JPH0498147A - Double refraction measuring device - Google Patents

Abstract

PURPOSE:To eliminate need for a mechanism, for mechanically and accurately moving a phase compensating plate, by using a method in which a phase difference between pieces of polarization, transmitted a double refractional specimen and mutually orthogonal is measured, and the phase difference is electrically canceled with a phase shifter using an electro-optic effect. CONSTITUTION:Incident light from a semiconductor laser 1 to a light wave-guide passage 4 is made e.g. a TE mode. Applied voltage to the electrodes of a mode converter 3 and a phase shifter 5 is adjusted with a polarization control means in a base 2 so that a laser beam 7 incident to a specimen 8 can be made circularly polarized light. A phase difference between TE and TM modes produced by the double refraction of the specimen 8 is adjusted so that output current from a photodiode 16 can be made zero. The adjustment is made by making feedback to each applied voltage of the phase shifter 5 or a phase shifter 11. Because the relation between applied voltage to the phase shifter and a phase shift quantity is known, reversely a phase difference produced with the specimen 8, that is a double refraction quantity, can be learnt from the value of the applied voltage of the phase shifter as a result of adjusting so as to make output current from the diode 16 zero.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to measuring the birefringence or film thickness of a transparent material.
This invention relates to a birefringence measuring device.

[Conventional technology]

A conventional device of this type had the following configuration.

A polarizer is placed in front of the sample, and an analyzer is placed after the sample, and measurements are performed in a so-called cross-direction state in which the polarization directions of the polarizer and analyzer are perpendicular to each other. If the sample has birefringence or no birefringence, the amount of light that passes through the analyzer is zero, but if the sample has birefringence, the light after passing through the sample is generally elliptically polarized, so some of the light is Transmit through the analyzer. To measure the birefringence, a Babinet-Soleil plate (Babjnet-3oleil com
For example, when the phase compensation plate is placed between the sample and the polarizer, it is set at an angle of 45° with the direction of polarization of the polarizer. Then, the phase compensation plate is adjusted so that the amount of light transmitted through the analyzer is zero in order to cancel the phase difference generated in the sample.

Then, by reading the amount of movement of the phase compensation plate, the phase difference due to birefringence generated in the sample can be determined.

[Invention or problem to be solved]

However, in the above technique, a phase compensation plate such as a Babinet Soleil plate is used, and the phase compensation plate requires a mechanism to precisely adjust it mechanically, so the configuration of the measuring device is complicated. The entire device is expensive, and mechanical adjustment requires time, which increases the measurement time.

The present invention was made in view of these problems, and since the device corresponding to the phase compensation plate does not have a mechanical adjustment mechanism,
It is an object of the present invention to provide a new birefringence measurement device that has a simple configuration, can be manufactured at low cost as a whole, and can significantly shorten measurement time.

[Means to solve problems]

For the above purpose, the present invention includes a first substrate including a waveguide instead of a polarizer and a polarization control means for controlling the polarization state of guided light using an electro-optic effect, and an optical waveguide and a guided light instead of an analyzer. A second substrate including a polarization control means for controlling the polarization state of the light using an electro-optic effect and a polarization separation means for separating different polarized lights, and a laser beam 7 emitted from the first optical waveguide 4 is projected onto a sample 8. and a light projecting means 6 for transmitting the laser beam 7 that has passed through the sample to the second optical waveguide 1.
The birefringence of the sample is measured by a birefringence measuring device characterized by comprising a focusing means 9 for focusing the light onto the incident end face of the sample.

[Effect]

In the present invention, the phase difference between mutually orthogonal polarized lights transmitted through a sample having birefringence is reduced by using a polarization control means using an electro-optic effect and a phase softer included in the first substrate and the second substrate. Since it is electrically canceled, there is no need for a mechanism for precisely moving the phase compensation plate mechanically as in the past. [Embodiment] Figure 1 shows the first embodiment of the present invention. 4 and 12 are a first substrate and a second substrate respectively made of dielectric crystals having an electro-optic effect such as lithium niobate (L+Nb0s) or lithium tantalate (LiTa03), and 4 and 12 are made of known methods such as impurity diffusion or ion exchange a first optical waveguide and a second optical waveguide, respectively formed by the method;
3 and I3 are a first mode converter and a second mode converter using an electro-optic effect, respectively, and 5 and 11 are a first phase shifter and a second phase shifter using an electro-optic effect, respectively.

The combination of the first mode converter 3 and the first phase shifter 5 is the polarization control means in the first substrate 2, and the combination of the second phase shifter 11 and the second mode converter 13 is the polarization control means in the second substrate 10. This is polarization control means. The hatched portions of each of the first mode converter 3, first phase shifter 5, second phase softer 11, and second mode converter 13 indicate electrodes. Various configurations are known for this electrode configuration depending on the substrate orientation or the propagation direction of light, and an example of X-cut Y propagation is shown here. By adjusting the voltage applied to each electrode of the polarization control means on the first substrate 2, the polarization state of the light emitted from the first optical waveguide 4 can be arbitrarily adjusted. Similarly, the second board IO
By adjusting the voltage applied to each electrode of the polarization control means in , the polarization state of the light incident on the second optical waveguide 12 from the focusing means 9 can be arbitrarily adjusted. The respective drive circuit portions of the first mode converter 3, first phase shifter 5, second phase shifter 11, and second motor converter 13 are omitted. 14 are different polarized lights (T
This is a mode splitter for separating IE mote and TM mote, and is composed of a double mote area and a Y branch 15. 1 is a semiconductor laser.

Of course, not only semiconductor lasers but also gas lasers are very good.
Semiconductor laser is preferred. Reference numerals 16 and 17 are a first photodiode and a second photodiode for detecting the intensity of guided light, respectively. Of course, as long as the photodetector is for detecting the intensity of light, a photodetector tube such as a multiplier or the like may be used, but it is preferable to use a photodiode. Reference numeral 6 denotes a light projecting means for projecting the laser light 7 emitted from the first optical waveguide 4 onto the sample 8. For example, a selfoc lens manufactured by Nippon Sheet Glass Co., Ltd. is used to create the parallel light beam 7. It will be done. 9 is a second laser beam 7 that has passed through the sample.
As a focusing means for focusing the light onto the incident end face of the optical waveguide 12, the above-mentioned Selfoc lens or the like is used.

The principle of birefringence measurement according to the present invention will be explained using FIG. The incident light from the semiconductor laser I to the first optical waveguide 4 is assumed to be in TE mode, for example. The polarization control means in the first substrate 2 includes, for example, applying voltages to the respective electrodes of the first mode converter 3 and the first phase shifter 5 so that the laser beam 7 incident on the sample 8 becomes circularly polarized light. is adjusted. The polarization control means in the second substrate IO includes, for example, a second phase shifter 11 so that when circularly polarized light is incident on the second optical waveguide 12, the light incident on the mode splitter 14 becomes the TB mode. Second
It is assumed that the voltage applied to each electrode of the mode converter 13 is adjusted. The mode splitter 14 transmits, for example, the TE mode to one optical waveguide 18 of the Y branch 15.
The TM mode is separated into the other optical waveguide 19 of the Y branch I5. When the sample 8 is not present, the light incident on the second optical waveguide 12 is circularly polarized light, and at this time, the light incident on the mode splitter 14 becomes the TE mode, and all the guided light is branched to, for example, one optical waveguide 18. Therefore, the output current from the first photodiode 16 is 70. If the sample 8 has birefringence, the light incident on the second waveguide 12 will generally be elliptically polarized light, and the phase difference between the TE and Th1 modes will not be 90°. Therefore, the light incident on the mode splitter 14 contains both TE and TM acid components, and the output of the first photodiode 16 does not become zero.

At this time, the TE mode caused by the birefringence of sample 8, T
The phase difference between the M modes can be adjusted so that the output current from the first photodiode 16 is zero, but this is done by adjusting the phase difference between the first phase shifter 5 and the second phase shifter 11, respectively. This is done by feeding back to the applied voltage. Since the relationship between the voltage applied to the phase shifter and the amount of phase shift is known, conversely, the relationship between the voltage applied to the phase shifter and the amount of phase shift is
The phase difference generated by the sample 8, that is, the amount of birefringence can be determined from the value of the voltage applied to the phase shifter as a result of adjusting the output current from the sample 6 to zero.

FIG. 2 shows a second embodiment of the present invention, in which the same symbols as in FIG. 1 represent the same effects. The materials for the first substrate 2 and the second substrate IO include gallium arsenide (GaAs) and indium phosphide (InP).
By using a compound semiconductor such as ), the semiconductor laser l, the first photodiode 16, and the second photodiode 17 can be monolithically integrated on the substrate. 3a and 13a are a first moat converter and a second mode converter using an electro-optic effect, respectively, and 5a and Ila are a first phase shifter and a second phase shifter using an electro-optic effect, respectively.

first mode converter 3a, first phase shifter 5a,
The hatched portions of the second phase shifter 11a or the second mode converter 13a indicate electrodes, and various configurations are known for each electrode configuration depending on the substrate orientation or the propagation direction of light. These are, for example, gallium arsenide (G
aAs) substrate orientation is <100> and propagation direction is <110>
> direction, and these structures operate in the same way as the first embodiment. The principle of birefringence measurement in the second embodiment is similar to that in the first embodiment.

In the first and second embodiments, if one phase shifter is added to either the first substrate 2 or the second substrate IO, the amount of phase shift that can cancel the phase shift caused by the sample can be increased. It can be used as a phase shifter exclusively for cancellation.

〔Effect of the invention〕

As described above, according to the present invention, the phase difference between mutually orthogonal polarized lights transmitted through a sample having birefringence is measured, and the phase difference generated in the sample is electrically canceled by a phase shifter using an electro-optic effect. Since this method is used, there is no need for a mechanism for precisely moving the phase compensation plate mechanically as in the past.

Therefore, the configuration of the measuring device becomes extremely simple, and the entire device can be manufactured at low cost. Furthermore, since the phase chic is driven electrically, the measurement time can be significantly shortened. Furthermore, in the present invention, since the entire device is constructed using an optical integrated circuit, it is extremely small and lightweight compared to conventional devices, and thus can be applied to in-line measurement. Furthermore, since the optical integrated circuit can be manufactured by a batch process, an extremely inexpensive birefringence measuring device can be realized.

In particular, when using a dielectric crystal with a large electro-optic effect such as lithium niobe (LiNbO3) or lithium tantalate (LiTa03) for the first substrate 2 and the second substrate 10, the optical integrated circuit itself Furthermore, it is smaller, lighter, and easier to manufacture.

In particular, when a compound semiconductor such as gallium arsenide (Ga'As) or indium phosphide (InP) is used for the first substrate 2 and the second substrate IO, the semiconductor laser I is placed on the first substrate 2, Since it is possible to monolithically form the first photodiode 16 and the second photodiode 17 on the substrate IO, there is no need for alignment at all when connecting the semiconductor laser and the photodiode to the substrate.
The entire device can be manufactured at low cost.

In particular, since the polarization control means is composed of the mode converter 3 and the phase shifter 5, the structure is simple, and
Easy to manufacture.

In particular, if either the first substrate 2 or the second substrate 10 is provided with a phase shifter that uses an independent electro-optic effect in addition to the polarization control means, it can be used as a phase shifter exclusively for canceling the phase shift amount. This makes it easier to calibrate measured values.

[Brief explanation of drawings]

FIG. 1 is a plan view of a first embodiment of the device according to the invention;
FIG. 2 is a plan view of a second embodiment of the device according to the invention. [Explanation of symbols of main parts] 2 is a semiconductor laser, 2 and 10 are a first substrate and a second substrate, respectively, 4 and 12 are a first optical waveguide and a second optical waveguide, respectively, 3 and 13 are respectively A first mode converter and a second mode converter, 5 and 11 a first phase shifter and a second phase shifter, respectively, 6 a light projection means, 7 a laser beam, 9 a focusing means, 14 a mode splitter, 16
and 17 are a first photodiode and a second photodiode, respectively.

Claims (7)

[Claims] (1) A first substrate including a laser, an optical waveguide for propagating the laser light emitted from the laser, and a polarization control means for controlling the polarization state of the guided light using an electro-optic effect; A light projection means for projecting the emitted light onto the sample, a focusing means for focusing the laser light projected by the light projection means and transmitted through the sample, and an optical waveguide/guide for propagating the laser light focused by the focusing means. A second substrate including polarization control means for controlling the polarization state of wave light using an electro-optic effect and polarization separation means for separating guided different polarized lights, and a laser that propagates through an optical waveguide included in the second substrate. A birefringence measuring device characterized by comprising a photodetector that detects the intensity of light. (2) The first substrate and the second substrate are lithium niobate (LiNbO_3) or lithium tantalate (L
2. The birefringence measurement device according to claim 1, wherein the birefringence measuring device is a dielectric crystal having an electro-optic effect such as iTaO_3). (3) The first substrate and the second substrate are made of gallium arsenide (Ga
2. The birefringence measuring device according to claim 1, wherein the birefringence measuring device is a compound semiconductor such as As) or indium phosphide (InP). (4) The birefringence measuring device according to claim 1 or 3, wherein the semiconductor laser 1 is monolithically integrated on the first substrate. (5) The birefringence measuring device according to any one of claims 1 and 3, wherein the photodetector is monolithically integrated on the second substrate. (6) The birefringence measuring device according to any one of claims 1 to 5, wherein the polarization control means includes a mode converter and a phase shifter. (7) Claims 1 to 6, characterized in that the first substrate or the second substrate is provided with a phase shifter using an independent electro-optic effect, separate from the polarization control means. The birefringence measuring device described in .