Surface plasmon based photonic (or plasmonic) circuits merge electronics and photonics at the nanoscale, creating the ability to combine the superior technical advantages of photonics and electronics on the same chip. Recent work has demonstrated their remarkable applications in subwavelength optics, data storage and transmission, light harvesting and generation, and microscopy, as well as bioapplications. Plasmonics has become one of the most intensive research subjects in recent years, and much effort has been made to develop novel and efficient waveguiding structures and plasmonic materials. We will first review some major progress in subwavelength plasmonic waveguides and plasmonic materials. Then, focusing on the applications of a class of promising alternative plasmonic materials, transparent conducting oxides, we will introduce some of our up-to-date study, especially on electro-absorption modulators and beam steering.
Recent research on epsilon-near-zero (or index-near-zero) materials has revealed their promising applications in
optoelectronics. We explore a novel waveguide structure, namely “epsilon-near-zero-slot waveguide”, by utilizing
transparent conducting oxides as the active medium, which can be tuned between epsilon-near-zero and epsilon-farfrom-
zero by accumulation carriers, resulting in sharp effective index change. We propose laser beam steering by taking
advantage of this epsilon-near-zero-slot waveguide structure. With about 60°steering angle being achieved, this
waveguide structure has the advantages of ultra high speed and compact dimension, as well as easy fabrication.
We demonstrate greatly enhanced light absorption by monolayer graphene over a broad spectral range, from visible to
near infrared, based on attenuated total reflection (ATR). The designed structure consists of two dielectric media and
monolayer graphene between them. Up to 42.7% light absorption has been achieved by this structure. Moreover, when
applying electrolyte gel, electric double layers are formed at the graphene-gel interface, which leads to the change of
graphene’s electrical properties as well as optical properties. As a result, light absorption of graphene can be manually
modulated. This design may help build electro-optic modulators for applications in communications, sensing and
spectroscopy.
We explore tunable plasmonic metamaterials for electro-optic modulator applications based on ITO-based multilayer
structures. Two different structures are investigated, and modulation depth up to 38.8% can be achieved. Preliminary
results are presented for the real time response of an ITO/electrolyte gel/doped Si modulator. Furthermore, another
modulator configuration is investigated by substituting electrolyte gel by high-k dielectric material (HfO2).
A multilayer metal-insulator (MMI) stack system is viewed as an anisotropic metamaterial to exhibit plasmonic behavior
and a candidate of "metametal". The dispersion of the fundamental super mode propagating along the boundary between
an MMI stack and a dielectric coating is theoretically studied and compared to that of surface waves on a single metalinsulator
boundary. The conditions to obtain artificial surface plasmon frequency are thoroughly investigated, and the
tuning of effective surface plasmon frequency is verified by electromagnetic modeling. The design rules would bring
important insights into layer-by-layer metamaterial development related to superlenses, optical lithography, nanosensing
and imaging.
The classical self-imaging effect can be observed for a periodic object with a pitch larger than the diffraction limit of an
imaging system. In this paper, we show that the self-imaging effect can be achieved in an indefinite metamaterial even
when the period is much smaller than the diffraction limit in both two-dimensional and three-dimensional numerical
simulations, where the paraxial approximation is not applied. This is attributed to the evanescent waves, which carry the
information about subwavelength features of the object, can be converted into propagating waves and then conveyed to
far field by the metamaterial, where the permittivity in the propagation direction is negative while the transverse ones are
positive. The indefinite metamaterial can be realized and approximated by a system of thin, alternating multilayer metal
and insulator (MMI) stack. As long as the loss of the metamaterial is small enough, deep subwavelength image size can
be achieved.
We demonstrate integrated plasmonic devices on silicon-on-insulator (SOI) substrate for photon-plasmon conversion
and plasmonic mode transformation at near-infrared frequency. The plasmonic junction converts photons to surface
plasmons and then back to photons with 7.35 dB conversion loss, and has successfully focused multimode plasmonic
propagation to deep subwavelength (80 nm by 50 nm) single mode propagation with 2.28 dB/μm propagation loss. The
integration approach leads to a robust and versatile platform for 3D nanoplasmonic gauges potentially functional in
ultra-fast communications and optical sensing.
The Talbot effect (or the self-imaging effect) can be observed for a periodic object with a pitch larger than the diffraction
limit of an imaging system, where the paraxial approximation is applied. In this paper, we show that the super Talbot
effect can be achieved in an indefinite metamaterial even when the period is much smaller than the diffraction limit in
both two-dimensional and three-dimensional numerical simulations, where the paraxial approximation is not applied.
This is attributed to the evanescent waves, which carry the information about subwavelength features of the object, can
be converted into propagating waves and then conveyed to far field by the metamaterial, where the permittivity in the
propagation direction is negative while the transverse ones are positive. The indefinite metamaterial can be
approximated by a system of thin, alternating multilayer metal and insulator (MMI) stack. As long as the loss of the
metamaterial is small enough, deep subwavelength image size can be obtained in the super Talbot effect.
In this paper, we propose an optical switch based on a metal-insulator-metal plasmonic waveguide with Si3N4 core sandwiched between two gallium (Ga) metal layers. Combining the unique structural phase transition property of gallium, within a total length of only 400 nm, an extinction ratio as high as 7.68 dB can be achieved in the proposed nanoplasmonic structure. The phase transition may be achieved by changing the temperature of the waveguide or by external light excitation.
Due to the large transverse mode size in the frequency regime far below plasma frequency, some important applications
of surface plasmons in the THz or microwave frequency regime have been limited where deep subwavelength optical
devices are a critical technique. Here we experimentally demonstrated focusing and guiding electromagnetic (EM) waves
in a 3D spoof surface plasmonic waveguide, which is a row of rectangular rods patterned on an aluminum slab. The
maximum of the mode size can be mapped in the middle plane of two neighboring rods. The mode size slightly varies
with different frequencies and minimizes at 0.04λ-by-0.03λ at 2.25 GHz. Moreover, due to the tight binding of surface
waves, the decrease of the waveguide width does not significantly affect the dispersion of the guided modes. This fact
enables the mode tapering in the transverse direction from a wide waveguide into deep subwavelength waveguide with
high efficiency. To this end, a tapered spoof surface plasmonic waveguide was fabricated as the input is the uniform
spoof surface plasmonic waveguide and its performance was investigated in experiments. From the experimental results,
as the EM waves propagate in the taper, the mode size becomes smaller and smaller with the intensity gradually
increasing, and eventually EM waves are coupled into the deep subwavelength mode.
We propose integrated waveguides for terahertz (THz) and mid-infrared (MIR) applications on wafer platform. Based on
the prototype of spoof plasmonic waveguides consisting of textured metallic surface, we explore the possibility of
coating periodic metallic pattern with silicon (at 0.6 THz) or germanium (at MIR region of 30 THz) to further shrink the
relative mode size of propagation spoof plasmonic waves. Numerical modeling via 3D finite-difference time-domain
(FDTD) has shown deep sub-wavelength mode confinement in transverse directions to smaller than λ/50 by λ/50, with an
estimated propagation loss of less than 0.1 dB for each repetitive unit.
We propose a "slot-to-slot" coupler to convert power between optical and metal-insulator-metal (MIM) plasmonic
modes. Coupling efficiency of larger than 60% is obtained from 2D FDTD simulation. Based on this prototype, a quasi-MIM plasmonic junction is demonstrated using e-beam lithography onto an SOI substrate. The junction is formed by
depositing a thin layer of gold (~20 nm) on part of a dielectric slot. When probed by 1520-nm laser, coupling efficiency
of 36% is achieved for a 500-nm long quasi-MIM junction. Optical modulation is under investigation by pumping the
device using visible light to change the optical property of gold.
In this paper, ultra low cross talk is achieved by using a resonant cavity at the intersection between two strip waveguides
formed in a square lattice photonic crystal structure (PhC). Two PhC structures are studied: one consists of cylindrical
rods and another consists of cubic rods. The Q-Factor of the cavity is changed by increasing the number of rods that form
the cavity and by decreasing the spacing between the waveguide and the cavity. Our two dimensional simulation results
show that the latter method resulted in cross talk reduction of more than 21 dB for both structures. The overall cross talk
was -90.50 dB for the cylindrical rods structure and -105.0 dB for the cubic rods structure. The optimized PhC structures
were fabricated on a silicon-on-insulator platform. The rods were buried in silicon oxide in order to maximize the
photonic band gap and provide index guiding in the vertical direction.
We experimentally demonstrate subwavelength resolution imaging at microwave frequencies by a three-dimensional (3D) photonic crystal flat lens using full 3D negative refraction. The flat lens is made of a body-centered cubic photonic crystal (PhC) whose dispersion at the third band results in group velocity opposite to phase velocity for
electromagnetic waves. The photonic crystal was fabricated in a layer-by-layer process. Two different sources (monopole and pinhole) were used as imaged objects and a monopole detector was employed for detection in the image region. By scanning the detector, we obtained the images of the pinhole and monopole sources, seperately. The image of the pinhole sources had subwavelength feature size in all three dimensions, which predicts a 3D imaging capability of the flat lenses. An image of two pinhole sources with subwavelength spacing showed two resolved spots, which further verified subwavelength resolution.
We present our experimental demonstration of self-collimation inside a three-dimensional (3D) simple cubic photonic crystal at microwave frequencies. The photonic crystal was designed with tailored dispersion property and fabricated by a high precision computer-controlled machine. The self-collimation modes were excited by a grounded waveguide feeding and detected by a scanning monopole. Self-collimation of electromagnetic waves in the 3D photonic crystal was demonstrated by measuring the 3D field distribution, which was shown as a narrow collimated beam inside the 3D photonic crystal whereas a diverged beam in the absence of the photonic crystal.
We demonstrate an efficient prism coupling method to couple nonplanar infrared waves into a 2-D planar photonic-crystal (PhC) device, such as a PhC waveguide (PhCW). A coupling efficiency of 31.1% is obtained experimentally. Results from finite-difference time-domain (FDTD) modeling are shown to closely match the results measured in a fabricated sample.
We demonstrate nondefect mid-infrared waveguides based on the self-collimation effect in photonic crystals (PhCs). Due to the spatial dispersion properties serving to confine and route light, propagation loss as low as 2.56 dB/mm is obtained in a silicon-on-insulator (SOI)-based waveguide. The efficiency, together with their ability of arbitrary and structureless routing of electromagnetic beams, of these self-collimation devices provide a potential candidate for miniaturizing devices.
In this paper, we demonstrate the design and fabrication of a planar lens based on the dispersion property of a photonic crystal. When a photonic crystal is illuminated with a low frequency within its dispersion diagram it behaves very similar to an isotropic material, whose resultant index is kept a constant, and is determined by the ratio of high index material and low index material. To validate our design, we performed the experiment in millimeter regime, where the photonic crystal lens was fabricated using a CNC micro-milling machine, and a millimeter wave imaging system was built based on a vector network analyzer. For the lens, we have observed its ability to collimate an incident point source both in the amplitude and phase.
In this paper we present self-collimation in three-dimensional (3D) photonic crystals (PhCs) consisting of a simple cubic structure. By exploiting the dispersive properties of photonic crystals, a cubic-like shape equi-frequency surface (EFS) is obtained. Such surfaces allow for structureless confinement of light. Due to the degeneracy of propagation modes in a 3D structure, self-collimation modes can be distinguished from other modes by launching a source with a particular polarization. To this end, we found that polarization dependence is a key issue in 3D self-collimation. The results hold promise for high-density PhCs devices due to the lack of structural interaction. Finally, a novel method for the fabrication of three-dimensional (3D) simple cubic photonic crystal structures using conventional planar silicon micromachining technology is presented. The method utilizes a single planar etch mask coupled with time multiplexed sidewall passivation and deep anisotropic reactive ion etching in combination with isotropic etch processes to create three-dimensional photonic crystal devices. Initial experimental results are presented.
Micro-optics offers the ability to realize massively parallel, surface-normal interconnects at the chip scale. In this context, we investigate the integration of a 10-Gbytes/s, 850-nm vertical-cavity surface-emitting laser (VCSEL) with a 2×2 array of continuous surface profile, diffractive optical elements to demonstrate a prototype system that incorporates 3-D, highly dense, parallel optical interconnects. The integration is achieved using a novel conductive polymer-based flip-chip process, which is implemented using conventional fabrication techniques. We present experimental results from the design, fabrication, integration, and characterization of the prototype system.
Using the special dispersion properties of photonic crystals (PhCs), we present a promising novel coupling device, the terahertz (THz) planar photonic crystal (PhC) lens. Three-dimensional finite-difference time-domain (3D-FDTD) calculations show a 90% power transfer from a 100 mm waveguide to a 10 mm waveguide, and experimental results confirm its high efficiency. Furthermore, the PhC lens couples the wave into a PhC line-defect waveguide is also reported. These achievements manifest the usefulness of the PhC lens as an effective approach to couple the wave into future THz circuits.
We present a method for coupling from a single mode fiber, or fiber ribbon, into an SOI waveguide for integration with silicon opto-electronic circuits. The coupler incorporates the advantages of the tapered waveguides and prism couplers, yet offers the flexibility of planar integration. The coupler can be fabricated on a double polished silicon wafer using direct polishing or grayscale photolithography. Tapered waveguides or J-couplers are then used as lateral mode converters. An experimental setup with a rotational stage and a pneumatic plunger has been built for adjusting the incident angle and tunnel layer thickness, which are key factors in determining the coupling efficiency. When optimal coupling is achieved on the setup, the coupler can be packaged using epoxy bonding. Thus, a fiber-waveguide parallel coupler or connector can be easily constructed. Electromagnetic calculation predicts a coupling efficiency of 77%(-1.14dB insertion loss) for a silicon-to-silicon coupler with a uniform tunnel layer. The coupling efficiency is experimentally achieved to be 46%(-3.4dB insertion loss) excluding the loss in silicon and the reflections from the input surface and output facet.
AlGaAsSb/AlGaSb heterostructures offer the ability to realize high-performance devices for 1550 nm high-speed optical interconnect applications. In this context, we present the design, fabrication, integration and characterization of 10 GHz p-i-n photodetectors in this material system. This effort has involved an investigation into inductively coupled plasma (ICP) etching of these materials and the development of a novel process for their conductive polymer based flip chip die attach.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.