How are lenses for optical applications different from ordinary glass lenses?

What is the difference between optical glass and ordinary glass?

In optics, glass and lenses are commonly used components or consumables for lenses, prisms, mirrors, windows, etc. So what is the difference between optical lenses and glass and lenses in daily life?

Three thousand years ago, Egyptian and Chinese civilizations were able to manufacture glass, but it was not until the 13th century that people began to apply glass to glasses and mirrors. Since the 16th century, due to the development of astronomers and navigation, the great scientists Galileo, Newton, Descartes and others used glass to make telescopes and microscopes. In the 17th century, chromatic aberration in optical systems became the core problem of optical instruments. In order to solve this problem, people added lead oxide to the glass species, and a piece of ordinary glass became a piece of glass. Achromatic lenses. In 1768, French scientists made uniform optical glass by stirring with clay rods, and since then the optical glass manufacturing industry has been opened. In the 19th century, several developed capitalist countries directly established their own optical glass factories

From 1953 to 1957, Pilkington and Pickerstaff invented the revolutionary float glass technology, enabling the first continuous production of complete, high-quality glass in the same process.

Then, Japan applied continuous smelting to optical instruments. In 1965, Japan's HOYA company first realized the continuous melting production of BK7 optical glass without streaks and bubbles. Continuous melting is divided into raw material melting pool, clarifying pool, stirring and homogenizing pool, and finally the leakage material is released.

After the standardization of the optical glass industry, it is mainly divided into radiation-proof optical glass, radiation-resistant optical glass, ultraviolet and infrared optical glass, colorless optical glass, colored optical glass, and optical quartz glass.

Among them, there are also four key preparation technology components development, physical and chemical testing, melting process, and melting equipment. Among them, the optical glass melting technology also includes single crucible melting, continuous melting and so on.

It can be said that ordinary glass and optical glass, the biggest difference is the following:

1. The processing process, materials and production process are very different from ordinary glass.

2. Optical lenses follow different applications, and their appearance is very different from ordinary glass, which can be recognized by the naked eye.

3. The performance of optical glass is highlighted in the control of light in all wavelength bands, while ordinary glass only has control over the visible light band, and is often more concerned about durability and practicality

Ordinary glass is generally used for mirrors or decorations, such as windows, glass doors, handicrafts, and glasses lenses are not ordinary glass, glasses or contact lenses. Color lenses are divided into optical devices/medical equipment, and glasses without prescription are divided into decorations.

Optical lenses have a wide range of applications, covering information, optics, light sources, photovoltaics, and semiconductor industries. Optical lenses are important basic materials and play a key role, such as special performance optical glass for high-end optical lenses, synthetic quartz glass for photomask substrates in the semiconductor field, large-size laser neodymium glass for laser fusion devices, infrared thermal Infrared chalcogenide glass for camera lens, etc.

The following introduces several optical lenses/glasses:

1. Quartz glass optical lens

Quartz optical glass is generally used for various optical components in the wavelength range of 190nm~2300nm.

Synthetic quartz glass is a very high-end optical material with excellent high temperature resistance (its softening point is close to the melting point of platinum, and its thermal expansion coefficient is extremely small, only 1/6 of ceramic and 1/20 of ordinary glass.), Excellent spectral characteristics (high transmittance from ultraviolet to infrared, especially in the ultraviolet and deep ultraviolet spectral range is not available in general optical glass.), high dielectric electric field strength (low dielectric loss And extremely low conductivity, it is an excellent insulating material.), high purity (the total content of metal ions in synthetic quartz glass can be controlled within 1 × 10-6.) and so on.

The preparation technologies of high-quality synthetic quartz glass mainly include electrofusion method, gas fusion method, chemical vapor deposition (CVD), plasma chemical vapor deposition (PCVD) and so on. The most commonly used method is chemical vapor deposition.

Hubei Feilihua Quartz Glass Co., Ltd. and the research team of Professor Zheng Lili from Tsinghua University have mastered the complete technical chain of high-efficiency deposition and synthesis of quartz glass by multi-lamp CVD method of organosilicon D4 through four years of independent research and development, and with the help of multi-physics model simulation research (including equipment and process), that is, precision feeding and air supply system, large-diameter soot body deposition process, soot body vitrification and sintering process, and production equipment. -3.4 μm) ≥ 80%, the overall performance preparation has reached the international advanced level.

Additional knowledge:

1. Low refraction special dispersion optical glass

The characteristics of low-dispersion fluorine-phosphorus glass combine the advantages of fluoride glass and phosphate glass, with ultra-low refractive index, ultra-low dispersion and high special relative partial dispersion value, and has excellent achromatic performance, especially for long focal length complex. Achromatic lens as an alternative to CaF2 fluoride crystals.

However, there is a difficult problem in the preparation of low-dispersion fluorine-phosphorus glass, that is, fluorine-phosphorus glass contains a large amount of volatile fluoride components, which are volatile and cause local unevenness of the glass. In addition, the platinum crucible is seriously eroded, and platinum particles are easily melted into the glass. .

Special low-dispersion glass can improve the geometric accuracy of imaging, while expanding the imaging field of view and reducing the complexity of the system, reducing the number of lenses, simplifying and optimizing the structure of the optical system, and reducing its volume and weight. Therefore, it is regarded as a key optical material for long focal length, large field of view and high-definition optical systems.

In 2019, Hubei Xinhua Optical Information Materials Co., Ltd. developed a new fluorophosphorus glass H-FK95, with a refractive index (nd) of 1.43700, a dispersion coefficient (ud) of 95.1, the lowest dispersion, the highest Abbe number, and a large anomaly Dispersion and excellent optical achromatic ability can simplify and optimize the optical imaging system and improve the imaging quality.

At present, the supply of fluorine phosphor glass products is in short supply, and it is widely used in high-definition video surveillance (150 million units/year), vehicle lenses (with an annual growth rate of 30%), projectors (8 million units/year), digital and SLR cameras ( (accounting for about 30% of the total optical demand) and other fields have important applications.

2. Infrared chalcogenide glass

In recent years, chalcogenide glass is considered as a new generation of infrared optical lens material. Common infrared optical materials mainly include ZnSe crystal, Si single crystal, Ge single crystal, chalcogenide glass, fluoride and so on.

Chalcogenide glass is an infrared optical material with excellent performance. It is mainly composed of S, Se, and Te in the VIA group of the periodic table, and a certain amount of other metalloid elements (Ga, Ge, As, Sb, etc.) are introduced. The oxygen-free glass can be divided into three systems: sulfur-based (S) glass, selenium-based (Se) glass, and tellurium-based (Te) glass.

Chalcogenide glass is an amorphous substance with weak covalent bond properties compared to oxide glass; the band gap is 1-3 eV, which is smaller than oxide glass (~10 eV), and has semiconducting properties .

In addition, chalcogenide glass also has excellent infrared transmittance, high optical nonlinearity, low phonon energy, light-induced effect, semiconductor characteristics, fast ion conductivity characteristics, etc., and can be used in automotive night vision devices, infrared imaging Instruments, life detectors, infrared shoulder-fired missiles, night vision gun sights and other fields.

Chengdu Guangming Optoelectronics Co., Ltd. and Ningbo University have realized the large-scale production of high-quality infrared chalcogenide glass, and solved the batch and stable preparation technology of Φ100-200 mm chalcogenide glass. The refractive index uniformity of the developed chalcogenide glass product is 2.0 x10-5, batch refractive index error <4x10-4, the performance index has reached the international advanced level.

In addition to the above introduction, there is another application technology of chalcogenide glass - precision molding. In 2003, Dr. Zhang Xianghua of French Umicore Company first realized the precision molding technology of Ge22As20Se58 and Ge20Sb15Se65 chalcogenide glass spherical and aspherical lenses. The shape error of the molded sample (the difference between the molded surface and the design surface) is less than 0.5 μm, which is comparable to that of a single-point diamond lathe. The machining accuracy is comparable, and it has been supplied to BMW high-end car night vision devices in batches.

There are two types of precision molding methods: single-station and multi-station. The Japanese Toshiba 211V single-station molding machine of Ningbo University has the advantages of large molding diameter and high precision, but the molding efficiency is low.

Chalcogenide glass has certain advantages in the design of athermalized infrared optical system. The optical/mechanical parameter changes of the optical lens and its metal casing material when the temperature changes together determine the infrared image quality change. The application environment of the infrared optical system is relatively harsh, and it is necessary to improve the optical design in a targeted manner for environmental temperature changes, so as to reduce the problem of image quality degradation such as shifting and defocusing of the infrared optical system due to the change of the refractive index in the temperature changing environment.

Typical applications of chalcogenide glass in athermalized infrared optical systems include telephoto long-wave infrared telescope objective lenses and molded aspherical lenses based on chalcogenide glass.

Chalcogenide glass lenses are currently the largest in the civilian security monitoring and temperature measurement thermal imager market. Due to the localization of domestic infrared detectors and cost reduction, and monitoring product suppliers such as Hikvision and Dahua have begun to set foot in the field of infrared night vision, sulfur The purchase volume of glass in the domestic market is gradually increasing, and the annual demand will exceed 10 tons in the future. The development of civilian vehicle night vision systems will create greater demand for chalcogenide glass.