| 1. |
- Larsson, Anders, 1957, et al.
(författare)
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VCSEL modulation capacity: Continued improvements or physical limits?
- 2017
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Ingår i: 6th IEEE Photonics Society Optical Interconnects Conference, OI 2017. - 9781509050154 ; , s. 53-54
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Konferensbidrag (refereegranskat)abstract
- The short-reach optical interconnects used in datacenters and high-performance computing systems are dominated by VCSEL and multimode fiber (MMF) links 1 . The VCSEL-MMF technology is the most cost and power efficient and offers the smallest footprint. VCSELs operating at 25-28 Gbit/s are in production 2 while research has extended the VCSEL modulation bandwidth to 30 GHz 3 (Fig.1) and enabled OOK-NRZ data transmission up to 57 Gbit/s at 25°C 4 and 50 Gbit/s at 85°C 5 , without equalization or forward-error-correction (FEC). A VCSEL energy dissipation below 100 fJ/bit has been demonstrated at 25-50 Gbit/s 3 (Fig.1). The need for higher interconnect capacity raises the question whether the speed and dynamics of VCSELs can be further improved or whether physical limits preventing this have been reached. Higher speed VCSELs would enable higher lane rates and therefore reduced number of lanes and increased bandwidth density for a given aggregate interconnect capacity.
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| 2. |
- 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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| 3. |
- Haglund, Erik, 1985, et al.
(författare)
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High-power single transverse and polarization mode VCSEL for silicon photonics integration
- 2019
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 27:13, s. 18892-18899
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement. We demonstrate a 6.5 mW single transverse and polarization mode GaAs-based oxide-confined VCSEL at 850 nm. High power is enabled by a relatively large oxide aperture and an epitaxial design for low resistance, low optical loss, and high slope efficiency VCSELs. With the oxide aperture supporting multiple polarization unrestrained transverse modes, single transverse and polarization mode operation is achieved by a transverse and polarization mode filter etched into the surface of the VCSEL. While the VCSEL is specifically designed for light source integration on a silicon photonic integrated circuit, its performance in terms of power, spectral purity, polarization, and beam properties are of great interest for a large range of applications.
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| 4. |
- Jahed, Mehdi, 1988, et al.
(författare)
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Monolithic Multi-Wavelength VCSEL Arrays with Uniform Performance by Intra-Cavity Phase Tuning
- 2021
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Ingår i: Conference Digest - IEEE International Semiconductor Laser Conference. - 0899-9406.
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Konferensbidrag (refereegranskat)abstract
- We demonstrate monolithic multi-wavelength VCSEL arrays with wavelengths set by intra-cavity phase tuning. Precise channel spacing is achieved by Ar-ion etching. Uniform performance over an array is achieved by spectral matching and balancing of wavelength dependent gain, DBR reflectances and optical confinement factor.
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| 5. |
- Jahed, Mehdi, 1988, et al.
(författare)
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Precise setting of micro-cavity resonance wavelength by dry etching
- 2019
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Ingår i: Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics. - : American Vacuum Society. - 2166-2754 .- 2166-2746. ; 37:3
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Tidskriftsartikel (refereegranskat)abstract
- With an intracavity phase tuning technique, the authors demonstrate <2 nm precision in wavelength setting of vertical-cavity surface-emitting laser (VCSEL) microresonators in the wavelength range 1040-1070 nm using an Ar ion-beam etching process with subnanometer precision in etch depth. This postgrowth fabrication technique for controlling the wavelength of individual VCSELs is promising for the development of monolithic multiwavelength VCSEL arrays with precisely defined wavelengths for wavelength division multiplexed (WDM) optical interconnects and the assembly of compact and high-capacity WDM transmitters.
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| 6. |
- Jahed, Mehdi, 1988
(författare)
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VCSEL and Integration Techniques for Wavelength-Multiplexed Optical Interconnects
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- GaAs-based vertical-cavity surface-emitting lasers (VCSELs) are dominating short-reach optical interconnects (OIs) due to their high modulation speed, low power consumption, circular output beam and low fabrication cost. Such OIs provide the high bandwidth connectivity needed for interconnecting servers and switches in data centers. With the rapidly increasing use of Internet-based applications and services, higher bandwidth connectivity and higher aggregate capacity VCSEL-based OIs are needed. Until now, this has been achieved mostly through an increase of the lane rate by higher speed VCSELs and higher order modulation formats. Furthermore, spatial-division-multiplexing has proven effective for increasing the aggregate capacity. Much higher capacity can be achieved by multiple wavelengths per fiber, known as wavelength-divisionmultiplexing (WDM). Moreover, smaller footprint and higher bandwidth density WDM transceivers can be built using monolithic multi-wavelength VCSEL arrays with densely spaced VCSELs. This requires a VCSEL technology where the wavelength of individual VCSELs can be precisely set in a post-epitaxial growth fabrication process and a photonic integrated circuit (PIC) for multiplexing and fiber coupling. Flip-chip integration over grating couplers (GCs) is considered for interfacing VCSELs with waveguides on the PIC. In this thesis, an intra-cavity phase tuning technique is demonstrated for setting the resonance wavelength of VCSELs in a monolithic array with an accuracy in spacing of <1 nm. Uniform performance over the array is achieved by spectral matching and balancing of mirror reflectances, optical confinement factor and optical gain. Single transverse and polarization mode VCSELs, as required for flip-chip integration over GCs, with a record output power of 6 mW are also demonstrated. Finally, an investigation of angled flip-chip integration of a VCSEL over a GC on a silicon photonic integrated circuit (Si-PIC) is presented. Dependencies of coupling efficiency and optical feedback on flip-chip angle and size of the VCSEL die are studied using numerical FDTD simulations. Moreover, flip-chip integration of a VCSEL over a GC on a Si-PIC is experimentally demonstrated. The insertion loss from the VCSEL at the input GC to a singlemode fiber, multimode fiber or flip-chip integrated photodetector over the output GC was measured and quantified. The latter forms an on-PIC optical link.
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| 7. |
- Jahed, Mehdi, 1988
(författare)
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VCSEL Techniques for Wavelength-Multiplexed Optical Interconnects
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The majority of global data communication is taking place within data centers where data is stored and processed and where the largest part of the power used for global networking is consumed. With the rapidly increasing use of Internet-based applications and services, data centers are equipped with a larger number of servers and switches requiring higher bandwidth connectivity. Optical interconnects (OIs) are used to provide the connectivity needed. Short-reach OIs are dominated by 850 nm GaAs-based vertical-cavity surface-emitting lasers (VCSELs) due to their low fabrication cost, low power consumption, high modulation speed, and circular output beam. With the need for even higher bandwidth connectivity, large efforts have been invested in the development of VCSEL-based OIs offering higher aggregate capacity. Until now, higher capacity has been achieved mostly through an increase of the lane rate by higher speed VCSELs and higher order modulation formats. Furthermore, spatial division multiplexing (SDM), using parallel fibers or multicore fibers, has proven effective for increasing the aggregate capacity. With these techniques, it is expected that the OI capacity will saturate at the 1 Tbit/s level. Capacity beyond the limits of current technologies is expected by also exploring the wavelength dimension, referred to as wavelength division multiplexing (WDM). This calls for the development of high-speed VCSELs at multiple wavelengths. To also enable the very small footprint transceivers and high bandwidth density needed as transceivers move closer to the switch AISC, the multiple wavelength VCSELs should be in a monolithic array. This requires a VCSEL technology where the wavelength of individual VCSELs can be precisely set in a post-growth fabrication process. As an integration platform for multiplexing and fiber coupling we envision a photonic circuit on Si with Si3N4 waveguides and grating couplers for VCSEL integration. With such waveguides being single mode and the grating couplers being polarization sensitive, the VCSELs in the array should be single transverse and polarization mode, in addition to having a high modulation bandwidth. In this thesis, an intra-cavity phase tuning technique, based on an Ar ion-beam etching process with sub-nm precision, is demonstrated for setting the resonance wavelength of VCSEL resonators with <2 nm precision in the wavelength range 1040-1070 nm. Single transverse and polarization mode VCSELs with a record output power of 6 mW are also demonstrated. Suppression of higher order transverse modes and the orthogonal polarization state is achieved by etching a shallow mode filter in the surface of the VCSEL.
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| 8. |
- Jahed, Mehdi, 1988, et al.
(författare)
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VCSEL Wavelength Setting by Intra-Cavity Phase Tuning - Numerical Analysis and Experimental Verification
- 2021
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Ingår i: IEEE Journal of Quantum Electronics. - 0018-9197 .- 1558-1713. ; 57:6, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- Monolithic multi-wavelength VCSEL arrays, with wavelengths of individual VCSELs precisely set in a post-epitaxial growth process, would enable compact multi-color light sources and transmitters for various sensing and datacom applications. Here we report on a numerical study of the requirements of spectral matching and balancing of DBR reflectances, optical confinement factor, and optical gain for uniformity of threshold current and slope efficiency over wavelength with wavelength set by intra-cavity phase tuning. The requirements are verified by an experimental demonstration of intra-cavity phase tuned VCSELs in the spectral range 1043-1067 nm with a wavelength spacing of 8 ± 1 nm enabled by precise Ar ion-beam etching. Small variations of threshold current and slope efficiency are achieved by close to ideal spectral matching and balancing. The VCSELs are GaAs-based with a dielectric SiO2/TiO2 top-DBR. We conclude that high uniformity of threshold current and slope efficiency is demanding in terms of spectral matching and balancing and requires not only very precise etching for intra-cavity phase tuning and precise thickness of the layers in the dielectric top-DBR, but also precise thickness and composition of the layers in the epitaxial semiconductor part.
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