Communication between computing systems is recognized as the main limitation to increasing the speed of all-electronic systems beyond levels currently achieved in existing supercomputers. Optical interconnects hold great promise in eliminating current communication bottlenecks because of properties that stem from optics inherent parallelism. Wavelength-division multiplexing (WDM) technology, by which multiple optical channels can be simultaneously transmitted at different wavelengths through a single optical transmission medium is a useful means of making full use of optics parallelism over a wide wavelength region. In this talk, we review the working principles of wavelength division (de) multiplexers (WD(D)M) for optoelectronic interconnection in high-throughput optical links and address the optical design issues of Wd9D)Ms. Several grating-based WD9D)M structures are analyzed. We report experimental data for several versions of WD(D)Ms which exhibit low insertion loss, high reliability, and low cost.
A demonstration of hybrid integration of a 1 X 12 metal- semiconductor-metal (MSM) photo-detector array and polyimide channel waveguides via 45 degree(s) total-internal-reflection micro-coupler is reported here. MSM photo-detector array was fabricated on a semi-insulated GaAs wafer. The two-layer polyimide waveguide array was constructed using Ultradel 9120D for core and Ultradel 9020 for lower cladding layer. The photodetectors are integrated to operate in the conventional vertical illumination mode. We have measured the external quantum-efficiency and 3 dB bandwidth of the integrated MSM photo-detectors to be 0.4 A/W and 2.648 GHz, respectively. The aggregate 3 dB bandwidth of the 12-channel integrated system is 32 GHz.
We report the design and formation of a high-performance polymer waveguide array with 45-degree micro-mirror couplers for achieving fully-embedded board-level optoelectronic interconnects. We have used Si CMOS process compatible polymer as the fabrication material, which is relatively easy to process and has low propagation loss at 850 nm wavelength. 45-degree total interior reflection micro-mirror couplers fabricated within the channel waveguides provide surface-normal light coupling between the waveguide and the optoelectronic devices, thus forming a fully-embedded 3D optoelectronic interconnect. We have demonstrated a hybrid optoelectronic integrated system of GaAs MSM photodetector array and polymer channel waveguide array with 45-degree micro-mirror couplers, showing an aggregate 3 dB bandwidth of 32 GHz.
Erbium doped polymer waveguide amplifier for operation at 1.55 micrometers was studied. A fluorinated polyimide was doped with Er ions using ion implantation. The samples were irradiated at room temperature by 320 keV Er2+ and 160 keV Er+ ions. Doses used were 1 by 1015/cm2 and 1 by 1014/cm2 respectively. The implanted samples were characterized using Rutherford Backscattering and SIMS analysis. The implanted ion profile was nearly Gaussian with range of 0.25 micrometers for the 320 keV implant and 0.12 micrometers for the 160 keV implant. A Gaussian implanted ion profile, matched with the electric field profile of the waveguide mode, can enhance the efficiency of energy transfer between the waveguide mode and the active ions. The implant depth of Er in polyimide at the energies used is shallow. In order to achieve the overlap with the electric field profile, a two layer waveguide amplifier structure is proposed. Such doping and waveguide fabrication techniques are compatible with the existing silicon technology.
We report the fabrication and processing of thin film MSM silicon photo-detector and thin film VCSEL for optoelectronic interconnects. These two components, together with polyimide wave-guide can be used in constructing the high sped, low power, low cost optical interconnection system. Such a system will provide the fast board level data transmission. The DC and AC characteristics of thin film silicon MSM photo-detector, and the I-V and L-I characteristics of thin film VCSEL are measured.
Neodymium (Nd) doped polymer based optical amplifiers have been studied. NdCl3.6H2O and Nd(III) hexafluoracetylacetonate were used as dopants. Photoluminescence at 0.89 micrometers , 1.06 micrometers and 1.33 micrometers from Nd ions in polyimide was detected. Phase separation with possible formation of liquid crystal polymer was observed in NdCl3.6H2O doped polyimide. Thin film waveguides and multimode channel waveguides were fabricated using a novel planarizing technique to reduce scattering losses. Optical gain of about 5.4 dB at 1.06 micrometers was demonstrated in a 5 cm long NdCl3.6H2O doped polyimide channel waveguide.
A multifunctional polymeric deice capable of performing functions such as electro-optic modulation, optical amplification, and electro-optic switching simultaneously is described. All three modules can be built on a single substrate. A novel polymeric modulator with structure based on 1 X 2 Y-fed directional coupler is demonstrated. The results of preliminary investigations on optical amplifiers are presented.
Novel optical memory systems offer ultra large storage capacity and with fast access time. The current commercial system can produce in access of 300 Mb/s aggregate data rate and near future system will yield aggregate data rates on the order of 1-10 Gb/s. However, full exploitation of this feature is possible only if memory to processor interface is fast enough to handle such a data rate. In this presentation, a unique optoelectronic interconnect architecture based on WDM and WDDM are described.
We report the formation of polyimide-based H-tree waveguides for a multi-GBit/sec optical clock signal distribution in a Si CMOS process compatible environment. Such a clock distribution system is to replace the existing electronic counterpart associated with high-speed supercomputers such as Cray T-90 machine. A waveguide propagation loss of 0.21 dB/cm at 850 nm was experimentally confirmed for the 1-to-48 waveguide fanout device. The planarization requirement of the optical interconnection layer among many electrical interconnection layers makes the employment of tilted grating a choice of desire. Theoretical calculation predicts the 1-to-1 free-space to waveguide coupling with an efficiency as high as 95 percent. Currently, a coupling efficiency of 35 percent was experimentally confirmed due to the limited index difference between guiding and cladding layers. Further experiments aimed at structuring a larger guiding/cladding layer index differences are under investigation. To effectively couple an optical signal into the waveguide through the tilted grating coupler, the accuracy of the wavelength employed is pivotal. This makes the usage of the vertical cavity surface-emitting lasers (VCSELs) and VCSEL arrays the best choice when compared with edge-emitting lasers. Modulation bandwidth as high as 6 GHz was demonstrated at 850 nm. Such a wavelength is compatible with Si-based photodetectors.
Guided-wave optics is a promising way to deliver high-speed clock-signal in supercomputer with minimized clock-skew. Si- CMOS compatible polymer-based waveguides for optoelectronic interconnects and packaging have been fabricated and characterized. A 1-to-48 fanout optoelectronic interconnection layer (OIL) structure based on Ultradel 9120/9020 for the high-speed massive clock signal distribution for a Cray T-90 supercomputer board has been constructed. The OIL employs multimode polymeric channel waveguides in conjunction with surface-normal waveguide output coupler and 1-to-2 splitters. Surface-normal couplers can couple the optical clock signals into and out from the H-tree polyimide waveguides surface-normally, which facilitates the integration of photodetectors to convert optical-signal to electrical-signal. A 45-degree surface- normal couplers has been integrated at each output end. The measured output coupling efficiency is nearly 100 percent. The output profile from 45-degree surface-normal coupler were calculated using Fresnel approximation. the theoretical result is in good agreement with experimental result. A total insertion loss of 7.98 dB at 850 nm was measured experimentally.
We report the formation of polyimide-based H-tree waveguides for a multi-GBit/sec optical clock signal distribution in a Si CMOS process compatible environment. Such a clock distribution system is to replace the existing electronic counterpart associated with high-speed supercomputers such as Cray T-90 machine. A waveguide propagation loss of 0.21 dB/cm at 850 nm was experimentally confirmed for the 1-to-48 waveguide fanout device. The planarization requirement of the optical interconnection layer among many electrical interconnection layers makes the employment of tilted grating a choice of desire. Theoretical calculation predicts the 1-to-1 free-space to waveguide coupling with an efficiency as high as 95 percent. Currently, a coupling efficiency of 35 percent was experimentally confirmed due to the limited index difference between guiding and cladding layers. Further experiments aimed at structuring a larger guiding/cladding layer index differences are under investigation. To effectively couple an optical signal into the waveguide through the tilted grating coupler, the accuracy of the wavelength employed is pivotal. This makes the usage of the vertical cavity surface-emitting lasers (VCSELs) and VCSEL arrays the best choice when compared with edge-emitting lasers. Modulation bandwidth as high as 6 GHz was demonstrated at 850 nm. Such a wavelength is compatible with Si-based photodetectors.
Si-CMOS compatible polymer-based waveguides for optoelectronic interconnects and packaging have been fabricated and characterized. A 1-to-48 fanout optoelectronic interconnection layer (OIL) structure based on Ultradel 9120/9020 for the high-speed massive clock signal distribution for a Cray T-90 supercomputer board has been constructed. The OIL employs multimode polymeric channel waveguides in conjunction with surface-normal waveguide output coupler and 1-to-2 splitter. A total insertion loss of 7.98 dB at 850 nm was measured experimentally.
Surface relief gratings with tilted grating profiles have been studied for efficient optical signal coupling for polymeric waveguide based optoelectronic interconnects. In this article the theoretical formulation used to calculate the diffraction efficiency in a pre-defined direction is discussed. The designed gratings provide an effective unidirectional surface-normal optical coupling for polymer-based optoelectronic interconnects. The gratings with a tilt-angle of 32 degrees and periods ranging from 0.5 to 3 micrometers were fabricated. Both surface-normal input and output grating couplers have been demonstrated in polyimide waveguides on silicon substrate.
We report for the first time, 3D tapered polymeric waveguides fabricated by the compression-molding technique. The waveguides presented herein provide a feasible solution to bridge discrete optoelectronic devices having the apertures of a few microns to hundreds of microns. One-cm long tapered channel waveguides with the cross-sections of 5 micrometers X 5 micrometers at one end and 100 micrometers X 100 micrometers at the other end were fabricated. These waveguides have a propagation loss of 0.5 dB/cm when the 632.8 nm He-Ne laser light is coupled from the small end and of 1.1 dB/cm when coupled from the large end. By confining the energy to the fundamental mode, when coupling from large end to the small end, a low-loss packaging can be achieved bidirectionally.
We report for the first time, 3D tapered polymeric waveguides fabricated by the compression-molding technique. Compression-molded polymeric waveguides presented herein provide a feasible solution to bridge discrete optoelectronic devices having the apertures of a few microns to hundreds of microns in both horizontal and vertical directions. One-cm long tapered channel waveguides with the cross-sections of 5 micrometers X 5 micrometers at one end and 100 micrometers X 100 micrometers at the other end were fabricated. These polymeric channel waveguides have a propagation loss of 0.5 dB/cm when the 632.8 nm He-Ne laser light is coupled from the small end to the large end and of 1.1 dB/cm when coupled from the large end to the small end. By confining the energy to the fundamental mode, when coupling from large end to the small end, a low-loss packaging can be achieved bidirectionally.
The enhancement of the third order susceptibilities (chi) (3) and second order molecular hyperpolarizabilites < (gamma) > in a series of covanlently stacked dimer and trimer macrocycles (SiPc and SiNc) was observed throught he phase conjugated signals from DFWM measurements at both 1064 and 532 nm. The FWHM of the phase conjugated signals at 532 nm is much smaller than those at 1064 nm and those of the reference compound CS2. The < (gamma) > values at both wavelengths as a function of number of the monomer units (n) have an approximate n3 dependence, differing only in the scaling constant. The origin of such enhancement is discussed and compared to those in 1D (pi) -conjugated systems.
A series of new silicon phthalocyanine monomers containing two or more hydroxyl groups has been synthesized by axial etherification of [PcSi(OH)2] with various polyfunctional alcohols, where R is a residue generated from an appropriate alcohol namely, ethylene glycol, glycerol, triethanolamine, triethylene glycol, 1,4-bis(2- hydroxyethyl)piperazine and N,N-bis(2-hydroxyethyl) isonicotinamide. All derivatives are soluble in common organic solvents such as chloroform and dioxane, and exhibit low absorptions in the visible spectral region. The dimer [RO(SiPcO)2R] and trimer [RO(SiPcO)3R] of triethanolamine have also been synthesized to investigate structure-property relationships. The above derivatives can be processes into thin polymeric films either by reacting with a diisocyanate compound or with a reactive polysiloxane. Third- order nonlinear optical properties of the above derivatives are described.
KEYWORDS: Polymers, Luminescence, Optical fibers, Signal detection, Proteins, Molecular self-assembly, Glasses, Chemiluminescence, Molecules, Chemical elements
We discuss the molecular self-assembly on optical fibers in which a novel method for protein attachment to the sensing tip of the fiber is used. Our objective is to assemble a conjugated polythiophene copolymer as an attachment vehicle. Subsequent attachment of the photodynamic phycobiliprotein serves as the fluorescence probe element. Following our earlier experiments from Langmuir-Blodgett deposition of these polymeric materials as thin films on glass substrates, we extended the technique to optical fibers. First, the bare fiber surface is silanized with a C18 silane compound. The copolymer (3-undecylthiophene-co-3- methanolthiophene, biotinylated at the methanol moiety) assembly on the fiber is carried out presumable through van der Waals interactions between the hydrophobic fiber surface and the undecyl alkyl chains on the polymer backbone. A conjugated Str-PE (streptavidin covalently attached to phycoerythrin) complex is then attached to the copolymer via the conventional biotin-streptavidin interaction. The conjugated polymer not only supports the protein but, in principle, may help to transduce the signal generated by phycoerythrin to the fiber. Our results from fluorescence intensity measurements proved the efficacy of this system. An improved methodology is also sought to more strongly attach the conjugated copolymer to the fiber surface, and a covalent scheme is developed to polymerize and biotinylate polythiophene in situ on the fiber surface.
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