Fabrication of Y-junction waveguides using proton beam writing

Miura, Kenta*; Sato, Takahiro; Ishii, Yasuyuki; Koka, Masashi; Uehara, Masato*; Kiryu, Hiromu*; Takano, Katsuyoshi*; Okubo, Takeru; Yamazaki, Akiyoshi; Kada, Wataru; Yokoyama, Akihito; Kamiya, Tomihiro; Hanaizumi, Osamu*

We develop optical waveguides using Proton Beam Writing (PBW). In this study, Y-junction PMMA film waveguides at 1.55 m were fabricated using PBW. First, an SiO film was deposited as an under-cladding on an Si substrate using radio-frequency sputtering. After a PMMA film was spin-coated on the SiO film, the sample was baked at 120 C. The thickness of PMMA film became 10 m by repeating these processes twice. Next, a Y-junction waveguides with the width of 8 m and branching angle of 2 were drawn in the PMMA film on the condition of the dose of 100 nC/mm using PBW having a 1.7 MeV proton beam with the current of 10 pA and the size of about 1 m. Finally, a 10-m thick PMMA film was deposited again on the sample as an upper-cladding layer by spin-coating. The observation of an optical microscope showed that an objective Y-junction was successfully drawn using PBW. To observe near field patterns (NFPs), the laser light of wavelength at 1.55 n was injected through a single-mode fiber (SMF) from one side of the edge of the waveguide cleaved both sides of the sample. The two independent NFPs were observed form each branching waveguide using a vidicon camera at the opposite side of the waveguide. The observation result of the two NFPs with an optical power intensity ratio of 1:0.98 demonstrated that the light of 1.55 m was divided at almost equal ratio by this Y-junction.