| 1. |
- Dai, Daoxin, 1979-
(author)
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Designs and simulations of silicon-based microphotonic devices
- 2005
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Doctoral thesis (other academic/artistic)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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| 2. |
- Dai, Daoxin, et al.
(author)
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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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In: IEEE Journal of Selected Topics in Quantum Electronics. - 1077-260X .- 1558-4542. ; 11:2, s. 439-443
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Journal article (peer-reviewed)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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| 3. |
- Dai, Daoxin, et al.
(author)
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Reduction of multimode effects in an SOI-based etched diffraction grating demultiplexer
- 2005
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In: Optics Communications. - : Elsevier BV. - 0030-4018 .- 1873-0310. ; 247:4-6, s. 281-290
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Journal article (peer-reviewed)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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| 4. |
- Gao, Ying, et al.
(author)
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Phase-tunable polarization division multiplexing DPSK receiver using a single demodulator
- 2009
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In: Passive Components and Fiber-based Devices VI. - : SPIE - International Society for Optical Engineering. - 9780819480323 ; , s. 763003-
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Conference paper (peer-reviewed)abstract
- We report a new design of differential phase-shift keying (DPSK) receivers which utilize a single demodulator to receive polarization division multiplexed signals. More than 20 dB extinction-ratio can be achieved by optimizing the phase detuning with a polarization controller in the receiver. Experimental demonstrations using 20 Gb/s polarization multiplexed DPSK signals and 2 15-1 pseudorandom binary sequence are conducted to show the performance of the proposed receiver. After 60 km of optical fiber transmission, the receiver has less than 3 dB power penalty at bit-error rate (BER) of 10-9.
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| 5. |
- Gao, Ying, et al.
(author)
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Phase-tunable polarization division multiplexing DPSK receiver using a single demodulator
- 2009
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In: 2009 Asia Communications and Photonics Conference and Exhibition, ACP 2009. - Washington, D.C. : OSA. - 9781557528773 ; , s. 5377237-
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Conference paper (peer-reviewed)abstract
- We report a new differential phase-shift keying (DPSK) receiver design which utilizes a single demodulator and can receive polarization division multiplexed signals. This system provides less than 3 dB power penalty at bit-error rate (BER) of 10-9 after 60 km of optical fiber transmission.
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| 6. |
- Hu, Xin, et al.
(author)
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Compact Dual-Band Rat-Race Coupler Based on a CompositeRight/Left Handed Transmission Line
- 2009
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In: Metamaterials and plasmonics. - Dordrecht : Springer. - 9781402094057 ; , s. 281-287
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Conference paper (peer-reviewed)abstract
- A general model for dual band rat-race couplers is presented through an odd-even mode analysis approach. The requirements for the impedances and electrical lengths of the branches are derived. To verify this model, a dual-band rat-race coupler is designed utilizing the balanced composite right/left handed transmission line. The whole structure is much more compact than the existing dual-band rat-race couplers and easy to fabricate. The simulated results are given. Return loss and port isolation of better than -30 dB are achieved at the central frequencies of both operating bands. Furthermore, the requirements of equal amplitude and balanced phase conditions are well fulfilled (within 0.5 dB and 5) over a frequency range of almost 50 and 90 MHz at the two central frequencies.
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| 7. |
- Hu, Xin, et al.
(author)
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Compact dual-band rejection filter based on complementary meander line split ring resonator
- 2009
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In: Progress in Electromagnetics Research Letters. - 1937-6480. ; 8, s. 181-190
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Journal article (peer-reviewed)abstract
- A general model for dual band rat-race couplers is presented through an odd-even mode analysis approach. The requirements for the impedances and electrical lengths of the branches are derived. To verify this model, a dual-band rat-race coupler is designed utilizing the balanced composite right/left handed transmission line. The whole structure is much more compact than the existing dual-band rat-race couplers and easy to fabricate. The simulated results are given. Return loss and port isolation of better than -30 dB are achieved at the central frequencies of both operating bands. Furthermore, the requirements of equal amplitude and balanced phase conditions are well fulfilled (within 0.5 dB and 5) over a frequency range of almost 50 and 90 MHz at the two central frequencies.
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| 8. |
- Hu, Xin, et al.
(author)
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Dual-Band-Rejection Filter Based on SplitRing Resonator (SRR) and Complimentary SRR
- 2009
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In: Microwave and optical technology letters (Print). - : Wiley. - 0895-2477 .- 1098-2760. ; 51:10, s. 2519-2522
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Journal article (peer-reviewed)abstract
- A novel concept of a compact, low insertion-loss dual-band-rejection filter (DBRF) is proposed, and its equivalent circuit model is given. The filter consists of single split ring resonators (SRRs) on the top of the host microstrip line and Complimentary SRR etched on the back ground plane. The dimensions of the structure are as small as 1.4 cm × 2 cm, while high frequency selectivity is achieved at both band edges due to the presence of two transmission zeros. The filter has an insertion loss of better than 1 dB, a return loss of larger than 10 dB in the passband from 3.3 to 4.0 GHz, and two rejections of greater than 30 dB within 2.5-2.6 and 5.2-5.6 GHz.
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| 9. |
- Hu, Xin, et al.
(author)
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Equivalent Circuit of Complementary Split-Ring Resonator Loaded Transmission Line
- 2009
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In: Microwave and optical technology letters (Print). - : Wiley. - 0895-2477 .- 1098-2760. ; 51:10, s. 2432-2434
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Journal article (peer-reviewed)abstract
- In this article, a circuit model is proposed for the complementary split-ring resonators (CSRRs) loaded transmission line, and comparisons between the results derived from the equivalent circuit model and the experimental results are given and a good agreement between them over a wide frequency band supports the effectiveness of F the proposed modeling methodology. Both the results show the negative f permittivity at the vicinity of the resonance frequency of CSRR. By comparing the results of different periodic length (i.e., the capacitance per-unit-cell of the host microstrip line is changed), the validity of the equivalent circuit is further confirmed.
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| 10. |
- Hu, Xin, et al.
(author)
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Lattice type transmission line of negative refractive index
- 2008
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In: Journal of Zhejiang University. Science A. - 1862-1775. ; 9:2, s. 289-292
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Journal article (peer-reviewed)abstract
- In this letter, we introduce a novel passive transmission line of negative refractive index (i.e., left-handedness) based on identical symmetrical lattice type structures [thus called "lattice type transmission line" (LT-TL)]. The dispersion characteristic and the transmission response of the proposed LT-TL are analyzed. While all the other left-handed passive transmission lines are of high pass, the present passive left-handed transmission line is of low pass. Compared with a conventional transmission line, the LT-TL has a phase shift of 180 degrees in the entire wide pass-band.
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