Optical image measuring apparatus for forming an image of an object to be measured based on interference light

An optical image measuring apparatus, comprising:

• a light source for emitting a light beam;
• an optical interference system that divides the light beam emitted from the light source into signal light propagating through the object to be measured and reference light propagating through a predetermined reference object, shifts a frequency of the signal light and a frequency of the reference light relative to each other, and then superimposes the signal light propagating through the object to be measured and the reference light propagating through the predetermined reference object on each other to produce the interference light;
• optical path divider operable to drive an optical path of the interference light produced by the interference optical system into a plurality of optical paths to produce a plurality of interference light beams;
• at least one intensity modulator operable to modulate an intensity of at least one of the interference light beams at a predetermined frequency, which is provided on at least one first optical path of the plurality of optical paths;
• a plurality of photo detectors each provided on each of the plurality of optical paths, where at least one first photo detector of the plurality of photo detectors which is provided on the first optical path receives at least one interference light beam whose intensity is modulated and converts the received interference light beam into an electrical signal to be outputted and at least one second photo detector of the plurality of photo detectors which is provided on at least one second optical path other than the first optical path receives at least one interference light beam and converts the received interference light beam into an electrical signal to be outputted;
• and
• calculator operable to calculate an intensity of a direct current component based on the electrical signal outputted from the photo detector provided on a predetermined optical path of the plurality of optical paths,
• wherein an image, of the object to be measured is formed based on the interference light beams propagating on the plurality of optical paths,
• wherein the intensity modulator modulates the intensity of the interference light beam at a frequency which is not synchronized with a beat frequency of the interference light beam, and
• the calculator time-averages the electrical signal outputted from the photo detector based on the interference light beam whose intensity is modulated at the frequency to calculate the intensity of the direct current component.

An optical image measuring apparatus for forming an image of an object to be measured based on interference light, comprising:

• a light source for emitting a light beam;
• an optical interference system that divides the light beam emitted from the light source into signal light propagating through the object to be measured and reference light propagating through a predetermined reference object, shifts a frequency of the signal light and a frequency of the reference light relative to each other, and then superimposes the signal light propagating through the object to be measured and the reference light propagating through the predetermined reference object on each other to produce the interference light;
• intensity modulator operable to modulate an intensity of the interference light at a predetermined frequency;
• photo detector operable to receive the interference light whose intensity is modulated and converting the received interference light into an electrical signal to be outputted;
• calculator operable to calculate an intensity of a direct current component composed of background light of the interference light and at least one of an intensity and/or phase of an alternating current component of the interference light based on the electrical signal outputted from photo detector;
• and
• light receiving time changer operable to change a light receiving time of the interference light beam received by the photo detector between a first light receiving time equal to or longer than a beat period of the interference light beam and a second light receiving time shorter than the beat period in accordance with the beat period,
• wherein the calculator
• time-averages an electrical signal outputted from the photo detector to calculate the intensity of the direct current component when the light receiving time is changed to the first light receiving time by the light receiving time changer, and
• calculates at least one of the intensity and/or phase of the alternating current component based on an electrical signal outputted from the photo detector when the light receiving time is changed to the second light receiving time and the direct current component whose intensity is calculated corresponding to the first light receiving time.