CN117761945A - Superlattice for reducing photorefractive effect of ferroelectric crystal - Google Patents
Superlattice for reducing photorefractive effect of ferroelectric crystal Download PDFInfo
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- CN117761945A CN117761945A CN202311791318.1A CN202311791318A CN117761945A CN 117761945 A CN117761945 A CN 117761945A CN 202311791318 A CN202311791318 A CN 202311791318A CN 117761945 A CN117761945 A CN 117761945A
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- 239000000463 material Substances 0.000 abstract description 17
- 230000003313 weakening effect Effects 0.000 abstract 1
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- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 description 12
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- 230000005621 ferroelectricity Effects 0.000 description 2
- 229910052749 magnesium Inorganic materials 0.000 description 2
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- WSMQKESQZFQMFW-UHFFFAOYSA-N 5-methyl-pyrazole-3-carboxylic acid Chemical compound CC1=CC(C(O)=O)=NN1 WSMQKESQZFQMFW-UHFFFAOYSA-N 0.000 description 1
- 229910013641 LiNbO 3 Inorganic materials 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
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- WYOHGPUPVHHUGO-UHFFFAOYSA-K potassium;oxygen(2-);titanium(4+);phosphate Chemical compound [O-2].[K+].[Ti+4].[O-]P([O-])([O-])=O WYOHGPUPVHHUGO-UHFFFAOYSA-K 0.000 description 1
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Abstract
The invention discloses a superlattice structure for reducing photorefractive effect of ferroelectric crystal, wherein main laser is transmitted in the ferroelectric crystal, the superlattice structure comprises a plurality of groups of auxiliary domain structures arranged in the ferroelectric crystal, each group of auxiliary domain structures generates auxiliary light by using the main laser, and domains of the auxiliary domain structures are arranged along the transmission direction of the main laser; each group of auxiliary domain structures comprises two sections of auxiliary optical domain structures which are sequentially arranged, wherein the two sections of auxiliary optical domain structures are a first auxiliary optical domain structure and a second auxiliary optical domain structure. The invention realizes weakening of the photorefractive effect of the ferroelectric material by designing the superlattice structure capable of generating the blue-violet laser in the ferroelectric material, thereby improving the laser spot shape in the ferroelectric material and reducing the phenomena of unstable power and the like caused by the photorefractive effect.
Description
Technical Field
The invention relates to the technical field of photoelectrons, in particular to a superlattice for reducing the photorefractive effect of ferroelectric crystals.
Background
Ferroelectric is a crystal in which some crystals have spontaneous polarization in a certain temperature range, and the spontaneous polarization direction thereof can be reversed by reversing the direction of an external electric field, and this property of the crystal is called ferroelectricity, and a crystal having ferroelectricity is called ferroelectric. Ferroelectric materials have many applications in piezoelectric, dielectric, pyroelectric, electro-optic, nonlinear optics, and the like. There are many kinds of ferroelectric materials, including single crystal, polycrystal, inorganic, organic, and the like. Ferroelectric optical crystals mainly include lithium niobate (LiNbO 3), lithium tantalate (LiTaO 3), potassium titanyl phosphate (KTiOPO 4), and the like. These optical crystals have nonlinear optical effects, electro-optical effects, abnormal photovoltaic effects and photorefractive effects. In terms of the electro-optic effect, the most important application field is the information industry, and a high-speed electro-optic modulator formed by adopting electro-optic crystals is widely applied to the optical communication industry; in the nonlinear optical effect, the most important application field is laser frequency conversion, for example, green lasers, which are widely used in the laser processing field, convert infrared laser light into 532nm laser light by the frequency doubling effect.
When the ferroelectric optical crystal is used, laser needs to pass through the crystal to act, and particularly in some high-power applications, high-intensity laser easily causes effects such as thermal lens, photorefractive and the like, so that the shape of the laser in the crystal is changed, the original shape cannot be maintained, the conversion efficiency in the use process is further influenced, and even irreversible damages such as crystal damage, fragmentation and the like are generated. And, the better the intrinsic optical quality of the ferroelectric crystal material, the fewer impurities, the higher the nonlinear efficiency and the more obvious the photorefractive effect. For example, in a high-power optical parametric oscillator, a focused 1064nm pump laser is easy to generate self-focusing and light spot deformation in a periodically polarized lithium niobate crystal (PPLN), so that the laser oscillation in a cavity is affected, the output laser power is unstable, and the higher power output is affected; in nonlinear waveguides, such as proton exchange, titanium diffusion or thin film lithium niobate waveguides, due to small mode volume, high optical power density, and common near infrared refraction phenomena caused by two-photon absorption equivalent are also common, and phenomena such as zero drift, unstable output, increased loss, waveguide damage and the like of waveguide devices such as thin film lithium niobate modulators are easily caused.
At present, a method of doping ions, such as doping magnesium (Mg: CLN) in lithium niobate, or increasing the working temperature to more than 100 ℃ is mainly adopted to reduce the photorefractive effect of the ferroelectric. Since Mg-CLN can be operated at room temperature after magnesium doping, the first proposal is currently generally adopted. However, even after doping techniques are employed, the photorefractive effect still exists during high power operation. A method for eliminating light spot distortion in a ferroelectric optical crystal is proposed by CN115857202a, which adopts blue-violet light irradiation to reduce photorefractive effect and eliminate light spot distortion; the method needs to adopt an extra blue-violet light source, and has high cost.
Disclosure of Invention
The invention aims to: the invention aims to provide a superlattice for reducing the photorefractive effect of ferroelectric crystals, so as to reduce the photorefractive effect of ferroelectric materials and reduce the phenomenon of unstable power caused by the photorefractive effect.
The technical scheme is as follows: the superlattice structure for reducing the photorefractive effect of the ferroelectric crystal comprises a plurality of groups of auxiliary domain structures arranged in the ferroelectric crystal, wherein each group of auxiliary domain structures utilizes the main laser to generate auxiliary light, and domains of the auxiliary domain structures are arranged along the transmission direction of the main laser; each group of auxiliary domain structures comprises two sections of auxiliary optical domain structures which are sequentially arranged, wherein the two sections of auxiliary optical domain structures are a first auxiliary optical domain structure and a second auxiliary optical domain structure; the wavelength of the auxiliary light is 300nm-500nm.
Further, the positions of the auxiliary domain structures meet the coherent superposition principle of phase matching, so that the blue-violet light phase generated by each auxiliary domain structure is coherent and constructive.
Further, each section of auxiliary domain structure is a chirp domain structure, or a periodic domain structure, or a quasi-periodic domain structure, or a non-periodic domain structure, or a random periodic domain structure or a cascade domain structure.
Further, when the main laser is light with a single wavelength, the first auxiliary light domain structure multiplies the frequency of the main laser to generate frequency-doubled light, and the second auxiliary light domain structure multiplies the frequency of the main laser and the frequency-doubled light to generate frequency-doubled auxiliary light.
Further, when the main laser is broadband light, each section of the auxiliary domain structure is a chirped domain structure or a quasi-periodic domain structure or an aperiodic domain structure.
Further, the first auxiliary optical domain structure multiplies the frequency of the main laser to generate frequency-multiplied light, and the second auxiliary optical domain structure multiplies the frequency-multiplied light to generate frequency-multiplied broadband auxiliary light.
Compared with the prior art, the invention has the following remarkable effects:
1. the invention does not need to adopt an extra blue-violet light source, thereby reducing the cost and the volume and being more convenient to use; the blue-violet light generated by frequency multiplication/frequency combination is transmitted in a collinear way with the main laser, the space mode is overlapped with the main laser, and the effect can be achieved only by small power;
2. the superlattice structure capable of generating blue-violet laser is designed in the ferroelectric material, so that the photorefractive effect of the ferroelectric material is weakened, the laser spot shape in the ferroelectric material can be improved, and the phenomena of unstable power and the like caused by the photorefractive effect can be reduced.
Drawings
FIG. 1 is a schematic illustration of the coaxial illumination mode of the present invention;
FIG. 2 (a) is a schematic diagram of the light spot in a ferroelectric crystal with high power and without assist light irradiation;
FIG. 2 (b) is a schematic diagram showing the distortion of the light spot in the ferroelectric crystal when the power is high;
FIG. 2 (c) is a schematic diagram of the light spots in the ferroelectric crystal after irradiation with assist light at a higher power;
FIG. 3 is a schematic diagram of the domain polarization scheme of example 1;
FIG. 4 is a schematic view of a thin film lithium niobate waveguide in example 2;
FIG. 5 is a schematic diagram of a wideband domain polarization scheme for a thin film lithium niobate waveguide.
Detailed Description
The invention is described in further detail below with reference to the drawings and the detailed description.
In order to solve the problems in the prior art, the invention provides a method for manufacturing a periodically polarized domain structure in a ferroelectric superlattice, generating blue-violet laser through nonlinear effects such as frequency multiplication or difference frequency and the like, exciting carriers in a ferroelectric material, and improving the conductivity of the ferroelectric material, thereby reducing the change of a photoinduced electric field and a photoinduced refractive index in the material and improving the photorefractive threshold of the material.
The reason for distortion of the laser in ferroelectric crystals is mainly abnormal photovoltaic and photorefractive effect, and charges generated locally by irradiation of a laser (hereinafter referred to as main laser) spot in the crystals cannot be neutralized, so that the refractive index tensor of the crystals is changed, and the shape of the spot is deformed. The basic principle of the invention is that blue-violet light/ultraviolet light (called auxiliary light hereinafter) with short wavelength is generated through domain structure design to irradiate a facula distortion area, a large number of carriers are excited in the crystal, and charges generated by photovoltaic energy are neutralized.
The wavelength of the auxiliary light is between 300nm and 500nm, such as 355nm, 387nm, 405nm, 450nm, 473nm and the like, and the generation mode comprises, but is not limited to, frequency multiplication, frequency combination, difference frequency, OPA, OPG, OPO and other second-order nonlinear processes.
The generation of the assist light is achieved by the design of the domain structure of the ferroelectric superlattice, including but not limited to periodic, quasi-periodic, non-periodic, random periodic, cascaded, etc. structures.
The main principle of domain structure design of the ferroelectric superlattice is as follows:
(1) The periods of the domain structures are arranged along the transmission direction of the main laser, the periods are distributed in the longitudinal area of the transmission of the main laser, the phase matching inverted lattice vectors generated by the periods are very small, only auxiliary blue-violet light with the magnitude smaller than mW is generated, and the power of the main laser is basically not influenced;
(2) The domain structures are distributed in the transmission direction of the main laser in a segmented manner, each segment only occupies a very small length, so that the main laser transmission is not influenced, and all positions of the main laser transmission play a role in assisting the main laser transmission;
(3) The preferable design scheme of the domain structure is a quasi-periodic, non-periodic and other broadband nonlinear matching scheme, and the purpose is to adapt to transmission main lasers with more wavelengths;
(4) The sectional design of the domain structure needs to ensure that the distribution position of each section follows the coherent superposition principle of phase matching, so that the blue and violet light phase generated by each section of domain structure is the same, thereby enabling the intensity to be coherent and constructive and increasing the generation intensity of the blue and violet light;
(5) If the ferroelectric material needs to design a phase matching domain inversion for the main laser, an additional blue-violet light generating inverted lattice vector can be added to the domain inversion design of the main laser.
Example 1
This embodiment is designed for periodic domain structures in bulk ferroelectric crystals. As shown in fig. 1, a periodically poled lithium niobate crystal, abbreviated as PPLN, is used to generate a new frequency laser beam under the pumping of a main laser beam (e.g., 1064 nm). The main laser is Gaussian beam near the fundamental mode, enters the crystal after being focused by the lens, and the light spot is shown in fig. 2 (a); when the power is strong, the light spot in the crystal is distorted as shown in fig. 2 (b); after irradiation with the assist light, the spot is as shown in fig. 2 (c). The target auxiliary light wavelength adopted by the invention is 355nm, and is realized by the main laser through the frequency multiplication and frequency combination process, and the required power is 1mW.
Since the main laser is 1064nm laser with fixed wavelength, the domain structure design is realized by adopting cascade domains with single periods at two ends, and the specific scheme is shown in fig. 3.
As shown in fig. 3, 1064 main laser is used to generate 1550nm laser at the difference frequency, the polarization period of the main laser required domain is about 30 μm, and the quality of the beam is deteriorated due to photorefractive effect during transmission. In order to reduce the photorefractive effect, fig. 3 adopts a design scheme of an auxiliary domain structure: each set of auxiliary domain structures is a two-segment superlattice including a first auxiliary optical domain structure 1 and a second auxiliary optical domain structure 2, and after being separated by a distance, the first auxiliary optical domain structure 1 and the second auxiliary optical domain structure 2 are repeated, generating 355nm triple frequency light. The first auxiliary optical domain structure 1 is used for carrying out frequency multiplication on main laser to generate 532nm frequency multiplication light, and the domain polarization period is about 7 mu m; the second auxiliary optical domain structure 2 is used for generating 355nm ultraviolet light with frequency doubling of three times by frequency combination of the main laser and the frequency doubling light, and the domain polarization period is about 1.7 mu m. Because the required inverted lattice vector is small, in order to reduce the polarization difficulty, high-order polarization periods, such as 3, 5, 7-order periods of 1.7 μm, and the like, can be adopted for matching, and the 7-order period is 11.9 μm. The polarization periods are all approximate values and need to be calculated specifically according to specific materials and environmental temperatures. The number of the auxiliary optical domain structures is not limited to two, and the auxiliary optical domain structures can be repeated for a plurality of times according to the requirements (namely, the number of segments m of the auxiliary optical domain structures is more than or equal to 2).
Example 2
This embodiment is a domain polarization scheme for a thin film lithium niobate waveguide modulator. As shown in fig. 4, in the same manner as in example 1, in order to eliminate the distortion of the main laser light in the thin film lithium niobate modulator, the auxiliary light of 387nm was transmitted along the waveguide. In the embodiment, the auxiliary light adopts four times of the frequency of 1550nm of the main laser and adopts a two-stage scheme of frequency multiplication and frequency multiplication.
As shown in fig. 5, the primary laser 1550nm frequency doubling adopted by the thin film lithium niobate waveguide auxiliary light is generated by the third auxiliary light domain structure 3 and the fourth auxiliary light domain structure 4 shown in the previous figures. Specifically, since the main laser wavelength of the thin film lithium niobate modulator is not strictly 1550nm, a four-frequency chirp, quasi-periodic and non-periodic structure of a broadband needs to be designed to match with the frequency multiplication process of the broadband. Specifically, the third auxiliary optical domain structure 3 of the broadband can adopt chirp, quasi-periodic, non-periodic and other structures to realize broadband frequency multiplication of 1500nm-1600nm and generate frequency multiplication light of 750nm-800nm, for example, the period range of the chirp structure is 18 μm-21 μm. Specifically, the fourth auxiliary optical domain structure 4 of the broadband can adopt chirp, quasi-periodic, non-periodic structures and the like to realize broadband frequency multiplication of 750nm-800nm and generate frequency multiplication light of 375nm-400nm, for example, the period range of the chirp structure is 2 μm-2.7 μm. Also, similar to example 1, since the required inverted lattice vectors of the third auxiliary optical domain structure 3 and the fourth auxiliary optical domain structure 4 are small, in order to reduce the polarization difficulty, a high-order polarization period, for example, a period of 3, 5, 7, etc. steps of 2 μm, and a period of 7 steps of 14 μm may be used for matching. The polarization periods are all approximate values and need to be calculated specifically according to specific materials and environmental temperatures. The auxiliary optical domain structure is not limited to two, and can be repeated for a plurality of times according to the requirement (namely, the number of segments n of the auxiliary domain structure is more than or equal to 2).
Claims (6)
1. The superlattice structure for reducing the photorefractive effect of the ferroelectric crystal, wherein main laser light is transmitted in the ferroelectric crystal, is characterized by comprising a plurality of groups of auxiliary domain structures arranged in the ferroelectric crystal, each group of auxiliary domain structures generates auxiliary light by using the main laser light, and domains of the auxiliary domain structures are arranged along the transmission direction of the main laser light; each group of auxiliary domain structures comprises two sections of auxiliary optical domain structures which are sequentially arranged, wherein the two sections of auxiliary optical domain structures are a first auxiliary optical domain structure (1) and a second auxiliary optical domain structure (2); the wavelength of the auxiliary light is 300nm-500nm.
2. The superlattice structure for reducing a photorefractive effect of a ferroelectric crystal according to claim 1, wherein a plurality of sets of said auxiliary domain structures are positioned to satisfy a phase-matched coherent superposition principle such that blue-violet light phases generated by each set of said auxiliary domain structures are coherent and constructive.
3. The superlattice structure for reducing a photorefractive effect of a ferroelectric crystal according to claim 1, wherein each of said auxiliary domain structures is a chirped domain structure, or a periodic domain structure, or a quasi-periodic domain structure, or a non-periodic domain structure, or a random periodic domain structure, or a cascade domain structure.
4. A superlattice structure for reducing the photorefractive effect of a ferroelectric crystal according to claim 3, wherein when the main laser light is light of a single wavelength, the first auxiliary light domain structure (1) multiplies the main laser light to generate frequency-doubled light, and the second auxiliary light domain structure (2) multiplies the main laser light and the frequency-doubled light to generate frequency-doubled auxiliary light.
5. A superlattice structure for reducing the photorefractive effect of a ferroelectric crystal according to claim 3, wherein when the main laser is broadband light, each of said auxiliary domain structures is a chirped domain structure, or a quasi-periodic domain structure or an aperiodic domain structure.
6. The superlattice structure for reducing a photorefractive effect of a ferroelectric crystal according to claim 5, wherein said first auxiliary optical domain structure (1) multiplies a primary laser light to generate a doubled light, and said second auxiliary optical domain structure (2) multiplies said doubled light to generate a quadrupled broadband auxiliary light.
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