We propose the design and fabrication of nanophotonic optical routing channels using three-dimensional photonic crystals (PhCs) operating at telecommunication wavelengths. The fabrication method involves patterning a single planar etch mask and custom-tuned isotropic reactive-ion etching with passivation to create an array of spherical voids with three-dimensional symmetry. Introducing planar defects in the buried PhC lattice can create the optical routing channels. The dispersion properties of the embedded silicon three-dimensional (3D) PhC are utilized for the optical interconnect
design. The proposed design has sub-micron routing capability and flexibility with overlay and arbitrary routing. The optoelectronic circuits can be fabricated using CMOS technology on the surface and the source and emitters can be flip chip bonded to emit down, through the silicon layer. The beam coupling can be done using angled mirror facets. The guiding mechanism is based on the three-dimensional self-collimation effect.
We report our progress on the fabrication of three-dimensional (3D) photonic crystals to operate at near-infrared (IR) wavelengths using conventional planar silicon micromachining. The method involves patterning a single layer of planar etch mask and a custom etch process to create a 3D array of spherical voids. The etch mask is patterned in polymethyl methacrylate (PMMA) using conventional deep-UV contact photolithography and then transferred to a silicon dioxide (SiO2) hard mask. The 3D spherical voids are fabricated using a sequence of etching and passivation steps. In the etch step performed in a fluorine-based inductively coupled plasma-etching system, first a layer of spherical voids is created. Then, the spherical voids are passivated by dry silicon oxidation. A subsequent anisotropic removal of oxide at the bottom of the sphere is achieved by high-energy ion bombardment thus enabling the creation of etch mask for the successive layers. Plasma chemistry with high selectivity to oxide is utilized for opening the subsequent layer of spherical voids. By repeating these steps, buried 3D array of spherical voids is obtained. This way, a 3D structure with simple cubic symmetry can be obtained from an etch mask initially patterned with a square lattice of circular holes. Our fabrication method has numerous advantages over alternative approaches as it is based on the well-established CMOS mass fabrication technology, which is compatible with the next generation optoelectronic circuits.
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.
In this paper, we present self-collimation in three-dimensional (3D) photonic crystals (PhCs) that consist of a simple cubic structure. By exploiting the dispersive characteristics of the photonic crystals, we demonstrate the ability to achieve structureless (defect-free) confinement of light. We also verify that polarization dependence is a key issue in 3D self-collimation. The results hold promise for the 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. It overcomes the disadvantages of the methods hitherto reported in the literature for the fabrication of 3D photonic crystal devices, which include high complexity of multi-step processes, tight alignment tolerances, long turnaround times, and incompatibility with an integrated photonics platform. The method utilizes a single planar etch mask coupled with time multiplexed sidewall passivating deep anisotropic reactive ion etching along with isotropic etch process to create three-dimensional photonic crystal devices. Initial experimental results are presented.
In this paper, we review the confinement mechanism of self-collimation in planar photonic crystals. In this mechanism, an approximately flat equi-frequency contour (EFC) below the light cone of the planar photonic crystal can be used to laterally confine the light and total internal reflection (TIR) provides vertical confinement. To this end, self-collimation in both low-index and high-index planar photonic crystals are investigated using the three-dimensional (3D) finite-difference time-domain (FDTD) method and the 3D iterative plane wave method (PWM). It is found that low-loss self-guiding is achievable in both the valence and conduction bands for high-index planar photonic crystals. However, for low-index planar photonic crystals, low-loss self-guiding can be only observed in the valence band. Experimental results show a propagation loss of as low as 1.1 dB/mm for the self-guiding in a high-index planar photonic crystals.
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.
KEYWORDS: Etching, Photonic crystals, Silicon, Anisotropic etching, Photomasks, Micromachining, Lithography, Deep reactive ion etching, Reactive ion etching, Microelectromechanical systems
In this paper, we present a novel method for the fabrication of three-dimensional (3D) photonic crystal structures using conventional planar silicon micromachining technology. It overcomes the disadvantages of the methods hitherto reported in the literature for the fabrication of 3D photonic crystal devices, which include high complexity of multi-step processes, tight alignment tolerances, long turnaround times, and incompatibility with an integrated photonics platform. The method utilizes a single planar etch mask coupled with time multiplexed sidewall passivating deep anisotropic reactive ion etching along with isotropic etch process to create three-dimensional photonic crystal devices. In the process, anisotropic etching is followed by isotropic etching leading to the formation of sphere like voids. This step is followed by sidewall polymer deposition and local removal of the polymer from the bottom of the spheres that allows the etch process to be repeated and produce many layers. For the etch mask initially patterned with a square lattice, the etch sequence methodology explained above yields a 3D structure with simple cubic symmetry. Theoretical calculations predict that this structure should possess a complete photonic band gap. Optimization of the photonic band gap can be achieved by using different lattices (square, triangular, hexagonal) as the etch mask to produce photonic crystals with different crystalline structures. Further, by utilizing this fabrication scheme, photonic crystals over a wide range of the electromagnetic spectrum (<3Thz to >300Thz) can be fabricated by scaling the etch times and the mask dimensions.
In this paper we discuss the design and implementation of integrated planar optical devices realized by exploiting the unique dispersion properties of photonic crystal (PhC) devices. In particular, we demonstrate the ability to focus and spatially route optical beams in the absence of channelized structures. By this we mean that these devices do not contain any form of lateral confinement, in the sense of a physical structure, other than the dispersion properties of the crystal lattice. To this end, lateral control is imposed on the propagating wave by virtue of engineering the band structure of the photonic crystal lattice. Our approach to this effort is based on engineering the dispersion diagram of a given periodic structure outside of its band gap. As such, this allows for the determination of unique propagation characteristics and corresponding devices, as we show in theoretical simulations and experimental results.
Optimization of the photonic bandgap in finite-height photonic crystal (PhC) slab structures requires high-fill-factor lattices. We present a method for fabrication of high-fill-factor PhC devices in silicon-on-insulator (SOI) substrates using electron-beam lithography and high-aspect-ratio reactive-ion etching (RIE). We achieve 8:1 aspect-ratio PhC structures with 60-nm vertical membrane walls using a custom deep reactive-ion etching process in a conventional low-end RIE with patterned resist as the only etch mask. We present examples of various PhC devices fabricated using this method including a high-efficiency coupling structure for PhC waveguides.
In this paper we present the development of several new and novel fabrication methods for the realization of two-dimensional photonic crystal devices in silicon slab waveguides. We begin by presenting a process for the fabrication of high fill-factor devices in silicon-on-insulator wafers. Next, we present a grayscale fabrication process for the realization of three-dimensional silicon structures, such as tapered horn couplers. We then present the fabrication of suspended silicon slabs using a co-polymer process based on direct write electron beam lithography and silicon sputtering. And lastly, we conclude by presenting an alternate method for realizing PhC devices in a silicon slab based on a combination of wet and dry etching processes in bulk silicon wafers.
As processor speeds enter the Gigahertz regime, the disparity between processing time and memory access time plays an increasingly important role in the overall limitation of processor performance. Furthermore, as the components continue to shrink in size, the limitations in interconnect density and bandwidth serve to exacerbate communication bottlenecks. To address these issues, we propose a 3D architecture based on through-wafer vertical optical interconnects. Our system is monolithically fabricated on a single host substrate and preserves the VLSI-scale of integration by using meso-scopic diffractive optical elements for beam fan-out and signal distribution at the chip level.
This paper proposes use of the hybrid JPEG/recursive block coding (JPEG/RBC) algorithm in low bit rate image coding and presents a quantization matrix (QM) design for the DST blocks that can be used for a wide range of low DST bit rates. The data rate optimization problem encountered in the JPEG/RBC algorithm is discussed and an empirical ratio of the bit rates for the DCT and the DST blocks is obtained for low bit rate image coding. Subjective evaluation of images coded at low bit rates placed JPEG/RBC in the top group of three algorithms among those submitted for possible inclusion as the next generation bandwidth compression algorithm in the National Imagery Transmission Format Standard.
JPEG has already found wide acceptance for still frame image compression. The quantization matrices (QMs) play a critical role in the performance of the JPEG algorithm but there has been a lack of effective QM design tools. As a result, sub-optimal QMs have commonly been used and JPEG has been judged to be inappropriate for some applications. It is our contention that JPEG is even more widely applicable than `common knowledge' would admit. This paper describes a low-cost design tool that has been developed and is currently being successfully applied to design QMs for various sensors including IR, SAR, medical, scanned maps, and fingerprints.
KEYWORDS: Image compression, Autoregressive models, Visualization, Image processing, Quantization, Visual information processing, Signal to noise ratio, Image quality standards, Radon, Chemical elements
The tile effect is an artifact which considerably degrades the visual quality of the images coded at bit rates less than 1 bpp. A new algorithm called JPEG/RBC which is based on a two source decomposition of a noncausal model fits closely within the broad framework of the JPEG standard. Preliminary results indicate substantial improvement in performance and bit rates in addition to the mitigation of the tile effect.
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