Supermode noise of harmonically mode-locked erbium fiber lasers with composite cavity

Abstract

Abstract-The supermode noise of a harmonically mode-locked erbium-doped fiber laser with composite cavity is investigated both theoretically and experimentally. We propose a simple model based on the transfer function of the composite cavity. From this model, the frequencies of the cavity modes and their frequency-dependent losses are determined. A comprehensive experimental study of the composite cavity laser is carried out, covering a wide range of path-length differences between both arms of the fiber interferometer that form the composite cavity. Experimental results are in good agreement with our model. In particular, the path length difference determines periodic frequency windows within which supermodes of the composite cavity are observed. Outside these windows, supermodes are not detectable. Our results show quite remarkably that, although the number of supermodes is reduced with respect to the simple cavity, no measurable reduction of the overall supermode noise is obtained, contrary to what has recently been suggested [1].

Experimental investigation of the cavity modulation frequency detuning effect in an active harmonically mode-locked fiber laser

“…As we detuned the modulation frequency by 10 kHz, weak amplitude fluctuations appeared on top of the mode-locked pulses due to supermode noise induced by the frequency detuning effect, as shown in Fig. 3(b) [14]. The supermode noise is clearly shown in the inset of Fig.…”

“…There are many theoretical and experimental studies on this issue [10][11][12][13][14][15][16]. It has been shown that modulation frequency detuning causes pulse width broadening, phase noise, and output power reduction [17,18].…”

Frequency synchronization of Fourier domain harmonically mode locked fiber laser by monitoring the supermode noise peaks

“…Supermode noise in harmonically mode locked lasers has been discussed extensively [15][16][17][18][19]. In a laser harmonically mode locked to the N-th order, the lasing cavity supports N sets of phase locked cavity modes, called supermodes.…”

“…The beatings between these supermodes introduce intensity fluctuation between the consecutive pulses in the output of the harmonically mode locked laser. Different methods have been proposed to reduce the intensity fluctuation which include adopting a composite cavity to select only one set of the supermodes [16,18], using adaptive loss compensation [19], etc.…”

“…the optimal operation point of the laser is not unique. The function of supermode noise suppression schemes [16,18,19] is to render the laser to operate near one of these optimal points.…”