Optical reflectometry using integrated VCSEL photodiode chip

A method of testing an optical waveguide to determine a distance in the optical waveguide of an occurrence of interest, the method comprising:

• at a VCSEL, emitting an optical pulse into a waveguide;
• receiving at a photodiode disposed in the same epitaxial structure as the VCSEL a reflection of the pulse such that the reflection of the pulse passes through the VCSEL and onto the photodiode, wherein the reflection is caused by an occurrence of interest affecting the waveguide;
• measuring an amount of time between when the pulse was emitted and when the reflection was received;
• correlating the amount of time to a distance in the waveguide, wherein the distance is, at least approximately, a distance to the occurrence of interest;
• at the VCSEL, emitting a wavelength modulated optical signal into the waveguide;
• receiving at the VCSEL a reflection of the wavelength modulated optical signal, wherein the reflection is caused by the occurrence of interest affecting the waveguide at a particular wavelength and wherein the reflection being received at the VCSEL causes a change in the VCSEL output;
• detecting the change in the VCSEL output;
• correlating the change in VCSEL output to a distance in the waveguide, wherein the distance is, at least approximately, a distance to the occurrence of interest;
• and
• determining the distance in the optical waveguide to the occurrence of interest based on the correlation of the change in VCSEL output to the distance in the waveguide or based on the correlation of the amount of time to the distance in the waveguide.

A test apparatus configured to test for occurrences of interest along an optical waveguide, the test apparatus comprising:

• a VCSEL;
• a pulse generator coupled to the VCSEL configured to cause the VCSEL to emit an optical pulse into a waveguide;
• a photodiode disposed in the same epitaxial structure as the VCSEL;
• a timer communicatively coupled to the VCSEL and the photodiode, wherein the timer is configured to measure an amount of time between when a pulse is emitted by the VCSEL and when a reflection of the pulse passes through the VCSEL and onto the photodiode, wherein the reflection is caused by an occurrence of interest affecting the waveguide;
• a modulating generator selectively coupled to the VCSEL, the modulating generator configured to modulate the wavelength of the VCSEL, and wherein the pulse generator is selectively coupled to the VCSEL such that a generator is selectively coupled to the VCSEL;
• and
• analyzing circuitry selectively coupled to the photodiode, the analyzing circuitry configured to detect changes in the VCSEL output and wherein the timer is selectively coupled to the photodiode such that either the analyzing circuitry or the timer circuitry can be operatively coupled to the photodiode.