Patent ID: 6141360
Filing Date: 2000-10-31
Classification: H01S

Abstract:
A tunable wavelength laser light source apparatus comprising:a first optical reflection member comprising a diffraction grating having a predetermined wavelength resolution;a second optical reflection member comprising a half-mirror, said second optical reflection member being provided opposite to the first optical reflection member at a first predetermined distance, whereby an optical cavity is formed between the first and second optical reflection member, said optical cavity having an optical cavity mode standing with a free spectrum range FSR1=.lambda..sup.2 /2nL (where .lambda. is a light wavelength, n is a refractive index, and L is a cavity length which corresponds to the first predetermined distance), and said half-mirror allowing part of light from inside the optical cavity to be transmitted therethrough to outside of the optical cavity and allowing reflection light from outside of the optical cavity to return therethrough to the optical cavity;an optical gain medium comprising a semiconductor laser having ends coated with anti-reflection coatings, said optical gain medium being provided between the first and second optical reflection members, whereby a laser light source is provided, which oscillates in the optical cavity mode;a third optical reflection member comprising a feedback mirror for returning to the optical cavity as said reflection light the part of the light transmitted from inside the optical cavity through said half-mirror to outside the optical cavity, said third optical reflection member being provided opposite to the second optical reflection member at a second predetermined distance which is set to be far smaller than the first predetermined distance based on a predetermined full width at half maximum which defines the predetermined wavelength resolution of the diffraction grating, whereby a compound cavity is provided, said compound cavity having a compound cavity mode standing with a predetermined free spectrum range FSR2=.lambda..sup.2 /2nL (where .lambda. is a light wavelength, n is a refractive index, and L is a light path length which corresponds to the second predetermined distance), and said compound cavity mode emphasizing the optical cavity mode of the optical cavity, which stands at intervals of FSR2;a variable mechanism comprising a piezoelectric element for varying the second predetermined distance by changing a position of the third optical reflection member on an optical axis; anda rotation mechanism for changing a center of a wavelength discrimination curve thereof, which has the predetermined full width at half maximum which defines the predetermined wavelength resolution of diffraction grating, by rotating the diffraction grating, thereby to select one of a plurality of oscillation wavelengths standing in the compound cavity mode of the compound cavity, effecting a single mode oscillation, and for sweeping the compound cavity mode in wavelength in cooperation with the variable mechanism;wherein the compound cavity mode is generated when an electromagnetic field inside of the optical cavity is coupled in phase to a reflection electromagnetic field from the third reflection member; andwherein oscillation gain becomes high at a wavelength at which the compound cavity mode stands, and original modes which are due to the optical cavity are suppressed, thereby ensuring that oscillation starts with the compound cavity mode selected by rotation of the diffraction grating.