Hyoji Kim

Timing jitter optimization of mode-locked Yb-fiber lasers toward the attosecond regime

We demonstrate ultra-low timing jitter optical pulse trains from free-running, 80 MHz repetition rate, mode-locked Yb-fiber lasers. Timing jitter of various mode-locking conditions at close-to-zero intracavity dispersion (-0.004 to +0.002 ps(2) range at 1040 nm center wavelength) is characterized using a sub-20-attosecond-resolution balanced optical cross-correlation method. The measured lowest rms timing jitter is 175 attoseconds when integrated from 10 kHz to 40 MHz (Nyquist frequency) offset frequency range, which corresponds to the record-low timing jitter from free-running mode-locked fiber lasers so far. We also experimentally found the mode-locking conditions of fiber lasers where both ultra-low timing jitter and relative intensity noise can be achieved.

Sub-100-as timing jitter optical pulse trains from mode-locked Er-fiber lasers

We demonstrate sub-100-as timing jitter optical pulse trains generated from free-running, 77.6 MHz repetition-rate, mode-locked Er-fiber lasers. At -0.002(±0.001) ps2 net cavity dispersion, the rms timing jitter is 70 as (224 as) integrated from 10 kHz (1 kHz) to 38.8 MHz offset frequency, when measured by a 24 as resolution balanced optical cross correlator. To our knowledge, this result corresponds to the lowest rms timing jitter measured from any mode-locked fiber lasers so far. The measured result also agrees fairly well with the Namiki-Haus analytic model of quantum-limited timing jitter in stretched-pulse fiber lasers.

Reduction of timing jitter and intensity noise in normal-dispersion passively mode-locked fiber lasers by narrow band-pass filtering.

Fiber lasers mode-locked with normal cavity dispersion have recently attracted great attention due to large output pulse energy and femtosecond pulse duration. Here we accurately characterized the timing jitter of normal-dispersion fiber lasers using a balanced cross-correlation method. The timing jitter characterization experiments show that the timing jitter of normal-dispersion mode-locked fiber lasers can be significantly reduced by using narrow band-pass filtering (e.g., 7-nm bandwidth filtering in this work). We further identify that the timing jitter of the fiber laser is confined in a limited range, which is almost independent of cavity dispersion map due to the amplifier-similariton formation by insertion of the narrow bandpass filter. The lowest observed timing jitter reaches 0.57 fs (rms) integrated from 10 kHz to 10 MHz Fourier frequency. The rms relative intensity noise (RIN) is also reduced from 0.37% to 0.02% (integrated from 1 kHz to 5 MHz Fourier frequency) by the insertion of narrow band-pass filter.

Sub-20-Attosecond Timing Jitter Mode-Locked Fiber Lasers

We demonstrate 14.3-attosecond timing jitter [integrated from 10 kHz to 94 MHz offset frequency] optical pulse trains from 188-MHz repetition-rate mode-locked Yb-fiber lasers. In order to minimize the timing jitter, we shorten the non-gain fiber length to shorten the pulsewidth and reduce excessive higher-order nonlinearity and nonlinear chirp in the fiber laser. The measured jitter spectrum is limited by the amplified spontaneous emission limited quantum noise in the 100 kHz-1 MHz offset frequency range, while it was limited by the relative intensity noise-converted jitter in the lower offset frequency range. This intrinsically low timing jitter enables sub-100-attosecond synchronization between the two mode-locked Yb-fiber lasers over the full Nyquist frequency with a modest 10-kHz locking bandwidth. The demonstrated performance is the lowest timing jitter measured from any free-running mode-locked fiber lasers, comparable to the performance of the lowest-jitter Ti:sapphire solid-state lasers.

Gigahertz repetition rate, sub-femtosecond timing jitter optical pulse train directly generated from a mode-locked Yb:KYW laser

We show that a 1.13 GHz repetition rate optical pulse train with 0.70 fs high-frequency timing jitter (integration bandwidth of 17.5 kHz-10 MHz, where the measurement instrument-limited noise floor contributes 0.41 fs in 10 MHz bandwidth) can be directly generated from a free-running, single-mode diode-pumped Yb:KYW laser mode-locked by single-wall carbon nanotube-coated mirrors. To our knowledge, this is the lowest-timing-jitter optical pulse train with gigahertz repetition rate ever measured. If this pulse train is used for direct sampling of 565 MHz signals (Nyquist frequency of the pulse train), the jitter level demonstrated would correspond to the projected effective-number-of-bit of 17.8, which is much higher than the thermal noise limit of 50 Ω load resistance (~14 bits).

1.13-GHz Repetition Rate, Sub-Femtosecond Timing Jitter, CNT-Mode-Locked Ultrafast Yb:KYW Laser

We show 1.13-GHz repetition rate, 0.70-fs timing jitter optical pulse train directly generated from diode-pumped, CNT-mode-locked Yb:KYW laser. The measured jitter is the lowest for GHz pulse trains, and is suitable for high-resolution analog-to-digital conversion.

Timing jitter reduction in self-similar Yb-fiber lasers via narrow intra-cavity bandpass filtering

Timing jitter reduction in self-similar Yb-fiber lasers is achieved by intra-cavity bandpass filtering. The laser changes from self-similar to dissipative soliton regime, while the timing jitter is reduced from 14.6-fs to 2.8-fs [10 kHz-30 MHz].

Progress in ultrafast fiber lasers for ultralow-jitter signal sources

We introduce the most recent progress in the optimization of ultrafast fiber lasers for building ultralow timing jitter signal sources. Using a sub-20-attosecond-resolution timing jitter measurement technique, we optimize the timing jitter of optical pulse trains from mode-locked Er-fiber and Yb-fiber lasers to 70 attoseconds and 175 attoseconds, respectively, when integrated from 10 kHz to 40 MHz offset frequency. To our knowledge, these results correspond to the lowest rms timing jitter demonstrated from fiber lasers so far, the equivalent phase noise of which is comparable to that of the best microwave sources available, with much reduced cost and engineering complexity.

Ultra-low timing and intensity noise from mode-locked Yb-fiber lasers at close-to-zero intra-cavity dispersion

We demonstrate ultra-low timing and intensity noise from mode-locked Yb-fiber lasers. The measured rms timing jitter and relative intensity noise are 187 attoseconds and 0.057 %, respectively, integrated from 10 kHz to 40 MHz.