JPH08285690A - Depolarization device and light power measuring device using the depolarization device - Google Patents

Abstract

PURPOSE: To prevent a depolarization device from being influenced by an unknown polarization condition of incident light rays by providing it with a means by which the light to be measured is made to parallel rays and are separated into orthogonal linear polarization components and emitted, a means by which received orthogonal linear polarization components are exchanged into circular polarization, and a light receiving element for photoelectrically converting the circular polarization beams. CONSTITUTION: The light 81 to be measured that has been emitted from a light connector 80 is made parallel rays by a collimate lens 14, and they are made incident on a polarization beam spitter 16. The rays of p-wave component 17p straightforwardly transmitted through the beam splitter 16 are incident on one surface of a 1/4 wavelength plate 20. On the other hand, the rays of s-wave component 17s reflected by 90deg are reflected at right angles by a prism 18, and are also incident on one surface of the wavelength plate 20. Since the wavelength plate 20 is installed in such an optical arrangement that the direction of the optical axis of the crystal thereof makes 45deg to the p-wave component 17p and s-wave component 17s, both the linear polarized rays of the p-wave component 17pa and s-wave component 17s are together converted into circularly polarized rays and emitted. An condenser lens 22 converges the circularly polarized beams from the wavelength plate 20 on the light- receiving surface of a light-receiving element 50.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for photoelectrically converting absolute optical power without being affected by the unknown polarization state of incident light.

[0002]

2. Description of the Related Art FIG. 3 shows an example of the configuration of a conventional optical power measuring device. The measured light source 100 is a light source with an unknown polarization state. The configuration is the optical connector 80 and the optical fiber 35.
And the light receiving element 50 and the amplification display section 70. The amplification display unit 70 includes an IV converter 71, an amplifier 72, an AD converter 74, an optical power calculation unit 76, and a display unit 78.

The light source 100 to be measured is connected to an optical connector 80, emitted from the open end face of an optical fiber 35 as spatial light, and gives an incident light beam 30 having a certain incident angle θ to a light receiving element (photodiode) 50. , Is converted into a current signal proportional to the incident power and output.

In the light receiving element 50, the photoelectric conversion efficiency generally varies depending on the polarization state of the incident light (non-polarized light, random polarized light, linearly polarized light, circularly polarized light) depending on the crystal plane direction. This deviation may cause a deviation of about several percent depending on the element used. Therefore, the absolute optical power of the measured light source 100 may not be accurately measured.

Upon receiving a weak current signal from the light receiving element 50, the IV converter 71 of the amplification display unit 70 converts the current input into a voltage signal, the amplifier 72 amplifies the voltage signal, and the AD converter 7
After being quantized into a digital signal by 4, the optical power calculation unit 76
After being converted into optical power by, the display unit 78 digitally displays the optical power level.

[0006]

As described above, there is a difference in photoelectric conversion efficiency depending on the polarization state of the light beam incident on the light receiving element 50. This is not preferable in a measuring instrument which should measure the absolute optical power of the measured light source 100 accurately, which is a difficulty in measurement. Therefore, an object of the present invention is to realize a photoelectric conversion device that is not affected by the unknown polarization state of incident light.

[0007]

In order to solve the above-mentioned problems, in the structure of the present invention, the light 81 to be measured is received, converted into parallel rays, and then converted into orthogonal linearly polarized (P-wave, S-wave) components. A configuration is provided in which a means for separating and outputting is provided, a means for receiving the two orthogonal linearly polarized light beams and converting both light beams into circularly polarized light, and a light receiving element 50 for receiving the two circularly polarized light beams and performing photoelectric conversion are provided. Use it as a means. This makes it possible to realize a photoelectric conversion device that is not affected by the unknown polarization state of the incident light beam when converting the optical power of the unknown polarization state into an electric signal.

FIG. 1 shows the configuration of the first solving means according to the present invention. In the present invention, the collimating means 14 for converting the light to be measured 81 into parallel rays is provided, and the polarization beam splitter 16 for receiving the parallel rays and separating and emitting the orthogonal linearly polarized light (P wave, S wave) components is provided. Is provided with a quarter-wave plate 20 that receives linearly polarized light rays orthogonal to each other and has an optical arrangement in which both light rays are 45 degrees with respect to the optical axis direction (reference axis) of the crystal, and converts both light rays into circularly polarized light. A component means for receiving the two circularly polarized beams and condensing them on the light receiving surface of the light receiving element 50 (condensing lens 22) is provided.

FIG. 2 shows the configuration of the second solving means according to the present invention. In the present invention, the collimating means 14 for converting the light to be measured 81 into parallel rays is provided, receives the parallel rays, and branches into an ordinary ray that advances straight along the incident optical axis and an extraordinary ray parallel to the incident optical axis, and A beam dissipating prism 24 for emitting parallel light beams of linearly polarized light components 25p and 25s orthogonal to each other is provided to receive the linearly polarized light beams orthogonal to each other and the optical axis direction of the crystal (reference axis).
On the other hand, the optical arrangement is such that both light rays are 45 degrees, and a quarter wave plate 20 for converting both light rays into circularly polarized light is provided as a constituent means.

In addition to the above configuration, there is a configuration in which an optical power measuring device is provided with an amplification display section 70 which receives a current signal from the light receiving element 50, amplifies it, converts it into an optical power level and displays it. The amplification display unit 70 has a configuration in which a current signal from the light receiving element 50 is received, the IV converter 71 converts the current input into a voltage signal, the amplifier 72 amplifies the voltage signal, and the AD converter 74 a digital signal. There is a realization means for digitally displaying the level of the optical power on the display unit 78 after it is quantized into the optical power and converted to the optical power by the optical power calculation unit 76.

[0011]

The collimating lens 14 has the function of making the light 81 to be measured into parallel rays, which allows the polarization beam splitter 16 to separate the light into orthogonal polarization components. Example 1
The polarization beam splitter 16 has a function of receiving parallel rays of an unknown polarization state and separating and outputting them into orthogonal linearly polarized light components (P wave, S wave). The beam dissipating prism 24 of the second embodiment splits and outputs an ordinary ray that goes straight on the incident optical axis and an extraordinary ray that is parallel to the incident optical axis as parallel rays of linear polarization components 25p and 25s that are orthogonal to each other. It has an effect.

The quarter-wave plate 20 receives two linearly polarized light rays that are orthogonal to each other, and gives an optical arrangement in which both light rays have an optical axis direction (reference axis) of 45 degrees so that both light rays are circular. It has the effect of converting to polarized light and outputting. Condensing lens 22
Has a role of condensing two circularly polarized beams so that one light receiving element 50 receives the light.

[0013]

【Example】

(Embodiment 1) In the first embodiment of the present invention, a light beam of unknown polarization state is separated into orthogonal polarization components (P wave, S wave) using a polarization beam splitter, and each is converted into circular polarization. It is a constituent means for eliminating the polarization dependency by photoelectrically converting the light rays that are collected later.

An example of the configuration of the optical power measuring device is, as shown in FIG. 1, an optical connector 80 and a collimating lens 14.
, Polarization beam splitter 16, prism 18, and 1
/ 4 wavelength plate 20, condenser lens 22, and light receiving element 50
And an amplification display unit 70. The optical connector 80, the light receiving element 50, and the amplification display unit 70 are the same as those in the related art.

The collimator lens 14 has an optical connector 80.
The light 81 to be measured emitted from is converted into parallel rays, which are then incident on the polarization beam splitter 16.

Polarizing beamsplitters
The prism 16 is composed of a pair of right-angled prisms attached to each other.
It is an optical element that is branched into two linearly polarized light components (P wave, S wave). A dielectric multilayer coating layer having a thickness of several wavelengths is formed on the inclined surface of this prism so as to have a polarization effect. For this reason, the measurement wavelength λ range is applicable only in a finite narrow wavelength range. The light beam of the P wave component 17p that has passed through this straight line enters one surface of the quarter wavelength plate 20. On the other hand, the light beam of the S wave component 17s reflected at 90 degrees is reflected at a right angle by the prism 18 and is incident on one surface of the quarter wavelength plate 20 in the same manner.

The quarter-wave plate 20 is for converting linearly polarized light into circularly polarized light, and has two orthogonal P-wave components 17p.
Alternatively, with respect to the S wave component 17s, the optical axis direction (reference axis) of the crystal is set in an optical arrangement in which both light beams are 45 degrees.
As a result, both the linearly polarized light of the P wave component 17p and the linearly polarized light of the S wave component 17s are both converted into circularly polarized light and emitted.

The condenser lens 22 is the quarter wavelength plate 20.
The two circularly polarized light beams from are focused on the light receiving surface of the light receiving element 50. Here, since both light rays have the same circular polarization, the photoelectric conversion efficiency in the light receiving element 50 is always constant, and it is possible to detect the optical power that is not affected by the polarization state.

After that, the light receiving element 50 is processed in the same manner as in the conventional case.
The IV converter 7 receives the weak current signal photoelectrically converted by
The current input is converted into a voltage signal by 1, amplified by the amplifier 72, quantized into a digital signal by the AD converter 74, converted into optical power by the optical power calculation unit 76, and then displayed by the display unit 78. Is displayed digitally.

(Embodiment 2) In the second embodiment of the present invention,
A beam dissipating prism is used to separate a ray of unknown polarization state into two components, an ordinary ray and an extraordinary ray, which are orthogonal to each other. This is a means for eliminating the polarization dependence.

An example of the configuration of the optical power measuring device is, as shown in FIG. 2, an optical connector 80 and a collimating lens 14.
And the beam displaying prism 24, 1 /
The four-wave plate 20, the light receiving element 50, and the amplification display section 70 are included. The optical connector 80, the collimator lens 14, the quarter wavelength plate 20, the light receiving element 50, and the amplification display unit 70 are the same as those in the first embodiment.
Is the same as

Beam Displaying Prism (be
am displacing prism) 24 is a polarizer utilizing the birefringence characteristic of calcite that splits and outputs incident light into two parallel linearly polarized light components (P wave, S wave) whose polarization planes are orthogonal to each other. An ordinary ray that travels straight along the optical axis and an extraordinary ray that is parallel to the incident optical axis are branched and emitted as orthogonal linearly polarized light components. The separation distance between the two beams is, for example, 2.7 mm. Since it is a birefringent element, it can be used in a wide wavelength range. This receives parallel rays from the collimator lens 14 and splits and emits them into two parallel linearly polarized light components 25p and 25s which are orthogonal to each other.

The ¼ wavelength plate 20 receives the two parallel rays and converts the linearly polarized light into circularly polarized light in the same manner as in the first embodiment and outputs the circularly polarized light.

The light-receiving element 50 has a light-receiving surface (for example, 3) that can receive both parallel rays from the quarter-wave plate 20.
Photoelectric conversion is performed by one light receiving element 50 using a light receiving element having a light receiving surface of mm or more). This eliminates the need for light collecting means. Of course, a configuration in which a condenser lens is inserted as in the first embodiment may be adopted. Since both light rays photoelectrically converted by the light receiving element 50 are the same circularly polarized light, the photoelectric conversion efficiency of the light receiving element is always constant and is not affected by the polarization state.

After that, in the same manner as the conventional one, the light receiving element 50
The IV converter 7 receives the weak current signal photoelectrically converted by
The current input is converted into a voltage signal by 1, amplified by the amplifier 72, quantized into a digital signal by the AD converter 74, converted into optical power by the optical power calculation unit 76, and then displayed by the display unit 78. Is displayed digitally.

In the above description of the first embodiment, the case where the prism 18 is used for 90-degree reflection has been described, but a reflector such as a mirror may be used instead, and the same operation can be performed.

[0027]

Since the present invention is configured as described above, it has the following effects. The collimator lens 14 has an effect of converting the measured light 81 into parallel rays and allowing polarization separation by the polarization beam splitter 16. The polarization beam splitter 16 of the first embodiment has an effect of receiving parallel rays of an unknown polarization state and separating and outputting the parallel linearly polarized light components (P wave, S wave). The beam dissipating prism 24 according to the second embodiment has linear polarization components 25p and 25s in which an ordinary ray that goes straight on the incident optical axis and an extraordinary ray that is parallel to the incident optical axis are orthogonal to each other.
The effect of branching out as parallel rays of

The quarter-wave plate 20 receives two orthogonal linearly polarized light rays and arranges them so that the optical axis direction (reference axis) of the crystal is 45 degrees for both light rays. It has the effect of converting to polarized light and outputting. The condenser lens 22 is
By condensing the two circularly polarized beams, one light receiving element 50 can receive light.

[Brief description of drawings]

FIG. 1 is a configuration example of an optical power measuring device according to a first embodiment of the present invention.

FIG. 2 is a configuration example of an optical power measuring device according to a second embodiment of the present invention.

FIG. 3 is a configuration example of a conventional optical power measuring device.

Claims (5)

[Claims] 1. A light receiving device for converting an optical power of an unknown polarization state into an electric signal, further comprising means for receiving a light to be measured, converting the light into parallel rays, and separating and emitting the linearly polarized light components orthogonal to each other. A means for receiving two linearly polarized light beams orthogonal to each other and converting the two light beams into circularly polarized light; and a light receiving element for receiving the two circularly polarized light beams and performing photoelectric conversion. Depolarizer. 2. A light receiving device for converting an optical power of an unknown polarization state into an electric signal, further comprising collimating means for converting the light under measurement into parallel light rays, receiving the parallel light rays, and separating and emitting the linearly polarized light components orthogonal to each other. A quarter-wavelength which is provided with a polarization beam splitter for receiving the above-mentioned orthogonal linearly polarized light rays and has an optical arrangement in which both light rays are 45 degrees with respect to the optical axis direction of the crystal, and converts both light rays into circularly polarized light. A depolarizing device comprising: a plate; and a condensing unit that receives the two circularly polarized beams and condenses them on a light receiving surface of a light receiving element. 3. A light receiving device for converting an optical power of an unknown polarization state into an electric signal, wherein collimating means for converting the light under measurement into parallel light rays is provided, and the parallel light rays are received and the incident optical axis is moved straight. A beam dissipating prism that splits a light ray and an extraordinary ray parallel to the incident optical axis and emits it as a parallel ray of linearly polarized light components orthogonal to each other is provided. An optical depolarizer having the optical arrangement in which both rays are 45 degrees with respect to the axial direction, a quarter-wave plate for converting both rays into circularly polarized light, and having the above. 4. In addition to the structure according to claims 1, 2, and 3,
An optical power measuring device provided with an amplification display section (70) which receives a current signal from a light receiving element, amplifies it, converts it into an optical power level, and displays it. 5. The amplification display section (70) receives the current signal from the light receiving element, converts the current input into a voltage signal with an IV converter, amplifies it with an amplifier, and quantizes it into a digital signal with an AD converter. 5. The optical power measuring device according to claim 4, further comprising means for digitally displaying the level of the optical power on the display unit after converting the optical power to the optical power by the optical power calculation unit.