THORLABS TLD001 User manual

HA0184T
TLD001
Laser Diode Driver
Kinesis User Guide
Original Instructions

T-Cube Laser Diode Driver
Contents
Chaper 1 Overview ................................................................................................... 1
1.1 Introduction ........................................................................................ 1
1.2 Power Supply Options ....................................................................... 2
1.3 Kinesis Software Overview ............................................................... 2
1.3.1 Introduction ............................................................................................. 2
1.3.2 Kinesis Server ........................................................................................ 3
1.3.3 Software Upgrades ................................................................................. 4
Chaper 2 Safety .......................................................................................................... 5
2.1 Safety Information ............................................................................. 5
2.2 General Warnings .............................................................................. 5
2.3 Warnings Relating To Laser Safety .................................................. 6
Chaper 3 Getting Started ........................................................................................... 7
3.1 Mechanical Installation ...................................................................... 7
3.1.1 Environmental Conditions ....................................................................... 7
3.1.2 Mounting Options ................................................................................... 7
3.1.3 Removing the Baseplate ........................................................................ 8
3.2 Rear Panel Connections Overview ................................................... 9
3.2.1 Rear Panel Description ........................................................................... 9
3.3 Power Supply Connection ................................................................ 9
3.3.1 Supply Voltage and Current Requirements ............................................ 9
3.3.2 Connection To A Standalone Power Supply ........................................ 10
3.3.3 Configuring The Unit to the Laser Diode .............................................. 11
3.3.4 Laser Diode Polarity ............................................................................. 11
3.3.5 Connecting the Photodiode with Bias ................................................... 13
3.3.6 Laser Diode Drive Current Limit ........................................................... 13
3.3.7 Photodiode Current (IPD) Range ......................................................... 15
3.3.8 Optimization of the PD Current Gain .................................................... 15
3.3.9 Calibrating the Power Display .............................................................. 16
3.3.10 Summary .............................................................................................. 17
3.3.11 Using the Safety Interlock and Key Switch ........................................... 18
Continued...

T-Cube Laser Diode Driver
Chaper 4 Standalone Operation .............................................................................. 20
4.1 Introduction ...................................................................................... 20
4.2 Control Panel Buttons and Indicators .......................................... 20
4.3 Set Up Preparation ........................................................................... 21
4.4 Front Panel Set Up Procedure ........................................................ 22
4.5 Manual Operation Tutorial .............................................................. 28
4.6 Error Codes ...................................................................................... 28
4.7 Output Potentiometer Operation .................................................... 28
4.8 Mode Button Operation ................................................................... 29
4.8.1 Constant Current Mode (CONST I) ...................................................... 29
4.8.2 Constant Power Mode (CONST P) ....................................................... 29
Chaper 5 PC Operation - Tutorial ............................................................................ 30
5.1 Introduction ...................................................................................... 30
5.2 Install The Software ......................................................................... 30
5.3 Set Up Preparation ........................................................................... 31
5.4 Set Up Via The GUI Panel ................................................................ 32
5.5 Modulation of the Laser Diode Output ........................................... 35
Chaper 6 Software Reference ................................................................................. 37
6.1 GUI Panel .......................................................................................... 37
6.2 Settings Panel .................................................................................. 39
6.2.1 Control Tab .......................................................................................... 40
6.2.2 Max Current Tab .................................................................................. 42
6.2.3 Photodiode Tab ................................................................................... 43
6.2.4 Advanced Tab ..................................................................................... 44
Appendices
Appendix A Rear Panel Connector Pinout Details ....................................45
Appendix B Preventive Maintenance .........................................................47
Appendix C Specifications ..........................................................................48
Appendix D Regulatory ................................................................................49
Appendix E Thorlabs Worldwide Contacts ................................................51

Page 1 17874-D03
T-Cube Laser Diode Driver
Chapter 1 Overview
1.1 Introduction
The TLD001 T-cube is a versatile, high precision laser diode/LED driver, designed to
drive a wide range of semiconductor laser diodes. It supports operating currents of up
to 200 mA, a hig h compliance voltage of 8 Vol ts and both constant current and
constant power operating modes. As a member of the T-cube family of products, the
TLD001 allows both standalone use or PC-based operation via USB interface.
This laser diode driver is a highly compact yet fully functional unit. It is provided with
a USB interface for easy PC control and also a manual interface panel containing a 5
digit 7 Segment display, adjustment potentiometer, Mode, Display and Laser ON
buttons, and safety key switch.
The unit can be set to control either the injection current or the optical output power
of the laser diode.
For convenience the footprint of this unit has been kept to a minimum, measuring only
120mm x 60mm x 47mm (4.8" x 2.4" x 1.8") and with the facility to directly mount to
the optical table. The manual controls for this unit are conve niently located on the
upper surface. The Mode and Display buttons allow the various operating modes to
be selected easily. There is also a key switch and interlock connector fitted to thi s
compact unit for use in laser applications requiring such functionality.
Fig. 1.1 T-Cube laser diode driver (TLD001)
USB connectivity provides easy 'Plug and Play' PC controlled operation - multiple T-
Cube units can be connected to a single PC via standard USB hub technology, or by
using the T-Cube Controller Hub (see over). Co upling this wi th the user friendly
Kinesissoftware (supplied) allows the user to get up and running in a short space of
time. Advanced custom app lications and sequences are a lso possible using the

Rev A Nov 2017 Page 2
Chapter 1 Overview
extensive programming environment also supplied. This p rogramming library is
compatible with many development tools such as LabView, Visual Basic, Visual C++,
C++ Builder, LabWindows/CVI, Matlab and Delphi.
See Section 1.3. for a full description of the Kinesis system software.
In the remainder of this handbook, the Tutorial section (Chapter 5) provides a good
initial understanding on using the unit, and the reference section (Chapter 6) covers
all operating modes and parameters in detail.
1.2 Power Supply Options
Thorlabs offers a compact, two-way power supply unit (TPS002), allowing up to two
Laser Diode driver T-Cubes to be powered from a single mains outlet.
As a further level of convenience when using these Controllers, Thorlabs also offers
the 3-channel and 6-channel K-Cube Controller Hubs (KCH301 and KCH601). These
products have been designed specifically with multiple Cube operation in mind, in
order to simplify issues such as cable management, power supply routing, multiple
USB device communications and different optical table mounting scenarios.
The K-Cube Controller Hub comprises a sl im base-plate type carrier with ele ctrical
connections located on the upper surface to accept the Cubes.
Internally the Controller Hub contains a fully compliant USB 2.0 hub circuit to provide
communications for all Cubes – a single USB connection to the Controller Hub is all
that is required for PC control. The Controller Hub also provides power distribution for
the Cubes, requiring only a single power connection.
1.3 Kinesis Software Overview
1.3.1 Introduction
The K-Cube range of controllers share many of the benefits. These include USB
connectivity (allowing multiple units to be used together on a single PC), fully featured
Graphical User Interface (GUI) panels, and extensive software function libraries for
custom application development.
The Kinesis software suite provides a flexible and powerful PC based control system
both for users of the equipment, and software programmers aiming to automate its
operation.
The User Interface allows full control of all settings and operating modes enabling
complete ‘out-of-box’ operation without the need to de velop any further custom
software. It provides all of the necessary system software services such as generation
Caution
The KCH301 and KCH601 Controller Hubs have been designed primarily for
use with the K-Cube range of controller units. T-Cube controllers such as the
TDC001 TEC Controller can still be used on this hub, but will require an adapter
plate (KAP102) before they can be fitted.

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T-Cube Laser Diode Driver
of GUI panels, communications handling for multiple USB units, and logging of all
system activity to assist in hardware trouble shooting. The Kinesis server is also used
by software developers to a llow the creation of advanced automated positioning
applications very rapidly and with great ease. The server is described in more detail
in the following section.
1.3.2 Kinesis Server
Kinesis controls are re-usable compiled software components that supply both a
graphical user interface and a pro grammable interface. Many such Co ntrols are
available for Windows applications development, providing a large range of re-usable
functionality. For example, there are Controls available that can be used to
manipulate image files, connect to the intern et or simply pro vide user in terface
components such as buttons and list boxes.
With the Kinesis system, .Net Controls are deployed to allow direct control over (and
also reflect the status of) the range of electronic controller units, including the Piezo
K-Cube. Software applications that use .Net Controls are often referred to as 'client
applications'. A .Net Co ntrol is a language independent software component.
Consequently the controls can b e incorporated into a w ide range of software
development environments for u se by client application developers. Development
environments supported include Visual Basic, Labview, Visual C++, C++ Builder,
HPVEE, Matlab, VB.NET, C#.NET
and, via VBA, Microsoft Office applications such as
Excel and Word.
Consider the Control supplied for a TLD001 Laser Diode driver unit .
This Control provides a complete user graphical instrument panel to allow the Laser
Diode unit to be manually operated, as well as a complete set of software functions
(often called methods) to allow all parameters to be set and laser control operations
to be automated by a client application. The instrument panel reflects the curre nt
operating state of the driver unit to which it is associated. Updates to the panel take
place automatically when a user (client) application is making software calls into the
same Control. For example, if a client application instructs the associated Laser Diode
Control to set a pa rticular output power, progress is monitored automatically by
changing power readout on the graphical interface, without the need for further
programming intervention.

Rev A Nov 2017 Page 4
Chapter 1 Overview
The Kinesis software provides a rich set of graphical user panels and programmable
interfaces allowing users and client application developers to interact seamlessly with
the hardware. Each of the co ntrollers has an associated GUI Control and these are
described fully in the handbook for the associated controller.
Fig. 1.2 System Architecture Diagram
Refer to the main Kinesis Soft ware online help file, for a co mplete programmers
guide. This is available either by pressing the F1 key when running the Kinesis server,
or via the Start menu, Start\Programs\Thorlabs\Kinesis\.Net API Help.
1.3.3 Software Upgrades
Thorlabs operate a policy of continuous product development and may issue software
upgrades as necessary. The latest software can be downloaded from the ‘services’
section of www.thorlabs.com.

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T-Cube Laser Diode Driver
Chapter 2 Safety
2.1 Safety Information
For the continuing safety of the operators of this equipment, and the protection of the
equipment itself, the operator should take note of the Warnings, Cautions and Notes
throughout this handbook and, where visible, on the product itself.
The following safety symb ols may be used throughout the handbook and on the
equipment itself.
2.2 General Warnings
Warning: Risk of Electrical Shock
Given when there is a risk of injury from electrical shock.
Warning
Given when there is a risk of injury to users.
Caution
Given when there is a risk of damage to the product.
Note
Clarification of an instruction or additional information.
Warning
If this equipment is used in a manner not specified by the manufacturer, the
protection provided by the equipment may be impaired. In particular, excessive
moisture may impair operation.
Spillage of fluid, such as sample solutions, should be avoided. If spillage does
occur, clean up immediately using absorbant tissue. Do not allow spilled fluid to
enter the internal mechanism.

Rev A Nov 2017 Page 6
Chapter 2 Safety
2.3 Warnings Relating To Laser Safety
Warning
In itself, this laser driver does not produce any laser radiation, and Thorlabs has
no control over the rating of the laser diodes this product may be used to drive.
It is the users responsibility to ensure that the appropriate protection is used,
and that standard safety precautions observed. The users attention is drawn to
the following precautions:
Inappropriate use of any Laser product could result in permanent eye damage.
To prevent injury, all personnel in the vi cinity of the laser driver should wear
appropriate eye protection.

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T-Cube Laser Diode Driver
Chapter 3 Getting Started
3.1 Mechanical Installation
3.1.1 Environmental Conditions
Location Indoor use only
Maximum altitude 2000 m
Temperature range 5oC to 40oC
Maximum Humidity Less than 80% RH (non-condensing) at 31°C
To ensure reliable operation the unit should not be e xposed to corrosive agents or
excessive moisture, heat or dust.
If the unit has been stored at a low temperature or in an environment of high humidity,
it must be allowed to reach ambient conditions before being powered up.
3.1.2 Mounting Options
The T-Cube Laser Driver is shipped with a ba seplate fitted, ready to be bolted to a
breadboard, optical table or similar surface.
If required, the baseplate can be removed and the unit can be stood on rubber feet -
see Section 3.1.3.
For multiple cube system s, a USB controller hub is available - see Section 1.2. for
further details. Full instructions o n the fitting and use o f the controller hub are
contained in handbook for the product.
Warning
Operation outside the foll owing environmental limits may ad versely affect
operator safety.
Caution
When siting the unit, it should be positioned so as not to impede the operation
of the control panel buttons.
Ensure that proper airflow is maintained to the rear of the unit. Do not cover the
ventilation holes in the case.
Note
During its operation the T-Cube Laser Driver dissipates some heat that causes a
temperature rise inside the unit. This in turn, can reduce the precision of the unit
slightly, especially at high output currents. For the highest level of precision it is
therefore beneficial to mount the unit onto the optical table (or other metal surface)
where the large metal surface of the table will conduct most of the heat away from
unit. Mounting the unit on the TCH002 hub will also have the same benefit

Rev A Nov 2017 Page 8
Chapter 3 Getting Started
3.1.3 Removing the Baseplate
In order to help mounting the unit to an optical table, a baseplate is provided with the
unit. However, if the unit is required to be operated free-standing (for example on a
bench), the baseplate can be removed and rubber feet fitted.
The baseplate must be removed before the rubber feet (supplied) can be fitted, or the
unit is connected to the USB controller hub.
Fig. 3.1 Removing The Baseplate
1) Using a hexagon key, remove the bolts securing the unit to the baseplate. Retain
the bolts for future use if the baseplate is refitted.
2) Turn the unit upside down.
3) Remove the backing paper from the rubber feet (supplied) taking care not to touch
the exposed adhesive surface.
4) Position the feet as desi red, then press and hold for a fe w seconds until the
adhesive has bonded.
5) The unit may now be used freestanding, sitting on its rubber feet.
Detail A
Detail B
Baseplate attachment screws

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T-Cube Laser Diode Driver
3.2 Rear Panel Connections Overview
3.2.1 Rear Panel Description
Fig. 3.2 Rear Panel Connections
PD RANGE – These micro switches are used to set the current range appropriate for
the photo diode being used 10 mA, 1 mA, 100 µA or 10 µA. - see Section 3.3.7.
LD OUT (9-Pin D-Type) – The ‘LD OUT’ connector exposes a number of electrical
terminals used when connecting the laser diode or photo diode - see Section 3.3.4.
It also exposes the Interlock connection, which must be closed before the laser diode
can be turned on - see Section 3.3.11. For pin out details, see Appendix A.2
MOD IN (SMA connector) – Modulation or analog control input, -10V to +10V - see
Section 5.5.
3.3 Power Supply Connection
3.3.1 Supply Voltage and Current Requirements
Note
Thorlabs supply a variety of SMA to BNC and SMC to BNC adaptor and extension
cables. Please see our catalog, or visit www.thorlabs.com for further details.
Warning
Exceeding the power supply maximum voltage, or connecting a reverse polarity
voltage can cause permanent damage to the unit and could result in personal
injury.
Supply Minimum Maximum Max Operating Current
+5V +4.9V +5.1V 400 mA
+15V +14.5V +15.5V 250 mA
-15V -14.5V -15.5V 250 mA
LD OUT MOD IN
PD RANGE
10μA
100μA
1mA
10mA 12345
6789

Rev A Nov 2017 Page 10
Chapter 3 Getting Started
3.3.2 Connection To A Standalone Power Supply
Fig. 3.3 Front Panel Power Supply Connector
1) Using the front panel connector as shown above, connect the unit to a regulated
DC power supply of the rating detailed in Section 3.3.1.
2) Switch on the Power Supply unit.
3) The Version number of the embedded software is displayed for a few seconds.
4) If the unit is to be used with a PC, connect the USB cable.
Thorlabs offers a compact, two-way power supply unit (TPS002), allowing up to two
Laser Diode driver T-Cubes to be powered from a single mains outlet. However, if an
external supply is to be used, see Appendix A.1 for power supply connector pin out
details.
Warning
The unit must be connected only to a DC supply as detailed in Section 3.3.1.
Connection to a supply of a different rating may cause damage to the unit and
could result in injury to the operator.
Caution
If an external power supply is used, ensure that the 3 supply voltages are turned
on and off simultaneously. Applying the supply voltages with a large (> 1s)
delay between them can result in the laser diode driver cube showing an
incorrect reading.
USB POWER
DC ±15V, +5V

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T-Cube Laser Diode Driver
3.3.3 Configuring The Unit to the Laser Diode
Before the laser diode controller can be used, it must be configured to operate with
the specific laser diode it i s intended to drive. T he following section explains why
certain parameters must be set for specific types of laser diode. The set up procedure
may be performed manu ally, using the top panel buttons (see Section 4.4.) o r
remotely via a PC (see Section 5.4.).
The configuration process consists of the following main steps:
- setting the laser diode polarity,
- setting the maximum laser current,
- adjusting the photodiode range and gain,
- optical power calibration.
These steps only need to be done once for a given laser diode. Once the setup has
been completed, the TLD001 stores the corresponding parameters in non-volatile
memory and they are loaded automatically at each power-up.
3.3.4 Laser Diode Polarity
Laser diodes are manufactured in a variety of packages and pin configurations, with
or without an internal photodiode. In addition, normally one terminal of the laser diode
is connected to the metal case and commoned with either the anode and cathode of
the photodiode.
The TLD001 has been designed to drive all the possible configurations but care is
needed to ensure that the l aser diode is connected to the controller correctly.
Although the TLD001 provides some protection against some common wiring errors,
some faults, such as accidentally swapping the laser diode and the photodiode or
connecting the laser diode with reverse po larity can still cause damage to the laser
diode module.
For the lowest noise and highest level of protection, the case of the laser diode
package should always be connected to the electrical system ground. Since normally
the case will also be electrically connected to either the anode or the cathode of the
laser diode, this results in two common configurations: anode grounded (AG) and
cathode grounded (CG). This can be established from the laser diode data sheet and
the device should be connected to the D-type connector on the TLD001 accordingly.
Additionally, in most cases either the anode or the cathode of the internal photodiode
(if there is one) is also connected to the case, resulting in four possible configurations,
as shown in Fig. 3.4.

Rev A Nov 2017 Page 12
Chapter 3 Getting Started
.
Fig. 3.4 Laser diode connections
Whilst these four config urations are the most commonly found, in some cases the
laser diode, or the photodiode or both are isolated, i.e. electrically not connected to
the case. For these types of laser diode to be used with the TLD001 unit, one terminal
of the laser diode and/or photodiode MUST BE grounded externally, ideally as close
to the case as possible.
Fig. 3.5 Floating laser diode & photodiode connections
The polarity of the laser diode may be set via the top panel buttons (see Section 4.4.)
or through the GUI settings panel (see Section 5.4.):
Note
In this case, the ground connection (pin 3) may be connected to the anode (pin 8) or
the cathode (pin 7) of the laser diode, and to the anode (pin 4) or the cathode (pin 2)
of the photodiode. In order to prevent measuring errors, this connection should be
made as close as possible to the laser diode.
LD PD LD PD LD PD LD PD
Anode Grounded Anode Grounded Cathode Grounded Cathode Grounded
LD OUT Connector
1 23 45
6789
1 23 45
6789
1 2345
6789
1 2345
6789
LD PD
LD OUT Connector
1 23 45
6789

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T-Cube Laser Diode Driver
3.3.5 Connecting the Photodiode with Bias
There are 2 modes of operation for photodiodes; zero bias (photovoltaic mode) or
reverse bias (photoconductive mode). When operating with zero bias, light falling on
the diode causes a current across the device, leading to forward bias which in turn
induces "dark current" in the opposite direction to the p hotocurrent. The normal
operating mode for the TLD001 is photovoltaic (zero bias) mode.
With reverse bias, a b attery is connected in series with the photodiode to hold the
device in reverse bias. This is normally done to improve the transient response (i.e.
speed) of the photodiode. If the photodiode is to be operated with reverse bias, the
battery can be connected as shown in Fig. 3.6 below.
Fig. 3.6 Battery connections for biassed operation
3.3.6 Laser Diode Drive Current Limit
Setting the maximum current the unit can output under any operating conditions
ensures that the laser diode cannot be damaged by accidental overdriving. Individual
laser diodes show a very large production spread, and the maximum current that a
given device can be operated at varies from device to device.
From an electrical point of view, laser diodes are similar to LEDs, in that both devices
are semi conductor diodes that emit light. However, while LEDs are ve ry simple to
use, require no device-to-device characterization, and are rel atively resilient to
damage, laser diodes need far more sophisticated driver electronics.
For example, most common small LEDs work reasonably well at 10mA. Laser diodes
on the other hand, need to be individually set to an operating current. Furthermore,
because of their inherent sensitivity to the operating conditions, some devices may
not produce any laser light at a particular current, while others may become damaged
at the same current.
In addition, it is helpful to consider the output powe r versus drive current
characteristics of laser diodes as shown on the next page.
AG with Bias CG with Bias
LD OUT PIn No.
2
_
+
4
+
_

Rev A Nov 2017 Page 14
Chapter 3 Getting Started
Fig. 3.7 Laser Diode Power v Current Characteristics
Fig. 3.7 shows a typical laser diode power v current be havior. At currents be low a
certain ‘threshold current’, the laser diode produces very little optical power. Once a
threshold current is exceeded, the output power starts increasing very rapidly. At a
particular current the optical power reaches a maximum value specified for the
device, and any further increase can easily damage the laser diode, even if it occurs
only for a very short length of time (a few % above the maximum operating current for
a microsecond can cause a catastrophic failure).
The threshold current and maximum operating current vary from device to device,
therefore the operating conditions for individual laser diodes must b e set very
carefully. The threshold and maximum operating current values are also very
sensitive to te mperature, therefore it is recomme nded that laser diodes are n ot
operated above 80% of their rated maximum output power.
Generally, unless the electrical parameters of the given laser diode are already known
(i.e. the diode has been characterized), the drive current li mit must be d erived by
experiment. This involves connecting an optical power meter to the laser diode and
continually monitoring the optical power whilst gradually increasing the drive current,
taking care to stay within the maximum optical power quoted by a safe margin (usually
20%).
In general, setting the maximum current must be performed with extreme caution. The
process is complicated by the temperature dependence of the laser power: as the
laser diode chip warms up, the optical power decreases. This can create a potentially
dangerous situation during current limit adjustment. The problem is that since during
the current limit adjustment the laser chip warms up, the ma ximum laser c urrent
adjustment will be made for a warm laser diode chip. If now the laser diode is turned
off, allowed to cool down and then turned back on again with the maximum la ser
current applied, the cold laser diode chip will produce a much higher optical power
40
30
20
10
10 20 30 40 50
O/P Power
(mW)
Forward current (mA)
25°C 60°C
limit

Page 15 17874-D03
T-Cube Laser Diode Driver
output. If thi s exceeds the limit specified for the laser diode, the device can get
damaged.
3.3.7 Photodiode Current (I
PD
) Range
Regardless of whether the photodiode is operated in zero bias or reverse bias mode,
the current range applicable to the photodiode selected must be set.
This is because each photodiode produces a different photocurrent, and therefore it
is not possible to cover all possible devices with a single range. For photodiodes that
are part of a laser diode package, the photocurrent produced at the rated maximum
power is normally published in the data sheet, so setting the range can be done easily.
The unit has 4 settings to accommodate photodiode current ranges from 1 0µA to
10mA. The range can be selected using the micro switches accessible via the rear
panel.
Fig. 3.8 Rear panel PD RANGE micro switches
The photodiode current range is normally done with the laser diode operating at the
drive current limit, when the photodiode will produce a specific photo current. If this
photocurrent value is known, the PD RANGE switches on the rear panel can simply
be set to the correct range. If the photocurrent value is not known, then the procedure
involves switching the TLD001 into a special PD RANGE adjustment mode and trying
all ranges from 10mA downwards. The unit will indicate whether a given range is too
high, too low, or correct. - see Section 4.4. or Section 5.4.
3.3.8 Optimization of the PD Current Gain
Optimization of the PD Current Gain, is an automated process performed internally
by the unit, and should be performed only after the PD RANGE has been adjusted.
In the Kinesis system, the software “dem and” of how m uch current (in constant
current mode) or optical power (in closed loop mode) is being generated by the laser
Note
It is not unusual for the published value to be specified with a factor of 4 tolerance
(e.g. min. 0.5mA, max 2.0mA) and sometimes the values may fall in different ranges.
In other instances, for example when an external photodiode is used, the range may
not be known. Even if the range is unknown, the TLD001 offers a quick and simple
procedure to allow the correct range to be set.
10 1 0.1
PD RANGE
1 2 3 4 5 6
ON DIP
Range 10μA
10 1 0.1
PD RANGE
1 2 3 4 5 6
ON DIP
Range 100μA
10 1 0.1
PD RANGE
1 2 3 4 5 6
ON DIP
Range 1mA
10 1 0.1
PD RANGE
1 2 3 4 5
ON DIP
Range 10mA

Rev A Nov 2017 Page 16
Chapter 3 Getting Started
diode is set by a digital to analog converter (DAC). This DAC produces a voltage that
the software can set to be between zero and a fixed reference voltage.
When constant po wer mode is selected , a cl osed loop controller is set up that
continuously reads the photocurrent and adjusts the laser power accordingly, so that
the photocurrent is always equal to a “setpoint” value (the optical power is kept
constant by keeping the photocurrent constant.). To enable the full range of the DAC
to be used, the photodiode current readings must b e “normalized”, so that the full
range (i.e. maximum photocurrent) corresponds to the DAC full range. The “optimize
current gain” button carries out this normalization.
For example, assume the DAC generates a vo ltage between zero a nd 5 Volts
maximum.
In a pa rticular set up, we may find tha t at maximum optical power, the photodiode
produces 25 µA. When the “Optimize TIA current gain” button is pressed, the system
adjusts the photodiode TIA gain to 0.2 V / µA so that the photodiode amplifier outputs
5 Volts.
In another setup, the photodiode produces a different current for max optical power,
so a different photodiode amplifier gain is required.
For convenience, it is preferable to initiate the optimization process from the GUI
Settings panel because this is more visually intuitive - see Section 5.4. (once the unit
has been configured to work with the chosen laser diode, further operation can then
be performed without a PC). However, it is also possible to perform the optimization
process from the top panel buttons, without a control PC - see Section 4.4.
3.3.9 Calibrating the Power Display
The displayed power is derived from the photodiode current, and the relationship
between these parameters will differ between laser diodes. Therefore, the power
display must be tuned to the diode being driven before the output power of the laser
diode can be shown or adjusted accurately. This can be achieved via the front panel
configuration menu (see Section 4.4.) or by entering a Watts/Amps calibration factor
in the GUI Settings panel (see Section 5.4.).

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T-Cube Laser Diode Driver
3.3.10 Summary
1) For the TLD001 unit to dri ve a la ser diode satisfactorily, the fol lowing pre-
requisites must be met:
•Either the anode or the cathode of the laser diode must be connected to ground.
•If a particular laser diode has the anode or cathode connected to the case, then this
terminal is the grounded terminal.
•Most laser diodes also have a built in photodiode. If the photodiode is present, then
its anode or cathode must also be connected to ground.
•In most cases, if the laser diode is supplied in a package with a built in photodiode,
one of the photodiode terminals will be connected to the case. This configuration
is dictated by the package.
•You must not use a ‘floating’ photodiode. Either the anode or cathode must be
connected to the system ground.
2) The displayed power is derived from the Photodiode current, which is wavelength
and temperature dependent. The wavelength also varies wi th temperature.
Therefore, the power readout will not be stable unless a TEC stabilized mount
(such as the LDM90) and compatible controller (TTC001) is used.