Patent attributes
An etalon functioning as a Fabry-Perot resonator is formed by bonding a quartz crystal bulk having a pair of Z-cut surfaces and a compensation bulk having a pair of Z-cut surfaces with one of the Z-cut surfaces of the quartz crystal bulk facing one of the Z-cut surfaces of the compensation bulk, reflection films being formed on the other of the Z-cut surfaces of the quartz crystal bulk and the other of the Z-cut surfaces of the compensation bulk, respectively. As for the compensation bulk, a LiCAF having a characteristic that (1/n)*(∂n/∂T)+α becomes negative, n being the refractive index, T the temperature and α the linear expansion rate, and a ratio of the optical length of the quartz crystal bulk to that of the compensation bulk being approximately set to |(1/n)*(∂n/∂T)+α|:3×10−6.
