As shown in the following figure, in the optical distribution network (ODN) of optical communication networks, there is a core passive component that always occupies a key position. It undertakes the important task of optical power distribution and builds a channel for optical medium transmission between the network-side OLT and the user-side ONU. This component is the optical fiber Splitter.
There are three main technical routes for optical fiber splitters: FBT (coupler), PLC planar waveguide technology, and micro-optical technology platform. Today, we will focus on the widely used PLC Splitter and disassemble this core component of optical communication from principle, structure, fabrication, parameters to application.
1. What are the differences in core technologies between PLC and FBT?
Although both are fiber optic splitters, PLC and FBT technologies have obvious differences in performance and application, with the core differences concentrated in working bands and power distribution:
· PLC Splitter: Can operate in the full band of 1260-1650nm, can achieve uniform distribution of optical energy, and is the mainstream choice for large-scale optical network deployment;
· FBT Splitter: The working bandwidth is less than that of PLC, but its advantage is that it can achieve non-uniform random distribution of port energy (such as 1:99, 30:70, etc.). Splitters based on FBT technology are often referred to as couplers.
For short, choose PLC for full-band compatibility and power sharing, and FBT for custom power distribution in special scenarios.
2. Core Structure of PLC splitter, three key components
Let's start with the breakdown of the PLC structure. The core components and packaging structure are as follows:
As can be seen from the above figure, the core composition of the PLC splitter is not complicated. It is mainly composed of three core components, combined with outer sealing steel pipe and other packaging structures. The overall structure is clear and each component performs its own function:
1.Pigtail: One or two optical fibers are fixed in a D-type capillary glass tube with UV and then ground at a specific Angle. The core purpose of the grinding is to reduce the reflected light and increase the return loss (RL);
2.FA fiber array: Insert the fiber tape into the V-Groove, cover the plate and glue it, then grind and polish it at an Angle of about 8 degrees. The V-groove is used to precisely position the fiber distance. It should be noted here that the MT-FA series commonly used in 400G/800G/1.6T high-speed transceiver modules have higher requirements for appearance and precision, while the multi-channel FA used in NPO/CPO has much higher PITCH precision requirements than the FA used in PLC;
3 PLC splitter chip.
The PLC chip is the most core part of the entire device and also the most technically challenging part. The PLC chip is formed on a quartz or special glass substrate using chemical vapor deposition (PECVD) or ion exchange to create a specific optical waveguide path. To achieve a uniform or non-uniform division of an incident optical waveguide into different numbers of output optical waveguides, such as 2, 4, 8, 16, 32, 64, etc., to achieve the branching function of the optical signal, and to form a PLC optical chip through device packaging and precision grinding. Since the peak period of PLC splitter construction in China has passed, this is just a brief mention. As for how the overall PLC chip is designed and how it is controlled at the chip level, interested friends can choose whether they need to go further in the process of building the knowledge system and choose as needed.
3. General production process of PLC splitters, the key lies in the control of details
The production of Pigtail and FA belongs to the basic component process. The processes of various manufacturers are largely the same, with the main differences being in detail control and the level of automation. With the three core components of Pigtail, FA and PLC chip already in place, the general packaging process of PLC splitters can refer to the industry standard process, which is centered around core steps such as component bonding, dispensing fixation, optical inspection and packaging molding. The control of details at each step directly affects the final performance of the device.
The above are the common steps in the industry as follows. They do not include the detailed and confidential controls of each company and are for reference only.
4. PLC Splitter Core Parameters, 1×N/2×N Specifications Overview:
Since we talked about the core optical parameters of passive products in the title of the previous section, "Core Optical Parameters of Passive Products", it will be much easier for us to describe the specifications here.
The mainstream specifications of PLC splitters are 1×N and 2×N. The core parameters cover operating wavelength, insertion loss, loss uniformity, return loss, etc., which are also key indicators for measuring device performance. The following are industry-wide standard parameters (which may be slightly adjusted by different manufacturers according to chip, process and customer requi
5. A variety of packaging forms to fit different application scenarios
The core of the PLC splitter is 1×N/2×N bare device or mini module, while the external package form is designed specifically based on the actual application scenarios to meet the different deployment requirements of FTTX. The mainstream package forms include:
Bare device, Mini Module, BOX Module, Direct Tray Type, Wall-mounted, Cassette, Rack-mountable, Two in one, LGX metal box, etc.
In simple terms, the core components remain the same, and the package form is matched as needed, allowing the PLC splitter to adapt to different installation environments such as computer rooms, corridors, and outdoors.
6. Standards and reliability These specifications are mandatory requirements
The production and testing of PLC splitters must follow international, national and industry standards. Mainstream common standards include:
Domestic standards: YD/T 2000.1-2009 (Planar Optical Waveguide Optical Power splitter), YDT1117-2001 (Technical conditions for All-Fiber Branch Devices);
International standards: GR-1209-CORE (General Requirements for Passive Optical Components), GR-1221-CORE (Requirements for reliability Assurance of Passive Optical Components).
Among them, the Telcordia standard is an important industry reference, mainly conducting reliability tests from both environmental and mechanical dimensions. It covers 2000 hours of wet heat, 2000 hours of high and low temperature storage, 20 cycles of thermal shock, mechanical shock, vibration, 70N cable tensile strength, water immersion, salt spray, cable torsion/side tension, high power transmission and many other tests. Only by passing all these tests can the long-term stable operation of the device be guaranteed.
7. Core application scenarios, PON technology + FTTX standard configuration
The main application scenario of PLC splitters is FTTX (Fiber to the Building, Fiber to the Home, Fiber to the desktop, etc.) based on PON technology, which serves as the core of the ODN network to achieve efficient distribution of optical signals, connect OLT and numerous ONUs, and is an indispensable key component in the large-scale deployment of fiber broadband and fiber communication.
Thought Moment: In some high-speed multimode scenarios, why do FBT-made couplers not work, while micro-optical-made couplers do?
Finally, there is a small issue in the industry that all optical communication colleagues can consider: When terminal customers configure certain high-speed multi-mode transceiver modules, the tape-pull FBT coupler cannot work properly in multi-mode scenarios, but it can work when switched to a micro-optical coupler. What is the reason behind this? Leave a comment and we'll reveal the answer later ~ or you can just solve it.
Conclusion:
PLC fiber splitters, as one of the cores of passive components for optical communication, have become the mainstream choice for FTTX network deployment
