Electro-optic modulator

Abstract

An electro—optic modulator comprising a semiconductor material which is equipped with an index of refraction that is dependent on an electric field applied to the modulator, characterized in that the semiconductor material is provided as a ferroelectric, ferrielectric, or antiferroelectric Van der Waals material with a layered crystal structure that breaks inversion symmetry, wherein the semiconductor material is selected for having an energy bandgap (Eg) in the range of 0.5 eV to 7 eV at °C.

Description

Electrooptic modulator The invention relates to an electrooptic modulator comprising a semiconductor or insulator material which is equipped with an index of refraction that is dependent on an electric field applied to the modulator. Electrooptic modulators are used in photonic devices and instruments, and can be used to modulate information on light beams from a wide variety of sources, in particular, lasers. The variable index of refraction. that is dependent on the electric field is also known as the Pockels effect, when the variability of the index is predominantly large and linear. Examples of useful crystals that exhibit a linear electrooptic effect include GaAs, CdTe (cubic crystals), KDP (Potassium Dihydrogen Phosphate), ADP (Ammonium. dihydrogen. phosphate tetragonal), LiNb03 and LiTa03 (trigonal). Because the Pockels coefficients are different for the ordinary and extraordinary polarizations of the lightbeam that is modulated, the electrooptic modulator functions as a voltage controlled variable wave retarder. There is a continuous quest for an improved electrooptic modulator, which brings better results in terms of 0 high data transmission speed, which is crucial for highspeed Internet, 5G networks, and data centers . low power consumption, providing energy savings and increased battery life in portable devices . signal quality to minimize transmission errors . compact size and increasing the possibility to integrate with other semiconductors . wide bandwidth for support of advanced communications protocols 0 high stability and reliability improving the quality of communications _ 2 _ . small latency to improve speed in switching between states. Such an improved electrooptic modulator is particularly desirable in fields like telecommunications, data communications and photonics, but is also relevant to construction and aerospace (i.e. windows and lenses). One of the desirable aspects is to have a electrooptic modulator of which the refraction index is more sensitive to the electric field that is applied to the modulator. The current prior art electrooptic modulator employs LiNbOg, which shows the best known sensitivity uptodate. It is an object of the invention to in particular improve the sensitivity of the refraction index in relation to the applied electric field to the modulator. To surpass the state of the art, this invention aims to rely on a newly discovered electrooptic effect which extends beyond the known Pockels and Kerr effects. The Pockels effect is a directionally dependent linear variation in the refractive index of an optical medium that occurs in response to the application of an electric field. The Kerr effect is a weak, thirdorder non linear variation in the refractive index of an optical medium that is wavelength independent an also occurs in response to the application of an electric field. The current invention instead aims to rely on a previously unknown, seemingly non linear, effect which. we will coin. as the MKAeffect or el Mrabet, van der Eolk, Ali effect. According to an aspect of the invention an electrooptic modulator may be provided comprising a semiconductor material which is equipped with an index of refraction. that is dependent on. an electric field applied to the modulator. The semiconductor material is provided as a ferroelectric, ferrielectric, or antiferroelectric Van der Waals material with a layered crystal structure that breaks inversion symmetry. The _ 3 _ semiconductor material is selected for having an energy bandgap (Eg) in the range of 0.5 eV to '7 eV at 20 °C. The electrooptic modulator may be designed, such as means of its thickness, to exhibit a 103 10l refractive index point change per volt. Wherever refractive index is referred. to, also separate from these examples, the effect pertains to at least one of inplane or outofplane refraction. For the sake of completeness a layered structure here refers to a material composed of individual layers stacked upon each other, forming an overall threedimensional (3D) crystal lattice. Each of these layers is typically a twodimensional (2D) plane where atoms are strongly bonded together, but the bonding between the layers is weaker. The thickness of the material determines the refractive index point change. The optical effect is believed to become pronounced for the materials having a thickness of 1 300 nm. This particular range is relevant for photonic applications. Most preferably the material can be chosen to have a thickness in the range of 10 200 nm. The material here would then be allowed to be purposed as a waveguide. In. the latter range the material, such. as demonstrated. for CIPS, is believed to exhibit an improved refractive index point changes 0.001 0.5 per volt for incident wavelengths within the range of 2001700 nm, such as at least one of incident wavelength of 210.6, 632.8, 1550 and 1688.3 nm. The newly found effect, wherein the refractive index changes as function of thickness and wavelength, has been demonstrated in the thickness range of 14.09 nm to 160.89 nm for CIPS, i.e. CuIansa While CuInP256 is the primary stoichiometry, CuzlnzP256 = 1:1:1, there are other stable variations in CIPS, such as (1x):(1+y):1, wherein x,y = 0 - 1, preferably 0 _ 4 _ 0,1. It stands to reason that x,y = 1 may be excluded from the former range. The person skilled in the art will recognize the latter range as deviations within the same structural framework rather than distinct stable compounds. It is also alternatively possible to achieve the above ratios through substitutional or intercalation doping, as long as one does so without substantially disrupting the lattice.. It is expected that materials which share the aforementioned properties of CTPS also exhibit this behavior. Using these materials we can improve the sensitivity of the electrooptic modulator which paves the way for improvement on other issues as nntioned above. The electrooptic modulator of the invention is therefore provided. with. the features of one or :more of the appended claims. Optionally, the electroobject modulator of the invention is characterized. in that the modulator substantially comprises CTPS. It is found that in comparison with the prior art, the electrooptic modulator of the invention. has a sensitivity which is several orders of magnitude higher than the prior art electrooptic modulator. The invented electrooptic modulator can exhibit a llkl index point change per volt, whereas the prior art modulator sensitivity is 104 index point change per volt. The improved. results are in particular achievable when the CTPS material comprises a thickness in the range from ~200 nm to 10 nm. Even beyond CTPS. The accompanying drawings, which is incorporated into and forms a part of the specification, illustrates results achieved with an embodiment of the present invention and, together with the description, serves to explain the _ 5 _ principles of the invention. The drawings are only for the purpose of illustrating and is not to be construed as limiting the invention. In the drawings, graphs are shown of the refractive index(n) versus thickness at incident wavelengths of 210.6,632.8, 1550 and 1688.3 nm. .Also shown are the absorption, extinction, complex dielectric function and dielectric loss for completeness. Data. is thus available for the range between 210.6 nm and 1688.3 nm showing the afore described MKAeffect in CIPS. The relevant Figures are 1, 3, 5 and 7. Figure 21 shows the refractive index(n) versus thickness at an incident wavelength of 300 nm.. The figures show a significant change in the refractive index of the ordinary optical axis in comparison with the extraordinary optical axis of the electrooptic modulator of the invention, at all applied wavelengths employing the material CTPS for the electrooptic modulator. The change in the refractive index can be clearly seen across a film thickness range from 160.89 nm to 14.09 nm. This particular range is relevant for photonic applications. The figures also show the extinction coefficient K at the before mentioned. wavelength. as a function. of thickness (in nanometers) for a material. The extinction coefficient, K is related. to the material's ability to absorb light at this wavelength, and it is shown for both inplane (squares) and outofplane (circles) orientations. The relevant Figures are 2, 4, 6 and 8. The figures further show the dielectric loss (represented as 82 / 81 at the before mentioned. wavelengths as a function of thickness (in nanometers) for the material. The dielectric loss is plotted separately for inplane (squares) and outof _ 6 _ plane (circles) measurements. The relevant Figures are 11, 14, 17 and 20. Lastly, the figures show both the real and imaginary part of the dielectric function 81 and 82 respectively for the previously :mentioned. wavelengths as a function. of thickness (in nanometers) for the material, with separate measurements for inplane (squares) and outofplane (circles) directions. The relevant Figures are 9, 10, 12, 13, 15, 16, 18 and 19. The dielectric function itself is a complex number, typically written as: =1+i2 where: o 81 (the real part) represents the material's ability to store electric energy (its dispersive properties). o 82 (the imaginary part) represents the losses in the material due to absorption. It is believed that the data on CTPS supports the presence of the effect in similarly layered Thiophosphate structures CuCerse, AgVste, AgCerse, and CuVste. Since these materials have comparable bonding, spacing, and stacking patterns, electrooptical effects observed in CTPS provide a foundational understanding of similar effects in these materials. CTPS data is further believed to support same electrooptical effects ill MnPSm VPS CrPS CoPS NiPS FePsg, TiPS3, and CuP83 due to the shared layered crystal structure. Oxyhalides, MOXZ, where M = Nb, Ta, or V; X = C1, Br or 1, namely exhibit layered structures sufficiently similar to thiophosphates. These are all ferroelectric, ferrielectric, or antiferroelectric Van. der Waals materials having a layered crystal structure that breaks inversion symmetry, wherein the semiconductor material is selected for having an energy bandgap (Eg) in the range of 0.5 eV to 7 eV _ 7 _ 20 at 0C. In closing it is posited that the possible 103 10l refractive index point change per volt at selected thicknesses far exceeds the Kerr effect. Kerr is pertains to electric dipole alignment from. an external field. The inventions is showing an electrooptical effect in materials which are known to already have electric dipole ordering for all of the thicknesses explored herein. The Kerr effect also does not or is not known to change with thickness in any way similar to the observed changing index of refraction. Finally, the Kerr effect is wavelength independent since it only driven by the internal induced dipole moment alignment. Its on or off for nearly all electromagnetic radiation below a materials band gap size. The present invention demonstrates wavelength dependence. The MKAeffect is seemingly far larger for shorter wavelengths approaching the bandgap size and it decreases as wavelength increases. Although. the invention. has been. discussed. in the foregoing with reference to EHI exemplary embodiment (Hf the invention, the invention is not restricted to this particular embodiment which can be varied in many ways without departing from the invention. The discussed exemplary embodiment shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary the embodiment is merely intended to explain the wording of the appended claims without intent to limit the claim to this exemplary embodiment. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using this exemplary embodiment. Variations and modifications of the present invention will be obvious to those skilled. in the art and. it is intended. to _ 8 _ ver in the appended claims all such modifications and uivalents. The entire disclosures of all references, plications, patents, and publications cited above are hereby corporated by reference. Unless specifically stated as being sential above, none of the various components or the terrelationship thereof are essential to the operation. of e invention. Rather, desirable results can be achieved by bstituting various components and / or reconfiguration of eir relationships with one another. _ 9 _

Claims

1. An electrooptical modulator comprising a semiconductor material that is provided with a refractive index that depends on an electric field applied to the modulator applied, characterized by the fact that the semiconductor material is provided as a ferroelectric, ferrieelectric or antiferroelectric Van der Waals material with a layered crystal structure that breaks inversion symmetry, where the semiconductor material is selected to have an energy bandgap (Eg) to have in the range of 0.5 eV to 7 eV at 20°C.

2. The electrooptical modulator of conclusion l, where the semiconductor material substantially comprises a crystal that belongs to the ABPQg family, where A is at least one metal is, like a transition metal element, that a has an oxidation state of +1 (M+), where B has at least one metal is, like a main group metal element, that a has an oxidation state of +3 (M3+), and X is a chalcogen selected from the group consisting of sulfur (S), tellurium (Te) and selenium (Se).

3. The electrooptical modulator of claim 2, where the semiconductor material is selected from the group consisting of CuInPä, CuCrPä, AgVPä%, AgCrPä and CuVPä.

4. The electrooptical modulator of conclusion l, where the material is CuInP256, where copper and indium are have a ratio in the range of 0.8:11:0.8, such as substitution or intercalation doping comprising without the schedule to significantly disrupt.

5. The electrooptical modulator of conclusion l, where the semiconductor material substantially comprises a crystal that belongs to the APZXG family, where A.at least one metal is, like a transition metal element, that has an oxidation state has from +4 (M4+) and X a chalcogene is selected from the group consisting of sulfur (S), tellurium (Te), and selenium (Se).

6. The electrooptical modulator of claim 5, _ 10 _ where the semiconductor material is selected from the group consisting of SanTeg, SnP2S6, SanSe6, GeP2S6, GePzTe6 and GePzSe6.

7. The electrooptical modulator of conclusion l, where the semiconductor material substantially comprises a crystal that belongs to the APXg family, where A.at least one metal is with an oxidation state of +2 (M2+) or a combination of metals with an oxidation state of +1 (M1+) and +3 (M3+), and where X is a chalcogen selected from sulfur (S), tellurium (Te) and selenium (Se).

8. The electrooptical modulator of claim 7, where the semiconductor material is selected from the group consisting of MnPS3, VPS3, CrPS3, CoPS3, NiPS3, FePS3, TiPS3 and CuPS3.

9. The electrooptical modulator of conclusion l, where the semiconductor material substantially comprises a crystal that belongs to the .AOXz family, where A. a transition metal cation is selected from the group consisting of niobium (Nb), tantalum (Ta) and vanadium (V), and X is a halide selected from chlorine (Cl), bromine (Br) or iodine (I).

10. The electrooptical modulator of claim 9, where the semiconductor material is selected from the group consisting of NbOClz, NbOBrg, NbOIz, TaOClz, TaOBrz, TaOIz, VOClz, VOBrz and V012.

11. The electrooptical modulator of one of the previous conclusions, where the material comprises a thickness in the range of 300 nm to 1 nm, preferably 200 nm to 10 nm.

12. Electrooptical modulator according to one of the conclusions III, characterized by the variability of the refractive index occurs with incident light with a wavelength in the range of 210.6 nm to 1688.3 nm, such as at least one of 210.6, 300, 632.8, 1550 and 1688.3 nm.

13. Electrooptical modulator comprising a semiconductor material that is equipped with a refractive index that depends on an electric field applied to the modulator applied, characterized by the electrooptical _ ll _ modulator substantial CIPS comprises, i.e. CuIanSa l4. Electrooptical modulator according to conclusion l3, where the CIPS material comprises a thickness in the range of 160.89 nm to 14.09 nm. 5 15. Electrooptical modulator according to claim 13 or 14, where the variability of the refractive index occurs at incident light with a wavelength of approximately 300 nm.

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