JP2006292674A - Method and device for monitoring optical power, and optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for monitoring optical power capable of reducing the number of part items and fused connection points to reduce a loss as the whole system, and also to provide a device therefor and an optical device incorporating the device therein. <P>SOLUTION: In this method for monitoring optical power, an optical fiber for monitoring is arranged in the vicinity of the fused connection point of a measured optical fiber to make scattered light emitted from the fused connection point get incident, and scattered light power is measured through the monitoring optical fiber to monitor the input and output optical powers of the measured optical fiber. This optical power monitoring device of the present invention has the monitoring optical fiber arranged to make the scattered light emitted from the fused connection point get incident, in the vicinity of the fused connection point of the measured optical fiber, and a light detecting means for measuring the scattered light power through the monitoring optical fiber. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical power monitoring method and apparatus for measuring the optical power of an optical fiber to be measured, and in particular, the loss of the entire system is reduced by reducing the number of components and the number of fusion splicing points. The present invention relates to an optical power monitoring method, an optical power monitoring apparatus, and an optical device incorporating the apparatus.

  For optical devices, particularly optical devices using optical fibers with optical amplification characteristics doped with functional materials that enhance optical amplification or nonlinear optical effects, the optical power of pumping light, outgoing light, and reflected light Is an important parameter for device performance, so the propagation power of the optical fiber through which these lights propagate, that is, the measured optical fiber (incident light (input), outgoing light (output), and reflected light (reflected return light)) Is generally monitored (see, for example, Patent Document 1).

In the conventional optical power monitoring method, a part of each of input light, output light and reflected light is branched by a fiber coupler at a predetermined branching ratio, and this branched light is used as an optical signal or a photodiode (hereinafter referred to as PD). In most cases, it is converted to an electrical signal and monitored.
FIG. 2 illustrates a conventional optical power monitor device. In this conventional apparatus, an optical fiber coupler 2 is inserted into and connected to a connection portion of an optical fiber 1 to be measured so that light can be extracted from the optical fiber 1 to be measured with a predetermined branching ratio. It is configured to measure the light intensity by leading to no PD. In FIG. 2, reference numerals 3 and 4 denote fusion splice points (hereinafter referred to as connection points).
JP-A-5-264344

  Optical devices using optical fibers on the input / output side can be easily connected by fusion-bonding the optical fibers when connecting the modules. For example, in the case of a fiber laser that uses the optical amplification characteristics of a rare earth-doped optical fiber, the output side fiber of the pump light source and the input side of the rare earth-doped optical fiber are fusion-spliced to make the pump light incident on the rare earth-doped optical fiber. It can be easily connected. However, in this type of optical device, when it is necessary to monitor the pumping light power or the like of the optical fiber 1 to be measured, as shown in FIG. Since it must be inserted between the incident sides of the optical fiber, two connection points 3 and 4 are required. Therefore, since one connection point is added as compared with the case where monitoring is not required, connection loss also occurs at two locations.

  The present invention has been made in view of the above circumstances, and an optical power monitoring method, an optical power monitoring apparatus, and the apparatus capable of reducing the loss of the entire system by reducing the number of components and the number of fusion splicing points. The purpose is to provide an optical device incorporating the above.

  In order to achieve the object, a monitoring optical fiber is disposed in the vicinity of the fusion splicing point of the optical fiber to be measured so that scattered light emitted from the splicing splicing point can be incident, and the scattering is transmitted through the optical monitoring optical fiber. There is provided an optical power monitoring method characterized by monitoring the propagation optical power of an optical fiber to be measured by measuring the optical power.

  In the optical power monitoring method of the present invention, it is preferable to adjust the distance between the fusion splicing point and the tip of the monitoring optical fiber so that the light receiving power of the monitoring optical fiber is appropriate.

  Further, the present invention provides a monitor optical fiber disposed so that scattered light emitted from the fusion splicing point can be incident in the vicinity of the fusion splicing point of the optical fiber to be measured, and scattered light transmitted through the monitoring optical fiber. There is provided an optical power monitoring device comprising a light detection means for measuring power.

  In the optical power monitoring device of the present invention, the tip of the monitoring optical fiber is fixed with an adhesive having a refractive index higher than the cladding refractive index of the optical fiber to be measured together with the fusion splicing point of the optical fiber to be measured. The adhesive is preferably covered and fixed with a heat-shrinkable reinforcing sleeve.

  In the optical power monitoring device of the present invention, the tip of the monitoring optical fiber is covered with a reinforcing rod together with a fusion splicing point of the optical fiber to be measured, and the optical fiber to be measured is inside the reinforcing rod. It is preferably fixed by an adhesive having a refractive index higher than the clad refractive index.

  In the optical power monitoring apparatus of the present invention, it is preferable that the light detection means is a PD that converts light transmitted through a monitoring optical fiber into an electrical signal.

  Further, the present invention is an optical device having an optical amplification function or a nonlinear optical effect, and has the optical power monitor device according to any one of claims 3 to 6, and can measure the propagation optical power of the optical fiber to be measured. An optical device is provided.

  The optical device of the present invention preferably includes an optical fiber for optical amplification doped with a functional material that enhances the optical amplification effect.

  The functional material is preferably at least one selected from the group consisting of rare earth ions such as erbium, ytterbium, lanthanum, cerium, praseodymium, and neodymium.

Unlike the conventional branching means, the optical power monitoring method of the present invention receives scattered light caused by the connection loss leaking from the connection point existing in the optical fiber to be measured by the monitoring optical fiber, and Since the optical power of the optical fiber under test can be monitored by guiding the light to the light detection means, an optical fiber coupler is not used, no wasteful connection loss occurs, and the work is inexpensive. A good optical power monitoring method can be provided.
The present invention is particularly applicable to an optical device such as an optical fiber laser using an optical fiber having an optical amplification characteristic with high input / output optical power.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1A and 1B show an embodiment of an optical power monitor device according to the present invention, FIG. 1A is a configuration diagram of an optical power monitor device 11, and FIG. The optical power monitoring device 11 of the present embodiment is capable of making scattered light 18 emitted from the connection point 12 be incident in the vicinity of the fusion splicing point 12 (hereinafter abbreviated as a connection point) of the optical fibers 10A and 10B to be measured. The monitor optical fiber 13 is arranged, and a PD 16 is provided as a light detection means for measuring the scattered light power transmitted through the monitor optical fiber 13.

  In the optical fibers 10A and 10B to be measured, two optical fibers are fusion-bonded at the connection point 12, and signal light, excitation light, amplified light, etc. are propagated to the optical fiber, and the optical power of the portion is measured. There is no particular limitation as long as it is an optical fiber portion that requires monitoring. For example, in a fiber laser, an optical fiber amplifier, or the like, a connection portion between an optical fiber for output from a pumping light source and an input side of a rare earth-doped optical fiber for amplification is assumed. The connection point 12 of the optical fibers 10A and 10B to be measured is obtained by removing the coating of each optical fiber end, butting the end faces of the optical fiber bare wires made of quartz glass, aligning the optical axes, and using a fusion splicer. Are formed by fusion splicing.

  In the example shown in FIG. 1, one of the measured optical fibers 10A and 10B is one of the measured optical fibers 10A that is an output side optical fiber of a laser diode 17 (hereinafter referred to as LD) that is an excitation light source, and the other. The optical fiber 10B to be measured is an input side optical fiber such as a rare earth doped optical fiber having an optical amplification function, and the optical power of the input light from the LD 17 to the other optical fiber 10B to be measured is shown.

  In this optical power monitor device 11, the distal end portion of the monitoring optical fiber 13 is disposed adjacent to the connection point 12 of the optical fibers 10 A and 10 B to be measured, and the vicinity of the connection point 12 and the distal end portion of the monitoring optical fiber 13. Are surrounded and fixed by an adhesive 15 having a refractive index higher than the clad refractive index of the optical fibers 10A and 10B to be measured, and a heat-shrinkable reinforcing sleeve is placed on the adhesive 15 and is covered by heat shrinkage. It is fixed by that.

  In the optical device, each module is connected by fusion splicing between optical fibers. In the conventional technique, it is possible to adjust the fusion splicing condition and reduce the connection loss to a certain value, but the connection loss cannot be avoided. Light due to the connection loss is scattered in the form of leakage light in the propagation direction, and scattered light 18 is emitted from the connection portion 12. If the optical characteristics and fusion splicing conditions of the optical fibers 10A and 10B to be measured are constant, the light power distribution of the scattered light 18 is also constant.

  The present invention utilizes the inevitable connection loss, and installs the tip of the monitoring optical fiber 13 in the vicinity of the connection point 12 of the optical fibers to be measured 10A and 10B to be monitored in the light propagation direction. The scattered light 18 resulting from the connection loss is received. As described above, since the distribution of the scattered light power caused by the connection loss is constant, the light reception power of the monitoring optical fiber 13 installed at a predetermined position near the connection point 12 is also constant. That is, since the correlation between the scattered light power received by the monitoring optical fiber 13 and the optical power propagating through the optical fibers to be measured 10A and 10B (hereinafter referred to as propagation optical power) is constant, the monitoring optical fiber By measuring the scattered light power received at 13 with the PD 16, the propagation light power can be easily estimated, and the propagation light power can be easily monitored.

As the method for fixing the monitoring fiber 13, there are the following two methods.
1) After the monitoring optical fiber 13 is installed at a predetermined position, the reinforcing sleeve 14 is provided with an adhesive 15 together with the tip of the monitoring optical fiber 13 and the vicinity of the connection point 12 of the optical fibers 10A and 10B to be measured. Cover and fix by heat shrinking.
2) After the monitoring optical fiber 13 is installed at a predetermined position, the monitoring optical fiber and the vicinity of the connection point 12 of the optical fibers 10A and 10B to be measured are covered with a reinforcing rod, and adhesive is applied from both ends of the reinforcing rod. Inject and cure.
The adhesive 15 used in 1) and 2) is preferably an adhesive having a refractive index higher than the cladding refractive index of the optical fibers 10A and 10B to be measured.

  In the vicinity of the connection point 12, the power distribution of the scattered light 18 varies depending on the spatial position. Therefore, after the tip of the monitoring optical fiber 13 is installed at a predetermined position, it is important to fix the position without changing the position. It is. In other words, if the tip position of the monitoring optical fiber 13 is constant, the correlation between the received light power and the propagation light power to be monitored becomes constant, and the propagation light power is indirectly determined by the received light power of the monitoring optical fiber 13. Can be monitored automatically.

  Usually, the fusion splicing between optical fibers includes a step of removing the end coating of the optical fiber, which is called pretreatment. That is, in the vicinity of the connection point 12, the optical fiber remains in a bare wire state made of quartz glass. In order to protect the connecting portion 12, the connecting portion 12 is usually re-coated and reinforced with a reinforcing sleeve (also referred to as a heat-shrinkable tube) that has been previously passed through an optical fiber and provided with a hot-melt adhesive. .

  Therefore, in the present invention, after the monitoring optical fiber 13 is installed at a predetermined position, the distal end portion of the monitoring optical fiber 13 and the vicinity of the connection portion 12 of the optical fibers 10A and 10B to be measured are covered with the reinforcing sleeve 14 together. By doing so, the monitoring optical fiber 13 can be installed and fixed simultaneously with the reinforcement of the connection portion 13 by the procedure of the reinforcement process that is normally required without additional equipment or processes.

  In the present invention, it is preferable that the refractive index of the adhesive is higher than the cladding refractive index of the optical fiber on the input / output side. In the present invention, the propagation light power of the optical fibers 10A and 10B to be measured is monitored by receiving the scattered light power caused by the connection loss in the vicinity of the connection point 12. Therefore, it is assumed that the scattered light 18 caused by the connection loss is leaked to the external space in the vicinity of the connection point 12. However, when the refractive index of the adhesive 15 covering the vicinity of the connection point 12 is lower than the refractive index of the cladding of the optical fibers 10A and 10B to be measured, the scattered light 18 once emitted from the core is an adhesive having a low refractive index. It is reflected, returns to the optical fiber again, and propagates in the form of the cladding mode through the cladding of the optical fiber. Therefore, in order to scatter the connection loss near the connection point 12 to the external space, it is desirable that the refractive index of the adhesive 15 used in the present invention is higher than the cladding refractive index of the optical fibers 10A and 10B to be measured.

  On the other hand, the types of the internal hot melt adhesive for the commercially available reinforcing sleeve are limited. When selection of an adhesive (for example, selection of a refractive index) is required, a tip of the monitoring optical fiber 13 and light to be measured are replaced with a reinforcing rod such as a glass rod instead of the heat-shrinkable reinforcing sleeve 14. A method is effective in which the vicinity of the connection point 12 of the fibers 10A and 10B is collectively covered, a predetermined adhesive is injected from both ends of the rod, and then fixed by curing. Moreover, the adhesive used at this time is not limited to a hot-melt adhesive, and for example, a commercially available ultraviolet curable resin may be used.

  As the above-mentioned adhesive, it is preferable to use an adhesive that has little absorption in the wavelength band of the propagation light of the optical fibers 10A and 10B to be measured. In both of the above-described two fixing methods, since the adhesive 15 needs to be filled in the reinforcing sleeve 14, the adhesive is scattered due to the connection loss, depending on the wavelength of the propagation light to be monitored. There is also a possibility that the light 18 is absorbed. When an adhesive having a large absorption in the wavelength band of the propagation light to be monitored is used, the absolute value of the light receiving power of the monitoring optical fiber 13 is reduced to the lower detection limit due to the absorption by the adhesive, and detection / response cannot be performed. In addition to the fear, the absorbed optical power becomes thermal energy, and a large amount of heat may be generated, and there is a possibility that the reinforcing resin itself in the connection portion may burn. Therefore, the adhesive used in the present invention is preferably an adhesive that absorbs less in the wavelength band of the propagation light to be monitored.

In the present invention, it is preferable that the optical signal from the monitoring optical fiber 13 is received by the PD 16 and converted into an electrical signal.
In addition, it is preferable to adjust the distance between the connection point 12 and the tip of the monitoring optical fiber 13 so that the light receiving power of the monitoring optical fiber is appropriate.

  In this optical power monitor device 11, the optical signal from the monitoring optical fiber 13 may be directly monitored. However, when the control circuit of the optical device is an electric circuit, the optical signal is received by the PD chip or the like from the direct monitor. It is common to monitor an element after converting an optical signal into an electric signal. Also in the present invention, when the control circuit of the optical device is applied to an electric circuit, it is desirable that the optical signal from the monitoring optical fiber 13 is converted into an electric signal by the PD 16. Further, when the optical power received by the PD 16 is weak, it is preferable to install an electric amplifier circuit on the control circuit of the PD 16.

  In addition, elements such as PD have an allowable maximum power, and there is a risk that the elements will be destroyed if the power exceeds this. If there is a possibility that the light receiving power of the PD 16 may exceed the allowable maximum power, it is of course possible to insert a normal attenuation optical fiber in the portion before the light receiving of the PD 16. However, in the present invention, the light receiving power of the PD 16 is appropriate. It is desirable to adjust the installation position of the distal end of the monitoring optical fiber 13, that is, the distance between the distal end of the monitoring optical fiber 13 and the connection point 12 so as to be a proper amount. Basically, the farther the tip of the monitoring optical fiber 13 is from the connection point 12, the smaller the received light power (see Example 1 described later).

  This optical power monitoring device 11 is in principle applicable to optical devices using optical fibers on all input / output sides, but in particular, light doped with a functional material that enhances optical amplification or nonlinear optical effect. It is desirable to apply to optical devices such as fiber lasers and optical fiber amplifiers using optical fibers having amplification characteristics.

  In an optical device such as a fiber laser having an optical amplification characteristic having high input / output optical power, since the absolute value of the input / output optical power is large, the connection loss is also large. For example, in the case of a high power fiber laser, the output side optical power is often 10 W or more. In that case, even if the connection loss on the output side is only 0.1 dB, the absolute power is 200 mW or more. Even if 0.01% of the connection loss is received, the optical power is -16 dB, which is a level that can be sufficiently detected.

  In addition, the functional material that enhances the above-described optical amplification function includes rare earth elements such as erbium (Er), ytterbium (Yb), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), and the like. It is desirable to include at least one rare earth ion.

[Example 1]
The apparatus shown in FIG. 1 was manufactured and the input optical power from the LD was monitored.
As the light source, an LD having a center wavelength of 980 nm and a maximum output of 500 mW was used. A single-mode optical fiber having a cut-off wavelength of 940 nm and a mode field diameter of 6.7 μm was used as the optical fiber on the input side and output side, which are optical fibers to be measured. The connection loss at the connection point between the input and output side optical fibers was adjusted to be 0.1 dB (about 11.4 mW).
The monitoring optical fiber is a multimode optical fiber having a core diameter of 50 μm, a cladding diameter of 125 μm, and a numerical aperture (NA) of 0.2. Along with the output optical fiber, a tip is installed near the connection point, and then commercially available. The hot-melt adhesive was fixed with a reinforcing sleeve provided inside.
Using the above apparatus, the power of the LD of the light source was made constant at 500 mW, and the light receiving power of the monitoring optical fiber was monitored with a power meter while changing the distance from the connection point to the tip of the monitoring optical fiber. The result is shown in FIG.
The horizontal axis in FIG. 3 is the distance from the connection point to the tip of the monitoring optical fiber, and the vertical axis is the light receiving power of the monitoring optical fiber. It can be seen that the scattered light power that can be received varies depending on the position of the tip of the monitor optical fiber.
In addition, the position where the light receiving power is maximum is not a position close to the connection point but a position separated by a certain distance. This is because the scattered light caused by the connection loss is radiated at an angle (which varies depending on the NA) and emerges in an oblique direction from the connection point, so that the power distribution is not maximum in the immediate vicinity of the connection point. .

[Example 2]
In the apparatus shown in FIG. 1, the distance from the connection point to the tip of the monitoring optical fiber was kept constant at 2 mm, the power of the LD of the light source was changed from 100 mW to 500 mW, and the received light of the monitoring optical fiber was monitored. The result is shown in FIG. However, for comparison, the LD output power unit of the light source on the horizontal axis is converted from mW to dBm.
The horizontal axis in FIG. 4 is the output power of the LD as the light source, and the vertical axis is the light reception power of the monitoring optical fiber. From the results of FIG. 4, it can be seen that the output power can be monitored from the received light power of the monitoring optical fiber installed at a fixed position.

1 shows an embodiment of an optical power monitoring device according to the present invention, where (a) is a configuration diagram of the optical power monitoring device, and (b) is an enlarged cross-sectional view of a main part. It is a block diagram which shows the conventional optical power monitor apparatus. 6 is a graph showing the relationship between the distance from the connection point measured in Example 1 to the tip of the monitoring optical fiber and the light receiving power. It is a graph which shows the relationship between the output power of the light source measured in Example 2, and the light reception power of the optical fiber for a monitor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10A, 10B ... Optical fiber to be measured, 11 ... Optical power monitor apparatus, 12 ... Connection point (fusion splicing point), 13 ... Monitoring optical fiber, 14 ... Reinforcement sleeve, 15 ... Adhesive, 16 ... PD (light detection) Means), 17 ... LD, 18 ... scattered light.

Claims (9)

  By disposing a monitoring optical fiber in the vicinity of the fusion splicing point of the optical fiber to be measured so that scattered light emitted from the splicing splicing point can be incident, and measuring the scattered light power through the optical monitoring optical fiber An optical power monitoring method characterized by monitoring the propagation optical power of an optical fiber to be measured.   2. The optical power monitoring method according to claim 1, wherein a distance between the fusion splicing point and the tip of the monitoring optical fiber is adjusted so that a light receiving power of the monitoring optical fiber is appropriate.   An optical fiber for monitoring arranged so that scattered light emitted from the fusion splicing point can be incident in the vicinity of the fusion splicing point of the optical fiber to be measured, and light for measuring the scattered light power transmitted through the monitoring optical fiber And an optical power monitor device.   Reinforcement in which the tip of the monitoring optical fiber is fixed with an adhesive having a refractive index higher than the clad refractive index of the optical fiber to be measured together with the fusion splicing point of the optical fiber to be measured, and the adhesive is thermally contracted The optical power monitor device according to claim 3, wherein the optical power monitor device is fixed by being covered with a sleeve.   The tip of the monitoring optical fiber is covered with a reinforcing rod together with the fusion splicing point of the optical fiber to be measured, and an adhesive having a refractive index higher than the cladding refractive index of the optical fiber to be measured inside the reinforcing rod The optical power monitor device according to claim 3, wherein the optical power monitor device is fixed by an agent.   6. The optical power monitoring apparatus according to claim 3, wherein the light detection means is a photodiode for converting light transmitted through a monitoring optical fiber into an electric signal.   An optical device having an optical amplification effect or a nonlinear optical effect, comprising the optical power monitor device according to any one of claims 3 to 6, and configured to be able to measure a propagation optical power of an optical fiber to be measured. An optical device characterized by that.   8. The optical device according to claim 7, further comprising an optical fiber for optical amplification doped with a functional material that enhances an optical amplification effect. 9. The optical device according to claim 8, wherein the functional material is at least one selected from the group consisting of rare earth ions such as erbium, ytterbium, lanthanum, cerium, praseodymium, and neodymium.

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