This PDF file contains the front matter associated with SPIE Proceedings Volume 12575, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Ultrafast-ultralong ring fiber lasers represent a new passively mode-locked laser architecture reliant on the use of Raman-assisted nonlinearity management over cavities extending tens of kilometers and fast, polarization-insensitive saturable absorption. These new sources are capable of supporting the generation of stable pulses shorter than 200 fs with ultra-low repetition rates of a few tens of kHz, overcoming previous limitations to pulse duration and peak power imposed by dispersive effects. The unique characteristics of this new family of ultrafast fiber oscillators makes them suitable for a broad range of applications. In this invited talk we will review some of the latest advances on the topic, focusing on the optimal design and implementation of such lasers.

We present the development of SOI waveguides with low-loss (~1.5 dB/cm) single-moded guidance over an octave of frequency. Broadband single-moded guidance is needed for on-chip mid-infrared spectroscopy and this cannot be provided by conventional waveguide geometries in standard material platforms. The reported waveguides require a simple fabrication process flow and will be widely applicable to different mid-infrared wavelength bands for a variety of sensing applications. We further present a low-loss bend design (0.179 ± 0.031 dB/90°) that overcomes the inherently large bending loss of the waveguides, which is a limiting factor in the utility of the waveguides. We consider different prospective designs for the use of these waveguides in a circuit for a sensing device.

Due to the high need for renewable energy on a worldwide scale, significant research ha s been done on how to use solar energy as a source of free and clean energy. The energy produced is mostly released as electromagnetic radiation with a spectral range of 0.2 to 3 m. New technologies are being developed to harvest this energy while overcoming the limitations of conventional PV devices. These new devices are called nano-antennas (rectenna). Nanoantennas are used to absorb electromagnetic wave radiation especially unused parts of solar radiation (IR region) and the thermal radiation from objects and convert it to electric current and vice versa. Here, a novel design of an "E"-shaped nano-antenna for energy harvesting is introduced and analyzed by using the three-dimensional (3D) finite-difference time-domain (FDTD) method. The key issue in the design of an “E"-shaped nano-antenna for energy harvesting is based on the excitation of surface plasmon polaritons (SPP) through the doped silicon arms of the E shape placed on an Al₂O₃ substrate to obtain wideband behavior in IR region. In this paper, doped silicon was used instead of noble metal as a plasmonic material with optical resonances in the infrared. The width and length of doped silicon arms are v aried to get the best performance. Doped nanocrystals (NCs) have received more attention lately because through doping the free carrier densities can be changed gradually and active tenability can be achieved.

Description and implementation case study of low etendue, ultra-bright, and noncoherent laser-based light source (1150 lm, 8000 cd) built on a 5W blue LD and single crystal phosphor for high-efficiency technical applications.

Whispering gallery mode microspheres have garnered considerable attention due to their applications in signal processing and telecommunications. Unique properties such as high quality factor and small mode volume of whispering-gallery mode microspheres make them suitable for laser applications with a low pumping power requirement and narrow emission linewidth. Tellurite glass is a promising material for making microlasers because of its high transparency range, high refractive index, and it has been proven as a good host for rare earth ions leading to powerful and broad stimulated emission cross section. We reported lasing in Er³⁺ doped tellurite glass microspheres fabricated using the plasma torch method. 15Na₂O₂5WO₃60TeO₂ doped with 0.5 mol% Er³⁺ is used for the fabrication of microspheres. Laser light from the pump is coupled to the microsphere through a half and a full tapered fiber. An optical spectrum analyzer receives the counter propagating light from the microsphere. A pump laser of 980 nm is used to achieve the laser emission at 1570 nm.

Silicon photonics has established itself as a key integration platform, leveraging high-quality materials and large-scale manufacturing using mastered toolsets of complementary metal-oxide-semiconductor (CMOS) foundries. Chip-scale photonics offer unique promises for dense integration of versatile optical functions through compact and high-performance building blocks. Integrated photonics is now competing technology for many applications, spanning from telecom/datacom and interconnects up to quantum sciences and light detection and ranging (LIDAR) systems, among others. However, the lack of low-loss input/output chip interfaces can be prohibitive to successfully deploy multi-diverse device applications. Low coupling loss is essential in reducing overall power budget in photonic systems, impacting on-chip integration level. The light coupling from an off-chip environment into the planar waveguide platforms has always been a challenging research problem since the early years of integrated photonics. Optical interfaces formed on a photonic chip surface, rather than implemented on a chip edge, have been widely used to access photonic circuits with optical fibers or enabling free-space coupling of light beams. Surface gratings can be positioned at arbitrary locations and/or arranged in pre-defined patterns on the chip, facilitating wafer-scale testing and optical packaging. In this work, we present our recent progress in the development of silicon-based surface gratings for use in fiber-to-chip and free-space beam coupling. In particular, we discuss prospective design approaches to develop low-loss surface grating couplers implemented on silicon-on-insulator (SOI), silicon nitride (SiN), and hybrid silicon-silicon nitride (Si-SiN) platforms, allowing to approach a coupling loss below -1 dB. Among these, we also cover contemporary advances in compact silicon metamaterial nano-antennas for dense optical phased arrays, obtaining high a diffraction performance (> 90%) and wideband operation (> 200 nm) simultaneously.

Silicon nitride (SiN) has emerged as an important waveguide platform to implement integrated photonic circuits for a wide range of applications, including telecommunications, nonlinear optics, and quantum information. The SiN platform is compatible with a CMOS fabrication and provides attractive properties such as low propagation loss and increased tolerance to fabrication errors. However, a comparatively low index contrast is a challenge for coupling light off-chip using surface grating couplers. Compared to silicon waveguides, reduced grating scattering strength limits attainable coupling efficiency since the size of the radiating beam is significantly larger compared to near-Gaussian optical mode of standard SMF-28 optical fibers. In this work, we present, both theoretically and experimentally, a set of robust uniform and apodized grating couplers implemented in 400 nm SiN platform. Grating couplers operate with TE polarization at telecom C-band, with measured coupling losses between -4 dB to -3 dB near 1550 nm wavelength. Prospectively, our designs can be further optimized by using sub-wavelength grating metamaterial engineering and self-focusing topology, with simulated fiber-chip coupling loss as low as -1.6 dB. Our results pave the way towards development of highly efficient and robust off-chip coupling interfaces in SiN platform.

The production of surface relief gratings plays a crucial role in nano-structuring today. Applications range from laser mirrors to manufacturing of waveguides for mixed and augmented reality. Augmented (AR) and mixed reality (MR) applications have recently gained large interest. For in- and out-coupling optics, mainly Slanted Relief Gratings (SRG) are used. Nano-imprint lithography (NIL) is one way to produce such optical gratings.^{[1], [2], [3]} For this procedure, NIL master stamp is pressed into a polymer for replication of the pattern. These NIL master stamps have to be structured previous to the NIL process. The manufacturing of those masters is realized by a pattern transfer of a masked substrate by ion beam etching technology. This technology enables the tilting of the substrate in the respect to the ion beam, the so-called incident angle of the ions, and, hence, the slant angles can be defined. Additionally, applying different process parameters, such as ion energy, beam current density and the mixture of process gas, the ratio between the physical, anisotropic etching and chemical isotropic etching can be adjusted. This ratio defines the shape of the slanted gratings. Two types of ion beam process are available, the Reactive ion beam etching (RIBE) for structuring the complete substrate surface simultaneously and the reactive ion beam trimming (RIBT) a locally resolved etching method enabling manufacturing of slanted gratings with both varying slant angle and varying trench depth. This work shows process results for these two manufacturing approaches.

Micro-ring resonators (MRR) are basic photonic components, which serve as crucial building blocks for a variety of devices, e.g. integrated sensors, external cavity lasers, and high speed photonic data transmitters. Silicon nitride photonic platforms are particularly appealing in this field of application, since this waveguide material enables on-chip photonic circuitry with (ultra-) low losses in the NIR as well as across the whole visible spectral range. In this contribution we investigate key performance properties of MRRs in the wavelength range around 850 nm, such as free spectral range (FSR), quality factor (Q factor) and extinction ratio. We systematically investigate a large parameter space given by the MRR radii, coupling gaps between ring and bus waveguide, as well as waveguide width. Furthermore, we compare key properties such as the Q factor between low pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD) Si₃N₄ platforms and find enhanced values for LPCVD ring resonators reaching nearly a Q factor of 10⁶.The fabrication is carried out with standard CMOS foundry equipment, utilizing photolithography and reactive ion etching on 250 nm thick silicon nitride films. As cladding material, high density PECVD silicon oxide is deposited prior to the waveguide onto bare silicon and a sputtered oxide serves as upper cladding. With this process toolbox full CMOS backend compatibility is achieved when considering only PECVD Si₃N₄ waveguide material. In terms of manufacturability, special focus is put on the die-to-die as well as on wafer-to-wafer variability of the performance parameters, which is crucial when considering mass production of MRR devices. Finally, the experimental findings are compared to finite difference time domain (FDTD) simulations of the MRR circuits revealing excellent agreement when considering the manufacturing variability.

Optical transceivers that function under a high-speed rate condition are demanded to have more optical power ability to overcome the power losses which is a cause of the need of using a larger RF line connected to the Mach-Zehnder modulator for fulfilling the high-speed condition. The classic solution to this problem is to use a better power laser with a high level of 120 milliwatts. However, this solution can be complicated for a photonic chip circuit due to the high cost and nonlinear effects, which can increase the system noise. Therefore, we propose a better solution to increase the power level using a 4x1 power combiner which is based on multimode interference using a silicon nitride slot waveguide structure. Results show that the combiner can function well over the O-band spectrum with high combiner efficiency of at least 98.1% and after a short light coupling propagation of 28.8 μm. This new study shows how it is possible to obtain a transverse electric mode solution for four Gaussian coherent sources using Si3N4 slot waveguides technology. This new technology can be utilized for combining multiple coherent sources that work with a photonic chip at the O-band range.

Increasing data rates in the wireless access require high-bandwidth signal processing, which might be problematic for electronics. One solution is provided by high-bandwidth photonic signal processing in integrated silicon photonic devices. The transformation of electrical into optical signals and sometimes the photonic signal processing itself require a modulator. Especially silicon photonic ring modulators have the potential to significantly enhance the signal processing performance for large-scale integrated photonic circuits, since they have a very low footprint and power consumption. Nevertheless, densely packed integrated photonic devices show thermal crosstalk, which may lead to problems of heat dissemination in the chips. Here we will show, that a deep trench is a suitable method to avoid this problem. We present simulation results of crosstalk mitigation for ring modulators and show the improvement in the transmission characteristics.

To match the growing demand for data transmission capacities, silicon photonic tunable multichannel filters with architectures like ring resonators or Bragg gratings are the leading technology. However, their performance, especially the channel count, is often limited by the free spectral range or fabrication difficulties due to small size grating teeth (~ 150 nm). The long-period waveguide gratings (LPWGs) with periodicity ~ μm can be a promising alternative to overcome these limitations. In this context, we propose a four-channel wavelength division (de) multiplexer (WDM) based on cascaded LPWG geometry, operating in the C-band of telecommunication. The proposed structure consists of four cascaded LPWGs in which each LPWG comprises two parallel waveguides made of silicon and titanium dioxide (TiO₂) with apodized gratings placed in between having a length of 720 μm. The 3-dB bandwidth of each channel is found to be 1.59 nm with a small insertion loss of -0.1 to -0.6 dB owing to the unique spectral property of LPWG. The channel spacing is decided through the efficient tuning with the metallic heaters placed on top of each grating due to the high and opposite thermo-optic coefficient of silicon and TiO₂. A minimum spacing of 268 GHz between two consecutive channels is achieved with a power consumption of 30 mW. The cross-talk between the channels is found to be < -20 dB even with ± 10 nm random errors in the waveguide’s width along the propagation direction. The proposed structure possesses great potential towards dense WDM application.

The work presented here demonstrated and analyzed an angled multimode interference (AMMI) waveguide optical switch with a feedback network to reduce the length of the device. The optical power in the MMI different ports was controlled by changing the phase using an optical shifter. The MMI waveguide was symmetrically excited in forward direction, giving a single symmetrical image at the output port. This signal is then split into two equal halves using a Y-junction. Each half is guided in a single mode ring-like waveguide to be coupled to the MMI as feedback sources. According to the phase shift between the two rings, the signal can be switched to one of the output ports. A 25 μm tapered waveguide was used to change the spot size and reduce the optical losses, the tapers width for the inputs and outputs was optimized to be Wt =2.1 μm to fit our 6 μm MMI width. Angled ports were used for backward excitation. The angle between the ports and the MMI at the input was optimized at an angle of 8⁰. The MMI optimized length is 127.1 μm and extinction ratio of the proposed design was 18.2 dB and 16.5 dB for the two outputs ports at an operation wavelength of 1.55 μm.

Our work presents research of the optical Ge-Si glass composition doped with Er³⁺, Yb³⁺ ions and Bi optically active centers (BACs), which are useful for optically amplifiers for a double C- and U-band. The luminescence response in the 1500 – 1700 nm range was tested with various types of glass with different content of modifier and activators in the 1500 – 1700 nm range. The maxima of the luminescence intensity and the spectral full width were determined by modified reflex spectrum method measurement. The prepared Ge-Si glass doped with Er³⁺ ions and BACs exhibited strong and balanced emission in the 1520 – 1680 nm range after pumping at 1480 nm. The specific balanced optical differential gain of up to 0.2 dB/cm in the C-band and simultaneously 0.2 dB/cm in the U-band was measured. The measured results prove that the investigated germano-silicate glasses doped with Er³⁺ and Bi ions are promising for optical amplifiers working in the optical C- and U-bands.

Gas sensing is critical in the detection of hazardous gases in the environment as well as medical disorders. Today the world faces energy and climate challenges which increase the demand for sensors that can sense harmful emissions in surrounding environments and manage fuel exhausts from stationary plants and transportation. Metal-oxide, capacitance, and electrochemical-based gas sensors are among the various gas-detecting techniques. Among these sensing techniques, the optical method is particularly important since it is a quick, dependable, and extremely sensitive way of sens e. Therefore, this research is motivated by a desire to build a nano-optical gas sensor to meet the internet of things (IoT) needs, but on the condition that it is manufactured using CMOS technologies. The plasmonic nanoantenna on-Chip will be used as a gas sensor relying on the dielectric nanoparticles with high refractive index properties which demonstrate high electromagnetic mode coupled with significant localized surface plasmon resonance (LSPR) confined in a nanometric volume. The changing of the refractive index of the surrounding medium will exhibit a shift in the resonance wavelength or affect the peak of the field intensity. The nanoantenna proposed is composed of highly doped silicon and placed on a dielectric layer. We use several nanoantenna models to resonate in the mid-infrared spectrum, where each gas has its fingerprint. The numerical calculations were performed using the Lumerical commercial tool based on the 3D Finite Difference Time Domain (FDTD) approach.

This paper introduces a mid-wavelength infrared (MWIR) lens design which has both function of high-speed scanning and optical zooming for Infrared Search and Track (IRST) System. For scanning function, a reflecting mirror is integrated within the optical system to stabilize the light-of-sight of the optical axis in integration time. This scanning mirror is placed in front of an imager group which focus the light onto the image surface. To perform the optical zooming function, an afocal telescope is place conjugated with the scanning mirror so that the optical lens design can change the focal length without affecting the scanning function. The field of view in scanning mode is 19.0° x 23.6° for a single frame while in optical zooming mode, the field of view can be change to 5.9° x 4.8° at minimum which makes the optical zoom power of 4X. All optical configurations of the system are designed to work with a F/#2 SXGA (1280 x 1024) cooled detector having a pixel pitch of 15μm.

Faced with the challenges of the energy crisis and climate change, green facades are becoming an increasingly important tool in building architecture. They allow the physical shading of building walls, promote evapotranspiration in summer and increase the thermal insulation in winter. An optimal water and nutrition supply is a fundamental requirement for an effectively working facade greening, which needs appropriate caretaking. In order to keep the use of human resources for maintenance work and the associated costs as low as possible, automatic detection of the plant condition is required. This study provides a remote optical detection method to determine the irrigation condition of plants by measurements of VIS, NIR, and MIR spectra of reflected and emitted radiation by the plant leaves during accelerated senescence. The senescence was accelerated by increased temperature and reduced humidity in a climate chamber, as well as on cut leaves with no water supply. Vegetation indices were investigated with respect to their sensitivity to changes in the plant vitality due to lack of water. An advanced vegetation index trained on time-lapse data was developed, which shows a high sensitivity regarding slight changes in the plant leaf reflectivity and allows conclusions to be drawn about the changes in plant vitality caused by water shortage.

We investigate the calculation of resonance modes of a VCSEL with a Riesz projection eigenvalue solver. The eigenvalue solver is based on the principle of contour integration where for the solution of scattering problems physical right sides are used. Here, it is investigated how numerical parameters impact the performance of the method, where we focus on the computation of the fundamental VCSEL mode.

Active plasmonic switches with broadband operating range are proposed based on arrays of gold nanodisc-dimers (NDD) with asymmetry in terms of sequentially increasing diameters, in combination with vanadium dioxide (VO₂) as a phase change material. On exposing light, voltage, or heat the layer of VO₂ changes its state from semiconductor to metal. This transition causes considerable changes in the optical characteristics which subsequently alters the reflectance spectra of the designed NDD based plasmonic switches. Thus, efficient broadband switching with high extinction ratios is obtained over a vast wavelength ranges in the near-infrared spectrum. These switches can be employed as the elementary devices in optical networks or can also be used as switching components in integrated photonic circuits.

The detection of environmentally harmful gases and medical conditions depends heavily on gas sensing. The optical approach for sensing is particularly important among traditional sensing techniques since it is a quick, dependable, and extremely sensitive manner of sensing. The traditional noble metals utilized for plasmonic resonances suffer from high radiative losses as well as fabrication challenges, such as shifting the resonance positions into the mid-infrared regions and compatibility with the existing complementary metal-oxide-semiconductor (CMOS) manufacturing platform. In this study, we show that mid-infrared localized surface plasmon resonances (LSPR) can occur using thin SiO₂ films. It is demonstrated that by simulating micrometer-sized antennas in a SiO₂ chip, the mid-infrared LSPR can be further increased and spectrally extended to the mid-infrared spectrum. The optical gas sensor based on SiO₂ is frequently used to detect a wide range of gases, including NH₃ and O₃. These gases often exhibit peak absorption in the infrared (IR) spectrum. Since SiO₂ can also function as an infrared photodetector, we consider that our results will open the way for the direct integration of plasmonic sensors with the on-chip CMOS platform, considerably improving the prospect of the mass manufacture of high-performance plasmonic sensing systems. A silicon-dioxide nanoantenna is placed on a dielectric substrate to form the suggested nanoantenna. Different shapes and gap dimensions for resonant nanoantenna structures in the mid-infrared range are studied and numerically analyzed. The silicon-dioxide nanoantenna shows high localized field intensity in the midinfrared range.