- Email: [email protected]
Optical via for silicon photonic 3D-integrations
Optics Communications 452 (2019) 200–202
Contents lists available at ScienceDirect
Optics Communications journal homepage: www.elsevier.com/locate/optcom
Optical via for silicon photonic 3D-integrations Tianhua Lin a,b , Qin Han a , Tao Chu c ,∗ a b c
Institute of Semiconductors, Chinese Academy of Sciences, No. A35, Qinghua East Rd, Haidian, Beijing 100083, China University of Chinese Academy of Sciences, 19A Yuquan Rd, Shijingshan, Beijing 100049, China College of Information Science and Electronic Engineering, Zhejiang University, 38 Zheda Rd, Hangzhou 310027, China
ARTICLE
INFO
Keywords: Silicon photonics Silicon nitride Grating coupler Optical via
ABSTRACT We proposed an optical via through which both O- and C-band lights can be coupled from a fiber into different waveguide layers of a silicon photonic chip with multiple waveguide layers. The optical via consists of two grating couplers with various structures in different waveguide layers; these couplers are optimized through particle swarm optimization. From a single fiber, coupling efficiencies of −6.01 and −4.15 dB at 1300 and 1536 nm, respectively, were experimentally obtained for the two grating couplers.
1. Introduction Si3 N4 waveguides are widely considered in the construction of complementary metal–oxide–semiconductor (CMOS) compatible silicon photonic integrated circuits owing to their low propagation loss, thermal-optic efficiency [1], and nonlinear susceptibility [2]. Waveguides, arrayed waveguide gratings (AWGs) [3], microring-resonators [4], and other devices have been studied based on Si3 N4 materials. Further, with developments in large-capacity optical communications, the integration level of photonic chips has increased and the demand for 3-D photonic chips [5] with multiple waveguide device layers for future applications is growing. Si3 N4 waveguide devices are expected to be used in the fabrication of 3-D integrated photonic chips as Si3 N4 films can easily be deposited layer by layer in fabrication processes. However, the issue of coupling lights between waveguides in different layers and optical fibers has not been accurately solved. A popular method of evanescent-wave coupling [6] usually requires a very thin inter-cladding layer between waveguides in vertically neighboring Si3 N4 layers; the thin inter-cladding layer also induces crosstalk due to the unneeded evanescent-wave coupling between waveguides in neighboring layers. Thus, there is an urgent requirement of an optical device that can couple lights between multiple layers and between layers and fibers. In this letter, we introduce a new device that is used to couple lights between a fiber and two Si3 N4 device layers working at O- and C-band light wavelengths. The device can be easily expanded to more than two layers, and is named optical via as it functions as an electrical via in CMOS integrated chips. It was designed using dual-layer grating structures and can be easily fabricated through CMOS-compatible processes. The experimental results show that the coupling efficiencies of the optical via are −6.01 and −4.15 dB at 1300 and 1536 nm, respectively. ∗
The optical via could become a necessary device in future multilayer silicon photonic circuits. 2. Design and simulations Fig. 1 shows the schematic of the proposed device comprising two Si3 N4 device layers on a Si substrate separated with cladding SiO2 layers. Two grating couplers were implanted on the Si3 N4 layers to couple O- and C-band lights into waveguide devices at different layers. The section sizes of Si3 N4 waveguides were selected as 500 nm × 800 nm to satisfy the single-mode light propagating conditions. Thus, the thickness of each Si3 N4 layer was selected to be 500 nm. The grating couplers were designed as follows [7]: nef f
2𝜋 2𝜋 2𝜋 − − 𝑛𝑐𝑙𝑎𝑑𝑑𝑖𝑛𝑔 𝑠𝑖𝑛𝜃 = 0 𝜆 𝛬 𝜆
(1)
where 𝜆 is the wavelength of the incident light. When the O- and Cband lights are considered, 𝜆 = 1310 and 1550 nm, respectively. 𝛬, 𝑛ef f , and 𝑛cladding are the grating period, effective index, and cladding index of the grating couplers, respectively, and 𝜃 is the incident angle of the fiber. The equations only fit perfectly at one wavelength as designed. When the wavelength changes, a mismatch can be depicted as follows: ( ) 2𝜋 2𝜋 2𝜋 𝑀 = nef f − − 𝑛𝑐𝑙𝑎𝑑𝑑𝑖𝑛𝑔 𝑠𝑖𝑛𝜃 𝜆 𝛬 𝜆 ) ( 2𝜋 2𝜋 2𝜋 − nef f − − 𝑛𝑐𝑙𝑎𝑑𝑑𝑖𝑛𝑔 𝑠𝑖𝑛𝜃 (2) 𝜆 + 𝛥𝜆 𝛬 𝜆 + 𝛥𝜆 where 𝛥𝜆 is the wavelength change. Eq. (2) can be simplified as follows:
𝑀=
( ) 2𝜋 𝑛ef f − 𝑛cladding 𝛥𝜆
Corresponding author. E-mail address: [email protected] (T. Chu).
https://doi.org/10.1016/j.optcom.2019.07.031 Received 22 February 2019; Received in revised form 28 June 2019; Accepted 14 July 2019 Available online 16 July 2019 0030-4018/© 2019 Elsevier B.V. All rights reserved.
𝜆2
(3)
T. Lin, Q. Han and T. Chu
Optics Communications 452 (2019) 200–202
Fig. 1. Schematic of the optical via. The devices comprise two Si3 N4 device layers on a Si substrate, separated with SiO2 cladding layers. Two grating couplers were implanted on the Si3 N4 layers. The period (𝛬), etch depth (D), etch width (W) of both layers, and the shift (S) of the top layers are indicated.
Fig. 2. Simulated coupling electric field of our design at (a) 1550-nm wavelength light incident and (b) 1310-nm wavelength light incident.
Obviously, the mismatch is inversely proportional to the square of the wavelength. This implies that the O-band wavelength light has a larger mismatch compared with the C-band light. The larger the mismatch is, the smaller the incident light is affected by the grating structure. Therefore, the C- and O-band grating couplers were placed on the top and bottom layers to mitigate the influence of the bottom layer coupling efficiency from the top layer grating structures. The fiber incident angle was selected to be 4◦ to avoid second-order diffraction. The particle swarm optimization algorithm was applied to optimize the parameters of the optical via. The sum of coupling efficiency at both 1310- and 1550-nm wavelengths was selected as the figure of merit (FOM) to optimize the structure. The devices were simulated using 2-D finite-difference time-domain (FDTD) solvers from Lumerical Solutions, Inc. The pitch, duty cycle, and etch depth of the O-band grating coupler are the most significant parameters that affect the coupling efficiency of the O-band light collectively. They were selected as 800 nm, 0.53, and 300 nm, respectively. The pitch, duty cycle, and etch depth of the C-band grating coupler are the most significant parameters that affect the coupling efficiency of the C-band light collectively. They were selected as 990 nm, 0.6, and 374 nm, respectively. Furthermore, the thicknesses of buried oxide (BOX), intercladding, cladding layers, and the shift of top layer affect both the O-band and C- band coupling efficiencies slightly. They were selected as 1.53, 0.94, 0.5 and −0.59 μm, respectively. The FOM converged at a sum efficiency of 92% through 500 generations of optimization. Fig. 2 shows the electric fields of light propagating in the Si3 N4 waveguides and gratings at different layers of the chip. The simulated results of coupling efficiencies are shown in Fig. 3. The maximum coupling efficiencies of the O- and C-band grating couplers are 3.9 and 3.0 dB at 1310- and 1550-nm wavelengths, respectively. The crosstalk was calculated as 22 and 16 dB at 1310- and 1550-nm wavelength. Adiabatic tapers with lengths of 100 μm were used to connect the gratings with Si3 N4 waveguides with widths of 800 nm [8].
Fig. 3. Simulated coupling efficiencies of the two grating couplers.
top Si3 N4 layer was also fabricated using the same process. Finally, a cladding layer of 500-nm-thick SiO2 was deposited on the top. Fig. 4 shows the microphotograph and scanning electron microscopy image of the top view of the device, the fabrication process of which is also compatible with the CMOS process. The patterns on the top and bottom layers were aligned with the Au alignment marks fabricated on the bottom Si3 N4 layer in advance. To evaluate the alignment error, we fabricated Vernier marks on both layers. In our fabricated samples, an alignment error of 40 nm was corrected in the chip through shift compensations, and a simulation was performed to evaluate the influence of coupling efficiencies caused by the shift. As shown in Fig. 5, when the top layer shifts from the optimized position of −2 μm to 2 μm, the coupling efficiency of 1310 nm shows a periodic fluctuation of 0.1 dB. In contrast, when the bottom layer shifts from −2 μm to 2 μm, the coupling efficiency of 1550 nm shows a periodic fluctuation of 0.5 dB. These periodic fluctuations were caused by the periodic structures of the gratings. To characterize the devices, one side of the testing structure is the optical via, and the other sides are separated O-band and C-band grating couplers, as shown in Fig. 4. The coupling efficiencies and crosstalk of the optical via were measured and are shown in Fig. 6. Maximum coupling efficiencies of −6.01 and −4.15 dB were obtained at 1300- and 1536-nm wavelengths, respectively. Crosstalks of no more than −22 and −17 dB at the O-band and C-band were obtained, respectively. The measured coupling efficiencies are worse than the
3. Fabrication and experimental results A 1.53-μm-thick BOX layer was first deposited on a Si substrate through plasma enhanced chemical vapor deposition (PECVD). Next, the first Si3 N4 waveguide device layer was deposited through PECVD, after which electron beam lithography was used to draw the device layout on a photoresist, and inductively coupled plasma etching was used to transfer the pattern to the device layer. An inter-cladding layer of 940-nm-thick SiO2 then covered the bottom Si3 N4 layer. The 201
T. Lin, Q. Han and T. Chu
Optics Communications 452 (2019) 200–202
simulated results, and show slight shifts between the peak wavelengths. These shifts are considered to be caused by the fabrication errors. Owing to a small incident angle, there is a strong reflection on the longer wavelength where a Fabry–Perot (F–P) ripple was observed. The F–P ripples have intervals inversely proportional to the length of the F–P cavity, which, in our test structure, comprises the taper and the waveguide connector between the taper. In application, the length and complexity of the optical circuits are significantly larger than those of our test optical circuits, and thus could have very small F–P ripple intervals and depleted reflection; this in turn could result in the nonappearance of the F–P patterns. It is worth noting that the coupling efficiency of C-band increases and that of the O-band decreases compared with those of the separated grating couplers. This is due to the interaction between the two grating couplers. The bottom layer grating positively influences the top layer as if the bottom layer acted as a Bragg reflector [9]. The top layer grating negatively influences the bottom layer because the light field through the top layer has a phase distortion. 4. Conclusions Fig. 4. Microphotograph and SEM image of the optical via.
In this study, we designed and fabricated an optical via to couple a fiber and two Si3 N4 device layers with O- and C-band lights. The device could be easily fabricated using a CMOS-compatible process. The coupling efficiencies were obtained as −6.01 and −4.15 dB at 1300 and 1536 nm, respectively. The crosstalks were measured to be no more than −22 and −17 dB at O-band and C-band, respectively. In the future, an apodized design [10] of the grating couplers can be applied to advance the coupling efficiencies.
Funding This work was supported by the National Key Research and Development Program of China [grant numbers 2016YFB0402505]. References [1] R. Amatya, C.W. Holzwarth, M.A. Popović, F. Gan, H.I. Smith, F. Kärtner, R.J. Ram, Low Power Thermal Tuning of Second-Order Microring Resonators, Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies, Optical Society of America, Baltimore, Maryland, 2007, p. CFQ5. [2] K. Ikeda, R.E. Saperstein, N. Alic, Y. Fainman, Thermal and kerr nonlinear properties of plasma-deposited silicon nitride/silicon dioxide waveguides, Opt. Express 16 (2008) 12987–12994. [3] D. Dai, Z. Wang, J.F. Bauters, M.C. Tien, M.J.R. Heck, D.J. Blumenthal, J.E. Bowers, Low-loss Si3N4 arrayed-waveguide grating (de)multiplexer using nano-core optical waveguides, Opt. Express 19 (2011) 14130–14136. [4] H. Cai, A.W. Poon, Optical manipulation and transport of microparticles on silicon nitride microring-resonator-based add–drop devices, Opt. Lett. 35 (2010) 2855–2857. [5] M. Raburn, L. Bin, K. Rauscher, O. Yae, N. Dagli, J.E. Bowers, 3-D photonic circuit technology, IEEE J. Sel. Top. Quantum Electron. 8 (2002) 935–942. [6] J.F. Bauters, M.L. Davenport, M.J.R. Heck, J.K. Doylend, A. Chen, A.W. Fang, J.E. Bowers, Silicon on ultra-low-loss waveguide photonic integration platform, Opt. Express 21 (2013) 544–555. [7] T.K. Gaylord, M.G. Moharam, Analysis and applications of optical diffraction by gratings, Proc. IEEE 73 (1985) 894–937. [8] Y. Fu, T. Ye, W. Tang, T. Chu, Efficient adiabatic silicon-on-insulator waveguide taper, Photonics Res. 2 (2014) A41. [9] D. Taillaert, P. Bienstman, R. Baets, Compact efficient broadband grating coupler for silicon-on-insulator waveguides, Opt. Lett. 29 (2004) 2749–2751. [10] S. Ruizhi, G. Hang, A. Novack, M. Streshinsky, A.E.-J. Lim, L. Guo-Qiang, T. Baehr-Jones, M. Hochberg, High-efficiency grating couplers near 1310 nm fabricated by 248-nm DUV lithography, IEEE Photonics Technol. Lett. 26 (2014) 1569–1572.
Fig. 5. Influence of the shifting of layers along the x direction on the coupling efficiencies.
Fig. 6. Measured coupling efficiency and crosstalk of the optical via.
202
Contents lists available at ScienceDirect
Optics Communications journal homepage: www.elsevier.com/locate/optcom
Optical via for silicon photonic 3D-integrations Tianhua Lin a,b , Qin Han a , Tao Chu c ,∗ a b c
Institute of Semiconductors, Chinese Academy of Sciences, No. A35, Qinghua East Rd, Haidian, Beijing 100083, China University of Chinese Academy of Sciences, 19A Yuquan Rd, Shijingshan, Beijing 100049, China College of Information Science and Electronic Engineering, Zhejiang University, 38 Zheda Rd, Hangzhou 310027, China
ARTICLE
INFO
Keywords: Silicon photonics Silicon nitride Grating coupler Optical via
ABSTRACT We proposed an optical via through which both O- and C-band lights can be coupled from a fiber into different waveguide layers of a silicon photonic chip with multiple waveguide layers. The optical via consists of two grating couplers with various structures in different waveguide layers; these couplers are optimized through particle swarm optimization. From a single fiber, coupling efficiencies of −6.01 and −4.15 dB at 1300 and 1536 nm, respectively, were experimentally obtained for the two grating couplers.
1. Introduction Si3 N4 waveguides are widely considered in the construction of complementary metal–oxide–semiconductor (CMOS) compatible silicon photonic integrated circuits owing to their low propagation loss, thermal-optic efficiency [1], and nonlinear susceptibility [2]. Waveguides, arrayed waveguide gratings (AWGs) [3], microring-resonators [4], and other devices have been studied based on Si3 N4 materials. Further, with developments in large-capacity optical communications, the integration level of photonic chips has increased and the demand for 3-D photonic chips [5] with multiple waveguide device layers for future applications is growing. Si3 N4 waveguide devices are expected to be used in the fabrication of 3-D integrated photonic chips as Si3 N4 films can easily be deposited layer by layer in fabrication processes. However, the issue of coupling lights between waveguides in different layers and optical fibers has not been accurately solved. A popular method of evanescent-wave coupling [6] usually requires a very thin inter-cladding layer between waveguides in vertically neighboring Si3 N4 layers; the thin inter-cladding layer also induces crosstalk due to the unneeded evanescent-wave coupling between waveguides in neighboring layers. Thus, there is an urgent requirement of an optical device that can couple lights between multiple layers and between layers and fibers. In this letter, we introduce a new device that is used to couple lights between a fiber and two Si3 N4 device layers working at O- and C-band light wavelengths. The device can be easily expanded to more than two layers, and is named optical via as it functions as an electrical via in CMOS integrated chips. It was designed using dual-layer grating structures and can be easily fabricated through CMOS-compatible processes. The experimental results show that the coupling efficiencies of the optical via are −6.01 and −4.15 dB at 1300 and 1536 nm, respectively. ∗
The optical via could become a necessary device in future multilayer silicon photonic circuits. 2. Design and simulations Fig. 1 shows the schematic of the proposed device comprising two Si3 N4 device layers on a Si substrate separated with cladding SiO2 layers. Two grating couplers were implanted on the Si3 N4 layers to couple O- and C-band lights into waveguide devices at different layers. The section sizes of Si3 N4 waveguides were selected as 500 nm × 800 nm to satisfy the single-mode light propagating conditions. Thus, the thickness of each Si3 N4 layer was selected to be 500 nm. The grating couplers were designed as follows [7]: nef f
2𝜋 2𝜋 2𝜋 − − 𝑛𝑐𝑙𝑎𝑑𝑑𝑖𝑛𝑔 𝑠𝑖𝑛𝜃 = 0 𝜆 𝛬 𝜆
(1)
where 𝜆 is the wavelength of the incident light. When the O- and Cband lights are considered, 𝜆 = 1310 and 1550 nm, respectively. 𝛬, 𝑛ef f , and 𝑛cladding are the grating period, effective index, and cladding index of the grating couplers, respectively, and 𝜃 is the incident angle of the fiber. The equations only fit perfectly at one wavelength as designed. When the wavelength changes, a mismatch can be depicted as follows: ( ) 2𝜋 2𝜋 2𝜋 𝑀 = nef f − − 𝑛𝑐𝑙𝑎𝑑𝑑𝑖𝑛𝑔 𝑠𝑖𝑛𝜃 𝜆 𝛬 𝜆 ) ( 2𝜋 2𝜋 2𝜋 − nef f − − 𝑛𝑐𝑙𝑎𝑑𝑑𝑖𝑛𝑔 𝑠𝑖𝑛𝜃 (2) 𝜆 + 𝛥𝜆 𝛬 𝜆 + 𝛥𝜆 where 𝛥𝜆 is the wavelength change. Eq. (2) can be simplified as follows:
𝑀=
( ) 2𝜋 𝑛ef f − 𝑛cladding 𝛥𝜆
Corresponding author. E-mail address: [email protected] (T. Chu).
https://doi.org/10.1016/j.optcom.2019.07.031 Received 22 February 2019; Received in revised form 28 June 2019; Accepted 14 July 2019 Available online 16 July 2019 0030-4018/© 2019 Elsevier B.V. All rights reserved.
𝜆2
(3)
T. Lin, Q. Han and T. Chu
Optics Communications 452 (2019) 200–202
Fig. 1. Schematic of the optical via. The devices comprise two Si3 N4 device layers on a Si substrate, separated with SiO2 cladding layers. Two grating couplers were implanted on the Si3 N4 layers. The period (𝛬), etch depth (D), etch width (W) of both layers, and the shift (S) of the top layers are indicated.
Fig. 2. Simulated coupling electric field of our design at (a) 1550-nm wavelength light incident and (b) 1310-nm wavelength light incident.
Obviously, the mismatch is inversely proportional to the square of the wavelength. This implies that the O-band wavelength light has a larger mismatch compared with the C-band light. The larger the mismatch is, the smaller the incident light is affected by the grating structure. Therefore, the C- and O-band grating couplers were placed on the top and bottom layers to mitigate the influence of the bottom layer coupling efficiency from the top layer grating structures. The fiber incident angle was selected to be 4◦ to avoid second-order diffraction. The particle swarm optimization algorithm was applied to optimize the parameters of the optical via. The sum of coupling efficiency at both 1310- and 1550-nm wavelengths was selected as the figure of merit (FOM) to optimize the structure. The devices were simulated using 2-D finite-difference time-domain (FDTD) solvers from Lumerical Solutions, Inc. The pitch, duty cycle, and etch depth of the O-band grating coupler are the most significant parameters that affect the coupling efficiency of the O-band light collectively. They were selected as 800 nm, 0.53, and 300 nm, respectively. The pitch, duty cycle, and etch depth of the C-band grating coupler are the most significant parameters that affect the coupling efficiency of the C-band light collectively. They were selected as 990 nm, 0.6, and 374 nm, respectively. Furthermore, the thicknesses of buried oxide (BOX), intercladding, cladding layers, and the shift of top layer affect both the O-band and C- band coupling efficiencies slightly. They were selected as 1.53, 0.94, 0.5 and −0.59 μm, respectively. The FOM converged at a sum efficiency of 92% through 500 generations of optimization. Fig. 2 shows the electric fields of light propagating in the Si3 N4 waveguides and gratings at different layers of the chip. The simulated results of coupling efficiencies are shown in Fig. 3. The maximum coupling efficiencies of the O- and C-band grating couplers are 3.9 and 3.0 dB at 1310- and 1550-nm wavelengths, respectively. The crosstalk was calculated as 22 and 16 dB at 1310- and 1550-nm wavelength. Adiabatic tapers with lengths of 100 μm were used to connect the gratings with Si3 N4 waveguides with widths of 800 nm [8].
Fig. 3. Simulated coupling efficiencies of the two grating couplers.
top Si3 N4 layer was also fabricated using the same process. Finally, a cladding layer of 500-nm-thick SiO2 was deposited on the top. Fig. 4 shows the microphotograph and scanning electron microscopy image of the top view of the device, the fabrication process of which is also compatible with the CMOS process. The patterns on the top and bottom layers were aligned with the Au alignment marks fabricated on the bottom Si3 N4 layer in advance. To evaluate the alignment error, we fabricated Vernier marks on both layers. In our fabricated samples, an alignment error of 40 nm was corrected in the chip through shift compensations, and a simulation was performed to evaluate the influence of coupling efficiencies caused by the shift. As shown in Fig. 5, when the top layer shifts from the optimized position of −2 μm to 2 μm, the coupling efficiency of 1310 nm shows a periodic fluctuation of 0.1 dB. In contrast, when the bottom layer shifts from −2 μm to 2 μm, the coupling efficiency of 1550 nm shows a periodic fluctuation of 0.5 dB. These periodic fluctuations were caused by the periodic structures of the gratings. To characterize the devices, one side of the testing structure is the optical via, and the other sides are separated O-band and C-band grating couplers, as shown in Fig. 4. The coupling efficiencies and crosstalk of the optical via were measured and are shown in Fig. 6. Maximum coupling efficiencies of −6.01 and −4.15 dB were obtained at 1300- and 1536-nm wavelengths, respectively. Crosstalks of no more than −22 and −17 dB at the O-band and C-band were obtained, respectively. The measured coupling efficiencies are worse than the
3. Fabrication and experimental results A 1.53-μm-thick BOX layer was first deposited on a Si substrate through plasma enhanced chemical vapor deposition (PECVD). Next, the first Si3 N4 waveguide device layer was deposited through PECVD, after which electron beam lithography was used to draw the device layout on a photoresist, and inductively coupled plasma etching was used to transfer the pattern to the device layer. An inter-cladding layer of 940-nm-thick SiO2 then covered the bottom Si3 N4 layer. The 201
T. Lin, Q. Han and T. Chu
Optics Communications 452 (2019) 200–202
simulated results, and show slight shifts between the peak wavelengths. These shifts are considered to be caused by the fabrication errors. Owing to a small incident angle, there is a strong reflection on the longer wavelength where a Fabry–Perot (F–P) ripple was observed. The F–P ripples have intervals inversely proportional to the length of the F–P cavity, which, in our test structure, comprises the taper and the waveguide connector between the taper. In application, the length and complexity of the optical circuits are significantly larger than those of our test optical circuits, and thus could have very small F–P ripple intervals and depleted reflection; this in turn could result in the nonappearance of the F–P patterns. It is worth noting that the coupling efficiency of C-band increases and that of the O-band decreases compared with those of the separated grating couplers. This is due to the interaction between the two grating couplers. The bottom layer grating positively influences the top layer as if the bottom layer acted as a Bragg reflector [9]. The top layer grating negatively influences the bottom layer because the light field through the top layer has a phase distortion. 4. Conclusions Fig. 4. Microphotograph and SEM image of the optical via.
In this study, we designed and fabricated an optical via to couple a fiber and two Si3 N4 device layers with O- and C-band lights. The device could be easily fabricated using a CMOS-compatible process. The coupling efficiencies were obtained as −6.01 and −4.15 dB at 1300 and 1536 nm, respectively. The crosstalks were measured to be no more than −22 and −17 dB at O-band and C-band, respectively. In the future, an apodized design [10] of the grating couplers can be applied to advance the coupling efficiencies.
Funding This work was supported by the National Key Research and Development Program of China [grant numbers 2016YFB0402505]. References [1] R. Amatya, C.W. Holzwarth, M.A. Popović, F. Gan, H.I. Smith, F. Kärtner, R.J. Ram, Low Power Thermal Tuning of Second-Order Microring Resonators, Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies, Optical Society of America, Baltimore, Maryland, 2007, p. CFQ5. [2] K. Ikeda, R.E. Saperstein, N. Alic, Y. Fainman, Thermal and kerr nonlinear properties of plasma-deposited silicon nitride/silicon dioxide waveguides, Opt. Express 16 (2008) 12987–12994. [3] D. Dai, Z. Wang, J.F. Bauters, M.C. Tien, M.J.R. Heck, D.J. Blumenthal, J.E. Bowers, Low-loss Si3N4 arrayed-waveguide grating (de)multiplexer using nano-core optical waveguides, Opt. Express 19 (2011) 14130–14136. [4] H. Cai, A.W. Poon, Optical manipulation and transport of microparticles on silicon nitride microring-resonator-based add–drop devices, Opt. Lett. 35 (2010) 2855–2857. [5] M. Raburn, L. Bin, K. Rauscher, O. Yae, N. Dagli, J.E. Bowers, 3-D photonic circuit technology, IEEE J. Sel. Top. Quantum Electron. 8 (2002) 935–942. [6] J.F. Bauters, M.L. Davenport, M.J.R. Heck, J.K. Doylend, A. Chen, A.W. Fang, J.E. Bowers, Silicon on ultra-low-loss waveguide photonic integration platform, Opt. Express 21 (2013) 544–555. [7] T.K. Gaylord, M.G. Moharam, Analysis and applications of optical diffraction by gratings, Proc. IEEE 73 (1985) 894–937. [8] Y. Fu, T. Ye, W. Tang, T. Chu, Efficient adiabatic silicon-on-insulator waveguide taper, Photonics Res. 2 (2014) A41. [9] D. Taillaert, P. Bienstman, R. Baets, Compact efficient broadband grating coupler for silicon-on-insulator waveguides, Opt. Lett. 29 (2004) 2749–2751. [10] S. Ruizhi, G. Hang, A. Novack, M. Streshinsky, A.E.-J. Lim, L. Guo-Qiang, T. Baehr-Jones, M. Hochberg, High-efficiency grating couplers near 1310 nm fabricated by 248-nm DUV lithography, IEEE Photonics Technol. Lett. 26 (2014) 1569–1572.
Fig. 5. Influence of the shifting of layers along the x direction on the coupling efficiencies.
Fig. 6. Measured coupling efficiency and crosstalk of the optical via.
202