Concomitant with the increasing use of mass storage and high speed services, the deployment of optical fiber infrastructures has been increasing, and accordingly, malfunction frequency, such as the cutting and bending of optical fiber has also been increasing by various environment variables. But problems have arisen in distinguishing the exact location of damage, and in the increase in the number of repairs and dispatch expenses caused by the complex structure of optical fiber, which has resulted in monitoring systems for optical fiber becoming more popular.
Currently, if a malfunction occurs with an optical fiber, a technician is sent to the site, and operates a commodity Optical Time Domain Reflectometer (OTDR) at the edge of the broken optical fiber. Because this repair method demands a lot of time and money, monitoring the optical fiber in real time is required to improve upon that method.
OTDRs for monitoring optical fiber in real time have been studied for two types, the Line care, and the embedded OTDR. The Line care type simply uses an additional device with the existing optical network infrastructure. Therefore, development of the embedded OTDR combined with the OTDR function on an existing optical transceiver is required to decrease the size of hardware, and diagnose the condition of the optical fiber in real time.
In this study, an Optical Sub-Assembly (OSA) embedded in the optical transceiver is formally modeled and analyzed, by separating the data and OTDR functions.
This OSA structure needs the OTDR function, a bidirectional transceiver with single wavelength, and uses an optical splitter. It requires sufficient distance between the active devices constituting the OSA, so that the data optical source, which is the existing optical transceiver, can be aligned together inside the optical module. Therefore, we selected the active alignment method using the TO-can package.
We defined essential components embodying the OTDR and data functions to design such an OSA, and formed separately embodied devices as one optical module through optical analysis. We then calculated the alignment range that showed the best efficiency in the designed structure.
Chapter 4 evaluates the reliability of the design, and analyzes the production features, by conducting an OSA production and alignment experiment to evaluate the designed structure.
As a result, the size of the manufactured OSA module is 24x16x8 mm, and comparison of the designed and experimental values showed that the error rate was less than 10% for the Laser Diodes (LDs), and less than 5% for the Photodiodes (PDs), with over 90% reliability. Also, the OSA module alignment experiment confirmed that the LD-to-single mode fiber (SMF) coupling efficiency was OTDR LD: max 23%, Data LD: max 25.9%, and SMF-to-PD coupling efficiency was OTDR PD: max 40.6%, Data PD: max 63.6%

These results by modeling through optical analysis confirmed the possibility of producing an optical module for commercialization, when numerous optical sources and PDs are accumulated as one OSA. When the OTDR function is embedded in the existing optical transceiver, the condition of the optical fiber can be diagnosed at the In-service state in real time.