JPH0560615A - Light spectrum analyzer - Google Patents

Abstract

PURPOSE:To automate setting of an optimum range. CONSTITUTION:An output of a Michelson interferometer 11 is amplified by an amplifier 12, an amplified output thereof is converted into a digital signal by an A/D converter 13, the digital signal is subjected to fast Fourier transform and a spectrum thus obtained is converted into a power spectrum by a power computing element 17. The power spectrum is integrated over all of frequency bands by an integrating element 18, an amplification gain of the amplifier 12 and/or a conversion gain of the A/D converter 13 is altered in accordance with an integrated value thus obtained, and thereby an optimum range is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical spectrum analyzer for converting an output of an interferometer into a digital signal and Fourier-transforming the digital signal to analyze input light.

[0002]

2. Description of the Related Art In an optical spectrum analyzer, input light is incident on a Michelson interferometer, the interference light is converted into an electric signal, the electric signal is amplified by an amplifier as necessary, and the amplified output is AD-converted. A digital signal is converted into a digital signal by a detector, and the digital signal is subjected to fast Fourier transform to obtain a signal in the frequency domain, that is, a spectrum is obtained, and various analyzes are performed on the input light.

[0003]

In order to set the optimum sensitivity to the input light, that is, to determine the optimum range,
The spectrum of the input light is analyzed and displayed, the range is changed appropriately by looking at the display, that is, the amplification gain of the amplifier or the conversion gain of the AD converter is changed, and the spectrum analysis of the input light is performed again. Was repeated to set the optimum range. Since such an operation is performed, in order to obtain the optimum range, it is often necessary to perform the measurement five times.
Since the Michelson interferometer mechanically moves a mirror to obtain interference light within a predetermined range, it is difficult to perform at high speed, and one measurement takes a relatively long time. For this reason, it is not preferable to perform the measurement many times for setting the optimum range because the measurement time as a whole becomes long.

[0004]

According to the present invention, the spectrum obtained by Fourier transform is converted into a power spectrum, the power spectrum is integrated over the entire frequency band, and the range is set according to the integrated value. Be seen.

[0005]

FIG. 1 shows an embodiment of the present invention. The input light is incident on the Michelson interferometer 11, the interference light is converted into an electric signal and output, the electric signal is amplified by the amplifier 12, and the amplified output is converted into a digital signal by the AD converter 13. The digital signal is digital filter 1
4 or not, and is supplied to the fast Fourier transformer 15 for fast Fourier transform, and the spectrum obtained by the transform is displayed on the display 16.

In the present invention, the fast Fourier transformer 1
The spectrum obtained from 5 is converted into a power spectrum by the power calculator 17, and the power spectrum is integrated by the integrator 18 over the entire frequency band. The amplification gain of the amplifier 12 and / or the conversion gain of the AD converter 13 is set according to the integrated value, and the optimum range is automatically set.

That is, in the measurement, first, the range is set appropriately, that is, the integral power of the input light is estimated, and the range is set with the power as a reference power level. After setting the range, the input light is measured, the integral value of the power spectrum is obtained as described above, the difference between the integral value and the reference power level of the setting range is obtained, and the range setting is changed according to the difference. .. For example, when the integral value is too large, the range is lowered according to the integral when the integral value is too large, and control is performed as if the integral value was set as the reference power level from the beginning.

If the reference power level (setting range) initially set is extremely different from the power of the input light, it may not be possible to set the optimum range even with one measurement. In this case, the display spectrum of the display 16 is displayed. Since it is blunt, it can be understood that the range is not the optimum range, and rerange setting (remeasurement) may be performed. However, in general, it is often known how much the power of the measured light is, and if the range is set as the reference power level at the start of measurement, it is optimal for one measurement. The range is automatically set.

[0009]

As described above, according to the present invention, 1
The power spectrum is obtained from the spectrum obtained by one measurement, this is integrated, the range is set by the integrated value, the optimum range setting is obtained by one measurement, and the total measurement time becomes shorter. Also, the measurement operation becomes simple.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

Claims (1)

[Claims] 1. The output of the interferometer is converted into a digital signal,
In the optical spectrum analyzer for Fourier transforming the digital signal, a means for converting the spectrum obtained by the Fourier transform into a power spectrum, a means for integrating the converted power spectrum over the entire frequency band, and a means for integrating the power spectrum An optical spectrum analyzer comprising means for setting a measurement range according to an integrated value and.