This PDF file contains the front matter associated with SPIE Proceedings Volume 12425, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

The physics taking place in optomechanical cavities can be used to operate on microwave signals in the optical domain, which belongs to the realm of microwave photonics. Here we review our recent work on the processing of microwave signals via optomechanical cavities built on silicon chips. Using a silicon optomechanical crystal cavity with a mechanical mode in the phonon lasing regime, we show that the generated microwave tone displays a phase noise low enough to be used in practical applications. We also demonstrate frequency conversion of realistic data streams making use of the inherent nonlinear behavior of the cavity. We also discuss how the long-term stability of the resulting optomechanical microwave oscillator can be improved by locking two different mechanical modes and bringing them to the phonon lasing states. These results suggest that ultra-compact optomechanical cavities show potential application in photonics-enabled next-generation wireless networks and satellite communications.

We report on a waveguide-type chromatic dispersion compensator comprising a pair of arrayed-waveguide gratings and an array of 100 fixed delay lines. The compensator was fabricated with a silica waveguide with the relative index difference of 2.3%. We connected the first arrayed-waveguide grating output to the second arrayed-waveguide grating input through the delay lines. Each demultiplexed wavelength component at the first arrayed-waveguide grating experiences assigned delay for the dispersion compensation and is again multiplexed at the second arrayed-waveguide grating. The compensator can trim the dispersion of ten channels with spacing of 2.0 nm. The obtained dispersion compensation value and bandwidth at each channel were about -53 ps/nm and 1.6 nm, respectively. The compensator is helpful to the dispersion compensation for high-speed intensity-modulated signals including on-off keying and pulse amplitude modulation signals.

This work proposes the design of optical SR latch. The fundamental component of the latch is a micro-ring resonator (MRR), which utilizes a plasma dispersion effect with an applied reverse bias voltage to tune its resonance wavelength. The proposed SR latch is made up of two identical micro-ring resonators with similar doped regions and the same logic mode of operation. The memory properties are realized by implementing the feedback loop between the input and output of the circuit. A time-varying simulation is carried out by applying two pseudorandom electrical input signals S and R into the circuit at a data rate of 25 Gbps. The work concludes with a comparative analysis between two optical SR latches (NOR-based and NAND-based).

We treat operational principles and resulting properties of periodic photonic lattices. These lattices can be fashioned in the lab as 2D or 1D patterned films on substrates or modeled as membrane particle arrays for simplest geometry. Even though the basic periodic element, namely the diffraction grating, has been known for 100+ years, new solutions and applications based on periodic spatial modulations continue to appear. In recent literature, corresponding assemblies and devices are called metamaterials or metasurfaces. Current lithographic technology enables fabrication of spatial modulations on subwavelength scales in one, two, or three dimensions. The resulting diffractive optical elements or metasurfaces may support waveguide modes when designed with proper refractive indices and dimensions. Waveguide modes that are guided or quasi-guided in waveguide gratings experience stopbands and passbands as the light frequency is varied. Associated with these leaky bands, there appear resonant bright channels and non-resonant dark channels in the spectra. The bright state corresponds to a high reflectivity guided-mode resonance (GMR) whereas the dark channel represents a bound state in the continuum (BIC). We review past results placing these physical observations in historical context. The BIC states correspond to symmetry-blocked resonance channels. In earlier work, the BIC was often referenced as the non-leaky band edge. We show theoretical dispersion charts and experimental sampling of those revealing GMR and BIC channels. Along similar lines, recent results show experimental lattice band dynamics of simple resonance systems. Finally, the connection of the classic Rytov effective medium formalism to the GMR/BIC states is presented. We show that all key resonancelattice properties are embodied in Rytov-equivalent homogeneous waveguides. This interesting fact overwhelmingly proves the waveguide character of the lattice systems.

Integration of photonic circuits on silicon offers a unique opportunity to address the scaling of inter- and intra-chip communications in an energy-efficient and cost-effective manner. Mode-division multiplexing (MDM) is deemed as one of the most promising technologies to increase aggregated data bandwidth and avoid a communication capacity crunch. In this invited talk, we review our latest advances on integrated silicon mode multiplexers, including new topologies based on subwavelength grating (SWG) metamaterials for extended broadband operation and higher-order mode support. Specifically, we report on an ultra-broadband multiplexer based on a phase shifter and a multimode interference (MMI) coupler both engineered with subwavelength metamaterials. Experimental measurements of a complete multiplexer-demultiplexer link show losses lower than 2 dB and crosstalk below -17 dB over a bandwidth of 245 nm (1427 – 1672 nm).

In this paper, we present an overview of our innovative computational methodology based on statistical learning optimization to optimize highly efficient and robust metasurface designs. We have optimized highly efficient single- and multi-functional devices. In addition, we have extended our multi-objective optimization to account for manufacturing imperfections.

The identification of chemicals from their mid-infrared spectra has a wide range of applications, such as forensics and environmental monitoring. This is generally done using laboratory benchtop tools, such as the Fourier transform infrared spectrometer. Although such systems offer high performance, alternative platforms offering reduced size, weight, and cost can enable a host of new applications. In this presentation, we will describe our recent work on a compact microspectrometer platform for chemical identification.

In this presentation we will describe the technologies developed at the Jet Propulsion Laboratory for space remote sensing applications in mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) spectral regions. Remote sensing and characterization of high temperature targets on the Earth’s surface is required for many cross-disciplinary science investigations and applications including fire and volcano impacts on ecology, the carbon cycle, and atmospheric composition. For decades this research has been hindered by insufficient spatial resolution and/or detector saturation of satellite sensors operating at short and mid-infrared wavelengths (1-5μm) where the spectral radiance from high temperature (<800 K) surfaces is most significant. To address this critical need, the Jet Propulsion Laboratory and partnering institutions are developing a compact modular high dynamic range (HDR) multispectral imager concept, with the flexibility to operate in the short, mid- or long-wavelength infrared spectral bands.

LiDAR sensors are key to ensure safety and efficiency of autonomous vehicles and mobile robotic systems. But current commercial LiDAR technologies cannot face the issues in terms of costs, reliability and form factors that are hindering widespread adoption. Steerlight, a CEA-Leti spin-off, develops a new generation of on-chip LiDARs that relies on Frequency Modulated Continuous Wave (FMCW) and Silicon Photonics. FMCW provides instantaneous depth and velocity acquisition while Silicon Photonics enables the integration of the optical and electronics functionalities on a single chip. This paper will first describe the proposed silicon photonics based architecture. Subsequently, various demonstrations will illustrate the roadmap towards miniature and scalable LiDARs. Such features will contribute to making a wide range of devices smarter and safer, beyond the automotive and robotics markets.

Optical phased arrays (OPAs) have seen frequent implementation in applications requiring beam steering such as light detection and ranging (LiDAR) and free-space optical communications. These applications require narrow beamwidths and large steering ranges which are seldom found simultaneously. Grating sidelobes found in the far field patterns limit the steering range of an OPA due to the uniformly pitched elements spacing of < λ/2. Here we implement an array design that exploits the rotational symmetry of adjacent subarrays to suppress the sidelobes for both planar and circular sub-array lattices, greatly enhancing the OPA’s steering range.

Non-contact detection of photoacoustic signals is important for various applications, particularly in medical sensing and imaging, where contact methods can be uncomfortable or risky for the patient. Techniques using optical detection of vibrations, such as laser doppler vibrometers (LDVs), have been proven to be a key component for enabling non-contact photoacoustic sensing. However, most LDV systems rely on fiber-based or free-space optics, which can be unwieldy and expensive, especially for multiple location sensing. In this work, we present a compact, photonic integrated circuit (PIC)-based homodyne LDV system for the detection of photoacoustic signals. The system is fabricated on a silicon-on-insulator platform, which has the potential to be low-cost in case of medium or large volume production. To generate the photoacoustic signals, we used a 532 nm pulsed laser directed towards a target embedded in a silicone phantom designed to mimic the acoustic properties of human tissue. The target consists of an ink-solution-filled channel, which absorbs the excitation light and generates acoustical signals within the phantom through the photoacoustic effect. After performing a series of measurements with different ink concentrations, we found a good correlation between the photoacoustic signals detected by the on-chip detectors and the absorption of the target. Our system was able to detect ink solutions with absorption values as low as 5 cm⁻¹, an order of magnitude lower than the typical absorption of whole blood at 532 nm. These results demonstrate that PIC-based LDVs can be used to realize compact and low-cost non-contact detection for photoacoustic biomedical sensing applications.

A new approach for determining the concentration composition of a multi-element media using a micro-ring resonator (MRR) is proposed which allows for noise removal as well as moderately higher average accuracy. This method uses two neural networks, namely a convolutional neural network (CNN) and a deep neural network (DNN). The CNN differentiates the transmission spectrum from the noise. This spectrum is used to obtain selected features before being fed into the DNN, which determines the concentration of each chemical in the analyte. Both models are trained to work with a silicon on-insulator ring resonator operating between the infrared wavelengths of λ=1.46 μm to λ=1.6μm on mixtures of water, ethanol, methanol, and propanol by using simulation data obtained from finite difference eigenmode, although the same approach can be used with other designs and chemical combinations. The CNN was trained using the MRR transmission spectra superimposed with white Gaussian noise as well as Poisson noise to mimic various noise sources, while the DNN underwent training on the extracted features. Average Root-Mean-Square Error was for a range of concentrations from 0.0357-75% is 5.531%.

OLED-on-Silicon technology has reached industry maturity for OLED (organic light emitting diode) microdisplays, e.g., in near-to-eye applications. Anyway, there is a huge amount of further applications, which can be addressed with an organic frontplane on an integrated CMOS backplane, e.g., OPD (organic photo diode). This paper will report on latest results in the field of OPD-on-silicon sensing as well as OLED-on-silicon displays, sketching up the impact of a universal photonic platform comprising emitters, photodetectors and CMOS driving and read-out circuitry, based on application scenarios.

Wavelength stabilization of external cavity lasers is a of key importance to exploit their sub-kHz intrinsic linewidth. In this work we demonstrate < 20 dB optical phase noise reduction at acoustic frequencies using a simple off-the-shelf electronic feedback loop. The novelty here is that we exploit an on-chip optical frequency discriminator (OFD) in Si3N4 (TriPleX), based on an aMZI with a path length difference of 1.4 m, having less than 10 dB loss. The used setup has a bandwidth of approximately 1 MHz, allowing for wavelength modulation depth in the order of tens of MHz.

In metallic mirror Micro-opto-electro-mechanical system (MOEMS) Fabry Pérot interferometer (FPI) chips, sticking and non-reversible pull-in of the two mirrors is lowering the lifetime of the component. Adding 10 nm of atomic layer deposited (ALD) of semiconducting titanium dioxide (TiO₂) coating over the cavity of the mirror decreased the static charge inside the mirror cavity preventing sticking of the mirrors and the mirrors survived actuated to pull-in for more than 1000 times. As too thick layers can optically lower the performance of the mirror and overly thin layers would not decrease the static charge, we studied three different TiO₂ thicknesses of 3 nm, 5 nm, and 10 nm. In conclusion, 10 nm TiO₂ layer does not optically interfere in the FPI´s performance and it has the best conductivity of all tested TiO2 film thicknesses.

Future remote imaging systems promise spectroscopic functionalities extending well beyond the visible wavelengths. This allows real-time spectral information to be gathered from multiple wavelength bands which is highly attractive for numerous remote sensing spectroscopy/imaging applications and aids target recognition. This paper briefly presents a micro-electromechanical systems (MEMS) based electrically tuneable adaptive filter technology developed for the technologically important infrared (IR) bands of the electromagnetic spectrum and reports on the progress towards extension to the significantly longer wavelength THz band. The demonstrated concepts focus on merging MEMSenabled dynamic modulation with the spectral sensitivity and selectivity of metamaterials, as well as on the possibility of adopting the rapidly evolving 3D printing technologies.

In this paper, we present an improved version of an Application-Specific Photonic Integrated Chip for solving Partial Differential Equations (PDEs). This novel chip is designed to solve PDEs with specific reflecting boundary conditions, by means of a series of integrated mirrors at the edges.

Emerging applications such as light detection and ranging (LiDAR), on-chip interconnect and neuromorphic photonics demand higher complexity and integration density in photonic integrated circuits (PICs). Conventional InP PICs, although offers seamless integration of actives and passives, cannot meet this demand. In this talk, a InP membrane photonics platform will be presented and its recent progress will be reviewed. It features sub-micron waveguides together with native amplifiers. Therefore it has potential to achieving active-passive photonic integration with order-ofmagnitude higher density and complexity.

LiDAR, or light detection and ranging, is an active remote sensing system that accurately survey the surrounding environment. As the essential component of a LiDAR system, an optical phased array (OPA) plays a fundamental role in beamforming. Generally speaking, OPAs usually require a narrow beam width and a large steering range. Grating lobes are found to be limiting the steering range due to the inherently large uniform element spacing in the traditional phased array design. In this work, we provide design solutions to suppress and eliminate the grating lobes of three types of OPAs: rectangular, circular, and randomly distributed OPAs.

An Optoelectronic Millimeter Wave MOSFET consists of an MOS transistor, a millimeter wave generating diode and a laser / LED in the drain region, and photon / microwave sensors in the well / substrate regions. The MOSFET, millimeter wave diode, laser, and sensors are integrated as one transistor. When a gate voltage and a drain voltage are applied, the MOSFET is turned on, so as the millimeter wave diode, laser, and sensors. If the MOSFET is turned off, all devices are turned off. Nonlinear optical computing of multiple bandwidths and much higher speeds can be accomplished. A different millimeter wave photonic CMOS model, which generates multiple nonlinear optical and microwave spectrums, is needed. In this report we will look into detailed circuit design using the new nonlinear photonic RF transistor model, including designs of AND / OR / NOR / XOR / OP AMP logic gates. Nonlinear optical filters and polarization are used in these deigns, which are different from traditional IC design.