Abstract
This work reports on an investigation of the optical feedback in an InAs/InGaAs passively mode-locked quantum dot (QD) laser epitaxially grown on silicon. Under the stably-resonant optical feedback condition, experiments demonstrate that the radio-frequency linewidth is narrowed whatever the bias voltage applied on the saturable absorber (SA) is; on the other hand, the effective linewidth enhancement factor of the device increases with the reverse bias voltage on the SA, hence it is observed that such an increase influences the mode-locking dynamic and the stability of device under optical feedback. This work gives insights for stabilizing epitaxial QD mode-locked lasers on silicon which is meaningful for their applications in future large-scale silicon electronic and photonic applications requiring low power consumption as well as for high-speed photonic analog-to-digital conversion, intrachip/interchip optical clock distribution and recovery.
Highlights
Ultrafast laser sources are of strong interest in various applications such as optical clocks [1], length metrology [2], optical communications [3] and high performance data centers [4]
To understand the influence of external cavity length on the laser performance, figure 5 depicts the quantum dot (QD)-mode-locked lasers (MLL) peak frequency and RF linewidth as a function of optical delay line length under -35 dB feedback strength, rext, with the device operated at twice threshold with -1 V (a) and -5 V (b) applied to the saturable absorber (SA)
Our results demonstrate that a large reduction of RF linewidth takes place in the optimum feedback condition, which corresponds to the integer resonant operation when the optical length of the external cavity is a multiple of that of the laser cavity [27, 42]
Summary
Ultrafast laser sources are of strong interest in various applications such as optical clocks [1], length metrology [2], optical communications [3] and high performance data centers [4]. Low relative intensity noise [7], narrow spectral linewidth [8, 9], high tolerance to external feedback [10], and remarkable temperature stability [11] have been demonstrated, amongst other attributes In this context, monolithic mode-locked lasers (MLL) with QD gain regions are reliable sources for generating ultra-short pulses, which are useful for a large number of applications such as communications, metrology, and clock distribution in future computer processors. Any error in timing appears as an error in the sampled signal itself, greatly reducing the dynamic range of the sampled signal To this end, mode-locking technique is ideal solution to generate ultra-short pulses to overcome this issue [12,13,14].
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