Low-DOP depolarizer for linearly polarized light independent of direction of vibration

Depolarizer is a key device in polarization sensitive optical systems, by which a completely or partially polarized light is converted into unpolarized one. An artificial polarization-dependent delay is employed substitute for polarization maintaining fiber, a compact depolarizer for linearly polarized light with any direction of vibration is proposed. Before being depolarized, the incident linearly polarized light is converted into an elliptical polarized light by a quarter-wave plate and is divided into two orthogonal polarized parts always with equal intensity, so that the depolarizer is independent of the optical field direction of incident light. The depolarization performance evolution with the order of quarter-wave plate, center wavelength and optical field direction of incident light is calculated. Low DOP (2.6%), low insertion loss (0.6 dB) and small insertion loss fluctuation (0.11 dB) are obtained for a linearly polarized light with 0.13 nm spectral width. Theoretical analyses and experimental results show that proposed depolarizer has low DOP, low insertion loss and small insertion loss fluctuation, and can be operated in a wide spectral band.