Optical device and analyzing apparatus

An optical device comprising:

• a first projection group and a second projection group that are electrically conductive projections and that are arranged along a direction parallel to a virtual plane, wherein
• the first projection group is provided in a first area, and the second projection group is provided in a second area adjacent to the first area,
• the first projection group is arranged at a first period, and the second projection group is arranged at a second period different from the first period,
• the first period and the second period are shorter than a wavelength λ1 of an incident light,
• the incident light includes a first light that is incident on the first projection group at a first angle with respect to a vertical line directed to the virtual plane and a second light that is incident on the second projection group at a second angle different from the first angle with respect to the vertical line, and
• a material of the first and second projection groups, the first and second periods, and the first and second angles are determined so as to make both a first resonant wavelength of first surface plasmon resonance at the first projection group and a second resonant wavelength of second surface plasmon resonance at the second projection group the wavelength λ1.