Shai Gertler

Optical nonreciprocity plays a key role in almost every optical system, directing light flow and protecting optical components from backscattered light. Controllable forms of on-chip nonreciprocity are needed for the robust operation of increasingly sophisticated photonic integrated circuits (PICs) in the context of classical and quantum computation, networking, communications, and sensing. However, it has been challenging to achieve wideband, low-loss optical nonreciprocity on-chip. In this paper, we demonstrate strong coupling and Rabi-like energy exchange between photonic bands, possessing a continuum of modes, to unlock nonreciprocity and frequency translation over wide optical bandwidths in silicon. Using a traveling-wave phonon field to drive indirect interband photonic transitions, we demonstrate band hybridization that enables an intriguing form of nonreciprocal dissipation engineering. Using the …

Integrated photonics could bring transformative breakthroughs in computing, networking, imaging, sensing, and quantum information processing, enabled by increasingly sophisticated optical functionalities on a photonic chip. However, wideband optical isolators, which are essential for the robust operation of practically all optical systems, have been challenging to realize in integrated form due to the incompatibility of magnetic media with these circuit technologies. Here, we present the first-ever demonstration of an integrated non-magnetic optical isolator with terahertz-level optical bandwidth. The system is comprised of two acousto-optic frequency-shifting beam splitters which create a non-reciprocal multimode interferometer exhibiting high-contrast, nonreciprocal light transmission. We dramatically enhance the isolation bandwidth of this system by precisely dispersion balancing the paths of the interferometer. Using this approach, we demonstrate integrated nonmagnetic isolators with an optical contrast as high as 28 dB, insertion losses as low as -2.16 dB, and optical bandwidths as high as 2 THz (16 nm). We also show that the center frequency and direction of optical isolation are rapidly reconfigurable by tuning the relative phase of the microwave signals used to drive the acousto-optic beam splitters. With their CMOS compatibility, wideband operation, low losses, and rapid reconfigurability, such integrated isolators could address a key barrier to the integration of a wide range of photonic functionalities on a chip. Looking beyond the current demonstration, this bandwidth-scalable approach to nonmagnetic isolation opens the door to …

New strategies to convert signals between optical and microwave domains could play a pivotal role in advancing both classical and quantum technologies. Through recent studies, electro-optomechanical systems have been used to implement microwave-to-optical conversion using resonant optical systems, resulting in transduction over limited optical bandwidth. Here, we present an optomechanical waveguide system with an integrated piezoelectric transducer that produces electro-optomechanical transduction over a wide optical bandwidth through coupling to a continuum of optical modes. Efficient electromechanical and optomechanical coupling within this system enables bidirectional optical-to-microwave conversion with a quantum efficiency of up to 54.16 dB. When electrically driven, this system produces a low voltage acousto-optic phase modulation over a wide (100 nm) wavelength range. Through optical-to-microwave conversion, we show that the amplitude-preserving nature inherent to forward Brillouin scattering is intriguing and has the potential to enable new schemes for microwave photonic signal processing. We use these properties to demonstrate a multi-channel microwave photonic filter by transmitting an optical signal through a series of electro-optomechanical waveguide segments having distinct resonance frequencies. Building on these demonstrations, such electro-optomechanical systems could bring flexible strategies for modulation, channelization, and spectrum analysis in microwave photonics.

An optical amplifier device employing a Mach-Zehnder Interferometer (MZI) that reduces the amount of residual pump power in the optical output of the amplifier is disclosed. The MZI amplifier employs two geometrically linear optical amplifier arms or two multi-spatial-mode racetrack optical amplifiers to amplify a signal with a pumping beam, with the signal output port having extremely low levels of residual pump power. The MZI optical amplifier is a silicon photonic integrated circuit, with all optical amplifiers, couplers, phase shifters, and optical attenuators formed of silicon photonic integrated circuit elements. The MZI optical amplifier may include one, two, or three MZI stages, and multiple MZI optical amplifiers may be used in parallel or sequentially to achieve higher overall signal gain or power. The MZI optical amplifier may employ Brillouin-scattering-based amplifiers, Raman-based integrated waveguide optical …

We demonstrate wideband strong coupling between two photonic bands via electrically-driven acousto-optic scattering. Based on this system, we demonstrate a non-magnetic, low-loss (< 1 dB) and broadband (59 GHz 10 dB isolation bandwidth) optical isolator.

Physical design refers to mathematical optimization of a desired objective (e.g. strong light--matter interactions, or complete quantum state transfer) subject to the governing dynamical equations, such as Maxwell's or Schrodinger's differential equations. Computing an optimal design is challenging: generically, these problems are highly nonconvex and finding global optima is NP hard. Here we show that for linear-differential-equation dynamics (as in linear electromagnetism, elasticity, quantum mechanics, etc.), the physical-design optimization problem can be transformed to a sparse-matrix, quadratically constrained quadratic program (QCQP). Sparse QCQPs can be tackled with convex optimization techniques (such as semidefinite programming) that have thrived for identifying global bounds and high-performance designs in other areas of science and engineering, but seemed inapplicable to the design problems of wave physics. We apply our formulation to prototypical photonic design problems, showing the possibility to compute fundamental limits for large-area metasurfaces, as well as the identification of designs approaching global optimality. Looking forward, our approach highlights the promise of developing bespoke algorithms tailored to specific physical design problems.

We report nonreciprocal wave propagation with~ 10dB nonreciprocity over a 32 nm optical bandwidth based on inter-band acousto-optic scattering within a silicon photonic waveguide system.

We demonstrate an efficient non-magnetic optical isolator based on electrically-driven inter-band acousto-optic scattering in an AlN-on-SOI photonic device. The isolator exhibits< 1 dB insertion loss and 10 dB of isolation over a 50 GHz bandwidth.

Optomechanical systems show great potential as quantum transducers and information storage devices for use in future hybrid quantum networks. In this context, optomechanical strong coupling can enable efficient, high-bandwidth, and deterministic transfer of quantum states. While optomechanical strong coupling has been realized at optical frequencies, it has proven difficult to identify a robust optomechanical system that features the low loss and high coupling rates required for more sophisticated control of mechanical motion. In this paper, we demonstrate strong coupling in a Brillouin-based bulk cavity optomechanical system in both the single-mode and the multimode strong-coupling regime, which leads to a useful device both for applications in quantum information and for investigating decoherence phenomena in bulk acoustic wave resonators. Using nontrivial mode hybridizations in the strong-coupling …

Devices and systems for opto-acoustic signal processing are described herein. In one embodiment, the device may include a structure configured to laterally confine travelling acoustic phonons (hypersound) throughout, a first multimode optical waveguide embedded within the structure, and an acoustic phonon emitter within the structure, where the first multimode optical waveguide is selected to couple to the acoustic phonons (hypersound) confined within the structure. In one embodiment, the system may include a first light source optically coupled to a proximal end of the first multimode optical waveguide, the first light source emitting a probe wave having a frequency ωp (1), and a driver configured to drive the acoustic phonon emitter to emit acoustic phonons (hypersound).

The growing demand for bandwidth makes photonic systems a leading candidate for future telecommunication and radar technologies. Integrated photonic systems offer ultra-wideband performance within a small footprint, which can naturally interface with fiber-optic networks for signal transmission. However, it remains challenging to realize narrowband (∼MHz) filters needed for high-performance communications systems using integrated photonics. In this paper, we demonstrate all-silicon microwave-photonic notch filters with 50× higher spectral resolution than previously realized in silicon photonics. This enhanced performance is achieved by utilizing optomechanical interactions to access long-lived phonons, greatly extending available coherence times in silicon. We use a multi-port Brillouin-based optomechanical system to demonstrate ultra-narrowband (2.7 MHz) notch filters with high rejection (57 dB) and …

The canonical beam splitter—a fundamental building block of quantum optical systems—is a reciprocal element. It operates on forward-and backward-propagating modes in the same way, regardless of direction. The concept of nonreciprocal quantum photonic operations, by contrast, could be used to transform quantum states in a momentum-and direction-selective fashion. Here we demonstrate the basis for such a nonreciprocal transformation in the frequency domain through intermodal Bragg scattering four-wave mixing (BSFWM). Since the total number of idler and signal photons is conserved, the process can preserve coherence of quantum optical states, functioning as a nonreciprocal frequency beam splitter. We explore the origin of this nonreciprocity and find that the phase-matching requirements of intermodal BSFWM produce an enormous asymmetry (76×) in the conversion bandwidths for forward and …

We present narrowband RF-photonic filters in an integrated silicon platform. Using Brillouin interactions, the filters yield narrowband (∼ MHZ) filter bandwidths with high signal rejection, and demonstrate tunability over a wide (∼ GHz) frequency range.

In this dissertation, we explore the possibilities offered by the unique properties of Brillouin scattering to implement signal-processing operations in photonic devices. Brillouin scattering| the coupling of light and sound waves| enables access to long-lived acoustic modes directly from the optical domain and results in processes very different compared with other optical systems. Furthermore, when utilized to process microwave signals, Brillouin-active photonic systems are compelling for their ability to bridge the vastly different frequency scales of microwave and optical signals.

Musical Acoustics and Instrument Design, a course taught in the Yale Center for Engineering Innovation and Design (CEID), explores the principles of acoustic and electronic musical instruments using a highly interactive hands-on approach that takes optimal advantage of the resources available in an academic makerspace. Targeting undergraduate students with a wide range of backgrounds in music and engineering, the course provides an understanding of the theory of musical instruments, how they are designed, and a practical knowledge of the tools and technology used to build them. The culmination of the course is the design and construction of an original instrument by each student. The course was co-taught by Larry Wilen and Konrad Kaczmarek, faculty in Mechanical Engineering and the Department of Music, respectively. Shai Gertler was the teaching fellow and Antonio Medina was a student in the class, now a Design Fellow in the CEID.Milo was a music and math major, and a carillon aficionado. His initial idea was to create a set of keys that looked like a carillon keyboard, but could also simulate the feel of playing a carillon, with lower notes having a different resistance and inertia comparedto higher ones. He experimented with various electromechanical systems and eventually settled upon a simple geared motor with a built in encoder, with a metal bar (the “key”) attached to the motor shaft. The system was interfaced to a teensy microprocessor and motor drivers. By employing feedback and physical modeling in his code, he could simulate just about any mechanical system; Due to time constraints, Milo settled on just 4 motors …

As self-sustained oscillators, lasers possess the unusual ability to spontaneously synchronize. These nonlinear dynamics are the basis for a simple yet powerful stabilization technique known as injection locking, in which a laser’s frequency and phase can be controlled by an injected signal. Because of its inherent simplicity and favorable noise characteristics, injection locking has become a workhorse for coherent amplification and high-fidelity signal synthesis in applications ranging from precision atomic spectroscopy to distributed sensing. Within integrated photonics, however, these injection-locking dynamics remain relatively untapped—despite significant potential for technological and scientific impact. Here, we demonstrate injection locking in a silicon photonic Brillouin laser. Injection locking of this monolithic device is remarkably robust, allowing us to tune the laser emission by a significant fraction of the …

Microwave photonic systems are compelling for their ability to process signals at high frequencies and over extremely wide bandwidths as a basis for next generation communication and radar technologies. However, many applications also require narrow-band filtering operations that are challenging to be implemented using optical filtering techniques, as this requires reliable integration of ultra-high quality factor optical resonators. One way to address this challenge is to utilize long-lived acoustic resonances, taking advantage of their narrow-band frequency response to filter microwave signals. In this article, we examine new strategies to harness a narrow-band acoustic response within a microwave-photonic signal processing platform through the use of light-sound coupling. Our signal processing scheme is based on a recently demonstrated photon-phonon emitter-receiver device, which transfers …

We demonstrate multi-pole RF-photonic filters in an integrated silicon platform. Using Brillouin interactions, the filters yield a narrow passband (~ MHZ), high out-of-band rejection (70 dB), and can be tuned over a wide range (GHz).

The ever-increasing demand for high speed and large bandwidth has made photonic systems a leading candidate for the next generation of telecommunication and radar technologies. The photonic platform enables high performance while maintaining a small footprint and provides a natural interface with fiber optics for signal transmission. However, producing sharp, narrow-band filters that are competitive with RF components has remained challenging. In this paper, we demonstrate all-silicon RF-photonic multi-pole filters with∼ 100× higher spectral resolution than previously possible in silicon photonics. This enhanced performance is achieved utilizing engineered Brillouin interactions to access long-lived phonons, greatly extending the available coherence times in silicon. This Brillouin-based optomechanical system enables ultra-narrow (3.5 MHz) multi-pole response that can be tuned over a wide (∼ 10 GHz …

Characterizing ultrashort optical pulses has always been a critical but difficult task, which has a broad range of applications. We propose and demonstrate a self-referenced method of characterizing ultrafast pulses with a multimode fiber. The linear and nonlinear speckle patterns formed at the distal end of a multimode fiber are used to recover the spectral amplitude and phase of an unknown pulse. We deploy a deep learning algorithm for phase recovery. The diversity of spatial and spectral modes in a multimode fiber removes any ambiguity in the sign of the recovered spectral phase. Our technique allows for single-shot pulse characterization in a simple experimental setup. This work reveals the potential of multimode fibers as a versatile and multi-functional platform for optical sensing.