Device performing optical coherence tomography

Abstract

An apparatus for performing optical coherence tomography (OCT) includes an interferometer (1) comprising a sample arm (2) to which light can be guided to a sample (3), a reference arm (4) to which light can be guided on a reference section, and a detector (5) capable of detecting interference light signals from the two arms (2, 4), relating to the problem of identifying and compensating for Z-direction drift of the OCT signal caused by temperature changes within the apparatus for performing optical coherence tomography, preferably such identification and compensation should be performed automatically, and characterized in that an internal and / or sample-insensitive calibration target (6) is provided, and light can be guided toward the calibration target on a monitoring section (7).

Description

Technical Field

[0001] The present invention relates to an apparatus according to the generic concept of claim 1.

Background Art

[0002] The name, optical coherence tomography (in English, "Optical Coherence Tomography", usually abbreviated as OCT), is interpreted as an imaging method. Using this method, two-dimensional and three-dimensional images can be obtained from an optically scattering structure. In this method, usually, light having a certain bandwidth is split into two partial light beams in a beam splitter. The first partial light beam is incident on a test sample or object, and the second partial light beam passes through a reference section. The light reflected from the sample or reference interferes with the reference light beam. The sample is inspected by a so-called A scan that resolves the sample axially from the signal from the interference, that is, resolves the sample at a depth along the optical axis of the first partial light beam.

[0003] Normally, the axial shift of the OCT image that may result from a varying temperature difference between the sample arm and the reference arm is not compensated.

[0004] In this case, therefore, it is disadvantageous that the absolute position of the OCT image in the Z direction varies with the temperature difference. Thus, any calibration that depends on the Z position of this apparatus has an error or may have an error. Even in an apparatus that does not depend on calibration, post-adjustment of the Z position may be required in some cases.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, at the root of the present invention is the problem of identifying and compensating for the Z-direction drift of the OCT signal caused by temperature variations within an apparatus that performs optical coherence tomography. Preferably, the identification and compensation should be performed automatically.

Means for Solving the Problems

[0006] The present invention solves the above-mentioned problems with the features of claim 1.

[0007] According to the present invention, first, a calibration target must be provided inside the instrument and / or insensitive to the sample, and it has been found that light can be guided towards the calibration target on the monitoring section.

[0008] Furthermore, it was found that this allows for extremely high-speed Z-direction calibration scans against a fixed calibration target inside the instrument during the original imaging process. Preferably, the Z-direction calibration scan can be performed using a scanner.

[0009] Against this backdrop, it was found that if the reference signal and sample signal originate from components, and these components are exposed to various temperatures, or if the reference interval is exposed to a different temperature than the sample interval, the calibration target will appear at various image depths.

[0010] Furthermore, it was found that if the path length between the additional calibration target and the original sample position differs beyond the OCT image depth, an appropriate additional reference interval can be introduced into the interferometer.

[0011] Furthermore, it was found that the OCT signal of the calibration target preferably appears at a constant image depth that is automatically detected. Also, since both the two reference intervals and the sample interval are exposed to the same temperature fluctuations, the difference in the detected image depths corresponds to the original imaging shift.

[0012] Finally, it was found that variations in path length differences that occur between the reference vibration and the sample signal must be taken into consideration or calibrated so that these variations can be distinguished from variations due to temperature drift.

[0013] The monitoring section may correspond entirely or partially to the sample arm or sample section. This allows for particularly reliable automatic compensation of temperature drift. The calibration target may be positioned within the sample section.

[0014] A monitoring device may be provided within the apparatus. Preferably, the measurement is started manually using a user-controlled method, or automatically without operator intervention. The monitoring device detects the OCT signal of the calibration target as a deviation from a reference point at a specific depth in the OCT scan or OCT image, and changes the optical path length of the sample arm and / or reference arm. As a result, the OCT scan or OCT image is not affected by the deviation of the calibration target's OCT signal, or the display of the sample in the display device may be applied in this manner. This ensures that the OCT scan always remains at the desired position in the Z direction. Similarly, quantitative measurement data can be determined from the OCT data, and various imaging patterns can be recorded. Manual readjustment is no longer necessary.

[0015] Optical path length changing units may be placed on the sample arm and / or reference arm to change the optical path length of the light guided by each arm. Path length adjustment is performed by optical path length changing units, so-called delay lines, located within the sample arm and / or reference arm. To compensate for temperature drift, the path length difference between the sample arm and the reference arm is matched. The Z-direction drift of the OCT signal is compensated for by this device.

[0016] The optical path length of the sample arm and the optical path length of the monitoring path may be equal, or they may differ by less than the image depth. This allows for particularly reliable compensation of temperature drift with a simple optical structure.

[0017] The optical path lengths of the sample arm and the monitoring section may differ, and therefore two reference sections may be provided. This allows both the two reference sections and the multiple sample sections—that is, the sample section of the inspected sample and the sample section of the calibration target, and therefore the monitoring section—to be exposed to the same temperature changes.

[0018] The calibration target may be light-scattering. This allows the calibration target to be detected optically well when the light source illuminates it.

[0019] The calibration target may be configured as a retroreflector. The calibration target inside the instrument must scatter light sufficiently strongly. When the calibration target is configured as a retroreflector, it is designed to contribute to improving the signal-to-noise ratio (SNR).

[0020] An additional lens can be used to focus on the calibration target.

[0021] The sample arm and the reference arm may be spatially separated from each other, at least partially. In this case, the apparatus has an optical block in which a calibration target is placed. The sample arm and monitoring section are located at least partially or completely outside the optical block. In this way, the sample arm and monitoring section can be exposed to a first temperature substantially or completely together, while the reference arm can be exposed to a second temperature substantially or completely. The optical block may preferably be configured as a movable component unit.

[0022] A monitoring device may be used to alternately or simultaneously guide light onto the calibration target and onto the sample, or onto a portion of the sample arm that can face the sample. This allows for a calibration scan in the Z direction.

[0023] The monitoring device may output a portion of the light from the sample arm immediately before the end of the optical fiber-guided sample arm, and guide a portion of that light to a calibration target coupled to the optical fiber. This allows calibration scanning to be performed with the assistance of the optical fiber. The optical fiber can maintain or suppress polarization particularly well. The interferometer can be constructed as a free-flow optical system or with optical fibers, but a construction with optical fibers is advantageous.

[0024] The monitoring device may have at least one scanner, an optical switch or a coupler. The scanner can perform a calibration scan in the Z direction. The switch or coupler can connect multiple reference arms if necessary.

[0025] The light emerging from the light source can be guided by a splitting device to both the sample arm and the reference arm. At this time, the light reflected from the sample can be returned from the optical block through the sample arm to the integrating device in order to interfere with the light from the reference arm. Thereby, the sample arm and the reference arm can be at least partially separated from each other.

[0026] In this context, the sample arm may be divided into a first sample arm portion and a second sample arm portion. At this time, an optical path length changing unit is arranged between these sample arm portions, and the optical path length changing unit is arranged between the splitting device and the integrating device. In this way, the optical path length changing unit can be arranged in a space region occupied by a temperature different from the temperature in the space region where the optical block is arranged.

[0027] Two reference arm portions can be connected to the reference arm by a coupler or an optical switch, and each reference arm portion becomes a part of the reference arm. In this way, the reference arm can be implemented singly or doubly according to the position of the calibration target.

[0028] The optical path length changing unit may be arranged between the splitting device and the integrating device within the reference arm. In this way, the optical path length changing unit can be arranged in a space region occupied by a temperature different from the temperature in the space region where the optical block is arranged.

[0029] Alternatively or additionally, the optical path length changing unit may be arranged between the splitting device and the coupler or optical switch within the reference arm. In this way, the reference arm can be implemented singly or doubly according to the position of the calibration target.

[0030] The sample arm may be divided into a first sample arm section and a second sample arm section. In this case, the optical path length changing unit is placed between these sample arm sections, and the path changing unit is placed between the dividing device and the optical block. In this way, the optical path length changing unit can be placed in a spatial region with a temperature different from that of the spatial region where the reference arm is located. The optical path length changing unit can be positioned facing the sample.

[0031] The arrangement may include the type of apparatus described herein, a first spatial region occupied by a first temperature, and a second spatial region occupied by a second temperature, wherein the optical block is positioned in the second space so as to spatially face the sample under test. This allows for the movable separation of multiple optical components, exposing some of the optical components to the first temperature and other parts to the second temperature.

[0032] The drawing shows the following: [Brief explanation of the drawing]

[0033] [Figure 1] Figure 1 is a schematic diagram of a conventional interferometer when the sample arm is exposed to a low temperature, i.e., cold air, and the reference arm is exposed to a high temperature, i.e., warm air. [Figure 2] Figure 2 is a graph showing the dependence of the Z-direction shift of the OCT signal on the temperature difference between the sample arm and the reference arm. [Figure 3] Figure 3 is a schematic diagram of the optical block, which is extended around the calibration target. [Figure 4] Figure 4 is a schematic diagram of an interferometer in which optical path length changing units are located in both the sample arm and the reference arm. [Figure 5] Figure 5 is a schematic diagram of the apparatus when the optical path length changing unit is optically positioned behind the sample within the sample arm. [Figure 6] Figure 6 is another schematic diagram of the apparatus in which the optical path length changing unit is positioned behind the sample within the sample arm, and the reference arm may be configured in a double configuration. [Figure 7] Figure 7 is a schematic diagram of the apparatus when the optical path length changing unit is located within the reference arm. [Figure 8] Figure 8 is another schematic diagram of the apparatus in which the optical path length changing unit is located within the reference arm, and the reference arm may be configured in a double configuration. [Figure 9] Figure 9 is a schematic diagram of the apparatus when the optical path length changing unit is positioned on the sample side within the sample arm. [Figure 10] Figure 10 is a schematic diagram of the apparatus in which the path rerouting unit is positioned towards the sample within the sample space, and the reference arm can be configured in a double configuration. [Modes for carrying out the invention]

[0034] Figure 1 shows a schematic diagram of a conventional optical coherence tomography (OCT) apparatus. The apparatus includes an interferometer 1 comprising a sample arm 2 to which light can be guided to a sample 3, a reference arm 4 to which light can be guided along a reference section, and a detector 5 to which interference signals from the two arms 2 and 4 can be detected. Furthermore, a light source 11 is provided.

[0035] In this regard, Figure 1 shows the arrangement of the prior art, which includes a first spatial region W occupied by a first temperature and a second spatial region K occupied by a second temperature. Since the reference arm 4 and the sample arm 2 are separated from each other within the interferometer, a temperature difference may occur between these two units.

[0036] Figure 2 shows the effect of heating the reference arm 4 while keeping the sample arm 2 at room temperature. The measurement results show that the temperature difference between the sample arm 2 and the reference arm 4 of the interferometer causes a drift or shift in the Z direction of the OCT signal.

[0037] Figure 2 shows, based on the graph, that when the sample arm length is 6m and the heating temperature is approximately 20°C, the drift in the Z direction during heating is 4mm. In Figure 2, the x-axis indicates temperature in °C, and the y-axis indicates the peak position of the OCT signal in mm.

[0038] To compensate for the effects described above, the apparatus shown in Figure 1 is extended around the calibration target 6 inside the instrument and / or insensitive to the sample, and light can be guided on the monitoring section 7 toward its calibration marker.

[0039] Figure 3 shows the calibration target 6 assigned to the optical block 9. The sample arm 2 passes through the optical block 9. Light is guided towards the calibration target 6 over the monitoring section 7. The monitoring section 7 may correspond entirely or partially to the sample arm 2 or the sample section.

[0040] In this context, Figure 4 shows a schematic diagram of an apparatus for performing optical coherence tomography (OCT). The apparatus includes an interferometer 1 comprising a sample arm 2 to which light can be guided to a sample 3, a reference arm 4 to which light can be guided along a reference section, and a detector 5 capable of detecting interference signals from the two arms 2 and 4.

[0041] The device is equipped with an internal and / or sample-insensitive calibration target 6, and light can be guided toward this calibration target on the monitoring section 7, as schematically shown in Figure 3.

[0042] The optical path length of sample arm 2 and the optical path length of monitoring section 7 may be equal, or they may differ by less than the image depth.

[0043] Calibration target 6 is a light-scattering type. Calibration target 6 is configured as a retroreflector.

[0044] Figure 4 schematically shows that a monitoring device 8 is also provided. This monitoring device detects the OCT signal of the calibration target 6 as a deviation from a reference point at a certain depth in the OCT scan or OCT image.

[0045] The monitoring device 8 can change the optical path length of the sample arm 2 and / or reference arm 4 so that the OCT scan or OCT image is not affected by the shift in the OCT signal of the calibration target 6, preferably by manually starting the measurement in a user-controlled manner, or by automatically starting the measurement without the influence of the operator.

[0046] The monitoring device 8 has the display of sample 3 adjusted accordingly within the display device, and the optical path lengths of sample arm 2 and / or reference arm 4 can be alternately changed so as not to be affected by Z-direction misalignment.

[0047] Figure 4 is a supplement to Figure 3, further showing that optical path length changing units 4a, 2a, or delay lines are introduced, respectively, to compensate for the aforementioned thermal effects on the reference arm 4 and / or sample arm 2, and that the optical block 9 is extended around the calibration target 6.

[0048] Each sample arm 2 and / or reference arm 4 is assigned an optical path length changing unit 2a, 4a, respectively, to change the optical path length of the light guided within each arm 2, 4.

[0049] In some cases, the optical path length changing unit 2a for sample arm 2 may be assigned to sample arm 2, or the optical path length changing unit 4a for reference arm 4 may be assigned to reference arm 4. If significant, it is also possible that optical path length changing units are assigned to both arms 2 and 4, respectively.

[0050] Using the monitoring device 8, light can be guided alternately or simultaneously to the calibration target 6 and the sample 3, or to a portion of the sample arm 2 that can face the sample 3.

[0051] The monitoring device 8 may output a portion of the light from the sample arm 2 immediately before the end of the optical fiber guided sample arm, and guide a portion of that light to the calibration target 6 coupled to the optical fiber. This makes it possible to realize a device with an optical fiber configuration.

[0052] Figure 3 further shows that the monitoring device 8 according to Figure 4 includes at least one scanner 10 to perform a calibration scan in the Z direction.

[0053] Figures 5 to 10 schematically show the arrangement of the apparatus, a first spatial region W occupied by the first temperature, and a second spatial region K occupied by the second temperature. In this arrangement, the optical block 9 is positioned within the second spatial region K so as to spatially face the sample 3 under test.

[0054] Figures 5 to 10 show, based on various embodiments of the apparatus, that the sample arm 2 and the reference arm 4 are spatially separated from each other, at least partially. In this configuration, the apparatus has an optical block 9, within which the calibration target 6 is located. The sample arm 2 and the monitoring section 7 are located at least partially or completely within the optical block 9, while the reference arm 4 is located at least partially or completely outside the optical block 9.

[0055] Figures 5 to 10 show that the light emitted from the light source 11 can be guided to both the sample arm 2 and the reference arm 4 by the splitting device 12. In this case, the light reflected from the sample 3 can be returned to the integrating device 13 via the sample arm 2, starting from the optical block 9, in order to interfere with the light from the reference arm 4.

[0056] In Figures 5 and 6, the sample arm 2 is divided into a first sample arm portion 2.1 and a second sample arm portion 2.2, respectively. The optical path length changing unit 2a is positioned between the sample arms 2.1 and 2.2, and between the splitting device 12 and the integrating device 13.

[0057] In Figure 6, two reference arm sections 4.1 and 4.2 can be connected to the reference arm 4 by a coupler 14 or optical switch, and each of the reference arm sections 4.1 and 4.2 becomes part of the reference arm 4.

[0058] Figures 5 and 6 specifically show that the optical path length changing unit 2a is positioned behind the sample 3 within the sample arm 2. The reference arm 4 must be configured as a single or double arm depending on the position of the calibration target 6. In this case, a second reference arm can be realized or implemented by either a coupler 14 or a switch.

[0059] In Figures 7 and 8, the optical path length changing unit 4a is positioned within the reference arm 4 between the splitting device 12 and the integrating device 13.

[0060] In Figure 8, the optical path length changing unit 4a is located within the reference arm 4 between the splitting device 12 and the coupler 14 or optical switch.

[0061] Figures 7 and 8 show that the optical path length changing unit 4a may be located within the reference arm 4. The reference arm 4 must be mounted in single or double configuration depending on the position of the calibration target 6.

[0062] In the two reference arm sections 4.1 and 4.2, the optical path length changing unit 4a must be located in a common path between the reference arm sections 4.1 and 4.2. In this case, the second reference arm 4.2 can be realized or implemented through either the coupler 14 or the switch. Therefore, the optical path length changing unit 4a is optically positioned in the reference arm 4 before the splitting position, specifically before the coupler 14.

[0063] In Figures 9 and 10, the sample arm 2 is divided into a first sample arm portion 2.1 and a second sample arm portion 2.2. The optical path length changing unit 2a is positioned between the sample arm portions 2.1 and 2.2, and is located between the splitting device 12 and the optical block 9.

[0064] Figures 9 and 10 show that the optical path length changing unit 2a is positioned toward the sample 3 in the sample arm portion 2.1. In this case, it should be noted that the optical path length changing unit 2a is deployed in a double stroke.

[0065] The reference arms must be mounted either in single or double configuration depending on the position of the calibration target 6. In this case, the second reference arm 4.2 may be realized or mounted through either the coupler 14 or the switch.

[0066] The optical path lengths of sample arm 2 and monitoring section 7 may differ, and therefore two reference sections may be provided. Advantageously, the optical path length to calibration target 6 is as long as the optical path length to sample 3, eliminating the need for a second reference. To avoid significantly increasing noise and to keep the signal-to-noise ratio of the original sample signal as low as possible, the output of the second reference arm section should be kept as low as possible, or it should be implemented by a switch.

[0067] The interferometer may be configured as a free-ray optical system or within an optical fiber, in which case the optical fiber configuration is advantageous. Furthermore, it is advantageous to place the calibration target 6 within the instrument. [Explanation of Symbols]

[0068] 1 Interferometer 2 Sample Arms 2.1 First sample arm section 2.2 Second sample arm section 2a Optical path length changing unit for sample arm 3 Samples 4 Reference Arm 4.1 First reference arm section 4.2 Second reference arm section 4a Reference arm optical path length changing unit 5 detectors 6 Calibration target 7. Monitoring section 8. Monitoring device 9 Optical Blocks 9a Collimator 10 Scanners 11 Light source 12 Splitting device 13. Integrated device 14 Combiner

Claims

1. An apparatus for performing optical coherence tomography (OCT), the apparatus comprising an interferometer (1) having a sample arm (2) for guiding light to a sample (3), a reference arm (4) for guiding light along a reference section, and a detector (5) capable of detecting interference light signals from the two arms (2, 4), The apparatus is characterized in that it is provided with an internal and / or sample-insensitive calibration target (6), and light is guided to the calibration target (6) on a monitoring section (7).

2. The apparatus according to claim 1, characterized in that the monitoring section (7) corresponds completely or partially to the sample arm (2) or the sample section.

3. The apparatus according to claim 1 or 2, characterized in that a monitoring device (8) is provided, and by either manually starting the measurement in a user-controlled manner, or by automatically starting the measurement without the influence of the operator, the monitoring device detects the OCT signal of the calibration target (6) as a deviation from a reference point at a specific depth in the OCT scan or OCT image, and changes the optical path length of the sample arm (2) and / or the reference arm (4), so that the OCT scan or the OCT image is not affected by the deviation of the OCT signal of the calibration target (6), or the display of the sample in the display device is applied in such a manner.

4. The apparatus according to any one of claims 1 to 3, characterized in that optical path length changing units (2a, 4a) for changing the optical path length of the light guided within each of the arms (2, 4) are assigned to the sample arm (2) and / or the reference arm (4).

5. The apparatus according to any one of claims 1 to 4, characterized in that the optical path length of the sample arm (2) and the optical path length of the monitoring section (7) are equal or differ by an amount less than or equal to the image depth.

6. The apparatus according to any one of claims 1 to 5, characterized in that the optical path length of the sample arm (2) and the optical path length of the monitoring section (7) are different, and therefore two reference sections are provided.

7. The apparatus according to any one of claims 1 to 6, characterized in that the calibration target (6) is light-scattering.

8. The apparatus according to any one of claims 1 to 7, characterized in that the calibration target (6) is designed as a retroreflector.

9. The apparatus according to any one of claims 1 to 8, characterized in that the sample arm (2) and the reference arm (4) are separated from each other in at least a certain section, the apparatus comprises an optical block (9), the calibration target (6) is located within the optical block, the sample arm (2) and the monitoring section (7) are located at least partially or completely within the optical block (9), and the reference arm (4) is located at least partially or completely outside the optical block (9).

10. The apparatus according to any one of claims 1 to 9, characterized in that the monitoring device (8) guides light alternately or simultaneously onto the calibration target (6) and the sample (3), or into the cross-section of the sample arm (2) that turns toward the sample (3).

11. The apparatus according to any one of claims 1 to 10, characterized in that the monitoring device (8) separates a portion of the light from the sample arm (2) immediately in front of the end of the sample arm guided by the optical fiber, and guides the portion of the light to a calibration target (6) coupled to the optical fiber.

12. The apparatus according to any one of claims 1 to 11, characterized in that the monitoring device (8) has at least one scanner (10), an optical switch or a coupler (14).

13. The apparatus according to any one of claims 1 to 12, characterized in that light emitted by a light source (11) is guided in the splitting device (12) into both the interior of the sample arm (2) and the interior of the reference arm (4), and the light reflected from the sample (3) can be returned from the optical block (9) through the sample arm (2) to the integrating device (13) in order to interfere with the light from the reference arm (4).

14. The apparatus according to claim 13, characterized in that the sample arm (2) is divided into a first sample arm portion (2.1) and a second sample arm portion (2.2), an optical path length changing unit (2a) is positioned between the sample arm portions (2.1, 2.2), and the optical path length changing unit (2a) is positioned between the dividing device (12) and the integrating device (13).

15. The apparatus according to any one of claims 1 to 14, characterized in that two reference arm portions (4.1, 4.2) can be switched into the reference arm (4) by a coupler (14) or an optical switch, and each of the reference arm portions (4.1, 4.2) becomes part of the reference arm (4).

16. The apparatus according to any one of claims 13 to 15, characterized in that the optical path length changing unit (4a) is located within the reference arm (4) between the splitting device (12) and the integrating device (13), and / or the optical path length changing unit (4a) is located within the reference arm (4) between the splitting device (12) and the coupler (14) or optical switch.

17. The apparatus according to any one of claims 13 to 16, characterized in that the sample arm (2) is divided into a first sample arm portion (2.1) and a second sample arm portion (2.2), an optical path length changing unit (2a) is positioned between the sample arm portions (2.1, 2.2), and the optical path length changing unit (2a) is positioned between the dividing device (12) and the optical block (9).

18. An arrangement comprising the apparatus according to any one of claims 1 to 17, a first spatial region (W) where a first temperature is maintained, and a second spatial region (K) where a second temperature is maintained, wherein an optical block (9) to be spatially turned toward the sample to be examined (3) is located within the second spatial region (K).

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