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Abstract A coupled class‐B laser system is presented to obtain a nonlinear emitter. Its bistability was theoretically predicted, and numerically illustrated to demonstrate by a typical bistable curve diagram. The bistable system exhibits some typical nonlinear dynamic behaviours, such as hyperchaos, quasi‐period as well as coexistent scenarios, and shows a route to a single‐period away from hyperchaos. The hyperchaotic states are diagnosed to find by Lyapunov exponent. The hyperchaotic four‐scroll strange attractor was illustrated to be characterized by ergodicity, complexity, and randomness. The result has a reference value for a bistable optical device, a hyperchaotic emitter, and their applications.

A coupled class‐B laser system is presented to obtain a nonlinear emitter. Its bistability was theoretically predicted, and numerically illustrated to demonstrate by a typical bistable curve diagram. The bistable system exhibits some typical nonlinear dynamic behaviours, such as hyperchaos, quasi‐period as well as coexistent scenarios, and shows a route to a single‐period away from hyperchaos. The hyperchaotic states are diagnosed to find by Lyapunov exponent. The hyperchaotic four‐scroll strange attractor was illustrated to be characterized by ergodicity, complexity, and randomness. The result has a reference value for a bistable optical device, a hyperchaotic emitter, and their applications. [ABSTRACT FROM AUTHOR]

The laser frequency stabilization technology is very important in the development of laser applications, and the improvement of this technology has tend to further expectations for portability and low cost, in addition to the realization of strict frequency control. In this context, we construct a dual-cavity laser frequency stabilization system based on an intracavity dual-mode self-reference mechanism. With this approach, we achieve remarkable results with a laser frequency drift of about 6.6 kHz and an Allen deviation (ADEV) of 10−13 levels over an integration time scale from 0.01 s to 1000 s. Notably, the solution achieves one of the best results without the need for an external reference structure. This work provides a way to realize wavelength-stabilized laser sources by interlocking two DFB lasers. This approach is distinguished by its simplicity and cost-effectiveness, making it a promising option for a variety of applications outside of the laboratory environment.

Laser diodes are widely used in research and industrial applications in areas such as measurements, communications and health. In most of these applications, stability in the emitted light power is required. This can be realized by modifying the internal parameters, such as the current supply, by using an analog automatic power control (APC). This research presents the design and analysis of a feedback laser driver (digital APC system) based on a proportionall–integral (PI) controller. The controller's theoretical design acting on the supply current in a laser was obtained by algebraically solving the general equations of a PI controller over a laser described as a steady-state system. The required steady-state model can be determined from the lightl–current curve obtained either from the laser data sheet or experimentally. A posterior numerical analysis shows that the proportional gain of the PI controller is only limited numerically by the reciprocal of the slope efficiency of the laser when the characteristic time of the system is greater than the sampling period. Finally, the APC model was tested in an experimental setting using a laser diode ADL-65052TL at several temperatures. The results show that the proposed relations for the proportional gain and the integral time are valid, achieving the desired power stability with a drift of less than 0.1 % . [ABSTRACT FROM AUTHOR]

• Efficient and user-friendly thermal simulation instructions for side-pumped lasers. • Reliable laser mode matching in the resonant was computed and designed. • Pulses lasers with high repetition- rates and excellent stability were obtained. • Potentially beneficial applications like PLIF and laser remote sensing. A theoretical and experimental investigation is conducted on a high repetition-rate side-pumped burst-mode Nd:YAG laser. The absorbed pumping power distribution and laser resonator are meticulously optimized to enlarge the area of the fundamental mode and improve thermal stability. With the 1 ms pumping duration and a pumping frequency of 10 Hz, the pulsed laser's burst energy, peak power, and pulse width achieve 0.29 J, 347 kW, and 16 ns, respectively, with the Q-switched repetition rate of 50 kHz. The minimum coefficient of variation for the laser pulse train remains below 5 %. This study represents the first demonstration of a long-term reliable output from a high-energy, nanosecond-pulsed, side-pumped Nd:YAG burst laser operating at 50 kHz. [ABSTRACT FROM AUTHOR]

This work presents a stable and reliable turnkey continuous-wave laser system for a Yb/Ba multispecies trapped-ion quantum computer. The compact and rack-mountable optics system exhibits high robustness, operating over a year without realignment, regardless of temperature changes in the laboratory. The overall optical system is divided into a few isolated modules interconnected by optical fibers for easy maintenance. The light sources are frequency-stabilized by comparing their frequencies with two complementary references: 1) a commercial Fizeau wavelength meter and 2) a high-finesse optical cavity. This scheme enables automatic frequency stabilization for days with a sub-MHz precision.

We study improvements of the Self-Injection Locked (SIL) distributed feedback (DFB) semiconductor laser phase noise as well as integral linewidth on the amount of the SIL feedback and show that SIL reduces the laser noise nearly equally in a broad frequency range, spanning from 1 Hz to 10 MHz. In our experiment SIL operation is supported by a tunable resonant reflector consisting of a high quality factor (high-Q) monolithic whispering gallery mode resonator (WGMR) supplied with a controllable attenuator. Using the experimental setup we validated theoretical formula describing the SIL spectral purity and identified practical parameters of the system allowing reaching the phase noise limit resulting from the fundamental thermodynamic noise of the resonator. We show that the linewidth improvement due to SIL effect is drastically impacted by the frequency spectral dependence of the phase noise of the laser and that it drops significantly in a flickering laser. We also confirmed that the thermorefractive coefficient as well as mode volume of the WGMR imposes the major limitations on the SIL performance. Low intracavity absorption is needed to suppress the attenuation-related thermal effects in the cavity. [ABSTRACT FROM AUTHOR]

We report on a Q-switched Er-doped all-fiber laser based on a solution-processed Ti3C2Txsaturable absorber (SA). Ti3C2Tx is transferred to the fiber core region by optical deposition process through thermal effect. The Ti3C2Tx SA is clamped between two optical fiber connectors, which is flexible to integrate into the laser oscillator. The modulation depth and saturation incident fluence are measured to be ~3% and $\sim 53.31~\mu \text{J}$ /cm2 at 1550 nm wavelength region, respectively. At a threshold pump power of 190mW, we get self-started stable Q-switched operation with single-pulse energy of 22.17 nJ and pulse duration of $\sim 7.07~\mu \text{s}$. With the pump power varing from 190 to 280 mW, the repetition frequency (RF) changes from 52.8 kHz to 62.79 kHz. The maximum average output power is 2.14 mW, which corresponds to the single-pulse energy of 34.03 nJ. The short-term stability is obtained by measuring the RF and temporal sequences of output pulse for 12 hours. Moreover, the long-term stability is demonstrated by measuring the output power and repetition rate for one week, showing the highly stable operation of the Ti3C2Tx fiber laser, for the first time as far as we know. [ABSTRACT FROM AUTHOR]

In this paper, we present an experimental study of the metrological stabilization of a solid-state frequency comb for embedded metrology applications. The comb is a passively mode-locked laser diode based on InGaAs/InP Quantum-dash structure emitting optical lines into a 9 nm bandwidth centered at $1.55~\mu \text{m}$ with a repetition rate of 10.09 GHz. The frequency stabilization is achieved by optical injection locking of the comb with an external cavity laser diode referenced onto a metrological frequency standard. One observes the transfer of the spectral purity from the injection laser to the neighbouring modes of the injected one as well as the transfer of stability to the adjacent modes. The measurement of the long term stability highlights a frequency noise with random walk behavior specific of the passive mode locking process. Demonstration of sidebands of the injection laser at the repetition frequency of the comb also makes it possible to propose a transfer mechanism and to consider a complete stabilization of the frequency comb at a metrological stability level. [ABSTRACT FROM AUTHOR]

The rotation of circular and annular pyrolytic graphite (PG) disks levitating above circular magnet arrays can be used for a novel method of magnetic manipulation, whereas the condition of stable levitation has not been figured out yet. In this article, a method to analyze the diamagnetic forces sustained by levitated PG is proposed to investigate the mechanism of stable levitation. When using this method, the whole PG disk is divided into multiple regions according to the distribution of magnetic field in order to determine the resultant diamagnetic force. With the help of the method, the exclusive levitation height of PG disk was determined, and the relationship between the relative size of circular and annular disks to magnet and its ability of stable levitation was clarified. The proposed method is the first one able to investigate the position stability of levitated PG and provides insights into local forces without heavy workload of finete element method (FEM) calculation. The analysis results are verified by the simulation of distribution of potential energy and can be a new way of magnetic manipulation. [ABSTRACT FROM AUTHOR]

Laser diodes are widely used in research and industrial applications in areas such as measurements, communications and health. In most of these applications, stability in the emitted light power is required. This can be realized by modifying the internal parameters, such as the current supply, by using an analog automatic power control (APC). This research presents the design and analysis of a feedback laser driver (digital APC system) based on a proportionall–integral (PI) controller. The controller’s theoretical design acting on the supply current in a laser was obtained by algebraically solving the general equations of a PI controller over a laser described as a steady-state system. The required steady-state model can be determined from the lightl–current curve obtained either from the laser data sheet or experimentally. A posterior numerical analysis shows that the proportional gain of the PI controller is only limited numerically by the reciprocal of the slope efficiency of the laser when the characteristic time of the system is greater than the sampling period. Finally, the APC model was tested in an experimental setting using a laser diode ADL-65052TL at several temperatures. The results show that the proposed relations for the proportional gain and the integral time are valid, achieving the desired power stability with a drift of less than 0.1%.

We propose and demonstrate a technique to vastly reduce the linewidth of a commercially available semiconductor laser operating at 1550 nm by locking it to an all-fiber Mach-Zehnder interferometer (MZI) with a short path length imbalance. The long term linewidth was reduced from 20 kHz to the single and even sub Hz level. Very narrow linewidths can only be measured by beating two separate, nominally identical lasers. To this end, we employ two lasers configured in a unique, counter propagating configuration, both locked to two different fringes of the MZI. The beat between the two locked lasers proves the extremely narrow linewidth of each laser. In order to detect and compensate for the noise caused by mechanical and thermal fluctuations of the fibers, we use the beat signal as an input to a servo loop that feeds a piezo electric fiber stretcher stabilizing the MZI. [ABSTRACT FROM AUTHOR]

Ultra-stable lasers serve as the backbone for the most advanced optical metrology scientific experiments, enabling the ability to laser interferometry or atomic spectroscopy at the highest levels of precision, thanks to the rapid development of laser wavelength stabilization techniques based on optical or electrical feedback from an external reference such as absorption line or optical cavity. With the increasing interest in making these scientific systems portable and applying it outside of the laboratory, it still remains an open question as to how to realize a laser source that can reach the high wavelength stabilization and still remain sufficiently compact and portable for field use. Here, we describe a wavelength stabilization fiber laser with intracavity reference mechanism, by utilizing the beat note of dual modes inside the laser cavity as the laser wavelength drift reference signal. A laser wavelength drift less than 5 kHz and ADEV 10−13 level at integration time scales from 0.01s to 1000s is achieved, which is to-date the best results for the laser wavelength stabilization without the external frequency reference. The outcome of this work presents a new way to achieve an ultra-stable laser with a simpler, lower cost feature. It offers new insights to promote the highest precision optical metrology scientific application outside of the laboratory, and also gives the possibilities of applying the ultra-stable laser source into a wider range of industrial application. [ABSTRACT FROM AUTHOR]

Bifurcation analysis and dynamical system studies are carried out to find the stability regime and chaotic scenario in electron acoustic waves in relativistic degenerate plasma. We have obtained the quantum hydrodynamic model and obtain the Korteweg–de Vries equation describing the nature and characteristics of solitary structures. The amplitude modulated envelop soliton formation due to external perturbations has been studied by analyzing the nonlinear Schrodinger equation. Further to study the stability factors and the parametric range for such stability, the dynamical system is studied and bifurcation analysis has been carried out. The chaotic behavior of the system is studied through largest Lyapunov exponent (LLE). This work will find application in theoretically predicting the stable modes in many solar plasma and stellar plasma applications and in laser plasma in future. [ABSTRACT FROM AUTHOR]

Catastrophic optical mirror damage (COMD) is one of the main failure mechanisms limiting the reliability of GaAs based laser diodes. Here, we compare the facet stability of ZnSe-passivated ridge-waveguide lasers (RWLs) that are cleaved in air and subsequently cleaned using atomic hydrogen with RWLs that are cleaved in ultra-high vacuum. RWLs cleaved in ultra-high vacuum show a superior performance and reach power densities up to 58 MW/cm2 under extended continuous wave operation at 1064 nm. This is attributed to the reduction of defects at the interface between ZnSe and the cleaved facet as evidenced by transmission electron microscopy and X-ray diffraction. [ABSTRACT FROM AUTHOR]

Based on the experimental platform of an L-band normal-dispersion mode-locked fiber laser, we report the first observation, to the best of our knowledge, of the collision of dissipative solitons (DSs) and concomitant state transition with chaotic behavior by the dispersive Fourier transform technique (DFT). The gain depletion and recovery of Er3+ in L-band cause the DSs that are close to each other to experience different gain spectra, thus giving them different central wavelengths and group velocities. As a result, collisions occur and lead to transitions between different pulsation and stable DS state. The experimental results provide new insights into the complex multi-soliton dynamics under unstable mode-locking conditions. It is confirmed that more than one soliton solution can coexist in a multi-pulse situation related with the gain dynamics. Our experimental results extend the exploration of multisoliton and soliton pulsation in laser state transition, and contribute to the study of soliton stability and laser dynamics. [ABSTRACT FROM AUTHOR]

Due to low cost and ease of manufacture, the combined sensor consisted of a camera and a 1D laser range finder is commonly used in many engineering applications. Especially in aerospace field, this type of combined sensor is important to earth observation and deep space exploration. This article proposes a novel extrinsic calibration method to get the accurate and stable calibration results of camera-1D laser range finder combined sensor. Firstly, an accuracy criterion named with directional comprehensive criterion is proposed to solve the less constraint in traditional calibration methods, which can evaluate the inconsistencies in the 1D laser ranging direction and the mean reprojection error in the 2D image plane direction fully. Then, according to the proposed directional comprehensive criterion, a novel robust extrinsic calibration framework is presented, which removes the observation data with large errors automatically and utilizes a stability criterion as the termination condition. The simulation experiments and real data experiments reveal that the proposed method is effective, which is superior to the existing methods. [ABSTRACT FROM AUTHOR]

A stabilized coherent narrow-linewidth Brillouin random fiber laser with low lasing noise is proposed and investigated experimentally, which employs stimulated Brillouin scattering and Rayleigh scattering in optical fibers to provide the gain and the random distributed feedback, respectively. The stabilized lasing output with suppressed noise is realized utilizing a simple structure of a double-coupler fiber ring resonator, which is composed of a section of single-mode fiber and two optical couplers with different coupling ratios. Compared with the existing free-running Brillouin random fiber lasers, much more stabilized laser output can be obtained as the double-coupler fiber ring resonator effectively acts as a narrow-bandwidth mode filter through the Vernier effect that constrains the dense random longitudinal modes competition within a small frequency range. In the experiment, a stable ultra-narrow linewidth of approximately 586.4 Hz is obtained from the laser output. Statistical analysis of mode hopping in the proposed laser indicates a great improvement in multi-mode resonances and frequency jitters with the imbedding of the ring resonator. In addition, measurement results of relative intensity noise and frequency noise of the proposed laser showcase a great suppression in mode-competition-induced lasing instability and a significant improvement in the noise level compared to the free-running Brillouin random fiber lasers. The proposed all-fiber-based stabilization technique makes a step forward for developing practically robust and reliable Brillouin random fiber lasers. Such a stabilized highly coherent narrow-linewidth laser source with low cost and low power consumption will find promising applications in high-resolution spectrometers, microwave photonics, and optical sensing. [ABSTRACT FROM AUTHOR]

The paper is focused on a systematic investigation of the circuits for active stabilization of the frequency offset between two semiconductorn ultra-accurate fiber optic time transfer systems. The frequency offset is increased up to 50 GHz, which can be achieved not only with relatively low-noise integrated tunable laser assemblies, but also with ordinary, telecom-grade, distributed feedback lasers. The paper starts by determining the general frequency accuracy and stability, required to keep the uncertainty contribution of the stabilization circuit at a negligible level (assumed here as 1 ps) compared to other contributions of the overall uncertainty of the link calibration. Next, the technical details of the essential building block of the system discussed, which is required to convert the high-frequency offset to lower frequencies to allow convenient frequency measurement, are analyzed. Experimental circuits built with commercially available millimeter wave integrated circuits were tested with the frequency offset complying with telecom dense wavelength division multiplex standards, equal to 12.5 GHz, 25 GHz and 50 GHz. It was found that such stabilization circuits can cause substantial systematic errors, which are related to lasers’ phase noise and the operation with low input optical powers (below −39 dBm in evaluated circuits). These effects were investigated experimentally in detail and countermeasures were proposed. [ABSTRACT FROM AUTHOR]

A 3-D printed narrowband bandpass filter based on spherical dual-mode resonators is presented in this article. It is designed for output multiplexers (OMUXs) using high- $Q$ spherical dual-mode resonators. Realization is by laser powder bed fusion (L-PBF) technology of Invar alloy chosen for its low coefficient of thermal expansion (CTE). Using PBF circumvents the alloy’s manufacturability issues associated with its hardness in machining and free forming. Compared with polymer-based vat photopolymerization technology, PBF allows for direct metal manufacture of complex monolithic microwave components with better thermal-mechanical properties and higher power-handling capability. Using Invar can further help achieve high temperature stability of the filter in high-power operation. To demonstrate the proposed solution, detailed thermal-RF test at different temperatures was carried out. The experimental results of a 0.47% fourth-order silver-plated Invar filter with two transmission zeros verify the design and manufacturing. An insertion loss of 1 dB and an effective temperature coefficient of less than 2 ppm/K were achieved. [ABSTRACT FROM AUTHOR]

Chip-scale atomic clocks (CSACs) have been extensively investigated and many prototypes or products have been realized as time sensors. Researchers focus on improving the frequency stability performance, reducing the volume and the power consumption of CSACs. To the best of our knowledge, the physics packages reported until now are all assembled from discrete components. This traditional assembly method has a very low efficiency and causes variations among different physics packages. In this article, we propose a wafer-level assembled physics package for CSACs based on three dimensional (3-D) wafer-level packaging (WLP) and microelectromechanical system (MEMS) technologies. The components of the physics package are all fabricated on wafers. These wafers are integrated together vertically and then diced into separate physics packages. The proposed method has the advantages of high uniformity among different physics packages and high efficiency. And it improves the utilization rate of wafers by reducing the unused area. Thus, the production cost is reduced considerably. The volume of the proposed functional physics package is less than 8 mm3. The prototype chip-scale atomic clock incorporating the proposed physics package reveals the coherent population trapping (CPT) linewidth of 1.8 kHz and the total power consumption of about 20mW. The frequency stability is about $6.1 \times 10^{-12}$ @1000s. The observed results demonstrate promising performance of the wafer-level assembled physics package. The approach described in this article reveals a viable method for batch production for its low cost, high efficiency and high product uniformity. [ABSTRACT FROM AUTHOR]

We describe the design and implementation of a compact laser system for the pulsed optically pumped (POP) rubidium (Rb) cell atomic clock. The laser system includes packaged optics for sub-Doppler absorption, acousto-optic modulation and light beam expansion, and dedicated electronics for laser diode reliable single-mode operation and laser frequency stabilization. With beat measurements between two identical laser systems, the laser frequency stability was found to be ${3.0}\times {10}^{-{12}}$ for averaging times from 1 to 60 s and it reached ${3.5}\times {10}^{-{12}}$ at 10 000 s averaging time. Based on the compact laser system, the short-term stability of the Rb cell atomic clock in pulsed regime was approximately ${2.7}\times {10}^{-{13}}\,\, {\tau }^{-\text {1/2}}$ , which is in reasonable agreement with the estimated ${2.37}\times {10}^{-{13}}\,\, {\tau } ^{-\text {1/2}}$. The compact laser system is significant in terms of the development of transportable and high-performance Rb atomic clock prototypes. [ABSTRACT FROM AUTHOR]

Finding and identifying the minimal number of sensor nodes for a sensor network is one of the most basic problems for the implementation of distributed state estimators. Despite a plethora of research studied sensor networks, most of them ignored this problem or assumed the considered sensor network comes with an ideal number of sensor nodes. We revisit this problem in the current paper. To this end, the minimal number of sensor nodes problem is first formalized and a novel observability condition, namely, minimal nodes uniform observability (MNUO), is then proposed. Next, this MNUO is applied to study the stability issues of the distributed Kalman filtering algorithm. In what follows, under the condition of MNUO, conditions to ensure its stability are given and the results about the relation of the filtering performance before and after selecting the minimal number of sensor nodes are obtained. Finally, optimization solutions and an example are given to find the minimal number of sensor nodes for a sensor network. [ABSTRACT FROM AUTHOR]

Extremum-Seeking Control (ESC) is a technique used to stabilize systems to optimal operating conditions. The adjustment of the controller parameters is not usually reported. In this paper we present a computational model for frequency stabilization of a laser source using ESC. The model is based on a saturated absorption spectroscopy experiment used to reference the frequency of the laser light to an atomic transition in Cesium atoms. By using this model, we were able to study the performance and adjust the parameters of the controlled system. This model was succesfully validated using an experimental open loop configuration. The model was then used to predict stable configurations of the controlled system, to be implemented in the experimental setup. As a result, we were able to get the laser frequency locked to a Cs atomic transition in the laboratory with a relative stability in frequency of 6x10-8. [ABSTRACT FROM AUTHOR]

A frequency-stabilized narrow-linewidth external cavity diode laser (ECDL) at the wavelength of the R18 carbon dioxide (CO2) absorption line for space-borne CO2 detection LIDAR is reported. The ECDL module based on the fiber Bragg grating (FBG) is integrated in a compact butterfly package, emitting at the wavelength of 1572.02 nm and provides continuous tunability of 22 GHz. A polarization-maintaining all-fiber ring resonator is used as a transfer cavity to transfer the long-term stability of a metrological frequency reference at 1550.12 nm to the target wavelength. The combination of narrowing linewidth technique and frequency stability transfer technique enables lasing with an intrinsic Lorentzian linewidth of 15 kHz as well as a relative frequency stability on the order of $10^{-12}$ for averaging time from 1 to 1000 s (minimum of $2.1\times 10^{-12}$ at 2 s). [ABSTRACT FROM AUTHOR]

Laser-driven white light illumination is considered as the next generation of high brightness white light source. The most common way to achieve laser-based white light is using a blue laser to excite phosphor/ silicone converter (reference converter). However, the relatively low thermal conductivity of phosphor limits most of the heat to its surface and cannot be dissipated effectively. In this work, a converter with copper sintering powder framework/paraffin (CPSF/P) embedded into the phosphor/silicone is proposed. As an internal heat transfer channel, copper powder sintering framework (CPSF) transfers heat to paraffin coated in porous skeleton, and then paraffin absorbs the generated heat through solid–liquid phase transition, which effectively dissipates the heat concentrated on the phosphor surface and improves its thermal stability. Under high-power laser excitation of 7.74 W, the surface temperature of the reference converter is up to 660 °C, while the maximum temperature of the CPSF/P converter is only 139 °C, which is reduced by 521 °C (78.9%). The results show that the proposed CPSF/P converter can withstand higher excitation power and show better thermal stability than the reference converter, which is helpful to obtain higher color stability. This provides an efficient heat dissipation scheme for high-power laser-driven lighting. [ABSTRACT FROM AUTHOR]

We present a continuously tunable single-frequency continuous wave (CW) Ti:Sapphire (Ti:S) laser with modulation-free-locked intracavity lithium niobate (LiNbO3) birefringent etalon (BE), which is implemented by detecting the polarization state variation of the reflected laser beam from the BE. After the BE is stably locked, the continuous frequency-scanning range up to 40 GHz is obtained within the tuning range of 300 nm while the resonator length of the Ti:S laser is continuously scanned. Because the modulation signal is unnecessary in the presented Ti:S laser system, the influences of the extra modulation signal on the intensity noise as well as the frequency noise of the laser are thoroughly eliminated and the modulation-noise-free continuously tunable single-frequency CW Ti:S laser is successfully attained. [ABSTRACT FROM AUTHOR]

In this work, a facile growing laser-scribed graphene (LSG) process is successfully demonstrated, which can pattern in situ sulfur (S)-doped porous graphene electrodes on a flexible sodium lignosulfonate (SLS)-coated polyethersulfone (PES) film. The typical microsupercapacitors (MSCs) based on S-doped porous graphene deliver an ultrahigh areal capacitance of 55.4 mF cm−2, and have good long-term cycle stability with 85.2% capacitance retention after 10000 cycles. Moreover, these devices exhibit superb mechanical flexibility and outstanding modular integration capability. This novel fabrication approach can be extended to other heteroatom-doped electrode materials for application in high-performance energy storage devices. [ABSTRACT FROM AUTHOR]

As a member of the MXene family, tungsten carbide (WC), with its unique physical structure and excellent optical properties, possesses enormous development potentials in ultrafast optoelectronics. In this letter, A WC film saturable absorber (SA) is successfully demonstrated to induce passive Q-switching in an erbium-doped fiber laser (EDFL). The WC nanoparticles (NPs) are synthesized by a hydrothermal method. Stable Q-switched pulses are generated at 1558 nm with a threshold pump power of 141 mW, after inserting the prepared WC film into the EDFL ring cavity. As the pump power ranges from 141 mW to 193 mW, the repetition rate increases from 32.34 kHz to 35.8 kHz, while the pulse duration decreases from $5.5~\mu \text{s}$ to $4.16~\mu \text{s}$. When the pump power reaches a maximum power of 193 mW, the corresponding maximum pulse energy and output power are 81 nJ and 2.9 mW, respectively. To our best knowledge, this is the first report of utilizing WC as SA to achieve Q-switched pulses. Our research results provide a new reference for the realization of pulsed laser using MXene materials and reveal that WC has immense applications in nonlinear optics and ultrafast laser technology, which greatly broadens the frontier of materials for optoelectronic techniques. [ABSTRACT FROM AUTHOR]

Developing compact and stable 2 $\mu \text{m}$ ultrafast laser sources is important for generating mid-inferred frequency combs. Here, we report on a simple, compact and reliable thulium-doped fiber laser based on figure-of-9 mode-locking. Self-starting and stable mode-locked operation is achieved with 0.30 nJ pulse energy and 128 fs pulse width under 121.3 MHz repetition rate. The generated pulses centered at 1990 nm have a 3 dB bandwidth of 39.4 nm. The laser has been assembled into a $197\times 78\times 20$ mm3 fiber box under temperature-control. The repetition rate was phase locked over 20 h with a fluctuation standard deviation of 192.5 $\mu $ Hz. Such compact and highly-reliable mid-inferred laser could be used beyond laboratory and promote numerous critical applications including dual-comb spectroscopy, ranging and frequency calibration. [ABSTRACT FROM AUTHOR]

Three sets of bottom-gate (BG) nanocrystalline silicon (nc-Si:H) thin-film transistors (TFTs) with amorphous silicon nitride (a-SiNx:H) as the gate dielectric were produced under various nc-Si:H plasma deposition conditions. Chromium (Cr) and aluminum (Al) were used as the gate electrodes in each TFT set. The effects of the gate electrode on the nc-Si:H TFT performance, particularly on its electrical stability, were studied. For each TFT set, Al-gated TFTs resulted in the higher mobility, lower subthreshold slope, and better stability compared to the Cr-gated TFTs. The impact of the Cr- or Al-gate underlayer on the surface and bulk properties of a-SiNx:H and nc-Si:H films was analyzed in detail considering back channel etching (BCE) characteristics, electrical, scanning electron microscope (SEM), Raman, grazing angle X-ray diffraction (GAXRD), and Fourier transform infrared-attenuated total reflection (FTIR-ATR) measurements. Structural differences were recognized in a-SiNx:H and nc-Si:H films grown in the BG TFT sequence depending on the type of the gate electrode. Based on these findings, possible reasons were proposed to explain the superiority of the Al over Cr as the gate electrode for nc-Si:H TFTs. [ABSTRACT FROM AUTHOR]

To investigate the effect of photon-induced carrier transition mechanism on switch stability, the time jitters of 2-mm-gap gallium arsenide photoconductive semiconductor switches (GaAs PCSSs) are compared when triggered by lasers of two different wavelengths, i.e., 1064 and 532 nm. The time jitter model is proposed to clarify the synergy of the multiple adjustable macroparameters of trigger conditions. The carrier valley occupation rates with respect to bias electric field are simulated, where the influence of the microprocedures, i.e., carrier generation, carrier intervalley transition, and carrier transportation, is considered. Our experimental results illustrate that the time jitter of the GaAs PCSS exhibits a nonmonotonous behavior and obtains a local minimum at $\sim 3$ kV/cm for 1064 nm; however, it shows a monotonous decrease to a constant value at about 3 kV/cm for 532 nm. Our analysis indicates that the discrepancy in GaAs PCSS time jitter is attributed to the difference in the relative fluctuation of the carrier velocity affected by the carrier valley occupation rate. This article is of great significance in optimizing the stability of GaAs PCSS and pulse power system by adjusting the macroparameters in the time jitter model. [ABSTRACT FROM AUTHOR]

We experimentally and theoretically demonstrate a new method to obtain a single-mode operation in long cavity lasers. The method is based on suppressing non-lasing modes in the time domain by attenuating their intensity beating with the lasing mode. This suppression is implemented in our experiments by adding into the cavity an intensity modulator, which is controlled by the photo-detected beating signal. We have demonstrated the method in a long Erbium-doped fiber ring laser with a ring cavity length of about 13 m. Single-mode operation without mode-hopping was obtained for a long time duration of about 100 minutes. Although Erbium-doped fiber amplifiers are homogeneously broadened at room temperature, a single-mode operation was achieved in several cavity modes, which do not have the highest small-signal gain. A theoretical model, based on a small-signal stability analysis, is given. The model indicates that the control delay should be accurately chosen. [ABSTRACT FROM AUTHOR]

We demonstrate a novel, robust and compact fiber laser mode-locked by nonlinear polarization evolution (NPE) in polarization-maintaining (PM) fibers. The reflectivity of the artificial saturable absorber (SA) is analyzed to explain the mode-locking mechanism in the laser cavity. Experimentally, three linear laser schemes that feature repetition rates 94 MHz, 124 MHz and 133 MHz are systematically investigated. When the pump power is 1100 mW, the 124-MHz laser cavity delivers highly stable pulses with a single-pulse energy of 0.92 nJ. After the compression, the pulse duration obtained from the 124-MHz fiber laser is 250 fs, while the corresponding transform-limited pulse duration is 124 fs. The highest fundamental repetition rate that could be achieved in our experiment is 133 MHz, as mentioned above. The noise characterization has been performed with different cavity lengths and therefore different net-cavity dispersion. The 68-fs timing jitter and the 0.01% relative intensity noise (RIN) of the 133-MHz fiber laser have been realized integrated from 1 kHz to 10 MHz. Furthermore, the root-mean-square (RMS) power fluctuation is 0.35% in 2 hours, which implies superior stability of the output power. Thus, this linear fiber oscillator provides a competitive low-noise light source for optical applications appropriate for complex environments. [ABSTRACT FROM AUTHOR]

Stable output and beam profile at high power laser operation is a prime requirement for precision high-end manufacturing. The stability of laser charateristics during power scaling in a single-oscillator is limited by several unavoidable non-linear effects. Hence, kW-level power scaling through multiple amplification stages or using signal combination are feasible solutions. In a master oscillator power amplifier (MOPA) architecture, pump-signal combiner with high pump coupling efficiency and low loss signal transmission maintaining seed beam quality during coupling from a single mode fiber into a large mode area fiber, is an important component. In this respect, an effective method of fabricating mode-field matched pump-signal combiner has been presented employing a section of intermediate fiber, having adiabatically tapered core and uniform cladding, along with a conventional signal fiber (termed hybrid signal fiber) inside the input fiber bundle to obtain effective mode-field matching of signal light in between the input fiber bundle and the output fiber. Additionally a taper-less signal combiner design has been proposed for scaling laser power through incoherent combination. The reduced-clad signal fiber with low loss core guidance supports bundling of the input fibers inside an economic low-OH silica tube to obtain good transmission efficiency and beam profile. [ABSTRACT FROM AUTHOR]

The closed-loop method based on the Faraday effect is realized with a low coherence-noise resonator in resonance fiber optic gyro (RFOG). The resonator based on spun-fiber (SF) is designed and fabricated, which not only has the advantage of low coherent optical noises, but also has an outstanding circularly state of polarization (CSOP) maintaining ability that lays the foundation for the realization of a closed-loop method based on the Faraday effect. As the core component of the Faraday-based method, the Faraday coil is reasonably designed to meet the requirements of the sufficient frequency shift and power stability. In addition, the interval control method that is conducive to the improvement of system stability is applied to control Faraday coil for the first time. The experimental results show that the method we proposed can effectively achieve high-reciprocity and linear equivalent frequency shift by Faraday coil. Also, the short-term and long-term stability of Faraday-based RFOG system have been improved compared with other closed-loop methods, which provides a simple and efficient method for RFOG closed-loop signal processing. [ABSTRACT FROM AUTHOR]

Operation stability is the main challenge that current existing saturable absorbers (SAs) are facing. In this paper, we report on two low chemical activity saturable absorbers, the tellurium dioxide and antimony trioxide thin film, for stable femtosecond pulse generation in 2 μm region. The nonlinear absorption of two oxides at 2 μm was firstly revealed and the extraordinary mode-locking performance based on two oxides was demonstrated. The phase noise and amplitude noise were also measured and analyzed, and the integrated RMS relative intensity noise was found to be 0.0196% and 0.0218% for TeO2 thin film and Sb2O3 thin film respectively. Great thermal stability and long-term stability were also confirmed. Heating the oxides coated area in atmosphere for hours and the lasers still could be mode-locked. Compared to low dimensional materials, the oxides proposed in this paper could be more suitable for robust mode locking in harsh environment. The broadened working conditions tolerance also enables new applications for optical modulators. [ABSTRACT FROM AUTHOR]

In this paper, we report the existence of Eckhaus instability in laser cavities with harmonically swept filters, of which Fourier Domain Mode Locked (FDML) laser is an important example. We show that such laser cavities can be modeled by a real Ginzburg Landau equation with a frequency shifting term arisen from the cavity dispersion. We analytically derived a solution of the governing equation and analyzed its stability. We found that the cavity dispersion introduces a continuous frequency shift to the laser signal such that it will be eventually pushed outside the stable region and trigger the Eckhaus instability. We show that the repeated triggering of the Eckhaus instability in the laser cavities is the dominant effect that leads to the high frequency fluctuations in FDML laser output, which is the unique feature of such laser cavities and intrinsically limits the signal quality of the FDML lasers with nonzero cavity dispersion. [ABSTRACT FROM AUTHOR]

Integrating photonics with CMOS electronics in silicon is essential to enable chip-scale, electronic-photonic systems that will revolutionize classical and quantum communication and computing systems. However, the lack of an on-silicon isolator, capable of blocking unwanted back reflections and ensuring the stable operation of the laser, precluded many previous demonstrations from providing single-chip solutions. For most optical systems employing a laser, magneto-optic isolators have been indispensable, but such isolators are incompatible with silicon. To stabilize on-chip lasers, reflections-cancellation circuits were proposed as a way to reduce the reflections going back to the laser. Yet, a stable laser against time-varying back reflections was never demonstrated. Here we demonstrate a stable quantum well-distributed feedback (QWDFB) laser against slowly time-varying reflections using a reflections-cancellation circuit (RCC) on a foundry-produced, silicon-photonic (SiP) chip. The optical spectrum and the relative intensity noise (RIN) of the laser when the RCC was running is comparable to when an isolator was used. By accurately locking the laser in a stable optical feedback regime, the RCC further enhances the QWDFB laser performance by reducing its linewidth by a factor of 100, down to 3 kHz. Both results are enabled using novel techniques in the design, calibration, tuning, and control of the proposed SiP RCC. The optical insertion loss of the RCC is less than 1.5 dB for reflections smaller than −20 dB and can yield isolation ranges of up to 64 dB. Our device paves the way towards the mass production of fully integrated, low-cost electronic-photonic silicon chips without attaching magneto-optic isolators between the laser and the SiP chip. [ABSTRACT FROM AUTHOR]

This paper investigates a novel method for the in-situ evaluation of the low-frequency magnetic field fluctuation in an atomic comagnetometer (ACM). An in-situ magnetic field measurement model is first established for the hybrid atomic spin ensembles in the ACM based on the simplified Bloch equations. Then, the ACM is transformed into an in-situ magnetometer by employing a large longitudinal magnetic field and a transversal alternating current (AC) magnetic field, respectively. This in-situ magnetometer is sensitive to the magnetic field fluctuation along the detection laser direction according to the established measurement model and can realize the magnetic field measurement sensitivity of 88fT/Hz1/2 at 0.1Hz. Finally, the low-frequency magnetic field fluctuation is evaluated with this in-situ magnetometer, whose influence on the stability of the ACM is also analyzed by the Allan variance method. The experimental results show that the contribution of the magnetic field fluctuation along the detection laser direction to the stability of the ACM is about 0.0068 deg/h, which means that the magnetic field error still has a non-negligible effect on the stability of the system. This new in-situ magnetic field measurement method has the advantages of simple operation and no need to replace the atomic vapor cell, which provides an effective means of the magnetic field error evaluation for the ACM. [ABSTRACT FROM AUTHOR]

We measure the electrical performance and stability of indium tin zinc oxide (ITZO) thin-film transistors (TFTs), respectively, covered with a passivation layer (PVL) of aluminum oxide (Al2O3) or scandium oxide (Sc2O3) prepared by pulsed laser deposition (PLD). The devices with the Sc2O3 PVL exhibit both satisfactory electrical performance and stability with a field effect mobility of 16.4 cm2/Vs, threshold voltage of 1.0 V, subthreshold swing of 0.09 V/decade, and especially, a minimum threshold voltage shift of 0.7 and −1.6 V under negative bias temperature stress (NBTS) and positive bias temperature stress (PBTS), respectively. This may be attributable to the suppression of oxygen vacancy formation and excellent capacity to protect the channel from environmental effects. Although the devices with the Al2O3 PVL show similar electrical performance, their stability is worse than that of the devices with Sc2O3. This shows the excellent potential of Sc2O3 thin films as a PVL. [ABSTRACT FROM AUTHOR]

We investigate the application of Ramsey spectroscopy for the development of a microcell atomic clock based on coherent population trapping (CPT). The dependence of the central Ramsey-CPT fringe properties on key experimental parameters is first studied for optimization of the clock’s short-term frequency stability. The sensitivity of the clock frequency to light-shift effects is then studied. In comparison with the continuous-wave (CW) regime case, the sensitivity of the clock frequency to laser power variations is reduced by a factor up to 14 and 40.3 for dark times of 150 and $450~\mu \text{s}$ , respectively, at the expense of intensity 3.75 times higher for short-term stability optimization. The dependence of the clock frequency on the microwave power is also reduced in the Ramsey case. We demonstrate that the Ramsey-CPT interrogation improves the clock Allan deviation for averaging times higher than 100 s. With a dark time of $450~\mu \text{s}$ , a clock fractional frequency stability of $3.8 \times 10^{-12}$ at 104 s is obtained, in comparison with the level of $8\times 10^{-11}$ obtained in the standard CW case, in similar environmental conditions. These results demonstrate that Ramsey-based interrogation protocols might be an attractive approach for the development of chip-scale atomic clocks (CSACs) with enhanced mid- and long-term stability. [ABSTRACT FROM AUTHOR]

We demonstrate a hybrid solution for simultaneous transfer of ultra-stable optical frequency, RF frequency and time signal on a 100 km fiber spool with the same wavelength based on coherent demodulation and optical phase-lock-loop (OPLL). The one pulse per second (1PPS) is encoded by phase and RF frequency is encoded with an intensity modulator. The noise caused by fiber link is compensated by the round-trip method. And the bad effect on optical frequency caused by optical phase modulation (PM) can be cleaned using OPLL. When the fiber link is stabilized, the transferred time deviation (TDEV) can be 2.4E-11@1s and 1.9E-12@104s, RF frequency stability can achieve 8.0E-14@1s and 2.5E-17@104s, the modified Allan deviation (MDEV) of cleaned optical frequency can be 1.4E-16@1s and 1.6E-19@104s. [ABSTRACT FROM AUTHOR]

The conditions securing stability in configurations that employ gain media, carry vital information for the operation and functionality of the respective systems. These constraints are determined for a generic photonic setup comprising two concentric, passive or active, cylindrical impedance metasurfaces, by assuming their size small compared to the oscillation wavelength. Such an approximation, permits the analytical determination of the unstable poles across the complex frequency plane, which is otherwise a computationally cumbersome task. The absorbing and scattering response of the structure, when excited by various primary sources, unveils the dynamics behind the supported resonances and reveals the limits in its performance while respecting stability restrictions. The reported results may assist substantially the modeling and stable design of devices involving this ubiquitous cylindrical component in numerous applications spanning from radiation pattern control and angular momentum transformation to active cloaking and reconfigurable wavefront manipulation. [ABSTRACT FROM AUTHOR]

Considering the compensation of thermo-optic coefficients (TOC) between GaN-based cavity and TiO2 photonic crystal (PhC) layer, we have theoretically designed a photonic crystal surface emitting laser (PCSEL) with temperature-insensitive wavelength. The structure includes a freestanding GaN membrane with embedded multiple InGaN/GaN quantum well (QW) layer and the top TiO2 PhC layer. The high refractive index (RI) of PhC and the freestanding membrane cavity structure cooperate to enable a stronger field-coupling in PhC, thus fulfill the athermal coupling condition. Interestingly, the wavelength temperature dependence is only 0.0015 nm/°C for such PCSEL with a 82% PhC confinement factor, and its athermal property is proportional to the field confinement factor in TiO2 PhC layer. To illustrate, a general formula has been developed after the investigations of thermo-optic effect and thermal expansion effect. [ABSTRACT FROM AUTHOR]

We propose a method to continuously frequency shift a target laser that is frequency stabilized by a reference laser, which is several hundreds of nanometers detuned. We demonstrate the technique using the $\mathrm {5S_{1/2}} \rightarrow \mathrm {5P_{3/2}} \rightarrow \mathrm {29D_{5/2}}$ Rydberg transition in 87Rb vapor and lock the 482 nm target laser to the 780 nm reference laser using the cascaded electromagnetically induced transparency signal. The stabilized frequency of the target laser can be shifted by about 1.6 GHz by phase modulating the reference laser using a waveguide-type electro-optical modulator. This simple method for stable frequency shifting can be used in atomic or molecular physics experiments that require a laser frequency scanning range on the order of several GHz. [ABSTRACT FROM AUTHOR]

Random fiber lasers (RFLs), featuring a simple open cavity but with unique lasing characteristics, have captured considerable attention in the past several decades. Particularly, RFLs assisted by the passive feedback exhibit excellent robustness and compactness owing to the combination of active amplification and passive feedback from random distributed Rayleigh scattering. However, RFLs with the aid of the passive feedback reported previously are primarily operating in the near-infrared wavelength region of 1.1 μm or 1.5 μm based on the ytterbium or erbium doped active fibers. Here, we propose and demonstrate a random fiber laser configuration combining the passive feedback from a piece of single mode fiber with the active gain based on the thulium doped fiber, and extend the operation wavelength to the critically important mid-infrared wavelength band of ∼2 μm. The spectral and temporal characteristics of the lasing output are evaluated and compared with those generated in a single pass amplification structure and a conventional resonant structure. Our results show that the passive feedback assisted RFL has a stabilized lasing wavelength and notably suppressed temporal dynamics. This work not only advances the development of RFLs, but also provides a promising strategy to achieve mid-infrared laser emission with a comparatively low relative intensity noise. [ABSTRACT FROM AUTHOR]

We report the design and performance of a single frequency all-fiber distributed feedback (DFB) laser sources employing fiber Bragg gratings (FBGs) emitting in the 2- $\mu$ m region. Output powers up to 65 mW CW and optical signal-to-noise ratios of $>$ 65 dB/0.05 nm are obtained. The emission wavelength of the DFB–FBG laser can be fine-tuned with picometer accuracy over a range of 0.6 nm by controlling the pump power and laser temperature. The single frequency source is amplified with polarization-maintaining Ho- or Tm-doped fiber amplifiers to an output power of 1 W CW at 2051 nm or 0.7 W CW at 2039 nm. Heterodyne measurements yield instantaneous laser linewidths of 5 kHz FWHM for both native and amplified signals. [ABSTRACT FROM AUTHOR]