一文看透几种AR光波导方案原理、制程、难点、优势及主要玩家.....

Overview of AR Waveguide Solutions: Principles, Processes, Challenges, Advantages, and Key Players

光波导因具有体积/透光率/清晰度等优势明显，有望成为主流AR光学方案。

据悉，光波导AR眼镜包括显示模组、波导片和耦合器三部分，显示模组发出的光线通过耦入器件进入光波导，在波导内以全反射的形式向前传播，最后通过耦出器件耦出光波导进入人眼成像。

按照耦入耦出器件的不同，光波导可分为几何光波导和衍射光波导，其中几何光波导以阵列光波导为主导，衍射光波导又分为表面浮雕光栅光波导（SRG）和体全息光波导（VHG）

Waveguides are set to become the mainstream AR optical solution due to their significant advantages in size, light transmission, and clarity.

Reportedly, AR glasses with waveguides include three parts: the display module, the waveguide plate, and the coupler. Light emitted from the display module enters the waveguide through the input coupler, propagates forward within the waveguide through total internal reflection, and finally exits through the output coupler, entering the human eye to form an image.

According to different couplers, waveguides can be divided into geometrical waveguides and diffractive waveguides. Geometrical waveguides are mainly array waveguides, while diffractive waveguides are further divided into surface relief grating waveguides (SRG) and volume holographic waveguides (VHG).

光波导方案在体积、透光率、清晰度、视场角等方面均具备优势，有望成为主流AR光学方案。

阵列光波导：成像效果优秀，量产难度较大

• 阵列光波导：成像效果优秀，二维扩瞳解决了光机体积与视场角、EyeBox的矛盾。

A. 一维扩瞳：光线通过反射镜耦入波导片，在波导片中经过多轮全反射后到达半透半反镜面，部分光线反射耦出进入人眼，未耦出光线透过镜面到达下个镜面，重复反射/透射过程，直至最后一个镜面将剩余光线全部耦出到人眼。一维扩瞳阵列光波导能将EyeBox从4mm扩大到10mm+，且杂散光少，光线调制均匀，成像质量、色彩以及对比度水平较高。

Waveguide solutions offer advantages in size, light transmission, clarity, and field of view (FOV), making them likely to become the mainstream AR optical solution.

Array Waveguides: Excellent Imaging, Difficult to Mass Produce

• Array Waveguides: Excellent imaging performance with high production difficulty.

A. One-Dimensional Expansion: Light enters the waveguide plate through a reflector, undergoes multiple total reflections within the plate, reaches a semi-reflective mirror where part of the light reflects out into the eye, and the rest transmits to the next mirror. This process repeats until all light is coupled out. One-dimensional expansion array waveguides can expand the EyeBox from 4mm to over 10mm, with minimal stray light, uniform light modulation, high imaging quality, color, and contrast.

Principle of Array Waveguide (One-Dimensional Expansion)

B. 二维扩瞳：在两个区域分别设置反射阵列，第一个区域实现一个方向的扩瞳，同时将光束传导至第二个区域，进行另一个方向的扩瞳，可以是纵向→横向扩瞳，也可以是横向→纵向扩瞳。二维扩瞳阵列光波导解决了光机体积与视场角、EyeBox的核心矛盾，能够有效增加EyeBox和视场角（可达50%+），显著减小光机体积，更好地满足消费级用户对AR眼镜的形态体积以及成像效果的要求。 

Two-Dimensional Expansion: Reflector arrays are set in two regions; the first region achieves expansion in one direction and transfers the light to the second region for expansion in the other direction, which can be longitudinal to lateral expansion or lateral to longitudinal expansion. Two-dimensional expansion array waveguides solve the core conflict between optical engine size and FOV/EyeBox, effectively increasing the EyeBox and FOV (by more than 50%), significantly reducing the size of the optical engine, and better meeting consumer demands for AR glasses' shape, size, and imaging performance.

Two-Dimensional Expansion in Array Waveguides

C. 优势总结：阵列光波导除了拥有光波导共有的轻薄化优势外，相比于已量产的表面浮雕光栅衍射光波导，其成像效果更为优秀（杂散光少/色彩均匀/EyeBox&视场角较大/分辨率高），几乎无漏光问题（1%-5%），且光损较低，可以减小光机功耗增加续航。

• 核心问题：量产难度大，明暗条纹影响美观。

A. 量产难度大：阵列波导制作涉及镜面镀膜、贴合、切割等流程，阵列镜面膜层多达几十层且每个镜面反射/透射比不同，需要镀不同层数的膜，贴合合时多镜面间平行度要求极高，总良率难以保证，此外，贴合后的切割角度也会影响成像质量。若采用二维扩瞳技术，量产难度进一步提升，理论上量产成本比一维扩瞳高4-5倍。

Advantages Summary: Besides the general lightweight advantages of waveguides, array waveguides offer superior imaging performance compared to mass-produced surface relief grating diffractive waveguides (less stray light, uniform color, larger EyeBox and FOV, high resolution), with almost no light leakage (1%-5%), and low light loss, which can reduce optical engine power consumption and increase battery life.

Core Issues: High production difficulty and bright and dark stripes affecting aesthetics.

A. High Production Difficulty: Manufacturing array waveguides involves processes like mirror coating, bonding, and cutting. Each mirror requires different layers of coating, and the alignment of multiple mirrors must be precise, making it challenging to maintain high yields. Additionally, the cutting angle after bonding affects imaging quality. Two-dimensional expansion further increases production difficulty, with theoretical production costs being 4-5 times higher than one-dimensional expansion.

Array Waveguide Manufacturing Process

B. 明暗条纹：半透半反镜面阵列天然存在明暗条纹，影响美观。

• 技术升级关键：

1）键合技术升级：分子键合技术代替传统胶水贴合，即利用分子间范德华力使镜片紧密平整地贴合，加强键合强度、提升贴合面平整度，且不受胶水折射率影响，由于贴合玻璃片数量较多、精度要求较高，实际工艺流程中仍有较大难度。

 2）镀膜、键合等核心环节自动化设备的开发；

3）支持屈光度定制，代替外加近视镜片的方案，更加轻薄化。

• 阵列光波导主要玩家：

A. Lumus：全球阵列光波导龙头，与Meta、苹果等密切合作。率先提出二维扩瞳阵列光波导技术，先后推出Maximus和Z-Lens两款二维产品，Z-lens分辨率2K*2K，亮度3000nit，FOV 50°，光机体积缩小约50%，可粘合动态聚焦透镜（缓解VAC问题）和近视镜片，无漏光炫光问题。

B. Bright and Dark Stripes: Semi-reflective mirror arrays naturally have bright and dark stripes, affecting aesthetics.

Key Technologies for Improvement:

1. Bonding Technology Upgrade: Replacing traditional glue bonding with molecular bonding, which uses Van der Waals forces to tightly and smoothly bond the lenses, enhancing bonding strength and flatness without being affected by glue refractive index. Due to the large number of bonded glass pieces and high precision requirements, there are still significant challenges in the actual process.

2. Development of Automated Equipment: For core processes such as coating and bonding.

3. Support for Refractive Power Customization: Replacing additional myopia lenses with a more lightweight design.

Key Players in Array Waveguides: A. Lumus: A global leader in array waveguides, closely collaborating with Meta, Apple, and others. They pioneered two-dimensional expansion array waveguide technology, launching Maximus and Z-Lens two-dimensional products. Z-Lens offers 2K*2K resolution, 3000 nits brightness, 50° FOV, and a reduced optical engine size by about 50%. It can also bond dynamic focus lenses (mitigating VAC issues) and myopia lenses, with no light leakage or glare issues.

B. 水晶光电：2016年参与Lumus B轮融资，与Lumus、肖特共同推动二维阵列光波导量产落地。

C. 其他国内厂商：灵犀微光、珑璟光电、理湃光晶、谷东科技等厂商在阵列波导均有布局，量产年产能在10万片左右，主要针对一维扩瞳产品，二维产品处于小批量/在研阶段。

表面浮雕光波导：量产难度较低，彩虹效应等问题亟待解决

• 成像原理：

A. 表面浮雕光栅（Surface Relief Grating，SRG）：具有周期性变化结构/凹槽的光栅结构，一般分为一维光栅（矩形光栅/倾斜光栅/闪耀光栅等）和二维光栅（柱状光栅等).

B. Crystal-Optoelectronics: Participated in Lumus's Series B financing in 2016, promoting the mass production of two-dimensional array waveguides with Lumus and Schott.

C. Other Domestic Manufacturers: Companies such as Lingxi Microvision, Longjing Optics, Lipai Optics, and Gudong Technology are also developing array waveguides, with an annual production capacity of around 100,000 pieces, mainly targeting one-dimensional expansion products. Two-dimensional products are in small-scale production or research stages.

Surface Relief Grating Waveguides: Easier to Mass Produce, Issues with Rainbow Effect

Imaging Principle: A. Surface Relief Grating (SRG): Features gratings with periodic structures/grooves. They are generally divided into one-dimensional gratings (rectangular gratings/inclined gratings/blazed gratings, etc.) and two-dimensional gratings (columnar gratings, etc.).

Types of Surface Relief Gratings

B. 衍射原理：光束入射光栅后会被分束为多个不同方向的衍射级次，通过调节光栅周期/占空比/深度等参数优化衍射效率，能使得某个方向的衍射光束具有最高衍射效率（通常选择非0衍射级次作为工作级次），实现光束定向传输。 

Diffraction Principle: When a light beam enters a grating, it is split into multiple diffraction orders in different directions. By adjusting parameters such as grating period, duty cycle, and depth, the diffraction efficiency can be optimized to ensure that the diffraction beam in a particular direction has the highest efficiency (usually selecting a non-zero diffraction order as the working order), thereby achieving directional light transmission. 

Diffraction Principle 

C. 表面浮雕光波导原理：基于上述衍射原理，通过表面浮雕光栅耦入波导片，在波导片中全反射后通过表面浮雕光栅耦出进入人眼，实现一维扩瞳，二维扩瞳一般通过转折光栅或二维光栅实现。

Principle of Surface Relief Grating Waveguides: Based on the aforementioned diffraction principle, light is coupled into the waveguide plate through a surface relief grating. The light then undergoes total internal reflection within the waveguide plate and is coupled out through the surface relief grating into the human eye, achieving one-dimensional expansion. Two-dimensional expansion is generally achieved through turning gratings or two-dimensional gratings. 

Principle of Surface Relief Grating Waveguides 

• 衍射光波导二维扩瞳：

A. 转折光栅：转折光栅二维扩瞳IP主要由微软和Vuzix持有，体全息光波导厂商Digilens也采用类似的转折光栅技术，如下图，光束从入射光栅进入转折光栅，转折光栅实现水平扩瞳的同时将光束反射进入出射光栅，最终由出射光栅完成垂直扩瞳和耦出过程。

Diffractive Waveguide Two-Dimensional Expansion:

A. Turning Grating: The two-dimensional expansion IP for turning gratings is mainly held by Microsoft and Vuzix. Volume holographic waveguide manufacturer Digilens also uses similar turning grating technology. As shown in the figure below, the light beam enters the turning grating from the incident grating. The turning grating achieves horizontal expansion while reflecting the light beam into the output grating, where vertical expansion and the coupling-out process are completed.

Turning Grating Two-Dimensional Expansion 

B. 二维光栅：以WaveOptics柱状光栅扩瞳为例，光束通过入射光栅进入波导片后，通过出射光栅（二维光栅）实现多方向的扩束以及光束的耦出。二维光栅设计难度非常高，需要控制耦出光线的均匀性，相比于转折光栅，二维光栅扩瞳减少了光损耗，增大了出射光栅面积，有效扩大EyeBox范围。

Two-Dimensional Grating: Using WaveOptics' columnar grating expansion as an example, the light beam enters the waveguide plate through the incident grating and achieves multi-directional expansion and coupling out of the light beam through the output grating (two-dimensional grating). The design of two-dimensional gratings is very challenging, requiring control of the uniformity of the coupled-out light. Compared to turning gratings, two-dimensional grating expansion reduces light loss, increases the area of the output grating, and effectively expands the EyeBox range.

Two-Dimensional Grating Two-Dimensional Expansion 

• 表面浮雕光波导量产难度较低：

1）母版制备：基于半导体加工工艺，旋涂抗蚀剂层—干涉/电子束曝光—反应离子刻蚀—去除抗蚀剂层。

2）批量生产：一般采用紫外线纳米压印光刻法批量生产，母版—步进母版—旋涂压印胶—结构压印—紫外线曝光固化—功能性图层覆盖波导—激光切割。

• 前沿工艺：

A. 残胶层控制：纳米压印过程中往往会留下残胶层，而残胶层对光学性能有影响，因此需要尽量减小甚至去除残胶层，2023年Digilens发布的SRG+工艺能够实现无残胶层的SRG结构。

Surface Relief Grating Waveguides: Easier to Mass Produce:

1. Master Preparation: Based on semiconductor processing techniques, involving spin coating a resist layer, interference/electron beam exposure, reactive ion etching, and removal of the resist layer.

2. Mass Production: Generally adopts ultraviolet nanoimprint lithography for bulk production, involving the steps of master preparation, stepper master preparation, spin coating imprint resin, structural imprinting, ultraviolet exposure curing, covering the waveguide with functional layers, and laser cutting.

Advanced Processes: 

A. Residual Layer Control: The nanoimprint process often leaves a residual layer, which affects optical performance. Therefore, it is necessary to minimize or even remove the residual layer. The SRG+ process released by Digilens in 2023 can achieve SRG structures without a residual layer.

B. 纳米压印+刻蚀（NIL+Etching）：将低折射率树脂作为后期干法刻蚀的可牺牲层，纳米压印后用干法刻蚀将残胶层刻透并刻蚀至下方玻璃层，再将树脂纳米压印胶去除。这种工艺的光栅折射率RI可达2.0以上，可靠性更高，但工艺难度和成本都更高。

• 材质：树脂vs玻璃。树脂密度仅为玻璃的1/4-1/3，且具备抗摔等特性，23年魅族、努比亚等AR眼镜均采用树脂SRG光波导。树脂的缺陷在于折射率低，树脂折射率普遍为1.74，而玻璃材质可达2.0，影响fov和色彩均匀性。从成本角度，树脂成本理论上较玻璃低，但由于目前良率较低，成本优势并不明显。

• 核心问题：彩虹效应， 视场角小，光效低，漏光。

A. 彩虹效应：相同的光栅周期，波长越长衍射角越大（R>G>B），因此不同波长的TIR（Total internal reflection）往返长度不同，反弹次数不同（R<G<B），红光fov被限制在较低范围内，而蓝光fov相对较大，此外，同一颜色的衍射效率也会受入射角度影响，两个因素共同导致视场角和动眼框范围内RGB比例不均匀，即出现彩虹效应。

B. 视场角小：受入射角限制影响，当前SRG产品视场角普遍在20-30°。

C. 光效低：光损较为严重，平均光效水平在0.3%-1%，需要高亮度的显示屏配合使用。（倾斜光栅和闪耀光栅衍射效率较高）

D. 漏光：光在出瞳区域会通过透射和反射进入前方外界环境，使得镜片呈现使用画面，泄漏用户隐私。

• 多层光波导vs单层光波导：设计多个波导片（一般二或三层），分别传输不同波长范围的光，可以改善颜色均匀性，减小彩虹效应，增大视场角，但不可避免会增加系统的重量和厚度。从产品应用来看，单色显示的SRG单层波导方案技术和量产难度较低，应用较多，全彩显示更多采用两层波导方案，重量和成本较三层方案更优，后续如何采用单层波导实现均匀全彩显示是各大厂商努力的方向。

• B. Nanoimprint + Etching (NIL+Etching): This process uses low-refractive-index resin as a sacrificial layer for subsequent dry etching. After nanoimprinting, the residual layer is etched through to the underlying glass layer using dry etching, and the resin imprint glue is removed. This technique achieves a grating refractive index (RI) of over 2.0, offering higher reliability, but it also comes with greater complexity and cost.

• Materials: Resin vs. Glass: Resin has a density of only 1/4 to 1/3 of glass and is impact-resistant. AR glasses from brands like Meizu and Nubia in 2023 use resin SRG waveguides. However, resin's low refractive index (commonly 1.74 compared to glass's 2.0) affects FOV and color uniformity. From a cost perspective, resin is theoretically cheaper than glass, but current low yields negate its cost advantage.

• Core Issues: Rainbow Effect, Small FOV, Low Light Efficiency, Light Leakage.

• A. Rainbow Effect: With the same grating period, longer wavelengths have larger diffraction angles (R > G > B), leading to different total internal reflection (TIR) lengths and bounce times for different wavelengths (R < G < B). This restricts the red light FOV to a lower range, while blue light FOV is relatively larger. Additionally, the diffraction efficiency of the same color is affected by the incident angle, causing uneven RGB ratios within the FOV and eye box, resulting in the rainbow effect.

• B. Small FOV: Limited by the incident angle, current SRG products generally have a FOV of 20-30°.

• C. Low Light Efficiency: Significant light loss, with average light efficiency levels of 0.3%-1%, requiring high-brightness displays for compensation. Inclined and blazed gratings have higher diffraction efficiency.

• D. Light Leakage: Light in the exit pupil area can transmit and reflect into the external environment, making the lens display the usage screen and compromising user privacy.

• Multi-Layer Waveguides vs. Single-Layer Waveguides: Designing multiple waveguide plates (typically two or three layers) to transmit different wavelength ranges can improve color uniformity, reduce the rainbow effect, and increase the FOV. However, this inevitably adds weight and thickness to the system. From a product application perspective, single-layer waveguides for monochrome displays are more technically feasible and easier to mass produce, while full-color displays more commonly use two-layer waveguides, offering better weight and cost efficiency compared to three-layer solutions. The future goal for manufacturers is to achieve uniform full-color displays with single-layer waveguides.

体全息光波导：理论优势明显，材料&工艺要求高

• 体全息光栅（Volume Holographic Grating，VHG）原理：通过双光束全息曝光技术在介质中形成干涉条纹，从而获得折射率周期性变化的光栅结构，当介质的厚度远大于光波长时这种结构称为体全息光栅。体全息光波导基于衍射原理，将体全息光栅作为光线耦入和耦出的器件。体全息光波导包括反射式和透射式，其中反射式方案应用更多。

• 全彩-体全息波导：使用三色激光器同时加工，或采用多层波导片方案分离RGB光路，提升色彩均匀性。

•  二维扩瞳：与SRG光波导类似，分为转折光栅和二维矢量两个路径。

• 体全息光波导理论优势：1）衍射效率更高：理论上在满足布拉格条件时，体全息光栅衍射效率可达100%；2）成像更优：由于体全息本身的角度选择性和波长选择性，不存在漏光问题，可通过光机和光栅设计优化幅减弱彩虹效应；3）可能打破视场角限制：采用特殊全息材料可打破波导基体折射率带来的视场角限制；4）量产成本低：无需投资SRG纳米压印方案中制作母版的机器和母版制作的成本，在复用性和降本上有明显优势。

Volume Holographic Waveguides: Clear Theoretical Advantages, High Material & Process Requirements

Volume Holographic Grating (VHG) Principle: VHGs are formed by creating interference fringes in a medium using dual-beam holographic exposure, resulting in a grating structure with periodic changes in refractive index. When the medium's thickness is much greater than the wavelength of light, it is called a volume holographic grating. VHG-based waveguides use these gratings as light couplers for input and output. Volume holographic waveguides include reflective and transmissive types, with the reflective type being more commonly used.

Full-Color Volume Holographic Waveguides: Full-color VHGs are processed using tricolor lasers simultaneously or by adopting multi-layer waveguide plates to separate RGB light paths, enhancing color uniformity.

Two-Dimensional Expansion: Similar to SRG waveguides, VHGs can achieve two-dimensional expansion through turning gratings or two-dimensional vector paths.

Theoretical Advantages of Volume Holographic Waveguides:

1. Higher Diffraction Efficiency: Theoretically, VHGs can achieve 100% diffraction efficiency under Bragg conditions.

2. Superior Imaging: Due to VHGs' inherent angular and wavelength selectivity, there is no light leakage issue. The optical design can reduce the rainbow effect.

3. Potential to Break FOV Limitations: Special holographic materials can overcome the FOV limitations imposed by the waveguide substrate's refractive index.

4. Low Production Costs: VHGs do not require the expensive machinery and master-making costs associated with SRG nanoimprint solutions, offering significant advantages in reusability and cost reduction.

• 体全息光波导制造：

A. 将感光胶涂布在玻璃/树脂基底上曝光制造，或在膜片上制造成全息光栅后复合或转移到玻璃/树脂波导上。

B. 索尼卷对卷工艺：1）双束干涉曝光法在光敏聚合物薄膜上形成体全息图案；2）通过注射成型获得塑料波导；3）体全息薄膜与塑料波导对准贴合后切割成指定图案；4）配色，将红、蓝波导和绿色波导对准并用UV树脂封装固定。

Manufacturing of Volume Holographic Waveguides: A. Coating a photosensitive adhesive on a glass/resin substrate followed by exposure to create the holographic pattern, or creating the holographic grating on a film and then laminating or transferring it onto a glass/resin waveguide. B. Sony's Roll-to-Roll Process:

1. Using dual-beam interference exposure to form a volume holographic pattern on a photosensitive polymer film.

2. Obtaining plastic waveguides through injection molding.

3. Aligning and bonding the volume holographic film with the plastic waveguide, followed by cutting into the specified pattern.

4. Color matching by aligning and sealing the red, blue, and green waveguides with UV resin.

Sony's Roll-to-Roll Process for Volume Holographic Waveguides

C. Digilens波导印刷工艺：核心是超高折射率全息光聚合物（光聚合物+液晶），工艺分为母版制作和波导印刷，灵活性高，可实现数字化模板设计。

• 量产难点：体全息光栅是基于材料特性而开发的制程工艺，因此核心难点在于全息材料的选择和制备，材料将直接影响全息涂层均匀性和波导Fov等光学性能。此外，实际量产时曝光/生产的环境稳定性要求非常严格，湿度/温度/流通性都会影响效果。

• 主要玩家：海外代表公司包括索尼、Digilens、Akonia（苹果收购），国内包括水晶光电、谷东科技、三极光电等。

• C. Digilens Waveguide Printing Process: The core material used is a high-refractive-index holographic photopolymer (photopolymer + liquid crystal). The process is divided into master production and waveguide printing, offering high flexibility and enabling digital template design.

• Mass Production Challenges: Volume holographic gratings are developed based on the characteristics of the materials used. Therefore, the key challenge lies in the selection and preparation of holographic materials, which directly impact the uniformity of the holographic coating and the optical performance of the waveguide's FOV. Additionally, the stability of the exposure/production environment during actual mass production is crucial, as factors such as humidity, temperature, and airflow can significantly affect the results.

• Key Players: Major players include Sony, Digilens, and Akonia (acquired by Apple) overseas. In China, key companies include Crystal-Optoelectronics, Gudong Technology, and Sanji Optoelectronics.

Key Players in Volume Holographic Waveguides