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Title:Development of high-speed vertical-cavity surface-emitting diode laser and vertical-cavity transistor laser for shortreach optical interconnects
Author(s):Wang, Hsiao-Lun
Director of Research:Feng, Milton
Doctoral Committee Chair(s):Feng, Milton
Doctoral Committee Member(s):Dallesasse, John M; Jin, Jianming; Bayram, Can
Department / Program:Electrical & Computer Eng
Discipline:Electrical & Computer Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Abstract:Commercialization of vertical-cavity surface-emitting lasers (VCSELs) in the mid-1990s replaced light-emitting diodes and provided more reliable and cost-effective optical interconnects (OIs) with improved data rate from 100 Mb/s to 1 Gb/s. The transition from proton isolated VCSEL to oxide confined VCSEL further advanced the data rate from 1 Gb/s to 10 Gb/s, and now 25 Gb/s NRZ oxide VCSELs are adopted in optical transceiver products for data centers. This dissertation investigates the 50 Gb/s NRZ oxide VCSEL development for next-generation OIs. Wide temperature range operation is important for VCSELs because commercial optical transceivers are required to be functional from 0 °C to 70 °C. We present temperature-dependent measurement and analysis of 50 Gb/s oxide VCSELs where L-I-V, spectrum and junction temperature from room temperature to 115 °C are included. The device demonstrates 30 GHz bandwidth at RT and over 20 GHz at 115 °C. The bandwidth reduction is attributed to the increased carrier recombination and photon lifetime at higher temperature. Bit error ratio (BER) measurements are used to correlate data rate with device optical bandwidth at each temperature. Multimode transmission within VCSEL-based optical links has resulted in limited reach due to modal dispersion. In this dissertation, three types of 50 Gb/s oxide VCSELs, namely multimode (MM), reduced mode (RM) and single mode (SM), are fabricated to study their modal effect and measure their highest data rate versus distance up to 1 km in OM4 fiber using a real-time bit error rate tester. While the MM and RM VCSELs suffer from modal dispersion and their data rate over distance is below the typical effective modal bandwidth (EMB) limits of OM4 fiber, the SM VCSEL demonstrates a series of record performances that exceed the EMB limit of 4700 MHz*km. Finally, progress on process development of a vertical-cavity transistor laser (VCTL) is presented. The high threshold current issue present in previous devices is identified and attributed to the low-Q cavity formed below the emitter contact. We present the modified layout and process flows of VCTL to resolve the trench oxidation problem. Future work is outlined to achieve energy-efficient and room-temperature operation.
Issue Date:2020-08-19
Rights Information:Copyright 2020 Hsiao-Lun Wang
Date Available in IDEALS:2021-03-05
Date Deposited:2020-12

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