A surface plasmon laser and a method for preparing the same

Abstract

The present invention belongs to the field of surface plasmon nanolasers, and particularly relates to a surface plasmon laser based on a pair of silver nanowires for a Fabry-Perot cavity. The laser includes a single-crystalline pair of silver nanowires, a gain medium, and a super-smooth metal film. An isolation layer is provided on the super-smooth metal film, the gain medium is disposed on the isolation layer, and the single-crystalline pair of silver nanowires are respectively disposed on both sides of the gain medium, so that the pair of silver nanowires and the super-smooth gold film form a surface plasmon resonance cavity of a composite structure, providing strong electric field confinement and directional scattering characteristics. The surface plasmon laser proposed by the present invention has a simple preparation process and is easy to operate. It can effectively convert pump light into surface plasmons and well confine them in the resonance cavity, realizing efficient excitation of the laser, obtaining an ultra-low excitation threshold, and being more suitable for micro-nano on-chip optical integration; by virtue of the scattering directivity of the surface plasmon resonance cavity, the problem of poor directivity of the plasmon laser can be improved. The present invention expands the application of surface plasmon lasers in the field of integrated optics.

Description

Technical Field

[0001] The present invention belongs to the field of surface plasmon nanolasers, and particularly relates to a novel surface plasmon laser based on silver nanowires for a Fabry - Perot cavity and a preparation method thereof. Background Art

[0002] Laser is the light amplification by stimulated emission of radiation, which has the advantages of high intensity, high directivity and monochromaticity. Since the advent of the first laser in 1960, lasers have played a crucial role in various fields of scientific research and daily life. In the past few decades, with the rapid development of laser technology and the increasing demand for laser applications, people have focused on developing lasers with higher peak power, shorter pulse duration, smaller cavity size and wider spectral range. Among them, in order to continuously miniaturize and micro - miniaturize lasers, a large number of researchers have designed and prepared a series of complex structures such as heterostructures, quantum wells, vertical - cavity surface - emitting lasers, microdisks, photonic crystals, etc., and have achieved great success in reducing the laser from the macroscopic scale to the wavelength level by reducing the cavity size. However, the cavity size is essentially limited by the optical diffraction limit. How to break through the diffraction limit and further reduce the mode volume of the laser to the sub - wavelength and deep sub - wavelength scale has become a research hotspot in the current integrated chip field.

[0003] Surface plasmon polaritons (SPPs) are electromagnetic modes formed by the interaction between electromagnetic fields and free electrons on the metal surface. It can confine electromagnetic waves at the sub - wavelength scale, thereby breaking through the diffraction limit of light, enabling micro - nano optical devices based on surface plasmon polaritons to control the transmission and processing of optical information at the sub - wavelength scale, and thus providing a powerful platform for the development of all - optical integrated nano - optical devices. In 2003, Bergman and Stockman proposed the concept of achieving surface plasmon amplification by stimulated emission of radiation (SPASER) using a plasmonic resonance cavity, and the size of this cavity will be reduced far below the diffraction limit of light in vacuum. The ultra - tight confinement characteristics of the optical field in the plasmonic cavity play a crucial role in realizing ultra - compact cavity modes, ultrafast laser modulation, and significantly enhancing the absorption and emission efficiency of the gain material in the cavity, thus further promoting the development of the forefront technology of lasers.

[0004] However, since the excitation of surface plasmons requires the introduction of metal, it means that the laser has the disadvantage of high loss. Among them, the loss of metal is divided into: scattering loss of internal free electrons and absorption loss of photons; scattering loss caused by the surface roughness of the metal film. This results in a relatively high threshold for surface plasmon lasers, severely limiting their practical applications. In the past two decades, in order to overcome the disadvantage of the high threshold of surface plasmon lasers, researchers have carried out a large number of scientific studies. However, most of them focus on planar plasmon lasers, and few researchers pay attention to the characteristics of more complex low-dimensional plasmon lasers. This difference may be because complex surface plasmon waveguides or cavities not only require a large grain size and good grain uniformity, but also need to ensure the processing of highly precise geometric shapes, such as wedge-shaped, groove-shaped and other structures, to reduce the scattering loss introduced by complex processing. However, complex geometric shapes such as grooves and wedges usually require nanomachining processes such as focused ion beam etching technology. This method is difficult to prepare, has a high processing cost, and inevitably introduces surface structure defects, thereby increasing the threshold of the plasmon laser and greatly reducing its application value. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the novel surface plasmon laser proposed by the present invention can improve the problems of high threshold and poor directivity of the plasmon laser by virtue of the strong electric field confinement characteristics and scattering directionality of the surface plasmon resonance cavity.

[0006] According to one aspect of the present invention, the present invention provides the following technical solutions:

[0007] A surface plasmon laser based on a silver nanowire pair for a Fabry-Perot cavity, the laser comprising a single-crystalline silver nanowire pair, a gain medium, and a super-smooth metal film. An isolation layer is provided on the super-smooth metal film, the gain medium is disposed on the isolation layer, and the single-crystalline silver nanowire pair is respectively disposed on both sides of the gain medium, so that the silver nanowire pair and the super-smooth metal film form a surface plasmon resonance cavity with a composite structure, providing strong electric field confinement and directional scattering characteristics.

[0008] As a preferred embodiment of the surface plasmon laser based on a silver nanowire pair for a Fabry-Perot cavity according to the present invention, wherein: the single-crystalline silver nanowire pair is made by directionally transferring and assembling single silver nanowires through a micro-nano manipulation arm.

[0009] As a preferred embodiment of the surface plasmon laser based on a silver nanowire pair for a Fabry-Perot cavity according to the present invention, wherein: the gain medium is a semiconductor nanowire or a monolayer two-dimensional material.

[0010] As a preferred embodiment of the surface plasmon polariton laser based on silver nanowires and Fabry-Perot cavity of the present invention, wherein: the gain medium is any semiconductor material in the visible to near-infrared band.

[0011] As a preferred embodiment of the surface plasmon polariton laser based on silver nanowires and Fabry-Perot cavity of the present invention, wherein: the gain medium is preferably gallium arsenide / indium gallium arsenide multi-quantum disk nanowires grown by vapor-liquid-solid growth mechanism.

[0012] As a preferred embodiment of the surface plasmon polariton laser based on silver nanowires and Fabry-Perot cavity of the present invention, wherein: the diameters and lengths of the gallium arsenide / indium gallium arsenide multi-quantum disk nanowires are 200 nm and 2 μm respectively;

[0013] As a preferred embodiment of the surface plasmon polariton laser based on silver nanowires and Fabry-Perot cavity of the present invention, wherein: the gain medium is preferably a monolayer two-dimensional material exfoliated by mechanical method, and the thickness of the monolayer two-dimensional material is 0.8 nm, and the length and width are 20×20 μm 2 。

[0014] As a preferred embodiment of the surface plasmon polariton laser based on silver nanowires and Fabry-Perot cavity of the present invention, wherein: the ultra-smooth metal film is made by combining thermal evaporation and template stripping method, and the ultra-smooth metal film is configured to be 1 μm 2 with Ra = 0.25 nm within the range.

[0015] As a preferred embodiment of the surface plasmon polariton laser based on silver nanowires and Fabry-Perot cavity of the present invention, wherein: the diameters and lengths of the silver nanowires are 100 - 400 nm and 10 - 40 μm respectively; the thickness of the ultra-smooth metal film is 50 nm, and the length and width are 2×2 cm 2 。

[0016] According to another aspect of the present invention, the present invention also provides the following technical solutions:

[0017] A preparation method of a surface plasmon polariton laser, the specific steps are as follows:

[0018] S1: Use the template stripping method to prepare an ultra-smooth metal film on the SiO2 / Si substrate;

[0019] S2: Adopt atomic layer deposition technology to deposit an Al2O3 isolation layer on the mechanically exfoliated ultra-smooth metal film;

[0020] S3: Transfer the gain medium to the ultra-smooth metal film with the isolation layer;

[0021] S4: Transfer two silver nanowires to both sides of the gain medium in sequence using a tungsten wire probe with a diameter of hundreds of nanometers to form a laser containing a surface plasmon resonance cavity.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. The present invention transfers silver nanowires to a super-smooth metal film at a fixed point. Compared with nano-processing techniques such as focused ion beam etching and electron beam lithography, this method has the characteristics of simple process, easy operation, strong controllability, low cost, and easy popularization, and completely avoids the structural scattering loss caused by processing defects. In addition, compared with traditional surface plasmon lasers, the laser proposed by the present invention can effectively convert pump light into surface plasmons and confine them well in the resonance cavity, realizing efficient excitation of lasers. Finally, a surface plasmon laser with an ultra-low threshold (threshold of 250 W / cm2 in Example 1 and 4.3 W / cm2 in Example 2) is obtained.

[0024] 2. The present invention uses a micro-nano manipulation arm combined with a self-made tungsten wire probe with a diameter of hundreds of nanometers. With the help of the tungsten wire probe with a diameter of hundreds of nanometers, the cavity length of the resonance cavity can be conveniently and flexibly adjusted. Compared with traditional plasmon lasers, flexible adjustment of the cavity length can be achieved, and then it can be integrated with semiconductor gain materials of various sizes and bandgap energies, realizing a surface plasmon laser with adjustable emission in the visible to near-infrared band.

[0025] 3. For the novel surface plasmon laser preparation method and the prepared laser proposed by the present invention, the silver nanowire pair and the super-smooth metal film form a composite structure surface plasmon resonance cavity. With the help of the scattering directivity of the surface plasmon resonance cavity, the problem of poor directivity of plasmon lasers can be improved. The surface plasmon resonance cavity and gain medium material described in the present invention are easy to purchase and have low prices, the preparation is controllable and the operation difficulty is low, and the preparation cost is relatively low, greatly increasing its application value. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0027] Figure 1(a) is an example diagram of the assembly structure of a plasmon resonance cavity formed by a single-crystal silver nanowire pair - super-smooth metal film of the present invention;

[0028] Figure 1(b) is the scattering spectrum diagram of the resonance cavity of the present invention;

[0029] Figure 2(a) is an example diagram of the results of the novel surface plasmon resonance cavity described in Embodiment 1 of the present invention for a monolayer two-dimensional material laser;

[0030] Figure 2(b) is the laser spectrum diagram of the novel surface plasmon resonance cavity described in Embodiment 1 of the present invention for a monolayer two-dimensional material laser;

[0031] Figure 3(a) is an example diagram of the results of the novel surface plasmon resonance cavity described in Embodiment 2 of the present invention for a gallium arsenide / indium gallium arsenide semiconductor nanowire laser;

[0032] Figure 3(b) is the laser spectrum diagram of the novel surface plasmon resonance cavity described in Embodiment 2 of the present invention for a gallium arsenide / indium gallium arsenide semiconductor nanowire laser. Detailed implementation manners

[0033] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0034] It should be noted that if there are directional indications (such as up, down, left, right, front, back...) involved in the embodiments of the present invention, the directional indications are only used to explain the relative position relationship and movement conditions between components in a specific posture (as shown in the drawings). If the specific posture changes, the directional indications will also change accordingly.

[0035] A preparation method of a surface plasmon laser, and the specific method steps are as follows:

[0036] S1: Prepare a super-smooth metal film on a SiO2 / Si substrate using the template stripping method;

[0037] S2: Deposit an Al2O3 isolation layer on the super-smooth metal film peeled mechanically by atomic layer deposition technology;

[0038] S3: Transfer the gain medium to the super-smooth metal film with the isolation layer;

[0039] S4: Use a tungsten wire probe of hundreds of nanometers to transfer two silver nanowires to both sides of the gain medium in sequence to form a laser containing a surface plasmon resonance cavity.

[0040] Embodiment 1

[0041] Surface plasmon laser based on silver nanowire pairs for a Fabry - Perot cavity. The laser has a surface plasmon resonance cavity. The laser includes single - crystal silver nanowire pairs, a gain medium, and an ultrasmooth metal film. An isolation layer is provided on the ultrasmooth metal film, the gain medium is disposed on the isolation layer, and the single - crystal silver nanowire pairs are arranged on both sides of the gain medium.

[0042] In the surface plasmon laser, the diameter and length of the silver nanowires are 100 - 400 nm and 10 - 40 μm respectively; the gain material is monolayer WSe2, with a thickness and size of 0.8 nm and 20×20 μm respectively. 2 The thickness of the metal film is 50 nm, the material is gold, and the length and width are 2×2 cm. 2 The performance of the surface plasmon laser is studied using the above parameters.

[0043] Using a bottom - up assembly process, first, an ultrasmooth metal film with a thickness of 50 nm is prepared by the template stripping method. Then, an aluminum oxide isolation layer with a thickness of 4 nm is deposited on both the top and bottom of the mechanically exfoliated single - layer two - dimensional material using atomic layer deposition technology. Finally, two silver nanowires are sequentially transferred onto the single - layer two - dimensional material using a self - made tungsten wire probe with a diameter of hundreds of nanometers to form a laser containing a surface plasmon resonance cavity.

[0044] The designed surface plasmon laser is placed at a low temperature of 4K for optical testing. As shown in Fig. 2(b), as the pump power increases, when the pump power density reaches 250 W / cm 2 , a narrow - line - width laser peak appears on the background of a broad fluorescence spectrum, demonstrating the threshold characteristic of laser emission.

[0045] Example 2

[0046] Surface plasmon laser based on silver nanowire pairs for a Fabry - Perot cavity. The laser has a surface plasmon resonance cavity. The laser includes single - crystal silver nanowire pairs, a gain medium, and an ultrasmooth metal film. An isolation layer is provided on the ultrasmooth metal film, the gain medium is disposed on the isolation layer, and the single - crystal silver nanowire pairs are arranged on both sides of the gain medium.

[0047] In the surface plasmon laser, the diameter and length of the silver nanowires are 100 - 400 nm and 10 - 40 μm respectively; the gain material is gallium arsenide / indium gallium arsenide semiconductor nanowires, with a diameter and length of 200 nm and 2 μm respectively; the thickness of the metal film is 50 nm, the material is gold, and the length and width are 2×2 cm. 2 The performance of the surface plasmon laser is studied using the above parameters.

[0048] Using a bottom-up assembly process, first, a 50-nm-thick ultra-smooth metal film is prepared by the template stripping method. Then, an 8-nm-thick aluminum oxide isolation layer is deposited on the ultra-smooth metal film by atomic layer deposition technology. Finally, a gallium arsenide / indium gallium arsenide semiconductor nanowire and two silver nanowires are sequentially transferred onto the metal film using a self-made tungsten wire probe with a diameter of hundreds of nanometers to form a laser containing a surface plasmon resonance cavity.

[0049] According to the steps described in Example 1, the designed surface plasmon laser is placed at a low temperature of 4K for optical testing. The threshold characteristics of the emitted laser and the phenomenon of linewidth narrowing are shown in Figure 3.

[0050] Compared with the plasmon lasers obtained by nano-fabrication processes such as focused ion beam etching and electron beam lithography, the surface plasmon laser proposed in the present invention is simple to fabricate, has a flexible adjustable cavity length, is inexpensive and easy to promote, and overcomes the high threshold phenomenon caused by the inherent ohmic loss of metals and the structural scattering loss of other surface plasmon lasers. The plasmon laser proposed in the present invention can convert the pump light into surface plasmons and confine them well in the resonance cavity, realizing the efficient excitation of the laser, and finally realizing a plasmon laser with an ultra-low threshold. The present invention can conveniently and flexibly adjust the cavity length of the resonance cavity with a self-made tungsten wire probe with a diameter of hundreds of nanometers, and then integrate it with semiconductor gain materials of various sizes and bandgap energies, realizing a surface plasmon laser with adjustable emission in the visible to near-infrared band. The novel surface plasmon laser proposed in the present invention can improve the problem of poor directivity of the plasmon laser by virtue of the scattering directionality of the surface plasmon resonance cavity. Therefore, the method described in the present invention greatly expands the application of surface plasmon lasers in the field of integrated optics.

[0051] In summary, the above are only the preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A surface plasmon laser based on a Fabry - Perot cavity with silver nanowires, characterized in that: The laser is based on the silver nanowire pair Fabry-Perot cavity technology. The laser includes a single-crystal silver nanowire pair with a pentagonal cross-section, a gain medium, and a super-smooth metal film. An isolation layer is provided on the super-smooth metal film, and the gain medium is disposed on the isolation layer. The single-crystal silver nanowire pair is respectively disposed on both sides of the gain medium, so that the silver nanowire pair and the super-smooth gold film form a surface plasmon resonance cavity of a composite structure, providing strong electric field confinement and directional scattering characteristics.

2. The surface plasmon laser based on a Fabry - Perot cavity using silver nanowires according to claim 1, wherein: The single-crystal silver nanowire pair is made by directionally transferring and assembling single silver nanowires with a micro-nano manipulation arm.

3. The surface plasmon laser based on a silver nanowire for a Fabry - Perot cavity according to claim 1, wherein: The gain medium is a semiconductor nanowire.

4. A surface plasmon laser based on a Fabry - Perot cavity using silver nanowires according to claim 1, characterized in that: The gain medium is any semiconductor material in the visible to near-infrared band.

5. A surface plasmon laser based on a Fabry - Perot cavity using silver nanowires according to claim 1, characterized in that: The gain medium is a gallium arsenide / indium gallium arsenide multi-quantum disk nanowire grown by a vapor-liquid-solid growth mechanism.

6. The surface plasmon laser based on a Fabry - Perot cavity using silver nanowires according to claim 5, wherein: The diameter and length of the gallium arsenide / indium gallium arsenide multi-quantum disk nanowire are respectively 200 nm and 2 μm.

7. A surface plasmon laser based on a Fabry - Perot cavity using silver nanowires according to claim 1, characterized in that: The gain medium is a monolayer two-dimensional material exfoliated by a mechanical method. The thickness of the monolayer two-dimensional material is 0.8 nm, and the length and width are 20×20 μm2.

8. The surface plasmon laser based on a Fabry - Perot cavity using silver nanowires according to claim 1, characterized in that: The super-smooth metal film is made by combining thermal evaporation and template stripping methods, and the super-smooth metal film is configured to have Ra = 0.25 nm within a range of 1 μm2.

9. The surface plasmon laser based on a Fabry - Perot cavity using silver nanowires according to claim 8, wherein: The diameter and length of the silver nanowire are respectively 100 - 400 nm and 10 - 40 μm; the thickness of the super-smooth metal film is 50 nm, and the length and width are 2×2 cm2.

10. A method for preparing a surface plasmon laser according to any one of claims 1-9, and the specific preparation method steps are as follows: S1: Use the template stripping method to prepare a super-smooth metal film on a SiO2 / Si substrate; S2: Adopt atomic layer deposition technology to deposit an Al2O3 isolation layer on the mechanically exfoliated super-smooth metal film; S3: Transfer the gain medium to the super-smooth metal film with an isolation layer; S4: Use a tungsten wire probe with a diameter of hundreds of nanometers to sequentially transfer two silver nanowires to both sides of the gain medium to form a laser containing a surface plasmon resonance cavity.

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