Frequency-domain optical coherence tomography with extended field-of-view and reduction of aliasing artifacts
The present disclosure provides an OCT imaging system to reduce or eliminate frequency-domain aliasing artifacts. The frequency is shifted using a carrier frequency to define a sampling range substantially centered on the carrier frequency. An image of the sample is generated from a displayed imaging range that consists of a subset of the frequencies within the sampling range. Furthermore, the system may be configured to determine the carrier frequency such that a Nyquist frequency corresponding to the shifted frequency is extended beyond either an upper or a lower bound of an OCT quality envelope corresponding to the first portion of light. Additionally, the carrier frequency may be determined such that a lower bound of the OCT quality envelope is greater or less than a zero-frequency DC limit.
1. A method of optically imaging a sample utilizing a frequency-domain optical coherence tomography (OCT) system comprising a wavelength-swept light source, the method comprising the steps of:
illuminating the sample with a first portion of light emitted by the wavelength-swept light source;
illuminating a reference plane with a second portion of light emitted by the wavelength-swept light source;
shifting a frequency of at least one of the first portion of light or the second portion of light to define a sampling range including a set of frequencies; and
generating a displayed imaging range from the sampling range, the displayed imaging range consisting essentially of only a subset of the set of frequencies within the sampling range.
2. The method of claim 1 , wherein the sampling range (i) extends from a first frequency to a second frequency and (ii) is substantially centered on a carrier frequency.
3. The method of claim 2 , wherein the second frequency has a numerical value greater than a numerical value of the first frequency.
4. The method of claim 2 , wherein the displayed imaging range (i) extends from a third frequency, having a numerical value greater than a numerical value of the first frequency, to a fourth frequency, having a numerical value less than a numerical value of the second frequency, and (ii) is substantially centered on the carrier frequency.
5. The method of claim 4 , wherein the fourth frequency has a numerical value that is greater than a numerical value of the third frequency.
6. The method of claim 2 , wherein the carrier frequency is negative.
7. The method of claim 6 , wherein the step of shifting a frequency of at least one of the first portion of light or the second portion of light comprises (i) using a negative frequency shift in an acousto-optical frequency shifter or (ii) reversing a phase shift associated with a sample arm and a reference arm.
8. The method of claim 1 , wherein the step of shifting the frequency of at least one of the first portion of light or the second portion of light comprises:
determining a carrier frequency; and
shifting the frequency of the first portion of light based on the determined carrier frequency,
wherein a Nyquist frequency corresponding to the first portion of light is extended beyond either an upper or a lower bound of an OCT quality envelope corresponding to the first portion of light.
9. The method of claim 8 , wherein a lower bound of the OCT quality envelope is greater than a zero-frequency DC limit of the first portion of light.
10. The method of claim 9 , wherein the step of generating the displayed imaging range from the sampling range comprises omitting frequencies from the set of frequencies where aliasing occurs.
11. The method of claim 9 , wherein the subset of frequencies in the displayed imaging range includes between 5 and 95 percent of the frequencies in the set of frequencies in the sampling range.
12. The method of claim 9 , wherein the subset of frequencies in the displayed imaging range includes between 25 and 75 percent of the frequencies in the set of frequencies in the sampling range.
13. The method of claim 9 , wherein the subset of frequencies in the displayed imaging range includes between 40 and 60 percent of the frequencies in the set of frequencies in the sampling range.
14. The method of claim 8 , further comprising shifting the frequency of the second portion of light based on the determined carrier frequency.
15. A method of optically imaging a sample utilizing a frequency-domain optical coherence tomography (OCT) system comprising (i) an optical source for emitting output light over a range of wavelengths and (ii) an interferometer for detecting interference over a sampling range of frequencies each associated with a different depth within the sample, the method comprising:
illuminating the sample with a first portion of the output light;
illuminating a reference plane with a second portion of the output light; and
associating larger depths within the sample with more negative frequencies within the sampling range;
wherein the sampling range extends from a first frequency to a second frequency and is substantially centered on a carrier frequency.
16. The method of claim 15 , further comprising generating an image of the sample based on a displayed imaging range, the displayed imaging range consisting essentially of a subset of the frequencies of the sampling range.
17. The method of claim 15 , wherein the step of associating larger depths within the sample with more negative frequencies within the sampling range comprises shifting a frequency of at least one of the first portion of light or the second portion of light by a negative carrier frequency.
18. The method of claim 17 , wherein the second portion of light is shifted by the carrier frequency such that a corresponding sampling range extends from a first frequency to a Nyquist frequency, wherein the first frequency is different than the zero-frequency DC limit.
19. The method of 15 , the method further comprising filtering reflections of the first portion of light from the sample with at least one of a high-pass filter and a low-pass filter.