How to manufacture high-precision optical guide tubes.

How to manufacture high-precision light guide tube rods 

High-precision light guide rods are core optical components based on the principle of total internal reflection, which efficiently and distortion-free transmit light. They are widely used in high-end fields such as laser equipment, medical endoscopes, precision detection instruments, and display modules. Their precision directly determines the light transmission efficiency, spot uniformity, and overall performance of the equipment. Manufacturing requires breakthroughs in multiple technical difficulties such as material purification, forming accuracy, and surface treatment. The following is UltraOpto's standardized and replicable manufacturing process for high-precision light guide rods, strictly controlling every precision node throughout the process to ensure that the products meet the requirements of high-end optical systems. 

I. Core Premise: Selection and Pre-treatment of High-purity Raw Materials 

The quality of high-precision light guide tubes is determined from the source of raw materials. It is necessary to prioritize ensuring the high light transmittance, low impurity content and stress-free nature of the materials, which is the foundation for achieving efficient light guidance. 

1.Raw material selection 

Select the appropriate material based on the application scenario: ① Visible light/near-infrared scene (400nm - 2000nm): Use high-purity BK7 optical glass and fused silica, with a purity of ≥ 99.99% and a transmittance of ≥ 92% (uncoated), free of bubbles, streaks, and impurities; ② Infrared scene (2μm - 15μm): Use germanium (Ge) and calcium fluoride (CaF₂) crystals to ensure high transmittance in the infrared band, low dispersion, and high resistance to laser damage; ③ High-end precision scene: Use imported high-borosilicate glass or single-crystal quartz to further enhance optical uniformity. 

2. Raw Material Pretreatment 

Double purification and stress relief of raw materials: Firstly, vacuum melting and ion purification processes are adopted to remove trace impurities (metal ions, bubbles) in the raw materials, reducing light loss. Then, high-temperature annealing treatment is carried out. BK7 glass is held at 450-500°C for 12-18 hours, and fused silica is held at 600-700°C for 24 hours. The temperature is reduced at a rate of 0.5-1°C per hour to completely eliminate internal stress in the raw materials, preventing deformation and cracking during subsequent processing, and ensuring that light does not distort during the guiding process. 

II. Key Processes: Forming and Dimensional Accuracy Control 

The dimensional accuracy of the light guide tube (outer diameter, inner diameter, length, and roundness) directly affects its compatibility with the equipment and the light transmission path. It is necessary to achieve micron-level precision control through precise forming processes. 

1.Precision forming (core process) 

Two core forming processes are adopted to meet different precision requirements: ① High-end precision type: A combined process of melt drawing and CNC grinding is used. The pre-treated raw materials are heated to the melting state (820℃ for BK7 glass and 1710℃ for fused silica), and the drawing speed is precisely controlled (0.1-0.5mm/s) by a precision drawing machine to ensure uniform outer diameter of the tube and rod. Subsequently, the inner and outer walls of the tube and rod are finely ground by a CNC grinding machine, with the outer diameter tolerance controlled within ±0.005mm, the roundness ≤ 0.003mm, and the length tolerance ±0.01mm. ② Industrial precision type: A precision extrusion forming process is adopted, combined with custom molds, to achieve mass production, with an outer diameter tolerance of ±0.01mm, meeting the demands of mid-to-high-end industrial scenarios. 

2. End Face Forming and Grinding 

The two end faces of the light guide tube are crucial for the incidence and emission of light. It is necessary to ensure that the end faces are flat and perpendicular to the tube axis. A super-precision end face grinding machine is used in combination with diamond grinding paste to precisely grind and polish the two end faces. The perpendicularity of the end faces is controlled to be no more than 0.001mm/m to prevent light from deviating when it enters. At the same time, the end faces are chamfered (chamfer ≤ 0.05mm) to prevent edge chipping and reduce light scattering. 

III. Core Assurance: Super-precision Surface Treatment and Polishing 

The surface quality of the inner and outer walls of the light guide tube directly determines the total reflection efficiency and light loss. It is necessary to achieve a scratch-free and highly smooth surface through ultra-precision polishing technology. 

1.Ultra-precision polishing of the inner wall 

The inner walls of the tubes and rods are polished in all directions by using a dedicated ultra-precision polishing machine for inner walls, in combination with nano-scale polishing liquid (cerium oxide, diamond nano-abrasives), and through a flexible polishing head. The entire process is carried out in a 100-level clean workshop to prevent dust and impurities from adhering. After polishing, the surface roughness of the inner wall Ra is ≤ 0.05nm, with no scratches or pits, meeting the ISO 10110-7 standard (scratches ≤ 10/5, pits ≤ 0.03mm), ensuring that light can achieve efficient total reflection within the tubes and rods, with light loss ≤ 0.5%/m. 

2. Outer Wall Polishing and Protection 

The outer wall is processed with chemical mechanical polishing (CMP) technology. After polishing, the surface roughness Ra is no more than 0.1nm, enhancing the appearance texture and mechanical stability of the tube and rod. Then, a scratch-resistant and anti-fouling coating is applied to the surface to improve wear resistance (Mohs hardness ≥ 6) and prevent the adhesion of external dust and moisture, ensuring long-term stability in use. 

IV. Precision Inspection: Comprehensive Quantitative Control in All Dimensions to Eliminate Substandard Products 

The inspection of high-precision light guide tube rods should cover three core dimensions: size, surface quality, and optical performance. High-precision inspection equipment should be used to conduct a full inspection of each product to ensure that the precision meets the standards. 

1.Dimensional accuracy inspection 

High-precision diameter gauges (with an accuracy of ±0.001mm), roundness measuring instruments, and length measuring devices are used to comprehensively inspect the outer diameter, inner diameter, roundness, length, and perpendicularity of the tubes and rods. Each parameter must meet the design standards. Non-conforming products are directly removed to ensure dimensional consistency. 

2. Surface Quality Inspection 

The surface roughness, scratches and pits on the inner and outer walls are inspected by a high-power microscope (magnification ≥ 1000 times) and a surface roughness tester to ensure there are no surface defects that affect the light guiding performance. Meanwhile, ultrasonic scanning is used to detect whether there are any tiny bubbles or cracks inside the tube and rod to ensure there are no internal defects in the product. 

3. Optical Performance Testing 

The laser transmission efficiency tester is used to measure the transmission efficiency of light after passing through the tube and rod, ensuring that it is ≥98% (after coating with an anti-reflective film); the light spot uniformity tester is used to verify the uniformity of the emitted light spot (uniformity ≥95%), avoiding problems such as light spot distortion and uneven brightness; at the same time, the light loss is detected to ensure that it meets the design requirements (≤0.5%/m). 

V. Cleaning, Packaging and Traceability 

Precision cleaning 

The composite process of ultrasonic cleaning and vacuum drying is adopted. The surface of the tube and rod is cleaned step by step with deionized water, anhydrous ethanol and acetone to remove polishing powder, oil stains and impurities. Then, vacuum drying is carried out at 80-100℃ for 2 hours to ensure that there is no residue on the surface and the cleanliness reaches the 100-level standard. 

Vacuum Packaging and Traceability 

In a 100-level clean environment, the finished products are vacuum-packed with desiccants inside to prevent moisture and dust during transportation and storage. Each finished product comes with a complete test report, including all key indicator data such as dimensions, surface quality, and optical performance, ensuring full traceability from raw materials to finished products and allowing customers to use them with confidence. 

UltraOpto Manufacturing Advantages 

We have optimized the entire process of forming, polishing and inspecting for the manufacturing of high-precision light guide tubes, breaking through the industry's pain points of "dimensional accuracy and surface quality" and "transmission efficiency and light loss". According to customer needs, we can customize the size, material, length and coating scheme of the tubes (coating anti-reflection films on the input and output ends to enhance transmission efficiency), which are suitable for high-end scenarios such as laser equipment, medical endoscopes and precision detection. We ensure that each product has high stability, high precision and high efficiency in light guiding performance, providing core support for high-end optical systems.