KR20060066267A - Apparatus for measuring the refractive index profile of optical devices using confocal scanning microscopy - Google Patents

Abstract

An apparatus for measuring refractive index of an optical element using the optical element principle according to the present invention includes: position adjusting means for adjusting an optical element to measure the refractive index in the X, Y, and Z directions; A light emitting diode (LED) for outputting source light of a single wavelength; Circular symmetric beam output means for converting and outputting the source light output from the LED into a circular symmetric beam; Parallel light output means for converting the circular symmetric beam into parallel light and outputting the parallel light; A first λ / 2 wavelength plate through which the parallel light is transmitted; A polarizing beam splitter for splitting light transmitted through the first λ / 2 wavelength plate; A first [lambda] / 4 wavelength plate for outputting light in a circularly polarized state from the light transmitted through the polarization beam splitter; A focusing lens for focusing light in a circular polarization state output from the first λ / 4 wavelength plate on a measurement cross-section of the optical device; The light reflected from the measuring cross section of the optical device is input through the focusing lens, the first λ / 4 wavelength plate, and the polarizing beam splitter, and the power of the reflected light is measured, and the measuring cross section of the optical device is measured from the power of the reflected light. And reflective photodetecting means for calculating a refractive index.

Confocal scanning microscope, reflectance, refractive index, optical waveguide, optical element

Description

Apparatus for measuring the refractive index profile of optical devices using confocal scanning microscopy}             

1 is a block diagram showing an apparatus for measuring refractive index of an optical device using a confocal scanning microscope principle according to an embodiment of the present invention;

2 is a block diagram of a circular symmetric beam output means according to another embodiment of the present invention;

3 is a view showing parallel light output from a collimation lens;

4 is a configuration diagram in which the refractive index measuring means according to the polarization state according to an embodiment of the present invention is added,

5 is a view of measuring the power of the light reflected from the measurement cross-section of the optical device while moving the piezoelectric actuator with the optical device up and down near the focal length of the focusing lens,

Figure 6 is a graph showing the results of measuring the refractive index distribution of the multi-mode optical fiber by using the refractive index measuring apparatus of the optical device according to the present invention.

   <Brief description of symbols for the main parts of the drawings>

101; LEDs 102, 103; lens

104; Single mode optical fiber 105; Collimation Lens

106; λ / 4 wavelength plate 107; Polarizing Beam Splitter

108; Transmission photodetector 109; λ / 2-wavelength plate

110; Mirror 111; Focusing lens

112; Piezoceramic actuator 113; Optical element

114; Oil 115; lens

116; Reflective photodetector

The present invention relates to an apparatus for measuring the refractive index of an optical device, and more particularly, to an apparatus for measuring the refractive index of an optical device core using the principle of a confocal scanning microscope.

The optical fiber and optical waveguide are composed of a high refractive index core portion and a low refractive index cladding portion, and light is transmitted through the high refractive index core. Depending on the size of the core and the value of the refractive index, the conditions under which the light travels will change. Therefore, when developing and evaluating the characteristics of optical fibers and optical waveguides, it is necessary to accurately measure the refractive index of the core. In particular, the multimode optical fiber used in the Gigibit ethernet is directly related to the refractive index and the transmission capacity of the optical fiber, and it is necessary to accurately measure the refractive index distribution of the optical fiber in order to increase the transmission capacity of the optical fiber. In addition, since the structure of the optical device including the optical fiber and the optical waveguide is a complex structure of less than micron, a technique for accurately measuring refractive index with a spatial resolution of less than micron is required.

A conventional method of measuring the refractive index of an optical fiber is the RNF (Refracted Near-Field) method. This RNF method is commercialized and sold by several companies. This RNF method will be described. The cross section of the optical fiber to be measured is immersed in an oil having the same refractive index as that of the clad, and the laser beam is irradiated to the cross section of the optical fiber immersed in the oil. Then, the laser beam is refracted by the refractive index of the optical fiber, and the refractive index of the optical fiber is measured by measuring the refractive angle of the laser beam.

In this RNF method, when the size of the laser beam is small, the spatial resolution becomes high, but it is difficult to accurately measure the refractive angle. When the size of the laser beam is increased to accurately measure the refractive angle, the spatial resolution becomes low. That is, there is a structural limitation in simultaneously increasing the accuracy and spatial resolution of the refractive index. In addition, this RNF method has a disadvantage in that a measurement error due to oil occurs because the degree of refraction of the laser beam is changed depending on the state of oil. In addition, this RNF method has a disadvantage that the preparation procedure for measuring the refractive index of the optical fiber is complicated, takes a long measurement time, and can apply only a sample in the form of an optical fiber.

In addition to this RNF method, other measurement methods have been proposed. Most other prior art also immerses the cross section of the optical fiber in oil to eliminate measurement errors caused by the refractive index difference between the clad and air. However, since the degree of refraction of the light changes depending on the state of the oil, there is a disadvantage that a measurement error caused by the oil occurs.

SUMMARY OF THE INVENTION The object of the present invention devised to solve the above problems of the prior art is to provide an apparatus for directly measuring the refractive index of an optical device directly without being affected by oil.

In addition, another object of the present invention is to provide a measuring device that can be applied to all types of optical devices, and to increase the accuracy and spatial resolution of the refractive index at the same time.

An apparatus for measuring refractive index of an optical element using a confocal scanning microscope principle according to the present invention for achieving the above object comprises: position adjusting means for adjusting an optical element to measure the refractive index in the X, Y, and Z directions;

A light emitting diode (LED) for outputting source light of a single wavelength;

Circular symmetric beam output means for converting and outputting the source light output from the LED into a circular symmetric beam;

Parallel light output means for converting the circular symmetric beam into parallel light and outputting the parallel light;

A first λ / 2 wavelength plate through which the parallel light is transmitted;

A polarizing beam splitter for splitting light transmitted through the first λ / 2 wavelength plate;

A first [lambda] / 4 wavelength plate for outputting light in a circularly polarized state from the light transmitted through the polarization beam splitter;

A focusing lens for focusing light in a circular polarization state output from the first λ / 4 wavelength plate on a measurement cross-section of the optical device;

The light reflected from the measuring cross section of the optical device is input through the focusing lens, the first λ / 4 wavelength plate, and the polarizing beam splitter, and the power of the reflected light is measured, and the measuring cross section of the optical device is measured from the power of the reflected light. It characterized in that it comprises a reflective light detection means for calculating the refractive index of.

Hereinafter, an apparatus for measuring refractive index of an optical device using a confocal scanning microscope principle according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The present invention proposes an apparatus for measuring the refractive index of an optical device using the principle of confocal scanning microscope. As an attempt to apply a confocal scanning microscope to the refractive index measuring apparatus of an optical fiber, the paper "Measuring method for the refractive index profile of optical glass fibers" W. Eickhoff, E. Weidel, Opt. Quantum Electron. 7, 109-113, 1975, but the prior art is currently in the state of research and commercialization has been suspended due to technical limitations, such as low spatial resolution and unable to obtain a stable power output of the light source.

On the other hand, the present invention proposes a technique for modifying the confocal scanning microscope to a structure suitable for measuring the refractive index of the optical device, and measuring the refractive index of the optical device by using a newly configured refractive index measuring device.

1 is a block diagram illustrating an apparatus for measuring refractive index of an optical device using a confocal scanning microscope principle according to an embodiment of the present invention.

In this embodiment, the optical element is used as a generic term including all optical fibers, optical waveguides, general optical elements, optical materials, and the like.

The refractive index measuring apparatus of the optical element includes a position adjusting means for positioning the optical element 113 for measuring the refractive index in the X, Y, and Z directions, and a light emitting diode (LED) 101 for outputting source light having a single wavelength. A circular symmetric beam output means for converting the source light emitted from the LED 101 into a circular symmetric beam, parallel light output means for converting the circular symmetric beam into parallel light, and the parallel light The λ / 2 wavelength plate 106 to be transmitted, the polarizing beam splitter 107 for dividing the light transmitted through the λ / 2 wavelength plate 106, and the polarizing beam splitter 107 transmit Λ / 4 wavelength plate 109 through which light is transmitted and outputting light in a circularly polarized state, a mirror 110 in which light in a circular polarization state output from the λ / 4 wavelength plate 109 is reflected, and A focusing lens 111 for focusing the light reflected from the mirror 110 on the measurement cross-section of the optical device 113 is provided.

The refractive index measuring apparatus of the optical element further includes a transmission light detector 108 for detecting the power of the source light reflected by the polarization beam splitter 107.

The LED 101 outputs source light of a single wavelength of 658 nm.

The light focused on the measurement section of the optical device 113 is reflected and provided to the reflected light detecting means through the focusing lens 111, the mirror 110, the λ / 4 wavelength plate 109, and the polarization beam splitter 107. . The reflected light detecting means includes a lens 115 for collecting the reflected light reflected from the measuring cross section of the optical element 113, and a reflected light detector 116 for detecting the power of the collected reflected light.

The circular symmetric beam output means includes a lens 102 for collecting the source light output from the LED 101, a lens 103 for injecting the light collected from the lens 102 into the single mode optical fiber 104, and a lens ( It is provided with a single mode optical fiber 104 for receiving light through the 103 to output a circular symmetric beam. The parallel light output means is implemented with a collimation lens 105. Using the LED 101 configured as described above, the circular symmetric beam output means 102, 103, 104 and the parallel light output means 105, the beam quality that can obtain a stable source optical power and the highest spatial resolution Can be obtained.

The position adjusting means includes a piezoelectric actuator (PZT) 112 for attaching an optical element to be measured and adjusting the position in the Z direction, and an XY scanner for positioning the piezoelectric actuator 112 in the X and Y directions.

The opposite cross section of the measurement cross section of the optical element 113 is immersed in oil 114 having the same refractive index as the clad. The reason is that the opposite cross section of the measurement cross section of the optical element is immersed in oil 114 to remove it since the reflected light reflected back from the interface with air can affect the measured value.

Referring to the operation of the refractive index measuring apparatus of the optical device using the confocal scanning microscope principle according to an embodiment of the present invention configured as described above are as follows.

When the LED 101 generates source light having a wavelength of 658 nm, the lens 102 collects the source light, and the lens 103 injects the collected source light into the single mode optical fiber 104. In the visible region, light passing through the single mode fiber is output in the form of a circular symmetric beam. The collimation lens 105 makes this circular symmetric beam into parallel light. The parallel light passing through the collimation lens 105 passes through the lambda / 2 wavelength plate 106, which adjusts the amount of light transmitted through the polarization beam splitter 107.

The light transmitted from the polarization beam splitter 107 passes through the λ / 4 wavelength plate 109, the mirror 110, and the focusing lens 111 and focuses on the measurement cross-section of the optical device 113 with a beam of 1 μm or less. )do. Light reflected from the polarization beam splitter 107 is incident on the transmission photodetector 108. The transmission photodetector 108 measures the power of the source light to check the power stability of the source light.

The optical element 113 attached to the piezoelectric ceramic actuator (PZT) 112 moves up and down near the focal length of the focusing lens 111, and the light reflected from the optical element 113 is focused on the focusing lens 111 and the mirror ( The light incident on the reflected light detector 116 passes through the 110, the λ / 4 wavelength plate 109, and the polarization beam splitter 107. The reflected light incident on the reflected light detector 116 is maximized when the measurement cross section of the optical element is located at the focal length of the focusing lens 111. By adjusting the XY scanner and the piezoceramic actuator 112, the two-dimensional surface refractive index distribution of the optical device can be measured.

At this time, the relationship between the reflectance and the refractive index of the light reflected from the measurement cross-section of the optical device is shown in Equation 1 below.

Where n is a refractive index and R is a reflectance of light reflected from the measurement cross section of the optical device.

The reflected light detector 116 measures the power of the reflected light. When describing the method of obtaining the reflectance from the power of the reflected light, first, the reflectance-independent values are analyzed from the values reflected from the reference sample surface whose refractive index is known. By removing it, the reflectance on the surface of the reference sample is found. Then, when applied to the power of the reflected light of the optical device to be measured later, the pure reflectance of the optical device to be measured can be known. The method of calculating the reflectance from the power of this reflected light follows a conventional method.

2 is a block diagram of a circular symmetric beam output means according to another embodiment of the present invention. The circular symmetric beam output means is implemented as a single mode optical fiber 20 whose cross section in contact with the LED 101 is formed in the shape of a lens 21. The single mode optical fiber 20 collects the source light generated from the LED 101 into the cross section of the lens shape 21 and passes it through the single mode optical fiber. As described above, the light passing through the single mode optical fiber 20 in the visible light region is output in a circular symmetric beam shape, and the collimation lens 105 makes the circular symmetric beam into parallel light. When the source light generated from the LED 101 is directly incident to the single mode optical fiber 20 as shown in FIG. 2, the number of parts to be used can be reduced, and errors caused by the alignment of the lenses 102 and 103 can be eliminated. Can be.

3 is a diagram illustrating parallel light output from the collimation lens 105.

4 is a configuration diagram in which the refractive index measuring means according to the polarization state according to an embodiment of the present invention is added.

The refractive index measuring means according to the polarization state is a λ / 4 wave plate 31 for converting the circularly polarized light generated by the polarization beam splitter 107 and the λ / 4 wave plate 109 into linearly polarized light, and λ / And a? / 2 wavelength plate 32 for outputting linearly polarized light in various states from the linearly polarized light passing through the four wavelength plate 31. In addition, the refractive index measuring means further includes a polarizer 33 for transmitting a desired linearly polarized signal in the linearly polarized light of various states output from the λ / 2 wavelength plate 32. When the thus obtained linearly polarized light is incident on the measurement cross section of the optical device and the refractive index distribution is measured, the change in the refractive index distribution according to the polarization state can be measured.

FIG. 5 is a diagram illustrating a measurement of the power of light reflected from a measuring section of an optical device by moving a piezoelectric ceramic actuator (PZT) 112 having an optical device up and down near a focal length of the focusing lens 111. The present invention does not use a separate feedback system in order to place the measurement section of the optical device at the focal length of the focusing lens 111. However, when the piezoceramic actuator (PZT) 112 is moved near the focal length of the focusing lens 111, the reflected light is maximized when the measuring section of the optical element is positioned at the focal length of the focusing lens 111. The position where the power of light is maximized and its maximum value are stored. In addition, if the power of the reflected light is measured in the same manner while adjusting the position of the optical device with the XY scanner, the two-dimensional refractive index distribution of the measurement cross section of the optical device is obtained.

Figure 6 is a graph showing the results of measuring the refractive index distribution of the multi-mode optical fiber by using the refractive index measuring apparatus of the optical device according to the present invention. A multimode optical fiber having a core size of 13.5 μm and a difference in refractive index between the core and the cladding of 0.0328 is measured using a measuring apparatus according to the present invention. 6A is a two-dimensional measured value, and (b) is a one-dimensional measured value.

Although the technical spirit of the present invention has been described above with reference to the accompanying drawings, it is intended to exemplarily describe the best embodiment of the present invention, but not to limit the present invention. In addition, it is obvious that any person skilled in the art may make various modifications and imitations without departing from the scope of the technical idea of the present invention.

As described above, according to the present invention, accurate refractive index measurement is possible in a short time. In addition, the present invention can be applied to all types of optical devices such as optical waveguide devices, optical devices, and optical materials, as well as optical fiber types, and thus can be applied to all fields requiring surface refractive index distribution values.

Claims (11)

Position adjusting means for positioning the optical element to measure the refractive index in the X, Y, and Z directions; A light emitting diode (LED) for outputting source light of a single wavelength; Circular symmetric beam output means for converting and outputting the source light output from the LED into a circular symmetric beam; Parallel light output means for converting the circular symmetric beam into parallel light and outputting the parallel light; A first λ / 2 wavelength plate through which the parallel light is transmitted; A polarizing beam splitter for splitting light transmitted through the first λ / 2 wavelength plate; A first [lambda] / 4 wavelength plate for outputting light in a circularly polarized state from the light transmitted through the polarization beam splitter; A focusing lens for focusing light in a circular polarization state output from the first λ / 4 wavelength plate on a measurement cross-section of the optical device; The light reflected from the measuring cross section of the optical device is input through the focusing lens, the first λ / 4 wavelength plate, and the polarizing beam splitter, and the power of the reflected light is measured, and the measuring cross section of the optical device is measured from the power of the reflected light. An apparatus for measuring refractive index of an optical element using a confocal scanning microscope principle, characterized in that it comprises reflective photodetecting means for calculating a refractive index of the optical fiber. The refractive index of an optical device using a confocal scanning microscope principle according to claim 1, further comprising a transmission photodetector which transmits the first λ / 2 wavelength plate and detects the power of light reflected by the polarization beam splitter. Measuring device. The method of claim 1, wherein the circular symmetric beam output means, A first lens for collecting the source light output from the LED, a second lens for injecting the light collected from the first lens into a single mode optical fiber, and converting the light incident through the second lens into a circular symmetric beam An apparatus for measuring refractive index of an optical element using a confocal scanning microscope principle, characterized in that it comprises the single mode optical fiber to be outputted. The method of claim 1, wherein the circular symmetric beam output means, Refractive index measuring apparatus of the optical element using the confocal scanning microscope principle, characterized in that the cross section in contact with the LED is a single-mode optical fiber formed in the shape of a lens. The method of claim 1, wherein the parallel light output means, An apparatus for measuring refractive index of an optical device using a confocal scanning microscope principle, characterized in that it is a collimation lens. The method of claim 1, wherein the position adjusting means, Refractive index of the optical device using a confocal scanning microscope principle comprising a piezoelectric ceramic actuator (PZT) for attaching the optical device and positioning in the Z direction, and an XY scanner for positioning the piezoelectric actuator in the X and Y directions. Measuring device. 7. The method of claim 6, wherein the piezoelectric actuator moves the optical element in the Z direction near the focal length of the focusing lens, and the reflective photodetector calculates the refractive index as the maximum value of the power of the incident reflected light. An apparatus for measuring refractive index of an optical device using a confocal scanning microscope principle. The second λ / 4 wave plate according to claim 1, wherein the circularly polarized light output from the first λ / 4 wave plate is converted into linearly polarized light and output. And a second [lambda] / 2 wave plate for outputting linearly polarized light in polarized state to the focusing lens. The refractive index of an optical device using a confocal scanning microscope principle according to claim 8, further comprising a polarizer which transmits a desired linearly polarized light of the light output from the second λ / 2 wavelength plate and outputs it to the focusing lens. Measuring device. The method of claim 1, wherein the reflected light detecting means calculates the reflectance (R) of the reflected light from the power of the reflected light, and calculates the refractive index (n) by applying the reflectance (R) to the following equation. An apparatus for measuring refractive index of an optical device using a confocal scanning microscope principle. [Equation]

The apparatus of claim 1, further comprising an oil having the same refractive index as that of the clad of the optical device for immersing the opposite end surface of the measurement section of the optical device.

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