JP2005294570A - Optical fiber amplifier, second harmonic generator, light generation method, and second harmonic generation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-power light suitable as a fundamental wave for second harmonic generation in a simplified way and with high efficiency. <P>SOLUTION: An optical fiber amplifier 102 and a resonator 106 are constituted of a first optical fiber 101 and a second optical fiber 105, each doped with neodymium ions (Nd<SP>3+</SP>). An exciting light 115 from an exciting light source 113 is projected into one of the optical fibers as an exciting light, and the portion of the exciting light not absorbed by the neodymium ions is projected into the other optical fiber as an exciting light for the generation of lights each having a wavelength of 920 nm±20 nm. The light is oscillated in the resonator 106, and is passed through a bandwidth-narrowing element installed in the oscillation path for conversion into a narrowband light, amplified in the optical fiber amplifier 102, and then outputted. Furthermore, the output of the optical fiber amplifier 102 is passed through a nonlinear element for the generation of a second harmonic light. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical fiber amplifying device using an optical fiber with a predetermined ion added to a core portion, and a second harmonic generation device using the optical fiber amplifying device, and in particular, is incident on an optical fiber as excitation light. The present invention relates to a second-order harmonic generation method capable of effectively utilizing the generated light and efficiently generating desired light as the second-order harmonic.

  Optical fiber amplifiers can amplify light as it is and output it with high power, and have been widely used as light sources for electronic devices that use light sources as well as signal transmissions.

  In an optical fiber amplifier, for example, when excitation light having a predetermined wavelength is incident on an optical fiber in which rare earth ions are added to the core portion, the rare earth ions are excited to transition their energy levels and relax to lower levels. The phenomenon of generating light of a predetermined wavelength is used.

  FIG. 10 is a diagram for explaining the principle, and shows a situation when neodymium ions (Nd3 +) are added to the core portion as an optical fiber and light having a wavelength of 810 nm is incident on the core portion as excitation light. Yes.

  That is, Nd3 + absorbs 810 nm, transitions from the ground level 4I9 / 2 to 4F5 / 2, immediately relaxes to 4F3 / 2, and then relaxes to the ground level 4I9 / 2. Emits light near 920 nm. Amplification (or oscillation, which will be described later) uses this transition, but is in a so-called quasi-three-level state and emits light when the distribution density of the ground level 4I9 / 2 is high. Light near the wavelength of 920 nm is reabsorbed and lost. Therefore, in order to amplify (or oscillate) near the wavelength of 920 nm, it is necessary to reduce the distribution density of the ground level 4I9 / 2 as much as possible.

  That is, if a large amount of pumping light is incident on the optical fiber and the pumping light density is increased, a large amount of Nd3 + is excited from the ground level, thereby reducing the distribution density of the ground level 4I9 / 2. Is possible.

  When an optical fiber doped with Nd3 + is pumped from its end face, the pumping light is absorbed by Nd3 + and decreases exponentially. If the fiber length is long, the pumping light density is not sufficient at the end, and the loss with respect to light near the wavelength of 920 nm increases.

  Therefore, the fiber length of the optical fiber constituting the optical fiber amplifier is set to a length at which excitation is sufficiently performed. Therefore, a part of the pumping light passes through the optical fiber as it is and is output to the outside without being absorbed by Nd3 +.

  As described above, in the conventional optical fiber amplifier, all of the pumping light is not utilized, and a part of the pumping light is output without being used as it is, and is discarded as a result. There was room.

  As an optical fiber amplifier, many proposals have been conventionally made (for example, Patent Documents 1 and 2), but no proposal has been made to effectively utilize a portion where excitation light incident on an optical fiber is not utilized.

Furthermore, a proposal has been made in the past to generate visible light as a second harmonic using near-infrared light as a fundamental wave using an optical fiber (for example, Patent Document 3). There is a demand for the realization of proposals that are not sufficient and further improved.
JP 2000-503476 JP-A-5-107573 JP 2003-258341 A

  As described above, in the conventional optical fiber amplifier, no proposal has been made to effectively utilize the portion of the light incident as the excitation light that is output as it is without being absorbed by the added ions. There was room. Furthermore, the second harmonic generation device using an optical fiber is not always satisfactory in terms of efficiency, and the realization of a highly efficient device has been demanded.

  The present invention has been made in view of the above points, and optically couples an optical fiber amplifier and a resonator composed of an optical fiber, and makes pump light incident on one of the optical fibers for absorption. The pump light that has not been made is incident on the other optical fiber as pump light, and the light generated by resonance in the resonator is introduced into the optical fiber amplifier to be amplified so that the pump light can be used effectively. It is an object of the present invention to provide an optical fiber amplifier and a second harmonic generation device configured to convert light output after being amplified by the optical fiber amplifier into light having a different wavelength by a non-linear element and output the light. And

  The optical fiber amplifying device of the present invention includes a first optical fiber that outputs first light having a wavelength of 920 nm ± 20 nm when neodymium ions (Nd3 +) are added to a core portion and excitation light is incident on the core portion. And an optical fiber amplifier having neodymium ions (Nd3 +) added to the core and pumping light incident on the core so that the wavelength is the same as that of the first light and narrower than the first light. A resonator having a second optical fiber configured as a resonator that generates the second light by resonance, an excitation light source, the optical fiber amplifier, and the resonator are optically coupled, and the excitation Excitation light from a light source is incident on either the first optical fiber or the second optical fiber, and the excitation light that has not been absorbed by the neodymium ions (Nd3 +) is incident on the other optical fiber. Incident as the excitation light to the bar, characterized in that it further has the second light generated by the resonator anda optical means to be incident on the first optical fiber.

  The second harmonic generation device of the present invention outputs the first light having a wavelength of 920 nm ± 20 nm when neodymium ions (Nd3 +) are added to the core portion and excitation light is incident on the core portion. An optical fiber amplifier having one optical fiber, neodymium ions (Nd3 +) are added to the core, and excitation light is incident on the core so that the first light has the same wavelength as the first light. A resonator having a second optical fiber configured as a resonator that generates second light having a narrower band than light by resonance, a pumping light source, the optical fiber amplifying means, and the resonator are optically coupled. In addition, the excitation light from the excitation light source is incident on either the first optical fiber or the second optical fiber, and the excitation light that has not been absorbed by the neodymium ions (Nd3 +) in the incident excitation light. The other First optical means that enters the optical fiber as the pumping light and further causes the second light generated by the resonance means to enter the first optical fiber; and the first optical means that is amplified by the optical fiber amplifier. And second optical means for generating and outputting third light having a wavelength of 460 nm ± 10 nm by allowing the first light to pass through the non-linear element.

  In addition, the light generation method of the present invention includes the first light that outputs first light having a wavelength of 920 nm ± 20 nm by adding neodymium ions (Nd3 +) to the core portion and incident excitation light on the core portion. An optical fiber amplifier having a fiber, and neodymium ions (Nd3 +) are added to the core portion, and pump light is incident on the core portion, so that the second light having the same wavelength as that of the first light and a narrow band. Optically coupling a resonator having a second optical fiber generated by resonance, and exciting the pumping light by injecting it into one of the first and second optical fibers; Injecting the pumping light not absorbed by the optical fiber into which the pumping light is incident into the other optical fiber as pumping light, and amplifying the second light generated by the resonator by the optical fiber amplifier. Output Tsu and-flops, characterized in that it was equipped with.

  Furthermore, in the second harmonic generation method of the present invention, neodymium ions (Nd3 +) are added to the core portion, and excitation light is incident on the core portion to output first light having a wavelength of 920 nm ± 20 nm. An optical fiber amplifier having a first optical fiber and neodymium ions (Nd3 +) are added to the core portion, and excitation light is incident on the core portion, so that the wavelength is the same as that of the first light and a narrow band. A resonator having a second optical fiber that generates second light by resonance is optically coupled, and pumping light is incident on one of the first and second optical fibers to be excited. The step of causing the pumping light that has not been absorbed by the optical fiber into which the pumping light has been incident to enter the other optical fiber as the pumping light, and the second light generated by the resonator is the optical fiber. Amplify with amplifier And outputting the light output from the optical fiber amplifier through a non-linear elements, characterized by comprising the steps of: obtaining a second harmonic of the light output from the optical fiber amplifier.

  According to the present invention, the pumping light that has not been absorbed by the optical fiber amplifier or the optical fiber of the resonator is incident on the other optical fiber as the pumping light, and the resonator is generated by pumping the optical fiber. It is configured to generate light of the same wavelength and narrow band, and is configured to amplify the light generated by this resonator by guiding it to an optical fiber amplifier. It is possible to provide an optical fiber amplifying device capable of obtaining a high output.

  In addition, the light amplified by the optical fiber amplifier is used as the fundamental wave, and it is configured to generate the second harmonic by passing it through a non-linear element, so light of the desired wavelength can be generated easily and efficiently. It is possible to provide a second harmonic generation device capable of performing the above.

Hereinafter, an embodiment of an optical fiber amplifier according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing an optical fiber amplifying apparatus 100 of the present invention. In the figure, reference numeral 101 denotes a first optical fiber constituting the optical fiber amplifier 102, and neodymium ions (Nd3 +) are added to the core portion thereof.

  Optical elements 103 and 104 are disposed at both ends of the first optical fiber 101, respectively. The optical elements 103 and 104 function as a condensing lens or a collimator lens according to the direction of light passing therethrough.

  Reference numeral 105 denotes a second optical fiber that constitutes the resonator 106, and neodymium ions (Nd3 +) are added to the core portion of the second optical fiber as in the first optical fiber 101. In addition, dielectric mirrors 107 and 108 are pressed and connected to both ends of the second optical fiber 106, respectively.

  The dielectric mirrors 107 and 108 have a function of transmitting light having a wavelength near 810 nm and 1.06 μm and partially reflecting light having a wavelength of 920 nm. Further, optical elements 109 and 110 are disposed in proximity to the dielectric mirrors 107 and 108, respectively. The optical elements 109 and 110 also function as a condensing lens or a collimator lens depending on the direction of light passing therethrough.

  The optical element 109 is optically coupled to the optical element 104 disposed at the end of the first optical fiber 101, and the optical element 104 collimates the light from the first optical fiber 101. The optical element 109 collimates the light from the dielectric mirror 107 and outputs it to the optical element 104.

  Further, a polarizing prism 111 is disposed so as to face the optical element 110 on the dielectric mirror 108 side, and a diffraction grating 112 is further provided so as to face the polarizing prism 111. The diffraction grating 112 is, for example, arranged in a Littrow arrangement, and together with the second optical fiber 105, forms a dielectric mirror 107 on the opposite side of the second optical fiber 105 and an optical resonator 106 near a wavelength of 920 nm. The polarizing prism 111 is in the optical resonator 106 and has a function of increasing the loss of one of the linearly polarized waves that are orthogonal to each other.

  Further, a semiconductor laser light source 113 that generates laser light having a wavelength of about 810 nm as excitation light is provided. The laser light of about 810 nm from the laser light source 113 is reflected by the filter 114 and led to the optical element 103. The filter 114 is a filter that separates the vicinity of the wavelength of 810 nm and the vicinity of 920 nm, and is composed of a dielectric mirror, which reflects the vicinity of the wavelength of 810 nm and transmits the vicinity of the wavelength of 920 nm as it is.

  The operation of the optical fiber amplifying apparatus 100 configured as described above will be described. Laser light 115 having a wavelength of about 810 nm from the semiconductor laser light source 113 is incident on the core portion of the first optical fiber 101 through the filter 114 and the optical element 103.

  In the first optical fiber 101, neodymium ions (Nd3 +) at the core of the first optical fiber 101 are excited by absorbing incident light having a wavelength of about 810 nm and generate light having a wavelength of 920 nm ± 20 nm. On the other hand, a part of the excitation light 115 near the wavelength of 810 nm is emitted from the first optical fiber 101 as it is without being absorbed by neodymium ions (Nd3 +), and passes through the optical elements 104 and 109 and the dielectric mirror 107. The light enters the core portion of the second optical fiber 105.

  In the second optical fiber 105, neodymium ions (Nd3 +) at the core absorb and excite incident light 115 having a wavelength of about 810 nm, and generate light having a wavelength of 920 nm ± 20 nm. Since this light is reflected by the dielectric mirror 108 and propagates in the second optical fiber 105 in the reverse direction, the pumping light density in the second optical fiber 105 is increased and a sufficient pumping state is obtained.

  A part of the light having a wavelength of 920 nm ± 20 nm generated in the second optical fiber 105 is transmitted through the dielectric mirror 108 and is derived as light 116 from the optical element 110 to the diffraction grating 112 via the polarizing prism 111. Then, the light is folded by the diffraction grating 112 and led out again to the polarizing prism 111 as light 117. The light 117 emitted from the polarizing prism 111 is collected by the optical element 110, led to the dielectric mirror 108, passes through the dielectric mirror 108, and enters the second optical fiber 105.

  The light 117 incident on the second optical fiber 105 passes through the core part, is reflected by the opposite dielectric mirror 107, and is again diffracted from the dielectric mirror 108 via the optical element 110 and the polarizing prism 111. It reaches the grating 112, is folded back here, and is incident on the second optical fiber 105. As described above, light having a wavelength of 920 nm ± 20 nm generated in the second optical fiber 105 is alternately reflected between the dielectric mirror 107 and the diffraction grating 112, and as a result, the resonator 106 oscillates. It will be.

  The light generated by the oscillation operation is narrowed to FWHM (Full Width Half Maximum) <0.5 nm by the diffraction grating 112, and further processed to be linearly polarized by the polarizing prism 111. 118 is emitted from the dielectric mirror 107, collimated by the optical element 109, further condensed by the optical element 104, and incident on the first optical fiber 101.

  Since the first optical fiber 101 is pumped at a high pumping density as described above, it functions as a high gain amplifier for light near the wavelength of 920 nm, and the incident light 118 is amplified to high power light. Then, the light 119 near the wavelength of 920 nm is emitted from the first optical fiber 101. The light 119 emitted from the first optical fiber 101 is collimated by the optical element 103 and transmitted through the filter 114 to be output.

  Since the output light 119 has a narrow band and is linearly polarized, it is optimal for use as a fundamental wave of, for example, a second harmonic generation (SGH).

  According to the optical fiber amplifying apparatus of the present invention described above, the pumping light that has not been absorbed by the optical fiber amplifier is used as the pumping light for the optical fiber that constitutes the resonator. It can be used without.

In addition, a diffraction grating is arranged outside the pair of dielectric mirrors arranged at both ends of the resonator optical fiber, and the oscillation path is configured by the dielectric mirror and the diffraction grating across the optical fiber. It is possible to minimize the influence of the loss by using a band narrowing element such as a diffraction grating that can cause the above problem in an optical oscillation system that has no problem even with a small output.
As described above, according to the optical fiber amplifying apparatus of the present invention, it is possible to provide a high-power and high-efficiency laser beam.

  In the above description, the structures of the first and second optical fibers 101 and 105 are not described in detail. However, as the optical fibers 101 and 105, the optical fibers 101 and 105 are for excitation high propagation whose refractive index is lower than that of the core portion. It is preferable to use a so-called double clad structure provided with a clad. According to this, since a higher level of excitation light can be incident, a higher level output can be obtained.

  FIG. 2 is a diagram showing an example in which the first and second optical fibers 101 and 105 have a double clad structure. As shown in the figure, the optical fibers 101 and 105 are provided with a core portion 201 at the center thereof, a first cladding 202 formed on the outside thereof, and a second cladding 203 formed on the outside thereof. . The first clad 202 has a function of propagating excitation light, and an outer portion of the light spot collected by the optical element is incident and propagated and outputted as it is. For this purpose, the refractive index of the first clad 202 is set to be lower than the refractive index of the core portion 201 and further set to be higher than the refractive index of the second clad 203.

  By using such an optical fiber having a double clad structure, it is possible to propagate pumping light, so that it is possible to generate a large output light. However, particularly when applied to the second optical fire bar 105. By setting the cutoff wavelength of the core portion to be shorter than the wavelength 920 nm ± 20 nm generated by oscillation, the resonator can be easily oscillated in a single mode.

  Furthermore, it is desirable that the first and second optical fibers 101 and 105 are polarization maintaining fibers. That is, as shown in FIG. 3, the core part 301 is formed in the cross-sectional ellipse shape. With such a configuration, since the propagation speed is different between light having polarization in the minor axis direction of the core 301 and light having polarization in the major axis direction, polarization can be maintained. By using such an optical fiber, linearly polarized light with less unnecessary orthogonal components can be obtained. In FIG. 3 as well, the optical fibers 101 and 105 are formed in a double clad structure, and have a first clad 302 and a second clad 303.

  Further, according to the embodiment shown in FIG. 1, the diffraction grating 112 is used to narrow the light generated in the resonator 106. However, the band is narrowed using other elements. It may be.

  In other words, for example, an etalon can be used instead of the diffraction grating. FIG. 4 is a diagram showing an embodiment of a resonator 106 using an etalon. In FIG. 4, the same components as those in FIG. An etalon 401 is disposed so as to receive the light 116 that has passed through the polarizing prism 111, and a mirror 402 that totally reflects the light 117 having a wavelength of about 920 nm that has passed through the etalon 401 is provided.

  The light 117 reflected by the total reflection mirror 402 is incident on the second optical fiber 105 via the polarizing prism 111, the optical element 110, and the dielectric mirror 108, and is reflected by the dielectric mirror 107 on the opposite side to be dielectric. The light returns through the body mirror 108, the optical element 110, and the polarizing prism 111, and is reflected by the total reflection mirror 402 again. The oscillation operation is performed by repeating the above.

  In this embodiment, the narrow band light of FWHM <0.5 nm can be obtained by the steep filter characteristic of the etalon 401.

  Further, even when a fiber Bragg grating (FBG) is used, narrow band light can be generated similarly. FIG. 5 is a diagram showing the embodiment, and the same components as those in FIG.

  In FIG. 5, an optical fiber 501 including an FBG and an optical element 502 disposed between the optical fiber 501 and the polarizing prism 111 are provided.

  The light 116 that has passed through the polarizing prism 111 is collected by the optical element 502 and is incident on an optical fiber 501 having an FBG. The optical fiber 501 has a function of totally reflecting FWHM <0.5 nm of light in the vicinity of a wavelength of 920 nm by the FBG, whereby a narrow band light 117 having a wavelength of 920 nm is led to the optical element 502, where collimation is performed. Then, the light is emitted to the polarizing prism 111 and is incident on the second optical fiber 105 through the optical element 110 and the dielectric mirror 108.

  The incident light 117 is reflected by the dielectric mirror 107 and returned, and finally, an oscillation operation for generating light having a wavelength near 920 nm and a narrow band is performed.

  Further, as means for narrowing the band of light generated by oscillation, an optical fiber added with unexcited neodymium ions (Nd3 +) can be applied. FIG. 6 shows an embodiment thereof. In FIG. 6, the same components as those in FIG. In the embodiment of FIG. 6, an optical fiber 601 to which neodymium ions (Nd 3 +) are added is provided, an optical element 602 is provided between the optical fiber 601 and the polarizing prism 111, and the optical element of the optical fiber 601 is further provided. A mirror 603 that totally reflects light in the vicinity of a wavelength of 920 nm is provided at the end opposite to 602.

  The light 116 that has passed through the polarizing prism 111 is collected by the optical element 602, is incident on the core portion of the optical fiber 601, reaches the mirror 603 as it is, and is reflected back to return to the optical element 602 as a light 117. 111 enters the second optical fiber 105 via the optical element 110. Also in this embodiment, an oscillation operation in which light is repeatedly reflected between the dielectric mirror 107 and the mirror 603 is performed.

  In this embodiment, excitation light having a wavelength of about 810 nm that is incident on the second optical fiber 105 without being absorbed by the first optical fiber 101 shown in FIG. 1 is neodymium in the core portion of the second optical fiber 105. Ions (Nd3 +) are excited, but are reflected by the dielectric mirror 110 and are not emitted from the dielectric mirror 110. Therefore, excitation light is not incident on the optical fiber 601 and neodymium ions (Nd3 +) are not excited.

  When the resonator 106 oscillates, a standing wave is generated inside. At this time, in the second optical fiber 105 in which neodymium ions (Nd3 +) added to the core are excited, spatial hole burning of gain occurs, and a number of longitudinal modes filling this spatial hole burning are established. Bandwidth expands. However, in the optical fiber 601, since the added ions are not excited, loss burning due to standing waves occurs inside, so that it becomes difficult to stand in an opposite phase for other longitudinal modes. As a result, the light 117 emitted through the optical fiber 601 has a narrow band.

  As described above, in the embodiment shown in FIGS. 4 to 6, the band of light generated by the oscillation operation of the resonator 106 can be surely set to the narrow band.

  In the embodiment shown in FIG. 1, the excitation light 115 near the wavelength of 810 nm generated by the semiconductor laser light source 113 is first incident on the first optical fiber 101 and is not absorbed by the first optical fiber 101. The pump light 115 is configured to be incident on the second optical fiber 105, but the pump light 115 is first incident on the second optical fiber 105, and the portion that has not been absorbed is incident on the first optical fiber 101. It can also be configured to.

  FIG. 7 shows an embodiment in which the pumping light from the semiconductor laser light source 113 is first incident on the second optical fiber 105. In FIG. 7, the same components as those in FIG. In the embodiment shown in FIG. 7, a filter 114 is disposed between the optical element 110 and the polarizing prism 111, and the light 115 having a wavelength of 810 nm generated from the semiconductor laser light source 113 is reflected by the filter 114. It is configured to enter the second optical fiber 105 through the optical element 110 and the dielectric mirror 108.

  As a result, neodymium ions (Nd3 +) added to the core of the second optical fiber 105 are excited to generate light having a wavelength of 920 nm ± 20 nm, but the excitation light 115 that has not been completely absorbed by the neodymium ions (Nd3 +). Passes through the dielectric mirror 107 and enters the first optical fiber 101 through the optical elements 109 and 104.

  Thereby, neodymium ions (Nd3 +) added to the core portion are excited, and the first optical fiber 101 generates light having a wavelength of 920 nm ± 20 nm.

  On the other hand, the light having a wavelength of 920 nm ± 20 nm generated by the second optical fiber 105 is reflected by the dielectric mirror 107, passes through the second optical fiber 105, reaches the dielectric mirror 108, and this dielectric The light passes through the mirror 108 and is led to the diffraction grating 112 through the optical element 110 and the polarizing prism 111 as light 116.

  In the diffraction grating 112, the incident light 116 is returned as light 117, which is incident on the second optical fiber 105 again via the polarizing prism 111, the optical element 110, and the dielectric mirror 108.

  As described above, the resonator 106 operates to oscillate light between the dielectric mirror 107 and the diffraction grating 112. As described with reference to FIG. 1, the diffraction grating 112 has a function of narrowing a band of light generated by oscillation, and the polarizing prism 111 converts the signal into a signal having a predetermined linear polarization.

  The light 118 having a wavelength of 920 nm ± 20 nm and a linearly polarized wave generated by the oscillation operation of the resonator 106 passes through the dielectric mirror 107 and enters the first optical fiber 101 through the optical elements 109 and 104. Then, it is amplified, emitted from the first optical fiber 101 as light 119, collimated by the optical element 103, and output.

  According to this embodiment, since a large level of excitation light can be incident on the second optical fiber 105, a large level of light can be generated by the oscillation operation of the resonator 106. The gain of the optical fiber 101 as an amplifier need not be so high.

  Also in the embodiment shown in FIG. 7, in order to narrow the band of light generated by oscillation, as in the embodiment shown in FIGS. 4 to 6, an optical fiber equipped with an etalon and FBG, or A configuration using an optical fiber that is not excited by adding ions to the core can be adopted.

  Further, in the embodiment shown in FIG. 1 and FIG. 7, the first optical fiber constituting the optical fiber amplifier and the second optical fiber constituting the resonator are coupled by the optical elements 104 and 109. However, the end portions of the optical fibers 101 and 105 may be directly connected with a mirror having characteristics equivalent to those of the dielectric mirror 107 interposed therebetween.

  FIG. 8 is a diagram showing an optical fiber coupling portion configured as described above. A dielectric mirror 801 is directly formed on either the end of the first optical fiber 101 or the end of the second optical fiber 105. Further, the end of the other optical fiber is pressed against the dielectric mirror 801 for connection.

  In this embodiment, since the first optical fiber 101 and the second optical fiber 105 are directly coupled, the light can be efficiently propagated to the other optical fiber. It is.

  Note that an optical fiber using neodymium ions (Nd3 +) has a relatively large gain with respect to a wavelength of 1.06 μm, and therefore easily oscillates at that wavelength. This wavelength of 1.06 μm is at the same level as the oscillation near the 920 nm in the upper level. Therefore, if oscillation occurs, the efficiency may be reduced. Therefore, the end face of the first optical fiber 101 for amplification is cut or polished obliquely so that light emitted from the inside of the fiber to the outside is emitted in a radiation mode at the fiber end face to suppress oscillation. It is also possible.

  As described above, in the optical fiber amplifying device shown in FIG. 1 and FIG. 7, the light 119 amplified and output by the first optical fiber 101 is narrow band and linearly polarized. It is optimal as a fundamental wave for generating harmonics.

  FIG. 9 is a diagram showing an embodiment of an apparatus for generating the second harmonic using the light 119 amplified and outputted in the embodiment shown in FIG. 1 as a fundamental wave. In the figure, the same components as those in FIG.

  In FIG. 9, a non-linear crystal 902 is disposed through the optical element 901 so as to receive the light 119 from the first optical fiber 101 that has passed through the filter 114, and further receives light that has passed through the non-linear crystal 902. In addition, a filter 904 is arranged via an optical element 903.

  The non-linear crystal 902 has a function of converting incident light 119 having a wavelength of about 920 nm into light 905 including the second harmonic, for example, a lithium niobium added with magnesium oxide having a periodically poled structure. A beet crystal (PPMgLN) or the like is suitable.

  The optical element 901 has a function of collecting the light 119 transmitted through the dielectric mirror 114 and causing it to enter the nonlinear crystal 902. The optical element 903 collimates the light 905 emitted from the nonlinear crystal 902. And has a function of leading to the filter 904. Further, the filter 904 has a function of separating the second harmonic 906 from the light 905 derived through the optical element 903, and is configured by a dielectric mirror, for example. That is, the fundamental wave is transmitted as it is and the second harmonic is reflected.

  By the action of the non-linear crystal 902, the light 119 having a wavelength of 920 nm ± 20 nm passing therethrough becomes the light 905 including the vicinity of the wavelength of 460 nm, and this light 905 is changed by the filter 904 from the fundamental wave 905 having the wavelength of 920 nm ± 20 nm. Separated into second harmonics 906. The second harmonic 906 is so-called blue laser light having a wavelength of around 460 nm.

  According to the embodiment shown in FIG. 9, since it receives light of a narrow band and linearly polarized light at a wavelength of 920 nm ± 20 nm, which is amplified to a large level, from the first optical fiber 101, the second order is very efficient. Harmonics can be generated and output.

  In the apparatus shown in FIG. 9 as well, the optical fibers 101 and 105 having the construction shown in FIGS. 2 and 3 can be applied, and the means shown in FIG. It is possible to apply.

  As described above, according to the present invention, pumping light from a pumping light source is incident on and pumped into either an optical fiber for amplification or an optical fiber for resonator, and the pumping light that has not been absorbed by the optical fiber. In order to excite the other optical fiber, and further configured to interpose an element for narrowing the light generated by oscillation in the oscillation path constituted by the optical fiber for the resonator, The pump light can be used without waste, and the influence of the loss of the band narrowing element can be suppressed, so that a high-efficiency, large output, narrow band second harmonic is generated from the optical fiber for amplification. It is possible to emit light suitable for the fundamental wave to be generated.

The figure which shows one Embodiment of the optical fiber amplifier which concerns on this invention. The figure which shows one Embodiment of the optical fiber applied to the apparatus of FIG. The figure which shows other embodiment of the optical fiber applied to the apparatus of FIG. The figure which shows other embodiment of the narrow banding means applied to the apparatus of FIG. The figure which shows further another embodiment of the narrow banding means applied to the apparatus of FIG. The figure which shows further another embodiment of the narrow banding means applied to the apparatus of FIG. The figure which shows other embodiment of the optical fiber amplifier concerning the present invention. FIG. 8 is a view showing another embodiment of a coupling means for optically coupling optical fibers in the apparatus shown in FIGS. 1 and 7. The figure which shows the 2nd harmonic generator concerning this invention. The figure for demonstrating the principle of the light generation by excitation of an optical fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Optical fiber amplifier 101 ... 1st optical fiber 102 ... Optical fiber amplifier 103,104 ... Optical element 105 ... 2nd optical fiber 106 ... Resonator 107,108 ... Dielectric mirror 109,110 ... Optical element 111 ... Polarizing prism 112 ... Diffraction grating 113 ... Semiconductor laser light source 114 ... Filter 401 ... Etalon 501 ... Optical fiber with FBG 601 ... Non-excited optical fiber 902 ... Non-linear crystal

Claims (6)

An optical fiber amplifier having a first optical fiber that outputs a first light having a wavelength of 920 nm ± 20 nm when neodymium ions (Nd3 +) are added to the core part and excitation light is incident on the core part;
Neodymium ions (Nd3 +) are added to the core portion, and excitation light is incident on the core portion, so that the second light having the same wavelength as the first light and a narrower band than the first light is resonated. A resonator having a second optical fiber configured as a resonator to generate;
An excitation light source;
The optical fiber amplifier and the resonator are optically coupled, and the pumping light from the pumping light source is incident on either the first optical fiber or the second optical fiber. An optical system in which excitation light that has not been absorbed by the neodymium ions (Nd3 +) is incident on the other optical fiber as the excitation light, and the second light generated by the resonator is incident on the first optical fiber. Means,
An optical fiber amplifying apparatus comprising:   The optical fiber amplifying apparatus according to claim 1, wherein the resonator includes a band narrowing element in a resonance path. An optical fiber amplifier having a first optical fiber that outputs a first light having a wavelength of 920 nm ± 20 nm when neodymium ions (Nd3 +) are added to the core part and excitation light is incident on the core part;
Neodymium ions (Nd3 +) are added to the core portion, and excitation light is incident on the core portion, so that the second light having the same wavelength as the first light and narrower than the first light is resonated. A resonator having a second optical fiber configured as a resonator to generate;
An excitation light source;
The optical fiber amplifying means and the resonator are optically coupled, and the pumping light from the pumping light source is incident on either the first optical fiber or the second optical fiber. Among them, the excitation light that has not been absorbed by the neodymium ions (Nd3 +) is incident on the other optical fiber as the excitation light, and the second light generated by the resonance means is incident on the first optical fiber. First optical means;
Second optical means for generating and outputting third light having a wavelength of 460 nm ± 10 nm by passing the first light amplified by the optical fiber amplifier through a nonlinear element;
A second-order harmonic generator characterized by comprising:   The second-order harmonic generator according to claim 3, wherein the resonator includes a band narrowing element in a resonance path. An optical fiber amplifier having a first optical fiber that outputs a first light having a wavelength of 920 nm ± 20 nm when neodymium ions (Nd3 +) are added to the core part and excitation light is incident on the core part, and a core The second light that is generated by resonance by adding a neodymium ion (Nd3 +) to the portion and the excitation light is incident on the core portion to generate second light having a wavelength equivalent to that of the first light and a narrow band. Optically coupling a resonator having a fiber, and injecting excitation light into one of the first optical fiber and the second optical fiber, and exciting the excitation light;
Entering the pumping light that has not been absorbed by the optical fiber into which the pumping light is incident into the other optical fiber; and
Amplifying and outputting the second light generated by the resonator by the optical fiber amplifier;
A light generation method comprising: An optical fiber amplifier having a first optical fiber that outputs a first light having a wavelength of 920 nm ± 20 nm when neodymium ions (Nd3 +) are added to the core part and excitation light is incident on the core part, and a core The second light that is generated by resonance by adding a neodymium ion (Nd3 +) to the portion and the excitation light is incident on the core portion to generate second light having a wavelength equivalent to that of the first light and a narrow band. Optically coupling a resonator having a fiber, and injecting excitation light into one of the first optical fiber and the second optical fiber, and exciting the excitation light;
Entering the pumping light that has not been absorbed by the optical fiber into which the pumping light is incident into the other optical fiber; and
Amplifying and outputting the second light generated by the resonator by the optical fiber amplifier;
Obtaining the second harmonic of the light output from the optical fiber amplifier through the nonlinear element through the light output from the optical fiber amplifier;
A second-order harmonic generation method comprising:

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