As silicon photonics-based circuit designs transition from lab to fab, an end-to-end automated measurement flow is required to address a unique combination of high flexibility in test conditions and high volume. This paper describes such a flow for process design kit (PDK) development in the state-of-the-art 300 mm CMOS-compatible silicon photonics foundry at the Albany NanoTech Complex in Albany, NY. Presenting details of this measurement flow will offer considerable cost and time savings to new users in this area. The measurement flow begins at the layout stage, where users can instantiate various combinations of pre-characterized padsets that contain DC/RF pads and optical couplers, which are compatible with the automated electro-optic setup used for measurements. These padsets are offered via two options: (1) a script-based layout builder tool or (2) a parametric cell in a “Measurement Design Kit” offering in a design automation platform, which is an analog to a PDK. Special marker layers are added to the padsets, whose coordinates are extracted after the layout is complete. The coordinates are then passed to fiber positioners on the semi-automated prober while performing measurements. Electro-optic measurements are performed across the wafer using vertical coupling, which is well-suited for large-scale measurements. The wafer is placed on a 300 mm prober with automated fiber positioners that can optimize optical coupling across six degrees of freedom. The electro-optic measurement setup is based on the Keysight Photonic Application Suite. It includes a tunable laser, polarization synthesizer, and multi-channel detectors that measure transmission in both TE and TM polarizations. A lowloss optical switch matrix is programmed to switch connections between lasers and detectors to 16 grating couplers in the padset. The entire measurement setup, including the prober and instruments, is driven using the Python-based SweepMe! automation framework, which is modular and allows for the easy creation of test plans.
In this work we explain the methodology and techniques for building an end-to-end design enablement (DE) platform from component design to process design kit (PDK) release for silicon photonics-based photonic integrated circuit (PIC) design. Elements of the DE include: component design, layout and test site development, measurement infrastructure and PDK development. Our methodology builds on the best practices followed in CMOS and RF foundries but adds unique features specific to silicon photonics. The DE flow is developed on the American Institute for Manufacturing Integrated Photonics’ (AIM Photonics) 300 mm silicon photonic technologies manufactured in a limited-volume foundry at the Albany Nanotech Complex, in Albany, NY. For component development, the AIM Photonics PDK offers a process stack file supported in Lumerical platform that applies linewidth corrections and doping information to imported layouts increasing the efficiency and accuracy of the design. For test sites, an automated layout and connectivity framework is explained that allows users to generate a layout from spreadsheet inputs that is also compatible with automated waferscale measurements. AIM Photonics PDKs include layout, models and design-rule-check (DRC) tools that are offered across multiple platforms. The DRC decks are offered in commercial tools such as Cadence and Synopsys, as well as KLayout. We present features of layouts and communication with schematics. In addition, we also explain techniques for processing and analyzing measured statistical data and extracting platform specific compact models. Presenting this methodology to the wider community is integral to the mission of AIM Photonics and will be of immense benefit particularly to small organizations engaged in prototype development.
The reduction of optical loss for integrated photonics I/O is an important area of active research. Edge coupling (end-firing) is a key I/O technology, having advantages over grating couplers in terms of spectral bandwidth and lower insertion loss1. Low-loss edge coupling into silicon waveguides will be critical to datacenters and telecommunications systems in order to help accommodate the aggressive growth of data analytics applications2. In this work, we investigate the coupling losses from optical fiber (SMF-28) into on-chip silicon waveguides using silicon nitride edge couplers with varying chip facet angles. The expected losses were simulated using Three Dimensional Finite-Difference Time-Domain (3D-FDTD) modelling and measured experimentally to close the design-fabrication loop. The chips were produced within a state-of-the-art 300 mm CMOS foundry, using edge couplers from the foundry Process Design Kit (PDK). During optimization of the photolithography and dry etching process, the facet angle deviation from 90° was minimized. Insertion loss of the SiN edge coupler was investigated via transmission measurements utilizing both cleaved fibers and fiber V-grooves. Facet angles varied from approximately 75°–90° were tested for insertion loss and trends were consistent with the 3D-FDTD modelling. Measurements were performed over a range of 1450–1650 nm using a tunable laser source and optical power meter. In addition, facet insertion loss was isolated by using propagation loss data from an in-line testing tool that measured silicon waveguides propagation losses, on wafer and in the same wavelength band.
A novel process design kit (PDK) offering providing seamless access to the Albany NanoTech Complex’s 300mm foundry with a mission to promote silicon photonics technology is demonstrated. Unlike traditional pure-play foundries, we have developed a framework that allows our PDKs to contain libraries developed by internal and external domain experts. In addition to integrated Electronic Photonic Design Automation (EPDA) platforms, our PDK is also released in an alternate PIC design flow that the lowers the cost barrier for organizations. Further, our PDKs target a broad application space that includes telecom as well emerging areas such as sensors and quantum photonics – all with the ability for onboard light sources. A PDK from American Institute of Manufacturing (AIM Photonics) will be discussed that demonstrates these features.
The American Institute for Manufacturing Integrated Photonics (AIM Photonics) runs a silicon photonics multi-project wafer (MPW) program providing riders with access to silicon photonic devices and circuits fabricated in a state-of-the-art 300 mm CMOS line. Current MPW offerings include both silicon and silicon nitride waveguides, GHz modulation/detection, electro-optic switches and filters, low-loss edge coupling, three metal levels, and supports operation in the O, C, and L bands. Often propagation loss is not prioritized for active MPW runs in favor of other key parameters such as modulation speeds, photodiode responsivity, device size, spectral bandwidths, etc. However, for areas such as quantum technology, sensors, LiDAR, and data communications it is an imperative to incorporate both low-loss waveguides and active devices on a single die. These application areas require lower propagation losses because they either use single photons, high Q resonators, and/or require high efficiency coupling for lasers/SOAs. As part of our updated MPW integration, we have demonstrated losses of 1.1 dB/cm in Si strip waveguides and 0.4 dB/cm in SiN strip waveguides, a reduction of 1.4 dB/cm and 1.6 dB/cm, respectively, from our published MPW values.
There is significant interest in developing laser wavelengths between 700 and 800 nm that may then be frequency doubled to the UV for applications in spectroscopy and atomic physics. We present our most recent results on both a 739 nm AlGaAs/AlGaInP VECSEL, where we demonstrate 150 mW of CW power suitable for frequency doubling to the Yb+ cooling transition at 369.5 nm, and a 780nm AlGaAs/AlGaInP VECSEL which was utilised in a novel demonstration of second harmonic generation in a Zinc-indiffused MgO:PPLN waveguide. In the latter we have generated 1 mW of power at 390 nm.
We report on the fabrication and characterization of Er:YGG films suitable for waveguide amplifiers that could in principle be used in integrated path differential absorption lidar systems. Presented is our fabrication technique, comprising pulsedlaser- deposition growth of ~10 μm-thick crystalline films, their channeling via ultraprecision ductile dicing with a diamond-blade, producing optical quality facets and sidewalls, and amplifier performance. Net gain at 1572 nm and 1651 nm is obtained for the first time in Er-doped YGG waveguide amplifiers. Additionally, in a channel waveguide a maximum internal gain of 3.5 dB/cm at the 1533nm peak was realized. Recent crystal film quality improvements promise further performance enhancements needed for the intended application for high-peak power sources in the 1.6-μm spectral region targeting Earth observation systems for monitoring greenhouse gases.
We demonstrate the fabrication of a mechanically robust planarised fibre-FHD optical composite. Fabrication is achieved through deposition and consolidation of optical grade silica soot on to both an optical fibre and planar substrate. The consolidated silica acts in joining the fibre and planar substrate both mechanically and optically. The concept lends itself to applications where long interaction lengths (order of tens of centimetres) and optical interaction via a planar waveguide are required, such as pump schemes, precision layup of fibre optics and hybrid fibre-planar devices. This paper considers the developments in fabrication process that enable component development.
Integrated optics is becoming increasingly important for applications in quantum information processing, quantum
sensing and for advanced measurement. Intrinsically stable and low-loss it provides essential routing and coupling for
quantum optical experiments offering functions such as interconnects, couplers, phase delays and routing. Silica-onsilicon
has particular attractions, and in this work the fabrication approaches and advantages of the technique will be
explored. In particular, UV direct writing of waveguides and Bragg gratings proves useful for its rapid-prototyping
capability and its ability to provide grating for characterization of components for loss, birefringence and coupling ratio.
This review concentrates on the fabrication of planar waveguide devices, and ways in which direct UV writing provides
important functionality. Examples of applications of silica-on-silicon waveguides include quantum enhanced
interferometry, teleportation, boson sampling as well as hybrid operation for single photon detection with transition edge
sensors directly placed onto waveguide devices.
Ductile regime dicing has been used to machine a variety of optical materials to produce waveguides for lasers, multimode
interference devices and non-linear devices. However, few papers discuss the properties of the machining, either
qualitatively or quantitatively. In this work ductile regime dicing of germanium, Yttrium Aluminum Garnet (YAG),
lithium niobate and silicon for photonic applications are reported. Machining parameters are discussed, surface
micrographs shown, and surface roughnesses are calculated for each sidewall machined. The sidewall average surface
roughnesses (Sa) were measured to be 2.1 nm for germanium, 3.5 nm for YAG, 7.9 nm for lithium niobate and 8.6 nm
for silicon.
An optomechanical dual cantilever device has been fabricated with applications as a displacement sensor and variable attenuator. A novel fabrication approach using a precision dicing saw has benefits for fabrication time, cost and energy consumption. The displacement sensor sensitivity is 0.8 dB/micron and a suppression ratio of 25 dB is obtained when the device is used as an attenuator.
The authors present a direct UV writing approach to fabricate fiber Bragg gratings (FBGs) and gratings in
photolithographic waveguides. The technique uses two coherent UV beams, which are focused to a small spot (~7μm
diameter) at the point at which they overlap. The resulting interference pattern at the foci consists of fringes which are
used to define several grating planes per exposure, giving greater design flexibility and a significantly larger accessible
spectral range compared to traditional approaches. The typical index contrast during grating fabrication is observed to be
4.7×10-3, at writing speeds of 8 mm/min.
We have demonstrated two monolithically integrated Bragg grating based accelerometers, both with the optical path and mechanical structure being made from the same substrate. The unique fabrication techniques, Direct UV Writing and precision dicing, used to create the glass microcantilevers are discussed. We show experimental results from two different Bragg grating based interrogation systems, one utilizing a single Gaussian apodized Bragg grating and the other utilizes two spectrally matched Bragg gratings forming a Fabry-Pérot interferometer. Sinusoidal accelerations were applied to both devices and their sensitivities were found to be 0.67±0.035 mV/g and 14.0±0.44 mV/g for the single Bragg grating and Fabry-Pérot interferometer respectively.
Preparation of high quality facets for low-loss coupling is a significant production issue for integrated photonics, usually requiring time consuming lapping and polishing. Recently, the development of precision dicing saws with diamond impregnated blades has allowed the achievement of optical grade surfaces in optical materials based on dicing alone. In this report we investigate the optimization dicing conditions to achieve optical quality surfaces in a silica-on-silicon planar substrate and show what can be achieved by correct selection of machining parameters.
Tilted Bragg gratings (TBGs) have been shown to have a number of practical uses in planar geometries, demonstrating polarization capabilities and allowing excitation of surface plasmons. Fabrication and characterization of TBGs has been carried out in silica-on-silicon waveguides to highlight potential planar applications. An initial investigation into the coupling behaviour of TBGs has been undertaken, with greater than -20 dB coupling achieved for even small angle gratings (5 °). Experimental analysis of these TBG systems provides insight into future applications of the planarized devices.
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