JP2007173346A - Laser system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the possibility of damaging a semiconductor laser by preventing laser oscillation from happening at a wavelength of a fiber laser providing a gain peak. <P>SOLUTION: A laser system includes a wavelength division multiplex combiner disposed between a semiconductor laser and a fiber Bragg grating. The wavelength division multiplex combiner separates incident light incident on the wavelength division multiplex combiner to the light of the predetermined wavelength and to light having gain peak wavelength different from the laser oscillation wavelength of the fiber laser, and prevents the light of the wavelength of the gain peak different from the laser oscillation wavelength from returning to the semiconductor laser. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laser system, and more particularly to a laser system using a fiber laser using an optical fiber itself as a laser device.

  In recent years, fiber lasers using optical fiber itself as a laser device by adding a laser-active element to optical fiber glass used in optical communications have been applied to microfabrication technologies in the electronics industry such as semiconductor manufacturing processes. Various proposals have been made with the aim of achieving this goal.

Specifically, a fiber laser is one in which a core of an optical fiber is doped with rare earth ions such as erbium ions and yttrium ions as a laser active medium, and the optical fiber itself constitutes a laser resonator. It was made to do.

FIG. 1 is a conceptual structural explanatory diagram of a conventional laser system using such a fiber laser.

  This conventional laser system 100 is coupled to a fiber laser 102 in which the core of the optical fiber is doped with a laser active medium and the optical fiber itself constitutes a laser resonator, and an end 102 a on the incident side of excitation light in the fiber laser 102. And the semiconductor laser 104 that makes the excitation light incident on the end portion 102a, and the condensing light that is arranged after the end portion 102b on the emission side of the laser beam in the fiber laser 102 and collects the laser beam emitted from the end portion 102b. A lens 106, a dielectric multilayer mirror 108 that is disposed downstream of the condensing lens 106 and transmits part of the laser beam condensed by the condensing lens 106 and reflects the remainder to provide optical feedback, and a fiber laser 102 is disposed at the end 102b of the laser 102 so that the laser oscillation wavelength To nearly 100% of the fiber Bragg grating to identify the laser oscillation wavelength has a reflectance (Fiber Bragg Grating: FBG) is configured to have a 110.

Here, the wavelength of the excitation light generated by the semiconductor laser 104 is λ ₁ . The laser oscillation wavelength excited by the excitation light having the wavelength λ ₁ and reflected by the fiber Bragg grating 110 is λ _2, and the gain peak wavelength of the fiber laser 102 is λ ₃ . That is, the fiber laser 102 has gains at the wavelengths λ ₂ and λ ₃ , but the wavelength λ ₃ has a larger gain.

Further, the dielectric multilayer mirror 108 transmits only a part of the light having the wavelength λ ₂ (for example, the transmittance is 10%) and outputs the laser beam to the outside. Accordingly, the remainder of the light having the wavelength λ _{2 and} the light having the wavelength λ ₃ are reflected by the dielectric multilayer mirror 108 and returned to the fiber laser 102 via the condenser lens 106 to be optically fed back.

In the above configuration, according to the conventional laser system 100, when the excitation light having the wavelength λ ₁ is incident from the semiconductor laser 104 to the end portion 102a of the fiber laser 102, the laser active medium is excited by the excitation light, and the fiber Bragg grating. 110 lasing at the wavelength lambda ₂ is reflected by, the light of the wavelength lambda ₂ emitted from the end portion 102b is condensed by the condenser lens 106, a portion is transmitted through the dielectric multilayer film mirror 108 It is emitted as a laser beam to the outside.

However, in the conventional laser system 100 described above, the light with the wavelength λ ₃ of the gain peak of the fiber laser 102 is also reflected by the dielectric multilayer mirror 108, and the light with the wavelength λ ₃ passes through the condensing lens 106 to the fiber. The light is returned to the laser 102 and returned. For this reason, strong laser oscillation occurs at the wavelength λ ₃ of the gain peak of the fiber laser 102 between the dielectric multilayer mirror 108 and the light emitting surface of the semiconductor laser 104, and the light emitting surface of the semiconductor laser 104 may be damaged. There was a problem.

  Further, it has been pointed out that the above-described conventional laser system 100 has poor reliability due to the occurrence of damage to the semiconductor laser 104.

In general, a wavelength division multiplex coupler (WDM Coupler) is disposed as a wavelength separation fiber device between a fiber laser and a semiconductor laser that generates excitation light, and the excitation light and laser oscillation of wavelength λ ₁ are arranged. it was often done to separate the wavelength serving wavelength lambda ₂ of light. However, even with such a technique, the light having the wavelength λ ₃ of the gain peak of the fiber laser is not separated, so that strong laser oscillation occurs at the wavelength λ ₃ of the gain peak of the fiber laser, which may damage the semiconductor laser. Could not be resolved.

Note that the prior art that the applicant of the present application knows at the time of filing a patent application is not an invention related to a known literature invention, so there is no prior art document information to be described.

  The present invention has been made in view of the above-mentioned various problems of the prior art, and its object is to prevent laser oscillation from occurring at the wavelength of the gain peak of the fiber laser. Thus, a laser system that eliminates the possibility of damaging the semiconductor laser is provided.

  Another object of the present invention is to provide a laser system with improved reliability by eliminating the possibility of damaging the semiconductor laser.

  In order to achieve the above object, the laser system according to the present invention uses a wavelength division multiple coupler that separates the gain peak wavelength of the fiber laser and the wavelength of the excitation light, and uses an unnecessary laser at the gain peak wavelength of the fiber laser. Oscillation is suppressed and damage to the light emitting surface of the semiconductor laser is prevented in advance.

  That is, the laser system according to the present invention is such that a wavelength division multiplex coupler is disposed between an end portion on the incident side of excitation light in a fiber laser and a semiconductor laser that makes the excitation light incident on the end portion. This wavelength division multiplex coupler does not separate the pumping light wavelength from the laser oscillation wavelength, but separates the pumping light wavelength from the fiber laser gain peak wavelength to provide a fiber laser gain peak. The light of the wavelength is not returned to the fiber laser.

  In addition, the laser system according to the present invention uses a long-period diffraction grating that functions as a band-block filter by coupling the wavelength near the gain peak of the gain fiber of the incident light to the cladding, and gain of the incident light. The optical feedback from the end face of the semiconductor laser in the wavelength region near the gain peak of the fiber is suppressed.

Among these inventions, the invention described in claim 1 is a fiber laser in which a laser active medium is doped in an optical fiber core and the optical fiber itself constitutes a laser resonator, and one end of the fiber laser is predetermined. A semiconductor laser that injects excitation light of a wavelength of the fiber, a fiber Bragg grating that is disposed on the one end side of the fiber laser and that reflects the light of the laser oscillation wavelength to identify the laser oscillation wavelength, and the fiber laser And a dielectric multilayer mirror that reflects light emitted from the other end and is disposed between the semiconductor laser and the fiber Bragg grating. Wavelength division multiplex coupler Separates light incident on the wavelength division multiplex coupler into light having a predetermined wavelength and light having a gain peak wavelength different from the laser oscillation wavelength of the fiber laser, and is different from the laser oscillation wavelength. The gain peak wavelength light is not returned to the semiconductor laser.

  According to a second aspect of the present invention, in the first aspect of the present invention, a nonlinear optical element is disposed between the other end portion side and the dielectric multilayer mirror. It is what you do.

  According to a third aspect of the present invention, the invention according to any one of the first and second aspects of the present invention is characterized in that the other end side and the dielectric multilayer mirror are provided. A passive fiber is arranged between them.

  According to a fourth aspect of the present invention, there is provided a fiber laser in which a core of an optical fiber is doped with a laser active medium so that the optical fiber itself constitutes a laser resonator, and at one end of the fiber laser. A semiconductor laser that receives excitation light of a predetermined wavelength; a fiber Bragg grating that is disposed on the one end side of the fiber laser and that reflects the light of the laser oscillation wavelength to identify the laser oscillation wavelength; and the fiber In a laser system having a dielectric multilayer mirror that is disposed on the other end side of the laser and reflects light emitted from the other end portion, disposed between the semiconductor laser and the fiber Bragg grating Long-period diffraction grating, and the long-period diffraction grating is incident The wavelength of the gain fiber vicinity of the gain peak of the light coupled into the cladding which acts as a band block filter is obtained so as to suppress the optical feedback from the semiconductor laser end surface in said wavelength range.

  According to a fifth aspect of the present invention, in the fourth aspect of the present invention, a nonlinear optical element is disposed between the other end side and the dielectric multilayer mirror. It is what you do.

  According to a sixth aspect of the present invention, the invention according to any one of the fourth or fifth aspect of the present invention is characterized in that the other end portion side and the dielectric multilayer mirror are provided. A passive fiber is arranged between them.

  According to the present invention, there is an excellent effect that laser oscillation does not occur at the wavelength of the gain peak of the fiber laser, and there is no possibility of damaging the semiconductor laser.

  In addition, according to the present invention, since there is no possibility of damaging the semiconductor laser, an excellent effect that the reliability can be remarkably improved is achieved.

  Hereinafter, an example of an embodiment of a laser system according to the present invention will be described in detail with reference to the accompanying drawings.

  In the following description, the same or corresponding configurations are denoted by the same reference numerals, and the description of the overlapping configuration and operation will be omitted as appropriate.

FIG. 2 is an explanatory diagram of a conceptual configuration of a laser system according to an example of the embodiment of the present invention.

  The laser system 10 according to the present invention and the conventional laser system 100 are such that the laser system 100 couples the semiconductor laser 104 to the end 102 a of the fiber laser 102, whereas the laser system 10 is connected to the end of the fiber laser 102. They are different in that the semiconductor laser 104 is coupled to the unit 102a via the wavelength division multiplex coupler 12.

  More specifically, in the laser system 10, the wavelength division multiplex coupler 12 is coupled to the end 102 a, and the wavelength division multiplex coupler 12 is disposed between the semiconductor laser 104 and the fiber Bragg grating 110. become.

The wavelength division multiplex coupler 12 separates the light incident on the wavelength division multiplex coupler 12 into light having the wavelength λ ₁ of the pumping light and light having the wavelength λ ₃ of the gain peak of the fiber laser 102.

The semiconductor laser 104 and the wavelength division multiplex coupler 12 are coupled by a passive fiber 14 having no gain. The wavelength division multiplex coupler 12 is connected to a passive fiber 16 having no gain for separating light having a wavelength λ ₃ separated from light incident on the wavelength division multiplex coupler 12. The passive fiber 16 is terminated so as not to reflect light of wavelength lambda _3.

In the above configuration, according to the laser system 10, when excitation light having the wavelength λ ₁ is incident on the end 102 a of the fiber laser 102 through the passive fiber 14 and the wavelength division multiplex coupler 12 from the semiconductor laser 104, the excitation is performed. are excited laser active medium and lasing at the wavelength lambda ₂ reflected by the fiber Bragg grating 110 by light, the light of the wavelength lambda ₂ emitted from the end portion 102b is condensed by the condenser lens 106, one that The part passes through the dielectric multilayer mirror 108 and is emitted to the outside as a laser beam.

At this time, the laser system 10, also the light of the wavelength lambda ₃ of the gain peak of the fiber laser 102 by the dielectric multilayer film mirror 108 is reflected, fiber laser 102 light of the wavelength lambda ₃ via a condenser lens 106 The light is returned to and returned to the light.

Here, the light of wavelength λ ₃ returned to the fiber laser 102 by the dielectric multilayer mirror 108 is separated by the wavelength division multiplex coupler 12 and terminated so as not to reflect the light of wavelength λ _3. 16 is guided.

Accordingly, since the light of wavelength λ ₃ does not reciprocate within the fiber laser 102, the laser oscillation at the wavelength λ ₃ in the fiber laser 102 is prevented in advance, and thus the semiconductor laser 104 is also prevented from being damaged. Is done.

  Further, according to the laser system 10, since the semiconductor laser 104 is not damaged in this way, the reliability as the system can be improved.

Further, the fiber laser 102, when prevents laser oscillation at a wavelength lambda _3, because there is no adding components to the fiber laser 102, it does not lower the efficiency of laser oscillation.

As the wavelength division multiplex coupler 12, for example, a so-called fusion type may be used, and the bandwidth of the wavelength to be separated is about several nm. Therefore, with respect to the wavelength λ _2, no particular defining the specification.

Here, a quartz-based optical fiber with the addition of Yb ions as fiber laser 102 and the wavelength lambda ₁ is the wavelength of about 975nm of excitation light of the semiconductor laser 104, and, if the wavelength lambda ₂ is to laser oscillation is 1017nm Will be described.

The fiber laser 102, which is a silica-based optical fiber to which Yb ions are added, has a gain sufficient to cause laser oscillation at a wavelength of 1017 nm, but its wavelength λ ₃ is at a wavelength of about 1030 nm.

The fiber Bragg grating 110 is highly reflective when the wavelength λ ₂ for laser oscillation is 1017 nm, and the width of the reflection band (reflection band width) is about 0.1 nm.

On the other hand, the dielectric multilayer mirror 108 generally has a reflection bandwidth of several tens of nanometers, and has a high reflectance for both the wavelength 1017 nm (wavelength λ ₂ ) and the wavelength 1030 nm (wavelength λ ₃ ). .

Therefore, the light having a wavelength of 1030 nm (wavelength λ ₃ ) reflected by the dielectric multilayer mirror 108 reaches the wavelength division multiple coupler 12 without being reflected by the fiber Bragg grating 110.

Then, the light having a wavelength of 1030 nm (wavelength λ ₃ ) reaching the wavelength division multiplex coupler 12 is separated by the wavelength division multiplex coupler 12 and terminated so as not to reflect the light of wavelength 1030 nm (wavelength λ ₃ ). The light is guided to the passive fiber 16 and the occurrence of laser oscillation at a wavelength of 1030 nm (wavelength λ ₃ ) in the fiber laser 102 is prevented in advance.

Next, FIG. 3 is a conceptual structural explanatory diagram of a laser system according to another example of the embodiment of the present invention.

  In the laser system 20 and the laser system 10 according to the present invention, the laser system 10 does not include a nonlinear optical element between the condenser lens 106 and the dielectric multilayer mirror 108, whereas the laser system 20 Both are different in that a nonlinear optical element is disposed between the condenser lens 106 and the dielectric multilayer mirror 108.

Semitransparent mirror More specifically, in the laser system 20, half the light of wavelength lambda ₂ is in which the wavelength lambda ₂ reflected on the rear stage of the condenser lens 106, i.e., light of the wavelength lambda _2/2 is to be transmitted 22 is disposed, and a non-linear optical element 24 that generates a second harmonic is disposed between the semi-transmissive mirror 22 and the dielectric multilayer mirror 108.

Therefore, according to the laser system 20, the laser beam having the laser oscillation wavelength λ ₂ (for example, 1017 nm) collected by the condenser lens 106 is reflected by the semi-transmissive mirror 22 and enters the nonlinear optical element 24. is, is reflected by the dielectric multilayer film mirror 108 is intended to be emitted to the outside through the non-linear optical element 24 and the semi-transparent mirror 22, thereby the laser oscillation wavelength wavelength serving wavelength of lambda ₂ half lambda _2/2 A laser beam (for example, 508.5 nm) can be efficiently generated, and damage to the semiconductor laser 104 can be prevented.

In each of the above-described embodiments, a long period diffraction grating may be arranged instead of the wavelength division multiplex coupler 12. FIG. 4 is an explanatory diagram of the long-period diffraction grating, and FIG. 5 is a graph illustrating an example of characteristics of the long-period diffraction grating.

  A fiber Bragg grating (FBG) as a reflection element generally used has a grating vector of +/− 2k which is a difference between an incident wave (wave number vector k) and a reflected wave (wave number vector−k) at a reflection wavelength. That is, the grating pitch is about a half of the wavelength in the fiber, that is, a period of about 0.3 μm if it has a 1 μm band reflection band.

  In contrast, a long-period diffraction grating (LPG: long period grating) has a long grating period. This is because it is coupled to a crack mode propagating in the same direction. The light coupled to the cladding is attenuated due to loss due to the jacket, etc. As a result, the long-period grating is attenuated by coupling only a specific wavelength to the cladding, and acts as a band-block filter for a specific wavelength band It is.

  Therefore, by replacing this long-period diffraction grating with the wavelength division multiplex coupler 12 in each of the above-described embodiments, the long-period diffraction grating becomes near the gain peak of the gain fiber in the light incident on the fiber laser 102. The wavelength is coupled to the cladding and functions as a band-block filter to suppress optical feedback from the end face of the semiconductor laser 104 in the wavelength range.

Although not particularly illustrated, a passive fiber having no gain is connected between the end 102 b of the fiber laser 102 and the condensing lens 106, and the light emitted from the passive fiber is collected by the condensing lens 106. You may make it light.

  The present invention can be used for microfabrication and inspection of a fine structure in the field of electronic industry.

FIG. 1 is an explanatory diagram of a conceptual configuration of a conventional laser system using a fiber laser. FIG. 2 is an explanatory diagram of a conceptual configuration of a laser system according to an example of the embodiment of the present invention. FIG. 3 is a conceptual structural explanatory diagram of a laser system according to another example of the embodiment of the present invention. FIG. 4 is an explanatory diagram of a long period diffraction grating. FIG. 5 is a graph showing an example of characteristics of the long-period diffraction grating.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Laser system 12 Wavelength division multiple coupler 14 Passive fiber 16 Passive fiber 20 Laser system 22 Semi-transmission mirror 24 Nonlinear optical element 100 Laser system 102 Fiber laser 102a End part 102b End part 104 Semiconductor laser 106 Condensing lens 108 Dielectric multilayer film Mirror 110 Fiber Bragg Grating

Claims (6)

A fiber laser in which an optical fiber core is doped with a laser active medium and the optical fiber itself constitutes a laser resonator;
A semiconductor laser that makes excitation light of a predetermined wavelength incident on one end of the fiber laser;
A fiber Bragg grating that is arranged on the one end side of the fiber laser and reflects the light of the laser oscillation wavelength to identify the laser oscillation wavelength,
A dielectric multilayer mirror that is disposed on the other end side of the fiber laser and reflects light emitted from the other end;
A wavelength division multiple coupler disposed between the semiconductor laser and the fiber Bragg grating;
The wavelength division multiplex coupler separates light incident on the wavelength division multiplex coupler into light having the predetermined wavelength and light having a gain peak wavelength different from the laser oscillation wavelength of the fiber laser, A laser system characterized by not returning light having a gain peak wavelength different from the laser oscillation wavelength to the semiconductor laser. The laser system according to claim 1, wherein
A laser system, wherein a non-linear optical element is disposed between the other end side and the dielectric multilayer mirror. The laser system according to claim 1 or 2,
A passive fiber is disposed between the other end side and the dielectric multilayer mirror. A fiber laser in which an optical fiber core is doped with a laser active medium and the optical fiber itself constitutes a laser resonator;
A semiconductor laser that makes excitation light of a predetermined wavelength incident on one end of the fiber laser;
A fiber Bragg grating that is arranged on the one end side of the fiber laser and reflects the light of the laser oscillation wavelength to identify the laser oscillation wavelength,
A dielectric multilayer mirror that is disposed on the other end side of the fiber laser and reflects light emitted from the other end;
Having a long period diffraction grating disposed between the semiconductor laser and the fiber Bragg grating;
The long-period diffraction grating couples a wavelength near the gain peak of the gain fiber of the incident light to the cladding, functions as a band-block filter, and suppresses optical feedback from the end face of the semiconductor laser in the wavelength range. A laser system characterized by The laser system according to claim 4, wherein
A laser system, wherein a non-linear optical element is disposed between the other end side and the dielectric multilayer mirror. The laser system according to any one of claims 4 and 5,
A passive fiber is disposed between the other end side and the dielectric multilayer mirror.

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