Nanophotonic phase noise filter in silicon

Narrow-linewidth light sources have far-reaching applications from communication1 to metrology2–4. Benchtop linewidth reduction methods such as feedback5,6 and feed-forward7,8 schemes have been used to reduce the linewidth of lasers. The feedback scheme typically has a limited bandwidth and depends on the laser characteristics and the feed-forward scheme is highly sensitive to gain and delay mismatches. Here, we report the demonstration of an integrated nanophotonic phase noise filter, which can be placed after a low-cost laser to significantly suppress its phase noise independent of the light source. The hybrid-integrated electronic–photonic system measures and suppresses the phase noise of the input light using an electronic–photonic loop without interacting with the light source. Using the integrated phase noise filter, laser linewidth reduction from 2.55 MHz to 4 kHz and from 200 kHz to 320 Hz is demonstrated. The silicon photonic and complementary metal–oxide–semiconductor (CMOS) electronic chips were hybrid-integrated within a footprint of 3 mm2. An optoelectronic device that measures and suppresses the phase noise of a source has been realized in an integrated silicon platform.