an amplifier is connected to its own input with the resonator as a bandpass filter. After reaching steady-state oscillation, the feedback circuit is disrupted by a fast microwave switch, and the transient signal, which emanates from the resonator, is detected using down-conversion. The Fourier transform of the resulting time-dependent signal yields directly the resonance profile of the resonator. Albeit the method being highly accurate, this comes with a conceptual simplicity, ease of implementation, and lower circuit cost. We compare existing methods for this type of measurement to explain the sensitivity of the present technique, and we also make a prediction for the ultimate accuracy for the resonator Q and f 0 determination.

Wavelength-Tunable and Highly Stable Perovskite-Quantum-Dot-Doped Lasers with Liquid Crystal Lasing Cavities.

This study applies a low-cost solvothermal method to synthesize all-inorganic (lead-free cesium tin halide) perovskite quantum dots (AIPQDs) and to fabricate AIPQD-doped lasers with cholesteric liquid crystal (CLC) lasing cavities. The lasers present highly qualified lasing features of low threshold (150 nJ/pulse) and narrow line width (0.20 nm) that are attributed to the conjunction of the suppression of photoluminescence (PL) loss caused by the quantum confinement of AIPQDs and the amplification of PL caused by the band-edge effect of the CLC-distributed feedback resonator. In addition, the lasers possess highly flexible lasing-wavelength tuning features and a long-term stability under storage at room temperature and under high humidity given the protective role of CLC. These advantages are difficult to confer to typical light-emitting perovskite devices. Given these merits, the AIPQD-doped CLC laser device has considerable potential applications in optoelectronic and photonic devices, including lighting, displays, and lasers.

Outcome of special vibration controller techniques linked to a cracked beam

• Analytical solution and numerical simulation of non-linear differential equations. • Multiple scale perturbation technique is used to obtained the first order approximation. • PPF, IRC and NIPPF controllers to reduce the vibration. • Stability study subjected to external excitation. • Effect of different parameters in the system. This paper presents a comparison between three different controller methods added to a cracked beam under the action of a harmonic excitation. Those three controllers are Positive Position Feedback (PPF), Integral Resonant Control (IRC) and Nonlinear Integral Positive Position Feedback (NIPPF) which be added to the measured system. The multiple scales method (MSM) is applied for getting the approximate solution on behalf of measured design. This method is effective to solve the major equations of measured system. Stability and effect of different coefficients of the system are demonstrated. The approximate solution response is established via numerical simulation outcome. NIPPF controller is the best one gives better results compared to the other two controllers in decreasing the high amplitude of the system. Comparison between mathematical solution and numerical simulation are considered. Relationship of formerly available papers is considered.

Stabilization of self-mode-locked QDash lasers subject to simultaneous continuous-wave optical injection and optical feedback.

In this paper, we report stabilization of self-mode-locked two-section quantum-dash lasers on the widest range of delay using simultaneous optical injection and optical feedback. With continuous-wave optical injection, various wavelengths spanning a range from 1568 to 1578nm were investigated and optimum wavelengths (1571.210 to 1572.710) yielding the narrowest RF linewidth and reduced timing jitter of slave laser were identified. In addition, the dependence of RF linewidth and pulse repetition rate on injected wavelength was further explored. Our results indicate that simultaneous optical feedback and optical injection significantly improves the RF linewidth across the widest delay range compared to optical feedback alone. Under fully resonant feedback and optimum injection parameters, a minimum RF linewidth of 1kHz (instrument limited) was achieved with simultaneous optical injection plus optical feedback, which was >2× lower than optical feedback alone and more than 100× lower than free-running. This stabilization technique is implemented in an all-optical arrangement without optical/electrical conversion, which is ideal for high-repetition-rate devices and photonic integration.

Deep-Ultraviolet Hyperbolic Metacavity Laser.

Given the high demand for miniaturized optoelectronic circuits, plasmonic devices with the capability of generating coherent radiation at deep subwavelength scales have attracted great interest for diverse applications such as nanoantennas, single photon sources, and nanosensors. However, the design of such lasing devices remains a challenging issue because of the long structure requirements for producing strong radiation feedback. Here, a plasmonic laser made by using a nanoscale hyperbolic metamaterial cube, called hyperbolic metacavity, on a multiple quantum-well (MQW), deep-ultraviolet emitter is presented. The specifically designed metacavity merges plasmon resonant modes within the cube and provides a unique resonant radiation feedback to the MQW. This unique plasmon field allows the dipoles of the MQW with various orientations into radiative emission, achieving enhancement of spontaneous emission rate by a factor of 33 and of quantum efficiency by a factor of 2.5, which is beneficial for coherent laser action. The hyperbolic metacavity laser shows a clear clamping of spontaneous emission above the threshold, which demonstrates a near complete radiation coupling of the MQW with the metacavity. This approach shown here can greatly simplify the requirements of plasmonic nanolaser with a long plasmonic structure, and the metacavity effect can be extended to many other material systems.

Lasing With Resonant Feedback in Weakly Modulated Parity-Time Symmetric Lattices

We report on the lasing action in weakly modulated parity-time (PT) symmetric lattices. At the exceptional point in PT-symmetric lattices, the amplitude and phase of unidirectionally scattered waves are independently and flexibly determined by the PT modulations, thus, providing a distinctive route to construct a lasing mode in finite systems with weakly modulated structures. It is revealed that the resonant feedback mechanism plays a crucial role in building up the lasing action. Our finding would enrich the singularity dynamics in the weakly modulated PT systems.

Experimental and Theoretical Investigation of the Polymer Optical Fiber Random Laser with Resonant Feedback

Abstract1D random fiber laser is a novel fiber‐based laser, which exhibits many unique optical properties and shows great promise for various applications including speckle‐free imaging. A multimode and coherent polymer optical fiber random laser (POFRL) is successfully fabricated by doping TiO2 nanoparticles and Rh640 perchlorate dyes in the core of a polymer optical fiber (POF). The waveguide effect provided by the POF greatly increases the multiscattering events for light propagation and results in laser cavity with much shorter length than the scattering mean free path. As an illustration of potential applications, a clear speckle‐free imaging is demonstrated using the POFRL as the illumination source. Furthermore, a four‐level Monte Carlo method‐based numerical model is proposed to describe the lasing dynamics in POFRL. The model supports the experimental work in the research field of POFRL.

Continuous-wave operation in directly patterned perovskite distributed feedback light source at room temperature.

We report a directly patterned perovskite distributed feedback (DFB) resonator and show narrow amplified spontaneous emission (ASE) at pump powers as low as 0.1 W/cm2 under continuous-wave (CW) optical pumping conditions at room temperature. Compared to the pristine thin film photoluminescence spectrum, a 16-fold reduction in emission linewidth in the MAPbI3 DFB cavity was observed. The direct nanostructuring of perovskites was achieved by thermal nanoimprint lithography. Our findings pave the way toward realizing CW pumped perovskite lasers at room temperature and energy-efficient perovskite light sources.

Distributed Feedback Lasers Based on MAPbBr3

AbstractHybrid perovskite semiconductors hold great promise as low‐cost, yet high performance gain media for lasers. Distributed feedback (DFB) resonator structures are a key to unlock low laser threshold levels, which are essential on the way to the first electrically operated perovskite laser diode. Here, the first DFB lasers based on methylammonium lead bromide (MAPbBr3) thin films, with a linear photonic grating imprinted into the MAPbBr3 active layers is presented. High‐Q Bragg resonator gratings with a periodicity of 300 nm are directly patterned by thermal nanoimprinting into thin films of MAPbBr3 at a temperature as low as 100 °C. A notable effect of the imprinting process is a substantial flattening of the initially very rough polycrystalline perovskite layers to layers consisting of large crystals on the order of tens of microns with a surface roughness of 0.6 nm. The smooth surface affords a significantly lowered threshold for the onset of amplified spontaneous emission due to reduced scattering. In optically pumped DFB laser structures, very low lasing thresholds of 3.4 µJ cm−2 are achieved. It is foreseen that these results will influence research on perovskite‐based optoelectronic devices beyond lasers, e.g., light emitting diodes and solar cells.

Delta-Sigma Digitization and Optical Coherent Transmission of DOCSIS 3.1 Signals in Hybrid Fiber Coax Networks

We first demonstrate delta-sigma digitization and coherent transmission of data over cable system interface specification (DOCSIS) 3.1 signals in a hybrid fiber coax (HFC) network. Twenty 192-MHz DOCSIS 3.1 channels with modulation up to 16384QAM are digitized by a low-pass cascade resonator feedback (CRFB) delta-sigma analog-to-digital converter (ADC) and transmitted over 80-km fiber using coherent single-λ 128-Gb/s dual-polarization (DP) quadrature phase-shift keying (QPSK) and 256-Gb/s DP-16QAM optical links. Both one-bit and two-bit delta-sigma digitization are implemented and supported by the QPSK and 16QAM coherent transmission systems, respectively. To facilitate its practical application in access networks, the coherent system is built using a low-cost narrow-band optical modulator and RF amplifiers. Modulation error ratio (MER) larger than 50 dB is successfully demonstrated for all 20 DOCSIS 3.1 channels, and high-order modulation up to 16384QAM is delivered over fiber for the first time in HFC networks. The raw DOCSIS data capacity is 54 Gb/s with net user information ~45 Gb/s. Moreover, the bit error ratio (BER) tolerance is evaluated by measuring the MER performance as BER increases. Negligible MER degradation is observed for BER up to 1.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> and 1.7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> for one-bit and two-bit digitization, respectively.

Giant enhancement of emission efficiency and light directivity by using hyperbolic metacavity on deep-ultraviolet AlGaN emitter

Despite the demands of growth, the development of deep-ultraviolet (UV) light-emitting diodes (LEDs) still suffers from the fundamental limits of material defects and the anisotropic optical property of AlGaN multiple quantum-wells (MQWs), resulting in an extremely low emission output. Here, we present a novel approach to address this issue by using a nanoscale hyperbolic metacavity on the deep-UV LED, where the resonant modes of metacavity are excited. An intense plasmon field is consequently feedback to the MQW. This strong resonant mode feedback allows the dipoles of MQW recombine directionally, thereby achieving enhancements of radiative emission rate by a factor of 160 and quantum efficiency by a factor of 3.5. It also shows the capability of metacavity in tailoring the direction of light emission, leading to a 520% increase in total emission intensity and 148% increase in emission extraction. A small divergence angle of 65° of LEDs is therefore demonstrated. Our study clearly shows that the use of metacavity is a promising candidate for the highly-desired efficiency and directivity deep-UV applications, and the metacavity effect can be extended to other nanoscale devices, such as nanolaser, single photon source, nano-biosensor, and nano-antenna.

Diverse Regimes of Mode Intensity Correlation in Nanofiber Random Lasers through Nanoparticle Doping

Random lasers are based on disordered materials with optical gain. These devices can exhibit either intensity or resonant feedback, relying on diffusive or interference behaviour of light, respectively, which leads to either coupling or independent operation of lasing modes. We study for the first time these regimes in complex, solid-state nanostructured materials. The number of lasing modes and their intensity correlation features are found to be tailorable in random lasers made of light-emitting, electrospun polymer fibers upon nanoparticle doping. By material engineering, directional waveguiding along the length of fibers is found to be relevant to enhance mode correlation in both intensity feedback and resonant feedback random lasing. The here reported findings can be used to establish new design rules for tuning the emission of nano-lasers and correlation properties by means of the compositional and morphological properties of complex nanostructured materials.

An Efficient All‐Plastic Organic Waveguide Solid‐State Laser Devices with Distributed Bragg Reflector

Organic dye or polymer waveguide laser is a promising next‐generation solid‐state laser device, because they are not only easily and inexpensively fabricated as laser sources, but also have high potential for bio‐sensing for hazardous materials and environments. The active layer and the effective resonator consist of all‐organic materials, which can be processed by solution‐casting or spin‐coating. Here, laser performances of all‐plastic organic waveguide solid‐state laser devices are reported with Bragg mirror and micro‐cavity, both being fabricated by the relief gratings. Waveguide consists of a high quantum yield organic dye of pyrromethene 567 as a lasing emitter and a cellulose acetate (CA) film as a waveguide matrix. The distributed Bragg reflector (DBR) region and the distributed feedback (DFB) resonator as a micro‐cavity are fabricated in the waveguide devices using a negative photoresist SU‐8 by an interference technique. The performances of lasing threshold and slope efficiency for both organic waveguide devices with DBR region and DFB resonator are evaluated. The slope efficiency of 2.01% and the lasing threshold of 45 µJ cm−2 are measured for the waveguide device with DBR region, whereas the waveguide device with DFB resonator gives the slope efficiency of 0.72% and the lasing threshold of 140 µJ cm−2.

All-inorganic perovskite-based distributed feedback resonator.

Halide perovskite materials have rapidly emerged as outstanding optoelectronic materials for solar cells, light-emitting diodes (LEDs), and lasers. Compared to hybrid organic-inorganic perovskites, all-inorganic perovskites have shown unique merits that may contribute to the ultimate goal of developing electrically-pumped lasers. In this paper, we demonstrate a distributed feedback (DFB) resonator using an all-inorganic perovskite thin film as the gain medium. The film has a gain coefficient of 161.1 cm-1 and a loss coefficient of 30.9 cm-1. Excited by picosecond pulses, the microstructured all-inorganic perovskite film exhibits a single-mode emission at 654 nm with a threshold of 33 μJ/cm2. The facile fabrication process provides a promising route towards low-cost single-mode visible lasers for many practical applications.