Thorlabs LDC4020 High-Power 20 A Precision Laser Diode Controller

Thorlabs LDC4020 High-Power 20 A Precision Laser Diode Controller

The Thorlabs LDC4020 is a high-power precision laser diode controller designed to operate compatible laser diodes at currents up to 20 A. It provides an 11 V compliance voltage and supports constant-current, constant-power, continuous-wave, modulated, and quasi-continuous-wave operating configurations.

The LDC4020 accommodates laser diodes with either anode-grounded or cathode-grounded polarity. Its 13W3 mixed D-sub laser output includes high-current connections, laser-voltage sensing, photodiode feedback inputs, and interlock connections. A compatible cable or custom connection assembly rated for at least 20 A is required for safe operation at the controller’s maximum output.

For optical power regulation, the controller accepts feedback from a photodiode, thermopile, sensor amplifier, or compatible optical power meter with an analog voltage output. Users can operate a laser diode at a fixed electrical current or close an optical feedback loop to maintain a selected photodiode current, sensor voltage, or calculated optical power.

Features and Benefits of the Thorlabs LDC4020

The Thorlabs LDC4020 provides flexible control and monitoring for professional laser diode systems requiring high current, programmable operation, and integrated protection.

• 20 A laser current capacity: Drives compatible high-power laser diodes over a current range from 0 A to 20 A.
• 11 V compliance voltage: Supports compatible laser diodes and laser assemblies within the controller’s available output envelope.
• Constant-current operation: Regulates laser diode current using the controller’s internal current loop.
• Constant-power operation: Regulates optical output using feedback from a photodiode or voltage-output optical sensor.
• Photodiode feedback: Provides selectable 2 mA and 20 mA monitor-current ranges with configurable polarity and reverse-bias voltage.
• Thermopile input: Supports voltage measurement ranges of 10 mV, 100 mV, 1 V, and 10 V.
• Internal modulation generator: Produces sine, square, or triangle modulation from 20 Hz to 50 kHz.
• External modulation input: Accepts a DC-coupled control signal for laser current, optical power, or wavelength-control applications.
• QCW pulse operation: Supports internally or externally triggered laser pulses with widths from 100 µs to 1 second.
• Computer control: Provides USB 2.0, USBTMC, SCPI commands, and compatible VXIpnp instrument drivers.

High-Power Laser Diode Current Control

The LDC4020 provides a laser diode current range from 0 A to 20 A with an 11 V compliance voltage. The front-panel setting resolution is 1 mA, while remote-control resolution is 320 µA.

Laser current accuracy is specified as ±0.1% of the reading plus 8 mA. Typical RMS ripple and noise are below 10 mA over a bandwidth from 10 Hz to 10 MHz. Typical 24-hour current drift is below 1 mA at a constant ambient temperature.

The adjustable laser current limit protects the connected diode from excessive drive current. The LDC4020 current-limit range extends from 20 mA to 20 A, with 1 mA front-panel resolution and 320 µA remote-control resolution. Current-limit accuracy is specified as ±0.12% of the reading plus 12 mA.

Constant-Current and Constant-Power Modes

In constant-current mode, the LDC4020 closes an internal current-control loop and maintains the selected laser diode current. The controller displays the configured current and the measured output current, allowing users to monitor the electrical drive conditions applied to the laser.

In constant-power mode, the controller uses an external optical feedback signal to regulate laser output. The feedback source can be a photodiode producing a current signal or a thermopile, sensor amplifier, or optical power meter producing a voltage signal.

When the responsivity of the connected sensor is entered, the LDC4020 can calculate and display optical power in watts. Photodiode responsivity can be configured from 0.01 mA/W to 10 A/W, while voltage-sensor responsivity can be configured from 0.01 mV/W to 500 V/W.

Photodiode Feedback Input

The LDC4020 provides selectable photodiode current ranges of 0 mA to 2 mA and 0 mA to 20 mA. The 2 mA range offers higher sensitivity, while the 20 mA range accommodates photodiodes producing greater monitor current.

Photodiode polarity can be configured for anode-grounded or cathode-grounded operation. The controller can also supply a reverse-bias voltage from 0 V to 10 V, with polarity determined by the selected photodiode grounding configuration.

The photodiode input uses a transimpedance amplifier with an approximately zero-ohm virtual-ground input. The sensor can connect through the main 13W3 laser output connector or the rear-panel optical-sensor BNC input.

Thermopile and Voltage-Sensor Feedback

Voltage-output optical sensors can be connected through the 13W3 mixed D-sub connector or rear-panel optical-sensor BNC input. Available measurement ranges are 10 mV, 100 mV, 1 V, and 10 V.

The voltage input has a 1 MO impedance and supports thermopiles, sensor amplifiers, and compatible optical power meters with an analog voltage output. The selected range should match the expected sensor signal to provide the desired balance of range and resolution.

The controller can use the measured voltage as the feedback variable in constant-power mode. When the sensor response is entered, the LDC4020 calculates the corresponding optical power and permits power-based setpoint and limit configuration.

Internal and External Modulation

The internal direct-digital-synthesis generator provides sine, square, and triangle waveforms. On the LDC4020, the available internal modulation frequency range is 20 Hz to 50 kHz, and modulation depth can be adjusted from 0.1% to 100%.

The rear-panel external modulation input is DC coupled and accepts signals up to ±10 V. In constant-current mode, external modulation is added to the laser current setpoint. In constant-power mode, the external signal is applied to the selected optical power feedback setpoint.

The LDC4020 constant-current modulation input has a small-signal 3 dB bandwidth from DC to 50 kHz with a 0.2 O load. The constant-current modulation coefficient is 2 A/V with a ±5% tolerance.

Quasi-Continuous-Wave Pulse Operation

The LDC4020 supports quasi-continuous-wave operation in constant-current mode. QCW pulses can be generated using the internal timing source or triggered by an external signal applied to the rear-panel QCW pulse input.

Pulse width can be configured from 100 µs to 1 second with 1 µs resolution. For internal triggering, the pulse period can be adjusted from 1 ms to 5 seconds, corresponding to repetition rates from 1 kHz down to 0.2 Hz.

The rear-panel trigger output tracks the programmed QCW pulse width and provides a TTL or 5 V CMOS-compatible signal. This output can synchronize compatible oscilloscopes, power meters, data-acquisition systems, and external test equipment.

Laser Diode Protection

The Thorlabs LDC4020 includes multiple protection functions designed to help safeguard the connected laser diode and optical setup.

• Key switch: Prevents unauthorized activation of the laser current output.
• Programmable switch-on delay: Provides an adjustable delay from 0 to 60 seconds before current is applied.
• Soft start: Helps protect the laser diode from undesired current peaks during output activation.
• Adjustable current limit: Restricts the maximum laser diode current in constant-current and constant-power modes.
• Voltage protection: Switches off the output when the configured laser-voltage threshold is reached.
• Interlock circuit: Prevents operation unless the external interlock loop is closed.
• Open-circuit detection: Initiates an emergency shutdown if the laser diode connection is interrupted.
• Electronic shorting: Shorts the laser diode electronically while the current output is disabled.
• Overtemperature protection: Switches off the output if the controller exceeds its permitted internal temperature.
• LD Enable input: Allows external safety or temperature-monitoring equipment to inhibit laser operation.

Four-Wire Laser Voltage Measurement

The LDC4020 supports four-wire laser diode voltage measurement to reduce errors caused by voltage drop along the high-current output cables. Dedicated voltage-sensing conductors can be connected close to the laser diode terminals independently of the main current-carrying conductors.

The laser voltage measurement range is 0 V to 14 V. Front-panel resolution is 1 mV, remote resolution is 160 µV, and measurement accuracy is specified at ±20 mV.

Adjustable laser overvoltage protection extends from 1 V to 11 V with 1 mV resolution and ±50 mV accuracy. The protection threshold should be configured appropriately for the connected laser diode.

USB Interface and Automated Control

The LDC4020 includes a USB 2.0 Full Speed interface supporting USBTMC and USBTMC-USB488 protocols. Its SCPI-compliant command set enables integration with automated laboratory, characterization, and production systems.

Compatible VXIpnp instrument drivers support programming environments such as NI LabVIEW, NI LabWindows/CVI, Microsoft Visual Studio, and Microsoft Visual Studio .NET. A suitable VISA library with USBTMC support is required for computer communication.

Remote operation can be used for setting laser current, configuring optical feedback, reading current and voltage, adjusting modulation, controlling QCW parameters, monitoring status, and retrieving error information.

Typical Applications

The Thorlabs LDC4020 Laser Diode Controller is suitable for professional applications such as:

• High-power laser diode current control
• Laboratory laser diode characterization
• Constant optical power regulation
• Laser diode burn-in and life testing
• Laser module development and qualification
• Pulsed and quasi-continuous-wave laser operation
• Laser wavelength modulation
• Photonics research and development
• Optical component production testing
• Automated laser diode measurements
• Semiconductor laser evaluation
• High-power optical source development

Product Overview

Brand	Thorlabs
Model	LDC4020
Product Family	LDC4000 Series
Product Category	High-Power Precision Laser Diode Controller
Laser Current Range	0 A to 20 A
Compliance Voltage	11 V
Operating Modes	Constant current, constant power, CW, modulated, and QCW
Feedback Sensors	Photodiode and thermopile or compatible voltage-output optical sensor
Computer Interface	USB 2.0 with USBTMC and SCPI support
Primary Application	Precision control and monitoring of compatible high-power laser diodes

 

Laser Current Control Specifications

Specification	Details
Laser Diode Current Range	0 A to 20 A
Compliance Voltage	11 V
Current Setting Resolution	1 mA from the front panel; 320 µA through remote control
Current Measurement Resolution	1 mA from the front panel; 320 µA through remote control
Current Accuracy	±(0.1% of reading + 8 mA)
Typical Ripple and Noise	Less than 10 mA RMS from 10 Hz to 10 MHz
Typical 24-Hour Drift	Less than 1 mA at constant ambient temperature
Current-Limit Range	20 mA to 20 A
Current-Limit Resolution	1 mA from the front panel; 320 µA through remote control
Current-Limit Accuracy	±(0.12% of reading + 12 mA)

 

Optical Feedback Specifications

Specification	Details
Photodiode Current Ranges	0 mA to 2 mA and 0 mA to 20 mA
Photodiode Measurement Resolution, 2 mA Range	1 µA from the front panel; 32 nA through remote control
Photodiode Measurement Resolution, 20 mA Range	10 µA from the front panel; 320 nA through remote control
Photodiode Accuracy, 2 mA Range	±(0.08% of reading + 0.5 µA)
Photodiode Accuracy, 20 mA Range	±(0.08% of reading + 5 µA)
Photodiode Reverse-Bias Voltage	0 V to 10 V
Photodiode Input Impedance	Approximately 0 O virtual ground
Voltage-Sensor Ranges	0 mV to 10 mV, 0 mV to 100 mV, 0 V to 1 V, and 0 V to 10 V
Voltage Input Impedance	1 MO

 

Modulation and QCW Specifications

Specification	Details
Internal Modulation Waveforms	Sine, square, and triangle
Internal Modulation Frequency	20 Hz to 50 kHz
Internal Modulation Depth	0.1% to 100%
External Modulation Input Range	Maximum ±10 V
External Modulation Input Impedance	Greater than 10 kO
Constant-Current Modulation Bandwidth	DC to 50 kHz with a 0.2 O load
Constant-Current Modulation Coefficient	2 A/V ±5%
QCW Pulse-Width Range	100 µs to 1 second
QCW Pulse-Width Resolution	1 µs
QCW Repetition-Period Range	1 ms to 5 seconds
QCW Repetition-Rate Range	0.2 Hz to 1 kHz
QCW Trigger	Internal or external rising-edge trigger

 

Laser Voltage and Monitoring Specifications

Specification	Details
Voltage Measurement Principle	Four-wire measurement supported
Laser Voltage Measurement Range	0 V to 14 V
Laser Voltage Resolution	1 mV from the front panel; 160 µV through remote control
Laser Voltage Accuracy	±20 mV
Overvoltage Protection Range	1 V to 11 V
Overvoltage Protection Resolution	1 mV
Overvoltage Protection Accuracy	±50 mV
Current Monitor Output	500 mV/A ±5%
Current Monitor Load Resistance	Greater than 10 kO

 

Interfaces and Connections

Connection	Interface
Laser, Photodiode, Interlock, and Status	Female 13W3 mixed D-sub jack
LD Enable Input	BNC
QCW Pulse Input	BNC
Trigger Output	BNC
Optical Sensor Input	BNC
External Modulation Input	BNC
Analog Current Monitor Output	BNC
USB Interface	USB Type B
Digital I/O	Six-pin Mini-DIN with four separately configurable lines
Chassis Ground	4 mm banana jack
Mains Input	IEC 60320

 

Electrical, Mechanical, and Environmental Specifications

Specification	Details
Line Voltage	100 V to 120 V AC ±10% or 200 V to 240 V AC ±10%
Line Frequency	50 Hz to 60 Hz ±5%
Maximum Power Consumption	600 VA
Dimensions Without Operating Elements	263 mm wide x 122 mm high x 307 mm deep
Dimensions With Operating Elements	263 mm wide x 122 mm high x 345 mm deep
Weight	5.5 kg
Operating Temperature	0 °C to 40 °C, non-condensing
Storage Temperature	-40 °C to 70 °C
Relative Humidity	Maximum 80% up to 31 °C, decreasing to 50% at 40 °C
Maximum Operating Altitude	Below 2000 m
Warm-Up Time for Rated Accuracy	30 minutes

 

Compatible Accessories

Accessory	Description
CAB4006	Shielded 20 A cable with male 13W3 mixed D-sub connectors for compatible high-power laser diode mounts
CON4005	20 A mixed 13W3 D-sub connector kit with high-current contacts
CAL-LDC4000	Recalibration service for an LDC4000 Series controller
TED4015	Compatible temperature controller for supported temperature-window protection

 

Connection and Compatibility Considerations

The LDC4020 can deliver up to 20 A through its 13W3 mixed D-sub laser output. The connector contacts, wiring, laser mount, and cables used in the output circuit must be rated for the required current. The CAB4006 cable is the documented Thorlabs connection cable for compatible high-power laser diode mounts.

Laser diode polarity must be configured correctly before the output is enabled. The LDC4020 supports both anode-grounded and cathode-grounded devices, but an incorrect polarity selection or wiring arrangement can damage the connected diode.

The laser current limit, overvoltage threshold, interlock, and applicable power limits should be configured before operation. The controller’s protection functions do not replace proper electrical design, heat sinking, temperature control, laser safety procedures, or compatibility verification.

Calibration Before Shipment

When calibration is technically applicable and supported, the Thorlabs LDC4020 is calibrated before shipment. Calibration may include verification of laser current accuracy, current measurement, current limits, laser voltage measurement, voltage protection, photodiode inputs, voltage-sensor inputs, modulation response, monitor output, and USB communication.

Following successful calibration, the controller may include a calibration label, calibration certificate, and associated measurement data, depending on the selected calibration service and equipment condition.

If formal calibration is unavailable or not included, the LDC4020 receives comprehensive functional and performance testing. Testing may include power-up, display and controls, current-output operation, current limiting, voltage measurement, photodiode and thermopile inputs, internal modulation, external modulation, QCW triggering, interlock response, LD Enable input, digital I/O, and USB communication.

The exact calibration scope, measurement data, output cable, connector kit, supplied documentation, firmware version, and service records should be confirmed before purchase when these items are required for laboratory, production, regulatory, or quality-management applications.

Buyer Considerations

The Thorlabs LDC4020 is a high-current laser diode controller intended for compatible laser diodes and mounts. Buyers should confirm that the 20 A current range, 11 V compliance voltage, laser polarity, 13W3 connection, feedback sensor, modulation requirements, and protection settings match the intended laser assembly.

The LDC4020 does not include an integrated thermoelectric temperature controller. A separate compatible temperature controller may be required to stabilize the laser diode mount and support temperature-window protection.

The LDC4020 should not be confused with the LDC4005, which provides a lower 5 A current range and different noise and modulation characteristics. Buyers should review the unit’s display, controls, output connector, BNC interfaces, cooling fan, USB port, calibration status, and included accessories before purchase.

Why Buy from AssetRelay?

AssetRelay supplies professional equipment and product solutions for fiber optic, telecom, laboratory, production, inspection, cleaning, RF/microwave, electronic test, and photonics applications. The Thorlabs LDC4020 supports engineers, laboratories, production facilities, procurement teams, and service organizations that require precision control of compatible high-power laser diodes.

Buyers should review the available product photographs, physical condition, 13W3 output connector, BNC interfaces, included cables, connector kit, firmware information, calibration status, and laser diode compatibility before purchase.

Only accessories specifically identified in the product listing should be considered included. A suitable 20 A output cable, connector kit, laser diode mount, temperature controller, optical sensor, USB cable, interlock hardware, and supporting test equipment may be required separately.