Analysis of the development and status quo of advanced optical processing technology1

　　 Now it is not difficult to find that almost all military weapon systems are equipped with various photoelectric sensor devices, and in these photoelectric sensor devices, more or less various styles of optical components are used. From the materials of a survey report made by the US Army, we know that from 1980 to 1990, the US military laser and infrared thermal imaging products required 1,147,700 pieces of various optical parts, of which 635,900 pieces of spherical optical parts were not used. There are 234,600 spherical optical parts, 181,000 flat optical parts, and 96,200 polyhedral scanning mirrors. Take the M1 tank as an example. It uses about 90 lenses, 30 prisms, and various mirrors, windows and laser components. Another example is a small AN/AVS-6 pilot night vision goggles that uses 9 aspherical optical parts and 2 spherical optical parts.

　　 Since the 1970s, military optical technology represented by infrared thermal imaging and high-energy lasers has developed rapidly. Military optical systems require not only good image quality, but also small size, light weight, and simple structure. This is a severe test for the optical processing industry. In order to keep up with the development of the times and design and produce high-quality optical imaging systems, the optical parts processing industry carried out large-scale technological revolution and innovation activities in the 1970s, and researched and developed many new optical parts processing methods, such as aspheric surfaces. Processing method of optical parts. In the past 10 years, new optical parts processing technology has been further promoted and popularized. At present, the optical parts processing technologies commonly used abroad mainly include:

　　 Computer numerical control single point diamond turning technology, optical glass lens molding technology, optical plastic molding technology, computer numerical control grinding and polishing technology, epoxy resin replication technology, electroforming technology... and traditional grinding and polishing technology.

2. Computer numerical control single point diamond turning technology

　　 Computer numerical control single point diamond turning technology is an aspheric optical part processing technology that was first developed by the US National Defense Research Institute in the 1960s and promoted and applied in the 1980s. It uses natural single crystal diamond tools on ultra-precision CNC lathes. Under the precise control of the machine tool and the processing environment, it directly uses diamond tools to single-point turning to process aspheric optical parts that meet the optical quality requirements. This technology is mainly used to process small and medium-sized infrared crystals and optical parts of metal materials. Its characteristics are high production efficiency, high processing accuracy, good repeatability, suitable for mass production, and processing costs are significantly lower than traditional processing technologies. Optical parts with a diameter of less than 120mm processed by this diamond turning technology have a surface accuracy of 1/2～1l, and the root mean square value of the surface roughness is 0.02～0.06mm.

At present, the materials that can be processed by diamond turning technology are: non-ferrous metals, germanium, plastics, infrared optical crystals (mercury cadmium telluride, cadmium antimonide, polysilicon, zinc sulfide, zinc selenide, sodium chloride, potassium chloride, chloride Strontium, magnesium fluoride, calcium fluoride, lithium niobate, KDK crystal) electroless nickel, beryllium copper, germanium-based chalcogenide glass, etc. The above materials can directly meet the requirements of optical surface quality. This technology can also process glass, titanium, tungsten and other materials, but at present it cannot directly meet the requirements of optical surface quality and requires further grinding and polishing.

In addition to directly processing spherical and aspheric optical parts, computer numerical control single-point diamond turning technology can also be used to process various optical parts forming molds and optical parts bodies, such as processing glass molding molds, copy molds, and optical plastics. Injection molding mold and machine body for processing and replicating epoxy optical parts, etc. This technology is combined with ion beam polishing technology to process high-precision aspheric optical parts; combined with hard carbon coating process and epoxy resin replication technology, it can produce relatively inexpensive precision aspheric mirrors and lenses. If grinding accessories are added to the diamond lathe or ceramic tools are used, precision fixtures are installed, and diamond cutting is performed at a low temperature of -100°C, the application range of this technology will be further expanded. At present, the Optical Center of the University of Arizona has used this technology to replace the traditional manual processing technology, but when processing glass optical parts, it cannot be directly ground into an optical mirror that meets the quality requirements, and flexible polishing is still required.

The technical and economic effects of single-point diamond turning of optical parts are very obvious. For example, when processing a 90° off-axis parabolic mirror with a diameter of 100mm, if the traditional grinding and polishing process is used, the surface accuracy can reach up to 3mm (5l), and the processing time takes 12 Monthly, the processing cost of each parabolic mirror is 50,000 US dollars.

　　 Using the diamond turning method, it can be completed in 3 weeks, the processing cost is only 4 thousand US dollars, and the surface accuracy can reach 0.6μm (1λ). Honeywell of the United States used this technology to process the tetrahedral scanning mirror of the AN/AAD-5 infrared reconnaissance device. The size of each side of the rotating mirror is 88.9\’’203.2mm, the flatness of each side is required to be 1/2, and the angular accuracy is 90°±42. With a lathe, 124 scanning rotating mirrors were processed in 15 months, and the quality met the design technical requirements. Each rotating mirror saves US$2,770 compared to processing with traditional processing methods. Honeywell used this process to produce 200 tetrahedral rotating mirrors, saving a total of nearly 900,000 US dollars. In addition, 100,000 plane mirrors were processed for the AN/AAD-5 infrared reconnaissance device, saving more than 10 million US dollars. During the 10 years from 1980 to 1990, the processing cost of 4 kinds of military optical parts, including plane (50\''50mm), polyhedron (diameter 90mm), spherical surface (diameter 100mm), and aspherical surface (diameter 125mm), was based on a conservative economy. According to calculation results, the US Department of Defense has saved a total of about 400 million US dollars.