Photonic Circuitry Research Articles

Genetically optimized on-chip wideband ultracompact reflectors and Fabry–Perot cavities

Reflectors are an essential component for on-chip integrated photonics. Here, we propose a new method for designing reflectors on the prevalent thin-film-on-insulator platform by using genetic-algorithm optimization. In simulation, the designed reflector with a footprint of only 2.16 μm×2.16 μm can achieve ∼97% reflectivity and 1 dB bandwidth as wide as 220 nm. The structure is composed of randomly distributed pixels and is highly robust against the inevitable corner rounding effect in device fabrication. In experiment, we fabricated on-chip Fabry–Perot (FP) cavities constructed from optimized reflectors. Those FP cavities have intrinsic quality factors of >2000 with the highest value beyond 4000 in a spectral width of 200 nm. The reflectivity fitted from the FP cavity resonances is >85% in the entire wavelength range of 1440–1640 nm and is beyond 95% at some wavelengths. The fabrication processes are CMOS compatible and require only one step of lithography and etch. The devices can be used as a standard module in integrated photonic circuitry for wide applications in on-chip semiconductor laser structures and optical signal processing.

Genetic-algorithm-optimized wideband on-chip polarization rotator with an ultrasmall footprint.

Polarization control of light waves is an important technique in optical communication and signal processing. On-chip polarization rotation from the fundamental transverse-electric (TE00) mode to the fundamental transverse-magnetic (TM00) mode is usually difficult because of their large effective refractive index difference. Here, we demonstrate an on-chip wideband polarization rotator designed with a genetic algorithm to convert the TE00 mode into the TM00 mode within a footprint of 0.96 μm ×4.2 μm. In simulation, the optimized structure achieves polarization rotation with a minimum conversion loss of 0.7dB and the 1-dB bandwidth of 157nm. Experimentally, our fabricated devices have demonstrated the expected polarization rotation with a conversion loss of ∼2.5 dB in the measured wavelength range of 1440-1580nm, where the smallest value reaches ∼2 dB. The devices can serve as a generic approach and standard module for controlling light polarization in integrated photonic circuitry.

Efficient Nonlinear Metasurface Based on Nonplanar Plasmonic Nanocavities

Since their discovery in the 1960s, nonlinear optical effects have revolutionized optical technologies and laser industry. Development of efficient nanoscale nonlinear sources will pave the way for new applications in photonic circuitry, quantum optics and biosensing. However, nonlinear signal generation at dimensions smaller than the wavelength of light brings new challenges. The fundamental difficulty of designing an efficient nonlinear source is that some of the contributing factors involved in nonlinear wave-mixing at the nanoscale are often hard to satisfy simultaneously. Here, we overcome these limitations by developing a new type of nonplanar plasmonic metasurfaces, which can greatly enhance the second harmonic generation (SHG) at visible frequencies and achieve conversion efficiency of ∼6 × 10–5 at a peak pump intensity of ∼0.5 GW/cm2. This is 4–5 orders of magnitude larger than the efficiencies observed for nonlinear thin films and doubly resonant plasmonic antennas. The proposed metasurface cons...

Plasmonic Waveguide-Integrated Nanowire Laser

Next-generation optoelectronic devices and photonic circuitry will have to incorporate on-chip compatible nanolaser sources. Semiconductor nanowire lasers have emerged as strong candidates for integrated systems with applications ranging from ultrasensitive sensing to data communication technologies. Despite significant advances in their fundamental aspects, the integration within scalable photonic circuitry remains challenging. Here we report on the realization of hybrid photonic devices consisting of nanowire lasers integrated with wafer-scale lithographically designed V-groove plasmonic waveguides. We present experimental evidence of the lasing emission and coupling into the propagating modes of the V-grooves, enabling on-chip routing of coherent and subdiffraction confined light with room-temperature operation. Theoretical considerations suggest that the observed lasing is enabled by a waveguide hybrid photonic-plasmonic mode. This work represents a major advance toward the realization of application-oriented photonic circuits with integrated nanolaser sources.

Diamond on aluminum nitride as a platform for integrated photonic circuits

Diamond offers superior material properties for realizing advanced integrated optical components. Particularly attractive is its wide transparency window which covers visible and infrared wavelengths. To take advantage of the potential for broadband waveguiding, diamond needs to be surrounded by broadband transparent cladding materials. Here we use diamond deposited onto aluminum nitride as a platform for integrated optics. We demonstrate essential photonic circuitry for coupling light into on‐chip waveguides and show transmission both in the near‐infrared and visible wavelength range. Our approach holds promise for functional diamond devices that cover spectral regions up to the mid‐infrared.Left: Scanning electron micrograph of a diamond waveguide with an overlay of the mode profile. Right: material stack consisting of polycrystalline diamond (PCD) on aluminum nitride (AlN) on silicon (Si) (not to scale).

Colloidal nanophotonics: the emerging technology platform

Dating back to decades or even centuries ago, colloidal nanophotonics during the last ten years rapidly extends towards light emitting devices, lasers, sensors and photonic circuitry to manifest itself as an emerging technology platform rather than an entirely academic research field.

Plasmonic ridge waveguides with deep-subwavelength outside-field confinements

Subwavelength plasmonic waveguides are the most promising candidates for developing planar photonic circuitry platforms. In this study a subwavelength metallic ridge waveguide is numerically and experimentally investigated. Differing from previous plasmonic waveguides, the metallic strip of the subwavelength ridge waveguide is placed on a thick metal film. It is found that the surface-plasmon-polariton (SPP) waveguide modes result from the coupling of the corner modes in the two ridge corners. The bottom metal film has a great influence on the SPP modes, and nearly all the evanescent fields of the SPP modes are tightly confined outside the ridge waveguide. Simulations show that 50% of the total power flow in the SPP mode can be confined outside the ridge waveguide with an area of only about λ2/20. The propagation length is still about 10 times the plasmon wavelength. Through comparison with a metallic strip placed directly on the dielectric substrate, the proposed ridge waveguide exhibits a much higher sensing performance. This plasmonic ridge waveguide with deep-subwavelength outside-field confinements is of significance in a range of nano-optics applications, especially in nanosensing.

Electroluminescence Enhancement via Grating on a Si-based Plasmonic Metal-Insulator-Semiconductor Tunnel Junction

ABSTRACTHere we fabricated and characterized a CMOS compatible metal-insulator-semiconductor (MIS) plasmonic tunnel junction for Si-based photonic circuitry. A grating structure was realized on MIS plasmonic tunnel junction via focused-ion-beam milling (FIB) to increase the intensity of the light emission that occurs during inelastic electron tunneling. Approximately 65 times higher intensity of light emission is achieved with the grating structure during the measurements.

Combined System for Efficient Excitation and Capture of LSP Resonances and Flexible Control of SPP Transmissions

We propose a compact combined system which supports compound spoof surface resonances due to the coupling between spoof surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs). The system is composed of ultrathin metallic spiral structures for discrete LSP resonances and an ultrathin corrugated metallic strip to guide continuous SPP modes. We demonstrate both theoretically and experimentally that the LSP resonances can be efficiently excited and captured by the SPP waveguide, while the SPP transmissions can be judiciously controlled by the LSP structures. The spoof SPP-LSP combined system may find potential applications in sensing and integrated photonic circuitry in the microwave and terahertz frequencies.

Microring-based multi-chip WDM photonic module.

We report on a packaged prototype of a WDM photonic transceiver. It is an all-solid state hybrid assembly based on 130nm SOI photonic circuitry integrated with a 40nm CMOS VLSI driver. Our prototype supports eight tunable WDM channels operating at 10Gb/s, each capable of both transmitting and receiving data on the same chip. We discuss two options to close the link using the optical fiber or a waveguide bridge chip. We provide integration details and supporting link measurement data to describe packaged photonic module and its power efficient functionality with its on-chip power per channel averaging 1.3pJ/bit, excluding off-chip laser electrical power.

The rise of the GeSn laser

The development of a group IV semiconductor laser that is CMOS-compatible represents a step towards the creation of fully integrated electronic and photonic circuitry.

Near thresholdless laser operation at room temperature

The development of a thresholdless laser operating above room temperature (RT) is key for the future replacement of electronics with photonic integrated circuits, enabling an increase of several orders of magnitude in computing speeds. Recently, thresholdless lasing characteristics at low temperature (4 K) have been demonstrated. However, for practical applications, RT laser emission becomes necessary. Here we report experimental evidence that is compatible with a laser based on InAsSb quantum dots embedded in a photonic-crystal microcavity that exhibits an ultralow-power threshold (860 nW) and high efficiency (β =0.85), thus operating in the near-thresholdless regime at RT in the 1.3 μm spectral window. The results open up a wide range of opportunities for RT applications of ultralow threshold lasers, such as integrated photonic circuitry or high sensitivity biosensors.

Ultrafast all-optical modulation with hyperbolic metamaterial integrated in Si photonic circuitry.

The integration of optical metamaterials within silicon integrated photonic circuitry bears significantly potential in the design of low-power, nanoscale footprint, all-optical functionalities. We propose a novel concept and provide detailed analysis of an on-chip ultrafast all-optical modulator based on an hyperbolic metamaterial integrated in a silicon waveguide. The anisotropic metamaterial based on gold nanorods is placed on top of the silicon waveguide to form a modulator with a 300x440x600 nm(3) footprint. For the operating wavelength of 1.5 μm, the optimized geometry of the device has insertion loss of about 5 dB and a modulation depth of 35% with a sub-ps switching rate. The switching energy estimated from nonlinear transient dynamic numerical simulations is 3.7 pJ/bit when the transmission is controlled optically at a wavelength of 532 nm, resonant with the transverse plasmonic mode of the metamaterial. The switching mechanism is based on the control of the hybridization of eigenmodes in the metamaterial slab and the Si waveguide.

Unidirectional Lasing Emerging from Frozen Light in Nonreciprocal Cavities

We introduce a class of unidirectional lasing modes associated with the frozen mode regime of nonreciprocal slow-wave structures. Such asymmetric modes can only exist in cavities with broken time-reversal and space inversion symmetries. Their lasing frequency coincides with a spectral stationary inflection point of the underlying passive structure and is virtually independent of its size. These unidirectional lasers can be indispensable components of photonic integrated circuitry.

Manipulating Bloch surface waves in 2D: a platform concept-based flat lens

At the end of the 1970s, it was confirmed that dielectric multilayers can sustain Bloch surface waves (BSWs). However, BSWs were not widely studied until more recently. Taking advantage of their high-quality factor, sensing applications have focused on BSWs. Thus far, no work has been performed to manipulate and control the natural surface propagations in terms of defined functions with two-dimensional (2D) components, targeting the realization of a 2D system. In this study, we demonstrate that 2D photonic components can be implemented by coating an in-plane shaped ultrathin (∼λ/15) polymer layer on the dielectric multilayer. The presence of the polymer modifies the local effective refractive index, enabling direct manipulation of the BSW. By locally shaping the geometries of the 2D components, the BSW can be deflected, diffracted, focused and coupled with 2D freedom. Enabling BSW manipulation in 2D, the dielectric multilayer can play a new role as a robust platform for 2D optics, which can pave the way for integration in photonic chips. Multiheterodyne near-field measurements are used to study light propagation through micro- and nano-optical components. We demonstrate that a lens-shaped polymer layer can be considered as a 2D component based on the agreement between near-field measurements and theoretical calculations. Both the focal shift and the resolution of a 2D BSW lens are measured for the first time. The proposed platform enables the design of 2D all-optical integrated systems, which have numerous potential applications, including molecular sensing and photonic circuits. Controlling Bloch surface waves in a multilayer dielectric yields a new platform for creating two-dimensional photonic circuitry. Libo Yu and co-workers from the Swiss Federal Institute of Technology in Lausanne used an ultrathin (λ/15) polymer coating to modify the local effective refractive index of a dielectric multilayer stack that guides Bloch surface waves. Careful design of the shape of a polymer layer makes it possible to deflect, diffract and focus the waves within a planar geometry. The researchers used this approach to construct a flat lens capable of operating at a wavelength of 1.5 µm, and used a multiheterodyne scanning near-field optical microscope to observe the near-field behavior of the platform. They say that many other forms of photonic component should be possible.

Optimizing silicon-plasmonic waveguides for $$\chi ^{(3)}$$ χ ( 3 ) nonlinear applications

Hybrid silicon-plasmonic waveguides constitute an appealing platform for integrated photonic circuitry. They merge the technical maturity and prevalence of the SOI platform with the subwavelength confinement of plasmonic waveguides, essential for accessing enhanced nonlinear response at micron length-scales. Employing full-wave numerical simulations complemented with Schrodinger equation techniques, we propose nonlinear waveguide designs for Kerr-effect applications exhibiting minimized impairments due to free-carrier effects, thus raising the power-ceiling imposed on standard silicon waveguides.

An ultra-small silicon laser

A micrometre-sized laser has been demonstrated in silicon, the most ubiquitous material of the electronics industry. The device operates at microwatt power levels and could open routes to compact photonic integrated circuits. See Letter p.470 Silicon is the workhorse of the microelectronics industry, but its performance as a 'photonic' material is not exceptional. Nevertheless, much progress has been made in imparting useful optical properties to silicon, culminating in the realization of an all-silicon laser. Yasushi Takahashi and colleagues now present a new architectural twist on the silicon laser, showing how the incorporation of a photonic-crystal nanocavity into such a structure can drastically reduce both the size and the threshold power (the power at which it starts to behave as a laser) of the resulting device — both features that are essential for large-scale integration with other photonic and electronic circuitry.

Recent Advances in Organic One‐Dimensional Composite Materials: Design, Construction, and Photonic Elements for Information Processing

Many recent activities in the use of one-dimensional nanostructures as photonic elements for optical information processing are explained by huge advantages that photonic circuits possess over traditional silicon-based electronic ones in bandwidth, heat dissipation, and resistance to electromagnetic wave interference. Organic materials are a promising candidate to support these optical-related applications, as they combine the properties of plastics with broad spectral tunability, high optical cross-section, easy fabrication, as well as low cost. Their outstanding compatibility allows organic composite structures which are made of two or more kinds of materials combined together, showing great superiority to single-component materials due to the introduced interactions among multiple constituents, such as energy transfer, electron transfer, exciton coupling, etc. The easy processability of organic 1D crystalline heterostructures enables a fine topological control of both composition and geometry, which offsets the intrinsic deficiencies of individual material. At the same time, the strong exciton-photon coupling and exciton-exciton interaction impart the excellent confinement of photons in organic microstructures, thus light can be manipulated according to our intention to realize specific functions. These collective properties indicate a potential utility of organic heterogeneous material for miniaturized photonic circuitry. Herein, focus is given on recent advances of 1D organic crystalline heterostructures, with special emphasis on the novel design, controllable construction, diverse performance, as well as wide applications in isolated photonic elements for integration. It is proposed that the highly coupled, hybrid optical networks would be an important material basis towards the creation of on-chip optical information processing.

Epitaxial GaN Microdisk Lasers Grown on Graphene Microdots

Direct epitaxial growth of inorganic compound semiconductors on lattice-matched single-crystal substrates has provided an important way to fabricate light sources for various applications including lighting, displays and optical communications. Nevertheless, unconventional substrates such as silicon, amorphous glass, plastics, and metals must be used for emerging optoelectronic applications, such as high-speed photonic circuitry and flexible displays. However, high-quality film growth requires good matching of lattice constants and thermal expansion coefficients between the film and the supporting substrate. This restricts monolithic fabrication of optoelectronic devices on unconventional substrates. Here, we describe methods to grow high-quality gallium nitride (GaN) microdisks on amorphous silicon oxide layers formed on silicon using micropatterned graphene films as a nucleation layer. Highly crystalline GaN microdisks having hexagonal facets were grown on graphene dots with intermediate ZnO nanowalls via epitaxial lateral overgrowth. Furthermore, whispering-gallery-mode lasing from the GaN microdisk with a Q-factor of 1200 was observed at room temperature.

Integrated Silicon Nanophotonic Data Processing Devices: A Brief Review

Significant scientific efforts are constantly invested in the attempts to develop photonic circuitry integrated in microelectronic chip. Such circuitry should be capable of realizing fundamental processing building blocks such as modulators (or transistors) and logic gates in order to improve the performance of an optics communication short and/or long range links. The improvement is to be obtained in the sense of reduced power dissipation, lower noise level and increased information bandwidth. This paper reviews some of the technologies involved in those efforts. Specifically we focus on silicon based integrated nanophotonic modulation devices (based upon plasma dispersion as well as fundamental non linear processes in silicon) as well as passive devices for directing and spectrally filtering light via silicon nanophotonic crystal structures. The patents mentioned in this review relate to the realization of nanophotonic logic gates for data processing, they are related to photonic nano communication link apparatus, apparatus and method for switching, modulation and dynamic control of light transmission using photonic crystals and to modulator-based photonic chip-tochip interconnections for dense three-dimensional multichip module integration. Keywords: Integrated optics, optical circuitry, silicon.