Interferometer aplanatism adjusting method and measuring method based on electrorheological wavelength semiconductor laser

Abstract

The invention belongs to the related technical field of optical measurement, and discloses an interferometer aplanatism adjustment method and measurement method based on electrorheological wavelength semiconductor laser, and the adjustment method comprises the steps: changing the input current of a semiconductor laser according to a preset mode, and obtaining the fringe movement direction and movement amplitude of an interference image; adjusting the optical path of the reference arm or the optical path of the measuring arm, changing the input current to obtain the moving direction and the moving amplitude of the fringes, and comparing the moving direction and the moving amplitude with the moving direction and the moving amplitude of the fringes obtained before the optical path is adjusted; adjusting the optical path of the reference arm or the optical path of the measuring arm next time according to a comparison result until the movement amplitude of the fringes is smaller than a preset threshold value, and determining the state as an aplanatism state. After the optical path of the reference arm or the optical path of the measuring arm is adjusted, the optical path of the reference arm or the optical path of the measuring arm is further adjusted on the basis of feedback of the moving direction and the moving amplitude of the interference image under the current change, finally the aplanatism state is achieved, and establishment of aplanatism adjustment evaluation judgment indexes is achieved.

Description

Technical Field

[0001] This invention belongs to the field of optical measurement technology, and more specifically, relates to an optical path adjustment method and measurement method for an interferometer based on a current-varying wavelength semiconductor laser. Background Technology

[0002] With continuous improvements in semiconductor laser theory and manufacturing processes, semiconductor lasers, characterized by their small size, low cost, light weight, low power consumption, and strong integration capabilities with other semiconductor devices, are finding increasingly wider applications in fields such as fiber optic communication, laser printing, consumer electronics, and industrial processing. However, semiconductor lasers are less commonly used in interferometric measurements, primarily due to the instability of their output wavelength and angle, which leads to severe phase drift in the resulting interference images. For measurement systems requiring stable interferometric phase output over extended periods, semiconductor lasers struggle to meet the requirements, thus limiting their application.

[0003] This limitation is particularly pronounced in applications using classical optical instruments based on the principle of interference. These interferometers are simple in structure, offer high accuracy in measuring optical path difference, and have wide applications in optical metrology. However, using semiconductor lasers as the light source for such interferometers inevitably faces the limitation of phase drift in the interference image, as mentioned earlier. Theoretically, one solution is to adjust the measuring arm and reference arm of the interferometer to an equal optical path, thus ensuring that the interference phase output is unaffected by wavelength drift. However, this method has significant problems. Currently, there is no effective method for evaluating equal optical path; it can only be evaluated by measuring distance with calipers or tape measures, but this method has large errors and cannot meet the micrometer-level error tolerance requirements for equal optical path measurement. This has prevented a breakthrough in the application of semiconductor lasers in precision interferometry. Summary of the Invention

[0004] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides an interferometer equal optical path adjustment method and measurement method based on current-varying wavelength semiconductor lasers. This addresses the problem that existing interferometers lack an effective equal optical path evaluation method, leading to difficulties in adjusting the equal optical path states of the measuring arm and reference arm, thus limiting the application of semiconductor lasers in interferometers. The aim is to establish an effective equal optical path evaluation index, improve the convenience of equal optical path adjustment, and thereby realize the application of semiconductor lasers in interferometric measurements.

[0005] To achieve the above objectives, according to one aspect of the present invention, an optical path adjustment method for an interferometer based on a current-varying wavelength semiconductor laser is provided, wherein the interferometer uses a semiconductor laser as a light source, and the interferometer includes a reference arm and a measuring arm; the optical path adjustment method for the interferometer includes: Under the initial reference arm optical path and the measurement arm optical path, the input current of the semiconductor laser is changed according to the preset mode to change the wavelength, and the initial fringe movement direction and movement amplitude of the interference image before and after the wavelength change are obtained. Adjust the optical path of the reference arm or the optical path of the measuring arm, change the input current of the semiconductor laser according to the preset mode, and obtain the fringe movement direction and amplitude of the interference image after optical path adjustment; The direction and magnitude of fringe movement after optical path adjustment in the interference image are compared with the direction and magnitude of fringe movement before optical path adjustment. Based on the comparison results, the optical path of the reference arm or the optical path of the measuring arm is adjusted again. This process is repeated until the input current of the semiconductor laser is changed according to the preset mode after adjustment, and the amplitude of the stripe movement is less than the preset threshold. At this point, the state of equal optical path is determined.

[0006] According to the optical path adjustment method for interferometers based on current-variable wavelength semiconductor lasers provided by the present invention, the optical path of the reference arm or the optical path of the measuring arm is adjusted in the next iteration based on the comparison results, specifically including: If the direction of fringe movement after optical path adjustment in the interference image is the same as the direction of fringe movement before optical path adjustment, and the magnitude of movement is smaller than the magnitude of movement before optical path adjustment, it indicates that it is approaching the point of equal optical path. Then, the same strategy should be used to adjust the optical path of the reference arm or the optical path of the measuring arm next time. If the direction of fringe movement after optical path adjustment in the interference image is the same as the direction of fringe movement before optical path adjustment, and the magnitude of movement is greater than the magnitude of movement before optical path adjustment, it indicates that the fringe is moving away from the point of equal optical path. In this case, the opposite strategy should be used to adjust the optical path of the reference arm or the optical path of the measuring arm next time. If the direction of fringe movement after optical path adjustment in the interference image is opposite to the direction of fringe movement before optical path adjustment, it indicates that the equal optical path point has been crossed. In this case, the optical path of the reference arm or the optical path of the measuring arm will be adjusted between the optical path position after optical path adjustment and the optical path position before optical path adjustment.

[0007] According to the interferometer equal optical path adjustment method based on current-varying wavelength semiconductor laser provided by the present invention, when a situation of crossing equal optical path points occurs, the adjusted optical path position of the reference arm optical path or the measurement arm optical path and the optical path position before adjustment are taken as the position interval of the equal optical path point. The midpoint of the interval is taken as the position of the reference arm optical path or the measurement arm optical path for the next adjustment, and the fringe movement direction of the interference image at the midpoint of the interval is obtained. The midpoint of the interval is used to replace the positions at both ends of the position interval where the fringe movement direction is the same to form a new position interval where the equal optical path point is located. The optical path adjustment is repeated in a loop until the obtained fringe movement amplitude is less than a preset threshold, and then it is determined to be an equal optical path state.

[0008] According to the optical path adjustment method for interferometers and other devices based on current-variable wavelength semiconductor lasers provided by the present invention, changing the input current of the semiconductor laser specifically involves: A resistor with a controllable resistance is connected in series between the semiconductor laser and the voltage source. By adjusting the resistance value, the input current of the semiconductor laser can be changed.

[0009] The optical path adjustment method for interferometers based on semiconductor lasers provided by the present invention further includes, before acquiring the original fringe movement direction and amplitude of the formed interference image: Based on the optical path lengths of the reference arm and the measuring arm obtained from the measurement distance, the optical path lengths of the reference arm or the measuring arm are adjusted to make their measurement distances close.

[0010] According to the optical path adjustment method for interferometers based on current-variable wavelength semiconductor lasers provided by the present invention, the specific method for changing the input current of the semiconductor laser according to a preset mode is as follows: Reduce the input current of the semiconductor laser to obtain the direction and magnitude of fringe movement in the interference image when the current decreases; or increase the input current of the semiconductor laser to obtain the direction and magnitude of fringe movement in the interference image when the current increases.

[0011] According to the optical path adjustment method for interferometers based on current-variable wavelength semiconductor lasers provided by the present invention, changing the input current of the semiconductor laser according to a preset mode specifically involves: using a three-point method to change the input current of the semiconductor laser, thereby obtaining the fringe movement direction and amplitude of the interference image under the change of input current when fringe drift occurs; specifically including: First, the input current is set to a first preset current to obtain the first phase of the interference image; then, the input current is set to a second preset current to obtain the second phase of the interference image; then, the input current is set to the first preset current again to obtain the third phase of the interference image; based on the first phase, the second phase, and the third phase, the fringe movement direction and amplitude of the interference image under the change of input current when there is fringe drift are determined. Wherein, the first preset current is greater than the second preset current, and the direction and magnitude of the fringe movement in the interference image are obtained when the input current decreases; or, the first preset current is less than the second preset current, and the direction and magnitude of the fringe movement in the interference image are obtained when the input current increases.

[0012] According to the optical path adjustment method for interferometers based on current-variable wavelength semiconductor lasers provided by the present invention, the difference between the average value of the first and third phases and the second phase is used as the shift amplitude value of the interference image under the change of input current, and the positive or negative sign of the difference represents the fringe shift direction; the shift amplitude value Specifically as follows: ; in, For the first phase, For the second phase, This is the third phase.

[0013] The optical path adjustment method for interferometers based on current-variable wavelength semiconductor lasers provided by the present invention is specifically as follows: When the input current is the first preset current or the second preset current, multiple interference images are acquired and the light intensity is averaged in the spatial domain to obtain the averaged interference image. The phase of the averaged interference image is then obtained by Fourier transform as the corresponding phase. The shift amplitude of the interference image under a single change of input current is then determined by calculating the corresponding phase. The input current is changed repeatedly using the three-point method, and the average of the shift amplitude values ​​of the interferogram under the multiple changes of input current is taken as the final shift amplitude value.

[0014] According to another aspect of the present invention, an interferometer measurement method based on current-varying wavelength semiconductor laser is provided, comprising: firstly, adjusting the interferometer to equal optical path using the interferometer equal optical path adjustment method based on current-varying wavelength semiconductor laser as described in any of the above claims, and then performing measurements based on the adjusted interferometer.

[0015] In summary, compared with the prior art, the optical path adjustment method and measurement method based on current-variable wavelength semiconductor laser interferometer provided by the present invention are as follows: 1. A method for equal optical path adjustment in interferometers based on current-variable wavelength semiconductor lasers is proposed. This method utilizes the characteristic that changes in current lead to changes in laser wavelength, which in turn cause changes in the direction and amplitude of interference image movement. After adjusting the optical path of the reference arm or the measurement arm, the optical path of the reference arm or the measurement arm is further adjusted based on the feedback of the direction and amplitude of interference image movement under current changes, ultimately achieving an equal optical path state. This establishes an evaluation and judgment system for equal optical path adjustment, thereby realizing the equal optical path state adjustment of the measurement arm and the reference arm of the interferometer and expanding the application of semiconductor lasers in interferometers. 2. A specific guidance strategy for the next adjustment under various conditions is proposed when comparing the changes in the direction and amplitude of fringe movement in interference images. By comparison, the position of the equal optical path can be accurately determined, and the adjustment can be made towards the equal optical path point. When the equal optical path point is crossed, the position range of the equal optical path point is determined by the optical path position of each adjustment, and the midpoint of the range is used as the position of the next adjustment. By repeating this process, the equal optical path point can be found efficiently and accurately, and equal optical path adjustment can be achieved. 3. In order to suppress and eliminate the slow wavelength drift of semiconductor lasers, a three-point method is proposed to change the input current of semiconductor lasers to obtain the fringe shift direction and amplitude of the interference image under the change of input current. This is beneficial to eliminate the effects of temperature-induced phase drift and vibration, and improve the accuracy of obtaining the fringe shift amplitude in the interference image under the change of current. 4. In order to suppress and eliminate the influence of environmental vibration on interference fringes, a method is proposed to use multiple interferograms to perform light intensity averaging in the spatial domain to obtain the averaged interference image. Then, the corresponding phase is obtained through Fourier transform. This method is beneficial to eliminate the influence of environmental vibration on interference fringes and improve the accuracy of fringe phase acquisition. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of an interferometer system based on a current-varying wavelength semiconductor laser, provided in an embodiment of the present invention.

[0017] Figure 2 This is a schematic diagram showing the corresponding phase changes caused by current variations under different optical path differences in an embodiment of the present invention.

[0018] Figure 3 The flowchart provided in this embodiment of the invention illustrates the process of adjusting the optical path length according to changes in current, taking the increase of the optical path length of the reference arm as an example.

[0019] Figure 4 This is a schematic diagram illustrating the process of obtaining the phase shift direction and amplitude changes caused by current changes using the three-point method according to an embodiment of the present invention.

[0020] Figure 5 This is a schematic diagram illustrating the phase change caused by the three-point current in an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0022] Please see Figure 1 This embodiment provides an interferometer optical path adjustment method based on a current-variable wavelength semiconductor laser. The interferometer uses a semiconductor laser as its light source and includes a reference arm and a measuring arm. The interferometer optical path adjustment method includes: Under the initial reference arm optical path and the measurement arm optical path, the input current of the semiconductor laser is changed according to the preset mode to change the wavelength, and the initial fringe movement direction and movement amplitude of the interference image before and after the wavelength change are obtained. Adjust the optical path of the reference arm or the optical path of the measuring arm, change the input current of the semiconductor laser according to the preset mode, and obtain the fringe movement direction and amplitude of the interference image after optical path adjustment; The direction and magnitude of fringe movement after optical path adjustment in the interference image are compared with the direction and magnitude of fringe movement before optical path adjustment. Based on the comparison results, the optical path of the reference arm or the optical path of the measuring arm is adjusted again. This process is repeated until the input current of the semiconductor laser is changed according to the preset mode after adjustment, and the amplitude of the stripe movement is less than the preset threshold. At this point, the state of equal optical path is determined.

[0023] This embodiment of the study found that changes in the supply current of a semiconductor laser will cause changes in the output wavelength of the semiconductor laser, thereby causing a shift in the interference fringes in the interference pattern. Furthermore, increasing the supply current of the semiconductor laser increases the output wavelength, and decreasing the supply current decreases the output wavelength. When the optical paths of the reference arm and the measuring arm are not equal, for example, when the optical path of the measuring arm is greater than that of the reference arm, the increase in laser output wavelength due to increased current will cause the interference pattern to shift in one direction, denoted as L, while the decrease in laser output wavelength due to decreased current will cause the interference pattern to shift in the opposite direction, denoted as R. The greater the optical path difference, the greater the shift. Conversely, when the optical path of the reference arm is greater than that of the measuring arm, the increase in laser output wavelength due to increased current will cause the interference pattern to shift in the direction of R, while the decrease in laser output wavelength due to decreased current will cause the interference pattern to shift in the direction of L. Again, the greater the optical path difference, the greater the shift.

[0024] Furthermore, when the optical path lengths of the two arms are equal, changing the current magnitude will not shift the interference pattern even if the laser output wavelength changes. Therefore, this embodiment proposes to determine the optical path difference state after optical path adjustment based on changes in the direction and amplitude of the interference pattern fringes' movement. Starting from the initial optical path difference state of the two arms, the current magnitude is changed in each state, and the direction and amplitude of the interference pattern fringes' movement are recorded under the same current magnitude change. The changes in the direction and amplitude of the interference pattern fringes' movement guide the next adjustment of the optical path lengths of the two arms. When the interference pattern fringes stop moving, the equal optical path state is determined, thereby achieving equal optical path adjustment.

[0025] As an alternative implementation, the optical path of the reference arm or the optical path of the measuring arm is adjusted next time based on the comparison results, specifically including: If the direction of fringe movement after optical path adjustment in the interference image is the same as the direction of fringe movement before optical path adjustment, and the magnitude of movement is smaller than the magnitude of movement before optical path adjustment, it indicates that the image is approaching the point of equal optical path. In this case, the same strategy should be used to adjust the optical path of the reference arm or the optical path of the measuring arm next time. For example, if the current strategy is to increase the optical path of the reference arm or the optical path of the measuring arm, the same strategy of increasing the optical path of the reference arm or the optical path of the measuring arm can be used next time. If the current strategy is to decrease the optical path of the reference arm or the optical path of the measuring arm, the same strategy of decreasing the optical path of the reference arm or the optical path of the measuring arm can be used next time.

[0026] If the direction of fringe movement after optical path adjustment in the interference image is the same as the direction of fringe movement before optical path adjustment, and the magnitude of movement is greater than the magnitude of movement before optical path adjustment, it indicates that the fringe is moving away from the equi-optical-path point. In this case, the opposite strategy should be used to adjust the optical path of the reference arm or the optical path of the measuring arm next time. For example, if the current strategy is to increase the optical path of the reference arm or the optical path of the measuring arm, the next strategy can be to decrease the optical path of the reference arm or the optical path of the measuring arm. If the current strategy is to decrease the optical path of the reference arm or the optical path of the measuring arm, the next strategy can be to increase the optical path of the reference arm or the optical path of the measuring arm.

[0027] If the direction of fringe movement after optical path adjustment in the interference image is opposite to the direction of fringe movement before optical path adjustment, it indicates that the equal optical path point has been crossed. In this case, the next adjustment should be made between the optical path position after adjustment and the optical path position before adjustment for either the reference arm or the measuring arm. For example, if the current strategy is to increase the reference arm or measuring arm optical path, the next adjustment should decrease it; if the current strategy is to decrease it, the next adjustment should increase it. This continues until the interference image stops moving, indicating that the optical paths of the reference arm and the measuring arm are now equal.

[0028] Furthermore, when a situation occurs where the optical path crosses the equal optical path point, the adjusted optical path position of the reference arm or the measurement arm and the optical path position before adjustment are taken as the position interval of the equal optical path point. The midpoint of the interval is taken as the position of the reference arm or the measurement arm optical path for the next adjustment, and the fringe movement direction of the interference image at the midpoint of the interval is obtained. The midpoint of the interval is used to replace the positions at both ends of the position interval where the fringe movement direction is the same to form a new position interval where the equal optical path point is located. The optical path adjustment is repeated in a loop until the obtained fringe movement amplitude is less than a preset threshold, at which point it is determined to be an equal optical path state.

[0029] As an alternative implementation method, changing the input current of the semiconductor laser specifically involves connecting a resistor with a controllable resistance in series between the semiconductor laser and the voltage source. By adjusting the resistance value, the input current of the semiconductor laser can be changed.

[0030] refer to Figure 1 In this embodiment, the interferometer system uses a semiconductor laser LD1 as the system light source. A voltage source AOV1 is used as the power supply for the semiconductor laser. A computer-controllable resistor R1 is connected in series between the semiconductor laser LD1 and the voltage source AOV1. The adjustable resistor value can be controlled by the computer to change the power supply current to the semiconductor laser. The light beam emitted by the semiconductor laser light source passes through beam splitter BS1, with one part incident on the reference arm and the other part on the measuring arm. In the reference arm, the beam is reflected back to the beam splitter by beam splitter BS2 and corner prism TP1. In the measuring arm, the beam is reflected back to the beam splitter by corner prism TP2. The light signals reflected back from the reference arm and the measuring arm interfere at beam splitter BS1. An industrial camera is used as a sensor to acquire the interference image output by the interferometer, and is connected to a computer to transmit the interference image to the computer for phase calculation.

[0031] When the optical path length of the reference arm is not equal to that of the measuring arm, by adjusting the current, it can be seen that the collected interference fringes move left and right as the current changes. Moreover, the magnitude of the movement is positively correlated with the difference in optical path length between the reference arm and the measuring arm, that is, the greater the difference in optical path length, the greater the magnitude of the movement.

[0032] In a specific experiment, the corresponding phase changes caused by current variations under different optical path differences are illustrated in the diagram below. Figure 2 As shown, when the optical path length of the reference arm is greater than that of the measuring arm, when the current increases, the phase shift direction when the optical path length of the reference arm is 1 mm greater than that of the measuring arm is the same as the phase shift direction when the optical path length of the reference arm is 0.8 mm greater than that of the measuring arm. The phase shift amplitude is greater than that when the optical path length of the reference arm is 0.8 mm greater than that of the measuring arm.

[0033] When the current increases, the phase shift direction when the optical path length of the reference arm is 1 mm longer than that of the measuring arm is opposite to the phase shift direction when the optical path length of the measuring arm is 0.8 mm longer than that of the reference arm, and the phase shift amplitude is larger.

[0034] When the current increases, the phase shift direction when the optical path length of the measuring arm is 1 mm longer than that of the reference arm is the same as the phase shift direction when the optical path length of the measuring arm is 0.8 mm longer than that of the reference arm. The phase shift amplitude is larger than that when the optical path length of the measuring arm is 0.8 mm longer than that of the reference arm.

[0035] As an alternative implementation, before acquiring the original fringe movement direction and amplitude of the formed interference image, the method further includes: adjusting the optical path of the reference arm or the optical path of the measuring arm based on the optical path of the reference arm obtained by the measurement distance, so that the measurement distances of the two are close.

[0036] In this embodiment, before adjusting the optical path of the reference arm or the optical path of the measuring arm, the optical path of the reference arm can be adjusted by measuring the optical path distance, i.e., the distance between the corner bevel prism of the reference arm and the beam splitter, thus limiting the optical path difference to a small range. It is understood that this step can be performed before determining the direction of movement of the interference image. This is to coarsely adjust the optical path difference, narrow the range for fine adjustment, and save time. This step can be selected according to the actual situation.

[0037] Specifically, the optical path adjustment process is as follows: Figure 3 As shown, under the initial reference arm optical path and measurement arm optical path of the interferometer, the resistance value of the programmable resistor R1 is changed by computer control. The direction and size of the interference fringe movement under this state are recorded and set as the original fringe state.

[0038] Taking adjusting the optical path of the reference arm to achieve equal optical path as an example, it is impossible to determine whether to increase or decrease the optical path of the reference arm. A trial-and-error method can be used. First, increase the optical path of the reference arm by moving the corner cube prism TP1 along the +Y direction. Then, change the resistance value of the programmable resistor R1 and record the direction and magnitude of the current interference fringe movement before and after the resistance change. Compare the current fringe movement state with the original fringe movement state. Two situations will occur. In the first situation, if the current state has the same fringe movement direction as the original state, but the movement magnitude is reduced, it means that increasing the optical path of the reference arm is moving towards the equal optical path point. The new adjustment direction of the optical path of the reference arm should be the same as the previous adjustment direction. By adjusting the reference arm in this way, it will eventually cross the equal optical path point, that is, the fringe movement direction will be reversed. In the second situation, if the current state has the same fringe movement direction as the original state, but the movement magnitude is increased, it means that increasing the optical path of the reference arm is moving away from the equal optical path point. In this case, the adjustment direction of the optical path of the reference arm should be opposite to the previous adjustment direction. By continuously adjusting in the opposite direction, it will eventually cross the equal optical path point as well.

[0039] When crossing points of equal optical path length occurs, the phase shift directions before and after the change in optical path length are opposite. In this case, the midpoint LR1 between the two positions LR and LR' of the reference arm before and after the change in optical path length is taken as the new reference arm position. The phase shift direction at the new position is observed. Then, LR1 replaces the position in LR and LR' with the same phase shift direction, that is, keeping the two positions with opposite phase shift directions as a new pair of positions to form the position interval of the equal optical path length point. This substitution is repeated continuously until a position with negligible phase shift can be found, that is, the basically equal optical path length position.

[0040] As an optional embodiment, changing the input current of the semiconductor laser according to a preset mode specifically involves: reducing the input current of the semiconductor laser in each optical path state of the reference arm and the measurement arm, and obtaining the fringe movement direction and amplitude of the interference image when the current is reduced; or increasing the input current of the semiconductor laser, and obtaining the fringe movement direction and amplitude of the interference image when the current is increased.

[0041] Furthermore, changing the input current of the semiconductor laser according to the preset mode specifically involves: in order to suppress and eliminate the slow wavelength drift of the semiconductor laser, the input current of the semiconductor laser is changed using the three-point method, thereby obtaining the fringe movement direction and amplitude of the interference image under the change of input current when fringe drift occurs; to eliminate the effects of phase drift caused by temperature and vibration, the actual fringe movement amount and direction are obtained using the three-point method, as detailed in the following implementation method. Figure 4 As shown. Specifically includes: First, the input current is set to a first preset current to obtain the first phase of the interference image; then, the input current is set to a second preset current to obtain the second phase of the interference image; then, the input current is set to the first preset current again to obtain the third phase of the interference image; based on the first phase, the second phase, and the third phase, the fringe movement direction and amplitude of the interference image under the change of input current when there is fringe drift are determined. Wherein, the first preset current is greater than the second preset current, and the direction and magnitude of the fringe movement in the interference image are obtained when the input current decreases; or, the first preset current is less than the second preset current, and the direction and magnitude of the fringe movement in the interference image are obtained when the input current increases.

[0042] Specifically: When the input current is the first preset current or the second preset current, multiple interference images are acquired and the light intensity is averaged in the spatial domain to obtain the averaged interference image. The phase of the averaged interference image is then obtained by Fourier transform as the corresponding phase. The shift amplitude of the interference image under a single change of input current is then determined by calculating the corresponding phase. The input current is changed repeatedly using the three-point method, and the average of the shift amplitude values ​​of the interferogram under the multiple changes of input current is taken as the final shift amplitude value.

[0043] The difference between the average value of the first and third phases and the second phase can be used as the amplitude of the shift in the interference image under the change of input current. The sign of the difference indicates the direction of fringe shift.

[0044] Taking a first preset current greater than a second preset current as an example, in a specific embodiment, the value of the programmable resistor is first adjusted to reduce the resistance, so that the semiconductor laser is in a high-current power supply state. 100 interferograms are collected, and the light intensity is averaged in the spatial domain to obtain an averaged interferogram. Then, the phase of the single-frame interferogram is obtained by using the Fourier transform method. Then, the value of the programmable resistor was adjusted to increase the resistance, so that the semiconductor laser was in a low-current power supply state. 100 interferograms were collected, and the light intensity was averaged in the spatial domain to obtain an averaged interferogram. Then, the phase of the single-frame interferogram is obtained by using the Fourier transform method. Finally, adjust the programmable resistor to reduce its resistance, bringing the semiconductor laser back to a high-current power supply state. Collect 100 interferograms, average the light intensity in the spatial domain, and then obtain the phase of a single frame interferogram using the Fourier transform method. ; Shift value Specifically as follows: ,in, For the first phase, For the second phase, This is the third phase. From this, we can obtain... To further eliminate the influence of phase drift and other factors, the above steps were repeated 5 times to obtain the desired result. , , , and , for 5 times Averaging This allows us to obtain the amount and direction of stripe movement, where... The absolute value represents the amount of movement. The positive or negative sign indicates the direction of movement.

[0045] The diagram illustrating the phase change caused by the three-point current is shown below. Figure 5 As shown. and The phase values ​​should be equal, but due to phase drift, they cannot reach the same level. The three-point method can minimize the impact of this phase drift.

[0046] As an optional initial optical path adjustment direction, you can first decrease the optical path of the reference arm, first decrease the optical path of the measuring arm, or first increase the optical path of the measuring arm. The adjustment method is basically the same as increasing the optical path of the reference arm; it will not be elaborated here.

[0047] In this embodiment, taking the initial increase of the reference arm optical path and the monitoring of the direction and amplitude of the interferogram fringe movement as a function of current as an example, the process of equal optical path adjustment is as follows: Figure 3 As shown, it includes: Under the current optical path difference condition, the resistance is changed to control the change in current, and the direction and amplitude of the interference fringe movement, i.e. the phase shift, are recorded as the original state. Increase the optical path length of the reference arm; record the direction and amplitude of the interference fringe movement after changing the current magnitude following the change in the optical path length of the reference arm; compare the original fringe movement direction and amplitude with the fringe movement direction and amplitude after changing the optical path length of the reference arm. If the movement direction is the same as the original fringe, but the movement amplitude is reduced, then increase the optical path of the reference arm; If the movement direction is the same as the original fringe, but the movement amplitude is increased, or if the movement direction is opposite to the original fringe, then the optical path of the reference arm is reduced. Record the previous state of the stripe change with current as the original state; After changing the optical path length of the reference arm, record the direction and amplitude of the interference fringes movement when the current magnitude is changed; determine whether the interference fringes move when the current magnitude changes; if they move, continue to compare and perform the next adjustment. If no movement is made, the optical path has been adjusted to be equal, and the adjustment is complete.

[0048] In other embodiments, an interferometer measurement method based on semiconductor lasers is also provided. The interferometer measurement method based on semiconductor lasers includes: firstly, adjusting the interferometer to equal optical path using the interferometer equal optical path adjustment method based on semiconductor lasers as described in any of the above embodiments, and then performing measurements based on the adjusted interferometer.

[0049] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for adjusting the optical path length of an interferometer based on a current-varying wavelength semiconductor laser, wherein, The interferometer uses a semiconductor laser as its light source and includes a reference arm and a measuring arm; its key feature is that the optical path adjustment method of the interferometer includes: Under the initial reference arm optical path and the measurement arm optical path, the input current of the semiconductor laser is changed according to the preset mode to change the wavelength, and the initial fringe movement direction and movement amplitude of the interference image before and after the wavelength change are obtained. Adjust the optical path of the reference arm or the optical path of the measuring arm, change the input current of the semiconductor laser according to the preset mode, and obtain the fringe movement direction and amplitude of the interference image after optical path adjustment; The direction and magnitude of fringe movement after optical path adjustment in the interference image are compared with the direction and magnitude of fringe movement before optical path adjustment. Based on the comparison results, the optical path of the reference arm or the optical path of the measuring arm is adjusted again. This process is repeated until the input current of the semiconductor laser is changed according to the preset mode after adjustment, and the amplitude of the stripe movement is less than the preset threshold. At this point, the state of equal optical path is determined.

2. The optical path adjustment method for interferometers based on current-variable wavelength semiconductor lasers as described in claim 1, characterized in that, Based on the comparison results, the optical path of the reference arm or the optical path of the measuring arm will be adjusted for the next time, specifically including: If the direction of fringe movement after optical path adjustment in the interference image is the same as the direction of fringe movement before optical path adjustment, and the magnitude of movement is smaller than the magnitude of movement before optical path adjustment, it indicates that it is approaching the point of equal optical path. Then, the same strategy should be used to adjust the optical path of the reference arm or the optical path of the measuring arm next time. If the direction of fringe movement after optical path adjustment in the interference image is the same as the direction of fringe movement before optical path adjustment, and the magnitude of movement is greater than the magnitude of movement before optical path adjustment, it indicates that the fringe is moving away from the point of equal optical path. In this case, the opposite strategy should be used to adjust the optical path of the reference arm or the optical path of the measuring arm next time. If the direction of fringe movement after optical path adjustment in the interference image is opposite to the direction of fringe movement before optical path adjustment, it indicates that the equal optical path point has been crossed. In this case, the optical path of the reference arm or the optical path of the measuring arm will be adjusted between the optical path position after optical path adjustment and the optical path position before optical path adjustment.

3. The optical path adjustment method for interferometers based on current-variable wavelength semiconductor lasers as described in claim 2, characterized in that, When a situation occurs where the optical path crosses the equal optical path point, the adjusted optical path position of the reference arm or the measurement arm and the original optical path position are taken as the location interval of the equal optical path point. The midpoint of the interval is taken as the position of the reference arm or the measurement arm optical path for the next adjustment, and the fringe movement direction of the interference image at the midpoint of the interval is obtained. The midpoint of the interval is used to replace the positions at both ends of the location interval where the fringe movement direction is the same to form a new location interval where the equal optical path point is located. The optical path adjustment is repeated in this way until the obtained fringe movement amplitude is less than the preset threshold, at which point the equal optical path state is determined.

4. The optical path adjustment method for interferometers based on current-varying wavelength semiconductor lasers as described in claim 1, characterized in that, The specific steps to change the input current of the semiconductor laser are as follows: A resistor with a controllable resistance is connected in series between the semiconductor laser and the voltage source. By adjusting the resistance value, the input current of the semiconductor laser can be changed.

5. The optical path adjustment method for interferometers based on current-variable wavelength semiconductor lasers as described in claim 1, characterized in that, Before obtaining the original fringe movement direction and amplitude of the formed interference image, the following steps are also included: Based on the optical path lengths of the reference arm and the measuring arm obtained from the measurement distance, the optical path lengths of the reference arm or the measuring arm are adjusted to make their measurement distances close.

6. The optical path adjustment method for interferometers based on current-variable wavelength semiconductor lasers as described in any one of claims 1-5, characterized in that, The specific steps for changing the input current of the semiconductor laser according to the preset mode are as follows: Reduce the input current of the semiconductor laser to obtain the direction and magnitude of fringe movement in the interference image when the current decreases; or increase the input current of the semiconductor laser to obtain the direction and magnitude of fringe movement in the interference image when the current increases.

7. The optical path adjustment method for interferometers based on current-variable wavelength semiconductor lasers as described in claim 6, characterized in that, Changing the input current of the semiconductor laser according to the preset mode specifically involves using the three-point method to change the input current of the semiconductor laser, thereby obtaining the direction and amplitude of fringe movement in the interference image under the change of input current when fringe drift occurs; specifically including: First, the input current is set to a first preset current to obtain the first phase of the interference image; then, the input current is set to a second preset current to obtain the second phase of the interference image; then, the input current is set to the first preset current again to obtain the third phase of the interference image; based on the first phase, the second phase, and the third phase, the fringe movement direction and amplitude of the interference image under the change of input current when there is fringe drift are determined. Wherein, the first preset current is greater than the second preset current, and the direction and magnitude of the fringe movement in the interference image are obtained when the input current decreases; or, the first preset current is less than the second preset current, and the direction and magnitude of the fringe movement in the interference image are obtained when the input current increases.

8. The optical path adjustment method for interferometers based on current-variable wavelength semiconductor lasers as described in claim 7, characterized in that, The difference between the average of the first and third phases and the second phase is used as the amplitude of the shift in the interferometric image under the change of input current. The sign of the difference represents the direction of fringe shift. Specifically as follows: ； in, For the first phase, For the second phase, This is the third phase.

9. The optical path adjustment method for interferometers based on current-variable wavelength semiconductor lasers as described in claim 7, characterized in that, Specifically: When the input current is the first preset current or the second preset current, multiple interference images are acquired and the light intensity is averaged in the spatial domain to obtain the averaged interference image. The phase of the averaged interference image is then obtained by Fourier transform as the corresponding phase. The shift amplitude of the interference image under a single change of input current is then determined by calculating the corresponding phase. The input current is changed repeatedly using the three-point method, and the average of the shift amplitude values ​​of the interferogram under the multiple changes of input current is taken as the final shift amplitude value.

10. An interferometer measurement method based on current-varying wavelength semiconductor laser, characterized in that, include: First, the interferometer is adjusted to the same optical path using the interferometer equal optical path adjustment method based on current-varying wavelength semiconductor laser as described in any one of claims 1-9, and then measurements are performed based on the adjusted interferometer.

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