Since my phD with EIT (first experimental demonstration of electromagnetically induced transparency in solids) in 1995, I have been working in the area of nonlinear quantum optics such as slow light and light storage using rare-earth doped solids. Since 2006, I have been designated as a director of Photon Information Processing (PIP) by the Korean government, where the research topic is 1. photon logic gates and 2. quantum memory. For the photon logic gates, I proposed digital all-optical logic gates based on slow light and nondegenerate four-wave mixing, where the four-wave mixing efficiency can reach higher than 100%. It was published in APL in 2008 and registered a patent in 2010. For the quantum memory, I for the first time demonstrated EIT-based light storage using slow light phenomenon in PRL in 2002. Due to the lower efficiency and single-mode operation in time time domain, however, I needed to propose optically locked photon echoes for a multi-mode ultralong quantum memory protocol: Nature Photonics in 2009. This ulltralong quantum memory is absolutely required for quantum repeaters based on DLCZ protocol. The optically locked photon echo proposal was experimentally demonstrated in NJP in 2012. In 2012, I also presented a simple method of double rephasing technique combined with the optical locking in PRA Rapid Comm. I am still pursuing quantum memory research for the potential applications of DLCZ-based quantum repeaters. By the way, in the fall of 2013, I have organized Quantum Optics Workshop 2013 held in Jeju, S. Korea (http://qow.or.kr).