Development of 10 Gb/s Tunable Transponder Module
By Hiroyuki Itohara *, Masafumi Tabara * and Nobuya Shinoda *Because transponder modules of fixed (non-tunable) wavelength have been usedin DWDM transmission, a number of module varieties corresponding to the number of individual wavelengths must be provided. A tunable transponder module has been accordingly developed, incorporating a tunable CW LD, wavelength locker, modulator, controller andreceiver into a compact package. It is compliant with the 300-pin MSA de fact industrial standard.
With these tunable transponder modules, the number of module varieties is reduced by a factorof as much as eight.

ABSTRACT1.

INTRODUCTION2.

The capacity of optical communication networks is being
increased due to the vast growth in internet traffic originating in North America in the 1990s. This evolution is primarily due to wavelength division multiplexing (WDM)
technology, which propagates plural optical signals on asingle optical fiber, as well as to optical fiber amplification(OFA) technology.
The transponder module is one of the key components
making up a long-haul WDM transmission system, andintegrates optical transceiver, electrical multiplexer/demultiplexer and control circuits into a compact package. Since
the commonly used transponder module is not tunable inwavelength, a number of transponder module varieties
corresponding to the number of individual wavelengths
must be provided. With a 10 Gb/s transponder module,
the number of module varieties can be reduced by a factorof as much as eight due to wavelength tunability.
Accordingly a 10 Gb/s tunable transponder module has
been developed by the authors, and is reported in thispaper.
Mux/DeMUX

OFA

λ1

λ2

λ2

λ3

λ3λnλnOFA

Mux/DeMUX

OFA

OFA

Optical fibertransmission lineOFA

XC

Figure 1

Mux/DeMUX

λ1

λ1

λ2

λ2

λ3λ3λnλnTerminal Station * Only one direction isrepresented out of the bi- Transponder card
directional transmission
practically used.

Transponder card

*2.1 Applications
Transponder modules are used in a variety of opticaltransmission systems, but here we wish to focus on longhaul WDM transmission systems as the major application.
Figure 1 shows an example of long-haul transmission. At
the terminal station, uncolored optical signals from a crossconnect switch (XC) are converted to different wavelengths from λ 1 to λ n . Each colored optical signal isprocessed by the multiplexer (MUX) for single fiber transmission, followed by OFA, and then transmitted by opticalfiber. Figure 2 shows an example of the transmission
equipment, in which there are a number of transponder
cards corresponding to necessary numbers of wavelengths which convert from 1310 nm signals to 1500 nm(λ1 to λn) signals and vice-versa. Each transponder card
contains two transponder (TRP) modules, one for shortreach (SR TRP) and one for long-reach (LR TRP). The
optical signal is converted via electrical signals by the twoTRPs. The uncolored optical signal (10 Gb/s) is received
at the SR TRP and subdivided into 16 lines of 622 Mb/s

Mux/DeMUXXCλ1

APPLICATIONS AND FUNCTIONS

Terminal Station

Example of long-haul transmission.

WT Team, FITEL-Network Lab., R&D Div.

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Development of 10 Gb/s Tunable Transponder Module

λ 1310λ 1310λ 1310λ 1310λ 15xxSR TRP

λ 15xxSR TRP

Applicable distance
Short distance transmission on the client side

SR (Short-Reach)

inside terminal stations

LR TRP
λ 15xxSR TRPLR TRPSR TRPLR TRPSR TRPLR TRP

λ 15xxOFA

IR (Intermediate-Reach)

Intermediate distances up to 40 km
Point-to-point long-distance transmissions up toLR (Long-Reach)

80 km or long-haul transmissions with OFA

λ 15xxTransponder card
Transmission equipment

Figure 2

Example of transmission equipment.

electrical signals for output. The 622 Mb/s signals are subjected to forward error correction, monitoring, etc. outside
the transponder module, and again multiplexed to a 10Gb/s signal at the LR TRP. The 10 Gb/s signal is converted to an optical signal of a particular wavelength for WDM
transmission.
2.2 Functions
Each transponder module installed on the transponder
card has following functions.
• converts a 10 Gb/s electrical signal into a 10 Gb/s
optical signal• converts a 10 Gb/s optical signal into a 10 Gb/s electrical signal• multiplexes 16 lines of 622 Mb/s electrical signals into
a 10 Gb/s signal• demultiplexes a 10 Gb/s electrical signal into 16 linesof 622 Mb/s signals

3.

Classification of transponders.

ClassLR TRP

MUX/DeMUX

λ 1310Table 1

Network side

Client side

STANDARD AND CLASSIFICATION

3.1 Standardization
Eleven transponder vendors have organized the MSA
group, and released Issue 1 of the 300-pin 10 Gb/s
Transponder MSA Document in April 2002. The latest
release is Issue 4 of August 2003. The document is a defact industrial standard, even for transponder vendors thatare not member of the MSA group, and various transponders compliant with the 300-pin MSA standard have beenreleased. Following are the basic items standardized inthe 300-pin MSA.
• Electrical signal interfaces such as data, clock, controland alarm• Power supply• Type of electrical connector (Meg-array 300-pin connector)• Pin assignment of electrical 300-pin connector• Physical dimensions

3.2 Classification
Transponder modules are classified according to thetransmission distance as shown in Table 1. SR transponders are mainly used to the client side inside terminal stations. IR transponders are used for transmission overmedium distances up to 40 km. LR transponders are used
for long-distance transmissions from 40 to 80 km, and with
OFA for even greater distances. Since 10 Gb/s transmission over 1310 nm single mode fiber is degraded bywavelength dispersion, external modulator is used for IRand LR transponders. The developed tunable transponder
module uses a Mach-Zender type external modulator for
long-haul transmission with OFA.

4.

FEATURES

The developed tunable transponder has a tunable wavelength over 8 channels at 50 GHz spacing, reducing thenumbers of transponder varieties for transponders
required by a factor of eight.
4.1 Structure
The structure of the tunable transponder module is shownin Figure 3.
On the transmission side, 16 lines of 622 Mb/s electricalsignals supplied from outside the transponder module aremultiplexed into a 10 Gb/s electrical signal. This 10 Gb/ssignal is then converted to an optical signal by a tunable
DFB LD and Mach-Zender type modulator.
The tunable DFB LD provides wavelength tunability
over eight channels (wavelengths) for 50 GHz spacingwith wavelength locker integrated, and Mach-Zender typeexternal modulator with LiNbO3 achieves the higher optical extinction ratio required for long-haul transmission.

10-Gb/s tunable transponder module
I2C Buscontroller

Tunable LD(with locker)

622Mbps×16
electrical

622Mbps×16electrical

16:1
Serializer

RF driver1:16
Deserializer
CDR

Limiting
AMP

LN
Modulator

Pin-PD.

10Gb/s optical

10Gb/s optical

MSA 300pin

Figure 3

Structure of tunable transponder module.

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Development of 10 Gb/s Tunable Transponder Module

Table 2

Specifications of tunable transponder.

ItemCondition@±1000 ps/nm

Loss budget

9.95/10.66/10.709 Gb/s

Power consumption+3.3 V, +5.0 V, -5.2 V

Operating temperature Case temperature

On the receiver side, the 10 Gb/s optical signal isreceived and converted into an electrical signal by PIN-PD(Photodiode), followed by adjustment by means of a limiting amplifier to the optimum level, and is then divided into
16 lines of 622 Mb/s electrical signals by a deserializer.
To control the thermally tunable LD, external modulator
and alarms, a microprocessor is installed. Controls andalarms can be communicated to an external controller not
only by parallel interface but also over an I2C serial businterface.
4.2 Appearance
The appearance of the transponder module is shown in
Figure 4. Though there are physical limitations to incorporating a DFB LD and Mach-Zender type modulator into themodule, the same compact size as for SR and IR
transponder modules (88.9×114.3×14.5 mm) has beenachieved. The case is made of aluminum alloy for effective heat dispersion.

5.

-5~70°C

Excluding heat sink

3.5 × 4.5 ×0.53 inchand projecting part(88.9×114.3×13.5 mm)

Output power

PRBS231 -1

Min. +5 dBm

Extinction ratio

PRBS231 -1

Min. +11 dB

Size

Wavelength1530~1620 nm
8 ch × 50 GHz

Tunability
BER 10 -12 average

Sensitivity@0 ps/nm
BER 10 -12 average

Overload

Min. -17 dBm
Min. -4 dBm

10dB/D1540nm

4.3 Specifications
Table 2 shows the specifications of the tunable transponder. Transmission rates includes the SONET/SDH standard 9.95 Gb/s, and 10.66 and 10.709 Gb/s are also available for the forward error correction (FEC) rate, which iscommonly used for long-haul transmission.
More than +5 dBm of optical output and less than -17
dBm of sensitivity makes possible a loss budget of over
22 dB at zero dispersion and over 20 dB at dispersion of±1000 ps/nm in transmission.

Typ. 14 W

Optical output

Appearance of tunable transponder.

Min. 20 dB
Min. 22 dB@0 ps/nmTransmission rate

Figure 4Specifications

1542.5nm

1545nmWavelength

Figure 5

Trace of wavelength tuning.

(a) Channel 1 at 25°C (1541.35 nm)(b) Channel 8 at 25°C (1544.13 nm)(c) Channel 1 at -5°C (1541.35 nm)(d) Channel 1 at 70°C (1541.35 nm)

EVALUATION

5.1 Wavelength Tuning
A thermally tunable LD in the transponder module isdeployed, so that the wavelength is changed by controlling the temperature. Figure 5 shows the trace of varying
wavelength from channel 1 (1541.35 nm) to channel 8(1544.13 nm) after locking in each channel.
5.2 Transmission Characteristics
Figure 6(a) shows the eye pattern at channel 1 and Figure6(b) is the eye pattern at channel 8 at a case temperatureof 25°C. Figure 6(c) and (d) shows the eye pattern atchannel 1 at case temperatures of -5°C and 70°C. At eachwavelength and temperature, good extinction ratios ofover 13 dB are achieved.

Figure 6

Eye patterns.

5.3 Receiver Characteristics
As receiver characteristics, Figure 7 shows the bit error
ratio (BER) vs. optical input level for 0~60 km optical fibertransmission; (a) and (b) show the measurements atchannel 1 and 8 at a case temperature of 25°C; (c) and(d) show the measurements at channel 8 and 1 at casetemperatures of -5°C and 70°C. In all cases, the BER of
10-12 is achieved at an optical input level of less than -19

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96Development of 10 Gb/s Tunable Transponder Module

dBm. In addition, the dispersion penalty due to opticalfiber is less than 0.5 dB. Good receiver performance isachieved.

6.

(a) Channel 1 at 25°C (1541.35 nm)(b) Channel 8 at 25°C (1544.13 nm)

CONCLUSION

A 10 Gb/s tunable transponder with 8-ch wavelength tunability at 50-GHz spacing has been developed andachieved good transmitter and receiver performance overthe desired wavelength tuning range at the desired temperature range.
The development of this tunable transponder is strongly
expected to contribute to greater economy and flexibility in
WDM transmission systems.

REFERENCES(c) Channel 8 at -5°C (1544.13 nm)

Figure 7(d) Channel 1 at 70°C (1541.35 nm)

1) 300pin MSA Group: Reference Document for 300pin Transponder
Edition 4 (14 August 2002)
2) I2C Reference Document for 300pin MSA10G and 40G
Transponder Edition 3 (24 July 2002)
3) ITU-T G.691 Optical interface for single channel STM-64, STM256 system and other SDH systems with optical amplifier
4) ITU-T G.692 Optical interface for multichannel systems with optical amplifiers

Bit error ratio vs. optical receiving power.

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