Identical Laser Research Articles

Integrated Resonant Electro‐Optic Comb Enabled by Platform‐Agnostic Laser Integration

AbstractThe field of integrated photonics has significantly impacted numerous fields including communication, sensing, and quantum physics owing to the efficiency, speed, and compactness of its devices. However, the reliance on off‐chip bulk lasers compromises the compact nature of these systems. While silicon photonics and III‐V platforms have established integrated laser technologies, emerging demands for ultra‐low optical loss, wider bandgaps, and optical nonlinearities necessitate other platforms. Developing integrated lasers on less mature platforms is arduous and costly due to limited throughput or unconventional process requirements. In response, a novel platform‐agnostic laser integration technique is proposed, utilizing a singular design and process flow, applicable without modification to a diverse range of platforms. Leveraging a two‐step micro‐transfer printing method, nearly identical laser performance is achieved across platforms with refractive indices between 1.7 and 2.5. Experimental validation demonstrates strikingly similar laser characteristics between devices processed on lithium niobate and silicon nitride platforms. Furthermore, the integration of a laser with a resonant electro‐optic comb generator on the thin‐film lithium niobate platform is showcased, producing over 80 comb lines spanning 12 nm. This versatile technique transcends platform‐specific limitations, facilitating applications like microwave photonics, handheld spectrometers, and cost‐effective Lidar systems, across multiple platforms.

High-Throughput Microstructural Characterization and Process Correlation Using Automated Electron Backscatter Diffraction

The need to optimize the processing conditions of additively manufactured (AM) metals and alloys has driven advances in throughput capabilities for material property measurements such as tensile strength or hardness. High-throughput (HT) characterization of AM metal microstructure has fallen significantly behind the pace of property measurements due to intrinsic bottlenecks associated with the artisan and labor-intensive preparation methods required to produce highly polished surfaces. This inequality in data throughput has led to a reliance on heuristics to connect process to structure or structure to properties for AM structural materials. In this study, we show a transformative approach to achieve laser powder bed fusion (LPBF) printing, HT preparation using dry electropolishing and HT electron backscatter diffraction (EBSD). This approach was used to construct a library of > 600 experimental EBSD sample sets spanning a diverse range of LPBF process conditions for AM Kovar. This vast library is far more expansive in parameter space than most state-of-the-art studies, yet it required only approximately 10 labor hours to acquire. Build geometries, surface preparation methods, and microscopy details, as well as the entire library of >600 EBSD data sets over the two sample design versions, have been shared with intent for the materials community to leverage the data and further advance the approach. Using this library, we investigated process–structure relationships and uncovered an unexpected, strong dependence of microstructure on location within the build, when varied, using otherwise identical laser parameters.

10-dB squeeze laser tuneable over half a nanometer around 1550 nm.

Lasers for generating monochromatic light beams with sideband spectra in strongly squeezed vacuum states are the basis for aspired optical continuous-variable quantum computers. We have developed a "squeeze laser" that produces 10 dB squeezed vacuum states at a wavelength of 1550 nm, the latter being tunable by 0.5 nm without losing the high squeeze factor. Several identical squeeze lasers can thus be combined to realise wavelength-division multiplexing. Our squeeze laser uses the mature technology of parametric down-conversion in a periodically poled KTP crystal placed in a cavity that resonates both the squeezed field and the second harmonic pump field. Unlike previous realisations, we achieve the double resonance and phase matching by individually optimising and controlling the temperatures of two sections of the crystal body. The wavelength range is currently limited by the tuneability of the 1550 nm master laser.

Chaos Synchronization of InGaAsP Lasers

The optical output of a semiconductor laser can fluctuate chaotically by modulating its direct current in limited conditions of the modulated current signal parameters in terms of modulation frequency and modulation index. In this work, single, double, and chaotic pulses of an InGaAsP laser with direct current modulation, are numerically presented through a bifurcation diagram. Numerically, the unidirectional optical coupling system realizes chaotic synchronization between two identical InGaAsP lasers with direct current modulation, as the transmitter/receiver configuration. The transmission time for transmitting light from the transmitted laser to the received laser is essential for controlling the quality of chaos synchronization. The transmission time applies on the order of nanoseconds. Chaos synchronization quality is estimated by a correlation plot and calculated by the cross-correlation coefficient. This study observed the best synchronization quality (complete chaos synchronization) when the two lasers are identical. On the other hand, the chaotic synchronization between two non-identical InGaAsP lasers was investigated. In this case, complete chaos synchronization is not found, and the quality of chaotic synchronization was observed to decrease as the mismatch between the parameters of the two lasers increased.

Optical frequency averaging of light.

The use of averaging has long been known to reduce noise in statistically independent systems that exhibit similar levels of stochastic fluctuation. This concept of averaging is general and applies to a wide variety of physical and man-made phenomena such as particle motion, shot noise, atomic clock stability, measurement uncertainty reduction, and methods of signal processing. Despite its prevalence in use for reducing statistical uncertainty, such averaging techniques so far remain comparatively undeveloped for application to light. We demonstrate here a method for averaging the frequency uncertainty of identical laser systems as a means to narrow the spectral linewidth of the resulting radiation. We experimentally achieve a reduction of frequency fluctuations from 40 Hz to 28 Hz by averaging two separate laser systems each locked to a fiber resonator. Only a single seed laser is necessary here as acousto-optic modulation is used to enable independent control of the second path. This technique of frequency averaging provides an effective solution to overcome the linewidth constraints of a single laser alone, particularly when limited by fundamental noise sources such as thermal noise, irrespective of the spectral shape of noise.

Synchronization and multistability in a network of diffusively coupled laser models

Synchronization phenomena refer to the emergence of common temporal patterns among clusters of interacting units in a complex network. In information transmission, lasers’ synchronization plays a key role in facilitating information communication. This paper is devoted to studying the synchronization of globally coupled identical laser models via the linear and nonlinear forms of diffusive couplings. In this regard, the master stability function and time-averaged synchronization error are employed as the analytical and numerical approaches to examine complete synchronization. Apart from the complete synchrony, the constructed networks are explored to find other synchronization patterns and multistability. The results obtained from the master stability function analysis, which are further approved by the numerical outcomes, show that when coupled through the linear diffusive function, the interacting laser models achieve complete synchrony in a small value of the coupling parameter. However, in the nonlinear case, complete synchronization cannot be attained. Moreover, multistability can be observed in different network states, including cluster synchronization, chimera, and solitary states.

High-Precision Wavelength Tuning of GeSn Nanobeam Lasers via Dynamically Controlled Strain Engineering.

The technology to develop a large number of identical coherent light sources on an integrated photonics platform holds the key to the realization of scalable optical and quantum photonic circuits. Herein, a scalable technique is presented to produce identical on-chip lasers by dynamically controlled strain engineering. By using localized laser annealing that can control the strain in the laser gain medium, the emission wavelengths of several GeSn one-dimensional photonic crystal nanobeam lasers are precisely matched whose initial emission wavelengths are significantly varied. The method changes the GeSn crystal structure in a region far away from the gain medium by inducing Sn segregation in a dynamically controllable manner, enabling the emission wavelength tuning of more than 10nm without degrading the laser emission properties such as intensity and linewidth. The authors believe that the work presents a new possibility to scale up the number of identical light sources for the realization of large-scale photonic-integrated circuits.

Revealing the Evolution from Q-Switching to Mode-Locking in an Erbium-Doped Fiber Laser Using Tungsten Trioxide Saturable Absorber

Passively Q-switching and mode-locking technologies can generate short pulses with durations that differ by several orders of magnitude widely used in different applications. Recently, Q-switching and mode-locking realized in an identical laser cavity with saturable absorbers was reported. The analysis of pulse conversion is helpful for us to further understand the pulse dynamics of a laser. In this paper, the pulse evolution from Q-switching, Q-switched mode-locking to mode-locking, is demonstrated by using a tungsten trioxide saturable absorber in a ring-cavity erbium-doped fiber laser. Firstly, self-started Q-switching at 1563 nm is observed, the repetition rate continuously increases, and the duration decreases when the pump power increased. Then, with an adjusting intra-cavity state of polarization under a high pump power level, stable Q-switched mode-locking pulses evolved from Q-switching, are observed. The amplitude of the emerged pulse sequence with a period of 36.8 ns, determined by cavity length, is modulated by the Q-switched envelope with the period of 10.3 μs. By optimizing the intracavity polarization carefully, stable continuous wave mode-locking operation is achieved eventually. To the best of our knowledge, this is the first experimental demonstration of Q-switching and mode-locking, respectively, in an identical transition-metal-oxides-based pulsed fiber laser without modification of cavity structure.

Femtosecond-comb based 10 MHz-to-optical frequency link with uncertainty at the 10−18 level

The International System of Units (SI) definition of the ‘second’ is likely to be redefined in the optical frequency region in the near future. Therefore, uncertainty reduction in the frequency link between 10 MHz, which is used in the frequency link with an artificial satellite, and the ultrastable laser for observing clock transitions in optical clocks, is an important issue for numerical determination in the new definition and for International Atomic Time operation after the redefinition. We have evaluated all the possible uncertainty factors in the frequency link with a femtosecond comb between 10 MHz and an optical frequency and obtained the lowest uncertainty yet reported of 3.9 × 10−18 by temperature-stabilizing RF multipliers and by using temperature insensitive coaxial cables. Furthermore, we have validated the uncertainty of the frequency link by simultaneously measuring an optical frequency of an identical laser using two femtosecond combs referenced to a common 10 MHz source and confirmed to be consistent with the evaluated uncertainty.

Ultra-narrow bandwidth and large tuning range single-passband microwave photonic filter based on Brillouin fiber laser

A scheme to perform ultra-narrow filter bandwidth and high frequency selectivity microwave photonic filter (MPF) with wide tuning range is proposed and experimentally demonstrated. The ultra-narrow bandwidth of the MPF is implemented by a Brillouin laser resonator, which is composed of a cascaded ring Fabry–Pérot (CR-FP) resonator formed by a main cavity with a cavity length of 100 m and a secondary cavity with a cavity length of 10 m. A Brillouin laser resonator is formed by the main cavity to obtain an extremely narrow comb-shaped Brillouin gain spectrum. The Vernier effect of the double ring cavity can effectively suppress the side modes, thereby realizing the narrow linewidth Brillouin laser filtering. Besides, two identical tunable lasers provide the stimulated Brillouin scattering (SBS) pump light and optical carrier signal for this device respectively. After the interaction between the Brillouin gain spectrum and the optical modulation signal, the filter passband can be stably tuned by simply changing the wavelength of SBS pump light. The experimental results show that the microwave photonic filter can be stably tuned in the frequency range of 0–20 GHz, the out-of-band rejection ratio is about 20 dB, and the minimum 3 dB bandwidth is about 114 Hz.

Phase noise measurements and diagnoses of a large array of fiber lasers by PISTIL.

One of the most promising solutions to access high power laser chains is to achieve a coherent combination of a large number of elementary lasers. To interfere constructively, these laser sources should be identical and operate under the same conditions. However, despite these efforts, differential delays appear in the course of time, which must be compensated for. While designing the required correction system, knowing the behavior of a laser as a function of the environmental conditions is not crucial, whereas having access to the differences in the behaviors of identical lasers is, leading to difficulties in modeling. The purpose of this paper is to illustrate how a large set of lasers can be simultaneously analyzed to estimate their variations and optimize a correction system. The X-Coherent Amplified Network laser relies on 61 fiber amplifiers, which are as identical as possible. This state of the art femtosecond digital laser therefore appears as an ideal candidate to study a large number of fiber lasers working under controlled conditions.

Controllable spin-dynamic scenarios on zigzag carbon cross structure

We investigate the spin-dynamic properties of two carbon cross structures assembled from two carbon chains with two Ni atoms attached. Both the global spin transfer through the long-distance carbon cross and the local spin flip on the single Ni atom are achieved within the subpicosecond regime, demonstrating the feasibility of individual intrasite and intersite spin manipulation. We investigate the dependence of the two different types of spin-dynamics processes on an external magnetic field, and we compare them by analyzing the spin features of the populated intermediate states. The comparison explains well the addressability of the local spin flip and the conservation of the global spin transfer. In addition, by applying two identical laser pulses, we successfully enhance the sensitivity of the local spin flip with respect to the external magnetic field, which yields a higher spatial resolution of the individual spin addressing. The present investigation is a significant step towards integrated all-optical logic circuits based on nano-spintronics.

Enhanced Prediction Performance of Reservoir Computing Based on Mutually Delay-Coupled Semiconductor Lasers via Parameter Mismatch

As an efficient information processing method, reservoir computing (RC) is essential to artificial neural networks (ANNs). Via the Santa Fe time series prediction task, we numerically investigated the effect of the mismatch of some critical parameters on the prediction performance of the RC based on two mutually delay-coupled semiconductor lasers (SLs) with optical injection. The results show that better prediction performance can be realized by setting appropriate parameter mismatch scenarios. Especially for the situation with large prediction errors encountered in the RC with identical laser parameters, a suitable parameter mismatch setting can achieve computing performance improvement of an order of magnitude. Our research is instructive for the hardware implementation of laser-based RC, where the parameter mismatch is unavoidable.

An Ultra-Coherent Semiconductor Laser Locked to a Short Delay Fiber Mach-Zehnder Interferometer With Active Fiber Noise Cancellation

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.

Independent effects of laser power and scanning speed on IN718's precipitation and mechanical properties produced by LBPF plus heat treatment

The laser energy density was believed to control microstructure and mechanical properties of additive-manufactured Inconel 718 (IN718) alloy. However, in this study, remarkable differences were found in the microstructures, tensile mechanical properties, and fracture surfaces of industrial IN718 alloy (with densities higher than 99.75%), which were fabricated by Laser Powder Bed Fusion (LPBF) processes with almost identical laser energy densities and the same standard heat treatment. The results show that these deviations are primarily ascribed to the independent effects of laser power and scanning speed during LPBF-processes on the precipitation of IN718 alloy. The reasons for these variations are discussed based on the thermal history of melt pool and pre-solidified layer during the LPBF-process, which were further analyzed and supported by computational fluid dynamics simulation based on the finite volume method.

Spectroscopic VUV diagnostics of high-temperature iron plasmas using the comparison method

We report the development of a new comparison method used to estimate the electron temperature T e of heavy-element plasmas and high-temperature iron laser-produced plasmas. To this end, two laser-produced plasmas – magnesium plasmas and iron plasmas – were studied at identical laser radiation fluxes on the target. Plasma diagnostics was performed using X-ray spectra of H- and He-like Mg ions. VUV spectra of Fe ions were recorded in the wavelength range 15 – 150 Å As a result, the change in the structure of the VUV spectra of Fe ions as a function of T e in the range of 100 – 400 eV was studied. These data are necessary for diagnosing plasma sources containing the iron element.

A Compact Laser System for the Pulsed Optically Pumped Rubidium Cell Atomic Clock

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 3.0×10-12 for averaging times from 1 to 60 s and it reached 3.5×10-12 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 [Formula: see text], which is in reasonable agreement with the estimated [Formula: see text]. The compact laser system is significant in terms of the development of transportable and high-performance Rb atomic clock prototypes.

Nanosecond laser-induced controllable oxidation of TiB2–TiC ceramic composites for subsequent micro milling

Laser-induced controllable oxidation coupled with micro-milling (LOMM) provides a feasible way to machine difficult-to-machine materials such as TiB 2 –TiC ceramic composites. The oxidation mechanism of the material under laser irradiation represents the fundamental issue of LOMM. In this paper, laser-induced controllable oxidation of spark plasma sintered TiB 2 –TiC ceramic composites as the workpiece material was studied. A three-dimensional finite element model was established based on ABAQUS/CAE 6.14 software to simulate the effect of laser parameters on temperature field distribution and was verified by experiments. The influence of laser processing parameters and assisted gas atmospheres on the oxidation behavior of TiB 2 –TiC ceramic composites was investigated. Results revealed that the irradiated temperature which had a significant impact on oxidation behavior, increased with an increment of the laser fluence and decreased with an increment of scanning speed with other laser parameters fixed. In addition, based on experimental analysis, the thickness of the oxide-layer increased with an increase of laser fluence and reduced with increasing laser scanning speed. At a laser fluence of 10.78J/cm 2 and scanning speed of 1 mm/s as well as in an oxygen-rich atmosphere, a loose and porous oxide-layer was produced on the irradiated surface. Cross-section thicknesses of the oxide-layer and sub-layer reached 63 μm and 22 μm, respectively. Moreover, the thickness of the oxide-layer was 22 μm in air surroundings and hardly be found in argon and nitrogen atmospheres under identical laser parameters, which indicated that oxygen content had a significant influence on the oxidation reaction of the material. The products of the oxide-layer were mainly composed of rutile- and anatase-TiO 2 . Furthermore, the hardness of the sub-layer was 9.6 ± 0.7 GPa at a laser fluence of 10.78J/cm 2 and scanning speed of 1 mm/s, which was far lower than that of the substrate with a hardness of 20 ± 0.7 GPa. This study provides a theoretical basis for subsequent micro-milling.

Failure mechanism analysis based on laser-based surface treatments for aluminum-polyamide laser joining

The development of strong metal to polymer assemblies is currently an important research subject thanks to its prominence to develop lightweight structures. Furthermore, laser welding is known to be a fast, reliable, and versatile joining process, and it was demonstrated recently that it can be applied to such metal to polymer systems. To enhance the mechanical properties of the laser-joined aluminum-polyamide (Al-PA) specimens, laser polishing and laser ablation processes have been implemented on the aluminum surface before joining. The polyamide surface was also treated with the laser beam, separately. The surfaces were tested by several characterization techniques before and after each surface treatment. Then aluminum and polyamide samples with different surface treatments have been joined with an identical laser joining process. The mechanical properties of the joints in single lap shear configuration are reported and the failure mechanisms are discussed based on micro-computed x-ray tomography imaging of joined specimens and microscopic analysis before failure. Results show that both surface treatments of aluminum significantly improve the shear load of the joint; however, with different failure mechanisms. Polyamide surface treatment and increasing degree of crystallinity are effective when combined with the laser polishing of the Al surface. This combination is responsible for further enhancement of the shear load of the joint to the limit of base metal strength which is approximately 60 % improvement compared to the untreated samples. Finally, energy dispersive X-ray mapping shows the physicochemical bonding between aluminum oxide and polyamide at the interface.

Effect of a helium gas atmosphere on the mechanical properties of Ti-6Al-4V alloy built with laser powder bed fusion: A comparative study with argon gas

In metal additive manufacturing, the microstructures and associated mechanical properties of metal specimens can be controlled over a wide range. Although process parameters are considered important in the fabrication of functional parts, the effect of atmospheric gas has not been comprehensively documented. In laser powder bed fusion (LPBF), gas flow is used to eliminate fumes generated by laser irradiation. Simultaneously, the gas removes heat from the laser-irradiated part, which is exposed to high temperature. In this study, we investigated the capacity of helium as an alternative to argon, which is conventionally used as the LPBF atmosphere gas. He has a higher thermal conductivity and lower gas density than Ar, which may result in enhanced heat removal from the Ti-6Al-4V alloy during fabrication. Numerical simulations suggest a greater cooling rate under He flow. Further, the material built under He flow contained finer α' martensite grains and showed improved mechanical properties compared to those fabricated under Ar flow, despite the identical laser irradiation conditions. Thus, He gas is advantageous in LPBF for fabricating products with superior mechanical performance through microstructural refinement, and this is a result of its capacity for cooling and fume generation inhibition. Therefore, this study reveals the importance of the choice of atmospheric gas because of its effects on the characteristics of metallic specimens fabricated using LPBF.