Gain analysis of optically-pumped Si nanocrystal waveguide amplifiers on silicon substrate

Abstract

The SiO(2)/SiO(x)/SiO(2) strip-loaded waveguide on Si substrate with buried Si nanocrystals (Si-ncs) in SiO(x) layer is demonstrated to show the Si-nc dependent optical gain. The amplified spontaneous emission (ASE) spectrum at 750-850 nm is observed with central wavelength of 805 nm and 3dB spectral linewidth of 140 nm. The optical net modal gain and loss coefficients of 85.7 cm(-1) and 21 cm(-1), respectively, are determined from the waveguide length dependent ASE intensity. By attenuating 785-nm laser diode signal to inject the pumped SiO(2)/SiO(x)/SiO(2) strip-loaded waveguide, a small-signal power gain of 13.5 decibel (dB) is obtained. Increasing the laser diode power shows a significantly reduced power gain with a saturated output power due to the finite density of the optically pumped Si-ncs. The fitting of power-dependent gain with a gain-saturated amplifier model reveals a peak gain of 35 dB and a saturation power of 1.1 nW for the SiO(2)/SiO(x):Si-nc/SiO(2)/Si strip-loaded waveguide. Similar output saturation is also observed with increasing pumping power. With the presence of optical gain in the optically pumped Si-ncs, the intended application will be the monolithic integration of the Si-nc based optical waveguide amplifier with the other on-board photonic integrated circuits for the future optical interconnect communication.