  The demand for high-performance chip-scale lasers has driven rapid growth in
integrated photonics. The creation of such low-noise laser sources is critical
for emerging on-chip applications, ranging from coherent optical
communications, photonic microwave oscillators remote sensing and optical
rotational sensors. While Brillouin lasers are a promising solution to these
challenges, new strategies are needed to create robust, compact, low power and
low cost Brillouin laser technologies through wafer-scale integration. To date,
chip-scale Brillouin lasers have remained elusive due to the difficulties in
realization of these lasers on a commercial integration platform. In this
paper, we demonstrate, for the first time, monolithically integrated Brillouin
lasers using a wafer-scale process based on an ultra-low loss Si3N4/SiO2
waveguide platform. Cascading of stimulated Brillouin lasing to 10 Stokes
orders was observed in an integrated bus-coupled resonator with a loaded Q
factor exceeding 28 million. We experimentally quantify the laser performance,
including threshold, slope efficiency and cascading dynamics, and compare the
results with theory. The large mode volume integrated resonator and gain medium
supports a TE-only resonance and unique 2.72 GHz free spectral range, essential
for high performance integrated Brillouin lasing. The laser is based on a
non-acoustic guiding design that supplies a broad Brillouin gain bandwidth.
Characteristics for high performance lasing are demonstrated due to large
intra-cavity optical power and low lasing threshold power. Consistent laser
performance is reported for multiple chips across multiple wafers. This design
lends itself to wafer-scale integration of practical high-yield, highly
coherent Brillouin lasers on a chip.
