JPH02262023A - Optical spectrum analyzer - Google Patents

Abstract

PURPOSE:To improve measuring accuracy of the intensity of light to a large extent in addition to accuracy in wavelength by adjusting the gain so that the intensity of light from a measuring photodetector which is changed to reference light agrees with the intensity of light from a calibrating photodetector. CONSTITUTION:The intensity of reference light (d) having a reference wavelength is detected with a calibrating photodetector 16. Then an optical switch 11 is switched, and the reference light (d) is split into a Fabry-Perot type spectroscope 1. The intensity of the split light is detected with a measuring photodetector 2. A gain-adjustment control means 15a which is provided in a data processing part 15 is adjusted so that the intensity of the light from the calibrating photodetector 16 agrees with the intensity of the split reference light (d). Thereafter, the optical switch 11 is switched so as to select light to be measured (a). The light to be measured is split in the Fabry-Perot type spectroscope 1. The light is converted into the optical intensity in the measuring photodetector 2. The gain is adjusted, and the intensity is automatically corrected to the correct optical intensity.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical spectrum analyzer using a Fabry-Perot type spectrometer, and in particular, the installation in a Fabry-Perot resonator is important because mechanical errors such as accuracy may affect measurement results. This invention relates to an optical spectrum analyzer that removes effects.

[Prior Art] A Fabry-Perot spectrometer incorporating a Fabry-Perot resonator is used as an optical spectrum analyzer to accurately determine the wavelength characteristics of light with a relatively narrow wavelength bandwidth, such as a laser beam used in optical communications. An optical spectrum analyzer using

Such an optical spectrum analyzer is configured as shown in FIG. 3, for example. Meanwhile, the constant light a of the subject 1111 manually applied from the outside is incident on the Fabry-Perot spectrometer 1. The Fabry-Perot spectrometer 1 separates the incident light a to be measured into light intensities (spectrums) at each wavelength λ. The light separated by the Fabry-Perot spectrometer 1 is converted into a light intensity signal by a measurement light receiver 2 formed of a photodiode or the like. The light intensity signal outputted from the M1 constant light receiving lid 2 is amplified by an amplifier 3, then converted to a digital value by an A/D converter 4, and inputted to a data processing section 5.

The data processing unit 5 is composed of a type of microcomputer, and edits the light intensity I (λ) at each wavelength λ inputted from the A/D converter 4 and sends it to the display 6.

The display 6 shows each input light intensity! (λ) is displayed with the wavelength λ on the horizontal axis.

Further, the data processing unit 5 sends a voltage signal C to the Fabry-Perot spectrometer 1 via the D/A converter 7 to control the al constant wavelength λ.

As is well known, the Fabry-Perot spectrometer 1 is shown in Fig. 4(a).
It has the following configuration. That is, in a Fabry-Perot resonator formed by a pair of parallel plates 8a and 8b with high reflectivity arranged opposite to each other, piezoelectric elements 9a are placed at multiple locations on the back surface of one parallel plate 8b.
, 9b are mounted on one side, and the other side of each piezoelectric element 9a, 9b is fixed to a frame (not shown). The other parallel plate 8a is also fixed to the frame. Then, each piezoelectric element 9a, 9b receives D/
A voltage signal C converted into a DC value by an A converter 7 is applied.

In the Fabry-Perot spectrometer 1 having such a configuration,
When light g enters the parallel plate 8a perpendicularly from the back surface of the parallel plate 8a, as shown in the figure, the light g is repeatedly reflected between the two parallel plates 8a and 8b, forming a kind of resonance state. be done. 1/2 of the wavelength λ of the incident light g is the parallel plate 8a.

8b, the incident light passes through the parallel plate 8b on the opposite side and is output. Therefore, if the interval is fixed and the wavelength λ of the input light is changed,
When the wavelength of the light output from the parallel plate 8b on the opposite side is analyzed, as shown in FIG.
A peak 10 occurs at each wavelength Δλ called S R (Free Spectral Range).

Therefore, the piezoelectric elements 9a, 9b illustrating the spacing
The resonant wavelength can be changed continuously by changing it by applying a voltage signal C to . In other words, it becomes a sweep type filter, and the position of the peak 10 changes. Therefore, when the wavelength range included in the light to be measured is limited to a range narrower than the FSR, the wavelength λ of the light output from the parallel plate 8b at the interval is uniquely determined.

Peak 10 in FIG. 4(b) has a very sharp peak waveform. Therefore, by controlling the voltage signal C applied from the data processing unit 5 to the Fabry-Perot spectrometer 1, it is possible to control the wavelength λ of the light output from the Fabry-Perot spectrometer 1 with very high precision. becomes.

[Problems to be Solved by the Invention] However, the optical spectrum analyzer shown in FIG. 3 still has the following problems.

That is, in this Fabry-Perot spectrometer 1, a desired wavelength resolution and a desired light intensity (spectrum) 4
In order to obtain a -1 constant volume, the pair of parallel plates 8a and 8b constituting the Fabry-Perot resonator shown in FIG. 4(a) require very high optical positioning accuracy. That is, when the incident light g enters the parallel plate 8a at a slight angle, when the parallelism of the parallel plates 8a and 8b decreases, or when the incident light g is not completely parallel, but has a spread. In this case, even if light having a beautiful wavelength characteristic as shown in FIG. 5(a) as shown in FIG. 5(b),(c),(d) depending on the incomplete positioning of the resonator.
The wavelength characteristics are significantly different from those of . Therefore, in this optical spectrum analyzer, the light intensity (
There was a problem in which the measurement accuracy of spectrum level) was significantly reduced.

However, as described above, the task of accurately optically positioning each of the parallel plates 8a and 8b within the Fabry-Perot spectrometer 1 is very complicated and requires a great deal of effort and time.

Further, even if the installation is performed with high accuracy, there is a problem that the installation position may become incorrect after long-term use, resulting in a decrease in the initial accuracy.

Furthermore, there is also a concern that the optical component may thermally expand due to temperature rise, resulting in a decrease in dimensional accuracy.

Therefore, the light intensity (spectrum level) at each wavelength
It has been difficult to maintain high measurement accuracy at all times.

The present invention was made in view of these circumstances, and
2 for proofreading! By comparing the state where the quasi-light passes through the Fabry-Perot spectrometer and the state where it does not pass, the actual A
By correcting the light intensity at each wavelength obtained at the same wavelength, it is possible to significantly improve the measurement accuracy of the light intensity at each wavelength in addition to the wavelength l1llJ constant accuracy, even without the need for complicated positioning adjustments of optical components. Our primary objective is to provide an optical spectrum analyzer that can always maintain high measurement accuracy.

[Means for solving the problem] In order to solve the above problems, the optical spectrum analyzer of the present invention includes a Fabry-Perot spectrometer using a Fabry-Perot resonator, and a 73) Switch the light incident on the J-travel receiver that detects the light intensity of the light, the calibration receiver that detects the light intensity of the reference light, and the Fabry-Perot spectrometer to either the reference light or the measured light. and a gain that adjusts the light intensity output from the measurement receiver when the light switch selects the reference light so that it matches the light intensity detected by the calibration receiver. The device is equipped with an adjustment control means and a display that displays the light intensity whose gain has been adjusted by the gain 2j adjustment control means.

[Function] In the optical spectrum analyzer configured in this way, the light intensity of the reference light having the reference wavelength, for example, is detected by the calibration light receiver. Next, the optical switch is switched and the reference light is separated into spectra using a Fabry-Perot spectrometer. Then, the light intensity at the separated reference wavelength is detected and read by a measuring light receiver. Here, since the reference light has only the wavelength component of the reference wavelength, the light intensity output from the calibration receiver matches the light intensity at the base wavelength spectrographed by an ideal Fabry-Perot spectrometer. It should be done. Therefore, the gain may be adjusted so that the light intensity detected by the calibration light receiver matches the light intensity of the separated reference light.

When the light to be measured is selected using the optical switch, the ΔP1 constant light is separated by the Fabry-Perot spectrometer, converted to light intensity by the measurement receiver, and gain adjusted to automatically produce the correct light intensity. is corrected accordingly.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

Figure 1 shows an outline of the optical spectrum analyzer of the present invention (1
FIG. 3 is a schematic diagram showing η formation. The same parts as in FIG. 3 are given the same reference numerals.

Measured light a input from the outside is input to the Fabry-Perot spectrometer 1 via the optical switch 11.

Reference numeral 12 in the figure is a reference light source 12 that outputs a reference light d having a reference wavelength λ0, which is composed of a DFB (distributed feedback) laser oscillator or the like, and the reference light d output from this reference light source 12 is connected to another optical switch. The optical switching device 1 via the device 13
1. The optical switch 11 switches and selects the light to be incident on the next Fabry-Perot bone optical device 1 between the constant light a and the reference light d.

The Fabry-Perot spectrometer 1 has a structure shown in FIG. The light separated by the Fabry-Perot spectrometer 1 is converted into a light intensity signal by the β1 constant light receiver 2 formed by a photodiode or the like. The output light intensity signal is gain adjusted by a gain adjuster 14, then converted to a digital light intensity value by an A/D converter 4, and inputted to a data processing unit 15 composed of, for example, a microcomputer. This data processing section 15 connects the Fabry-Perot spectrometer 1 to the D/A converter 7.
A voltage signal C that controls the measurement wavelength λ is sent out via the wavelength λ.

On the other hand, the reference light d output from the reference light source 12 is incident on the calibration light receiver 16 also formed by a photodiode via the optical switch 13, converted into a light intensity signal, and then amplified by the amplifier 17. The A/D converter 18 converts it into a digital light intensity value. The light intensity value Ao of this reference light d is input to the data processing section 15.

A display 6 made of, for example, a CRT display device or the like is connected to this data processing section 15 for displaying measurement results. The display 6 shows each corrected light intensity at each wavelength λ input from the data processing unit 15! (λ) is displayed with the wavelength λ on the horizontal axis.

Note that each of the optical switches 11 and 13 is switched and controlled by a switching operation by an operator in the data processing section 15. Further, the gain of the gain adjuster 14 is controlled by a control command from the data processing section 15 (gain adjustment control means 15a).
.

Next, the operating procedure of the optical spectrum analyzer configured as shown in FIG. 1 will be explained.

First, the reference light source 12 is driven to output the reference light d having the wavelength characteristics shown in FIG. 2(a), and the optical switch 13 is switched to the calibration light receiver 16 side. Then, the reference light d having only the reference wavelength λ0 is incident on the calibration light receiver 16. Then, the amplifier 17 outputs a light intensity signal e having the waveform shown in FIG. 2(b), and the A/D converter 18 outputs a light intensity signal e.
The optical intensity value AO corresponding to the signal level of
5. The data processing unit 15 stores the light intensity Ao corresponding to the reference light d.

Next, the optical switch 13 is switched to the Fabry-Perot spectrometer 1 side, and the optical switch 11 is switched to the reference light d side. Then, the reference light d outputted from the reference light source 12 and having only the reference wavelength λ0 and having the wavelength characteristics shown in FIG. . The Fabry-Perot spectrometer 1 separates the incident reference light d into wavelengths λ. The light separated by the Fabry-Perot spectrometer 1 is converted into a light intensity signal f by the measurement receiver 2, and then converted by the gain adjuster 14 into a light intensity signal f at the peak level A shown in FIG. 2(C). and input to the A/D converter 4. This A/D converter 4 converts the input optical intensity signal f into an A/D converter at a predetermined sampling period corresponding to each wavelength λ.
The data processing unit 1 converts the light intensity values at each wavelength λ.
Send to 5.

The data processing unit 15 reads the peak light intensity A corresponding to the reference wavelength λ0 from among the light intensity values at each input wavelength λ. Next, the data processing unit 15 compares the light intensity Ao of the previously stored reference light d that does not pass through the Fabry-Perot spectrometer 1 with the light intensity A read this time, so that the light intensity A is equal to the light intensity Ao. If not, the gain of the gain adjuster 14 is changed so that the light intensity A changes in a direction closer to the light intensity Ao. Then, the reference light d is spectrally measured again using the Fabry-Perot spectrometer 1, and the obtained light intensity value A is compared with the previous light intensity Ao. Then, ap1 determined light intensity A
When the light intensity matches the reference light intensity Ao, the gain adjuster 1
4 gain adjustment is completed.

Note that the gain adjustment process of the gain adjuster 14 is automatically performed according to a control program. Further, as described above, the reference light d has the reference wavelength λ. Therefore, the light intensity Ao outputted from the calibration light receiver 16 via the A/D converter 18 is equal to the wavelength component of the reference light d separated by the ideal Fabry-Perot spectrometer 1. It is assumed that the light intensity matches the light intensity A at the reference wavelength λ0.

When the gain adjustment of the gain adjuster 14 is completed, the reference light [
12 is cut off, and the optical switch 11 is switched to the constant light a side of 11#1.

This completes the adjustment operation of the Fabry-Perot spectrometer 1 in this optical spectrum analyzer.

When the adjustment operation is completed, it becomes possible to start the normal spectral +111 constant for the 11111 constant light a.

According to such an optical spectrum analyzer, before starting the actual spectroscopic measurement of the constant light a, the light intensity A of the reference light d that has passed through the Fabry-Perot spectrometer 1 is measured by the Fabry-Perot spectrometer 1. The gain of the gain adjuster 14 is adjusted to match the light intensity Ao, which is the base light intensity that does not pass through.

Therefore, each parallel plate 8a in the Fabry-Perot resonator constituting the Fabry-Perot spectrometer 1.

As long as the positional accuracy of the parallelism etc. of 8b is maintained above a certain level, the light intensity at each wavelength λ of the light to be measured a can be adjusted even if the positional accuracy is not strictly adjusted. (spectrum level) can be measured accurately.

In addition, since the adjustment work using the reference light d can be easily performed, if it is performed at regular intervals or every time a measurement is started, it is sufficient to prevent the measurement accuracy from decreasing due to changes in the optical spectrum analyzer over time or temperature changes. It becomes possible to deal with it. Therefore, the best measurement accuracy can always be maintained.

Although the case where the reference light d is used has been described above, the same n1 constant accuracy can be maintained even if the unmodulated measured light a is used instead of the reference light.

In addition, in the embodiment, the gain adjuster 14 was provided upstream of the A/D converter 4 to adjust the gain of the analog light intensity signal output from the n1 constant light receiver 2, but this gain adjustment After the light intensity signal is converted into a digital value by the A/D converter 4, the gain is adjusted by software in the data processing unit 15 according to a control program. It is also possible.

[Effects of the Invention] As explained above, the optical spectrum analyzer of the present invention is capable of measuring the respective light intensities in a state in which a reference light for calibration having a reference wavelength passes through a Fabry-Perot spectrometer and in a state in which it does not pass through the Fabry-Perot spectrometer. A gain adjuster inserted in the signal path of the measurement photodetector is adjusted so that the values match. Therefore, in addition to the wavelength measurement accuracy, the A of the light intensity at each wavelength is
It is also possible to greatly improve the accuracy of determining Δallj, and there is an advantage that a high accuracy of determining Δallj can always be maintained even without complicated positioning adjustments of optical components.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a schematic configuration of an optical spectrum analyzer according to an embodiment of the present invention, Fig. 2 is a waveform diagram for explaining the operation of the embodiment, and Fig. 3 is a diagram showing a conventional optical spectrum analyzer. The block diagram shown in FIG. 4 is a diagram for explaining the operation of a general Fabry-Perot spectrometer.
FIG. 5 is a waveform diagram for explaining the problems of the conventional optical spectrum analyzer. 1... Futebriperot spectrometer, 2... i'lPj
Light receiver/indicator for regular light receiver, 11... Optical switch, 1
2... Reference light source, 14... Gain adjuster, 15...
- Data processing section, 16... Calibration light receiver. Applicant's agent Patent attorney Takehiko Suzue (a) (b) (c) (d) Figure 5

Claims (1)

[Claims] A Fabry-Perot spectrometer (1) using a Fabry-Perot resonator, a measurement receiver (2) that detects the light intensity of the light separated by the Fabry-Perot spectrometer, and a measurement receiver (2) that detects the light intensity of the reference light. an optical receiver (16) for switching between the reference light and the measured light the light incident on the Fabry-Perot spectrometer; gain adjustment control means (15a) for adjusting the gain so that the light intensity output from the measurement light receiver matches the light intensity detected by the calibration light receiver when switching is selected; and the gain adjustment control means An optical spectrum analyzer comprising: a display (6) for displaying the light intensity whose gain has been adjusted by the means;