High Gain Submicrometer Optical Amplifier at Near-Infrared Communication Band

Nanoscale near-infrared optical amplification is important but remains a challenge to achieve. Here we report a unique design of silicon and erbium silicate core-shell nanowires for high gain submicrometer optical amplification in the near-infrared communication band. The high refraction index silicon core is used to tightly confine the optical field within the submicron structures, and the single crystalline erbium-ytterbium silicates shell is used as the highly efficient gain medium. Both theoretical and experimental results show that, by systematically tuning the core diameter and shell thickness, a large portion of the optical power can be selectively confined to the erbium silicate shell gain medium to enable a low loss waveguide and high gain optical amplifier. Experimental results further demonstrate that an optimized core-shell nanowire can exhibit an excellent net gain up to $31\mathrm{dB}{\mathrm{mm}}^{-1}$, which is more than 20 times larger than the previously reported best results on the micron-scale optical amplifiers.

Figure 1

(a) Schematic of the core-shell nanostructure. (b) The silicon core diameter-dependent effective index for guided modes that are supported in the core-shell Si-EYS nanowires at the wavelength of 1550 nm. (c) Simulated power percentage confined in the core-shell Si-EYS nanowire. (d) Simulated power percentage contained in the shell region.

Figure 2

(a)–(f) Optical electrical-field distribution images for HE11 mode with core diameters of 0 nm, 100 nm, 200 nm, 300 nm, 400 nm, and 600 nm (total diameter, 600 nm).

Figure 3

Microstructure characterization of the Si-EYS core-shell nanowires. (a) Typical SEM images of part of a single nanowire, and (b) its locally amplified image. (c) Cross-sectional TEM image of the wire, and its corresponding two-dimensional element mapping (d)–(g). (h) Typical HRTEM image collected at the core-shell interface of the wire [red rectangle area in (c)].

Figure 4

(a) Guided length-dependent propagation loss at wavelengths of 1590 nm, 1620 nm, and 1534 nm, along a core-shell nanowire with a diameter of 600 nm (core diameter, 300 nm) and a length of $60\mu \mathrm{m}$. (b) Guided length-dependent propagation loss at wavelength 1590 nm along four different nanowires with diameter of 600 nm and core diameters of 0 nm, 200 nm, 300 nm, and 400 nm. The solid lines in (a) and (b) are the linear fit of these measured data.

Figure 5

(a) Typical spectra of the guided PL (black) only with the pump laser on; the probe laser at 1534 nm or 1543 nm, and the total output with both the probe and the pump lasers are present (pumped at 36 mW). (b) Pump power-dependent net gain for the wires with core diameters of $\mathrm{d}=200\mathrm{nm}$, 300 nm, and 400 nm (wire diameter is 600 nm). (c) Silicon core diameter-dependent maximum net gain (black dot, pumped at 56 mW) and positive net gain threshold (blue rectangular) for different silicon core diameters.