Embodiments of the present disclosure generally relate to the field of processing electromagnetic signals. More particularly, embodiments of the present disclosure relate to the field of modulating electromagnetic signals.
Typically, in optical communication networks, modulated light is transmitted through a fiber optic medium. The fiber is perceived as a waveguide, guiding the modulated light (represented as an electromagnetic wave) from one point to another.
In order to convey information from one end of the fiber optic to its other end, light is modulated and conveyed in its modulated form. The most basic modulation technique is an on-off keying (“OOK”) (also known as light/dark). When such a modulation is used, light is considered as a single bit of “1” whereas dark is considered as a single bit of “0”. OOK is the most common and basic modulation technique, and is widely used in optical communications. OOK is the simplest form of amplitude-shift keying modulation that represents digital data as the presence or absence of a carrier wave. In its simplest form, the presence of a carrier (i.e. presence of light) for a. specific duration represents a binary “1”, while its absence (i.e. darkness) for the same duration represents a binary “0”. Some more sophisticated modulation schemes vary these durations to convey additional information.
While OOK is a very simple and a straightforward type of modulation, yet, it is associated with some implementation challenges, especially when used in optical communications. These challenges are translated into limitations in bandwidth/information rate, power efficiency and overall attainable communication range.
Amplitude modulation of electromagnetic signals is commonly used nowadays and OOK is typically carried out in Radio Frequency (RF) systems using an AM transmitter as a source oscillator, followed by a variable gain amplifier. The oscillator output is fed as an input to the amplifier, while the modulating signal controls the amplifier gain. This way, the output signal is amplitude modulated. A schematic diagram exemplifying a typical RF AM modulator is demonstrated in
When optical systems are concerned, the scheme is somewhat different. The source oscillator is typically a laser, emitting a very narrow band of coherent light. By applying an “on and off” DC biasing of the laser, its output is switched between light and dark—thereby achieving the required OOK modulation. A schematic diagram exemplifying a typical OOK transmitter is illustrated in
Still, simple AM modulation schemes, and in particularly OOK type of modulation for optical signals, involves several drawbacks, among which:
Therefore, the present invention. seeks to provide a novel solution to amplitude modulation of electromagnetic signals, and in particularly to OOK modulation of light, a solution which overcomes many of the drawbacks associated with prior art OOK schemes.
The disclosure may be summarized by referring to the appended claims.
In view of the drawbacks of conventional methods, it is an object of the present invention to provide unique and innovative method and system for modulating electromagnetic signals.
It is another object of the present disclosure to provide a method and an apparatus for carrying out amplitude modulation by loading the propagating electromagnetic field, rather than turning on and off the signal generating source.
It is another object of the disclosure to provide a method and an apparatus which rely on using one or more antennas provided with a changeable non-linear load, thereby changing the impedance matching between the antenna and the medium in order to obtain the desired modulation.
Other objects of the present disclosure will become apparent from the following description.
According to one embodiment, there is provided a system configured to amplitude modulate electromagnetic signals, wherein the system comprising at least one antenna coupled to a respective electrical load configured to be provided with one or more modulating signals, and wherein the electromagnetic signals are amplitude modulated in accordance with impedance matching between the at least one antenna and its respective load.
In the following description reference is made at times to amplitude modulation of light. It should be understood however that the system and method described herein are applicable for the entire electromagnetic spectrum, and thus when reference is being made to light modulation, still it should be understood as encompassing an applicable range as the case may be of the full electromagnetic spectrum, and riot only to the part of the electromagnetic spectrum associated with visible light.
According to another embodiment, the load of the at least one antenna is a non-linear load, and is DC biased by at least one of the one or more modulating signals. A non-linear load as used herein through the specification and claims is used to denote a load where the current-voltage relationship (i.e. the I(V) function) cannot be described by a linear equation. Such a load, exhibits a differential load (dV/dI) that varies with the DC bias point of the load.
In accordance with another embodiment, the load of the at least one antenna is a metal-insulator-metal (MIM) load.
By yet another embodiment, the electromagnetic signals are optical signals.
According to another embodiment, the system further comprising a waveguide for conveying the electromagnetic signals (in their unmodulated and,/or modulated form) along a pre-defined path.
According to still another embodiment, the system further comprises a modulating signal source and at least one blocker (e.g. a. series of chokes) operative to block the electromagnetic signals received by the at least one antenna from reaching the modulating signal source.
By yet another embodiment, the system comprising a plurality of antennas each coupled to a respective MIM load, and wherein. the antennas are arranged serially along the waveguide, and wherein the same modulating signal is applied to each of the MIM loads, thereby enabling serial modulation of the electromagnetic signals as they propagate through the waveguide, by the plurality of antennas.
According to another aspect, there is provided a system configured to amplitude modulate electromagnetic signals, wherein the system comprising a plurality of antennas each coupled to a respective MIM load and configured to be provided with a respective modulating signal, and wherein each of the respective modulating signals is applied to each of the MIM loads, thereby obtaining amplitude modulation of the electromagnetic signals in accordance with impedance matching between each of the plurality of antennas and its respective load.
In accordance with another embodiment, the plurality of antennas is arranged along a waveguide and the system is configured to enable amplitude modulation of the electromagnetic signals by the plurality of antennas, as the electromagnetic signals propagate along the waveguide (e.g. serial modulation).
By yet another embodiment, at least two of the modulating signals provided to the plurality of antennas, are different from each other.
According to still another embodiment, the load coupled to each of the plurality of antennas is a non-linear load which is DC biased by a respective modulating signal provided to each of the plurality of antennas.
In accordance with another embodiment of this aspect of the invention, the electromagnetic signals are optical signals.
According to yet another aspect of the invention there is provided a method for amplitude modulating electromagnetic signals, wherein the method comprises the steps of:
providing at least one antenna coupled to a respective load;
providing modulating signals to the at least one respective load, for enabling amplitude modulation of the electromagnetic signals;
amplitude modulating the electromagnetic signals in accordance with impedance matching between the at least one antenna and its respective load.
According to another embodiment of this aspect, the step of amplitude modulating the electromagnetic signals comprises applying a non-linear load which is DC biased by the modulating signals to the respective load of the at least one antenna.
In accordance with another embodiment, the respective load of the at least one antenna is a metal-insulator-metal (MIM) load.
By yet another embodiment, the electromagnetic signals are optical signals.
In accordance with still another embodiment, a plurality of antennas are provided, each coupled to a respective MIM load, wherein the plurality of antennas are arranged in a serial configuration along a waveguide, and wherein the step of amplitude modulating the electromagnetic signals comprises applying the same modulating signal to each of the respective MIM loads, thereby enabling serially modulating the electromagnetic signals as they propagate through the waveguide, by the plurality of antennas.
The accompanying drawings, which are incorporated herein and constitute a part of this specification, illustrate several embodiments of the disclosure and, together with the description, serve to explain the principles of the embodiments disclosed herein.
Some of the specific details and values in the following detailed description refer to certain examples of the disclosure. However, this description is provided only by way of example and is not intended to limit the scope of the invention in any way. As will be appreciated by those skilled in the art, the claimed method and device may be implemented by using other methods that are known in the art per se. In addition, the described embodiments comprise different steps, not all of which are required in all embodiments of the invention. The scope of the invention can be summarized by referring to the appended claims.
The following description relates to a method and an apparatus for implementing a unique and innovative approach of light modulation. The approach demonstrated in the following description is based on loading the propagating electromagnetic field, rather than on switching the light source on and off. The loading of the electromagnetic field is done by placing one or more antennas in the field, and actively changing its loading. Thus, actively changing the impedance matching between the antenna and the medium, and consequently changing the power being transferred between. the medium and the antenna(s).
Let us now consider a setup, where an antenna is placed in a medium where an electromagnetic wave is propagating.
Assuming that the antenna is properly designed, the electromagnetic wave will induce AC currents across the antenna, as propagates therethrough.
Next, the energy balance of this setup is analyzed. To do so, let us consider the following two extreme scenarios:
Scenario 2: the antenna is loaded with a perfectly matched load. The term “a perfectly matched load” as used herein is used to denote a load that would cause absorption of all the electromagnetic energy picked by the antenna. In this case, the antenna absorbs the energy it has picked (i.e. absorption mechanism), and consequently the propagating electromagnetic field energy would be decreased by the very same amount of energy that was picked by the antenna. This scenario is presented in
A basic principle of the proposed solution relies on coupling one or more antennas to the electromagnetic field while allowing the electromagnetic waves to propagate along a waveguide. As the wave propagates, it is coupled to the antenna(s) along the waveguide. When coupled to the antenna(s), the electromagnetic wave may either go through or be reflected (it would go through for example, if the antenna(s) is/are not properly loaded, and would be reflected to the electromagnetic field either under open or short load conditions); or be absorbed by the antenna(s), if it/they is/are properly loaded.
Changing the electrical loading of the antenna(s), allows to amplitude modulate the electromagnetic field, as will be further explained.
An antenna coupled to a non-linear electrical load, may reflect different electro-magnetic loads by changing the DC bias of the non-linear load, for example, in case where an antenna coupled to a Metal-Insulator-Metal (MIM) structure, is used. MIM devices are well known in the art. They are two-port passive electrical devices, where two metals are separated from each other by a thin insulator. As voltage is applied across the metals, current appears to flow through the insulator utilizing the effect called ‘tunneling effect’. It can be shown that tunneling is a non-linear effect (as the current increases exponentially as a result of a linear increase in the voltage), and thus a MIM acts as a non-linear electrical load.
When coupling a MIM device (structure) to an antenna feed point, the loading perceived by the antenna is the differential load (dV/dI) as reflected by the MIM device. It can be shown that by DC biasing the MIM structure, different loads shall be reflected to the antenna—hence different impedance matching points are formed.
There are certain advantages that are associated with the solution described hereinabove, when compared with prior art OOK type of modulation schemes. Some of the main advantages are the following:
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein, for example cases where the optical signals are conveyed to the antenna via a waveguide/optical fiber in the addition or in the alternative of being conveyed in free space. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
Filing Document | Filing Date | Country | Kind |
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PCT/IL2016/051295 | 12/4/2016 | WO | 00 |
Number | Date | Country | |
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62264328 | Dec 2015 | US |