Data
sheet
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2.5 Gb/s Transmitter
Module - DWDM
The MT25W transmitter module provides an easy to use self-
contained optical source for Dense Wavelength Division
Multiplexed (DWDM) applications up to 2.7 Gb/s data rates.
The module requires +5 V, +3.3 V, 0V supplies and PECL/ECL
data input to operate, and so allows non-DWDM optical links
to be upgraded very easily. Internal control circuitry ensures
that the optical source remains within optical power and
wavelength limits over variations in temperature, power, and
over life. The MT25 W conforms to ITU-T G.692 (submitted
for approval) STM-16 Long Haul and Telcodia OC-48 Long
Reach specifications for data links to 160 km and beyond.
Over 40 wavelengths are available, specified
as per the ITU grid at 100 GHz channel spacing, covering
the C-band EDFA window.
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Features
Up to 2.7 Gb/s
Optical link lengths to 3000
ps/nm & beyond
ITU 100 GHz grid compliant
100 pm wavelength stability
over life
0 to +85C operation
High reliability optical components
Monitor functions for laser status
Laser disable function and
automatic mean power control
Source wavelengths available
covering the EDFA window
Microprocessor control
OPTICAL DEVICE
TXSD
DATA
DATA
LBC MONITOR
Laser ALARM
TEMP MONITOR
TEMP ALARM
Vcc
Vtec
Gnd
MODN INPUT
TEMP
CONTROL
CIRCUIT
THERMO-
COOLER
ELECTRIC
S
MONITOR
& ALARMS
CIRCUIT
LASER DRIVE
AND CONTROL
CIRCUIT
Figure 1: Transmitter block diagram
Functional description
The module is comprised of an hermetically packaged 1550 nm BH Laser device with optical isolation,
laser drive, automatic laser power control, and monitoring circuitry.
The laser package uses a Thermo-Electric Cooler (TEC) to maintain constant laser temperature and
wavelength. The microprocessor-based control circuit also provides temperature monitoring, alarm
outputs and internal fault diagnostics.
The module features high speed complementary data inputs which are AC coupled and have internal
50
termination, transmitter disable input, modulation input for wavelength tagging, alarm and monitor
supervisory outputs.
The optical output is via a single mode pigtail which can be fitted with a variety of single mode
optical connectors.
The module operates from a 5 V supply, with a 3.3 V supply for the TEC to minimise power dissipation.
The module is very compact and incorporates an advanced integral heatsink.
Transmitter operation
Optical power control
A single silicon IC provides the laser drive, modulation, and mean power control. This IC maintains
a constant output power by using the backfacet diode as the feedback element in a closed loop
control system.
Data input (DATA/ DATA)
The inputs are AC coupled and terminated with 50 W. This provides 100 W differential impedance. The
recommended input signal must meet the required voltage swing for PECL/ECL. Due to the high speed
nature of this product it is vital that high speed design rules are followed in the design of the system
board. Follow the recommended user interfaces.
This transmitter is not suitable for burst mode operation and unbalanced data patterns may affect the
automatic constant power circuit.
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Transmitter operation (continued)
Transmitter disable (TXSD)
Transmitter operation can be disabled by applying a CMOS Logic 1 level to the TXSD pin. An internal
pull-down resistor allows the TX Disable pin to be left unconnected, in which case the laser is enabled.
When disabled, the output power is < -40 dBm.
Laser Bias Current Monitor (LBCM)
The LBCM provides an analog voltage output corresponding to the laser bias current. The LBCM
output is referenced to ground and indicates the change of laser threshold as the laser ages. The
LBCM output is buffered; use with high impedance loads to reduce errors and dissipation.
Laser alarm (LASA)
The Laser alarm is an Active High CMOS level output. The Laser alarm is activated when the optical
output power is outside of operations limits.
Temperature alarm (TEMP ALARM)
The temperature alarm is an active high CMOS level output. The temperature alarm is activated when
the laser temperature is 1.6 C above or below normal laser operating temperature. This is a high
current output and can drive alarms directly.
Modulation input (MOD'N)
The modulation input allows for the use of a low frequency tone (10-500 GHz) for modulation
of the "1"s level.
This input must be driven from a 50
source, and is AC coupled internally. Over driving this input can
cause waveform distortion; limit modulation depth to 5-10%. If unused, connect this input to 0 V
to prevent noise pickup.
Two wire interface (TWCK, TWDA)
The module can be configured using a two-wire communication interface. TWCK carries the clock
signal generated by the external master. TWDA carries the serial data stream.
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Power supplies
The module operates from a single rail power supply of
+5.0 V nominal. The Thermo-Electric Cooler is supplied
from a separate pin (Pin 16 Vtec). The TEC operates with
a 3.3 V supply for a wide operating temperature range.
This low voltage ability is used to reduce the power
dissipation of the module.
Filter the supply to the module well and as noise free
as possible to prevent any possible interference with
the module (see the recommended system interface).
The supply feeds to the module and TEC must be of low
DC impedance with minimal voltage drop at the maximum
values of module and TEC current. For maximum
EMI screening, the case is electrically connected to
the Gnd pins.
Specification
Stresses beyond those in Table 2: "Absolute maximum
ratings" may cause permanent damage to the module.
These are stress ratings only and functional operation
of the module at these or any other conditions beyond
those indicated in the operational sections of the
specifications is not implied. Exposure to absolute
maximum rating conditions for extended periods
may affect the module's reliability.
Pin #
Name
Pin #
Name
1
Gnd
20
Two-wire Data
2
Data
19
Two-wire Clock
3
Data
18
Gnd
4
Gnd
17
Vcc
5
Laser Disable
16
Vtec
6
Vcc
15
Temperature Alarm
7
Vcc
14
No internal connection
8
Vcc
13
Laser Alarm
9
Modulation Input
12
Laser Bias Current Monitor
10
Gnd
11
No user connection
Pinout
Table 1: Module pinout
Parameter
Min
Max
Unit
Operating Case Temp
0
+85
C
Shipping/storage Temp
-40
+85
C
Relative Humidity
95
%RH
Applied Voltage (Any Pin)
-0.5
6.0
V
Lead Soldering Temp
250
C
Lead Soldering Time
10
S
Fibre Bend Radius
30
mm
Table 2: Absolute maximum ratings
Gnd pins are connected to the module case. Do not make any connection to pin 11.
Pins 19 & 20 can be connected to ground if the two wire interface is not being used.
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Physical dimensions
Parameter
Min
Max
Unit
Bend Radius
30
mm
Mode Field Diameter
8.8
9.8
m
Cladding Diameter
122
128
m
Concentricity Error
0.5
m
Pigtail Length (Typical)
1
950
1050
mm
Table 3: Fibre pigtail
Figure 2: Mechanical outline
Mechanical outline
All dimensions in mm unless otherwise stated, general tolerance = 0.25 mm
Note 1: Other pigtail fibre lengths are available on request.
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