Ring Laser Research Articles

Dual-Wavelength Passively Q-Switched Erbium-Doped Fiber Laser Incorporating Calcium Carbonate Nanoparticles as Saturable Absorber

This study experimentally demonstrates the operation of a dual-wavelength passively Q-switched erbium-doped fiber laser that incorporates CaCO3 nanoparticles as a saturable absorber (SA). The SA was prepared by using the drop-casting method, wherein CaCO3 nanoparticles were embedded in a polyvinyl alcohol (PVA) polymer to form a CaCO3/PVA film SA. The film was integrated into a ring laser cavity with a 976 nm pump to generate Q-switched pulses. The properties of the SA were examined experimentally, and its modulation depth is approximately 47%. As the pump power increased from 180 mW to 270 mW and the pulse repetition rate increased from 12.67 kHz to 21.3 kHz, the corresponding pulse width decreased from 35.27 μs to 18.74 μs. The signal-to-noise ratio was approximately 25 dB, highlighting the laser’s stability. The results indicate that the proposed CaCO3/PVA SA is suitable for realizing portable Q-switched lasers.

Variations in the Earth’s rotation rate measured with a ring laser interferometer

Variations in the Earth’s rotation rate measured with a ring laser interferometer

Photonic molecule based on coupled ring quantum cascade lasers

Photonic molecules—particular systems composed of coupled optical resonators—emulate the behavior of complex physical systems exhibiting discrete energy levels. In this work, we present a photonic molecule composed of two strongly coupled, mid-infrared ring quantum cascade lasers. We explore both experimentally and numerically the key features of the photonic molecule such as the energy level splitting of bonding and antibonding supermodes. Due to the large size of the resonators, the energy splitting results in bands containing tens of modes. Each of these modes is furthermore doubly degenerate with respect to the direction of propagation, namely, clockwise and counterclockwise. We explore several methods to carefully break these symmetries of the system in a controlled manner by introducing spatial and temporal asymmetries in the pumping scheme of the ring lasers. By employing these techniques, we achieve a high degree of precision in the dynamic control of the photonic molecule. Owing to their inherent suitability for on-chip integration, this class of devices may enable applications as varied as mid-infrared sensors or a rich playground for studying non-Hermitian photonics and quantum optics with quantum cascade lasers.

High-power laser beam shaping using a metasurface for shock excitation and focusing at the microscale.

Achieving high repeatability and efficiency in laser-induced strong shock wave excitation remains a significant technical challenge, as evidenced by the extensive efforts undertaken at large-scale national laboratories to optimize the compression of light element pellets. In this study, we propose and model a novel optical design for generating strong shocks at a tabletop scale. Our approach leverages the spatial and temporal shaping of multiple laser pulses to form concentric laser rings on condensed matter samples. Each laser ring initiates a two-dimensional focusing shock wave that overlaps and converges with preceding shock waves at a central point within the ring. We present preliminary experimental results for a single ring configuration. To enable high-power laser focusing at the micron scale, we demonstrate experimentally the feasibility of employing dielectric metasurfaces with exceptional damage threshold, experimentally determined to be 1.1 J/cm2, as replacements for conventional optics. These metasurfaces enable the creation of pristine, high-fluence laser rings essential for launching stable shock waves in materials. Herein, we showcase results obtained using a water sample, achieving shock pressures in the gigapascal (GPa) range. Our findings provide a promising pathway towards the application of laser-induced strong shock compression in condensed matter at the microscale.

Study on Dual-Wavelength Wide-Spectrum Erbium-Doped Fiber Ring Laser for Optical Fiber Interferometric Sensing System

In this paper, a novel dual-wavelength wide-spectrum erbium-doped fiber ring laser (EDFRL) for optical fiber sensing system is proposed and experimentally demonstrated. The output of EDFRL is theoretically simulated and classified depending on the theoretical analysis of laser threshold condition into “excited state” and “nonexcited state”. The influence of pump wavelength, fiber laser configuration, EDF length and output coupling ratio of EDFRL is discussed. The EDFRL pumped at 1480 nm wavelength and backward-pumped mode could achieve the stable maximum wide-spectrum output power. The output power fluctuation is lower than 0.06 dB and the center wavelengths shift is less than 0.01 nm. The practicability of EDFRL in a hybrid M-Z and Sagnac interferometer optical fiber sensing system is demonstrated through the comparison of SLD and EDFRL. Consequently, the EDFRL proposed in this study is expected to replace the traditional SLD in the optical fiber interferometric sensing system at a lower cost.

The One-Way Linear Effect, a first order optical effect

In the One-Way Linear Effect, the round-trip time interval T0′ taken by light to propagate around a moving linear closed contour, is measured by a device. If the contour changes velocity by Δv, the round-trip interval T′(X′,Δv) turns out to depend on the device position X′ and Δv. The variation ΔT′=T′(X′,Δv)−T0′, related to Δv/c, is experimentally observable by means of standard interferometry, ring laser techniques, or high precision time-delay detectors of light pulses. Being sensitive to velocity variations, if experimentally confirmed the One-Way Linear Effect may have relevant applications in inertial guidance systems and related areas. Furthermore, the One-Way Linear Effect can be used to confirm Lorentz invariance by testing relative simultaneity versus absolute simultaneity.

Aspects of Sitall SO-115M Use in the Fabrication of the Optical Components of He–Ne Ring Lasers

Aspects of Sitall SO-115M Use in the Fabrication of the Optical Components of He–Ne Ring Lasers

Sodium-doped InP/ZnSeS/ZnS quantum dots as a saturable absorber for passive Q-switched fiber lasers

In this work, sodium-doped InP/ZnSeS/ZnS (InP–Na) QDs was fabricated by thermal injection method for the first time. The nonlinear optical properties were first demonstrated by realizing a modulation depth of 7.85% and saturable intensity of 2.2 MW cm−2 by two-detector method. The Q-switching operations were carried out by integrating InP–Na QDs as saturable absorber (SA) in a fiber laser ring cavity system. Q-switched laser pulses with a pulse width of 139 ns were generated. The ability of effective pulse width compression can be attributed to the short exciton recovery time of SA, as confirmed by transient absorption and time-resolved photoluminescence. This is the first demonstration of Na-doped InP/ZnSeS/ZnS QDs and using it as SA for generating ultrafast laser pulses. Therefore, this study extends the research scope of InP-based QDs in optical communications, nonlinear photonics and ultrafast photonics.

Passively Q-switched Er3+-doped fiber laser based on double-transition metal MAX phase TiNbAlC saturable absorber

We demonstrated a stable passively Q-switched fiber laser operation at 1531.57 nm using a double-transition metal MAX phase TiNbAlC saturable absorber. The prepared saturable absorber’s modulation depth, saturation intensity, and non-saturation loss are 1.75%, 0.089 MW/cm2, and 32.81%, respectively. Using the TiNbAlC saturable absorber within an erbium-doped fiber laser ring cavity, stable Q-switched pulses with a central wavelength of 1531.57 nm, and a 3-dB bandwidth of 1.43 nm are acquired. The minimum pulse duration and the maximum single pulse energy are 3.18 μs and 51.56 nJ, respectively. Furthermore, the maximum repetition rate is 37.9 kHz with a signal-to-noise ratio of 50 dB. Our results indicate that double-transition metal MAX phase TiNbAlC can be an excellent saturable absorber candidate for an ultrashort pulse fiber laser.

Frequency noise of laser gyros

Laser gyros are powerful tools used to test the predictions of the general theory of relativity. The precision of a measurement of the rotation rate with a laser gyro is limited by the frequency noise of the beat between two counterpropagating modes of a ring laser. The frequency noise of a single mode of a laser is limited by quantum mechanical constraints because it is related to the maximum precision with which the phase of a coherent state can be measured. If two modes are not correlated, the variance of the fluctuations of the difference of their frequencies is the sum of the variance of the frequency noise of the two modes. If the two modes are correlated, this result does not hold any longer. In this paper, we show that a laser gyro has mechanisms capable of dynamically locking the two modes together without forcing them to the same frequency. The lock of modes decouples the noise of the beat note from the frequency noise of the individual modes, thus allowing the realization of sub-shot noise laser gyros.

Area theorem in a ring laser cavity

Area theorem in a ring laser cavity

Versatile wavelength tunable noise-like pulse generation from an erbium doped fiber laser using an intra-cavity Michelson interferometer

We report, versatile wavelength tunable mode locked noise-like pulses (NLP) from an erbium doped fiber ring laser, using a novel intra-cavity Michelson interferometer (MI) as a tunable filter. Our results demonstrate independent control of the central wavelength and the bandwidth using fine and coarse controls in one arm of the MI. The central wavelength is continuously tunable across the entire C-band (1530 nm to 1566 nm), while the bandwidth can be varied from 3 nm to 19.5 nm. The NLPs have a repetition rate of 1.307 MHz with pulse energies of ∼1 nJ. Additionally, harmonic mode-locked states and NLP pairs can also be produced using the same laser. On account of the adaptable output spectrum, we believe, such lasers will be useful for a variety of applications including sensing, spectroscopy and optical coherence tomography. The MI-based fiber laser can also serve as an ideal platform for gaining insight and exploring the rich dynamics of NLPs.

Integrated Fiber Ring Laser Temperature Sensor Based on Vernier Effect with Lyot-Sagnac Interferometer.

The Vernier effect created using an incorporated Lyot-Sagnac loop is used to create an ultra-high sensitivity temperature sensor based on a ring laser cavity. Unlike standard double Sagnac loop systems, the proposed sensor is fused into a single Sagnac loop by adjusting the welding angle between two polarization-maintaining fibers (PMFs) to achieve effective temperature sensitivity amplification. The PMFs are separated into two arms of 0.8 m and 1 m in length, with a 45° angle difference between the fast axes. The sensor's performance is examined both theoretically and experimentally. The experimental results reveal that the Vernier amplification effect can be achieved via PMF rotating shaft welding. The temperature sensitivity in the laser cavity can reach 2.391 nm/°C, which is increased by a factor of more than eight times compared with a single Sagnac loop structure (0.298 nm/°C) with a length of 0.8 m without the Vernier effect at temperatures ranging from 20 °C to 30 °C. Furthermore, unlike traditional optical fiber sensing that uses a broadband light source (BBS) for detection, which causes issues such as low signal-to-noise ratio and broad bandwidth, the Sagnac loop can be employed as a filter by inserting itself into the fiber ring laser (FRL) cavity. When the external parameters change, the laser is offset by the interference general modulation, allowing the external temperature to be monitored. The superior performance of signal-to-noise ratios of up to 50 dB and bandwidths of less than 0.2 nm is achieved. The proposed sensor has a simple structure and high sensitivity and is expected to play a role in biological cell activity monitoring.

Lock-in phenomena in non-Hermitian coupled systems

Coupled-mode theory has been widely employed in various branches of photonics, such as nano-photonics and non-Hermitian optics. Here we show that it can also be used as an effective physical model for clarifying various optical mode lock-in phenomena, which have been revealed to essentially originate from non-Hermitian degeneracies. We discuss the lock-in effects in physical systems through prototypical examples of optical feedback self-injection frequency lock-in technology and lock-in phenomena of ring laser gyroscopes (RLGs). Seemingly unrelated effects have been unified through one general non-Hermitian mode coupling model. Furthermore, based on our theoretical framework, we have uncovered the underlying mechanism of lock-in in RLGs and analyzed how this effect can be systematically suppressed or even eliminated

Ultra-Short Pulse-Train Generation of 30-GHz Repetition Rate Using Rational Harmonic Mode Locking and Nonlinear Polarization Rotation

A 30-GHz pulse-train is generated using the rational harmonic mode-locking technique, experimentally, using a Mach–Zehnder Lithium Niobate modulator. The width of the pulses is then reduced from 5.8-ps to 1.9-ps by incorporating nonlinear polarization rotation. This phenomenon arises due to the very high nonlinear behavior of the photonic crystal fiber (PCF) added to the ring laser cavity. Numerically solving the Generalized Nonlinear Schrödinger Equation provided insights into the pulse evolution behavior. The relative polarization angle and length of the PCF were varied to study their effects on the pulse-width.

Hybrid Mode-Locked Fiber Ring Laser Using Graphene Saturable Absorbers to Generate 20 and 50-GHz Pulse Trains

Optical pulses at high repetition rates are generated using rational harmonic mode locking and saturable absorber made of graphene nanoparticles in a fiber laser. The pulse generation from the fiber laser is modeled by solving the Generalized Nonlinear Schrodinger Equation. The computation involved varying the various saturable absorption parameters, such as linear and nonlinear absorption coefficients. Experimentally stable pulse trains at 20 GHz and 50 GHz are generated with a pulse width of ∼ 2.7 ps. This result agrees with the simulation.

LIFT of cell spheroids: Proof of concept

The application of spheroids in tissue engineering has a number of advantages over conventional cell suspensions and 2D cultures. One of the methods for tissue and organ fabrication from spheroids is bioprinting. As one of bioprinting methods, laser-induced forward transfer (LIFT) has received much attention in terms of cell printing, while its potential has not been realized for spheroid patterning yet. In this paper, the authors have shown for the first time the practical applicability of LIFT for spheroid transfer with high survival rates and printing precision. For this, a special optical device, a piShaper, was used to change the laser energy distribution to non-Gaussian profile which allowed for mitigating the negative effects of laser radiation on the spheroids during LIFT. The authors showed that non-Gaussian energy distribution in the laser spot in the form of double ring led to higher post-printing viability of spheroids than in case of conventional Gaussian energy distribution in laser beam. Subsequently, using the double ring laser spot geometry, the spheroids were bioprinted in the form of simple geometric figures: line, triangle, and square. Overall, LIFT bioprinting of spheroids has demonstrated a strong potential as the precise, safe, and reproducible method for biofabrication that can be potentially used for making tissue-engineered bioequivalents or building specific organ-on-a-chip platforms.

Noise-like pulses in dispersion-controlled fiber lasers

Noise-like pulse generation in ring lasers in which the anomalous dispersion of the cavity fiber is partially compensated by using a normal-dispersion fiber has been studied by numerical simulation. Solitons moving in this cavity are periodically subjected to temporal compression in the anomalous-dispersion fiber and expansion in the normal-dispersion fiber. It has been found that in these lasers, stationary solitons become unstable and passive mode locking occurs through the emission of bunched noise-like pulses consisting of chaotically evolving solitons. The results are relevant to the development of noise-like pulse generation and methods for controlling lasing regimes.

Coherent optical gyroscope on the basis of the bidirectional ultra-short pulse Erbium ring fiber laser

A gyroscopic effect has been studied in the bidirectional ultra-short pulse erbium-doped fiber ring laser hybridly mode-locked with a co-action of a Single-Walled Carbon Nanotube-based saturable absorber (SWCNT-SA) and Nonlinear Polarization Evolution introduced by means of the short-segment polarizing fiber. Owing to the Kerr nonlinearity contribution through self-phase modulation and self-steepening effects to the carrier-to-envelope phase slip of both clockwise (CW) and counterclockwise (CCW) solitons, wideband controllable tuning of a gyroscope bias point has been demonstrated by means of an appropriate adjustment of either intracavity polarization or pump power. Angular velocity detected ranges from 0.12 deg/s to 360 deg/s while the highest rotation sensitivity reaches 7 kHz/(deg/s) for 0.79 m2 single-coil ring gyroscope being in agreement with the calculated scale factor value. The gyroscope dead band with upper limit of ≈5.15 deg/s corresponding to the beat-note frequency of ≈15 kHz has been detected during clockwise rotation of the gyroscope. The highest gyroscope resolution of ≈0.01 deg/s=38 deg/h has been estimated on the basis of the bias point drift measurement.

Liquid-Core-Microtubule-Enhanced Laser Sensor for High-Resolution Temperature Measurement

We present a fiber laser temperature sensor based on temperature dependence whisper gallery mode-based microcavity. Three different thermo-optic coefficient liquids are injected into a thin wall thickness microtubule for different temperature sensitivity of whisper gallery mode shift. The sensor temperature sensitivity increases with the absolute value of the liquid core thermo-optic coefficient. The theoretical model of whisper gallery mode temperature response is analyzed. A liquid core microtubule is inserted into the erbium-doped fiber ring laser cavity as the optical filter and sensing unit simultaneously, so the lasing wavelength can be used to detect the temperature change of the medium. Due to the narrow spectral width of sensing laser, a high sensing resolution system is experimentally confirmed. With the combination of liquid core to increase the sensitivity and fiber ring laser cavity to increase sensing resolution, the high sensitivity 112.8 pm/°C of sensing system is demonstrated and the thermal resolution is 8.16 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> °C.