Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1997-05-07
1999-08-03
Hantis, K P
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
356328, G01J 328
Patent
active
059332352
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an optical spectrum analyzer and to a spectrometer apparatus using a detector array and, more particularly, to improvements in the wavelength accuracy of an optical spectrum analyzer and improvements in the power level accuracy, as well as improvements for extension of the range of measured wavelengths.
BACKGROUND ART
The prior art optical spectrum analyzer indicates the average value of light power existing within a finite slit width, or a finite spectral width.
A spectrograph using a detector array has been urged to display the output from each device as it is, for the following reason. The spectrum of light under measurement is assumed to have an arbitrary shape. The spectral shape does not always have a 1:1 relation to the output from the device array.
Accordingly, it has been difficult to estimate the real spectral shape from the output from the device array.
Furthermore, the wavelength resolution and the range of measured wavelengths are determined by the number of the devices of the array, the pitch, the focal distance of the focusing mirror, and other factor. Trade-offs are made between the wavelength resolution and the range of measured wavelengths. Therefore, if one is improved, then the other is deteriorated. It is impossible to improve both at the same time.
In view of the foregoing, the present invention has been made. It is an object of the present invention to provide an optical spectrum analyzer which assumes that light under investigation is an assemblage of monochromatic light rays (light whose spectral linewidth is much narrower than the resolution of the instrument such as laser light) and which can find the center wavelength of the monochromatic light and the total power by performing simple arithmetic operations from the outputs from adjacent devices of a device array.
It is another object of the invention to realize an optical spectrum analyzer capable of measuring ASE noise buried in laser light and of equivalently improving the dynamic range.
It is a further object of the invention to realize a spectrometer apparatus which is applicable to an optical spectrum analyzer and which is provided with a plurality of incident ports, or slits, to extend the range of measured wavelengths while maintaining desired wavelength resolution.
DISCLOSURE OF THE INVENTION
The first-mentioned object is achieved in accordance with the teachings of the invention by an optical spectrum analyzer comprising a spectrometer apparatus, an arithmetic unit for calculating the center wavelength from output signals from light-receiving devices of a device array and from the light power distribution at an incident port by interpolation and for calculating the total power, and a display unit for displaying values of the center wavelength and total power. The spectrometer apparatus directs light introduced from an incident port at the light-dispersing device. Light going out of the light-dispersing device is focused onto the device array.
In this structure, the outputs (theoretical values) from the photo detector devices have been previously calculated. It is assumed that the n-th device of the device array produces a maximum output and deviates from the center of the outgoing beam impinging on the device array by an amount of .DELTA.x. The relation between the amount of deviation .DELTA.x and the associated photo detector device is found in advance.
If values are obtained by actual measurements, the amount of deviation .DELTA.x is found from the above relation. Then, the center wavelength is found. Also, the total power can be calculated from the theoretical values of the outputs from the photo detector devices and from the values obtained by actual measurements.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of main portions of an optical spectrum analyzer according to the invention;
FIG. 2 is a diagram illustrating the relation between a device array and outgoing beam;
FIG. 3 is a flowchart illustrating the operation;
FIG. 4 is a diagram illustrati
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patent: 4375919 (1983-03-01), Busch
patent: 4983039 (1991-01-01), Harada et al.
patent: 5357343 (1994-10-01), Lowne et al.
Izumi et al "Wavelength . . . Pollutants" J. Phys. E. Sci. Instrument vol. 4, No. 1, Jan. 1981
Arihara Mamoru
Sampei Yoshihiro
Suzuki Yasuyuki
Tachikawa Yoshihiko
Hantis K P
Kojima Moonray
Yokogawa Electric Corporation
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