JP2012044224A - Optical amplifier and laser beam source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a practical optical amplifier having high gain, and to provide a laser beam source device.SOLUTION: An optical fiber which is composed of a quartz based glass as a main component and added with Yb ions in at least a part of a core region, is used as each of a first optical amplifying waveguide 41 and a second optical amplifying waveguide 42. The first optical amplifying waveguide 41 is excited by excitation beams wave-guiding the core region and optically amplifies and outputs the beams input at an input end. The second optical amplifying waveguide 42 is excited by the excitation beams wave-guiding the core region and a first clad region, and inputs, optically amplifies, and outputs the beams optically amplified in the first optical amplifying waveguide 41.

Description

  The present invention relates to an optical amplifying device that optically amplifies light input to an input end and outputs the light from an output end, and a laser light source device including such an optical amplifying device.

  A laser light source that oscillates laser light includes a laser resonator in which a laser medium that emits emitted light when supplied with excitation energy is disposed on a resonance optical path, and a Q switch that modulates the resonator loss of the laser resonator And excitation means for continuously supplying excitation energy to the laser medium.

  In this laser light source, when the cavity loss of the laser resonator is set to a large value by the Q switch means, the inversion distribution of the laser medium is enhanced by the excitation energy supply by the excitation means, and then the laser is turned by the Q switch means. When the resonator loss of the resonator is set to a small value, stimulated emission occurs in a short time in the laser medium disposed on the resonance optical path of the laser resonator. This stimulated emission light is output as laser light from the laser resonator to the outside. Such a laser light source is capable of outputting pulse laser light having a high peak power, and thus is widely used for electronic / mechanical processing applications, medical laser scalpels, measurement applications such as length measurement, and the like.

  For example, as a method for realizing a Q switch, a method of effectively modulating the reflectance of a reflecting mirror constituting a laser resonator using an optical switch (AO switch) based on an acousto-optic (AO) effect is generally used. . As the laser medium, an optical fiber (Yb-Doped Fiber, hereinafter referred to as “YbDF”) in which Yb ions are added to the optical waveguide region is used (see Non-Patent Documents 1 and 2). In this case, excitation light having a wavelength of 975 nm band or a wavelength of 915 nm band is used as excitation energy supplied to the laser medium.

  In the optical fiber laser light source configured as described above, an inversion distribution is formed in YbDF with the supply of excitation light, and ASE (Amplified Spontaneous Emission) light is generated from this YbDF. The application and stop of the RF voltage to the AO switch are repeated, thereby modulating the resonator loss of the laser resonator. For example, in the period when the RF voltage is not applied to the AO switch, the resonator loss of the laser resonator increases and laser oscillation does not occur. On the other hand, in the period when the RF voltage is applied to the AO switch, laser resonance occurs. The resonator loss of the resonator becomes small, laser oscillation occurs, the energy that has been accumulated in the YbDF as an inversion distribution until then is released all at once, and a high-power optical pulse is generated.

  The Q switch can be realized not only by the optical fiber laser light source as described above but also by a solid laser light source or a gas laser light source. However, the optical fiber laser light source is practical because it has few spatial coupling parts, is highly reliable, is compact, and has a stable and good beam quality. However, as compared with a solid-state laser light source (particularly, a disk laser light source), an optical fiber laser light source usually has a resonator length as long as several meters. In the case of a Q switch, it propagates through the laser resonator. Since the time is several tens of ns, there is a disadvantage that an optical pulse having a shorter width cannot necessarily be generated.

  In order to solve such problems, a directly modulated semiconductor laser light source or an externally modulated optical fiber laser light source is used as a seed light source, and pulse laser light output from this seed light source is optically amplified by an optical amplifying device. The thing of the structure to perform is known (refer nonpatent literatures 3 and 4). In the configuration of the laser light source device including such a seed light source and an optical amplification device, the degree of freedom of the pulse width and the repetition frequency is increased.

M. J. Weber, et al, "Dependenceof the stimulated emission cross section of Yb3 + on host glasscomposition", IEEE J. of Quantum Electron., Vol.QE19, No.10, pp.1600-1608,1983 R. Paschotta, et al, "Lifetimequenching in Yb-doped fibers", Optics communications, vol.136, pp.375-378,1997 A. Babushkin, et al, "Multi-kilowatt peak power pulsed fiber laser with precise computer controlledpulse duration for materials processing", Proc. Of SPIE Vol.5709, pp98-102 A. J. W. Brown, "Fiber laserdevelopment at Aculight Corporation", Proc. 63rd Laser Processing Society, 2005

  However, the inventor of the present application has found that a laser light source device having such a seed light source and an optical amplifying device has the following problems.

  That is, when a directly modulated semiconductor laser light source is used as a seed light source, considering that the beam quality of the output pulsed laser light is maintained at the diffraction limit, the semiconductor laser light source is of a transverse single mode. Is desirable. However, the horizontal single-mode semiconductor laser light source has a maximum output of 200 mW at most that oscillates in a wavelength region (1064 nm band) where Yb has gain. Also, the current value that can be modulated at high speed in a band of several hundred MHz is limited. Further, although a method of outputting a high peak power with a gain switch is also conceivable, it is not desirable to output a constant high peak power from the viewpoint of the reliability of the semiconductor laser light source. Due to these restrictions, the peak power of the seed light source is limited to about 100 to 200 mW. Even when an externally modulated optical fiber laser light source is used as a seed light source, the peak power needs to be suppressed to about 100 mW at most from the viewpoint of the reliability of an electro-optical element such as LNO used for external modulation. There is.

  As a result, when the peak of the output pulse is required to be several k to several tens kW (for example, when used for laser processing, or as a light source for outputting a fundamental wave for generating the second harmonic or the third harmonic) When used), the optical amplifying device provided downstream of the seed light source needs to have a gain exceeding 40 dB. This gain is close to the highest class even in the field of optical communications and is very high. Even if clad excitation generally used in an industrial optical fiber laser light source is performed, the gain that can be earned by one stage of YbDF is limited to about 30 dB due to saturation by ASE light other than signal light.

  Therefore, it is preferable that the optical amplifying apparatus has a multistage configuration of two or more stages, and an element having a loss spectrum for removing ASE light is inserted between the stages. In this case, since the level of the signal light to be amplified is still small, the YbDF in the previous stage does not need clad pumping that requires expensive fiber coating or special pumping light coupling means, and is generally spread in the field of optical communication. It is desirable from the viewpoint of cost and power consumption to use a pumping system using pumping light propagating through the core of the optical fiber.

  However, Non-Patent Documents 3 and 4 do not disclose design items related to the glass composition of YbDF suitable for these different excitation methods. In the first place, as for the glass composition of YbDF, as described in Non-Patent Documents 1 and 2, it is only an individual study on stimulated emission cross section and absorption cross section or excitation lifetime, and the target is borate, phosphate glass, etc. In many cases, however, the glass is not suitable for practical use, and there has been no detailed investigation of the composition of industrially important quartz glass. Moreover, there was no mention of the compatibility between composition and excitation mode.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a practical optical amplifying device and a laser light source device having high gain.

  An optical amplifying device according to the present invention is an optical amplifying device that optically amplifies light input to an input end and outputs it from an output end. (1) The main component is made of silica glass, a core region, and the core A Yb ion is added to at least a part of the core region, and is excited mainly by excitation light guided through the core region, while propagating light input to the input end to the core region. A first optical amplifying waveguide that amplifies and outputs light; and (2) a main component is made of silica glass, a core region, a first cladding region that surrounds the core region, and a first cladding that surrounds the first cladding region. Yb ions are added to at least a part of the core region, and are mainly excited by the pumping light guided through the core region and the first cladding region, and are amplified in the first optical amplifying waveguide. A second optical amplifying waveguide that inputs the amplified light and outputs the amplified light while propagating the light to the core region; and (3) a first optical amplifying waveguide and a second optical amplifying waveguide, respectively. And an excitation light supply means for supplying excitation light to the light source. Further, the additive concentration of Al positive ions in the first optical amplifying waveguide is higher than the additive concentration of Al positive ions in the second optical amplifying waveguide. In the optical amplification device according to the present invention, it is preferable that the excitation lifetime of the first optical amplification waveguide is longer than that of the second optical amplification waveguide. The excitation lifetime of the first optical amplifying waveguide is preferably 1 msec or longer. Moreover, it is preferable that the excitation lifetime of the first optical amplifying waveguide is 1 msec or longer.

  Alternatively, the optical amplifying device according to the present invention is an optical amplifying device that optically amplifies the light input to the input end and outputs from the output end, (1) the main component is made of quartz glass, and the core region, And Yb ions are added to at least a part of the core region, and are mainly excited by the excitation light guided through the core region and propagate the light input to the input end to the core region. And a first optical amplifying waveguide that amplifies and outputs the light, and (2) the main component is made of silica glass, and includes a core region, a first cladding region surrounding the core region, and the first cladding region. A Yb ion is added to at least a part of the core region, and is excited mainly by excitation light in a 915 nm band guided through the core region and the first cladding region. A second optical amplifying waveguide that inputs light amplified in the optical waveguide, outputs the amplified light while propagating the light to the core region, and (3) a first optical amplifying waveguide and a second optical waveguide And an excitation light supply means for supplying excitation light to each of the optical amplifying waveguides. Further, the addition concentration of Al positive ions in the first optical amplification waveguide is higher than the addition concentration of Al positive ions in the second optical amplification waveguide, and the spectrum of the absorption cross section of the second optical amplification waveguide. The secondary peak in the wavelength 915 nm band is preferably higher than the secondary peak in the wavelength 915 nm band in the spectrum of the absorption cross section of the first optical amplifying waveguide. In the optical amplifying device according to the present invention, it is preferable that the secondary peak in the wavelength 915 nm band, which is specified by the height of the main peak in the spectrum of the absorption cross section of the second optical amplifying waveguide, is higher than 25.1%. It is.

  In the optical amplifying device according to the present invention, each of the first optical amplifying waveguide and the second optical amplifying waveguide is made of silica glass as a main component, and Yb ions are added to at least a part of the core region. Yes. The excitation light supplied to the first optical amplifying waveguide by the excitation light supply means guides the Yb ions added to the first optical amplifying waveguide through the core region of the first optical amplifying waveguide. Excited. The excitation light supplied to the second optical amplifying waveguide by the excitation light supplying means is guided through the core region and the first cladding region of the second optical amplifying waveguide and added to the second optical amplifying waveguide. Excited Yb ions are excited. The amplified light input to the input end is optically amplified in the first optical amplifying waveguide and further amplified in the second optical amplifying waveguide, and the amplified light is output from the output end. The additive concentration of Al positive ions in the first optical amplifying waveguide is higher than the additive concentration of Al positive ions in the second optical amplifying waveguide. Alternatively, the secondary peak of the wavelength 915 nm band in the spectrum of the absorption cross section of the second optical amplifying waveguide is higher than the secondary peak of the wavelength 915 nm band in the spectrum of the absorption cross section of the first optical amplifying waveguide. Such an optical amplifying device has a high gain and can be practical. The positive ions added to the first optical amplifying waveguide and the second optical amplifying waveguide may be La instead of Al.

  A laser light source device according to the present invention includes a laser light source that outputs laser light, and the optical amplification device according to the present invention that amplifies the laser light output from the laser light source. In the laser light source device according to the present invention, the laser light output from the laser light source is output after being optically amplified by the optical amplifying device. Since the optical amplification device has a high gain, this laser light source device can output a high-power laser beam.

  The optical amplifying device according to the present invention has a high gain and is excellent in practical use, and can be suitably used particularly for processing applications.

It is a schematic block diagram of the laser light source apparatus 1 which concerns on this embodiment. It is a block diagram of the optical amplification apparatus 3 which concerns on this embodiment. 6 is a chart summarizing compositions and excitation lifetimes of YbDF-A, YbDF-B, and YbDF-C. It is a figure which shows the spectrum of each stimulated emission cross section of YbDF-A, YbDF-B, and YbDF-C. It is a figure which shows the spectrum of each absorption cross section of YbDF-A, YbDF-B, and YbDF-C. 6 is a chart summarizing gains of YbDF-A and YbDF-B. 6 is a chart summarizing signal light power and residual pumping light power of YbDF-A and YbDF-B, respectively. It is a graph which shows the relationship between the secondary peak height of the spectrum of the absorption cross-sectional area normalized with each Al concentration of YbDF-A, YbDF-B, and YbDF-C and the main peak. It is a block diagram of 3 A of optical amplifiers which concern on other embodiment.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a schematic configuration diagram of a laser light source device 1 according to the present embodiment. The laser light source device 1 shown in this figure has a MOPA (Master Oscillator Power Amplifier) configuration, and includes a laser light source 2 and an optical amplification device 3. The laser light source 2 outputs laser light and is, for example, a laser diode. The optical amplifying device 3 optically amplifies the laser light output from the laser light source 2. In the laser light source device 1, the laser light output from the laser light source 2 is output after being optically amplified by the optical amplifying device 3.

  FIG. 2 is a configuration diagram of the optical amplifying device 3 according to the present embodiment. The optical amplifying device 3 shown in this figure optically amplifies the light input to the input end 11 and outputs it from the output end 12, and includes optical isolators 21 to 23, optical couplers 31 and 32, first optical amplification. The optical waveguide 41, the second optical amplifying waveguide 42, the band pass filter 50, the optical branching device 60, and the excitation light source 70 are provided. An input terminal 11 of the optical amplifying device 3 inputs laser light output from the laser light source 2.

  In order from the input end 11 to the output end 12, the optical isolator 21, the optical coupler 31, the first optical amplifying waveguide 41, the optical isolator 22, the bandpass filter 50, the optical coupler 32, and the second optical amplifying waveguide 42 are provided. An optical isolator 23 is disposed. An optical branching device 60 is connected to both the optical coupler 31 and the optical coupler 32, and a pumping light source 70 is connected to the optical branching device 60.

  Each of the optical isolators 21 to 23 allows light to pass in the forward direction from the input end 11 to the output end 12, but does not allow light to pass in the reverse direction. The optical coupler 31 outputs the amplified light reaching from the optical isolator 21 to the first optical amplifying waveguide 41 and also outputs the pumping light reaching from the optical splitter 60 to the first optical amplifying waveguide 41. . The optical coupler 32 outputs the amplified light reaching from the bandpass filter 50 to the second optical amplifying waveguide 42 and also outputs the pumping light reaching from the optical splitter 60 to the second optical amplifying waveguide 42. To do.

  Each of the first optical amplifying waveguide 41 and the second optical amplifying waveguide 42 is an optical waveguide in which the main component is made of silica glass and Yb ions are added to at least a part of the core region. Yb-doped optical fiber (YbDF). The first optical amplifying waveguide 41 receives the light to be amplified and the pumping light output from the optical coupler 31, is excited by the pumping light to optically amplify the light to be amplified, and the amplified light is supplied to the optical isolator 22. Output. The second optical amplifying waveguide 42 receives the amplified light and the pumping light output from the optical coupler 32, is excited by the pumping light to optically amplify the amplified light, and the amplified light is supplied to the optical isolator 23. Output.

  In particular, the first optical amplifying waveguide 41 includes a core region and a cladding region surrounding the core region, and Yb ions are added to at least a part of the core region. The light input to the input terminal is amplified and output. The second optical amplifying waveguide 42 includes a core region, a first cladding region that surrounds the core region, and a second cladding region that surrounds the first cladding region, and at least a part of the core region contains Yb ions. The light that has been added, is excited by the pumping light guided through the core region and the first cladding region, and is optically amplified in the first optical amplifying waveguide 41 is further amplified and output.

  Further, each of the first optical amplifying waveguide 41 and the second optical amplifying waveguide 42 contains trivalent positive ions other than Yb ions. The positive ion addition concentration in the first optical amplification waveguide 41 is higher than the positive ion addition concentration in the second optical amplification waveguide 42. The positive ions are preferably Al3 + ions. The secondary peak of the wavelength 915 nm band in the spectrum of the absorption cross section of the second optical amplifying waveguide 41 is higher than the secondary peak of the wavelength 915 nm band in the spectrum of the absorption cross section of the first optical amplifying waveguide 42. Is preferred. The excitation lifetime of the first optical amplification waveguide 41 is preferably longer than the excitation lifetime of the second optical amplification waveguide 42. The excitation lifetime of the first optical amplifying waveguide 41 is preferably 1 msec or longer.

  The band pass filter 50 is provided on the optical path between the optical isolator 22 and the optical coupler 32, selectively transmits the light amplified and output in the first optical amplifying waveguide 41, and has other wavelengths. Light (ASE light) is blocked. The optical branching device 60 divides the pumping light output from the pumping light source 70 into two, outputs one of the branched pumping light to the optical coupler 31, and outputs the other pumping light to the optical coupler 32. The excitation light source 70 outputs excitation light having a wavelength capable of exciting Yb ions contained in each of the first optical amplifying waveguide 41 and the second optical amplifying waveguide 42, and preferably includes a laser diode. . The excitation light source 70, the optical branching device 60, the optical coupler 31, and the optical coupler 32 function as excitation light supply means for supplying excitation light to the first optical amplifying waveguide 41 and the second optical amplifying waveguide 42, respectively.

  The optical amplifying apparatus 3 configured as described above operates as follows. The excitation light of the wavelength 975 nm band or wavelength 915 nm band output from the excitation light source 70 is branched into two by the optical branching device 60. One pumping light obtained by branching by the optical splitter 50 is supplied to the first optical amplifying waveguide 41 through the optical coupler 31, and the other pumping light is supplied to the second optical amplifying waveguide 42 through the optical coupler 32. To be supplied.

  Light to be amplified having a wavelength of 1064 nm input to the input end 11 is input to the first optical amplifying waveguide 41 through the optical isolator 21 and the optical coupler 31, and is optically amplified in the first optical amplifying waveguide 41. The The light amplified in the first optical amplifying waveguide 41 is input to the second optical amplifying waveguide 42 via the optical isolator 22, the bandpass filter 50, and the optical coupler 32, and this second optical amplifying waveguide 42 is supplied. Further optical amplification is performed in the waveguide 42. The light amplified in the second optical amplifying waveguide 42 is output from the output end 12 via the optical isolator 23.

  Next, the first optical amplifying waveguide 41 and the second optical amplifying waveguide 42 will be described more specifically. Each of the first optical amplifying waveguide 41 and the second optical amplifying waveguide 42 is an optical waveguide in which the main component is made of silica glass and Yb ions are added to at least a part of the core region. Yb-doped optical fiber (YbDF). Hereinafter, examples of YbDF (YbDF-A, YbDF-B, YbDF-C) that can be used as the first optical amplifying waveguide 41 or the second optical amplifying waveguide 42 will be described.

  FIG. 3 is a chart summarizing the compositions and excitation lifetimes of YbDF-A, YbDF-B, and YbDF-C. The chart also shows the height of the secondary peak (normalized secondary peak) normalized by the height of the main peak of the absorption cross section. YbDF-A is obtained by adding 3807 wtppm of Yb element and 5.66 wt% of Al element to the core region. YbDF-B is obtained by adding 5486 wtppm of Yb element and 0.27 wt% of Al element to the core region. YbDF-C is obtained by adding 10571 wtppm of Yb element and 2.54 wt% of Al element to the core region. When the compositions of YbDF-A and YbDF-B are compared, the difference in Yb concentration is small, but the difference in Al concentration is large. The Al concentration of YbDF-A is higher than the Al concentration of YbDF-B. As a result, the excitation lifetime of YbDF-A was 1.5 msec, the excitation lifetime of YbDF-B was 0.8 msec, and the former was approximately twice the latter. Longer excitation lifetimes are generally advantageous for improving power conversion efficiency because the excitation power that serves as a threshold for shifting from absorption to amplification is kept low.

  FIG. 4 is a diagram showing spectra of the stimulated emission cross sections of YbDF-A, YbDF-B, and YbDF-C. FIG. 5 is a diagram showing absorption cross-sectional spectra of YbDF-A, YbDF-B, and YbDF-C. These spectra are standardized with a main peak value near 100 at a wavelength of 975 nm. Compared with YbDF-A, YbDF-B has a higher absorption peak in the wavelength 915 nm band and better absorption efficiency of excitation light in the wavelength 915 nm band. Compared with YbDF-A, YbDF-B has a second peak of the stimulated emission cross section on the long wavelength side. Therefore, when it is desired to make the oscillation wavelength longer than 1080 nm (such as when it is saturated very strongly, it is This is advantageous when the diameter ratio between the core and the clad exceeds 10.

  In each of YbDF-A and YbDF-B, the absorption cross section is the largest in the wavelength 975 nm band. From this point, it can be said that the 975 nm band is preferable as the excitation light wavelength. However, in the case of cladding excitation, the required current of the multimode excitation laser diode used as the excitation light source 70 is several A to several tens of A, and the amount of heat generation is large. It is possible, and water cooling is required in some cases. At this time, the temperature fluctuation of the laser diode is not negligible, and the wavelength of the excitation light output from the laser diode becomes unstable. As a result, the excitation in the wavelength 975 nm band with a narrow absorption spectrum width causes a large deterioration in absorption efficiency when the pumping light wavelength fluctuates, which in turn leads to a deterioration in power conversion efficiency. On the other hand, although the secondary peak in the wavelength 915 nm band has a low peak value but is wide, the influence of the excitation light wavelength fluctuation can be ignored. Therefore, in the case of cladding excitation, it is considered that wavelength 915 nm band excitation is desirable.

  Next, the gains of YbDF-A and YbDF-B when excited by pumping light having a wavelength of 975 nm that propagates through the core region will be described. FIG. 6 is a chart summarizing the gains of YbDF-A and YbDF-B. Here, both YbDF-A and YbDF-B have a mode field diameter of 4.6 μm at a wavelength of 1.064 μm, a diameter of a Yb-added region of 2.4 μm, and an absorption cutoff at a wavelength of 975 nm. The area was 248 dB / m, the length was 6 m, and it was excited by excitation light having a wavelength of 975 nm band propagating through the core region.

  In the case of pumping with pumping light propagating in the core region, a single mode wavelength 0.98 μm band pumping laser diode module that is widely used for optical communication can be used as a pumping light source. Therefore, the excitation light wavelength was set to 975 nm. The power of the excitation light injected into each of YbDF-A and YbDF-B was 100 mW, 200 mW, or 400 mW. The excitation direction was forward excitation. The light to be amplified was assumed to have a wavelength of 1064 nm, a peak power of 200 mW, a pulse train with a duty ratio of 10,000, and an average power of -17 dBm.

  As shown in FIG. 6, for YbDF-A, the gain is 16.8 dB when the pumping light power is 100 mW, and the gain is 21.6 dB when the pumping light power is 200 mW. When the power was 400 mW, the gain was 24.1 dB. For YbDF-B, the gain is 9.1 dB when the pumping light power is 100 mW, the gain is 17.9 dB when the pumping light power is 200 mW, and the pumping light power is 400 mW. The gain was 22.4 dB.

  In YbDF-A and YbDF-B, when the pumping light power is 100 mW, the difference in the threshold of the pumping power greatly affects, the gain of YbDF-A is about 16.7 dB, and the gain of YbDF-B is 9 dB. There was a difference of almost twice between the two. When the pumping light power is 400 mW, the influence of the difference in threshold between the two is reduced and the difference is reduced, but the gain of YbDF-A is still large due to the difference in the shape of the stimulated emission cross section and the absorption cross section. Further, even if the difference is small at the beginning of operation, YbDF-A can be said to be more advantageous in consideration of the effect of deterioration of the pumping laser diode during the period of years and the pumping light power decreasing.

  Next, gains of YbDF-A and YbDF-B when clad excitation is performed with excitation light of a wavelength of 915 nm band will be described. FIG. 7 is a chart summarizing the signal light power and residual pumping light power of YbDF-A and YbDF-B, respectively. The difference in the absorption cross-sectional area peak in the wavelength 915 nm band affects the cladding excitation in which the overlap between the excitation light mode field and the Yb addition region is small. Therefore, the following cases were examined. Here, both YbDF-A and YbDF-B have a mode field diameter of 14 μm at a wavelength of 1.064 μm, a diameter of a Yb-added region of 12 μm, a cladding diameter of 125 μm, and a wavelength of 975 nm. The absorption cross-sectional area was 64 dB / m, the length was 5 m, and was excited by excitation light having a wavelength of 915 nm band propagating through the core region and the first cladding region.

  In the case of excitation by excitation light propagating through the core region and the first cladding region, the excitation light wavelength is preferably in the 915 nm band as described above. Therefore, the excitation light wavelength was set to 915 nm. The power of excitation light injected into each of YbDF-A and YbDF-B was 40 mW. The excitation direction was reverse excitation with excellent excitation efficiency. For the light to be amplified, the wavelength was set to 1064 nm, and the average power was set to +17 dBm on the assumption that the light was sufficiently amplified before reaching the wavelength.

  As shown in FIG. 7, for YbDF-A, the power of the output signal light from which the amplified light is amplified is 23.7 W, and the power of the residual pumping light is 5.8 W. As for YbDF-B, the power of the output signal light that is optically amplified from the amplified light was 24.5 W, and the power of the residual pumping light was 3.5 W. Compared with YbDF-B, the average output of YbDF-A is lower by 0.8W. The reason for this is that, compared with YbDF-B, YbDF-A has a small absorption coefficient at a wavelength of 915 nm as can be seen from the absorption cross section spectrum shown in FIG. This is because 5.8 W) is about 60% larger. Thus, if the residual pumping light power is large, it may cause damage to the laser light source 2 located upstream of the optical amplifying device 3, and the danger increases.

  FIG. 8 is a graph showing the relationship between the Al concentration of each of YbDF-A, YbDF-B, and YbDF-C and the secondary peak height of the absorption cross section spectrum normalized by the main peak. The lower the Al concentration, the higher the height of the secondary peak near the wavelength of 915 nm. On the other hand, as seen in the specifications of the JDSU 6390 series, which has the highest share in the world as a pumping laser diode, there is also a wavelength variation of about 915 ± 8 nm on the pumping laser diode side. Here, at the longest wavelength of 923 nm within the variation range, the absorption cross-sectional area of YbDF-B is higher than that of YbDF-A as shown in FIG. 5, but substantially matches YbDF-C. Therefore, if the worst wavelength variation (923 nm) in the specification of the pump laser diode is assumed, the Al concentration is the same for both YbDF-B and YbDF-C. However, if there is a difference in Al concentration beyond this, the effect at the secondary peak of the absorption cross section appears. Therefore, it is desirable that the Al concentration of the Yb-doped fiber is at most YbDF-C or less for the purpose of cladding excitation.

  As described above, YbDF-A has a pumping power and signal light power as low as several mW to several hundreds mW, and a preamplifier upstream of the signal path that can set the wavelength of pumping light to 975 nm (that is, in FIG. It is preferable to apply to the first optical amplifying waveguide 41). On the other hand, YbDF-B has high pumping power and signal light power of several W to several tens of W, and the booster amplifier downstream of the signal path where the pumping light wavelength must be around 915 nm (ie, the first amplifier in FIG. 2). It is preferable to apply to the two-light amplifying waveguide 42). The excitation direction of the second optical amplifying waveguide 42 is preferably reverse excitation.

  Therefore, it is more preferable that the optical amplifying device 3A having the configuration shown in FIG. 9 is used as the optical amplifying device 3 in FIG. FIG. 9 is a configuration diagram of an optical amplifying device 3A according to another embodiment. Compared with the configuration of the optical amplifying device 3 shown in FIG. 2, the optical amplifying device 3A shown in FIG. 9 is different in that an optical coupler 33 is provided instead of the optical coupler 32, and an optical branching device 60 is provided. The difference is that an excitation light source 71 and an excitation light source 73 are provided instead of the excitation light source 70.

  The optical coupler 33 is provided between the second optical amplifying waveguide 42 and the optical isolator 23, and passes the light amplified and output in the second optical amplifying waveguide 42 to the optical isolator 23. Then, the excitation light reaching from the excitation light source 71 is output to the second optical amplifying waveguide 42. The excitation light source 71 is connected to the optical coupler 31 and outputs excitation light having a wavelength of 975 nm band. The pumping light source 73 is connected to the optical coupler 33 and outputs pumping light having a wavelength of 915 nm.

  The optical amplifying device 3A configured as described above operates as follows. Excitation light of a wavelength of 975 nm band output from the excitation light source 71 is supplied from the forward direction to the first optical amplifying waveguide 41 (YbDF-A) via the optical coupler 31, and the first optical amplifying waveguide 41 It is confined in the core region and guided. The pumping light of the wavelength 915 nm band output from the pumping light source 73 is supplied from the reverse direction to the second optical amplifying waveguide 42 (YbDF-B) via the optical coupler 33, and this second optical amplifying waveguide. It is confined in the 42 core region and the first cladding region and guided.

  Light to be amplified having a wavelength of 1064 nm input to the input end 11 is input to the first optical amplifying waveguide 41 through the optical isolator 21 and the optical coupler 31, and is optically amplified in the first optical amplifying waveguide 41. The The light amplified in the first optical amplifying waveguide 41 is input to the second optical amplifying waveguide 42 through the optical isolator 22 and the band pass filter 50, and further in the second optical amplifying waveguide 42. Optically amplified. The light amplified in the second optical amplifying waveguide 42 is output from the output terminal 12 via the optical coupler 33 and the optical isolator 23.

  In addition, although the case where Al was added together with Yb was shown above, an equivalent effect is expected if it is a trivalent positive ion such as La. Moreover, in place of the above YbDF-B, an Al-free additive may be used.

DESCRIPTION OF SYMBOLS 1 ... Laser light source device, 2 ... Laser light source, 3, 3A ... Optical amplifier, 11 ... Input end, 12 ... Output end, 21-23 ... Optical isolator, 31, 32, 33 ... Optical coupler, 41 ... 1st light Amplifying waveguide, 42... Second optical amplifying waveguide, 50... Bandpass filter, 60 .. optical branching device, 70, 71, 73.

Claims (7)

An optical amplifying device for optically amplifying light input to an input end and outputting from an output end,
The main component is made of silica glass, includes a core region and a cladding region surrounding the core region, and Yb ions are added to at least a part of the core region, and the excitation light mainly guides the core region. A first optical amplifying waveguide that is excited by the optical amplifier and that amplifies and outputs the light input to the input end while propagating to the core region;
The main component is made of silica-based glass, and includes a core region, a first cladding region surrounding the core region, and a second cladding region surrounding the first cladding region, and at least a part of the core region contains Yb ions. Added, pumped mainly by pumping light guided through the core region and the first cladding region, and input light amplified in the first optical amplifying waveguide, and propagates the light to the core region A second optical amplifying waveguide that amplifies and outputs the light while
Excitation light supply means for supplying excitation light to each of the first optical amplification waveguide and the second optical amplification waveguide;
The optical amplifying apparatus, wherein an additive concentration of Al positive ions in the first optical amplifying waveguide is higher than an additive concentration of Al positive ions in the second optical amplifying waveguide.   2. The optical amplifying device according to claim 1, wherein an excitation lifetime of the first optical amplifying waveguide is longer than an excitation lifetime of the second optical amplifying waveguide.   2. The optical amplifying device according to claim 1, wherein an excitation lifetime of the first optical amplifying waveguide is 1 msec or longer. An optical amplifying device for optically amplifying light input to an input end and outputting from an output end,
The main component is made of silica glass, includes a core region and a cladding region surrounding the core region, and Yb ions are added to at least a part of the core region, and the excitation light mainly guides the core region. A first optical amplifying waveguide that is excited by the optical amplifier and that amplifies and outputs the light input to the input end while propagating to the core region
The main component is made of silica-based glass, and includes a core region, a first cladding region surrounding the core region, and a second cladding region surrounding the first cladding region, and at least a part of the core region contains Yb ions. The light that is pumped by the 915 nm band pumping light that is guided mainly through the core region and the first cladding region and is optically amplified in the first optical amplifying waveguide is input, and the light is input to the core. A second optical amplifying waveguide for optical amplification and output while propagating to the region;
Excitation light supply means for supplying excitation light to each of the first optical amplification waveguide and the second optical amplification waveguide;
The addition concentration of Al positive ions in the first optical amplification waveguide is higher than the addition concentration of Al positive ions in the second optical amplification waveguide,
The secondary peak of the wavelength 915 nm band in the spectrum of the absorption cross section of the second optical amplification waveguide is higher than the secondary peak of the wavelength 915 nm band of the spectrum of the absorption cross section of the first optical amplification waveguide. A characteristic optical amplification device.   5. The optical amplification according to claim 4, wherein the secondary peak in the wavelength 915 nm band normalized by the height of the main peak in the absorption cross section spectrum of the second optical amplifying waveguide is higher than 25.1%. apparatus.   5. The optical amplifying apparatus according to claim 1, wherein positive ions added to the first optical amplifying waveguide and the second optical amplifying waveguide are La instead of Al. 6. A laser light source device comprising: a laser light source that outputs laser light; and the optical amplifying device according to claim 1 that optically amplifies the laser light output from the laser light source.

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