JPH01100403A - Light source apparatus for interferometer - Google Patents

Abstract

PURPOSE:To miniaturize a laser head and to prevent the generation of the shift of an optical axis by environmental change, by guiding the laser beam emitted from a laser beam source to a plane-of-polarization preserving fiber. CONSTITUTION:The laser beam condensed by a condensing lens part is introduced into a plane-of-polarization preserving fiber 5. One end part 5a of the plane-of-polarization preserving fiber 5 is connected to the laser head 3 provided to a stage 1 and the laser beam propagating through the plane-of-polarization preserving fiber 5 is emitted from one end part 5 thereof and converted to parallel beam by a collimator lens 4 to be introduced into an interference optical system 2. Since the laser head 3 is constituted of the collimator lens 4 and one end part 5a of the plane-of-polarization preserving fiber 5, miniaturization and wt. reduction are achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a light source device for an interferometer that supplies a laser beam to an interference section that divides the beam into at least two beams and causes them to interfere.

(Prior Art) FIG. 9 is a schematic configuration diagram of an optical interferometer equipped with a conventional interferometer light source device. In the figure, 51 is a stage, and this stage 51 includes an interference optical system 52 and A gas laser device 53 that is a laser head that emits laser light to the interference optical system 52 is installed. Reference numeral 54 denotes a wavelength stabilization control unit that stably maintains the wavelength of the laser light emitted by the gas laser device 53. This wavelength stabilization control unit 54 and the gas laser device 53 (laser head) constitute an interferometer light source device. There is. Reference numeral 55 denotes a calculation device that calculates the movement distance of the movable mirror 52b from the interference light received by the receiver 52a and displays the calculated movement distance on the display section 55a. 52d is a reference mirror, and 52c is a splitter that divides the beam into a reference beam and a measurement beam.

Now, when a laser beam is emitted from the gas laser device 53 and the movable mirror 52b is moved, brightness and darkness occur on the light receiving surface of the receiver 52a due to the interference of the laser beam, and the calculation device 55 counts the number of brightness and darkness and moves the mirror 52b. The distance traveled by mirror 52b is measured.

(Problems to be Solved by the Invention) By the way, in order to accurately measure the moving distance of the movable mirror 52b, the gas laser device 53. Movable mirror 52b, receiver 52
Optical axes such as a must be aligned with high precision. However, in the above device, the gas laser device 53
Since it is large and heavy, its own weight will cause it to reach stage 5.
1 becomes deflected, the optical axes of these optical axes, which have been aligned with high precision, become misaligned, resulting in a problem in which measurement errors become large. Furthermore, it has been proposed to separate the gas laser device 53 from the stage 51 and guide the laser beam emitted from the gas laser device 1i53 to the interference optical system 52 using a reflecting mirror. Since the direction of the reflective surface changes with changes in the environment and the optical axes shift, there is a problem that it is vulnerable to changes in the environment.

Further, a device using a semiconductor laser has been proposed, but in this case, the oscillation wavelength is easily affected by the injection current and operating temperature, so it is necessary to stabilize the oscillation wavelength. Control to stabilize this oscillation wavelength requires either a Fabry-Perot etalon plate, an atomic/molecular absorption cell, etc., which serves as a wavelength standard, and a half mirror 2 reflector, a condensing lens, etc. be. In addition, a cooling element, an accompanying thermistor, etc. are required to stabilize the operating temperature. For this reason, although the semiconductor laser itself is extremely small, the laser head mounted on the stage has hardly been miniaturized, making it impossible to solve the above-mentioned problems.

(Object of the Invention) Therefore, the present invention has been made in view of the above problems, and provides a light source device for an interferometer that allows the laser head to be made smaller and does not cause deviation of the optical axis due to changes in the environment. The purpose is to

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention includes a laser light source unit that emits a laser beam, and receives the laser light from the laser light source unit and divides the laser beam into at least two beams. It is equipped with a polarization-maintaining fiber that leads to an interference section that causes interference.

(Function) With the above configuration, the laser light emitted from the laser light source is guided to the interference part by the polarization maintaining fiber.

(Example) Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a conceptual diagram showing the arrangement of an optical system of an optical interference device that implements a light source device for an interferometer according to the present invention. In FIG. 1, 1 is a stage on which an interference optical system 2 is mounted;
A laser head 3 emits a laser beam to the interference optical system 2, and is provided with a collimator lens 4. The interference optical system 2 includes a divider 2a and a reference mirror 2b as in the conventional case.

It is composed of a moving fi2c, a light receiving sensor 2d, etc.

6 is a semiconductor laser device; 7 is a wavelength stabilization control device that stabilizes the oscillation wavelength of the laser light emitted by the semiconductor laser device 6; 8 is a device that calculates the moving distance of the movable mirror 2a of the interference optical system 2;
A calculation device 9 is a power source that displays the calculated movement distance on the display section 8a.

These semiconductor laser devices 6. Wavelength stabilization control device7. The arithmetic unit 8 and the like are housed in one case K. By the way, the semiconductor laser device 6° wavelength stabilization control device 7. A light source device for an interferometer is constituted by a polarization maintaining fiber 5, which will be described later.

FIG. 2 shows a schematic configuration diagram of the semiconductor laser device 6. In the figure, 11 is a semiconductor laser, 13 is an electronic cooling element for forcibly cooling the semiconductor laser 11, and 1
4 is a heat sink, and 15 is a thermistor for detecting the temperature of the semiconductor laser 11. 16 is a collimator lens unit that converts the laser beam emitted from the semiconductor laser 11 into a parallel beam;
17 is a half mirror that splits the parallel light beam made into a parallel light beam by the collimator lens section 16; 118 is a filter that serves as a wavelength standard for detecting fluctuations in the wavelength of the laser beam; 19;
2 is a condenser lens that focuses the light beam transmitted through the filter 18; 20 is a light receiving sensor that receives the light beam focused by the condenser lens 19;
0 monitors the fluctuation of the oscillation wavelength. and.

The wavelength stabilization control device 7 controls the injection current of the semiconductor laser 11 based on the output signal of the light receiving sensor 20, thereby stabilizing the oscillation wavelength. That is,
If the oscillation wavelength of the laser beam fluctuates for some reason, the light beam passing through the filter 18 is attenuated according to the wavelength fluctuation, so the output signal of the light receiving sensor 2G becomes smaller, and the wavelength stabilization control device E7 adjusts its output. Based on the signal, the injection current is quickly controlled in a direction that reduces fluctuations in the oscillation wavelength.

21 is a condenser lens that divides the light beam transmitted through the half mirror 17; a half mirror 122 is a condenser lens that focuses the light beam divided by the 8th mirror 21; 23 is a light receiving sensor that receives the light beam that has been focused by the condenser lens 22; Fluctuations in the oscillation output are monitored by the light receiving sensor 23. The wavelength stabilization control device 7 also controls the current flowing through the electronic cooling element 13 based on the output signal of the light receiving sensor 23, and adjusts the operating temperature of the semiconductor laser 11 so as to keep the oscillation output stable. ing. 24
is a focusing lens section that focuses the light beam transmitted through the half mirror 21. Normally, the NA of a polarization preserving fiber is extremely small, so the focal length of this focusing lens section 24 is greater than or equal to the focal length of the collimator lens section 16. .

Note that the above-mentioned collimator lens section 16 and focusing lens section 2
4 constitutes a relay lens section. The laser beam focused by the focusing lens section 24 is introduced into the polarization maintaining fiber 5. The polarization maintaining fiber 5 has a core 5b in a cladding 5a having an elliptical cross section (see FIG. 7), and 25 is a connector. One end 5a of the polarization preserving fiber 5 is connected to the laser head 3 provided on the stage l, and the laser beam propagating through the polarization preserving fiber 5 is emitted from the one end 5a and is transmitted through the collimator lens 4. The laser beam is made into a parallel light beam and introduced into the interference optical system 2.

Since the laser head 3 is composed of a collimator lens 4 and one end 5a of a polarization maintaining fiber 5, it is extremely small and lightweight.

Then, as the movable mirror 2c of the interference optical system 2 is moved, the laser beam reflected by the movable mirror 2c and the laser beam reflected by the reference mirror 2b interfere with each other, as in the conventional case, and this interference light The light is received by the light receiving sensor 2d, and the moving distance of the movable mirror 2c is measured.

By the way, the laser light emitted from the semiconductor laser 11 is mostly linearly polarized light, but it is spontaneous emission light.

A small amount of unpolarized light is also included. Since interferometers use coherent light for measurement, the unpolarized light causes noise, and the polarization ratio (
The higher the ratio (linearly polarized light component/non-polarized light component), the better. In order to increase the polarization ratio, the laser beam emitted from the semiconductor laser 11 may be collimated so that NA (=sin θ) becomes small, as shown in FIG. However, if the NA is made small, a light beam (laser light) emitted from the semiconductor laser 11 with a large emission angle is discarded, resulting in a large energy loss. The fourth @ shows a graph showing the relationship between polarization ratio, NA, and optical output.

However, as shown in FIG. 5, even if a collimator lens section 16 with a large NA is used, a condensing lens section 24 having a focal length longer than the focal length of the collimator lens section 16 is provided afterwards to create a polarization-maintaining fiber. If the laser beam is incident on the fiber 5, the same effect as when the NA is made small can be obtained, and furthermore, the laser beam propagating through the polarization preserving fiber 5 and emitted from the other end 5a has a polarization ratio. This is improved (because non-polarized light components are easily attenuated in the polarization preserving fiber 5). Therefore, the semiconductor laser 11
Even if a laser beam emitted from a large exit angle is picked up, the laser beam is focused by the condenser lens section 24 and made to enter the polarization preserving fiber 5.

Since the polarization maintaining fiber 5 acts as a polarizer and increases the polarization ratio, it is possible to obtain a laser beam with less energy loss and a high polarization ratio, which is extremely convenient for interferometers etc. that use coherent light. .

In the above embodiment, the laser head 3 has a collimator lens 4.
and one end 5a of the polarization-maintaining fiber 5, it is extremely small and lightweight, and unlike conventional methods, the stage does not bend due to the weight of the laser head, resulting in large measurement errors. , since the laser beam is not introduced into the interference optical system 2 using a reflecting mirror or the like,
The optical axes of the laser head 3 and the interference optical system 2 will not be misaligned due to environmental changes.

Further, in the above embodiment, the semiconductor laser device 6, the wavelength stabilization control device 7, and the arithmetic device! 8 are housed in the same case, the cords connecting each device are shortened, and the noise carried by the cords is reduced. In addition, since the semiconductor laser device 6 is provided in a separate case from the stage 1, almost no heat from the semiconductor laser 11 or the heat sinks 12, 14 is conducted to the laser head 3, and the stage 1
There is no thermal effect on the

FIG. 6 shows a second embodiment in which a collimator lens 4 and an interference optical system 2 are connected to a
It was made to exist. This 1-crystal optical axis 3 made of 3 λ/4 plates
The angle between 1a and the long axis 5c of the ellipse of the core 5b of the polarization maintaining fiber 5 is 45° as shown in FIG. In the figure, 32 is a polarizing beam splitter, 33
．． 34 is the first. The second light receiving sensor 35 is a half mirror.

Now, when linearly polarized laser light is emitted from the laser head 3, this laser light is turned into circularly polarized light by the λ/4 plate 31, and the P polarized light component and the S polarized light component of this circularly polarized light are π/
A phase difference of 2 occurs. This circularly polarized laser beam is split into a reference beam and a measurement beam by the half mirror 35, and these beams are reflected by the reference boundary and the movable mirror and return to the half mirror 35, where the P-polarized component of the measurement beam is divided into a reference beam and a measurement beam. The P-polarized light component of the reference light beam, the S-polarized light component of the measurement light beam, and the S-polarized light component of the reference light beam interfere with each other, and the interfered light beams enter the polarizing beam splitter 32.

The P polarized light component of this incident interference light beam passes through the polarizing beam splitter 32 and is received by the first light receiving sensor 33, and the S
The polarized light component is reflected by the slope 32 a of the polarizing beam splitter 32 and is received by the second light receiving sensor 34 .

1st. The second light receiving sensors 33 and 34 output light receiving signals according to the amount of light received.

When the movable mirror is moved, for example, in the direction of the arrow, each time the difference between the reference optical path length and the measurement optical path length becomes a half-integer multiple of the wavelength, that is, each time the moving distance of the movable mirror increases by λ/2. bL Since brightness and darkness occur due to interference between the reference light beam and the measurement light beam, 1. The second light-receiving sensors 33 and 34 output sinusoidal light-receiving signals corresponding to the brightness and darkness of the light-receiving sensors, as shown in FIG. by the way.

Since the P-polarized light component and the S-polarized light component of the interference light beam incident on the polarizing beam splitter 16 have a phase difference of π/2, the first.
A phase difference of π/2 occurs in the light reception signals output from the second light reception sensors 33 and 34 (see FIG. 8).

These received light signals are converted into pulse signals (Q, S in Figure 8) which become H level when the level is higher than a predetermined level, and count pulses are generated at the rise and fall of these pulse signals as shown in T in Figure 8. By generating such count pulses and counting the count pulses, the moving distance of the movable mirror can be measured with an accuracy of λ/8.

Also, when the movable mirror moves in the direction of arrow B, S
After the signal shown at becomes H level, the signal shown at Q becomes H level (if you are moving in the direction of the arrow, Q
(after S becomes H level), the moving direction of the movable mirror can be detected from this. In addition, λ
14 plate 31 may be installed at any position indicated by the broken line.

(Effects of the Invention) Since the present invention is configured as described above, the laser head can be made small and lightweight, and the optical axis can be changed without causing any deflection of the stage. No deviation occurs. Therefore, it is possible to accurately measure the moving distance of the movable mirror.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing the arrangement of the optical system of an optical interference device implementing the interferometer light source device according to the present invention, FIG. 2 is a schematic configuration diagram of a semiconductor laser device, and FIG. 3 is an explanation of NA. figure,
Figure 4 is a graph showing the relationship between polarization ratio, NA, and optical output, Figure 5 is an explanatory diagram for improving the polarization ratio, Figure 6 is an explanatory diagram of the second embodiment, and Figure 7 is λ An explanatory diagram showing the relationship between the crystal optical axis of the /4 plate and the core of the polarization preserving fiber,
FIG. 8 is an explanatory diagram of the relationship between the output signal of a light receiving sensor and a pulse, and FIG. 9 is an explanatory diagram of an optical interference device equipped with a conventional light source device for an interferometer. 5...Polarization preserving fiber 11...Semiconductor laser 16...Collimator lens section 24...Focusing lens section Fig. 5 Fig. 6 Fig. 8

Claims (4)

[Claims] (1) A light source for an interferometer, comprising: a laser light source section that emits a laser beam; and a polarization preserving fiber that receives the laser beam from the laser light source section, divides it into at least two beams, and guides them to an interference section where they interfere. Device. (2) The laser light source section includes a laser light source that emits laser light, and a relay lens section that focuses the laser light emitted from the laser light source and makes it enter the polarization-maintaining fiber. A light source device for an interferometer according to claim 1. (3) The relay lens section includes a collimator lens section that converts the laser beam emitted from the laser light source into a substantially parallel beam, and a focusing lens section that makes the laser beam emitted from the collimator lens section enter the polarization preserving fiber. The light source device for an interferometer according to claim 2, characterized in that it has the following. (4) The light source device for an interferometer according to claim 3, wherein the focal length of the focusing lens section is longer than the focal length of the collimator lens section.