Characterization of the noise and correlations in harmonically mode-locked lasers

Abstract

In a harmonically mode-locked laser multiple optical pulses propagate inside the laser cavity. The noise in different pulses inside the laser cavity is in general correlated. Information regarding the sign and magnitude of the noise correlations is contained in the distribution of the spectral weight among the supermode noise peaks that appear in the pulse energy and timing noise spectral densities. We show that the supermode noise spectrum obtained experimentally by measurement of the photodetector current noise spectral density can be used to determine the correlations in the energy and the timing noise of different pulses in the laser cavity. We also present simple models for the timing noise in harmonically mode-locked lasers that demonstrate the relationship between the noise correlations and the supermode noise peaks.

Observation of 200th harmonic with fractional linewidth of 10−10 in a microwave frequency comb generated in a tunneling junction

“…18) are used with microwave spectrum analyzers to characterize ultrafast lasers. 19 The frequency comb in a STM is also generated by optical rectification, so studies of the effects of laser noise on photodetection of mode-locked ultrafast laser pulses may be applied to the MFC in a STM. The analysis of photodetection suggests that each harmonic is Lorentzian with a linewidth proportional to the square of the harmonic number.…”

Characterization of regenerative stabilized actively mode-locked fiber laser incorporating a saturated amplifier in feed-back chain

“…For example, it causes mode-locking at the fundamental cavity frequency (f c ) instead of its Nth ( ¼4) harmonic (f N ), resulting in every 4th pulse to be of higher amplitude than the rest. This phenomenon is referred in literature as the occurrence of super-modes [22], where more than one mode is competing inside the cavity. Fig.…”

Semiconductor mode-locked lasers as pulse sources for high bit rate data transmission

“…Even though the gigahertzrepetition-rate mode-locked erbium-doped fiber laser literature reports timing jitters of < 10 fs (100 Hz to 1 MHz, 1 ps pulse width) [61], 16 fs (100 Hz to 100 kHz, 3 ps) [66], 120 fs (100 Hz to 10 MHz, 1 ps) [51], the total timing jitter should be integrated out to half the repetition-rate of the laser (i.e. 10 Hz to 5 GHz) [58,67], and hence the total timing jitter of these sources are not well characterized since these integration ranges do not include the supermode timing jitter. In section 4.4, the design path towards sub-66 fs timing jitter sources will be outlined to enable multi-terabit per second transmission rates.…”

“…harmonically mode-locked lasers [67] -Neighboring pulses arise independently from ASE similar to a gain-switched laser (assuming that there are no coupling effects such as gain saturation effects and reflections), but the pulses are highly correlated every round-trip since it is the same pulse, similar to a fundamentally mode-locked laser. Hence the noise correlation function in a harmonically mode-locked laser is a mix between the gain-switched laser and fundamentally mode-locked laser correlation functions.…”

“…Rather than explain how to interpret the rf spectra in detail, we refer the reader to recent papers in the literature [67,70]. The main point is that one must make assumptions about correlations of the pulse-to-pulse timing jitter and amplitude noise before the rf spectrum can be interpreted correctly and a valid rms timing jitter number can be obtained.…”