MODULATOR

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates generally to the modulation of electromagnetic radiation, and more specifically to materials for controlling the transmissivity of light and methods thereof.

BACKGROUND OF THE INVENTION

[0002] The ability to control the transmissivity of transparent materials is a valuable functionality that opens up a new realm of possibilities in light modulating devices and is used, for example, in controllable shading of buildings, in projectors and in optical display systems. Generally, three main methods are used to adjust transmissivity involving: photochromic (PC) materials, electrochromic (EC) materials, and liquid crystals (LC).

[0003] PC materials are used in transparent surfaces, which are frequently used in eyeglasses, and can change their transmissivity in response to ambient light. These materials have relatively long transition times for a change in its transmissivity, e.g. from being transparent to opaque, and vice versa - often in the range of seconds. In addition, the transmissivity of PC materials cannot be controlled by electrical voltage, but the transmissivity is modulated by environmental conditions, for example adjacent light sources.

[0004] EC materials can undergo a change in their transmissivity in response to the application of an electrical voltage. A change to the modulation of electromagnetic radiation using EC materials can be achieved in just under a second. However, applications, such as medical imaging and display applications, require much shorter transition times. Further, EC materials may allow the modulation of specific wavelengths resulting in tinted lenses, since they affect the colors that are transferred through it in the transparent and the opaque state. In addition, the use of EC materials is limited to light in the visible range and near IR wavelengths. However, there is no concept that allows the use of EC materials in the modulation of light in the mid-to- long IR range.

[0005] LCs are materials which include ellipsoidal particles that can change their orientation in response to an applied electric field. By doing so, the structure behaves as a polarization rotator, which in combination with an additional polarizer can attenuate the transmitting light locally. The transition rate of an LC screen is relatively fast (e.g., in the range of milliseconds) and the attenuation can vary from 50% to a complete blockage. However, a significant drawback of LCs is their maximum transmissivity of only 50%, which is too low for certain optical applications. In addition, the pixel size (on which the LCD grid is based) is limited to a minimal size of few microns. Consequently, the pattern of the LCD surface has a periodicity pitch of few microns, larger than a wavelength in the visible range, which might result in scattering effects and chromatic aberrations.

[0006] Thus, there remains a need for the provision of an optical amplitude modulator that is characterized in allowing dynamic changes to the transmissivity of electromagnetic radiation, in particular, achieving a fast and complete change in transmissibility from a transparent state to an opaque state and vice versa.

SUMMARY OF THE INVENTION

[0007] The summary does not necessarily identify key elements nor limit the scope of the invention, but merely serves as an introduction to the following description.

[0008] Advantages and improvements of the invention may include an optical amplitude modulator that can dynamically control its transmissivity of electromagnetic radiation upon application of a defined voltage but can maintain a level of transmissivity when the applied voltage is turned off.

[0009] Embodiments may improve optical modulators by allowing a modulation ranging from a transparent state to an opaque state responsive to the application of a defined voltage.

[0010] The following is a simplified summary providing an initial understanding of the invention.

[0011] Some embodiments of the invention may include an optical amplitude modulator, including: a first conductive terminal; a second conductive terminal; a transparent insulator layer; and a transparent semiconductor layer; wherein the insulator layer and the semiconductor layer are sandwiched between the first terminal and the second terminal; and wherein a transmissivity of electromagnetic radiation through the insulator layer and the semiconductor layer is dynamically controllable according to a voltage applied between the first terminal and the second terminal. [0012] Alternative embodiments of the invention may include an optical amplitude modulator, including: a first conductive terminal; a second conductive terminal; a transparent insulator layer; and two layers of a transparent semiconductor layer; wherein the insulator layer is sandwiched between the two semiconductor layers; wherein the two semiconductor layers are each electrically connected to a different of the first and second terminal; and wherein a transmissivity of electromagnetic radiation through the insulator layer and the two semiconductor layers is dynamically controllable according to a voltage applied between the first terminal and the second terminal.

[0013] In an embodiment, the semiconductor layer is an n-type semiconductor layer configured to: increase the transmissivity of electromagnetic radiation through the insulator layer and the semiconductor layer responsive to an application of a negative voltage between the first terminal and the second terminal; and reduce the transmissivity of electromagnetic radiation through the insulator layer and the semiconductor layer responsive to an application of a positive voltage between the first terminal and the second terminal.

[0014] In an embodiment, the semiconductor layer is a p-type semiconductor layer configured to: reduce the transmissivity of electromagnetic radiation through the insulator layer and the semiconductor layer responsive to an application of a negative voltage between the first terminal and the second terminal; and increase the transmissivity of electromagnetic radiation through the insulator layer and the semiconductor layer responsive to an application of a positive voltage between the first terminal and the second terminal.

[0015] In an embodiment, the semiconductor layer comprises a plurality of separated sublayers interwoven with the insulator layer, and each of the plurality of sublayers is operably connected to either the first terminal or the second terminal.

[0016] In an embodiment, the plurality of sublayers are alternately connected to the first terminal and the second terminal.

[0017] In an embodiment, the plurality of sublayers includes both n-type and p-type semiconductor sublayers.

[0018] In an embodiment, the n-type sublayers are operably connected to the first terminal and the p-type sublayers are operably connected to the second terminal.

[0019] In an embodiment, each sublayer has a thickness of between 10-40 nm. [0020] In an embodiment, the first terminal and the second terminal are formed from one or more metals selected from titanium, gold, silver, aluminum or indium tin oxide “ITO”.

[0021] In an embodiment, the insulator layer is formed from one or more oxides or sulfides, selected from silicon dioxide “SiO2”, tantalum pentoxide “Ta20s”, titanium dioxide “TiO2”, hafnium oxide “HfO ”, zinc sulfide “ZnS”, aluminum oxide “AI2O3”, or magnesium oxide “MgO”.

[0022] In an embodiment, the semiconductor layer comprises one or more impurities selected from phosphorus, arsenic, antimony, boron or indium.

[0023] Some embodiments of the invention may include an optical shutter comprising the optical amplitude modulator as described herein.

[0024] Some embodiments of the invention may include a method of dynamically controlling the transmissivity of electromagnetic radiation through the insulator layer and the semiconductor layer of the optical amplitude modulator, the method comprising: applying a voltage between the first terminal and the second terminal to selectively vary the transmissivity of the optical amplitude modulator by: generating an accumulation of electrons at an interface between the semiconductor layer and the insulator layer, repelling electrons from the interface between the semiconductor layer and the insulator layer; or a combination thereof.

[0025] In an embodiment, the electromagnetic radiation is a long-wave infrared radiation comprising a wavelength of between 8pm and 14pm.

[0026] In an embodiment, the optical amplitude modulator is configured to maintain a selected level of transmissivity when an applied voltage between the first terminal and the second terminal is turned off.

[0027] These, additional, and/or other aspects and/or advantages of the present invention are set forth in the detailed description which follows; possibly inferable from the detailed description; and/or learnable by practice of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which: [0029] Figure 1 illustrates an optical arrangement of an optical amplitude modulator, according to an embodiment of the present invention;

[0030] Figure 2 is a graph illustrating an example of a band diagram during the accumulation, according to an embodiment of the present invention;

[0031] Figure 3 is a graph illustrating an example of a band diagram during the depletion, according to an embodiment of the present invention;

[0032] Figure 4 is an illustration of an absorption mechanism proceeding via an interband transition, according to an embodiment of the present invention;

[0033] Figure 5 is an illustration of an absorption mechanism proceeding via an intraband transition, according to an embodiment of the present invention;

[0034] Figure 6 shows an example of a circuit diagram depicting an optical switch in accumulation mode according to an embodiment of the present invention;

[0035] Figure 7 shows an example of a circuit diagram depicting an optical switch in depletion mode according to an embodiment of the present invention;

[0036] Figure 8 illustrates a capacitor structure of an oxide layer between two conducting plates, in accordance with the prior art;

[0037] Figure 9 illustrates a capacitor structure of an oxide layer between an n-type semiconductor and a p-type semiconductor, according to an embodiment of the present invention; and,

[0038] Figure 10 illustrates an optical amplitude modulator, according to an embodiment of the present invention.

[0039] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0040] In the following description, various aspects of the present invention will be described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the present invention. However, it will also be apparent to one skilled in the art that the present invention may be practiced without the specific details presented herein. Furthermore, well known features may be omitted or simplified in order not to obscure the present invention.

[0041] With specific reference now to the drawings in detail, it is stressed that the particulars shown are for the purpose of example and solely for discussing the preferred embodiments of the present invention, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention. The description taken with the drawings makes apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

[0042] Before explaining the embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following descriptions or illustrated in the drawings. The invention is applicable to other embodiments and may be practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

[0043] As used herein, “terminal”, “first terminal” or “second terminal” may refer to a layer that is a conductor or includes conductive material.

[0044] In the electronic industry, the most commonly used switching device is the Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET). MOSFET devices have already been produced in mass production and do not consume energy in static states. Therefore, they are the most preferred switches for integrated circuit electronics.

[0045] In this invention, the principle of a MOS capacitor structure to modulate conductivity is used and combined with semiconductors to control intra-band transitions in optical amplitude modulators. In other words, a switchable absorption mechanism may be used to raise electrons to a higher energy level within the conduction band. Thereby, depletion or accumulation of charge carriers may affect the probability of absorption. As a result, a change in the probability of absorption may allow modulating the absorption coefficient in real-time using field effects, predominantly modulation of the electrical conductivity of a material by the application of an external electric field.

[0046] Semiconductors are commonly used in optical electronic devices, mainly exploiting the inter-band transitions, to create lasers, LEDs, and various modulators. To control the absorption/emission of electromagnetic radiation, these devices may require a constant flow of electrons. Thus, such devices consume energy even when they are at a steady state.

[0047] At lower frequencies, GHz for example, the absorbance is primarily dominated by the conductance of the material. Since semiconductors can change their conductivity using the field effect, they are suitable candidates for amplitude attenuators. As the frequency increases, the absorption coefficient resulting from the conductance may decrease, and thus, other absorption mechanisms may be dominant. For example, in the visible range of electromagnetic radiation, absorption may be dominated by inter-band transitions.

[0048] It is therefore an object of embodiments of the invention to incorporate semiconductors into MOS capacitor structures to control intra-band transitions to modulate the absorption coefficient in real-time using field effects.

[0049] Some embodiments of the invention may include an optical amplitude modulator, including: a first transparent conductive terminal; a second transparent conductive terminal; a transparent insulator layer; and a transparent semiconductor layer; wherein the insulator layer and the semiconductor layer are sandwiched between the first terminal and the second terminal; and wherein a transmissivity of electromagnetic radiation through the insulator layer and the semiconductor layer is dynamically controllable according to a voltage applied between the first terminal and the second terminal.

[0050] A semiconductor layer may be an n-type semiconductor layer configured to: increase the transmissivity of electromagnetic radiation through the insulator layer and the semiconductor layer responsive to an application of a negative voltage between the first terminal and the second terminal; and reduce the transmissivity of electromagnetic radiation through the insulator layer and the semiconductor layer responsive to an application of a positive voltage between the first terminal and the second terminal.

[0051] A semiconductor layer may be a p-type semiconductor layer configured to: reduce the transmissivity of electromagnetic radiation through the insulator layer and the semiconductor layer responsive to an application of a negative voltage between the first terminal and the second terminal; and increase the transmissivity of electromagnetic radiation through the insulator layer and the semiconductor layer responsive to an application of a positive voltage between the first terminal and the second terminal.

[0052] In some embodiments, optical amplitude modulators of the invention may be prepared using known fabrication methods that are based on standard deposition techniques, e.g. sputtering, thermal evaporation, CVD, PE-CVD, etc.. These techniques are used in chip fabrication centers in the production of integrated circuits and are known to be low cost at mass production.

[0053] The transmissivity of an optical modulator of the invention may be controlled by application of an electrical voltage to its terminals, e.g. to its conductor layers. Optical amplitude modulators of the invention may be based on a semiconductor structure, which does not consume energy in a steady state. Since an optical amplitude modulator of the invention may be configured to maintain its transmissivity in the absence of a current flow through the optical modulator, its use as an optical amplitude modulator in battery powered cameras may reduce energy consumption, e.g. compared to optical modulators that are based on conventional modulators that require a constant current flow to maintain their transmissivity state.

[0054] In some embodiments, the optical amplitude modulators of the present invention may be used as solid-state optical shutters. Thereby, the absorption of electromagnetic radiation by a semiconductor is required to be a function of the charge carrier density. At long-wave infrared (LWIR) wavelengths (8-14 pm), interband transitions in the semiconductor may not occur and the main reason for absorption of electromagnetic radiation are ohmic losses. Mechanistically, the absorption of electromagnetic radiation may be related to the presence of currents caused by the incident electric field that are induced by the conductivity of the semiconductor.

[0055] Said currents transform the electric field to heat (phonons in the lattice). Thus, the conductivity of a semiconductor may depend on the electrons and holes density within the lattice of the semiconductor. By applying an electric field on a semiconductor, the free charge carriers density in the semiconductor, and, thus, a semiconductor’s conductivity can be modulated. Upon application of an electric field to a semiconductor, an accumulation layer or a depletion layer is created depending on the fields polarity and the free-charge carrier type.

[0056] Thus, in one embodiment, optical amplitude modulators of the invention may allow the generation of accumulation layers to achieve an absorption of electromagnetic radiation that may result in a change of conductivity in the semiconductor.

[0057] The accumulation layers of semiconductors may be tuned in its ability to interact with charge carriers to absorb light at optical frequencies (e.g. electromagnetic radiation in the range of 400 nm to 14 pm). However, accumulation layers are very thin (e.g. less than 20 nm) and, thus, each layer has a limited capability in the modulation of the absorbance of an optical amplitude modulator. Some embodiments of the invention may include optical amplitude modulators that may overcome the problem since they may include a longer path in the absorbing medium while requiring a low voltage for changes in the absorption. Accordingly, a layered structure of semiconductors and oxides may allow modulation of an optical amplitude modulator in order to achieve a desired modulation depth, e.g. an opaque state or a transmissible state of the optical modulator. The proposed structures of the invention may not consume energy in their steady state - when the capacitor structure is fully charged - and changes to the transmissivity may be dependent on the capacitance of the structure. For example, for small devices, the switching time can be very short, e.g. in the order of microseconds or milliseconds.

[0058] Some embodiments of the invention may include an optical shutter including an optical amplitude modulator as described herein. A solid-state, voltage controlled optical shutter of the invention may be beneficial and valuable for a variety of applications. For example, bolometric sensors rely on a mechanical shutter to perform Non-Uniformity-Correction (NUC) as an initializing step of its calibration. By replacing the classical mechanical shutter with an electronically controlled optical shutter, this process may be much more efficient in terms of duration, reliability, cost, and volume.

[0059] Moreover, an optical shutter can be implemented on a wafer level package, which may reduce the duration and efficiency of the manufacturing process. Additionally, an optical shutter can be arranged in the form of an array of pixels, and therefore, it can attenuate incoming light locally. This type of optical shutter can be used to improve the dynamic range of cameras (either in the visible range or IR) by attenuating hot spots, e.g., the sun or a strong lamp.

[0060] An optical amplitude modulator may be integrated into a meta-material, e.g. a dynamic-neutral-density-filter (DNDF) to improve the switching speed, heat dissipation and angular dependency. An optical modulator based on accumulation layers and the DNDF may be especially suitable for LWIR imaging systems. At present, in these systems, inter-band transitions do not occur, however fast absorptionbased shutters are necessary to improve the dynamic range and to avoid "sunburn" effects.

[0061] Figure 1 illustrates a general structure of an optical amplitude modulator 100 according to an embodiment of the present invention. Optical amplitude modulator 100 may include a first conductive terminal and a second conductive terminal, e.g. first conductive terminal 101 and second conductive terminal 107. For an optical device, conductive terminals 101 and 107 may be made from transparent conducting material that may allow the transmittance of electromagnetic radiation in a desired wavelength spectrum. Conductive terminals 101 and 107 may be, for example, formed from one or more metals, such as titanium, gold, silver, aluminum or indiumtin oxide (ITO). Conductive terminals 101 and 107 may embed, encompass or border a transparent insulator layer, e.g. insulator 103 and a transparent semiconductor layer, e.g. semiconductor 105. Insulator layer 103 and semiconductor layer 105 may be sandwiched between terminal 101 and terminal 107. Insulator layer 103 may be formed from one or more oxides or sulfides, for example an insulator or insulator layer may be selected from silicon dioxide “SiCh”, tantalum pentoxide “Ta2Os”, and titanium dioxide “TiCh”, hafnium oxide “HfCh”, zinc sulfide “ZnS”, aluminum oxide “AI2O3”, or magnesium oxide “MgO”. Insulator 103 may be an oxide layer and may be located between terminal 101 and semiconductor 105. A semiconductor of an optical amplitude modulator may be adjusted in its composition based on a specific wavelength area of electromagnetic radiation that is applied to the optical amplitude modulator. For example, for electromagnetic radiation having a wavelength between 8-14 pm, a suitable semiconductor 105 may include germanium “Ge”. For example, the conductivity of an un-doped germanium semiconductor may be much higher compared to a silicon “Si” semiconductor due to higher charge carrier mobility (3900 cm ² /V for Ge compared to 1400 cm ² /V for Si) and higher intrinsic carrier density (three orders of magnitude greater for Ge compared to Si). Additionally, Si has an internal phonon absorption at a wavelength of about 12 pm. Thus, internal absorption can make Si unsuitable as a semiconductor in a modulator that includes a plurality of semiconductor layers when exposed to electromagnetic radiation in the range between 12-14 pm. Semiconductor 105 may include one or more impurities selected from phosphorus, arsenic, antimony, boron or indium. When a voltage is applied on terminals 101 and/or 107, insulator 103 may prevent a current flow from the first terminal 101 into the semiconductor 105.

[0062] Semiconductors have an electrical conductivity that may lie between an insulator and a conductor. Their conducting properties may be tuned by the introduction of impurities that are introduced into their lattice structure, commonly referred to as doping. Thereby, a semiconductor containing free holes in its lattice structure may be commonly referred to as a p-type and a semiconductor containing free electrons in its lattice structure is commonly referred to as an n-type semiconductor. When an n-type semiconductor is used as a semiconductor 105 in an optical amplitude modulator 100 and a positive voltage is applied between conductors 101 and 107, electrons may be attracted to terminal 101 and may accumulate at the interface between the semiconductor 105 and insulator 103 - commonly referred to as “accumulation”.

[0063] Figure 2 is a graph illustrating an example of a band structure 200 during an accumulation of electrons between terminal 201 and terminal 207. Conduction band 210 is located at a higher energy level than fermi energy level 212 and valence band 214. However, a high electron density near the first terminal 201 may lead to a reduction of the energy level of conduction band 210 closer to the first terminal 201 (thus closer to the oxide layer) and the energy level of the conduction band 210 may be reduced to Fermi level 212. The probability of occupying a state is a function of the distance between the state and the Fermi level 212. Thus, valence bands 214 that are closer to the Fermi level 212 may be more likely to occupy states with electrons. Accordingly, the reduction of the energy level of conduction band 210 may increase the number of electrons in the conduction band 210 and, thus, the number of electrons in close proximity to the gate.

[0064] Figure 3 is a graph illustrating an example of a band structure 300 during a depletion of electrons between a first terminal 301 and a second terminal 307, herein also referred to as “depletion mode”. [0065] When a voltage that is applied between terminals 301 and 307 is negative, the electrons may be repelled from terminal 307 and positive static ions, commonly referred to as "holes" remain in the lattice of a semiconductor. As a result, as shown in Fig. 3, conduction band 310 is moved to higher energy levels when in close proximity to second terminal 307 in relation to Fermi level 312, thereby lowering the electron density near terminal 301 and, thus, the probability to populate conduction band 310 with electrons from valence band 314 may be decreased.

[0066] When the magnitude of negative voltage in the depletion mode is further increased, at some point, holes may start to accumulate near the insulator to create a p-type semiconductor in a small region of the semiconductor. The depletion mode arising due to high negative voltage may be referred to as inversion and may occur when an energy level 316 (F^/2), as shown in Fig. 3 may cross the Fermi level 312. Generally, for p-type semiconductors, the depletion mode can be observed for negative voltages and the accumulation mode can be observed for positive voltages that are applied to terminals 301 and 307. Unlike the n-type semiconductors which may be dominated in its operation by the provision of electrons in the semiconductor at the interface to the insulator, the p-type semiconductors modulate their conductive behavior primarily due to the generation of holes in the semiconductor at the interface to the insulator.

[0067] Accordingly, for an n-type semiconductor layer, an increase in transmissivity of electromagnetic radiation through an optical amplitude modulator may be observed for an application of a negative voltage between first terminal 101 and second terminal 107; and a reduction in the transmissivity of electromagnetic radiation through an optical amplitude modulator may be observed for an application of a positive voltage between the first terminal 101 and the second terminal 107.

[0068] For a p-type semiconductor layer, a reduction in the transmissivity of electromagnetic radiation through an optical amplitude modulator may be observed for an application of a negative voltage between a first terminal 301 and a second terminal 307; and an increase in the transmissivity of electromagnetic radiation through an optical amplitude modulator may be observed for an application of a positive voltage between a first terminal and a second terminal, e.g. conductor layers 101 and 107. [0069] Mechanistically, two absorption mechanisms may be observed in semiconductors when a positive or negative voltage is applied: inter-band transition and intra-band transition.

[0070] Figure 4 is an illustration of an absorption mechanism 400 proceeding via an inter-band transition. In this mechanism, a photon incident on the semiconductor may be absorbed and may lead to the movement of an electron from the valence band 414 to the conduction band 410 and an electron hole in the valence band, thereby generating an electron-hole pair. To excite an electron from the valence band to the conduction band, the photon wavelength (or, equivalently, its energy) should be higher than the semiconductor's bandgap.

[0071] Figure 5 is an illustration of an absorption mechanism 500 proceeding via an intra-band transition. In an intra-band transition, a photon’s energy may be absorbed by an electron that is already in the conduction band 510. The electron may shift to a higher energy state and may produce heat as it drops back to the ground state within the conduction band 510. This absorption mechanism may rely on the presence of electron vacancies in higher energy states of the conduction band and may be commonly observed in metals, or for lower incident field frequencies (e.g. in the GHz or THz magnitude) leading to inter-band or internal phonon transitions.

[0072] Inter-band transitions may suggest that any photon with sufficient energy can be absorbed, regardless of the electric field applied to the material.

[0073] However, for example, using n-type semiconductors, electron accumulation may mean that the charge carrier density in the conduction band may be increased and depletion means that the charge carrier density at the conduction band may be decreased. In a case where the bandgap of a semiconductor is larger than the wavelengths of the electromagnetic radiation (photons) that are transmitted through the device, inter-band transitions cannot occur.

[0074] In addition, when a semiconductor has vacant states that are located at high energy levels within the conduction band, a semiconductor would have an absorption coefficient whose value may be predominantly influenced by intra-band transitions. As a result, such a semiconductor would absorb light according to the Beer-Lambert law. However, in a case where the device may be depleted from its charge carriers, no electrons may be available to absorb photons. Under these conditions, the material may become transparent. [0075] Figure 6 shows an example of a circuit diagram depicting an optical amplitude modulator 600 in an accumulation mode. Accumulation of free charge carriers 611 may lead to an increase in electron density in the lattice of semiconductor 605 at the interface to insulator 603 and may increase the absorption of the optical amplitude modulator 600 resulting in an increased opacity of the modulator.

[0076] Figure 7 shows an example of a circuit diagram depicting an optical amplitude modulator 700 in a depletion mode. Depletion of the free charge carriers 711 may lead to a rise in non-mobile positive charges that are bound to the lattice in the semiconductor 705 at the interface to the insulator 703 and may increase the transparency of the optical amplitude modulator 700. The positive charges in figure 7 may be ions that are generated by the removing electrons from the semiconductor 705. Since the positively charged ions may be bound to the lattice structure of the semiconductor 705, they do not contribute to the conduction or absorption.

[0077] Figure 8 shows an example of a parallel plate capacitor 800, as known in the prior art. Capacitor 800 may include an insulator 803 that is embedded between a conductors 801 and 807.

[0078] The capacity C of such capacitor 800 can be calculated according to example formula 1. Capacity C may be equivalent to a product of vacuum permittivity e ₀ , relative permittivity of the insulator (e.g. an oxide) e _ox and plates area A, divided by spacing d between the plates.

[0079] Charge Q applied to the plate of capacitor 800 may be equal to the capacity of the capacitor multiplied by the positive voltage, as outlined in example formula 2:

(2) Q = CV

[0080] The charge density per area Q may be expressed as the ratio of charge Q per plate area A as shown in example formula 3.

[0081] Figure 9 shows an example of capacitor 900 that comprises an insulator 903 that may be embedded between a semiconductor 901, e.g. an n-type semiconductor, and semiconductor 905, e.g. a p-type semiconductor.

[0082] Comparing capacitor 800 of figure 8 to capacitor 900 of figure 9, replacement of the two metallic plates - conductors 801 and 803 - of capacitor 800 by thin semiconductors, e.g. semiconductors 901 and 905, as shown in figure 9 may result in charges that are either accumulated near the surface or depleted.

[0083] In the depletion mode, the depth t _dep can be extracted according to the initial doping concentration according to example formula 4. Thereby n represents the electron concentration in a case of a n-type semiconductor and q represents the charge of an electron (approximately q = 1.602 ■ 10 ^-19 6):

Q

(4) t ep

^K = qn

[0084] For a p-type semiconductor, substituent h may represent the hole concentration and the depth t _dep for a p-type semiconductor may be calculated as outlined in example formula 5:

[0085] In case of accumulation, however, depth t _dep is not dependent on the doping and is approximately t _acc = 10 nm.

[0086] In view of the accumulation layers, the concentration of free charge carriers arising due to accumulation may be expressed as outlined in example formula 6:

[0087] Accordingly, the conductivity a may be calculated via example formula 7. Conductivity a may be equal to the product of electron mobility q and electron concentration for an n-type semiconductor.

(7) a = qqn

[0088] The absorption coefficient resulting from the conductivity may be calculated using example formula 8, which can be derived from the Drude-model of electrical conduction. Thereby, e _r is the dielectric constant of the semiconductor, f is the incident field frequency and T is the average collision time:

[0089] By analysis of example formula 7, the absorbance decreases with respect to higher field frequencies f. Thus, the modulation of a field with high frequency f is more complex, for example for electromagnetic radiation in the visible range or NIR range. For the LWIR regime, however, the expression of the absorbance using the absorption coefficient may be sufficient.

[0090] Referring back to figure 9, the absorption from capacitor 900 shown in figure 9 may be observed in a limited accumulation area between 10-40 nm. Accordingly, since there is only one accumulation layer for each semiconductor, the absorbance of an optical amplitude modulator comprising a single system of semiconductor and insulator may be limited.

[0091] To increase the absorbance of an optical modulator, the number of semiconductor layers within an insulator of an optical amplitude modulator could be increased as outlined in figure 10.

[0092] Figure 10 illustrates an optical amplitude modulator 1000 including: a first conductive terminal, e.g. conductor 1001; a second conductive terminal, e.g. conductor 1007; a transparent insulator, e.g. insulator 1003; a transparent semiconductor that includes a plurality of semiconductor sublayers 1005 and 1006. Transparent insulator 1003 may be sandwiched between first conductor 1001 and second conductor 1007. A transmissivity of electromagnetic radiation through the optical amplitude modulator may be dynamically controllable according to a voltage that may be applied between a first terminal 1001 and a second terminal 1007. Optical amplitude modulator 1000 may include insulator 1003 that may include a plurality of semiconductor sublayers 1005 and 1006 that may be located within insulator 1003.

[0093] A semiconductor layer may include a plurality of separated semiconductor sublayers 1005 and 1006 that are interwoven with insulator layer 1003, and each of the plurality of semiconductor sublayers is operably connected to either the first terminal or the second terminal, e.g. terminal 1001 and terminal 1007. For example, a plurality of semiconductor sublayers may include both n-type and p-type semiconductor sublayers. The plurality of semiconductor sublayers 1005 and 1006 may be alternately connected to the first terminal and the second terminal.

[0094] n-Type semiconductor sublayers, e.g. sublayers 1006, may be operably connected to a first terminal, e.g. terminal 1001, and p-type semiconductor sublayers, e.g. sublayers 1005, may be operably connected to a second terminal, e.g. terminal 1007. For example, n-type semiconductors 1006 may be operably connected to terminal 1001 that is negatively charged to accumulate negative charges and p-type semiconductors and p-type semiconductors 1005 may be operably connected to terminal 1001 that is positively charged to accumulate positive charges. Each sublayer of the plurality of semiconductor sublayers may be substantially surrounded by insulator 1003.

[0095] Electromagnetic radiation may pass through optical amplitude modulator 1000 transversal or substantially perpendicular to the orientation of sublayers 1005 and 1006 and may penetrate optical amplitude modulator 1000 substantially parallel to the orientation of terminals 1001 and 1007. The number of semiconductor sublayers 1005 and 1006 may be adjustable. Thus, the higher the number of semiconductors sublayers 1005 and 1006, the higher the number of sublayers that electromagnetic radiation may penetrate and the broader the range of transmissivity that can be dynamically controlled by the optical amplitude modulator 1000.

[0096] Switching times for an optical amplitude modulator 1000 as shown in FIG. 10 may be dependent on the number of semiconductor sublayers. For example, for an optical amplitude modulator 1000 as shown in Fig. 10, having a length 1009 set as 1 cm and a height 1008 set as 1 cm and including 25 semiconductor sublayers 1005 and 1006 (each of the sublayers having a thickness of approximately 25 nm), a switching time may be about 50 milliseconds. For example, for an optical amplitude modulator 1000 as shown in Fig. 10, having a length 1009 of 100 pm and a height 1008 of 100 pm and that includes 25 semiconductor sublayers 1005 and 1006, a switching time may be in the range of microseconds.

[0097] Voltage that may be applied to terminals 1001 and 1007 of optical amplitude modulator 1000 may lead to an accumulation, e.g. within an area of 10-40 nm for each of semiconductor sublayers 1005 and/or 1006. Thereby, the voltage that may be applied to terminals 1001 and 1007 may be equal in every capacitor structure that may exist in the layered structure.

[0098] Some embodiments of the invention may include a method of dynamically controlling the transmissivity of electromagnetic radiation through the optical amplitude modulator. The method may comprise the application of a voltage (e.g. a voltage of up to 20 V) between the first terminal, e.g. conductor 1001, and the second terminal, e.g. conductor 1007, to selectively vary the transmissivity of the optical amplitude modulator, such as optical amplitude modulator 1000. For example, the transmissivity of an optical amplitude modulator, such as optical amplitude modulator 1000, may be varied by generating an accumulation of electrons at an interface between the semiconductor layer and the insulator layer. For example, the transmissivity of an optical amplitude modulator, such as optical amplitude modulator 1000, may be varied by repelling electrons from the interface between the semiconductor layer and the insulator layer. For example, the transmissivity of an optical amplitude modulator, such as optical amplitude modulator 1000, may be varied by a combination of generating an accumulation of electrons at an interface between the semiconductor layer and the insulator layer and repelling electrons from the interface between the semiconductor layer and the insulator layer.

[0099] Electromagnetic radiation that is used to dynamically control the transmissivity of the optical amplitude modulator may be a wavelength in the optical regime commonly referred to as “visible light” (400 nm-750 nm), or up the long-wave infrared radiation including a wavelength of between 8 pm and 14 pm. The optical amplitude modulator may be configured to maintain a selected level of transmissivity when the voltage between the first terminal and the second terminal is turned off.

[0100] An optical amplitude modulator may be operably connected to a substrate, for example a substrate that includes silicon “Si” or germanium “Ge”. A substrate may be transparent for a specific range of electromagnetic radiation that is modulated by the modulator, e.g. SiCh may be a suitable substrate for electromagnetic radiation in the optical regime “visible light” (400 nm -750 nm).

[0101] The aforementioned flowchart and diagrams illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each portion in the flowchart or portion diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the portion may occur out of the order noted in the figures. For example, two portions shown in succession may, in fact, be executed substantially concurrently, or the portions may sometimes be executed in the reverse order, depending upon the functionality involved, It will also be noted that each portion of the portion diagrams and/or flowchart illustration, and combinations of portions in the portion diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

[0102] As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system or an apparatus. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.”

[0103] The aforementioned figures illustrate the architecture, functionality, and operation of possible implementations of systems and apparatus according to various embodiments of the present invention. Where referred to in the above description, an embodiment is an example or implementation of the invention. The various appearances of “one embodiment,” “an embodiment” or “some embodiments” do not necessarily all refer to the same embodiments.

[0104] Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the invention may be described herein in the context of separate embodiments for clarity, the invention may also be implemented in a single embodiment.

[0105] Reference in the specification to “some embodiments”, “an embodiment”, “one embodiment” or “other embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least some embodiments, but not necessarily all embodiments, of the inventions. It will further be recognized that the aspects of the invention described hereinabove may be combined or otherwise coexist in embodiments of the invention.

[0106] It is to be understood that the phraseology and terminology employed herein is not to be construed as limiting and are for descriptive purpose only.

[0107] The principles and uses of the teachings of the present invention may be better understood with reference to the accompanying description, figures and examples.

[0108] It is to be understood that the details set forth herein do not construe a limitation to an application of the invention.

[0109] Furthermore, it is to be understood that the invention can be carried out or practiced in various ways and that the invention can be implemented in embodiments other than the ones outlined in the description above.

[0110] It is to be understood that the terms “including”, “comprising”, “consisting” and grammatical variants thereof do not preclude the addition of one or more components, features, steps, or integers or groups thereof and that the terms are to be construed as specifying components, features, steps or integers. [0111] If the specification or claims refer to “an additional” element, that does not preclude there being more than one of the additional element.

[0112] It is to be understood that where the claims or specification refer to “a” or “an” element, such reference is not be construed that there is only one of that element.

[0113] It is to be understood that where the specification states that a component, feature, structure, or characteristic “may”, “might”, “can” or “could” be included, that particular component, feature, structure, or characteristic is not required to be included.

[0114] Where applicable, although state diagrams, flow diagrams or both may be used to describe embodiments, the invention is not limited to those diagrams or to the corresponding descriptions. For example, flow need not move through each illustrated box or state, or in exactly the same order as illustrated and described.

[0115] Methods of the present invention may be implemented by performing or completing manually, automatically, or a combination thereof, selected steps or tasks.

[0116] The term “method” may refer to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the art to which the invention belongs.

[0117] The descriptions, examples and materials presented in the claims and the specification are not to be construed as limiting but rather as illustrative only.

[0118] Meanings of technical and scientific terms used herein are to be commonly understood as by one of ordinary skill in the art to which the invention belongs, unless otherwise defined.

[0119] The present invention may be implemented in the testing or practice with materials equivalent or similar to those described herein.

[0120] While the invention has been described with respect to a limited number of embodiments, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of some of the preferred embodiments. Other or equivalent variations, modifications, and applications are also within the scope of the invention. Accordingly, the scope of the invention should not be limited by what has thus far been described, but by the appended claims and their legal equivalents.