Autofocus apparatus

A method for automatically operating an autofocus apparatus, the method comprising:

• illuminating a light beam to a splitter for splitting the light beam into a first portion of a light signal and a second portion of a light signal;
• inputting the first portion of the light signal to a balance detector;
• coupling an fiber optic circulator to the second portion of the light signal at a first port, to an optical collimator at a second port, and to a balance detector at the third port, wherein the light signal in the fiber optic circulator travels only from the first port to the second port and from the second port to the third port;
• directing a light beam from the second port of the fiber optic circulator onto a sample by the light collimator through a Dichroic mirror and a microscope objective, wherein the sample is placed on an adjustable microscopy stage;
• capturing the reflected light beam signal by the microscope objective and sending to the balance detector through the optical collimator and into the second port and out of the third port of the fiber optic circulator;
• converting the light signal reflected off of a substrate that the sample is placed on, into an analog voltage signal by the balance detector;
• and
• processing the output of the balance detector, so as to allow the desired separation between the sample and objective to be maintained.