Broadband frequency combs with mode spacings of 1 GHz provide a valuable resource for optical frequency metrology and astrophotonics. Significant average powers are often needed to reach the pulse energies required for supercontinuum generation at 1 GHz repetition rates, putting this beyond the reach of most simple ultrafast lasers. Here, by using dispersion-engineered Si₃N₄ waveguides, we report octave-spanning comb generation from 539 to 1078 nm (−20 dB bandwidth) pumped with a three-element 1 GHz Ti:sapphire laser powered by a single laser diode. Laser repetition-rate stability of 790 mHz is achieved over a 1-hour duration, and carrier-envelope-offset control and stabilization to a single-frequency cw laser is presented. The system offers a simple route to a coherent, broadband supercontinuum spanning the visible to the near-infrared, with potential as an enabling technology for optical frequency metrology, quantum timekeeping, and astrophysical spectrograph calibration.
Color symmetry breaking in a nonlinear optical microcavity
Luca O. Trinchão,
Alekhya Ghosh,
Arghadeep Pal,
Haochen Yan,
Toby Bi,
Shuangyou Zhang,
Nathalia B. Tomazio,
Flore K. Kunst,
Lewis Hill, et al.
Spontaneous symmetry breaking leads to diverse phenomena across the natural sciences, from the Higgs mechanism in particle physics to superconductors and collective animal behavior. In photonic systems, the symmetry of light states can be broken when two optical fields interact through the Kerr nonlinearity, as shown in early demonstrations with counterpropagating and cross-polarized modes. Here, we report the first observation of color symmetry breaking in an integrated silicon nitride microring, where spontaneous power imbalance arises between optical mode at different wavelengths, mediated by the Kerr effect. The threshold power for this effect is as low as 19 mW. By examining the system's homogeneous states, we further demonstrate a Kerr-based nonlinear activation-function generator that produces sigmoid-, quadratic-, and leaky-ReLU-like responses. These findings reveal previously unexplored nonlinear dynamics in dual-pumped Kerr resonators and establish new pathways towards compact, all-optical neuromorphic circuits.
