Operating a Variable Delay Line

This page describes how Standard OEM laser engines and Axsun Integrated Engines can operate a miniature motorized Variable Delay Line (VDL) if the optional driver electronics are installed.

Before you Begin

Insure these prerequisites are met before using the VDL optical module per the instructions listed below:

VDL Optical Module Installation

With the Laser Engine powered OFF, plug the VDL optical module's electrical connector into the corresponding receptacle on the laser driver board. The beige 2x5-pin VDL connector is unique and can only be plugged into one receptacle on the laser driver board. Also connect the VDL module's fiber connector(s) to your optical network as desired.

Power ON the Laser Engine. Confirm successful connection between the Laser Engine and the host PC via OCT Host or the Hardware Control Tool. For example OCT Engine (i.e. the laser driver board) will be listed in the Connected Boards: indicator in the lower left region of the OCT Host window:

VDL Operation

Adjustment of the optical delay provided by the VDL optical module is achieved by movement of a retroreflector mounted on a carriage actuated linearly by a stepper motor turning a lead screw. The user sends commands to the Laser driver board microcontroller firmware which then controls the stepper motor motion.

There is no linear encoder present, hence the controller firmware must register itself with the actual physical position of the carriage by moving it to one extreme until it triggers a limit switch. This process is called homing or zeroing the VDL. Once the VDL has been homed, the firmware tracks the carriage position by accumulating all issued steps in the positive and negative directions. The homed position is considered the 0.00 mm delay point.

IMPORTANT! For accurate motion control of the VDL, the homing operation must be performed after each power-on cycle of the Laser driver board (i.e. any time the device firmware is rebooted).

Commands to a) go home, b) move to an arbitrary position within the total range, and c) get the current VDL position are available in the Axsun GUI Tools (OCT Host or the Hardware Control Tool) or can be sent by a user's custom application using either the AxsunOCTControl_LW or AxsunOCTControl APIs:

VDL controls on the OCT Host GUI are located on the VDL Motor tab. Buttons and input fields are provided to Home the VDL, Move it in a Relative or Move it in an Absolute fashion by a desired distance, or Stop VDL motion in progress. The current status of the VDL is also shown. Any requests to move the VDL to a position which is outside of its allowable delay range (0 to 15 mm) will be ignored.

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