Second harmonic generation device with monolayer m0s 2 having near-perfect conversion efficiency

Abstract

The invention relates to an integrated photonic device (100) configured for near-perfect second harmonic generation (SHG) at a resonant optical wavelength λ. The device includes a substrate (S), a first (101) and second (109) distributed Bragg reflector (DBR) made of alternating layers with different refractive indices (103, 105), and a monolayer of MoS2 (ML MoS2) as the nonlinear material sandwiched between identical insulating layers (102). The device utilizes a Fabry-Perot cavity configuration, enhancing the electric field at λ, ensuring maximum SHG efficiency. The phase matching condition is satisfied due to the sub-nm thickness of MoS2 layer of 0.62 nm. The device is an SHG device with an input at 1550 nm and an output at 775 nm, with SHG conversion efficiencies higher than 99%. Ultra high nonlinear susceptibility of MoS2 also optimizes SHG performance, and the device is therefore very efficient for photonic applications.

Description

SECOND HARMONIC GENERATION DEVICE WITH MONOLAYER M0S2 HAVING NEAR-PERFECT CONVERSION EFFICIENCYCROSS-REFERENCES TO RELATED SYSTEMS

[0001] This application claims priority to Indian provisional patent application no. 202441025035 entitled SECOND HARMONIC GENERATION DEVICE WITH MONOLAYER M0S2 on 28 March, 2024.FIELD OF THE INVENTION

[0002] The invention generally relates to photonics and in particular it is related to non-linear optics and photonic crystal.DESCRIPTION OF THE RELATED ART

[0003] Second Harmonic Generation (SHG) is the lowest-order optical nonlinear (NL) conversion process where two photons of the same frequency combine to generate a photon of twice that frequency. This is a special case of sum frequency generation. SHG is used extensively to get coherent light sources in new spectral domains. For example, 532 nm laser output is generated by pumping high intensity of more common 1064 nm laser into KTP (KTiOPCL) or KDP (KH2PO4) crystals. In addition, SHG is used in autocorrelators to accurately and directly measure the duration and width of ultra-short pulses and plays a critical role in quantum studies in stabilizing optical frequency combs.

[0004] In bulk crystal under non-depleted pump regime, the SHG signal power grows with the light-matter interaction strength which depends directly on propagation distance in the NL crystal, material’s second order nonlinear susceptibility (%(2)), and the pump power. With a typical value of ~ 10 pm / V for %(2), one normally needs sample thickness of a few mm for conversion efficiency >10%. In addition, careful phase matching between the pump and the signal is required for enhanced conversion efficiency. A conversion efficiency of 80 % requires KDP or KTP of nearly cm thickness and such thick crystals are not suitable for compact devices or on-chip applications. The conversion efficiency can be improved by increasing the effectivepump power with resonant cavities such as whispering gallery mode resonators, on-chip micro ring resonators, micro disks or photonic crystal cavities and this concept is utilized in earlier designs. The cavity increases the local electric field strength, and thus light-matter interaction is enhanced. Although in microscale devices the conversion efficiency has been predicted to be 44% in simulations, only 15% was realized in the experiments, owing to the lack of proper in and out power coupling, low Q-factor of the resonators, and low values of %(2)in most common materials like AIN (4.7 pm / V). periodically poled lithium niobate (PPLN) (19.5 pm / V). GaAs (110 pm / V) and Alo.3Gao.7As (100 pm / V). Efficiencies at near infrared frequencies are mostly low (-10%) and the intensity for optimum conversion is mostly high. Novel materials and / or designs needed for improving efficiency and lowering the threshold intensity for optimum efficiency.

[0005] Ever since graphene has been demonstrated to possess interesting electronic and optical properties, a larger number two-dimensional (2D) materials have been explored for a number of properties including optical nonlinearity. Particularly, the monolayer 2D materials lack the inversion symmetry, a key requirement for finite %(2). An extremely large value of 105pm / V for %(2)in monolayer (ML) M0S2 at 810 nm wavelength has been deduced from SHG measurements. Recently, in spontaneous parametric down conversion (SPDC) measurements, a ML of M0S2 was interpreted to have a value of 104pm / V at 875 nm and 6xl03pm / V at 775 nm. However, / 2’ became smaller for larger odd number of M0S2 layers and nearly zero for even number of M0S2 layers. Despite large / 2’. the optical pathlength in this ML material is less than a nm, and hence the SHG or SPDC conversion is not efficient. An approach to increase either the effective pathlength and / or the effective electric field strength, is needed to exploit the large nonlinearity.

[0006] Therefore, the innovation solves previous method issues through advanced techniques that improve both nonlinear efficiency performances and compact device functionality. The invention addresses nonlinear conversion in thin materials and offers new designs that maximize SHG efficiency while avoiding large crystal thickness combined with excessive intensity requirements.SUMMARY OF THE INVENTION

[0007] Devices and methods for near-perfect second harmonic optical conversion are presented. In various embodiments, the present invention relates to an integrated photonic device (100) configured to provide near-perfect second harmonic generation (SHG) operating at a resonant optical wavelength X. The device comprises a substrate (S) and a first distributed Bragg reflector (DBR) (101) formed by alternating layers of materials with different refractive indices (103, 105). The thickness of these layers is specifically designed to be X / 4m,2, where ni and are the refractive indices of the corresponding layer. A monolayer (107) of M0S2 (ML M0S2) is used as the nonlinear material, sandwiched between two identical insulating layers (102) with a thickness of Z / 4113- where n is the refractive index of the insulating layer. So, the total thickness of the cavity is X / 2n3. The device further includes a second distributed Bragg reflector (DBR) (109) formed by alternating layers of different reflective index (103, 105), where light of wavelength X is configured to enter the device through the second DBR (109) and light of second harmonic of X / 2 is configured to be transmitted through the first DBR (101) and reflected through the second DBR (109).

[0008] In some embodiments, the high refractive index (103) material of the DBRs is Sb2S3, while the low refractive index (105) material is SiCU.

[0009] In various embodiments, the thickness of the M0S2 layer (107) is 0.62 nm.

[0010] In some embodiments, the number of alternating layers (103, 105) in both the first and second DBRs is carefully selected to achieve near-complete second harmonic conversion. For example, the insulating layers (102) may be made of hexagonal boron nitride (h-BN), with Sb2S3as the high refractive index (103) material and SiCh as the low refractive index (105) material. In some embodiments, the first DBR (101) has 13 sets of alternate high and low refractive index materials along with an additional capping layer of Sb2S3, and the second DBR (109) includes 9 sets of alternate high and low refractive index materials along with an additional capping layer of Sb2S3. The device is designed to operate at an input wavelength of 1550 nm and produce an output at 775 nm.

[0011] In some embodiments, the use of h-BN is an insulating layer (102) between the DBRs ensuring that the M0S2 is placed at the middle of the cavity where the electric field is maximized, leading to greater SHG efficiency. At a pump intensity of 10 kW / cm2, the device is capable of achieving a SHG conversion efficiency greater than 99%, with the cavity quality factor reaching approximately 1,960,000.

[0012] In various embodiments, the ultra-high second-order nonlinear susceptibility of the ML M0S2, which is 104pm / V, contributes to the device's impressive SHG performance and thus an attractive, highly efficient solution for second harmonic generation in photonic applications.

[0013] This, and other aspects are disclosed herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings are provided to better illustrate the present invention, and they form an integral part of the detailed description of the invention, in which:

[0015] FIG 1 illustrates device design for SHG conversion using a monolayer M0S2 (ML M0S2) sandwiched between hexagonal boron nitride (h-BN) layers and placed in a cavity formed by Distributed Bragg Reflectors (DBRs).

[0016] FIG. 2A illustrates SHG conversion through bulk BBO crystal demonstrating the superiority of the device in FIG 1.

[0017] FIG 2B illustrates SHG conversion through BBO in a cavity created by two Distributed Bragg Reflectors (DBRs) again demonstrating the superiority of the device in FIG 1.

[0018] FIG 2C illustrates SHG conversion using a monolayer M0S2 (ML M0S2) sandwiched between hexagonal boron nitride (h-BN) layers and placed in a cavity formed by DBRs.

[0019] FIG. 3A shows the variation of second harmonic power conversion efficiency as a function of propagation length in a phase matched BBO crystal.

[0020] FIG. 3B shows the variation of SHG conversion efficiency as a function of pump intensity in a phase matched BBO crystal.

[0021] FIG. 4 shows Second harmonic conversion using a symmetric and asymmetric DBR with BBO in the cavity.

[0022] FIG. 5 shows the electric field enhancement (left axis) and the refractive index profile (right axis) inside the cavity with monolayer M0S2 at the middle of the cavity.

[0023] FIG. 6A shows the calculated SHG conversion efficiency using monolayer M0S2 in a DBR cavity as a function of pump intensity.

[0024] FIG. 6B shows the second harmonic conversion efficiency plotted as a function of wavelength for different pump intensities in case of monolayer M0S2 in a DBR cavity.

[0025] FIG. 7 shows the comparison between the SHG conversion efficiency curves from the structures with cavity filled by BBO with that filled by h-BN / MoS2 / h- BN stack.

[0026] FIG. 8 shows the SHG conversion efficiency variation with angle of incidence of the pump at the critical intensity of SHG conversion efficiency for normal incidence with monolayer M0S2 in a DBR cavity.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from its scope.

[0028] Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of "a", "an", and "the" include plural references. The meaning of "in" includes"in" and "on." Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein.

[0029] The present subject matter of this invention discloses a photonic second harmonic generation (SHG) device and method using a monolayer M0S2 (ML M0S2) in a resonant cavity system to enhance SHG conversion efficiency. The device uses a resonant cavity with Distributed Bragg Reflectors (DBRs) formed by quarterwavelength thickness layers of alternate high and low refractive index materials, and insulating h-BN layer of total half wavelength thickness as the cavity. SHG conversion is improved with the use of the nonlinear properties of the ML M0S2 which is placed at the center of the cavity where the electric field is maximum. Phase-matching condition is satisfied due to the sub-nm thickness of ML M0S2. The device and method are further disclosed with reference to the drawings.

[0030] As illustrated in FIG. 1, the invention discloses in its various embodiments an integrated photonic device 100 configured for near-perfect second harmonic generation (SHG) operating at a resonant optical wavelength X. The device includes a substrate S, over which a first distributed Bragg reflector (DBR) (101) formed by alternating layers of different reflective index materials 103, 105 is placed. These layers have a thickness of X / 4m,2. where m and are the refractive indices of the corresponding high and low refractive index materials. The device next includes a monolayer M0S2 107 (ML M0S2) material placed as the nonlinear material, sandwiched between identical insulating layers 102. The thickness of the insulating layers is X / 4ns, where ns is the refractive index of the insulating layer. A second distributed Bragg reflector (DBR) (109) formed by alternating layers of different refractive index (103, 105) is placed over the sandwiched monolayer material 107 and cavity materials 102. The device operates by allowing light of wavelength X to enter the device through the second DBR 109, interact with the M0S2, and to generate a second harmonic signal at a wavelength of X / 2. The second harmonic light is transmitted through the first DBR 101 and reflected through the second DBR 109.

[0031] In some embodiments, the thickness of the M0S2 layer 107 is 0.62 nm.

[0032] In various embodiments, the number of sets of alternating layers 103, 105 in the first or the second DBR is configured to achieve near-complete second harmonic conversion from the device. The high refractive index material 103 comprises Sb2S? and the low refractive index material 105 is SiO2. The insulating layers (102) are hexagonal boron nitride (h-BN). The first DBR 101 has 13 sets of alternate high and low refractive index materials, along with an additional capping layer of the high refractive index material Sb2S3. The second 109 DBR includes 9 sets of alternate high and low refractive index materials, with an additional capping layer of high refractive index material Sb2S3. The device is configured to operate at an input wavelength of 1550 nm and generate an output at 775 nm.

[0033] In various embodiments of the device, the high refractive index material 103 comprises Sb2S? and the low refractive index material 105 is SiO2. In various embodiments, the configuration of the first 101 and second 109 DBRs forms a Fabry- Perot cavity, which enhances the electric field at the resonant wavelength X. The use of h-BN as insulating layers (102) is configured to fill the cavity between the two DBRs and the MoS2is placed at the middle of it where the electric field is at a maximum. This placement ensures that the device achieves maximum conversion efficiency. The phase matching condition is automatically satisfied due to the ultra-thin nature of the MoS2monolayer, contributing to efficient SHG.

[0034] In various embodiments, the device is configured to have a SHG conversion efficiency greater than 99% at a pump intensity of 10 kW / cm2. The quality factor of the cavity is about 1,960,000. In various embodiments, the device uses ML MoS2as a nonlinear material due to its ultra-high second-order nonlinear susceptibility of 104pm / V. which is crucial for achieving efficient second harmonic generation. This configuration exploits light confinement and electric field strength inside the cavity, so that the SHG process is maximized for high efficiency and minimal loss.

[0035] The invention has multiple advantages, as further discussed here. This invention offers several key elements for improving the efficiency of second harmonic generation (SHG). Increase in the second-order nonlinear effect is achieved by using monolayer MoS2(ML MoS2) in the specially designed resonant cavity, enabling a quite sufficient SHG conversion rate at the same time, even with lower pump intensitycompared to traditional devices. The incorporation of both ML M0S2 and the electric field enhancement due to cavity at the pump wavelength (1550 nm) allows the device to achieve the conversion efficiency of around 99% at a pump power of 10 kW / cm2. The phase matching condition is fulfilled automatically due to the sub-nm thickness of monolayer M0S2. The device is also capable of being engineered to perform the inverse transformation, which has the potential to be used for generation of sources of entangled photons for quantum technology. This approach represents a major step forward in photonic devices, overcoming the limitations of traditional bulk crystals and opening up new possibilities for compact, high-efficiency SHG systems.

[0036] EXAMPLES

[0037] EXAMPLE 1: Design of the Photonic Device

[0038] COMSOL Multiphysics software is used for optical modelling. A pump at 1550 nm is used to produce a signal at 775 nm. Three cases of FIG. 2(A), (B) and (C) are considered to show the superiority of the invention. FIG. 2(A) shows SHG conversion through the industry workhorse bulk BBO, 2(B) BBO in a cavity created by two DBRs, and 2(C), which is our actual invention, a ML M0S2 sandwiched between h- BN and placed in the cavity made of the DBRs used in case 2(B). To avoid the Fresnel loss and the consequent SHG efficiency, the perfectly matched layer (PML) is placed on top of all systems. However, for realistic predictions and comparison, air is the entry surface for the other two cases. In the case 2(A) bulk BBO crystal of length 10 pm is used assuming perfect phase matching between the pump and the SHG wavelengths in order to estimate the maximum possible conversion. For cases 2(B) and 2(C), the DBRs are made of quarter wavelength thick alternating layers of high index Sb S and low index SiO2 and the cavity is total half wavelength thick. Cavity in fig 2(B) is filled with BBO. The thickness of a ML M0S2 in FIG 2(C) is 0.62 nm and the rest of cavity is filled with h-BN. Optionally, h-BN may be replaced by SiO2. The location of M0S2 is adjusted so that it is placed where the electric field inside the cavity reaches the maximum. The introduction of M0S2 causes a shift in the resonant frequency that is greater than the resonance linewidth because of the high quality factor resonance. Therefore, by suitably modifying the cavity length or changing the angle of incidence, the resonance frequency is tuned to the desired value.

[0039] EXAMPLE 2: Optical modelling and SHG simulations using COMSOL Multiphysics

[0040] Optical modelling is done using COMSOL Multiphysics software. It is assumed that a signal at 775 nm is produced by a pump at 1550 nm. The design satisfies the phase-matching condition inherently for the ML M0S2. The normal incidence SHG simulations are done in COMSOL Multiphysics with a linearly polarized plane wave as the source of the 1550 nm pump. The SHG conversion efficiency predicted is greater than 99% at a pump intensity of 10 kW / cm2. For comparison, first, the calculations are carried out for conversion through bulk BBO. The defect-mediated and free carrier absorption in BBO was neglected. FIG. 3A shows the variation of second harmonic power conversion efficiency as a function of propagation length in a perfectly phase matched BBO crystal at pump intensity 100 kW / cm2. The calculated SHG efficiency is only 2.5 x W8% for a 10 pm long crystal. Higher conversion efficiency is possible with thicker BBO since conversion varies quadratically with length in low conversion regions. FIG. 3B shows the variation of SHG conversion efficiency as a function of pump intensity for a 10 pm -thick BBO crystal. There can be around 70% conversion with an unrealistically high-power of 1012kW / cm2pump intensity.

[0041] EXAMPLE 3: SHG conversion efficiency of BBO in resonant cavity with DBRs

[0042] For moderate conversion with realistic intensity levels, either thickness has to be increased to cm or a resonant cavity has to be employed. Since the length of the nonlinear medium cannot be increased beyond the phase matching length, cavity with appropriate Q-factor is chosen to increase light intensity by orders of magnitude. The DBRs are made of Sb2S? with a higher-index of 2.77 and SiO2 with a lower index of 1.45. The calculations performed with BBO (of thickness 470 nm) in the cavity. FIG. 4 displays the calculated performance. When the DBR mirrors have equally high reflectivity (symmetric mirrors), we get a Q-factor -970,000 with N = 9 number of DBR periods on each side and the intensity dependent SHG efficiency (FIG. 4, lower curve) is predicted to reach a maximum value of 36% at 10 MW / cm2of intensity. When the DBR mirrors have unequal but high reflectivity (asymmetric mirrors), much larger Q-factor -1,960,000 is obtained with Ni = 9 and N2 = 13 DBR periods on each side andthe intensity-dependent SHG efficiency is predicted to reach a maximum value of 71% at 1 MW / cm2. Although the output intensity level is reasonable, the materials would experience thermal runaway problem because of free carrier and defect mediated absorption not considered here.

[0043] EXAMPLE 4: Evaluation of SHG property using ML M0S2 in cavity

[0044] Finally, the SHG property of a ML M0S2 in the cavity is evaluated. SinceML thickness of 0.62 nm is much smaller than cavity thickness, the NL material has to be appropriately sandwiched, preferably with a low index material, to fill the cavity. M0S2 is routinely used with h-BN which has an index of 2.08, and a sandwich structure made of h-BN / MoS2 / h-BN to fully occupy the cavity is considered. The introduction of a single layer M0S2 approximately at the midpoint of the cavity, which is filled with half wavelength thick h-BN, functions as a defect layer within the structure. The presence of the defect layer induces a shift in the cavity resonance towards longer wavelength. In order to achieve the cavity resonance to the targeted 1550 nm, it is necessary to reduce the cavity length appropriately. Other option to tune the resonance frequency is to change the angle of incidence instead of reduction of cavity length. This will keep the M0S2 at the maximum of electric field to avail the maximum SHG conversion. FIG. 5 shows the electric field enhancement (left axis) and the refractive index profile (right axis) inside the cavity to illustrate the location of M0S2 (index 2.93). A / J2’ value of 104pm / V for M0S2 is used in calculations.

[0045] EXAMPLE 5: SHG conversion efficiency and coupled-mode theory

[0046] The calculated SHG conversion efficiency as a function of pump intensity is shown in FIG. 6A. It is predicted that SHG conversion efficiency of >99% can be achieved with a monolayer M0S2 at a much lower pump intensity of 10 kW / cm2. In FIG. 6B the second harmonic conversion efficiency is plotted as a function of pump wavelength for different pump intensities. A couple of observations are made, (1) The efficiency falls rapidly as the central wavelength is changed because of the high Q- cavity resonance. For wavelengths away from the central wavelength, the cavity electric field enhancement decreases and hence conversion efficiency also decreases. (2)Similarly, the FWHM increases as the intensity increases as expected from the coupled mode theory.

[0047] The skewed bell shape of the intensity-dependent SHG conversion efficiency (FIG. 6A) curve can be explained by the coupled-mode theory of Askin and its extension to SHG in a resonant cavity by Kozlovsky. As per this theory, the maximum conversion happens when the impedance is matched — in- and out- coupling of the cavity are equal. The in-coupling is determined by (1 - ri) where ri is the reflectivity of the entry mirror and the out coupling by (1 - rm) where rmis the effective reflectivity of the cavity excluding the entry mirror. The rmis a product of the reflectivity of the exit mirror, the transmission through the cavity, and the SHG conversion in the nonlinear material. For asymmetric cavity, the reflectivity of the entry mirror is taken lower than that of the exit mirror. At low intensities, SHG conversion is low and as a result the out-coupling is far smaller the in-coupling, leading to low conversion efficiency. At very high intensities, the SHG conversion is very high which results in larger out-coupling and the impedance -matching not satisfied, leading to lower SHG efficiency. Only at intermediate intensities, both coupling can be equal to achieve the impedance-matching condition which leads to highest SHG conversion. For symmetric cavity, since the reflectivity of the two mirrors are equal, and as long as there is SHG conversion, the impedance matching will never be achieved and as a result SHG conversion will be less compared to the asymmetric case. Since outcoupling varies with pump power, the SHG conversion curve will attain a maximum when in- and out- couplings are closest being equal.

[0048] EXAMPLE 6: Comparison of SHG conversion efficiency in BBO and M0S2 Systems

[0049] It is instructive to compare the SHG conversion efficiency curves from the structures with cavity filled by BBO with that filled by h-BN / MoS2 / h-BN stack, shown in FIG. 7. It is noted that the peak efficiency improves from -71% to >99%. More noticeably, the critical intensity for peak efficiency reduces by a factor 102even when the Q-factor of the cavity remains almost the same. From coupled mode theory we know that the critical intensity is proportional to the square of the product of the thickness of nonlinear material and the / 2’. For the thickness and / 2’ values used,critical intensity for M0S2 should be smaller than that for BBO by a factor of 43. However, the predicted larger reduction of 100 arises from the ability to place 0.62 nm- thick M0S2 at the peak electric field in cavity, whereas the 470 nm thick BBO sees an averaged-out effective electric field which is smaller than the peak value.

[0050] EXAMPLE 7: Suitable LASER and application of SHG device in fiber coupled device

[0051] All the results we have discussed till now were for normal incidence only. For off normal incidence the cavity will gradually go out of resonance. FIG. 8 shows the variation of conversion efficiency as a function of angle of incidence and it shows a FWHM of about 0.11 degree. Most of the lasers emit gaussian beams which has a finite divergence angle determined by the beam waist. But at the beam waist position the LASER beam is perfectly plane wave. The extent over which the beam is plane wave is called as the depth of focus, equal to twice the Rayleigh range. So, for the optimal performance of the device, we can place the device within the depth of focus centered around the beam waist. As a realistic example, let’s take a situation which ensures optimal beam parameters for sufficient conversion efficiency with negligible effect of off-normal angle of incidence. Consider a LASER of spot size 2 mm focused by a lens of focal length 25 mm. As a result of this configuration, we can get a beam diameter of nearly 24.7 micron and depth of field nearly 617 pm. As the total device size is less than 10 pm, we can place it cantered at the beam waist where the beam will be nearly parallel. At the end of the device the beam divergence angle is calculated to be 0.07 degree which is well within the required range of incidence angle for efficient conversion. At this position, a LASER of 10-100 mW power can provide the required intensity for this near-complete conversion. This method is also applicable for fiber coupled second harmonic conversion by fabricating it on the exit side of the fiber. While the finite numerical aperture of the fiber causes a part of the light to go out of resonance, this method still offers a practical and straightforward way to design a fiber optic cable integrated second harmonic source.

[0052] EXAMPLE 8: Design of cavity structure for enhanced SHG conversion efficiency

[0053] A realistic cavity structure (100) is designed which provides SHG conversion efficiency of more than 99%, shown in FIG. 6A, with the corresponding critical pump power 10 kW / cm2at 1550 nm. These values are several orders of magnitude better than the state of art systems. Since SPDC is an inverse process of SHG, it is expected the design would form a basis for high brightness and high efficiency entangled photons source as well.

Claims

WE CLAIM:

1. An integrated photonic device (100) configured to provide near-perfect second harmonic generation (SHG) operating at a resonant optical wavelength A. comprising: a substrate S; a first distributed Bragg reflector (DBR) (101) formed by alternating layers of different refractive index (103, 105), wherein the thickness of these layers is A / 4m,2 where n i. and m are the refractive indices of the corresponding layer; a monolayer (107) M0S2 (ML M0S2) as nonlinear material, sandwiched between two identical insulating layers (102) having thickness A / 4113 where n , is the refractive index of the insulating layer; and a second distributed Bragg reflector (DBR) (109) formed by alternating layers of different refractive index (103, 105), wherein, light of wavelength A is configured to enter the device through the second DBR (109) and light of second harmonic of / 2 is configured to be transmitted through the first DBR (101) and reflected through the second DBR (109).

2. The device (100) as claimed in claim 1, wherein the high refractive index (103) material comprises Sb2S3 and the low refractive index (105) is SiC>2.

3. The device (100) as claimed in claim 1, wherein the thickness of the M0S2 (107) is 0.62 nm.

4. The device (100) as claimed in claim 2, wherein the number of sets of alternating layers (103,105) in the first or the second DBR is configured to achieve near complete second harmonic conversion from the device.

5. The device (100) as claimed in claim 4, wherein the insulating layers (102) are hexagonal boron nitride (h-BN); the different refractive index materials comprise a high refractive index (103) material Sb2S3 and a low refractive index (105) SiCh; the number of sets of alternate high and low refractive index materials in the first DBR (101) is 13 with an additional capping layer of Sb2S3;the number of sets of alternate high and low refractive index materials in the second DBR (109) is 9 with an additional capping layer of Sb2S3, wherein the device is configured to operate at an input A. of 1550 nm and generate an output at 775 nm.

6. The device (100) as claimed in claim 5, wherein the use of h-BN as insulating layers (102) is configured to fill the cavity between the two DBRs and the M0S2 is placed at the middle of it where the electric field is at a maximum.

7. The device (100) as claimed in claim 5, wherein the SHG conversion efficiency is greater than 99% at a pump intensity of 10 kW / cm2, and the quality factor of the cavity is about 1,960,000.

8. The device (100) as claimed in claim 6, wherein ML M0S2 is used as a nonlinear material due to its ultra-high second order nonlinear susceptibility of 104pm / V.

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