KR20150043773A

KR20150043773A - Manufacturing Method of Plastic Optical Fiber Employing In-Line Hole for Sensor, and Plastic Optical Fiber Sensor Using It

Info

Publication number: KR20150043773A
Application number: KR20130122586A
Authority: KR
Inventors: 박재희; 신종덕
Original assignee: 계명대학교 산학협력단
Priority date: 2013-10-15
Filing date: 2013-10-15
Publication date: 2015-04-23

Abstract

The present invention relates to a manufacturing method of plastic optical fiber employing in-line hole for the sensor, and plastic optical fiber sensor using it and comprises: a step of placing a plastic optical fiber (POF) on a workbench of a micro drilling machine and fixating the POF with a vice; and a step of forming a hole on the in-line part of the POF that has a radius of 0.1 mm-0.5 mm with the micro drilling machine. The present invention provides a manufacturing method of plastic optical fiber employing in-line hole for the sensor that is easy to manufacture, that has low manufacturing costs, and that can enhance the performance of the sensor. A POF manufactured this way can be used in micro refractive index sensor of dispersion sensor as well as in-line attenuators of local area communication networks.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic optical fiber sensor using a plastic optical fiber and a plastic optical fiber sensor using the plastic optical fiber,

The present invention relates to a method of manufacturing a plastic optical fiber for a sensor and an optical fiber sensor using the same, and more particularly, to a method of manufacturing a plastic optical fiber for a sensor in which a linear hole is formed in a millimeter or less and a plastic optical fiber sensor using the plastic optical fiber .

Plastic Optical Fiber (POF) has many advantages such as low cost, effective weight, low weight, electromagnetic wave interference, excellent processability, etc., which are used in local area network and low-end products and disposable sensor products. Most commercial POFs are those made of PMMA with a core diameter of about 1 millimeter with core and cladding refractive indices of 1.49 and 1.41, respectively. In the region where the loss of the POF is the lowest, the inexpensive light sources can be easily obtained as the visible light region, and since the POF sensors operate in the multi mode, the use of the light intensity changes in most cases has a simple advantage.

The proposed POF based sensors are as follows. The bending type sensor is a sensor using a phenomenon in which the bending is increased according to the pressure applied to the surroundings and the intensity of the received light is reduced. The sensors were used to measure driver's reflexes, refractive index, and ambient pressure. The tapered sensor is made by tapering the optical fiber and is used to measure the refractive index, the amount of gas and the amount of chemical substance by using the optical power damping by the refraction generated in the taper region according to the refractive index of the surrounding medium . The side machining type is a sensor that polishes the side of the optical fiber to a certain depth of the core and uses optical power attenuation generated in this portion depending on the medium. This sensor was also used for refractive index measurement and liquid level measurement. The surface plasmon resonance type is a sensor using a resonance wavelength that varies depending on the refractive index of the medium, by fabricating a buffer layer and a metal layer on a side polished POF. This sensor was also applied to measure refractive index, amount of chemical substance, and so on.

The above sensor structures are long in length from several centimeters to several tens of centimeters, require low sensitivity, difficult to manufacture the sensor, and expensive equipment for manufacturing the sensor.

Smaller, more simple, hole-based sensor structures use single-mode silica optical fibers, and use femtosecond lasers as fabrication equipment to fabricate holes in single-mode silica fiber optics with diameters of 10 μm or less. One of the methods is to irradiate the femtosecond laser in a direction perpendicular to the optical axis of the fiber to form a hole. In this case, a conical hole is formed, and the upper part is opened and the lower part is closed. On the other hand, after chemically etching the hole with a femtosecond laser, holes with a constant diameter and through the optical fiber can be fabricated. Since these sensors use a single-mode silica optical fiber to fabricate microholes, the holes may be too small, which may lead to inaccurate measurement results, high cost of equipment and complicated fabrication processes.

Korean Patent Publication No. 10-2010-0095252

SUMMARY OF THE INVENTION An object of the present invention to solve the above problems is to provide a method of manufacturing a plastic optical fiber for a sensor in which a manufacturing method is simple and a linear hole is formed in which the sensor performance can be improved while the manufacturing cost is low and a plastic optical fiber Sensor.

According to a first aspect of the present invention, there is provided a method of manufacturing a plastic optical fiber for a sensor having a linear hole, the method comprising: placing a plastic optical fiber (POF) oil on a workbench of a micro drilling machine, Wow; Forming a hole having a radius of 0.1 mm to 0.5 mm in the micro-drilling machine on an in-line of the plastic optical fiber secured with the vise.

In the step (c), it is preferable that at least two holes are formed, and the drill of the drilling machine is preferably an end mill bit.

According to a second aspect of the present invention, there is provided an optical fiber sensor, wherein an optical fiber manufactured by any one of the above-described manufacturing methods is used.

The present invention provides a manufacturing method of a plastic optical fiber in which a manufacturing method is simple, a linear hole for a sensor is formed so that the manufacturing cost is low and the sensor performance can be improved.

In addition, the plastic optical fiber manufactured by such a method can be used for a very small refractive index sensor or a dispersion sensor, as well as for various products such as an in-line attenuator of a local area network.

FIG. 1 is a view showing a flow of a method of manufacturing a plastic optical fiber with a line-shaped hole according to an embodiment of the present invention,
Fig. 2 is a characteristic diagram for a plastic optical fiber (POF) having a linear hole,
FIG. 3 is a schematic view showing an experimental apparatus for forming a line-shaped hole according to an embodiment of the present invention and an apparatus for measuring the transmittance of a sensor for different liquids,
4 is a graph showing data measured at 670 nm and two transmittance data calculated analytically.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and how to accomplish it, will be described with reference to the embodiments described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. The embodiments are provided so that those skilled in the art can easily carry out the technical idea of the present invention to those skilled in the art.

In the drawings, embodiments of the present invention are not limited to the specific forms shown and are exaggerated for clarity. Also, the same reference numerals denote the same components throughout the specification.

The expression "and / or" is used herein to mean including at least one of the elements listed before and after. Also, singular forms include plural forms unless the context clearly dictates otherwise. Also, components, steps, operations and elements referred to in the specification as " comprises "or" comprising " refer to the presence or addition of one or more other components, steps, operations, elements, and / or devices.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

1 is a view showing a flow of a method of manufacturing a plastic optical fiber for a sensor in which a line-shaped hole is formed according to an embodiment of the present invention. As shown in FIG. 1, in the method of manufacturing a plastic optical fiber with a sub-millimeter linear hole according to an embodiment of the present invention, a plastic optical fiber (POF) is placed on a workbench of a micro- drilling machine, and the plastic optical fiber is fixed with a vise (S100); And forming a hole having a radius of 0.1 mm to 0.5 mm on the in-line of the plastic optical fiber fixed with the vise by the micro-drilling machine (S200).

In order to increase the resolution in the plastic optical fiber for sensor in which the line-shaped hole used in the sensor is conventionally formed, the hole size is increased (0.1 mm to 0.5 mm) in the embodiment of the present invention and micro- By proposing a method of forming multiple holes in order to increase the sensitivity of the sensor while maintaining the physical strength of the sensor structure, the method can be used not only in a simple manufacturing method but also in a sensor capable of improving the sensor performance while having a low manufacturing cost And a method of manufacturing a plastic optical fiber in which a line-shaped hole is formed.

Experimental and analytical results

Hereinafter, embodiments of the present invention for measuring the refractive index of the hole-based optical fiber sensor have been described. Fig. 2 is a characteristic diagram for a plastic optical fiber (POF) having a linear hole. In POF, the refractive indexes of the core and the cladding are 1.49 and 1.41, the core diameter 2a is 1.48 mm, and the wavelength of the light source used in the experiment is 670 nm, there are more than one million modes. Therefore, the interpretation of this structure should be explained in terms of ray optics.

Since the optical fiber is cylindrical symmetrical, only the upper half is considered from the optical fiber axis in the present invention. From the center of the hole, L (

) Θ _A of each hole by a distance in contact with the optical fiber at a position on the light axis A (

) And the complementary critical angle &thetas; _B (

) Is not blocked by the hole and propagates without loss. This is defined as the base transmittance. r _h is the radius of the hole, a is the radius of the core, and θ _c is the critical angle. The optical power of the light rays satisfying the condition that the total reflection occurs at the interface between the core and the cladding after passing through the hole as the light ray C is added to the base light transmittance and becomes the transmittance of the optical fiber structure. The transmittance means the ratio of the optical power at the left input end of the optical fiber to the optical power at the right output end.

If the hole is small, the base transmittance is increased but the change in the optical power due to the change in the refractive index of the hole decreases. This is the case with low resolution. On the other hand, as the hole increases in size, the base transmittance decreases, but the change in transmittance increases with the change in the refractive index of the hole. This is the case when the resolution is high. Therefore, the hole size has a considerable influence on the resolution of the sensor.

Since the refractive index of the liquid filling the holes is lower than that of the optical fiber core in most cases, the holes have the same function as a concave lens for dispersing the incident light. If incident light travels close to the optical fiber axis and passes through the hole and enters at an angle greater than the critical angle at the core / cladding interface, it will propagate without loss.

If the output angle, θ _o, is equal to or less than the critical angle, this ray will be lost due to refraction at the interface. Within the angular range of the angle θ with respect to the ray propagating in the fiber core through the hole, the transmittance of the sensor is calculated by the following equation:

Here,? _H is an angle between the optical fiber axis and the point at which the light ray C reaches the hole, measured from the center of the hole. For? _{0, max} =? _c ,

From Equation (2), θ _{h, max} are obtained by numerical analysis and then inserted again into Equation (1) to obtain θ _{i, max} , which is the maximum incident angle at which the ray can propagate without loss through the hole. Table 1 shows the maximum angles calculated for the refractive indices of different materials filling the holes. The transmittance of the sensor structure is easily obtained under the following assumptions.

1) Refractive index difference between the optical fiber core and the material filling the hole is not large, so Fresnel reflection at the input / output boundary of the hole / optical fiber core is ignored. 2) only the rays in the meridian direction are considered uniquely, 3) the mode distribution is uniform, and 4) there is no scattering due to the hole surface roughness.

Therefore, the transmittance of the sensor is expressed by Equation (3) below.

The maximum input angle increases with the refractive index as shown in [Table 1]. This clearly shows that as the refractive index increases, the light travels more through the hole, leading to a higher transmittance.

FIG. 3 shows an experimental apparatus for forming a line-shaped hole according to an embodiment of the present invention and an apparatus for measuring sensor transmittance for different liquids. The 1 m long POF has cladding and core diameters of 1.5 and 1.48 mm, respectively. The refractive indices of the core and the cladding are 1.49 and 1.41, respectively. The output light of a 670nm laser diode is focused on the input of the POF with a 20x microscope lens. The POF is fixed in vise and is located under the high speed drill bench. As the drill bit, an end mill bit having a diameter of 0.6 mm was used.

The POF output power was measured with an optical power meter. Before drilling, the output power of the optical fiber was measured and used as a reference power for calculating the transmittance. The holes were drilled and then injected into the holes in the order of the liquid having the lowest refractive index and the liquid having the highest refractive index. The liquid was injected from the top of the hole using a pipette.

In order to obtain accurate results, the liquid after measurement was absorbed by using paper and blown again to dryness. After that, it was confirmed again that the output power had the same value as the refractive index of the hole filled with air. Then proceeded to the next liquid. The liquids used in the experiments were water (n = 1.33), n-dodecane (n = 1.42), and 99% glycerol (n = 1.47). All of these refractive index values are given at 589.3 nm. After the permeability measurement was completed, the POF was removed from the vise and washed, and a hole diameter of about 0.35 mm at the center was measured by a digital microscope. Some scratches were observed inside the holes due to the drill bit.

Figure 4 shows the transmittance measured at 670 nm and the analytically calculated transmittance. As shown in Fig. 4, the sensor transmittance is increased in proportion to the refractive index as expected. It is observed that the calculated transmittance is higher than the measured transmittance. This difference is due not only to ignoring the Fresnel reflection at the interface of the hole, ignoring the skew ray, uniform mode distribution, increasing the scattering due to hole surface roughness during the drilling process, 670nm), the value of the refractive index of the liquid is less than the given value at 589.3nm.

This difference also tends to increase as the difference in refractive index between the liquid and the optical fiber core increases. For example, the difference for glycerol is 3.89 ± 0.22%. However, for n-dodecane and H2O, 4.86 ± 0.88% and 6.14 ± 0.44%, respectively. This phenomenon appears to be due to the fact that scattering becomes larger in holes filled with a medium having a lower refractive index due to hole surface roughness. The sensor sensitivity was about 13.4 dB / RIU in the 1.33 to 1.42 refractive index range. Performance is slightly less than that of a microhole refractive index sensor fabricated on a single mode silica fiber of similar structure, but it is clear that increasing the hole size or making multiple holes will further improve the performance.

As described above, the present invention proposes a method of manufacturing a hole-based plastic optical fiber sensor of less than a millimeter manufactured by drilling in POF. In the present invention, the sensor proposed by the embodiment is applied to the measurement of the refractive index. The transmittance of the sensor structure was evaluated to investigate the sensing characteristics of the proposed sensor as a refractive index sensor. To evaluate the transmittance of the sensor structure, the analytical results of the transmittance were derived using the ray optics under the following assumptions. 1) The refractive index difference between the optical fiber core and the hole is not so large, so that the Fresnel reflection at the input / output interface of the core is ignored. 2) only the rays in the direction of the meridian are considered, 3) the mode distribution is uniform, and 4) there is no scattering due to the hole surface roughness. Induced transmittance results show that hole size affects sensor resolution. Therefore, in order to increase the resolution, it is necessary to generate a larger hole, but when the hole size is increased, the physical strength is lowered. To compensate, it is desirable to use several holes with smaller diameters to maintain physical strength and lead to higher resolution.

A hole having a radius of 0.35 mm was produced by using a 0.6-mm-diameter micro-bit in a POF having an outer diameter of 1.5 mm. The liquids used in the experiments were water (n = 1.33), n-dodecane (n = 1.42), and 99% glycerol (n = 1.47). The difference between experimental and calculated results is less than 6%. Considering the assumptions used in the derivation of the transmittance and the fact that the liquid refractive index values at the 670 nm wavelength used in the experiment are lower than the wavelength of 589.3 nm, the experimental results and the calculated results are surprisingly consistent.

Therefore, the optical fiber having a sub-millimeter hole based on the POF of the present invention can be used with various kinds of optical fiber sensors such as a very small refractive index sensor, a liquid level sensor, a gas sensor, a dispersion sensor, Of-line attenuator.

While the invention has been shown and described with respect to the specific embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. Anyone with it will know easily.

Claims

Placing a plastic optical fiber (POF) oil on a workpiece of a micro drilling machine and fixing the plastic optical fiber with a vise;
And forming a hole having a radius of 0.1 mm to 0.5 mm in the micro-drilling machine on an in-line of the plastic optical fiber fixed with the vise. Way.

The method according to claim 1,
The step (c)
And at least two or more holes are formed in the plastic film.

The method according to claim 1,
Wherein the drilling of the drilling machine uses an end mill bit. &Lt; RTI ID = 0.0 > 11. < / RTI >

The plastic optical fiber sensor according to any one of claims 1 to 3, wherein the optical fiber is used.