Optical Passive Devices: The Key Cornerstones in Optical Communication

In the era of booming optical communication technology, optical passive devices, as the core components of fiber-optic communication equipment, are playing an indispensable role. They are like the precise gears in the optical communication network, silently yet crucially facilitating the efficient transmission of information. Widely used in long-distance communication, regional networks, fiber-to-the-home (FTTH), video transmission, and fiber-optic sensing, the performance of these devices directly impacts the stability and reliability of the entire optical communication system.

在光通信技术蓬勃发展的今天，光无源器件作为光纤通信设备的核心组成部分，正发挥着不可或缺的重要作用。它们宛如光通信网络中的精密齿轮，无声无息却又至关重要地推动着信息的高效传输，广泛应用于长距离通信、区域网络、光纤到户、视频传输以及光纤感测等众多领域，其性能的优劣直接影响着整个光通信系统的稳定性和可靠性。

                                       

                                                                                                                   1.1光通信系统关系图

Main Types and Characteristics of Optical Passive Devices

光无源器件的主要类型与特点

Fiber Optic Connectors: The Vital Flexible Connection Links

光纤活动连接器：灵活连接的关键纽带

Fiber optic connectors are the fundamental elements enabling the flexible connection between fibers. They come in a wide variety of types, including FC, SC, ST, LC and other types of adapters, each with PC, UPC, APC three forms, along with a variety of models and specifications of patch cords available, with the core number ranging from single-core to 12-core.

光纤活动连接器是实现光纤之间灵活连接的基础元件，其种类繁多，包括 FC、SC、ST、LC 等多种类型的适配器，每种适配器又具备 PC、UPC、APC 三种形式，同时还有各种型号和规格的尾纤可供选择，芯数从单芯到 12 芯不等。

             

The structure mainly consists of connector plugs, fiber jumpers, converters, transformers, etc. The manufacturing process of the connector plug's ferrule has extremely high requirements. For example, the outer diameter of the ferrule is Ф2.499±0.0005mm, the micropore diameter is Ф126±0.5μm, and the micropore eccentricity is <1μm. These parameters directly affect the connection quality. Ceramic ferrules are widely used due to their excellent temperature stability, wear resistance, and corrosion resistance. However, there are some cases in the market where plastic is used to impersonate ceramic, so careful identification is required.

其结构主要由连接器插头、光纤跳线、转换器、变换器等部分组成。连接器插头的插针体制作工艺要求极高，例如插针外径为 Ф2.499±0.0005mm，微孔直径 Ф126±0.5μm，微孔偏心量＜1μm 等，这些参数直接影响着连接的质量。陶瓷插针材料因具有出色的温度稳定性、耐磨性和抗腐蚀能力而被广泛应用，但市场上也存在部分塑料冒充陶瓷的情况，需谨慎辨别。

In terms of performance indicators, insertion loss and return loss are the key considerations. The smaller the insertion loss, the better. High-quality products usually have an insertion loss of less than 0.3dB. It is affected by various factors such as fiber core misalignment, tilt, end face gap, Fresnel reflection, different fiber core diameters, and different numerical apertures. Return loss is an important indicator reflecting the influence of reflected light. APC-type plugs, through special spherical contact and bevel processing, can achieve a return loss of more than 60dB, effectively reducing the interference of reflected light on the light source and the system. Repeatability and interchangeability are also important indicators of connector performance. Stable products should have a repeatability of less than ±0.1dB, and the interchangeability should be controlled within ±0.15dB, which reflects the rationality of the connector's structural design and manufacturing process.

在性能指标方面，插入损耗和回波损耗是关键考量因素。插入损耗越小越好，优质产品的插入损耗一般小于 0.3dB，它受到纤芯错位、倾斜、端面间隙、菲涅耳反射、纤芯直径不同以及数值孔径不同等多种因素影响。回波损耗则是反映反射光影响的重要指标，APC 型插头通过特殊的球面接触和斜面加工，可使回波损耗达到 60dB 以上，有效减少反射光对光源和系统的干扰。重复性和互换性也是衡量连接器性能的重要标志，性能稳定的产品重复性应小于 ±0.1dB，互换性控制在 ±0.15dB 以内，这体现了连接器结构设计和加工工艺的合理性。

Optical Splitters: The Core Hubs for Signal Distribution

光分路器：信号分配的核心枢纽

Optical splitters are responsible for the coupling, branching, and distribution of optical signals in the optical network system and are extremely important passive devices. They are commonly represented by M×N to indicate the number of input and output ports. In the fiber-optic CATV system, 1×2, 1×3, and 1×N optical splitters are widely used.

光分路器在光网络系统中承担着光信号的耦合、分支与分配任务，是极为重要的无源器件，常用 M×N 表示其输入输出端口数量，在光纤 CATV 系统中，1×2、1×3 及 1×N 光分路器应用广泛。

                                                   

                                                                                                                         1.2  1分8微分光分路器

According to the principle, they can be divided into fiber type and planar waveguide type. Among them, the fused-taper fiber coupler has become the mainstream in the market due to its simple manufacturing process, low price, stable connection, and adaptability to environmental changes. Its splitting principle is based on the coupling of the evanescent field between fibers and the change of fiber radius. By controlling the twist angle and stretching length during the fusion and tapering process, different splitting ratios can be achieved. However, in the traditional manufacturing process, due to the inconsistent thermal expansion and contraction of the curing adhesive, quartz substrate, and stainless steel tube, the optical splitter is prone to damage in the outdoor environment, resulting in poor stability.

按原理可分为光纤型和平面波导型，其中熔锥型光纤耦合器凭借制作简单、价格低廉、连接稳固且适应环境变化等优势，成为市场主流。其分光原理基于光纤间消逝场耦合及半径改变，通过控制熔融拉锥过程中的扭转角度和拉伸长度来实现不同分光比例。然而，传统工艺中因固化胶与石英基片、不锈钢管热胀冷缩程度不一致，导致光分路器在野外环境易损坏，稳定性较差。

The main technical indicators of optical splitters include insertion loss, additional loss, splitting ratio, and isolation. For example, the additional loss of a 1*N single-mode standard optical splitter increases with the increase of the splitting number, which is 0.2dB for 2 ports and can reach 1.2dB for 16 ports. The splitting ratio is related to the transmission optical wavelength. For example, the splitting ratio of a certain optical splitter may be 50:50 at a wavelength of 1.31μm and change to 70:30 at a wavelength of 1.5μm. Therefore, the wavelength must be specified when ordering. Isolation is of great significance for system performance and is usually required to be above 40dB to avoid signal interference between optical paths.

光分路器的主要技术指标包括插入损耗、附加损耗、分光比和隔离度等。例如，1*N 单模标准型光分路器的附加损耗随分路数增加而增大，2 路时为 0.2dB，16 路时可达 1.2dB。分光比与传输光波长相关，如某光分路器在 1.31μm 波长下分光比为 50:50，在 1.5μm 波长下可能变为 70:30，因此订购时需明确波长。隔离度对于系统性能意义重大，通常要求达到 40dB 以上，以避免光路间的信号干扰。

Optical Attenuators: The Powerful Tools for Signal Intensity Regulation

光衰减器：信号强度调控的利器

Optical attenuators are indispensable in the fiber-optic CATV system. There are mainly four series in the market: fixed type, step adjustable type, continuously adjustable type, and intelligent type.

光衰减器在光纤 CATV 系统中不可或缺，市场上主要有固定式、步进可调式、连续可调式及智能型四种系列。

                 

                             1.3 多模在线可调衰减器

The attenuation principles are diverse. The displacement-type optical attenuator controls the attenuation amount by adjusting the alignment accuracy of the fiber connection. The transverse displacement type is often used in the manufacture of fixed attenuators and has a high return loss (generally greater than 60dB). The axial displacement type is used in the manufacture of some fixed and small variable attenuators. The thin-film type attenuator utilizes the relationship between the reflection of light on the metal thin film surface and the film thickness to achieve attenuation. By changing the film thickness, fixed or variable attenuators can be made. The attenuator with an attenuation sheet directly fixes the attenuation sheet on the fiber end face or in the optical path and can also be used to make fixed or variable attenuators.

其衰减原理多样，位移型光衰减器通过调整光纤对接精度来控制衰减量，横向位移型常用于固定衰减器制作，回波损耗高（一般大于 60dB）；轴向位移型则用于部分固定和小型可变衰减器制作。薄膜型衰减器利用光在金属薄膜表面反射与薄膜厚度关系实现衰减，通过改变薄膜厚度可制成固定或可变衰减器。衰减片型衰减器则是将衰减片固定在光纤端面或光路中，同样可用于制作固定或可变衰减器。

In terms of performance indicators, attenuation amount and insertion loss are important parameters. The attenuation amount of a fixed optical attenuator is actually its insertion loss. For variable attenuators, the lower the insertion loss, the better. High-quality products have an insertion loss of less than 1.0dB, and ordinary products with an insertion loss of less than 2.5dB can be used. The attenuation accuracy of mechanical adjustable attenuators is usually ±0.1 times the attenuation amount, and the fixed attenuator has higher accuracy. Return loss is also a key indicator. High-performance attenuators have a return loss of more than 45dB to reduce the impact of reflected light on the system.

性能指标方面，衰减量和插入损耗是重要参数。固定光衰减器衰减量即插入损耗，可变衰减器插入损耗越低越好，高质量产品在 1.0dB 以下，普通产品小于 2.5dB 即可使用。衰减精度对于机械式可调衰减器通常为衰减量的 ±0.1 倍，固定式衰减器精度更高。回波损耗也是关键指标，高性能衰减器回波损耗在 45dB 以上，以减少反射光对系统的影响。

Optical Switches: The Intelligent Hubs for Optical Path Switching

光开关：光路切换的智能枢纽

Optical switches play a crucial role in optical path control and can be divided into mechanical and non-mechanical types. Mechanical optical switches change the optical path by moving the fiber or optical elements. They have the advantages of low insertion loss (generally less than 1.5dB), high isolation (generally greater than 45dB), and being unaffected by polarization and wavelength, dominating the market. Non-mechanical optical switches change the refractive index of the waveguide by using electro-optical, magneto-optical, acousto-optical, or thermo-optical effects to change the optical path. They have the advantages of short switching time, small size, and being convenient for optical integration or optoelectronic integration, but they have large insertion loss and low isolation.

光开关在光路控制领域发挥着关键作用，可分为机械式和非机械式两大类。机械式光开关依靠光纤或光学元件移动切换光路，具有插入损耗低（一般小于 1.5dB）、隔离度高（一般大于 45dB）、不受偏振和波长影响等优点，在市场中占据主导地位。非机械式光开关利用电光、磁光、声光或热光效应改变波导折射率实现光路切换，开关时间短、体积小，便于光集成或光电集成，但插入损耗大、隔离度低。

      

                                                              1.4 光开关

In the CATV optical network, optical switches can ensure the uninterrupted operation of the system. For example, when the main optical transmitter fails, the optical switch can connect the backup optical transmitter to the system within a very short time (less than 1ms) to ensure the normal transmission of cable TV signals. In addition, in fiber-optic transmission networks, optical switching systems, optical device testing, and fiber-optic sensing networks, optical switches can also realize the intelligent distribution and exchange of information, improving the stability and reliability of the system operation.

在 CATV 光网络中，光开关可确保系统不间断工作。例如，当主用光发射机故障时，光开关能在极短时间（小于 1ms）内将备份光发射机接入系统，保障有线电视信号正常传输。此外，在光纤传输网络、光交换系统、光器件测试及光纤传感网络中，光开关也能实现信息分配与交换的智能化，提升系统工作的稳定性与可靠性。

Wavelength Division Multiplexers: The Key Technologies for Capacity Expansion

波分复用器：容量扩充的关键技术

Wavelength division multiplexing technology enables the simultaneous transmission of multiple optical signals with different wavelengths in a single fiber, greatly increasing the fiber transmission capacity and reducing costs. Wavelength division multiplexers, as the core devices for realizing this technology, play an important role in optical path multiplexing and demultiplexing. They combine optical signals of different wavelengths for transmission and accurately separate the multiplexed optical signals at the receiving end.

波分复用技术通过在一根光纤中同时传输多个不同波长的光信号，大幅提升了光纤传输容量，降低了成本。波分复用器作为实现该技术的核心器件，在光路中承担着合波与分波的重要功能，将不同波长光信号汇集传输并在接收端准确分离。

               

                                1.5 WDM在网络中的运用

Most products on the market are of the diffraction grating type. The main indicators include insertion loss, crosstalk loss, wavelength spacing, and the number of multiplexed channels. The insertion loss is generally around 1 - 5dB, and the crosstalk loss needs to be greater than 20dB to ensure good separation of signals of different wavelengths. By using wavelength division multiplexing technology, only a small number of multiplexing and demultiplexing devices need to be added at the transmitting and receiving ends to fully utilize the existing optical cable resources, realize multi-channel transmission, and effectively expand the communication capacity, bringing significant economic benefits.

市场上多数产品为衍射光栅型，其主要指标包括插入损耗、串音损耗、波长间隔和复用路数等。插入损耗一般在 1 - 5dB 左右，串音损耗需大于 20dB，以确保各波长信号的良好分隔。采用波分复用技术，只需在收发端增加少量合波、分波设备，就能充分利用现有光缆资源，实现多路传输，有效扩充通信容量，带来显著经济效益。

Optical Splice Boxes, Optical Distribution Boxes, and Optical Termination Boxes: The Guarantees for Optical Path Connection

光接头盒、光配线箱与光终端盒：光路连接的保障

In the process of optical cable connection and equipment connection, optical splice boxes, optical distribution boxes, and optical termination boxes play a vital role. The optical splice box is used for connecting long-distance optical cables, ensuring connection strength and adapting to various environments. It has sealing and waterproof functions and can be installed horizontally or vertically. To ensure connection strength, the connecting optical cables are first reinforced with steel wires, and then each fused fiber is arranged in layers with a patch panel. For one optical cable input and one output, a 11 splice box is selected. If it is one optical cable input and N optical cable outputs, a 1N splice box is selected. When the number of optical cable cores exceeds 16 pairs, it is necessary to specify the number of optical cable cores when ordering to facilitate the addition of fiber heat shrinkable sleeves and fiber trays inside.

在光缆连接与设备配接过程中，光接头盒、光配线箱和光终端盒起着至关重要的作用。光接头盒用于长距离光缆连接，确保连接强度并适应各种环境，具备密封和防水功能，可根据光缆进出数量选择不同规格，如 11 或 1N 接头盒，对于大芯数光缆还需注意内部光纤热收缩套管和托板的配置。

                              

                                                        1.6 盒式接头盒

The optical distribution box is suitable for the distribution and equipment connection of optical cables with more than 16 cores entering the room. It integrates active connectors, flanges, and optical splitters, facilitating the fixation of optical cables and the flexible distribution of optical signals. The optical termination box is used for the connection of optical cables with less than 16 cores entering the room and connecting to optical equipment. One end is connected to the outdoor optical cable, and the other end is connected to the optical equipment through patch cords.

光配线箱适用于 16 芯以上光缆进入室内后的分配与设备配接，集成了活动接头、法兰盘和光分路器等部件，方便固定光缆并实现光信号的灵活调配。光终端盒则用于 16 芯以下光缆入室后的设备连接，一端连接室外光缆，另一端通过尾纤连接光设备。

Testing and Quality Assurance of Optical Passive Devices

光无源器件的测试与质量保障

The testing of optical passive devices is a crucial link to ensure product performance and quality. Different testing methods and equipment have significant impacts on the accuracy, reliability, and operability of test results.

光无源器件的测试是确保产品性能和质量的关键环节，不同测试方法和设备对测试结果的精度、可靠性和可操作性影响显著。

In a common testing system, the selection of the light source is of utmost importance. For testing purposes, a laser light source with a power of 0dBm or a broadband source with -10dBm/nm is sufficient, but attention should be paid to parameters such as power stability, coherence length, and signal-to-noise ratio. The erbium-doped fiber ring-based tunable laser has a coherence length of only 15 cm, which can effectively avoid optical path interference and improve test stability. Its signal-to-spontaneous emission noise ratio (S/SSE) reaches 75dB, making it suitable for testing devices with a large dynamic range. For broadband sources, the spectral stability is a key parameter.

在常见测试系统中，光源选择至关重要。用于测试的激光光源功率 0dBm 或宽谱源 -10dBm/nm 即可满足要求，但需注意功率稳定度、相干长度和信噪比等参数。基于掺铒光纤环的可调谐激光器相干长度仅 15 厘米，可有效避免光路干涉，提高测试稳定性；其信噪比（S/SSE）达 75dB，适用于大动态范围器件测试。宽谱源则需关注波谱稳定度。

The material (such as Ge, Si, InGaAs, etc.) and area of the power meter detector affect its performance. A low-polarization-dependent-response detector is suitable for PDL testing. A large-area detector (>3mm²) is beneficial for light reception, but the bare fiber adapter may cause the fiber to touch the detector, affecting the test repeatability and reliability. Although the fusion splicing method increases the operation, it can ensure long-term stability. The wide-aperture integrating sphere detector technology can avoid many problems of traditional detectors and improve test repeatability.

功率计探测器材料（如 Ge、Si、InGaAs 等）和面积影响其性能，低偏振反映度探测器适合 PDL 测试。大面积探测器（＞3mm²）利于受光，但裸光纤适配器可能导致光纤触及探测器，影响测试重复性和可靠性，熔接方式虽增加操作但能确保长期稳定性。宽口径积分球探测器技术则可避免传统探测器的诸多问题，提升测试重复性。

The parameters of the polarization controller, such as the scanning period, the area covered on the Poincare sphere, and the optical power fluctuation, affect the test accuracy. In particular, the optical power fluctuation will interfere with the PDL test results.

偏振控制器的扫描周期、覆盖 Poincare 球面积、光功率波动等参数影响测试准确性，特别是光功率波动会干扰 PDL 测试结果。

In addition, there are multiple ways to build a testing system. The traditional method of building a system by controlling instruments with a computer and the module assembly system each have their own advantages and disadvantages. The module assembly system, such as EXFO's IQS - 12004B DWDM testing system, combines multiple test units organically, has fast data transmission, convenient operation, and good scalability. It can achieve high-precision testing and obtain multiple parameter curves and crosstalk matrices, demonstrating the advantages of an advanced testing system.

此外，测试系统搭建方式也有多种，传统计算机控制仪表搭建和模块组装系统各有优劣。模块组装系统如 EXFO 的 IQS - 12004B DWDM 测试系统，将多个测试单元有机结合，数据传输快、操作方便、扩容性好，可实现高精度测试并得出多项参数曲线和串扰矩阵，展示了先进测试系统的优势。

Applications and Development Prospects of Optical Passive Devices

光无源器件的应用与发展前景

Optical passive devices are widely used in the field of optical communication. From the long-distance transmission of the backbone network to the last mile of the access network, and to the high-speed interconnection inside the data center, these devices are indispensable. They not only play a key role in fiber-optic communication trunk lines, optical switching access networks, DWDM, OADM, OTDM and other systems but also have diverse applications in many fields such as fiber-optic sensing, medical treatment, industrial manufacturing, and transportation. For example, they are used for measuring physical and chemical quantities such as displacement, vibration, temperature, and pressure, as well as in medical devices such as laser scalpels and medical endoscopes, and in optical communication links in automotive and aerospace applications.

光无源器件在光通信领域的应用极为广泛，从骨干网络的长距离传输到接入网的最后一公里，再到数据中心内部的高速互联，都离不开这些器件的支持。它们不仅在光纤通信干线、光交换接入网、DWDM、OADM、OTDM 等系统中发挥关键作用，还在光纤传感、医疗、工业制造、交通运输等众多领域实现了多样化应用，如位移、振动、温度、压力等物理化学量的测量，激光手术刀、医用内窥镜等医疗设备，以及汽车光通信系统、航空航天中的光通信链路等。

With the continuous development of information technology, higher requirements are placed on the capacity, speed, and reliability of optical communication systems. Optical passive devices will develop towards integration, miniaturization, and high performance to meet the future needs of optical communication. For example, more accurate wavelength division multiplexers will enable more wavelength multiplexing, further increasing the fiber transmission capacity. More advanced optical switch technologies will reduce insertion loss, increase switching speed, and achieve more flexible optical path control. New optical attenuators will have higher attenuation accuracy and a wider dynamic range to adapt to complex optical signal regulation scenarios. At the same time, with the continuous emergence of new materials and new processes, the performance of optical passive devices will continue to be optimized, and the cost will gradually decrease, providing strong support for the popularization and application expansion of optical communication technology and promoting the global information and communication infrastructure to a new height.

随着信息技术的不断发展，对光通信系统的容量、速度和可靠性提出了更高要求。光无源器件将朝着集成化、小型化、高性能化方向发展，以满足未来光通信的需求。例如，更高精度的波分复用器将实现更多波长的复用，进一步提升光纤传输容量；更先进的光开关技术将降低插入损耗、提高切换速度，实现更灵活的光路控制；新型光衰减器将具备更高的衰减精度和更宽的动态范围，适应复杂的光信号调控场景。同时，随着新材料、新工艺的不断涌现，光无源器件的性能将不断优化，成本将逐步降低，为光通信技术的普及和应用拓展提供有力支撑，推动全球信息通信基础设施迈向新的高度。

In the grand blueprint of optical communication, optical passive devices are undoubtedly the cornerstones for building high-speed, stable, and intelligent optical networks. With their diverse types, excellent performance, and wide applications, they promote the efficient transmission of information in optical fibers and lay a solid foundation for the digital process of human society. In the future, with the continuous innovation of technology, optical passive devices will continue to lead the development of the optical communication industry and open a more brilliant era of information interconnection.please refer to the official website www.optical-solution.com or contact Yuki< zgsales1@optical-solution.com >.

在光通信的宏伟蓝图中，光无源器件无疑是构建高速、稳定、智能光网络的基石。它们以多样的类型、卓越的性能和广泛的应用，推动着信息在光纤中的高效传输，为人类社会的数字化进程奠定了坚实基础。未来，随着技术的持续创新，光无源器件将继续引领光通信行业的发展，开启更加璀璨的信息互联新纪元。订购详情，请见官网www.optical-solution.com，或联系邮箱:Yuki.