JP6846752B2 - Laser output control device using an optical attenuator with variable attenuation - Google Patents

Description

The present invention relates to a laser output control device using an optical attenuator with a variable attenuation amount.

Laser light is widely used in fields such as processing equipment and medical equipment, and it is required to precisely control the output (power energy) of a laser in order to advance the technology and ensure safety.
Generally, in order to control the laser output, the output of the laser oscillation is controlled by adjusting the laser excitation current in the laser device itself, or the desired output is obtained by adjusting the optical attenuator installed outside the laser device. It is known to control to be.
In the output control of laser oscillation, high-precision control is realized, such as the laser output obtained by limiting the current control resolution causes stepwise changes, and the heat generated by the laser device itself causes output instability. It's difficult to do.
Therefore, when precise output adjustment is required, an element that attenuates light, such as an absorption filter, a reflector, and a polarization separating element, is installed in the optical path after the laser is emitted from the laser device, and the laser passes through the element. It is common to change the output of light to adjust it to the desired value.

Further, a system has also been proposed in which these dimming elements are combined with an actuator or the like and the amount of light attenuation is controlled by an external signal to actively change the intensity of light passing through the elements.
In such a system, an absorption filter with a gradient in density is moved to change the incident position of the laser light, the substrate is rotated to change the incident angle of the laser light, and the polarization direction of the light is rotated to change the polarization separation element. The amount of light is changed by transmitting light, but it was difficult to apply it to high-intensity laser light.

That is, the absorption filter type is not suitable as a high-intensity laser light attenuator because it is easily damaged by heat generated by absorption of laser light.
In addition, the type that rotates a transparent substrate and utilizes the angle dependence of the reflectance caused by the difference in refractive index between the substrate material and the surroundings has high durability, but has a strong polarization dependence on the reflectance, so it is usually unpolarized. The characteristics of high-intensity lasers, which use polarized light or randomly polarized light, are uncertain and cannot function as an attenuator.
In addition, the type that rotates the polarization direction of light has low durability of the polarizing element and has the constraint that the light to be controlled is limited to linearly polarized light. Therefore, the industrial high output of randomly polarized light represented by a fiber laser. Not applicable to lasers. Even if a polarizing element having a high laser proof stress exists, the laser output to be controlled is inevitably less than half of the original laser output by separating and extracting only the linearly polarized light component. Such output loss is also undesirable from an energy efficiency standpoint in applications that require higher laser power, such as laser machining.

In this way, all existing laser output adjustment and control technologies have technical issues such as low durability and limited control targets, and at present, they have high intensity and a wide variety of polarization states. In the industrial high-power laser, there is no effective means for controlling the output with high accuracy.
For this reason, for example, at a laser processing site, it has been difficult to suppress momentary fluctuations in laser output due to temperature changes due to morning and evening and seasons, operating conditions of equipment, and residual heat. In laser machining, if the output becomes unstable, the machining state also becomes unstable, which leads to deterioration of product quality and yield. Therefore, a technology for stabilizing high-power laser light for machining with high accuracy. There has been a strong demand for a technique for freely and precisely controlling the desired value.

By the way, in order to construct an optical element having high durability against high-intensity laser light, it is sufficient to reduce heat generation of the element itself by using a material having low light absorption. That is, the principle of dimming may be based on the reflection / transmission of the element instead of the light absorption, and as a means for making the amount of light attenuation variable by using a material having such a small light absorption, near-field by a prism or the like. It is conceivable to utilize the coupling characteristics of field light.

Patent Document 1 describes that a monitor light is detected from a beam splitter by a photodetector to stabilize a laser output.
Patent Document 2 describes that evanescent light is generated between a convex lens and a right-angle prism to obtain a laser intensity distribution according to the convex shape of the convex lens.
Non-Patent Document 1 describes that a radio wave having a wavelength of several centimeters is used to change the transmittance and reflectance by generating and coupling an evanescent wave (light).

Japanese Unexamined Patent Publication No. 5-145163 Japanese Unexamined Patent Publication No. 2009-27325

J.J. Brady, et al., “Penetration of Microwaves into the Rarer Medium in Toral Reflection”, J. Opt. Soc. Am, Vol.50, No.11, pp.1080-1084, 1960.

Light attenuation utilizing the coupling characteristics of near-field light will be described with reference to FIG.
When light is incident on the slope from the inside of the prism A at an angle that causes total internal reflection, near-field light (evanescent light) is generated on the outside of the slope. This near-field light has the property that it is localized in the range of wavelength from the vicinity of the slope (the surface where the near-field light is generated) and does not propagate in the normal direction of the generation surface. The intensity of near-field light is highest on the surface of the generation surface of prism A, and is exponentially attenuated according to the distance from the generation surface. Here reach the near-field light (oozing length) d _p is the wavelength of light lambda, n ₁ the refractive index of the _prism, the incident angle of the laser beam of the refractive index of the surrounding n _2, the prism slopes If θ _in , it is given by the following equation.
d _p = λ / 2π / (n ₁ ² · sin ² θ _in −n ₂ ² ) ^1/2

By the way, when an object that scatters light is brought close to a region where near-field light exists, the near-field light binds to the object, loses its localization, and propagates in space. The intensity of this spatially propagating light depends on the intensity of near-field light at the position of the scatterer. At this time, the output of the light reflected in the prism A is a value obtained by subtracting the output of the propagating light from the output of the incident light. That is, when the light absorption of the prism material is negligible, output P _in of the incident _light, outputs the P _r of the reflected _light, the output of the scattered transmitted light when the P _t, the following relation holds.
P _in = _Pr + P _t
Introducing prism B as scatterers, when the coupling surface that slopes incident light P _in to prism A, the light distribution of which is branched into a transmitted light P _t to the reflected light P _r and the prism B of the prism A A vessel (beam splitter) is formed.

If the slopes of prisms A and B that generate and combine proximity field light are called a pair of "opposing surfaces", the reflectance to prism A and prism B can be changed by changing the distance between the facing surfaces. In principle, the transmittance to the prism can be adjusted between 100% to 0% and 0% to 100%, respectively.
_{Further, when the incident angle θ in} of the light from the inside of the prism A to the slope is changed, the exudation length of the near-field light changes, and the intensity of the light reaching the coupling surface of the prism B changes. Similarly, the reflectance and the transmittance can be adjusted by this.

FIG. 2 shows changes in reflectance and transmittance with respect to the distance [nm] between the facing surfaces of the prisms A and B when the prisms A and B are right-angle prisms made of optical glass BK7 and the laser wavelength is 1.1 μm. The lines show the theoretical values and the plots show the experimental values. The incident angle is set to 45 °.
On the other hand, FIG. 3 shows a change in transmittance (line: theoretical value, plot: experimental value) when the exudation length of near-field light is changed by adjusting the angle of incidence on the slope of prism A.

Based on this principle, it is possible to construct an optical attenuator that adjusts the transmittance and reflectance with a transparent material that does not absorb light, so durability against high-intensity laser light, which has been a conventional problem, can be expected. That is, if a system that detects the output of the laser beam and feeds it back to the setting of the attenuation amount by using the mechanism for adjusting the interval and the angle described above is constructed, the output of the laser beam can be maintained at a constant value with high accuracy, or is desired. It is possible to realize an operation such as quickly changing to the value of, and to realize a laser output control device that can be applied to high-intensity laser light.

However, in order to control the reflection / transmittance based on this principle, it is necessary to align the near-field light generation surface and the coupling surface on the order of wavelength level and set the distance. The target was limited to infrared rays and radio waves with long wavelengths. In other words, application to visible to near-infrared laser light, which is in high industrial demand, requires nanometer-order optical alignment, advanced adjustment skills by skilled workers, and precise multi-axis (translation, tilting) stages and jigs. Since equipment such as actuators is indispensable, it is difficult to miniaturize, and it takes time and cost, it has been a barrier to practical use.

Therefore, an object of the present invention is to achieve both high accuracy and low cost of optical alignment, which is indispensable for constructing a near-field optical attenuator in the visible to near-infrared wavelength region, and to achieve high intensity in the wavelength region. The purpose is to realize a laser light output control device based on a highly durable variable attenuation variable light attenuator applicable to a laser, and to realize miniaturization, cost reduction, and high performance of this device.

In order to solve this problem, in the laser output control device of the present invention, the facing surfaces are brought into close contact with each other directly or via a spacer having a predetermined thickness so that the distance between the facing surfaces is initially set. By rotating the two prisms A and B integrated and the integrated prisms A and B while maintaining the distance between the opposing surfaces of the light, and adjusting the incident angle of light, the prisms A and B An adjustment mechanism that adjusts the ratio of light output that emits prisms A and B by generating and combining near-field light between facing surfaces, an optical sensor that detects the output value of light that emits prisms A and B, and light. It is composed of an arithmetic control device that controls an adjustment mechanism based on a detection signal of a sensor and changes the ratio of light outputs emitted from prisms A and B.

According to the present invention, the near-field light generation surface and the coupling surface of the prisms A and B can be aligned with high accuracy and without requiring a high level of skill, and the visible to near-red color, which is in high industrial demand, can be aligned. It is possible to realize a highly durable optical attenuator with a variable attenuation amount, which can be applied to a high-intensity laser of an external wavelength, and a laser output control device using the optical attenuator, which can reduce the size and cost.

FIG. 1 is a diagram showing a basic principle of controlling reflection / transmittance by generation and coupling of near-field light. FIG. 2 is a diagram showing changes in the reflection / transmittance of the system with respect to the distance [nm] between facing surfaces in the alignment of the prisms A and B. FIG. 3 is a diagram showing changes in the transmittance of the system with respect to the angle of incidence [°] on the prism facing surface. FIG. 4 is a plan view of the alignment of the prisms A and B according to the first embodiment. FIG. 5 is a side view from a direction along the facing surface in the alignment of the prisms A and B according to the first embodiment. FIG. 6 is a diagram showing an example of a laser beam output control system using an optical attenuator with a variable attenuation amount according to the first embodiment. FIG. 7 is a diagram showing an example of a beam sampler formed by determining the distance between the facing surfaces of the prisms A'and B'. FIG. 8 shows fluctuations in laser power (before the control system is incident) when a stepwise and drifting disturbance of about ± 10% is intentionally applied, and when this disturbance is suppressed by applying Example 1. It is a comparative figure of the laser power fluctuation (after the control system is emitted). FIG. 9 is a plan view of Example 2 in which prisms A and B are fixed via an actuator element 7 that is deformed by an external signal to adjust the distance between facing surfaces and make the transmission (reflectance) rate variable. .. FIG. 10 is a diagram showing a configuration example of the third embodiment in which the beam sampler is integrated. FIG. 11 is a diagram showing a configuration example of Example 4 in which the angle of light incident on the near-field light generation surface is changed. FIG. 12 is a diagram showing a change in transmitted light intensity when the rotating stage is operated in a range of ± 15 ° based on an angle perpendicularly incident on the leg surface of the right-angle prism A. In FIG. 13, semi-cylindrical prisms A and B are formed into a cylindrical body with a spacer 6 interposed therebetween, and the cylindrical bodies of the prisms A and B are rotated while being housed in the annular space of the fixed transparent bearing element 9. It is a figure which shows the attenuator structure of Example 4 in which the incident angle to the facing surface is variable. FIG. 14 is a diagram showing a configuration example of a laser light output control system using an optical attenuator with a variable attenuation amount according to the fourth embodiment. FIG. 15 is a diagram showing an example in which a polygonal prism is adopted. FIG. 16 is a diagram showing Example 5 in which a wedge-shaped or other spatial change is applied between the facing surfaces of the prisms A and B, and the amount of attenuation is variable depending on the incident position of the laser beam.

[Example 1]
In the first embodiment, the output of the laser beam is controlled by changing the distance between the facing surfaces of the prisms A and B by a variable stage.
First, the alignment of the prisms A and B will be described with reference to the drawings.
4 and 5 show a plan view and a side view from a direction along the facing surface in the alignment of the prisms A and B, respectively. In this embodiment, right-angled prisms having the same shape are used as the prisms A and B, and the surfaces (bottom surfaces) of the prisms A and B forming the hypotenuse in FIG. 4 are arranged so as to face each other. It is used as a generation surface and a connection surface.

When performing alignment, first, the facing surfaces of the prisms A and B are brought into close contact with each other. In this state, the alignment of each axis is optimized between the near-field light generation surface of prism A and the near-field light coupling surface of prism B, the distance between the facing surfaces is the minimum, and the parallelism between the facing surfaces is small. Corresponds to the maximum ideal state.
Next, the packed layer S is formed as shown in FIG. 5 in order to complement the space created between the prisms A and B for which the alignment has been optimized and the stages SA and SB where the alignment error remains. In this embodiment, an appropriate amount of the uncured adhesive forming the packed bed S is applied to the fixed surfaces of the stages SA and SB, and then the prism A is placed on the stage SA while maintaining the close contact between the facing surfaces of the prisms A and B. Then, the prism B is held on the stage SB. When the adhesive is cured in this state, the prisms A and B are fixed on the stages SA and SB, respectively, while maintaining the optimum alignment.

In the normal procedure, prisms A and B are fixed on the stages SA and SB, respectively, and then the alignment of the stages SA and SB is adjusted and optimized. Even if it requires skill and time and is performed automatically, high-cost equipment such as multi-axis stages and actuators, computers and optimization programs that control them are indispensable.
On the other hand, in this embodiment, in the stage before fixing the prisms A and B to the stages SA and SB, respectively, the facing surfaces of the prisms A and B are kept in close contact with each other to create a state in which the alignment is adjusted. deep. The misalignment remaining between the prisms A and B and the stages SA and SB in this state is complemented by the packed bed S, which eliminates the complicated and costly alignment technique described above. Strictly speaking, in this embodiment, there is a deviation between the optical axis passing through the prisms A and B and the operating axis of the stage, but this is a level that does not affect the performance as an optical attenuator.
Then, after the adhesive as the packing layer is cured, the stage SB is moved straight in a certain direction with this state as the reference initial position, so that the distance between the facing surfaces of the prisms A and B is maintained at a high degree of parallelism. It can be changed. In particular, by operating the prism B side, it is possible to control the reflectance to the prism A and the transmittance to the prism B while maintaining the optical axis of the beam emitted by reflection or transmission.

In this embodiment, right-angled prisms having the same shape are used as the prisms A and B, but prisms of other forms or prisms of different sizes may be used, and various facing surfaces of the prisms may be selected. You may.
As the material of the packing layer, in addition to the above-mentioned uncured liquid adhesive, a clay-like material that plastically deforms along the shape of the gap between the prisms A and B and the stages SA and SB is used as the filling layer. A method of fixing by applying an external force with a jig may also be used.

FIG. 6 shows an example of a laser beam output control system using an optical attenuator with a variable attenuation amount according to this embodiment. In the optical attenuator 1 aligned as described above, the laser beam is incident on the leg surface of the prism A, totally reflected on the slope, and the output of the laser beam emitted from the other leg surface is controlled. A part (several% or less) of the light output of the emitted light is extracted using a beam sampler 2 or the like, and detected using a photoelectric type or thermal type optical sensor 3. The detected optical output signal is input to the arithmetic control device 4, and sends a control command to the actuator drive circuit 5 of the stage SB according to the difference from the target value. As the actuator controlled by the actuator drive circuit 5, a piezo aquaturer or the like capable of high-speed and high-precision position control is suitable.
Here, when the monitor signal of the reflected light exceeds the target value, the stage SB is operated so as to increase the coupling amount of the near-field light, that is, to narrow the distance between the facing surfaces of the prisms A and B. On the other hand, when the value is lower than the target value, the stage B is operated so as to reduce the coupling amount of the near-field light, that is, to increase the distance between the facing surfaces.

Here, the specifications of the beam sampler 2 and the optical sensor 3 constituting the control system are selected according to the characteristics and purpose of the laser beam to be controlled. For example, when the laser beam to be controlled is unpolarized or randomly polarized, it is desirable to use a beam sampler 2 or an optical sensor 3 having no polarization dependence in its characteristics. Further, when aiming at higher speed control, it is desirable to use a photoelectric type having high response characteristics and high sensitivity for the optical sensor 3. Further, in consideration of the efficiency of the control system, in order to prevent the light output after control from being reduced by extracting an unnecessarily large amount of monitor light, the beam sampler 2 is provided with the optical sensor 3 for the monitor. It is desirable to give the maximum branching ratio while considering S / N.

By the way, since the photoelectric optical sensor has a quick response and high sensitivity, it can obtain highly accurate monitor performance, but it is not suitable for detecting high-intensity laser light in terms of durability and sensitivity level. Therefore, when the photoelectric sensor is used as an optical sensor 3 for a monitor for controlling a high-power laser, it is necessary to sufficiently attenuate the light incident on the sensor to an appropriate intensity level and extract the light. .. Therefore, as the beam sampler 2, a robust beam sampler having high durability against high-intensity laser light and having a high branching ratio is required.
Usually, as a beam sampler, a glass substrate in which an approximate branching ratio can be obtained by the difference in refractive index between air and glass, or a dielectric multilayer film in which reflectance and transmittance are controlled are used. However, the branching ratios obtained by these are at most several% and 0.01%, respectively, and the branching ratio is not sufficient depending on the laser output level to be controlled. For example, if 1 kW laser light is extracted with a 0.01% beam sampler, the output of the monitor light will be 100 mW, but the output is still too high to be received by the photoelectric sensor, so further attenuation (high branch ratio) will occur. Desired.
It is conceivable to install a plurality of the above glass substrates and dielectric multilayer films to gradually weaken the light incident on the monitor sensor to increase the total attenuation rate, but the optical system becomes large and complicated. As a result, the practicality is lowered and stray light is generated, so that high monitor performance cannot be obtained.

In this way, in order for the feedback control system by the arithmetic control device 4 to function with high accuracy, the damping factor (branch ratio) can be stably maintained regardless of the laser output to be controlled, and at the same time, control is performed. A beam sampler having a high branching ratio capable of extracting monitor light while minimizing a decrease in the target laser output is required.
Therefore, it is preferable to use it as a beam sampler by utilizing the principle of the near-field optical coupling type optical attenuator of the present invention.
That is, as shown in FIG. 7, a robust spacer 6 having a specific thickness is interposed at a position that does not block the laser optical path, such as a corner between the facing surfaces of the prisms A'and B', and the prisms A', B' The distance between the facing surfaces is determined by mechanically fixing the facing surfaces with a jig or an adhesive in a state where the facing surfaces are in close contact with the spacer 6. The distance between the facing surfaces of the prisms A'and B'may be adjusted to a desired attenuation factor by using a low-intensity measurement laser beam, or may be obtained after the adhesive used has been cured. The attenuation factor may be measured in advance.
This makes it possible to construct a beam sampler that is compact, highly durable, robust, and has excellent stability.

FIG. 8 shows fluctuations in laser power (control system incident) when a randomly polarized laser with a high-intensity beam (approximately 2 kW / cm ² ) is intentionally subjected to stepwise and drift-like disturbances of about ± 10%. The results of comparing the previous) and the laser power fluctuation (after the control system is emitted) when the disturbance is suppressed by applying this embodiment to the laser beam are shown by adding a time axis.

According to this embodiment, the same level of fluctuation occurs for a short time with respect to the instantaneous step-like disturbance of the laser power to be controlled, but the feedback control by the arithmetic control device 4 instantly converges to the target value. It was confirmed that the fluctuation amount of the laser output can be significantly reduced to less than 0.1% in the standard deviation without being affected by the gentle drift-like disturbance.

In this embodiment, in order to support random polarization, the specifications are set so that the polarization dependence of the beam sampler 2 for the monitor and the optical sensor 3 is minimized.
Further, in the construction of the translation mechanism that changes the distance between the facing surfaces of the prisms A and B, by giving an angle δ between the facing surfaces and the operating axis of the translation stage, the movement amount X of the stage B is relative to the movement amount X of the stage B. The distance between the facing surfaces becomes X · sinδ, and the speed is reduced. This makes it possible to optimize the accuracy and speed of light attenuation control according to the positioning accuracy and speed of the stage.
In this experiment, in order to confirm the linearity of the actual movement distance with respect to the movement command of the stage, a He-Ne laser beam was introduced between the facing surfaces of the prisms A and B at an incident angle that does not totally reflect, and the interference obtained was obtained. The distance between the facing surfaces was evaluated based on the waveform.

According to this embodiment, even if it is a high-intensity laser beam for processing or a randomly polarized laser, the laser output can be highly accurate simply by installing a control system as shown in FIG. 6 in the optical path. It is possible to control the fluctuation and effectively suppress the fluctuation and maintain the desired value.
In the verification assuming application to a high-power laser, a beam with a wavelength of 1.1 μm, an output of 100 W, and a diameter of 1 mm in TEM00 mode can be used, and the amount of attenuation can be adjusted even for a high-intensity beam of ^{about 20 kW / cm 2.} It was confirmed that.

If the transmission / reflectance of the beam sampler 2 and the sensitivity of the sensor 3 are calibrated in advance by an experiment, the laser power after the control output can be measured with high accuracy. That is, when a desired laser power value is input to the calculation unit, it is possible to construct a traceable laser irradiation device that outputs the laser power as it is with high accuracy.

Further, in this embodiment, a constant target value is set, the output fluctuation of the incident laser light is absorbed by feedback control, and a constant laser output is emitted, but the target value is changed with time and emitted. The laser output may be controlled to change in various ways.
For example, in the case of a laser processing device, a map corresponding to the position of the stage on which the work (workpiece) is mounted and the required laser irradiation amount is programmed, linked with the operation of the stage, and the laser is used depending on the location. Advanced laser irradiation technology such as changing the output becomes possible.
By controlling in this way, the cutting speed can be controlled according to the dimensions of the parts, the range of processing can be limited, and the laser heating temperature can be selectively changed depending on the part, so that the heating furnace can be used many times. It is expected that the laser processing technology will become more sophisticated, such as replacing the heat treatment performed in the process with a single laser device and shortening the process.
In addition, by shortening the warm-up time until the output of the laser device stabilizes at the start of the production line, it is possible to contribute to energy saving and improvement of production efficiency in the factory.

Further, in the above embodiment, the light totally reflected by the prism A and emitted is targeted for output control, but the transmitted light to the prism B may be targeted for control. In that case, the adjustment of the distance between the opposing surfaces between the prisms A and B by the actuator drive circuit 5 is in the opposite direction, and the output of the transmitted light is increased by reducing the distance between the opposing surfaces between the prisms A and B, and the prism A is used. By increasing the distance between the facing surfaces between B and B, the output of transmitted light is reduced.
In particular, the case where the reflection side is the control target is suitable when it is desired to control the output of high-intensity laser light with high resolution and high accuracy. On the other hand, the case where the transmitted light is the control target is suitable for a case where it is desired to extract a part of the originally high-intensity laser light with high accuracy at a weak level.
Further, as shown in FIG. 2, it is possible to optimize the operation of the control system according to the control target by utilizing the characteristic that the gradient of the characteristic curve of the reflection / transmittance obtained by the distance between the facing surfaces changes. is there. That is, when the output of the laser beam to be controlled varies greatly, the control width is prioritized and the attenuation is controlled in the region where the gradient of the characteristic curve is large, and the controlled object is relatively stable and the output is more accurate. When control is required, it is possible to give priority to control resolution and control the amount of attenuation in a region where the slope of the characteristic curve is gentle.

[Example 2]
In this embodiment, the prisms A and B are directly fixed to each other via an actuator element that is deformed by an external signal, so that the distance between the facing surfaces can be adjusted without using a mechanical stage or the like, and the transmission (reflectance) rate can be adjusted. It is variable.
FIG. 9 shows a side view seen from a direction along the facing surface. A rod-shaped piezo element that expands and contracts when a voltage is applied is used as the actuator element 7, and the piezo element is expanded and contracted with one end fixed to the prism A and the other end fixed to the prism B. As a result, the distance between the facing surfaces of the prisms A and B is adjusted, and the amount of transmission and reflection attenuation is variable.

Similar to the first embodiment, the prisms A and B are brought into close contact with each other to optimize the alignment, and the piezo elements are placed between the facing surfaces at positions that do not block the optical paths of the laser beams of both prisms while maintaining the state. It is arranged, and both ends thereof are fixed with an adhesive to the side surfaces orthogonal to the facing surfaces of the prisms A and B, respectively. The adhesive is preferably an epoxy-based adhesive that can obtain sufficient mechanical strength.
When the prism A is fixed with a holder or the like, the prism B is supported on the prism A via a piezo element. By expanding and contracting the piezo element in this state, the distance between the facing surfaces of the prisms A and B can be adjusted.

At this time, if the prisms A and B are supported by a plurality of piezo elements, the operating force increases according to the number of elements, and faster and more stable position control of the prism B is possible.
In order to change the distance between the facing surfaces while maintaining the parallelism between the facing surfaces of the prisms A and B, it is indispensable to match the displacement amounts of the plurality of piezo elements. This is possible by separately grasping the relationship between the transmission rate for each surface location and the command signal (applied voltage in the case of a piezo element) to the actuator element 7.
Furthermore, by giving different displacements to multiple actuators, it is possible to intentionally break the parallelism between the facing surfaces and change the transmittance of transmitted and reflected light depending on the position in the facing surfaces, which is a laser. It can also be applied to a control device for a beam cross-sectional intensity profile (laser light intensity distribution in a plane orthogonal to the optical axis).

The actuator element 7 includes a piezoelectric material such as a voltage-controlled piezo element as described above, an actuator element in which the distance between bottom surfaces is changed by temperature control using a linear expansion coefficient, and a moisture-sensitive material such as hydrogel. It is possible to use a material whose thickness is variable depending on the humidity, a material which is displaced by electromagnetic wave (light) irradiation (a material that absorbs electromagnetic waves (light) other than the controlled laser wavelength), and the like. As a method of installing the actuator, in addition to the method of installing the actuator on the side surface of the prism as in the above embodiment, a thin film actuator material is spacerd at a position in the facing surfaces of the prisms A and B so as not to block the optical path of the laser beam. It may be in the form of intervening as in.

According to this embodiment, the distance between the facing surfaces of the prisms A and B can be controlled without using high-precision stages, and the moving part is significantly reduced in weight, so that the damping amount control speed (response). Gender) improves. At the same time, if the moving parts are small and lightweight, the robustness of the system against mechanical external forces such as drops and impacts will be improved, so high practicality in the field can be expected. Further, at the time of assembly, as in the case of the first embodiment, a compact optical attenuator with a variable attenuation amount can be constructed simply and with high accuracy without the need for a precise alignment work.

[Example 3]
In the third embodiment, the laser light output control device is made compact by combining prisms A and B having variable reflection / transmittance and prisms A'and B'with fixed reflection / transmittance. , FIG. 10 shows a plan view.
Two sets of a variable attenuation light attenuator composed of right-angle prisms A and B and a fixed attenuation light attenuator composed of right-angle prisms A'and B'are prepared. , A part that adjusts the optical output by changing the distance between the facing surfaces and a part that maintains the distance between the facing surfaces and functions as a beam sampler with a constant branching ratio are combined.

Here, by optically connecting the leg surface on the light emitting side of prism A of the first attenuator and the leg surface on the light incident side of prism A'of the second attenuator, two sets of optical attenuators Is integrated.
Since the connecting portion of the prism suppresses the reflection of light due to the difference in refractive index, both leg surfaces may be polished with high precision to be in an optical contact state, or may be fixed with a highly transparent optical adhesive. Further, it is also effective to interpose the refractive index matching oil and fix it from the outside with a jig or the like, or to construct a non-reflective film such as a dielectric multilayer film on both of the connecting surfaces.

In this embodiment, the attenuator is arranged so that the incident direction and the exit direction of the light entering the optical output control device are parallel to each other. However, by changing the direction of the attenuator on the exit side, for example, the incident light It is also possible to construct a "corner cube type" light output control device that controls the output of the light to a desired value and then returns it to the direction in which it came, or a "beam steering type" light output control device that bends and emits light in any direction after control. is there.
Further, in this embodiment, the prisms A (near-field light generating side) of the two sets of attenuators are arranged close to each other or in close contact with each other, but these may be integrated from the beginning. That is, instead of the two prisms A and A', one parallelogram prism is used, and the amount of attenuation is controlled and the monitor light is extracted on the two slopes.

In this way, the variable attenuator (prism A, B) that adjusts the light output and the fixed attenuator (prism A', B') that extracts the monitor light are made compact, and the monitor sensor 3 branches a small amount of light. By installing it in the immediate vicinity of the prism B', which functions as a beam sampler that allows light to pass through, the elements of the control system can be integrated into a small size that fits in the palm of your hand. The miniaturization and weight reduction of the operating unit for control and the adoption of a high-speed, high-sensitivity photoelectric type for the monitor photodetector contributes to high-speed feedback control and improves control performance. At the same time, the cost is reduced by reducing the number of parts in the system, and the mechanical robustness is ensured by reducing the size and weight, which improves the practicality.
Although FIG. 10 shows an example in which the second embodiment is adopted as the variable attenuator (prisms A and B), the integrated prism A and the prism A'prism B'are adopted in the first embodiment. It may be placed on the stage SA and the prism B may be placed on the stage SB.

[Example 4]
In the fourth embodiment, while maintaining a constant distance between the facing surfaces of the prisms A and B, the incident angle of light on the near-field light generating surface of the prism A is changed to reach the coupling surface of the prism B. The amount of attenuation is adjusted by adjusting the intensity of the field light.
FIG. 11 shows a configuration example. On the rotating stage 8, prisms A and B, which maintain the distance between facing surfaces by a spacer 6 having a thickness d and are integrated by fixtures at both corners, are installed, and the actuator mechanism (micrometer,) of the rotating stage 8 is installed. By operating the motor, reduction mechanism, etc.) manually or by the drive circuit 5, the incident angle θ _in of light on the proximity field generation surface of the prism A is changed within a predetermined rotation angle range.
At this time, the rotation axis is set near the near-field light generation position of the incident side prism A. The integrated prisms A and B are installed on the rotating stage 8 by adhesion or the like so as to rotate around this axis.

Specifically, the right-angled prisms A and B of BK7 are brought into close contact with each other with an aluminum foil spacer 6 having a thickness of 0.8 μm interposed therebetween, and both are mechanically fixed by a fixing jig or an adhesive.
After the distance between the bottom surfaces is fixed in this way, it is installed on the rotating stage 8 and the rotating stage is operated within a range of ± 15 ° based on the angle perpendicularly incident on the leg surface of the prism A. FIG. 12 shows a change in the transmitted light intensity when the light intensity is increased. Here, the leg surfaces of the prisms A and B into which the laser light is incident and emitted are coated with a coating that suppresses the reflectance within a range of an incident angle of ± 30 °.

In the region where the rotation angle Φ is less than about −5 °, the total reflection condition is not satisfied on the prism A slope and the near-field light is not generated, so that no attenuation occurs and the incident light on the prism A maintains almost the intensity. It is transmitted from prism B as it is.
In this example, with an angle change of about 10 °, the transmitted light intensity changes by about 30 dB (1/1000), which corresponds to an attenuation of 3 dB (50%) per °. At present, the highest performance angular resolution of the automatic rotation stage is available in less than 1 second (= 1 ° / 3600), and by changing the angle of incidence on the attenuator, a wide range is available. It is possible to realize a highly accurate laser light output control system.

In order to set a desired distance between the facing surfaces, in addition to interposing the spacer 6, a film having a predetermined thickness is formed on one or both prism facing surfaces by vapor deposition or the like, and then the facing surfaces are brought into close contact with each other. You may. Further, one or both prism facing surfaces may be formed into a concave shape by chemical etching, mechanical polishing, or the like.
Further, in order to secure the stability of the damping amount, it is necessary to improve the positioning accuracy of the rotary stage 8. In the case of the manual rotary type using a micrometer or the like, a return spring is incorporated in the rotary mechanism. , It is preferable to eliminate backlash.
On the other hand, in the case of an automatic rotation type using a piezo or a motor, the rotation angle can be controlled with high accuracy by feedback-controlling the actuator drive circuit 5 in combination with an angle detection sensor such as a rotary encoder. is there.

However, when the right-angled prisms A and B are used as in this embodiment, when the rotation angle exceeds a certain range, the light of the emitted light is emitted due to the refraction generated at the refractive index boundary surface (leg surface) between the prisms A and B and the surroundings. Axis deviation cannot be ignored.
For example, when a laser beam having a wavelength of 1064 nm is incident on an attenuator composed of a right-angle prism of BK7 glass having a side of 25 mm, the transmitted light axis shifts by ± 0.7 mm when the incident angle is changed within a range of ± 5 °. To do.
Such an optical axis shift adversely affects the alignment of all optical systems installed after this, and directly leads to a decrease in the performance of the optical system. For example, in a laser processing apparatus, it causes deformation of the focused spot and deviation of the irradiation position, which leads to a decrease in processing accuracy.
That is, the optical attenuator is ideally required to cause no change in parameters other than the output of the laser beam before and after the attenuation.

In order to avoid the optical axis shift and the distortion of the beam shape before and after such attenuation, the structure is such that the incident / exit angle of light is always maintained at 0 ° at the refractive index interface other than the facing surfaces of the prisms A and B. And it is sufficient.
Therefore, as an example, as shown in FIG. 13, the prisms A and B are formed into a semi-cylindrical shape, fixed and integrated with a spacer 6 interposed therebetween to form a cylindrical body, and then the prisms A and B are housed in the central portion. The structure is such that an annular space with a slight gap 10 is formed between the transparent bearing element 9 having a cylindrical space. The transparent bearing element 9 is immovable independently of the rotation of the prisms A and B, and the gap formed between the outer surface of the cylindrical prisms A and B and the inner surface of the transparent bearing element 9 is formed. It is filled with optical oil.

In this way, while matching the materials of the prisms A and B with the material of the transparent bearing element 9 and the refractive index of the optical oil, the entrance / exit portion of the laser light is set as the outer surface of the flat transparent bearing element 9, and the incident / exit portion is formed. By arranging the angles so as to be 0 °, it is possible to suppress the optical axis shift and the focusing of light on the side surfaces of the semi-cylindrical prisms A and B.
As the optical oil, oil-immersed oil for microscopes with adjusted refractive index is used to achieve both mechanical lubrication and matching of refractive index, and there is no optical axis shift or beam shape distortion, and near-field control by incident angle control. It is possible to construct a field-optical coupling type variable optical attenuator.
FIG. 14 shows an example of a laser light output control device using an optical attenuator with a variable attenuation amount according to this embodiment.

Further, in FIG. 15, a polygonal prism is adopted as a device for changing the transmittance without using an element for optical axis shift or beam shape correction. In this example, as the prisms A and B, a regular dodecagonal prism divided into two by a diagonal line is used. The incident angle and emission angle of the laser light at the refractive index interface of the light incident / exit portions of the prisms A and B are reset every 30 ° of the stage rotation angle and return to 0 °. There is no change in beam shape.
On the other hand, the reflected light from the facing surface of the prism A may be used as the emitted light. In this case, the direction of the emitted light can be changed by rotating the facing surface in order to adjust the reflectance. it can.

[Example 5]
In this embodiment, a spatial change such as a wedge shape is given between the facing surfaces of the prisms A and B, and the amount of attenuation is variable depending on the incident position of the laser beam.
In FIG. 16, the bottom surfaces of the prisms A and B are held in contact with each other at the upper left corners of the prisms A and B, and are held in contact with each other. By interposing a spacer 6 having an increasing thickness, the distance between the two facing surfaces is continuously increased from the upper left end side to the lower right end as in d1 to d2.

With this configuration, the amount of light attenuation changes depending on the incident position of the laser beam on the prism A.
That is, in FIG. 15, when it is desired to obtain a small reflectance (large transmittance), it is above the prism A, while when it is desired to obtain a large reflectance (small transmittance), it is below the prism A. A laser beam is incident.

For this purpose, it is necessary to accurately adjust the incident position of the laser beam with respect to the prism A, and after maintaining the incident angle constant, the incident position of the laser beam with respect to the prisms A and B, or the prism A with respect to the laser beam. , A positioning mechanism 11 capable of adjusting the position of B is provided. At this time, by operating the positioning mechanism in parallel with the facing surface of the prism A, the amount of attenuation can be made variable while maintaining the optical axis of the light reflected on the prism A.

By the way, as shown in FIG. 2, the change in reflectance or transmittance with respect to the distance between the facing surfaces of the prisms A and B is not linear, and is steep from the state where the facing surfaces are in close contact to the distance of about the wavelength of light. However, at longer distances, the change in reflectance or transmittance gradually slows down, the reflectance gradually approaches 100%, and the transmittance gradually approaches 0%.
With such non-linear characteristics, it is difficult to adjust the position to appropriately obtain the desired reflection / transmittance. Therefore, processing is performed so that the shape of one or both of the opposing surfaces of the prisms A and B is a gently convex (concave) curved surface.
As a result, it is possible to make the change in the distance between the bottom surfaces gentle and to make the change in reflectance or transmittance with respect to the change in the distance between the bottom surfaces between the prisms A and B a linear characteristic.
When the prism facing surface is processed into a curved surface, the characteristic that the change in the transmittance (reflectance) rate changes continuously with respect to the laser incident position can be obtained, but on the facing surfaces of the prisms A and B, by vapor deposition or the like. By forming a thin film on the order of nanometers in a stepped manner with different thicknesses, it is possible to give a stepwise change in the transmittance (reflectance) with respect to the incident position of the laser beam.

As described above, according to the present invention, a variable optical attenuator using near-field light can be constructed with high accuracy and low cost, and by constructing a laser output control device using this, a laser output control device can be constructed. In addition to the conventional problem of increasing the laser strength of the control device, the size and weight can be reduced and the cost can be reduced. According to this, it is possible to realize a highly practical laser output control system that precisely controls the output of a high-intensity laser, and it is expected that various laser application technologies using the system will be developed.

A, B Prism SA, SB Stage A', B'Beam sampler prism 1 Optical attenuator 2 Beam sampler 3 Optical sensor 4 Arithmetic control device 5 Actuator drive circuit 6 Spacer 7 Actuator element 8 Rotating stage 9 Transparent bearing element 10 Gap 11 Positioning mechanism

Claims (3)

Two integrated surfaces are integrated while maintaining a predetermined distance between the facing surfaces so that the distance between the facing surfaces is initially set by bringing the facing surfaces into close contact with each other directly or via a spacer having a predetermined thickness. Prism A, B,
By placing and rotating the integrated prisms A and B on a rotating stage and adjusting the incident angle of light, near-field light is generated and coupled between the facing surfaces of the prisms A and B. An adjustment mechanism that adjusts the ratio of light output that emits prisms A and B, and
An optical sensor that detects the output value of the light emitted from the prisms A and B, and
Based on the detection signal of the light sensor, to control the adjusting mechanism, and the operation control device for varying the prism A, the ratio of light output for emitting B,
Light output control device having a. The prisms A and B have a semi-cylindrical shape, and are fixed and integrated via a spacer to form a cylindrical body, and are provided with a transparent bearing element that is immovable independently of the rotation of the prisms A and B. By accommodating the prisms A and B in a cylindrical space formed in the central portion of the transparent bearing element, an annular space is formed between the outer surface of the prisms A and B and the inner surface of the transparent bearing element. The optical output control device according to claim 1, wherein the annular space is filled with optical oil. The prism A, B is a polygonal prism, light output control device according to claim 1, characterized that you to prism by fixing and integrated via the spacer.

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