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## 光纤/激光和简单配件

### 光纤简介

POF — Polymer Optical Fibers 聚合物光纤

Liquid Light Guide: The liquid light-guide is a flexible tube with a liquid core that is used as an alternative to a light guide made of thin silica or glass fiber bundle and provides excellent light transmission. The liquid light guides are highly flexible and do not break. The liquid light-guide has the cross-section of a pipe, thus has no packing losses like a fiber based light guides, which have spaces between the thin fibers where no light goes through.

Fiber Connector Adapters: Fiber Connector Adapters are receptacle-type adapters designed to extend cable length by joining two fiber optic patch cords together with low coupling loss.

### 从LED到平行光输出(光纤)

Fiber Coupler LED:

Fiber collimator (光纤准直器): 参考prizmatix网站，如下图

### Combiner/Splitter/Shutter/Couplers/Exapander

Beam Combiner
A beam combiner may be a combination of beam splitters and mirrors, or simply several beam splitters.

Diaphragm Shutters with Controller:

• Shutter Blades Open from the Center
• Uncoated or PTFE-Coated Stainless Steel Blades
• Manual or TTL Input Control

Multimode Fiber Optic Filter/Attenuator Mounts: [thorlabs]

• Reflective, Achromatic Design for 250 nm – 450 nm or 450 nm – 20 µm
• Mount Filters, Cuvettes (比色皿), or Variable Attenuator in the Optical Path
• Ideal for Ø200 µm to Ø1000 µm Core Multimode Fibers with ≤0.39 NA
• Models with FC/PC or SMA Connectors

Reflective Beam Expanders
Reflective Beam Expanders are modified Gregorian or Cassegrain mirror systems that offer broadband performance virtually free of chromatic and spherical aberration. A convex mirror is used to expand an incident beam onto a concave mirror, resulting in a larger collimated beam.

Triplet Fiber Optic Collimators/Couplers:

Aspheric Fiber Collimators:

### Beam Shaper

holoor

1

2

Filter/Mirror/Polarizer/Windows/Glass/Coating

• 带通滤波片(Bandpass Filters)
• 长通滤波片(Longpass Filters)
• 短通滤波片(Shortpass Filters)
• 吸热玻璃(Heat Absorbing Glasses )
• 冷镜(Cold Mirrors)
• 热镜(Hot Mirrors)
• 陷波滤波片(Notch Filters)
• 彩色基片滤光片(Color Substrate Filters)
• 二向色滤光片(Dichroic Filters)
• 中性密度滤波片(Neutral Density (ND) Filters)

### Filter/Mirror

Infrared cut-off filters, sometimes called IR filters or heat-absorbing filters, are designed to reflect or block near-infrared wavelengths while passing visible light. They are often used in devices with bright incandescent light bulbs (such as slide and overhead projectors) to prevent unwanted heating. There are also filters which are used in solid state (CCD or CMOS) video cameras to block IR due to the high sensitivity of many camera sensors to near-infrared light.

A Dichroic Filter is a type of filter used to transmit or reflect light, depending on the wavelength; light of a specific wavelength range is transmitted, while light of a different range is reflected or absorbed. Dichroic filters are commonly used for longpass and shortpass applications.

(1) Two dichroic mirrors are used in 3LCD systems to divide the light from the lamp into red, green, and blue. The base glass of these two mirrors is coated with a thin film that reflects only light of a specific wavelength.

### 1/4波片

(1) 四分之一波片的三种用法—知乎
(2) 1/4波片原理（Quarter-wave plate）—知乎

### 窗口材料Windows

Calcium fluoride is often used in spectroscopic windows and lenses due to its high transmission from 200nm to 7μm. Its low absorption and high damage threshold makes it a popular choice for excimer laser optics. Calcium fluoride’s low index of refraction allows it to be used without an anti-reflective coating. The Knoop hardness of calcium fluoride is 158.3. TECHSPEC® Calcium Fluoride (CaF2) Windows manufactured from vacuum UV grade calcium fluoride are commonly found in cryogenically cooled thermal imaging systems.

• Low Absorption, High Transmission UV Grade Calcium Fluoride
• Ideal for Applications Ranging from 200nm – 7μm
• Low Index of Refraction

Barium Fluoride (BaF2) Windows can be used in a variety of applications, such as infrared spectroscopy, due to their wide broadband transmission that extends from the deep ultraviolet to the long-wave infrared. Barium fluoride’s low index of refraction of 1.48 provides high transmission without the need for anti-reflection coatings. Barium fluoride windows can be used up to 800 °C in a dry environment, but prolonged exposure to moisture can degrade transmission in the ultraviolet range. While barium fluoride windows are less resistant to water than calcium fluoride, BaF2 windows are the most resistant optical fluoride to high-energy radiation, but feature lower UV transmittance. BaF2 has a Knoop hardness of 82.

• Excellent Transmission from 200nm – 12 μm
• Provide High Transmission without AR Coatings
• Sensitive to thermal shock

Lithium Fluoride (LiF) Windows provide high, flat transmission from 150nm to 6 μm. Lithium fluoride has excellent transmission in the vacuum ultraviolet (VUV) wavelength range of 150 – 200nm. Lithium fluoride also has a low index of refraction, allowing these windows to be used without an anti-reflection (AR) coating. Lithium Fluoride (LiF) Windows are ideal for use as UV transmission windows in spectroscopy applications, as a diffracting element in X-ray spectrometry, or as infrared windows for thermal imaging applications.

• High Transmission from 150nm – 6μm
• Excellent Vacuum UV (VUV) Transmission
• Low Index of Refraction
• sensitive to thermal shock and is attacked by atmospheric moisture at temperatures above 400°C.

Gorilla® Glass Windows are chemically strengthened to reduce the propagation of surface flaws. These thin windows feature superior surface quality and excellent scratch resistance. With greater than 90% transmission from 350 – 600nm, these windows are excellent protective covers for electronic displays in consumer and industrial applications. Gorilla® Glass Windows are widely used as protective cover glass for high-end display devices such as laptops, televisions and mobile phones. Due to their durable construction, they are ideal for even the most demanding applications.

• Chemically Strengthened Drawn Glass
• Highly Resistance to Surface Scratches
• Ideal for Electronic Displays

Sapphire Windows are manufactured from single crystal sapphire, making them ideal for demanding applications (such as laser systems) because of their extreme surface hardness, high thermal conductivity, high dielectric constant and resistance to common chemical acids and alkalis. Sapphire is the second hardest crystal next to diamond and, because of their structural strength, sapphire windows can be made much thinner than other common windows with improved transmittance. Chemically, sapphire is single crystal aluminum oxide (Al2O3) and is useful in a transmission range from 330 – 5500nm when uncoated. TECHSPEC® Sapphire Windows are available with anti-reflection (AR) coatings to improve performance in the visible, NIR, and IR spectra with coating options covering 400 – 5000nm.

• Features Extreme Surface Hardness Chemical Resistance
• Transmits Wavelengths Ranging From UV to Mid-Infrared
• Thinner and Stronger than Standard Glass Windows
• Anti-Reflection Coating Options Covering 400 – 5000nm Available

Sodium Chloride (NaCl) is a material commonly used in FTIR spectroscopy. NaCl is a relatively low cost cubic crystalline material that has excellent transmission from 250 nm – 16 μm. Over this large spectral range, its index of refraction ranges between 1.4 – 1.6. It is hygroscopic by nature and thus samples should not contain water. Sodium Chloride windows are sensitive to thermal shock but can be used in temperatures up to 400 °C. NaCl has a density of 2.17 g/cm3 and a Knoop Hardness of 18.2.

Potassium Bromide (KBr) is a material commonly used in FTIR spectroscopy. KBr has a slightly larger spectral range than Sodium Chloride (NaCl) and has excellent transmission from 250nm – 26 μm. Its index of refraction varies from 1.46 – 1.59 over this range. KBr is water soluble and its surfaces should be protected from exposure to moisture. Exposure to moisture will degrade the surface of the window. Potassium Bromide windows provide good resistance to mechanical shock, can be easily cleaved and can be used in temperatures up to 300 °C. KBr has a density of 2.75 g/cm3 and a Knoop Hardness of 7.0.

• Excellent Transmission from 250nm – 16μm
• Low Cost
• Ideal for FTIR Spectroscopy
• Potassium Bromide (KBr) Windows Also Available
• Excellent Transmission from 250nm – 26μm
• Good Resistance to Mechanical Shock
• Ideal for FTIR Spectroscopy
• Sodium Chloride (NaCl) Windows Also Available

TECHSPEC® Brewster Windows are designed to present a circular profile when oriented at Brewster’s angle (55.57 °). TECHSPEC® Brewster Windows feature laser grade surface quality and parallelism, in addition to limiting transmitted wavefront distortion to λ/10. When used at 55.57°, these windows minimize the loss of P-polarized light, ideal for use within laser cavities and for producing linearly polarized light.

• Reduce Loss of P-Polarized Light
• Circular Profile When Oriented at 55.57°
• Great for Use in Laser Cavities

TECHSPEC® Silicon (Si) Windows manufactured from optical grade silicon are popular for the 1.2 – 7μm spectral region due to their low cost and low density. Due to its low density (half that of germanium or zinc selenide), silicon is ideal for weight sensitive applications, especially those in the 1.65 – 5μm region. Density is 2.329 g/cm3 and Knoop Hardness is 1150, making it harder and less brittle than germanium. 热稳定性也更好(more thermally stable)

• Transmission from 1.2 – 7μm
• Available Uncoated or AR Coated for 1.65 – 5μm
• Ideal for Weight Sensitive Applications (密度小)
• No Birefringence. Birefringence can degrade IR imaging performance, so selecting a material that is not birefringent is important. Since silicon features a cubic crystalline structure, it will not exhibit birefringence.

Acrylic (PMMA) Plastic Windows are ideal for integration into lightweight optical systems. Compared to polycarbonate windows, acrylic windows are more scratch resistant and can be polished to restore optical quality but are more likely to chip or shatter. Acrylic (PMMA) Plastic Windows also provide a higher UV light transmission than polycarbonate and are recyclable. Acrylic windows are used in a wide variety of industrial and medical applications including aircraft windows, automobile headlights, and ophthalmological devices.

Polycarbonate Plastic Windows are a lightweight alternative to glass windows. Combining durability and high transmission, these windows are an ideal cost-effective solution for harsh environments and displays. Compared to PMMA acrylic windows, polycarbonate windows are more impact resistant and stronger but are more susceptible to scratches. Polycarbonate Plastic Windows feature lower water absorption and a higher softening temperature than PMMA, but their higher index of refraction leads to higher Fresnel reflections without AR coatings. Their strength and stability make these windows ideal for use in medical and industrial applications.

PMMA Plastic Windows

• Highly Scratch-Resistant
• High Visible Light Transmission
• Cost-Effective Alternative to Glass

Polycarbonate Plastic Windows

• High Visible Light Transmission
• Excellent Thermal Stability
• Durable and Lightweight

## 光学玻璃

### 简介

(1) Al2O3可以提高玻璃化学稳定性和机械强度；
(2) PbO和BaO可以增大玻璃折射率，但化学稳定性降低；
(3) 加入Na2O可以降低熔炼温度；
(4) As2O3可以澄清气泡；
(5) CdO可以改善玻璃的化学稳定性。
(6) Ta2O5，高折射低色散特种光学玻璃

(1) 色散
The dispersion is measured by a standard parameter known as

D光—黄光，587.6nm，钠光谱中的D线；
F光—蓝色，486.1nm，氢光谱中的F线 ；
C光—红光，656.3nm，氢光谱中的C线

(2) 折射率(Refractive Index)
Refractive Index is the ratio of the speed of light in a vacuum to the speed of light in the specified material – a description of how light slows down as it passes through an optical material. The refractive index for optical glasses, $$n_d$$, is specified at a wavelength of 587.6nm (Helium d-line). Materials with a low index of refraction are commonly referred to as “crowns”(冕牌玻璃-低折射率，低色散) whereas materials with a high index of refraction are referred to as “flints.” (火石玻璃)

(3) 透过率(Transmission)
Standard optical glasses offer high transmission throughout the entire visible spectrum and beyond in the near-ultraviolet and near-infrared ranges. Figure 1 shows internal transmission of 5mm thick substrates without Fresnel reflections. Transmission data was gathered using Edmund Optics’ spectrophotometers. Crown glasses tend to have better transmission in the NUV than do flint glasses. Flint glasses, because of their high index, feature higher Fresnel reflection loss and thus should always be specified with an anti-reflection (AR) coating.

(4) 折射率和色散的差别(Refractive Index Versus Dispersion)
Refractive Index is a measurement of how much light bends as it passes through a transparent object. Dispersion is a measurement of the difference between how far violet light bends versus red light. These two ends of the spectrum bend at different rates, which is why we see rainbows!

A higher refrective index always mean a higher dispersion rate?
No, the two of them are not directly propotionately related to them on a linear scale. 比如Cubic Zirconia的折射率大约2.15，钻石的折射率是2.4，但是实际上钻石的折射率低于Cubic Zirconia，Cubic Zirconia的阿贝数为33.54，钻石的为65.290323，所以Cubic Zirconia看起来颜色更炫。参考：What is Refractive Index Versus Dispersion?

### 镧玻璃

Lanthanum is used in many high index glasses; high index glass, when combined with other glass materials, improves dispersion and is utilized in many achromats and imaging lenses (消色差和成像透镜) to increase efficiency and improve image quality. 镧系玻璃是兴起于二战后的新型光学玻璃，主要是摄影物镜用，因为它折射率很高，可以在1.68到1.85左右，又有着比较大的阿贝数（意味着低色散）。在二战后那个时期，有1.7的折射率意味着你可以藐视一众原有的冕牌玻璃。存在疑问，折射率高，不应该是色散严重，阿贝数小吗？

• 原料昂贵；
• 成玻璃范围窄，氧化镧是非常容易导致玻璃在混熔降温过程中制造失败（析晶）的组分，加镧越多，折射率会越高，但析晶的风险也越大。
• 熔融混合物粘度低，侵蚀性强，形成的玻璃化学稳定性也不够好。

## 几何光学薄膜Coating/Film/Sheeting等

### Retroreflector(逆反射器)

x

(1) 自行车尾灯原理到底是什么?—知乎
(2) Retroreflector-Wiki

### Anti-Reflection (AR) Coatings

Due to Fresnel reflection, as light passes from air through an uncoated glass substrate approximately 4% of the light will be reflected at each interface. This results in a total transmission of only 92% of the incident light, which can be extremely detrimental in many applications (Figure 1). Excess reflected light reduces throughput and can lead to laser-induced damage in laser applications. Anti-reflection (AR) coatings are applied to optical surfaces to increase the throughput of a system and reduce hazards caused by reflections that travel backwards through the system and create ghost images. Back reflections also destabilize laser systems by allowing unwanted light to enter the laser cavity. AR coatings are especially important for systems containing multiple transmitting optical elements. Many low-light systems incorporate AR coated optics to allow for efficient use of light.

• $$\lambda/4$$ MgF2: The simplest AR coating centered at 550 nm (with an index of refraction of 1.38 at 550nm). MgF2 coating is ideal for broadband use though it gives varied results depending upon the glass type involved.
• VIS 0° 和 VIS 45°： VIS 0°（对于 0° 入射角）和 VIS 45°（对于 45° 入射角）为 425 – 675 nm 提供优化的透射率，将平均反射率分别降低到 0.4% 和 0.75%。对于可见光应用，VIS 0° AR 涂层优于 MgF2 。
• VIS-NIR：我们的可见光/近红外宽带减反射涂层经过特别优化，可在近红外区域产生最大透射率 (>99%)。
• Telecom-NIR：我们的电信/近红外是一种专门的宽带增透膜，适用于 1200 – 1600 nm 的流行电信波长。
• UV-AR 和 UV-VIS：紫外线镀膜应用于我们的紫外熔融石英镜片和紫外熔融石英窗，以提高其在紫外线区域的镀膜性能。
• NIR I 和 NIR II：我们的近红外 I 和近红外 II 宽带增透膜在普通光纤、激光二极管模块和 LED 灯的近红外波长范围内具有卓越的性能。
以上参考资料[Edmundoptics]

## Optical Lens/Grating

### Collimating mirror/lens (准直镜)

• Focus Collimated Light
• Collimate Light from a Point Source

• Parabolic reflector，最简单的类型，即抛物线的的长轴顶点(vertex)在reflector上，过该点的一段抛物线旋转就得到reflector。There are a few negatives associated using with using conventional parabolic mirrors, which are symmetric around the focal point (Figure 3). One is that the sides of the mirror generally obstruct access to the focus. Another is that when the mirror is used to collimate a divergent light source, the housing of the light source blocks a portion of the collimated beam. In particular, light emitted at small angles with respect to the optical axis of the mirror is typically obstructed. 于是人们又发明了Off-axis parabolic reflector；
• Off-axis parabolic reflector，一个圆形抛物面的大小理论上是无限的。任何实用的反射器都只使用它的一个部分。通常，该段包括抛物面的顶点，其曲率最大的地方，以及对称轴与抛物面相交的地方。然而，如果反射器被用来将传入的能量集中到接收器上，接收器的影子就会落到抛物面的顶点上，这是反射器的一部分，所以反射器的一部分被浪费了。This can be avoided by making the reflector from a segment of the paraboloid which is offset from the vertex and the axis of symmetry.
• 上图是off-axis parabolic mirror的示意图，以及Diagram of three types of reflector sights
• 另外还有一种可以接光纤的准直镜，如图上。The two ports on Thorlabs’ reflective collimators are not interchangeable. One port accepts an optical fiber connector and requires the highly divergent light of a point source. The other port is designed solely for collimated, free-space light

Parabolic Mirror Versus Spherical Mirror

• Parabolic mirrors perform better than spherical mirrors when collimating light emitted by a point source or focusing a collimated beam.
• Focusing Collimated Light
• Parabolic mirrors focus all rays in an incoming, collimated light beam to a diffraction-limited spot.
• Concave spherical mirrors  concentrate incoming collimated light into a volume larger than a diffraction-limited spot. The size of the spherical mirror’s focal volume can be reduced by decreasing the diameter of the incoming collimated beam.
• Collimating Light from a Point Source
• A point source emits light in all directions. When this highly divergent light source is placed at the focal point of a parabolic mirror, the output beam is highly collimated. If the point source were ideal, all reflected rays would be perfectly parallel with one another.
• When a point source is placed within a spherical mirror’s focal volume, the output beam is not as well collimated as the beam provided by a parabolic mirror. Different rays from the point source are not perfectly parallel after reflection from the spherical mirror, but two reflected rays will be more nearly parallel when they reflect from more closely spaced points on the spherical mirror’s surface. Consequently, the quality of the collimated beam can be improved by reducing the area of the reflective surface. This is equivalent to limiting the angular range over which the source in the focal volume emits light.
• Choosing Between Parabolic and Spherical Mirrors: A parabolic mirror is not always the better choice. Beam diameter, cost constraints, space limitations, and performance requirements of an application all influence selection. Beam diameter is a factor, since the performance of these two mirrors is more similar when the beam diameter is smaller. Parabolic mirrors are more expensive, since their reflective profiles are more difficult to fabricate. Parabolic mirrors are also typically larger. Improved performance may or may not be more important than the difference in cost and physical size.

### Ball Lenses (球透镜)

Ball lenses are great optical components for improving signal coupling between fibers, emitters, and detectors. They are also used in endoscopy(内视镜), bar code scanning, ball pre-forms for aspheric lenses (非球面镜), and sensor applications. Ball lenses are manufactured from a single substrate of glass and can focus or collimate light(使光线平行), depending upon the geometry of the input source. Half-ball lenses are also common and can be interchanged with full ball lenses if the physical constraints of an application require a more compact design.

To couple light from one fiber optic to another fiber optic of similar NA, two identical ball lenses can be used. Place the two ball lenses at the back focal length from the fibers

Thorlabs-介绍