A spectroscope or spectrometer for detecting a driving position of a main wavelength dispersive device using a diffraction line produced in that light from a light source having a narrow wavelength bandwidth is incident on a sub-wavelength dispersive device in an arrangement that a plane diffraction grating is used as the sub-wavelength dispersive device which is affixed on a driving axis in a manner of forming a suitable angle with the main wavelength dispersive device. When the main wavelength dispersive device is used between 0.degree. and 90.degree. , a diffraction angle of the sub-wavelength dispersive device comes within about 45.degree. . In such a range, the angular dispersion is not changed significantly, thus the interval between diffraction lines is hardly varied. For this reason, the width of a sub-detector can always be set at an optimum condition for raising the positional detecting accuracy while one or more diffraction lines are allowed to be incident.

A wavelength sub-dispersive device receives light from a standard light source producing light having a narrow bandwidth and having an intensity greater than that of light to be detected. The sub-dispersive device is provided for identifying the wavelength of the dispersed light by a main dispersive device, which is detected by a main detector. Light from the standard light source does not irradiate the main detector. If the main detector is irradiated with the light from the standard light source, the detection of the main detector is disturbed by its high intensity.

An analog-to-digital converter using a frequency tunable laser having output radiation of a frequency determined by the input voltage to the laser is described.

The present invention refers to a spectrometer device comprising a monochromator means, a light-measuring means receiving light from said monochromator means, and a calibration means comprising a calibration light source. The present invention provides a new spectrometer device whose light-measuring means comprises a plurality of light-measuring elements in an array extending in the direction of dispersion of the monochromator means, and whose calibration means carries out, on the basis of a spectral light measurement with the aid of the calibration light source, an association between the light-measuring elements and the wavelengths of the spectral light which is adapted to be detected by the respective light-measuring elements. These measures substantially facilitate the calibration and especially the automatic execution of said calibration, if desired simultaneously with a spectra measurement, and they improve the accuracy of the calibration.

A spectrometer is disclosed, in which plural entrance slits are mounted, and a reference light passing through one entrance slit and the light to be measured passing through the other entrance slit are simultaneously focused on a photo-sensitive surface of a detector through a diffraction grating and a focusing optical system, to measure the wavelength of the light to be measured precisely by using the reference light as a standard.