Chromatic Dispersion Limited Link Lengths for SWL and LWL Fiber Systems IEEE 802 Plenary Meeting Vancouver, BC November 11-15, 1996 David Cunningham, Leonid Kazovsky* and M. Nowell Hewlett-Packard Laboratories Filton Road Stoke Gifford Bristol BS12 6QZ UK Phone: +44 117 9228749 e-mail: dgc@hplb.hpl.hp.com  * On sabbatical at Hewlett-Packard Laboratories from Stanford University, Stanford, CA, 94305-4055
Outline Two basic effects of chromatic dispersion Pulse broadening Mode partition noise Penalties Additional effect of other noise terms Summary
Two basic effects of chromatic dispersion Chromatic dispersion is caused by the different propagation velocities of light components having different colours. It leads to two different effects: pulse spread, resulting in ISI; Mode Partition Noise (MPN)
Pulse broadening The value of the ISI-caused chromatic dispersion penalty (in db) can be estimated as follows[1]: αisi = 5 log [ 1 + 2 π ( B D L σ ) ] 2 where B is Baud rate, D is fiber chromatic dispersion coefficient, L is link length and σ is the RMS spectral width of laser
Mode partition noise Partitioning of laser power between laser modes does not change the total transmitted power and does not cause additional noise at the laser output. However, different laser modes travel at different velocities in the MMF. As a result, power fluctuations between modes lead to MPN at the fiber output. Â
Mode partition noise penalty The power penalty in db due to MPN can be estimated as [1]: 2 2 αmpn = 5 log [ 1 / ( 1 - Qa σmpn ) ] where A is the desired argument of 1/2-1 2 BER(Q) = [ Q ( 2 π ) ] exp( - Q / 2 ) and σmpn = (k / 2)[ 1 - exp{ - (π B D L σ ) } ] 2 Â σmpn is the MPN variance and the other terms as previously defined.
Penalties: Long Wavelength Lasers Near 1300nm D is approximately zero so D is estimated using: D = S ( λ0 - λd ) where S is the dispersion slope, λ0 is the source mean wavelength and λd is the MMF zero dispersion wavelength. Â
0 Optical Power Penalty (db) 0.5 1 1.5 Dispersion minimum 1300 nm Dispersion minimum 1320 nm Dispersion minimum 1300 nm Dispersion minimum 1320 nm Centre Wavelength (nm) Centre Wavelength (nm) 1250 1300 1350 1400 1250 1300 1350 1400 0 0.1 L 3 λd 1300 S. 0.102 10 12 Optical Power Penalty (db) 0.2 B. 1.25 10 9 MPN Penalty SMF, 3 km, 6 nm rms MPN Penalty SMF, 3 km, 4 nm rms Penalties: Long Wavelength Lasers, SMF, k=1
Optical Power Penalty (db) 0.05 λ0 1270, 1270.5.. 1355 S 0.093. 10 12 λd 1365 B. 1.25 10 9 6 nm rms 4 nm rms 6 nm rms 4 nm rms Centre Wavelength (nm) Centre Wavelength (nm) 1250 1300 1350 1400 1250 1300 1350 1400 Optical Power Penalty (db) 1 2 MPN Penalty 62MMF, 1 km MPN Penalty 62MMF, 2 km Penalties: Long Wavelength Lasers, 62MMF, k=1
1 10 23 1 10 22 1 10 21 1 10 20 1 10 19 1 10 18 BER 1 10 17 1 10 16 1 10 15 1 10 14 1 10 13 1 10 12 1 10 11-0. -0.ÀÆÀ2). -0.À2).ÀÆÀMODALÀNOISE 4 nm rms, k = 1, MSL = 0 4 nm rms, k = 0.5, MSL = 0 4 nm rms, k = 1, MSL = 0 4 nm rms, k = 0.5, MSL = 0 4 nm rms, k = 1, MSL = 1 db 4 nm rms, k = 0.5, MSL = 1 db Length (km) Length (km) Length (km) 0 2 4 6 0 2 4 6 0 2 4 6 1 10 21 1 10 21 1 10 20 1 10 20 1 10 19 1 10 19 1 10 18 1 10 18 1 10 17 1 10 17 1 10 16 1 10 16 BER 1 10 14 1 10 15 BER 1 10 14 1 10 15 1 10 13 1 10 13 1 10 12 1 10 12 1 10 11 1 10 11 1 10 10 1 10 10 1 10 9 1 10 9 BER vs Length (1300nm, -125 db/hz) 1 10 8 BER vs Length (1300nm, -116 db/hz) 1 10 8 BER vs Length (1300nm, -116 db/hz) Additional effect of other noise terms
Optical Power Penalty (db) 3 2 1 Penalties: Long Wavelength Lasers, SMF, k=1 Theoretical Penalty SMF, 2 nm rms Experimental results at a centre wavelength of 1285 at 1 Gb/s: 1 db penalty for 10 km of SMF 2 db penalty for 15 km of SMF Bit rate increased to 1.4 Gb/s and a BER floor at 10-12 observed. 1280 1285 1290 15 km 10 km Centre Wavelength (nm)
ISI, rms width 4 nm MPN, k=1 Sum ISI, rms width 2 nm MPN, k=1 Sum Link Length (km) Link Length (km) 0 0.1 0.2 0.3 0.2 0.25 0.3 0.35 0.4 0.45 0 0 Power Penalty (db) 4 2 Power Penalty (db) 4 2 6 6 MPN Penalty vs Dispersion (1.25 Gb/s) Dispersion Penalties versus length MPN Penalty vs Dispersion (1.25 Gb/s Penalties: Short Wavelength Lasers (770 nm ), 50MMF, k=1, B = 1.25 Gb/s, D = 140 ps/nm
0 0.1 0.2 0.3 0.4 Â ISI, rms width 4 nm MPN, k=1/2 Sum ISI, rms width 2 nm MPN, k=1/2 Sum Link Length (km) Link Length (km) 0.3 0.4 0.5 0.6 0.7 0 0 Power Penalty (db) 6 4 2 Power Penalty (db) 6 4 2 8 8 MPN Penalty vs Dispersion (1.25 Gb/s) Dispersion Penalties versus length MPN Penalty vs Dispersion (1.25 Gb/s) Penalties: Short Wavelength Lasers (770 nm ), 50MMF, k=0.5, B = 1.25 Gb/s, D = 140 ps/nm
Power Penalty (db) 10 5 0 ISI, rms width 4 nm MPN, k=1 Sum ISI, rms width 2 nm MPN, k=1 Sum Link Length (km) Link Length (km) 0 0.1 0.2 0.3 0.4 0.2 0.3 0.4 0.5 0.6 0 Power Penalty (db) 5 10 MPN Penalty vs Dispersion (1.25 Gb/s) Dispersion Penalties versus length MPN Penalty vs Dispersion (1.25 Gb/s) Penalties: Short Wavelength Lasers (840 nm ), 50MMF, k=1, B = 1.25 Gb/s, D = 100 ps/nm
ISI, rms width 4 nm MPN, k=1/2 Sum 0 0.2 0.4 0.6 6 4 2 Link Length (km) 8 0 Power Penalty (db) ISI, rms width 2 nm MPN, k=1/2 Sum Link Length (km) 0.4 0.6 0.8 1 0 2 Power Penalty (db) 6 4 8 MPN Penalty vs Dispersion (1.25 Gb/s) MPN Penalty vs Dispersion (1.25 Gb/s) Dispersion Penalties versus length Penalties: Short Wavelength Lasers (840 nm ), 50MMF, k=0.5, B = 1.25 Gb/s, D = 100 ps/nm
Mode Partition Noise - Experimental Set up ILX Temp. & current control GPIB control DUT 50MMF Variable attenuator BERT Power Meter 10% Photodiode 90% Clock & Data Recovery Laser temperature could be ramped or held constant
Experimental results 50MMF had high modal BW to ensure low ISI penalty. 300m 500m  700m 1km BER 1E-6 1E-7 1E-8 1E-9 1E-10 1E-11 BER measurement Laser a 1km 0km 0.5km -21-20 -19-18 -17-16 -15 Received Power (dbm)
Experimental Penalties: Short wavelength Lasers laser λ RMS width 300m 50MMF 500m 50MMF 700m 50MMF 1km 50MMF a 780nm 0.79nm - 1 db penalty - floor @ 10^-10 b 850nm 0.85nm - - - <1dB penalty c 850nm 1.13nm - - 1dB penalty (floor@10^-11 when MSL present) floor @ 10^-11 d 850nm 0.62nm floor @ 10^-11 floor @ 10^-9 - floor @ 10^-6 Â e 850nm 0.49nm - >1dB penalty (floor @ 10^-11 when MSL present) - floor @ 10^-9 À.OTÀMEASURED
1 10 14 1 10 15 1 10 16 1 10 17 1 10 18 1 10 19 1 10 20 1 10 21 1 10 22 1 10 23 Â -0. -0.ÀÆÀ2). -0.À2).ÀÆÀMODALÀNOISE 2 nm rms, k = 1, MSL = 0 2 nm rms, k = 0.5, MSL = 0 2 nm rms, k = 1, MSL = 0 2 nm rms, k = 0.5, MSL = 0 2 nm rms, k = 1, MSL = 1dB 2 nm rms, k = 0.5, MSL = 1 db Length (km) Length (km) Length (km) 0 0.5 1 0 0.5 1 0 0.5 1 1 10 13 1 10 14 1 10 15 1 10 16 1 10 17 1 10 18 1 10 19 1 10 20 1 10 21 1 10 20 1 10 19 1 10 18 1 10 16 1 10 17 1 10 15 1 10 12 1 10 13 1 10 14 BER 1 10 5 1 10 6 1 10 7 1 10 8 1 10 9 1 10 10 1 10 11 1 10 12 1 10 13 BER 1 10 5 1 10 6 1 10 7 1 10 8 1 10 9 1 10 10 1 10 11 1 10 12 BER 1 10 11 1 10 10 1 10 8 1 10 9 1 10 7 1 10 6 0.1 0.01 0.001 1 10 4 0.1 0.01 0.001 1 10 4 0.001 1 10 4 1 10 5 0.01 0.1 BER vs Length (770nm, -125 db/hz) BER vs Length (770nm, -116 db/hz) BER vs Length (770nm, -116 db/h Additional effect of other noise terms
Summary 6 lasers from different manufacturers for MMF data communication at Gb/s rates were tested: lasers were all edge emitters (Fabry-Perot) all exhibited penalties due to MPN and chromatic dispersion induce ISI Preliminary Recommendations: MPN must be taken into account in specifications LWL maximum RMS width of 4nm for 3km SMF links SWL maximum RMS width < 2nm for 500m links