| 11. |
- Dai, Daoxin, et al.
(författare)
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Compact silicon-on-insulator-based multimode interference coupler with bilevel taper structures
- 2005
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 44:24, s. 5036-5041
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Tidskriftsartikel (refereegranskat)abstract
- A novel compact silicon-on-insulator- (SOI-)based multimode interference (MMI) coupler with bilevel taper structures was designed. The MMI section and the S-bend sections of the input-output waveguides are deeply etched. The input-output waveguides connecting to single-mode fibers or other photonic light circuits are etched shallowly to yield single-mode operation. A bilevel taper is introduced in the transition region between the shallowly and deeply etched regions. It is predicted theoretically that this design will not only improve the quality of the self-imaging in the MMI section but will also make the structure compact. Both the excess loss and the nonuniformity of the MMI coupler are reduced. By use of a three-dimensional beam propagation method, the performance of a 1 × 4 MMI coupler based on a SOI is simulated as a numerical example of the novel design. The simulated nonuniformity and the excess loss are approximately 0.0285 and 0.2 dB, respectively.
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| 12. |
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| 13. |
- Dai, Daoxin, et al.
(författare)
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Deeply etched SiO2 ridge waveguide for sharp bends
- 2006
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 24:12, s. 5019-5024
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Tidskriftsartikel (refereegranskat)abstract
- A deeply etched SiO2 ridge waveguide including the buffer, core, and cladding is presented for realizing sharp bends. The present SiO2 ridge waveguide has a strong confinement at the lateral direction, while it has a weak confinement at the vertical direction. Due to the strong confinement, a sharp bend (with a very small bending radius of about 10 mu m) is obtained for an acceptable bending loss. A detailed analysis of the loss in a bent waveguide is given by using a finite-difference method. In order to reduce the transition loss, a narrow bending section with an optimal lateral offset is used. A low leakage loss is obtained by using wide straight waveguides, and linear tapers are used to connect the wide straight section and narrow bent sections.
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| 14. |
- Dai, Daoxin, et al.
(författare)
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Design and fabrication of ultrasmall arrayed waveguide grating multiplexers based on Si nanowire waveguides
- 2007
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Ingår i: Optoelectronics Letters. - : Springer Science and Business Media LLC. - 1673-1905. ; 3:1, s. 7-9
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Tidskriftsartikel (refereegranskat)abstract
- The large refractive index difference between Si and SiO2 makes it possible to realize ultrasmall photonic integrated circuits. A 5 × 5 ultracompact arrayed waveguide grating multiplexer based on 500×250 nm Si nanowire waveguides is designed and fabricated by using the technologies of E-beam writing and amorphous-Si deposition. The measured channel spacing is about 1.5 nm (close to the design value) and the channel crosstalk is about -8 dB.
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| 15. |
- Dai, Daoxin, 1979-
(författare)
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Designs and simulations of silicon-based microphotonic devices
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The characteristics of a silicon-on-insulator (SOI) rib waveguide, including the bending loss of a multimode bent waveguide and the birefringence of a rib waveguide, are analyzed by using a finite-difference method (FDM). Based on a detailed analysis for a multimode bent waveguide, an appropriately designed multimode bent waveguide for reducing effectively the bending loss of the fundamental mode is realized. The slab height and the rib width of an SOI rib waveguide are normalized with the total height of the silicon layer and a general relation between these two normalized parameters for a nonbirefringent SOI rib waveguide is established. Using this general relation, one can easily design a nonbirefringent SOI rib waveguide. The issue of multimode effect in the SOI-based microphotonic devices such as arrayed-waveguide gratings (AWGs), etched diffraction gratings (EDGs), and multimode interference (MMI) couplers is discussed in detail. Two kinds of taper structures are proposed for reducing the multimode effects in EDGs or MMI couplers. A bi-level taper is introduced to eliminate effectively the multimode effects in an EDG or an MMI coupler. The bi-level taper is very appropriate for an EDG demultiplexer since the Si layer is etched through simultaneously for both the grating and the bottom taper structure, and thus no additional fabrication process is required. For the simulation of an AWG demultiplexer, a fast simulation method based on the Gaussian approximation is proposed and two kinds of effective and accurate three-dimensional (3D) simulation modeling are developed. The first 3D model is based on Kirchhoff-Huygens diffraction formula. To improve the computational speed, the 3D model is reduced to a two-dimensional (2D) one by integrating the corresponding field distributions in the AWG demultiplexer along the vertical direction under an assumption that the power coupled to the higher order modes in the free propagation region (FPR) is negligibly small. The equivalent 2D model has an almost the same accuracy as the original 3D model. Furthermore, a reciprocity theory is introduced for the optimal designof a special structure used for flattening the spectral response of an AWG demultiplexer. In the second 3D simulation method, we combine a beam propagation method (BPM) and the Kirchhoff-Huygens diffraction formula. In this method, a 3D BPM in a polar coordinate system is used for calculating the light propagation in the region connecting the first FPR and the arrayed waveguides, and thus the coupling coefficient of each arrayed waveguide is calculated conveniently and accurately. In the simulation of the second FPR, due to the uniform arrangement of arrayed waveguides, only several arrayed waveguides are needed in the BPM window and thus the computational efficiency is improved.
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| 16. |
- Dai, Daoxin, et al.
(författare)
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Elimination of multimode effects in a silicon-on-insulator etched diffraction grating demultiplexer with bi-level taper structure
- 2005
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Ingår i: IEEE Journal of Selected Topics in Quantum Electronics. - 1077-260X .- 1558-4542. ; 11:2, s. 439-443
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Tidskriftsartikel (refereegranskat)abstract
- Multimode effects in the free propagation region (FPR) of an etched diffraction grating (EDG) demultiplexer based on silicon-on-insulator are analyzed. The insertion loss and the crosstalk increase due to these undesired multimode effects. A bi-level taper structure between the FPR and the input/output waveguides is proposed. It is shown that such a taper structure can reduce the multimode effects to an almost negligible level. At the same time, the 3-dB passband width is enlarged by increasing the rib width. No additional fabrication process is needed for an EDG with such a design.
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| 17. |
- Dai, Daoxin, et al.
(författare)
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Gain enhancement in a hybrid plasmonic nano-waveguide with a low-index or high-index gain medium
- 2011
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Ingår i: Optics Express. - 1094-4087. ; 19:14, s. 12925-12936
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical investigation of a nano-scale hybrid plasmonic waveguide with a low-index as well as high-index gain medium is presented. The present hybrid plasmonic waveguide structure consists of a Si substrate, a buffer layer, a high-index dielectric rib, a low-index cladding, a low-index nano-slot, and an inverted metal rib. Due to the field enhancement in the nano-slot region, a gain enhancement is observed, i.e., the ratio partial derivative G/partial derivative g > 1, where g and G are the gains of the gain medium and the TM fundamental mode of the hybrid plasmonic waveguide, respectively. For a hybrid plasmonic waveguide with a core width of w(co) = 30nm and a slot height of h(slot) = 50nm, the intrinsic loss could be compensated when using a low-index medium with a moderate gain of 176dB/cm. When introducing the high-index gain medium for the hybrid plasmonic waveguide, a higher gain is obtained by choosing a wider core width. For the high-index gain case with h(slot) = 50nm and w(co) = 500nm, a gain of about 200dB/cm also suffices for the compensation of the intrinsic loss.
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| 18. |
- Dai, Daoxin, et al.
(författare)
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Highly sensitive sensor based on an ultra-high-Q Mach-Zehnder interferometer-coup led microring
- 2009
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 26:3, s. 511-516
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Tidskriftsartikel (refereegranskat)abstract
- A high-Q Mach-Zehnder interferometer (MZI)-coupled microring is presented for optical sensing with high sensitivity and a large measurement range. By optimizing the length difference, between the two arms of the MZI coupler, the MZI-coupled microring with a high-Q factor and high extinction ratio is obtained. In the present example, the Q factor of the designed silicon-nanowire-based microring is as high as 1.8 x 10(5) when the silicon nanowire has a propagation loss L=2 dB/cm. Due to this high-Q factor, the sensitivity for the change Delta n of the effective refractive index is about 10(-5)-10(-6) by measuring the shift of the resonant wavelength. Because of the wavelength dependence of the coupling ratio of the MZI coupler, it is possible to have only one resonant wavelength with a high extinction ratio in a very large wavelength span [i.e., the quasi-free spectral range of the MZI-coupler microring], which offers a very large measurement range covering the refractive index change
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| 19. |
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| 20. |
- Dai, Daoxin, et al.
(författare)
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Integrated Silicon Photonic Nanocircuits and Technologies for Optical Interconnect and Optical Sensing
- 2012
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Ingår i: OPTOELECTRONIC INTEGRATED CIRCUITS XIV. - : SPIE-INT SOC OPTICAL ENGINEERING. - 9780819489081
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Konferensbidrag (refereegranskat)abstract
- Silicon-on-insulator (SOI) nanowires give a very promising way to realize ultrasmall photonic integrated devices because of the ability for ultrasharp bending as well as the CMOS compatibility. As a typical integrated-type (de) multiplexer, ultrasmall arrayed-waveguide gratings (AWG) are very attractive for many applications. We have developed several types of ultrasmall SOI-nanowire AWG with novel layouts. SOI nanowires also give a good platform for optical sensing with high sensitivity because of the enhanced evanescent field. We have developed SOI-nanowire-based optical sensors by using MZI (Mech-Zehnder interferometer)-coupled microrings and cascaded rings. We also note that the size of an SOI nanowire is still limited to the order of wavelength in each direction. In contrast, surface plasmon (SP) waveguides could provide a nano-scale waveguiding and confinement of light. However, the conventional nano-scale SP waveguides are usually quite lossy. We have proposed two types of novel hybrid plasmonic waveguides to achieve nano-scale optical confinement and low-loss light propagation. Due to the ultra-high optical confinement, sub-mu m-2 hybrid plasmonic devices (e. g., power splitters) are presented. It is also shown that hybrid plasmonic waveguide enables sub-mu m bending and thus sub-mu m resonator has been also demonstrated. The hybrid plasmonic waveguides offer a way to transfer both photonic and electronic signals along the same circuit, which is attractive for active components, e. g., tunable filters and optical modulators.
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