Error-free transmission over 1.1 km of OM4 multimode fibre is demonstrated at 20 Gbit/s bit rate using a narrow spectral width, high-speed 850 nm vertical-cavity surface-emitting laser

Andrekson, Peter

Gustavsson, Johan S.

Haglund, Erik

Larsson, Anders

Safaisini, Rashid

Szczerba, Krzysztof

Westbergh, Petter

Gustavsson, Johan

Chalmers Research

20 Gbit/s error-free operation of 850 nm oxide-confined VCSELs beyond 1 km of multimode fibre

Chalmers Publication Library

Chalmers Publication Library
20 Gbit/s error-free operation of 850 nm oxide-confined VCSELs beyond 1 km of
multimode fibre
This document has been downloaded from Chalmers Publication Library (CPL). It is the author´s
version of a work that was accepted for publication in:
Electronics Letters (ISSN: 0013-5194)
Citation for the published paper:
Safaisini, R. ; Szczerba, K. ; Haglund, E. et al. (2012) "20 Gbit/s error-free operation of 850
nm oxide-confined VCSELs beyond 1 km of multimode fibre". Electronics Letters, vol.
48(19),  pp. 1225-U81.
http://dx.doi.org/10.1049/el.2012.2306
Downloaded from: http://publications.lib.chalmers.se/publication/165237
Notice: Changes introduced as a result of publishing processes such as copy-editing and
formatting may not be reflected in this document. For a definitive version of this work, please refer
to the published source. Please note that access to the published version might require a
subscription.
Chalmers Publication Library (CPL) offers the possibility of retrieving research publications produced at Chalmers
University of Technology. It covers all types of publications: articles, dissertations, licentiate theses, masters theses,
conference papers, reports etc. Since 2006 it is the official tool for Chalmers official publication statistics. To ensure that
Chalmers research results are disseminated as widely as possible, an Open Access Policy has been adopted.
The CPL service is administrated and maintained by Chalmers Library.
(article starts on next page)
20 Gb/s error-free operation of 850 nm 
oxide-confined VCSELs beyond 1 km of 
multi-mode fibre  
 
R. Safaisini, K. Szczerba, E. Haglund, P. Westbergh, J.S. 
Gustavsson,  A. Larsson, and P.A. Andrekson 
 
Error-free transmission over 1.1 km of OM4 multimode fibre is 
demonstrated at bit rates up to 20 Gb/s using a narrow spectral width, 
high speed 850 nm vertical-cavity surface-emitting laser. 
 
 
Introduction: Vertical-cavity surface-emitting lasers (VCSELs) 
operating at 850 nm are well suited in data communication applications 
due to their numerous advantages [1]. Fast data transmission (20 -
25 Gb/s) over longer multimode fibre (MMF) (approaching 1 km) is a 
growing demand for applications such as intra building links in large 
office areas and data centers, where longer fibre links are required. 
 One of the main challenges of high bit rate (BR) transmission over 
long MMFs arises from their limited bandwidth caused by the effects of 
chromatic and modal dispersion [2]. One way of achieving longer 
distance transmission is improving the VCSEL modal properties to 
reduce its emission spectral width [3, 4].             
 There have been various efforts on increasing the error free 
transmission BR and/or distance for 850 nm VCSELs over MMFs. 
40 Gb/s back-to-back (BTB) and 35 Gb/s over 100 m of MMF using a 
23 GHz modulation bandwidth VCSEL was reported in [5]. Results 
from attempts at longer distance transmission by reducing the emission 
spectral width were recently reported for 500 m of MMF using an 
integrated mode filter [6] as well as 300 m [4] and 603 m [7] of MMF 
using a quasi-single mode VCSEL at 25 Gb/s. The latter also employed 
1 km of MMF to transmit at up to 17 Gb/s [8]. In addition, there is a 
report on 850 nm VCSEL transmission at 40 Gb/s over 2 km, but using 
an advanced photonic crystal fibre [9]. 
 Here we present results from our recent work on 20 Gb/s data 
transmission over 1.1 km of OM4 MMF using a high speed (~20 GHz 
modulation bandwidth) 850 nm VCSEL with a limited number of 
emission transverse modes and narrow spectral width. The top 
distributed Bragg reflector (DBR) reflectivity of the quasi single mode 
VCSEL was optimized for high output power and low damping of the 
modulation response. To the best of the authors’ knowledge, the BR-
distance product is the highest ever reported for a link employing a 
directly modulated VCSEL and MMF. 
 
VCSEL design and dc measurements: The VCSEL design was 
optimized for high modulation bandwidth as described in detail in [10]. 
The epitaxial layers were MOVPE grown on a semi-insulating GaAs 
substrate. Most of the bottom n-type DBR consists of Si-doped 
AlAs/AlGaAs layers to facilitate heat transport from the active region 
by using the high thermal conductivity binary compound. The active 
region contains five strained InGaAs/AlGaAs quantum wells for 
improved differential gain [1]. Alternating layers of C-doped AlGaAs 
with different Al contents were employed as top p-type DBR. The 
present structure utilizes a multi-oxide scheme to lower the parasitic 
oxide capacitance. The VCSEL aperture is defined during the device 
fabrication by wet-oxidizing two 98% Al content layers placed right 
above the active region in the top DBR, followed by four additional 
96% Al content shallow oxide layers for capacitance reduction. 
VCSELs were fabricated through a standard high speed VCSEL process 
flow including mesa formation, metal contact deposition, wet oxidation, 
and planarization. As the last processing step, the reflectivity of the 
output coupling DBR was reduced to raise the output power and the 
slope efficiency. This step led to an approximately 40% enhancement in 
the maximum output power and slope efficiency with only a minimal 
increase in threshold current. Having a higher launched optical power is 
crucial for transmission over longer fibres.  
 The light-current-voltage (LIV) characteristics of a VCSEL with 
~3 μm oxide aperture diameter measured at 20°C is presented in Fig. 1. 
The device show a slope efficiency of 0.64 W/A with 0.19 mA 
threshold current and a 2 mW maximum output power occurring at 
5.7 mA roll over current. The optical emission spectrum of the VCSEL 
at 2.7 mA is shown in the inset of Fig. 1. The device operated primarily 
in the fundamental mode with a sidemode suppression ratio >30 dB at 
bias currents below 1.5 mA and approximately 20 dB at 2.7 mA with 
0.29 nm RMS spectral width. This narrow spectral width reduces the 
effects of chromatic and modal dispersion in the fibre for long distance 
transmission. 
 
 
Fig. 1 LIV characteristics of the ~3 μm aperture VCSEL.  
Inset: Optical spectrum at 2.7 mA.  
 
Transmission experiments: Large signal modulation performance of the 
VCSEL was evaluated by measuring the eye diagrams and bit error 
rates (BERs) for BTB configuration and after 500, 800, and 1100 m of 
MMF. Non-return-to-zero data pattern with a 27-1 bits long 
pseudorandom binary sequence generated by a SHF 12103A bit pattern 
generator was fed to the VCSEL through a linear SHF 807 amplifier 
with 24 dB gain in combination with a total of 23 dB attenuation and a 
30 GHz SHF 120A bias-T via a high speed probe. The linear amplifier 
was utilized to suppress unwanted microwave reflections, while its 
additional gain was mainly cancelled out by the attenuator. The light 
output was then butt-coupled to a 62.5 μm core diameter MMF by 
maximizing the coupled power with ~50% coupling efficiency before 
either launching to a 50 μm core diameter OM4 MMF or directly to a 
photoreceiver for BTB measurement. The photoreceiver package 
contains a New Focus 1580 photodiode with 12 GHz bandwidth and an 
integrated transimpedance amplifier. Use of a photoreceiver package 
can effectively reduce the noise level and improve the signal quality. 
However, the available photoreceiver has a limited bandwidth and thus 
is a limiting factor for measuring at very high BRs. A JDSU OLA-54 
variable optical attenuator was placed before the photoreceiver to adjust 
the received power for the BER measurement. The output signal of the 
photoreceiver was then used to measure eye diagrams using an Agilent 
Infiniium DCA-J 86100C 70 GHz digital communications analyzer or 
to perform BER analysis using a SHF 11100B error analyzer. The 
VCSEL was biased at 2.7 mA with a peak-to-peak modulation voltage 
of 0.95 V. 
 
Results and discussion: Inverted eye diagrams for BTB, 500, 800, and 
1100 m transmission at 20 Gb/s are shown in Fig. 2. The corresponding 
BER results are presented in Fig. 3. Open eyes and error-free (BER<10-
12) operation at 20 Gb/s were achieved for up to 1100 m of MMF with a 
power penalty of ~2 dB at 1100 m transmission and a VCSEL energy 
dissipation of 280 fJ/bit. The BTB sensitivity is within 1 dB of the 
theoretical performance, accounting for the 12 GHz receiver bandwidth 
and the resulting intersymbol interference penalty. The eye diagrams 
after transmission over 1100 m of MMF suggest that fibre dispersion is 
not a limiting factor and even longer transmission distances should be 
possible. Unfortunately the received optical power was limited by fibre 
and connector losses. The reduced VCSEL spectral width directly 
reduces the effects of chromatic fibre dispersion while it indirectly also 
reduces the effects of modal dispersion since the quasi single mode 
VCSEL excites a reduced number of fibre modes. The eye diagrams 
also show the same amount of noise for both ones and zeros, suggesting 
that the relative intensity noise (and mode partition noise in particular) 
is not a limiting factor for these quasi-single mode VCSELs. 
 
1 
 
 
 
Fig. 2 Inverted eye diagrams of the received signal after BTB, 500, 800 
and 1100 m transmission on MMF. 
 
 
 
Fig. 3 BER results obtained for 20 Gb/s transmission over up to 1100 m 
of MMF. 
 
Conclusion: A high-speed, oxide-confined, quasi single mode 850 nm 
VCSEL has been fabricated and used in transmission experiments. 
Narrow spectral width and high output power allow for 20 Gb/s error-
free transmission over 1100 m of MMF as shown by open eye diagrams 
and BER measurements.   
 
Acknowledgments: The epitaxial VCSEL material was provided by IQE 
Europe Ltd. This work was supported by the Swedish Foundation for 
Strategic Research.  
 
 
 
R. Safaisini, K. Szczerba, E. Haglund, P. Westbergh, J.S. Gustavsson,  
A. Larsson M. Karlsson, and P.A. Andrekson (Department of 
Microtechnology and Nanoscience, Photonics Laboratory, Chalmers 
University of Technology, SE-41296 Göteborg, Sweden) 
 
E-mail: rashid.safaisini@chalmers.se  
 
 
References 
1  A. Larsson, “Advances in VCSELs for communication and sensing,” 
IEEE Journal of Selected Topics in Quantum Electronics, vol. 17, no. 6, 
pp. 1552–1567, Nov./Dec. 2011. 
 
2   A. Gholami, D. Molin, and P. Sillard, “Compensation of chromatic 
dispersion by modal dispersion in MMF- and VCSEL-based gigabit 
ethernet transmissions,” IEEE Photonics Technology Letters, vol. 21, 
no. 10, pp. 645–647, May 2009. 
 
3  P. Pepeljugoski, D. Kuchta, Y. Kwark, P. Pleunis, and G. Kuyt, 
“15.6-Gb/s transmission over 1 km of next generation multimode fiber,” 
IEEE Photonics Technology Letters, vol. 14, no. 5, pp. 717–719, May 
2002. 
 
4  G. Fiol, J. A. Lott, N. N. Ledentsov, and D. Bimberg, “Multimode 
optical fibre communication at 25 Gbit/s over 300 m with small 
spectral-width 850 nm VCSELs,” Electronics Letters, vol. 47, no. 14, 
pp. 810–811, Jul. 2011. 
 
5  P. Westbergh, J. S. Gustavsson, B. Kögel, Å. Haglund, A. Larsson, 
A. Mutig, A. Nadtochiy, D. Bimberg, and A. Joel, “40 Gbit/s error-free 
operation of oxide-confined 850 nm VCSEL,” Electronics Letters, vol. 
46, no. 14, pp. 1014–1015, Jul. 2010. 
 
6  E. Haglund, Å. Haglund, P. Westbergh, J. S. Gustavsson, B. Kögel, 
and A. Larsson, “25 Gbit/s transmission over 500 m multimode fibre 
using 850 nm VCSEL with integrated mode filter,” Electronics Letters, 
vol. 48, no. 9, pp. 517–518, Apr. 2012. 
 
7  J. A. Lott, P. Moser, A. Payusov, S. Blokhin, P. Wolf, G. Larisch, N. 
N. Ledentsov, and D. Bimberg, “Energy efficient 850 nm VCSELs 
operating error-free at 25 Gb/s over multimode optical fiber up to 600 
m,” IEEE Optical Interconnects Conference, May 2012. 
 
8  P. Moser, P. Wolf, J. A. Lott, G. Larisch, A. Payusov, A. Mutig, W. 
Unrau, N. N. Ledentsov, W. Hofmann, and D. Bimberg, “High-speed 
VCSELs for energy efficient computer interconnects,” Proc. SPIE, vol. 
8432, pp. 843202-1–843202-8, 2007. 
 
9  H. Hasegawa, Y. Oikawa, T. Hirooka, and M. Nakazawa, “40 Gbit/s-
2 km photonic crystal fibre transmission with 850 nm singlemode 
VCSEL,” Electronics Letters, vol. 43, no. 11, pp. 642–644, May 2007. 
 
10  P. Westbergh, J. S. Gustavsson, B. Kögel, Å. Haglund, and A. 
Larsson, “Impact of photon lifetime on high-speed VCSEL 
performance,” IEEE Journal of Selected Topics in Quantum 
Electronics, vol. 17, no. 6, pp. 1603–1613, Nov./Dec. 2011. 
 
2 
 


20 Gbit/s error-free operation of 850 nm oxide-confined VCSELs beyond 1 km of multimode fibre

Abstract

Similar works

Full text

Available Versions

Chalmers Research

Chalmers Publication Library