Continuous-wave (CW) laser-driven integrated Kerr microresonators enable broadband optical frequency combs with high repetition rates and low threshold power, in a compact footprint. A drawback of such microcombs is the low conversion efficiency from the pump laser to the comb lines, which is often in the few percent range or below. Here, complementing previously demonstrated approaches to increase conversion efficiency, we demonstrate a novel approach that leverages a chip-based rare-earth (Tm3+)-doped optical gain medium to boost the pump-to-comb conversion efficiency by more than one order of magnitude. Importantly, the gain medium does not require an additional pump laser, but recycles residual pump light from the Kerr-comb: the CW pump of the Kerr-comb (1610 nm) coincides with the pump wavelength of the on-chip gain medium, allowing unconverted pump power to be absorbed and transferred to the comb lines within gain window (1700 - 1900 nm). This enables a new class of highly efficient Kerr-combs for applications e.g. in data centers and optical computing.
Amplification of ultrafast optical pulses is key to a large number of applications in photonics. While ultrashort pulse amplification is well established in optical gain fibers, it is challenging to achieve in photonic-chip integrated waveguides, due to their inherent high-optical nonlinearity.
Here, we demonstrate for the first-time femtosecond pulse amplification on an integrated photonic chip. Our approach translates the concept of chirped pulse amplification to the chip level. Specifically, we leverage tailored all-normal dispersion, large mode-area gain waveguides to realize a low-nonlinearity, high-gain, short-length optical amplifier in which pulse propagation is dominated by dispersion. We show more than 17dB amplification of ultrashort pulses from a 1 GHz femtosecond source at center wavelength of 1815 nm. The amplified pulses have an on-chip output pulse peak power of 800 W with a pulse duration of 116 fs.
Compact laser sources are crucial for the next generation of photonic integrated circuits, where bulky mechanical components and other optical bench top systems can be realized on a single tiny chip. Similarly, biological sensing, environmental real-time monitoring and telecommunications all benefit from the advances seen in on-chip photonic components, in particular, active devices such as the amplifier and laser which have significant challenges in being implemented on a silicon substrate. The study of Erbium doped Aluminium Oxide (Al2O3:Er3+) has attracted significant interest from the research community due to its high solubility for rare-earth ions, wide optical transparency, and capability to be integrated as a hybrid coating or patterned into waveguides on a Si substrate using conventional fabrication techniques. Results point towards amorphous Al2O3 as an ideal candidate for further research into the discovery of amplifiers and lasers for photonic integrated circuits (PIC). Here, we report on the spectroscopic parameters as well as prospects for Al2O3:Er3+ doped films and their integration onto an existing low-loss waveguide platform for the realization of amplifiers and lasers. A review of past results will be given with pathways towards optimized films and improved laser performance in the future.
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