Modified Ring Resonator Research Articles

Power Efficiency Comparisons of Interchip Optical Interconnect Architectures

High-bandwidth interchip optical interconnect architectures have the potential to address increasing input-output bandwidth demands. This brief compares several optical interconnect architectures on the basis of power efficiency in 90- and 45-nm CMOS technologies. Under consideration are a near-term architecture consisting of discrete vertical-cavity surface-emitting lasers (VCSELs) with p-i-n photodetectors (PDs) and three long-term integrated photonic architectures that use waveguide metal-semiconductor-metal PDs and either electroabsorption modulator (EAM), ring resonator modulator (RRM), or Mach-Zehnder modulator (MZM) sources. An optimal current density methodology with normalized transistor parameters extracted from circuit simulations is applied to jointly optimize driver and receiver circuitry to minimize the total link power dissipation. The analysis results show that the VCSEL-based link is limited by VCSEL bandwidth and maximum power levels, rather than circuit bandwidth, and achieves a maximum of 24 Gb/s in both the 90- and 45-nm nodes. The EAM and the RRM are both attractive integrated photonic technologies capable of scaling data rates past 30 Gb/s at power efficiency levels near 0.5 mW/Gb/s in the 45-nm node and are primarily limited by coupling and device insertion losses. While the MZM offers robust operation due to its wide optical bandwidth, significant improvements in power efficiency must be achieved to become applicable for high-density applications.

Optical I/O Technology for Tera-Scale Computing

This paper describes both a near term and a long term optical interconnect solution, the first based on a packaging architecture and the second based on a monolithic photonic CMOS architecture. The packaging-based optical I/O architecture implemented with 90 nm CMOS transceiver circuits, 1 × 12 VCSEL/detector arrays and polymer waveguides achieves 10 Gb/s/channel at 11 pJ/b. A simple TX pre-emphasis technique enables a potential 18 Gb/s at 9.6 pJ/b link efficiency. Analysis predicts this architecture to reach less than 1 pJ/b at the 16 nm CMOS technology node. A photonic CMOS process enables higher bandwidth and lower energy-per-bit for chip-to-chip optical I/O through integration of electro-optical polymer based modulators, silicon nitride waveguides and polycrystalline germanium (Ge) detectors into a CMOS logic process. Experimental results for the photonic CMOS ring resonator modulators and Ge detectors demonstrate performance above 20 Gb/s and analysis predicts that photonic CMOS will eventually enable energy efficiency better than 0.3 pJ/b with 16 nm CMOS. Optical interconnect technologies such as these using multi-lane communication or wavelength division multiplexing have the potential to achieve TB/s interconnect and enable platforms suitable for the tera-scale computing era.

Split ring resonator sensors for infrared detection of single molecular monolayers

We report a surface enhanced molecular detection technique with zeptomole sensitivity that relies on resonant coupling of plasmonic modes of split ring resonators and infrared vibrational modes of a self-assembled monolayer of octadecanthiol molecules. Large near-field enhancements at the gap of split ring resonators allow for this resonant coupling when the molecular absorption peaks overlap spectrally with the plasmonic resonance. Electromagnetic simulations support experimental findings.

Multimode Waveguides Coupled to Single Mode Ring Resonators

A planar integrated optical device based on the interaction of two spatial eigenmodes with a single eigenmode ring resonator is presented. Solutions for the output mode amplitudes are determined theoretically and are shown to be strong functions of the relative phases of the two input modes. A device was fabricated in a polymer-silicon material system by a photolithographic process. The modal response as a function of wavelength is measured by the twin-fiber interferometer technique through fringe visibility. It is found that sharp visibility lineshapes may be achieved through the adjustment of input mode phase and twin-fiber spacing on the radiated output beam. These sharp lineshapes are also possible in the presence of high loss in the resonator. The on-chip test device incorporates a single mode to two-mode converter and a far-field wavefront sampler. The measured fringe visibility slope with respect to wavelength reaches a maximum value of 74 nm- 1 which is 56 nm-1 larger than a single mode waveguide coupled to a single mode microring with the same ring loss and 15 dB extinction ratio. Such sharp lineshapes in visibility may be exploited for optical applications in sensing, communications, and computing.

Multimode waveguide-cavity sensor based on fringe visibility detection

Fringe visibility detection of the interaction of two bus spatial eigenmodes with a resonant cavity is investigated for the purpose of achieving a sensor platform with high sensitivity. The power distribution between the bus waveguide eigenmodes is modulated by the interaction with the cavity and is detected via fringe visibility lineshapes produced by twin-fiber interferometry. A test device is fabricated in a polymer-silica material system by a photolithographic process and is characterized by measuring the fringe visibility change as a function of analyte refractive index. Fringe visibility modulation from a straight two-mode waveguide coupled to a single mode ring resonator exposed to an aqueous glucose solution demonstrates a visibility change of 1.57 per weight percent, compared to a transmission change of 0.19 per weight percent for a single mode waveguide critically coupled to a ring with similar intrinsic quality factor. The demonstrated change in fringe visibility is 8.2 times larger.

Bidirectional wavelength tuning of individual semiconductor quantum dots in a flexible rolled-up microtube

We consider a pair of artificial atoms with different ground-state energies. By means of finite element calculations, we predict that the ground-state energies can be tuned into resonance if the artificial atoms are placed into a flexible ring structure, which is elastically deformed by an external force. This concept is experimentally verified by embedding self-assembled quantum dots with low density into the wall of a rolled-up microtube ring resonator. We demonstrate that quantum dots can elastically be tuned in and out of resonance with each other or with the ring resonator modes.

Balun-BPF 특성 구현을 위한 3-단자 링-공진기의 해석

본 논문은 최근 발표된 이중 모드 링-공진기를 이용한 Balun-BPF를 3-단자 회로망 분석 방법을 이용하여 전체 어드미턴스 파라미터를 유도하고 이를 이용하여 Balun의 특성을 만족함을 수식적으로 증명하였다. BPF의 표준 설계법을 적용하여 손쉽게 임의의 특성을 갖는 Balun-BPF 설계가 가능하도록 Balun 동작 상태에서의 이미턴스 슬로프 파라미터를 도출하고, Balun-BPF 양단의 감쇄극 주파수를 예측하는 방법을 제시하였다. 회로 시뮬레이션과 실제 제작 측정을 통해 제안된 해석식들을 검증하였다. 제작된 Balun-BPF는 중심 주파수 2.46 GHz에서 71 MHz 대역폭과 삽입 손실 0.92 dB를 가지며, <TEX>$174{\sim}181^{\circ}$</TEX>의 위상 특성과 0.5 dB 이내의 크기 특성을 나타내었다. In this paper, we derived the Y-parameter of the recently reported Balun-BPF with a dual mode ring resonator by using the network analysis method. Using the derived Y-parameter we verified that the Balun-BPF structure satisfy the balun conditions. In order to design the Balun-BPF with arbitrary characteristics using the standard BPF design method with ease we derived the immittance slope parameters of the dual mode ring resonator with a load. The notch frequencies are also predicted. By designing with the proposed equations, simulating with a circuit simulator, fabricated and measured a Balun-BPF we confirmed the validation of the equations. The measured data shows bandwidth of 71 MHz and insertion loss of 0.92 dB at the center frequency of 2.46 GHz. It shows the phase imbalance of <TEX>$174{\sim}181$</TEX> degree and the magnitude imbalance within 0.5 dB.

New perturbation technique to generate split modes in electromagnetically coupled notch filters using different ring resonators

AbstractA new method for generating split modes in ring resonators, used as notch filters with three geometries (square, triangular, and circular), is introduced by varying the feed position of electromagnetically coupled feed line. The resonators are fabricated (all at 2.4 GHz nominally) on TMM4 (εr = 4.5, h = 0.762 mm) substrates and coupled electromagnetically to a 50 Ω microstrip feed line on separate TMM4 substrate. Only the latter has ground plane under it. The offset distance between the center of feed line and center of resonator is varied and changes in the resonant (notch) frequency, rejection (S21) of single and split modes are recorded at each offset position for all resonators. Experimental results are found to agree with simulated results to a greater degree for square and lesser for other two geometries. Frequency variations have much more disagreements. The angle of crossing between feed line and ring edges appears to be a critical factor. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1747–1752, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23483

Dielectric resonators and filters

High-performance DRs and filters are widely used in wireless and satellite communication systems due to their superior characteristics, such as high unloaded Q, excellent temperature stability, and smaller size compared to their air-filled counterpart. Temperature-stable high-Q dielectric materials with a wide range of dielectric constants from 20 to 100 are available. The properties of a DR such as resonant frequency and unloaded Q can be accurately determined by full-wave EM simulations. TEoi single-mode filters offer the advantages of design simplicity and flexibility in layout options over HEn dual-mode filters, while dual-mode filters have significiint advantages in the mass and volume of the products. Mixing the TEoi and HE\\ modes, dielectric loaded resonator filters achieve the advantages of dual-mode HEn DR filters and the excellent spurious performances of the TEqi mode ring resonator filters.

Surface plasmon resonance-assisted coupling to whispering-gallery modes in micropillar resonators

We report experiments and modeling of surface plasmon resonance (SPR)-assisted coupling to whispering-gallery modes in dielectric microresonators. Our experiments use a gold-coated glass-prism that is evanescently coupled to a 125-μm-diameter silica-micropillar resonator. We find nearly 12-fold enhancement in the whispering-gallery resonance extinction ratio in the vicinity of the SPR angle using a 50-nm gold-film. The measured trends of the enhancement, as a function of the laser-beam incident angle and the gold-film thickness, show good qualitative agreement with our modeling of SPR-assisted coupling to ring resonator modes. Our modeling suggests that the far-field interference between the SPR-enhanced microresonator mode field and the attenuated total internal reflected field from the prism gives the observed extinction ratio enhancement.

Three dimensionally confined optical modes in quantum-well microtube ring resonators

We report on microtube ring resonators with quantum wells embedded as an optically active material. Optical modes are observed over a broad energy range. Their properties strongly depend on the exact geometry of the microtube along its axis. In particular, we observe (i) preferential emission of light on the inside edge of the microtube and (ii) confinement of light also in the direction of the tube axis by an axially varying geometry, which is explained in an expanded waveguide model.

Nonplanar ring resonator modes: generalized Gaussian beams

Several findings on the modes of a nonplanar ring resonator have been carried out by utilizing the matrix method of generalized Gaussian beams. The widely used nonplanar ring resonator--a four-equal-sided nonplanar ring cavity with two curvature mirrors and two planar mirrors--has been chosen as an example. The overall stability maps of this typical nonplanar ring cavity with L/R ranging from 0 to infinity are calculated and described, while the total cavity length is L and the radius of the curvature mirrors is R. The stability map has also been found to have asymmetry with total image rotation rho ranging from 0 degrees to 360 degrees and 0<L/R<2. It has also been found that there still exist several stable regions in the extended region with L/R>2. The Gaussian modes of the nonplanar ring cavity have been found to have different characteristics with different design parameters such as rho and L/R. The azimuth angles of the major and minor axes of the spot size have been found to be variable with different design parameters such as rho and L/R and variable under different location of the nonplanar cavity. These interesting findings are totally different from the behavior of conventional planar stable resonators and are important to the cavity designs of nonplanar ring resonators.

Universal coupling between metal-clad waveguides and optical ring resonators

We demonstrate excitation of whispering gallery modes in optical ring resonators using a gold-clad pedestal planar waveguide structure. The gold-clad structure provides a strong evanescent field for light-coupling into the resonator while enabling low transmission loss throughout much of the visible and near-infrared region. This is advantageous compared to the previously demonstrated anti-resonant reflecting optical waveguide (ARROW) structure, which can only transmit a narrow wavelength band. We show that the height of the pedestal waveguide can be designed to optimize the coupling conditions for the ring resonator. This technology enhances the practicality of optical ring resonators for sensing devices, laser systems, and many other important applications.

Localised bending modes in split ring resonators

We present band diagrams for in-plane elastic waves propagating within a doubly periodic structure involving split ring resonators (SRR). From the Navier equations we derive that the lowest resonant frequencies are associated with localised bending modes solutions of a fourth-order differential equation in thin-bridges, which are responsible for the appearance of a low frequency stop band. Potential applications lie in the design of earthquake resistant systems.

Dual mode ring resonator band‐pass filter with wide stopband

AbstractIn this article, parallel‐coupled microstrip line (PCML) with ground plane aperture is used to improve the stopband performance of a stub tuned dual mode ring resonator band‐pass filter (BPF). The PCML with ground plane structure produces a wide‐band band‐pass response, whereas the stub tuned dual mode ring resonator produces sharp cutoff. The combined filter produces vastly improved filter characteristics. A prototype fabricated BPF having passband center frequency 5.71 GHz has a bandwidth of 40.6%. The upper stopband is extended over 6 GHz and there is no undesirable passband on the lower side of the main passband. Skirt selectivity of a single stage filter is at least 120 dB/GHz. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2216–2218, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21934

A modified ring dielectric resonator with improved mode separation and its tunability characteristics in MIC environment

In this paper, a novel dielectric-resonator (DR) structure, called a modified ring resonator, has been proposed. In a microwave integrated-circuit configuration, the ring DR shape is modified in such a way that, for the TE/sub 01/spl delta// mode, the nearest hybrid (or TM/sub 01/spl delta//) modes are pushed farther to provide a higher mode separation simultaneous to no deterioration of the Q factor in the mode of interest. Further, the tunability studies reveal that degradation of mode separation in the proposed configuration is much lower than the conventional ring resonator for the tuning range studied here. The configuration also offers versatility in choosing the substrate thickness, which otherwise is limited in a ring resonator.

A Novel Compact Dual-Band Bandpass Filter Using Dual-Mode Resonators

SUMMARY The paper reports a compact and high performance dualband bandpass filter (BPF) using two types of dual-mode resonators. The dual mode cross shaped resonator and the three dual mode ring resonators in the designed dual-band BPF are excited to control the first and second passband, respectively. It is shown that the designed and fabricated dualband BPF has narrow bandwidths and very sharp attenuation rate due to the existence of the transmission zeros. The frequency response of the designed dual-band BPF shows good agreement between the simulations and experiments.

Coupled-waves approach to the design and analysis of bragg and photonic crystal annular resonators

We utilize a novel coupled-waves approach to design and analyze various types of annular resonators based on Bragg and photonic crystal reflectors. Optimal grating profiles and their corresponding modal fields are found for specific cases such as disk and defect mode (ring) resonators. An excellent match is found between our analytic approximations and exact results obtained by the transfer matrix formalism and finite-difference time-domain simulations.

Simple analysis of the frequency modes for microstrip ring resonators of any general shape and correction of an error in the literature

AbstractUnlike the conventional magnetic‐wall model, a simple transmission‐line model unaffected by boundary conditions is used to calculate the frequency modes of ring resonators of any general shape such as annular, square, or meander. Moreover, it corrects an error in the literature concerning the frequency modes of the one‐port ring resonator. Also, it can be used to describe the dual‐mode behavior of the ring resonator, which the magnetic‐wall model cannot address well, especially for a ring resonator with complicated boundary conditions. Experiments show good agreement with theory. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 209–213, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11017

Polymer micro-ring filters and modulators

Micro-ring wavelength filters and resonant modulators using polymer materials at 1300 nm and 1550 nm are analyzed, designed, and demonstrated. The rings are integrated with vertically coupled input and output waveguides. The devices are fabricated using optical lithography. Filters with a finesse of 141 and free spectral range of 5 nm at 1300 nm and finesse of 117 with a free spectral range (FSR) of 8 nm at 1550 nm are demonstrated. Ring resonators with a Q as high as 1.3 /spl times/ 10/sup 5/ at 1300 nm are demonstrated. The filters can be temperature tuned at the rate of 14 GHz//spl deg/C. Resonant ring modulators, which use an electrooptic polymer, are demonstrated. The resonance wavelength voltage tunes at the rate of 0.82 GHz/V. The modulators have a bandwidth larger than 2 GHz. Using the resonant modulator, and open eye diagram at 1 Gb/s is demonstrated.