We propose a novel methodology employing deep photonic networks comprising cascaded Mach-Zehnder Interferometers (MZIs) to illustrate the proficiency of on-chip polarization handling. By applying gradient-based optimization techniques to tailor specific phase profiles within successive layers of MZIs, we demonstrate the functionality of devices adept at power division in both polarization-dependent and polarization-independent modalities. In silico simulations underscore the cutting-edge performance metrics achieved, encompassing a bandwidth exceeding 120 nm centered at 1550 nm, an extinction ratio surpassing 15 dB, and transmission bands characterized by flat-top profiles. These results prove the comprehensive capabilities of our deep photonic network ecosystem in polarization management, thereby unveiling promising prospects for advanced optical applications necessitating versatile polarization handling capabilities.
As guided-wave circuits continue to increase in complexity, designing efficient and compact on-chip building blocks for these circuits continues to be a crucial research and development objective for many photonic platforms. Despite this critical requirement, the best-performing devices still require computationally intensive simulations that can take up to days, with no guaranteed results. To address this challenge, we introduce a novel, data-driven, and extremely rapid eigenmode expansion (EME) method for designing compact and efficient integrated photonic devices. In contrast to typical EME, our method models a given waveguide geometry using a pre-calculated dataset of optical scattering matrices and effective indices, therefore easily parallelized to computational accelerators like GPUs. This results in individual device simulation times of 10s of milliseconds, representing a speedup of more than 1000x over traditional methods. We then couple this approach with nonlinear iterative optimization methods and demonstrate the design and optimization of highly efficient nanophotonic devices, including tapers, 3dB splitters, and waveguide crossings within ultra-compact footprints. For all three categories of devices, we verify the response of the final geometry using 3DFDTD simulations and demonstrate state-of-the-art metrics, including below 0.05dB of insertion loss, near-perfect mode matching to the desired output, and broadband operation capabilities of over 100nm. Our unique combination of efficient and physically accurate device simulation methods, together with nonlinear optimization, enables the design of high-performance and ultra-compact photonic building blocks. These capabilities present avenues for developing more complex and previously elusive optical functionalities with unprecedented computational efficiency.
Inverse design approaches with topology optimization can yield in highly efficient devices; however designing fabrication-compatible, broadband, yet simultaneously fabrication-tolerant devices still widely remains a challenge. Here, we design a broadband and fabrication-tolerant 10% silicon-based power tap using 3D-FDTD simulations and topology optimization, and demonstrate its experimental performance. The power tap has a compact footprint of 7.0 μm×3.1 μm, and achieves a broadband and spectrally flat operation from 1500 nm to 1600 nm. The device was specifically built to be fabrication-tolerant using an approach that maintains high performance under over-etch and under-etch scenarios by maximizing the contiguous area of the silicon layer in the final device. This tolerance was verified with 3D-FDTD simulations with 15 nm over-etch and under-etch modifications, demonstrating a change of less than 0.64 dB at either output port compared to the original device response at 1550 nm. The designed power tap was fabricated using a standard 220 nm thick silicon-on-insulator platform. The experimental measurements match closely with the design target and 3D-FDTD results, achieving state-of-the-art performance with excess losses as low as 0.23 dB and broadband operation. The output ports of the device also exhibit extremely flat spectra, where the transmission remains between 0.86 and 0.92 for the through port, and between 0.06 and 0.14 for the tap port throughout the 1500-1600 nm spectral range. These results represent the state-of-the-art experimental performance in compact power taps, and prove the effectiveness of fabrication-tolerant optimization.
Using a highly-scalable and physics-informed design platform with custom Mach-Zehnder interferometers (MZIs), we design and experimentally demonstrate a 1 × 2 wideband duplexer on silicon operating within 1450-1630 nm. The device is constructed from six layers of cascaded MZIs whose geometries are optimized using an equivalent artificial neural network, in a total timeframe of 75 seconds. Experimental results show below 0.72 dB deviation from the arbitrarily-specified target response, and less than 0.66 dB insertion loss. Demonstrated capabilities and the computational efficiency of our design framework pave the way towards the scalable deployment of custom MZI networks in communications, sensing, and computation applications.
We propose a deep photonic interferometer network architecture for designing fabrication-tolerant photonic devices. Our framework incorporates layers of variation-aware, custom-designed Mach-Zehnder interferometers and virtual wafer maps to optimize broadband power splitters under fabrication variations. Specifically, we demonstrate 50/50 splitters with below 1% deviation from the desired 50/50 ratio, even with up to 15 nm over-etch and under-etch variations. The significantly improved device performance under fabrication-induced changes demonstrates the effectiveness of the deep photonic network architecture in designing fabrication-tolerant photonic devices, and showcases the potential for improving circuit performance by optimizing for expected variations in waveguide width.
As the demand for scalable and complex on-chip nanophotonic devices with multi-wavelength and multi-mode optical functionalities increases, fast and efficient design algorithms have become an essential tool in silicon photonics. Although inverse design coupled with adjoint optimization has emerged as a powerful method to design such devices by requiring only two simulations in each iteration of the optimization process, these simulations still make up the vast majority of the necessary computations, and render the design of complex devices with large footprints computationally infeasible. Here, we present a substantial speed-up in the finite-difference frequency-domain (FDFD) simulations by introducing a factorization caching approach, and significantly reduce the computational requirements for device optimization. Specifically, we cache the symbolic and numerical factorizations of system matrices corresponding to discretized Maxwell’s equations, and re-use them throughout the entire optimization. Using this method, we reduce the majority of the computational operations in the FDFD simulations and drastically improve the simulation speeds. To demonstrate the resulting computational advantage compared to conventional FDFD methods, we show simulation speedups reaching as high as 8.5-fold in the design of broadband wavelength and mode multiplexers. These results present significant enhancements in the computational efficiency of inverse photonic design, and can greatly accelerate the use of machine-optimized devices in future photonic systems.
In this study, we propose on-chip deep photonic networks with custom-designed Mach-Zehnder interferometers (MZI), allowing for the design of devices with arbitrarily defined dispersion profiles. We demonstrate a custom simulation and optimization framework to optimize dispersion and transmission profiles of these MZI-based networks. We experimentally show a proof-of-concept two-port photonic network with a highly nonintuitive, triangular dispersion profile in the C-band, while simultaneously achieving a flat band transmission with less than 0.7 dB insertion loss. We also demonstrate capabilities with multi-port photonic networks to enhance design freedom for customizable dispersion profiles, opening up new possibilities for on-chip dispersion engineering.
Recent integrated optical phased array architectures, results, and applications will be reviewed. Beam-steering optical phased arrays monolithically integrated with on-chip rare-earth-doped lasers and heterogeneously integrated with CMOS driving electronics will be shown. Passive integrated optical phased arrays that focus radiated light to tightly-confined spots in the near field and that generate quasi-Bessel beams will be discussed. Finally, integrated-phased-array-based visible-light holographic displays will be proposed as a scalable solution towards the next generation of augmented-reality head-mounted displays; passive near-eye holographic displays, visible-light liquid-crystal modulators, and liquid-crystal-based visible-light phased arrays will be presented.
Mode-locked lasers provide extremely low jitter optical pulse trains for a number of applications ranging from sampling of RF-signals and optical frequency combs to microwave and optical signal synthesis. Integrated versions have the advantage of high reliability, low cost and compact. Here, we describe a fully integrated mode-locked laser architecture on a CMOS platform that utilizes rare-earth doped gain media, double-chirped waveguide gratings for dispersion compensation and nonlinear Michelson Interferometers for generating an artificial saturable absorber to implement additive pulse mode locking on chip. First results of devices at 1.9 μm using thulium doped aluminum-oxide glass and operating in the Q-switched mode locking regime are presented.
We report ultra-narrow-linewidth erbium-doped aluminum oxide (Al2O3:Er3+) distributed feedback (DFB) lasers with a wavelength-insensitive silicon-compatible waveguide design. The waveguide consists of five silicon nitride (SiNx) segments buried under silicon dioxide (SiO2) with a layer Al2O3:Er3+ deposited on top. This design has a high confinement factor (> 85%) and a near perfect (> 98%) intensity overlap for an octave-spanning range across near infrared wavelengths (950–2000 nm). We compare the performance of DFB lasers in discrete quarter phase shifted (QPS) cavity and distributed phase shifted (DPS) cavity. Using QPS-DFB configuration, we obtain maximum output powers of 0.41 mW, 0.76 mW, and 0.47 mW at widely spaced wavelengths within both the C and L bands of the erbium gain spectrum (1536 nm, 1566 nm, and 1596 nm). In a DPS cavity, we achieve an order of magnitude improvement in maximum output power (5.43 mW) and a side mode suppression ratio (SMSR) of > 59.4 dB at an emission wavelength of 1565 nm. We observe an ultra-narrow linewidth of ΔνDPS = 5.3 ± 0.3 kHz for the DPS-DFB laser, as compared to ΔγQPS = 30.4 ± 1.1 kHz for the QPS-DFB laser, measured by a recirculating self-heterodyne delayed interferometer (RSHDI). Even narrower linewidth can be achieved by mechanical stabilization of the setup, increasing the pump absorption efficiency, increasing the output power, or enhancing the cavity Q.
One of the key challenges in the field of silicon photonics remains the development of compact integrated light sources. In one approach, rare-earth-doped glass microtoroid and microdisk lasers have been integrated on silicon and exhibit ultra-low thresholds. However, such resonator structures are isolated on the chip surface and require an external fiber to couple light to and from the cavity. Here, we review our recent work on monolithically integrated rare-earth-doped aluminum oxide microcavity lasers on silicon. The microlasers are enabled by a novel high-Q cavity design, which includes a co-integrated silicon nitride bus waveguide and a silicon dioxide trench filled with rare-earth-doped aluminum oxide. In passive (undoped) microresonators we measure internal quality factors as high as 3.8 × 105 at 0.98 µm and 5.7 × 105 at 1.5 µm. In ytterbium, erbium, and thulium-doped microcavities with diameters ranging from 80 to 200 µm we show lasing at 1.0, 1.5 and 1.9 µm, respectively. We observe sub-milliwatt lasing thresholds, approximately 10 times lower than previously demonstrated in monolithic rare-earth-doped lasers on silicon. The entire fabrication process, which includes post-processing deposition of the gain medium, is silicon-compatible and allows for integration with other silicon-based photonic devices. Applications of such rare earth microlasers in communications and sensing and recent design enhancements will be discussed.
A key challenge for silicon photonic systems is the development of compact on-chip light sources. Thulium-doped fiber and waveguide lasers have recently generated interest for their highly efficient emission around 1.8 μm, a wavelength range also of growing interest to silicon-chip based systems. Here, we report on highly compact and low-threshold thulium-doped microcavity lasers integrated with silicon-compatible silicon nitride bus waveguides. The 200-μmdiameter thulium microlasers are enabled by a novel high quality-factor (Q-factor) design, which includes two silicon nitride layers and a silicon dioxide trench filled with thulium-doped aluminum oxide. Similar, passive (undoped) microcavity structures exhibit Q-factors as high as 5.7 × 105 at 1550 nm. We show lasing around 1.8–1.9 μm in aluminum oxide microcavities doped with 2.5 × 1020 cm−3 thulium concentration and under resonant pumping around 1.6 μm. At optimized microcavity-waveguide gap, we observe laser thresholds as low as 773 μW and slope efficiencies as high as 23.5%. The entire fabrication process, including back-end deposition of the gain medium, is silicon-compatible and allows for co-integration with other silicon-based photonic devices for applications such as communications and sensing.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.