Patent ID: 7365845
Filing Date: 2008-04-29
Classification: G01J

Abstract:
1. An optical spectrum analyzer comprising: a reference light source which radiates reference light having a known wavelength of maximum or minimum light intensity; a tunable wavelength filter which causes wavelength components contained in incident light to selectively exit therefrom and which changes the selected wavelength as time passes, wherein the incident light contains to-be-measured light from an external source thereof and the reference light radiated from the reference light source, and wherein the tunable wavelength filter includes: (i) a diffraction grating which receives the to-be-measured light and the reference light in a direction orthogonal to grooves of a diffraction surface of the diffraction grating and diffracts the to-be-measured light and the reference light, and (ii) a turning mirror having a reflection surface that confronts the diffraction surface of the diffraction grating, the turning mirror being formed to freely turn about an axis parallel to the grooves of the diffraction surface such that when the reflection surface of the turning mirror confronts the diffraction surface of the diffraction grating, the turning mirror receives diffracted light exiting from the diffraction grating in response to the to-be-measured light and to the reference light on the reflection surface and returns the diffracted light to the diffraction grating; light incident devices which cause the to-be-measured light to be directly incident, as a light component of the incident light, on the tunable wavelength filter along a first optical axis and which at the same time cause the reference light from the reference light source to be directly incident, as another light component of the incident light, on the tunable wavelength filter along a second optical axis different from the first optical axis; a light receiving device which simultaneously receives light, which results from the to-be-measured light and is caused to exit from the tunable wavelength filter, and light, which results from the reference light and is caused to exit from the tunable wavelength filter as well as simultaneously outputs an output signal in response to the to-be-measured light and an output signal in response to the reference light, wherein the light receiving device includes: (i) a first light receiving unit for receiving light exiting from the diffraction grating in a first specific direction in response to light resulting from the to-be-measured light and returned from the turning mirror of the tunable wavelength filter, and (ii) a second light receiving unit for receiving light exiting from the diffraction grating in a second specific direction in response to light resulting from the reference light and returned from the turning mirror of the tunable wavelength filter; a storage device which has a first memory and a second memory, and which stores spectrum data of the to-be-measured light and spectrum data of the reference light in respective predetermined portions of the first and second memories, the predetermined portions of the first and second memories having predetermined addresses, and the spectrum data being stored based on the output signals in response to the to-be-measured light and the reference light which are simultaneously output from the first and second light receiving units of the light receiving device, wherein the spectrum data is made to correspond to the wavelength that is selected by the tunable wavelength filter and changes as time passes; and a correction device which corrects the spectrum data of the to-be-measured light stored in the predetermined portion of the first memory of the storage device by using address values at which the spectrum data of the reference light stored in the predetermined portion of the second memory of the storage device is maximized or minimized, and known wavelengths corresponding to the address values, the spectrum data being corrected based on a wavelength that is selected by the tunable wavelength filter and changes as time passes; wherein the optical spectrum analyzer is arranged to continuously measure the to-be-measured light and in a wide wavelength range at a high speed while maintaining a high wavelength accuracy and without requiring an advance calibration processing to be performed, the optical spectrum analyzer performing measurement of the to-be-measured light accompanied by calibration processing of the correction devices for correcting wavelength information regarding the to-be-measured light based on the spectrum data of the to-be-measured light and the spectrum data of the reference light, which are obtained by causing the reference light having the known wavelength and the to-be-measured light to be incident on the tunable wavelength filter at all times; and wherein the turning mirror has reflection surfaces formed on both surface sides, and the diffraction grating comprises: