JPH0517627Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The invention relates to an optical signal detection device that detects an optical signal from an optical sensor that modulates the intensity of the measurement signal, and is intended to improve measurement accuracy. .

<Prior Art> As a means for measuring optical signals, a device as shown in FIG. 6, for example, is known. In FIG. 6, 10 is a photodiode that converts an optical signal into an electrical signal depending on the intensity of the light. The electric signal from this photodiode is amplified by an amplifier 12 and detected.

<Problems to be Solved by the Invention> In the photodetecting device as described above, as shown in FIG. 7, in the output of the amplifier 12, the fluctuating component to be measured appears above the fixed component. The amplifier is used under conditions such that it does not saturate even at the maximum light intensity, but if the variable component is small compared to the fixed component, the variable component may be buried in noise. When extracting only the variable component while suppressing the output of the fixed component, it is impossible to extract only the variable component with such a circuit because the photodiode outputs a current proportional to the light intensity.

The present invention was developed in view of the problems of the prior art described above, and aims to extract the variable component without being buried in noise by reducing the fixed component in the intensity-modulated light.

<Means for solving the problems> The structure of the present invention to solve the above problems is as follows.
A reference light source, a light branching device that branches light emitted from the reference light source into two directions, and one of the lights branched by the light branching device is incident and the light intensity changes in accordance with a change in a physical quantity. and a sensor that emits light having a fixed component; a phase intensity adjustment device that receives the other branched light and outputs light that has changed the phase and intensity of the incident light; and the phase intensity adjustment device. an optical coupling device that receives each output light from the sensor, combines these lights, and outputs light corresponding to a change in the physical quantity;
a photodetector that inputs light emitted from the optical coupling device and converts it into an electrical signal, and the phase intensity adjustment device is configured such that the phase of the light emitted from the phase intensity adjustment device is equal to that of the light emitted from the sensor. By adjusting the phase so that the phase is inverted in the optical coupling device with respect to the phase, and adjusting the light intensity so that the light intensity matches the light intensity of the fixed component, the optical coupling device It is characterized by emitting light whose fixed component is canceled out.

<Example> Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 1 shows the optical signal detection device of the present invention, where 1 is a reference light source that linearly polarizes laser light, and 2 is an optical branching device that branches light from the reference light source, such as a half mirror. . Reference numeral 3 denotes a sensor having a fixed component configured so that the light intensity changes in response to changes in physical quantities, and is configured as shown in FIG. 2, for example. In FIG. 2, 20 is a Si substrate, 21 is an optical waveguide made of SiO ₂ etc. formed on this substrate, and a notch 22 is provided in the middle of this optical waveguide, and the groove is cut into the groove by, for example, pressure. A shield 23 that moves in the direction is arranged. According to such a configuration, the intensity of the output light of the light from the reference light source that is incident on one end of the optical waveguide 21 changes due to the shielding body that moves according to the pressure.

Returning to FIG. 1, reference numeral 4 denotes a phase intensity adjustment device, which is configured as shown in FIG. 3, for example. In FIG. 3, 30 is a transparent substrate such as PLZT, and by providing transparent electrodes 31 on both sides of this substrate and applying an appropriate voltage from a power source 32, the phase of light passing through this substrate can be reversed. I can do it. 33 is, for example, an ND filter that can continuously attenuate the light intensity by rotating in the direction of the arrow. Although not shown in the figure, a known photodetection element for converting light into an electrical signal is provided downstream of the optical coupling device 5, and the electrical signal is configured to be monitored by, for example, an oscilloscope during the adjustment stage of the device. shall be taken as a thing.

FIG. 4 schematically shows the relationship between light intensity and time in the optical coupling device 5 shown in FIG. In the waveform, H is a fixed component and is the output level when the light intensity from the sensor reaches the minimum intensity. In addition, the dotted line B indicates the phase intensity adjustment device 4 necessary to cancel the fixed component H.
The fixed component H can be canceled out by shifting the waveform shown by the dotted line and superimposing it on the waveform A shown by the solid line to invert the phase. C is the envelope of A, and shows a state including a fixed component H.

Next, a method of adjusting the phase intensity adjusting device for canceling the fixed component will be explained. Note that it is assumed here that the light from the optical branching device is accurately split in half, and that there is no loss of light no matter which path it takes.

In the configuration shown in FIG. 1, when detecting an optical signal, the phase is first adjusted. Prior to adjustment, the ND is set so that the light emitted from the phase intensity adjustment device 4 among the lights branched by the optical branching device 2 is minimized (zero).
Keep the filter 33 rotating.

Next, the shield 23 is removed from the optical waveguide, and the light from the sensor 3 with the maximum light intensity enters the optical coupler 5.

When the optical signal from the optical coupler 5 is converted into an electrical signal by a known photodetector and inputted into an oscilloscope, an output at a certain level can be observed.

Next, the ND filter 33 of the phase intensity adjustment device 4
When rotated to maximize the output, if the phase is 180° out of phase with the light from the sensor, the output signal of the optical coupler 5 will be the minimum, and the output level of the oscilloscope will be the minimum.

Furthermore, when the phase matches the phase of the light from the sensor, the output signal of the optical coupler 5 becomes maximum and the output level of the oscilloscope also becomes maximum.

However, in reality, such coincidences are rare, so the output level of the oscilloscope is between the minimum and maximum levels.

When a voltage is applied to the transparent electrode to rotate the phase, the output of the oscilloscope increases or decreases, but the point at which the output reaches its minimum level is when the phases of the lights have rotated 180 degrees.

Next, adjust the strength.

The voltage applied to the transparent electrode is maintained at the voltage at the time when it reaches the minimum level, the shield 23 is inserted into the optical waveguide, and the light from the sensor 3 with the light intensity minimized enters the optical coupler 5. do.

Then, when the ND filter 33 is rotated in the direction of decreasing the light intensity and the output level of the oscilloscope reaches the minimum, the light intensity of the fixed component of the sensor and the light intensity from the ND filter 33 match, and in this state The fixed components of the sensor are canceled out.

When using the device, the voltage at which the level becomes the minimum is applied to the transparent electrode of the phase intensity adjustment device 4, and the rotation angle of the ND filter 33 is adjusted to match the rotation angle at that time.

FIG. 5 shows the output of the optical coupling device, and shows a state in which the fixed component shown in FIG. 4 is canceled out by the output from the phase intensity conversion device.

Here, the electric field strength E of light passing through the sensor can be expressed by the following equation.

E={A+B(t)}e ^-jwt ... A: Electric field strength (fixed component) when the light intensity is lowest B(t): Electric field strength component that varies with time ω: Angular frequency of light t: Time , the electric field strength E' of the light passing through the phase intensity adjustment device 4 can be expressed by the following equation.

E′=Ae ^-j(wt- 〓 ⁾ ...The light intensity I′ when the lights expressed above are interfered with is I′=|E+E′| ² |{A+B(t)}e ^-jwt +Ae ^{- j(wt-} 〓 ⁾ | ² = |B(t)e ^-jwt | ² = {B(t)} ² .... The light intensity after interference consists of only components that change over time, and components that do not change can be removed.

Note that the intensity I of light passing through the sensor can be expressed by the following equation.

I = | E | ² = A ² + 2A・B(t) + {B(t)} ² ... In the formula, A ² is a fixed component, and the light intensity component that changes over time is 2A・B(t) +{B
(t)} ² . Also, since the light intensity component after interference is {B(t)} ² as shown in the formula, there is no proportional relationship between these components, so the waveform will be distorted, but a correction circuit should be provided at the subsequent stage. It can be corrected by

In addition, in this example, a guided light blocking type is used as the sensor, and PLZT is used as the phase intensity modulation device.
I explained an example of combining an ND filter, but
Various methods can be used without being limited to this example.

<Effects of the invention> As described above in detail with the embodiments, according to the invention, by reducing the fixed component of the intensity-modulated light, the variable component can be detected without being buried in noise. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram showing one embodiment of the optical signal detection device of the present invention, FIG. 2 is an explanatory diagram showing an example of a sensor, FIG. 3 is an explanatory diagram showing an example of a phase intensity modulation device, and FIG. Figure 5 shows the light receiving state of the optical coupling device, Figure 5 shows the output from the optical coupling device, Figure 6 is an explanatory diagram showing a conventional optical detection device, and Figure 7 shows a conventional optical signal detection device. It is a figure which shows the output state of. 1... Reference light source, 2... Optical branching device, 3... Sensor, 4... Phase intensity adjustment device, 5... Optical coupling device.

Claims (1)

[Scope of utility model registration request] A reference light source, a light branching device that branches light emitted from the reference light source into two directions, and one of the lights branched by the light branching device is incident and the light intensity changes in accordance with a change in a physical quantity. and a sensor that emits light having a fixed component; a phase intensity adjustment device that receives the other branched light and outputs light that has changed the phase and intensity of the incident light; and the phase intensity adjustment device. an optical coupling device that receives each output light from the sensor, combines these lights, and outputs light corresponding to a change in the physical quantity;
a photodetector that inputs light emitted from the optical coupling device and converts it into an electrical signal, and the phase intensity adjustment device is configured such that the phase of the light emitted from the phase intensity adjustment device is equal to that of the light emitted from the sensor. By adjusting the phase so that the phase is inverted in the optical coupling device with respect to the phase, and adjusting the light intensity so that the light intensity matches the light intensity of the fixed component, the optical coupling device An optical signal detection device characterized by emitting light with a fixed component canceled out.