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Register a new userCounter-rotating cavity solitons in a silicon nitride microresonator
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We demonstrate the generation of counter-rotating cavity solitons in a silicon nitride microresonator using a fixed, single-frequency laser. We demonstrate a dual 3-soliton state with a difference in the repetition rates of the soliton trains that can be tuned by varying the ratio of pump powers in the two directions. Such a system enables a highly compact, tunable dual comb source that can be used for applications such as spectroscopy and distance ranging.
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The repetition rate of a Kerr comb comprising a single soliton in an anomalous dispersion silicon nitride microcavity is measured as a function of pump frequency tuning. The contributions from the Raman soliton self-frequency shift (SSFS) and from thermal effects are evaluated both experimentally and theoretically; the SSFS is found to dominate the changes in repetition rate. The relationship between the changes in repetition rate and pump frequency detuning is found to be independent of the nonlinearity coefficient and dispersion of the cavity. Modeling of the repetition rate change by using the generalized Lugiato-Lefever equation is discussed; the Kerr shock is found to have only a minor effect on repetition rate for cavity solitons with duration down to ~50 fs.
We investigate soliton generation dynamics with the influence of thermal effects. Either soliton annihilation or survival can occur in different trials with the same tuning method, and a spontaneous route to soliton formation is observed.
We demonstrate stable microresonator Kerr soliton frequency combs in a III-V platform (AlGaAs on SiO$_2$) through quenching of thermorefractive effects by cryogenic cooling to temperatures between 4~K and 20~K. This cooling reduces the resonators thermorefractive coefficient, whose room-temperature value is an order of magnitude larger than that of other microcomb platforms like Si$_3$N$_4$, SiO$_2$, and AlN, by more than two orders of magnitude, and makes soliton states adiabatically accessible. Realizing such phase-stable soliton operation is critical for applications that fully exploit the ultra-high effective nonlinearity and high optical quality factors exhibited by this platform.
We demonstrate an external cavity laser formed by combining a silicon nitride photonic integrated circuit with a reflective semiconductor optical amplifier. The laser uses an alignment tolerant edge coupler formed by a multi-mode waveguide splitter right at the edge of the silicon nitride chip that relaxes the required alignment to the III-V gain chip and equally splits the power among its two output waveguides. Both the ground and first order mode are excited in the coupler and reach the quadrature condition at the waveguide junction, ensuring equal power to be coupled to both. Two high-quality-factor ring resonators arranged in Vernier configuration close a Sagnac loop between the two waveguides. In addition to wideband frequency tuning, they result in a longer effective cavity length. The alignment tolerant coupler increases the alignment tolerance in the two directions parallel to the chip surface by a factor 3 relative to conventional edge couplers, making it ideal for gain chip integration via pick-and-place technology. Lasing is maintained in a misalignment range of $pm$6 $mu$m in the direction along the edge of the chip. A Lorentzian laser linewidth of 42 kHz is achieved.
By integrating the full Maxwells equations we predict the existence of gap solitons in a quadratic, Fabry-Perot negative index cavity. An intense, fundamental pump pulse shifts the band structure that forms when magnetic and electric plasma frequencies are different so that a weak, second harmonic pulse initially tuned inside the gap is almost entirely transmitted. The process is due cascading, which occurs far from phase matching conditions, and causes pulse compression. A nonlinear polarization spawns a dark soliton, while a nonlinear magnetization produces a bright soliton.
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