25 Gbit/s transmission over 500 m multimode fibre using 850 nm VCSEL with integrated mode filter

Abstract

An integrated mode filter in the form of a shallow surface relief was used to reduce the spectral width of a high-speed 850 nm verticalcavity surface-emitting laser (VCSEL). The mode filter reduced the RMS spectral width from 0.9 to 0.3 nm for a VCSEL with an oxide aperture as large as 5 mm. Because of reduced effects of chromatic and modal fibre dispersion, the mode filter significantly increases the maximum error-free (bit error rate , 10 212 ) transmission distance, enabling transmission at 25 Gbit/s over 500 m of multimode OM3+ fibre.Introduction: Multimode vertical-cavity surface-emitting lasers (VCSELs) operating at 850 nm have become well established light sources for optical interconnects in local area networks, storage area networks and high-performance computing owing to low power consumption, circular output beam, fast direct modulation at low currents and low-cost fabrication [1]. Recent years have seen an impressive increase in the speed of 850 nm GaAs-based VCSELs, reaching small signal modulation bandwidths exceeding 23 GHz and enabling error-free transmission at 40 Gbit/s back-to-back [2]. These devices show great promise as transmitters in future short-reach (rack-to-rack and boardto-board, 300 m) and very-short-reach (module-to-module and chipto-chip, 1 m) optical interconnects. Moreover, the low-cost 850 nm GaAs VCSEL technology also has the potential to be used at longer distances of several hundreds of metres, meeting the demand for longer optical interconnects in ever larger data centres. However, for transmission distances exceeding 300 m and data rates above 10 Gbit/s, the effects of modal and chromatic fibre dispersion significantly distort the signal [3]. At higher bit rates, reducing the effects of fibre dispersion becomes increasingly important, becoming a serious concern already at a distance of 100 m at ≥ 25 Gbit/s.In this Letter, we utilise an integrated mode filter to reduce the spectral width of a VCSEL and thereby mitigate the effects of fibre dispersion. The result is a significant increase in transmission distance, enabling error-free transmission at 25 Gbit/s over 500 m of OM3+ fibre. This is to our knowledge the first time an 850 nm VCSEL with an oxide aperture as large as 5 mm has been used to transmit such high bit rates over as long distance as 500 m.

Single-Mode, High-Speed, and High-Power Vertical-Cavity Surface-Emitting Lasers at 850 nm for Short to Medium Reach (2 km) Optical Interconnects

“…Such a device would let the VCSEL-based MMF AOC compete with the 1.3 μm DFB-based SMF AOC for the medium reach (2 km) optical interconnect market. Several methods, such as surface relief structures [12], [13], triangular holey structures [14], and antiresonant reflecting optical waveguide structures [15], have been utilized to fabricate VCSELs with a relatively large active diameter, a (near) single-mode, and high-output optical power performance. However, not all the reported single-mode and high-power VCSEL structures may be suitable for the highspeed applications.…”

Высокоскоростные Полупроводниковые Вертикально-Излучающие Лазеры Для Оптических Систем Передачи Данных (Обзор)

“…Наиболее перспективным направлением для контроля модового состава ВИЛ [81] является формирование поверхностного рельефа путем локального травления выводного зеркала на глубину, кратную толщине четвертьволнового слоя РБО. Однако с точки зре-ния существенного повышения быстродействия ВИЛ данный подход выигрыша не обеспечивает [82] и преимущественно применяется для повышения дальности передачи данных при сохранении приемлемо высокой скорости [83,84].…”

High-speed 850 nm VCSELs with 28 GHz modulation bandwidth for short reach communication

“…Above these primary oxide layers, four 96% Al-content layers are included in the DBR to reduce the parasitic oxide capacitance which otherwise can limit high-speed performance. The p-doped GaAs contact layer is designed as an antiphase layer which enables the possibility of mode filter integration and post fabrication tuning of the photon lifetime (τ p ) [11,12]. The optical reflection from the top GaAs/air interface is initially completely out-of-phase with reflections further down in the DBR, resulting in a low reflectivity and a short phonon lifetime.…”