Optical Transmitter Based on a 1.3-μm VCSEL and a SiGe Driver Circuit for Short-Reach Applications and Beyond

Abstract

Long-wavelength vertical-cavity surface-emitting lasers (LW-VCSELs) with emission wavelength in the 1.3-µm region for intensity modulation (IM)/direct detection optical transmissions enable longer fiber reach compared to C-band VCSELs, thanks to the extremely low chromatic dispersion impact at that wavelength. A lot of effort has been recently dedicated to novel cavity designs in order to enhance LW-VCSELs' modulation bandwidth to allow higher data rates. Another approach to further improve VCSEL-based IM speed consists of making use of dedicated driver circuits implementing feedforward equalization (FFE). In this paper, we present a transmitter assembly incorporating a fourchannel 0.13-µm SiGe driver circuit wire-bonded to a novel dual 1.3-µm VCSEL array. The short-cavity indium phosphide buried tunnel junction VCSEL design minimizes both the photon lifetime and the device parasitic currents. The integrated driver circuit requires 2.5-V supply voltage only due to the implementation of a pseudobalanced regulator; it includes a two-tap asymmetric FFE, where magnitude, sign, relative delay, and pulse width distortion of the taps can be modified. Through the proposed transmitter, standard single-mode fiber reach of 20 and 4.5 km, respectively, for 28-and 40-Gb/s data rate has been demonstrated with stateof-the-art power consumption. Transmitter performance has been analyzed through pseudorandom bit sequences of both 2 7 −1 and 2 31 −1 length, and the additional benefit due to the use of the driver circuit has been discussed in detail. A final comparison with stateof-the-art VCSEL drivers is also includedt.

Beyond 50 Gb/s Directly-Modulated Long-Wavelength VCSELs for Next-Gen Access Network

“…Moreover, high relaxation-resonance frequencies, and reduced parasitic effects guarantee high-speed modulations [6]. Both O and C band devices present a current aperture of about 5 µm and an effective cavity length of 2.5 µm leading to modulation bandwidths up to 20 GHz with relative intensity noise below -140 dB/Hz [4,5]. In Fig.…”

“…In order to further increase the line rate to 50 Gb/s, a suitable solution could be the adoption of fixed wavelength short-cavity (SC) VCSELs, reliable both in O and C bands and providing modulation bandwidths up to 17 GHz [4,5]. Since chromatic dispersion (CD) is the main impairment when increasing the serial rate beyond 25 Gb/s in an IM/DD system, we evaluate the resilience of DMT modulation for fiber lengths compliant with access distances in case of single sideband (SSB) filtering using suitable simulations.…”

DSP-free and real-time NRZ transmission of 50Gb/s over 15km SSMF and 64Gb/s back-to-back with a 1.3µm VCSEL

“…Fiber reaches for these applications range from 100m up to 2km for intra data center links and at least 10km for inter data center links. While many proposed solutions rely on external modulation implemented in III-V or Silicon Photonics material systems [2,3], links based on directly modulated VCSELs have the potential to provide low power, low cost and low complexity solutions [4][5][6][7][8][9][10]. In [4][5][6], short wavelength multimode VCSELs were reported that achieve bitrates as high as 100Gb/s.…”

“…However, transmission in the Cband is limited by chromatic dispersion in standard single-mode fiber (SSMF) and hence O-band VCSELs are promising to achieve a higher bitrate x distance product. In [10], a directly modulated link using a 1325nm VCSEL is reported, capable of reaching 28Gb/s using NRZ over 20km and 40Gb/s over 4.5km. Link performance is limited by the bandwidth of the O-band VCSEL, which is still less compared to state of the art C-band VCSELs.…”

“…Therefore, here we demonstrate a link using the same O-band VCSEL from [10], now combined with a transmitside analog 6-tap feedforward equalizer (FFE), without relying on any DSP. Bit-error rates (BERs) were measured in real-time (without any offline processing) and no optical amplification was used to overcome link losses.…”