Optics: measuring and testing – By light interference – Spectroscopy
Reexamination Certificate
2000-09-29
2003-07-15
Kim, Robert H. (Department: 2882)
Optics: measuring and testing
By light interference
Spectroscopy
Reexamination Certificate
active
06594019
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a data processor for a wavemeter which executes data processing to display optical frequencies/wavelengths of optical signals measured by the wavemeter and to a data processing method for the wavemeter.
2. Description of the Related Art
In recent years, a sudden increase in data communication demands has requested higher-capacity optical communications. In order to meet this request, the Wavelength Division Multiplexing (WDM) transmission technology has come into service and has been upgraded actively. Higher-performance wavemeters are in need in order to evaluate transmission systems and optical devices utilizing the WDM transmission technology.
In a conventional wavemeter used for evaluating transmission systems and optical devices utilizing the WDM transmission technology, a series of processing described below used to be repeated sequentially: digital interference signal data obtained via A/D sampling of interference signals input from an interferometer is temporarily stored in a buffer; the digital interference data stored in the buffer is read by the Digital Signal Processor (DSP) to convert the data to frequency data; and the frequency data is further converted to optical frequency data or optical wavelength data.
Some of the conventional wavemeters utilize the fast Fourier transform (FFT) processing when the DSP converts digital interference data to frequency data. In the FFT processing, chronological digital interference signal data is divided by predetermined period and output as frequency data.
However, as a feature of the FFT processing, discontinuous points present in chronological digital interference data cause frequency data to be displayed in the data obtained via FFT processing. To cope with this, a conventional FFT processing includes a process in which digital interference signal data prior to FFT processing is multiplied by a hamming windowing function coefficient for correcting discontinuous points.
However, for a conventional wavemeter used to evaluate transmission systems or optical devices utilizing the conventional WDM transmission technology, digital interference signal data was multiplied by the hamming windowing function coefficient for correcting data discontinuous points in order to prevent occurrence of data discontinuous points in the FFT-processed frequency data, prior to FFT processing in which the DSP converted digital interference signal data to frequency data.
Thus, the DSP perform operation processing in which digital interference signal data is multiplied by the hamming windowing function coefficient then the FFT processing in which the resulting data is converted to frequency data. This places a considerable processing load on the DSP and prolongs the processing time, thus presenting a problem that the processing time from the A/D sampling to completion of a series of data processing is prolonged.
The processing after the DSP does not execute its own data processing until the data processing in the preceding stage is complete. This also prolonged the processing time from the A/D sampling to output of data processing results.
SUMMARY OF THE INVENTION
An object of the invention is to provide a data processor for a wavemeter and a data processing method for the wavemeter, wherein the processing in which the DSP multiplies digital interference signal data by the hamming windowing function coefficient and the butterfly operation processing in the first stage are executed in parallel in order to reduce time required for a series of data processing concerning the wavemeter.
According to an aspect of the invention, there is provided a data processor for a wavemeter which processes interference signals of the optical signals in order to display optical frequencies/wavelengths of optical signals measured by the wavemeter, characterized in that the data processor comprises:
first data conversion means for converting the interference signals to digital interference signal data (for example, A/D sampler
3
in
FIG. 1
) and
second data conversion means for executing the fast Fourier transform processing including the hamming windowing function coefficient on digital interference signals converted by the first data conversion means to convert the digital interference signal data to frequency data (for example, DSP#A
5
in FIG.
2
).
According to the aspect of the invention, in a data processor for a wavemeter which executes data processing to display optical frequencies/wavelengths of optical signals measured by the wavemeter, the first data conversion means converts the interference signals to digital interference signal data and the second data conversion means executes the fast Fourier transform processing including the hamming windowing function coefficient on digital interference signals converted by the first data conversion means to convert the digital interference signal data to frequency data.
According to another aspect of the invention, there is provided a data processing method for a wavemeter which processes interference signals of the optical signals in order to display optical frequencies/wavelengths of optical signals measured by the wavemeter, characterized in that the data processing method comprises:
a first data conversion step for converting the interference signals to digital interference signal data and
a second data conversion step for executing the fast Fourier transform processing including the hamming windowing function coefficient on digital interference signals converted by the first data conversion step to convert the digital interference signal data to frequency data.
According to the another aspect of the invention, a data processing method for a wavemeter which executes data processing to display optical frequencies/wavelengths of optical signals measured by the wavemeter comprises:
a first data conversion step for converting the interference signals to digital interference signal data and a second data conversion step for executing the fast Fourier transform processing including the hamming windowing function coefficient on digital interference signals converted by the first data conversion step to convert the digital interference signal data to frequency data.
Thus, the processing in which digital interference signal data is multiplied by the hamming windowing function coefficient prior to fast Fourier transform processing can be omitted and the time required for a series of data processing concerning the wavemeter can be reduced, thus boosting the response time in displaying optical frequencies and optical wavelengths of optical signals.
In this case, according to the invention, a data processor for a wavemeter according to the first aspect of the invention, the second data conversion means may comprise storage means for storing the hamming windowing function coefficient.
According to the invention, the second data conversion means comprises storage means for storing the hamming windowing function coefficient.
In this case, according to the invention, a data processing method for a wavemeter according to the third aspect of the invention can be such that the second data conversion step stores the hamming windowing function coefficient in the storage means.
According to the invention, the second data conversion step stores the hamming windowing function coefficient in the storage means.
Thus, setting of an optimum fast Fourier transform processing depending on the characteristics of optical signals to be measured can be made with ease, thus facilitating change to specifications of the wavemeter.
REFERENCES:
patent: 5012815 (1991-05-01), Bennett, Jr. et al.
patent: 5627938 (1997-05-01), Johnston
patent: 5790250 (1998-08-01), Wang et al.
patent: 5890098 (1999-03-01), Kozaki et al.
Ichikawa Akio
Mogi Kenji
Ando Electric Co. Ltd.
Fish & Richardson P.C.
Kim Richard
Kim Robert H.
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