Output Spectrum Research Articles

Numerical analysis and experimental validation of nonlinear broadband monostable and bistable energy harvesters

Vibration based piezoelectric energy harvesting has been receiving more and more attention for supplying usable electrical energy to low-power electronic devices. This type of energy can produce the desired voltage to power any low electronic device or wireless sensor. But most of them provide lower voltage and insufficient power. In this paper, the nonlinear magnetic field is introduced to broaden the effective resonant bandwidth for overcoming this issue. The dynamic linear and nonlinear model of magnetic coupling piezoelectric vibration energy harvester is established based on the Hamilton principle, Euler-Bernoulli beam theory, piezoelectric theory, and Kirchhoff's law and law of mechanics. Numerical solutions of nonlinear energy harvesting systems are studied by using the Runge-Kutta method. The bifurcation diagram, Poincare map, power spectrum, and phase trajectory of voltage output are investigated with different excitation amplitudes and frequencies. Simulation of linear and nonlinear model were illustrated at given excitation levels. Simulation results show the harvesting performance can be improved by proper external magnetic coupling and potential energy function. The theoretical harmonic balance analysis results verify the numerical solution and influence the mechanism of excitation levels and interface resistances. Experimental verification is carried out to measure the nonlinear restoring force and examine the performance of nonlinear bistable and monostable energy harvesters. The experiment results show the nonlinear bistable and monostable energy harvesters can provide larger voltage and more power.

Comparison of the output spectrum for four models of devices with crossed fields

This paper considers four models of crossed-field devices: cylindrical magnetron, cylindrical magnetron diode, planar magnetron diode and planar magnetron. As is known, in crossed-field devices electrons move by cycloid-like trajectories and induced current arises. The spectral components of the induced current for every of the models are calculated. It has been found that the components of the induced current spectrum contain from one (planar magnetron diode) to eight (cylindrical magnetron diode) components. The calculated spectral components have been compared to the spectral components of the generation spectrum of the real device.
 Only one component whose frequency coincides with the cyclotron frequency was found in the induced current spectrum of the planar magnetron diode.
 The induced current spectrum in a planar magnetron has three components. These frequencies have a large difference with the frequency of magnetron generation for a microwave oven. Therefore, the models of the planar magnetron diode and the planar magnetron are not very suitable for simulating the operation of crossed-field devices.
 The induced current spectrum in a cylindrical magnetron diode contains eight components. The third harmonic is closest to the fundamental frequency of the microwave magnetron. In this case, the difference between the frequencies being compared is near 10 %. Therefore, the model of a cylindrical magnetron diode is not very suitable for modeling the operation of crossed-fields devices.
 Two components were found in the induced current spectrum of a cylindrical magnetron. The first harmonic is the closest to the fundamental frequency of the microwave magnetron. In this case, the difference between the frequencies being compared does not exceed 3 %. Such a small discrepancy between the calculated and real frequencies can be explained by the presence of a spatially periodic distribution of the electrostatic field. Thus, the cylindrical magnetron model is well suited for simulating the operation of crossed-fields devices.

Picosecond Pulse Tapered Fiber Amplifier Operated near 1030 nm with Peak Power up to 1 MW

We demonstrated an optimization of a picosecond fiber amplifier based on Yb-doped tapered fiber in a spectral range of 1030 nm. Nonlinear effects limiting peak power scaling (stimulated Raman scattering and four-wave mixing) were studied and factors affecting their threshold were established, such as gain, diameter profile along the length of taper, output mode field diameter, and numerical aperture of a pump. By determining the optimal amplification regime and manufacturing advanced tapered fibers, we amplified 13 ps pulses to a record-high peak power of 1 MW at a wavelength of 1029 nm directly at the output of the fiber at an average power of 13.8 W. Four-wave mixing was the limiting factor, and the total fraction of deleterious components in the output spectrum was ~2%. The quality of the output beam was close to being diffraction limited (M2 < 1.2).

Simulation Analysis on Optimization of Optical Fiber Communication Based on L+ Band

Nowadays, L+ band (1600-1650 nm) is widely used in optical communication, however, the traditional fiber amplifiers for L+ band can no longer meet the increasing demand, and it is crucial to select more suitable materials and optimize the peak power of the output spectrum. In this work, we determine the rate equation and power propagation equation corresponding to the three-energy-level structure by Er3+ doping phosphate glass, and select the appropriate pumping wavelength and power, and calculate the variation of amplified spontaneous emission spectra with the length of the fiber and the doping concentration using MATLAB programming. Finally, on this basis, genetic algorithm is used to optimize the fiber length and doping concentration, and the parameter values to maximize the peak power of the output spectrum are successfully obtained, and the performance is compared with that of the traversing parameter method, which provides a reference for the design and optimization of fiber amplifiers.

Optimization of the Peak Power of the Output Spectrum of Spontaneous Emission Spectrum Amplified by O-Band Fiber

As the demand for information and communication continues to increase, the optimization and improvement of optical fiber communication has been a key focus of scientific research, with profound impacts on multiple fields, including military, aerospace, industrial, and daily communications. Based on the in-depth understanding and establishment of the rate equation and power propagation equation of each energy level system, this study explores the influence of fiber length and doping concentration on amplifying spontaneous emission spectrum under certain pump power. With a comprehensive understanding of its characteristics, analog annealing algorithms are employed to optimize the length and doping concentration of the fiber to maximize the peak power of the output spectrum. This research provides an important contribution to the further development and efficiency improvement of optical fiber communication in the future. It is concluded that for the O-band, the output peak of high power can provide greater signal strength, thereby increasing the transmission distance and bandwidth capacity of the signal. This is essential for applications such as long-distance communications, high-speed data transmission, and multi-channel transmission.

Observation of operation states and wavelength-switching in spatiotemporal mode-locked lasers

The construction and investigation of spatiotemporal mode-locked (STML) lasers offer us an opportunity to comprehend and analyze exceedingly intricate high-dimensional nonlinear physical phenomena that underlie diverse behaviors. While the exploration of coherent mode-locking, such as multimode solitons, has been progressing in depth, there remains a dearth of understanding regarding random pulses or extreme events within STML lasers. In this study, an STML laser was constructed and implemented with two operating regimes. The laser demonstrated mutual switching between noise-like pulses and dissipative soliton states, accompanied by corresponding changes in the output spectrum. The transition of the laser's output spectrum from a single wavelength to a synchronous dual-wavelength at noise-like pulses operation was observed for the first time, as far as we all know. These findings contribute to a deeper understanding of spatiotemporal mode-locked lasers.

Modelling and experimental characterization of double layer InP/AlGaInP quantum dot laser

Spectrum of an InP/AlGaInP self- assembled double-layer quantum dot (QD) laser fabricated by metal–organic vapor-phase epitaxy is theoretically and experimentally investigated. A bimodal QD size distribution (small and large QD groups) was detected which is formed during the fabrication. A model is proposed based on rate equations accounting for the superposition of two inhomogeneous QD groups. The total output power and the power spectral density (PSD) of the fabricated QD laser are experimentally characterized at room temperature. The output spectrum is segmented into the sum of two Gaussians curves (super Gaussian) belonging to the small and large QD groups. The peak PSD and the spectral width of each group are extracted and their dependency on the injected current density is analysed. The peak of the large QDs is found to be dominant at small current while the peak of the small QDs dominated at high current alongside a reduction in its spectral width leading to lasing based on them. This behaviour is attributed to the saturation of the large QDs energy levels due to its relatively long radiative lifetime. The experimental analysis is in a good agreement with the theoretical results.

Multi-pulse random fiber laser with wide tuning range in L-band based on tunable band-pass filter and electro-optic modulator

In this paper, a L-band random fiber laser (RFL) with wide tuning range based on tunable band-pass filter (TBF) and electro-optic modulator (EOM) is proposed and studied. The L-band erbium-doped fiber amplifier (L-EDFA) is added to output L-band laser, and a wavelength tunable band-pass filter is used to generate tunable wavelength output. When the pump power is increased from 50mW to 350mW, the output spectra are all chaotic multi-wavelengths. After the filter being added, a stable narrow-band single-wavelength laser can be output in the range of 1564–1618 nm. An EOM is added to introduce actively Q-switched. When the pump power is 50mW, a stable single pulse output can be observed on the oscilloscope. When the pump power is 100mW, the output pulse is double pulse. When the pump power exceeds 100mW, three pulses or four pulses phenomenon appears. The adjustable multi-pulse laser has a wide application prospect in pulse coding, secure communication and other fields.

Continuous-Wave and Mode-Locked Operation of an In-Band Pumped Tm,Ho,Lu:CaGdAlO4 Laser

We investigate in-band pumping of a Tm,Ho,Lu:CaGdAlO4 laser using a Raman-shifted Er-fiber laser (1678 nm), in the continuous-wave (CW) and mode-locked (ML) regimes. A maximum output power of 524 mW is obtained in the CW regime with a 5% output coupler at an absorbed pump power of 2.04 W, corresponding to a slope efficiency of 27.9%. A maximum CW wavelength tuning range of 160 nm at the zero level, from 1984 to 2144 nm, is obtained with a 0.2% output coupler. In the ML regime, pumping with 5.5 W (unpolarized), the average output power (0.2% output coupler) reaches 148 mW at a repetition rate of ~96 MHz. The output spectrum is centered at 2071.5 nm with a FWHM of 21.5 nm (σ-polarization). The pulse duration amounts to 218 fs (time-bandwidth product equal to 0.327).

Experimental investigation of high-power broadband all-fiber nanosecond superfluorescent source

In this work, we demonstrate a broadband nanosecond superfluorescent fiber source (ns-SFS) with an average power of several hundred watts and an adjustable repetition frequency of 25 kHz–100 kHz. To figure out a suitable active fiber length for ns-SFS seed, the impact of active fiber length on the output spectrum of SFS is investigated theoretically and experimentally. The results indicate an evident redshift in the central wavelength of output spectrum with increasing fiber length. By scaling the power of the ns-SFS seed employing three amplifier stages, the maximum average power and pulse energy are obtained with a value of 463 W, 17.6 mJ, respectively. To the best of our knowledge, this work is the first demonstration of a broadband ns-SFS amplifier with output power exceeding hundred watt and pulse energy exceeding 10 mJ.

Tunable force transduction through the Escherichia coli cell envelope.

The outer membrane (OM) of Gram-negative bacteria is not energised and so processes requiring a driving force must connect to energy-transduction systems in the inner membrane (IM). Tol (Tol-Pal) and Ton are related, proton motive force- (PMF-) coupled assemblies that stabilise the OM and import essential nutrients, respectively. Both rely on proton-harvesting IM motor (stator) complexes, which are homologues of the flagellar stator unit Mot, to transduce force to the OM through elongated IM force transducer proteins, TolA and TonB, respectively. How PMF-driven motors in the IM generate mechanical work at the OM via force transducers is unknown. Here, using cryoelectron microscopy, we report the 4.3Å structure of the Escherichia coli TolQR motor complex. The structure reaffirms the 5:2 stoichiometry seen in Ton and Mot and, with motor subunits related to each other by 10 to 16° rotation, supports rotary motion as the default for these complexes. We probed the mechanism of force transduction to the OM through in vivo assays of chimeric TolA/TonB proteins where sections of their structurally divergent, periplasm-spanning domains were swapped or replaced by an intrinsically disordered sequence. We find that TolA mutants exhibit a spectrum of force output, which is reflected in their respective abilities to both stabilise the OM and import cytotoxic colicins across the OM. Our studies demonstrate that structural rigidity of force transducer proteins, rather than any particular structural form, drives the efficient conversion of PMF-driven rotary motions of 5:2 motor complexes into physiologically relevant force at the OM.

Ultrasensitive, dynamic, and online monitoring photonic sensors for protein conformation

The monitoring of molecular dynamic transition and protein conformation changes is important for some neurodegenerative diseases (NDs) and has attracted much attention due to its ability to reveal the pathological mechanism of several NDs. Here, a label-free optical detection method with an ultrahigh refractive index sensitivity (S) and dynamical S tuning range was developed to provide a novel technology roadmap for the online monitoring of protein conformation. The real-time conformation variation process was transduced into a visualization optical signal, allowing it to be monitored. The biosensor prototype was constructed by the cross-overlapping of two rows of square capillaries on a gold mirror to form two microcavities with different free spectral ranges (denoted as the sensing and reference cavities). The coupling of the resonance mode between the two microcavities induced the generation of the Vernier effect and the magnifying of S, presented in the form of a modulated envelope in the spectrum. S values ranged from −17,256 nm/RIU to 93,937 nm/RIU, indicating that the biosensor could not only realize large dynamic tuning ranges but also an ultrahigh S. The conformation changes of silk proteins from the random coil to the β–sheet were sensitively monitored by the output spectrum after it was stimulated with ethanol solution. This ultrasensitive biosensor (which is both label-free and optical) provides a novel and supplementary technique to monitor the structural and conformation changes process of proteins. The results reveal its significant potential for clinical diagnosis, healthcare, pharmaceutical screening, and food security.

Optimal Conditions for a Multimode Laser Diode with Delayed Optical Feedback in Terahertz Time-Domain Spectroscopy

Recent studies have indicated that terahertz time-domain spectroscopy (THz-TDS) can stably and efficiently acquire output spectra using an affordable and compact multimode laser diode (MMLD) with delayed optical feedback as the light source. This research focused on a numerical analysis of the optimal conditions for employing an MMLD with delayed optical feedback (a chaotic oscillating laser diode) in THz-TDS utilizing multimode rate equations. The findings revealed that the intermittent chaotic output generated by the MMLD, characterized by concurrent picosecond pulse oscillations lasting several tens of picoseconds, proved to be highly effective for THz-TDS. By appropriately setting the amounts for the injection current and optical feedback and the delay time for the optical feedback, intermittent chaotic oscillation could be attained within a considerably broad parameter range. The generation of intermittent chaotic oscillations was confirmed by observing their characteristic asymmetric spectral shapes. Moreover, both the MMLD output spectrum and the THz-TDS output spectrum exhibited consistently stable shapes at the microsecond scale, demonstrating the attractor properties inherent in an MMLD with delayed optical feedback.

Study on the sensing characteristics of Salinity-Temperature-Depth based on SNS-FBG cascade

A Salinity-Temperature-Depth sensor based on SNS-FBG cascade is proposed for optical fiber Salinity-Temperature-Depth sensing structure for marine applications to realize measurement of three parameters. The sensor consists of a single mode fiber(SMF) -no-core fiber(NCF) -SMF structure cascaded with two fiber Bragg gratings. The experiment detects the three parameters by monitoring the wavelength drift of the output spectrum of the sensor. The experimental results show that the salinity sensitivity is 0.027nm/‰, the temperature sensitivity is 11.98 pm/°C and the depth sensitivity is 1.71 nm/MPa. The proposed Salinity-Temperature-Depth sensor can detect the Salinity-Temperature-Depth by monitoring of the wavelength with the characteristics of low cross-sensitivity, simple production and has the advantages of three-parameter sensing.

Narrow linewidth and wideband tunable continuous-wave terahertz generator based on difference frequency generation with DAST crystal.

A narrow linewidth and wideband tunable continuous-wave terahertz generator with DAST crystal has been demonstrated in this paper. Two narrow-linewidth CW fiber lasers were used as the pump sources for difference frequency generation. The terahertz wave can be continuously tunable in the range of 1.1-3 THz. The maximum output power of 2.79nW was obtained at 2.568 THz. The linewidth of the output THz wave was estimated to be 56.5 MHz by fitting transmission spectrum of CO gas at 450 Pa pressure around 80.52 cm-1 with the Vogit gas model. Furthermore, the output spectra at room temperature and pressure was in good agreement with the air absorption lines in Hitran database. Moreover, the narrower absorption characteristic spectrum of 2-Deoxy-D-Glucose sample has been obtained through the spectrum measurements. Therefore, it could promote the practical prospect of tunable CW-THz source, which will have good potential in THz high-precision spectroscopic detection and multispectral imaging.

An enhanced chromatic dispersion probe for simultaneous measurement of dual-axis absolute and relative displacement with nanometric resolutions

This paper presents an enhanced chromatic dispersion probe for simultaneous measurement of dual-axis absolute and relative displacement with nanometric resolutions based on a 4f optical system and a signal processing algorithm. In the 4f optical system, a light source is generated by a pinhole in such a way that the employed pinhole is placed on the focal planes of the two achromatic lenses, aimed at generating a low-pass filter in the frequency domain. With a smaller pinhole, side lobes of the measured spectra are effectively suppressed and the signal-to-noise ratio is optimized, resulting in an expanded absolute measurement range and improved resolution of the two axes, and an enhanced relative measurement resolution of the dual-axis. A signal processing algorithm is proposed in such a way that in the spectral curvature region of the dual-axis output spectra, the original fitted spectrum is replaced by a linear fitting line and a newly-intersected wavelength can be obtained, resulting in an expanded measurement range of the relative displacement of the dual-axis. Numerical simulation and experiments have indicated that the absolute measurement range has been expanded to 225 μm with an enhanced resolution of 40 nm, and the measurement range of the relative displacement of the dual-axis has been expanded to 370 μm with an enhanced relative measurement resolution of 90 nm.

NUMERICAL SIMULATION OF ENHANCED OPTICAL FREE SPECTRAL RANGE THROUGH INTEGRATED FANO-MICRORING CONFIGURATION

A numerical analysis of the integrated Fano-microring (IFM) racetrack resonator spectrum was performed to investigate the enhancement of the optical system’s free spectral range (FSR). The FSR is an important optical property which can contribute to the high sensitivity of optical devices. The IFM refers to the combination of Fano resonance produced in the output spectrum through the interaction of Fabry–Perot resonance and circulation resonance. This work focuses on the study of inducing Fano resonance in the microring resonator to optimize the FSR of the system. The results show that the integration of two resonances can produce a Vernier output spectrum, which significantly enhanced the FSR of the system without any need for additional ring waveguides. This work also compared the IFM resonance with the conventional microring resonance. In this simulation, the optimized FSR obtained by the IFM configuration was 266.55 nm, which is five times higher than the conventional microring configuration.

A Review of Progress about Birefringent Filter Design and Application in Ti:sapphire Laser

All-solid-state tunable lasers have been widely used in many fields including multi-photon microscopy, time-resolved photoluminescence, atomic physics, and so on owing to their broadband output spectrum range, good beam quality, and low noise. To cover the broad fluorescent line of the laser crystal as much as possible, a birefringent filter (BRF) is always the most popular candidate for acting as a tuning element. In this review, the tuning characteristics of BRF and the design rule as well as its progress in practical application are summarized. Especially, it is worth noting that laser crystal itself begins to act as the BRF for wavelength tuning except for its gain characteristic, which has paved a new way for developing a kind of novel tunable laser. We believe that this review will not only provide a valuable reference for the design of BRF but also lay the foundation for developing a new application of BRF.

Microwave Photon Emission in Superconducting Circuits

Quantum computing requires a novel approach to store data as quantum states, opposite to classical bits. One of the most promising candidates is entangled photons. In this manuscript, we show the photon emission in the range of microwave frequencies of three different types of superconducting circuits, a SQUID, a JPA, and a JTWPA, often used as low-noise parametric amplifiers. These devices can be operated as sources of entangled photons. We report the experimental protocol used to produce and measure microwave radiation from these circuits, as well as data simulations. The collected spectra are obtained by performing single-tone measurements with a direct rf pump on the devices; the output spectra at low powers (below −100 dBm) are well interpreted by the dynamical Casimir model, while at high powers (above −100 dBm) the system is well described by the Autler–Townes fluorescence of a three-level atom.

Closed-form expressions for the pure time delay in terms of the input and output Laguerre spectra

The pure time delay operator is considered in continuous and discrete time under the assumption of the input signal being integrable (summable) with square. Then the input and the output signals are uniquely given by their Laguerre spectra. It is shown that a discrete convolution operator with polynomial Markov parameters constitutes a common description of the delay operator in the continuous and discrete case. Closed-form expressions for the delay value in terms of the output and input Laguerre spectra are derived. The expressions hold for any feasible value of the Laguerre parameter and can be utilized for e.g. building time-delay estimators that allow for non-persistent input. A simulation example is provided to illustrate the principle of Laguerre-domain time-delay modeling and analysis with perfect disturbance rejection.