Data
sheet
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2.5 Gb/s Tunable
Transmitter Module -
DWDM, 100 GHz
The MT25T transmitter module is a completely self-
contained optical source for Dense Wavelength Division
Multi-plexed (DWDM) applications up to 2.7 Gb/s data rates.
The MT25T allows non-DWDM optical links to be upgraded
very easily. A key feature is that the module can operate at
one of four wavelengths on adjacent 100 GHz ITU channels
and is fully configurable through a two-wire communication
interface. The MT25T conforms to Telcordia OC-48 Long
Reach specifications for data links to 160 Km (3000ps/nm)
and beyond. Over 40 wavelengths are available as specified
by the ITU grid at 100 GHz channel spacing covering the
C-band EDFA window.
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Features
Four wavelengths from
single module
Advanced interface
for complete configuration
Up to 2.7 Gb/s
ITU 100 GHz grid compliant
0 to +70C operation
High reliability optical
components
Optical Link lengths
to 3000 ps/nm & beyond
Source Wavelengths available
covering the C-band
EDFA window
OPTICAL DEVICE
LASER DRIVE
AND CONTROL
CIRCUIT
TEMP
CONTROL
CIRCUIT
THERMO-
COOLER
ELECTRIC
MONITORS
& ALARMS
CIRCUIT
TXSD
DATA
DATA
LBCM
LASA
Vcc
Vtec
Gnd
MODN
EILF
TEMA
TWDA
TWCK
Figure 1: Transmitter block diagram
Functional description
Power supply requirements are +5 V Vcc, +5 V Vtec and 0 V. The module has high speed complementary
data inputs (PECL/ECL) which are AC coupled and have internal 50
termination, transmitter disable
input, modulation input for wavelength tagging, alarm and monitor supervisory outputs, Etalon in lock
output flag. The optical output is via a single mode pigtail which can be fitted with a variety of single
mode optical connectors.
The module comprises of a hermetically packaged 1550 nm BH Laser device with optical isolation and
Etalon wavelength feedback. This ensures that the optical source remains within optical power and
wavelength limits over variations in temperature and over life. Internal circuitry and a microprocessor
control the operation of the module and by using a Thermo-Electric Cooler (TEC) ensures the correct
laser temperature to achieve constant wavelength based on true wavelength feedback from the Etalon
filter. The microprocessor provides a two-wire communication interface allowing customer configuration of
the desired channel as well as monitoring of operating conditions and alarms.
Transmitter operation
Optical power control
The on board microprocessor provides fully automatic integrated power and wavelength control using the
Etalon output signals as feedback. This approach enables a controlled start and inter-channel protection,
as well as normal constant power control.
Transmitter disable (TXSD)
Transmitter operation can be disabled by applying a CMOS Logic 1 level to the TXSD pin. The laser can
be disabled by the modules microprocessor in the event of gross failure. When disabled, output power is
guaranteed < -40 dBm. The transmitter disable can be activated by the module microprocessor for gross
failure of the temperature or laser circuits. In this case the microprocessor sets the Laser Alarm,
Temperature Alarm and Etalon-in-lock flag and maintains the transmitter disable until a power on reset or
toggle of TXSD.
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Transmitter operation (continued)
Data input (DATA, DATA)
The inputs are internally AC coupled and terminated with 50
. This provides 100
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.
Modulation input (MODN)
The modulation input allows for the use of a low frequency tone (10-500 kHz) for modulation of the
"1"s level. This input is AC coupled and must be driven from a 50
source. Over driving this input can
cause waveform distortion. 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 with 7-bit address capability.
TWCK carries the clock signal generated by the external master. TWDA carries the serial data stream.
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; but 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 active when the optical output
power is outside of operation limits.
Temperature alarm (TEMA)
The temperature alarm is an active high CMOS level output. The temperature alarm is activated when the
laser temperature is approximately 1C above or below normal laser operating temperature for Etalon
lock. This is a high current output and can drive alarms directly.
Etalon in lock flag (EILF)
This output provides a CMOS level indication of when the wavelength is locked to the reference wavelength
under Etalon control.
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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 20 Vtec). Ensure the supply to
the module is well filtered 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 module and
TEC currents. For maximum EMI screening, the case is
electrically connected to the 0 V (Gnd) pins.
Gnd pins are connected to the module case.
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
24
Two-wire Data
2
Data
23
Two-wire Clock
3
Data
22
Gnd
4
Gnd
21
Vcc
5
Laser Disable
20
Vtec
6
Vcc
19
Temperature Alarm
7
Vcc
18
No internal connection
8
Vcc
17
Laser Alarm
9
Modulation Input
16
Laser Bias Current Monitor
10
Gnd
15
Etalon in Lock Flag
11
A4
14
A1
12
A3
13
A2
Pinout
Table 1: Module pinout
Parameter
Min
Max
Unit
Operating Case Temp
0
+70
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
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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 available on request
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