CN203574219U - Separation pulse broadening optical device based on cascaded polarization beam split - Google Patents

Abstract

The utility model discloses a separated pulse stretching optical device based on cascaded polarization beam splitting. The device is composed of three-stage stretching units connected through optical paths, and the three-stage stretching units are: the first-stage stretching unit fs/ps— 10ps, the second stage stretching unit 10ps-100ps and the third stage stretching unit 100ps-ns, each stage stretching unit is composed of several stretching subunits, the structure of the stretching subunits is based on the principle of polarization beam splitting, so that lasers with different polarization states Different optical paths in space or in optical fibers, or different refractive indices introduced in birefringent crystals, to achieve precise control of the delay between sub-pulses. After N stretching sub-units, an initial pulse is finally decomposed into 2 ^N sub-pulse to achieve high-magnification pulse stretching.

Description

Split pulse stretching optical device based on cascaded polarization beam splitting

technical field

The utility model belongs to the technical field of high-energy lasers, in particular to a high-magnification polarization separation type pulse broadening and pulse polarization beam combining structure, in particular to a separated pulse broadening optical device based on cascaded polarization beam splitting.

Background technique

Realizing high-power, high-peak-intensity laser pulses has always been an important research direction in the field of laser technology. In many emerging applications, such as laser wakefield acceleration, X-ray, γ-ray, electron and photon beam generation and other related strong field-matter interactions, for laser pulses, it is necessary to meet the average power and Extremely high single pulse energy, for example, laser wakefield acceleration mostly requires a peak power density of 10 ¹⁸ W/cm ² or higher.

Although it is now possible to achieve continuous laser output with an average power of 10 kW in a single fiber, for pulsed lasers, due to various nonlinear effects in the fiber, such as stimulated Raman scattering, stimulated Brillouin scattering, self-phase In the presence of modulation, four-wave mixing, etc., the energy limit of ultrashort pulses with pulse widths less than picoseconds is about 1 mJ; for long pulses with pulse widths of several nanoseconds, limited by the damage threshold of optical materials such as quartz, Its peak energy density is difficult to exceed 50 J/cm ² .

A series of applications require ultra-short and ultra-intense lasers with high single-pulse energy and high peak power density. The pulse energy or pulse peak power that a single fiber can withstand, even a double-clad fiber with a large mode field or a photonic crystal fiber, is limited by the damage threshold of the material. Moreover, the amplification of ultrashort pulses needs to avoid nonlinearities in the fiber as much as possible. The impact of the effect. It can be used to divide an ultrashort laser pulse into several (such as thousands or tens of thousands) sub-pulses, increase the pulse repetition rate as much as possible, reduce the energy of a single pulse, and realize the conversion of ultrashort pulse laser to quasi-continuous laser , so that the adverse effect of the nonlinear effect related to the pulse energy during the amplification process can be reduced, and finally the high-energy ultrashort laser pulse is obtained through the pulse beam combining and compression device. In terms of technical implementation, there are mainly two problems: one is how to achieve high-magnification pulse splitting, and decompose a main pulse into thousands or tens of thousands of sub-pulses separated in the time domain; the other is how to control the separated laser sub-pulses After amplification, it can be synthesized into a main pulse. It is required that no additional phase noise or sub-pulse delay jitter is carried in the pulse synthesis, and the nonlinear phase shift of the pulse during the amplification process is required to be as small as possible.

The traditional ultrashort pulse stretching device, such as the chirped pulse stretching device that introduces dispersion management according to the different propagation speeds of light with different frequency components in the material, adopts the spatial structure of gratings or prisms, and can convert femtosecond and picosecond levels The ultrashort pulse is stretched to the nanosecond level, and the chirped stretched pulse is amplified to perform pulse compression. This chirped pulse amplification and compression technology has been developed so successfully that it has become a mainstream technology in the field of ultrafast science and technology. However, the above-mentioned structure has high requirements on the spectral width of the incident pulse, and it is not suitable to accurately control the amount of broadening. Narrow, cumulative high-order dispersion has the disadvantage of being incompressible. The application of chirped pulse amplification technology to the laser pulse amplification system with an all-fiber structure faces great difficulties, and it is difficult to achieve ultrashort laser pulse amplification greater than 1mJ.

Utility model content

The purpose of this utility model is to provide a split pulse stretching optical device based on cascaded polarization beam splitting in order to overcome the problems and shortcomings in the above-mentioned prior art. Laser pulses of polarization states introduce different optical paths or refractive indices, so that a single ultrashort pulse is decomposed into two sub-pulses with different polarization states and separated in time. Each of the decomposed sub-pulses is then decomposed again to again obtain two temporally separated pulses with different polarization states. After each decomposition, an ultrashort pulse will be decomposed into two. After N times of decomposition, the initial ultrashort pulse will be decomposed into 2 ^N sub-pulses. By optimizing each decomposition process, different polarization states The difference in optical path or refractive index introduced by the laser can precisely control the delay between each sub-pulse, and realize high-magnification time-domain stretching of pulses at arbitrary intervals.

The purpose of this utility model is achieved in that:

A separate pulse stretching optical device based on cascaded polarization beam splitting, characterized in that the device is composed of three-stage stretching units connected through optical paths, and the three-stage stretching units are: the first-stage stretching unit fs/ps-10ps, the second-stage stretching unit The second-level stretching unit is 10ps-100ps and the third-level stretching unit is 100ps-ns. Each level of stretching unit is composed of several stretching subunits, and its stretching subunit structure is one of the following structures:

⑴. It consists of a birefringent crystal and a polarization controller. After the pulse passes through the polarization controller, it enters from one side of the birefringent crystal and exits from the other side of the crystal.

⑵. It consists of two birefringent crystals of the same size and a polarization controller. After the pulse passes through the polarization controller, it enters from one birefringent crystal and exits from the other birefringent crystal;

(3) Consists of a loop mirror, a polarization controller, a polarization beam splitter, a delayer and two mirrors, the pulse is incident from the input end of the loop mirror, and exits from the output end of the loop mirror;

(4) Consists of a polarization controller, a polarization beam splitter, a delayer and two Faraday rotating mirrors, the pulse is incident from one port of the polarization beam splitter, and exits from the other port of the polarization beam splitter;

⑸. It is composed of a polarization controller, two polarization beam splitters, a delayer and two mirrors. The pulse enters from one polarization beam splitter and exits from the other polarization beam splitter.

⑹. It consists of a polarization controller, two polarization beam splitters and two mirrors. The pulse enters from one polarization beam splitter and exits from the other polarization beam splitter;

⑺. It consists of a polarization controller, two polarization beam splitters and four mirrors. The pulse enters from one polarization beam splitter and exits from the other polarization beam splitter;

(8) Composed of a polarization controller, two bonded polarization beam splitters and a tapered crystal or glass, the pulse enters from one polarization beam splitter and exits from the other polarization beam splitter;

⑼. It consists of a polarization controller, two polarizing beam splitters bonded together and two mirrors. The pulse enters from one polarizing beam splitter and exits from the other polarizing beam splitter.

The polarization controller is a half-wave plate, that is, a half-wave plate, or a stress-type optical fiber polarization controller.

The polarization beam splitter, polarization controller, delayer, loop mirror, reflector or Faraday rotating reflector is a spatial structure or an all-fiber structure with pigtails.

The delay introduced by the first-stage stretching unit of the utility model to different polarization states is very small, generally 1-2 picoseconds, and the corresponding space length is less than 1 mm, so the pulse stretching subunit structure based on birefringence is adopted, After the superposition of three or four sub-unit structures, the femtosecond pulse can be stretched to the order of 10 ps (wherein the femtosecond pulse will undergo chirped pulse broadening through the optical device); the second-stage stretching unit introduces different polarization states The delay is generally tens of picoseconds, and the spatial structure based on the polarization beam splitter is commonly used. By precisely controlling the spatial optical path difference between the two mutually perpendicular polarization state pulses after separation, the pulse of about 10 ps can be stretched to 100 ps; the third stage The delay introduced by the stretching unit for different polarization states is relatively large. The fiber delay structure is commonly used to control the length of the delay fiber and introduce a large optical path difference to realize the stretching of 100 ps pulses to the order of several nanoseconds. the

The stretching sub-unit structure of the utility model can be superimposed continuously. By controlling the optical path difference introduced by each level of stretching unit, the function of pulse separation and stretching at any distance can be realized, and the pulse can be stretched from femtoseconds/picoseconds to dozens or hundreds. Nanosecond or even quasi-continuous long pulses are beneficial to achieve high-energy pulse amplification, improve the energy utilization efficiency of pump light, reduce the peak power of the amplified pulse to avoid possible damage to the amplified medium by high peak power pulses, and reduce the amplification process. Non-linear B integral, and suppress the noise associated with the amplification process.

The utility model advantage is as follows:

(1) Compared with the traditional stretcher based on gratings and prisms, the optical path structure of the utility model is simple, easy to realize and good in stability.

(2) In the optical path of the present utility model, the incident angle of the laser pulse is vertical incident or 45-degree reflection, which does not need to precisely control the incident angle, reduces alignment requirements, and is easy to integrate.

(3) The stretching amount of each stretching unit can be precisely controlled by the length of the delay crystal or delay fiber in the stretching subunit structure, which is easy to adjust.

(4) The stretching of the utility model has nothing to do with the width of the pulse spectrum. Compared with the traditional stretcher that relies on dispersion to achieve stretching, the utility model has wider versatility and has no requirements for the spectrum of the incident laser pulse.

⑸ Separate pulse broadening reduces the energy of a single pulse and avoids device damage caused by excessive pulse energy during high-power amplification.

6. According to different polarization states, it has different optical paths to achieve pulse stretching. Compared with traditional dispersion-based stretchers, it hardly introduces nonlinear effects such as high-order dispersion, which is conducive to subsequent compression to achieve ultrashort pulses.

⑺. The broadened pulse has a stable polarization state, and can obtain stable conversion efficiency in polarization-sensitive applications such as frequency doubling.

⑻. A Faraday rotating mirror is added to the output end of the stretching subunit structure, and the reversely transmitted beam passes through the subunit structure, which can realize the beam combining of polarization splitting pulses, that is, the unit structure simultaneously realizes pulse splitting and broadening and splitting pulse combining .

⑼. By superimposing and broadening the subunit structure, the stretching amount can be precisely controlled, and the ultrashort pulse can be stretched to the nanosecond level, and the stretching rate is high.

⑽. The utility model has no requirements on the incident spectrum, does not affect the spectral distribution of the laser pulse during the broadening process, and can be used for simultaneous broadening and compression of multi-band pulses.

⑾. The utility model is simple, and the devices used are all conventional devices, which is convenient for integration and high-energy amplification, and is suitable for obtaining high-stability, high-power laser output in green and ultraviolet bands.

Description of drawings

Figure 1 is a schematic diagram of a high-magnification polarization-separated broadening structure;

Fig. 2 is the structural diagram of equal-spaced high-magnification polarization-separated pulse stretching in Embodiment 1;

Fig. 3 is a structural diagram of high-magnification polarization-separated pulse stretching at arbitrary intervals in Embodiment 2;

Figure 4-9 shows the stretching structure based on birefringent crystals, which is suitable for pulse stretching of the first-level stretching unit (fs/ps—10ps) (in which femtosecond-level pulses will undergo chirped pulse stretching through optical devices), specifically for:

FIG. 4 is a structural diagram of a polarization broadening subunit based on a birefringent crystal;

Figure 5 is a two-stage polarization broadening structure diagram based on birefringent crystals;

Figure 6 is a multi-level birefringent crystal-based polarization broadening structure diagram;

Fig. 7 is another subunit structure diagram based on birefringent crystal polarization broadening;

Fig. 8 is another structural diagram based on two-stage polarization broadening of birefringent crystals;

Fig. 9 is another structural diagram based on polarization broadening of multi-level birefringent crystals;

Figure 10-19 shows the space stretching structure, which can precisely adjust the delay time to realize high-magnification polarization pulse separation stretching, which is suitable for the pulse stretching of the second stage (10ps-100ps) or the third stage stretching unit (100ps-ns), Specifically:

Fig. 10 is a structural diagram of a widening subunit of a single polarization beam splitter;

FIG. 11 is another structural diagram of a widening subunit of a single polarization beam splitter;

Fig. 12 is a kind of stretching subunit structural diagram of band optical delay device;

Fig. 13 is a broadening structure diagram of a two-stage single polarization beam splitter;

Fig. 14 is a widening structure diagram of a multi-stage single polarization beam splitter;

Fig. 15 is a structure diagram of a broadening subunit of two separate polarization beam splitters with a delay crystal;

Fig. 16 is a structural diagram of the widening subunits of two separated polarization beam splitters;

Fig. 17 is a structural diagram of a widening subunit of an adhesive polarizing beam splitter;

Fig. 18 is another structural diagram of the widening subunit of the bonded polarization beam splitter;

Figure 19 is a structural diagram of a widening subunit of an all-fiber single polarization beam splitter;

Figure 20-25 shows the all-fiber stretching structure, which is suitable for the pulse stretching of the third-level stretching unit (100ps-ns), specifically:

FIG. 20 is a structural diagram of a widening subunit of a single polarization beam splitter with an all-fiber structure;

Figure 21 is a widening structure diagram of a single polarization beam splitter with a two-stage all-fiber structure;

Figure 22 is a widening structure diagram of a single polarization beam splitter with a multi-stage all-fiber structure;

Fig. 23 is a widening structure diagram of a multi-stage bonded polarizing beam splitter;

Fig. 24 is a structural diagram of a widening subunit of an all-fiber two polarization beam splitter;

Fig. 25 is a structural diagram of multi-stage all-fiber stretching.

Detailed ways

The utility model is further described in conjunction with the accompanying drawings, but not limited to the following embodiments.

Referring to Fig. 1, the utility model adopts three-level widening to realize the pulse widening of fs/ps to the order of several nanoseconds, and the three-level widening unit is: the first level widening unit (fs/ps-10ps), the second Level stretching unit (10ps-100ps) and third level stretching unit (100ps-ns). Among them, the delay introduced by the first-stage stretching unit for different polarization states is very small, generally 1-2 ps, and the corresponding space length is less than 1 mm. Therefore, the pulse stretching subunit structure based on birefringence is adopted. After three or four stretches The superposition of the sub-unit structure realizes the femtosecond pulse broadening to the order of 10ps (wherein the femtosecond pulse will undergo chirped pulse broadening through the optical device); the delay introduced by the second-level stretching unit for different polarization states is generally For tens of picoseconds, the spatial structure based on the polarization beam splitter is commonly used. By precisely controlling the spatial optical path difference between two mutually perpendicular polarization state pulses after separation, the pulse of about 10 ps can be stretched to 100 ps; the third-stage stretching unit pairs different The delay introduced by the polarization state is large, and the fiber delay structure is commonly used to control the length of the delay fiber and introduce a large optical path difference to realize the stretching of the 100 ps pulse to the order of several nanoseconds or even longer.

Example 1

Refer to Fig. 2, which is a structural diagram of equal-spaced high-magnification polarization-separated pulse stretching, including three stages of stretching, and each stage of stretching is composed of four cascaded stretching subunits. The used devices include a birefringent crystal 13 , a half-wave plate 11 , a mirror 4 , a spatial polarization beam splitter 1 , a delay fiber 7 , and a Faraday rotating mirror 10 with a pigtail. The initial incident pulse is decomposed into two sub-pulses whose polarization directions are perpendicular to each other and with the same amplitude through a stretching subunit, and then passes through the next stretching subunit, and the half-wave plate between the two stretching subunits is adjusted so that the first broadening The polarization direction of the pulse output by the subunit is rotated by 45 degrees, and then enters the second broadening subunit, or the polarization control of the laser pulse is realized by arranging the crystal space orientation angle, so that the birefringent crystals or polarization beam splitters adjacent to the front and rear stages The rotation axis of the device is the laser pulse propagation direction, and the axial angle is 45 degrees (in this case, the half-wave plate 11 can be omitted). At the same time, the number of birefringent crystals in the second stretching subunit is twice the number of birefringent crystals in the first stretching subunit. According to the structure shown in the figure, the polarization direction of the incident pulse of each stretching subunit is equal to the outgoing pulse of the previous one. Rotated by 45 degrees, or the angle between the incident planes of the adjacent polarization beam splitters in the front and rear stages is 45 degrees (in this case, the half-wave plate 11 can be omitted). The number of birefringent crystals in each stretching sub-unit is twice the number of birefringent crystals in the previous stretching sub-unit. After four stretching sub-units in the first stage, an initial pulse is separated into 16 sub-pulses. The length of the crystal is reasonably selected so that the delay introduced by every two crystals is 1 ps, and after the first stage of broadening, the length of the pulse time domain is 16 ps.

Afterwards, the separated pulses are broadened by four second-stage polarization beam splitters. Before each widening subunit, there is a polarization controller to adjust the polarization direction of the incident pulses to ensure that the two pulses after passing through the polarization beam splitter 1 All have the same intensity, and the spatial optical path difference introduced by each stretching subunit is twice the optical path difference of the previous stretching unit. After cascading four stretching subunits, the 16 pulses that will be incident are realized at the output Separated into 256 sub-pulses, for example, the delay distance of each stretching sub-unit can be precisely adjusted, so that the first stretching sub-unit introduces a delay of 16ps, and the final pulse time domain length at the output end is 256ps.

Then, the pulse output from the second-stage pulse stretching is incident into the third-stage stretching composed of four fiber-based delay units. In each stretching subunit, the length of the delay fiber is equal to the delay of the previous stretching subunit. 2 times that of the optical fiber, precisely adjust the length of the delay fiber in each stretching sub-unit, so that the first stretching sub-unit introduces a delay of 256ps, and finally at the output end, 256 initial pulses are decomposed into 4096 sub-pulses, and each sub-unit The interval between the pulses is the same, for example, the interval can be set to 1 ps, and the total time domain width is 4.096 ns, which realizes high-magnification equal-interval pulse-separated stretching.

Example 2

Refer to Fig. 3, which is a structural diagram of high-magnification polarization separation pulse stretching at any interval, including three stages of stretching, and each stage of stretching is composed of four cascaded stretching subunits. The used devices include a birefringent crystal 13 , a half-wave plate 11 , a mirror 4 , a spatial polarization beam splitter 1 , a delay fiber 7 , and a Faraday rotating mirror 10 with a pigtail. The initial incident pulse passes through the first stretching subunit, and is decomposed into two subpulses whose polarization directions are perpendicular to each other and with the same amplitude. The polarization direction of the pulse output by the first stretching subunit is rotated by 45 degrees, and then enters the second stretching subunit. According to the structure shown in the figure, the polarization direction of the incident pulse of each stretching subunit is rotated by 45 degrees relative to the outgoing pulse of the previous one. degree, or realize the polarization control of the laser pulse through a special spatial orientation angle arrangement, so that the birefringent crystals or polarization beam splitters adjacent to the front and rear stages take the laser pulse propagation direction as the rotation axis, and the axial angle is 45 degrees (in this case case, the half-wave plate 11 can be omitted). Afterwards, the separated pulses are broadened by four second-stage polarization beam splitters. Before each widening subunit, there is a polarization controller to adjust the polarization direction of the incident pulses to ensure that the two pulses after passing through the polarization beam splitter 1 All have the same intensity, and the spatial optical path difference introduced by each stretching sub-unit is arbitrary. After passing through the cascaded four stretching units, the pulse output from the second-stage pulse stretching is incident on the four fiber-based delay units. In the third stage of stretching, an initial pulse is decomposed into 4096 sub-pulses finally at the output. Since the delay introduced by each level of broadening can be freely controlled by adjusting the length of the birefringent crystal, the length of the spatial optical path or the length of the delay fiber, it is possible to achieve high-magnification pulse-separated broadening at any interval.

Figure 4-9 shows the stretching structure based on birefringent crystals, which is suitable for the first-level (fs/ps-10ps) pulse stretching, and realizes the stretching of femtosecond and picosecond ultrashort pulses to 10ps by polarization separation order of magnitude. For a delay of less than 1 ps, the corresponding spatial optical path difference is less than one millimeter, and the length can not be precisely controlled by using a widening structure based on spatial delay or optical fiber delay. In birefringent crystals, the difference in refractive index between two beams of light polarized perpendicular to each other is small, and the length of birefringent crystals is also limited by crystal processing, generally less than 50mm, and it is impossible to introduce a delay greater than 50ps. The concrete structure of accompanying drawing 4-9 is introduced respectively below:

FIG. 4 is a structural diagram of a birefringent crystal polarization broadening subunit, including a birefringent crystal 13 and a half-wave plate 11 . After the initial pulse passes through the half-wave plate 11, it is incident on the birefringent crystal 13, and is decomposed into the ordinary light with the same propagation direction and the extraordinary light with the changed propagation direction. Due to the birefringence effect, the ordinary light and the extraordinary light have the same The polarization states are perpendicular to each other, and the refractive index of the two beams of light in the crystal is also different, so the propagation speed of the two beams of light is also different. By selecting different birefringent crystals, rationally designing the angle between the optical axis of the crystal and the incident direction and the length of the crystal, the optical path difference between ordinary light and extraordinary light can be precisely controlled, and an incident pulse can be separated into two polarizations perpendicular to each other. subpulse. Due to the birefringence effect, ordinary light and extraordinary light travel in different directions and are separated in space. After the first birefringent crystal, a birefringent crystal of exactly the same size is placed, and its optical axis direction is the same as that of the first birefringent crystal. The optical axes of the two crystals are symmetrical about the common plane of the two crystals, which can realize the compensation for the spatial separation of the ordinary light and the extraordinary light, and converge the two beams of light into one beam in space. By adjusting the half-wave plate 11, the relative intensities of the two sub-pulses change accordingly.

FIG. 5 is a structural diagram of polarization broadening of two birefringent crystals, including a birefringent crystal 13 and a half-wave plate 11 . The initial incident pulse passes through the first stretching subunit, and is decomposed into two subpulses whose polarization directions are perpendicular to each other and with the same amplitude, and then passes through the next stretching subunit, adjusting the half-wave plate between the two stretching subunits so that The polarization direction of the pulse output by each stretching subunit is rotated by 45 degrees, or the polarization control of the laser pulse is realized through a special spatial orientation angle arrangement, so that the birefringent crystals adjacent to the front and rear stages take the propagation direction of the laser pulse as the rotation axis, and the axial angle is 45 degrees (in this case, the half-wave plate 11 can be omitted), and then incident to the second broadening subunit, at the same time, the number of birefringent crystals of the second broadening subunit is the birefringence of the first broadening subunit Twice the number of crystals, according to the structure shown in the figure, can realize the separation of one pulse into four sub-pulses, and the amplitude of each pulse is a quarter of the original pulse.

FIG. 6 is a structural diagram of multiple birefringent crystals for polarization broadening, including a birefringent crystal 13 , a half-wave plate 11 , and a mirror 4 . The initial incident pulse passes through the first stretching subunit, and is decomposed into two subpulses whose polarization directions are perpendicular to each other and with the same amplitude, and then passes through the next stretching subunit, adjusting the half-wave plate between the two stretching subunits so that The polarization direction of the pulse output by each stretching subunit is rotated by 45 degrees, or the polarization control of the laser pulse is realized through a special spatial orientation angle arrangement, so that the birefringent crystals adjacent to the front and rear stages take the propagation direction of the laser pulse as the rotation axis, and the axial angle is 45 degrees (in this case, the half-wave plate 11 can be omitted), and then incident to the second broadening subunit, at the same time, the number of birefringent crystals of the second broadening subunit is the birefringence of the first broadening subunit Twice the number of crystals, according to the structure shown in the figure, the polarization direction of the incident pulse of each stretching subunit is rotated by 45 degrees relative to the previous outgoing pulse, and the number of birefringent crystals in each stretching subunit is the same as that of the previous stretching Twice the number of birefringent crystals in the sub-units, and through N stretched sub-units, an initial pulse is separated into 2 ^N sub-pulses. The function of the mirror 4 is only to change the layout of the optical path.

FIG. 7 is a structural diagram of another subunit for polarization broadening of a birefringent crystal, including a birefringent crystal 13 and a half-wave plate 11 . After the initial pulse passes through the half-wave plate 11, it is incident on the birefringent crystal 13, and the angle between the incident direction and the optical axis is reasonably designed to ensure that the decomposed ordinary light and extraordinary light travel in the same direction in the crystal. Due to the effect of birefringence, ordinary light and extraordinary light have polarization states perpendicular to each other, so the propagation speeds of the two beams of light are also different. By selecting different birefringent crystals and rationally designing the crystal length, the optical path difference between ordinary light and extraordinary light can be precisely controlled, and an incident pulse can be separated into two sub-pulses whose polarizations are perpendicular to each other. By adjusting the half-wave plate 11, the relative intensities of the two sub-pulses change accordingly.

FIG. 8 is another structural diagram of polarization broadening of two birefringent crystals, including a birefringent crystal 13 and a half-wave plate 11 . The initial incident pulse passes through the first stretching subunit, and is decomposed into two subpulses whose polarization directions are perpendicular to each other and with the same amplitude, and then passes through the next stretching subunit, adjusting the half-wave plate between the two stretching subunits so that The polarization direction of the pulse output by each stretching subunit is rotated by 45 degrees, or the angle between the incident surfaces of adjacent birefringent crystals is 45 degrees (in this case, the half-wave plate 11 can be omitted), and the incident At the same time, the number of birefringent crystals in the second broadening subunit is twice the number of birefringent crystals in the first widening subunit. According to the structure shown in the figure, one pulse can be separated into four subunits. Pulses, each one-fourth the amplitude of the initial pulse.

FIG. 9 is another structural diagram of polarization broadening of multiple birefringent crystals, including a birefringent crystal 13 , a half-wave plate 11 , and a mirror 4 . The initial incident pulse passes through the first stretching subunit, and is decomposed into two subpulses whose polarization directions are perpendicular to each other and with the same amplitude, and then passes through the next stretching subunit, adjusting the half-wave plate between the two stretching subunits so that The polarization direction of the pulse output by each stretching subunit is rotated by 45 degrees, or the angle between the incident surfaces of adjacent birefringent crystals is 45 degrees (in this case, the half-wave plate 11 can be omitted), and the incident To the second stretching subunit, at the same time, the number of birefringent crystals in the second stretching subunit is twice the number of birefringent crystals in the first stretching subunit. According to the structure shown in the figure, the incident pulse polarization of each stretching subunit The direction is rotated by 45 degrees relative to the previous outgoing pulse, and the number of birefringent crystals in each broadening subunit is twice the number of birefringent crystals in the previous widening subunit. After N-level widening subunits, an initial The pulse is separated into 2 ^N sub-pulses. The function of the mirror 4 is only to change the layout of the optical path.

Figure 10-19 is a space stretching structure, which can withstand higher power, and is suitable for the second-level (10ps-100ps) or third-level (100ps-ns) pulse stretching to the unit, and realizes the picosecond-level super Short pulses are broadened to hundreds of picoseconds or even nanoseconds by polarization separation. The stretching sub-unit with spatial structure can finely control the stretching amount. The specific structures in Figure 10-19 are introduced below:

A structure diagram of a broadening subunit of a single polarization beam splitter shown in FIG. 10 , including a space-structured polarization beam splitter 1, a space-structured circulator 2, a delay crystal or glass 3, a mirror 4, and a half-wave plate 11. The pulse is incident from the input port of the circulator 2, exits from the transmission port of the circulator 2, passes through the half-wave plate 11, and then enters the polarization beam splitter 1, and adjusts the half-wave plate 11 so that the The pulse is equally divided into two beams of sub-pulses whose polarizations are perpendicular to each other. One pulse is directly reflected by the mirror 4, and the other pulse first passes through the delay crystal or glass 3, and then is reflected by the mirror. After reflection, it passes through the delay crystal again. Or glass 3, after the two pulses are reflected, they are converged into a beam of light on the polarization beam splitter 1 along the incident direction, pass through the half-wave plate 11, enter from the transmission port of the circulator 2, and finally pass through the third beam of the circulator 2 ports exit. After the polarization beam splitter 1, the two pulses are spatially separated, and the optical paths they travel are different. By adjusting the length of the spatial optical path or the length of the delay crystal or glass 3, the optical path difference of the two pulses can be precisely controlled, and then through When the mirror is reversely incident on the polarization beam splitter 1, the two pulses overlap in space and are separated into two sub-pulses in time according to the optical path difference. The sub-pulses have the same amplitude, which is half of the original pulse.

FIG. 11 is a structure diagram of another broadening subunit of a single polarization beam splitter, including a spatially structured polarization beam splitter 1 , a delay crystal or glass 3 , a Faraday rotating mirror 9 , and a half-wave plate 11 . The pulse passes through the half-wave plate 11 and is incident on the polarization beam splitter 1. The half-wave plate 11 is adjusted so that the pulse incident on the polarization beam splitter 1 is equally divided into two beams of sub-pulses whose polarizations are perpendicular to each other, and one pulse directly passes through the Faraday Reflected by the rotating mirror 9, the other pulse first passes through the time-delay crystal or glass 3, and then is reflected by the Faraday rotating mirror 9. After reflection, it passes through the time-delay crystal or glass 3 again. After the two pulses are reflected, they travel along the incident direction Converge again on the polarization beam splitter 1 to form a beam of light. Since the polarization direction of each pulse is rotated by 90 degrees compared with the initial incident time, the converged laser pulses are output from another port of the polarization controller. The two pulses overlap in space, and are separated into two sub-pulses in time according to the optical path difference. The sub-pulses have the same amplitude, which is half of the original pulse.

Figure 12 is a structural diagram of a broadening subunit with a fiber delay device, including a spatially structured polarization beam splitter 1, a delay fiber 7, a Faraday rotating mirror 10 with a pigtail, a half-wave plate 11, and an optical fiber collimator Device 14. The pulse passes through the half-wave plate 11 and is incident on the polarization beam splitter 1. The half-wave plate 11 is adjusted so that the pulse incident on the polarization beam splitter 1 is equally divided into two beams of sub-pulses whose polarizations are perpendicular to each other. A collimator 14, coupled to the optical fiber, is directly reflected by the Faraday rotating reflector 10 with a pigtail, and another pulse passes through the fiber collimator 14, first coupled into the delay fiber 7, and then passes through the Faraday rotating reflector with a pigtail 10 reflection, after reflection, pass through the delay fiber 7 again, after the two pulses are reflected, they are converged into a beam of light again on the polarization beam splitter 1 along the incident direction, since the polarization direction of each pulse is compared with that of the initial incident, are rotated by 90 degrees, so the converged laser pulses are output from the other port of the polarization controller. The two pulses overlap in space, and are separated into two sub-pulses in time according to the optical path difference. The sub-pulses have the same amplitude, which is half of the original pulse.

Figure 13 is a broadening structure diagram of two single polarization beam splitters. The initial incident pulse undergoes a broadening and is separated into two sub-pulses. By controlling the length of the second time-delay glass or crystal, the second time-delay glass or crystal is used to introduce The optical path difference is twice that of the first one, which can realize the stretching that separates an initial pulse into four sub-pulses according to polarization.

Figure 14 is a broadening structure diagram of multiple single polarization beam splitters. The initial incident pulse undergoes a broadening and is separated into two sub-pulses. By controlling the length of the second time-delay glass or crystal, the second one introduces different polarization states The optical path difference is twice that of the first one, which can realize the expansion of separating an initial pulse into two according to polarization, and then separating it into four sub-pulses. The optical path difference introduced by each subsequent stretching unit for different polarization states is twice that of the previous one. Through the superposition of N stretching units, one pulse can be stretched into 2 ^N sub-pulses.

Fig. 15 is a structure diagram of a broadening subunit of two separate polarization beam splitters with a time-delay crystal, including two space-structured polarization beam splitters 1, a time-delay glass or crystal 3, two mirrors 4, and a half-wave plate 11. The pulse passes through the half-wave plate 11 and is incident on the polarization beam splitter 1. The half-wave plate 11 is adjusted so that the pulse incident on the polarization beam splitter 1 is equally divided into two beams of sub-pulses whose polarizations are perpendicular to each other. One pulse directly passes through a Reflected by the mirror 4, the other pulse first passes through the delay crystal or glass 3, and then reflected by another mirror 4. After the two pulses are reflected, they converge into a beam of light on another polarizing beam splitter 1, and the two pulses The pulses overlap in space and are separated into two sub-pulses in time according to the optical path difference. The sub-pulses have the same amplitude, which is half of the original pulse.

FIG. 16 is a structural diagram of the broadening subunits of two separated polarization beam splitters, including two space-structured polarization beam splitters 1 , four mirrors 4 , and a half-wave plate 11 . The pulse passes through the half-wave plate 11 and is incident on the polarization beam splitter 1. The half-wave plate 11 is adjusted so that the pulse incident on the polarization beam splitter 1 is equally divided into two beams of sub-pulses whose polarizations are perpendicular to each other. One pulse directly passes through a Reflected by the mirror 4, the other pulse passes through two mirrors 4 to introduce a longer optical path, and then reflected by a mirror 4. After the two pulses are reflected, they converge into a beam of light on another polarizing beam splitter 1 , the two pulses coincide in space, and are separated into two sub-pulses in time according to the size of the optical path difference. The amplitude of the sub-pulses is the same, which is half of the initial pulse.

Fig. 17 is a structural diagram of a bonded polarizing beam splitter widening subunit, including two spatial polarizing beam splitters 1 bonded together, and 45-degree cone angle glass bonded on the two polarizing beam splitters A prism adjusts the light path, and a half-wave plate 11 . Adjust the half-wave plate 11 so that the sub-pulse intensities of the two polarization states after separation are consistent. The structure shown in the figure can make the two sub-pulses separated by polarization recombine on the next polarization beam splitter. By adjusting the length of the longitudinal glass, it can Adjust the interval between the two separated sub-pulses.

FIG. 18 is another structure diagram of a bonded polarization beam splitter widening subunit, including two spatial polarization beam splitters 1 , two mirrors 4 , and a half-wave plate 11 bonded together. The pulse passes through the half-wave plate 11 and is incident on a polarizing beam splitter 1. The half-wave plate 11 is adjusted so that the pulse incident on the polarizing beam splitter 1 is equally divided into two beams of sub-pulses whose polarizations are perpendicular to each other, and one pulse directly passes through In another polarizing beam splitter, another pulse passes through two mirrors 4, introduces a certain optical path, and then reflects to another polarizing beam splitter. The two pulses are converged on the second polarizing beam splitter, overlap each other in space, and are separated into two sub-pulses in time according to the size of the optical path difference. The amplitude of the sub-pulses is the same, which is half of the original pulse.

Figure 19 is a broadening structure diagram of a multi-stage bonded polarization beam splitter. The structure shown in Figure 18 is continuously superimposed, and the half-wave plate in front of each unit structure is adjusted, or the laser pulse is realized through a special spatial orientation angle arrangement. Polarization control, so that the adjacent polarization beam splitters of the front and rear stages take the laser pulse propagation direction as the rotation axis, and the axial angle is 45 degrees, so that the incident light of each stage can be separated into two beams with the same amplitude according to the polarization state perpendicular to each other. The sub-pulse can expand one pulse into 2 ^N sub-pulses through N stretching unit structures.

Figure 20-25 is an all-fiber stretching structure, which is suitable for the third-level (100ps-ns) pulse stretching unit, which realizes the stretching of ultrashort pulses on the picosecond level to the nanosecond level through polarization separation, and uses a delay fiber The stretching sub-unit is suitable for pulse stretching with a relatively large delay, and the specific structures of accompanying drawings 20-25 are introduced respectively below:

Figure 20 is a structural diagram of a widening subunit of an all-fiber single polarization beam splitter, 6 is a circulator with a fiber structure, 12 is a manual or electric polarization controller, 5 is a polarization beam splitter with a fiber structure, and 7 is a delay Optical fiber, 8 is the reflecting mirror with pigtail. The pulse is incident from the input port of the circulator 6, exits from the transmission port of the circulator 6, passes through the polarization controller 12, and then enters the polarization beam splitter 5, and adjusts the polarization controller 12 so that the pulse incident on the polarization beam splitter 5 The pulse is equally divided into two beams of sub-pulses whose polarizations are perpendicular to each other. One pulse is directly reflected by the reflector 8, and the other pulse first passes through the delay fiber 8, and then is reflected by the reflector. After reflection, it passes through the delay fiber 7 again. After the two pulses are reflected, they converge again on the polarization beam splitter 5 along the incident direction to form a beam of light, pass through the polarization controller 12, enter from the transmission port of the circulator 6, and finally exit from the third port of the circulator 6. The two pulses after the polarization beam splitter 5 are spatially separated, and the optical paths they travel are different. By adjusting the length of the delay fiber 7, the optical path difference of the two pulses can be precisely controlled, and then incident on the With the polarizing beam splitter 5, the two pulses overlap in space, and are separated into two sub-pulses in time according to the optical path difference. The sub-pulses have the same amplitude, which is half of the original pulse.

FIG. 21 is a structural diagram of a broadening subunit of a single polarization beam splitter with an all-fiber structure, including a four-port polarization beam splitter 5 with a fiber structure, a delay fiber 7 , a Faraday rotating mirror 10 with a pigtail, and a polarization controller 12 . The pulse passes through the polarization controller 12 and is incident on the polarization beam splitter 5. The polarization controller 12 is adjusted so that the pulse incident on the polarization beam splitter 5 is equally divided into two beams of sub-pulses whose polarizations are perpendicular to each other. The rotating mirror 10 is reflected, and the other pulse first passes through the delay fiber 7, and then is reflected by the Faraday rotating mirror 10 with pigtails. After reflection, it passes through the delay fiber 7 again. After the two pulses are reflected, the Converge again on the polarization beam splitter 5 to form a beam of light. Since the polarization direction of each pulse is rotated by 90 degrees compared with the initial incident time, the converged laser pulses are output from another port of the polarization controller. The two pulses overlap in space, and are separated into two sub-pulses in time according to the optical path difference. The sub-pulses have the same amplitude, which is half of the original pulse.

Figure 22 is a broadening structure diagram of two single polarization beam splitters with an all-fiber structure. The initial incident pulse undergoes a broadening and is separated into two sub-pulses. By controlling the length of the second delay fiber, the second pulse for different polarization states The introduced optical path difference is twice that of the first one, which can realize the stretching that separates an initial pulse into four sub-pulses according to polarization.

Figure 23 is a broadening structure diagram of a single polarization beam splitter with multiple all-fiber structures. The initial incident pulse undergoes a broadening and is separated into two sub-pulses. By controlling the length of the second delay fiber, the second pulse for different polarization states The introduced optical path difference is twice that of the first one, which can realize the expansion of separating an initial pulse into two according to polarization, and then separating it into four sub-pulses. The optical path difference introduced by each subsequent stretching unit for different polarization states is twice that of the previous one. Through the superposition of N stretching units, one pulse can be stretched into 2 ^N sub-pulses.

FIG. 24 is a structure diagram of a stretching subunit of an all-fiber two polarization beam splitter, including a polarization beam splitter 5 with a two-fiber structure, a delay fiber 7 , and a polarization controller 12 . The pulse passes through the polarization controller 12 and is incident on the polarization beam splitter 5. The polarization controller 12 is adjusted so that the pulse incident on the polarization beam splitter 5 is equally divided into two beams of sub-pulses whose polarizations are perpendicular to each other, and one pulse is directly incident on the Another polarization beam splitter 5, the other pulse first passes through the delay fiber 7, and then enters another polarization beam splitter 5, the two pulses converge into one beam of light, the two pulses overlap in space, and the time is according to the optical path The magnitude of the difference is split into two sub-pulses with the same amplitude, which is half of the original pulse.

Figure 25 is a structural diagram of multiple all-fiber stretching. The initial incident pulse is split into two sub-pulses after a stretching. By controlling the length of the second delay fiber, the second optical path difference introduced for different polarization states is the second Twice that of one, it can realize the expansion of separating an initial pulse into two according to the polarization, and then separating it into four sub-pulses. The optical path difference introduced by each subsequent stretching unit for different polarization states is twice that of the previous one. Through the superposition of N stretching units, one pulse can be stretched into 2 ^N sub-pulses.

Claims (3)

1. discrete pulse broadening Optical devices based on cascade polarized beam splitting, it is characterized in that this device is formed by connecting by light path by three grades of broadening unit, described three grades of broadening unit are: first order broadening unit fs/ps-10ps, second level broadening unit 10ps-100ps and third level broadening unit 100ps-ns, every grade of broadening unit forms by several broadening subelements, and what its broadening sub-unit structure was lower array structure is a kind of:

(1), a birefringece crystal and a Polarization Controller, consist of, pulse is after Polarization Controller, from the one side incident of birefringece crystal, from the another side outgoing of crystal;

(2), two blocks of onesize birefringece crystals and a Polarization Controller, consist of, pulse is after Polarization Controller, from a birefringece crystal incident, from another piece birefringece crystal outgoing;

(3), an annular mirror, a Polarization Controller, a polarization beam apparatus, a delayer and two speculums, consist of, pulse is from the input incident of annular mirror, from the output outgoing of annular mirror;

(4), a Polarization Controller, a polarization beam apparatus, a delayer and two faraday rotator mirrors, consist of, pulse is from a port incident of polarization beam apparatus, from another port outgoing of polarization beam apparatus;

(5), a Polarization Controller, two polarization beam apparatus, a delayer and two speculums, consist of, pulse is from a polarization beam apparatus incident, from another polarization beam apparatus outgoing;

(6), a Polarization Controller, two polarization beam apparatus and two speculums, consist of, pulse is from a polarization beam apparatus incident, from another polarization beam apparatus outgoing;

(7), a Polarization Controller, two polarization beam apparatus and four speculums, consist of, pulse is from a polarization beam apparatus incident, from another polarization beam apparatus outgoing;

(8), by crystal or the glass combination of a Polarization Controller, two polarization beam apparatus that are bonded together and a taper, formed, pulse is from a polarization beam apparatus incident, from another polarization beam apparatus outgoing;

(9), a Polarization Controller, two polarization beam apparatus that are bonded together and two speculums, consist of, pulse is from a polarization beam apparatus incident, from another polarization beam apparatus outgoing.

2. device according to claim 1, is characterized in that described Polarization Controller is that 1/2nd wave plates are half-wave plate or stress type optical fiber polarization controller.

3. device according to claim 1, is characterized in that described polarization beam apparatus, Polarization Controller, delayer, annular mirror, speculum or faraday rotator mirror are space structure or with all optical fibre structure of tail optical fiber.

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