Publications by authors named "Youjian Song"

40 Publications

Orbital-angular-momentum-resolved diagnostics for tracking internal phase evolution in multi-bound solitons.

Opt Express 2021 May;29(11):16686-16694

The generation of multi-bound solitons is a fascinating subject of investigation in many conservative and dissipative systems, such as photonics, fluid mechanics, Bose-Einstein condensates, and so on. In this study, we demonstrate the successful extraction of phase dynamics between solitons in bound multiple solitons with up to seven constituents in a mode-locked Er laser system. By mapping the internal phase motions of multi-bound solitons to the spatial phase movement of cylindrical vector beams using orbital angular momentum (OAM)-based diagnostics, different categories of internal pulsations are revealed. We show that bound state of four solitons exhibits linear drifting relative phase evolution dynamics; while for bound multiple solitons with constituents from five to seven pulses, stationary relative phase dynamics are observed. These findings highlight the possibility of the OAM-based method access to the internal motion of multi-soliton molecules with more freedom of degrees and fuel the analogy with research on chemistry molecule complex.
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http://dx.doi.org/10.1364/OE.424602DOI Listing
May 2021

Route to stable dispersion-managed mode-locked Yb-doped fiber lasers with near-zero net cavity dispersion.

Opt Express 2020 Sep;28(20):29766-29774

We numerically investigate the stability of a dispersion-managed mode-locked Yb-doped fiber laser of near-zero net cavity dispersion. The instability is primarily due to the filtering effect of the chirped fiber Bragg grating. The size of the unstable region is dependent on the modulation depth of the saturable absorbers. At modulation depth higher than 30%, stable mode-locking can operate throughout the dispersion region. Based on the simulation results, stable mode-locking around zero cavity dispersion is experimentally viable by a SESAM with a 34% modulation depth. The fiber laser can generate laser pulses with a 17-nm spectral bandwidth and a 139-fs dechirped pulse duration.
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http://dx.doi.org/10.1364/OE.403456DOI Listing
September 2020

Optical frequency comb noise spectra analysis using an asymmetric fiber delay line interferometer.

Opt Express 2020 Mar;28(7):9232-9243

A simple and practical apparatus enabling repetition rate (frep) noise, carrier-envelope frequency (fceo) noise and n optical comb mode (νn) noise spectra measurements with high precision is established. The frep and νn noise spectra are measured by a fiber delay line interferometer, while fceo noise spectrum is measured by an f-2f interferometer. We utilize this apparatus to characterize the noise performance of an Er-fiber optical frequency comb (OFC) and analyze the origin of dominant noise sources. Moreover, this apparatus provides a powerful tool for diagnosing noise dynamics intrinsic in mode-locked lasers and OFCs. To this end, we uncover the anti-correlation between frep and fceo noise as well as the impact of servo loops on noise characteristics in the stabilized OFC.
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http://dx.doi.org/10.1364/OE.386231DOI Listing
March 2020

Pulse dynamics manipulation by the phase bias in a nonlinear fiber amplifying loop mirror.

Opt Express 2019 May;27(10):14705-14715

Pulse dynamics controlling is of great importance for high quality pulse generation in ultra-short pulse fiber lasers. The pulse quality characteristics in terms of pulse duration, energy, chirp profile, tunability, as well as noise feature substantially depend on intracavity pulse propagation dynamics. Here we found that a nonlinear amplifying loop mirror mode-locked thulium-doped fiber laser can switch among enabling operation conventional soliton, stretched-pulse soliton and dissipative soliton regimes only by manipulating an intracavity phase bias device. This provides a simple approach to tailoring ultra-short laser characteristics to different applications.
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http://dx.doi.org/10.1364/OE.27.014705DOI Listing
May 2019

Timing jitter reduction through relative intensity noise suppression in high-repetition-rate mode-locked fiber lasers.

Opt Express 2019 Apr;27(8):11273-11280

We reported the timing jitter reduction of an 882 MHz mode-locked NPE Yb:fiber lasers through active relative intensity noise suppression. The timing jitter spectra measurements based on balanced optical cross-correlation (BOC) technique show a reduction of ~10 dB in the Fourier frequency range from ~3 kHz to ~30 kHz with a unity-gain crossing point of 80 kHz. The results verify the theoretical prediction that the relative intensity noise (RIN) induced timing jitter by self-steepening effect dominates the jitter performance below ~100 kHz. Further comparison with the analytic model shows that the effect of RIN decays below ~3 kHz. Thus, the timing jitter reduction is not obvious at low frequency. To the best of our knowledge, this is the first experimental report on the timing jitter reduction through active RIN suppression in high-repetition-rate mode-locked fiber lasers.
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http://dx.doi.org/10.1364/OE.27.011273DOI Listing
April 2019

Intracavity cylindrical vector beam generation from all-PM Er-doped mode-locked fiber laser.

Opt Express 2019 Mar;27(6):8808-8818

We demonstrate a practical method that is used to generate on-demand first- and higher-order cylindrical vector beams, in the 1550 nm band, directly from an all polarization maintaining mode-locked Er-fiber laser. On demand typical 1st order CVBs, including the radially and azimuthally polarized beams, can be easily achieved by properly adjusting the angle of a half-wave plate with respect to the fast axis of the vortex wave plate. The spatial beam mode can be flexibly switched with no disturbance on the time domain mode-locking output. The laser outputs the desired vector beams at 1571 nm with a spectral bandwidth at full-width at half-maximum of 32 nm. The mode-locked laser pulses have a repetition rate of 74.9 MHz. Moreover, the proposed method can be easily extended to create higher-order CVBs. Our research provides a convenient way to generate ultrafast pulses in highly flexible-controlled structured modes, which is essential for optical fabrication and light trapping applications.
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http://dx.doi.org/10.1364/OE.27.008808DOI Listing
March 2019

Active f-to-2f interferometer for record-low jitter carrier-envelope phase locking.

Opt Lett 2019 Feb;44(4):1060-1063

The f-to-2f interferometer plays a key role for carrier-envelope phase (CEP) measurement and subsequent stabilization. The CEP measurement typically relies on the application of two optical nonlinearities, namely supercontinuum generation and second-harmonic generation. Then the cascadation of these nonlinearities often leads to signal levels on the order of a few photons per pulse. We experimentally demonstrate that the introduction of optical gain into the infrared arm of an f-to-2f interferometer can mitigate this detection bottleneck and improve signal-to-noise ratios by 20 dB compared to purely passive schemes. We further show that this measure allows for residual phase jitters between the carrier and envelope of about 10 mrad, corresponding to record-breaking timing jitters in the single attosecond regime. Moreover, the method appears generally applicable to a wide range of oscillators in the near-infrared and may enable stable CEP locking of mode-locked oscillators that so far have resisted stabilization. Finally, we propose a parametric variant of the active f-to-2f interferometer that can be used for laser amplifiers with kilohertz repetition rates and below.
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http://dx.doi.org/10.1364/OL.44.001060DOI Listing
February 2019

All-polarization-maintaining dual-wavelength mode-locked fiber laser based on Sagnac loop filter.

Opt Express 2018 Oct;26(22):28302-28311

We demonstrate an all polarization-maintaining (PM) fiber based dual-wavelength mode-locked Er-fiber laser. A nonlinear amplifying loop mirror (NALM) with an intracavity nonreciprocal phase shifter is used for self-started mode-locking. A short segment of PM fiber is angle-spliced to the NALM, functioning as a PM Sagnac loop filter, thus enabling dual-wavelength mode-locking. The wavelength separation is solely determined by the angle-spliced PM fiber length. Stable dual-wavelength mode-locking operation is switchable between 1570/1581 nm and 1581/1594 nm. The two-color pulse trains oscillating in the same cavity have an inherent offset repetition rate of ~1 kHz owing to cavity dispersion, allowing future high precision dual-comb applications with a simple and robust configuration.
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http://dx.doi.org/10.1364/OE.26.028302DOI Listing
October 2018

Femtosecond laser pulse generation with self-similar amplification of picosecond laser pulses.

Opt Express 2018 Oct;26(20):26411-26421

Compressing picosecond laser pulses to the femtosecond level is an attractive shortcut for obtaining femtosecond laser pulses. However, dechirped pulses generated by nonlinear compression with self-phase modulation (SPM) show obvious pedestals, which are induced by nonlinear chirp accumulation in spectral broadening process and cannot be easily suppressed. Here, we report systematic numerical simulations and experimental studies on self-similar amplification of picosecond pulses in a short gain fiber for obtaining ~100-fs laser pulses with nearly transform-limited (TL) temporal quality. It is demonstrated that self-similar amplification with picosecond seed pulses is only sensitive to pulse duration and pulse energy. Based on this optimization guideline, we built a compact self-similar amplification fiber system with a picosecond fiber laser as the seed source. This system outputs 66-fs pulses with 6.1-W average power at a repetition rate of 30 MHz. Due to the linear chirp produced in self-similar evolution process, compressed pulses show nearly TL temporal quality. It promises an efficient way of obtaining high-quality femtosecond laser pulses from a picosecond laser source.
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http://dx.doi.org/10.1364/OE.26.026411DOI Listing
October 2018

Timing jitter of high-repetition-rate mode-locked fiber lasers.

Opt Lett 2018 Sep;43(18):4382-4385

We characterize the timing jitter of the pulse trains from 880 MHz Yb-doped nonlinear polarization rotation mode-locked fiber lasers based on a balanced optical cross-correlation method. Jitter spectral density at different net-cavity dispersions has been characterized, and the near-zero dispersion shows the lowest rms timing jitter (10 fs rms, integrated from 30 kHz to 5 MHz). The measurements have been compared with analytical models. The comparison shows that the RIN-coupled timing jitter by nonlinearity is the dominated origin of the measured timing jitter below ∼100  kHz, while amplified spontaneous emission noise makes a major contribution in the high frequency range above hundreds of kilohertz. To the best of our knowledge, this is the first high-precision timing jitter characterization for the ∼gigahertz level repetition rate mode-locked fiber lasers. The results will be of great importance for further improving the laser performance for many applications.
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http://dx.doi.org/10.1364/OL.43.004382DOI Listing
September 2018

High-detectivity optical heterodyne method for wideband carrier-envelope phase noise analysis of laser oscillators.

Opt Lett 2018 Jul;43(13):3108-3111

Broadband characterization of the carrier-envelope phase (CEP) noise spectral density of free-running mode-locked lasers is essential for advanced low-noise optical frequency comb designs. Here we present a direct method that utilizes an optical heterodyne beat between a pair of repetition-rate-locked mode-locked lasers for CEP noise characterization, without requiring an f-2f interferometer or nonlinear optical conversion steps. A proof-of-principle experiment in a femtosecond Yb-fiber laser achieves CEP noise spectral density characterization with >270  dB dynamic range over a Fourier frequency range from 5 mHz to 8 MHz. The measurement noise floor is well below 1  μrad/√Hz, enabling dependable detection down to a quantum-limited noise floor. The method can resolve various noise mechanisms that cause specific CEP noise spectral shapes. The underlying mechanisms are further analyzed in terms of spurious temporal correlation to distinguish between technical and stochastic noise signatures. Moreover, a Hadamard deviation analysis reveals a varying degree of frequency stability in the measured CEP time series.
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http://dx.doi.org/10.1364/OL.43.003108DOI Listing
July 2018

Single-polarization large-mode-area fiber laser mode-locked with a nonlinear amplifying loop mirror.

Opt Lett 2018 Jun;43(12):2848-2851

The generation of high-power ultrashort pulses from a passively mode-locked fiber laser is reported based on the combination of a single-polarization large-mode-area (LMA) photonic crystal fiber with a nonlinear amplifying loop mirror design. The introduction of a non-reciprocal phase shift in the loop mirror enables self-starting of the mode-locked laser, while the polarizing LMA fiber supports environmentally stable high-power operation. Mode locking in the soliton-like, stretched-pulse, and all-normal-dispersion regime is characterized. The laser generates stable pulses with up to 2 W average power at a 72 MHz repetition rate, corresponding to a single-pulse energy of 28 nJ. The output pulses are dechirped to a near transform-limited duration of 152 fs. The proposed fiber oscillator presents an alternative approach to high-power ultrafast laser sources, along with environmental stability.
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http://dx.doi.org/10.1364/OL.43.002848DOI Listing
June 2018

Dual-comb spectroscopy with a single free-running thulium-doped fiber laser.

Opt Express 2018 Apr;26(8):11046-11054

We demonstrate dual-comb spectroscopy in the vicinity of 2 µm wavelength based on a single dual-wavelength dual-comb Thulium-doped fiber laser. The shared laser cavity ensures passively maintained mutual coherence between the two combs due to common mode environmental noise rejection. In a proof-of-principle experiment, the absorption characteristics caused by the water in the optical path that composes the dual-comb spectrometer are measured. The retrieved spectral positions of the water absorption dips match with the HITRAN database.
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http://dx.doi.org/10.1364/OE.26.011046DOI Listing
April 2018

Observation of subfemtosecond fluctuations of the pulse separation in a soliton molecule.

Opt Lett 2018 Apr;43(7):1623-1626

In this work, we study the timing instability of a scalar twin-pulse soliton molecule generated by a passively mode-locked Er-fiber laser. Subfemtosecond precision relative timing jitter characterization between the two solitons composing the molecule is enabled by the balanced optical cross-correlation (BOC) method. Jitter spectral density reveals a short-term (on the microsecond to millisecond timescale) random fluctuation of the pulse separation even in the robust stationary soliton molecules. The root-mean-square (rms) timing jitter is on the order of femtoseconds depending on the pulse separation and the mode-locking regime. The lowest rms timing jitter is 0.83 fs, which is observed in the dispersion managed mode-locking regime. Moreover, the BOC method has proved to be capable of resolving the soliton interaction dynamics in various vibrating soliton molecules.
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http://dx.doi.org/10.1364/OL.43.001623DOI Listing
April 2018

Intensity and temporal noise characteristics in femtosecond optical parametric amplifiers.

Opt Express 2017 Dec;25(25):31263-31272

We characterize the relative intensity noise (RIN) and relative timing jitter (RTJ) between the signal and pump pulses of optical parametric amplifiers (OPAs) seeded by three different seed sources. Compared to a white-light continuum (WLC) seeded- and an optical parametric generator (OPG) seeded OPA, the narrowband CW seeded OPA exhibits the lowest root-mean-square (RMS) RIN and RTJ of 0.79% and 0.32 fs, respectively, integrated from 1 kHz to the Nyquist frequency of 1.25 MHz. An improved numerical model based on a forward Maxwell equation (FME) is built to investigate the transfers of the pump and seed's noise to the resulting OPAs' intensity and temporal fluctuation. Both the experimental and numerical study indicate that the low level of noise from the narrowband CW seeded OPA is attributed to the elimination of the RIN and RTJ coupled from the noise of seed source, being one of the important contributions to RIN and timing jitter in the other two OPAs. The approach to achieve lower level of noise from this CW seeded OPA by driving it close to saturation is also discussed with the same numerical model.
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http://dx.doi.org/10.1364/OE.25.031263DOI Listing
December 2017

Noise characteristics of high power fiber-laser pumped femtosecond optical parametric generation.

Opt Express 2017 Oct;25(20):24594-24603

We study, both numerically and experimentally, the relative intensity noise (RIN) and timing jitter characteristics of optical parametric generation (OPG) process in MgO-doped periodically poled LiNbO (MgO:PPLN) pumped by fiber femtosecond laser. We directly characterize the RIN, and measure timing jitter spectral density of the OPG process based on the balanced optical cross-correlator (BOC) technique for the first time as well, which are both in a fairly good agreement with numerical simulation. Both the numerical and experimental study reveals that OPG can suffer from a smaller intensity fluctuation but a lager temporal jitter when it is driven into saturation. Furthermore, we demonstrate that with a 30 mW CW diode laser injection seeding the OPG output results in superior noise performance compared to the vacuum fluctuations seeded OPG.
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http://dx.doi.org/10.1364/OE.25.024594DOI Listing
October 2017

Intensity noise suppression in mode-locked fiber lasers by double optical bandpass filtering.

Opt Lett 2017 Oct;42(20):4095-4098

We show that the relative intensity noise (RIN) of a mode-locked fiber laser can be suppressed below a -140  dB/Hz level for the entire >20  Hz offset frequency range by a proper combination of intra-cavity and extra-cavity optical bandpass filters. When a 12-nm-bandwidth intra-cavity filter and a 16-nm-bandwidth extra-cavity filter are employed for a polarization-maintaining-nonlinear-amplifying-loop-mirror (PM-NALM)-based Er-fiber laser, the RIN spectrum level is suppressed by ∼30  dB in the low offset frequency range. The resulting integrated rms RIN is only 0.0054% [1 Hz-1 MHz]-to our knowledge, one of the lowest integrated RIN performances for any mode-locked laser reported so far. Besides the simplicity, this double-filtering approach has an additional advantage: unlike active pump-laser feedback methods, it does not have any resonant peaks in the stabilized RIN spectrum. In addition to the RIN suppression, with intra-cavity bandpass filtering, the integrated rms timing jitter is also reduced from 7.29-fs (no-filter) to 2.95-fs (12-nm intra-cavity filter) [10 kHz-1 MHz] in the soliton PM-NALM laser.
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http://dx.doi.org/10.1364/OL.42.004095DOI Listing
October 2017

Programmable controlled mode-locked fiber laser using a digital micromirror device.

Opt Lett 2017 May;42(10):1923-1926

A digital micromirror device (DMD)-based arbitrary spectrum amplitude shaper is incorporated into a large-mode-area photonic crystal fiber laser cavity. The shaper acts as an in-cavity programmable filter and provides large tunable dispersion from normal to anomalous. As a result, mode-locking is achieved in different dispersion regimes with watt-level high output power. By programming different filter profiles on the DMD, the laser generates femtosecond pulse with a tunable central wavelength and controllable bandwidth. Under conditions of suitable cavity dispersion and pump power, design-shaped spectra are directly obtained by varying the amplitude transfer function of the filter. The results show the versatility of the DMD-based in-cavity filter for flexible control of the pulse dynamics in a mode-locked fiber laser.
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http://dx.doi.org/10.1364/OL.42.001923DOI Listing
May 2017

Practical 24-fs, 1-μJ, 1-MHz Yb-fiber laser amplification system.

Opt Express 2017 Apr;25(7):7559-7566

We develop a practical femtosecond polarization-maintaining fiber laser amplification system with a standard double-cladding fiber technique, enabling 24-fs transform-limited pulses with 1-μJ pulse energy at a 1-MHz repetition rate. The laser system is based on a hybrid amplification scheme. Chirped-pulse amplification is employed in the pre-amplifier stage to supply high-quality pulses with enough energy for the main-amplifier, where nonlinear amplification is utilized to broaden the output spectrum. To obtain a dechirped pulse with high quality and short duration, a pre-shaper is inserted between the two amplification stages to adjust the pre-chirp, central wavelength, and pulse energy of the signal pulses in the main amplifier for optimizing pulse evolution. As a result, temporal pedestal free sub-ten-cycle high-energy laser pulses can be routinely obtained. In the end, the advantages of this novel laser source are demonstrated in the experiments on enhanced damage effect to cells co-cultured with gold nanorods.
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http://dx.doi.org/10.1364/OE.25.007559DOI Listing
April 2017

Excess carrier-envelope phase noise generation in saturable absorbers.

Opt Lett 2017 Mar;42(6):1068-1071

Attosecond spectroscopy and precision frequency metrology depend on the stabilization of the carrier-envelope phase (CEP) of mode-locked lasers. Unfortunately, the phase of only a few types of lasers can be stabilized to jitters in the few-hundred millirad range. In a comparative experimental study, we analyze a femtosecond Ti:sapphire laser and three mode-locked fiber lasers. We numerically demodulate recorded time series of the free-running carrier-envelope beat note. Our analysis indicates a correlation between amplitude and frequency fluctuations at low Fourier frequencies for essentially all lasers investigated. While this correlation typically rolls off at frequencies beyond 100 kHz, we see clear indications for a broadband coupling mechanism in one of the fiber lasers. We suspect that the observed coupling mechanism acts to transfer intracavity power fluctuations into excess phase noise. This coupling mechanism is related to the mode-locking mechanism employed and not to the gain medium itself. We further verify this hypothesis by numerical simulations, which identify resonances of the saturable absorber mirror as a possible explanation for the coupling mechanism. Finally, we discuss how to avoid a detrimental influence of such resonances.
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http://dx.doi.org/10.1364/OL.42.001068DOI Listing
March 2017

Reference-free, high-resolution measurement method of timing jitter spectra of optical frequency combs.

Sci Rep 2017 01 19;7:40917. Epub 2017 Jan 19.

School of Mechanical and Aerospace Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Korea.

Timing jitter is one of the most important properties of femtosecond mode-locked lasers and optical frequency combs. Accurate measurement of timing jitter power spectral density (PSD) is a critical prerequisite for optimizing overall noise performance and further advancing comb applications both in the time and frequency domains. Commonly used jitter measurement methods require a reference mode-locked laser with timing jitter similar to or lower than that of the laser-under-test, which is a demanding requirement for many laser laboratories, and/or have limited measurement resolution. Here we show a high-resolution and reference-source-free measurement method of timing jitter spectra of optical frequency combs using an optical fibre delay line and optical carrier interference. The demonstrated method works well for both mode-locked oscillators and supercontinua, with 2 × 10 fs/Hz (equivalent to -174 dBc/Hz at 10-GHz carrier frequency) measurement noise floor. The demonstrated method can serve as a simple and powerful characterization tool for timing jitter PSDs of various comb sources including mode-locked oscillators, supercontinua and recently emerging Kerr-frequency combs; the jitter measurement results enabled by our method will provide new insights for understanding and optimizing timing noise in such comb sources.
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http://dx.doi.org/10.1038/srep40917DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5244383PMC
January 2017

Quantum-limited timing jitter characterization of mode-locked lasers by asynchronous optical sampling.

Opt Express 2017 Jan;25(1):10-19

We demonstrate a novel time domain timing jitter characterization method for ultra-low noise mode-locked lasers. An asynchronous optical sampling (ASOPS) technique is employed, allowing timing jitter statistics on a magnified timescale. As a result, sub femtosecond period jitter of an optical pulse train can be readily accessible to slow detectors and electronics (~100 MHz). The concept is applied to determine the quantum-limited timing jitter for a passively mode-locked Er-fiber laser. Period jitter histogram is acquired following an eye diagram analysis routinely used in electronics. The identified diffusion constant for pulse timing agrees well with analytical solution of perturbed master equation.
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http://dx.doi.org/10.1364/OE.25.000010DOI Listing
January 2017

Ultra-flat supercontinuum generated from high-power, picosecond telecommunication fiber laser source.

Appl Opt 2016 Nov;55(33):9384-9388

An ultra-flat, high-power supercontinuum generated from a picosecond telecommunication fiber laser was presented. The pulse from a carbon nanotube mode-locked oscillator was amplified using an Er-Yb codoped fiber amplifier. The output of the system achieved an average power of 2.7 W, with the center wavelength at 1564 nm and a FWHM of 6 nm in the spectral domain. By passing this amplified high-power pulse through a 4.6 m highly nonlinear photonic crystal fiber, an ultra-flat supercontinuum spanning 1600-2180 nm is generated. And the average power of the supercontinuum achieves 1 W.
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http://dx.doi.org/10.1364/AO.55.009384DOI Listing
November 2016

Spectral and temporal breathing self-similar evolution in a fiber amplifier for low-noise transform-limited pulse generation.

Opt Lett 2016 Nov;41(22):5286-5289

We demonstrate a simple scheme for high-power low-noise high-contrast ultrashort pulse generation. It is enabled by the spectral and temporal breathing self-similar pulse evolution with an optimized negative pre-chirp. Experiments and simulations indicate the enhanced tolerances of this scheme to the gain-shaping distortions and pump fluctuations. It can lead to ∼16% increase in the compressed pulse quality with more than a two times wider spectrum and ∼31% reduction in the root-mean-square (rms) relative intensity noise (RIN). Transform-limited pulses as short as 36 fs are generated with the rms RIN of 0.029% (1 kHz-5 MHz) from a 2 m Yb-fiber amplifier.
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http://dx.doi.org/10.1364/OL.41.005286DOI Listing
November 2016

Long-term stable coherent beam combination of independent femtosecond Yb-fiber lasers.

Opt Lett 2016 Nov;41(22):5142-5145

We demonstrate coherent beam combination between independent femtosecond Yb-fiber lasers by using the active phase locking of relative pulse timing and the carrier envelope phase based on a balanced optical cross-correlator and extracavity acoustic optical frequency shifter, respectively. The broadband quantum noise of femtosecond fiber lasers is suppressed via precise cavity dispersion control, instead of complicated high-bandwidth phase-locked loop design. Because of reduced quantum noise and a simplified phase-locked loop, stable phase locking that lasts for 1 hour has been obtained, as verified via both spectral interferometry and far-field beam interferometry. The approach can be applied to coherent pulse synthesis, as well as to remote frequency comb connection, allowing a practical all-fiber configuration.
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http://dx.doi.org/10.1364/OL.41.005142DOI Listing
November 2016

Few-femtosecond timing jitter from a picosecond all-polarization-maintaining Yb-fiber laser.

Opt Express 2016 Jan;24(2):1347-57

We characterize the timing jitter of a picosecond all-polarization-maintaining (all-PM) Yb-fiber laser using the optical cross-correlation method. For the 10 MHz all-normal dispersion mode-locked laser with ~0.5 nm spectral bandwidth, the measured high-frequency jitter is as low as 5.9 fs (RMS) when integrated from 10 kHz to the Nyquist frequency of 5 MHz. A complete numerical model with ASE noise is built to simulate the timing jitter characteristics in consideration of intracavity pulse evolution. The mutual comparison among simulation result, analytical model and experiment data indicate that the few femtosecond timing jitter from the picosecond fiber laser is attributed to the complete elimination of Gordon-Haus jitter by narrow bandpass filtering by a fiber Bragg grating (FBG). The low level of timing jitter from this compact and maintenance-free PM picosecond fiber laser source at a low MHz repetition rate is promising to advance a number of femtosecond-precision timing and synchronization applications.
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http://dx.doi.org/10.1364/OE.24.001347DOI Listing
January 2016

Characterization and analysis of timing jitter in normal-dispersion mode-locked Er-fiber lasers with intra-cavity filtering.

Opt Express 2015 Aug;23(17):22898-906

We characterize and analyze the timing jitter of normal-dispersion mode-locked Er-fiber lasers with intra-cavity filtering. The timing jitter of Er-fiber lasers with 9-nm bandpass filters operating at + 0.0084 ps(2) is measured to be 3.46 fs (rms) when integrated from 10 kHz to 10 MHz offset frequency, which is similar to the jitter level of typical stretched-pulse or soliton Er-fiber lasers. The numerical simulation based on split-step Fourier transform method shows that the measured high-frequency jitter is quantum noise-limited performance. We also develop an analytical model for filtered normal-dispersion fiber lasers by modifying the well-established noise model of stretched-pulse fiber lasers. The analytical modeling reveals that the jitter performance is improved mostly by reducing the chirp parameter by intra-cavity filtering. Both numerical simulation and analytical model fit fairly well with the measured timing jitter result.
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http://dx.doi.org/10.1364/OE.23.022898DOI Listing
August 2015

Effect of timing jitter on time-of-flight distance measurements using dual femtosecond lasers.

Opt Express 2015 Jun;23(11):14057-69

The cross correlation between a pair of femtosecond lasers with slightly different repetition rates enables high precision, high update rate time-of-flight (TOF) distance measurements against multiple targets. Here, we investigate the obtainable ranging precision set by the timing jitter from femtosecond lasers. An analytical model governing dual femtosecond laser TOF distance measurement in the presence of pulse train timing jitter is built at first. A numerical study is conducted by involving typical timing jitter sources in femtosecond lasers in the following. Finally, the analytical and numerical models are verified by a TOF ranging experiment using a pair of free running femtosecond Er-fiber lasers. The timing jitter of the lasers is also characterized by an attosecond resolution balanced optical cross correlation method. The comparison between experiment and numerical model shows that the quantum-limited timing jitter of femtosecond lasers sets a fundamental limit on the performance of dual femtosecond laser TOF distance measurements.
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http://dx.doi.org/10.1364/OE.23.014057DOI Listing
June 2015

High power tunable femtosecond ultraviolet laser source based on an Yb-fiber-laser pumped optical parametric oscillator.

Opt Express 2015 Mar;23(5):6181-6

We report a high average power tunable 51 MHz femtosecond ultraviolet (UV) laser source based on an intra-cavity sum frequency mixing optical parametric oscillator (OPO) pumped by a fiber laser. The UV laser is generated by sum frequency generation (SFG) between the second harmonic of a mode-locked Yb-fiber laser and the signal of the OPO. A non-collinear configuration is used in the SFG to compensate the group velocity mismatch, and to increase the SFG conversion efficiency dramatically. Tunable ultraviolet pulses within the wavelength range from 385 to 400 nm have been produced with a maximum average power of 402 mW and a pulse width of 286 fs at 2 W Yb-fiber laser pump, corresponding to 20.1% near-infrared to UV conversion efficiency at 387 nm. To our knowledge, this is the first demonstration of tunable femtosecond UV pulse generation from a fiber laser pumped OPO, and is also the highest average power tunable UV femtosecond pulses from an OPO.
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http://dx.doi.org/10.1364/OE.23.006181DOI Listing
March 2015

On the origin of flicker noise in carrier-envelope phase stabilization.

Opt Lett 2014 Dec;39(24):6989-92

The origin of a 1/f noise contribution in the long-term carrier-envelope phase (CEP) measurements of mode-locked lasers is discussed. Using two different collinear interferometers for the out-of-loop characterization of feed-forward stabilized Ti:sapphire oscillators, we suppress a possible technical origin of 1/f noise to the extent possible. Both measurements indicate a lower limit of CEP frequency noise of 1  mHz/√Hz. Investigating several possible origins of this noise floor, we find a good agreement with a quantum noise mechanism that is directly induced by intracavity-amplified spontaneous emission (ASE). These findings enable direct access to ASE noise in short-pulse oscillators, which is very hard to characterize via repetition rate fluctuations. Finally, we discuss the possible consequences for frequency-comb-based timekeeping and frequency metrology, as well as for attosecond science.
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http://dx.doi.org/10.1364/OL.39.006989DOI Listing
December 2014
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