- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Symmetry Properties and Coexistence of the Mode-Locked States in Semiconductor Lasers
摘要： Coexistence of multiple dynamical states of operation is known in multimode lasers. In this work, we examine the symmetry properties of various laser models based on the delay differential equation (DDE) approach [1], and explain a vast class of experimental observations in mode-locked semiconductor lasers. In these models, the complex electric field amplitude ( )E t is presented by the equation having the form: 1 (cid:16) (cid:74) (cid:5) E t ( ) exp( (1) where dot means differentiation with respect to time, (cid:74) is the width of a Lorentzian bandwidth limiting element T(cid:77)(cid:32) (cid:58) is the term accounting the frequency detuning (cid:58) between one of the (such as a filter or gain profile); cavity modes and the transmittance peak of the filter; T is the cold cavity round trip time; is a function describing gain, saturable losses or/and nonlinearity. ) i R t T E t T (cid:77) R t T(cid:16) E t ( ) (cid:32) (cid:16) (cid:16) (cid:16) (cid:14) ) ( ( ) ( ) The phase parameter (cid:77) is 2(cid:652)-periodic translationally symmetrical. Continuous variation of the phase parameter (cid:77) allows for ‘unwrapping’ and overcoming this periodicity, unveiling translational symmetry in the system. The translational symmetry explains the appearance of multiple coexisting branches in the system, and multistability of the invariant solutions. We study this effect for several different systems, namely, a mode- locked single-section semiconductor laser, a mode-locked semiconductor laser with optical feedback, and a figure-eight semiconductor laser with a nonlinear amplifying loop mirror. By means of numerical continuation technique, we show that variation of the frequency detuning is the key to unveiling translationally symmetrical branches of laser mode-locked regimes, and their multistability. The multistable operations can demonstrate either slightly different repetition rates or/and very different temporal pulse profiles varying from Gaussian pulses to square waves. In order to corroborate our theoretical results experimentally, we explore single-section semiconductor quantum dash (Qdash) laser, and demonstrate switching and coexistence of two mode-locked operation states. The mode-locked regime repetition rate decreases with the pump current as a result of a thermally induced increase of the cavity length (see Fig. 1(a)). At 150 mA, the rf spectrum jumps discretely by approximately 2 MHz. This is accompanied by a jump in the optical spectrum of approximately 2 nm. After the jump, the repetition rate starts to decrease again until the next jump. This change of the cavity length induces the variation of the longitudinal mode spacing and, therefore, detuning between the dominant cavity mode and the peak of the gain profile, physically corresponding to the parameter (cid:77) in the model. The numerical bifurcation diagram plotted for the repetition rate evolution of the mode-locked operation is shown in Fig. 1(b), and the corresponding time traces are given in Fig. 1(c). The translational symmetry is ubiquitous in DDE laser models, and possibly, more effects of multistability related to multimode laser operation can be explained in this way.
关键词： delay differential equation,symmetry properties,mode-locked states,semiconductor lasers,multistability
更新于2025-09-12 10:27:22
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Passively Mode-Locked Self-Frequency Doubling Yb:LGSB Laser
摘要： Non-centrosymmetric crystals exploited as host matrices for rare earth active ions simultaneously enable a self-frequency doubling (SFD) process. In case of ytterbium doping it allows to obtain laser radiation at 1 μm and its SFD signal covering green spectral range. This mechanism is particularly interesting in case of mode-locked oscillators as the intensity within the crystal is much higher, thus increasing the conversion efficiency. Moreover, it can be also employed for cascaded χ(2) processes. Nevertheless, despite more than 20 years of development of Yb-doped mode-locked bulk lasers there are very few demonstrations of femtosecond oscillators with SFD properties [1-3]. One of the recently introduced non-centrosymmetric Yb3+-doped active media is LaxGdyYbzScw(BO3)4 (x + y + z + w = 4; shortly Yb:LGSB) crystal [4,5]. This novel scandium borate compound is a negative uniaxial crystal and it exhibits strong second order nonlinearity (point group 32). The nonlinear coefficient d11 amounts to 2.1 pm/V, which is much higher than in case of previously investigated SFD crystals [1-3]. Moreover, its emission spectrum is relatively broad and thus it is a very promising candidate for femtosecond SFD, which, to the best of our knowledge, has never been demonstrated with this gain medium before. Here, we demonstrate the first mode-locked operation of a laser based on an Yb:LGSB gain medium. The scheme of the X-shaped resonator cavity is depicted in Fig. 1a. An investigated c-cut 2.55 mm-long La0.681Gd0.308Yb0.129Sc2.882(BO3)4. crystal was grown by Czochralski method [4]. It was pumped by a 1 W fiber-coupled single-mode laser diode with central wavelength of 979 nm. Due to lack of the AR-coatings it was inclined under Brewster’s angle. As a saturable absorber we used a semiconductor saturable absorber mirror (SESAM) with 0.6% modulation depth and 10 ps relaxation time. In order to obtain stable soliton mode-locked operation the anomalous dispersion of -1650 fs2 was introduced to the cavity by the Gires-Tournois-interferometer (GTI) mirrors. The output coupler transmission was 0.8%. In this configuration the laser emitted 6.8 nm broad spectrum centered at 1070 nm (Fig. 1b), which corresponds to transform-limited pulse duration of 180 fs. The output average power was equal to 32 mW with repetition rate of 89 MHz. During mode-locked operation we could also observe a self-frequency doubled signal. Due to the low reflectivity of the employed mirrors in the green, the strongest SFD signal was detected after one of folding mirrors. The second harmonic spectrum is shown in the inset of the Fig. 1b. The fringes originate from the fact that SFD was not phase-matched in this case [3]. The work was supported by National Science Centre (NCN, Poland; grant 2015/18/E/ST7/00296) and by Ministry of Research and Innovation of Romania (CNCS-UEFISCDI, grant PN-III-P4-ID-PCE-2016-0853 within PNCDI III).
关键词： Yb:LGSB,mode-locked laser,non-centrosymmetric crystals,femtosecond oscillator,self-frequency doubling
更新于2025-09-12 10:27:22
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Femtosecond-Driven Up-Conversion in a Radially Poled LiNbO <sub/>3</sub> Microresonator
摘要： Nowadays, there are plenty of different techniques developed for the generation of Optical Frequency Combs (OFCs), but Mode Locked Laser (MLL) OFC is still the most commonly used and commercially available one [1]. Although MLLs are capable of producing very high-peak power OFCs with femtosecond pulse durations, it is sometimes challenging to apply them directly for a number of reasons. First, MLLs typically produce OFCs with repetition frequencies (fr) below 1 GHz, so additional filtering of the unwanted modes is required for the applications in telecommunications, astrocombs etc. Second, many spectral regions – namely mid-infrared, visible and ultraviolet – are difficult to access by MLLs, which implies the use of external parametric up- and down-conversion. One promising platform for such spectral transfer is high Q-factor optical microresonators based on second order (χ(2)) nonlinear crystals, since not only do they provide the desired spectral transfer, but also open up opportunities for the miniaturization of the system. In addition, such microresonators support whispering gallery modes that possess very low mode volumes, making it possible to enhance nonlinear (χ(2)) processes. This is a significant advantage over the already existing bulk analogs.
关键词： Mode Locked Laser,microresonators,second harmonic generation,femtosecond pulses,Optical Frequency Combs
更新于2025-09-12 10:27:22
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - A Multiple-Waveguide Mode-Locked Chip-Laser Architecture
摘要： Frequency combs and analogue to digital sampling are emerging applications that can benefit from advances in elegant, compact, and high performance miniature mode-locked lasers. By virtue of their ‘chip-scale’, and multiplicity of adjacent waveguides, compact cavity planar waveguide devices are suited to efficiently operate in the ~0.5 GHz to 10 GHz pulse regimes. The ultra-fast chip laser platform we have pioneered is based on direct inscription of sub-surface large mode-area waveguides into rare-earth doped fluorozirconate (ZBLAN) glass chips. Multiple waveguides per chip are rapidly written via computer numerically controlled (CNC) ultra-fast laser inscription (ULI); a flexible and advancing waveguide fabrication technique. The guided-wave confinement of these fiber like structures in this bulk gain media ensures efficient pump and cavity mode overlap, robust alignment, and single transverse mode operation. Our initial mode-locking experiments focused on erbium doped ZBLAN chips (sensitized by Yb). These lasers display reasonable cw laser performance, a large single transverse-mode, a wide tunable range covering 1510-1590 nm, and a zero-dispersion wavelength of 1650 nm, thereby reducing the requirement for dispersion compensation. The erbium ytterbium cerium co-doped ZBLAN chips have been demonstrated to produce transform limited mode-locked output near 1.55 μm, with pulse lengths down to 180 fs, and operation up to 3 GHz. In recent work we have also demonstrated cw mode-locking near 1 μm based on Yb doped ZBLAN chip lasers. This talk will provide an overview of chip fabrication, cavity design, mode-locking configuration, and mode-locking results we have achieved. By taking advantage of the multiple waveguide channels, we have demonstrated a cavity that could simultaneously operate adjacent mode-locked erbium lasers using all common cavity components. By slightly modifying one of the cavity lengths, the dual mode-locked laser was shown to operate as an ultra-stable dual frequency comb. This laser possessed the highest mutual coherence reported to date for a passively stabilised dual-comb laser.
关键词： waveguide,ZBLAN glass,frequency combs,ultra-fast laser inscription,mode-locked lasers
更新于2025-09-12 10:27:22
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Nd,Gd:SrF <sub/>2</sub> Laser Generating 600 fs Pulses at 0.9 W of Pump Power
摘要： Fluoride crystals (CaF2, SrF2) doped with neodymium Nd3+ and codoped with non-active ions as Y3+, La3+, or Gd3+ for breaking clusters of active ions, have become recently interesting active media for the diode-pumped mode-locked lasers. They possess broader emission spectra as well as longer fluorescence lifetime in comparison with widely used crystals such as Nd:YAG or Nd:YVO4. The femtosecond Nd,Y:SrF2 laser generating 97 fs pulses was reported in the Ti:sapphire pumped system [1]. We have reported continuously mode-locked operation of this laser pumped by a 2 W multimode laser diode and mode-locked using a semiconductor saturable absorber generating pulses with the duration of 258 fs [2]. In laser systems with La3+ codoped crystals, which have wider tunability than Y3+ codoped crystals, passively mode-locked 354 to 1200 fs and continuous-wave 1044 to 1081 nm tunable operation was reported in the system pumped by 4 W laser diode [3]. Recently a new Nd,Gd:SrF2 crystal has been investigated and the dual wavelength mode-locked picosecond operation was reported for pump power higher than 3.8 W [4]. We reported femtosecond operation of laser with this crystal and obtained pulses as short as 228 fs with output power of 2 x 50 mW in system pumped by 2 W laser diode for absorbed pump power of 1320 mW [5]. In the present contribution we report on operation of this novel laser with a Brewster cut crystal in passively mode locked regime for extremely low pump power. Laser system schematic is similar as in ref. [5] and is shown in Fig. 1. A 5 mm long Brewster cut 0.5%Nd, 5%Gd:SrF2 crystal was pumped by a multimode 2 W laser diode at 796 nm and passively mode-locked using a semiconductor saturable absorber mirror (SAM). Using a chirped mirror M3 with GDD equal to -650 fs2 it was possible to achieve continuously mode locked regime at absorbed pump power of only 320 mW, with output power of 2 x 12 mW behind the mirror M4 in linearly polarized beams with nearly Gaussian spatial profile and pulse duration of 740 fs (assuming sech2 pulse shape). For higher absorbed pump power of 632 mW (905 mW incident on the crystal) the total output power of 2 x 20 mW was achieved with a pulse duration of 600 fs. The autocorrelation curve is shown in Fig. 2 together with the measured spectrum 3.3 nm wide, and centered at 1051.5 nm. The absorbed pump power is 2 - 4 times smaller in comparison with our previous results. The calculated time-bandwidth product of 0.536 gives potential to get shorter pulses (down to 352 fs) with optimum GVD compensation.
关键词： diode-pumped,semiconductor saturable absorber mirror,femtosecond pulses,Nd,Gd:SrF2,mode-locked lasers
更新于2025-09-12 10:27:22
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Thermally Stabilized, Energy Efficient, All-Fiber Optical Frequency Comb
摘要： In recent years, optical frequency combs are gaining attention in many fields of science, e.g. frequency metrology, optical clocks, and high-resolution spectroscopy. Most sophisticated comb sources can be repetition rate stabilized down to 10-16 uncertainty in 1 s averaging time [1] (bounded by the stability of the reference clock). Therefore compact, low-cost and energy efficient fiber-based sources are highly demanded on the market [2]. Accurate thermal stabilization of the fiber laser cavity is the first step to obtain stable repetition frequency, which is critical for optical frequency comb spectroscopy schemes [3]. Moreover, cavity-enhanced spectroscopic techniques like Vernier spectroscopy requires additional detuning of the comb repetition rate from the cavity mode-spacing [4]. We report an experimental investigation of the performance of a Er-doped, low power, thermally stabilized, mode locked laser, utilizing graphene as a saturable absorber. The oscillator, depicted in Figure 1(a), consists of: a hybrid component comprising an output coupler, wavelength division multiplexer and isolator (TIWDM), saturable absorber, and a piezo-electric transducer (PZT). The laser based only on polarization maintaining (PM) fibers, without any free space components. The entire resonator and all components are placed on a custom-made heating plate with uniformly spread heating traces, which equally cover the entire board surface, ensuring perfectly homogenous heat distribution. For efficient thermal stabilization, the fibers are attached to the plate by acrylic adhesive thermopads. The resonator is placed in a 3D-printed enclosure. A custom-made thermal controller is responsible for thermalization of all oscillator components with long term stability better than 0.05°C. Additional tuning of the repetition rate in the range of 0 – 2.79 kHz is performed by means of a piezo stretcher driven with voltages from 0 to 150 V. The stretcher is based on a miniature, monolithic, multilayer piezo stack (5x5x50 mm), which stretches the Er-doped fiber by approximately 36 μm. The fundamental repetition rate (fc), resulting from the cavity length is equal to 124.6539196 MHz at 30°C (without any voltage applied to the PZT). The signal to noise ratio (SNR) in the radio frequency (RF) spectrum measured with 2.7 Hz resolution bandwidth (RBW) is at the level of 70 dB. The repetition rate of the laser can be detuned by 17 kHz via heating the resonator from 30 to 50°C. We believe that such compact, simple frequency combs with low power consumption are suitable for field applications. The presented work was funded by the Foundation for Polish Science (First TEAM/2017-4/39) co-financed by the European Union under the European Regional Development Fund. A.G. acknowledges the support of the Faculty of Electronics (grant “M?oda Kadra”).
关键词： optical frequency combs,fiber stretcher,thermal stabilization,graphene saturable absorber,mode locked laser
更新于2025-09-12 10:27:22
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Stochastic Soliton Quantization in Mode-Locked Fibre Laser
摘要： Soliton quantization is a natural, intrinsic and random consequence property of localized pulses in nonlinear systems. It is formed in the fiber laser in the form of dissipative solitons due to the gain competition between the solitons in the laser cavity. The observation of quantized separations between the solitons was predicted either due to the interaction between far separated solitons or due to the interaction between weakly overlapping pulses [1, 2]. It was first found experimentally in a nonlinear amplified loop mirror mode-locked fiber laser [3] and then in a nonlinear polarization rotation mode locking fiber laser [4, 5] with a requirement of high pump power of >400 mW. Here, we report for the first time the experimental demonstration of the stochastic temporal soliton quantization state regimes at a low range of the pump powers (~41 mW) using a carbon nanotube’s saturable absorber mode-locked fiber laser [6]. We found that the regimes and the total number of pulses in the cavity are highly sensitive to the pump power and the state of the polarization which could lead to several distinct regimes of pulse formation. However, for certain pumping powers which were 41 mW and specific orientation of the laser cavity polarization controller (PC), we observed pulse trains of several tenths of pulses as shown in the real-time spatiotemporal measurements in Fig. 1a. The pulse train consists of a stochastic quantized distribution with separation between pulses starting from about 3 ns to tenths of ps with a nonlinearly quantized separation, behaving between the localized soliton pulses as shown in Fg. 1b. The pulses are localized with a much broader temporal separation far from the main soliton pulse and condensed to a very narrow seperations nearer to it. By slightly increasing the pump power to ~88 mW and varying the PC, we obtained the second order of the stochastic soliton which also have a quantized temporal distribution without any undesirable distribution of types or interactions between neighboring solitons along 5000 roundtrip pulse train. The quantized soliton, actually, has formed intrinsically in the form of dissipative solitons due to large binding soliton states.
关键词： Soliton quantization,stochastic soliton,carbon nanotube saturable absorber,mode-locked fibre laser
更新于2025-09-12 10:27:22
-
Real-time characterization of spectral instabilities in a mode-locked fibre laser exhibiting soliton-similariton dynamics
摘要： the study of dissipative solitons in mode-locked lasers reveals a rich landscape of interaction dynamics resulting from the interplay of nonlinearity, dispersion and dissipation. Here, we characterize a range of instabilities in a dissipative soliton fibre laser in a regime where both conventional soliton and similariton propagation play significant roles in the intracavity pulse shaping. Specifically, we use the Dispersive fourier transform technique to perform real-time spectral measurements of buildup dynamics from noise to the generation of stable single pulses, phase evolution dynamics of bound state “similariton molecules”, and several examples of intermittent instability and explosion dynamics. These results show that the instabilities previously seen in other classes of passively mode-locked fibre lasers are also observed in the presence of strong nonlinear attraction of similariton evolution in an optical fibre amplifier.
关键词： explosion dynamics,Dispersive fourier transform,similariton molecules,intermittent instability,dispersion,nonlinearity,mode-locked lasers,dissipative solitons,dissipation
更新于2025-09-12 10:27:22
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Saturable Absorption with CNT Coupled WGM and Fabrication of Er-Doped Microresonator for on-Chip Mode-Locked Laser
摘要： Mode-locked (ML) fiber lasers are becoming key components in industry, because they provide high performance while being relatively inexpensive. The generation of high-repetition rate pulses is gaining interest but it remains a challenge to achieve a GHz repetition rate with fiber lasers. On the other hand, whispering-gallery-mode (WGM) microresonators allow the strong confinement of light and miniaturizing an ML laser into a WGM microresonator will enable us to achieve a high pulse repetition rate, a small footprint and on-chip integrability. In this work, we explore the possibility of a passive ML laser with the system shown in Fig. 1(a). There are two key technologies involved; one is saturable absorption (SA) and the other is laser gain in a microresonator. First, we verified numerically that we could realize an ML laser with our proposed carbon nanotube (CNT) coupled erbium (Er) doped microresonator, and the result is shown in Fig. 1(b). We modelled our system with a nonlinear Schr?dinger equation, where we took gain and SA (also loss (Q), Kerr effect, and dispersion) into account [2]. The result shows that a self-starting ML is possible with microresonator parameters. Next, encouraged by the numerical result, we experimentally demonstrated SA in a microtoroid. We grew CNTs selectively on a silica microtoroid by chemical vapor deposition and investigated the SA behavior (Fig. 1(c)). By performing a pump-probe like experiment we successfully characterized the SA behavior in a microresonator system. This is the first demonstration of SA in a WGM microcavity system [1]. We then fabricated an Er-doped active microtoroid by using the sol-gel method. The sol-gel method is one way of forming silica from a metal alkoxide precursor. Although sol-gel has been widely used, it is still a challenge to fabricate high-quality defect-free film on a Si wafer that allows us to fabricate an ultrahigh-Q WGM microresonator. Figure 1(d)-(f) shows the fabricated films. We found optimum parameters and obtained a clean film as shown in Fig. 1(g). By using this film, we fabricated an Er-doped WGM microresonator, where the Q was 1.2×106 at 1480 nm (Fig. 1(h)). We obtained clear up-conversion luminescence when we pumped the cavity at 1480 nm, which constitutes the first step towards ML lasing in such a WGM microresonator. In summary, these results provide a promising approach for realizing an on-chip high repetition rate ML WGM microresonator.
关键词： saturable absorption,sol-gel method,carbon nanotube,whispering-gallery-mode microresonators,erbium-doped microresonator,Mode-locked fiber lasers
更新于2025-09-11 14:15:04
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Modeling of the Ultra-Stable Operating Regime in Fourier Domain Mode Locked (FDML) Lasers
摘要： Fourier domain mode locked (FDML) ?ber lasers are broadband wavelength-swept ring systems with record sweep speeds. Lasing is achieved by synchronizing the roundtrip time of the optical ?eld in the ?ber delay cavity with the sweep period of a tunable Fabry-P′erot (FP) bandpass ?lter. Since their invention in 2006, FDML lasers have dramatically enhanced the capabilities of optical coherence tomography (OCT) and various sensing applications. However, the physical coherence limits, such as the maximum achievable coherence length, are yet unknown. An important breakthrough in reaching this limit is a recently experimentally demonstrated highly coherent operation mode over a bandwidth of more than 100 nm [1], referred to as the sweet spot. The sweet spot operation mode is characterized by nearly shot-noise limited ?uctuations in the intensity trace of the laser with signi?cantly enhanced coherence properties, whereas in conventional FDML laser systems the intensity trace is distorted by high frequency noise which negatively affects the coherence length. This ultra-low noise operating regime was generated by an almost perfect compensation of the ?ber dispersion with a manually ?ne tuned chirped ?ber Bragg grating and a highly synchronized sweep rate of the FP ?lter with an accuracy in the range of mHz. Polarization effects were controlled with a polarization maintaining semiconductor optical ampli?er (SOA) gain medium and a polarization controller.
关键词： Fourier domain mode locked (FDML) lasers,sweet spot operation mode,coherence length,semiconductor optical amplifier (SOA),polarization controller,optical coherence tomography (OCT)
更新于2025-09-11 14:15:04