Patent ID: 9054490
Filing Date: 2015-06-09
Classification: A61B,H01S

Abstract:
1. A tunable laser comprising: a first mirror and a second mirror; a gain medium arranged between the first mirror and the second mirror; a birefringence filter arranged between the first mirror and the second mirror; and an excitation device exciting the gain medium, wherein light that passes through the birefringence filter oscillates between the first mirror and the second mirror, wherein an oscillation wavelength is switched by rotating the birefringence filter, wherein the birefringence filter includes a first birefringent plate and a second birefringent plate, which have principal dielectric axes parallel to optical surfaces thereof, and wherein, in a transmission spectrum of the birefringence filter in a case where an angle formed by a principal dielectric axis of the first birefringent plate and a principal dielectric axis of the second birefringent plate is zero, when peaks at which a transmission is highest are defined as main peaks, peaks at which a transmission is second highest are defined as subpeaks, a stimulated-emission cross-section of the gain medium at the main peaks is denoted by σmain, and a stimulated-emission cross-section of the gain medium at the subpeaks is denoted by σsub, the principal dielectric axes of the first birefringent plate and the second birefringent plate are shifted from each other so that, at the subpeak at which (σsub−σmain)/σmain is largest, a relationship ln(1/R)×(σsub−σmain)/2σmain<ln(Tmain/Tsub) is satisfied, where a transmission at the subpeak is denoted by Tsub, a transmission at the main peaks is denoted by Tmain, and a reflectivity of the second mirror is denoted by R.