The scale and performance of solid-state beam steering photonic circuits intended for solid-state integrated LIDAR applications have increased significantly over the past decade, but the incorporation of a suitably powerful and low-cost light source remains a barrier to the breadth of applications for which this technology is suitable. In this work we demonstrate beam steering from a 24-channel optical phased array based on silicon nitride waveguides, directly optically coupled to a tapered laser diode based on InGaAsP operating at a wavelength of 905 nm and capable of 2 W of output optical power. In this proof-of-concept demonstration, we find experimentally the coupling loss to be approximately -8 dB.

A silicon photonics optical phased array with a two-dimensional matrix of antennas is experimentally demonstrated in which the unitary antennas are optimized such that light can be emitted over a high fraction of the overall array surface. This design strategy can be used to obtain a low divergence emitted beam containing a significant fraction of the total emitted power, at the expense of a reduced beam steering range. This type of device can be suited to phase front correction in optical wireless communications systems.

The autonomous driving capabilities of future vehicles is a key technology today. In order to provide optimal functionalities and safety, an additional sensor has to be integrated in complement to Radar and Cameras. The Lidar technology is today considered as the recommended choice [1],[2]. However, Lidars have to be compatible with mobile applications and particularly cars specifications in terms of footprint, beam scanning speed and accuracy for optimal detection at long range, performances in various temperature conditions and at least manufacturability at low cost. Several technologies are considered to provide the beam scanning going from the micro-optics[3] that remain slow and expensive due to high precision optics or MEMs[4] or Flash[5] technologies that are still at high cost and complex flow. This paper describes the work carried out at CEA-LETI to validate a complete process flow based on an Optical Phase Array[6],[7],[8] photonic circuit and the addition of TSV and back side processing coupled to a fine pitch flip chip on a silicon interposer, thus introducing 3D and advanced packaging processes to the Photonic on silicon technology. Photonic processing choices and realization will be discussed followed by results related to the introduction of the 3D and advanced packaging choices leading to a functional demonstrator designed to validate the beam steering performances an provide a real-time demonstration

We demonstrate the integration of a photonic circuit containing passive and active components into a piezoelectric-actuated micro cantilever. A 16-channel optical phased array operating at a wavelength of 905nm provides beam scanning over a range of 17 degrees in one dimension, while the inclination of the entire circuit and consequently the angle of the output beam in a second dimension can be independently modified over a range of up to 40 degrees via the piezoelectric actuator.

This paper presents experimental studies on heterodyne Frequency Modulated Continuous Wave (FMCW) signal reception for different optical heterodyne configurations including internal and external mixing between an incoming signal and a local oscillator. Signals and potential noise sources from a fibered FMCW Mach-Zehnder Interferometer (FMCW MZI) are theoretically evaluated. These optical estimations (signal and noise) of various power spectral densities (PSD) are converted into electrical unities to be compared to the measurements.The PSD are validated by using a known alternating voltage with controlled frequency and amplitude. This validation is used to compare the experimental and theoretical detection limits of different FMCW photodetectors, including a Photonic Integrated Circuit (PIC) detector developed and produced at CEA. The detection limit achieved with this PIC module closely matches with the expected theoretical performances. It validates the optical and electronic architecture and the achievements of CEA's design. The miniaturization of this operational detection module is underway. In the future, it will be located on a single chip alongside two Optical Phased Arrays (OPA), one for emission and the other for reception.

Using wafer level fabrication techniques, we combine silicon photonics and MEMS technologies to demonstrate the integration of an active photonic beam-steering circuit into a piezoelectric actuated micro cantilever. An optical phased array (OPA), operating at a wavelength of 905nm, provides output beam scanning over a range of 17° in one dimension, while the inclination of the entire circuit and consequently the angle of the output beam in a second dimension can be independently modified over a range of up to 40° via the piezoelectric actuator. This combination of existing commercial silicon technologies can provide continuous, low-divergence, solid-state beam scanning for sensing applications, while avoiding the disadvantages associated with the use of a widely tunable source laser.

This work reports the development of an enhanced 2D beam scanning by combining 200 mm silicon (Si) photonics and 200 mm Si MEMS technologies. It demonstrates the fusion of an active photonic beam-steering circuit within a piezoelectrically actuated micro-cantilever. Operating at a wavelength of 905 nm, the optical phased array (OPA) enables beam scanning up to 17 degrees in one dimension. Simultaneously, the circuit's inclination, in a second dimension, can be independently adjusted over a range of up to 40 degrees via the piezoelectric actuator. This paper will focus on the technological process that combines photonics and piezoelectric materials, as well as the possibility of tailoring the cantilever resonance frequencies via the dimensional parameters, to suit various target applications.

AbstractThree dimensional sensing is essential in order that machines may operate in and interact with complex dynamic environments. Solid-state beam scanning devices are seen as being key to achieving required system specifications in terms of sensing range, resolution, refresh rate and cost. Integrated optical phased arrays fabricated on silicon wafers are a potential solution, but demonstrated devices with system-level performance currently rely on expensive widely tunable source lasers. Here, we combine silicon nitride photonics and micro-electromechanical system technologies, demonstrating the integration of an active photonic beam-steering circuit into a piezoelectric actuated micro cantilever. An optical phased array, operating at a wavelength of 905 nm, provides output beam scanning over a range of 17° in one dimension, while the inclination of the entire circuit and consequently the angle of the output beam in a second dimension can be independently modified over a range of up to 40° using the piezoelectric actuator.

The development of an ideal optical system to support Mixed Reality and Augmented Reality (AR) applications has raised a lot of interest in the scientific community in the last decades. The perfect device remains an inaccessible target and researchers have to focus on the optimization of some specific behaviors. Several years ago, we introduced a disruptive display concept to push the device integration to the limit, with the suppression of the optical system. This allows the imaging process to be considered in a different way with a specific monitoring of the field of view. With this 'smart glass' concept, the glass is the display, and the image is formed directly onto the retina with a combination of refractive and diffractive effects. This conceptual target allowed us to define a technological roadmap to support our development. Technologies involved in this concept concern principally the field of Photonic Integrated Circuits in the visible range, digital/analogic holography and Liquid Crystal devices. We will present the current state of our research with a particular focus on the holographic display element. Recent results related to analogic pixelated hologram recording validate and question both our technological and conceptual approach. We will show images formed by sparse holographic pixel distributions with controlled angular characteristics that demonstrate the mix of refractive and diffractive effects. The transmission behavior of this holographic device will also be analyzed.

This work shows a methodology to simulate photonic integrated circuits (PIC) using commercial IC simulators. For this, all photonic devices are modelled using Verilog-A language including transmission and reflection of light. For each model, both polarizations, transverse electric (TE) and transverse magnetic (TM) polarized waves, are considered. The methodology allowing to simulate resonant and interference effects is presented. The sim-ulations of waveguide and ring resonator are shown. The extraction of a Mach-Zender Interferometer illustrates the modellization based on measurements in our Silicon technology.

This paper describes the design, fabrication, and experimental characterization of several photonic integrated components specifically made for a novel retinal projection concept for augmented reality applications. The retinal projection concept is based on the combination of integrated optics and holography to generate a self-focusing image on the retina. The photonic integrated circuit used for the retinal projector is made of several passive photonic components fabricated with stoichiometric Si 3 N 4 : single-mode strip waveguides, variable radius bent waveguides, MMI couplers (Multi-Mode Interference), diffraction grating couplers and waveguide crossings. The photonic components are designed to work in the visible spectrum at λ = 532 nm. They are compact and generally show low losses, which are the two main requirements to easily insert the photonic integrated circuit on wearable glasses and enhance the image quality of the retinal projector. Our photonic components can also find applications in a variety of other fields related to the visible spectrum, such as biophotonics, optical phased arrays, visible light communication and more.

We present development work relating to integrated optical phased arrays (OPA) for use in a 905nm time-of-flight (TOF) LIDAR system. Pseudo two-dimensional, single wavelength beam steering from a 7x32 channel silicon nitride-based photonic circuit was achieved, with optimized single-pass thermo-optic phase shifters with Pπ = 30mW. Direct optical coupling of a photonic chip to a 7 W tapered GaInAsP laser diode is also shown to suggest a pathway to achieving medium-to long-range integrated LIDAR using a low-cost light source.

We demonstrate an ultra-broadband 2x2 multimode interference (MMI) coupler leveraging subwavelength grating (SWG) nanostructures fabricated by immersion lithography. Excess loss of $\lt2$ dB, power imbalance $\lt1.5$ dB and phase error $\lt 5^{\circ}$ have been measured for a wavelength range of 1300 – 1680 nm. The small feature sizes, down to 75 nm, were well-defined using immersion lithography and optimized optical proximity correction.

We report a 256 channels 1D optical phased-array (OPA) based on plasma-dispersion effect. This system exhibits ultra-low power consumption (~1mW) revealing the potential of carrier-depletion scheme at low doping dose for solid-state LiDARs applications.

Near-eye displays have become a technology of high interest for Augmented, Virtual and Mixed reality due to the unique immersive experience they provide to the user. The majority of these devices use macroscopic optical elements that make them bulky and heavy. Our team has proposed a disruptive near-eye display concept that uses the self-focusing effect to project an image to the user’s retina. To form an image, emissive points are generated from a dense photonic integrated circuit embedded within the lens of a pair of smart glasses. In this work, we present the design of a dense routing architecture that addresses thousands of randomly distributed emissive points from a few hundred inputs. The circuit combines unbalanced waveguide splitter trees with a non-periodical addressing onto a dense waveguide network. We present the design optimization through numerical simulations and estimate the overall device performance based on simulation results. A waveguide interlayer crossing simulation indicates losses better than 0.003 dB/crossing, which guarantees low optical losses over thousands of crossings. By unbalancing correctly the splitter trees, we can obtain homogeneous power profiles over an emissive point distribution. The experimental validation of our design will be a major step towards the elaboration of a first prototype.

CEA aims at developing a compact 1550 nm Frequency Modulated Continuous Wave (FMCW) LiDAR on chip. In this paper, individual demonstrators, corresponding to three main components of a LiDAR (Light Distance And Ranging) system, are combined in a test bench: a FMCW laser source, an emission and reception Optical Phased Array (OPA) and an optical heterodyne detection module. Each component has been individually tested, but also evaluated in order to derive the system performance of a complete LiDAR. A test platform has been developed to calibrate an OPA fabricated at CEA platform, either in emission or in reception mode. The tested OPA includes 256 channels based on grating antennae, with 1.5 μm pitch and 256 thermo-optic phase shifters. More recently, this platform has been completed with a FMCW interferometer, where the FMCW LiDAR detection can be evaluated through a mixed propagation setup, composed of optical fibers and free space. Then, the OPA may be inserted into this setup. Therefore, the optical fiber FMCW interferometer has been optimized to detect the lowest signal (typically less than one hundred fW) and to estimate the signal-to-noise ratio (up to almost 30 dB) with low noise photodiodes. Performance has been compared to theoretical predictions. Then, our custom OPA is included inside this experimental setup in a free space propagation environment. The performance measurements extracted from the spectral analysis are in agreement with the expectations.

We experimentally demonstrate beam steering in an optical phased array (OPA) featuring a mixture of individual and cascaded phase modulator architecture embedded in the binary splitter tree. We show equivalent beam forming in a 16 channel OPA with 16 separate applied voltages and a cascaded 16ch OPA with 6 control voltages. A 32ch OPA with 10 control voltages is also demonstrated. These results illustrate a flexible means of designing an OPA with significantly fewer electrical connections than the optical channel count, while minimizing the impact of waveguide phase errors on the output beam quality.