KR19980085623A - Optical Fiber Damage Monitoring Device for Laser Transmission - Google Patents

Abstract

The present invention relates to an optical fiber connecting device comprising a visible light indicating laser (1) of a laser processing device and an optical fiber connecting device (6) for injecting the indicating laser into a laser transmission optical fiber by matching the optical path with the processing laser. In particular, the optical detector 8 for measuring the intensity of the indicating laser reflected from the optical fiber exit end surface after reciprocating the optical fiber, the photodetector 9 for measuring the output of the indicating laser, and the indicating laser are optical fibers. A polarization beam splitter 4 for maintaining the polarization before being incident on the beam and separating and detecting the indicating laser reflected from the optical fiber plane for each polarizing component, and a photodetector for measuring the output of the indicating laser. ) And the signal of the photodetector 8 for measuring the intensity of the laser reflected back from the optical fiber cross-section, and out of the preset threshold range. In the case of providing an optical fiber state monitoring device, characterized in that consisting of a signal processing device 10 for outputting an abnormal state of the optical fiber transmission state, by using the optical fiber connection device and laser for transmission used for laser welding, By selectively measuring the laser beams reflected from both ends of the optical fiber using a polarizer, it is possible to monitor the damage and contamination of the optical fiber in real time.

Description

Optical Fiber Damage Monitoring Device for Laser Transmission

The present invention relates to an optical fiber damage monitoring apparatus for laser transmission for monitoring in real time the damage state of the optical fiber for laser transmission during high power laser processing.

In general, laser processing technology has the advantage that the remote processing by the optical fiber long distance transmission is possible. Most laser remote processing is achieved by transmitting the laser light from the laser oscillator to the actual processing space by using the laser transmission fiber. In case of a problem in the state of the optical fiber during the processing, the high power laser light is out of the optical path and processed into the processing optical system. Not only does it cause damage, but it can also cause fatal damage to workers' safety.

Therefore, the real-time monitoring of the state of the laser transmission optical fiber is very important in the laser remote processing using the optical fiber, but most laser processing head portion is often installed in a bad condition such as a narrow space or a radiation zone, there is a problem that the monitoring is not easy.

In addition, conventional optical methods for monitoring a laser transmission optical fiber include a method of comparing a reflected optical signal by installing a separate photodetector next to a fiber coupler, and a separate optical fiber for monitoring next to the transmission optical fiber. There is also a method to monitor the alignment and damage by measuring the laser leaking through the cladding (additional).

Teleprocessing technology through fiber optic transmission of high power lasers began to spread in the 1980s, and fiber optic monitoring technology also began to be developed. However, due to the limitation that it is difficult to install a separate device in the work space, there is still no reliable optical fiber monitoring technology. Optical fiber monitoring in laser teleprocessing is a remote monitoring concept using fiber optics. Several methods have been developed. Conventional optical methods for monitoring high-power laser transmission optical fibers for processing include a separate photodetector (PHOTO-DETECTOR) next to the fiber coupler (FIBER COUPLER) as in US Patent 4,812,641 (HIGH POWER OPTICAL FIBER FAILURE DETECTION SYSTEM). By measuring and comparing the intensity of the laser light input to the optical fiber and the laser light output from the optical fiber, there is a method for monitoring the health of the optical fiber and the alignment of the optical system. This method basically uses the principle of monitoring the optical fiber's health by measuring the transmission of the optical fiber. In addition, U.S. Patent 5,319,195 (LASER SYSTEM METHOD AND APPARATUS FOR PERFORMING A MATERIAL PROCESSING OPERATION AND FOR INDICATION G THE STATE OF THE OPERATION) attaches a separate monitoring fiber next to the laser transmission fiber to measure the laser light leaking by CLADDING And a method of monitoring for damage. However, these methods have many limitations due to the complexity of installing separate optical fiber optics for monitoring in addition to the processing transmission fiber. Therefore, the real-time monitoring technology of the conventional optical fiber is composed of additional optical fiber optics. Due to this complexity, it was difficult to apply in actual field, and it was not universalized.

An object of the present invention for solving the above problems is to selectively transmit the laser beams reflected from both ends of the optical fiber by using a polarizer using a transmission optical fiber connection device and an indication laser used for laser welding. The present invention provides an optical fiber damage monitoring device for laser transmission that can monitor in real time the damage and contamination of the optical fiber.

That is, in the present invention, a polarizing beamsplitter is introduced into the surveillance optical system to separate the indicating laser signal reflected from both sides (the incidence part and the output part) of the end of the transmission fiber, and reflect from the optical fiber output surface to reciprocate the optical fiber. By measuring only the laser signal returning to the bottom row, a method of obtaining a signal having a high S / N ratio has been proposed. In addition, this method does not have to install a separate optical fiber to monitor the laser transmission optical fiber, and by installing several optical components such as a polarization beam splitter in the optical fiber connection device, it is possible to monitor the optical fiber for damage and contamination in real time. To help.

1 is a schematic diagram of an optical fiber state monitoring device

Figure 2 is a principle diagram of the monitoring laser signal using a polarizing beam splitter

3 shows the result of monitoring signal measurement when impurities are on the optical fiber ends

4 is a result of monitoring signal measurement when an impurity is deposited on an optical fiber end

5 shows the results of monitoring signal measurement when the optical fiber is bent and cut

Explanation of symbols for the main parts of the drawings

1: indicating laser 2: beam splitter

3: beam expander 4: polarized beam splitter

5: Band filter 6: Optical fiber connection device

7: Focusing lens 8, 9: Photodetector

10: signal processing device 11, 12: optical fiber

A feature of the present invention for achieving the above object is a visible light indicating laser 1 of a laser processing apparatus, and an optical fiber connecting apparatus optical system for causing the indicating laser to enter the laser transmission optical fiber by matching the processing laser with the optical path 6 In fiber optic connectors consisting of:

A first photodetector 8 for measuring the intensity of the indicating laser returned from the optical fiber exit cross section after reciprocating the optical fiber, a second photodetector 9 for measuring the output of the indicating laser, and the indicating laser Polarization beam splitter 4 for maintaining the polarization before the light is incident on the optical fiber and separating and detecting the instruction laser that is reflected and returned from the optical fiber plane by polarization components, and a second measuring output of the instruction laser. A signal that outputs an abnormality in the optical fiber transmission state when the signal is out of the preset threshold range by comparing / processing the signal of the photodetector 9 and the first photodetector 8 for measuring the intensity of the laser reflected from the cross section of the optical fiber. It consists of the processing apparatus 10.

As an additional feature of the present invention for achieving the above object, the polarizing beam splitter 4 has an indication laser that is transmitted by the polarization direction reflected from the incidence plane of the transmission optical fiber and is reflected from the emission plane of the transmission optical fiber. Is partially transmitted and partially reflected, so that the photodetector which detects the indicating laser reflected at the optical fiber cross section is configured to detect only the indicating laser reflected by the optical fiber exiting surface.

As an additional feature of the present invention for achieving the above object, the signal processing device 10 is a laser that reflects from the optical fiber cross-section is mixed with the light that is reflected or scattered from the processing specimen is reflected from the optical fiber exit cross-section If it is difficult to discriminate and measure only the signal, the output intensity of the indicating laser is modulated at a constant frequency and only the frequency component is processed from the measured laser signal, thereby eliminating the noise effect of the optical signal from the processed specimen.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

1 is a configuration diagram of an optical fiber connection device and a signal measuring device configured for optical fiber breakage and surface condition monitoring. The laser 1 for indicating the visible light of the laser processing device and the indicating laser are made to match the processing laser and the optical path. The optical fiber connector consisting of the optical system 6 for injecting into the transmission optical fiber, the second photodetector 9 for measuring the output of the indicating laser, and maintaining the polarization before the indicating laser enters the optical fiber. And a polarization beam splitter (4) for separating and detecting the indicating laser reflected by the optical fiber in terms of polarization components, and measuring the intensity of the indicating laser reflected from the optical fiber exit section after the optical fiber is reciprocated. 1 includes a photodetector 8 and a signal processing apparatus 10 for processing an indication laser intensity signal measured by two photodetectors.

Looking at the operation of the optical fiber damage monitoring device for laser transmission according to the present invention configured as described above, the processing laser from the oscillator is transmitted to the first optical fiber 11 is inserted into the processing specimen from the optical fiber connection device (6) 2 is transmitted to the optical fiber 12. In this step, the intensity of the indicating laser which is incident on the optical fiber (usually using a visible light diode laser) 1 and the indicating laser which is reflected from the optical fiber exiting surface returning to and returning from the optical fiber is measured. By comparing these two signals, it is possible to monitor the state of the optical fiber optical system.

In this case, the optical fiber for high power laser transmission is generally composed of four layers, the innermost layer of which is an optical fiber core part, the outermost part of which is a cladding part, the outer part of which is a buffer layer, and an outer part of the buffer layer. There is a protective tube. The core part of the optical fiber is made of high purity silica glass, and the refractive index is larger than that of the cladding part so that the laser beam is transmitted along the core without going out to the cladding part by total internal reflection. The refractive index of the buffer portion is larger than the cladding portion, so that when light exits the core through the cladding portion, it is transmitted through the buffer layer. This abnormal transmission causes many problems. If the optical fiber is broken or there are impurities in the surface or misalignment, the beam exits the core and rides through the buffer layer, thereby attenuating the laser signal of the core portion.

Therefore, this apparatus monitors the transmission state by comparing the laser signal of this core part with an input signal. In addition, the apparatus installs a polarizing beamsplitter in front of the laser to measure only the intensity of the indicating laser beam reflected back from the optical fiber output surface.

Referring to FIG. 2 attached to the measurement principle of the monitoring laser signal using the polarizing beam splitter operating as described above, when the beam polarized in the horizontal direction is incident on the optical fiber cross section is partially reflected from the incident surface and the exit surface of the optical fiber Come back. Since the beam reflected from the optical fiber incident surface is maintained in the horizontal direction, the first light detector 8 is not detected by just passing through the polarization beam splitter 4, but the beam reflected from the optical fiber exit surface is broken. As a result, it is reflected by the polarization beam splitter (partially about 1/2) and detected by the first photodetector 8.

Since this signal is a laser beam that has traveled back and forth through the fiber, it has information about the fiber condition. In other words, the proposed configuration eliminates the signal at the optical fiber incidence plane by introducing a polarizing optical component, and selectively detects only the signal reflected at the optical fiber exit face which has information on the state of the optical fiber. The S / N ratio is more than doubled to monitor the fiber condition.

At this time, the laser which is used a lot in laser processing is Nd: YAG laser or CO2 laser and is not visible to the naked eye because the wavelength is infrared region. Therefore, in the laser processing operation, an indication laser having a wavelength in the visible light region is installed / used by matching the optical path with the laser for the alignment of the optical system and the selection of the working position.

In other words, by monitoring the optical fiber transmission state by measuring the laser signal transmitted to the optical fiber reflected from the exit surface of the optical fiber, in this configuration that introduces a polarizer, the laser signal reflected from the optical fiber incident surface is removed and the laser signal reflected from the optical fiber entrance surface is removed. By selective measurement, the S / N ratio of the monitoring signal can be increased more than twice.

The present invention removes the indicating laser signal reflected from the optical fiber incident surface by introducing a polarizing optical component, and selectively detects only the indicating laser signal reflected from the optical fiber exit surface having information on the transmission state of the optical fiber. It increases the S / N ratio of more than twice and monitors the fiber condition.

The apparatus of the present invention actually confirmed the usability through experiments. The experiment used a step index high-power laser transmission optical fiber with a core diameter of 800um and obtained monitoring results in the case of impurities such as water at the end of the optical fiber and when the optical fiber was broken, thus proving that the optical system can be monitored in real time. It was.

That is, in order to prove the utility of the present invention, the optical fiber damage monitoring experiment was performed using a high power Nd: YAG laser transmission optical fiber and an indication laser (5mW, 633nm). In addition, the experiment was also modulated while modulating the output of the indicating laser in order to confirm that status monitoring is possible regardless of the output of the indicating laser. Mitsubishi's optical fiber (diaguide ST series step index MRT # ST800G-SY) with a core diameter of 800um was used, the photodetector used a PIN photo-diode, and a half width to selectively extract the indicating laser. A bandpass filter having a (FWHM) of 10 nm was used. The laser signal in this experiment was processed with a digital oscilloscope (lecroy 9304A).

3 shows the results of monitoring signal measurement experiments when water is applied to the optical fiber ends.

In the figure, ch.1 is the laser input signal, ch.2 is the signal returned through the optical fiber, and ch.D is the actual monitoring signal as the ratio of two signals (signal 2 / signal 1). The big change in the initial signal is the moment when water gets on the optical fiber output section, and the middle fluctuation shows the severe change in the laser reflectivity in the process of blowing water from the optical fiber end to compressed air.

FIG. 4 is a measurement result when modulating the intensity of a directing laser. The input signal and the output signal are experimentally modulated by the sine waveform of the output of the actual monitoring signal. Is the same as This characteristic means that when the indicating laser signal is mixed with other miscellaneous signals, for example, when the indicating laser signal is mixed with the optical signals generated by the plasma generated from the processed specimen, the intensity of the indicating laser is modulated to a specific frequency and only the signal at that frequency is measured. It can be used to remove the signal jam.

5 is a monitoring signal measurement result when the laser transmission optical fiber is bent and broken. It can be seen that the attenuation of the signal in the process of bending the optical fiber, and the signal attenuation after the break is also clearly shown. The results of this experiment show that the monitoring device can detect whether the laser processing part is contaminated or whether the laser transmission fiber is damaged.

When providing a laser transmission optical fiber damage monitoring device according to the present invention that operates as described above, using a transmission optical fiber connection device and an indication laser used for laser welding, the laser beams reflected from both ends of the optical fiber to the polarizer ( By selective measurement using a polarzer, it is possible to monitor the damage and contamination of the optical fiber in real time.

Claims (3)

In an optical fiber connecting device comprising a visible light indicating laser (1) of a laser processing device and an optical fiber connecting device (6) for injecting the indicating laser into a laser transmission optical fiber by matching the optical path with the processing laser: A first photodetector 8 for measuring the intensity of the indicating laser returned from the optical fiber exit cross section after reciprocating the optical fiber; A second photodetector 9 for measuring the output of the indicating laser; A polarization beam splitter 4 for maintaining the polarization before the instruction laser is incident on the optical fiber and detecting and separately detecting the instruction laser which is reflected from the optical fiber plane for each polarization component; And Comparing / processing the signals of the second photodetector 9 measuring the output of the indicating laser and the first photodetector 8 measuring the intensity of the laser reflected back from the optical fiber cross section, thus exceeding a preset threshold range. The optical fiber state monitoring device, characterized in that consisting of a signal processing device 10 for outputting an abnormal state of the optical fiber transmission state. 2. The polarizing beam splitter (4) according to claim 1, wherein the polarization beam splitter (4) transmits the indicating laser whose polarization direction is reflected at the entrance face of the transmission optical fiber, and partially transmits the indicating laser reflected at the exit face of the transmission optical fiber. And an optical detector (8) which is configured to reflect and detects the indicating laser reflected at the optical fiber cross-section, so as to detect only the indicating laser reflected by the optical fiber exiting surface. 2. The signal processing apparatus 10 of claim 1, wherein the signal processing device 10 is difficult to discriminate and measure only a laser signal reflected from an optical fiber cross-section due to mixing of the laser indicating the light reflected from the optical fiber exit cross-section with the light reflected or scattered from the processed specimen. In this case, the optical fiber state monitoring device, characterized in that to remove the noise effect of the optical signal from the processed specimen by modulating the output intensity of the indicating laser to a predetermined frequency and processing only the frequency component from the measured laser signal.