CTL200 v5+ User Guide

Last updated: 2023-05-10 PDF version
This user guide is for the CTL200 v5+. For previous versions, please refer to the <v5 guide.
CTL200v5 Digital butterfly laser diode controller user interface
CTL200v5 user interface

Laser connections

The CTL200-1 / CTL200-2 is compatible with Type 1 / Type 2 butterfly laser diodes. Note that it is only compatible with floating diodes.

Butterfly laser type 1 pin configuration
Butterfly laser type 1 pin configuration
Butterfly laser type 2 pin configuration
Butterfly laser type 2 pin configuration

Terminal block connections

  • RX, TX: Serial interface pins.
  • AI1, AI2: Auxiliary analog inputs between 0 and 2.5 V.
  • DO1, DO2: Digital outputs that replicate the status of LASER and TEMP LEDs on 3V3 logic levels.
  • LCK: Interlock pin.
  • VCC: 3V3 output supply pin. This pin is not designed to supply the CTL200.

Power supply

The CTL200 is provided with a 5.9 V / 3 A power supply. The CTL200 is supplied with 5 V or 6 V via the barrel connector. With 5 V power supply, compliance voltages are reduced by 1 V. To supply the board with 5 V supply, set the SW3 position to ON.

Important note: The VCC pin on the terminal block is not designed to supply the CTL200.

Configuration switch

  • Switch 1: When SW1 is ON, the user configuration is loaded at start-up. When SW1 is OFF, the default configuration is loaded at start up.
  • Switch 2: SW2 is used for firmware update. It should be kept OFF for normal operation.
  • Switch 3: SW3 is used to switch between power supplies. Set SW3 to ON when supplying the CTL200 with a 5 V power supply.
  • Switch 4: Unused.

Serial interface

The serial interface can be accessed either via the micro USB connector or via the TX and RX pins of the terminal block (3V3 logic level / 5V tolerant).

The serial interface is the only way to configure the CTL200 operating parameters. Once the configuration is done, it can be saved to the internal memory with the save command. If the configuration switch SW1 is ON at start up, the CTL200 will load the user-defined configuration and the serial interface is no longer needed.

The CTL200 can be controlled directly from a serial port terminal (e.g. Teraterm on Windows) with the following configuration:

  • Baud rate: 115200
  • Parity: None
  • Bits: 8
  • Stopbits: 1
  • Flow control: None

Note: If your computer does not recognize your controller, please see also this FAQ.

Example use of the serial port terminal

>>rtset 12000

Note: Each command must be followed by \r\n.

Graphical User Interface

A Graphical User Interface is available for Windows. The installer can be downloaded at this link. The GUI provides an effective mean of tuning the PID gains of the temperature controller.

CTL200 Digital butterfly laser diode controller graphical user interface
CTL200 graphical user interface


Command Description Type Unit Default Min Max
lason Disable | enable laser current R/W 0 0 1
ilaser Laser current. R/W mA 0.0 0.0
vlaser Laser voltage R V
ldelay Time between when the controller lights up and when the laser lights up R/W ms 1000.0 10.0 100000.0
ilmax Software current limit R/W mA 1000.0 0.0 1000.0
lckon Disable | enable interlock functionality R/W 0 0 1
lmodgain Laser current AIN1 modulation gain R/W mA/V 0 -100000.0 +100000.0
tecon Disable | enable TEC current R/W 0 0 1
tprot Disable | enable temperature protection R/W 1 0 1
rtset Thermistor resistance setpoint R/W Ω 10000.0 rtmin rtmax
rtact Actual value of thermistor resistance R Ω
itec TEC current R A
vtec TEC voltage R V
pgain Proportional gain of the temperature controller R/W 0.001 0.0 0.1
igain Integral gain of the temperature controller R/W 0.0001 0.0 0.1
dgain Differential gain of the temperature controller R/W 0.005 0.0 0.1
rtmin Minimum thermistor resistance. If temperature protection is enabled, the laser current is automatically disabled below this value. R/W Ω 5000.0 2000.0 50000.0
rtmax Maximum thermistor resistance. If temperature protection is enabled, the laser current is automatically disabled above this value. R/W Ω 15000.0 2000.0 50000.0
vtmin Minimum TEC voltage R/W V -2.0 -3.0 0.0
vtmax Maximum TEC voltage R/W V 2.0 0.0 3.0
tmodgain Temperature AIN2 modulation gain R/W Ω/V 0 -100000.0 +100000.0
iphd Photodiode current R mA 0.0 2.5
ain1 AI1 pin voltage R V 0.0 2.5
ain2 AI2 pin voltage R V 0.0 2.5
tboard Board temperature R °C
version Firmware version R v0.17
status Return lason, vlaser, itec, vtec, rtact, iphd, ain1, ain2. R
save Save configuration in internal memory (no argument) W
serial Return the serial number R
userdata write Write the user data (e.g. userdata write ABC) W 31 chars
userdata Read the user data R
brate UART baud rate R/W baud 115200 9600 460800
err Return the error code in hexadecimal format (no argument) R
errclr Clear the error code (no argument) W

Status LEDs

  • STATUS: Always ON during normal operation. Blinks when an error is detected (err > 0).
  • LASER: Turns ON when the photodiode current is above 10 µA.
  • TEMP: Turns ON when the thermistor resistance is within 1 Ω of the setpoint.

The digital outputs DO1 and DO2 replicate the status of LASER and TEMP LEDs on a 3V3 logic level.

Error codes

The command err returns a 32-bit number in hexadecimal representation which concatenates the detected errors (B0 is the Least Significant Bit):

  • B0: UART_BUFFER_OVERFLOW (err = 1)
  • B1: UART_CMD_BEFORE_PROMPT (err = 2)
  • B4: CMD_UNKNOWN (err = 10)
  • B5: CMD_INVALID_ARG (err = 20)
  • B7: INTERLOCK_TRIGGERED (err = 80)

Modulation inputs

The CTL200 has two current modulation inputs available on SMA connectors:

  • DC modulation input for modulation between DC and 10 MHz. A jumper allows to choose between 3 modulation gains (Low = 250 µA/V, Medium = 2.5 mA/V or High = 25 mA/V for the 200 mA version). Modulation range is between -1.3 V and +1.3 V for the Low and Medium modulation gain and between -1.3 V and 1.0 V for the High modulation gain (50 Ω input impedance).

  • AC modulation input for modulation above 100 kHz. Modulation range is ±5 V (50 Ω input impedance). Modulation gain is 20 mA/V.

Thermal management

The TEC voltage limits (vtmin and vtmax) and the thermistor resistance limits (rtmin and rtmax) provide an effective way of protecting the laser against thermal runaway. For reliable operation, the aluminium cooling base plate must be properly heatsunk.


An optional interlock functionality can be activated with the lckon 1 command. Laser current is then disabled when the LCK pin is pulled low. The figure below shows the use of the interlock with an external opto-isolator:

CTL200 Digital butterfly laser diode controller interlock
CTL200 interlock

Once laser current has been disabled, the serial command lason 1 must be sent to re-enable the laser current.

The behavior of the interlock pin can be inverted with the command lckon 3.

Analog modulation with AIN1 and AIN2

The analog input AIN1 can be used in conjunction with the command lmodgain (in mA/V) to modulate the laser current: ilaser' = ilaser + lmodgain x (V_AIN1 - 1.25 V).

The analog input AIN2 can be used in conjunction with the command tmodgain (in Ω/V) to modulate the laser temperature: rtset' = rtset + tmodgain x (V_AIN2 - 1.25 V).

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