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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]

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]

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]

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]

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]

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]

Harmonically mode-locked soliton fiber lasers have been intensively investigated in recent years due to their wide range of applications. Drawback of these lasers is relatively large timing jitter which is significantly higher than the timing jitter in lasers operating at fundamental frequency. We report the stabilizing frequency shift effect in harmonic mode-locking ring soliton fiber laser that is studied theoretically and numerically. It is known that a harmonic mode-locking regime in a fiber laser occurs due to interpulse repulsion, which leads to a uniform distribution of pulses in the cavity. We demonstrate that the frequency shift contributes to an increase in the hardness of interpulse interactions and can led to stabilization of the periodic arrangement of pulses. The experiment carried out confirms the theoretical predictions and the results of numerical simulation. [ABSTRACT FROM AUTHOR]

The theoretical framework of the Haus master equation of passive mode-locking is revisited. Reformulating the equation in the frequency domain as coupled ordinary differential equations, the complete set of fundamental soliton solutions is surveyed. For large values of anomalous dispersion, this leads to the well known bell-shaped solutions originally found by inverse scattering. Closer to zero dispersion, mode-locked spectra are affected by the available gain bandwidth, and solitons with Bessel-like temporal profiles are found. These spectrally caged solitons match previously unexplained pulse characterization measurements of few-cycle oscillators and mode-locked fiber lasers in the normal dispersion regime. Moreover, the frequency domain formalism suggests that a phase lock between the modes can even be established in the absence of saturable absorption. This finding may explain numerous mysterious experimental reports of mode-locking or comb formation in passive microring resonators and semiconductor lasers. Therefore our frequency-domain approach sheds new light into soliton physics from a completely different perspective. [ABSTRACT FROM AUTHOR]

A self-assembled quantum dot (QD) gain medium has multiple favorable material properties over conventional quantum well (QW) structures and bulk materials, including a large tolerance for material defects, reduced reflection sensitivity, nearly zero linewidth enhancement factor, low transparency current density, high temperature operation, and ultrafast gain dynamics useful for semiconductor mode-locked lasers and amplifiers. Here, we review the recent advances in the field of QD lasers and amplifiers with a focus on the direct growth on silicon (Si). Si photonics has found widespread application, particularly for high volume applications and for co-integration with CMOS electronics. [ABSTRACT FROM AUTHOR]

We report the first experimental observation, to the best of our knowledge, of soliton molecules in a robust all polarization-maintaining (PM) mode-locked fiber laser with a nonreciprocal phase bias that results in a low self-starting threshold and stable mode locking. Through elaborately tuning the waveplate in the cavity, calibrating the laser pulse from conventional soliton to soliton molecules is implemented, and versatile soliton molecules including harmonic soliton pairs, tightly or loosely bound soliton quartets, multipulse bound solitons are achieved and manipulated at different pump powers. Theoretical investigations are established to elucidate the soliton molecules spectral characteristics with various phase differences and time separations in the cavity that elicit good concurrence with achieved experimental results. The achieved results both rich the nonlinear dynamics in fiber lasers and pave the potential applications for this excellent architecture fiber laser. [ABSTRACT FROM AUTHOR]

In this letter, the design and characterization of an all-fiber femtosecond laser is reported that generates three wavelengths at 1030 nm, 1550 nm, and 1900 nm from a single cavity. The cavity is based on Er-doped fiber and it is mode-locked by a fiber coupled saturable absorber mirror. We take advantage of fiber optics nonlinearity to generate 1030 nm and 1900 nm wavelengths which can be amplified using well-known Yb-doped and Tm-doped amplifiers. The third output of the laser can be optimized to generate femtosecond pulses at a wide range of central wavelength from 1700 nm to 2000 nm. Since all three outputs of the laser are being generated from the same cavity, they can be easily synchronized to be used in various pump and probe applications. This approach reduces the size, power consumption and cost of the laser compared to three individual mode-locked cavities. The laser can be packaged in a 20 cm $\times20$ cm $\times20$ cm form factor. [ABSTRACT FROM AUTHOR]

The authors experimentally demonstrated the generation of mode‐locked pulses from all‐fibre erbium‐doped fibre laser cavity by using organic material, Alq3, as a saturable absorber (SA). The SA film was integrated into a ring fibre laser cavity to act as a mode‐locker. A mode‐locking operation was achieved in three different experiments with pulse width/repetition rate of 1.26 ps/3.36 MHz, 970 fs/3.36 MHz and 820 fs/4.9 MHz by using cavity length/optical coupler (OC) of 61.5 m/80:20 OC, 61.5 m /95:5 OC and 42 m/80:20 OC, respectively. All the experiments produced a soliton and a very stable mode‐locking operation at central wavelength of ∼1561 nm. The experiments confirmed that organic material can readily be used as SA for a mode‐locked operation in the 1.5 μm region. This demonstration might shed new insights into the potentials and techniques for developing ultrafast fibre lasers by using organic materials as SAs. [ABSTRACT FROM AUTHOR]

We report a ReSe2 passively mode-locked composite YVO4/Nd:YVO4 laser at 1.06 μm, which can stably generate pure continuous-wave mode-locking (CWML) operation at watt-level output. ReSe2, as a new type of 2-D transition metal dichalcogenides (TMDs), has the features of weak-layered dependence, broadband saturable absorption, low modulation depth and saturation intensity, which is beneficial to initiate robust CWML mechanism via nonlinear saturable absorption. By employing few-layered ReSe2 as saturable absorber, the nanosecond mode-locked pulses at fundamental repetition rate of 90.37 MHz was obtained experimentally in a composite YVO4/Nd:YVO4 laser. The maximum output power in pure CWML operation was as high as 1.1 W. The high-power CWML laser source shows potential applications in time-resolved spectroscopy, telecommunication and detection. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate a passively mode-locked all-fiber Tm laser with an all-fiber saturable absorber (SA) which operates based on the nonlinear multimode interference (NL-MMI) effect in a tapered graded-index multimode fiber (GIMF). The tapered GIMF SA demonstrates the nonlinear characteristics of modulation depth of 21.15%, and saturation fluence of $89.04~\mu \text{J}$ /cm2. We obtain stable fundamentally mode-locking operation at a pump threshold of 120 mW. The output soliton pulses have a center wavelength, spectral width, pulse duration and repetition rate of 1935 nm, 2.1 nm, 1.9 ps and 18.79 MHz, respectively. This is a simple, low-cost, stable, and convenient laser oscillator with many potential applications in eye-safe ultrafast photonics. [ABSTRACT FROM AUTHOR]

Polarization-maintaining (PM) all-fiber cavity is always essential to realize stable ultrafast-pulse generation. With the help of five sections of PM fibers with independently specific splicing angles, we successfully obtain a femtosecond pulse output from a PM Ytterbium-doped fiber laser (YDFL) mode-locked by the nonlinear polarization evolution (NPE) technique. Using a hybrid component, the PM all-fiber cavity can be greatly simplified. Ultrafast-pulses with 24.5-MHz repetition rate, 20-nm spectral bandwidth, and 260-fs pulse duration after external compression can be steadily generated. In comparison with the non-PM fiber cavity, the proposed YDFL has excellent long-term environmental stability, making it ideal for various practical applications. [ABSTRACT FROM AUTHOR]

Thulium-doped fiber laser (TDFL) is a versatile platform that can be engineered to produce laser sources with desired performance that target a vast number of applications, however its operation in the 1.7-μm region is still underdeveloped owing to the quasi-three-level nature of TDF emission. In this paper, we report a high energy noise-like pulse generation from a nonlinear polarization rotation (NPR) mode-locked TDFL. By using highly efficient core-pumping at 1650 nm and intra-cavity filtering component, stable mode-locking operation at 1750 nm is realized at a pump threshold of 1.5 W. With increasing the pump power to 5 W, the pulse width is stretched from 0.8 ns to 3.7 ns, while the monitored output power is linearly increased from 50 mW to 251 mW, corresponding to a maximum pulse energy of 321 nJ at the pulse repetition rate of 782 kHz. The long-term and shot-to-shot stability of the output are characterized to be 0.11 dB and 2.8% respectively. Noise-like pulse operation of the laser is confirmed by measuring the autocorrelation trace, which demonstrates a coherent peak on top of a wide pedestal. To the best of our knowledge, this is the first demonstration of high energy noise-like pulse generation from a TDFL at 1.7-μm band, enabling potential applications in for example spectroscopic analysis and material processing. [ABSTRACT FROM AUTHOR]

European Space Agency (ESA) considers picosecond mode-locked semi-conductor laser technology as a promising candidate for space applications in precision optical metrology systems. However, very challenging performance requirements should be met by such laser without additional amplification stages. In order to address this challenge, we realized two types of mode-locked edge emitting lasers operating at 990 nm wavelength. In particular, we demonstrate a very-long (13.5 mm) monolithic multi-section tapered laser reaching 201 pJ mode-locked pulses at low repetition frequency of 2.89 GHz with the pulse width that can be compressed down to 2.4 ps. We also report on a multi-section inverse bow-tie external cavity laser producing mode-locked pulses of 70 pJ energy and 6 ps width (0.73 fs after compressor) at 1.65 GHz pulse repetition frequency (PRF). The laser operates in an 80-mm-long external cavity. The PRFs of the two lasers can be continuously tuned over 9.8 and 9.1 MHz ranges, respectively. Active stabilization with a phase locking loop actuating on the driving current has allowed us to reach PRF relative stabilities of 1.15·10−10 and 2.9·10−10 on 1 s intervals for the two lasers. These performances fulfill the requirements of ESA for inter-satellite long distance measurements. [ABSTRACT FROM AUTHOR]

We experimentally demonstrated a method of generating continuously wavelength-switchable LP11 mode in an all-fiber laser. A Mach–Zehnder filter is constructed to provide a comb spectrum. A fused mode selective coupler (MSC) is used to obtain mode conversion and LP11 mode can be output successfully. The experiment result shows that, the proposed fiber laser can operate at single-, dual-, triple- and quadruple-wavelength with LP11 modes output by adjusting the polarization controllers (PCs). The wavelength ranges are adjustable, when the output of the proposed fiber laser are single-, dual-, and triple-wavelength. Besides, the interval of dual wavelengths is also adjustable to some extent. Due to the superior characteristics of the Mach–Zehnder filter and the MSC, the proposed wavelength-switchable fiber laser has the merits of good stability, high signal-to-noise ratio (SNR, higher than 36 dB) and high mode purity (high to 95%). [ABSTRACT FROM AUTHOR]

Enabling vehicles to communicate with other vehicles, infrastructure, pedestrians, and everything for use cases such as road safety, automatic driving, and infotainment is important for the future cellular networks. However, some vehicle-to-everything (V2X) services need secure transmissions and should be prevented from eavesdropping. Physical layer security, an information- theoretical framework, utilizes the randomness of underlying channels to ensure secrecy in the physical layer. Different from ground communications, unmanned aerial vehicles (UAVs) create line-of-sight connections to vehicles and mobile users making them an ideal platform to conduct physical layer security strategies. In this article, we embrace UAV to V2X communications to enhance the V2X security from the physical layer security's perspective. To be specific, we present security problems in V2X systems, highlight security threats in V2X networks, and illustrate some potential applications of UAVs in V2X security. Open problems for UAV-assisted V2X secure communications are also discussed. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides have recently been considered the candidates for saturable absorption materials due to their advantages in both electronic and optoelectronic. Compared with MoS2 and WS2, MoTe2 exhibits smaller bandgap. As a result, MoTe2 owns inherent advantages in the near-infrared applications. In this paper, the MoTe2 saturable absorber (SA) were prepared by the magnetron sputtering deposition method. Owing to the enhanced light-materials interaction between MoTe2 and evanescent field from the microfiber, the modulation depth of the MoTe2 SA was up to 26.97%. By assembling the MoTe2 SA into the erbium-doped fiber laser, the mode-locked fiber laser at 1.5 μm was demonstrated. The pulse duration of 111.9 fs was proved to be the shortest in the fiber lasers based on transition metal dichalcogenides. Moreover, the mode-locked fiber laser maintains the long-term stability. Our results suggest that the proposed MoTe2 SA is promising for the ultrashort pulse generation and stable system operation. [ABSTRACT FROM AUTHOR]

Fiber lasers have become one of the most important technologies in various industrial, medical, and scientific applications. However, their vulnerability to environmental disturbances, such as vibrations and thermal fluctuations, limits the range of practical operations outside the laboratory. In this letter, we report a simplified, all-normal dispersion, completely all-polarization-maintaining fiber integrated laser operating at 1030 nm. Our laser system employs a single-pump laser diode and an all-polarization maintaining fiber pulse compressor capable of generating 700-fs pulses with a pulse energy of 0.45 nJ. [ABSTRACT FROM AUTHOR]

The design and performance of a sub-10-picosecond source based on temporal focusing implemented with a lithium niobate phase modulator and a grating compressor are presented. The source is optimized taking into account spectral gain narrowing in subsequent amplifiers. It advantageously delivers low-repetition-rate pulses with tunable pulse duration, and its short-term jitter and long-term drift over extended periods of time are of the order of a few picoseconds. [ABSTRACT FROM AUTHOR]

The invention of optical frequency combs (OFCs) based on femtosecond (fs) mode-locked lasers has merged laser based spectroscopy with fs-laser technology. OFCs have triggered quantum leaps of advancement in photonics, physics, astronomy, and engineering, while also lending themselves to applications in medical and environmental fields. The key feature of OFCs is their ultrahigh frequency and time resolution. In this review, we introduce the concept behind OFCs and their sources, with a focus on stability and phase-noise performance. We conclude with a discussion of recent progress of a monolithic OFC, which provides ultralow free-running phase noise and an unprecedented frequency stability of 1 part in ${10^{19}}$ at a 1 s gate time. [ABSTRACT FROM AUTHOR]

Thin-disk technology uniquely enables the simultaneous scaling of both average and peak powers, while maintaining an excellent beam profile. It has been widely adopted in the 1-μm region, not only for continuous wave lasers but also for pulsed oscillators and amplifiers. However, the development of 2-μm thin-disk lasers is still at a very early stage, with passive mode locking having been demonstrated only recently. Here, we describe in detail a new femtosecond Ho:YAG thin-disk oscillator and recent power-scaling experiments that resulted in an average power of up to 25 W—the highest average power of any mode-locked oscillator in the 2-μm region. The future directions toward even higher average and peak power thin-disk oscillators are also discussed. [ABSTRACT FROM AUTHOR]

Q‐switched and mode‐locked fibre lasers have been successfully demonstrated in ytterbium‐doped fibre laser cavity by taking an advantage of the optical absorption of antimony telluride (Sb2 Te3) material. The Sb2 Te3 was embedded into polyvinyl alcohol to function as a saturable absorber (SA). A Q‐switching pulses train was obtained by incorporating the SA into the laser ring cavity configured with 3 dB coupler. The Q‐switching pulse repetition rate increases from 24.4 to 55 kHz as the pump power is increased from the threshold of 75.4–96.2 mW. The maximum pulse energy of 252.6 nJ is obtained at 82.3 mW pump power. On the other hand, by changing the output coupler to 10 dB coupler, a stable self‐started mode‐locking operation was then generated at pump power range from 47.8 to 89.4 mW with a fixed repetition rate of 24.2 MHz. At 89.4 mW pump power, the maximum output power and pulse energy are obtained to be around 18.6 mW and 0.8 nJ, respectively. The authors results display that the Sb2 Te3 material could also be developed as an effective SA for both Q‐switched and mode‐locked fibre lasers. [ABSTRACT FROM AUTHOR]

We experimentally study the pulse generation and the pulse train timing and amplitude stability of a monolithic passively mode-locked multisection quantum-well semiconductor laser. The laser emits a stable optical pulse train at a wavelength of 1070 nm and at a fundamental repetition rate of 20 GHz. Timing jitter and amplitude jitter analysis allows identifying distinct laser operating regimes of stable picosecond optical pulses. We obtain an ultra-low pulse-to-pulse timing jitter of 22 fs and find emission regimes which are unaffected by amplitude jitter. The lowest pulse width amounts to 2.6 ps, and the highest pulse peak power is estimated to be 556 mW at a low timing jitter of 170 fs and a negligible relative amplitude jitter of 0.05. [ABSTRACT FROM AUTHOR]

We report on the successful operation of a dissipative soliton fiber laser mode-locked with a bulk InGaAs-based saturable absorber mirror forming a resonant micro-cavity. Highly-chirped pulses with several nanojoules of energy are thus produced. Remarkably, the laser performances in terms of output power and amplitude stability are comparable to those obtained with their multiple-quantum-well-based counterparts. This letter suggests that this simplified approach for saturable absorber mirrors can be considered as a promising alternative regarding ultrafast optics applications. [ABSTRACT FROM PUBLISHER]

We present a method to discriminate stable mode-locked states of an all fiber erbium-doped laser based on nonlinear polarization rotation mechanism. The method has a balance between the accuracy and rapidness of the pulses discrimination. Mode-locked states are distinguished and confirmed by an amplitude discriminator, which reflects the repetition rate information of the pulses. An electronic polarization controller is used to precisely adjust the intracavity polarization states. The driving voltages of the electronic polarization controller at those mode-locked states are recorded as populations, and it is benefit to reduce the build-up time for mode locking. The populations are also recorded at operation temperature covering from 20 °C to 50 °C, which exhibits the repeatability and stability of the mode-locked states. Rapid self-tuning mode-locked fiber lasers could be achieved by the repeatability of the polarization settings under the stable temperature environment. [ABSTRACT FROM PUBLISHER]

We studied the optical comb peculiarities of the ultra-short dispersion-managed soliton generation in an erbium-doped all-fiber ring laser hybrid mode-locked with carbon:boron nitride single-walled nanotubes in the co-action with a nonlinear polarization evolution. A stable low-intensity-noise optical comb was obtained with a narrow single comb linewidth of 18.1 kHz based on dechirped 90-fs pulses with a repetition rate of 42.22 MHz, a spectral pulse width of 56 nm, and an average output power of 16.7 mW corresponding to 4.4-kW maximum peak power and 0.4-nJ pulse energy. [ABSTRACT FROM PUBLISHER]

We have designed and fabricated a Kerr frequency comb oscillator with 27.5 GHz repetition rate by pumping a whispering gallery mode crystalline resonator with a laser at 1560 nm center wavelength. The oscillator is stabilized to the Rb^87 D $_2$ line using frequency doubling with a periodically poled lithium niobate (PPLN) waveguide. Allan deviation of the repetition rate of the frequency comb was measured to be on the order of 10^{-11} at 1 s to 1000 s integration time. The long-term stability limitation is attributed to the frequency drift of the phase matching window of the PPLN structure as well as to mode interaction and associated drift of the resonator spectrum. [ABSTRACT FROM PUBLISHER]

We have reported a mode-locked pulse energy tunable ytterbium-doped fiber laser constructed by the polarization-maintaining (PM) fibers with a position-tunable focuser and a semiconductor-saturable absorber mirror (SESAM). The narrow bandwidth fiber Bragg grating in the cavity produces self-starting picosecond (ps) mode-locked operation. The linear laser cavity achieved tunable single pulse energy varied from 0.591 to 0.988 nJ, with a 24.7-MHz repetition rate and a 6.03-ps pulse duration at 1064.18 nm. High environmental stability is also confirmed by a high polarization extinction ratio over 17.8 dB. [ABSTRACT FROM PUBLISHER]

The optical injection locking (OIL) technique is proposed to reduce the phase noise of a carrier generated for a vertical-cavity surface-emitting laser (VCSEL)-based optoelectronic oscillator. The OIL technique permits the enhancement of the VCSEL direct modulation bandwidth as well as the stabilization of the optical noise of the laser. A 2-km delay line, 10-GHz optical injection-locked VCSEL-based optoelectronic oscillator (OILVBO) was implemented. The internal noise sources of the optoelectronic oscillator components were characterized and analyzed to understand the noise conversion of the system into phase noise in the oscillator carrier. The implemented OILVBO phase noise was -105.7 dBc/Hz at 10 kHz from the carrier; this value agrees well with the performed simulated analysis. From the computed and measured phase noise curves, it is possible to infer the noise processes that take place inside the OILVBO. As a second measurement of the oscillation quality, a time-domain analysis was done through the Allan's standard deviation measurement, reported for first time for an optoelectronic oscillator using the OIL technique. [ABSTRACT FROM AUTHOR]

The pulse repetition rate (RR) tuning and locking range (LR) as well as the pulse train timing stability of passively mode‐locked quantum‐well (QW) semiconductor lasers (SCLs) subject to single‐cavity optical self‐feedback (OFB) are investigated experimentally and by simulations. A simple and universal stochastic time‐domain model confirms the experimentally observed RR control and LR as well as timing jitter (TJ) improvement in QW SCLs subject to very long OFB cavities with lengths up to 73.1 m. In particular, the model allows predicting control potential and limits of the RR tuning, locking and TJ improvement depending on the choice of OFB delay length for time‐delay mode‐locked semiconductor laser stabilisation experiments. [ABSTRACT FROM AUTHOR]

An evaluation of the amplitude jitter and timing jitter for a regeneratively mode‐locked fibre laser via the use of the harmonic analysis approach is presented. The RF power spectrum of four harmonics derived from a 10 GHz mode‐locked pulse train was measured with high resolution. From a detailed analysis of the noise pedestal present in these harmonics, an amplitude jitter of ∼0.3% and an absolute timing jitter of ∼41 fs are obtained. [ABSTRACT FROM AUTHOR]

We demonstrate the short- and long-term stable operation of an all-polarization-maintained Fabry–Pérot cavity passively mode-locked fiber laser. The laser operates in an all-anomalous-dispersion solitonic regime. Laser stability is studied by a variety of measurements, which confirm the high stability of the laser in the temporal and spectral–both optical and electrical-domains. Pulse durations of 540 fs, period-relative time jitters of $\sim$0.015‰, and long-term uninterrumped operation with 0.4% variation (standard deviation) in the average output power are obtained. The highly stable operation of the laser oscillator was maintained after amplifying the laser output with a conventional EDFA. Pulse durations of $\sim$244 fs, period-relative time jitters of $\sim$0.019‰,  and an average output power of 20 mW were obtained after amplification, while maintaining the 100-dB signal-to-noise ratio of the laser oscillator measured at 500-Hz offset from the fundamental harmonic frequency. The theoretical validation of our experimental results is based on solutions of the Nonlinear Schrödinger Equation. We demonstrate that wavelength and z -position dependences of the active medium gain must be taken into account for an accurate correspondence with the experimental properties of the laser. [ABSTRACT FROM PUBLISHER]

We demonstrate a passively Q-switched erbium-doped fiber laser (EDFL) based on few-layer MoS2 as a saturable absorber (SA). Few-layer MoS2 is prepared by the chemical vapor deposition method. The prepared MoS2 is transferred onto the end face of a fiber connector to form a fiber-compatible MoS2-based SA. The saturation intensity and modulation depth of the MoS2 SA are measured to be 0.43 MW/cm2 and 33.2%, respectively. The Q-switched EDFL has an all-fiber linear cavity with two fiber Bragg gratings as the end mirrors. By inserting the MoS2 SA into the laser cavity, stable Q-switched operation is achieved at 1.55 μm. The laser has a pump threshold of 20.4 mW, a pulse repetition rate tunable from 10.6 to 173.1 kHz, and a minimum pulse duration of 1.66 μs. Our results show that few-layer MoS2 is a promising SA for Q-switching laser operation. [ABSTRACT FROM PUBLISHER]

Cross-phase modulation instability (XPMI) is experimentally observed in a fiber ring cavity with net normal dispersion and mode-locked by long fiber taper. The taper is deposited with reduced graphene oxide, which can decrease the threshold of XPMI due to the enhanced nonlinearity realized by 8-mm evanescent field interaction length and strong mode confinement. Experimental results indicate that the phase matching conditions in two polarization directions are different, and sidebands with different intensities are generated. This phase matching condition can be satisfied even the polarization state of the laser varies greatly under different pump strengths. [ABSTRACT FROM PUBLISHER]

We report a novel method to generate a stable and frequency-hopping-free microwave signal based on a mutually injection-locked dual-wavelength single-longitudinal-mode fiber laser and an optoelectronic oscillator (OEO), with the mutual injection locking realized by sharing an optical path consisting of a polarization modulator and a polarization-maintaining phase-shifted fiber Bragg grating. The two wavelengths from the fiber laser are injected into the OEO to lock the generated microwave signal, while the microwave signal from the OEO is fed back into the fiber laser to injection lock the two wavelengths. Thanks to the mutual injection locking, the operation stability of the fiber laser and the OEO are substantially improved. A microwave signal at 11.8 GHz with a phase noise of -105 dBc/Hz at a 10-kHz offset frequency is generated. A stable operation of the system without frequency shifting and hopping is demonstrated. [ABSTRACT FROM PUBLISHER]

In this paper, we designed the offset frequency locking and active frequency stabilization system for the continuous-wave (CW) and electro-optical Q-switched RF-excited waveguide CO2 lasers to provide an ideal light source for coherent radar. The CW laser is used as a local laser, and the pulsed laser is used as a main laser, which can produce Q-switched and cavity-dumped laser synchronously. A closed-loop laser frequency control system was used to stabilize the Q-switched laser at the gain curve center frequency and to lock the two lasers at a selected heterodyne frequency. The system includes two parts: 1) pulsed laser frequency stabilization and 2) offset frequency locking. The frequency stabilization part can keep the Q-switched laser oscillating at the peak of the gain curve by measuring the pulse build-up time continuously and controlling the cavity length. The offset frequency locking circuits keep the heterodyne frequency around the selected frequency by measuring the frequency of the beat signals and controlling the CW laser cavity length. In the experiment, the long-term frequency shift of the pulse laser was measured to be less than ±16 MHz and the offset frequency fluctuation was less than ±2 MHz when the frequency control system was in a closed-loop operation. [ABSTRACT FROM AUTHOR]

Square nanosecond mode-locking was demonstrated in a short-cavity polarization-maintaining (PM) fiber laser with a nonlinear amplifying loop mirror (NALM). Nonlinear phase shifts in the NALM enforced peak-power clamping and accordingly, the output pulse duration varied with the NALM gain. Gain competition of multipulse mode-locking was observed with short NALM loops. Such NALM-based mode-locking exhibited long-term stability against environmental disturbance. [ABSTRACT FROM PUBLISHER]

An erbium fiber oscillator with dominating gain fiber length and an intracavity pulse shaper is experimentally demonstrated. The Kerr nonlinear phase shift induced in the fibers is suppressed by the pulse shaper, enabling high-energy (8.9 nJ) high-compression efficiency (93%) pulses of less than 270 fs duration (after linear dechirping) at modest (320 mW) pump power. A stably mode-locked spectrum corresponding to 19 nJ, 83 fs transform-limited pulse is achieved at 720 mW pump power. Wave-breaking-free pulse energy can be further enhanced by introducing stronger spectral phase modulation via the pulse shaper if more pump budget is available. We also demonstrate manipulation of the central wavelength and bandwidth of the output pulse by intracavity spectral amplitude modulation via the pulse shaper. [ABSTRACT FROM PUBLISHER]

We report an environmentally stable nanotube mode-locked fiber laser producing linearly-polarized, nanosecond pulses. A simple all-polarization-maintaining fiber ring cavity is used, including 300 m of highly nonlinear fiber to elongate the cavity and increase intracavity dispersion and nonlinearity. The laser generates scalar pulses with a duration of 1.23 ns at a center wavelength of 1042 nm, with 1.3-nm bandwidth and at 641-kHz repetition rate. Despite the long cavity, the output characteristics show no significant variation when the cavity is perturbed, and the degree of polarization remains at 97%. [ABSTRACT FROM PUBLISHER]

In this paper, we present a systematic investigation of passive mode-locked InAs/InP quantum-dash lasers in terms of frequency and timing stability. Mode-locking features are analyzed using the frequency domain approach based on the concept of supermodes. It is shown that the phase of adjacent longitudinal modes is correlated over 1.3-THz frequency span. The observed strong coherence between modes enables low timing jitter and a long-term stability of the repetition rate frequency within 5×10-8 over 100 s. [ABSTRACT FROM PUBLISHER]

We present a timing jitter and amplitude noise characterization of a high-power mode-locked integrated external-cavity surface emitting laser (MIXSEL). In the MIXSEL, the semiconductor saturable absorber of a SESAM is integrated into the structure of a VECSEL to start and stabilize passive mode-locking. In comparison to previous noise characterization of SESAM-mode-locked VECSELs, this first noise characterization of a MIXSEL is performed at a much higher average output power. In a free-running operation, the laser generates 14.3-ps pulses at an average output power of 645 mW at a 2-GHz pulse repetition rate and an RMS amplitude noise of 0.15% [1 Hz, 10 MHz]. We measured an RMS timing jitter of 129 fs [100 Hz, 10 MHz], which represents the lowest value for a free-running passively mode-locked semiconductor disk laser to date. Additionally, we stabilized the pulse repetition rate with a piezo actuator to control the cavity length. With the laser generating 16.7-ps pulses at an average output power of 701 mW, the repetition frequency was phase-locked to a low-noise electronic reference using a feedback loop. In actively stabilized operation, the RMS timing jitter was reduced to less than 70 fs [1 Hz, 100 MHz]. In the 100-Hz to 10-MHz bandwidth, we report the lowest timing jitter measured from a passively mode-locked semiconductor disk laser to date with a value of 31 fs. These results show that the MIXSEL technology provides compact ultrafast laser sources combining high-power and low-noise performance similar to diode-pumped solid-state lasers, which enable world-record optical communication rates and low-noise frequency combs. [ABSTRACT FROM PUBLISHER]

We have developed a tunable semiconductor double-chirped mirror with high negative dispersion grown by molecular beam epitaxy. The simplified numerical plane-wave reflection transfer method was applied to design the dispersive mirror structure. The multilayer stack was grown of AlAs/GaAs materials and capped by an SiNx antireflective layer. The group delay dispersion as well as reflectivity characteristic were continuously tunable across the mirror surface from 1080 to 1000 nm. Within this range, the negative value of the dispersion changed from -3850±100 fs2 over the 6 nm band around 1080 nm to -2200±100 fs2 over 13 nm around 1000 nm with the reflectivity from the range of 99.0÷99.2%. The mirror performance was tested in a diode-pumped femtosecond Yb:KYW oscillator. [ABSTRACT FROM PUBLISHER]

We present a novel and detailed analysis of the locking range and the stability map for side-mode injection-locked in-plane semiconductor multimode lasers. By including the usually neglected unlocked modes in our model, we predict a multivalued locking range and stability map for this type of lasers. We also explain and relate, the previously noticed slave laser bistability phenomenon with the multivalued character of the locking range and stability map, and experimentally validate our findings. Moreover, we find that the unstable operating region, commonly found in literature by stability analysis of the injection-locked mode alone, is actually much smaller. [ABSTRACT FROM PUBLISHER]

Variation in the round-trip group delay through an intracavity prism pair is studied as a function of index variation in the gain medium. The resulting sensitivity to index perturbation gives insight into the degree to which pump noise will transfer to timing instability through this mechanism. General expressions for group-delay time change and slope are derived. It is found that thermal and nonlinear index changes in the gain crystal result in group-delay time sensitivities of 4.34 \times 10^-17 s/K and 1.25\times 10^-26 s\cdotcm^2/W, respectively, for a conventional 100-MHz Kerr-lens mode-locked laser. For a nominal temperature fluctuation of 1 K and a peak intensity variation of 5\times 10^8 W/m^2, this implies round-trip timing variation of 5\times 10^-17 s, which is very small, but not insignificant in today’s clock technology. [ABSTRACT FROM PUBLISHER]

A high-power neodymium-doped yttrium lithium fluoride (Nd:YLF) mode-locked 1.5-GHz laser currently used to drive the two photoinjectors of the Compact Linear Collider Test Facility project at the European Organization for Nuclear Research is described. A phenomenological characterization of the two powerful Nd:YLF amplifiers is presented and compared with the measurements. The laser system operates in a saturated steady-state mode. This mode provides good shot-to-shot stability with pulse train mean power in the 10 kW range. [ABSTRACT FROM PUBLISHER]