This paper will review the VCSEL performance requirements and link length limitations to support next generation 53Gbaud line rates with PAM-4 modulation for 100G per lane multi-mode optical links for both active optical cables and transceivers. VCSEL performance with bandwidth in excess of 25GHz and relative intensity noise lower than -145dB/Hz will be needed to enable this next generation of multi-mode links. VCSEL device performance and associated wear out life data will be included.
The development of robust next generation multi-mode VCSEL-based optical links requires an accounting of all penalties in the link. While limitations from fiber bandwidth can be overcome to a significant extent using equalization and forward error correction, noise in the link cannot be equalized. Measurements show that mode partition noise depends on launch condition, and the noise penalty can be decreased using devices with small k factor. Time and frequency domain characterization of mode power fluctuations shows that they occur primarily at frequencies below 5 GHz. These findings guide the development of VCSELs for 25GBaud PAM4 and higher bit rate applications.
This paper will review the device design and performance of Broadcom’s 50Gb/s PAM-4 VCSEL to enable the next generation of transceivers using a PAM-4 advanced modulation scheme at 25-28 GBd. The VCSEL has been optimized to minimize noise and improve dynamic performance for cleaner eyes. Preliminary wear out lifetime studies indicate that the time to 1% failure exceeds 10 years, making the VCSELs suitable for data communication applications.
Mode partition noise (MPN) can become the dominant limitation in 850 nm VCSEL-based multi-mode fiber (MMF) links at high data rates. Fluctuations in the partition of energy between the transverse modes of the VCSEL combined with the chromatic dispersion in the fiber leads to intensity noise at the receiver. The impact of MPN on non-equalized and equalized links has been studied with a numerical model of the VCSEL and MMF. The MPN in 25 Gb/s VCSELs has been investigated by examining noise in individual mode groups isolated using a thin film Fabry-Perot filter. The measured k factor below 0.15 should enable links significantly longer than 100 m at 25 Gb/s and higher data rates.
Avago’s 850nm VCSELs for applications requiring modulation at 25-28Gbps have been designed for -3dB bandwidths in excess of 19GHz over the extended temperature range of 0-85°C. The DBR mirrors have been optimized to minimize optical losses and thermal and electrical resistance. The active region is designed to provide superior differential gain for high optical bandwidth. In this paper we will describe the design for performance and manufacturability of Avago’s high speed 25-28Gbps VCSEL. Analysis of the high-speed modulation characteristics and results of wearout reliability studies will be presented. We will also discuss the manufacturability of this next generation of high performance, reliable lasers. The challenges of epitaxial growth and wafer fabrication along with the associated process control technologies will be described.
Avago’s 850nm oxide VCSEL for applications requiring modulation at 25-28G has been designed for -3dB bandwidths in excess of 18GHz over an extended temperature range of 0-85C. The VCSEL has been optimized to minimize DBR mirror thermal resistivity, electrical resistance and optical losses from free carrier absorption. The active region is designed for superior differential gain to enable high optical bandwidths. The small-signal modulation response has been characterized and the large-signal eye diagrams show excellent high-speed performance. Characterization data on other link parameters such as relative intensity noise and spectral width will also be presented.
In this paper we will discuss 14 Gb/s 850 nm oxide VCSEL performance and reliability. The device is targeted for the
16G Fibre Channel standard. The 14 Gb/s 850 nm oxide VCSEL meets the standard's specifications over the extended
temperature range to support transceiver module operation from 0C to 85C.
In this paper we report a 850nm oxide VCSEL operating at 20 Gbit/s (PRBS31) with a 5 dB Extinction Ratio,
based on a volume manufacturing platform with MOCVD grown GaAs/AlGaAs epi-material. We present
detailed time and frequency domain VCSEL characterization results, and a finite element simulation showing
good agreement with experimental data.
Directly modulated 850nm oxide VCSEL is a key enabling technology for short reach, high speed
data-communication applications. Current commercially available optical transceiver products operate at data rate
up to 10Gb/s per channel, for aggregate data rate of 70Gb/s and beyond, in the case of parallel optical data link.
High volume, low cost, over temperature optical modulation speed, spectral width, output power, thermal power
budget, large signal electrical interaction with the IC driver, and reliability are some of the key requirements
driving the 850nm oxide VCSEL development. In this paper, we discuss some of the engineering issues
investigated for developing a viable oxide VCSEL product operating at 10Gb/s per channel and higher data rate.
Super-luminescent laser diodes (SLD) in 800 to 1300 nm wavelength windows have been widely used in optical
coherence tomography (OCT) systems. The imaging resolution of OCT systems is proportional to the bandwidth of the
SLD light source. Here we present a new design to achieve broad bandwidth (>100nm at 1310nm) in one chip by using
two types of quantum wells.
The bandwidth of an SLD with a single active region is determined by the material bandwidth, confinement factor, and
the length of the active region. Neglecting spatial hole burning (SHB), the spectral density of amplified spontaneous
emission (ASE) can be the function of cavity length and spectral density of spontaneous emission and net gain. The main
factor that limits the ASE bandwidth is the net gain. The bandwidth of net gain has to be larger than 200 nm to obtain a
100 nm wide ASE spectrum if the ASE power is larger than several mW.
SLDs usually work at very high pump current (>400mA) to achieve high output power. From simulations, we found the
level of electron injection mainly determines the material gain. At the high injection level, large bandgap quantum wells
can get high gain and dominate the spectrum if the improper design is used. So in our design, we put the small bandgap
quantum wells at the N side to make the electron distribution in favor of long-wavelength material. Thus, and will be
balanced at high current injection level (>550mA). Figure 7 shows the measured spectrum of such structure. The
achieved spectral width is larger than 100nm and out put power is larger than 5 mW.
A unique design approach was proposed and applied to fabricate in a single chip ultra broad bandwidth and high power Superluminescent Emitting Diodes (SLEDs) at 820 nm, 1300 nm and 1550 nm windows. More than 2.5 mW, 20 mW, and 5mW of output power with a bandwidth of more than 50nm, 80 nm and 100 nm have been obtained for 820 nm, 1300 nm and 1550 nm wavelength windows, respectively. The devices were evaluated for optical coherence domain reflectometry (OCDR) and optical coherence tomography (OCT) applications, and coherence function data is quite good with a coherence measurement out to 10 mm with negligible artifacts.
Polarization-insensitive high power MQW superluminescent emitting diodes (SLEDs) were fabricated at 1300 nm with a very wide bandwidth of more than 60 nm and a very low spectrum modulation of 0.1 dB by combining high quality AR coating and several proprietary technologies including tilted cavity, window region and absorption region. Polarization dependence as low as 0.2 dB and more than 12 mW output power were obtained at 250 mA. The devices were evaluated for optical coherence domain reflectometer (OCDR) applications, and the coherence function data was quite good with a coherence measurement out to 10 mm with negligible artifacts. Devices with different cavity lengths were also fabricated and analyzed.