Method for controlling fiber growth in a laser heated pedestal growth system by controlling a laser power output, a pedestal feedstock rate of motion, and a draw rate

A method for controlling fiber growth in a laser heated pedestal growth system, the method comprising:

• providing a laser having a power output;
• measuring the power output to establish power output feedback data;
• controlling the power output using a first proportional, integral, derivative algorithmic controller which uses the power output feedback data as input to the first proportional, integral, derivative algorithmic controller;
• providing a pedestal feedstock having a melt end, where a molten zone is formed by heating the melt end via the laser beam according to the power output, and where the molten zone has a height;
• measuring the molten zone height at a fixed location relative to a focus of the laser beam to establish-molten zone height feedback data;
• controlling the molten zone height to control a pedestal feedstock rate of motion using a second proportional, integral, derivative algorithmic controller separate from the first proportional, integral, derivative algorithmic controller, the second proportional, integral, derivative algorithmic controller using the molten zone feedback data as input;
• drawing a fiber from the molten zone at a draw rate, where the fiber has a longitudinal length, and where the fiber has a drawing diameter;
• measuring the drawing diameter at a point proximal to the molten zone to establish a draw rate feedback data,
• controlling the draw rate to provide a desired drawing diameter using a third proportional, integral, derivative algorithmic controller separate from the first and second proportional, integral, derivative algorithmic controllers, using the draw rate feedback data as input to the third proportional, integral, derivative algorithmic controller.