| 1. |
- Caut, Alexander, 1994, et al.
(författare)
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Angled Flip-Chip Integration of VCSELs on Silicon Photonic Integrated Circuits
- 2022
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 40:15, s. 5190-5200
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Tidskriftsartikel (refereegranskat)abstract
- An investigation of angled flip-chip integration of a singlemode 850 nm vertical-cavity surface-emitting laser (VCSEL) on a silicon nitride photonic integrated circuit (PIC) is presented. Using numerical FDTD simulations, we consider the conditions under which the VCSEL can be integrated at an angle over a grating coupler with high coupling efficiency and low optical feedback. With both coupling efficiency and feedback decreasing with increasing angle, there is a trade-off. With co-directional coupling, first-order diffraction loss sets in at a critical angle, which further reduces the coupling efficiency. No such critical angle exists for contra-directional coupling. We also experimentally demonstrate angled flip-chip integration of GaAs-based 850 nm single transverse and polarization mode VCSELs over grating couplers on a silicon-nitride PIC. At the output grating coupler, light is either collected by an optical fiber or converted to a photocurrent using a flip-chip integrated GaAs-based photodetector. The latter forms an on-PIC optical link. We measured an insertion loss of 21.9, 17.6 and 20.1 dB with a singlemode fiber, multimode fiber and photodetector over the output grating coupler, respectively.
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| 2. |
- Caut, Alexander, 1994, et al.
(författare)
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Channel Scalability of Silicon Nitride (De-)multiplexers for Optical Interconnects at 1 μm
- 2024
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 42:1, s. 276-286
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an investigation of the channel scalability of silicon nitride (Si3N4)-based (de-)multiplexers in the 1-μm band (1015-1055 nm). We discuss 4-, 8- and 16-channel demultiplexers based on arrayed waveguide gratings (AWGs) and cascaded Mach-Zehnder interferometers (MZIs), with corresponding channel spacings of 8, 4 and 2 nm. Gaussian and flat-top response devices are considered for both technologies and we analyze the insertion loss, temperature sensitivity, response flatness, footprint and crosstalk (XT). We study the impact of the number of channels on the insertion loss and XT level. In the experimental part, we demonstrate a 4-channel Gaussian AWG. We also demonstrate 4-channel Gaussian and flat-top cascaded MZIs, based on multimode interferometers (MMIs) and directional couplers (DCs). The AWG is attractive due to its small footprint but its high manufacturing complexity makes the device more prone to fabrication defects, which can lead to higher loss and higher XT. For the Gaussian AWG and MZI, the XT level is approximately the same and increases with the number of channels from -28 to -23 dB at 4 and 16 channels respectively. The flat-top MZI has no extra-loss with respect to the flat-top AWG and has a better tolerance to high temperature operations. However, due to wavelength sensitive DCs, the XT of the flat-top MZI is higher than that of the flat-top AWG except for a 16-channel system.
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| 3. |
- Caut, Alexander, 1994
(författare)
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Design and Characterization of SiN-based integrated optical components for Wavelength Division Multiplexing
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To follow the trend of the data traffic and to limit the size of the hyperscale data centers, communication solutions offering small footprint, low cost and low power consumption are needed. Optical interconnects used in data centers are mostly short reach (approximately 100 m) based on GaAs-based 850 nm vertical-cavity surface emitting lasers (VCSELs) and OM4 multimode fibers (MMF). However, with 1 km-long optical links, the use of VCSEL-MMF at 850 nm becomes challenging at high data rates (Tb/s) due to large modal dispersion and high propagation loss. Therefore, other cost-effective methods are needed to compensate these limits. Single mode GaAs-based VCSELs have been demonstrated at 1060 nm of wavelength, where the chromatic dispersion is lower, for optical links ranging between 300 m and 10 km. This solution could be a better alternative than InP-based distributed feedback laser sources at 1310 nm in terms of cost and energy dissipation. As the modulation bandwidth of GaAs-based single mode VCSELs is limited to around 30 GHz, reaching the capacity target then requires a wavelength division multiplexing scheme with parallel single-core fibers (SCFs) or even multi-core fibers (MCFs). In this thesis we discuss different types of demultiplexers at 1060 nm of wavelength. The proposed designed demultiplexers are arrayed waveguide gratings (AWGs) and cascaded Mach-Zehnder interferometers (MZIs). These two technologies are compared in terms of transmission, bandwidth, crosstalk, and footprint with the number of output channels. Grating couplers at 1060 and 850 nm for on-chip coupling are also studied. The goal is to couple the light coming from a single mode fiber or a VCSEL with the lowest possible loss and back reflection.
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| 4. |
- Caut, Alexander, 1994, et al.
(författare)
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Polarization-insensitive silicon nitride photonic receiver at 1 μm for optical interconnects
- 2024
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Ingår i: IEEE Photonics Journal. - 1943-0655. ; 16:3, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- This paper demonstrates with FDTD simulations a silicon nitride polarization independent coarse wavelength division multiplexing (CWDM) receiver platform based on square waveguides for optical interconnects at 1 μm. Here, the channel spacing of the demultiplexers is much smaller than standard CWDM systems (25 nm) and is set to 8 nm. To avoid high waveguide propagation and radiation losses, several waveguide dimensions were considered. The 450 nm (width) x 450 nm (height) waveguide presented a good tradeoff between low loss and single-mode behavior and was therefore selected. The demultiplexer has a simulated polarization dependence on the waveguide's width variations of 0.17 nm/nm. In addition, we present edge coupler designs with coupling loss within 2.5 dB for TE and TM polarization.
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| 5. |
- Caut, Alexander, 1994, et al.
(författare)
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Polarization-Insensitive Silicon Nitride Photonic Receiver Based on Thin Waveguides for Optical Interconnects At 1 μm
- 2024
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Ingår i: IEEE Photonics Journal. - 1943-0655. ; 16:2, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- This paper demonstrates with simulations two polarization independent wavelength division multiplexing receiver platforms based on thin silicon nitride waveguides for optical interconnects at 1 μm. The chosen waveguide base geometry (width = 900 nm × height = 160 nm) is a good tradeoff between mode confinement and propagation loss. We first propose a design using a polarization splitter with an 1×4 demultiplexer based on an arrayed waveguide grating (AWG). This receiver has a reduced size and requires only one etching step. We later propose another simplified receiver design using a polarization splitter-rotator with two identical 1×4 demultiplexers based on cascaded Mach-Zehnder interferometers. The rotator is based on a thicker waveguide (width = 500 nm × height = 400 nm) and is partially etched to rotate the electric field by 90°. Thus, it requires the use of mode size converters at the in/output ports. To keep the fabrication complexity as low as possible for the second design, we limited ourselves to only two etching steps. Therefore, the thickness of the slab of the mode converters and of the rotator is the same as for the main 900 nm (wide) × 160 nm (thick) waveguide. The simulated extinction ratio of the polarization splitter at 1035 nm is 18 dB and the calculated TM-TE and TE-TM polarization conversion efficiency of the polarization rotator at 1035 nm is 99.9%.
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| 6. |
- Caut, Alexander, 1994
(författare)
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Silicon nitride-based integrated components for optical communication
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To follow the trend of the data traffic and to limit the size of the hyperscale data centers, communication solutions offering small footprint, low cost and low power consumption are needed. Optical interconnects used in data centers are mostly short reach (approximately 100 m) based on GaAs-based 850 nm vertical-cavity surface emitting lasers (VCSELs) and OM4 multimode fibers (MMF). However, with 1 km-long optical links, the use of VCSEL-MMF at 850 nm becomes challenging at high data rates (Tb/s) due to large modal dispersion and high propagation loss. Therefore, other cost-effective methods are needed to compensate these limits. Single mode GaAs-based VCSELs have been demonstrated at 1060 nm of wavelength, where the chromatic dispersion is lower, for optical links ranging between 300 m and 10 km. This solution could be a better alternative than InP-based distributed feedback laser sources at 1310 nm in terms of cost and energy dissipation. As the modulation bandwidth of GaAs-based single mode VCSELs is limited to around 30 GHz, reaching the capacity target then requires a wavelength division multiplexing scheme with parallel single-core fibers (SCFs) or even multi-core fibers (MCFs). In this thesis we discuss different types of demultiplexers at 1060 nm of wavelength. The proposed designed demultiplexers are arrayed waveguide gratings (AWGs) and cascaded Mach-Zehnder interferometers (MZIs). These two technologies are compared in terms of transmission, bandwidth, crosstalk and footprint with the number of output channels. Grating couplers at 1060 and 850 nm for on-chip coupling are also studied. The goal is to couple the light coming from a single mode fiber or a VCSEL with the lowest possible loss and back reflection.
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| 7. |
- Girardi, Marcello, 1991, et al.
(författare)
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3D Integration of Microcombs
- 2023
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Ingår i: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023.
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Konferensbidrag (refereegranskat)abstract
- Microcombs based on silicon nitride are a promising technology in applications such as sensing, metrology and telecommunication [1]. These applications often require to combine a nonlinear waveguide with a linear integrated processor on the same chip to perform functionalities such as splitting, demultiplexing, and optical buffering. However, there is a fundamental performance tradeoff between linear and nonlinear waveguides. For microcomb generation, thick waveguide cores are necessary to achieve the desired anomalous dispersion, while for linear operation a thin core improves the loss of a single mode (SM) waveguide [2]. The dissimilar requirements in waveguide thickness brings challenges for planar integrated technologies. Here, we propose and demonstrate wafer-level three-dimensional integration of microcombs using two different Si3N4 core thicknesses: a thick core featuring dispersion-engineered microcombs and a thinner core for linear processing (see Fig. 1a). This technology breaks off the fundamental tradeoff between loss and confinement in thick waveguides and opens the door to combine high-performance microcombs with ultra-low-loss silicon nitride waveguide technology [3]. We demonstrate this approach by efficiently coupling a microcomb between two layers of Si3N4 and demultiplexing a few lines with an arrayed waveguide grating (AWG) (Fig 1b).
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| 8. |
- Girardi, Marcello, 1991, et al.
(författare)
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Multilayer integration in silicon nitride: decoupling linear and nonlinear functionalities for ultralow loss photonic integrated systems
- 2023
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 31:19, s. 31435-31446
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Tidskriftsartikel (refereegranskat)abstract
- Silicon nitride is an excellent material platform for its extremely low loss in a large wavelength range, which makes it ideal for the linear processing of optical signals on a chip. Moreover, the Kerr nonlinearity and the lack of two-photon absorption in the near infrared enable efficient nonlinear optics, e.g., frequency comb generation. However, linear and nonlinear operations require distinct engineering of the waveguide core geometry, resulting in a tradeoff between optical loss and single-mode behavior, which hinders the development of high-performance, ultralow-loss linear processing blocks on a single layer. Here, we demonstrate a dual-layer photonic integration approach with two silicon-nitride platforms exhibiting ultralow optical losses, i.e., a few dB/m, and individually optimized to perform either nonlinear or linear processing tasks. We demonstrate the functionality of this approach by integrating a power-efficient microcomb with an arrayed waveguide grating demultiplexer to filter a few frequency comb lines in the same monolithically integrated chip. This approach can significantly improve the integration of linear and nonlinear optical elements on a chip and opens the way to the development of fully integrated processing of Kerr nonlinear sources.
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