The following section is the special issue for the 13th Japan–Finland Joint Symposium on Optics in Engineering (OIE2019) held on August 26–30, 2019 at two locations: Aalto University in Otaniemi, Espoo, Finland, and Kultuurikatel, Tallinn, Estonia. The special section contains 12 papers based on the presentations at the OIE2019, and it covers a wide range of fields including imaging, measurement, detectors, scattering, and signal processing. Each paper has been reviewed and accepted under the editorial policy of Optical Review. The total number of papers presented at the symposium was 56 including 1 plenary, 31 oral, and 24 poster presentations.

The OIE2019 was organized by Aalto University. OIE is an international symposium series in optics in engineering that started in Lappeenranta in 1995 and has been held in Tsukuba in 1997, Kajaani 1999, Suita 2001, Saariselkä 2003, Sapporo 2005, Tampere 2007, Tokyo 2009, Turku 2011, Utsunomiya 2013, Joensuu 2015, Sado 2017, and Espoo and Tallinn 2019. The aim of the symposium series is to provide a timely forum to share information on latest and innovative works on new photonics, technologies and device applications, and to promote the interaction between Finnish and Japanese scientists who are working in the fields of pure and applied optics and photonics.

The next 14th OIE (OIE’21) will be held in Hamamatsu, Japan. We hope that Finnish and Japanese researchers will meet and have valuable scientific discussions at the OIE symposium continuously.

Finally, we sincerely appreciate all the participants in the conference, the organizer, and the sponsors.