ATM-PON for Optical Communication
Special Edition on 21st Century Solutions
ATM-PON for Optical Communication
Transmission/Reception Optical Module
Miyuki KUDO*, Tokihiro TERASHIMA*, Tsutomu NAKAMURA**, Katsuyoshi NAITO***
Abstract
Recently, the term “IT revolution” has suddenly become well known and data communication networks represented by
the Internet have spread beyond the office and rapidly expanded its range to homes and individual users. The shape of
access system networks, that make it possible to provide service to each user, is diversifying. At the same time, there are
expectations that the FSAN (Full Service Access Networks) Group, which has been striving to quickly introduce an
economical high-speed, Broadband access system ATM-PON (Asynchronous Transfer Mode-based Passive Optical
Network) system as an optical transmission path for optical fibers will expand.1,2
FSAN is an organization centered on communications providers in America, Europe, and Japan. In order to have
common system specifications, this organization jointly investigated the issue from the development stage and aimed to
realize an optical access network that can flexibly respond to a wide variety of service demands. The ITU-T
(International Telecommunication Union, Telecommunication Standardization Sector) completed recommendations
G.983.1 and G.983.2 3,4, thereby establishing a unified world standard and establishing international standardization.
ATM-PON is a system that combines multimedia multiple speed multiplexing technology and ATM technology,
that has superior quality control functionality, with PON technology, that is expected to become more economical as
optical access networks are shared. System specifications must become common around the world in order to supply lowcost devices that make mass production possible before this system can expand. Lowering the cost of optical modules, which
account for most of the device cost, and developing mass production technology to secure supply are very important issues.
In this article, we would like to discuss the structure and characteristics of the low-cost 155.52 Mbps ONU (Optical
Network Unit) optical module that Oki developed for the ATM-PON system
ATM-PON System Overview
Structure of the ONU Optical Module
Figure 1 illustrates the structure of the ATM-PON system
stipulated in ITU-T recommendation G.983.1. This system consists of an OLT (Optical Line Terminal; an optical
subscriber terminating apparatus that multiple users have
on a network) and an ONU. The optical fiber that comprises the network is a one-core fiber that uses 1.3 µm band
single-mode fiber. The transmission format is an omnidirectional format that uses 1.3 µm band and 1.55 mm band
wavelength multiplexing. Upward signal light from ONU
to OLT uses the 1.3 µm band wavelength and has a transfer
rate of 155.52 Mbps. Downward signal light from OLT to
ONU uses the 1.55µm band and has a transfer rate of either
622.08 Mbps or 155.52 Mbps. The network that provides
optical cable from OLT to multiple users (ONU) consists
of an Optical Distribution Network (ODN). Optical branch
circuits such as optical splitters are used in this network.
The optical subscriber terminating apparatus ONU consists of a 1.55 µm band receiver, a photoelectric converter
(optical module) made up of 1.3 µm band emitters, and
electronic circuits.
Figure 2 illustrates the structure and outer appearance of
the recently developed ONU optical module. Table 1
indicates the module specifications. WDM (Wavelength
Division Multiplex) optical circuits, that multiplex and
demultiplex optical wavelengths of the 1.3 µm band and 1.5
mm band, use optical guided wave paths (Planar Lightwave
Circuit: PLC) that contain WDM filters. We selected the
PLC this time since, compared to the fiber coupler type or
space beam type, it has smaller integration, is suitable for
automating the assembly process and dominates in mass
production and cost reduction.
The WDM filters use polyimide filters to reduce costs.
We are able to multiplex/demultiplex the 1.3 µm band
wavelength and 1.5 µm band wavelength by inserting and
securing polyimide filters into dicing grooves at the PLC
branching locations. The polyimide filters follow the LWPF
(Long Wave Pass Filter) specifications. The 1.5 µm band
received wavelength input from the fiber passes through the
filters to be received by the reception PD (Photo Diode).
On the other hand, 1.3 µm band transmission LD (Laser
Diode) signal light is reflected by the filters, then is output
from the fiber.
Electrical cross-talk and optical cross-talk become a
problem with the ATM-ONU optical module since it
simultaneously drives transmission and reception. In order
*
Silicon Solutions Company, Components Div., Advanced Optical Devices Dept.,
Optical Module, Development Team 2
Silicon Solutions Company, Components Div., Advanced Optical Devices Dept.,
Optical Module, Development Team 2, Sub-team Leader
*** Silicon Solutions Company, Components Div., Advanced Optical Devices Dept.,
Optical Mudule, Development Team 2, Team Leader
**
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March 2001
OKI Technical Review 185
Vol. 68
Enterprise WDM Links
Enterprise
City
Hybrid Fiber Coax
Passive Optical Network
FSAN
Subscribers
OLT
ODN
ODN
ONU
ONU
Subscribers (Cable TV System)
ODN
1.3µm
ONU
Subscribers
1.5µm
Optical Access Network
OLT:Optical Line Termination
ODN:Optical Distribution Network
ATM-PON: Asynchronous Transfer Mode - Passive Optical Network
Figure 1: Structure of the ATM-PON System
to avoid the electrical cross-talk problem, the module we
introduce in this article employs an isolated mounting
structure that electrically insulates the transmission side
LD elements and the reception side PD elements from each
other. Since the transmission side LD and reception side
PD previously were mounted on the same Si substrate, it
was necessary to take steps such as separate the LD elements
and the PD elements by a sufficient distance or enhance the
GND in order to reduce electrical cross-talk. Therefore,
this structure was not conducive to realizing smaller size
and lower cost. However, we were able to strengthen the
electrical insulation by doing three things. First, use the
PLC as an insulator to isolate and connect the transmission
side Si substrate (1) that mounted the LD elements and
monitor PD elements, and the reception side Si substrate
(2) that mounted the reception PD elements. Second, pass
Si substrate (1) and Si substrate (2) mounted on PLCs
through a ceramic substrate. Third, mount them in a plastic
package along with a preamplifier. As a result, we were able
to further reduce the mounting distance between the LD
elements and the PD elements while avoiding the electrical
cross-talk problem. In other words, we made it possible to
miniaturize PLCs and achieve lower costs at the same time.
Regarding optical cross-talk however, it is necessary to
simultaneously satisfy transmission and reception especially in the transmission part that is detecting powerful
signals and in the reception part that is detecting weak
signals. Therefore, it is necessary for the reception part to
sufficiently block the 1.3 µm band wavelength, which is the
transmission wavelength. With this optical module, we
worked towards reducing cross-talk by inserting an LWPF
filter between the PLC reception terminal face and the
reception PD elements and coating the reception side Si
substrate (2) with stray light blocking resin potting.
Additionally, since the insulation structure we employed
made it possible to manage the yield of each component, we
became able to improve the yield of the overall module and
simplify our process management. As a result, we have
realized a cost reduction and can provide a module geared
towards mass production. The outer dimensions of the
module are as follows: 23.7 (L) ⫻ 8.2 (W) ⫻ 3.5 (H) mm.
Characteristics of the ONU Optical Module
Figure 3 illustrates the code error rate characteristics when
receiving a 155.52 Mbps signal. When simultaneously
transmitting and receiving, we were able to achieve a minimum light receiving sensitivity of -36dBm (BER=10-10) or
less in the temperature range from -40 to +85ºC and were
able to keep the resulting power penalty within 1dB. These
results sufficiently satisfy the minimum receiving light
sensitivity Class B and Class C specifications recommended
in ITU-T G983.1. Figure 4 illustrates the reception waveform (Pin = -35dBm, @25ºC). The reception light
sensitivity is 0.85 A/W (@25ºC), and the quantity of
fluctuation including the preamplifier is ±1dB or less
(@-40 to +85ºC). The light output characteristics of the
module were good as well. Fiber output Pf was 2.25 mW
(25 mA, @25ºC) and the tracking error was ±0.6dB or less
(@-40 to +85). Figure 5 illustrates the resulting light
output waveform. The results of the module internal return loss were also good. The return loss in the transmission wavelength was -15dB or less and the return loss in the
reception wavelength was -25dB or less.
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ATM-PON for Optical Communication
PRE-AMP
10-3
WDM filter
PLC-Chip
During Simultaneous
Transmission/Reception
Operation
PD-chip
Si-substrate(2)
Fiber Cover
-40ºC
25ºC
85ºC
Ceramic substrate
LD-Chip
MPD-Chip
Si-substrate(1)
Fiber
LD-Chip
PLC-Chip
Fiber Cover
Si-substrate(1)
PRE-AMP
PD-chip
Si-substrate(2)
Bit Error Rate
Fiber
Plastic Package
WDM filter
MPD-Chip
No Transmission
Operation
10-5
-40ºC
25ºC
85ºC
10-10
ClassC
ClassB
10-12
-40
-38
-36
-34
-32
Optical Input Power(dBm)
-30
Figure 3: Code Error Rate Characteristics (155.52 Mbps)
Conclusion
Figure 2: Structure and outer appearance of
ONU optical module
In this article, we introduced the low-cost 155.52 Mbps
ONU optical module that complies with international
standardization recommendation ITU-T G.983.1 for economical high-speed Broadband access system ATM-PON.
We confirmed being able to achieve sufficient characteristics in the module design evaluation and verification. The
most important topic for us will be achieving mass produc-
Rx Side
Tx Side
(Ta=-40 to 85°C)
Item
Transmission Rate
Light Output
Threshold Current
Center Wavelength
Spectrum Full Width at Half Maximum
Forward Voltage
Operating Current
Rising Time, Falling Time
Monitor Current
Monitor Dark Current
Tracking Errors
Power Supply Voltage
Light Receiving Sensitivity
Bias Voltage
Transimpedance
Rising Time, Falling Time
Return Loss
Symbol
Condition
Min. Value
Pf
Ith
␭c
⌬␭
Vop
Iop
CW
Pf=2.25mW, RMS
Pf=2.25mW, RMS(␴)
Pf=2.25mW
Pf=2.25mW
-2
tr, tf
Im
Id
Er
Pf=2.25mW
Pf=2.25mW
Ta=25°C
Im=const
@Pf=2.25mW (25°C)
Pin=3µW, Vcc=3.3V
Pin=0mW, Vcc=3.3+/-0.17V
10%-90%
␭=1480-1580nm
Vcc
Re
Vb
Zt
tr, tf
Rl
1270
80
-1
3.0
14
0.82
3.3
16
1.02
88
4
40
1360
5.8
1.45
80
Unit
Mbit/s
dBm
mA
nm
nm
V
mA
1
300
15
1
ns
µA
nA
dB
3.6
V
kV/W
V
dBΩ
ns
dB
Max. Value
1.22
3.9
20
Table 1: 155.52 Mbps ONU Optical Module Specifications
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Mean
155.52
March 2001
OKI Technical Review 185
Vol. 68
Figure 4: Light Reception Waveform (Pin = -35Bm, @25ºC)
tion that is geared towards generating business. We believe
that in order to accomplish this, we must secure reliability
for the module and must be flexible to respond to requests
for even lower cost modules. While anticipating the global
expansion of subsequent ATM-PON systems, we would
like to pay attention to the overall trend and expansion of
access systems.
References
1.
2.
3.
4.
Maeda, et al: Standardization Trend of High-speed
Broadband Access Networks, EIC Electronics Society
Newsletter, Vol. 83, No. 3, Pgs. 169-173, March,
2000.
Yokota, et al: Optical Access Systems, Oki Electric
Industry Co. Ltd. R&D Issue 182, Vol. 67, No. 1,
Pgs.19-22, April, 2000.
ITU-T Recommendation G.983.1 “Broadband optical access systems based on Passive Optical Networks
(PON)”, 1998.
ITU-T Recommendation G.983.2 “The ONT Management and Control Interface Specification for ATMPON,” COM 15-R44, June 1999.
Figure 5: Light Output Waveform (-40ºC to +85ºC)
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