Manufacturing method of 1.57-micron rectangular deep cut-off ultra-narrow band-pass optical filter

Abstract

The invention belongs to the technical field of a 1.57 micron laser and an application system thereof, and discloses a 1.57 micron rectangular deep cut-off ultra-narrow band pass filter manufacturing method, which comprises the following steps: (1) determining a theoretical film system; (2) making a template control file for automatic control of the coating machine by using the full-automatic coating machine according to the obtained theoretical film system structure; and (3) loading a selected coating material into the coating machine, and automatically finishing the manufacturing of the optical filter by the coating machine according to the selected template control file by adopting an eccentric monitoring control mode. According to the invention, the production efficiency of high-end optical film products with high requirements, such as rectangular deep cut-off ultra-narrow band pass filters, can be improved to a great extent, and particularly, the method has high practical value for the production of large-caliber filters.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of 1.57 micrometer laser and its application system, and relates to a method for manufacturing a 1.57 micrometer rectangular deep-cut-off ultra-narrow band pass filter. BACKGROUND

[0002] Laser has four optical characteristics of isotropy, high brightness, monochromaticity and high energy density. Due to the special characteristics of laser relative to ordinary light, laser and its application system play an increasingly important role in the development of modern society, and are widely used in various civil and military fields. In the optical system of laser and its application system, the optical elements through which the light path passes in the system generally need to be coated with optical thin films in order to meet the design requirements of the system.

[0003] The so-called optical thin film refers to selecting different optical refractive index coating materials, using physical or chemical deposition method to deposit different film materials on the surface of the to-be-coated film element according to the calculated thickness and sequence of optical principles, so that the element finally obtains the optical performance required by the system.

[0004] Band pass filter is a very important optical element in laser optical system. This type of filter is mainly used in various laser detectors and receiver systems. Along with the laser of the working wavelength, there are also various stray light in the environment, including natural light, various artificial lighting, etc., which basically contain light of each wavelength in the spectral range. The function of the band pass filter is to allow the laser signal of the working wavelength to pass through, while filtering out all other wavelengths of irrelevant light. The wavelength range allowed to pass through is the passband, and the wavelength range filtered out is the stopband.

[0005] The three main performance indicators of the band pass filter are:

[0006] 1. Rectangularity. The ideal band pass filter completely passes through the passband and completely cuts off the stopband, and the corresponding spectral curve in the passband is shaped like a rectangle. However, this result needs an infinite number of layers of thin films to approach. In actual production, the passband shape of the filter cannot be completely rectangular due to the influence of errors and the limited number of layers of the film system, and the degree of similarity of the passband shape to a rectangle is called rectangularity.

[0007] 2. Cut-off degree. The degree of energy suppression of the filter for the wavelength range of the stopband is called the cut-off degree. For any system, the higher the signal-to-noise ratio, the better the system performance. The signal-to-noise ratio is particularly important for laser receiving and detecting systems, because the spectral response range of the detector is generally much wider than the laser working wavelength. In order to obtain the highest signal-to-noise ratio, it is necessary to reduce the intensity of the stopband signal as much as possible, and the higher the cut-off degree of the filter in the stopband, the better.

[0008] 3. Bandwidth. Filter has different bandwidth according to the application requirements. Sometimes also use the filter peak transmittance half the wavelength difference on both sides of the passband, that is, half-width to characterize this index. Generally, the bandwidth of the bandpass filter is less than 10 nm, which is called ultra-narrow band filter.

[0009] The bandpass filter commonly used in laser system is an interference filter designed based on the Fabry-Perot principle. The interference filter selects two different refractive index materials as thin film materials, in which the material with high refractive index is defined as H, and the material with low refractive index is defined as L. The typical Fabry-Perot principle interference filter film system structure is: substrate / (HL)^m HnL(HL)^(m+1) / air, wherein m and n are positive integers, the unit thickness is one fourth of the working wavelength of the filter, and the specific value depends on the index requirements of the product to be obtained. The above structure is an interference cavity. Figure 4 The spectral test results of a typical 1.57 micron wavelength single-cavity bandpass filter in the prior art are described. From Figure 4 It can be seen that this simple design filter has the following limitations:

[0010] 1. Poor rectangularity. Due to the limitations of the design principle itself, the passband shape of the single-cavity interference filter is generally close to semicircular or even conical, resulting in a very narrow passband, which cannot provide a larger passband width when needed, resulting in low total laser energy transmittance. The problem caused by this in actual use is that the filter has poor temperature drift resistance. As we all know, the spectrum of the filter will drift with the change of temperature in actual use. After the single-cavity filter spectrum drifts with temperature, the transmittance at the working wavelength may change greatly, which is not conducive to the stability of the work.

[0011] 2. Poor cutoff. This is also caused by its design principle. From Figure 4 It can be seen that the single-cavity filter has a slow transition between the passband and the forbidden band, and the cutoff is very low.

[0012] In actual production of optical thin films, the workpiece to be coated is placed in a circular workpiece carrier above the film material to be evaporated. The workpiece carrier rotates at high speed during coating, and a monitoring piece is placed at the center. The coating process is controlled by monitoring the change in the intensity of the transmitted or reflected light signal of the monitoring piece with the thickness of the film material deposited. This method is the commonly used center monitoring method. The characteristic of this method is that the thin film at the monitoring point can meet the theoretical design to a high degree, but the farther away from the monitoring point, the greater the error caused by the position difference, ultimately resulting in that the thin film within a certain radius centered on the monitoring point can meet the design requirements, and outside the radius is a defective product or waste product. The area within the radius is called the coating effective area. Since multi-cavity filters have high requirements for error control, their effective area is much smaller than that of ordinary optical thin film products. The diameter of the umbrella stand or carrier of the coating machine for general optical thin films can easily reach more than 1.5 meters. Taking the M111 filter special coating machine produced by Japan Kogaku as an example, the diameter of the workpiece carrier is only 330 mm, and the actual usable area for coating multi-cavity filters is much smaller than the diameter. For high-requirement rectangular deep-cut ultra-narrow bandpass filters, the usable area diameter is only more than 20 mm.

[0013] At the same time, with the increase in the number of layers of the multi-layer film, the control precision during coating is also higher. Especially for multi-cavity filters, which are extremely sensitive to control errors, any slight mistake in the coating process can cause the multi-cavities to affect each other, resulting in the deformation or even collapse of the obtained product band, which becomes a waste product. How to control and reduce errors during actual coating will largely determine the quality of the obtained product. SUMMARY

[0014] (I) Invention purpose

[0015] The purpose of the present application is to overcome the deficiencies of the prior art and provide a manufacturing method for ultra-narrow bandpass filters with high production efficiency, which can improve the effective area and cutoff degree of the bandpass filter and effectively control the negative effects of errors.

[0016] (II) Technical solution

[0017] In order to solve the above technical problems, the present application provides a method for manufacturing a 1.57 micron rectangular deep-cut ultra-narrow bandpass filter, comprising the following steps:

[0018] (1) determining the theoretical film system, based on the typical film system structure of the multi-cavity filter, selecting Ta2O5 as the high refractive index material and SiO2 as the low refractive index material, defining the unit optical thickness of Ta2O5 and SiO2 at λ / 4 as H and L respectively, and using the film system design software Essential Macleod on the computer to determine the film system structure of the filter according to the performance parameters required by the ultra-narrow bandpass filter;

[0019] (2) using a full-automatic film coating machine with a quartz crystal oscillation film thickness controller, a high-precision optical film thickness controller and a radio frequency ion source auxiliary coating, according to the theoretical film system structure obtained above, a template control file for automatic control of the film coating machine is prepared;

[0020] (3) the selected film coating material is loaded into the film coating machine, and an eccentric monitoring control mode is adopted, and the film coating machine automatically completes the production of the optical filter according to the selected template control file.

[0021] (Three) beneficial effects

[0022] The 1.57-micron rectangular deep-cut ultra-narrow band pass filter production method provided by the above technical solution has the following beneficial effects compared with the prior art:

[0023] (1) Based on the single-cavity optical filter of the prior art, the multi-cavity optical filter is adopted, and the rectangularity can be well improved through the stacking of multiple single-cavity designs. While significantly compressing the transition region between the passband and the stopband, the stop degree is much higher than that of the single-cavity optical filter.

[0024] (2) The coating process of the optical filter is improved. According to the experience of multiple test results and the error analysis of the computer software, it is proved that using the process control method developed by the present application can effectively control the negative effects of errors and obtain actual products consistent with the theoretical design.

[0025] (3) The present application discards the commonly used center monitoring method and adopts the eccentric monitoring control mode, which effectively improves the effective area of the film coating.

[0026] (4) The method of selecting multi-cavity design in the present application obtains the theoretical design results with good rectangularity and high stop degree. In the actual production process, the eccentric monitoring method is used to limit and reduce the control error, and the products with large effective area and good uniformity are actually obtained, which can greatly improve the production efficiency of high-end optical thin film products such as rectangular deep-cut ultra-narrow band pass filters which require high requirements, especially for large-aperture optical filters of this type, which has high practical value. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The present application is a theoretical design curve diagram of a rectangular deep-cut ultra-narrow band pass filter working at 1570nm with a typical half-width of 5.2nm.

[0028] Figure 2 is a curve diagram of the test results of the actual product coated according to the process of the present application.

[0029] Figure 3The figure is a curve diagram of uniformity distribution of a large-diameter rectangular deep-cut-off ultra-narrow band pass filter plated according to the process of the present application.

[0030] Figure 4 The figure is a curve diagram of a typical single-cavity band pass filter of the prior art. DETAILED DESCRIPTION

[0031] In order to make the purpose, content and advantages of the present application more clear, the specific embodiments of the present application are described in further detail below in combination with the drawings and examples.

[0032] Referring to Figure 1 In order to solve the shortcomings of the single-cavity filter, for the application fields with very strict requirements on the performance of the filter, a multi-cavity filter design can usually be used to obtain better rectangularity, cut-off and required passband width through the superposition of multiple interference cavities. According to the theoretical design curve of a rectangular deep-cut-off ultra-narrow band pass filter working at 1570nm and having a typical half-width of 5.2nm, first, the theoretical film system is determined, based on the typical film system structure of the multi-cavity filter, Ta2O5 is selected as the high refractive index material and SiO2 is selected as the low refractive index material, with λ being 1570nm, and the unit optical thicknesses of Ta2O5 and SiO2 at λ / 4 being defined as H and L respectively. The performance parameters of the filter include a theoretical half-width with a distribution value of 5-5.4nm, and a region with an average transmittance of greater than or equal to 95% and a width of not less than 3nm. On a computer, the above H and L are simulated using the film system design software EssentialMacleod, and the film system structure of the filter is determined according to the performance parameters required by the ultra-narrow band pass filter as follows:

[0033] Substrate / (HLHLHLHLH4LHLHLHLHLHL)(HLHLHLHLH4LHLHLHLHLHL)

[0034] (HLHLHLHLH4LHLHLHLHL0.6H0.8L) / air.

[0035] The typical film system structure is: substrate / (HL)aHbL(HL)^(a+1)(HL)cHdL(HL)^(c+1)……(HL)mHnL(HL)^(m+1) / air, and the number of cavities and the specific parameters of each cavity in actual plating are determined by the performance parameters of the required product.

[0036] In actual production of the filter, a full-automatic coating machine with a quartz crystal oscillation film thickness controller, a high-precision optical film thickness controller and a radio frequency ion source is used. The coating machine can be selected from a NBPF-M0111 type narrow-band filter special coating machine produced by Japan Optical Corporation. Then, a template control file for automatic control of the coating machine is made according to the obtained theoretical film system. In this step, an eccentric monitoring control method is adopted. The selection of the monitoring point of the eccentric monitoring control method aims to obtain the largest possible coating effective area. The monitoring point can be a point on the circumference with a radius of 22 mm from the center of the workpiece carrier disc. The coating process is controlled by monitoring the transmission intensity of the point on the substrate to achieve the monitoring point. The areas on both sides of the monitoring point are close to the monitoring point. The selected coating materials Ta2O5 and SiO2 are loaded into the coating machine, the workpiece is placed in the workpiece carrier disc, and the coating machine is started. The coating machine automatically completes the production of the filter according to the selected template control file.

[0037] Figure 2 The spectral test results of a 1.57 micron wavelength 3-cavity band-pass filter actually produced by the present application are described. In which graph 1 is the test result of the center point of the actual product, and graph 2 is the theoretical design. As can be seen from the graph, the actually produced product can well meet the requirements of the theoretical design except that the passband transmittance is slightly lower than the theoretical value.

[0038] Figure 3 The uniformity distribution of the filter is described. For the produced 40 mm radius circular filter, three positions are selected for testing, i.e. the center of graph 3, the 20 mm radius point of graph 4 and the 40 mm radius point of graph 5. The test results show that the maximum wavelength difference of the produced filter is only 0.4 nm in the radial distribution, which has good uniformity, proving that the present application can be well applied to the production of large-aperture rectangular deep-cut-off ultra-narrow-band band-pass filters.

[0039] In this embodiment, after multiple tests and comparisons, the point with a radius of 22 mm from the center of the workpiece carrier disc is selected as the monitoring point. The advantages of the eccentric monitoring method are: first, the method actually monitors the average value of all points on the entire circumference at the radius on the high-speed rotating workpiece, thus reducing the error to a certain extent; second, since the areas on both sides of the monitoring point are close to the monitoring point, which is obviously stronger than the one-side area of the center monitoring method, the method can significantly improve the coating effective area. Through the above specially prepared process control method of the present application, the effective area radius of such filters can be improved to 40 mm, greatly improving the production efficiency and yield. From Figure 3 It can be seen that the maximum wavelength difference of the obtained product is only 0.4 nm within the effective area of 40 mm radius, which has good uniformity.

[0040] The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present application, and these improvements and modifications should also be considered as the protection scope of the present application.

Claims

1. A method for fabricating a 1.57-micron rectangular deep-cutoff ultra-narrow bandpass filter, characterized in that, Includes the following steps: (1) Determine the theoretical membrane system; (2) Using a fully automatic coating machine, based on the theoretical film structure obtained above, a template control file for the automatic control of the coating machine is created; (3) Load the selected coating material into the coating machine and use the eccentric monitoring control method. The coating machine will automatically complete the production of the filter according to the selected template control file.

2. The method for fabricating a 1.57-micron rectangular deep-cutoff ultra-narrow bandpass filter as described in claim 1, characterized in that, In step (1), based on the typical film structure of a multi-cavity filter, Ta2O5 is selected as a high refractive index material and SiO2 as a low refractive index material. With λ as 1570nm, the unit optical thickness of Ta2O5 and SiO2 at λ / 4 is defined as H and L, respectively. On a computer, the film structure of the filter is determined according to the performance parameters required by the ultra-narrow bandpass filter using the film design software EssentialMacleod.

3. The method for fabricating a 1.57-micron rectangular deep-cutoff ultra-narrow bandpass filter as described in claim 2, characterized in that, In step (1), the required performance parameters of the filter include: theoretical half-width, with a distribution value of 5 to 5.4 nm, and a width of not less than 3 nm for the region where the average transmittance of the passband is greater than or equal to 95%.

4. The method for fabricating a 1.57-micron rectangular deep-cutoff ultra-narrow bandpass filter as described in claim 3, characterized in that, In step (1), the determined filter film structure is as follows: Substrate / (HLHLHLHLH4LHLHLHLHLHL)(HLHLHLHLH4LHLHLHLHLHL) (HLHLHLHLH4LHLHLHLHL0.6H0.8L) / air.

5. The method for fabricating a 1.57-micron rectangular deep-cutoff ultra-narrow bandpass filter as described in claim 4, characterized in that, In step (1), the typical film structure of the filter is: substrate / (HL)^a H bL(HL)^(a+1)(HL)^c H dL(HL)^(c+1)……(HL)^m HnL(HL)^(m+1) / air. The number of cavities and the parameters of each cavity during actual deposition are determined by the performance parameters of the required product.

6. The method for fabricating a 1.57-micron rectangular deep-cutoff ultra-narrow bandpass filter as described in claim 5, characterized in that, In step (2), a fully automatic coating machine equipped with a quartz crystal oscillating film thickness controller, a high-precision optical film thickness controller, and a radio frequency ion source is used.

7. The method for fabricating a 1.57-micron rectangular deep-cutoff ultra-narrow bandpass filter as described in claim 6, characterized in that, In step (2), a template control file for automatic control of the coating machine is created using an eccentric monitoring control method.

8. The method for fabricating a 1.57-micron rectangular deep-cutoff ultra-narrow bandpass filter as described in claim 7, characterized in that, In step (2), a point on the circumference with a radius of 22mm from the center of the workpiece carrier is selected as the monitoring point. The coating process is controlled by monitoring the intensity of the transmitted light at this point on the substrate. The areas on both sides of the monitoring point are close to the monitoring point.

9. The method for fabricating a 1.57-micron rectangular deep-cutoff ultra-narrow bandpass filter as described in claim 8, characterized in that, In step (3), the selected coating materials Ta2O5 and SiO2 are loaded into the coating machine, the coated workpiece is placed in the workpiece carrier, the coating machine is started, and the coating machine automatically completes the production of the filter according to the selected template control file.

10. The application of a method for fabricating a 1.57-micron rectangular deep cutoff ultra-narrow bandpass filter based on any one of claims 1-9 in a 1.57-micron laser.

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