| 1. |
- Grabowski, Alexander, 1993, et al.
(författare)
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Impact of Carrier Transport and Capture on VCSEL Dynamics
- 2023
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Ingår i: IEEE Journal of Quantum Electronics. - 0018-9197 .- 1558-1713. ; 59:1, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- Using a vertical-cavity surface-emitting laser (VCSEL) equivalent circuit model based on two carrier rate equations to include effects of carrier dynamics, we study the impact of carrier transport and capture on the small- and large-signal modulation response of high-speed VCSELs. The model also accounts for parasitics, current-induced self-heating, and gain compression. A variation of the effective capture time from 1 to 15 ps is found to have a large impact on the small-signal modulation response, with the 3 dB bandwidth decreasing from 40 to 15 GHz and the response transitioning from under-damped to over-damped. This is primarily due to the increasing low frequency parasitic-like roll-off with increasing effective capture time. A significant effect on the optical waveforms produced by the VCSEL under 56 Gbit/s on-off keying (OOK) non-return-to-zero (NRZ) and pulse-amplitude modulation 4 (PAM4) modulation is observed, with a short effective capture time leading to horizontal eye closure caused by timing jitter (TJ) and intersymbol interference (ISI) and a long effective capture time leading to vertical eye closure caused by long rise- and fall-times. However, for high modulation speed, a short effective capture time is needed and the photon lifetime should be set for clear eye opening. We also show the impact of the effective capture time on the output power vs current characteristics and map the dependence of internal temperature, carrier densities, carrier escape and leakage rates, and spontaneous recombination rates on current for different effective capture times.
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| 2. |
- Grabowski, Alexander, 1993, et al.
(författare)
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Large-Signal Equivalent Circuit for Datacom VCSELs
- 2021
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 39:10, s. 3225-3236
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Tidskriftsartikel (refereegranskat)abstract
- Increasing the baud rate in optical interconnects (OIs) will require the use of more sophisticated driver and receiver electronics. This will help overcome the stagnated bandwidth of the Vertical-Cavity Surface-Emitting Laser (VCSEL) and the pin-photodetector. Next generation OIs operating at single lane rates of 50+ Gbaud will therefore require careful co-optimization of the electronics and the optoelectronics. To facilitate this work there is a need of an accurate equivalent circuit for the optoelectronic components, functioning over a broad drive current and ambient temperature range. The VCSEL is the most important and complex to model due to its non-linear behavior and strongly varying characteristics with drive current and ambient temperature. For this purpose, a large-signal equivalent circuit dedicated for high-speed datacom VCSELs has been developed and is presented here. The distributed electrical parasitics in the device layout are carefully considered, the intrinsic speed limitation from carrier transport effects in the Separate-Confinement-Heterostructure (SCH) and the carrier-photon interaction in the Quantum Wells (QWs) are included, and self-heating effects in the device are monitored. The circuit is purposely based on physical instead of empirical models so that it can provide usable feedback to VCSEL designers. For circuit demonstration, it is implemented in Keysight's Advanced Design System (ADS) software and thereafter applied to replicate the performance of a state-of-the-art 28-GHz-bandwidth VCSEL at different temperatures and drive currents. Comparison is made between simulated and measured steady-state characteristics, small-signal behavior, and large-signal response under 28 Gbaud On-Off-Keying (OOK) and Pulse-Amplitude-Modulation 4 (PAM4) modulation, showing good agreement.
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| 3. |
- Grabowski, Alexander, 1993, et al.
(författare)
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Large-Signal Equivalent Circuit for Datacom VCSELs – Including Intensity Noise
- 2022
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 40, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- Optical interconnects (OIs) continue to require more and more sophisticated driver and receiver electronics as higher baud rates are pushed in datacom, mainly due to the bandwidth stagnation of the optoelectronic components such as the vertical-cavity surface-emitting laser (VCSEL) in the transmitter as well as the photodetector (PD) in the receiver. Another important focus is maintaining high energy efficiency for the OIs. For both cases, a reliable equivalent circuit model for high-speed VCSELs is required for link optimization. This work is an extension of our previously presented large-signal VCSEL equivalent circuit model, where noise is added to the physical processes that the VCSEL model is based on. Thus, a new step is taken in the strive of developing an even more accurate physics-based large-signal VCSEL equivalent circuit model for datacom applications. Following a detailed description of the VCSEL noise modelling, a presentation is given on simulated results of VCSEL relative intensity noise (RIN) spectrum and eye diagrams under 28 Gbaud on-off keying (OOK) and pulse-amplitude 4 (PAM4) modulation, and that are compared with corresponding measurement results. Good agreement is found over a wide range of VCSEL driving conditions and temperatures. A 28-GHz-bandwidth VCSEL is applied for the demonstration, and the presented noise extended VCSEL equivalent circuit model was implemented in Verilog-A, and the simulations were performed using Cadence Spectre.
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| 4. |
- Jorgensen, A. A., et al.
(författare)
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Petabit-per-second data transmission using a chip-scale microcomb ring resonator source
- 2022
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Ingår i: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 16:11, s. 798-802
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Tidskriftsartikel (refereegranskat)abstract
- Optical fibre communication is the backbone of the internet. As essential core technologies are approaching their limits of size, speed and energy-efficiency, there is a need for new technologies that offer further scaling of data transmission capacity. Here we show that a single optical frequency-comb source based on a silicon nitride ring resonator supports data capacities in the petabit-per-second regime. We experimentally demonstrate transmission of 1.84 Pbit s–1 over a 37-core, 7.9-km-long fibre using 223 wavelength channels derived from a single microcomb ring resonator producing a stabilized dark-pulse Kerr frequency comb. We also present a theoretical analysis that indicates that a single, chip-scale light source should be able to support 100 Pbit s–1 in massively parallel space-and-wavelength multiplexed data transmission systems. Our findings could mark a shift in the design of future communication systems, targeting device-efficient transmitters and receivers.
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| 5. |
- Kaimre, Hans, 1996, et al.
(författare)
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Effects of Detuning on Wide-Temperature Behavior of 25 Gbaud 850 nm VCSELs
- 2023
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 12439
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Konferensbidrag (refereegranskat)abstract
- Emerging markets for optical interconnects with VCSEL-based transceivers require VCSELs with superior wide temperature performance. One of the prime parameters controlling the temperature dependence of VCSEL performance is wavelength detuning. We study the impact of detuning on the performance of 25 Gbaud class 850 nm VCSELs over a temperature range of -40 to 125°C, as applicable to e.g. automotive optical networking. Two VCSELs with different detuning, but otherwise identical, are compared. Basic static and dynamic performance parameters and their temperature dependencies are extracted. The results show that with appropriate detuning, sufficient performance at the temperature extremes and improved tolerance to temperature variations can be achieved. Excessive detuning to meet the more challenging high temperature performance requirements leads to insufficient low temperature performance.
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| 6. |
- Szczerba, Krzysztof, 1985, et al.
(författare)
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70 Gbps 4-PAM and 56 Gbps 8-PAM Using an 850 nm VCSEL
- 2015
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Ingår i: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 33:7, s. 1395-1401
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Tidskriftsartikel (refereegranskat)abstract
- We present 56 Gbps unequalized 8-pulse-amplitude-modulation (PAM) real-time transmission over 50 m of multimode fiber and 70 Gbps 4-PAM operation with offline equalization. FEC would be necessary in both schemes. The bit-rates are given taking into account the FEC overhead needed to reach a BER below 10-12. The experiments were performed with an 850 nm vertical cavity surface emitting laser with 20 GHz bandwidth and a 22 GHz photoreceiver. We show that 8-PAM modulation requires channel bandwidth comparable with the symbol rate to avoid excessive ISI penalty and that equalization of 4-PAM signal can significantly improve achievable bit-rates.
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| 7. |
- Szczerba, Krzysztof, 1985, et al.
(författare)
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70 Gbps 4-PAM and 56 Gbps 8-PAM using an 850 nm VCSEL
- 2014
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Ingår i: 2014 European Conference on Optical Communication, ECOC 2014; Cannes; France; 21 September 2014 through 25 September 2014. - 9782954944401 ; , s. Art. no. 6963923-
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Konferensbidrag (refereegranskat)abstract
- t We present 56 Gbps unequalized 8-PAM real-time transmission over 50 m of MMF and 70Gbps 4-PAM operation with offline equalization. The experiments were performed with an 850 nm VCSEL with 25 GHz bandwidth and a 22 GHz photoreceiver.
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| 8. |
- Szczerba, Krzysztof, 1985, et al.
(författare)
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Energy Efficiency of VCSELs in the Context of Short-Range Optical Links.
- 2015
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Ingår i: IEEE Photonics Technology Letters. - 1041-1135 .- 1941-0174. ; 27:16, s. 1749-1752
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Tidskriftsartikel (refereegranskat)abstract
- We present results from an investigation of theenergy efficiency of VCSELs under large signal modulation. We show that the most important factor influencing the energy consumption of the VCSELs is the required optical modulation amplitude, which drives other VCSEL design requirements. The required optical modulation amplitude also depends on the optical link design. Through this dependence it is possible to better understand the energy consumption of complete short range optical links.
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| 9. |
- Chen, Jingjing, 1982, et al.
(författare)
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An Energy Efficient 56 Gbps PAM-4 VCSEL Transmitter Enabled by a 100 Gbps Driver in 0.25 µm InP DHBT Technology
- 2016
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 34:21, s. 954-4964
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Tidskriftsartikel (refereegranskat)abstract
- Datacenters demand higher speed VCSEL-based optical interconnects at low power consumption. As a potential technology enabler, this paper presents a wide bandwidth and energy efficient multilevel PAM VCSEL driver implemented in an InP 0.25 μm double heterojunction bipolar transistor (DHBT) technology. The operational bandwidth of the driver is verified and error-free electrical data transmission up to 56 Gbps PAM-2 and 100 Gbps PAM-4 is demonstrated at a driver energy consumption less than 2 pJ/bit. The driver is integrated and tested with an in-house fabricated 850 nm VCSEL. Error-free 56 Gbps PAM-4 optical transmission at a transmitter energy consumption of 3.7 pJ/bit is demonstrated without equalization. This is the highest data rate reported for an integrated PAM-4 modulated VCSEL transmitter, while being the most energy efficient above 40 Gbps operation. Moreover, the VCSEL driver offers a pre-emphasis feature at PAM-2 operation for improved link throughput and receiver sensitivity.
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| 10. |
- Srinivasan, Muralikrishnan, 1991, et al.
(författare)
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End-to-End Learning for VCSEL-based Optical Interconnects: State-of-the-Art, Challenges, and Opportunities
- 2023
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 41:11, s. 3261-3277
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Tidskriftsartikel (refereegranskat)abstract
- Optical interconnects (OIs) based on vertical-cavity surface-emitting lasers (VCSELs) are the main workhorse within data centers, supercomputers, and even vehicles, providing low-cost, high-rate connectivity. VCSELs must operate under extremely harsh and time-varying conditions, thus requiring adaptive and flexible designs of the communication chain. Such designs can be built based on mathematical models (model-based design) or learned from data (machine learning (ML) based design). Various ML techniques have recently come to the forefront, replacing individual components in the transmitters and receivers with deep neural networks. Beyond such component-wise learning, end-to-end (E2E) autoencoder approaches can reach the ultimate performance through co-optimizing entire parameterized transmitters and receivers. This tutorial paper aims to provide an overview of ML for VCSEL-based OIs, with a focus on E2E approaches, dealing specifically with the unique challenges facing VCSELs, such as the wide temperature variations and complex models.
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