KR20210059310A - Ultrashort pulse laser apparatus using heating element - Google Patents

Abstract

The present invention relates to an ultra-short laser pulse generating device using a heating element. According to an embodiment, the ultra-short laser pulse generating device comprises: a gain medium made of an active optical fiber; an optical fiber connecting a first end and a second end of the gain medium to form an optical path; a pump light source for providing pump light toward a second end side of the gain medium; a light shield machine installed at a first end side of the gain medium in the optical path; a polarizing filter installed in the optical path and passing only one light of a polarization state; and a mode locking unit disposed adjacent to the optical fiber and including a plurality of heating modules individually including one or more heating elements and a power supply unit for applying power to each heating element of the plurality of heating modules.

Description

Ultrashort pulse laser apparatus using heating element

The present invention relates to a pulse laser generator, and more particularly, to a pulse laser generator capable of generating an ultra-short pulse laser using a heating element.

Lasers are used for precise measurement or processing, but ultrashort pulse lasers have recently begun to be widely used. Ultra-short pulse laser, also called femtosecond laser, is a laser with a very short pulse width from several femtoseconds to several picoseconds, and rarely causes thermal damage and cracks, so laser processing, display, bio, medical, and semiconductor that require ultra-precision processing. The demand is increasing in various fields such as.

Conventionally, a fiber laser device that generates an ultra-short pulse laser using a nonlinear polarization rotation (NPR) method generates ultra-short pulse lasers by inserting a plurality of polarizing plates inside to control polarization and rotating the polarizing plate. . However, when a polarizing plate is used, the laser device cannot be configured with only the optical fiber, but the laser light comes out of the optical fiber and passes through the polarizing plate and the optical system and is again condensed to the optical fiber. There is a problem in that the performance of the laser is deteriorated due to an increase in volume and misalignment of the optical system due to external vibration or temperature change.

Patent Document 1: Korean Patent Application Publication No. 2017-0069681 (published on June 21, 2017) Patent Document 2: Korean Patent Registration No. 10-1501509 (announced on March 11, 2015)

The present invention has been conceived to solve the above problem, and an object of the present invention is to provide an apparatus capable of generating an ultra-short pulse laser by controlling the polarization of laser light inside an optical fiber laser using a heating element.

According to an embodiment of the present invention, there is provided an apparatus for generating ultra-short laser pulses using a heating element, comprising: a gain medium made of an active optical fiber; An optical fiber connecting the first end and the second end of the gain medium to form an optical path; A pump light source providing a pump light to the second end side of the gain medium; An optical shield installed on the first end side of the gain medium of the optical path; A polarization filter installed in the optical path and passing only light in one polarization state; And a mode locking unit disposed adjacent to the optical fiber and including a plurality of heating modules each comprising one or more heating elements and a power supply unit for applying power to each heating element of the plurality of heating modules. Start a pulse generating device.

According to an embodiment of the present invention, there is provided an ultrashort laser pulse generator using a heating element, comprising: an optical fiber having a first end and a second end and forming a linear optical path; A gain medium disposed on the optical path and made of an active optical fiber; A pump light source providing a pump light to the first end side of the gain medium; A first reflector installed at the first end of the optical fiber and reflecting light at a predetermined reflectance; A second reflector installed at the second end of the optical fiber and selectively reflecting or passing light; A polarization filter installed in the optical path and passing only light in one polarization state; And a mode locking unit disposed adjacent to the optical fiber and including a plurality of heating modules each including one or more heating elements and a power supply for applying power to each heating element of each heating module. Disclosed is a laser pulse generator.

The pulsed laser generator according to an embodiment of the present invention does not require the use of a polarizing plate or other optical element to control polarization for generating pulses, and by applying heat to the optical fiber to adjust the polarization, the ultrashort pulse laser can be achieved with a simple configuration and low cost. Can be generated.

In addition, since the pulsed laser generator of the present invention can be composed of only optical fibers, there is no problem of deteriorating performance due to misalignment of the optical system due to external vibrations or environmental changes, and it is also possible to implement an ultra-short pulse laser device of a very small size. .

1 is an explanatory diagram of an ultrashort pulse laser generating apparatus according to an embodiment of the present invention;
2 is a diagram illustrating a change in refractive index of an optical fiber;
3 is a diagram illustrating a heating module according to an embodiment;
4 is a diagram illustrating a heating module according to an alternative embodiment;
5 is a view for explaining a heating module according to another alternative embodiment,
6 is a flowchart illustrating a method of generating an ultra-short pulse laser by heating a heating element according to an embodiment;
7 is a diagram showing an exemplary voltage waveform applied to a heating element;
8 is a flowchart illustrating a method of generating an ultra-short pulse laser by heating a heating element according to another embodiment;
9 to 11 are diagrams illustrating alternative embodiments of an ultrashort pulse laser generating apparatus.

The above objects, other objects, features, and advantages of the present invention will be easily understood through the following preferred embodiments related to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosed content may be thorough and complete, and the spirit of the present invention may be sufficiently conveyed to those skilled in the art.

In this specification, the singular form also includes the plural form unless specifically stated in the phrase. As used in the specification, "comprise" and/or "comprising" does not exclude the presence or addition of one or more other components.

Hereinafter, the present invention will be described in detail with reference to the drawings. In describing the specific embodiments below, a number of specific contents have been prepared to explain the invention in more detail and to aid understanding. However, readers who have knowledge in this field enough to understand the present invention It can be recognized that it can be used without specific content. In some cases, it is mentioned in advance that parts that are commonly known in describing the invention and are not significantly related to the invention are not described in order to avoid confusion in describing the invention.

Meanwhile, in the present specification, terms such as'light','light','laser','laser light', and'laser beam' will be used as the same meaning unless there is a particular benefit of distinction. Therefore, in the present specification, these terms are They can be substituted with each other.

1 is a schematic diagram of an ultrashort pulse laser generating apparatus according to an embodiment of the present invention. Referring to the drawings, an ultra-short pulse laser generator (hereinafter, simply referred to as a "laser generator") according to an embodiment includes an optical fiber 10, a pump light source 20, and a wavelength forming a ring-type closed path. A division multiplexer (WDM) 30, a gain medium 40, a light shield 50, a polarization filter 70, a coupler 80, and a mode lock unit 60 may be included.

The optical fiber 10 may be a general passive type optical fiber. Both ends of the optical fiber 10 are coupled with both ends of the gain medium 40 to form a closed path for a ring cavity type fiber laser.

The pump light source 20 generates pump light and supplies it to the gain medium 40. The pump light source 20 may be implemented as a laser diode (LD), for example, a wavelength division multiplexer (WDM) 30 by pumping light corresponding to the absorption light wavelength of 200 (for example, 980 nm). It is supplied to the gain medium 40 through.

The gain medium 40 may be composed of, for example, an active optical fiber. An active optical fiber is an optical fiber in which a rare earth element is added to the core of the optical fiber. There are several types of rare earth elements added to the active optical fiber, but erbium (Er), ytterbium (Yb), and thulium (Tm) can be used in general. For example, the gain medium 40 of an erbium doped fiber (EDF) has a wavelength of 980 nm or 1480 nm as an absorption band, a wide emission band centered on a wavelength of 1550 nm, and a ytterbium-doped optical fiber (Ytterbium The gain medium 40 of Doped Fiber, YDF) may have a wavelength of 980 nm as an absorption band and a wide emission band of several tens of nm around a wavelength of 1030 nm.

The light shield 50 is an optical element that passes light in only one direction, and is installed at one end side of the gain medium 40. The polarization filter 70 may be installed at any position in the optical path of the optical fiber 10 and may pass only light of one polarization state. The coupler 80 may divide a part of the light that has entered the coupler 80 and output it to the outside.

The mode locking unit 60 generates an ultra-short pulse laser by adjusting the polarization state of the laser light generated in the gain medium 40 and circulating through the optical fiber 10. In the present specification, the'ultra-short pulse' means, for example, a pulse having a frequency of several femto-seconds to several pico-seconds.

In one embodiment, the mode lock unit 60 is disposed adjacent to the optical fiber 10 and includes a plurality of heating modules each comprising one or more heating elements, a power supply unit 62 for applying a voltage to each heating module, and a power supply unit 62 ) And a control unit 61 for controlling. In the illustrated embodiment, the plurality of heating modules may be composed of two heating modules, that is, a first heating module HM1 and a second heating module HM2, which are sequentially arranged at the front and rear ends of the polarizing filter 70. . Each of the heating modules HM1 and HM2 may include one or more heating elements. However, depending on the specific embodiment, the number of heating modules, installation locations, and the number of heating elements may vary.

The laser generation process of the fiber laser according to the above-described configuration will be briefly described. First, pump light having a wavelength band between 900 nm and 1000 nm is generated by the pump light source 20 and supplied to the gain medium 40 through the WDM 30. The pump light excites the gain material doped in the active optical fiber of the gain medium 40 to have a high energy level, and the gain material in the excited active optical fiber falls from a high energy level to a low energy level and emits photons. For example, an erbium-doped optical fiber (EDF) emits laser light of 1550 nm, and a ytterbium-doped optical fiber (YDF) emits laser light of 1030 nm. At this time, the phase state or wavelength of each photon of the laser light is not constant and is a random state.

Among the generated photons, photons traveling from the gain medium 40 toward the light shield 50 are blocked by the light shield 50 and proceed only in the direction of the WDM 30 (ie, clockwise in FIG. 1). In the WDM 30, photons of 1550 nm (in the case of erbium) or 1030 nm (in the case of ytterbium) pass through the WDM 30 and proceed in the direction of the polarization filter 70, and the polarization in the polarization filter 70 is the same as the polarization filter. Only photons in the direction are transmitted. The polarization-filtered photons pass through the coupler 80 and the light shield 50 and proceed to the gain medium 40 again to form an optical cavity.

Photons incident on the active optical fiber of the gain medium 40 generate replicated photons of the same phase and wavelength from the excited gain material, and the photons continue to circulate through the optical cavity to generate replicated photons through an induced emission process. It generates laser light. The laser light generated at this time is a laser light having a single wavelength by copying and amplifying the photons that initially oscillated the laser. In this circulation process, the coupler 80 may emit laser light of a certain ratio to the outside as a laser output.

When the intensity of the laser light inside the optical cavity increases, nonlinear phenomena such as self-phase modulation, FWM (four-wave mixing), and Kerr effect occur according to the intensity of the light. The polarization state and frequency components of the laser light are changed. In addition to this nonlinear phenomenon, if the dispersion condition inside the cavity and the polarization condition of the light traveling inside the cavity are properly adjusted, it is possible to generate an ultrashort pulse laser with a pulse width between several femtoseconds and several picoseconds. I can.

In an embodiment of the present invention, a heating element capable of applying heat to a part of the optical fiber 10 is used to create a polarization state capable of generating such an ultra-short pulse. In this regard, FIG. 2 is a diagram showing a change in refractive index of an optical fiber by heating. FIG. 2(a) is a cross-section in the longitudinal direction of a part of the optical fiber 10, and FIG. 2(b) schematically shows a cross-section in the width direction. The most common and simple optical fiber is composed of a core 11 having a predetermined first refractive index n1 and a cladding 12 having a refractive index n2 smaller than the first refractive index n1 as shown in Fig. 2(a). . Since the first refractive index n1 is greater than the second refractive index n2, the laser light is propagated through the optical fiber while undergoing a total reflection process of light.

However, as shown in Fig. 2(b), when heat is applied to the optical fiber 10, the refractive index of the optical fiber is not uniform in the cross-section of the optical fiber, but varies with a temperature gradient. For example, as shown in Fig. 2(b), when heat is applied to the optical fiber in one direction of the X-axis, the surface of the clad 12 in this direction is heated and the refractive index of the clad 12 is lowered, and the axis ( That is, the propagation speed of light increases in the X-axis in the drawing and the speed decreases in the axis having a high refractive index (ie, the Y-axis in the drawing).

As described above, when the laser light passes through the heated region of the optical fiber 10, the speed at which light propagates between the X-direction polarization component and the Y-direction polarization component varies, and thereby, various polarizations depending on the degree of phase delay of each optical component. A state (linear polarization, elliptic polarization, circular polarization, etc.) is created.

Therefore, as shown in Fig. 1, a plurality of heating modules (HM1, HM2) each having one or more heating elements are arranged along the optical fiber 10, and the amount of heat applied to the optical fiber 10 by each of the heating elements of each heating module is calculated. By changing and combining variously, it is possible to create a specific polarization state in which an ultrashort pulse laser is generated.

In this case, preferably, some of the plurality of heating modules (HM1) are installed in the optical path in front of the polarizing filter 70, and some of the heating modules (HM2) are installed in the optical path in the rear of the polarizing filter 70 to adjust the polarization state. I can. In each heating module, at least one heating element is configured to be disposed along the optical fiber 10, and the number and installation position of the heating elements provided in each heating module may vary according to specific embodiments.

Now, various exemplary configurations of the first heating module HM1 will be described with reference to FIGS. 3 to 5. The configuration of the first heating module HM1 described below may be applied to the second heating module HM2 in the same or similar manner.

FIG. 3 is a view showing a first heat generating module HM1 according to an exemplary embodiment. FIG. 3(a) is a cross-section in the longitudinal direction and FIG. 3(b) is a schematic cross-section in the width direction.

Referring to the drawings, the first heating module HM1 is disposed in the thermally conductive case 63. The thermally conductive case 63 may be, for example, a case of a metal or alloy component having thermal conductivity. The thermally conductive case 63 is configured to surround the optical fiber 10 for a predetermined length. In the illustrated embodiment, the first heat generating module HM1 includes two heat generating elements, that is, a heat generating element 631 of a first channel and a heat generating element 632 of a second channel. In this specification, "channel" is a term used to distinguish heating elements in which the electric signals of the applied power (voltage or current) are different from each other. For example, even when several heating elements are included in one channel, these heating elements are the same. Voltage or current is applied, and different voltages or currents are applied between the heating elements of different channels.

The heating elements 631 of the first channel are arranged along the optical fiber 10 in the thermal conductive case 63, and the heating elements 632 of the second channel are formed of the first channel along the length direction of the optical fiber 10. It is arranged to be spaced apart from the heating element 631. The heating elements 631 and 632 of each channel are electrically connected to the power supply unit 62 by separate conductors 635, respectively.

In one embodiment, the heat sink 64 may be attached to at least one surface of the thermally conductive case 63. For precise polarization control, it is necessary to prevent the optical fiber 10 from being affected by external heat other than the heating element. Therefore, in order to prevent the heat accumulated inside the thermally conductive case 63 from affecting the optical fiber 10, a heat sink 64 is attached to at least one side of the thermally conductive case 63 to prevent the heat of the thermally conductive case 63. Can be configured to release quickly to the outside.

The length of each of the heating elements 631 and 632 is not particularly limited. In general, when the length of the heating element is longer, the length of the phase delay becomes longer, so that a small current can cause a lot of phase change, and when the length of the heating element is short, the phase delay is relatively small, so a larger current is required. Therefore, in order to reduce the amount of current, it is advantageous to configure the heating element long. However, in this case, since heat is applied to the optical fiber 10 over a long distance, the physical length of the optical fiber 10 expands, which may interfere with the phase delay or polarization state control. I can. Therefore, it is desirable to appropriately set the length of the heating element according to the specific embodiment, such as the material of the optical fiber or the size of the power to be applied.

FIG. 4 is a diagram illustrating a first heat generating module HM1 according to an alternative embodiment. FIG. 4(a) is a cross-section in the longitudinal direction and FIG. 4(b) schematically shows a cross-section in the width direction.

Referring to the drawings, a first heating module HM1 according to an alternative embodiment includes a heating element 631 of a first channel and a heating element 632 of a second channel in a thermal conductive case 63, and at least one It is the same as that of FIG. 3 in that the heat sink 64 is attached to the side, except that in the embodiment of FIG. 4, the heating element of each channel is composed of a pair of heating elements.

That is, in FIG. 4, the heating element 631 of the first channel is a pair of heating elements arranged side by side along the optical fiber 10 at a position symmetrical in the first radial direction around the optical fiber 10 in the thermal conductive case ( 631a, 631b). The heating element 632 of the second channel is disposed adjacent to the first heating element 631 along the longitudinal direction of the optical fiber 10, and, like the heating element 631 of the first channel, in a thermally conductive case. It is composed of a pair of heating elements arranged side by side along the optical fiber 10 at a position symmetrical in the first radial direction around the optical fiber 10.

In this way, when the heating elements of each channel are composed of a pair of heating elements arranged one at a position symmetrical in the radial direction with respect to the optical fiber 10, the refractive index is changed equally along the radial direction. That is, since the refractive index changes equally on the same axis in the radial direction, there is an advantage in that the change in polarization state can be quantitatively analyzed and controlled.

5 is a view for explaining a first heating module HM1 according to another alternative embodiment. FIG. 5(a) is a cross-section in the longitudinal direction, and FIGS. 5(b) and 5(c) are respectively shown in FIG. 5( The cross-section in the width direction when cut along the lines A-A' and B-B' in a) is schematically shown.

Referring to the drawings, the first heating module HM1 of FIG. 5 includes a pair of heating elements 631 of a first channel and a pair of heating elements 632 of a second channel in a thermally conductive case 63. It is the same as the configuration of FIG. 4 in that the heat sink 64 is attached to at least one side. However, in the embodiment of FIG. 5, the radial arrangement direction of the pair of heating elements 631 of the first channel and the radial arrangement direction of the pair of heating elements 632 of the second channel are different from the embodiment of FIG. There is a difference.

That is, in FIG. 5, the heating elements 631 of the first channel are a pair of heating elements arranged side by side along the optical fiber 10 at a position symmetrical in the first radial direction around the optical fiber 10 in the thermal conductive case ( 631a, 631b). The heating element 632 of the second channel is disposed adjacent to the first heating element 631 along the longitudinal direction of the optical fiber 10, and in the first radial direction around the optical fiber 10 in the thermal conductive case. It is composed of a pair of heating elements (632a, 632b) arranged side by side along the optical fiber 10 at a position symmetrical in the second radial direction perpendicular to the.

In this way, when the heating element 631 of the first channel and the heating element 632 of the second channel are arranged in different radial directions with respect to the optical fiber 10, there is an advantage of creating more diverse polarization states. When all the heating elements of all channels are arranged in the same radial direction, it is difficult to find a polarization condition for generating an ultrashort pulse laser because the polarization state changes along a limited path on the Poincare sphere representing the polarization state. There is a problem in that a relatively higher power (voltage or current) must be applied to each heating element in order to find a polarization condition. However, when the heating elements of the two channels are arranged vertically with each other in the radial direction as in the embodiment of FIG. 5, various polarization states can be created, so that the optimum polarization conditions for ultrashort pulse laser generation can be found, and relatively less power can be used. There are also advantages to using it.

In an exemplary embodiment, a process of finding an optimal pulse generation condition may be automated while changing an electric signal applied to a heating element of a plurality of channels until a pulse is generated. The pulse detection unit 90 detects a pulse from the laser output output from the coupler 80 and transmits it to the control unit 61, and the control unit 61 applies it to the heating element until a condition (mode lock) is achieved in which the pulse is generated. When an ultra-short pulse is detected while changing the losing current or voltage, the voltage or current applied to each heating element is stored as a voltage or current that satisfies the mode lock condition and maintains this voltage or current. In addition, when the mode lock condition of the laser is changed due to changes in the internal or external environment, the controller 61 may repeat the process of finding the mode lock condition described above again to find a new mode lock condition and generate the ultrashort pulse laser.

In this regard, FIG. 6 is a flowchart of an exemplary method of generating an ultrashort pulse laser by heating a heating element according to an exemplary embodiment.

Referring to the drawings, first, in step S110, a period of an electric signal to be applied to each channel is set. The period of the electric signal is set differently for each channel, and an example of such an electric signal is shown in FIG. 7. When the total number of heating element channels of the pulse generator 60 is four, as shown in Fig. 7(a), electric signals in the form of four triangular waves having different time periods may be applied to the heating elements of each channel. Since the time periods are different, many combinations of electric signal application conditions are created, so that various polarization states can be created.

The electric signal is not limited to a triangular wave type, and for example, a sine wave type electric signal may be applied. However, in the case of a sine wave, since the slope of the waveform is not constant over time, it is difficult to control polarization because the increase or decrease of heat generated by the heating element is not constant. . In an embodiment, the amplitude (V_2π) of the electric signal to be applied to each channel may be set to a voltage value such that a phase difference between two polarization components of light generated by heat generated by the electric signal is at least 2π or more.

In this case, preferably, each of the electric signals of each triangular waveform is formed of a waveform that increases by a unit step at every minute time interval. For example, Fig. 7(b) is an enlarged schematic view of the first channel applied electric signal V1 of Fig. 7(a) (however, the X-axis and Y in Figs. 7(a) and 7(b)). The axial scale is different), and as shown in Fig. 7(b), the electric signal V1 has a predetermined resolution (the Y-axis interval of each step) and may be composed of a waveform that increases by one step at a predetermined time interval. In one embodiment, the predetermined resolution (voltage interval of one step) may be a voltage interval when the phase difference between two polarization components of light generated by application of an electric signal is less than 2π/36 rad. . On the other hand, the electric signals (V2 to V4) applied to the second to fourth channels are not shown, but similar to Fig. 7(b), these electric signals are also composed of electric signals of step waveforms that increase by one step at predetermined time intervals. I will understand. However, at this time, since the slopes of the electric signals V1 to V4 are different from each other, it will be understood that the voltage increment (resolution) of one step of the electric signals V1 to V4 is different from each other.

Referring back to FIG. 6, after setting and storing the electric signals V1 to V4 to be applied to each channel as above, the pump light source 20 is turned on to generate a laser (S120). After that, the electric signal value of each channel set in the above step (S110) is read and the electric signal is simultaneously applied to each channel. That is, the first to fourth electrical signals (V1 to V4) of Fig. 7(a) are applied to each channel of the first to fourth channels, respectively, and at a predetermined time (e.g., voltage in the electric signal of Fig. 7(b)). It is determined whether a pulsed laser is generated (S140), and if the pulse is not generated, the size of each electric signal is increased by one step at each predetermined time interval (S160) and stored (S150). ) Repeat the operation of applying the electric signal to each channel again (S130) with the increased value.

If a pulse is generated, it is determined that the mode lock condition is satisfied, and the applied signal (voltage value) of each channel is stored at this time (S150), and thereafter, an electric signal is applied to each channel with this stored voltage value (S130). It maintains the mode lock condition and can continuously generate pulsed lasers.

8 is a flowchart of a method of generating an ultrashort pulse laser by heating a heating element according to another embodiment.

Referring to the drawings, in step S210, a period of an electric signal to be applied to each channel is set (S220), the pump light source 20 is turned on, and an electric signal is applied to each channel (S230), and this step is shown in FIG. Since it is the same as or similar to steps S110 to S130, a description will be omitted.

At this time, the electrical signals of all channels can be initially set to 0 in step S230, and the first voltage signal V_ch1 is increased by one step from 0 to a predetermined peak voltage V_2π in the heating element of the first channel. It is determined whether or not a pulsed laser is generated while applying (a first determination step of circulating S240, S250, S251, S290, S230, and S240).

If the pulsed laser is not generated in the first determination step, a second voltage signal V_ch2 is applied to the heating element of the second channel from 0 to the peak voltage V_2π in increments of a predetermined step. The entire first determination step is repeated for every step increase of (S240, S260, S261, S290, S230, S240).

If the pulsed laser is not generated even in the second determination step, a third voltage signal V_ch3 is applied to the heating element of the third channel from 0 to the peak voltage V_2π by increasing a predetermined step voltage. The entire second determination step is repeated every time the voltage signal increases by every step (a third determination step circulating S240, S270, S271, S290, S230, and S240).

And if the pulsed laser is not generated even in the third determination step, the fourth voltage signal V_ch4 is applied to the heating element of the fourth channel from 0 to the peak voltage V_2π in increments of a predetermined step. The entire third determination step is repeated every time the voltage signal is increased by every step (a fourth determination step circulating S240, S280, S281, S290, S230, S240).

If a pulse is generated while performing the first to fourth determination steps, it is determined that the mode lock condition is satisfied, and the applied signal (voltage value) of each channel at this time is stored (S290), and the stored voltage value thereafter. As an electrical signal is applied to each channel (S230), the mode lock condition is maintained and pulsed lasers are continuously generated.

Now, various modifications of the ultrashort pulse laser generating apparatus will be described with reference to FIGS. 9 to 11.

9 shows an apparatus for generating a pulsed laser according to an alternative embodiment of FIG. 1. Compared with FIG. 1, the laser generating apparatus of FIG. 9 replaced the polarizing filter 70 with a polarizing beam splitter (PBS) 75, and additionally installed a saturation absorber 100 disposed on the optical path.

The PBS 75 is an optical device that transmits or reflects a pulsed laser according to a polarization state. Therefore, depending on the polarization state of the pulsed laser, some of them pass through the PBS 75 and continue to circulate the optical fiber 10, and some of them can be reflected from the PBS 75 and sent out as laser output. Can be utilized according to.

Meanwhile, the saturable absorber (SA) 100 is an optical device capable of inducing pulse generation to facilitate pulse generation. The saturable absorber 100 is made of, for example, a semiconductor saturable absorber, carbon nanotubes, graphene, etc., and when light passes through the saturable absorber 100, light around the peak value of the pulse passes through. Both side areas of the pulse absorb and block. Therefore, whenever the laser light continuously passes through the saturation absorber 100, the pulse width gradually decreases, thereby generating a femtosecond-level pulse laser.

Meanwhile, it is not necessary to use the PBS 75 and the saturated absorber 100 at the same time in FIG. 9, for example, only the saturated absorber 100 may be added to the laser generating device of FIG. 1, or a polarization filter in the laser generating device of FIG. It goes without saying that a configuration simply replacing 70 with PBS 75 is also possible.

Fig. 10 shows an apparatus for generating a pulsed laser according to another alternative embodiment of Fig. 1; Compared with FIG. 1, the laser generating device of FIG. 10 further includes a delay line 110, a frequency comparator 120, and a control unit 130.

The delay line 110 may adjust the length of the optical path and may be disposed between the coupler 80 and the light shield 50, for example. The frequency comparator 120 receives the pulse generation frequency detected by the pulse detection unit 90 and compares it with a preset reference frequency, and the control unit 1130 makes the pulse generation frequency of the pulsed laser coincide with the reference frequency according to the comparison result. By controlling the delay line 110, the length of the optical path is adjusted.

In general, in a ring cavity type laser generator, a pulsed laser generates pulses with a period of c/L, where c is the speed of light and L is the total length of the ring cavity. However, the pulse generation period may change due to changes in the surrounding environment or optical elements. If the delay line 110 is adjusted to match the pulse generation frequency of the pulsed laser output as above to a preset reference frequency, the pulse is always pulsed at a constant pulse generation period. It becomes possible to create a laser.

11 shows an apparatus for generating a pulsed laser according to another alternative embodiment of the present invention.

1, 9, and 10 are a ring cavity type optical fiber laser generating device, but the mode locking part 60 of the present invention is also used in a linear cavity type optical fiber laser generating device as shown in FIG. Applicable, Fig. 11 schematically shows an exemplary laser generating device of this linear cavity type.

Referring to the drawings, the optical fiber 10, the pump light source 20, the WDM 30, the gain medium 40, the mode locking part 60, and the polarization filter 70 constituting the laser generating device of FIG. 11 are Since the components 10, 20, 30, 40, 60, and 70 of FIG. 1 correspond equally to each other, the same reference numerals are used, and a description thereof will be omitted.

In the linear type of FIG. 11, laser light is amplified while being reflected by reflectors 150 and 160 at both ends of the optical fiber 10. The reflector 150 is installed at the first end of the optical fiber 10 and reflects light at a predetermined reflectance. The second reflector 160 is installed at the second end of the optical fiber 10 and may selectively reflect or pass light.

Similar to the embodiment of FIG. 1, the mode locking unit 60 includes a plurality of heat generating modules and may be installed at the front and rear ends of the polarizing filter 70, respectively. In addition, although not shown in Fig. 11, as in Fig. 1, the mode lock unit 60 further includes a pulse detection unit (90 in Fig. 1) and a control unit (60 in Fig. 1) for detecting a pulse from the laser output. It is possible to control to apply an electric signal while varying to the heating element of each channel until it is generated.

In this case, each heat generating module of the mode locking unit 60 may have the configuration shown in FIGS. 3 to 5, and the method of FIG. 6 or FIG. 8 may be used as a specific method of generating a pulsed laser.

As described above, those of ordinary skill in the field to which the present invention pertains can understand that various modifications and variations are possible from the description of this specification. Therefore, the scope of the present invention is limited to the described embodiments and should not be defined, and should be defined by the claims to be described later, as well as those equivalent to the claims.

10: optical fiber 20: pump light source
30: WDM 40: gain medium
50: light shield 60: mode lock
70: polarization filter 80: coupler
90: pulse detection unit 100: saturated absorber
110: delay line 120: frequency comparator
130: control unit

Claims (15)

As an ultra-short pulse laser generator using a heating element,
A gain medium 40 made of an active optical fiber;
An optical fiber 10 connecting the first end and the second end of the gain medium to form an optical path;
A pump light source 20 providing a pump light toward the second end of the gain medium;
A light shield (50) installed on the first end side of the gain medium of the optical path;
An optical device installed in the optical path and allowing only light of one polarization state to pass through; And
Including; a mode locking unit 60 disposed adjacent to the optical fiber 10 and including a plurality of heating modules each comprising one or more heating elements and a power supply for applying power to each heating element of each heating module. Ultra-short pulse laser generating device characterized by. The method of claim 1,
The plurality of heating modules include a first heating module HM1 arranged along the optical fiber 10 at the front end of the optical device and a second heating module HM2 arranged along the optical fiber 10 at the rear end of the optical device. Ultra-short pulse laser generator comprising a. The method of claim 2,
The first heating module HM1 is disposed in a thermally conductive case 63 surrounding the optical fiber 10 for a predetermined length,
The first heating module HM1,
A pair of first heating elements 631 arranged side by side along the optical fiber 10 at a position symmetrical in the first radial direction around the optical fiber 10 in the thermal conductive case; And
The optical fiber 10 is disposed adjacent to the first heating element 631 along the longitudinal direction of the optical fiber 10, and the optical fiber 10 is symmetrical in the first radial direction around the optical fiber 10 in the thermal conductive case. A pair of second heating elements (632) arranged side by side along the; ultra-short pulse laser generating apparatus comprising a. The method of claim 2,
The first heating module HM1 is disposed in a thermally conductive case 63 surrounding the optical fiber 10 for a predetermined length,
The first heating module HM1,
A pair of first heating elements 631 arranged side by side along the optical fiber 10 at a position symmetrical in the first radial direction around the optical fiber 10 in the thermal conductive case; And
It is disposed adjacent to the first heating element 631 along the longitudinal direction of the optical fiber 10, and is symmetrical in a second radial direction perpendicular to the first radial direction around the optical fiber 10 in the thermal conductive case. A second heating element (632) arranged side by side along the optical fiber (10) at the position; Ultrashort pulse laser generating apparatus comprising a. The method of claim 2,
The mode locking unit 60 is a control unit that generates a control signal for applying voltages of different time periods to each of the heating elements of the plurality of heating modules based on the output laser output from the optical fiber 10 Including (61) further,
The mode locking unit,
Voltage signals having different time periods are simultaneously applied to each of the plurality of heating elements (S130), and at each predetermined time, it is determined whether a pulsed laser is generated (S140), and the voltage at this time when the pulsed laser is generated And storing each voltage value of the signal (S150), and applying a voltage signal to each of the plurality of heating elements with the stored voltage value. The method of claim 2,
The mode locking unit 60 further includes a control unit 61 for generating a control signal for applying different voltages to each of the plurality of heating elements based on the output laser output from the optical fiber 10, and ,
The mode locking unit,
The first heating element is increased by a predetermined step voltage from 0 to a predetermined peak voltage (V_2π), and the first voltage signal is applied to determine whether or not a pulse laser is generated (step 1),
If there is no pulse laser generation, the second heating element is increased by a predetermined step voltage from 0 to the peak voltage, and a second voltage signal is applied, but the step 1 is repeated with each increase (step 2),
If there is no pulse laser generation, the third heating element is increased by a predetermined step voltage from 0 to the peak voltage, and a third voltage signal is applied, but the step 2 is repeated with each increase (step 3),
When there is no pulse laser generation, the fourth heating element is increased by a predetermined step voltage from 0 to the peak voltage, and the fourth voltage signal is applied, but the third step is repeated (step 4) with each increase. Pulse laser generator. The method of claim 2,
A saturation absorber installed in the optical path, wherein the saturation absorber comprises at least one of a semiconductor saturation absorber, a carbon nanotube, and graphene. The method of claim 2,
Ultrashort pulse laser generator, characterized in that the optical element is one of a polarization filter (70) or a polarization beam splitter (PBS) (75). The method of claim 2,
A delay line 110 installed in the optical path;
A frequency comparator 120 comparing a pulse generation frequency of the pulsed laser output from the optical fiber 10 with a preset reference frequency; And
A control unit 130 for controlling the delay line 110 so that the pulse generation frequency of the pulsed laser and the reference frequency coincide based on the comparison result of the frequency comparator. As an ultra-short pulse laser generator using a heating element,
An optical fiber 10 having a first end and a second end and forming a linear optical path;
A gain medium 40 disposed on the optical path and made of an active optical fiber;
A pump light source 20 providing a pump light to the first end side of the gain medium;
A first reflector 150 installed at the first end of the optical fiber and reflecting light at a predetermined reflectance;
A second reflector 160 installed at the second end of the optical fiber and selectively reflecting or passing light;
An optical device installed in the optical path and allowing only light of one polarization state to pass through; And
Including; a mode locking unit 60 disposed adjacent to the optical fiber 10 and including a plurality of heating modules each comprising one or more heating elements and a power supply for applying power to each heating element of each heating module. Ultra-short pulse laser generating device characterized by. The method of claim 10,
The plurality of heat generating modules include a first heat generating module arranged at a front end of the optical element on an optical path and a second heat generating module arranged at a rear end of the optical element. The method of claim 11,
The first heating module is disposed in a thermally conductive case 63 surrounding the optical fiber 10 for a predetermined length,
The first heating module,
A pair of first heating elements arranged side by side along the optical fiber 10 at a position symmetrical in the first radial direction around the optical fiber 10 in the thermal conductive case; And
The optical fiber 10 is disposed adjacent to the first heating element 631 along the longitudinal direction of the optical fiber 10, and the optical fiber 10 is symmetrical in the first radial direction around the optical fiber 10 in the thermal conductive case. Ultra-short pulse laser generating apparatus comprising a; a pair of second heating elements arranged side by side along the line. The method of claim 11,
The first heating module is disposed in a thermally conductive case 63 surrounding the optical fiber 10 for a predetermined length,
The first heating module,
A pair of first heating elements arranged side by side along the optical fiber 10 at a position symmetrical in the first radial direction around the optical fiber 10 in the thermal conductive case; And
A position adjacent to the first heating element 631 along the longitudinal direction of the optical fiber 10 and symmetrical in a second radial direction perpendicular to the first direction around the optical fiber 10 in the thermal conductive case In the ultra-short pulse laser generating apparatus comprising a; a pair of second heating elements arranged side by side along the optical fiber (10). The method of claim 11,
The mode locking unit 60 is a control unit that generates a control signal for applying voltages of different time periods to each of the heating elements of the plurality of heating modules based on the output laser output from the optical fiber 10 Including (61) further,
The mode locking unit,
Voltage signals having different time periods are simultaneously applied to each of the plurality of heating elements (S130), and at each predetermined time, it is determined whether a pulsed laser is generated (S140), and the voltage at this time when the pulsed laser is generated And storing each voltage value of the signal (S150), and applying a voltage signal to each of the plurality of heating elements with the stored voltage value. The method of claim 11,
The mode locking unit 60 further includes a control unit 61 for generating a control signal for applying different voltages to each of the plurality of heating elements based on the output laser output from the optical fiber 10, and ,
The mode locking unit,
The first heating element is increased by a predetermined step voltage from 0 to a predetermined peak voltage (V_2π), and the first voltage signal is applied to determine whether or not a pulse laser is generated (step 1),
If there is no pulse laser generation, the second heating element is increased by a predetermined step voltage from 0 to the peak voltage, and a second voltage signal is applied, but the step 1 is repeated with each increase (step 2),
If there is no pulse laser generation, the third heating element is increased by a predetermined step voltage from 0 to the peak voltage, and a third voltage signal is applied, but the step 2 is repeated with each increase (step 3),
When there is no pulse laser generation, the fourth heating element is increased by a predetermined step voltage from 0 to the peak voltage, and the fourth voltage signal is applied, but the third step is repeated (step 4) with each increase. Pulse laser generator.

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