We report ultra-narrow-linewidth erbium-doped aluminum oxide (Al2O3:Er3+) distributed feedback (DFB) lasers with a wavelength-insensitive silicon-compatible waveguide design. The waveguide consists of five silicon nitride (SiNx) segments buried under silicon dioxide (SiO2) with a layer Al2O3:Er3+ deposited on top. This design has a high confinement factor (> 85%) and a near perfect (> 98%) intensity overlap for an octave-spanning range across near infrared wavelengths (950–2000 nm). We compare the performance of DFB lasers in discrete quarter phase shifted (QPS) cavity and distributed phase shifted (DPS) cavity. Using QPS-DFB configuration, we obtain maximum output powers of 0.41 mW, 0.76 mW, and 0.47 mW at widely spaced wavelengths within both the C and L bands of the erbium gain spectrum (1536 nm, 1566 nm, and 1596 nm). In a DPS cavity, we achieve an order of magnitude improvement in maximum output power (5.43 mW) and a side mode suppression ratio (SMSR) of > 59.4 dB at an emission wavelength of 1565 nm. We observe an ultra-narrow linewidth of ΔνDPS = 5.3 ± 0.3 kHz for the DPS-DFB laser, as compared to ΔγQPS = 30.4 ± 1.1 kHz for the QPS-DFB laser, measured by a recirculating self-heterodyne delayed interferometer (RSHDI). Even narrower linewidth can be achieved by mechanical stabilization of the setup, increasing the pump absorption efficiency, increasing the output power, or enhancing the cavity Q.
Nanxi Li, Purnawirman Purnawirman, E. Salih Magden, Gurpreet Singh, Neetesh Singh, Anna Baldycheva, Ehsan S. Hosseini, Jie Sun, Michele Moresco, Thomas N. Adam, Gerald Leake, Douglas Coolbaugh, Jonathan D. B. Bradley, and Michael R. Watts, "Ultra-narrow-linewidth erbium-doped lasers on a silicon photonics platform," Proc. SPIE 10537, Silicon Photonics XIII, 1053712 (Presented at SPIE OPTO: February 01, 2018; Published: 22 February 2018); https://doi.org/10.1117/12.2288791.
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