# Experimental Research on In Situ Uniaxial Tensile Response of Silica-Based PLC Optical Splitters
## 1 Introduction  
For a passive optical network (PON), such as an ethernet passive optical network (EPON), broadband passive optical network (BPON), and fiber to the x (FTTX), a fiber optic splitter is one of the essential components in the optical fiber link [1, 2]; the PLC optical splitter is one of the most common. Optical splitters are widely used for branching and combining optical signals [3]. Planar monolithically integrated photonic circuit technology, also known as planar lightwave circuits (PLC), is widely used to manufacture optical splitters [4]. PLC optical splitters have the advantages of high integration, good splitting uniformity, low temperature sensitivity, and low loss compared to traditional fused biconical taper optical splitters, so they are more widely used in FTTX transmission [5, 6]. In order to reduce the maintenance and operation costs of the optical network, high reliability PLC optical splitters are required [7]. The performance of the PLC optical splitter is mainly determined by the quality of the input/output fiber array and the PLC chip, as well as the fiber array-PLC chip connection technology [8, 9]. Soldering, laser welding, and adhesive connection are the three most popular connection techniques in PLC optical splitters packaging [10]. Among these, fiber array-PLC chip connection with UV-curable adhesives has become increasingly popular due to its advantages such as fast curing time, mass production, and low cost [11, 12]. However, the reliability of fiber array-PLC chip connection with adhesives is worthy of attention. The fiber array and the PLC chip are interconnected by a UV-curable adhesive, which is essentially a form of the adhesively-bonded joint, where the adhesively-bonded joint is the key area to achieve optical and mechanical interconnection, but is also the weak area of the PLC optical splitter, and is prone to damage and fracture leading to the failure of the optical performance of the device [13, 14]. PLC optical splitters, as a key component of PONs, are widely used and researched in recent years [6]. Previous work on the reliability of PLC optical splitters can be classified into two categories, one of which is to conduct environmental and mechanical reliability tests according to relevant standards, such as the Bellcore criterion (GR-1209/1221-CORE), to determine whether it has long-term stable optical performance, and to speculate on the cause of its failure [15; 16; 17]. The other is focused on the design, manufacturing, and packaging of PLC optical splitters [2; 18; 19]. However, previous studies usually only focus on the changes of the optical performance indexes of the device before and after the test, and there is a lack of relevant research on the failure behavior and failure mechanism of the device during the test. In addition, the existing studies seldom conduct in-depth research and analysis of specific weak areas, resulting in their failure characteristics still being unclear, especially from a local perspective. [PERSON] et al. [20] conducted temperature and humidity tests and drop tests on commercially available PLC optical splitters and concluded that the critical area of failure was at the adhesively-bonded joint between the fiber array and the chip, but they did not do further analysis of the damage evolution in this critical area. [PERSON] et al. [17; 21] conducted online experiments on PLC optical splitters, studied the real-time changes of its optical performance when it was subjected to temperature load and drop, analyzed the failure phenomena in the experiment, and put forward suggestions for packaging improvements. However, the specific weak areas and their failure characteristics have not been studied in-depth. For optical communication devices such as PLC optical splitters, its structure is compact and its size is small, especially the adhesive layer at the adhesively-bonded joint is usually very thin (tens or even several microns), and it has the functions of both mechanical and optical interconnection [9].