1. 
 Dai, Daoxin, et al.
(författare)

Accurate twodimensional model of an arrayedwaveguide grating demultiplexer and optimal design based on the reciprocity theory
 2004

Ingår i: Journal of the Optical Society of America A: Optics and Image Science, and Vision.  10847529. ; 21:12, s. 23922398

Tidskriftsartikel (refereegranskat)abstract
 An accurate twodimensional (2D) model is introduced for the simulation of an arrayedwaveguide grating (AWG) demultiplexer by integrating the field distribution along the vertical direction. The equivalent 2D model has almost the same accuracy as the original threedimensional model and is more accurate for the AWG considered here than the conventional 2D model based on the effectiveindex method. To further improve the computational efficiency, the reciprocity theory is applied to the optimal design of a flattop AWG demultiplexer with a special input structure.


2. 
 Dai, Daoxin, et al.
(författare)

Analysis of characteristics of bent rib waveguides
 2004

Ingår i: Journal of the Optical Society of America A.  07403232. ; 21:1, s. 113121

Tidskriftsartikel (refereegranskat)abstract
 With a perfectly matched layer boundary treatment, a semivectorial finitedifference method is used to calculate the eigenmodes of a singlemode (SM) or multimode (MM) bent rib waveguide. A detailed analysis is given for the dependence of the bending losses (including the pure bending loss and the transition loss) on geometrical parameters of the bent rib waveguide such as the rib width, the rib height, and the bending radius. The characteristics of the higherorder modes are analyzed. It is shown that the bending loss of the fundamental mode can be reduced effectively by increasing the width and height of the rib. For an integrated device, undesired effects due to the higherorder modes of a MM bent waveguide can be removed by appropriate choice of the geometrical parameters. An appropriately designed MM bent waveguide is used to reduce effectively the bending loss of the fundamental mode, and a lowloss SM propagation in a MM bent waveguide is realized when the bending losses of the higherorder modes are large enough.


3. 
 Dai, Daoxin, et al.
(författare)

Analysis of the birefringence of a silicononinsulator rib waveguide
 2004

Ingår i: Applied Optics.  00036935. ; 43:5, s. 11561161

Tidskriftsartikel (refereegranskat)abstract
 A detailed analysis of the polarization characteristics (birefringence) of a silicononinsulator (SOI) rib waveguide is given. The fundamental TE and TMpolarized modes of the SOI rib waveguide are calculated by a semivectorial finitedifference method. The rib width and the slab height of the SOI rib waveguide are normalized with respect to the total height of the silicon layer. A general relation between the two normalized parameters for a nonbirefringent SOI rib waveguide is obtained. According to this relation a nonbirefringent SOI rib waveguide can easily be designed. The fabrication tolerance for a nonbirefringent SOI rib waveguide is also analyzed, revealing that the tolerance can be increased by use of a larger total height of the silicon layer.


4. 
 Dai, Daoxin, et al.
(författare)

Calculation of the spectral response of an arrayedwaveguide gating demultiplexer with a wideangle beam propagation method in a cylindrical coordinate system
 2004

Ingår i: Optical and quantum electronics.  03068919. ; 36:11, s. 967979

Tidskriftsartikel (refereegranskat)abstract
 The spectral response of an arrayedwaveguide grating (AWG) demultiplexer is calculated by simulating the field propagation in the output section of an AWG with a wideangle beam propagation method (BPM) in a cylindrical coordinate system. As in a practical design of an AWG demultiplexer, each output waveguide consists of two straight sections connected by a bending section. The spectral response obtained by the present algorithm is more accurate than those obtained with two popular approximate methods, namely, the conventional overlapped integral method and the standard BPM for radially straight and infinitely long output waveguides. With the present algorithm, the dependence of the spectral response on the parameters of the output section is analyzed. The channel crosstalk and the 3 dB passband width of the spectral response depend mainly on the length of the first straight section, the end separation and the angular separation of the output waveguides. The bending section results in an asymmetrical spectral response with remarkable sidelobes which can be reduced by increasing the bending radius.


5. 


6. 
 Dai, Daoxin, et al.
(författare)

Compact silicononinsulatorbased multimode interference coupler with bilevel taper structures
 2005

Ingår i: Applied Optics.  00036935. ; 44:24, s. 50365041

Tidskriftsartikel (refereegranskat)abstract
 A novel compact silicononinsulator (SOI)based multimode interference (MMI) coupler with bilevel taper structures was designed. The MMI section and the Sbend sections of the inputoutput waveguides are deeply etched. The inputoutput waveguides connecting to singlemode fibers or other photonic light circuits are etched shallowly to yield singlemode 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 selfimaging 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 threedimensional 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.


7. 


8. 
 Dai, Daoxin, 1979
(författare)

Designs and simulations of siliconbased microphotonic devices
 2005

Doktorsavhandling (övrigt vetenskapligt)abstract
 The characteristics of a silicononinsulator (SOI) rib waveguide, including the bending loss of a multimode bent waveguide and the birefringence of a rib waveguide, are analyzed by using a finitedifference 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 SOIbased microphotonic devices such as arrayedwaveguide 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 bilevel taper is introduced to eliminate effectively the multimode effects in an EDG or an MMI coupler. The bilevel 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 threedimensional (3D) simulation modeling are developed. The first 3D model is based on KirchhoffHuygens diffraction formula. To improve the computational speed, the 3D model is reduced to a twodimensional (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 KirchhoffHuygens 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.


9. 
 Dai, Daoxin, et al.
(författare)

Elimination of multimode effects in a silicononinsulator etched diffraction grating demultiplexer with bilevel taper structure
 2005

Ingår i: IEEE Journal of Selected Topics in Quantum Electronics.  1077260X. ; 11:2, s. 439443

Tidskriftsartikel (refereegranskat)abstract
 Multimode effects in the free propagation region (FPR) of an etched diffraction grating (EDG) demultiplexer based on silicononinsulator are analyzed. The insertion loss and the crosstalk increase due to these undesired multimode effects. A bilevel 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 3dB passband width is enlarged by increasing the rib width. No additional fabrication process is needed for an EDG with such a design.


10. 
 Dai, Daoxin, et al.
(författare)

Gain enhancement in a hybrid plasmonic nanowaveguide with a lowindex or highindex gain medium
 2011

Ingår i: Optics Express.  10944087. ; 19:14, s. 1292512936

Tidskriftsartikel (refereegranskat)abstract
 A theoretical investigation of a nanoscale hybrid plasmonic waveguide with a lowindex as well as highindex gain medium is presented. The present hybrid plasmonic waveguide structure consists of a Si substrate, a buffer layer, a highindex dielectric rib, a lowindex cladding, a lowindex nanoslot, and an inverted metal rib. Due to the field enhancement in the nanoslot 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 lowindex medium with a moderate gain of 176dB/cm. When introducing the highindex gain medium for the hybrid plasmonic waveguide, a higher gain is obtained by choosing a wider core width. For the highindex 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.

