We review recent progress of an effort led by the Stojanović (UC Berkeley), Ram (MIT) and Popović (CU Boulder) research groups to enable the design of photonic devices, and complete on-chip electro-optic systems and interfaces, directly in standard microelectronics CMOS processes in a microprocessor foundry, with no in-foundry process modifications. This approach allows tight and large-scale monolithic integration of silicon photonics with state-of-the-art (sub-100nm-node) microelectronics, here a 45nm SOI CMOS process. It enables natural scale-up to manufacturing, and rapid advances in device design due to process repeatability. The initial driver application was addressing the processor-to-memory communication energy bottleneck. Device results include 5Gbps modulators based on an interleaved junction that take advantage of the high resolution of the sub-100nm CMOS process. We demonstrate operation at 5fJ/bit with 1.5dB insertion loss and 8dB extinction ratio. We also demonstrate the first infrared detectors in a zero-change CMOS process, using absorption in transistor source/drain SiGe stressors. Subsystems described include the first monolithically integrated electronic-photonic transmitter on chip (modulator+driver) with 20-70fJ/bit wall plug energy/bit (2-3.5Gbps), to our knowledge the lowest transmitter energy demonstrated to date. We also demonstrate native-process infrared receivers at 220fJ/bit (5Gbps). These are encouraging signs for the prospects of monolithic electronics-photonics integration. Beyond processor-to-memory interconnects, our approach to photonics as a “More-than- Moore” technology inside advanced CMOS promises to enable VLSI electronic-photonic chip platforms tailored to a vast array of emerging applications, from optical and acoustic sensing, high-speed signal processing, RF and optical metrology and clocks, through to analog computation and quantum technology.
The potentials of integrated optical systems for implementing compact and low power consumption yet highly sensitive
sensing systems have made them a viable candidate for integrated chemical and biological sensing applications. In these
integrated optical sensing systems, spectrometers have a significant role as a building block that enables on-chip
spectral analysis. Monitoring the spectral features of the signal using an on-chip spectrometer brings about a variety of
new sensing mechanisms and architectures in an integrated platform. Monitoring absorption spectra, measuring Raman
emission features, and tracking changes in spectral signatures as a result of environmental changes are some of the
schemes made possible by such spectral analysis. In this work, we implement superprism-based photonic crystal devices
in planar platforms as on-chip spectrometers. We use planar silicon platform in a silicon-on-insulator (SOI) wafers for
the infrared wavelength range. A silicon-nitride (SiN) planar platform is used for the near infrared and visible
wavelength ranges. In both SOI and SiN implementations, superprism-based spectrometers are experimentally
demonstrated and compared with grating spectrometers made in the same platform. The potentials of the demonstrated
spectrometers to meet the requirements of current and future applications in integrated optical sensing are briefly
discussed.
Photonic crystal waveguides (PCW) on silicon-on-insulator (SOI) are considered as a promising guiding platform with
flexible guiding properties for dense photonics integration. Although SOI is a versatile material for photonics
integration, PCWs fabricated on SOI substrates suffer from small guiding bandwidth due to the coupling to leaky TM-like
modes. The purpose of this work is to present a systematic approach to increase the low-loss guiding bandwidth of
PCWs on SOI. This has been achieved by reducing the interaction of low-group-velocity modes with the surrounding
photonic crystal. By this method the low-loss bandwidth of a W1 PCW is increased from 2.5 nm to 12 nm which is the
highest reported for this type of waveguide. We also present a detailed analysis of transmission properties of W1 PCWs
and elaborate on the coupling to TM-like guided modes present in the low-loss transmission bandwidth of this device.
When the periodic permittivity of two-dimensional (2D) photonic crystal (PC) can be separated in x- and y- coordinates,
one can consider the structure as two separate 1D photonic crystals, one of them being periodic in x coordinate and the
other in y coordinate. If it is possible to find a proper separable permittivity function, we can approximate a 2D PC with
two distinct 1D structures. One of the advantages is rapid calculation the density of state of a 2D PC. In this article an
analytical calculation of the density of states for such a 2D PC has been done with the aim of taking this advantage. For
calculating the density of states we use the effective resonance approach to analyze the 1D PC.
In this paper we analyze a disk-like quantum dot embedded in an engineered two-dimensional (2D) photonic crystal
cavity as an artificial atom. In this quantum dot electron and hole form an exciton where photon and electron-hole bound
state can interact. Within the engineered electromagnetic vacuum of the PBG material, the exciton can emit and reabsorb
a virtual poton. If the exciton energy lies near in the photonic band gap edge the exciton level splits into two levels. The
dressed state exciton exhibits a lower energy than that of bare exciton. Here energy associated with dressed exction is
evaluated.
Using polynomial expansion of electromagnetic fields has been already reported for extraction of E polarized defect
modes in two-dimensional photonic crystals. This approach is now applied to straight single-line defect optical
waveguides, where H polarized defect modes are analytically extracted for the first time. Electromagnetic fields are
expanded in accordance with the Floquet theorem, where each Floquet order is itself expanded in terms of Hermite
polynomials and finally a new set of linear ordinary differential equations with non-constant coefficients is obtained.
This set of equations is handled by employing differential transfer matrix method. In this fashion, algebraic and easy to
solve dispersion equations are derived, where each mode is effectively sought out in the Hilbert space spanned by
Hermite polynomials. Effective index theory based on static field approximation is also presented to show the strong
similarity between eigenmodes of photonic bandgap waveguides and those of slab waveguides with uniaxial anisotropic
claddings.
Analytical analysis of straight single-line defect optical waveguides in two dimensional photonic crystals based on expanding electromagnetic fields in terms of Hermite polynomials is reported. This novel electromagnetic field expression is substituted in Helmholtz equation, a new set of linear ordinary differential equations with variable coefficients are obtained, and by employing differential transfer matrix method; defect modes, i.e. the guided modes propagating in the line defect waveguide, are analytically derived. The validity of the results obtained by applying the proposed approach are confirmed by comparing them to those derived by using finite difference time domain method.
A novel approach for photonic crystals devices analysis, based on perturbation theory is reported. In this method the photonic crystal device is considered as the superposition of a parent lattice and a perturbing one. Then the solution is investigated in terms of the eigensolutions of the parent lattice. This way, one can easily obtain analytic expressions within the first order perturbation, describing the effects of different parameters on the eigensolutions of the structure. The perturbation theory employed in this work is typical of what is conventionally used in quantum mechanics literature. The proposed method is explicit, works fast, and does not involve complicated numerical calculations. Although this approach can be used to obtain some rules of thumb about the eigensolutions of the device within the first order perturbation approximation, it can be further followed to higher order perturbation terms for acquiring any desired level of accuracy. Since the presented method is mostly formulated analytically, not much computational effort is required for analyzing complex structures. In this paper the approach is described in detail and some examples are given to show the usefulness of it.
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