WO2009130894A1

WO2009130894A1 - Pulsed fiber laser light source, wavelength conversion laser light source, two-dimensional image display device, liquid crystal display device, laser machining device and laser light source provided with fiber

Info

Publication number: WO2009130894A1
Application number: PCT/JP2009/001826
Authority: WO
Inventors: 古屋博之; 楠亀弘一; 水島哲郎; 水内公典; 山本和久
Original assignee: パナソニック株式会社
Priority date: 2008-04-25
Filing date: 2009-04-22
Publication date: 2009-10-29

Abstract

A pulsed fiber laser light source (100) is provided with an LD (101) for a pump for outputting excitation light, and a laser oscillator. The laser oscillator includes a first fiber (103), which contains a laser activation material and permits the excitation light to enter from the LD (101); a second fiber (106), which contains a laser activation material and is to be a region which excitation light substantially does not reach; and a pair of fiber gratings (102, 104) which are optically connected to the first and the second fibers (103, 106) by sandwiching the first and the second fibers (103, 106). An input current which drives the LD (101) is interrupted so that a first peak of a light pulse outputted from the laser oscillator is formed and a second peak thereof is not formed.

Description

Pulse fiber laser light source, wavelength conversion laser light source, two-dimensional image display device, liquid crystal display device, laser processing device, and fiber laser light source

The present invention relates to a pulse fiber laser light source having high photoelectric conversion efficiency capable of generating a light pulse having a high output peak value, a wavelength conversion laser light source using the same, a two-dimensional image display device, a liquid crystal display device, and laser processing. The present invention relates to an apparatus and a laser light source with a fiber.

Up to now, solid-state lasers such as Nd: YAG laser and Nd: YVO ₄ laser have been mainly used as laser light sources for generating light in the 1 μm band, and laser processing machines using these lasers and these lights as fundamental waves. However, there is a problem that the larger the output, the more the laser medium needs to be cooled and the apparatus becomes larger. Therefore, a fiber laser light source capable of outputting W-class high-output light with a simple cooling mechanism has been attracting attention as a light source for welding and a fundamental wave light source of a wavelength conversion laser light source.

The basic laser operation of this fiber laser light source will be described below. First, excitation light from an excitation laser light source enters from one end of the fiber. The incident excitation light is absorbed by the laser active material contained in the fiber, and then the seed light of the fundamental wave is generated inside the fiber. The seed light of the fundamental wave is reflected back and forth many times in a resonator having a pair of reflection mirrors, a fiber grating formed in a fiber and a fiber grating formed in another fiber. At the same time, the seed light is amplified by the gain of the laser active substance contained in the fiber, the light intensity increases, the wavelength is selected, and laser oscillation occurs. Note that the fiber and the fiber are connected by a connecting portion, and the laser light source is current-driven by an excitation laser current source.

Also, after a part of the output light is separated by a beam splitter and received by a light receiving element for monitoring the output light, the output light is converted into an electrical signal and used. The output control unit adjusts the drive current of the laser light source with the excitation laser current source so that the intensity of the converted signal becomes an intensity at which a desired output can be obtained. Then, the intensity of the excitation light from the laser light source is adjusted, and the output intensity of the fundamental wave of the fiber laser light source is adjusted. As a result, so-called auto power control (hereinafter abbreviated as “APC”) in which the output intensity of the fiber laser light source is kept constant operates stably.

By the way, if the laser light source is a pulse light source having a high peak power, it can be applied to laser processing such as drilling and high-efficiency wavelength conversion. Is a continuous wave type, so its use is limited to laser welding. For example, in order to oscillate a light source using a fiber, a configuration in which a modulated seed light source is amplified by a fiber amplifier has become mainstream.

In addition, even when harmonics are generated from a fundamental wave generated by a fiber laser light source by a wavelength converter, a method of generating pulsed fundamental wave light having a high peak power at the same average output is a continuous light. Since the conversion efficiency from the fundamental wave to the harmonic can be improved by the wavelength conversion method, the pulse oscillation of the fiber laser light source greatly contributes to the efficiency improvement.

Such fiber laser light source pulsing has also been studied in the field of communication applications and the like. A main resonator and a sub-resonator are provided, an optical modulator is inserted into the resonator, and the optical modulator is used as the main resonator. Patent Document 1 describes a method of generating an optical pulse by matching beat phases of a resonator and a sub-resonator. In addition, a method of inputting a high-intensity optical pulse into an optical fiber having anomalous dispersion characteristics and generating a narrow-band optical pulse by the frequency shift effect is described in Patent Document 2, and is applied to a fiber grating portion of a fiber laser resonator. Patent Document 3 describes a method for providing a supersaturated absorption effect. On the other hand, Patent Document 4 also describes a modulation method for an excitation LD that does not generate an unexpected optical surge pulse.

FIG. 30 is a schematic diagram showing an example of the configuration of the conventional pulse fiber laser light source as described above. A pulse fiber laser light source 200 shown in FIG. 30 includes a pump LD 201,

fiber gratings

202 and 204, a fiber 203, and a modulation mechanism 301. The fiber 203 is composed of a double clad polarization maintaining fiber doped with Yb. The pump LD 201 excites the fiber 203 and inserts the modulation mechanism 301 into a resonator composed of a pair of

fiber gratings

202 and 204. , Generate a light pulse.

However, in the methods as disclosed in

Patent Documents

1 and 2 of the conventional example, it is possible to generate an optical pulse with an ultra-narrow band. However, as shown in the conventional configuration of FIG. Therefore, there is a problem that the efficiency as a light source is lowered because it is necessary to insert the modulation mechanism 301 in the light source or the excitation efficiency is low. Further, even when a supersaturated absorption band is provided in the resonator as in Patent Document 3, the loss in the resonator is increased, which causes a reduction in efficiency. In any of the above cases, in addition to the configuration of the fiber laser resonator that generates continuous light, a new member is required, which causes a problem of cost increase and deterioration of the member. It has been difficult to realize a wavelength conversion laser light source using a fiber laser light source.

Patent 2577785 JP-A-8-146474 JP-A-2005-174993 JP2007-142380

An object of the present invention is to provide a highly efficient pulse fiber laser light source with a simple configuration.

A pulsed fiber laser light source according to one aspect of the present invention includes an excitation laser light source that emits excitation light, a fiber member that includes a laser active substance, and that receives excitation light from the excitation laser light source, and sandwiches the fiber member. A laser resonator including a set of fiber gratings optically connected to the fiber member, wherein the fiber member is provided with a region where excitation light does not substantially reach, The input current for driving the laser light source is blocked so that the first peak of the light pulse emitted from the laser resonator is formed and the second peak is not formed.

In the above-described fiber laser light source, pulse oscillation can be performed without adding new expensive parts, so that a highly efficient pulse fiber laser light source can be realized with a simple configuration.

It is the schematic which shows the structure of the wavelength conversion laser light source in the 1st Embodiment of this invention. It is a figure which shows the transient response characteristic of the optical output generate | occur | produced from a fiber laser light source, when a rectangular pulse current is supplied to LD for pumps as an input current. It is a 1st figure which shows the change of the optical output when changing the pulse width of an input electric current in order to change the electric charge amount of an input. It is a 2nd figure which shows the change of the optical output when changing the pulse width of input current in order to change the electric charge amount of input. It is a 3rd figure which shows the change of the optical output when changing the pulse width of an input electric current in order to change the electric charge amount of an input. It is a 4th figure which shows the change of an optical output when changing the pulse width of an input electric current in order to change the electric charge amount of an input. It is a figure which shows an example of the single optical pulse generated by setting the pulse width and current value of a rectangular input current to predetermined values. It is a figure which shows an example of the optical output obtained by applying the input voltage which consists of several pulse voltage of a predetermined | prescribed period to pump LD, when input voltage is biased with the positive DC voltage. It is a figure which shows an example of the optical output obtained by applying the input voltage which consists of several pulse voltage of a predetermined | prescribed period to pump LD, when input voltage is biased with the negative DC voltage. It is a figure which shows the electric current waveform supplied to LD for pumps, and the optical output waveform generate | occur | produced from a pulse fiber laser light source. It is a figure which shows the actual electric current waveform supplied to LD for pumps, and the actual optical output waveform generate | occur | produced from a pulse fiber laser light source. It is the schematic which shows the main structures of the other pulse fiber laser light source used for the wavelength conversion laser light source by the 1st Embodiment of this invention. It is the schematic which shows the structure of the wavelength conversion laser light source in the 2nd Embodiment of this invention. It is a flowchart for demonstrating operation | movement of a pulse fiber laser light source when an optical pulse is radiate | emitted from the pulse fiber laser light source shown in FIG. It is the schematic which shows the structure of the other wavelength conversion laser light source by the 2nd Embodiment of this invention. It is a figure which shows the waveform of the pulse current of an input electric current, and the waveform of the optical output from the pulse fiber laser light source driven by this pulse current. It is the schematic which shows the structure of the wavelength conversion laser light source in the 3rd Embodiment of this invention. The output light waveform of the fiber amplifier of the wavelength conversion laser light source shown in FIG. 17, the seed light output waveform of the pulse fiber laser light source, the current waveform of the pump LD of the fiber amplifier, and the current waveform of the pump LD of the pulse fiber laser light source are shown. FIG. It is the schematic which shows the structure of the wavelength conversion laser light source in the 4th Embodiment of this invention. It is a schematic diagram which shows the condensing position of the fundamental wave in the conventional wavelength conversion element. It is a figure which shows the relationship between the position of a wavelength conversion element, and a fundamental wave power density by using the condensing position of a fundamental wave as a parameter. It is the figure which plotted (the power density of the 2nd harmonic x fundamental wave power density) with respect to the position of a wavelength conversion element using the condensing position of a fundamental wave as a parameter. It is a figure which shows the wavelength conversion characteristic of a prior art example and 4th Embodiment. It is the schematic which shows the structure of the wavelength conversion laser light source in the 5th Embodiment of this invention. FIG. 25 is a schematic diagram for explaining how the fundamental laser beam passes through the wavelength conversion laser light source shown in FIG. 24 while changing the incident angle to the wavelength conversion element. It is the schematic which shows the structure of the two-dimensional image display apparatus in the 6th Embodiment of this invention. It is the schematic which shows the structure of the liquid crystal display device in the 7th Embodiment of this invention. It is the schematic which shows the structure of the laser processing apparatus in the 8th Embodiment of this invention. It is the schematic which shows the laser light source with a fiber by the 8th Embodiment of this invention. It is a schematic diagram which shows an example of a structure of the conventional pulse fiber laser light source.

Hereinafter, a laser application apparatus according to an embodiment of the present invention will be described with reference to the drawings. In addition, what attached | subjected the same code | symbol in drawing may abbreviate | omit description.

(First embodiment)
FIG. 1 is a schematic diagram showing a configuration of a wavelength conversion laser light source according to the first embodiment of the present invention. The wavelength conversion laser light source shown in FIG. 1 includes a pulse fiber laser light source 100, an optical polarization maintaining fiber 105, an SHG (Second Harmonic Generation) module 110, an LD power supply 401, and a pulse generator 402. The pulse fiber laser light source 100 includes a pump. LD (excitation laser light source) 101,

fiber gratings

102 and 104, first fiber 103, second fiber 106, NA (aperture ratio) converter 107, and fiber 108 are provided.

The first fiber 103 is made of, for example, a double clad polarization maintaining fiber doped with Yb as a rare earth in the core portion, and the fiber length is 10 m. The pump LD 101 excites the first fiber 103 and oscillates laser light in a laser resonator composed of the first fiber 103, the second fiber 106, and the pair of

fiber gratings

102 and 104. In this way, the first fiber 103 is a double-clad polarization maintaining fiber doped with Yb, and by manipulating the characteristics of the

fiber gratings

102 and 104, the pulse fiber laser light source 100 can emit light of 1050 to 1170 nm. This laser active substance was selected because it can oscillate arbitrarily and can be applied to processing applications, wavelength conversion applications, and the like.

Further, in this embodiment, three single emitter laser diodes having a maximum output of 8 W and an oscillation wavelength of 975 nm are used as the pump LD 101. The fiber grating 102 is formed in a double clad polarization maintaining fiber in which germanium is added to the core portion, has improved sensitivity to ultraviolet light, and has characteristics of a center wavelength of 1064 nm, a reflection spectrum half width of 1 nm, and a reflectance of 98%. have. The fiber grating 104 is formed in a common single-mode polarization maintaining fiber (core diameter 9 μm, clad outer shape 125 μm) in which germanium is similarly added to the core portion, the center wavelength is 1064 nm, the reflection spectrum half-value width is 0. It has the characteristics of 05 nm and reflectivity of 10 to 15%.

Here, when the laser light emitted from the laser resonator is used as the fundamental wave of the wavelength conversion laser light source, in consideration of the conversion efficiency to visible light in the SHG module 110 which is a wavelength conversion element, the half width of the reflection spectrum is The thickness is preferably 0.1 nm or less, and more preferably in the range of 0.01 to 0.06 nm. In the study by the present inventors, it has been confirmed that when the reflection band of the fiber grating 104 is 0.05 nm or less, pulse oscillation is more stably performed. It has also been confirmed that when the mode field diameter of the rare earth-doped double clad fiber with respect to the oscillated laser beam is 8 to 13 μm, pulse oscillation is more likely to occur. This is because, even when the density of the rare earth ions that are laser active materials is the same, the amount of addition can be increased by an amount corresponding to an increase in the mode field diameter.

Also, when used as a fundamental wave of a wavelength conversion laser light source, it is desirable that the pulse fiber laser light source 100 of the present embodiment is used with a single polarized light (linearly polarized light). The reason why the linearly polarized light is used is that the wavelength conversion crystal in the SHG module 110 converts only one polarization component.

Thereafter, the optical pulse LP is introduced into the SHG module 110 by the optical polarization maintaining fiber 105 that propagates the oscillated light of around 1064 nm, and the SHG module 110 generates 532 nm light by the second harmonic generation.

The feature of the pulsed fiber laser light source 100 proposed in the present embodiment is that the Yb-doped fiber (first and second fibers 103 and 106) in the laser resonator is the second fiber that is not excited by the pumping light. 106 is present, and the NA converter 107 is inserted between the laser resonator and the pumping LD 101 which is an excitation light source. By driving a current waveform for driving the pump LD 101 at a predetermined rising speed and pulse width with respect to the laser resonator configured as described above, the laser resonator can be oscillated in a pulsed manner, and has a high peak power. An optical pulse LP can be obtained.

That is, in the present embodiment, since the second fiber 106, which is a Yb-doped polarization maintaining fiber that is not excited, is inserted into the laser resonator, the laser resonator self-absorbs the light itself oscillated and oscillation is not caused. It becomes stable. As the oscillation becomes unstable, the output light is easily pulsed. Here, if the rise of the excitation light incident on the laser resonator whose oscillation is unstable is a steep rise, a giant pulse can be generated by the relaxation oscillation of the second fiber 106 which is a Yb-doped fiber. By utilizing this fact, high-peak pulsed light can be repeatedly emitted by periodically and repeatedly exciting the laser resonator of this embodiment with pumping light having a steep rise characteristic.

Specifically, 98% or more of the pumping light emitted from the pump LD 101 is absorbed by the first fiber 103 which is a Yb-doped double clad polarization maintaining fiber portion, and the second fiber which is a Yb-doped polarization maintaining fiber portion. It is desirable that the structure 106 can reach only 2% or less of the excitation light so as to be a region where the excitation light does not substantially reach. In the present embodiment, a Yb-doped fiber (excitation light absorption: 1.8 dB / m) having a core diameter of 9 μm and a Yb ion concentration of 9 × 10 ²⁵ ions / m ³ is used. At this time, the length of the first fiber 103 is 9.5 m, and the length of the second fiber 106 is 5 m. Since these lengths are values that vary depending on the core diameter of the fiber and the Yb ion concentration, they can be changed depending on the configuration. However, the length of the second fiber 106 is 98% of the excitation light of the first fiber 103. It is desirable that the length be about 0.5 times the fiber length that absorbs the above.

Next, the NA converter 107 will be described. In the laser resonator described above, light having a high peak power oscillates, so the oscillated light passes through the fiber grating 102 on the pump LD 101 side and returns to the pump LD 101, and this return light destroys the pump LD 101. However, by inserting the NA converter 107 between the pump LD 101 and the fiber grating 102, it is possible to prevent destruction due to return light.

The mechanism of the NA converter 107 will be described below. The NA of the fiber 108 that propagates light from the pump LD 101 is 0.22, and the NA of the excitation light in the first fiber 103 that is the incident side fiber used for the laser resonator is 0.46, and the NA of the oscillated light is 0.46. NA is 0.1, and these lights propagate in the first fiber 103.

Generally, light propagating in a fiber is optically coupled with high coupling efficiency when propagating from a fiber having a small NA to a fiber having a large NA. For fibers with a small NA, the coupling efficiency is small. Therefore, between the pump LD 101 and the laser resonator (fiber grating 102), NA 0.25 (more than NA of the fiber 108 of the pump LD 101) to NA 0.46 (excitation in the first fiber 103 constituting the laser resonator). By inserting a multimode fiber (NA or less for light) as the NA converter 107, it is possible to prevent the oscillated light from flowing back to the pump LD 101.

Specifically, the NA for the return light in the laser resonator is 0.1, whereas the NA of the NA converter 107 is as large as 0.25 to 0.46. The NA of light is about 0.3. Thereafter, since the NA converter 107 is connected to the pump LD 101, the coupling efficiency to the fiber 108 that is the output side fiber of the pump LD 101 can be reduced with respect to the return light. At this time, when a multimode fiber is used as the NA converter 107, it is desirable to use a step index type multimode fiber having an NA of 0.3 to 0.46 and a length of about 1 to 5 m. .

As the NA converter 107, a “multi-mode combiner” used when pumping light input from a plurality of NA0.22 fibers, for example, 2 to 7 fibers, is combined into one NA0.46 fiber is used. You can also. By using the multi-mode combiner, in addition to the effect of reducing the return light to the pump LD 101 due to the difference in the NA of the fiber, the effect of reducing the return light due to the branching of the fiber can be obtained. Here, the NA of the plurality of fibers serving as the input port of the multimode combiner is equal to or greater than the NA of the fiber 108 on the pump LD 101 side, and the NA of one fiber serving as the output port of the multimode combiner is the laser resonance. It is preferable that it is below NA with respect to the excitation light of the 1st fiber 103 of a container. At this time, the input side fiber connected to the central portion of the output side fiber among the plurality of input side fibers connecting the LD 101 for the pump of the multimode combiner is greatly influenced by the return light. At least one of them is preferably not optically connected to the pump LD 101.

With the laser resonator configuration as described above, it is possible to form a resonator that is easily pulsated, but by pulse-modulating the current applied to the pump LD 101, it is possible to repeatedly oscillate the pulse. Become.

Here, the LD power supply 401 is a power supply that can realize a rapid rise with a rise speed of 1 to 15 ns. The LD power supply 401 forms a pulsed current waveform using the signal from the pulse generator 402 as a trigger. If the rising speed of the current applied to the pump LD 101 is as fast as about 100 ns, the laser resonator can be pulse-oscillated. For the sake of simplicity, a value of 1 to 15 ns is a necessary value. Here, as the rising speed of the current, for example, the time until the current reaches 0% to 100% (target value) can be used.

FIG. 2 is a diagram showing transient response characteristics of the optical pulse LP emitted from the pulse fiber laser light source 100 when a rectangular pulse current is supplied to the pump LD 101 as the input current IC. The change of the light pulse LP is shown.

As shown in FIG. 2, when the LD power supply 401 drives the pump LD 101 with a rectangular input current IC and the excitation light is incident on the laser resonator, the first peak P1 (light pulse LP) is output as an optical output after time T1. appear. Furthermore, if the input current IC is continuously injected, the second peak P2 occurs after T2 time, and after the transient response peak occurs, the light output is the light output corresponding to the current value Is of the rectangular input current IC. It becomes a steady value Ps.

The pulse fiber laser light source 100 according to the present embodiment cuts off the input current IC so that the first peak P1 and the second peak P2 of the optical pulse LP are not formed, thereby providing the first peak P1 as the optical output. It is characterized by emitting an optical pulse LP having only a single peak. Specifically, the pulse fiber laser light source 100 starts from the rise of the input current IC, and after the first peak P1 is formed after the light pulse LP is emitted, the end point is reached before the second peak is formed. The excitation may be performed in the provided section, and then the input current IC may be cut off. Further, the pulse fiber laser light source 100 is excited in the section where the end point is provided from the start of the input current IC to the arrival of the first peak P1 after the light pulse LP is emitted. The IC may be shut off. Further, the pulse fiber laser light source 100 may be cut off at the same time as the light pulse IP is emitted. For example, the first peak P1 of the light pulse IP is formed starting from the rise of the input current IC. In the meantime, excitation may be performed in the section where the end point is provided, and then the input current IC may be cut off.

Since the peak output after the second peak is lower than that of the first peak, high wavelength conversion efficiency cannot be obtained when wavelength conversion is performed using a wavelength conversion element. For this reason, it is desirable that the input current amount after T2 time be 20% or less of the input current amount when the first peak P1 is generated. In this case, the generation of the second peak P2 is prevented and the peak output is high. Only the first peak P1 can be generated.

The LD power supply 401 repeats a plurality of optical pulses LP as output light by applying the input current IC again and further driving the pump LD 101 after the input current IC is cut off and a predetermined time elapses. It can also be operated as it is emitted. With such a configuration, it is possible to continuously generate an optical pulse LP having a high output peak value as a pulse train. Note that the timing at which the input current IC is cut off is determined in advance based on the examination results described later, and is stored in advance in a predetermined memory in the LD power source 401.

3 to 6 are diagrams showing changes in the light output when the pulse width of the input current is changed in order to change the charge amount of the input. In each figure, a 10 A rectangular pulse current is applied to the pump LD 101 as an input current. The fiber length of the pulse fiber laser light source 100 is, for example, 10 m, and the core diameter of the fiber is 9 μm.

FIG. 3 shows the waveforms of the input current and the optical output when the pulse fiber laser light source 100 is operated by driving the pump LD 101 using a pulse having a charge amount of 55 μC (pulse width 5.5 μs) as the input current. FIG. In this case, since sufficient excitation light is not input, the pulse fiber laser light source 100 does not oscillate, and spontaneous emission light is slightly generated.

FIG. 4 shows the waveforms of the input current and the optical output when the pulse fiber laser light source 100 is operated by driving the pump LD 101 using a pulse having a charge amount of 65 μC (pulse width 6.5 μs) as the input current. FIG. In this case, the pulse fiber laser light source 100 reaches laser oscillation, and a single optical pulse having the first peak P1 is generated. The peak of the optical pulse P1 is the input current start time (input current rise time). 7 μs after.

FIG. 5 shows the waveforms of the input current and the optical output when the pulse fiber laser light source 100 is operated by driving the pump LD 101 using a pulse having a charge amount of 75 μC (pulse width 7.5 μs) as the input current. FIG. In this case, a single optical pulse having a larger first peak P1 is generated as compared with the example of FIG.

FIG. 6 shows the waveforms of the input current and the optical output when the pulse fiber laser light source 100 is operated by driving the pump LD 101 using a pulse having an electric charge of 85 μC (pulse width 8.5 μs) as the input current. FIG. In this case, an optical pulse with the second peak P2 in addition to the first peak P1 is generated, and the optical pulse has a waveform including a 2nd pulse.

In the above-described case shown in FIGS. 3 to 6, a single light pulse having a high peak value can be obtained under the input current conditions shown in FIG. Further, when the input current is a rectangular pulse train, an optical pulse train can be obtained for the optical pulse.

As described above, depending on the fiber length, the output of the excitation laser light source, and the like, if a charge amount 1.1 times or more of the charge amount input until the first peak P1 is generated is input, Peak P2 will occur. For this reason, it is desirable to block the input current so that the charge amount of the input current after the first peak P1 is generated is 20% or less of the charge amount until the first peak P1 is generated.

Similarly, when the time constant of the LD power source 401 as the input current source is large and the waveform of the input current has a tail, the charge amount of the input current after the first peak P1 is generated is the same as that before the first peak P1 is generated. It is desirable to reduce the input current so that the charge amount is 20% or less. Also, since the peak output of the first peak P1 is proportional to the amount of input current when the first peak P1 occurs, it is most desirable to use an input current source having a small time constant and excellent time response. It is desirable to cut off the input current between the occurrence of the peak P1 and before the occurrence of the second peak P2.

FIG. 7 is a diagram showing an example of a single optical pulse generated by setting the pulse width and current value of a rectangular input current to predetermined values. From the above examination results, the input current IC after the first peak P1 is generated so that the charge amount is 20% or less of the charge amount until the first peak P1 of the light pulse LP is generated as shown in FIG. When the pulse width and current value of the current IC are set and the input current is cut off after the first peak P1 occurs and before the second peak occurs, the output peak value PL of the first peak P1 may be increased. it can.

FIG. 8 and FIG. 9 are diagrams showing that the optical output is obtained by driving the pulse fiber laser light source 100 by applying an input voltage composed of a plurality of pulse voltages with a predetermined cycle to the pump LD 101. 8 is a diagram illustrating a case where the input voltage is biased with a positive DC voltage, and FIG. 9 is a diagram illustrating a case where the input voltage is biased with a negative DC voltage.

In the example shown in FIG. 8, the pump LD 101 is driven by an input voltage in which a positive DC voltage is superimposed on a pulse train having a period of 3 μs and a pulse width of 300 ns. With this input voltage, the optical output is an optical pulse having a half width of 50 ns as a pulse train. FIG. 9 shows that an optical pulse is output as a pulse train by applying an input voltage in which a negative DC voltage is superimposed on a pulse voltage having the same period of 3 μs and a pulse width of 300 ns as in FIG. In these examples, instead of shortening the pulse width, the drive waveform is controlled so that the integrated charge amount in the section where the current is input is the same by increasing the peak value of the input current (charge). ing.

Here, in the example shown in FIG. 9, a constant negative DC voltage is applied, but the input current is cut off after the input current is applied to the pump LD 101, and at the same time, the pump LD 101 has a voltage of 0.1 V or more and 0 A reverse voltage of 5 V or less (negative DC voltage) may be applied. By doing so, the half-value width of the optical output can be reduced to 40 ns or less, and the pulse can be narrowed. Further, since a high peak output is obtained as much as the pulse is narrowed, it is possible to increase the conversion efficiency when the wavelength of the laser beam generated by the pulse fiber laser light source 100 is converted as a fundamental wave.

In addition, although the period is 3 μs here, the period may be 5 μs or more. Thereby, further narrowing of the pulse and higher peaking are possible. Similarly, the period may be 11 μs or more. Thus, in addition to narrowing the pulse and increasing the peak, the stability of the pulse output is improved, so that it can be used for an image display device that requires high output stability.

With the above-described configuration, the excitation light for exciting the pulse fiber laser light source 100 can be stopped instantaneously. Therefore, in the present embodiment, it is possible to reliably generate a pulse train whose basic unit is an optical pulse having a single high output peak value not accompanied by a 2nd pulse. Furthermore, by appropriately setting the magnitude, waveform, period, etc. of the input current, it is also possible to generate optical pulses with a narrow pulse width as a pulse train, thereby realizing a wavelength conversion laser light source with higher wavelength conversion efficiency. Can do.

FIG. 10 shows the waveform of the light output generated from the pulse fiber laser light source 100 with respect to the waveform of the current applied to the pump LD 101. In the example shown in FIG. 10, the current waveform is modulated so that the rising speed is 5 ns, the pulse width is 300 ns, and the pulse interval is 5 μs. The result of driving the pump LD 101 with this current waveform is the actual pulse waveform shown in FIG. From FIG. 11, it can be seen that a stable repetitive pulse waveform is obtained as an optical output waveform by the LD current waveform.

With the above configuration, 1064 nm light with a peak power of about 500 W could be obtained in this embodiment. This 1064 nm light is converted into green light having a peak power of about 200 W by wavelength conversion using a nonlinear optical crystal like the SHG module 110. This pulse green laser beam has a peak power capable of performing laser marking or the like.

In the above description, 98% or more of the excitation light is absorbed by the first fiber 103 in order to make the second fiber 106 a region where the excitation light does not substantially reach. However, the present invention is particularly limited to this example. However, various modifications are possible. FIG. 12 is a schematic diagram showing a main configuration of another pulse fiber laser light source used in the wavelength conversion laser light source according to the present embodiment.

The difference between the pulse fiber laser light source 100a shown in FIG. 12 and the pulse fiber laser light source 100 shown in FIG. 1 is that the first fiber 103 and the second fiber 106 are made of a Yb-doped double clad polarization maintaining fiber. 103a and the second fiber 106a, and an excitation light absorption mechanism 302 that absorbs excitation light is provided between the first fiber 103a and the second fiber 106a. The other points are shown in FIG. This is the same as the pulse fiber laser light source 100 shown.

As shown in FIG. 12, an excitation light absorption mechanism 302 is inserted between the first fiber 103a and the second fiber 106a made of a Yb-doped double clad polarization maintaining fiber. In this case, after the excitation light propagates through the first fiber 103a, the excitation light is forcibly absorbed by the excitation light absorption mechanism 302. Therefore, the second fiber 106a can be made a region where the excitation light does not reach completely. . In this way, the same effect as described above can be obtained even when the excitation light is forcibly removed.

The configuration of the SHG module 110 will be described in detail in an embodiment described later. For wavelength conversion using a nonlinear optical crystal, the polarization state of light generated from the pulse fiber laser light source 100 is linearly polarized light. Need to be. As a method of making this linearly polarized light, a method using the difference in bending loss between the fast axis and the slow axis of the PANDA fiber, or by rotating the axial relationship between the fast axis and the slow axis of the fiber grating 102 and the fiber grating 104 by 90 °. A method of fusing fibers or using the birefringence of a fiber can be used.

Although not shown, a configuration using a reflecting member such as a mirror instead of the

fiber gratings

102 and 104 may be used. Further, since the fiber exit end face reflects Fresnel by about 3% unless an antireflection film or the like is particularly formed, it can be used instead of the fiber grating. By using a fiber grating, a highly efficient pulse fiber laser light source can be realized, but by using a mirror or Fresnel reflection at the emission end, a cheaper pulse fiber laser light source can be realized. .

(Second Embodiment)
FIG. 13 is a schematic diagram showing a configuration of a wavelength conversion laser light source according to the second embodiment of the present invention. The wavelength conversion laser light source 1000 of the present embodiment detects that an optical pulse has been generated from the pulse fiber laser light source 100b, and stops supplying current.

As shown in FIG. 13, the pulse fiber laser light source 100b includes a pump LD 101 that is an excitation laser light source that emits excitation light (not shown) and a laser active material, as in the first embodiment. A first fiber 103 that includes excitation light, a second fiber 106 that is not excited by the excitation light, and a pair of fibers that are optically connected with the first and

second fibers

103 and 106 interposed therebetween. And a half mirror 1002, a detection unit 1003, a control unit 1004, and a power source 1005.

The detection unit 1003 is disposed in the vicinity of the output end of the output side fiber grating 104 of the pair of

fiber gratings

102 and 104. A part of the optical pulse LP that is output light is branched by the half mirror 1002 and taken into the detection unit 1003. The pump LD and the power source 1005 are connected by a predetermined wiring, and the detection unit 1003 and the power source 1005 are connected to the control unit 1004 by a predetermined wiring and controlled.

In the pulse fiber laser light source 100b, the light pulse LP is emitted, and at the same time, the output light LP is emitted by cutting off the input current IC that drives the pump LD 101. The detection unit 1003 detects the optical output of the light pulse LP and outputs a detection signal DS to the control unit 1004. The control unit 1004 controls the power supply 1005 so as to cut off the input current IC. That is, when the detection signal DS is received by the control unit 1004, the control unit 1004 cuts off the input current IC supplied from the power source 1005 to the pump LD 101, as will be described later, in accordance with the content of the detection signal DS. It will be.

With such a configuration, the pulse fiber laser light source 100b with high photoelectric conversion efficiency capable of generating the optical pulse LP having a high output peak value as a pulse train can be realized with a simple configuration.

The wavelength conversion laser light source 1000 further includes an SHG module 110 including a wavelength conversion element that converts the fundamental wave into a harmonic wave using the output light LP from the pulse fiber laser light source 100b as a fundamental wave. Outputs harmonic light SP. By adopting such a configuration, it is possible to generate a pulse train having harmonic light pulses with higher conversion efficiency as a basic unit.

FIG. 14 is a flowchart for explaining the operation of the pulse fiber laser light source 100b when the optical pulse LP that is output light is emitted from the pulse fiber laser light source 100b shown in FIG. A specific operation of the pulse fiber laser light source 100b will be described with reference to FIGS.

First, the pump LD 101 is driven by a power source 1005, an input current IC is injected into the pump LD 101, and laser light (not shown) emitted from the pump LD 101 excites the pulse fiber laser light source 100b as excitation light. (Step S1). Here, for example, three single-emitter laser diodes having an oscillation wavelength of 975 nm are used as the pump LD 101 which is an excitation laser light source, and the maximum output of the pump LD 101 is 8 W.

Next, the excitation light excites the laser active substance of the pulse fiber laser light source 100b (step S2). Here, the first fiber 103 and the second fiber 106 are fibers having a fiber length of 10 m in which the core portion is doped with, for example, Yb (ytterbium) as a rare earth element to form a laser active material. A pair of

fiber gratings

102 and 104 corresponding to the mirrors of the laser resonator are provided with the second fiber 106 interposed therebetween.

In addition, for example, germanium is added to the core portion of the fiber grating 102 on the incident side of the pair of

fiber gratings

102 and 104 to improve sensitivity to ultraviolet light so that the grating can be easily formed. Yes. Further, the fiber grating 102 is formed as a laser resonator mirror so as to have, for example, a center wavelength of 1064 nm, a reflection spectrum half width of 1 nm, and a reflectance of 98%.

On the other hand, for example, germanium is similarly added to the core portion of the fiber grating 104 on the emission side, and the fiber grating 104 serves as a mirror of the laser resonator, with a center wavelength of 1064 nm, a reflection spectrum half width of 0.05 nm, and a reflectance. It is formed to have a characteristic of 10% or 15%.

When generating a fundamental wave from such a pair of

fiber gratings

102 and 104 to the SHG module 110, the reflection of the

fiber gratings

102 and 104 is considered in consideration of the wavelength conversion efficiency to the harmonics in the SHG module 110. The spectral width is desirably 0.01 nm or more and 0.06 nm or less. It has been confirmed that the pulse fiber laser light source 100b stably oscillates within this range.

Next, the optical pulse LP is emitted from the pulse fiber laser light source 100b configured as described above (step S3). At this time, the laser active substance of the pulse fiber laser light source 100b is excited by the excitation light to an energy level corresponding to the wavelength for oscillating the fundamental wave, and an inversion distribution is generated. Then, stimulated emission occurs, and the fundamental wave reciprocates while being amplified in the first fiber 103 and the second fiber 106 using the pair of

fiber gratings

102 and 104 as mirrors of the laser resonator, and the output side fiber grating. The light pulse LP is emitted from 104.

Next, the detection unit 1003 detects a part of the light pulse LP, and the control unit 1004 controls the power supply 1005 to cut off the input current IC supplied to the pump LD 101 (step S4). That is, a part of the optical pulse LP that is output light emitted from the pulse fiber laser light source 100 b is branched by the half mirror 1002 and detected by the detection unit 1003. The detection signal DS of the detection unit 1003 is transmitted to the control unit 1004 via a predetermined wiring, whereby the control unit 1004 cuts off the power source 1005 that drives the pump LD 101 and cuts off the input current IC. If it does so, since the excitation light which injects into the 1st fiber 103 from the LD 101 for pumps will be interrupted | blocked, the output light from the pulse fiber laser light source 100b will be interrupted | blocked.

Finally, by repeating the above steps S1 to S4, the light pulse LP is emitted as an optical pulse train instead of a single light pulse (step S5). In this way, a continuous optical pulse train having a predetermined cycle can be emitted.

By the way, most of the optical pulse LP of the output light passes through the half mirror 1002 and enters the SHG module 110 as a fundamental wave. Here, the SHG module 110 includes, for example, MgO: LiNbO ₃ (lithium niobate added with magnesium oxide), KTP (potassium titanyl phosphate), or MgO: LiTaO ₃ (magnesium) having a periodically poled structure. For example, added lithium tantalate).

Using such an SHG module 110, the optical pulse LP as a fundamental wave is wavelength-converted to an optical pulse SP as harmonic light. In this case, since the SHG module 110 performs wavelength conversion by the second-order nonlinear optical effect, the conversion efficiency improves as the spectrum width of the oscillation wavelength of the fundamental light pulse LP is narrower and the peak power is larger. As a result, the wavelength conversion laser light source 1000 operates with low power consumption. In this embodiment, an optical pulse LP having a peak power of 200 W and an oscillation wavelength of 1064 nm is used as a fundamental wave, and a green optical pulse SP having a peak power of 120 W and an oscillation wavelength of 532 nm is obtained as a harmonic. It has been.

Further, the transient response characteristic of the optical output of the output light LP from the pulse fiber laser light source 100b when a rectangular pulse current is supplied as an input current to the pump LD 101 is a diagram used in the description of the first embodiment. 2 can be used in the same way as in the first embodiment, and the changes in the input current and the optical output with respect to the time axis at this time are the same as in FIG.

That is, as described in the first embodiment, when the pump LD 101 is driven by the rectangular input current IC and the excitation light is incident, the first peak P1 of the light pulse LP is obtained as an optical output after T1 time. appear. Furthermore, if the input current IC is continuously injected, the second peak P2 occurs after T2 time. Hereinafter, after the peak of the transient response occurs, the light output indicates the steady value Ps of the light output corresponding to the current value Is of the rectangular input current IC.

Since the pulse fiber laser light source 100b of the present embodiment detects that the first peak P1 of the optical pulse LP of FIG. 2 has occurred by the detection unit 1003 and cuts off the input current IC, the first peak is used as the optical output. An optical pulse LP having a single peak of only P1 can be emitted.

Specifically, the detection unit 1003 detects the output peak value PL of the first peak P1 of the light pulse LP (see FIG. 7), and then the output value of the light pulse LP is 95% to 5% of the output peak value PL. It is preferable that the control unit 1004 cuts off the input current IC from the power supply 1005 at this time. With such a configuration, an optical pulse having a single high output peak value not accompanied by a 2nd pulse can be generated as the optical pulse LP, and a pulse train can also be generated.

In addition, by detecting that the output value of the optical pulse LP has fallen to a value in the range of 95% to 5% of the output peak value PL, the timing and setting for cutting off the input current IC can be facilitated, and wavelength conversion can be performed. The operation of the laser light source 1000 can be simplified. Also, with such a configuration, the excitation light for exciting the pulse fiber laser light source 100b can be stopped instantaneously, so that the optical pulse LP is reliably supplied with a single high output peak value not accompanied by a 2nd pulse. Can be generated as a pulse train whose basic unit is an optical pulse having

It should be noted that the configuration of the wavelength conversion laser light source that detects the occurrence of an optical pulse and stops the supply of current is not particularly limited to the above example, and various modifications are possible. FIG. 15 is a schematic diagram showing the configuration of another wavelength conversion laser light source according to the second embodiment of the present invention.

A wavelength conversion laser light source 1200 shown in FIG. 15 is different from the wavelength conversion laser light source 1000 shown in FIG. 13 in that a branch fiber 1202 is optically connected in the middle of the first fiber 103, and in addition to the detection unit 1003, a detection unit 1201. Is arranged in the vicinity of the branch fiber 1202. At this time, the detection unit 1201 extracts and detects a part of the fundamental wave of the pulse fiber laser light source 100c from a part of the branch fiber 1202, and the control unit 1004 receives the detection signal DD from the detection unit 1201, An input current IC output from 1005 to the pump LD 101 is controlled. In this case, the detection unit 1003 may be omitted.

With such a configuration, it is possible to accurately grasp the generation of the optical pulse LP including the peak value, so that the optical pulse LP having a single high output peak value can be used as a pulse train with a simpler device configuration. Can be generated. The detection unit 1201 may be arranged by being incorporated in a part of the branch fiber 1202.

Further, the wavelength conversion laser light source 1200 shown in FIG. 15 is different from the wavelength conversion laser light source 1000 shown in FIG. 13, and the pump LD 101 that is a laser light source is composed of a plurality of laser

light sources

101 a, 101 b, 101 c, and a plurality of lasers. One end of each of the

light sources

101a, 101b, and 101c is connected to one end of a coupling fiber 101d, and the other end of each coupling fiber 101d is connected to the input end of the fiber grating 102 on the input side of a set of fiber gratings by a combiner 1203. Is bound to. With such a configuration, the optical output of the pumping light can be increased to a predetermined magnitude, so that the optical pulse LP can be generated as a pulse train having a higher output optical pulse as a basic unit.

Further, the wavelength conversion laser light source 1200 shown in FIG. 15 is different from the wavelength conversion laser light source 1000 shown in FIG. 13 in that a polarization plane selection unit 1204 that selects the polarization plane of the laser light is arranged on the output end side of the second fiber 106. ing. With such a configuration, the light pulse LP can be generated as a pulse train having a light pulse with a uniform polarization plane as a basic unit. Then, when performing wavelength conversion in the SHG module 110, not only can the conversion efficiency be improved, but also the harmonic light SP with a uniform polarization plane can be output, which is optimal as a light source for a liquid crystal display device or the like.

By the way, obtaining the light pulse LP and the harmonic light SP having larger peak values from the wavelength conversion

laser light sources

1000 and 1200 can be realized by devising the waveform of the input current IC. FIG. 16 shows the waveform of the pulse current of the input current IC on the upper stage, and the pump LD 101 is driven by the pulse current having the shape of the input current IC and is pumped by the pumping light generated from the pump LD 101. The waveform of the light pulse LP, which is the light output from the light source 100b (or 100c), is shown in the lower part.

As shown in the upper part of FIG. 16, the input current IC is a pulse current composed of a trapezoidal wave that monotonously increases from the current value I1 to the current value (I2 + I3) over time. This pulse current is biased by a current value I3 as a direct current. In this way, by maximizing the current value immediately before cutting off the pulse current, as shown in the lower part of FIG. 16, the optical pulse having a single high output peak value P1 not accompanied by the 2nd pulse as the optical output. LP can be output. Further, by repeatedly inputting the current waveform shown in the upper part of FIG. 16 to the LD 101 for the pump, a pulse train having the optical pulse shown in the lower part of FIG. 16 as a basic unit can be generated. Note that the pulse current may be a triangular wave (state of I1 = I3) in which the current value increases monotonously.

(Third embodiment)
FIG. 17 is a schematic diagram showing a configuration of a wavelength conversion laser light source according to the third embodiment of the present invention. In this embodiment, the optical power LP1 from the pulse fiber laser light source 100 proposed in the first embodiment is used as seed light, and the seed light is further amplified by the fiber amplifier 1400, whereby the peak power can be further amplified. (Master Oscillator-Power Amplifier). The pulse fiber laser light source used in the present embodiment is not particularly limited to the above example, and other pulse fiber laser light sources may be used. This is the same for the other embodiments.

In this embodiment, since the output light LP2 generated from the pulse fiber laser light source 100 is used for wavelength conversion by the SHG module 110 made of a nonlinear optical crystal, it needs to be linearly polarized light. Therefore, the third fiber 1401 used in the fiber amplifier 1400 also needs to be a double clad polarization maintaining fiber in which the core portion is doped with Yb as a rare earth.

The pulse fiber laser light source 100 and the third fiber 1401 of the fiber amplifier 1400 are connected by a combiner 1402 provided with a port for introducing signal light. A plurality of pump LDs 1403 for exciting the fiber amplifier 1400 are also connected to the combiner 1402.

On the other hand, when the fiber amplifier 1400 is used, if the pump LD 1403 is continuously excited, light having a broad wavelength spectrum called ASE (Amplitude Spontaneous Emission) is generated, which causes an unexpected giant pulse. Therefore, the pulse generator 1405 and the LD power source 1404 can modulate the pump LD 1403 of the fiber amplifier 1400 using the signal TG of the pulse generator 402 that drives the pulse fiber laser light source 100 that generates seed light as a trigger. This is a feature of the embodiment.

18 shows the output light waveform of the fiber amplifier 1400 of the wavelength conversion laser light source shown in FIG. 17, the seed light output waveform of the pulse fiber laser light source 100, the current waveform of the pump LD 1403 of the fiber amplifier 1400, and the pulse fiber laser light source 100. The current waveform of the pump LD 101 for seed light is shown.

As shown in FIG. 18, the pulsed fiber laser light source 100 that generates seed light modulates the current waveform so that the rising speed is 5 ns, the pulse width is 300 ns, and the pulse interval is 10 μs, as in the first embodiment. is doing. On the other hand, as a current waveform for driving the pump LD 1403 of the fiber amplifier 1400, a current waveform having a pulse interval of 10 μs and a duty ratio of 50% is used by detecting the falling of the current of the pump LD 101. Specifically, the current waveform for driving the pump LD 1403 of the fiber amplifier 1400 is a waveform in which the LD current for exciting the fiber amplifier 1400 is applied to the pump LD 1403 after 5 μs from the falling of the current of the pump LD 101. ing.

In the example shown in FIG. 18, the falling timing D2 of the current waveform of the pump LD 101 that drives the pulse fiber laser light source 100 that outputs the seed light and the falling waveform of the current waveform of the pump LD 1403 that drives the fiber amplifier 1400 are shown. Although the timing D1 is matched, the falling timing D1 of the current waveform of the pump LD 1403 that drives the fiber amplifier 1400 is set to the rising timing D1 of the current waveform of the pump LD 101 that drives the pulse fiber laser light source 100 that outputs seed light. By setting the phase 1 to 5 ns earlier than the falling timing D2 (shifting the phase), the trailing edge DS of the output optical waveform from the fiber amplifier 1400 can be reduced. Thus, reducing the skirt DS at the time of falling has an important meaning in increasing the processing speed and processing accuracy, for example, when performing laser processing using a scanning mirror.

With this configuration, in this embodiment, a peak power 5 to 10 times that of the pulse fiber laser light source shown in the first embodiment can be obtained, and a 1064 nm light having a peak power of about 5 kW can be obtained. did it. This 1064 nm light is converted into green light having a peak power of about 2 to 3 kW by wavelength conversion using a nonlinear optical crystal in the SHG module 110. This pulse green laser beam has a peak power capable of performing metal laser trimming and the like.

In addition, the combination of the pulse fiber laser light source 100 and the fiber amplifier 1400 described in the present embodiment can reduce the heat generated from the

pump LDs

101 and 1403, and thus the heat dissipation structure can be simplified. There is also. In other words, in the case of the present embodiment, the

pump LDs

101 and 1403 are not always lit, so they are fixed to an aluminum heat sink and can be operated simply by forcing the outside air with a cooling fan. . As a result, a water cooling mechanism such as the conventional YAG laser and YVO ₄ laser becomes unnecessary, and the power consumption can be reduced. With the configuration of the present embodiment, it was possible to operate stably in the range of 0 to 60 ° C.

(Fourth embodiment)
FIG. 19 is a schematic diagram showing a configuration of a wavelength conversion laser light source according to the fourth embodiment of the present invention. In the present embodiment, a problem when infrared light generated from the pulse fiber laser light source 100 having the configuration shown in the first embodiment is wavelength-converted by a QPM-LN element and a solution to the problem will be described. Since the QPM-LN element has a large nonlinear optical constant, the conversion efficiency from the fundamental wave to the harmonic can be increased. However, the infrared light that becomes the fundamental wave due to the large nonlinear optical constant, It occurs even when ultraviolet light (third harmonic), which is the sum frequency of the converted green light (second harmonic), deviates from the phase matching condition. This ultraviolet light has the problem of causing green light absorption, causing green high power saturation and crystal breakage. In the present embodiment, this problem is solved as follows.

As shown in FIG. 19, in the wavelength conversion unit 1600, the fundamental wave BL emitted from the pulse fiber laser light source 100 is condensed on the wavelength conversion element 1601 by the condenser lens 1604, and the light emitted from the wavelength conversion element 1601 is The collimated lens 1605 converts the light into parallel light, and the dichroic mirror 1606 separates the remaining fundamental wave into the converted second harmonic SL. As the wavelength conversion element 1601, an Mg: LiNbO ₃ element having a polarization inversion structure with an element length of 25 mm is used. The temperature of the wavelength conversion element 1601 is managed by the Peltier element 1602, and the phase matching temperature is maintained.

FIG. 20 is a schematic diagram showing the condensing position of the fundamental wave in the conventional wavelength conversion element. The fundamental wave BL from the pulse fiber laser light source that generates the fundamental wave is collected in the wavelength conversion element 601 by the condenser lens 604. Shine. At this time, the focal point F2 of the beam is generally at the center of the wavelength conversion element 601. On the other hand, in the present embodiment, as shown in FIG. 19, a method of preventing crystal breakage by arranging the position of the focal point F1 in the vicinity of the end face of the wavelength conversion element 1601 is proposed.

FIG. 21 shows the relationship between the position (mm) from the center position of the wavelength conversion element 1601 and the fundamental wave power density (W / μm ² ) with the condensing position of the fundamental wave BL as parameter L1 (mm). . The parameter L1 indicates the distance from the left end face (incident side end face of the fundamental wave BL) of the wavelength conversion element 1601 to the focal position F1. From FIG. 21, it can be seen that the power density of the fundamental wave is the highest at the assumed condensing position.

From this result, the focusing position of the fundamental wave BL is further set as the parameter L1 (mm), and as a measure of the power density of the third harmonic wave, which is ultraviolet light, with respect to the position (mm) from the center position of the wavelength conversion element 1601. FIG. 22 is a diagram in which (second harmonic power density × fundamental wave power density) (arbitrary unit) is plotted. From FIG. 22, it can be seen that the intensity of the ultraviolet light increases rapidly when the condensing position L1 is 10 mm or more. From this result, it can be seen that the condensing position of the fundamental wave is preferably 10 mm or less from the end face of the wavelength conversion element 1601. Similarly, it can be seen that the length of the wavelength conversion element 1601 is preferably 0 to 10 mm. In this sense, it is preferable that the wavelength conversion element 1601 has an element length of 10 mm or less. However, the element length may be set to about 20 to 30 mm in consideration of a reduction in wavelength conversion efficiency.

FIG. 23 is a fundamental wave in the case where light is condensed at the center of the wavelength conversion element (L1 = 12.5 mm) and in the case where light is condensed at L1 = 0 mm as in the present embodiment. It is the figure which plotted the input-output characteristic of the green output (W) which is a 2nd harmonic with respect to a certain infrared input (W). From FIG. 23, in the conventional example, output saturation occurs when the second harmonic output becomes 3 W, but in this embodiment (L1 = 0 mm), the conversion efficiency is about 60%. Even when the second harmonic output is output up to 4 W, output saturation is not observed, and good results are obtained.

As described above, a wavelength conversion element made of a nonlinear optical crystal having a large nonlinear optical constant represented by an Mg: LiNbO ₃ element having a domain-inverted structure, for example, an effective nonlinear optical constant diff = 10 pm / V or more is used. When used, in the pulsed fiber laser light source 100 having a peak power of the fundamental wave light as large as kW or more as proposed in the present embodiment, the fundamental wave is condensed in order to prevent saturation of high green output and crystal breakdown. It is particularly effective that the position is a position of 0 to 10 mm from the incident side end face of the wavelength conversion element, and the length of the wavelength conversion element is 0 to 10 mm.

(Fifth embodiment)
FIG. 24 is a schematic diagram showing a configuration of a wavelength conversion laser light source 1900 according to the fifth embodiment of the present invention. FIG. 25 is a principal ray of a fundamental laser beam in the wavelength conversion laser light source 1900 shown in FIG. FIG. 10 is a schematic diagram illustrating only the ML and explaining how the fundamental laser beam passes while changing the incident angle to the wavelength conversion element 1905; In this embodiment, the pulsed fiber laser light source 100 proposed in the first embodiment is used as the fundamental wave laser light source 1901 shown in FIG. 24. However, the present invention is not particularly limited to the above example. A pulse fiber laser light source may be used.

The condensing point of the fundamental laser light (pulse light) emitted from the fundamental laser light source 1901 is controlled by the condensing optical system 1902, and between the reflecting mirrors composed of the first concave mirror 1903 and the second concave mirror 1904. Incident. The fundamental laser beam is incident on the wavelength conversion element 1905, and a part thereof is converted into the second harmonic (first pass).

Here, the first concave mirror 1903 has a coating that reflects the fundamental laser beam and transmits the second harmonic laser beam (wavelength conversion laser beam). The fundamental laser light and the second harmonic laser light pass through the wavelength conversion element 1905 and then reach the first concave mirror 1903, and the fundamental laser light is reflected and reenters the wavelength conversion element 1905, and the second Harmonic laser light (wavelength conversion laser light) is output to the outside. The fundamental laser beam reflected by the first concave mirror 1903 reenters the wavelength conversion element 1905, is partially converted into the second harmonic, and reaches the second concave mirror 1904 (second pass).

Next, at the second concave mirror 1904, the fundamental laser beam is reflected, reenters the wavelength conversion element 1905, is partially converted into the second harmonic, and reaches the first concave mirror 1903 (third pass). At this time, the second harmonic laser beam is output from the first concave mirror 1903, and the fundamental laser beam is reflected and reenters the wavelength conversion element 1905 (fourth pass). By repeating the above reflection and conversion, while the fundamental laser beam reciprocates between the two reflecting mirrors, the wavelength conversion element 1905 is repeatedly passed to generate the wavelength conversion laser beam.

In the present embodiment, the fundamental laser beam reciprocates several times to several tens of times depending on the curvature and arrangement conditions of the reflecting mirrors (first concave mirror 1903 and second concave mirror 1904) and the setting of the focusing optical system 1902. Thereafter, the reciprocation between the reflecting mirrors is stopped. The wavelength-converted laser light generated until the reciprocation is stopped is output from the first concave mirror 1903.

Here, the conversion efficiency η from the fundamental wave to the second harmonic in the wavelength conversion element 1905 is L, the interaction length of the wavelength conversion element 1905 is L, the power of the fundamental wave is P, and the beam cross-sectional area of the wavelength conversion element 1905 is A. When the deviation from the phase matching condition is Δk, it is expressed by the following equation.

η∝L ² P / A × sinc ² (ΔkL)

As can be seen from the above equation, the conversion efficiency is high in the region where the beam cross-sectional area is small, and the conversion efficiency at the beam waist position BW is remarkably high in the pass region of the wavelength conversion element 1905. In the present embodiment, the condensing optical system is such that the beam waist positions BW are scattered while the fundamental laser beam is reflected between the reflecting mirrors (the first concave mirror 1903 and the second concave mirror 1904). Reference numeral 1902 controls the beam waist position BW.

Here, when the beam waist position between the reflecting mirrors is concentrated, there arises a problem that the wavelength conversion element 1905 is broken due to light damage or the wavelength conversion becomes unstable at the concentrated position. In particular, when the focal lengths of the first concave mirror 1904 (first reflecting mirror) and the second concave mirror 1903 (second reflecting mirror) are represented by f1 and f2, the distance between the reflecting mirrors is (f1 + f2). In the arrangement (when the refractive index of the wavelength conversion element is not considered), the beam waist position is concentrated at the confocal point of the reflecting mirror, and optical damage and instability of wavelength conversion become a problem.

In this embodiment, the beam waist position BW is controlled by the condensing optical system 1902 so that a stable wavelength conversion laser can be output even when a confocal arrangement is used. That is, in the present embodiment, a beam waist is formed by the condensing optical system 1902 before the incidence of the first reflecting mirror (first concave mirror 1903) as shown in the figure, and the first and second reflecting mirrors (first A stable wavelength conversion laser beam can be obtained by performing wavelength conversion at different beam waist positions BW in the wavelength conversion element 1905 without forming a beam waist in several paths at the focal points of the concave mirror 1903 and the second concave mirror 1904). I am doing so. In this manner, the beam waist positions BW are scattered by the condensing optical system 1902 so that the wavelength conversion of the beam paths having different phase matching conditions at each beam waist position BW can be performed stably, and the wavelength conversion laser beam Can be taken out stably.

Specifically, in the present embodiment, a first concave mirror 1903 having a focal length f1: 25 mm and a second concave mirror 1904 having a focal length f2: 20 mm are used. Further, the incidence between the reflecting mirrors is performed by cutting the second concave mirror 1904 so as to be smaller than the first concave mirror 1903, and from this cut portion. The principal ray axis MA connecting between the centers of the reflecting mirrors indicates an optical axis connecting the centers of curvature between the reflecting mirrors as shown in FIG. The fundamental laser beam is incident on the wavelength conversion element 1905 and the first concave mirror 1903 so as to be parallel to the principal ray axis MA by the condensing optical system 1902. As the wavelength conversion element 1905, MgO: LiNbO ₃ (length: 26 mm, width: 10 mm) having a polarization inversion structure was used. The distance between the reflectors is 58.4 mm, and is slightly shifted from the confocal arrangement. The fundamental laser light repeatedly passes through the wavelength conversion element 1905 while changing the angle of incidence on the wavelength conversion element 1905 between the reflecting mirrors.

Here, the phase matching condition is a condition in which the phase of the wavelength converted light generated in the nonlinear optical material matches and the wavelength conversion efficiency is maximum (Δk = 0). The phase matching condition is determined by the wavelength of the laser beam, the refractive index of the nonlinear optical material, the incident angle of the laser beam, the period of the polarization inversion structure, and the like. Conventionally, when converting a certain wavelength, in order to match the phase matching conditions, the refractive index of the nonlinear optical material and the incident angle are adjusted according to the temperature. Therefore, Δk> 0 and a decrease in wavelength conversion efficiency is observed. In addition, if the wavelength of the laser beam is shifted, the phase matching conditions are different, so that readjustment and review of the configuration are necessary.

In this embodiment, since the incident angle to the wavelength conversion element 1905 is changed by the pass path, the wavelength of the laser light, the refractive index (temperature) of the nonlinear optical material, and the polarization inversion satisfying the phase matching condition by the pass path. Period etc. will change. For this reason, the wavelength conversion laser light source 1900 of the present embodiment has a plurality of phase matching conditions. As a result, when performing wavelength conversion of a fixed laser beam wavelength, there are multiple temperatures that satisfy the phase matching condition, and even if the temperature deviates from one phase matching condition, it matches the phase matching condition of the other pass path. This can compensate for the decrease in conversion efficiency.

Further, in this embodiment, the temperature satisfying the phase matching condition varies depending on the incident angle of the passing path in each path, and the total conversion efficiency is less likely to decrease even if the temperature changes. In the case of the configuration of the first embodiment or the like (only one path), the full width at half maximum of the conversion efficiency is 1.1 degrees, but the full width at half maximum of the conversion efficiency of the present embodiment is 2.6 degrees. And has an allowable width of more than twice. Further, the total conversion efficiency of the present embodiment has a higher value in a wider temperature range than the conventional configuration because the fundamental laser beam repeatedly enters the wavelength conversion element 1905. As a result, in this embodiment, the total conversion efficiency is high, and a conversion efficiency of 60% or more, which is twice the conversion efficiency of the conventional configuration, is achieved.

Further, in the wavelength conversion laser light source 1900 of this embodiment, the wavelength conversion element 1905 is disposed between two reflecting mirrors (a first concave mirror 1903 and a second concave mirror 1904) that reflect the laser light and have a curvature. The laser light is incident between the reflecting mirrors from a portion having no reflecting function by the condensing optical system 1902, and the laser light repeatedly passes between the reflecting mirrors while changing the incident angle to the wavelength conversion element 1905. Therefore, the wavelength conversion is repeated by changing the phase matching condition, and the condensing optical system 1902 controls the beam waist positions BW between the laser beam reflecting mirrors, and at least one of the reflecting mirrors converts the wavelength. Transmits light and emits a wavelength conversion laser. As a result, it is possible to have a plurality of phase matching conditions while having high conversion efficiency, so that the allowable range from the phase matching conditions such as temperature is expanded, and a wavelength conversion laser that is stable against environmental changes and the like can be obtained. Further, by interspersing the beam waist positions BW, it is possible to obtain a high-power wavelength-converted laser beam that eliminates optical damage and wavelength conversion instability.

In the present embodiment, a fiber laser having a center wavelength of 1064 nm and a full width at half maximum of 0.1 nm is used as the fundamental laser light source 1901. As the fundamental laser light source 1901, a solid laser, a semiconductor laser, a gas laser, a wavelength conversion laser, or the like can be used in addition to a fiber laser. In this embodiment, wavelength conversion to the second harmonic is performed. However, by selecting an appropriate laser light source, the present invention can be applied to wavelength conversion laser light sources such as sum frequency, difference frequency, and optical parametric oscillation. Can also be used.

In this embodiment, the distance D between the two reflecting mirrors (the first concave mirror 1903 and the second concave mirror 1904), the focal lengths of the two reflecting mirrors f1 and f2, and the wavelength conversion element 1905 When the length is L, this is a preferable form satisfying f1 + f2 <D <f1 + f2 + L. For example, in the present embodiment, D is 58.4 mm when f1: 25 mm, f2: 20 mm, and L: 26 mm. When there is a distance D between the reflecting mirrors in the above relationship, the two reflecting mirrors (the first concave mirror 1903 and the second concave mirror 1904) are close to the confocal arrangement, and the number of reciprocations of the beam path increases, and the wavelength conversion element Since the number of passes 1905 increases, the total conversion efficiency of the wavelength conversion laser light source 1900 can be increased.

Here, when the reflecting mirror is an asymmetric lens, the focal length of the reflecting mirror means the focal length in the direction in which the incident light beam between the reflecting mirrors is deviated from the principal ray axis MA. When the refractive index of the wavelength conversion element 1905 is n, it is particularly preferable that the distance D between the reflecting mirrors satisfies the following formula.

D ≠ f1 + f2 + (1-1 / n) × L (= confocal arrangement)

This confocal arrangement refers to the distance D at which the focal points of the two reflecting mirrors are at the same position. When the distance D between the reflecting mirrors is set to be a confocal arrangement, the laser beam may converge on the principal ray axis MA, causing optical damage and instability of wavelength conversion at high output. For this reason, it is preferable to set the distance D between the reflecting mirrors within a range of a position slightly deviated from the confocal arrangement. Specifically, the distance D is set at a position shifted by about 0.1 to 3 mm from the confocal arrangement. By making the distance shorter than the confocal arrangement within the above range, the number of reciprocations is ensured, the convergence of the focal position of the reflecting mirror is avoided, the laser light incident between the reflecting mirrors, and the second concave mirror 1904 (second The margin for the effective diameter of the reflecting mirror can be increased.

Further, the condensing optical system 1902 of the present embodiment includes a fiber collimator and a plano-convex lens. The condensing optical system 1902 collects the laser light in the wavelength conversion element 1905 except for the focal points of the two reflecting mirrors, and the beam waist positions BW during the reciprocation are scattered in the wavelength conversion element 1905. I have control. At the focal point of the two reflecting mirrors, there is an overlap of laser light, which may cause destruction of the wavelength conversion element and instability of wavelength conversion. Similarly, when wavelength conversion is concentrated in one place, the wavelength conversion element is destroyed and wavelength conversion is unstable.

Here, the wavelength conversion is strongly performed at the focused beam waist position, but in this embodiment, the beam waist position BW is interspersed other than the focal points of the two reflecting mirrors. By performing wavelength conversion at the scattered beam waist positions BW in this way, stable wavelength conversion laser light can be output. It should be noted that after the wavelength conversion is repeatedly performed at the beam waist positions BW where the laser beams are scattered, the beam waist positions BW of the laser beams may converge at the focal positions of the two reflecting mirrors.

In the present embodiment, the condensing optical system 1902 collects light between the reflecting mirrors of the first concave mirror 1903 and the second concave mirror 1904 before the laser light is reflected by the first concave mirror 1903. It is. By having a condensing point (beam waist position) between the reflecting mirrors before being reflected by the reflecting mirror, it is possible to form a beam waist with a large number of laser light paths that do not pass near the focal point of the reflecting mirror. As a result, a large number of beam waist positions BW can be arranged in a wide range as a laser beam path of the wavelength conversion element 1905. As a result, in the present embodiment, a large number of beam waist positions BW can be scattered over a wide range in the wavelength conversion element 1905, and stable wavelength conversion can be performed even at high output.

Further, this embodiment is a particularly preferable embodiment in which the light is condensed in the wavelength conversion element 1905 before being reflected by the reflecting mirrors (the first concave mirror 1903 and the second concave mirror 1904). As described above, the wavelength conversion before the reflection by the reflecting mirror may be performed to monitor the laser light whose wavelength is converted in the first pass of the wavelength conversion element 1905. In this case, since the wavelength-converted laser light that is not related to the reflecting mirror can be adjusted, a compact laser light source can be manufactured. Moreover, total conversion efficiency can be raised by performing wavelength conversion before reflecting with a reflective mirror.

In this embodiment, spherical concave mirrors are used for the two reflecting mirrors, but aspherical or flat reflecting mirrors may be used. In this case, at least one of the two reflecting mirrors has a curvature so that the laser beam is bent and reciprocated between the reflecting mirrors a plurality of times, and a laser beam beam waist is formed between the reflecting mirrors. To do. In the combination of the two reflecting mirrors, the laser light may be reflected a plurality of times, and the laser light may be incident on the wavelength conversion element 1905 with at least two types of incident angles.

Also, at least one of the reflecting mirrors transmits the wavelength-converted laser light in order to output the wavelength-converted laser light. In the present embodiment, the first concave mirror 1903 transmits the second harmonic whose wavelength has been converted. For example, the first concave mirror 1903 reflects the fundamental laser beam with the reflectance of the fundamental wave (1064 nm) of 99.5% and the transmittance of the second harmonic wave (532 nm) of 99%, and the second harmonic laser beam. Transparent. The second concave mirror 1904 reflects both the fundamental laser beam and the second harmonic laser beam with a reflectance of 99.5% of the fundamental wave (1064 nm) and a reflectance of 99% of the second harmonic (532 nm). . It is preferable that the reflectance of the reflecting mirror with respect to the laser beam (fundamental wave) is high because loss is reduced. The wavelength conversion laser light may be configured to transmit two reflecting mirrors, or may be configured to transmit only one.

In the present embodiment, MgO: LiNbO ₃ (PPLN) having a polarization inversion structure is used for the wavelength conversion element 1905, and the shape thereof may be a rectangular parallelepiped (for example, length 26 mm, width 10 mm, thickness 1 mm). This wavelength conversion element is made of a nonlinear optical crystal capable of performing wavelength conversion, and for example, a nonlinear optical crystal such as KTP, LBO, CLBO, or LT can be used. In particular, a wavelength conversion element having a polarization inversion structure and performing quasi-phase matching can be used in the wavelength conversion laser light source of the present invention because different phase matching conditions can be formed in the same element depending on the polarization inversion period. preferable. In this case, by having different phase matching conditions in the same element, it is possible to increase the allowable range for the temperature and wavelength of the wavelength conversion laser as a whole.

Further, the wavelength conversion element 1905 of the present embodiment is disposed so as to have an incident surface perpendicular to the principal ray axis MA. In the wavelength conversion element 1905, the domain-inverted structure is formed with a period parallel to the incident surface, and the domain-inverted period is about 7 μm. As described above, the polarization inversion period is not the same in the element, and the period and direction may be changed. On the incident / exit surface of the wavelength conversion element 1905, an AR coat of laser light (fundamental wave) and wavelength conversion laser light (second harmonic) is formed. As described above, the wavelength conversion element 1905 preferably forms an AR coat of laser light and wavelength conversion laser light in order to avoid unnecessary reflection between the reflecting mirrors.

In the present embodiment, for example, the effective diameter of the first concave mirror 1903 is φ5, the effective diameter of the second concave mirror 1904 is φ4, and the width of the wavelength conversion element 1905 for reciprocating the laser beam is 5 mm. With a long and compact shape, high-power wavelength-converted laser light can be stably output.

In the present embodiment, the diameter of the beam incident on the first concave mirror 1903 is φ0.3, and the diameter of the laser beam incident on the reflecting mirror is a small effective diameter (second concave mirror 1904). This is a preferred form that is 1/5 or less of the effective diameter. In this case, since the beam incident between the reflecting mirrors is sufficiently small with respect to the reflecting mirrors, the overlap of the laser light between the reflecting mirrors is alleviated and the number of round trips of the laser light between the reflecting mirrors is increased. be able to. By alleviating this overlap and increasing the number of reciprocations, it is possible to achieve both high output and high conversion efficiency even if it is compact. In the configuration of the present embodiment, when the incident beam diameter was made larger than 1/5 of the effective diameter of the reflecting mirror, the number of reciprocations was about 3, and the conversion efficiency was lowered. Here, the effective diameter of the reflecting mirror refers to the length in the longitudinal direction of the range where the laser beam hits the reflecting mirror.

In the present embodiment, the center wavelength λ of the fundamental laser light source 1901 is 1064 nm, the full width at half maximum Δλ is 0.1 nm, and the coherence length (λ ² / Δλ) is 11.3 mm. Since the distance D between the reflecting mirrors is 58.4 mm, the coherence length is less than twice the distance between the reflections. This embodiment is a preferred form in which the coherence length of the laser light is less than twice the distance between the reflecting mirrors. When the coherence length is more than twice the distance between the reflecting mirrors, interference occurs at the point where the laser beams reciprocating between the reflecting mirrors overlap, and the beam intensity becomes very strong. The strong beam intensity generated by the interference causes crystal destruction of the wavelength conversion element and instability of wavelength conversion. In the present embodiment, the coherence length of the laser light reciprocating between the reflecting mirrors is made shorter than the reciprocating distance, so that the problem of coherence that occurs in the case of this configuration can be solved.

At this time, as is apparent from FIG. 24 and FIG. 25, it can be seen that the beam path gradually moves from the outside to the inside of the wavelength conversion element 1905 which is a nonlinear optical crystal element. When wavelength conversion is performed, the generated harmonics may be absorbed to increase the temperature of the beam path. However, the harmonics output in this embodiment are large outside the wavelength conversion element 1905 and inside. It gets smaller as you go. Therefore, in the outer beam path, it is desirable that the temperature of the wavelength conversion element 1905 is low, and the temperature is higher as the temperature becomes closer to the inner side.

(Sixth embodiment)
FIG. 26 is a schematic diagram showing a configuration of a two-dimensional image display device according to the sixth embodiment of the present invention. The present embodiment is a two-dimensional image display device using a wavelength conversion green laser light source using any one of the above wavelength conversion laser light sources.

A two-dimensional image display device 2000 according to the present embodiment shown in FIG. 26 is an example in which the above-described pulse fiber laser light source is applied to an optical engine of a liquid crystal three-plate projector. The two-dimensional image display device 2000 includes an image processing unit 2002, a laser output controller 2003, an LD power source 2004, a red laser light source 2005R, a green laser light source 2005G, a blue laser light source 2005B, beam forming

rod lenses

2006R, 2006G, 2006B, and a relay lens 2007R. , 2007G, 2007B, folding mirrors 2008G, 2008B, two-

dimensional modulation elements

2009R, 2009G, 2009B for displaying images, polarizers 2010R, 2010G, 2010B, a combining prism 2011, and a projection lens 2012.

Laser light from each of the

laser light sources

2005R, 2005G, and 2005B is shaped into a rectangle by beam forming

rod lenses

2006R, 2006G, and 2006B, and the two-

dimensional modulation elements

2009R, 2009G, and 2009B for each color are formed by the

relay lenses

2007R, 2007G, and 2007B. Illuminate. An image modulated two-dimensionally with each color is synthesized by the combining prism 2011 and projected onto the screen from the projection lens 2012 to display an image.

The green laser light source 2005G is controlled by a laser output controller 2003 and an LD power source 2004 that control the output of green light. The green laser light source 2005G is a system in which the laser resonator is closed in the fiber, and suppresses a decrease in output with time and an output fluctuation due to an increase in the loss of the resonator due to external dust or reflection surface misalignment. Can do.

The image processing unit 2002 generates a light amount control signal for changing the output of the laser light according to the luminance information of the input video signal (video signal from TV, VIDEO, PC, etc.), and sends it to the laser output controller 2003. Playing a role. As a result, in this embodiment, the laser output controller 2003 and the LD power source 2004 control the red laser light source 2005R, the green laser light source 2005G, and the blue laser light source 2005B, and control the amount of light according to the luminance information, thereby controlling the contrast. It becomes possible to improve.

At this time, in the present embodiment, each

laser light source

2005R, 2005G, 2005B is pulse-driven, and the duty ratio (lighting time / (lighting time + non-lighting time)) of each

laser light source

2005R, 2005G, 2005B is turned on. ) Can be changed to adopt a control method (PWM control) that changes the average light quantity. Further, when the laser light source is used as a green light source used in a laser display, it may be configured to emit green laser light of 510 nm to 550 nm. With this configuration, green laser output light with high visibility can be obtained, and a color expression close to the primary color can be expressed as a display with good color reproducibility.

The configuration of the two-dimensional image display device is not particularly limited to the above example, and includes a plurality of laser light sources and a scanning unit that scans the laser light sources, and the laser light sources emit at least red, green, and blue, respectively. The laser light source may be configured so that at least the green light source among the laser light sources may be configured using any of the above-described pulse fiber laser light sources. Further, in addition to a mode of projecting from behind the screen (rear projection display), it is also possible to configure as a two-dimensional image display device having a front projection type configuration.

Also, the two-dimensional modulation element is not particularly limited to the above example, and it is of course possible to use a two-dimensional modulation element using a reflection type liquid crystal element, a galvano mirror, or a mechanical micro switch (MEMS) represented by DMD. . Furthermore, in a light modulation element that is less affected by the polarization component on the light modulation characteristics such as a reflective spatial modulation element, MEMS, and galvanometer mirror, it is necessary to use a polarization maintaining fiber such as a PANDA fiber when propagating harmonics through the optical fiber. However, when using a two-dimensional modulation device using liquid crystal, the optical modulation characteristics and polarization characteristics are greatly related. Therefore, a polarization maintaining fiber is used, and the light after wavelength conversion is linearly polarized light. It is desirable.

(Seventh embodiment)
FIG. 27 is a schematic diagram showing the configuration of the liquid crystal display device according to the seventh embodiment of the present invention. The liquid crystal display device 2100 of this embodiment is an example of a two-dimensional image display device using a backlight illumination device including any one of the above-described wavelength conversion laser light sources as a green light source.

As shown in FIG. 27, the liquid crystal display device 2100 includes a liquid crystal display panel 2101 and a backlight illumination device 2111 that illuminates the liquid crystal display panel 2101 from the back side. The liquid crystal display panel 2101 includes a polarizing plate 2102 and a liquid crystal panel 2103.

The laser light source 2112 of the backlight illumination device 2111 includes a plurality of

laser light sources

2112r, 2112g, and 2112b. The laser light source 2112 emits light sources that emit at least red (R), green (G), and blue (B), respectively. It consists of the structure used. That is, the R light source 2112r, the G light source 2112g, and the B light source 2112b emit red, green, and blue laser beams, respectively.

Here, a semiconductor laser device made of an AlGaInP / GaAs material with a wavelength of 640 nm is used for the R light source 2112r, and a semiconductor laser device made of a GaN material with a wavelength of 450 nm is used for the B light source 2112b. The G light source 2112g uses a green laser light source having a wavelength of 532 nm, which is configured using a green light source composed of any one of the wavelength conversion laser light sources described above.

As described above, the liquid crystal display device 2100 in this embodiment displays an image using the backlight illumination device 2111 and the R, G, and B light beams emitted from the backlight illumination device 2111. And a liquid crystal display panel 2101 to be performed. The backlight illuminator 2111 introduced a laser light source 2112 and an optical fiber 2113 that guides the R light, G light, and B light from the laser light source 2112 to the light guide plate 2115 through the light guide unit 2114. The light guide plate 2115 is uniformly filled with laser light of R light, G light, and B light, and emits laser light from a main surface (not shown). The G light source 2112g adds an optical component such as a condensing lens (not shown) to the wavelength conversion laser light source, and multi-beams of output light are condensed on the optical fiber 2113 and guided to the light guide plate 2115. I try to be.

With the above configuration, the present embodiment uses a pulsed fiber laser light source having a single high output peak value and high photoelectric conversion efficiency, so it has high brightness, excellent color reproducibility, and simple configuration with low consumption. An image display device with stable power can be realized.

(Eighth embodiment)
FIG. 28 is a schematic diagram showing a configuration of a laser processing apparatus according to the eighth embodiment of the present invention. In this laser processing apparatus, any one of the wavelength conversion laser light sources described above is used as a laser light source.

As shown in FIG. 28, the laser processing apparatus 2201 includes a laser light source 2202, a scan mirror 2203, and a stage 2204, and processes a processing target 2205. As the laser light source 2202, any one of the wavelength conversion laser light sources described above is used, and the laser light emitted from the laser light source 2202 is reflected by the scan mirror 2203 and irradiated onto the processing target 2205, thereby irradiating the laser on the processing target 2205. Move the position in the Y-axis direction. At the same time, the laser irradiation position on the processing target 2205 is moved in the X-axis direction by moving the stage 2204 on which the processing target 2205 is placed in the X-axis direction. With such a configuration, for example, by pulsing the laser light source 2202 at an arbitrary laser irradiation position, it is possible to mark an arbitrary pattern on the surface of the processing target 2205.

Further, by installing the processing object 2205 in the water tank and irradiating the laser beam on the surface of the processing object 2205 in the same manner as described above, it can be applied to laser peening and the like.

As described above, the laser processing apparatus 2201 of this embodiment can stably generate laser light with high beam quality and is preferably used as a light source used in a laser processing apparatus such as laser marking or laser peening. be able to. In laser peening, it is desirable to use a laser light source that generates light having a wavelength of 441 nm to 592 nm as wavelength conversion light. This prevents water from evaporating due to absorption of the laser light, and enables processing. A high laser peening effect on the irradiated surface of 2205 can be exhibited.

In this embodiment, a laser scanning type processing apparatus using a scan mirror is described. This is an example of a processing apparatus using the above-described wavelength conversion laser light source. For example, the fiber shown in FIG. The attached laser light source 2300 may be used.

29 includes a main body 2301, an output setting unit 2302, and a power switch 2306. The main body 2301 includes any one of the wavelength conversion laser light sources described above and an output control unit that controls the output of the laser light from the wavelength conversion laser light source, and sets the output of the laser light on the front panel. An output setting unit 2302 and a power switch 2306 for turning on / off the power are provided.

The laser light source with fiber 2300 causes the laser light generated by the wavelength conversion laser light source incorporated in the main body 2301 to enter the delivery fiber 2304 via the output connector 2303, and the delivery fiber 2304 emits from the wavelength conversion laser light source. The laser beam may be guided to the handpiece 2305, and an arbitrary irradiation surface may be irradiated from the handpiece 2305 with the outgoing beam EB that is a laser beam. By adopting such a configuration, it becomes possible to realize a laser light source with a fiber used for surgery or the like.

In each of the above embodiments, the pulse fiber laser light source uses a fiber doped with Yb as a rare earth element, but other rare earth elements such as Nd, Er, Dy, Pr, Tb, Eu, etc. At least one selected rare earth element may be used. Further, the doping amount of the rare earth element may be changed or a plurality of rare earth elements may be doped according to the wavelength and output of the wavelength conversion element.

In each of the above-described embodiments, a laser having a wavelength of 915 nm and a wavelength of 976 nm is used as the LD for pumping the pulse fiber laser light source. However, as long as the fiber laser can be excited, laser light sources other than these wavelengths are used. May be used. Further, as the wavelength conversion element, periodic polarization reversal MgO: LiNbO ₃ or the like was used, but wavelength conversion elements of other materials or structures, for example, potassium titanyl phosphate (KTP) or Mg: LiTaO ₃ or the like may be used.

From the above embodiments, the present invention is summarized as follows. That is, the pulse fiber laser light source according to the present invention includes an excitation laser light source that emits excitation light, a fiber member that contains a laser active substance, and is irradiated with excitation light from the excitation laser light source, and sandwiches the fiber member. A laser resonator including a set of fiber gratings optically connected to the fiber member, wherein the fiber member is provided with a region where excitation light does not substantially reach, The first peak of the light pulse emitted from the resonator is formed and blocked so that the second peak is not formed.

In this pulsed fiber laser light source, since the region where the excitation light does not substantially reach the fiber member is provided, the laser resonator self-absorbs the light itself oscillated and the oscillation becomes unstable, and the output light is It becomes a state that is easy to pulse. At this time, the input current for driving the excitation laser light source is cut off so that the first peak of the light pulse emitted from the laser resonator is formed and the second peak is not formed, so that it has a steep rise characteristic. By exciting the laser resonator with the excited light, high-peak pulsed light can be emitted. As a result, pulse oscillation is possible without adding new expensive parts, and a highly efficient pulse fiber laser light source can be realized with a simple configuration.

It is preferable that after the input current is cut off, the laser light source for excitation is again driven by the input current, so that the laser resonator repeatedly emits a plurality of light pulses.

In this case, since the laser resonator can be periodically and repeatedly excited with excitation light having a steep rise characteristic, high peak pulse light can be repeatedly emitted.

The fiber member preferably includes first and second fibers and an excitation light absorption mechanism that is disposed between the first and second fibers and absorbs excitation light.

In this case, after the excitation light propagates through the first fiber, the excitation light is absorbed by the excitation light absorption mechanism, so that the second fiber can be made an area where the excitation light does not reach.

The pulse fiber laser light source further includes a step index type multimode fiber that optically couples the excitation laser light source and the laser resonator, and the NA of the step index type multimode fiber is the excitation laser light source. It is preferable that it is NA or more with respect to the excitation light of the incident side fiber of the laser resonator.

In this case, since the light oscillated in the laser resonator can be prevented from flowing back to the excitation laser light source, it is possible to prevent the excitation laser light source from being damaged by the return light.

The pulse fiber laser light source further includes a multimode combiner that optically couples the excitation laser light source and the laser resonator, and NAs of a plurality of input ports of the multimode combiner are The NA of the output side fiber is equal to or greater than the NA of the output port of the multimode combiner, and is equal to or less than the NA of the pump light of the incident side fiber of the laser resonator, and at least one of the plurality of input ports of the multimode combiner. One is preferably not optically connected to the excitation laser light source.

In this case, in addition to the effect of reducing the return light to the excitation laser light source due to the difference in the NA of the fiber, the effect of reducing the return light due to the branching of the fiber can be obtained, and at least one input port has Since it is not optically connected to the excitation laser light source, the influence of the return light can be further reduced.

The rising speed of the input current applied to the excitation laser light source is preferably 1 ns to 100 ns. In this case, the laser resonator can be pulse-oscillated.

The pulse fiber laser light source further includes a detection unit that detects an optical output of the optical pulse, and a light source driving unit that applies the input current to the excitation laser light source, and the light source driving unit is based on the detection unit. It is preferable to cut off the input current based on the detection signal.

In this case, a pulse fiber laser light source with high photoelectric conversion efficiency capable of generating an optical pulse having a high output peak value as a pulse train can be realized with a simple configuration.

It is preferable that the detection unit detects an optical output of the optical pulse from a branch fiber optically connected in the middle of the fiber member.

In this case, since the generation of an optical pulse including a peak value can be accurately grasped, an optical pulse having a single high output peak value can be generated as a pulse train with a simpler device configuration.

The pulse fiber laser light source further includes an amplifier for amplifying an optical pulse emitted from the laser resonator, and the amplifier includes an amplification laser light source, a laser active material, and an amplification fiber having a polarization maintaining structure. And a combiner that optically couples the amplification laser light source and the amplification fiber, and the amplification fiber receives an optical pulse emitted from the laser resonator and passes through the combiner. Then, excitation light is incident from the amplification laser light source, and the drive current of the excitation laser light source and the drive current of the amplification laser light source are modulated in synchronization with a predetermined pulse width and a predetermined rising speed. It is preferable.

In this case, since a light pulse with a large peak power can be obtained, a pulse fiber laser light source can be used for processing such as metal laser trimming.

The fall timing of the drive current of the amplification laser light source is preferably earlier than the fall timing of the drive current of the excitation laser light source.

In this case, since the trailing edge of the output light waveform from the amplifier can be reduced, for example, when laser processing is performed using a scanning mirror, the processing speed and processing accuracy can be increased.

A wavelength conversion laser light source according to the present invention includes any one of the pulse fiber laser light source described above and a wavelength conversion element that converts the fundamental light emitted from the pulse fiber laser light source into a harmonic light. The condensing position is a position of 0 to 10 mm from the end face of the wavelength conversion element.

In this wavelength conversion laser light source, a pulsed fiber laser light source can be pulsed and wavelength conversion can be performed efficiently, and crystal destruction of the wavelength conversion element can be prevented. Therefore, a more reliable wavelength conversion laser light source can be obtained. realizable.

Another wavelength conversion laser light source according to the present invention includes the pulse fiber laser light source according to any one of the above, and a wavelength conversion element that converts fundamental light emitted from the pulse fiber laser light source into harmonic light, The length of the wavelength conversion element is 0 to 10 mm.

The wavelength conversion element preferably includes a nonlinear optical crystal having an effective nonlinear optical constant of 10 pm / V or more. In this case, it is possible to prevent green high-power saturation and crystal destruction in the wavelength conversion element.

A two-dimensional image display device according to the present invention controls the wavelength-converted laser light source according to any one of the above, a display unit that displays an image using laser light from the wavelength-converted laser light source, and the wavelength-converted laser light source. Controller.

In this two-dimensional image display device, green laser output light with high visibility can be obtained, and as a display with good color reproducibility, color representation close to the primary color can be achieved.

A liquid crystal display device according to the present invention includes a liquid crystal display panel, the wavelength conversion laser light source according to any one of the above, and a backlight illumination device that illuminates the liquid crystal display panel using laser light from the wavelength conversion laser light source. Is provided.

In this liquid crystal display device, a pulsed fiber laser light source having a single high output peak value and high photoelectric conversion efficiency is used, so that it has high brightness, excellent color reproducibility, a simple configuration and low power consumption and stable An image display device can be realized.

A laser processing apparatus according to the present invention includes the wavelength conversion laser light source according to any one of the above and an optical system that guides laser light emitted from the wavelength conversion laser light source to a processing target.

Since this laser processing apparatus can stably generate laser light with high beam quality, it is possible to realize a highly efficient laser processing apparatus that performs various laser processing such as laser marking and laser peening.

A fiber-attached laser light source according to the present invention includes any one of the wavelength conversion laser light sources described above and a light guide fiber member that guides laser light emitted from the wavelength conversion laser light source.

In this laser light source with a fiber, laser light can be irradiated onto an arbitrary irradiation surface from the tip of the light guide fiber member, so that a laser light source with a fiber used for surgery or the like can be realized.

According to the pulse fiber laser light source of the present invention, a pulse light source with high efficiency and high peak power can be obtained. Therefore, even when the outside air temperature or the like changes, it can be used as a stable and highly efficient pulse light source. In particular, a cooling system such as a Peltier element is not required for cooling the pump LD, and a pulsed fiber laser light source that can be used in an environment of room temperature to 40 ° C or room temperature to 50 ° C is realized only by forced air cooling using a heat sink and a cooling fan. Therefore, the conversion efficiency from the total input power to the optical output can be improved.

Claims

An excitation laser light source that emits excitation light;
Laser resonance including a fiber member containing a laser active substance and receiving excitation light from the excitation laser light source, and a set of fiber gratings optically connected to the fiber member with the fiber member interposed therebetween Equipped with
The fiber member is provided with a region where excitation light does not substantially reach,
A pulsed fiber laser light source characterized in that an input current for driving the excitation laser light source is blocked so that a first peak of an optical pulse emitted from the laser resonator is formed and a second peak is not formed. .
2. The laser resonator according to claim 1, wherein the laser resonator repeatedly emits a plurality of light pulses when the pumping laser light source is driven again by the input current after the input current is cut off. Pulse fiber laser light source.
The fiber member is
First and second fibers;
3. The pulse fiber laser light source according to claim 1, further comprising an excitation light absorption mechanism that is disposed between the first and second fibers and absorbs excitation light. 4.
A step index type multimode fiber that optically couples the excitation laser light source and the laser resonator;
The NA of the step index type multimode fiber is not less than the NA of the exit side fiber of the excitation laser light source and not more than the NA of the excitation light of the incident side fiber of the laser resonator. 4. The pulse fiber laser light source according to any one of 3 above.
A multi-mode combiner that optically couples the excitation laser light source and the laser resonator;
The NA of the plurality of input ports of the multimode combiner is equal to or greater than the NA of the output side fiber of the excitation laser light source, and the NA of the output port of the multimode combiner is the excitation light of the incident side fiber of the laser resonator. NA or less for
The pulse fiber laser light source according to any one of claims 1 to 3, wherein at least one of the plurality of input ports of the multimode combiner is not optically connected to the excitation laser light source.
6. The pulse fiber laser light source according to claim 1, wherein the rising speed of the input current applied to the excitation laser light source is 1 ns to 100 ns.
A detector for detecting the light output of the light pulse;
A light source driving unit for applying the input current to the excitation laser light source;
7. The pulsed fiber laser light source according to claim 1, wherein the light source driving unit cuts off the input current based on a detection signal from the detection unit.
The pulse fiber laser light source according to claim 7, wherein the detection unit detects an optical output of the optical pulse from a branched fiber optically connected in the middle of the fiber member.
An amplifier for amplifying an optical pulse emitted from the laser resonator;
The amplifier is
An amplification laser light source;
An amplifying fiber containing a laser active material and having a polarization maintaining structure;
A combiner for optically coupling the amplification laser light source and the amplification fiber;
The amplification fiber receives a light pulse emitted from the laser resonator and receives excitation light from the amplification laser light source via the combiner,
9. The drive current of the excitation laser light source and the drive current of the amplification laser light source are modulated in synchronization with a predetermined pulse width and a predetermined rising speed. The pulse fiber laser light source described in 1.
10. The pulse fiber laser light source according to claim 9, wherein the drive current fall timing of the amplification laser light source is earlier than the drive current fall timing of the excitation laser light source.
A pulse fiber laser light source according to any one of claims 1 to 10,
A wavelength conversion element that converts the fundamental light emitted from the pulse fiber laser light source into harmonic light, and
The wavelength conversion laser light source characterized in that the converging position of the fundamental wave light is a position of 0 to 10 mm from the end face of the wavelength conversion element.
A pulse fiber laser light source according to any one of claims 1 to 10,
A wavelength conversion element that converts the fundamental light emitted from the pulse fiber laser light source into harmonic light, and
The wavelength conversion laser light source, wherein the wavelength conversion element has a length of 0 to 10 mm.
The wavelength conversion laser light source according to claim 11 or 12, wherein the wavelength conversion element includes a nonlinear optical crystal having an effective nonlinear optical constant of 10 pm / V or more.
A wavelength-converted laser light source according to any one of claims 11 to 13,
A display unit for displaying an image using laser light from the wavelength conversion laser light source;
And a controller for controlling the wavelength conversion laser light source.
A liquid crystal display panel;
A wavelength-converted laser light source according to any one of claims 11 to 13,
A liquid crystal display device comprising: a backlight illumination device that illuminates the liquid crystal display panel using laser light from the wavelength conversion laser light source.
A wavelength-converted laser light source according to any one of claims 11 to 13,
An optical system for guiding a laser beam emitted from the wavelength conversion laser light source to a processing target.
A wavelength-converted laser light source according to any one of claims 11 to 13,
A laser light source with a fiber, comprising: a light guide fiber member that guides laser light emitted from the wavelength conversion laser light source.