JPH03189524A - Light wavelength characteristic measuring device - Google Patents

Abstract

PURPOSE:To simplify a measuring operation by providing a filter where an output from a photodetector is taken as an input and a cut-off frequency is set much smaller than the fourfold frequency of the rotational frequency of a 1/2 wavelength plate to pass a low band. CONSTITUTION:The 1/2 wavelength plate 2 is arranged perpendicular to measuring light from an input terminal 1 and rotated at a constant speed by a motor 3. Next, the light transmitted through the wavelength plate 2 is received by a spectroscope 4, where the light is spectrally splitted to the respective wavelength components, and the lightn outputted from the spectroscope 4 is converted into an electrical signal in the photodetector 5. Since the cut-off frequency is set much smaller than the fourfold frequency of the rotational frequency of the wavelength plate 2 in the LPF 6, the output of the LPF 6 is proportioned to a value averaged over the 1/4 cycle of a rotational angle alpha. With such constitution, the measuring operation is simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical wavelength characteristic measuring device whose measurement level does not change even if the polarization state of light changes.

[Conventional technology] Next, the number of grooves in the optical wavelength characteristic measuring device according to the conventional technology is
This will be explained using figures.

! ! In Figure 2, 11 is the measurement light input terminal, 12 is the spectrometer,
13 is a spectroscopic element control section, 14 is a polarizing element, 15 and 16 are photodetectors, 17 is a power measurement section, and 18 is a display section.

The spectrometer 12 receives the measurement light from the input terminal 11 and spectrally spectra it, and the spectroscopic element control section 13 controls the spectrometer 12 .

Each wavelength component separated by the spectrometer 12 is separated into two P-polarized light components and an S-polarized light component in two mutually different directions by a polarizing element 14.

The photodetectors 15 and 16 receive the P-polarized light and the S-polarized light separated by the polarizing element 14, and convert them into electrical signals corresponding to each optical power.

The power measurement section 17 includes a characteristic storage section 17A, a power calculation section 17B, and an optical wavelength control section 17G.
7 receives electric signals from the photodetectors 15 and 16, and calculates the power of 1 (measured) based on the diffraction efficiency for each polarized light component of the spectrometer 12 and the loss rate of the polarizing element 14.

The apparatus shown in FIG. 2 can extract only a specific wavelength component from the measurement light using the spectrometer 12 and measure its power. Also, while sequentially changing the transmission wavelength of the spectrometer 12,
By measuring the power one after another, the wavelength versus level characteristic of the measurement 31G can be determined.

Further, according to the apparatus shown in FIG. 2, after separating the output of the spectrometer 12 into two polarized components in different directions, the power of each component is measured, and then the polarization of the spectrometer 12 that has been measured in advance is Since the characteristics are corrected by calculation, the power of the measurement light can be measured without being affected by the polarization state of the measurement light.

[Problem to be solved by the invention] A diffraction grating is often used for the spectrometer ↓2 in FIG.

Diffraction gratings have the characteristic that their diffraction efficiency varies depending on the polarization state of light. In other words, a polarized light component P that is incident parallel to the direction of the grooves of the diffraction grating, and a polarized light component S that is incident perpendicular to the direction of the grooves of the diffraction grating.
The diffraction efficiency is different between the two.

Next, the characteristics of the diffraction grating will be explained with reference to FIG.

The horizontal axis in FIG. 3 is wavelength, and the vertical axis is relative diffraction efficiency. The solid curve is data for P polarization, and the dotted curve is data for S polarization.
This is polarization data.

Since the diffraction grating has the characteristics as shown in FIG. 3, the following problems occur in the optical wavelength characteristic measuring device.

(a) The measured power value varies depending on the polarization state of the measurement light, so the absolute value cannot be determined.

(b) If the measurement light is composed of multiple light components with different wavelengths and polarization states, the level difference between each wavelength component cannot be measured accurately.

Therefore, in order to solve these problems, the measuring device shown in FIG. 2 is used.

However, even if the measuring device shown in FIG. 2 is used, there are the following problems.

(1) Since expensive polarizing elements and complicated control circuits are required, the device becomes complicated and expensive, and adjustment is difficult.

(1) Before using the device, check the efficiency characteristics for each wavelength for the '0 component (between each of the diffraction gratings and polarizing elements).
, 11 must be determined and stored in the storage section of the control circuit.

An object of the present invention is to provide an optical wavelength characteristic measuring device that does not change the measurement level even if the polarization state of measurement light changes and is easy to implement.

[Means for Solving the Problem] In order to achieve this object, the present invention includes a 1/2 wavelength plate 2 disposed perpendicular to the IC (measurement), and a 1/2 wavelength plate 2 that is rotated at a constant speed. Motor 3 and L/2 wavelength plate 2
a spectrometer 4 that receives the transmitted light and separates it into each wavelength component; a photodetector 5 that converts the output light of the spectrometer 4 into an electrical signal; is 1/2
The filter 6 is set to be sufficiently smaller than four times the rotation frequency of the wave plate 2, and is provided with a filter 6 that passes low frequencies.

Next, the configuration of the optical wavelength characteristic measuring device according to the present invention will be explained in the first part.
This will be explained using figures.

In FIG. 1, 1 is an input terminal, 2 is a half-wave plate, 3 is a motor, 11 is a spectrometer, 5 is a photodetector, 6 is a filter, and 7 is an output terminal.

The 1/2 wavelength beam 2 is arranged at right angles to the measurement light from the input terminal 1, and is rotated by a motor 3 at a constant speed.

The spectrometer 4 receives the light transmitted through the 1/2 wavelength plate 2 and separates it into each wavelength component, and the photodetector 5 converts the output light of the spectrometer 4 into an electrical signal.

The filter 6 is a low-pass filter, and the cutoff frequency of the filter 6 is set to be sufficiently smaller than four times the rotation frequency of the half-wave plate 2.

[Action Co. Next, the operation of FIG. 1 will be explained.

The direction of the grooves in the diffraction grating of the spectrometer 4 is taken as the y-axis, and the direction perpendicular to the grooves is taken as the y-axis, and the electric field strength of the polarized component P of the light to be measured is E.
yn, the electric field strength of the polarization component S is E,.

If so, E. . , E y Q can be expressed as follows.

E, IC,: E cos O°cosωtE,,,
)=Es1nO−cos (ωt+φ)・・・・・・
...(1) Here, E is the amplitude of the electric field of the light to be measured, 0 is the inclination of the vibration direction of the electric field (direction of the polarization plane) from the X axis, ω
is the angular frequency, is the time, and φ is the phase difference between E , , 0 and E yO.

Next, the inclination angle of the fast axis of the 1/2 wavelength plate 2 with respect to xlIII is set as α, and the direction of the fast axis of the 1/2 wavelength plate 2 is set as
The direction of the low speed axis is the B axis.

The high-speed axis refers to the one of the two mutually orthogonal main axes of the half-wave plate 2 that transmits light at high speed relative to the other axis, and the low-speed axis is This is the axis that transmits light at a low speed to other objects.

A-axis component EAo and B-axis component EB of light expressed by equation (1)
o becomes as follows.

EAO=CO3α°E:+l”+sinαI E
,,.

=E[cosα0CO8O'CO8ωt+5incz
+5inO1CO8(Ckl t+φ)]E[1,,=
-5incz 0E,, n+coscLIEyn=
E [-5inα°cosO°C05(11t+cos
α1sjnOゝCO8((L) t+φ)]・・・・・・
(2) In the 1/2 wavelength plate 2, the (+1 phase of the slow axis is slower than the fast axis by π, fL), so the A-axis component E2 of the light transmitted through the 1/2 wavelength plate 2 .1, ■33 components Etl, are as follows.

EA l : EA +, i = E[cos α′C05O6CO8ωt+5i11α′
5inO′C05(ωt+φ)koE[,l=E13
・,・ = E [sir+ct 0cos e 0CO8(1
1 to -CO8α I Si mouth O + CO8 (ω +
φ) ]・・・・・・・・・(3) Return equation (3) to the xy coordinate system. That is, the X-axis component E, 21 and the y-axis component E, , 1 of the light transmitted through the half-wave plate 2 are E, 1=cosaIL':A1-5incz°EB.

=E[cos2α′C05O°cosωt+5in2
a 0sin(7ICO5((1) t+φ)]E,,
1=sincz IEA, IC03(E 0E, 1=
IE [! ;in2αIC06OICO8ω-ku2()S2 α 9 sin 0 8 cos (ω
+ φ ) ]・・・・・・・・・(・1) Next, the transmitted light according to equation (11) passes through the spectrometer 4
Think about Karasu. If the transmittance for the P component (X-axis component) of z:'t 4 is KP, and the transmittance for the S component (X-axis component) is , then the transmittance through the spectrometer 4, '0
X-axis component E2.0, y-axis component E5. U is E, = 1 (
,,・E,I = □′l3[cos2α′C08O0CO5ωL+5
in2 α1sinOTeO2(CLJ t+φ)]E
2 = ・Ey.

= K, I E [5in2 a 9
cos O' C08CLI shi-cos2 a
'5in(10CO8(CLI t+φ)]...
(5) The light according to equation (5) is guided to the photodetector 5 and its power is measured. Therefore, as the permittivity ε, let P be the X-axis component of the average power of () in formula (5), and let the X-axis component be I)1, and find P and P7. (6) After the photodetector 5, there is a filter 6 whose cutoff frequency is seven times smaller than four times the rotation frequency of the half-wave plate 2, so the output of the filter 6 is expressed by the formula (%). 6) P, and P,
is proportional to the average value over 1/4 period of the rotation angle α. This is because both equations (6) are periodic functions of 4α.

Therefore, the output of the filter 6 becomes a voltage proportional to P determined by the following equation.

d Equation (7) is unrelated to O and φ, which represent the polarization state of the measurement light. That is, the measured power will not be affected by the polarization state of the light source.

Although a case has been described in which a diffraction grating is used in the spectrometer 4, something other than a diffraction grating may be used in the spectrometer 4.

In that case, the directions of the P component (y-axis) and the S component (X-axis) may be appropriately determined for the spectrometer 4.

[Effects of the Invention] According to the present invention, the optical wavelength characteristic measuring device is composed of a 1/2 wavelength plate rotating at a constant speed, a spectrometer, a photodetector, and a filter, so that a difficult 1 m distance is not required.

Furthermore, since there is no need to measure and store the polarization characteristics of a spectrometer, the measurement work becomes simpler.

Therefore, according to the present invention, it is possible to provide an optical wavelength characteristic measuring device in which the measurement level does not change even if the polarization state of the measurement light changes.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an optical wavelength characteristic measuring device according to the present invention.
Figure 2 is a configuration diagram of a conventional optical wavelength characteristic measuring device.
FIG. 3 is an explanatory diagram of the characteristics of the diffraction grating. 1...Measurement light input terminal, 2...1/
2 wavelength plate, 3...Motor, 4...Spectrometer, 5...Photodetector, 6...Filter, 7... Output terminal.

Claims (1)

[Claims] 1. Half-wave plate (2) arranged at right angles to the measurement light
and a motor (3) that rotates the 1/2 wavelength plate (2) at a constant speed.
), a spectrometer (4) that receives the light transmitted through the 1/2 wavelength plate (2) and separates it into each wavelength component, and a photodetector (4) that converts the output light of the spectrometer (4) into an electrical signal.
5), and the output of the photodetector (5) is input, and the cut-off frequency is 1/2.
An optical wavelength characteristic measuring device characterized by comprising a filter (6) which is set to be sufficiently smaller than four times the rotation frequency of the wavelength plate (2) and which passes a low frequency band.