Optical wavelength meter

1. An optical wavelength meter, comprising:

an interferometer;

a laser configured to oscillate in a multi-longitudinal mode; and

a signal processor configured to calculate a wavelength of an input beam with reference to interference fringe information of a multi-longitudinal mode reference beam generated by the laser and interference fringe information of the input beam obtained from the interferometer.

2. The optical wavelength meter according to claim 1 , wherein the interferometer includes a Michelson interferometer.

3. The optical wavelength meter according to claim 1 , wherein the signal processor is configured to calculate the wavelength of the input beam by counting the number of interference fringes with reference to the interference fringe information of the multi-longitudinal mode reference beam and the interference fringe information of the input beam obtained from the interferometer.

4. The optical wavelength meter according to claim 1 , wherein the signal processor is configured to calculate the wavelength of the input beam by Fourier transform with reference to the interference fringe information of the multi-longitudinal mode reference beam and the interference fringe information of the input beam obtained from the interferometer.

5. The optical wavelength meter according to claim 1 , wherein a resonator mode spacing of the laser is 500 MHz or less.

6. The optical wavelength meter according to claim 1 , wherein the laser includes a multi-longitudinal mode He—Ne laser.

7. The optical wavelength meter according to claim 6 , wherein the He—Ne laser includes an unstabilized multi-longitudinal mode He—Ne laser.

8. The optical wavelength meter according to claim 1 , wherein the number of longitudinal modes in the multi-longitudinal mode reference beam is three or more.