Tunable microring resonator based on dielectric-loaded surface plasmon polariton waveguides

Integrated optical ring resonators are essential elemental components for integrated optical circuits. An ultrasmall thermo-optical microring resonator with two bus waveguide-configuration based on surface plasmon polariton waveguide is theoretically analyzed. The thermo-optical coefficient, the temperature-dependent amplitude attenuation coefficient and the temperature distribution properties of the waveguide are investigated numerically by finite element method. The critical resonant conditions of the microring resonator are discussed by considering the propagation losses in the plasmonic ring cavity. The transmission characteristics and the tunability of the ring resonator with different structural parameters are investigated. The results show that the proposed ring resonator with a low driving power and high efficient tunability has potential to develop nano-scope wavelength tunable channel drop filters, low power optical switches, attenuators, and other high compact integrated optical devices.     

Comparative study of the integration density for passive linear planar light-wave circuits based on three different kinds of nanophotonic waveguide

A theoretical analysis and comparison of the integration density are given for passive planar lightwave circuits based on three different kinds of nanophotonic waveguide, namely, photonic crystal waveguides, Si nanowire waveguides, and nanoslot waveguides. Two criteria for determining the integration density are used. One is the minimal decoupled separation between two parallel nanophotonic waveguides, and the other is the area occupied by a low-loss 90 degree turn. Some important functional components (such as Y branches and optical add-drop filters) are also chosen as basic elements to evaluate the integration density. It is shown that the integration densities of passive linear planar lightwave circuits based on these three kinds of nanophotonic waveguide are comparable.     

Phonon‐Assisted Electro‐Optical Switches and Logic Gates Based on Semiconductor Nanostructures

High‐performance nanostructured electro‐optical switches and logic gates are highly desirable as essential building blocks in integrated photonics. In contrast to silicon‐based optoelectronic devices, with their inherent indirect optical bandgap, weak light‐modulation mechanism, and sophisticated device configuration, direct‐bandgap‐semiconductor nanostructures with attractive electro‐optical properties are promising candidates for the construction of nanoscale optical switches for on‐chip photonic integrations. However, previously reported semiconductor‐nanostructure optical switches suffer from serious drawbacks such as high drive voltage, limited operation spectral range, and low modulation depth. High‐efficiency electro‐optical switches based on single CdS nanobelts with low drive voltage, ultra‐high on/off ratio, and broad operation wavelength range, properties resulting from unique electric‐field‐dependent phonon‐assisted optical transitions, are demonstrated. Furthermore, functional NOT, NOR, and NAND optical logic gates are demonstrated based on these switches. These switches and optical logic gates represent an important step toward integrated photonic circuits.     

Polymer micromachining for micro- and nanophotonics

Polymeric materials have been used in the fabrication of many high-performance, low cost photonic devices for optical communications, interconnects and sensors. The paper presents two low cost techniques for polymer based photonic components fabrication, such as waveguides, diffractive optical elements and optical modulators.We used both photopatternable (metal doped PVA) and nonphotopatternable polymers (PMMA and silicone polymers).The photosensitivity and, in the same time, refractive index of the poly(vinyl-alcohol) were modified through the addition inorganic/organic materials. These new light-sensitive nanocomposites can be easily spin coated onto variety of semiconductor substrates, and directly patterned to obtain channel waveguides and photonic integrated circuits.For nonphotopatternable polymers, two types of molds have been used: grooves etched in silicon or in silicon dioxide and photoresist molds. Rib waveguides and tunable modulators, voltage actuated, have been obtained using these techniques.     

A 0.2 V Micro‐Electromechanical Switch Enabled by a Phase Transition

Micro‐electromechanical (MEM) switches, with advantages such as quasi‐zero leakage current, emerge as attractive candidates for overcoming the physical limits of complementary metal‐oxide semiconductor (CMOS) devices. To practically integrate MEM switches into CMOS circuits, two major challenges must be addressed: sub 1 V operating voltage to match the voltage levels in current circuit systems and being able to deliver at least millions of operating cycles. However, existing sub 1 V mechanical switches are mostly subject to significant body bias and/or limited lifetimes, thus failing to meet both limitations simultaneously. Here 0.2 V MEM switching devices with ?10⁶ safe operating cycles in ambient air are reported, which achieve the lowest operating voltage in mechanical switches without body bias reported to date. The ultralow operating voltage is mainly enabled by the abrupt phase transition of nanolayered vanadium dioxide (VO₂) slightly above room temperature. The phase‐transition MEM switches open possibilities for sub 1 V hybrid integrated devices/circuits/systems, as well as ultralow power consumption sensors for Internet of Things applications.     

Near infrared photonic devices based on Er-doped GaN and InGaN

Er-doped III-nitride semiconductors have emerged as very attractive materials to achieve photonic devices with multiple functionalities for photonic integrated circuits (PICs). Optical sources and amplifiers based on these materials, particularly GaN and InGaN alloys, can operate at 1.54 μm and are expected to be temperature insensitive and have high signal gain with low noise. There is also the potential for these devices to be electrically pumped and to be integrated onto PICs, which is not possible with either Er-doped silica glasses or narrow bandgap semiconductors like InGaAsP. Here we present results on near infrared emitters and optical amplifiers based on Er-doped GaN/InGaN epilayers grown on different substrates by metal organic chemical vapor deposition (MOCVD). In particular, we report on chip-size current injected emitters and amplifiers fabricated by heterogeneously integrating Er-doped GaN/InGaN epilayers with UV nitride light-emitting diodes. The feasibility of developing electrically pumped optical amplifiers for PIC integration will also be discussed.     

Tunable electro-optical 2 × 2 photonic crystal beam splitter

A tunable electro-optical 2?×?2 beam splitter based on two-dimensional rod-type photonic crystals is presented. The beam splitter consists of two orthogonally crossed linear waveguides and a single center rod in square lattice photonic crystals. In order to create a linear waveguide, the radius of a line of rods is reduced. A single center rod is positioned at the intersection of the linear waveguides to divide the input lightwave into output ports. The switching mechanism is a change in the conductance of the waveguide region and hence modulating the guided modes. The tunable beam splitter can be applied to photonic integrated circuits.     

Integrated liquid-crystal switch for both TE and TM modes: proposal and design

An integrated optical switch is proposed and designed based on a weak-anchoring liquid-crystal (LC) cell with a substrate integrating planar lightwave circuits. It consists of a polarization splitter, two switchable polarization converters and a polarization combiner. The polarization splitter/combiner is a directional coupler with an etched slot and filled-in LC covering layer. The switchable polarization converters are straight waveguides with a designed length and covering LC. The proposed configuration is superior to the existing integrated LC switches, as it works for both the TE and TM modes.     

Baseband integrated acousto-optic frequency shifter/modulator module for fiber optic at 1.3 mum

A baseband integrated acoustooptic (AO) frequency shifter/modulator module that consists of a pair of titanium-indiffused proton-exchanged (TIPE) waveguide lenses and a pair of cascaded guided-wave AO Bragg cells has been realized in a Y-cut LiNbO(3) waveguide substrate 0.1 cmx1.0 cmx2.0 cm in size. A device module operating at the optical wavelength of 1.3 mum has provided a -3-dB tunable bandwidth of 120 MHz at baseband. The frequency-shifted or -modulated light propagates in a fixed direction, irrespective of the magnitude of frequency shift or modulation, and is focused into a spot (FWHM) of 6.2-mum size on the output edge of the waveguide. Accordingly, this optical frequency shifter/module can be directly interfaced with single-mode optical fibers to facilitate applications in fiber optic systems.     

InP-based IC technologies

The research and development of InP-based devices and integrated circuits (ICs) are driven by applications in broadband optical-fiber communications systems and microwave and millimeter-wave wireless systems. This paper describes recent progress on our InP-based device and IC technologies for 40-Gbit/s optical fiber communications and 10-Gbit/s class millimeter-wave wireless links. Device performance requirements for future 100-Gbit/s class ICs are then discussed along with our device technology roadmap. We also describe our latest 100-Gbit/s class optical fiber communication IC results.     

Monolithic integrated four DFB lasers array with a polymer-based combiner for WDM applications

Compact and low cost integrated photonic components will be of significant importance for a wider penetration of optical technologies into private customer access systems. Hybrid semiconductor/polymer integrated technologies are very promising to achieve this goal by virtue of the highly flexible nature of polymers at both molecular and material scale, of their compatibility with processing steps used in semiconductor technologies, and of their reasonably low cost. One example is an integrated semiconductor 4-wavelength laser array with a polymer based 1–4 passive optical combiner on the same substrate. The polymer waveguide structure is a polysulfone material stripe embedded in PMMA cladding layers, and the laser structure is a buried ridge stripe (BRS). The optical coupling between the active and passive elements is a butt-joint coupling via a reactive ion beam etched (RIBE) semiconductor mirror facet. Such a photonic integration simplifies the optical coupling between a laser array and single mode fibers, while reducing the packaging cost. This optical device has been achieved with interesting performances such as small dimension size (1.2 × 0.5 mm), low laser threshold current, and output powers for each laser from the polymeric waveguide port of at least 1.5 mW without additional on-chip optical amplification.     

Infrared Quantum Dots

Colloidal nanocrystals are quantum‐size‐effect tunable; offer an abundance of available surface area for electronic and chemical interactions; and are processible from organic or aqueous solution onto substrates rigid or flexible, smooth or rough, flat or curved, inorganic or organic (including biological), crystalline or amorphous, conducting, semiconducting, or insulating. With the benefit of over a decade's progress in visible‐light‐emitting colloidal‐quantum‐dot synthesis, physical chemistry, and devices, significant progress has recently been made in infrared‐active colloidal quantum dots and devices. This progress report summarizes the state‐of‐the‐art in infrared colloidal quantum dots, with an emphasis on applications and devices. The applications of interest surveyed include monolithic integration of fiber‐optic and free‐space‐communications photonic components with electronic substrates such as silicon and glass; in‐vivo biological tagging in infrared spectral bands in which living tissue is optically penetrable to a depth of 5–10 cm; solar and thermal photovoltaics for energy conversion; and infrared sensing and imaging based on non‐visible, including thermal, signatures. The synthesis and properties of quantum dots are first reviewed: photoluminescence quantum efficiencies greater than 50 % are achievable in solution, and stable luminescent dots are available in organic and aqueous solvents. Electroluminescent devices based on solution processing have been reported with external quantum efficiencies approaching 1 %. Photoconductive devices have been realized with 3 % internal quantum efficiencies, and a photovoltaic effect was recently observed. Electro‐optic modulation achieved by either field‐ or charge‐induced modification of the rate of optical absorption has been demonstrated based both on interband and intersubband (intraband) transitions. Optical gain from these processible materials with a threshold of 1 mJ cm^–2 and an optical net modal gain coefficient of 260 ± 20 cm^–1 have been reported.     

Polymeric thermo-optic space switches for optical communications

Solid state optical space switches based on the thermo-optic (t.o.) effect in polymeric optical waveguides have now reached the commercial stage. The application of these switches is in network protection and network reconfiguration functions for fiber optic communications systems. The requirements for these applications include polarization and wavelength independence, low insertion loss, low cross talk, low drive power with step-like (digital) response, millisecond switching times and small size. In addition the reliability of the component must meet the demanding requirements of telecom applications. It will be shown that polymeric t.o. space switches can meet all functional requirements due to the exceptional thermal and t.o. effects of polymers combined with their tunability and processing versatility. Furthermore, it will be shown that polymer optical chips components can withstand extreme lifetime tests with success.     

Effect of zinc content on the refractive index of Co-sputtered Zn-doped ITO films

In this study, we investigated the possibility of using Zn-doped ITO film as an alternative material for conventional SiO2 waveguides used in optical communication. The Zn-doped ITO films were deposited on quartz substrates using a combinatorial sputtering system, which yielded composition spread Zn-In-Sn-O (ZITO) films by co-sputtering two targets of ITO and ZnO. The Zn-doped ITO films deposited at room temperature exhibited an amorphous phase in the Zn content [Zn/(Zn+In+Sn)] range of 39-54 at%. The Zn-doped ITO films deposited at low oxygen partial pressure showed resistivity below 10(-3) ohms cm and optical transmittance of approximately 85% at 550 nm. The refractive index calculated by the Swanepoel method was found to be dependent on the Zn content in the Zn-doped ITO films. The calculated bending loss from the refractive index indicated that Zn-doped ITO could be utilized as a new waveguide material for various optical devices, such as optical splitters, wavelength division multiplexers (WDMs), optical modulators, and optical switches.     

Perfluorocyclobutyl Copolymers for Microphotonics

The copolymerization of aryl bis‐ and tris‐trifluorovinyl ether monomers yields aromatic perfluorocyclobutyl (PFCB) polymers, via thermally initiated step‐growth cycloaddition chemistry. PFCB polymers and their copolymers enjoy a unique combination of attributes well suited for applications in photonic technologies, such as broad tailorability of refractive indices and thermo‐optic coefficients, low transmission losses at 1300 and 1550 nm, high thermal, mechanical, and optical stability, and excellent melt and solution processability. Planar PFCB structures can be processed by direct micro‐transfer molding, which is a first step towards rapid soft‐lithographic fabrication of polymer planar lightwave circuits. Copolymerization chemistry and processing parameters and characterization, including thermal (T_g = 120–350 °C) and optical properties (refractive indices from 1.443 to 1.508 at 1550 nm; thermo‐optic coefficients dn/dT = –7×10^–5 K^–1 to –1.5 × 10^–4 K^–1), birefringence (< 0.003), and temporal stability of refractive index, are described.     

Control of modes coupling in photonic crystal waveguides by introducing asymmetry and long periodicity

The control of modes coupling in photonic crystal waveguides (PCWGs) is quite important because it's the basic working mechanism of many devices in optical integrative circuits, such as filters, switches, optical add drop multiplexers (OADMs), etc. Up to now, the researches of this area mostly focus on the modes coupling between two parallel PCWGs or between PCWGs and resonance cavities. In this paper, we proposed a new way of controlling modes coupling in PCWGs by introducing asymmetry and long periodicity. Because of the presence of asymmetry and long periodicity in PCWGs, some interesting modes coupling phenomena, which used to be forbidden in normal PCWGs, happen. Then a filter with a 1.42 nm full-width at the half value (FWHM) and an OADM with a 1.31 nm FWHM and a 0.34 dB insertion loss have been designed by utilizing the new modes coupling phenomena. Our researches not only provide a new way of controlling modes coupling in PCWGs but also benefit the design of many devices in optical integrative circuits greatly.     

Grains in Selectively Grown MoS2 Thin Films

Transition metal dichalcogenides (TMDCs) have recently been studied using various synthesis methods, such as chemical vapor deposition for large‐scale production. Despite the realization of large‐scale production with high material quality, a range of approaches have been made to solve the patterning issue of TMDCs focusing on the application of integrated devices; however, patterning is still under study to accurately represent nanoscale‐sized patterns, as well as the desired positions and shapes. Here, an insulating substrate is treated selectively with O₂ plasma, and MoS₂ growth is induced in the superhydrophilic area. Selectively well‐grown MoS₂ patterns are confirmed by atomic force microscopy and Raman and photoluminescence spectroscopy. In addition, the grain size, according to the growth size, and grain boundary are analyzed by annual dark field transmission electron microscopy (TEM) and spherical aberration‐corrected scanning TEM to confirm the selective growth. An analysis of the device performance and the optical properties reveals an enhancement with increasing grain size. This method presents the path of the growth technique for patterning, as well as the direction that can be applied to devices and integrated circuits.     

Thread‐Like CMOS Logic Circuits Enabled by Reel‐Processed Single‐Walled Carbon Nanotube Transistors via Selective Doping

The realization of large‐area electronics with full integration of 1D thread‐like devices may open up a new era for ultraflexible and human adaptable electronic systems because of their potential advantages in demonstrating scalable complex circuitry by a simply integrated weaving technology. More importantly, the thread‐like fiber electronic devices can be achieved using a simple reel‐to‐reel process, which is strongly required for low‐cost and scalable manufacturing technology. Here, high‐performance reel‐processed complementary metal‐oxide‐semiconductor (CMOS) integrated circuits are reported on 1D fiber substrates by using selectively chemical‐doped single‐walled carbon nanotube (SWCNT) transistors. With the introduction of selective n‐type doping and a nonrelief photochemical patterning process, p‐ and n‐type SWCNT transistors are successfully implemented on cylindrical fiber substrates under air ambient, enabling high‐performance and reliable thread‐like CMOS inverter circuits. In addition, it is noteworthy that the optimized reel‐coating process can facilitate improvement in the arrangement of SWCNTs, building uniformly well‐aligned SWCNT channels, and enhancement of the electrical performance of the devices. The p‐ and n‐type SWCNT transistors exhibit field‐effect mobility of 4.03 and 2.15 cm² V^?1 s^?1, respectively, with relatively narrow distribution. Moreover, the SWCNT CMOS inverter circuits demonstrate a gain of 6.76 and relatively good dynamic operation at a supply voltage of 5.0 V.     

Dynamic-single-mode Lasers

Recent progress in the dynamic-single-mode (DSM) semiconductor laser for long wavelength optical fibre communications is reviewed, and applications to wide-band optical fibre communication in the lowest loss wavelength region of 1·5–1·65 μm are studied. A DSM laser consists of a mode selective resonator and a transverse-mode-controlled waveguide, such as the narrow-striped distributed Bragg reflector (DBR) laser, to maintain a fixed axial mode under rapid direct modulation. The technology of monolithic integration for optical circuits is applied to realize some DSM lasers. The structures and properties of DSM lasers are reviewed.     

硅基光电集成材料及器件的研究进展

以硅基光电集成回路为主线，综述了不同的硅基光波导材料的制备技术和硅基光波导的制作工艺及其对光传输损耗的影响。分析了硅基光波导与锗硅光探测器集成用两种不同的耦合方式，阐明了波导与探测器集成的机理及设计理论基础。归纳出硅基键合激光器的四种技术方案，指出其共同优点是克服材料异质外延引起的晶格失配和热膨胀非共容，对实现OEIC行之有效。