| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- Dai, Daoxin, et al.
(författare)
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Reduction of multimode effects in an SOI-based etched diffraction grating demultiplexer
- 2005
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Ingår i: Optics Communications. - : Elsevier BV. - 0030-4018 .- 1873-0310. ; 247:4-6, s. 281-290
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Tidskriftsartikel (refereegranskat)abstract
- Multimode effects in the free propagation region (FPR) of a silicon-on-insulator (SOI)-based etched diffraction grating (EDG) demultiplexer are analyzed. In a conventional design, the power coupled to the higher order modes is considerable, which introduces a significant excess loss and crosstalk. It is shown that the multimode effects in an SOI EDG demultiplexer are much more detrimental than in an arrayed waveguide grating demultiplexer. Several methods for reducing the multimode effects are discussed. In particular, a laterally tapered structure between the FPR and the input/output waveguides is proposed as a simple and effective method for reducing the power coupled to the higher order modes and consequently reducing the multimode effects. The taper width is optimized to minimize the crosstalk.
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| 5. |
- He, Sailing, et al.
(författare)
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Some progress in integrated photonics
- 2005
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Ingår i: OPTOELECTRONIC DEVICES AND INTEGRATION. - : SPIE. - 0819455997 ; , s. 405-413
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Konferensbidrag (refereegranskat)abstract
- A review is presented on some progress we have made recently in planar integrated photonics including arrayed-waveguide gratings (AWGs) and etched diffraction gratings (EDGs), multimode interference (MMI) couplers/splitters, and spot-size converters. Some novel structures and design methods are summarized and presented.
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| 6. |
- Shi, Yaocheng, et al.
(författare)
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Design of a flat-field arrayed waveguide grating
- 2005
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Ingår i: Optoelectronic Devices and Integration. - : SPIE. ; , s. 500-507
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Konferensbidrag (refereegranskat)abstract
- A curved image plane is usually used in a conventional Rowland-type AWG For some applications (e.g., sensing), a straight image plane is desirable so that the output field at the image plane can be received directly with a detector-array. If one simply chooses a flat output plane (instead of a circular output curve) without optimization for a conventional AWG of Rowland circle type, some considerable aberrations will be introduced, which degrade the performances of the AWG The aberrations are calculated and analyzed with an optical path function. A three-stigmatic-point method is used to optimize the design of an AWG with a straight image plane and minimize the aberrations. In this design, the aberrations at three special wavelengths are removed. The first order aberrations at all wavelengths are also eliminated. An 80-channel flat-field AWG is designed as an example. The results show that the aberrations are reduced greatly and a good spectral response with tolerated side-lodes is obtained.
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| 7. |
- Shi, Yaocheng, et al.
(författare)
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Improved performance of a silicon-on-insulator-based multimode interference coupler by using taper structures
- 2005
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Ingår i: Optics Communications. - : Elsevier BV. - 0030-4018 .- 1873-0310. ; 253:4-6, s. 276-282
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Tidskriftsartikel (refereegranskat)abstract
- Multimode effects in a multimode interference (MMI) coupler based on silicon-on-insulator (SOI) are analyzed. Multimode interference in the vertical direction of an SOI-based MMI device degrades the self-imaging quality. Taper structures are introduced at the junction between input/output waveguides and multimode region to suppress the excitation of the undesired vertical modes. A 1 x 4 MMI coupler of low insertion loss (0.101 dB) and small non-uniformity (0.102 dB) is designed as a numerical example.
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