Abstract: An optical heterodyne detection system in accordance with an embodiment of the invention includes two optical receivers for separately measuring the power of an input signal and a local oscillator signal before the signals are combined. The measurements of the input signal and the local oscillator signal are then utilized to enhance the heterodyne signal to noise ratio by removing the intensity noise contributed by the input signal and the local oscillator signal. By measuring portions of the input signal power and the local oscillator signal power and then subtracting out the scaled quantities from the photocurrent measurement during signal processing, the signal to noise of the heterodyne signal is improved beyond that which is accomplished by known balanced receivers.

Abstract: A system and method for measuring the group delay of an optical device under test (DUT) utilizes an optical frequency counter in conjunction with a test interferometer to compensate for the non-uniform frequency changes of an input optical signal used by the test interferometer to measure the group delay. The group delay of the optical DUT is measured using the zero-crossings of an AC coupled heterodyne beat signal produced by the test interferometer from the input optical signal. In the measurement of the group delay, phase changes in the heterodyne beat signal caused by the non-uniform frequency changes of the input optical signal are compensated by using the measured optical frequency of the input optical signal. The optical frequency is detected by the optical frequency counter. The detected optical frequency is indicative of the non-uniform frequency changes of the input optical signal.

Abstract: A system and method for measuring the group delay of an optical device under test (DUT) utilizes an optical frequency counter in conjunction with a test interferometer to compensate for the non-uniform frequency changes of an input optical signal used by the test interferometer to measure the group delay. The group delay of the optical DUT is measured using the zero-crossings of an AC coupled heterodyne beat signal produced by the test interferometer from the input optical signal. In the measurement of the group delay, phase changes in the heterodyne beat signal caused by the non-uniform frequency changes of the input optical signal are compensated by using the measured optical frequency of the input optical signal. The optical frequency is detected by the optical frequency counter. The detected optical frequency is indicative of the non-uniform frequency changes of the input optical signal.