JP3106174B2 - Ellipsometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization analyzer used in fields such as optical fiber communication, optical measurement, and optical control.

[0002]

2. Description of the Related Art For example, in a conventional ellipsometer as shown in FIG.
0, the beam splitter 1 divides the reflected light B into transmitted light A and reflected light B, and the reflected light B passes through a λ / 4 wavelength plate 7 and a polarizer 8 to obtain a counterclockwise circularly polarized light component by the total reflection mirror 4. The transmitted light A is divided into transmitted light C and reflected light D by the beam splitter 2, and the reflected light D passes through the polarizer 9, and a 45 ° polarization component is obtained by the total reflection mirror 4. Further, the transmitted light C is divided into transmitted light E and reflected light F by the polarization beam splitter 3, and the reflected light F obtains a 90 ° polarization component by the total reflection mirror 4, and each light flux B, D, F, E Are detected by the respective photodetectors 6. In other words, in conventional optical fiber communication, a polarization analyzer for observing a rotation angle and a rotation direction of a polarized light conventionally includes a light component decomposer that decomposes a light beam using a large number of wedge-shaped prisms. Used to divide the polarized light beam into four polarized light components.

In such a conventional polarization analyzer utilizing reflection using a beam splitter, each beam splitter for splitting has a polarization characteristic and a phase jump, and does not hold phase information of incident light. . Further, in order to divide the input light into four equal parts, the first beam splitter and the second
Since the splitting ratio of the beam splitter must be changed, the polarization characteristic phase jumps from one to another.
As described above, the optical performance is not improved. This is inadequate for the purpose of analyzing the polarization of the input light,
The ellipsometer has a fatal defect.

[0004]

Therefore, according to the present invention, polarization analysis can be performed with a single photodetector without the polarization characteristic and phase jump caused by the optical component utilizing reflection as described above. It is an object to provide an ellipsometer.
It is another object of the present invention to provide a polarization analyzer without phase jump that can simultaneously detect and analyze polarized light in a plurality of wavelength ranges with a single detector.

[0005]

The present invention SUMMARY OF], in order to solve the technical problems described above, for the light flux to be analyzed polarized light, the first left-handed polarization characteristics with a quarter wave plate polarizer, a polarizer having a transmission axis of the second 0 ° direction, the rotation provided by the polarizer and tung Anahen photons equally spaced pitch circumferential angle has a transmission axis of the third 45 ° direction has a disc, further comprising an optical tuning device for tuning the rotation of the rotary disk and provided with one detector on the optical path of the light beams split by the polarizer of the rotary disk ; On the disc
Rotation at equal intervals to the next rotation angle position of each provided polarizer
Angle position of each polarizer with a specific wavelength filter
The present invention provides an ellipsometer characterized in that the groups are provided on the same rotating disk provided . Further, the said group of polarizers is 2
It is possible to analyze the polarization of each wavelength for a plurality of wavelengths.

[0006]

According to the ellipsometer of the present invention, the high-speed rotating disk 1
7, four light polarizers are used, and the four light polarizers divide the light into four light beams periodically. FIG.
Describes the basic configuration of the ellipsometer of the present invention. That is, FIG. 2 is a perspective view of the light splitting device of the ellipsometer of the present invention. A light beam 10 to be split passes through a lens 12 from an optical fiber 11 and passes through each polarizer 2 on a rotating disk 17.
As the rotating disk 17 rotates, it hits 1, 22, 23, and 24 sequentially, and sequentially passes through the polarizer. That is, a disk on which optical components and polarizers are arranged on the same pitch circle on the optical axis is rotated at high speed. In order to match the rotation angles harmoniously, the LED 18, the phototransistor 19 and the drill hole 2
The number of rotations can be measured by a photo interrupter consisting of 0, and the rotation angle position can be tuned by a motor 16 with an optical encoder. That is, the rotation angle position is measured by the optical encoder, and is synchronized with the measurement position of the photodetector. When rotated, the position of each polarizer optical component becomes unknown, so a photo interrupter is arranged to determine the initial measurement value.

The first polarizer 21 is a polarizer including a quarter-wave plate 31 having a FAST axis parallel to the X axis and having a transmission direction axis in a + 45 ° direction with respect to the X axis. .
The second polarizer 22 has a transmission direction axis of + 45 ° with respect to the X axis, and the third polarizer 23 has a transmission direction axis of X direction.
The fourth polarizer 24 is parallel to the axis and has only a drilled hole without any optical components. That is, a first counterclockwise polarization polarizer 21 having a quarter-wave plate 31 attached to a light beam to be subjected to polarization analysis, a second polarizer 22 having a transmission axis in the 0 ° direction, There is a rotating disk provided with a polarizer 23 having a third transmission direction axis of 45 ° and a perforated polarizer at equal pitch circumferential angles. Furthermore, the rotating disk 1
7, optical tuning devices 18, 19 for tuning the rotation of
20. Then, one detector 14 is provided on the optical path of the light beam split by each polarizer of the rotating disk.

The light beam from the single mode optical fiber 11 is collimated by a lens 12. The disk 17 on which the optical component polarizers are arranged on the same pitch circle on the optical axis is rotated at high speed. The rotation angle position is measured by the optical encoder and synchronized with the measurement position of the photodetector 14.
When rotated, the position of each optical component polarizer becomes unknown, so a photo interrupter for determining the initial measurement value is arranged.

Further, in the ellipsometer of the present invention, another combination polarizer is provided for each polarizer provided on the rotating disk on the same pitch circumference on the rotating disk. It is possible to provide a configuration in which polarized light having a wavelength different from the polarized light to be analyzed by the first polarizer can be simultaneously analyzed. That is, it is possible to measure not only one wavelength range but also a plurality of wavelength ranges. By additionally disposing a polarizer made of optical components having different wavelength characteristics on the same circumference, it is possible to measure two or more types of wavelength bands.

FIG. 3 is a perspective view showing the first and second combination polarizers and the optical path. Equipped with encoder and photo interrupter, on the same pitch circumference of the disc,
Polarizers and wavelength plates of different wavelength bands are attached, the rotation angle position is synchronized with the measurement position of the photodetector, and measurement is performed at a specific angle. That is, assuming that the transmission direction axis of the polarizer 23 is parallel to the X axis, the polarizer 22 and the polarizer 21
Indicates that the transmission direction axis is arranged at + 45 ° with respect to the X axis,
The FAST axis of the half-wave plate is arranged parallel to the X axis. On the other hand, in the polarizers 25, 26, 27, and 28 for measuring the second wavelength band, when the transmission direction axis of the polarizer 27 is parallel to the X axis, the polarizers 25 and 26 are aligned with the X axis. On the other hand, the transmission direction axis is arranged in the + 45 ° direction, and the FAST axis of the quarter-wave plate 31 is arranged parallel to the X axis.

The single mode optical fiber 11
From the lens is collimated by the lens 12. The disk 17 on which the polarizer of the optical component is arranged on the same pitch circle on the optical axis is rotated at high speed. The rotation angle position is measured by the optical encoder and measured in synchronization with the measurement position of the photodetector. When the rotating disk 17 is rotated, the positions of the polarizers of the respective optical components become unclear. Therefore, a photo interrupter is arranged in the same manner as described above to determine the initial measurement value.

Next, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

[0013]

Embodiment 1 FIG. 2 is a perspective view for explaining the positions of optical components and mechanical components in the ellipsometer of the present invention. Reference numeral 11 denotes a single mode optical fiber, and incident light enters the optical fiber 11 through the lens 12. 13 is a lens,
14 is a photodetector. Reference numeral 15 denotes a variable optical attenuator.
Is a motor with an optical encoder, 17 is a rotating disk, 18 is an LED (light emitting element), 19 is a phototransistor, 20 is a hole through which light from the LED (light emitting element) passes, and 21 is a hole. Is a first polarizer with a quarter-wave plate 31, 22 is a second polarizer, 23 is a third polarizer,
Reference numeral 24 denotes a drill hole without an optical component.

When the transmission direction of the third polarizer 23 is parallel to the X axis in orthogonal XY coordinates, the first polarizer 21 and the second polarizer 22
The transmission direction is arranged in the + 45 ° direction with respect to the X axis, and the FAST axis of the quarter wave plate 30 is arranged parallel to the X axis.

The light beam passing through the through hole 24 having no optical components is It, and the polarized light component passing through the third polarizer 23 is Ix.
The polarization component passing through the second polarizer 22 is I ₄₅ , and the polarization component passing through the first polarizer 21 with the quarter-wave plate 30 is _{IQ 45} . In the ellipsometer of the present invention, the four polarization components It, Ix, I ₄₅ and I ₄₅
Output _Q45 , calculate, and observe the polarization state.

As the optical encoder 16, a high-resolution optical encoder was used. As the phototransistor 19, a phototransistor having good high-speed response is used. Since the photodetector with good high-speed response has a small light receiving area, the lens 13
Is used to focus the light beam. The light beam is condensed by the lens 3 in order to be able to measure the modulated light of a high frequency of 10 MHz. To be able to measure 10MHz modulated light,
The gain is adjusted by light using a variable optical attenuator. Thereby, simplification and high performance of the operational amplifier circuit can be achieved.

When the rotating disk 17 is rotated by a motor, the passage time of the next drilling hole 24 that comes next when a signal is present in the photo interrupter can be measured by a photodetector. Drill hole 2
The pulse of the encoder is measured from the beginning of the passage of 4. Next, when the same hole comes, calculation is made from the pulse and the passage time so that light detection is performed at the center position of the hole. Using the center position as the encoder measurement origin, four light fluxes I
t, Ix, I ₄₅ and _{IQ 45} can be measured.

[0018]

Embodiment 2 FIG. 4 is a perspective view showing another example of the ellipsometer of the present invention. The polarized light beam to be analyzed enters from the single mode optical fiber 11, becomes a parallel light beam by the lens 12, and enters. Then, it hits a predetermined position of the optical component mounting rotary disk 17 that rotates at a high speed, and that position is located at the first polarizer 21, the second polarizer 22, the third polarizer 23, and the drill of the first embodiment. In each of the holes 24, as shown, a first polarizer 25, a second polarizer 26,
, And a drill hole 28 are provided. That is,
First polarizer 21, second polarizer 22, third polarizer 2
The combination of 3 and drill hole 24 is for a first wavelength and a first polarizer 25, a second polarizer 2
6. The combination of the third polarizer 27 and the drill hole 28 is for light of the second wavelength. And the variable attenuator 15,
The lens 13 and the photodetector 14 for condensing are as described in the first embodiment.
Is the same as The motor 16 with an optical encoder for adjusting the rotation of the rotating disk, the LED 18, the drill hole 20, and the photointerrupter of the phototransistor 19 are the same as those in the embodiment.

The first polarizers 21 and 25 have quarter-wave plates 31 and 32, respectively. As for the relationship between the axes of the respective optical components for the first wavelength light, assuming that the transmission direction of the third polarizer 23 is parallel to the X axis in the orthogonal XY coordinates, the first polarizer 21 and the second The polarizer 22 is at + 45 ° with respect to the X axis.
The transmission direction is arranged in the direction, and the FAS of the quarter wave plate 31
The T axis is arranged parallel to the X axis. Further, the same optical components are arranged for the light of the second wavelength. That is,
The light flux passing through the through hole 24 having no optical component is denoted by It,
The light flux passing through the polarizer 23 of the second polarizer 22
The light beam passing through the first polarizer having the quarter-wave plate 31 is denoted by I ₄₅ , and the optical beam passing through the first polarizer having the quarter-wave plate 31 is _denoted by I _Q45 .

In the ellipsometer of the present invention, these four light beams It, Ix, I ₄₅ and _{IQ 45} are outputted, calculation is performed, and the polarization state can be observed. In the ellipsometer of the present invention, an optical encoder having a high resolution is used. The phototransistor 19
It is necessary to use a device with good high-speed response. Since the photodetector having good high-speed response has a small light receiving area, the light is condensed by the condensing lens 13. In order to be able to measure the modulated light of a high frequency of 10 MHz, the variable light attenuator 15 is used, and the gain is adjusted with the light flux. This makes it possible to simplify the operational amplifier circuit and improve its performance. The adjustment is performed by the optical encoder, and the motor 16 with the optical encoder is rotated. That is, when there is a signal in the photo interrupter, the time required to pass through the next drill hole 24 is measured by the photodetector. The pulse of the encoder is measured from the beginning of the passage through the drill hole 24. Next, when it comes to the same hole, light is detected at the center position of the hole, and it can be calculated from the pulse and the transit time. The center position is set as the measurement origin by the encoder, and every 90 °, It, Ix, I ₄₅ , I _Q45
Can be measured.

[0021]

As described above, the following remarkable technical effects were obtained by the ellipsometer of the present invention. Firstly, the present invention has made possible a polarization analyzer which does not require a mirror, a prism and the like, has a small transmission loss, and has no polarization characteristics and no phase jump. Second, in the conventional ellipsometer, four light detectors are used.
Although it was necessary to adjust the dispersion of the performance of individual photodiodes, the ellipsometer of the present invention reduced the number of photodetectors to one. became. Third, there is therefore provided an ellipsometer with a simple structure. Fourth, since a variable optical attenuator is inserted, it is possible to measure high-speed modulated light from DC. Fifth, the present invention further provides an ellipsometer capable of measuring two or more wavelength bands.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an optical branching method used in a conventional ellipsometer.

FIG. 2 is an explanatory perspective view illustrating an optical branching method of the ellipsometer of the present invention.

FIG. 3 is a perspective explanatory view showing the concept of another example of the ellipsometer of the present invention.

FIG. 4 is an explanatory perspective view showing another example of the ellipsometer of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Single mode optical fiber 12, 13 Lens 14 Photodetector 15 Variable optical attenuator 16 Motor with optical encoder 17 Rotating disk 18 LED 19 Phototransistor 20 Drill hole 21, 22, 23 First, second and third
Polarizers 24, 28 Drilled holes without optical components 25, 26, 27 Second, first, second and third polarizers 30, 31 Quarter wave plate

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Nobutaka Namihira 2-1-1-15 Ohara, Kamifukuoka-shi, Saitama International Telegraph and Telephone Corporation Kami-Fukuoka Research Laboratory (56) References JP-A-5-10819 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01J 4/00-4/04

Claims (2)

(57) [Claims] 1. A quarter of a light beam to be subjected to ellipsometry
Polarizer of the first left-handed polarization characteristics with a wave plate, a polarizer having a transmission axis of the second 0 ° direction, the polarizer and tung Anahen photons having a transmission axis of the third 45 ° direction Has a rotating disk provided at a pitch circumferential angle of equal intervals, further has an optical tuning device for tuning the rotation of the rotating disk,
Then, the optical path of the light beams split by the polarizer of the rotary disk with one detector, the polarization provided in the disc on
At the next rotation angle position of the child, at the rotation angle position equidistant from each other,
Each polarizer group with a specific wavelength filter was provided
An ellipsometer characterized by being provided on the same rotating disk . Wherein the group of the polarizer has more than two groups, ellipsometer according to claim 1, characterized in that it is possible to analyze the respective wave polarization for the plurality of wavelengths.