Passive Mode-locking Regime Research Articles

Coherence Recovery in a Hybrid Partially Mode Locked III-V-on-Silicon Laser

We analyse the spectral properties of an optical frequency comb emitted by a III-V-on-silicon ring laser operated in the hybrid mode-locking regime. We demonstrate that the mode-locked laser has disparate responses to an external RF modulation depending on the saturable absorber bias and pump current. Firstly, we show that, when the mode-locking is fully achieved, the hybrid operation maintains the full mode-locking characteristics across the whole locking region. Secondly, starting from an incomplete passive mode-locking regime, and using the modulation frequency as a control parameter, we demonstrate the gradual improvement of the mode-locking characteristics within the locking tongue. This effect is maximized at the RF locking tongue boundary and manifests in an increase of the spectral width and a diminution of the modal linewidth dispersion.

Single-cycle-pulse generation in a coherently mode-locked laser with an ultrashort cavity

We theoretically investigate the possibility of a passive mode-locking regime in a two-section laser with an ultrashort cavity of the length around ten wavelengths of the medium resonant transition or even less. It is shown that such a regime is enabled through the coherent mode-locking phenomena arising due to the self-induced transparency when the gain and absorption bandwidths do not impose any restrictions on the duration of the generated pulse. Under such conditions, a laser with an ultrashort cavity could produce output pulses with the terahertz (THz) repetition rate and the duration up to a single optical cycle. Moreover, several scaling rules were derived, which allow for further shortening of the output pulse duration with the respective scaling of the media parameters.

Passive mode-locking operation of a diode-pumped Tm:YAG laser with a MoS2 saturable absorber

In this paper, we demonstrate the first passive mode-locking operations of a diode-pumped Tm:YAG laser with a MoS2 saturable absorber. In the absence of a MoS2 saturable absorber, the Tm:YAG laser produced a 2.68 W continuous-wave (CW) output power at 2013.8 nm. Under passive mode-locking regime, a maximum average output power of 0.2 W at a pulse repetition rate of 232.2 MHz and a pulse width of about 280 ps were achieved in the experiment. In addition, the near-diffraction limited beam qualities of the CW Tm:YAG laser were achieved.

Optical shutters for a compact femtosecond Yb:KYW laser

A stable passive mode-locking regime for a Yb3+ :KY(WO4)2 laser with optical pumping by a continuous diode laser was obtained using two types of optical shutter with a saturable absorber based on coupled GaAs/In0.25Ga0.75As/GaAs quantum wells. The shutters differed in their reflecting part: the first type was a semiconductor mirror and the second type was a dielectric one. The typical parameters of the mode-locking regime were as follows: a pulse duration of about 200 fs for both types of shutter, an average power of 2.54 W for the all-semiconductor shutter (SESAM) and 0.92 W for the dielectric mirror with a saturable absorber (DSAM). The efficiency relative to the incident pump power was 57% for the SESAM and 19% for the DSAM. The maximum pulse repetition rate was 982 MHz. The measured recovery time was about 2 ps for both saturable absorbers. The mirror damage threshold estimate for the SESAM was at least 8.87 mJ cm−2.

Mode-Locked Lasers with “Thin” Quantum Wells in 1.55 μm Spectral Range

We present the results of an experimental study of two-section semiconductor lasers with active region consisting of three 3.1 nm InGaAs/InGaAlAs quantum wells. Passive mode-locking regime with a repetition rate of 10 GHz is realized. Different approaches have been compared to determine the stability of pulse repetition.

Синхронизация мод в лазерах спектрального диапазона 1.55 mum на основе "тонких" квантовых ям

AbstractWe present the results of an experimental study of two-section semiconductor lasers with active region consisting of three 3.1 nm InGaAs/InGaAlAs quantum wells. Passive mode-locking regime with a repetition rate of 10 GHz is realized. Different approaches have been compared to determine the stability of pulse repetition.

1 GHz InP on-chip monolithic extended cavity colliding-pulse mode-locked laser.

A record low-repetition rate from an on-chip monolithic InP extended cavity colliding-pulse mode-locked laser is experimentally reported. The device, fabricated in generic InP-based active-passive integration technology, makes use of integrated mirrors to enable its use as a building block within a photonic integrated circuit. This structure allows us to generate an electrical frequency comb with mode spacing of 1GHz, determined by the 40.5mm long resonator. Passive and hybrid mode-locking regime conditions are experimentally demonstrated. In the passive regime, an electrical beat tone at the fundamental repetition rate with an electrical linewidth (LW) of 398kHz and a signal-to-noise ratio (SNR) >30 dB is measured. In the hybrid regime, the optical comb is locked to a continuous wave signal source, improving the LW of the generated signal and the SNR>40 dB.

Amplitude and Phase Noise of Frequency Combs Generated by Single-Section InAs/InP Quantum-Dash-Based Passively and Actively Mode-Locked Lasers

We investigate the amplitude and phase noise of an optical frequency comb based on InAs/InP quantum-dash mode-locked laser. The laser demonstrates low relative intensity noise (< −125 dB/Hz) and phase noise in the passive mode-locking regime. By actively mode-locking the laser, we observe a reduction in the flicker FM noise and timing jitter, as a result of which the optical linewidth decreases, and hence the effective bandwidth compatible with optical coherent systems increases by more than 50% to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 1.1$ </tex-math></inline-formula> THz.

A 40-GHz Colliding Pulse Mode-Locked Semiconductor Laser**Supported by the National Natural Science Foundation of China under Grant Nos 61335009, 61274046 and 61474111.

A monolithically active-passive integrated colliding pulse mode-locked semiconductor laser is demonstrated in the InGaAsP/InP material system. The device is mode locked at the second harmonic passive mode-locking regime with a wide mode-locking range. Pulse trains with the repetition rate of 40 GHz, 3-dB rf line width of 25 kHz, the pulse width of 2.5 ps, and a nearly transform-limited time-bandwidth product of 0.53 are obtained.

Wavelength-tunable prism-coupled external cavity passively mode-locked quantum-dot laser**Project supported by the National Natural Science Foundation of China (Grant No. 61274072) and the National High Technology Research and Development Program of China (Grant No. 2013AA014201).

A wavelength-tunable mode-locked quantum dot laser using an InAs/GaAs quantum-dot gain medium and a discrete semiconductor saturable absorber mirror is demonstrated. A dispersion prism, which has lower optical loss and less spectral narrowing than a blazed grating, is used for wavelength selection and tuning. A wavelength tuning range of 45.5 nm (from 1137.3 nm to 1182.8 nm) under 140-mA injection current in the passive mode-locked regime is achieved. The maximum average power of 19 mW is obtained at the 1170.3-nm wavelength, corresponding to the single pulse energy of 36.5 pJ.

Monolithically integrated 2.5 GHz extended cavity mode-locked ring laser with intracavity phase modulators.

A mode-locked extended cavity quantum well ring laser at 1.58μm with a repetition rate of 2.5GHz in the form of a photonic integrated circuit is presented. The device is realized using InP-based active-passive integration technology. The 33mm long cavity contains gain, saturable absorption, and passive waveguide sections as well as phase shifter sections to enable fine tuning of the spectral position of the lasing modes. Passive and hybrid mode-locked operation, along with the wavelength tuning of the laser modes, are experimentally demonstrated. In the passive mode-locking regime, a beat signal at the fundamental round trip frequency with a 3dB bandwidth of 6.1kHz is produced on a fast photo diode.

Continuously tunable Yb:KYW femtosecond oscillator based on a tunable highly dispersive semiconductor mirror.

The optimized nonuniform growth process was used to achieve spatially dependent reflectivity and dispersions characteristics in a highly dispersive semiconductor mirror. The mirror, together with a semiconductor saturable absorber mirror (SESAM), was used to demonstrate a tunable femtosecond Yb:KYW oscillator. In the passive modelocking regime the laser could be continuously tuned over 3.5 nm spectral band around 1032 nm with high resolution, maintaining the average output power above 140 mW.

Ultra-fast solitons in a long cavity multi-mode-fiber-based graphene mode-locked fiber laser with high slope efficiency

A few-layer graphene saturable absorber-based multi-mode fiber is used in a long-cavity fiber laser for passive mode-locking pulse generation. The saturable absorber has a large light–graphene interaction area, which increases its tolerance to pulse energy and decreases its saturable absorption threshold. The long-cavity fiber laser proposed has a high slope efficiency of ∼8.14%, and when the pumped power is increased to ∼355 mW, the laser can still operate at passive mode-locking regime with a high output power of ∼27.28 mW. The output pulses have the pulse energy of ∼3.2 nJ, pulse width of ∼883.9 fs, repetition rate of 8.5 MHz, and central wavelength of 1563.5 nm. Such a fiber laser has potential applications in optical communication, microsurgery and laser micromachining.

Broad wavelength tunability from external cavity quantum-dot mode-locked laser

Broadband wavelength tunability over 136 nm (between 1182.5 nm and 1319 nm) of picosecond pulses in passive mode-locked regime is demonstrated in a multi-section quantum-dot laser in external cavity configuration at room temperature. The maximum peak power of 870 mW with 15 ps pulse duration was achieved at 1226 nm wavelength.

Bandwidth optimization of a Carbon Nanotubes mode-locked Erbium-doped fiber laser

We present a new method to fabricate thin films using single-walled Carbon Nanotubes (SWCNT) and a urethane-based transparent polymer. We construct an Erbium-doped fiber laser to test our films as saturable absorbers to work as passive mode-locker. As results, pulse-trains were achieved and we carried on an optimization study involving total cavity dispersion, absorption strength of thin films incorporating SWCNT and laser bandwidth to produce broad bandwidths in passive mode-locking regime.

Comparison of the noise performance of 10 GHz repetition rate quantum-dot and quantum well monolithic mode-locked semiconductor lasers

Mode-locked lasers are commonly used in carrier-wave signal generation systems because of their excellent phase noise performance. Owing to the importance of this key parameter, this study presents a like-for-like comparison of the noise performance of the passive mode-locked regime of two devices fabricated with different material gain systems, one quantum well and the other quantum dot (QD), both with a monolithic all-active two-section mode-locked structure. Two important factors are identified as having a significant effect on the noise performance, the RF linewidth of the first harmonic and the shape of the noise pedestals, both depending on the passive mode-locked bias conditions. Nevertheless, the dominant contribution of the RF linewidth to the phase noise, which is significantly narrower for the QD laser, makes this material more suitable for optical generation of low-noise millimetre-wave carrier frequencies.

Features of mode locking in laser with quantum well in broad waveguide layer

Passive mode locking (PML) regimes in two-section lasers with quantum wells in broad waveguides operating at λ = 1.06 μm have been studied. The room temperature spectrum of the saturable absorber section retains exciton peak at the absorption edge, which decreases in amplitude shifts toward longer wavelengths by 18 meV when the reverse bias voltage is varied from 0 to 14 V. The PML regime is observed at relatively large voltages (above 9 V) that are necessary to compensate for the effect of band broadening in the gain section by the Stark shift of absorption in the reversely biased section. The PML regime exists, beginning with threshold values of the pumping current, and is characterized by a narrow RF signal with a 20-kHz linewidth. As the reverse bias voltage on the absorber section is increased, a low-frequency amplitude modulation superimposes on the mode-locked laser radiation.

CW and femtosecond operation of a diode-pumped Yb:BaY_2F_8 laser

We report for the first time on laser action of a diode-pumped Yb:BaY(2)F(8) crystal. Both CW and femtosecond operations have been demonstrated at room-temperature conditions. A maximum output power of 0.56 W, a slope efficiency of 34%, and a tunability range from 1013 to 1067 nm have been obtained in CW regime. Transform-limited pulse trains with a minimum duration of 275 fs, an average power of 40 mW, and a repetition rate of 83 MHz have been achieved in a passive mode-locked regime using a semiconductor saturable absorber mirror.

New ytterbium-phosphate glass for diode-pumped lasers

A new ytterbium laser glass based on an alumoborophosphate composition is developed. It is shown that the chemical and thermal stabilities of this glass are record-high for phosphate glasses and that its spectral and luminescent characteristics compare well with popular laser glasses. A mould of laser-quality glass doped with ytterbium with a concentration of 5×1020 cm-3 is synthesised. Active laser elements 5×5×2 mm in size are prepared from this glass for longitudinal diode pumping. These elements were used to fabricate a laser, whose output power in the cw regime reached 783 mW and maximum slope efficiency was 28.9%. Pulses with a duration of ∼150 fs and a peak power of about 5 kW are obtained in the passive mode-locking regime.

Luminescent and lasing characteristics of heavily doped Yb3+:KY(WO4)2 crystals

The luminescence decay times are measured taking into account reabsorption for KY(WO4)2:Yb(KYW:Yb) crystals with atomic concentrations of active ions from 0.2% to 30%. The radiative lifetime of Yb3+ ions was measured to be 233 μs. The cw output power of 1.46 and 1.62 W was achieved with the slope efficiency 52% and 47% for Yb:KYW lasers with the atomic concentration of Yb3+ ions equal to 10% and 30%, respectively. Using a semiconductor mirror with a saturable absorber (SESAM) in the passive mode-locking regime, pulses of duration 194 and 180 fs were obtained at wavelengths of 1042 and 1039 nm for crystals with Yb3+ concentrations equal to 10% and 30%, respectively, the average output power being 0.63 and 0.75 W.