Silicon nitride stress-optic microresonator modulator for optical control applications

Abstract

Modulation-based control and locking of lasers, filters and other photonic components is a ubiquitous function across many applications that span the visible to infrared (IR), including atomic, molecular and optical (AMO), quantum sciences, fiber communications, metrology, and microwave photonics. Today, modulators used to realize these control functions consist of high-power bulk-optic components for tuning, sideband modulation, and phase and frequency shifting, while providing low optical insertion loss and operation from DC to 10s of MHz. In order to reduce the size, weight and cost of these applications and improve their scalability and reliability, modulation control functions need to be implemented in a low loss, wafer-scale CMOS-compatible photonic integration platform. The silicon nitride integration platform has been successful at realizing extremely low waveguide losses across the visible to infrared and components including high performance lasers, filters, resonators, stabilization cavities, and optical frequency combs. Yet, progress towards implementing low loss, low power modulators in the silicon nitride platform, while maintaining wafer-scale process compatibility has been limited. Here we report a significant advance in integration of a piezo-electric (PZT, lead zirconate titanate) actuated micro-ring modulation in a fully-planar, wafer-scale silicon nitride platform, that maintains low optical loss (0.03 dB/cm in a 625 µm resonator) at 1550 nm, with an order of magnitude increase in bandwidth (DC - 15 MHz 3-dB and DC - 25 MHz 6-dB) and order of magnitude lower power consumption of 20 nW improvement over prior PZT modulators. The modulator provides a >14 dB extinction ratio (ER) and 7.1 million quality-factor (Q) over the entire 4 GHz tuning range, a tuning efficiency of 162 MHz/V, and delivers the linearity required for control applications with 65.1 dB·Hz2/3 and 73.8 dB·Hz2/3 third-order intermodulation distortion (IMD3) spurious free dynamic range (SFDR) at 1 MHz and 10 MHz respectively. We demonstrate two control applications, laser stabilization in a Pound-Drever Hall (PDH) lock loop, reducing laser frequency noise by 40 dB, and as a laser carrier tracking filter. This PZT modulator design can be extended to the visible in the ultra-low loss silicon nitride platform with minor waveguide design changes. This integration of PZT modulation in the ultra-low loss silicon nitride waveguide platform enables modulator control functions in a wide range of visible to IR applications such as atomic and molecular transition locking for cooling, trapping and probing, controllable optical frequency combs, low-power external cavity tunable lasers, quantum computers, sensors and communications, atomic clocks, and tunable ultra-low linewidth lasers and ultra-low phase noise microwave synthesizers.

Integrated stabilized lasers and circuits for atom cooling, trapping, and interrogation

“…Examples include Visible and IR SBS integrated lasers [23,24] and integrated reference cavities and modulators: Fig. 3 (a) 4-meter integrated coil-resonator for 36 Hz integral linewidth 1550 nm laser [29] and an integrated 3-meter 40 million Q coil-resonator yielding a 4.2 kHz linewidth at 674 nm [30], (b) 0.034 dB/m loss waveguides in a 200 mm wafer-scale Si3N4 integration platform realizing a 720 million Q resonator and 380 µW threshold SBS laser at 1550nm [17] (c) ultra-low loss PZT actuated ring modulator for photonic control [31], (d) 422 million Q resonator [32], and (e) a nonlinear cavity locked to an ultra-low loss cavity to reduce the Si3N4 Brillouin laser linewidth to 330 Hz integral linewidth and 6.5×10 -13 FFN at 8 ms [28].…”

Frequency agile photonic integrated external cavity laser

“…A monolithically integrated actuator (see Fig. 1(d)) comprises a piezo-electrical PZT actuator [15,44] for fast actuation and a microheater for alignment of a Vernier filter and wide wavelength tunability. Microheaters are fabricated in the bottom (ground) electrode layer which can be accessed through an opening of the PZT layer for wirebonding.…”

An Integrated Photon-Pair Source with Monolithic Piezoelectric Frequency Tunability

“…There have been previous demonstrations of frequency locking microresonators by feeding back a locking signal to the temperature of the microresonators, however the achievable bandwidth in such schemes is very small, typically only in the tens of Hertzs regime [49][50][51][52]. Focus has therefore moved away from such thermal locking schemes, with recent developments including piezoelectric frequency-locking schemes integrated on-chip [53]. However, the use of such devices as photon-pair sources has not yet been demonstrated.…”