THORLABS PICO D User manual

PICO D
USERS MANUAL

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Thorlabs Sweden AB, Göteborg, Sweden.
Document info:
740-OSL 103 XXX-PA1 PICO-D Maual.doc
LS 2/10/2005 7:41

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0 How to Handle PICO D
0.1 Safety Requirements
PICO D is a sensitive product and should be handled accordingly.
The requirements listed below have to be followed to avoid damage on PICO D or
personnel.
 Do not under any circumstances look into the optical output when the device is
operating. The laser radiation is not visible to the human eye, but it can seri-
ously damage your eyesight.
 Protect the equipment from external chocks and excessive vibrations.
 To avoid hazardous chocks, do not operate the PICO D if there are any signs of
damage to any part of the outer enclosure (covers, panels etc)
 Protect the equipment from rapid variation in temperature.
 The PICO D is not designed for outdoor use. Protect the equipment from rain
and snow. Make sure that the equipment is not exposed to dust, dusty air, con-
densing humidity (or equivalent).
 Always store and use the PICO D in a vertical position (as further described in
the manual).
 Handle with care when unpacking the PICO D.
 The original transport case, supplied by Thorlabs Sweden AB, should always be
used when sending PICO D to Thorlabs Sweden AB for service
 Use ESD wrist wrap when handling the PICO D.
 DO NOT use solvents on or near the equipment as it may damage the PICO D.
 Read this manual carefully before powering up PICO D or connecting the PICO
D to any other equipment .
 Handle all connectors, both electrical and optical, with care. DO NOT use un-
necessary force as this may damage the connectors.
 This is a class 1M laser product.

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0.2 ESD Precautions
All types of electronic components, particularly integrated circuits, are more or less
sensitive to Electrostatic Discharge (ESD). ESD is a general reason for failure of
electronic equipment. The total operating time can be reduced if precautions against
ESD-damage are not taken. See Figure 0-1.
WARNING ! Always wear an ESD wrist strap connected to the ESD terminal whenever han-
dling boards and units.
Figure 0-1 The ESD wrist strap. The wrist strap is connected to ground to
ensure that no electrostatic field is built up.

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Table of content
0HOW TO HANDLE PICO D 3
0.1 SAFETY REQUIREMENTS 3
0.2 ESD PRECAUTIONS 4
1INTRODUCTION 7
1.1 1.1 FEATURES AND OPTIONS:7
1.1.1 ACRONYMS AND ABBREVIATIONS 7
1.1.2 IMPORTANT AND WARNING MESSAGES 8
2SYSTEM DESCRIPTION AND INTERFACES 9
2.1 WHAT IS A TUNABLE LASER SOURCE (TLS)? 9
2.2 BRIEF SYSTEM OVERVIEW 9
2.3 BASIC OPERATION.10
2.4 MECHANICAL INTERFACE 11
2.4.1 MOUNTING OF PICO D 14
2.4.2 ENVIRONMENTAL CONDITIONS 15
2.5 ELECTRICAL INTERFACES 16
2.5.1 GROUNDING ISSUES 19
2.5.2 POWER SUPPLIES 20
2.5.3 DIGITAL CONTROL AND STATUS SIGNALS 21
2.5.4 ANALOG CONTROL SIGNALS 25
2.5.5 ELECTRICAL POWER AND SIGNAL CONNECTORS 28
2.6 OPTICAL INTERFACE 31
2.6.1 FIBER OPTICAL CONNECTOR 31
3OPERATION 32
3.1 SWITCHING ON THE PICO D 32
3.2 SWITCHING OFF THE PICO D 33
3.3 CALIBRATION OF PICO D 33
3.3.1 CALIBRATION METHODS 34
4MAINTENANCE & SERVICE 36
4.1 TRANSPORTING, STORAGING, PACKAGING AND UNPACKAGING 36
4.2 CLEANING 36
5TROUBLESHOOTING & FAQ 37
5.1 TROUBLESHOOTING, STEP-BY-STEP 37
6SUPPORT 38
APPENDIX A - MODEL DESCRIPTION TECHNICAL SPEC. 39

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APPENDIX B - MODE HOPS 41
APPENDIX C - DEFINITIONS, ACRONYMS AND ABBREVIATIONS 43
APPENDIX D - CHECK LIST FOR FAILURE REPORT 44

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1 Introduction
This manual describes how to interface and control the PICO D continuously tunable
laser source (TLS), designed and manufactured by Thorlabs Sweden AB is a flexible
OEM module intended for integration in to various fiber optic test and measurement
equipment, sensors and spectroscopy systems. It could be used in step or sweep
mode and the wavelength and optical power are controlled by a simple analog inter-
face.
The manual refers to other documents (e.g. product specification, packing instruc-
tions), which can be obtained from Thorlabs Sweden AB.
1.1 1.1 Features and options:
The Thorlabs Sweden AB offers a unique combination of broad wavelength range,
high tuning speed, linearity in sweep, high absolute accuracy and repeatability – re-
ferred to as "benchtop performance in a module". For the different options, please
refer to the PICO D specification (730 - OSL 103 XXXX) and for ordering informa-
tion, please refer to Appendix Fel! Hittar inte referenskälla.
Some of the highlighted features are described below.
 High absolute accuracy means no need for frequent calibrations
 Good repeatability results in consistent measurements
 Truly continuous, smooth tuning, i.e. small tuning speed variations, no back-
ward movements or mode hops, are important for many applications such as in-
terferometry and fiber sensing.
 Narrow linewidth is prerequisite for high-resolution interferometric, heterodyne
and spectroscopic measurements.
 Wide tuning range, covering one or two bands, eliminates the need for multiple
sources and offers flexible use.
 High tuning speed results in fast measurements, saves time and cost.
 Small form fit and the easy-to-integrate interface results in cost-effective sys-
tems, rapid implementation and flexibility
1.1.1 Acronyms and Abbreviations
The first time an abbreviation appears in the manual, the expanded form is shown,
followed by the abbreviation in parentheses, e.g. Electrostatic Discharge (ESD). The
abbreviated form is shown without parentheses when the expanded form is not
used. APPENDIX C contains a list of the acronyms and abbreviations and their ex-
panded forms.

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1.1.2 Important and Warning messages
Warning is used when an accident may occur if the safety precautions or the instruc-
tions are neglected. This type of accident may be fatal or cause serious injury. It may
also damage the product.
IMPORTANT
This is an example of an IMPORTANT message
WARNING ! This is an example of a warning message

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2 System Description and Interfaces
This chapter intended as an aid when designing a system containing PICO D. In or-
der to assure that PICO D will operate correctly and at the given specifications, the
requirements regarding handling an operation given in this manual have to be met.
2.1 What is a tunable laser source (TLS)?
A Tunable Laser Source (TLS) is a laser whose output wavelength could be swept
(continuous or random access) over a certain, and usually quite wide, wavelength
range. The PICO D can be tuned over typically 110 nm (albeit depending on the ac-
tual model of PICO D) which is sufficient for covering both the C- and L- wavelength
bands used in fiber optical communications systems. The TLS can be thought of as
an optical equivalent of a conventional electrical sweep oscillator. The acronym ECL
(External Cavity Laser), which reflects the technical design of the laser, is some-
times also used for describing the TLS function. However the acronym TLS has a
wider meaning since an ECL not necessarily is tunable.
TLS’s are frequently used in various measurement applications where a recording of
a certain measure versus wavelength is performed. Each application requires de-
tailed knowledge on some or all parameters characterizing a TLS (e.g. wavelength
range, side mode levels, spontaneous noise levels, line width, sweep characteris-
tics).
2.2 Brief system overview
PICO D, see Figure 2–1, is a Tunable Laser Source (TLS) based on a semiconduc-
tor laser mounted in a Littrow external cavity laser geometry. This tuning arrange-
ment allows high output power and large mode-hop-free tuning range.
The interface between PICO D and the user is analog. Analog voltages are used to
set the output wavelength and output optical power. By applying an analog voltage
to the interface the wavelength can be randomly tuned to any wavelength or con-
tinuously tuned (i.e. swept) between any wavelengths within the operational wave-
length range given in the specifications. The tuning is truly continuous due to the
construction of the tuning arrangement (i.e. no step motor drive). A stable voltage
source is required for supplying the analog control signals for setting output wave-
length and optical output power.
PICO D is fully controlled by its electronic control system and the user supplied ana-
log signals for setting output wavelength and optical output power. Furthermore,
PICO D requires an external DC power supply to be operational.

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1
234
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Figure 2–1 Schematic Radians PICO™. PICO is based on a Littrow resona-
tor. 1) Diffraction grating, 2) Intra-cavity collimating hybride (i.e.
refractive and diffractive combination) achromatic lens, 3) Laser
diode, 4) Output coupling optics including an isolator 5) Fiber op-
tics 6) Motor.
2.3 Basic operation.
PICO D is based on a patented low SSE Littrow external cavity laser geometry, c.f
Figure 2–1. The intra-cavity lens collimates the light emitted from the laser diode be-
fore the beam impinges on the diffraction grating. Wavelength selectivity is achieved
by tilting the diffraction grating. The tilting is controlled by a patented moving coil
(“motor”) arrangement. The beam reflected from the diffraction grating is directed
back to the laser diode. Thus, the laser resonator cavity is formed between the dif-
fraction grating and the leftmost side of the laser diode as seen in Figure 2–1. The
output beam is collimated and sent through an optical isolator before the beam is
launched into the optical fiber.
Due to the analog interface PICO D is easy to integrate in the user’s system configu-
ration. The user supplies an analog signal to tune (sweep) the laser between the
minimum and maximum wavelengths defining the tuning range. The tuning of PICO
D is truly continuous. The output wavelength of the laser will follow the applied ana-
log signal. Furthermore, by applying a constant voltage to the tuning input, the laser
will lase at a fixed wavelength. This implies that the laser can randomly access any
fixed wavelength within the tuning range.
The control system continuously monitors the angular position and the angular
speed of the mechanical arm onto which the grating is mounted. The outputs are fed
to the internal control circuitry. The wavelength control system is designed to:
 Follow a ramp (i.e. wavelength vs. time signal) without errors with short settling
times
 Clamp the laser at a fixed wavelength (i.e. a fixed angular position of the grating
arm) without errors

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 Obtain fast step response with short settling times when moving between fixed
wavelengths (“random access” tuning).
 Minimize errors in position due to external forces (i.e. vibrations, magnetic
fields)
The control system also monitors the optical output power in order to maintain a
constant optical output power throughout the tuning-range of PICO D. Using an ana-
log control port the user can set the optical output power.
The laser chip and the laser cavity are kept at constant temperature using a closed
loop thermo electrical cooler.
The inner metal casing functions as a body for the attachment of the different mod-
ules, such as fiber coupling-, laser unit, and sensor-mechanics. The outer casing is
made of metal and a layer of thermal isolating material. Furthermore there is a mag-
netic shield, made of a high permeability material, for preventing external magnetic
fields to interfere with the motor coils.
All lasers, and especially lasers having a resonator cavities defined by mechanical
tolerances, are delicate precision instruments and they must be handled accordingly.
PICO D is designed to withstand “normal” transportation and “normal” operation con-
ditions. Designer’s Guide
2.4 Mechanical interface
The PICO D is confined to a volume of maximum: 49 mm ×93 mm ×260 mm (W ×
H ×L) [49 mm ×93 mm ×274.1 mm if the locking mechanism belonging to the sig-
nal connector is included). The PICO D front panels, having bulkhead and pigtail op-
tical output respectively, are shown in Figure 2–3, and the side-view of PICO D is
shown in Figure 2–4.

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Warmairoutlet
Warmairoutlet
Coldairinlet
Coldairinlet
Figure 2–2 The PICO D case (bulk head version). All measures in millime-
ters.

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Bulkhead Pigtail
Figure 2–3 PICO D front panels. Both bulkhead (fiberoptical connector) and
pigtail options are available. All measures in millimeters. Com-
pare Figure 2–2.
Figure 2–4 Mechanical dimensions om PICO E, side view. All measures in
milliters. Compare Figure 2–2.

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2.4.1 Mounting of PICO D
The orientation of PICO D must be vertical during operation, see Figure 2–5, the ar-
row defined the vertical direction.
The four solid arrows in Figure 2–5 indicates the four threaded (M3) mounting holes
available on each long-side of the PICO D case. PICO D could be mounted either
using the holes on the left or right side of the case. All four mounting holes should be
used. The hole pattern is specified in Figure 2–6, the hole patterns on either long-
side of the unit are identical.
The weight of a PICO D unit is 1.8 kg.
Figure 2–5 PICO D physical layout. PICO D should always be mounted and
stored in vertical position, as indicated by the leftmost arrow in
the figure above. Optical bulkhead connecter is available at the
front, to the left. Electrical connectors for power and interface are
available at the back, to the right. The four solid arrows indicate
the threaded mounting M3 holes, see Figure 2–6. Compare
Figure 2–2.
WARNING ! The length of the M3 screws must not be longer than 3 mm (measured from the
outer

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Figure 2–6 Hole pattern, on both long-sides of PICO D (the hole pattern on
either side is identical) for mounting PICO E. The holes are
threaded M3, all measures in millimeters. Compare Figure 2–2.
2.4.2 Environmental Conditions
WARNING ! Sudden changes in temperature should be avoided as this may cause conden-
sation on the optical equipment that could have a negative influence on the
performance of the device.

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In order to ensure specified performance, the unit is designed to withstand environ-
mental influence according the following conditions.
The unit is tested according to the following (ETSI) standards with the exceptions
given below.
2.4.2.1.1 Storage, Transport and In operation
ETS 300 019-1-1.1 (Storage in partially temperature controlled locations.)
ETS 300 019-1-2.2 (Careful transport.)
ETS 300 019-1-3.1 (Stationary usage, weather protected, temperature controlled lo-
cations limited compliance, operating temperature)
2.4.2.1.2 Applicable EMC standards
EMC testing is done according to EN 61326-1 Annex A "Immunity test requirement
for equipment intented for use in industrial locations"
Emission according to EN 55022 class B
Imunity against radiation according to EN 61000-4-2, 4-3, 4-4, 4-5, 4-6, and 4-8
Imunity against radiation according to ENV 50204
2.4.2.1.3 Safety standards
EN 61010-1
UL 3101-1
According to IEC 60825-1 edition 1.2 2001-08 (laser safety) the PICO D is classified
as 1M.
IEC 825 (laser safety)
2.4.2.1.4 Exceptions and Extensions to Standards Compliance
Operating temperature range: +10 to +40 °C
Dew point: <26 °C non condensing environment (RH 85%) @ 30 °C
External vibration will gradually degrade the performance.
External magnetic field at the surface: Less than 6 µT at 30 - 200 Hz (5 A/m)
2.5 Electrical Interfaces
IMPORTANT
Read this chapter carefully before you connect PICO D to any voltage source.
PICO D is fully controlled and monitored by a set of analog and digital control1and
status2signals, see Figure 2–7.
1A control signal is defined as an input signal to PICO E (written to PICO D). The
control signals could be either analog or digital
2A status signal is defined as an output signal from PICO E (read from PICO D).

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Electrical power
Digital Control Signals
Analog Control Signals
Digital Status Signals
Figure 2–7 PICO D is controlled and monitored by a set of analog and digital
control and status signals.
The user needs to implement the following electrical connections:
 DC power +5, and ±15 V, see paragraph 2.5.1
 DC voltage, low noise, [ -10 V, 10 V] for setting the output wavelength, see
paragraph 2.5.4.1.
 DC voltage, low noise, [ -1 V, 10 V] for setting the optical output power level,
see paragraph 2.5.4.2.
 Setting appropriate digital control signals (0 V / 5 V logical levels), see para-
graph 2.5.3.1
 Reading the status of appropriate digital status signals (0 V / 5 V logical levels),
paragraph see 2.5.3.3.
The electrical signals are accessible via the two connectors located on the rear side
of PICO D, see Figure 2–8. The top (6 pin) connector connects the DC power supply
to PICO D and the lower (40 pin) connector contains all other electrical control and
status signals, see Figure 2–8.

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Power
connector
Signal
connector
Figure 2–8 Power (top) and signal (lower) connectors are located on the rear
side of PICO D. The full pin configuration of the PICO D power and
signal connectors are shown in Figure 2–15.
Table 2-1 This table list the signals used to control and monitor PICO D
Signal Type Note
_WAVELENGTH_TUNING Analog Control -10 V to + 10 V
_MODE_HOP_ADJUST Analog Control -10 V to + 10 V
_OPTICAL_POWER Analog Control -1 V to + 10 V
_MODE _HOP _ADJUST _ENABLE Digital Control On = 0 V
Off = +5 V
_OPTICAL_POWER_ENABLE Digital Control On = 0 V
Off = +5 V
_WAVELENGTH_TUNING ENABLE Digital Control On = 0 V
Off = +5 V
_COHERENCE _CONTROL ENABLE Digital Control On = 0 V
Off = +5 V
_CONSTANT _CURRENT _ENABLE Digital Control On = 0 V
Off = +5 V
_MODE _HOP _DETECT Digital status TRUE = 0 V
FALSE = +5 V
Duration time
> 100 µs
_SYSTEM _ERROR Digital status TRUE = 0 V
FALSE = +5 V

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Signal Type Note
_TEMPERATURE_ERROR Digital status TRUE = 0 V
FALSE = +5 V
Internal temperature
_WAVELENGTH _ERROR Digital status TRUE = 0 V,
FALSE = +5 V
_OPTICAL_POWER_ERROR Digital status TRUE = 0 V
FALSE = +5 V
2.5.1 Grounding issues
Before connecting PICO D to any electrical power or signal source care must be
taken to avoid ground loops. The ground loops may pick up noise and/or other dis-
turbances from the surrounding electromagnetic environment. Such disturbances
may lead to reduced performances (or malfunctioning) of PICO D.
There are two connectors on the rear side of PICO D, see Figure 2–8; one connec-
tor for electrical power, and one connector for the control and status signals. Both
connectors have pins connected to ground. ALL pins (see Table 2-10 and Table
2-11) labeled GND are physically joined inside PICO D.
We recommend that PICO D is connected to the (signal)ground via the electrical
power connector (in Table 2-10, all Row B pins are 0 V and physically joined). This
connection scheme ensures that the +5 V, +15 V and –15 V supplies can be used to
supply the user’s control electronics. However, a ground connection between the
Row B pins (in Table 2-10) and the ground of the user’s control electronics must be
made.
The three analog control voltages (TUNING_VOLTAGE, OPTICAL_POWER, and
MODE_HOP_ADJUST) are connected to differential input stages having high
CMRR. Hence, it is not recommended that any of the analog control voltages termi-
nals are grounded. See Figure 2–9.

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Figure 2–9 Recommended connection of electrical power and analog signals
to PICO D.
2.5.2 Power supplies
Three external power supplies are required to run the PICO D unit. Table 2-2 lists
the required voltages, and Table 2-3 list the requirements set on the power supplies,
and finally Table 2-10 lists the pin configuration of the DC power connector. The full
pin configuration of the PICO D power and signal connectors are shown in Figure 2–
15.
Table 2-2 DC-power supply
Voltage Comments
+5 V +5 volts supply
GND (+5 V) Return for +5V
connected to the circuit board ground
+15V +15 volts supply