Application Note
September 2000
Transitioning fr om the A2300 DFB
to the A1611A/B DFB Laser Module
Offerin g th e flexibility to accurate ly and cost-ef fectivel y address
the requirem ents of forward-p ath appli cations, the A1611A /B
module is optim ized to assi st OEM custo mers with 1310 nm
CATV transmitter design.
Introduction
The informati on off ered here is intended to aid in the
transition from the Agere Systems I nc. A2300 series to
the Agere A1611A/B series laser. Although similar in
function, size, and sha pe, the A2300 and A1611 family
of CATV lasers exhibit very distinct differences. More-
over, an indust ry standard pinout, higher power, better
performance, and ease of integration combine to make
the A1611A/B the laser module of choice when transi-
tioning from the dependable but aging A2300. This doc-
ument examines the basic diff erences ( and similarities),
methods for testing and test-fixture requirements, and
also illu strates the ease of integratin g the A1611A /B
in to a complete tr a ns m itter.
Laser Profiles
Both the A2300 and A1611A/B modules are analog
1310 nm DFB lasers mounted in a 14-pin industry-stan-
dard, butterfly-type package. Each is equipped with an
optical isolator, monito r photodiode, therm istor, and
thermoelectric cooling.
Optical Isolation
Reflections caus ed by a phenom enon suc h as Ray-
leigh scattering in long fiber-optic links is minimized
with built-in optical isolation. Reflected light enter ing
the laser module is attenuated by at leas t 40 dB.
This important feat ure is incorpor ated in al l v ersi ons
of t he A2300 as well as the A1611A/B lasers .
Pinouts and Impedances
The A2 300 mod ule offers two different pinout types,
each with a different RF drive impedance. One is
Agere’ s standard analog isolated laser module (ILM)
pinout , which has an input impedance of 75 Ω. The
75 Ω input impedance eliminates the need for ext er-
nal matching circuits and is achieved using an RF
transformer inter nal to the package.
The seco nd pinout type is the industr y s tand ard
OC-48 compatible package characterized by a 25 Ω
resistive-matched input impedan ce.
Similarly, the A1611A/B devi ce uses the OC-48
pinout with a characteristic input impedance of 25 Ω,
although only one pinout type and RF drive imp ed-
ance is offered.
The pin conf iguration fo r all module versions is pre-
sented in Figure 1 and side-b y- side pinout compari-
son is shown in Table 1.
2Agere Systems In c.
Application Note
September 2000
to the A1611A/B DFB Laser Module
Transitioning from the A2300 DFB
Laser Profiles (continued)
Pinouts an d Impe da nces (continued)
1-1159(F)
Figure 1. A2300 and A1611A/B Pin Configuration, All Versions
Tab l e 1. Indu stry- S t andard OC-48 Pinout wi th 25 Ω
ΩΩ
Ω Resistive Input Impedance vs. the ILM Pinout with 75 Ω
ΩΩ
Ω
Input Impedance
Models A1611 and A2300; 25 Ω
ΩΩ
ΩA2300; 75 Ω
ΩΩ
Ω
Pin
No. Description Pin
No. Description
1 Thermistor 1 Thermoelec tric Cooler (+)
2 Thermistor 2 Thermistor
3 Laser (dc Bias) Cathode (–) 3 MPD Anode (–)
4 MPD Anode (–) 4 MPD Catho de (+)
5 MPD Cathode (+) 5 Thermistor
6 Thermoelectric Cooler (+) 6 Case Grou nd
7 Thermoelectric Cooler(–) 7 Case Ground
8 Case Ground 8 Case Ground
9 Case Ground 9 Case Ground
10 Case Ground 10 Case Ground
11 Laser Anode (+) 11 Laser B ias and RF Input; 75 Ω
12 RF Input; 25 Ω (–) 12 NC
13 Laser Anode (+) 13 Laser Anode (+), Case Ground
14 Case Ground 14 Thermoelectric Cooler
1234567
141312111098
Agere Systems In c. 3
Application Note
September 2000 to the A1611A/B DFB Laser Module
Transitioning from the A2300 DFB
Laser Profiles (continued)
RF Modulation and Biasing
Both the A2300 42-c hannel CENELEC and A1611A/B
lasers use separat e pins f or RF modulation (pin 12) and
biasing (pin 3).
Unli ke the OC-48 pac kages, the A2300 ILM shares the
same pin (11) for biasing and m odulation . To keep RF
from fe eding into the laser bias power supply, a simple
circuit called the bias-T is necessary. A coil prevents
R F from feeding back into the bias supply. A capacit or
cou ples the modula ting signal to the laser cathode via
a 75 Ω matching transformer designed into the pack-
age.
1-1159(F)
Figure 2. A2300 NTSC IL M 75 Ω
ΩΩ
Ω RF Modulation and Biasing
1-1162(F)
Figure 3. A2300 and A1611A /B 25 Ω
Ω Ω
Ω R F Modula t ion an d Biasing
R F INPUT 75
Ω
FROM CONSTANT
BIAS CONTROL CIRCUIT
COIL
dc + R F
PIN 11
A2300 N TSC ILM
75
Ω
PIN 12
1611, A2300
25
Ω
PIN 3
75
Ω
TO
25
Ω
Z MATCHING
RF IN PUT 7 5
Ω
CONSTANT BIAS
CONTROL CIRCUIT
dc
44 Agere Systems In c.
Application Note
September 2000
to the A1611A/B DFB Laser Module
Transitioning from the A2300 DFB
Laser Profiles (continued)
Ext ernal Circuitry
Recent breakthrough s in coupling efficiency (light out
of the laser verses light into the fiber) have allowed the
A1611 to achieve higher optical output powers. This
advancement all ows f or longer fiber runs, makes more
optical splits possible, and thereb y reduces the number
of transmitters needed in the system. To maintain sta-
ble module operation over the entire operating temper-
ature range of –20 °C to + 65 °C, however, external
cont ro l ci rcuitry i s necessary.
Laser bias determines the optical output power. A
closed-loop feedback circuit, using a sample of the
optical output power provided by the built-in monitor
photodiode, maintains the bias current at the correct
level.
Similarly, chip temperature is maintained via an exter-
nal feedback circuit. The ther mo electric c ooler (TEC)
inside the laser pack age uses the Peltier eff e ct to trans-
fer heat from the chip to the package. Varying the
polarit y of the current al l ows laser chip heating and
cooling. In all cases , the laser package must be
attached to a heat sink to ensure proper laser cooling.
Agere can provide a set of boards (dc set) designed
speci fically to control laser bias and temperature. The
dc s et allows f or a quic k and easy solution to laser con-
trol when used in conjunction with Agere’s T3641 trans-
mitte r engine-com patible lasers (such as the A1611A/
B), as configured in Figure 4.
For more detailed information on laser control circuitr y
and theory of oper ation, please refer t o Laser Control
Circuits for A1611 Laser Module and T3641-Type Laser
Transmitter Subassembl y application note.
1-1160(F)
Figure 4. A1611A/B Bias and Tem pe rature Control Using Agere ’s dc Boards
T3641 PREDISTORTOR ENGINE
VR1
BIAS
ADJUST 9028-xxx
TEC bd.
TEC
ADUJUST
9383-xxx
BIAS bd.
9404-xxx
CONNECTOR bd.
1611
LASER
Agere Systems In c. 5
Application Note
September 2000 to the A1611A/B DFB Laser Module
Transitioning from the A2300 DFB
Link Testing
Link testi ng pla ys an important role in determining the
quality of a fiber link under real-world condi tions. The
link test can be used t o simulate actual customer condi-
tions such as carrier-noise ratio (CNR), distortion, fi ber
length, and other added passive losses.
Link testing als o pro vides a reliable method for compar-
ing the A2300 and A1611A/B de vices . The modules
were evaluated us ing a recently calibrated manufactur-
ing distort i on station, 25 km of fiber, and 2 dB of pas-
sive loss.
CNR and bias of both t ype lasers (A2300 and A161 1)
were set to the values found on th e A230 0 test data
sheet and distortion was measured. For 80-channel
loading, the A2300 e xhibited good CTB and acceptable
CSO perform anc e with the edge in both categorie s
going to the A1611. The measured CSO results for
110-channel l oading were ve ry marginal for t he A2300.
CTB was good in most cases. The A1611 passed both
CSO and CTB wit h good margins.
Link Test Setup E xample
The following procedure is preliminar y and is intended
to be used only as a guide for setting up an in-house
test station, which is shown in Figure 5.
First, the best bias must be deter mi ned. The best bias
is found primar ily by varyin g the laser bias in 10 mA
incr eme nts until the optimized power and distortion
point is f ound.
N ext, the correct fiber length must be inserted. This
length can be v aried to accommodate customer
requirements.
N ow the matrix generator can be set up for correct
channel loading. Once that is compl ete, CNR can be
measured and the RF drive le vel c an be adjusted to
meet the required CNR specifications.
Las tly, distortion (CSO, CTB) is measured. For disto r-
tion testing, optical power to the rece iver may have to
be reduc ed to prevent errors in meas ureme nt caused
by overdr iving the test receiver.
1-1164(F)
Figure 5. Link Test Hardware Configuration
LASER CO NTRO L BOX
TEST FIXTURE
1611 LASER OPTICAL
ATTENUATOR
OPTICAL RECEIVER
BANDP ASS FIL TERS
SPECTRUM ANALYZERMATRIX
GENERATOR
RF INPUT
66 Agere Systems In c.
Application Note
September 2000
to the A1611A/B DFB Laser Module
Transitioning from the A2300 DFB
Link Testing (continued)
Test Fixture Requirements
Different test fixtures are needed to fire-up each of the
three lase rs. The A2300 (ILM NTSC) uses a 257-type
test fixture. The A2300 (OC-48 CE NELEC) uses the
247-type test fixture. The A1611A/B uses a f i xture
(9331-xxx) manuf actured on site.
The 75 Ω version, as mentioned previously, will require
an external bias-T. Figure 6 shows how the fixt ure can
be used with the link test hardware setup.
The A2 300 CEN ELEC requires an impedance-m atc h-
ing pad or transformer when used with the 75 Ω output
matrix generator, as shown in Figure 7.
The A1611A/B test fixture can be optioned for 75 Ω or
50 Ω. It connects directly to the test hardware; bias-Ts
and external impedance matchi ng are not neede d.
A limited number of all test fixtures can be made avail-
able by Agere for short-ter m loan.
1-1164(F)
Figure 6. A2300 Test Fixture With Extern al Bias-T and 75 Ω
Ω Ω
Ω RF Input
1-1165(F)
Figure 7. A2300 CENELE C Test Fixture With Impedance-match ing P ad or Transformer and
75 Ω
Ω Ω
Ω RF Input
A2300
TO RECEIVE R
I LX L IGHT WAVE
LDC 39 00 OR
EQUIVALENT
BIAS-T
dc BIAS
RF IN 75 Ω
(F ROM MAT R IX)
A2300
TO RECEIVE R
I LX L IGHT WAVE
LDC 39 00 OR
EQUIVALENT
Z-MATCHING
RF IN 75 Ω
(F ROM MAT R IX) PAD OR XFMR
Agere Systems In c. 7
Application Note
September 2000 to the A1611A/B DFB Laser Module
Transitioning from the A2300 DFB
Matched Impedance
Most applications for the CATV laser call for a 75 Ω
impedance-m atc hed input. This problem is neatly
solved i n the A2300 IL M by an in-package matching
transformer. Lim iting the input impeda nce to 75 Ω,
although very useful , can sometime limit design flexibil-
ity.
The A1611A/B can easily be matched to most of the
commonl y used impedan ce requireme nts. A concep-
tual circuit showing the mos t common of the 25 Ω to
75 Ω requirements is shown in Figure 8. The heart of
the circuit is a simple, exter nal match ing transformer.
Board Integration
Board int eg rat ion can greatly reduce the time and
expense required when designing a comple te transmit-
ter. Many of the nec essary component s such as predi s-
tortion, am plification, and impedance matching can be
incorporated into a small form factor tr ansmitter engine.
When the engine is combined into a complete transmit-
ter design, however, new active components (such as
amplifiers) can add dis tortion. F eatures such as elec-
tronic fine-tuning of CS O and CTB ens ure the highest
le vels of performance .
The T36 41 transmitter engine consists of the A1611
laser mounted on the 9349 board. The 9349 board
includes a low-noise hybrid amp lifier, 75 Ω to 25 Ω
imp edance-m atchi ng circuitry, interfac e for connecting
laser control boards, and the latest i n-line predistortion
technology.
D ue to the prev iously me ntioned pinou t and imped-
ance matching incompatibilities, the A2300 ILM cannot
be used with t he T3641 engine . (The 75 Ω input i mped-
ance of the A2300 ILM is a mismatch f or the
75 Ω—25 Ω transformer used in the 9349 board). For
these reasons, the A2300 virtu ally requires a from-the-
ground-up design ef fort. A predistortion board alone,
des igned for use with the A2300 using the older split-
off pr edistortion technology, is still available for pur-
cha se. A separate board w ill have to be fabricated to
provide RF inputs, laser mounting, and control lines.
Summary
In view of the conven ient advantage s of the feature-
packed A1611A/ B laser module, including an industry
standard pinout, higher power , better performance, and
eas e of integration, transitioning from the maturing
A2300 t o the new-generation A1611A/B is the next log-
ical step.
1-1166(F)
Figu re 8. Concep t ual Circ u it Showi ng Typic al A1 611A/B Im pedance -matchi ng Requi rem e n t s
GNDGNDGND GND
C9C8C10
R1 GND
C10
GND
GND
1
2
COAX PAD
C7
1
3
2
T1
3/5 TURN
RF INPUT TO LASER
25
Ω
75
Ω
INPUT
Agere Systems Inc. reserves the right to make changes to the product(s) or information contained herein without notice. No liability is assumed as a result of their use or application.
Copyright © 2001 Agere Systems Inc.
A ll Rig hts Rese rved
September 2000
AP00-063OPTO
For additional inform ation, contact your A ger e S y s tems A ccount Mana ger or the following:
INTERNET: http://www.agere.com
E-MAIL: docmaster@agere.com
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Tel. (852) 312 9- 2000, FAX (852) 3129-2020
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Application Note
September 2000
to the A1611A/B DFB Laser Module
Transitioning from the A2300 DFB
Related Information
Descripti on Document Number
Introduc tion to the 3641-Type Transmitter Subassembly application note AP00-0 71OPTO
Las er Control Circuits fo r A1611A/ B Laser Module and the 3641-Type Las er Transmitte r
Subassembly a pplication note AP00-067OPTO
Mechanical Installation Requirem ents for the 3641-Type Transmitter Subassembly
application note AP00-069OPTO
Ele ctronic Fine Tuning of the 3641-Type Transmitter Subassem bly application note AP00-070OPTO
