Patent ID: 8848182

Claim:
An optical device comprising: a first projection group in which electrically conductive projections are arranged at a first period along a direction parallel to a virtual plane, wherein the first projection group is configured such that when light traveling in an incident direction inclined with respect to a vertical line directed to the virtual plane is incident on the first projection group, surface plasmon resonance is generated at a first resonance peak wavelength and a second resonance peak wavelength, a first resonance peak wavelength band including the first resonance peak wavelength includes an excitation wavelength λ 1 in surface-enhanced Raman scattering, a second resonance peak wavelength band including the second resonance peak wavelength includes a Raman scattering wavelength λ 2 in the surface-enhanced Raman scattering, and when an excitation frequency of the excitation wavelength λ 1 is k 1 , a Raman frequency of the Raman scattering wavelength λ 2 is k 2 , a dispersion curve of a surface plasmon polariton generated by the surface plasmon resonance is f(k), a light frequency of the incident h is ki, the first period is P 1 , and an incident angle between the incident direction and the vertical line is θ, the following relations are satisfied: f ( k 1)=2π /P 1 +ki× sin θ, and f ( k 2)=2π /P 1 −ki× sin θ.