Passive Photonic Components Research Articles

LPCVD Silicon Nitride Photonic Integrated Components Designed at 532 Nm Wavelength for a Novel Retinal Projection Concept and Visible Domain Applications

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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> : 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.

Subwavelength Grating‐Assisted Contra‐Directional Couplers in Lithium Niobate on Insulator

AbstractGrating‐assisted contra‐directional couplers are important optical components in photonic integrated circuits (PICs), which can serve as fundamental building blocks for optical (de)multiplexers, switches, filters, and splitters, among others. Recently, lithium niobate on insulator (LNOI) has emerged as an attractive PIC platform with many important active photonic circuit components demonstrated, including electro‐optic modulators and second‐harmonic wavelength converters. Nevertheless, the LNOI component toolbox still lacks some passive photonic circuit components to fulfill the requirements of future high‐performance PICs. In this contribution, a subwavelength grating‐assisted contra‐directional coupler (GACDC) is proposed, designed, and experimentally demonstrated in a silicon nitride‐loaded LNOI waveguide platform. As an example of its applications, a three‐channel wavelength‐division (de)multiplexer is fabricated and experimentally demonstrated by cascading several GACDCs, with a narrow wavelength spacing of 3.2 nm (400 GHz). The measured device insertion loss of each channel is about 2.5 dB with low interchannel crosstalk below −20 dB. A fabrication tolerance analysis is also carried out, indicating that the proposed GACDCs are tolerant to waveguide width variations.

Versatile Tunning of Compact Microring Waveguide Resonator Based on Lithium Niobate Thin Films

With the advancement of modulation technology and the requirement for device miniaturization and integration, lithium niobate on insulator (LNOI) can be a versatile platform for this pursuit, as it can confine the transmitted light at the nanoscale, leading to a strong light–matter interaction, which can sensitively capture external variations, such as electric fields and temperature. This paper presents a compact microring modulator with versatile tuning based on X-cut LNOI. The LNOI modulator equipped with electrodes with a coverage angle of 120∘ achieved a maximum electro-optic (EO) tuning efficiency of 13 pm/V and a maximum extinction ratio of 11 dB. The asymmetry in the static or quasi-static electro-optic tuning of the microring modulator was also analyzed. Furthermore, we measured the thermal-optic effect of the device with a sensitivity of 26.33 pm/∘C, which can potentially monitor the environment temperature or compensate for devices’ functional behavior. The demonstrated efficient and versatile compact microring modulator will be an important platform for on-chip active or passive photonic components, microring-based sensor arrays and integrated optics.

A short high-gain waveguide amplifier based on low concentration erbium-doped thin-film lithium niobate on insulator

One hotspot of integrated optics is how to realize a highly integrated and high-gain on-chip amplification system in a thin film of lithium niobate on insulator (TFLNOI). Here, a low erbium-doped TFLNOI waveguide amplifier with shorter length is demonstrated using the photolithography-assisted oblique-reactive ion etching technique. A maximum net internal gain of 5.4 dB in the small-signal-gain regime is measured at the peak emission wavelength of 1531.35 nm for a waveguide length of 1.5 mm and an erbium-doped concentration of 0.1 mol. %, indicating a gain per unit length of 36 dB cm−1. This work paves the way for the monolithic integration of diverse active and passive photonic components on the TFLNOI platform.

Hybrid-integrated high-performance microwave photonic filter with switchable response

The integrated microwave photonic filter (MPF), as a compelling candidate for next-generation radio-frequency (RF) applications, has been widely investigated for decades. However, most integrated MPFs reported thus far have merely incorporated passive photonic components onto a chip-scale platform, while all necessary active devices are still bulk and discrete. Though few attempts to higher photonic integration of MPFs have been executed, the achieved filtering performances are fairly limited, which impedes the pathway to practical deployments. Here, we demonstrate, for the first time to our knowledge, an all-integrated MPF combined with high filtering performances, through hybrid integration of an InP chip-based laser and a monolithic silicon photonic circuit consisting of a dual-drive Mach–Zehnder modulator, a high- Q ring resonator, and a photodetector. This integrated MPF exhibits a high spectral resolution as narrow as 360 MHz, a wide-frequency tunable range covering the S-band to K-band (3 to 25 GHz), and a large rejection ratio of &gt; 40 dB . Moreover, the filtering response can be agilely switched between the bandpass and band-stop function with a transient respond time ( ∼ 48 μs ). Compared with previous MPFs in a similar integration level, the obtained spectral resolution in this work is dramatically improved by nearly one order of magnitude, while the valid frequency tunable range is broadened more than twice, which can satisfy the essential filtering requirements in actual RF systems. As a paradigm demonstration oriented to real-world scenarios, high-resolution RF filtering of realistic microwave signals aiming for interference rejection and channel selection is performed. Our work points out a feasible route to a miniaturized, high-performance, and cost-effective MPF leveraging hybrid integration approach, thus enabling a range of RF applications from wireless communication to radar toward the higher-frequency region, more compact size, and lower power consumption.

On‐Chip Integrated Waveguide Amplifiers on Erbium‐Doped Thin‐Film Lithium Niobate on Insulator

AbstractOn‐chip light amplification with integrated optical waveguide fabricated on erbium‐doped thin‐film lithium niobate on insulator (TFLNOI) is demonstrated using the photolithography‐assisted chemomechanical etching (PLACE) technique. A maximum internal net gain of 18 dB in the small‐signal‐gain regime is measured at the peak emission wavelength of 1530 nm for a waveguide length of 3.6 cm, indicating a differential gain per unit length of 5 dB cm−1. This work paves the way to the monolithic integration of diverse active and passive photonic components on the TFLNOI platform.

40‐1: Invited Paper: New Liquid Crystal and Reactive Mesogens Mixtures for Passive and Active Photonic Components

We report the current state‐of‐the‐art in liquid crystal and reactive mesogen formulation properties and show how they relate to device performance for both passive and active photonic components for current and future non‐display applications. Development trends and trade‐offs of the formulation properties will be discussed looking into the future.

Shape optimization for the design of passive mid-infrared photonic components

Shape optimization techniques were first developed in the context of mechanical engineering and, more recently, applied to photonic components for data communication. Here, motivated by the growing application potential of mid-infrared photonics driven by chemical sensing and spectroscopy, we present the design by shape optimization of passive components operating in this wavelength range. A focus is placed on the creation of designs that are fabricable and robust to manufacturing uncertainties.

Silicon microdisk-based full adders for optical computing.

Due to the projected saturation of Moore's law, as well as the drastically increasing trend of bandwidth with lower power consumption, silicon photonics has emerged as one of the most promising alternatives that has attracted a lasting interest due to the accessibility and maturity of ultra-compact passive and active integrated photonic components. In this Letter, we demonstrate a ripple-carry electro-optic 2-bit full adder using microdisks, which replaces the core part of an electrical full adder by optical counterparts and uses light to carry signals from one bit to the next with high bandwidth and low power consumption per bit. All control signals of the operands are applied simultaneously within each clock cycle. Thus, the severe latency issue that accumulates as the size of the full adder increases can be circumvented, allowing for an improvement in computing speed and a reduction in power consumption. This approach paves the way for future high-speed optical computing systems in the post-Moore's law era.

Efficient on-chip integration of a colloidal quantum dot photonic crystal band-edge laser with a coplanar waveguide

High-density photonic integrated circuits (PICs) are expected to replace their current electronic counterparts in the future. The most crucial prerequisite for realizing successful PICs is to develop a low-loss coupling technique between active and passive photonic components based on various nanoscale materials and devices. Here we propose and demonstrate an on-chip integration technique in which a high-refractive-index layer constitutes the coplanar structural backbone across the entire PIC chip. To prove the concept, patterns of a two-dimensional photonic crystal (PhC) band-edge laser and grating couplers are engraved into the backbone layer, and colloidal quantum dots (CQDs) for optical gain are selectively deposited in the PhC area by a conventional lift-off process. Using optical excitation, we observe that the CQD–PhC structure emits coherent single-mode laser light, which is subsequently coupled to and propagates through an adjacent slab waveguide in the well-defined directions corresponding to the selected band-edge point, finally emerging through the grating coupler. Our study demonstrates a simple but highly suggestive PIC platform that automatically guarantees high coupling efficiencies between the micro- and nanophotonic devices to be integrated (through high degrees of modal matching in the vertical direction) and will therefore advance the development of high-density PIC technologies.

InP-Based Active and Passive Components for Communication Systems at 2 μm

Progress on advanced active and passive photonic components that are required for high-speed optical communications over hollow-core photonic bandgap fiber at wavelengths around 2 μm is described in this paper. Single-frequency lasers capable of operating at 10 Gb/s and covering a wide spectral range are realized. A comparison is made between waveguide and surface normal photodiodes with the latter showing good sensitivity up to 15 Gb/s. Passive waveguides, 90° optical hybrids, and arrayed waveguide grating with 100-GHz channel spacing are demonstrated on a large spot-size waveguide platform. Finally, a strong electro-optic effect using the quantum confined Stark effect in strain-balanced multiple quantum wells is demonstrated and used in a Mach-Zehnder modulator capable of operating at 10 Gb/s.

Passive Photonics in an Unmodified CMOS Technology With No Post-Processing Required

Passive photonic components consisting of sub-micrometer waveguides, grating couplers, and ring resonators are demonstrated in an unmodified commercial complementary metal-oxide-semiconductor (CMOS) process. Waveguides demonstrate propagation losses of approximately 1 dB/mm at 1.3-μm wavelengths. Grating couplers achieve better than -5.8-dB coupling efficiencies. Ring resonators exhibit Qs greater than 5000 with extinction ratios of more than 20 dB. Furthermore, due to the utilization of front-end-of-the-line design layers for creating the waveguide cores coupled with a relatively thick buried-oxide layer standard within the process, no post-processing is required at the chip or wafer level to achieve the reported device performance. Hence, for the first time, designers without processing capabilities may design custom CMOS photonic circuits for a broad range of applications. One such application which may appropriately leverage the low-cost platform could be disposable bio-photonic sensor arrays.

Hybrid plasmonic structures based on CdS nanotubes: a novel route to low-threshold lasing on the nanoscale

Nanowires and nanotubes could become important building blocks in advanced photonic systems owing to their fascinating optoelectronic properties and high compatibility with versatile chemical synthetic methods. Many intriguing studies have been enabled by applying these nanostructures in the construction of various types of active and passive photonic components. Successful examples are the recent demonstration of semiconductor and plasmonic lasers based on CdS nanowires (Duan et al 2003 Nature 421 241–5, Oulton et al 2009 Nature 461 629–32, Ma et al 2010 Nature Mater. 10 110–13), which generate and deliver intense coherent light down to and even below the diffraction-limited scale. Here in this paper, by carrying out a numerical investigation of a novel hybrid plasmonic structure that consists of a CdS nanotube sitting above a metal substrate separated by a nanometric MgF2 layer, we show theoretically that nanotube-based plasmonic structures can also act as highly efficient lasing sources. Optical properties of such a laser configuration including modal behaviour and the lasing threshold is investigated with regard to the variation of key geometrical parameters. Simulation results reveal that the employment of a CdS nanotube may result in improved optical performance compared with the conventional CdS-nanowire-based plasmon laser. Reduced lasing threshold with mitigated modal loss can be achieved simultaneously under carefully engineered geometries. We also explore the feasibility of combining nanowire- and nanotube-based active and passive components for on-chip integrations. As a simple demonstration, monolithic integration of a CdS nanotube laser with a CdS-nanowire-based passive component is shown numerically on a single chip. We expect that these studies could lay the foundations for nanotube- and nanowire-based hybrid integrated photonic components and circuits.

Giant optical anisotropy of oblique-aligned ZnO nanowire arrays

A combined method of modified oblique-angle deposition and hydrothermal growth was adopted to grow an optically anisotropic nanomaterial based on single crystalline ZnO nanowire arrays (NWAs) with highly oblique angles (75°-85°), exhibiting giant in-plane birefringence and optical polarization degree in emission. The in-plane birefringence of oblique-aligned ZnO NWAs is almost one order of magnitude higher than that of natural quartz. The strong optical anisotropy in emission due to the optical confinement was observed. The oblique-aligned NWAs not only allow important technological applications in passive photonic components but also benefit the development of the optoelectronic devices in polarized light sensing and emission.

Electron beam lithography writing strategies for low loss, high confinement silicon optical waveguides

The authors present a robust process for fabricating passive silicon photonic components by direct-write electron beam lithography (EBL). Using waveguide transmission loss as a metric, we study the impact of EBL writing parameters on waveguide performance and writing time. As expected, write strategies that reduce sidewall roughness improve waveguide loss and yield. In particular, averaging techniques such as overlap or field shift writing reduce loss, however, the biggest improvement comes from writing using the smaller field-size option of our EBL system. The authors quantify the improvement for each variation and option, along with the tradeoff in writing time.

Large-scale integrated photonics for high-performance interconnects

Moore's Law has set great expectations that the performance of information technology will improve exponentially until at least the end of this decade. Although the physics of silicon transistors alone might allow these expectations to be met, the physics of the long metal wires that cross and connect packages almost certainly will not. Global-level interconnects incorporating large-scale integrated photonics fabricated on the same platform as silicon microelectronics hold the promise of revolutionizing computing by enabling parallel many-core and network switch architectures that combine unprecedented performance and ease of use with affordable power consumption. Over the last decade, remarkable progress has been made in research on low-power silicon photonic devices for interconnect applications, and CMOS-compatible fabrication technologies promise a “Moore's Law for photonics” that could completely change the economics of integrated optics. In this survey, photonic technologies amenable to large-scale CMOS integration are reviewed from the perspective of high-performance interconnects operating over distance scales of 1mm to 100m. An overview of the requirements placed on integrated optical devices by a variety of modern computer applications leads to discussions of active and passive photonic components designed to generate, guide, filter, modulate, and detect light in the telecommunication bands. Critical challenges and prospects for large-scale integration are evaluated with an emphasis on silicon-on-insulator as a platform for photonics.

Passive photonic components using InP optical wire technology

The authors present the design, fabrication and characterisation of passive photonic components using InP optical wire technology. These components are straight and curved waveguides as well as Y-junctions. Their ultimate use is to be integrated within active nanophotonic functions and this is implicitly targeted in the different parts of this process work. First, propagation and excess losses because of a bend or Y-junction are modelled using a beam propagation method or a finite difference time domain method. Then, the technological process used to fabricate these components is presented; it is mainly based on e-beam direct writing and inductively coupled plasma deep etching. Finally, the different losses are measured and results are compared with the theory. The authors demonstrate, thus, that the use of submicron waveguides (or optical wire) can lead to very compact optical passive functions on InP since very small radius bends and wide angle Y-junctions showed almost low excess loss.

Guiding, modulating, and emitting light on Silicon-challenges and opportunities

Silicon photonics could enable a chip-scale platform for monolithic integration of optics and microelectronics for applications of optical interconnects in which high data streams are required in a small footprint. This paper discusses mechanisms in silicon photonics for waveguiding, modulating, light amplification, and emission. These mechanisms, together with recent advances of fabrication techniques, have enabled the demonstration of ultracompact passive and active silicon photonic components with very low loss.

Waveguide and guided-wave devices consisting of heterostructured photonic crystals

We report a strategy for the industrialization of photonic-crystal-based optical devices, starting with a review of the requirements for passive photonic crystal components. Although they have remarkable properties, such components are difficult to couple to/from optical fibers and have a relatively large propagation loss. We present an approach for meeting the requirements by using heterostructured photonic crystals fabricated by the autocloning technology. A low-loss, simple structured waveguide and sophisticated functional blocks (such as a resonator) can be integrated by a simple process. We first prepare a substrate patterned and corrugated by electron beam lithography and dry etching. Ta2O5/SiO2 multilayers are repeatedly deposited on the substrate, and no other process is needed to complete the chip. After dicing and polishing, the waveguide can be butt-jointed with an optical fiber, and the loss is estimated as 0.1 dB/mm. A resonator with Q = 11,700 is also demonstrated. Recent progress and the future outlooks for the technology are also discussed.