Widedynamic Range APD Burst Receiver for 2'4Gbits PON System

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Wide-dynamic Range APD Burst Receiver for
2.4Gbit/s PON System
Takashi Nakanishi, Ken-Ichi Suzuki, and Yoichi
Maeda
NTT Access Network Service Systems Laboratories,
NTT Corporation
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Contents
I. Background II. Burst receiver for PON
systems III. Application of APD burst
receiver IV. Experiment and results V.
Summary
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Background (1/3)

• PONs provide cost-effective access systems
  because the transmission fiber and the central
  office equipment can be shared by several
  customers.
• PON systems are popular as major FTTx systems
  around the world.

Access network
ONU
Optical splitter
Optical fiber
ONU
OLT
ONU
OLT Optical Line Terminal ONU Optical Network
Unit
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Background (2/3)
Demands placed on PON systems
Higher speed
Wider area

• Explosive spread of Internet applications
• Advent of new services such as IP phones,
  Video-on-Demand (VoD), and the home network

• OLT has to be able to accommodate as many
  customers as possible and as efficiently as
  possible.
• Increase transmission distance in areas with
  relatively low service demand.
• Increase splitting number in areas with
  relatively high service demand.

The above requirements can be satisfied by
expanding the allowable optical attenuation
range between OLT and optical network units
(ONUs)
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Background (3/3)
Increasing the optical transmission power
increases ONU cost, destroys the cost advantage
of PON systems
Using an optical amplifier before the optical
receiver
already studied burst-mode optical amplifier
based on a gain-clamped praseodymium-doped fiber
amplifier (PDFA)
Use an avalanche photo diode (APD) receiver
Access network
ONU
Optical splitter
Optical fiber
ONU
OLT
Optical amplifier
ONU
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Burst receiver for PON systems

• Downstream signals are continuous wave, but
  upstream signals are burst signals, so the OLT
  must be able to receive burst signals.

Optical splitter
ONU
OLT
Upstream wavelength 1310nm region
Differential distances between ONUs
Downstream wavelength 1490nm region
ONU
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Burst receiver for PON systems

• APD requirements in the OLT receiver
• Degradation in dynamic range because of strong
  optical input
• Interference of transient response signals

Strong burst
Optical burst signal with differential power
Dynamic range
Weak burst
Guard time
Preamble
Delimiter
Overhead
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Application of APD burst receiver to PON systems
Control the avalanche gain ( M ) by monitoring
the average power level of each burst signal
Strong inputlow voltage Weak inputhigh voltage
Level decision and generate APD bias control
signal
APD bias circuit
Input signal
Strong optical input makes dynamic range narrow
APD
Data decision
AGC circuit
Pre-amplifier
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Application of APD burst receiver to PON systems
Relationship between M and APD bias voltage in
this experiment.
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10
8
6
Multiplication factor
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2.5
2
0
10
15
20
25
30
35
40
VAPD V
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Application of APD burst receiver to PON systems
APD burst receiver must suppress other signals
within the 25.7 ns guard time.
G-PON upstream physical layer overhead
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Application of APD burst receiver to PON systems
G-PON optical interface specifications
1244Mbit/s upstream
G-PON DS 2.4Gbps US 1.2Gbps
Class B Sensitivity -28dBm Dynamic range 20dB
( )with control of ONU power level. using
APD receiver for OLT, ONU Tx minimum -7 dBm, ONU
Tx maximum -2 dBm, OLT Rx overload -7 dBm, OLT
Rx sensitivity -28 dBm.
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Our purpose
To achieve a burst receiver that has high
sensitivity and wide-dynamic range in PON
systems.
Our proposal
To control the avalanche gain by monitoring the
average power level of burst signals.
Our aim

• Improve the dynamic range of an APD burst
  receiver without increasing the burst overhead of
  a 2.4 Gbit/s G-PON system.
• Achieve receiver sensitivity of -28 dBm _at_ 2.4
  Gbit/s.

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Experimental setup
The optical burst signals were output by the AOM.
The output of APD circuit was measured by an
error detector and a sampling oscilloscope.
1km
APD circuit
1300nm
3dB coupler
3dB coupler
PC
LN
AOM
LD
data
burst
PPG
ED
LD
AOM
Laser Diode
Acoustic Optic Modulator
LN
PPG
Pulse Pattern Generator
LN Modulator
PC
ED
Polarization Controller
Error Detector
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Frame format
Proposed APD receiver requires a reset signal to
set M 10 for each burst signal.
ONU1 (-6dBm)
10 sequence
PN code
ONU2
Optical input
Overhead
Data
Reset signal
8 - 16bits
M
M2.5
M10
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TIA output without reset signal _at_ 1.2Gbps
Because following burst signal was strong.
influence of transient response signal was weak.
Because following burst signal was weak,
influence of transient response signal was strong.
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TIA output with reset signal _at_ 1.2Gbps
20ns
-6dBm
-30dBm
Influence of transient response signal was weak
because M was set to 10 by reset signal.
Close up
-6dBm
-30dBm
10ns
Influence of reset signal
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Frame format 2
To confirm interference of transient signals, we
inserted a 10 sequence between burst frames,
then measured BER.
ONU1 (-6dBm)
ONU2
10 sequence
PN code
Optical input
Start error count
128bits
1024bits
Reset signal
8 - 16bits
M10
M2.5
M
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BER result 1
-29.0
-29.2
-29.4

• Influence of transient response signals is not
  shown after 40bits.
• Supports 2.4Gbps application?

-29.6
Sensitivity for achieving 10-10 BER dBm
-29.8
-30.0
-30.2
-30.4
140
20
0
40
60
80
100
120
Number of transit bits from strong burst end bit
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TIA and LIM-AMP outputs with reset signal _at_
2.4Gbps
Influence of transient response signals is not
evident.
TIA output signal
LIM-AMP output signal
Received optical signal
Received optical signal
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BER result 2
Cont. signal (Freq. 1.2Gbps)
Burst LIM
10-4
Burst signal (Freq. 1.2Gbps)
Burst LIM
Cont. signal (Freq. 2.4Gbps)
Cont. LIM
10-5
Cont. signal (Freq. 2.4Gbps)
Burst LIM
PRBS 2(7)-1
10-6

• Bandwidth of burst LIM was not enough.
• To apply proposed APD to 2.4Gbps PON systems, we
  have to optimize the burst LIM.

10-7
bit error rate
10-8
10-9
10-10
10-11
10-12
10-13
-30
-31
-32
-33
-34
-35
-36
-40
-37
-38
-39
-24
-25
-26
-27
-28
-29
average received power dBm
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Summary

• We proposed to extend APD by adding M control and
  so create a high performance PON system.
• We confirmed that the transient response signal
  generated after the burst signal can be
  suppressed in the G-PON guard time of 2.4Gbit/s
  transmission rate.
• We also confirmed that it improved dynamic range
  (about 24 dB) _at_ 1.2Gbps.

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Thank you for your attention.