TWI620383B - Double polarization mode-locked laser system, gain module thereof and control method thereof - Google Patents

Abstract

The present invention provides a dual-polarization mode-locked laser system comprising an excitation light source for generating an excitation light; a mode-locking cavity adjacent to the excitation light source, and a gain medium disposed in the cavity and having an optical axis, Thereby causing the excitation light to enter the gain medium and generating an output of a self-mode-locked laser; and a stress applying device disposed in the resonant cavity adjacent to the gain medium and applying a heat to the gain medium Or stress, causing the gain medium to produce a birefringence phenomenon to produce a laser output having a bi-orthogonal polarization.

Description

Dual polarization mode-locked laser system, gain module thereof and control method thereof

This case relates to lasers, especially a dual polarization mode-locked laser.

Please refer to FIG. 1 , which is a schematic diagram of a conventional dual polarization laser. There is disclosed a resonant cavity 1 having a total reflection mirror 10 at one end and a partial reflection output mirror 13 opposite the total reflection mirror 10 at the other end. An optical axis A is formed between the total reflection mirror 10 and the partial reflection output mirror 13, and after the laser light gains to the required energy, the partial reflection output mirror 13 causes the laser light to be emitted from the resonance cavity 1. In order to achieve the effect of dual polarization, the conventional technique is generally achieved by two series of gain media, that is, the first gain medium 11 and the second gain medium 12, the polarization directions of which are perpendicular. If the dual polarization system is required to be outputted in a mode-locked mode, it is more necessary to strictly control the size of the first gain medium 11, the second gain medium 12, the material type, the placement position, the excitation light source, the size of the resonant cavity, and the like. Many variables are waiting. And usually the laser modes of the first and second gain media are different, so when the clamping effect is required, the distance between the two-sided mirrors in the resonant cavity must be the least common multiple of the respective half wavelengths, which leads to The resonant cavity is bulky and costly. The mode-locked laser output produced in Figure 1 is self-mode-locked. The (self-mode-locked) approach is achieved, and active-passive components, such as semiconductor saturable absorbers, can be used, but the architecture is more complex. Therefore, based on the above various inconvenient situations, there is a great need for a dual polarization mode-locked laser that can simplify the control of each component in the resonant cavity, a gain module used therein, a dual polarization control device, and The control method is to minimize the variation in the resonant cavity as much as possible, or to simplify the control method of the components in the resonant cavity.

For this reason, the applicant invented the "dual polarization mode-locked laser system and its gain module and its control method" in view of the lack of the prior art to improve the lack of the above-mentioned conventional means.

The object of the present invention is to create a new dual-polarization mode-locked laser device, system, method of generating the same, and a gain module applied thereto, by which the dual polarization can be produced using only one gain medium. The characteristic mode-locked laser does not need to be complicated by the use of more than one gain medium, such as the size of the gain medium, the type of material, the position of the excitation, the selection of the excitation source, the size of the cavity, etc., The use of the present invention makes it easy to obtain the output of a dual polarization mode-locked laser, reducing the cost of dual-polarization mode-locked lasers and, in turn, promoting the application of dual-polarization mode-locked lasers.

In order to achieve the above object, the present invention provides a dual polarization mode-locked laser system comprising: an excitation light source, which may be, but is not limited to, a mine The diode module generates an excitation light; a resonant cavity that can generate an output of the self-mode-locked laser is adjacent to the excitation light source module, and a gain medium is disposed in the resonant cavity and has an optical axis. Thereby causing excitation light to enter the gain medium; and a heat or stress applying device disposed in the resonant cavity adjacent to the gain medium and applying a heat or stress to the gain medium to cause the gain medium to generate double The phenomenon of refraction to produce a laser output with bi-orthogonal polarization.

In order to achieve the above object, the present invention further provides a gain module for a dual polarization mode-locked laser device, comprising: a gain medium having an optical axis; and a heat or stress applying device adjacent to the gain The medium is applied with a heat or stress to the gain medium to cause birefringence.

In order to achieve the above object, the present invention further provides a dual polarization control device for a laser gain module, comprising: a gain medium; and a positioning device for positioning the gain medium in the laser gain module; And a heat or stress applying device for applying a specific heat or stress to the gain medium to generate a specific birefringence phenomenon after passing through the gain medium.

In order to achieve the above object, the present invention further provides a method for controlling a dual polarized laser gain module, comprising: providing a gain medium; positioning the gain medium in the laser gain module; and the gain The medium imparts a specific heat or stress that produces a specific birefringence phenomenon as soon as a light passes through the gain medium.

1‧‧‧Resonance cavity

10‧‧‧ total reflection mirror

11‧‧‧First gain medium

12‧‧‧second gain medium

13‧‧‧Partial reflection output mirror

2‧‧‧Birefringent crystal

3‧‧‧gain medium

4‧‧‧Thermal application device

5‧‧‧Mechanical stress applying device, force applying mechanism

50‧‧‧ Fixed Department

50a‧‧‧First fixed department

50b‧‧‧Second fixed department

51‧‧‧ Force Department

51a‧‧‧First Force Department

51b‧‧‧Second Force Department

6‧‧‧Excitation source

7‧‧‧Coupling lens

8‧‧‧Main beam splitter

9‧‧‧polar polarizer

91‧‧‧First oscilloscope

92‧‧‧Second oscilloscope

A‧‧‧ optical axis

L‧‧‧Light

PM‧‧‧Power Meter

n _o ‧‧‧ ordinary light

n _e ‧‧‧ unusual light

1 is a schematic diagram of a conventional dual polarization mode-locked laser; FIG. 2 is a schematic diagram of a birefringence principle; FIG. 3 is a schematic diagram of a dual polarization crystal used as a gain medium; FIG. 4 is a schematic view of an embodiment of the present invention; 5 is a schematic view of another embodiment of the present invention; FIG. 6 is a schematic view of a system according to the present invention; FIG. 7 is a schematic view of an embodiment of mechanical stress application of the present invention; and FIG. 8 is another embodiment of the mechanical stress applying device of the present invention. FIG. 9 is a diagram showing relationship between excitation power and difference frequency according to the present invention; FIG. 10 is a diagram showing relationship between mechanical stress and difference frequency according to the present invention; FIG. 11 is a diagram showing heat and difference of the present invention; A relationship diagram between frequencies; and FIG. 12(A) and FIG. 12(B) are schematic diagrams showing a difference in repetition rate of dipolarized light of the present invention.

The following describes the embodiments of the "dual polarization mode-locked laser system and its gain module and its control method" in the present case. Please refer to the drawings, but the actual configuration and the method adopted do not have to be completely consistent with the method. In the description, those skilled in the art can make various changes and modifications without departing from the actual spirit and scope of the present invention.

Please refer to Figure 2 for a schematic diagram of the birefringence principle. It discloses a birefringent crystal 2, when a light L having a random polarization on the left side is incident on the crystal 2 at a non-perpendicular angle, the two polarization directions of light originally coincident (one is left and right polarization, and the other is up and down polarization). It will be separated by the different refractive indices of the two polarization directions. As shown on the right side of the crystal 2, the left and right polarized rays leave the crystal 2 according to the original path, so it is called ordinary light n _o , and the upper and lower polarized rays are The slightly lower path leaves the crystal 2, so it is called the extraordinary light n _e . At this point, there is a preliminary understanding of the effects of birefringence and dual polarization.

Please refer to FIG. 3, which is a schematic diagram of a dual polarization crystal used as a gain medium. The light passing through the dual-polarization gain medium 3 is outputted on the a-axis. Since the cross-section corresponding to the a-cut is the b-axis and the c-axis, and the two axes are unequal, the output light will be The phenomenon of polarization. If the output along the a-axis is, the polarization in a certain direction is particularly strong; but if it is output along the c-axis (c-cut), it is a random polarization. Therefore, when an isotropic crystal or a double polarizing medium 3 using c-cut is used as the gain medium, the output laser light is not polarized but is presented in a random polarization manner.

Please refer to Figure 4 and Figure 5. 4 is a schematic view of an embodiment of the present invention; and FIG. 5 is a schematic view of another embodiment of the present invention. Due to machine Mechanical stress or thermal stress can cause the isotropic crystal or c-cut direction crystal to be changed from the original random polarization to produce birefringence and double polarization, which means that two orthogonally polarized outputs are produced, as shown in Figure 2. The output shown. 4 and FIG. 5 respectively disclose a gain module including a resonant cavity 1 having a front mirror 10 at one end and a partial reflection output mirror 13 at the opposite end with a gain medium therebetween. 3, and the laser light is gradually increased in the gain medium 3 until the required value is emitted from the partial reflection output mirror 13. However, unlike the conventional technique shown in Fig. 1, the present invention has a heat or stress applying device, which is a heat applying device 4 in Fig. 4; and a mechanical stress applying device 5 in Fig. 5. 4, since the gain medium 3 generates heat during operation, cooling is required. Therefore, the heat application device 4 of the present invention also uses a cooling device as a main application example, and the gain medium 3 is cooled by a housing (Fig. It is not disclosed in the coating, and the effect of air cooling is achieved by using a blower such as a blower. Of course, the cooling effect can also be achieved by using liquid cooling, such as coating the gain medium 3 with a cooling casing (not shown), or placing the gain medium 3 in a cooling pool (not shown). In both, the effect of liquid cooling can be achieved. For the difference frequency relationship between the cooling temperature and the dual polarization and birefringence, please refer to FIG. 11 , which is a relationship diagram between the heat and the difference frequency of the present invention, wherein the transmission temperature control, the birefringence of the isotropic crystal, and the double polarization are seen. The phenomenon is controllable. For example, in some embodiments, as shown in Figure 11, the lower the cooling temperature, the higher the difference frequency, and there is almost no difference frequency phenomenon occurring at about 27.5 degrees Celsius. And between 22.5 degrees Celsius and 35 degrees, there is almost the same difference frequency. Therefore, it is possible to increase or decrease the temperature to achieve the difference frequency value desired by the user. However, the relationship between heat and difference frequency is positive or negative. The characteristics of the medium are not only those shown in Figure 11.

Please refer to FIG. 5, which is a schematic diagram of another embodiment of the present invention. The stress applying device disclosed therein is a mechanical stress applying device, which comprises a fixing portion 50, a urging portion 51, and a urging mechanism 5, and the fixing portion 50 and the urging portion 51 are disposed face to face, and the middle portion That is, the gain medium 3 is placed, and the fixing portion 50 is usually a body on which the gain medium 3 is placed. The urging mechanism 5 provides a thrust for pushing the urging portion 51 to move toward the fixing portion 50. It can be said that the urging portion 51 is biased in a direction toward the fixing portion 50, and the urging portion 51 is biased. The medium 3 is subjected to pressure. Therefore, the gain medium 3 generates a function of dual polarization and birefringence, and further outputs double-polarized laser light. Please refer to FIG. 10 for the difference frequency relationship between the application of stress and the dual polarization and birefringence, which is a relationship between the mechanical stress and the difference frequency of the present invention. It can be seen that if the rotary motion is changed into a linear motion by a screw, the force is calculated by the torque, and the higher the torque and the higher the frequency difference, the visible force is shown in FIG. The control, the birefringence of the isotropic crystal, and the double polarization phenomenon are controllable. Through the increase or decrease of the torque to achieve the difference frequency value that the user wants. In addition, in the embodiment of FIG. 5 or FIG. 4, an active-passive mode-locking component may be added to assist in generating a self-mode-locking laser, or a self-locking mode ray may be directly outputted by replacing the resonant cavity with the active-passive mode-locking component. Shoot.

Please refer to FIG. 6, which is a schematic diagram of the system of the present invention. In addition to the resonant cavity 1 and the gain medium 3 therein, an excitation light source 6 is included, which may be, but is not limited to, a diode laser generator as a power source, and the excitation light emitted by the excitation light source 6 may be It is not limited to pass through the coupling lens 7 in the gain medium 3. After the gain medium 3 generates a gain, a laser is generated in the resonant cavity 1, An optical axis A (refer to FIG. 1) is formed and output through the partially reflective output coupling mirror 13. The laser light is received by a power meter PM through a portion of a main beam splitter 8 to calculate the output power value, and the other portion of the laser light is passed through the polarizing beam splitter 9 to have a dual polarization generated by the gain medium 3. The laser light is separated according to the respective polarization directions, wherein the laser light of one polarization direction is incident on a first oscilloscope 91, and the laser light of the other polarization direction is incident on a second oscilloscope 92, which is usually a photosensitive element. As the main sensing element. Regarding the difference in the repetition rate of the two polarized lights, please refer to FIG. 12(A) and FIG. 12(B), which are schematic diagrams showing the difference in the repetition rate of the dipolarized light of the present invention. Fig. 12(A) shows polarization of forty-five degrees, and Fig. 12(B) shows polarization of one to five degrees. Both of the resolutions shown in the two figures are 100 ns/div, and the peak spacing in both figures is 3MHz. It can be seen that when two orthogonal polarized lights are at the same abscissa position (ie, at the same time point), the positions of the peaks are different, that is, a phenomenon of a beat frequency (also called a beat frequency) is generated. It can be seen that the present invention is characterized in that, since the resonant cavity used has a clamping effect, and the polarized light of the two polarizations comes from the same gain medium 3, the other characteristics are almost identical except that the repetition rate is slightly different. Therefore, the invention can be used to produce a dual-polarized laser output which is very simple, easy, fast and cost-effective, and can be applied to a large number of occasions. The gain medium 3 may be yttrium aluminum garnet (Nd: YAG).

Please refer to FIG. 7 and FIG. 8. FIG. 7 is a schematic view showing an embodiment of mechanical stress application according to the present invention; and FIG. 8 is a schematic view showing another embodiment of the mechanical stress applying device of the present invention. When the gain medium 3 is fixed in the resonant cavity (refer to FIG. 6) through a positioning device (not shown), it is used. A stress applying device (50a, 51a of Fig. 7; 50b, 51b of Fig. 8) applies mechanical stress to the gain medium 3 as uniformly as possible. In FIG. 7, the stress applying device is a first fixing portion 50a that cooperates with a first urging portion 51a, and the two L-shaped members that are substantially positive and negative with the respective recesses sandwich the gain medium 3 In the middle, the urging mechanism 5 (please refer to FIG. 5) biases the first urging portion 51a in the horizontal direction, and urges the first urging portion 51a to the gain medium 3 by pushing it. The force-applying mechanism can appropriately increase or decrease the pushing force. In FIG. 8, the stress applying device is a second fixing portion 50b and a second urging portion 51b, both of which have a V-shaped recess to sandwich the gain medium 3, and the urging mechanism 5 (please Referring to FIG. 5), the second urging portion 51b is biased in a vertical direction, and the second urging portion 51b is biased to the gain medium 3 by pushing, and the urging mechanism can be appropriately increased or decreased. Push the power. Further, in FIG. 7, the biasing force of the first urging portion 51a is parallel to the upper and lower sides of the gain medium 3, and in FIG. 8, the urging force of the second urging portion 51b is parallel to the pair of the gain medium 3. In the angular direction, the polarization angles of the dual polarizations generated by the two are also different, but the polarization angles of the dual polarizations of FIG. 7 or FIG. 8 are all orthogonal. In addition, the drawing planes of Figs. 7 and 8 are exactly opposite to the c-axis of the gain medium 3 (please refer to Fig. 3), and Fig. 5 can be said to be drawn directly opposite the a-axis or the b-axis, thereby showing that when mechanically When the stress is applied to the gain medium 3, the direction of the force applied is at an angle to the optical axis A, which is usually ninety degrees. In addition, the stress applying device of FIG. 7 or FIG. 8 can also directly fix the gain medium 3 as a jig, however, this will cause troubles in the subsequent adjustment of the matching relationship between the stress and the dual polarization, that is, the subsequent stress adjustment may cause the clamping. If the force is too large or too small, too much will damage the gain medium. If it is too small, the gain medium may shake and the output will be unstable. Accordingly, the present invention suggests separating the means for positioning the gain medium from the means for applying stress to facilitate a good output of the dual polarized laser.

Please refer to FIG. 9 , which is a diagram showing the relationship between the excitation power and the difference frequency according to the present invention. It can be seen that the higher the excitation power, the higher the repetition rate of the output polarized light. The experimental results represented by the circles also show that the power dependence of the input and output is almost the same as that of the linear regression, so the excitation power and the output dual polarization repetition rate are linear positive correlation.

Please refer to FIG. 10, which is a diagram showing the relationship between mechanical stress and difference frequency of the present invention. The mechanical stress is transmitted through the torsion force. It can be seen that when the torque is increased, the difference frequency also increases.

Please refer to FIG. 11 , which is a diagram showing the relationship between heat and difference frequency of the present invention. The temperature can be, but is not limited to, effected by cooling, and as the cooling changes, the difference frequency changes. As for the relationship between the heat and the difference frequency is positive correlation or negative correlation, it depends on the characteristics of the gain medium, which is not only shown in FIG.

In summary, the "dual polarization mode-locked laser device and the gain module thereof and the control method thereof" of the present invention basically apply an external force to a gain medium of a mode-locked laser to generate a dual polarization. Laser output. In addition, the force is usually based on mechanical stress or thermal stress. Of course, the situation can be implemented at the same time, so that the effect of outputting the dual-polarized mode-locked laser can be achieved very simply, and of course, it can be replaced as shown in FIG. Conventional technology. Therefore, through the device of the invention, the mode locking of the double-polarized laser can be easily completed, the structure and assembly are not too fine, the volume is smaller than the conventional technology, and the overall cost is also reduced, so the application and popularization of the laser for the present invention. With great contribution.

Example:

A dual polarization mode-locked laser system comprising: an excitation light source to generate an excitation light; a self-mode-locking cavity adjacent to the excitation light source, wherein a gain medium is disposed in the resonant cavity and has an optical axis So that the excitation light enters the gain medium and produces an output of a self-mode-locked laser; and a heat or stress applying device disposed in the resonant cavity adjacent to the gain medium and applying the gain medium A heat or stress is applied to cause the gain medium to produce a birefringence phenomenon to produce a laser output having a bi-orthogonal polarization.

2. The system of embodiment 1 wherein the stress applying means is a clamp for holding the gain medium.

3. The system of embodiment 1, further comprising a sensing module, the sensing module further comprising: a polarization beam splitter, the laser output is divided according to a polarization direction a first polarized light and a second polarized light; a first photosensitive element for sensing the first polarized light; and a second photosensitive element for sensing the second polarized light.

4. The system of embodiment 1, wherein the output of the self-mode-locked laser can also incorporate or replace the resonant cavity with a master-passive mode-locking component.

5. A gain module for a dual polarization mode-locked laser device, comprising: a gain medium having an optical axis; and a heat or stress applying device adjacent to the gain medium and applying the gain medium Give a hot or Stress, 俾 causes the gain medium to produce birefringence.

6. The gain module of embodiment 5 wherein the heat or stress applying means is a heater/cooler when the heat or stress applying means is applying heat.

7. The gain module of embodiment 5, wherein when the stress applying device applies mechanical stress, the stress applying device is a clamp that clamps the gain medium, and a direction of application of the clamp and the optical axis An angle greater than zero degrees is formed between them.

8. The gain module of embodiment 5 wherein the gain medium is yttrium aluminum garnet (Nd:YAG).

9. A dual polarization control apparatus for a laser gain module, comprising: a gain medium; a positioning device for positioning the gain medium in the laser gain module; and a stress applying device The gain medium is applied with a specific stress that produces a specific birefringence phenomenon as soon as a light passes through the gain medium.

10. A method for controlling a dual polarized laser gain module, comprising: providing a gain medium; positioning the gain medium in the laser gain module; and applying a specific stress to the gain medium, A specific birefringence phenomenon occurs after a light passes through the gain medium.

11. The invention of embodiment 1, 5, 9, or 10 wherein the crystal of the gain medium is arranged to be isotropic in a plane perpendicular to the optical axis.

The above embodiments are merely exemplified for convenience of explanation, and those who are familiar with the art are arbitrarily modified to do so, but they are not excluded. Please protect the scope of the patent.

Claims (6)

A dual polarization mode-locked laser system comprising: an excitation light source to generate an excitation light; a self-mode-locking resonant cavity adjacent to the excitation light source, wherein a resonant medium is disposed in the resonant cavity and has an optical axis, thereby Passing the excitation light into the gain medium and generating an output of a self-mode-locked laser, wherein the output of the self-mode-locked laser can also be added to or replaced by the active-passive mode-locking component; and a stress An application device is disposed in the resonant cavity adjacent to the gain medium and applies a stress to the gain medium to cause a birefringence phenomenon to generate a laser output having a bi-orthogonal polarization. The system of claim 1, wherein the stress applying device is a jig for holding the gain medium. The system of claim 1, further comprising a sensing module, the sensing module further comprising: a polarization beam splitter, the laser output is different according to a polarization direction And dividing into a first polarized light and a second polarized light; a first photosensitive element for sensing the first polarized light; and a second photosensitive element for sensing the second polarized light. A gain module for a dual polarization mode-locked laser device, comprising: a gain medium having an optical axis; and a heat or stress applying device adjacent to the gain medium and increasing The heat medium is subjected to a heat or stress which causes the gain medium to produce a birefringence phenomenon, wherein the heat or stress applying means is a heater/cooler when the heat or stress applying means applies heat. The gain module of claim 4, wherein when the heat or stress applying device applies mechanical stress, the heat or stress applying device is a clamp that clamps the gain medium, and the force of the clamp is An angle greater than zero degrees is formed between the direction and the optical axis. The gain module of claim 4, wherein the gain medium is yttrium aluminum garnet (Nd:YAG).