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Register a new userVisible light photonic integrated Brillouin laser
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Narrow linewidth visible light lasers are critical for atomic, molecular and optical (AMO) applications including atomic clocks, quantum computing, atomic and molecular spectroscopy, and sensing. Historically, such lasers are implemented at the tabletop scale, using semiconductor lasers stabilized to large optical reference cavities. Photonic integration of high spectral-purity visible light sources will enable experiments to increase in complexity and scale. Stimulated Brillouin scattering (SBS) is a promising approach to realize highly coherent on-chip visible light laser emission. While progress has been made on integrated SBS lasers at telecommunications wavelengths, barriers have existed to translate this performance to the visible, namely the realization of Brillouin-active waveguides in ultra-low optical loss photonics. We have overcome this barrier, demonstrating the first visible light photonic integrated SBS laser, which operates at 674 nm to address the 88Sr+ optical clock transition. To guide the laser design, we use a combination of multi-physics simulation and Brillouin spectroscopy in a 2 meter spiral waveguide to identify the 25.110 GHz first order Stokes frequency shift and 290 MHz gain bandwidth. The laser is implemented in an 8.9 mm radius silicon nitride all-waveguide resonator with 1.09 dB per meter loss and Q of 55.4 Million. Lasing is demonstrated, with an on-chip 14.7 mW threshold, a 45% slope efficiency, and linewidth narrowing as the pump is increased from below threshold to 269 Hz. To illustrate the wavelength flexibility of this design, we also demonstrate lasing at 698 nm, the wavelength for the optical clock transition in neutral strontium. This demonstration of a waveguide-based, photonic integrated SBS laser that operates in the visible, and the reduced size and sensitivity to environmental disturbances, shows promise for diverse AMO applications.
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Photonic systems and technologies traditionally relegated to table-top experiments are poised to make the leap from the laboratory to real-world applications through integration. Stimulated Brillouin scattering (SBS) lasers, through their unique linewidth narrowing properties, are an ideal candidate to create highly-coherent waveguide integrated sources. In particular, cascaded-order Brillouin lasers show promise for multi-line emission, low-noise microwave generation and other optical comb applications. Photonic integration of these lasers can dramatically improve their stability to environmental and mechanical disturbances, simplify their packaging, and lower cost. While single-order silicon and cascade-order chalcogenide waveguide SBS lasers have been demonstrated, these lasers produce modest emission linewidths of 10-100 kHz. We report the first demonstration of a sub-Hz (~0.7 Hz) fundamental linewidth photonic-integrated Brillouin cascaded-order laser, representing a significant advancement in the state-of-the-art in integrated waveguide SBS lasers. This laser is comprised of a bus-ring resonator fabricated using an ultra-low loss Si3N4 waveguide platform. To achieve a sub-Hz linewidth, we leverage a high-Q, large mode volume, single polarization mode resonator that produces photon generated acoustic waves without phonon guiding. This approach greatly relaxes phase matching conditions between polarization modes, and optical and acoustic modes. Using a theory for cascaded-order Brillouin laser dynamics, we determine the fundamental emission linewidth of the first Stokes order by measuring the beat-note linewidth between and the relative powers of the first and third Stokes orders. Extension to the visible and near-IR wavebands is possible due to the low optical loss from 405 nm to 2350 nm, paving the way to photonic-integrated sub-Hz lasers for visible-light applications.
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.
The interaction of optical and acoustic waves via stimulated Brillouin scattering (SBS) has recently reached on-chip platforms, which has opened new fields of applications ranging from integrated microwave photonics and on-chip narrow-linewidth lasers, to phonon-based optical delay and signal processing schemes. Since SBS is an effect that scales exponentially with interaction length, on-chip implementation on a short length scale is challenging, requiring carefully designed waveguides with optimized opto-acoustic overlap. In this work, we use the principle of Brillouin optical correlation domain analysis (BOCDA) to locally measure the SBS spectrum with high spatial resolution of 800 {mu}m and perform a distributed measurement of the Brillouin spectrum along a spiral waveguide in a photonic integrated circuit (PIC). This approach gives access to local opto-acoustic properties of the waveguides, including the Brillouin frequency shift (BFS) and linewidth, essential information for the further development of high quality photonic-phononic waveguides for SBS applications.
We present the first demonstration of a narrow linewidth, waveguide-based Brillouin laser which is enabled by large Brillouin gain of a chalcogenide chip. The waveguides are equipped with vertical tapers for low loss coupling. Due to optical feedback for the Stokes wave, the lasing threshold is reduced to 360 mW, which is 5 times lower than the calculated single-pass Brillouin threshold for the same waveguide. The slope efficiency of the laser is found to be 30% and the linewidth of 100 kHz is measured using a self-heterodyne method.
Brillouin laser oscillators offer powerful and flexible dynamics as the basis for mode-locked lasers, microwave oscillators, and optical gyroscopes in a variety of optical systems. However, Brillouin interactions are exceedingly weak in conventional silicon photonic waveguides, stifling progress towards silicon-based Brillouin lasers. The recent advent of hybrid photonic-phononic waveguides has revealed Brillouin interactions to be one of the strongest and most tailorable nonlinearities in silicon. Here, we harness these engineered nonlinearities to demonstrate Brillouin lasing in silicon. Moreover, we show that this silicon-based Brillouin laser enters an intriguing regime of dynamics, in which optical self-oscillation produces phonon linewidth narrowing. Our results provide a platform to develop a range of applications for monolithic integration within silicon photonic circuits.
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