CN114779382A - Volume Bragg grating wavelength beam combiner based on photo-thermal conversion glass and preparation method thereof - Google Patents

Volume Bragg grating wavelength beam combiner based on photo-thermal conversion glass and preparation method thereof Download PDF

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CN114779382A
CN114779382A CN202210708681.1A CN202210708681A CN114779382A CN 114779382 A CN114779382 A CN 114779382A CN 202210708681 A CN202210708681 A CN 202210708681A CN 114779382 A CN114779382 A CN 114779382A
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bragg grating
volume bragg
angle
beam combiner
wavelength
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CN114779382B (en
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晋帅
胡红雷
宋学智
嵇舒豪
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Hangzhou Tuozhi Photoelectric Technology Co ltd
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Hangzhou Tuozhi Photoelectric Technology Co ltd
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    • G02—OPTICS
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    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1847—Manufacturing methods
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
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Abstract

The invention discloses a volume Bragg grating wavelength beam combiner based on photo-thermal conversion glass and a preparation method thereof, wherein the preparation method comprises the following steps: establishing internal Bragg grating channel parameters of the beam combiner by using a coupled wave theory and a vector circle method, then obtaining an interference included angle of two beams of recording light in a medium according to a double-beam interference principle and obtaining an incident angle of the two beams of recording light in the mediumθ oi ' andθ ri '; then calculating to obtain the incident angles of the two beams of recording light outside the mediumθ oi Andθ ri (ii) a Finally based on the incident angleθ oi Andθ ri exposing the photo-thermal refractive glass to write corresponding wavelength lambdawThe volume bragg grating channel of (a); and carrying out thermal development treatment on the volume Bragg grating, carrying out crystal polishing on the two light-passing surfaces, and plating an anti-reflection film to obtain the volume Bragg grating wavelength beam combiner. The volume Bragg grating wavelength beam combiner prepared by the inventionThe laser beam combining device has the advantages of simple and compact structure, strong environmental adaptability, strong aging resistance and strong laser damage resistance, and can meet the requirements of high-power laser wavelength beam combination.

Description

Volume Bragg grating wavelength beam combiner based on photo-thermal conversion glass and preparation method thereof
Technical Field
The invention relates to the technical field of optical element manufacturing, in particular to a volume Bragg grating wavelength beam combiner based on photo-thermal conversion glass and a preparation method thereof.
Background
In order to improve the output quality and output power of laser beams, various optical components for wavelength combining have been developed. Among them, the wide application in the communication field is Wavelength Division Multiplexer (WDM), and the posture phase holographic grating WDM has the advantages of unique structure, high linear density, high spatial frequency, high diffraction efficiency, and the like, thereby becoming a hot point for research in the Wavelength Division Multiplexing field. At present, the body position phase holographic grating in WDM is prepared by respectively manufacturing a body position phase holographic transmission grating and a reflection grating based on heavy-cadmium-acid-salt gelatin on two sides of a BK7 substrate, and then packaging the gratings by epoxy resin.
The prior patents CN103592770A and CN208060867U disclose some preparation processes of body-phase holographic gratings, but the disclosed techniques mainly have the following problems: 1. the process is complex, and comprises the processes of BK7 substrate cleaning, gelatin solution preparation, gluing, aging, exposure, water washing, fixation, dehydration, blow-drying, packaging and the like; 2. the bichromate gelatin required for preparing the grating with higher diffraction efficiency is thicker, which reaches more than ten microns, and brings a challenge to the gluing technology; 3. the dichromated gelatin is an organic substance, the chemical stability of the dichromated gelatin has certain requirements on the temperature and the humidity of the environment, and the aging of the colloid is an unavoidable problem along with the time; 4. the dichromated gelatin has a low laser damage resistance threshold, is only suitable for low-power laser beam combination, and cannot meet the requirement of high-power laser beam combination.
With the increasing demand of high-power laser, researchers carry out beam combination research on the volume bragg grating based on the photothermal conversion glass in order to improve the adaptability of the volume phase grating to the environment, the long-term aging resistance and the laser damage resistance, and the reason is that the glass matrix has high environmental stability, the long-term aging resistance and the laser damage resistance threshold. However, the existing research is to design a laser beam combining system and experimentally verify the beam combining output capability, or is to carry out the most basic theoretical design research on the volume bragg grating, and does not relate to the manufacturing method of the wavelength beam combiner.
Accordingly, there is a need for improvements and developments in the art.
Disclosure of Invention
In view of the defects of the prior art, the invention aims to provide a volume bragg grating wavelength combiner based on photothermal conversion glass and a preparation method thereof, and aims to solve the problems that the existing dichromated gelatin-based wavelength combiner is complex in preparation process, and the prepared wavelength combiner is poor in environmental adaptability, easy to age and poor in laser damage resistance.
The technical scheme of the invention is as follows:
a method for preparing a volume Bragg grating wavelength beam combiner based on photo-thermal conversion glass comprises the following steps:
obtaining known parameters of a Bragg grating wavelength beam combiner of a volume to be designed, wherein the known parameters comprise incident light wavelength
Figure 670223DEST_PATH_IMAGE001
Angle of incidence
Figure 118522DEST_PATH_IMAGE002
The emergence angle after the action of the Bragg grating wavelength beam combiner to be designed
Figure 632680DEST_PATH_IMAGE003
Wavelength of photothermal conversion glass
Figure 699993DEST_PATH_IMAGE005
Has a refractive index of
Figure 45524DEST_PATH_IMAGE006
A degree of modulation of refractive index of
Figure 602407DEST_PATH_IMAGE007
；
According to incident of incident lightCorner
Figure 275965DEST_PATH_IMAGE009
And refractive index
Figure 271603DEST_PATH_IMAGE010
Calculating the angle of incidence inside the volume Bragg grating from the snell law of refraction
Figure 347006DEST_PATH_IMAGE011
And angle of departure
Figure 74791DEST_PATH_IMAGE012
；
According to the wavelength of incident light
Figure 625858DEST_PATH_IMAGE013
、Refractive index
Figure 97291DEST_PATH_IMAGE014
And angle of incidence within the volume Bragg grating
Figure 27201DEST_PATH_IMAGE015
And angle of departure
Figure 253783DEST_PATH_IMAGE016
Calculating the grating inclination angle of the volume Bragg grating by using a vector circle method
Figure 901933DEST_PATH_IMAGE017
And period of time
Figure 911477DEST_PATH_IMAGE019
；
Calculating the diffraction efficiency of volume Bragg grating according to Kogelnik coupled wave theory
Figure 86106DEST_PATH_IMAGE020
；
After the period and the fringe inclination angle of the volume Bragg grating are determined, the interference included angle of two beams of recording light in the medium is obtained according to the principle of double-beam interference
Figure 93377DEST_PATH_IMAGE021
；
Obtaining the incident angles of the two beams of recording light in the medium according to the interference included angle
Figure 556719DEST_PATH_IMAGE022
And
Figure 432271DEST_PATH_IMAGE023
；
based on the incident angles of the two beams of recording light in the medium
Figure 333844DEST_PATH_IMAGE024
And
Figure 636649DEST_PATH_IMAGE025
calculating and obtaining the incident angle of two beams of recording light outside the medium based on the snell principle
Figure 321708DEST_PATH_IMAGE026
And
Figure 876318DEST_PATH_IMAGE027
；
according to the calculated incidence angles of the two beams of recording light outside the medium
Figure 759960DEST_PATH_IMAGE028
And
Figure 436929DEST_PATH_IMAGE029
exposing the photo-thermal refractive glass to write corresponding wavelength
Figure 546967DEST_PATH_IMAGE030
The volume bragg grating channel of (a);
writing a plurality of volume Bragg grating channels corresponding to different wavelengths on the photo-thermal conversion glass according to the steps;
and carrying out thermal development treatment on the volume Bragg grating written in the channel, taking out the volume Bragg grating, carrying out fine polishing on the two light transmission surfaces, and plating an anti-reflection film to obtain the volume Bragg grating wavelength beam combiner.
The preparation method of the volume Bragg grating wavelength beam combiner based on the photothermal conversion glass comprises the step of calculating the incidence angle inside the volume Bragg grating according to the snell refraction law
Figure 498743DEST_PATH_IMAGE031
(ii) a Angle of departure of
Figure 705733DEST_PATH_IMAGE032
。
The preparation method of the volume Bragg grating wavelength beam combiner based on the photo-thermal conversion glass comprises the step of calculating the grating inclination angle of the volume Bragg grating by adopting a vector circle method
Figure 225707DEST_PATH_IMAGE033
With a period of
Figure 947676DEST_PATH_IMAGE034
。
The preparation method of the volume Bragg grating wavelength beam combiner based on the photothermal conversion glass comprises the step of calculating the diffraction efficiency of the volume Bragg grating to TE polarized light according to the Kogelnik coupled wave theory when the Bragg mismatch is zero
Figure 906404DEST_PATH_IMAGE035
Wherein
Figure 374426DEST_PATH_IMAGE037
，
Figure 455515DEST_PATH_IMAGE038
，
Figure 602462DEST_PATH_IMAGE039
the thickness of the volume bragg grating.
The preparation method of the volume Bragg grating wavelength beam combiner based on the photothermal conversion glass comprises the step of obtaining two beams of recording light in a medium according to a double-beam interference principleThe included interference angle is expressed as
Figure 36986DEST_PATH_IMAGE040
Wherein, in the process,
Figure 15306DEST_PATH_IMAGE041
in order to record the wavelength of light,
Figure 611503DEST_PATH_IMAGE043
the refractive index of the glass at the wavelength of the recording light.
The preparation method of the volume Bragg grating wavelength beam combiner based on the photothermal conversion glass comprises the step of obtaining the incidence angle of two beams of recording light in a medium according to the interference included angle and expressing the incidence angle as
Figure 245747DEST_PATH_IMAGE044
And
Figure 343016DEST_PATH_IMAGE045
。
according to the preparation method of the volume Bragg grating wavelength beam combiner based on the photothermal conversion glass, the incidence angle of two beams of recording light outside a medium is calculated according to the snell principle and is expressed as
Figure 316788DEST_PATH_IMAGE046
And
Figure 208521DEST_PATH_IMAGE047
。
the preparation method of the volume Bragg grating wavelength beam combiner based on the photothermal conversion glass comprises the step of carrying out thermal development treatment on the volume Bragg grating written into the channel, wherein the thermal development temperature is 450-550 ℃, and the thermal development time is 60-120 min.
The invention discloses a volume Bragg grating wavelength beam combiner based on photo-thermal conversion glass, which is prepared by adopting the preparation method of the volume Bragg grating wavelength beam combiner based on the photo-thermal conversion glass.
Has the advantages that: compared with the traditional dichromic acid gelatin phase holographic grating combiner, the invention has the advantages that multiple groups of grating channels are written into one piece of photothermal conversion glass, the structure is more compact, and the prepared volume Bragg grating wavelength combiner has better environmental adaptability, longer-time ageing resistance and higher laser damage resistance, and can meet the requirement of high-power laser wavelength combining. The preparation method of the volume Bragg grating wavelength beam combiner based on the photothermal conversion glass has fewer processes, is simple in flow control and is convenient for batch production.
Drawings
Fig. 1 is a flow chart of a method for manufacturing a volume bragg grating wavelength beam combiner based on photothermal conversion glass according to the present invention.
Fig. 2 is a schematic diagram of a wavelength combiner of a volume bragg grating.
FIG. 3 is a schematic diagram of a vector circle method.
FIG. 4 is a schematic view of the recording angle of the grating recording light inside the photothermal conversion glass.
FIG. 5 is a schematic diagram of a three-wavelength beam combiner of embodiment 1 with wavelengths of 450nm, 532nm, and 640 nm.
FIG. 6 is a graph of the angular spectrum of wavelengths 532nm and 640 nm.
FIG. 7 is a graph of spectra at 532nm and 640 nm.
FIG. 8 is an exposure schematic diagram of the fabrication of volume Bragg grating channels at 532nm and 640nm wavelengths.
Detailed Description
The invention provides a volume Bragg grating wavelength beam combiner based on photothermal conversion glass and a preparation method thereof, and the invention is further described in detail below in order to make the purpose, technical scheme and effect of the invention clearer and clearer. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Referring to fig. 1, fig. 1 is a flowchart of a method for manufacturing a volume bragg grating wavelength beam combiner based on photothermal conversion glass according to the present invention, and as shown in the figure, the method includes the steps of:
s10, obtaining the Bragg grating of the volume to be designedKnown parameters of a wavelength combiner, including incident light wavelength
Figure 330061DEST_PATH_IMAGE048
Angle of incidence
Figure 103457DEST_PATH_IMAGE049
The emergence angle after the action of the Bragg grating wavelength beam combiner to be designed
Figure 790790DEST_PATH_IMAGE050
Wavelength of photothermal conversion glass
Figure 994370DEST_PATH_IMAGE051
Has a refractive index of
Figure 337627DEST_PATH_IMAGE052
A degree of modulation of refractive index of
Figure 42277DEST_PATH_IMAGE053
；
S20, according to the incident angle of the incident light
Figure 725063DEST_PATH_IMAGE054
And refractive index
Figure 427439DEST_PATH_IMAGE055
Calculating the angle of incidence inside the volume Bragg grating from the snell law of refraction
Figure 54730DEST_PATH_IMAGE056
And angle of departure
Figure 438438DEST_PATH_IMAGE057
；
S30, according to the incident light wavelength
Figure 38046DEST_PATH_IMAGE058
、Refractive index
Figure 708062DEST_PATH_IMAGE060
And angle of incidence within the volume Bragg grating
Figure 963594DEST_PATH_IMAGE061
And angle of departure
Figure 947731DEST_PATH_IMAGE062
Calculating the grating inclination angle of the volume Bragg grating by using a vector circle method
Figure 464163DEST_PATH_IMAGE064
And period of time
Figure 446025DEST_PATH_IMAGE066
；
S40, calculating the diffraction efficiency of the volume Bragg grating to the TE polarized light according to the Kogelnik coupled wave theory
Figure 47908DEST_PATH_IMAGE067
；
S50, obtaining the interference included angle of the two beams of recording light in the medium according to the principle of double-beam interference after the period and the fringe inclination angle of the volume Bragg grating are determined
Figure 835735DEST_PATH_IMAGE068
；
S60, obtaining the incident angle of the two beams of recording light in the medium according to the interference angle
Figure 347619DEST_PATH_IMAGE069
And
Figure 359437DEST_PATH_IMAGE070
；
s70, recording light beam incident angle in medium
Figure 386299DEST_PATH_IMAGE071
And
Figure 915501DEST_PATH_IMAGE072
calculating the incidence of two beams of recording light outside the medium based on the snell principleCorner
Figure 140946DEST_PATH_IMAGE073
And
Figure 526928DEST_PATH_IMAGE074
；
s80, according to the calculated incidence angles of the two recording lights outside the medium
Figure 241418DEST_PATH_IMAGE075
And
Figure 167786DEST_PATH_IMAGE074
exposing the photo-thermal refractive glass to write corresponding wavelength
Figure 451000DEST_PATH_IMAGE076
The volume bragg grating channel of (a);
s90, writing a plurality of volume Bragg grating channels corresponding to different wavelengths on the photo-thermal conversion glass according to the steps;
s100, carrying out thermal development treatment on the volume Bragg grating written in the channel, taking out the volume Bragg grating, carrying out crystal polishing on the two light transmission surfaces, and plating an anti-reflection film to obtain the volume Bragg grating wavelength beam combiner.
Specifically, because the existing posture phase holographic grating based on dichromated gelatin can not meet the requirement of beam combination by a laser with higher power, the invention utilizes the characteristics of strong environmental adaptability, long-time ageing resistance and laser damage resistance of the photothermal conversion glass, and writes a plurality of groups of grating channels into one piece of photothermal conversion glass to prepare the volume Bragg grating wavelength beam combiner, so that the structure is simpler and more compact, and the volume Bragg grating wavelength beam combiner has better environmental adaptability, longer-time ageing resistance and higher laser damage resistance, and can meet the requirement of beam combination of high-power laser wavelength. The preparation method of the volume Bragg grating wavelength beam combiner based on the photothermal conversion glass provided by the invention has the advantages of fewer processes, simple flow control and convenience for batch production, and fills the technical blank of the prior art in the field.
In order to explain the preparation principle of the volume bragg grating wavelength beam combiner based on photothermal conversion glass, the embodiment will be described in detail with reference to the simplest single-channel volume bragg grating, and the wavelength beam combiner can realize the combination of 2 wavelengths, and it should be reminded that the beam combiner with more wavelengths is not the volume bragg grating channel.
As shown in fig. 2, incident light
Figure 211145DEST_PATH_IMAGE077
At an angle of incidence
Figure 212599DEST_PATH_IMAGE078
Incident direct penetration beam combiner to exit angle
Figure 942658DEST_PATH_IMAGE080
Outgoing, incoming light
Figure 18061DEST_PATH_IMAGE081
At an angle of incidence
Figure 11425DEST_PATH_IMAGE082
Incident light is also at an emergent angle after being subjected to grating action
Figure 562492DEST_PATH_IMAGE084
And (7) emitting. Wherein the grating period is
Figure 706029DEST_PATH_IMAGE086
With a thickness of
Figure 963835DEST_PATH_IMAGE087
The angle between the vector direction Kg of the grating and the normal is called the tilt angle of the grating
Figure 190417DEST_PATH_IMAGE089
Wavelength of photothermal conversion glass
Figure 572988DEST_PATH_IMAGE090
Has a refractive index of
Figure 848111DEST_PATH_IMAGE092
A degree of modulation of refractive index of
Figure 288320DEST_PATH_IMAGE093
。
Because the grating is used in air (the refractive index of air is 1), the incident angle inside the volume Bragg grating is calculated by the snell's law of refraction
Figure 357907DEST_PATH_IMAGE094
And angle of departure
Figure 493353DEST_PATH_IMAGE095
：
Figure 368905DEST_PATH_IMAGE096
(1) Wherein, in the process,θ i andθ o for the required external incident angle and emergent angle of the medium, a clockwise angle is defined as a positive angle, and a counterclockwise angle is defined as a negative angle.
As shown in fig. 3, the period and tilt angle of the grating are calculated according to the vector circle method (fig. 2):
Figure 601304DEST_PATH_IMAGE097
（2）。
in the non-absorption material, when the volume grating is calculated according to the Kogelnik coupled wave theory to obtain the maximum diffraction efficiency, the thickness of the grating
Figure 779475DEST_PATH_IMAGE099
And degree of modulation of refractive index
Figure 526851DEST_PATH_IMAGE101
The relationship that needs to be satisfied. Diffraction efficiency when the Bragg mismatch is zero
Figure DEST_PATH_IMAGE103
(TE polarization) can be expressed as:
Figure 815881DEST_PATH_IMAGE104
(3) wherein
Figure DEST_PATH_IMAGE105
，
Figure 433944DEST_PATH_IMAGE106
。
as can be seen from the above equation (3), once the angle and wavelength are determined, the period and tilt angle of the grating are determined to maximize the diffraction efficiency and the thickness of the grating
Figure 45667DEST_PATH_IMAGE099
And degree of refractive index modulation
Figure 218022DEST_PATH_IMAGE101
The product of (c) needs to be a constant. In selecting the thickness of the grating
Figure 169798DEST_PATH_IMAGE099
Attention is paid to the thickness of the grating
Figure 314471DEST_PATH_IMAGE099
The larger the angle selectivity curve is, the narrower the full width at half maximum is, which can limit the final efficiency of the light beam with the mrad-order divergence angle when the light beam is diffracted by the volume grating; thickness of grating
Figure 896762DEST_PATH_IMAGE099
The smaller the refractive index modulation degree of the grating
Figure 618731DEST_PATH_IMAGE101
The larger the need, while the manufacturing tolerances will be relatively large.
After the period and the fringe inclination angle of the volume bragg grating are determined, the interference included angle of two beams of recording light in the medium can be obtained according to the principle of double-beam interference:
Figure DEST_PATH_IMAGE107
(4) whereinwherein,
Figure 983984DEST_PATH_IMAGE108
in order to record the wavelength of light,
Figure 107798DEST_PATH_IMAGE110
is the refractive index of the glass at the wavelength of the recording light.
As shown in FIG. 4, the incident angles of two recording lights (object light and reference light) in the medium
Figure DEST_PATH_IMAGE111
And
Figure 533094DEST_PATH_IMAGE112
can be expressed as:
Figure DEST_PATH_IMAGE113
（5）；
then calculating the incident angles of the two beams of recording light outside the medium according to the snell principleθ oi Andθ ri ，
Figure 148883DEST_PATH_IMAGE114
（6）；
according to the calculated incidence angles of the two beams of recording light outside the medium
Figure DEST_PATH_IMAGE115
And
Figure 176882DEST_PATH_IMAGE116
exposing the photo-thermal conversion glass to write corresponding wavelength
Figure DEST_PATH_IMAGE117
The volume Bragg grating channels are written in a plurality of volume Bragg grating channels corresponding to different wavelengths on the photo-thermal conversion glass according to the steps, the volume Bragg grating is placed in a muffle furnace for thermal development after double-beam exposure, and when the diffraction efficiency does not reach a target value, the volume Bragg grating channels can be re-heated to improve the refractive index modulation degree of the volume Bragg grating channels
Figure DEST_PATH_IMAGE119
In order to achieve higher diffraction efficiency, if the repeated thermal development efficiency is not improved any more, the exposure needs to be improved, and in short, the exposure and the thermal development process are adjusted until the diffraction efficiency reaches a target value. And finally, performing fine polishing and plating an antireflection film with the used wavelength on the two light passing surfaces to obtain the volume Bragg grating wavelength beam combiner.
In some embodiments, in the step of performing the thermal development process on the volume bragg grating of the writing channel, the thermal development temperature is 450 ℃ and 550 ℃, and the thermal development time is 60-120 min. By way of example, the thermal development temperature is 500 ℃ and the thermal development time is 90 min.
In some embodiments, the amount of exposure is 80-120mJ/cm during the exposure of the photothermal conversion glass2But is not limited thereto.
In some embodiments, the invention further provides a volume bragg grating wavelength beam combiner based on photothermal conversion glass, which is prepared by the preparation method of the volume bragg grating wavelength beam combiner based on photothermal conversion glass. The volume Bragg grating wavelength beam combiner based on the photo-thermal conversion glass comprises a transmission volume Bragg grating which takes the photo-thermal conversion glass as a holographic recording medium, wherein the volume Bragg grating is provided with a plurality of grating channels. In multi-wavelength light, one beam of light directly passes through the beam combiner without being influenced by all grating channels, and other wavelength light is diffracted by the corresponding grating channels and then is emitted in the same direction as the light directly passing through the beam combiner, so that the purpose of multi-wavelength beam combination is achieved, and it can be known that if m wavelengths needing to be combined into beams are m, the number of the required grating channels is m-1.
The invention is further illustrated by the following specific examples:
example 1
The preparation method of the volume Bragg grating beam combiner based on the photo-thermal conversion glass is provided, and beam combination is carried out on three wavelengths of 450nm, 532nm and 640nm, wherein the polarization state of the three wavelengths is TE polarization. Fig. 5 is a schematic diagram of the structure and the used optical path of the three-wavelength beam combiner. In consideration of the compactness of the system (the incidence angle is not too large), light with the wavelength of 450nm is incident into the beam combiner at 0 degrees and is emitted out at 0 degrees, and the grating channel is not occupied. Light with wavelengths of 532nm and 640nm enters the beam combiner at 10 degrees and exits at 0 degrees. By definition, the angle of incidence for 532nm light is 10 and the angle of incidence for 640nm light is-10. The thickness d of the light-taking grating is 1mm, and the diffraction efficiency is 100%.
1. According to the above description of the application index, the volume bragg grating wavelength combiner can be designed as follows:
(A) measuring by using a refractometer and fitting by using a Cauchy model to obtain the photothermal conversion glass with the refractivity of 1.5301, 1.5048 and 1.4997 for the wavelengths of 325nm, 532nm and 640nm respectively;
(B) according to the above formulas (1) to (3) of the present application, parameters such as the incident angle, the period, the tilt angle, the refractive index modulation degree, etc. in the medium of the grating 1 and the grating 2 can be calculated as shown in table 1.
TABLE 1 table of parameters such as incident angle, period, tilt angle, refractive index modulation degree in medium of grating 1 and grating 2
Figure 296148DEST_PATH_IMAGE120
Then angular and spectral curves at 532nm and 640nm are obtained, see fig. 6 and fig. 7, respectively. When the diffraction efficiency reaches 100%, the angular half-widths of the wavelength beam combiner are respectively 0.21 degrees and 0.18 degrees, and the spectral half-widths are respectively 22nm and 32 nm. Therefore, when in use, the divergence angle of the wavelength beam combiner to the laser is required to be within dozens of mrad (the common collimated laser can reach); has enough spectrum half-width range and has low requirement on laser wavelength purity.
2. The manufacture of the three-wavelength beam combiner with the wavelengths of 450nm, 532nm and 640nm is realized by adopting an asymmetric ultraviolet double-light-path exposure system, and the steps are as follows:
532nm and 640nm volume Bragg grating channels can be obtained by calculation according to formulas (4) to (6), and the incident angles of the two beams of light outside the mediumθ oi Andθ ri (refer to fig. 3) are shown in table 2, respectively.
TABLE 2 preparation of 532nm and 640nm volume Bragg grating channels with angles of incidence of the two beams outside the mediumθ oi Andθ ri watch (A)
532nm 640nm
Incident angle of recording light 1θ ri 8°7′47″ -2°33′22″
Incident angle of recording light 2θ oi 2°1′29″ -7°37′48″
(B) The photo-thermal conversion glass with the surface finish-polished is subjected to grating structure preparation according to the calculated incidence angles of the recording light 1 and the recording light 2, and the exposure angle schematic diagram is shown in fig. 8. The thickness of the photothermal conversion glass is 1 mm. During exposure, a black light absorbing sheet is attached to the back surface of the photo-thermal conversion glass, and the glass and the black light absorbing sheet are adhered by adopting refractive index matching fluid and air is exhausted, so that the influence of back reflection on grating writing is reduced as much as possible;
(C) exposing the photo-thermal conversion glass at the recording light angle by adopting ultraviolet light with the wavelength of 325nm, writing a volume Bragg grating channel with the wavelength of 532nm, and then writing volume cloth with the wavelength of 640nmThe exposure of the Lag grating channel is 100mJ/cm2；
(D) And then placing the optical fiber in a muffle furnace at 500 ℃ for hot development for 90 minutes, taking out the optical fiber, performing fine polishing on two light passing surfaces, plating antireflection films at 450nm, 532nm and 640nm, and finishing the preparation of the Bragg grating wavelength beam combiner.
Embodiment 1 is only used to explain the development process of the volume bragg grating wavelength combiner, and the used wavelength, the incident angle, the exit angle, and the number of channels can be changed according to the actual application situation.
In conclusion, the volume Bragg grating wavelength beam combiner has the advantages that the structure is more compact by writing a plurality of groups of grating channels into the photo-thermal conversion glass, the prepared volume Bragg grating wavelength beam combiner has better environmental adaptability, longer time anti-aging capability and higher laser damage resistance, and the requirements of high-power laser wavelength beam combination can be met. The preparation method of the volume Bragg grating wavelength beam combiner based on the photothermal conversion glass has fewer processes, is simple in flow control and is convenient for batch production.
It is to be understood that the invention is not limited to the examples described above, but that modifications and variations may be effected thereto by those of ordinary skill in the art in light of the foregoing description, and that all such modifications and variations are intended to be within the scope of the invention as defined by the appended claims.

Claims (9)

1. A method for preparing a volume Bragg grating wavelength beam combiner based on photo-thermal conversion glass is characterized by comprising the following steps:
obtaining known parameters of a Bragg grating wavelength beam combiner of a volume to be designed, wherein the known parameters comprise incident light wavelength
Figure 852169DEST_PATH_IMAGE001
Angle of incidence
Figure 158516DEST_PATH_IMAGE003
The emergence angle after the action of the Bragg grating wavelength beam combiner to be designed
Figure 255785DEST_PATH_IMAGE004
Wavelength of photothermal conversion glass
Figure 695470DEST_PATH_IMAGE006
Has a refractive index of
Figure 118361DEST_PATH_IMAGE008
A degree of modulation of refractive index of
Figure 912004DEST_PATH_IMAGE010
；
According to the incident angle of incident light
Figure 547385DEST_PATH_IMAGE011
And refractive index
Figure 437981DEST_PATH_IMAGE013
Calculating the angle of incidence inside the volume Bragg grating from the snell law of refraction
Figure 641560DEST_PATH_IMAGE014
And angle of departure
Figure 781554DEST_PATH_IMAGE015
；
According to the wavelength of incident light
Figure 361571DEST_PATH_IMAGE017
、Refractive index
Figure 903411DEST_PATH_IMAGE018
And angle of incidence within volume Bragg grating
Figure 277892DEST_PATH_IMAGE019
And angle of departure
Figure 905182DEST_PATH_IMAGE020
Calculating the grating inclination angle of the volume Bragg grating by using a vector circle method
Figure 757732DEST_PATH_IMAGE022
And period of time
Figure 685236DEST_PATH_IMAGE023
；
Calculating the diffraction efficiency of the volume Bragg grating to the TE polarized light according to the Kogelnik coupled wave theory
Figure 230618DEST_PATH_IMAGE025
；
After the period and the fringe inclination angle of the volume Bragg grating are determined, the interference included angle of two beams of recording light in the medium is obtained according to the principle of double-beam interference
Figure 345205DEST_PATH_IMAGE027
；
According to the interference included angle, obtaining the incident angle of the two beams of recording light in the medium
Figure 329341DEST_PATH_IMAGE029
And
Figure 721140DEST_PATH_IMAGE030
；
based on the incident angles of two beams of recording light in the medium
Figure 827636DEST_PATH_IMAGE032
And
Figure 36376DEST_PATH_IMAGE034
calculating and obtaining the incident angle of two beams of recording light outside the medium based on the snell principle
Figure 886520DEST_PATH_IMAGE036
And
Figure 132825DEST_PATH_IMAGE037
；
according to the calculated incidence angles of the two beams of recording light outside the medium
Figure 144643DEST_PATH_IMAGE039
And
Figure 171505DEST_PATH_IMAGE040
exposing the photo-thermal conversion glass to write corresponding wavelength
Figure 435127DEST_PATH_IMAGE041
The volume bragg grating channel of (a);
writing a plurality of volume Bragg grating channels corresponding to different wavelengths on the photo-thermal conversion glass according to the steps;
and carrying out thermal development treatment on the volume Bragg grating written into the channel, taking out the volume Bragg grating, carrying out crystal polishing on the two light passing surfaces, and plating an anti-reflection film to obtain the volume Bragg grating wavelength beam combiner.
2. The method for preparing the volume Bragg grating wavelength beam combiner based on the photothermal conversion glass according to claim 1, wherein the angle of incidence inside the volume Bragg grating is calculated according to the snell's law of refraction
Figure 660572DEST_PATH_IMAGE042
(ii) a An angle of departure of
Figure DEST_PATH_IMAGE043
。
3. The method for preparing the volume Bragg grating wavelength beam combiner based on the photothermal conversion glass as claimed in claim 2, wherein the grating inclination angle of the volume Bragg grating is calculated by a vector circle method
Figure 249817DEST_PATH_IMAGE044
With a period of
Figure DEST_PATH_IMAGE045
。
4. The method for preparing a volume Bragg grating wavelength beam combiner based on photothermal conversion glass according to claim 3, wherein when the Bragg mismatch amount is zero, the diffraction efficiency of the volume Bragg grating on TE polarized light is calculated according to the Kogelnik coupled wave theory and expressed as
Figure 498395DEST_PATH_IMAGE046
Wherein
Figure DEST_PATH_IMAGE047
，
Figure 831288DEST_PATH_IMAGE048
，
Figure 114501DEST_PATH_IMAGE050
the thickness of the volume bragg grating.
5. The method for preparing the volume Bragg grating wavelength beam combiner based on the photothermal conversion glass as claimed in claim 4, wherein the interference angle of the two beams of recording light obtained according to the principle of two-beam interference inside the medium is expressed as
Figure DEST_PATH_IMAGE051
Wherein
Figure DEST_PATH_IMAGE053
in order to record the wavelength of light,
Figure DEST_PATH_IMAGE055
is the refractive index of the glass at the wavelength of the recording light.
6. The light-based of claim 5The method for preparing the volume Bragg grating wavelength beam combiner of the thermal folding glass is characterized in that the incident angle of two beams of recording light in a medium is obtained according to the interference included angle and is expressed as
Figure 77909DEST_PATH_IMAGE056
And
Figure DEST_PATH_IMAGE057
。
7. the method for preparing a volume Bragg grating wavelength beam combiner based on photothermal conversion glass according to claim 6, wherein the incidence angles of the two recording lights outside the medium are calculated according to the snell principle and expressed as
Figure 545275DEST_PATH_IMAGE058
And
Figure DEST_PATH_IMAGE059
。
8. the method as claimed in claim 1, wherein the step of performing thermal development on the Bragg grating written in the channel comprises performing thermal development at 550 ℃ and 450 ℃ for 60-120 min.
9. A volume Bragg grating wavelength beam combiner based on photo-thermal conversion glass is characterized by being prepared by the preparation method of the volume Bragg grating wavelength beam combiner based on the photo-thermal conversion glass according to any one of claims 1 to 8.
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