Abstract
This work investigates the performance of 1.3-μm quantum dot lasers epitaxially grown on silicon under optical feedback sensitivity with different temperature and doping profiles. Experiments show that these quantum dot lasers exhibit a very high degree of resistance to both incoherent and coherent optical feedbacks. 10 Gbps penalty-free transmissions are also unveiled under external modulation and at different temperatures. The paper draws attention on quantum dot lasers with p-doping that exhibit a better thermal resistance, a lower linewidth enhancement factor, a higher critical feedback level, and a better spectral stability with less intensity noise. Together, these properties make epitaxial quantum dot lasers with p-doping more promising for isolator-free and Peltier-free applications, which are meaningful for future high-speed photonic integrated circuits.
Highlights
Over the past decade, silicon (Si) photonics have been introduced to overcome the low efficiency and high energy consumption of metal wiring, in particular, for high-speed communication systems, optical interconnects, as well as board-to-board and chipto-chip integrated circuits.[1,2,3,4,5,6] Si exhibits a strong index contrast with silica (Δn ≈ 2) being an excellent candidate for an on-chip waveguide with strong light confinement, it cannot provide efficient light emission due to its indirect bandgap nature
Many efforts have been devoted to fabricate integrated light sources[5,7,8,9,10] either by considering hybrid integration of III-V semiconductor materials on Si or through direct heteroepitaxy onto Si or even germanium (Ge).[11–13]. While for the former, flip-chip or wafer bonding has already reported good performance,[14–16] it does not always allow making optical devices with enough compactness. Such hybrid lasers remain quite sensitive to coherent optical feedback from parasitic backreflections of the laser emission by the vertical grating couplers and the multiple passive and active interfaces/transitions between the III-V material and Si17–19 and to possible incoherent feedback originating from amplified spontaneous emission (ASE) noises generated by active building blocks such as semiconductor optical amplifiers (SOAs) or active waveguides that are often integrated in the same photonic integrated circuits (PICs).[20]
To further qualify the influence of p-doping on QD lasers subjected to optical feedback, this section is split into three parts: first, we remind the physical processes involved in the optical feedback and give some basic design rules for reaching feedback insensitive lasers; second, the impact of static optical feedback is studied without considering the modulation nor the transmission, allowing us to unveil how the optical feedback affects the spectral properties in both optical and radio-frequency (RF) domains; and in the last part, high-speed test bed experiments are performed with and without optical feedback
Summary
Scitation.org/journal/app feedback-insensitive transmitters is still a major objective for silicon photonics related applications. In order to meet the aforementioned requirements, semiconductor lasers monolithically grown on Si wafers, with low-cost, highyield, energy efficiency, and much better scalability, are still needed.[9] To this end, InAs/GaAs quantum-dot (QD) technology has been shown to be a promising solution for silicon integration. The inclusion of p-type doping contributes to eliminate gain saturation and to mitigate the thermal spread of holes,[33,34] leading to a rather temperature insensitive threshold current.[28,35–37]. Such a feature is illustrated, where the threshold currents, normalized to that at 293 K, are presented for the characterized temperature range from 288 K to 308 K. In order to better analyze the device operation well above threshold, the bias current used for both devices is maintained in what follows, if not specified, at 3 × Ith
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