Structure and method for modulating light

A structure includes a film having a plurality of nanoapertures and a semiconductor layer in connection with the film. The nanoapertures are configured to allow the transmission of a predetermined subwavelength of light through the film via the plurality of nanoapertures. The semiconductor layer facilitates the modulation of the predetermined subwavelength of light transmitted through the film. The structure also includes a carrier generator for modulating the predetermined subwavelength of light by generating charge carriers.

BACKGROUND

Recently, optical modulators and waveguides have garnered increased attention for a variety of applications, especially in data transmission, processing, and interconnects, with the thrust towards nanophotonics. One application of optical modulators is the transmission of information on computer chips. The trend is toward using wavelength division multiplexing (WDM) to transmit data in an optical system. WDM is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths, i.e., different colors of light, to carry different signals. This allows for a multiplication in capacity, in addition to making it possible to perform bidirectional communications over one strand of fiber. Optical modulators that may be used for WDM systems have the ability to modulate at specific wavelengths. However, conventional optical modulators are generally less wavelength sensitive. Modulators that are fabricated from lithium niobate generally are broadband and can modulate at different wavelengths, ranging from infrared to visible. But, these modulators, like other modulators, such as electro-absorption and micro-ring, suffer from issues in material compatibilities, optical coupling issues, and are complex to fabricate. Thus, due to the limitations of conventional optical modulators and other components of the conventional optical transmission system, such as detectors, different nano-wavelengths of light may not be used for the transmission of information.

One form of optical modulator, Schottky barrier modulators, typically include a semiconductor, such as silicon, or any III-V material such as GaAs, InP, AlGaAs, InGaAsP, GaN, InGaN, with an over-lying metal Schottky electrode. The interface between the semiconductor and the Schottky electrode is known as the Schottky energy barrier. In a Schottky modulator, carriers are generated in the semiconductor by forward-biasing the modulator. That is, a positive potential is applied to the metal with respect to the n-type semiconductor for generating carriers and changing the refractive index of the semiconductor. This, in turn, changes the wavelength of light that is permitted to pass through the subwavelength nano-holes in the metal. Depending on the incident wavelength, such as near infrared, the metal can be replaced with a highly delta doped p layer with subwavelength nano-hole arrays.

Conventional optical modulators, including lithium niobate electro-optic modulators, III-V electro-absorption modulators, and silicon micro-ring modulators, all suffer from several other drawbacks as well. First, conventional optical modulators incorporating wavelength selectivity are relatively difficult to fabricate. The wavelength selectivity in these modulators is usually accomplished by either precision growth of III-V epitaxial films such as III-V electro-absorption modulators or complex fabrication techniques to generate extremely smooth curved surfaces in silicon and coupling out with an optical waveguide in the case of silicon micro-ring modulators. This is a very limiting factor in applications where space is a premium or the need for low cost is important, such as applications for computer chips. Second, the complex fabrication process used for conventional optical modulators is excessively time-consuming and expensive. Moreover, inexpensive conventional optical modulators, such as lithium niobate modulators, do not allow selected wavelengths of light to be modulated.

DETAILED DESCRIPTION

Embodiments of structures and methods for detecting and modulating wavelengths of light are disclosed herein. The structures include a film having a plurality of nanoapertures, which are openings through the film configured to allow subwavelengths of light to be transmitted through the film. The film is generally metallic, however, in one example, the film may include a highly delta doped p-type semiconductor for operation in the near infrared subwavelengths. Subwavelengths of light are predetermined wavelengths of light ranging from 10 to 2000 nanometers (nm). Subwavelengths of light may refer to a specific wavelength, such as 436 nm, for example, or may also refer to narrow bands of wavelengths, such as 370-475 nm or 1300-1800 nm. While specific wavelengths are provided in these examples, a person having ordinary skill in the art will appreciate that subwavelengths of light may refer to other subwavelengths. Also, the nanoapertures may be configured to allow for the transmission of any predetermined subwavelengths of light through the film.

The structures described herein also include a semiconductor layer in connection with the film. For example, a surface of the semiconductor layer may be in direct contact with a surface of the film. The juxtaposition of the film and the semiconductor layer forms a Schottky contact and, when forward-biased, the film has a positive potential with respect to the semiconductor layer for an n-type semiconductor. When light is directed towards the film, the predetermined subwavelengths of light may pass through the nanoapertures and into the semiconductor layer. However, the electrical bias at the Schottky contact may be altered, thereby altering the carrier generation/depletion, to change the effective dielectric constant at the metal film-semiconductor interface, as discussed in greater detail below. This, in turn, modulates the light that is allowed to pass through the nanoapertures.

Modulating light includes altering an attribute of a wave of transmitted light. For example, modulating light may include increasing or decreasing the amplitude of the wavelength of light passing through the nanoapertures. Modulating may also include altering the transmission peak of the transmitted wavelength of light. For instance, a particular wavelength of light may be transmitting at 100% until it is modulated to transmit at 80%, 60%, etc.

The light may be modulated by altering the refractive index of the semiconductor layer. The refractive index of the semiconductor layer may be altered by carrier generation. Carrier generation refers to the generation of charge carriers, such as electrons and holes, which may be injected into the semiconductor layer to overcome the energy band gap of the semiconductor material, as is known in the art. A carrier generator may be used to initiate carrier generation by a number of different methods, including, but not limited to, optically, electrically, thermally, and chemically. For example, the refractive index of the semiconductor layer may be altered optically by directing another source of light towards the nanoapertures to initiate carrier generation and/or impinge on the nanoapertures. Impinging on the nanoapertures refers to reducing the transmission intensity of the light passing through the nanoapertures. In another example, the light may be modulated electrically by applying a voltage source to the semiconductor layer to deplete, or sweep out, carriers in order to change the refractive index.

The structures and methods described herein allow for the modulation of light with several advantages over previous optical modulators. For example, the structures described herein are highly wavelength sensitive. That is, the nanoapertures are configured to transmit only predetermined wavelengths of light. Thus, precise wavelengths of light may be modulated with a high degree of accuracy, as will be discussed in greater detail below. The structures described herein are also very compact. Therefore, a large number of structures may be placed on small surfaces, such as on computer chips. The structures described herein are also relatively easy to manufacture, because they require only a minimal number of different layers and materials.

FIG. 1Aillustrates a cross-sectional view of a structure100having a film102and a semiconductor layer104, according to an embodiment. The film102includes nanoapertures106, which are openings through the film102configured to allow one or more predetermined subwavelengths of light to be transmitted through the film102. For example, two different subwavelengths of light, such as λ1108and λ2109may be directed toward the film102. The nanoapertures106may be configured to allow the transmission of λ1108and/or λ2109through the film102. Thus, the nanoapertures106act as a filter by blocking the transmission of certain wavelengths of light through the film102, while allowing for the transmission of only predetermined subwavelengths of light, such as λ1108and/or λ2109. WhileFIG. 1Adepicts three nanoapertures, the film102may contain less than three or many more nanoapertures than the three shown inFIG. 1A.

As described above, the nanoapertures106are subwavelength, because they are configured to allow a predetermined subwavelength, or narrow band of subwavelengths, of light to pass through the film102. For example, the nanoapertures106may be configured to allow only λ1108, which may be the red spectrum of light ranging from approximately 580 to 680 nm, with a peak transmission wavelength being approximately 627 nm, to be transmitted through the film102. A person having ordinary skill in the art will appreciate that the nanoapertures106may be configured to allow any wavelength, or any band of wavelengths, of light to pass through the film102.

Configuring the nanoapertures106to allow a predetermined subwavelength to pass involves adjusting the periodicity of the nanoapertures106. Periodicity refers to the spacing between the nanoapertures106. The wavelength that the nanoapertures106are configured to transmit may be directly related to periodicity. This is due, in part, to the generation of standing waves over the surface of the nanoapertures106, which may be modified by altering periodicity to position the standing waves over the surface of the nanoapertures106. The diameter and shape of the nanoapertures may also effect the wavelength that the nanoapertures106are configured to transmit. For instance, the wavelength that a nanoaperture106transmits is generally about ten times larger than the diameter of the nanoaperture106, as discussed in greater detail below.

The geometric configuration of the nanoapertures106is not limited to circular. For instance, the nanoapertures106may be circular, oval, elongated slits, rectangular, etc. The nanoapertures106may also be patterned, corrugated, have annular rings, etc. For instance, the nanoapertures106may be surrounded with concentric circular grooves. Similarly, the nanoapertures106may each be configured to allow the same subwavelengths of light to pass through the film102or, alternatively, the film102may have nanoapertures106configured to allow any number of different subwavelengths of light to pass through the film102. The nanoapertures106may be provided as an array of nanoapertures106in the structure100. The array may be any shape, such as a square array or rectangular array. The nanoapertures106may also be provided as multiple arrays. Each array may be configured to allow a single subwavelength of the light108to be transmitted through the film102. For example, each array may be configured to allow a single color spectrum to be transmitted through the film102, such as red, green, blue, etc. In addition, a single modulator may have a chirped nanoaperture or a mixture of two or more sets of nanoapertures that can selectively detect multiple discrete wavelengths. For example, a single modulator may modulate wavelengths at 780 nm and 1550 nm only.

The nanoapertures106may have dimensions optimized for transmitting a particular subwavelength or optimized for a particular application. For instance, if the nanoapertures106are circular, they may have diameters ranging from 10 to 500 nm to detect different subwavelengths. In one embodiment, diameters of 155, 180, and 225 nm may allow for transmission of peak transmission wavelengths of 436, 538, and 627 nm, respectively. The nanoapertures106may be empirically configured to be approximately one-tenth the size of the wavelength of the light they are designed to pass. The nanoapertures106may be formed by any processes known in the art, including, but not limited to, any form of lithography, such as, electron beam or ion beam lithography and nanoimprinting lithography.

The film102may be formed from conductive materials, such as doped materials such as n- or p-type semiconductor and metals, for example, silver, gold, platinum, palladium, etc. The film102may be formed from a single material or from any combination of materials and may be homogenous or heterogeneous. The film106may have any dimensions. For example, in one embodiment, the film106may have a maximum thickness of approximately 50 nm. In other examples, the film102may have a thickness approximately within a factor of 5 of the diameter of the nanoapertures106.

The semiconductor layer104operates to facilitate in the detection and modulation of the subwavelengths of light that are transmitted through the film102and may be formed from any semiconductor material or any combination of materials known in the art. For example, the semiconductor layer104may be formed from an n-type semiconductor by doping a valence-four semiconductor with valence-five elements in order to increase the number of free (in this case negative) charge carriers or any III-V semiconductors. P-type semiconductor may also be used with appropriate bias, as is known in the art. The semiconductor layer104may be joined to the film102by any process known in the art, including thermal techniques, electron-beam or chemical deposition of the film104on the surface of the semiconductor layer104.

When the semiconductor layer104is connected to the film102, the transmission spectra of the nanoapertures106may be tuned by adjusting the periodicity and symmetry of the film102for the dielectric of the semiconductor layer104, as discussed above. For example, in a square array of nanoapertures106with a period of a0and peak transmissions of λmax, the normal incidence transmittance spectra can be identified approximately from the dispersion relation given by the following equation:

λmax=P43⁢(i2+ij+j2)⁢ɛm⁢ɛdɛm+ɛd
where the indices i and j are the scattering orders from the array and P is the periodicity, or the lattice period, of the array. The dielectric constant of the semiconductor layer104may shift the eigen-frequencies by a factor of f≈√{square root over (∈s)} where ∈sis the dielectric constant of the semiconductor material. Therefore, the nanoapertures106in the film102may be reconfigured to adjust to the effect of the semiconductor layer104. For example, the nanoapertures106may be reduced in size by a factor of f, set forth in the equation above, such that the subwavelengths of light passing through the nanoapertures106are shifted to be in resonance with the semiconductor layer104. Thus, the periodicity and size of the nanoapertures106are adjusted to allow for the predetermined subwavelengths of light, such as λ1108, to pass through the film102into the semiconductor layer104. For instance, as set forth above, the nanoapertures106may be approximately one-tenth the size of the wavelength and the periodicity, such as the number and placement of the nanoapertures106in an area, may be modified to determine the wavelength of the light that the nanoapertures106will pass. By forming the appropriate period for a standing wave of the surface plasmon, the light is enhanced at the nanoaperture106for that wavelength, much as the case for a photonic crystal structure.

The operation of the structure100is as follows. In an embodiment, the structure100is part of a photodetector operable to detect and modulate subwavelengths of light. For example, the structure100may allow for the detection of λ1108, which may be a wavelength of 538 nm. However, a person having ordinary skill in the art will appreciate that λ1108may be any subwavelength or narrow band of subwavelengths. AsFIG. 1Adepicts, λ1108is applied to the structure100. WhileFIG. 1Adepicts only a single arrow representing λ1108, it is to be understood that λ1108may be applied to the entire surface of the film102to contact each of the nanoapertures106. λ1108may originate from any source and may be applied to the structure100in any form. One source may include a laser or similar devices capable of producing a beam of light.

When λ1108comes into contact with the film102, λ1108may pass through the film102, via the nanoapertures106, to the semiconductor layer104. The precise wavelength of λ1108is predetermined because the nanoapertures106are configured to allow only those subwavelengths of light to pass through the nanoapertures106. Therefore, only λ1108may pass through the film102. Thus, the structure100may act as a photodetector to detect a specific subwavelength of light if the light has an energy of photons exceeding the bandgap of the semiconductor. Alternatively, if the light has an energy below the bandgap of the semiconductor, the semiconductor is transparent to the light, such as λ1108in this case. When it is determined that any light has reached the semiconductor layer104, the subwavelength of that light, λ1108, is automatically known, because the nanoapertures106are configured to allow only predetermined subwavelengths of light to pass through the film102to reach the semiconductor layer104.

λ1108may pass through the nanoapertures106by coupling to surface plasmons on the film104. Surface plasmons are waves that propagate along the surface of a substrate, usually a metallic substrate or heavily-doped dielectric substrate. Surface plasmons have the ability to interact with light to allow photons of the light to couple to the surface plasmons. Thus, surface plasmons have the unique capacity to confine light to very small dimensions to propagate the light. The transmission of λ1108through the nanoapertures106without coupling to surface plasmons drops off as the fourth power of the ratio of the diameter of the nanoapertures106and λ1108. However, with surface plasmon modes, if the nanoapertures106are arranged in an array where the period of the array is half the wavelength of the surface plasmon mode, a standing wave is formed and light is enhanced at the nanoaperture106, thereby allowing enhanced transmission through the nanoapertures106. In this manner, λ1108may pass through the film102by coupling to surface plasmons in the nanoapertures106.

As set forth above, the structure100may also facilitate the modulation of a subwavelength of light, such as of λ1108. For example, λ2109may be a modulating beam of light used as a carrier generator to modulate λ1108. For example, λ1108may be a subwavelength of approximately 800 nm, while λ2109is a weaker light at a different wavelength, such as 200 nm. λ2109may modulate λ1108by modulating the amplitude of λ1108. For example, λ2109may function as a carrier generator by initiating carrier generation and creating electron-hole pairs. When electron-hole pairs are injected into the semiconductor layer104, they alter the refractive index and the resonant frequency of the film102-semiconductor layer104interface, such that the nanoapertures106no longer pass light at the same wavelength. Thus, λ2109may modulate λ1108by altering the refractive index of the semiconductor layer104at the film102-semiconductor layer104interface. λ2109may also modulate λ1108by controlling the transmission peak of λ1108. For instance, λ2109may act like the gate of a transistor or the shutter of a camera by alternatively reducing and increasing the transmission peak of λ1108. As λ2109impinges on the nanoapertures106, the peak transmission λ1108may shift to 80%, 60%, and less.

The structure100, depicted inFIG. 1, may also include multiple semiconductor layers. For example, the structure100may include an intermediate semiconductor layer (not shown) disposed between the film102and the semiconductor layer104. The intermediate semiconductor layer may have a higher bandgap than the bandgap of the semiconductor layer104and may be used for tuning the nanoapertures106by altering the subwavelength of the light that the nanoapertures106are configured to allow transmission of. The nanoapertures106may be tuned, for example, by current injection, as set forth above. Embodiments having multiple semiconductor layers may be used in conjunction with a photodiode, such as a PIN (also known as p-i-n) semiconductor junction, where p is a p-type semiconductor, i is an intrinsic or not intentionally doped semiconductor, and n is an n-type semiconductor, as is known in the art. In this embodiment, nanoapertures may be formed in the p or n layer to act as a subwavelength filter, similar to the film102. However, in this embodiment, the nanoapertures may filter infrared frequencies.

FIG. 1Billustrates a cross-sectional view of a structure111having a film102, a semiconductor layer104, and a carrier generator115, according to an embodiment. The film102and the semiconductor layer104may be substantially similar, or identical, to the film102and the semiconductor layer104, described above with respect toFIG. 1A. The carrier generator115is a device for the generation of charge carriers, such as electrons and holes. The carrier generator115may include means for generating charge carriers either electrically, chemically, thermally, and/or biologically at the interface between the film102and the semiconductor104. For example, the carrier generator115may include a voltage source for applying an electric current to the semiconductor layer104, a heat source for increasing the temperature of the semiconductor layer104, etc. The carrier generator115modulates a subwavelength of light, such as the λ1108, by altering the refractive index of the semiconductor layer104at the film102-semiconductor layer104interface in the same manner as the modulating light source described above.

FIG. 1Cillustrates a cross-sectional view of a structure112having a film102, a semiconductor layer104, and a contact110, according to an embodiment. The film102and the semiconductor layer104may be substantially similar, or identical, to the film102and the semiconductor layer104, described above with respect toFIG. 1A. The contact110may be an ohmic contact or a region on the structure112that has been prepared so that the current-voltage (I-V) curve of the structure112is linear and symmetric. That is, the contact110may be a metallic material that creates an ohmic metal-semiconductor junction that does not rectify current.FIG. 1Cdepicts the contact110in connection with, and extending only partially along, the surface of the semiconductor layer104to allow light to transmit through the structure112. However, a person having ordinary skill in the art will appreciate that the contact110may be any reasonably suitable size and may be larger than the contact110depicted inFIG. 1Cwith openings in the contact110to allow light to pass through the structure112.

In another embodiment, the contact110may cover the whole back surface of semiconductor layer104to make an equipotential surface with the homogeneous Schottky barrier. One may use, for instance, transparent indium tin oxide (ITO) to form the contact110covering the entire back surface of the semiconductor layer104. When predetermined subwavelengths of light, such as λ1108, having photon energy exceeding the (direct) bandgap of the semiconductor layer104are transmitted through the nanoapertures106electron-hole pairs are created in the semiconductor layer104and absorb incident photons from the predetermined above bandgap light, which in this case is reverse-biased to sweep the electrons into the contact110, resulting in a photocurrent in the external circuit. This photocurrent may be detected to determine that the light has reached the semiconductor layer104. The subwavelength of the above bandgap light is automatically known when it is determined that light has reached the semiconductor layer104, because the nanoapertures106are configured to allow only those subwavelengths of the light to be transmitted through the film102, as described above. However, if the photon energy is less than the bandgap of the semiconductor layer104, the semiconductor layer104will be transparent to the photons and no photocurrent will be generated or detected. By forward-biasing the film102, when the film102is metal or a p-type semiconductor, with respect to the n-type semiconductor layer104, carrier generation at the film102-semiconductor layer104interface will change the transmission characteristics of the nanoapertures106, resulting in modulation of the impinging photons. Any suitable materials and processes known in the art for creating an ohmic contact may be used to create the contact110. For example, the contact110may be a sputtered or evaporated metallic pad that is patterned using photolithography.

Although not illustrated inFIG. 1C, the structure112may also include a measuring device for detecting and/or reading the photocurrent created in the structure112. For example, the measuring device may include an ampere meter connected to the contact110to detect a change in current responsive to the generation of the photocurrent in the semiconductor layer104due to the transmission of the light through the nanoapertures106. In another embodiment, a voltmeter may be used to measure the change in voltage across a load resistor due to the photocurrent generated in the semiconductor layer104.

FIG. 1Dillustrates a cross-sectional view of a structure113having a film102, a semiconductor layer104, a quantum well103, and a Bragg mirror105, according to an embodiment. The film102and the semiconductor layer104may be substantially similar, or identical, to the film102and the semiconductor layer104, described above with respect toFIG. 1A. The quantum well103represents a potential well for providing gain to compensate for any optical loss such as insertion loss. The quantum well103may be forward-biased to provide gain which is broadband, as is known in the art. The Bragg mirror105is any structure utilizing Bragg reflection principles to inhibit light, such as λ1108, from passing through the Bragg mirror105to create a resonant modulator where the extra round trips of the photon to the gain region increase the intensity, as is known in the art. For example, although depicted inFIG. 1Das a single layer, the Bragg mirror105may include an alternating sequence of layers of two different optical materials, with each optical layer thickness corresponding to one quarter of the wavelength for which the Bragg mirror105is designed. The quantum well103and the Bragg mirror105may be used to generate gain. That is, the quantum well103and the Bragg mirror105may be used to increase the total intensity output of the structure113in relation to the intensity input into the structure113, as is known in the art. The structure113is depicted as having both the quantum well103and the Bragg mirror105. However, the quantum well103and the Bragg mirror105may be used alone or in conjunction with each other in any of the structures depicted inFIGS. 1A-D.

FIG. 2illustrates a cross-sectional view of a structure200, according to an embodiment. The structure200includes a first film102ahaving first nanoapertures106a, a first semiconductor layer104a, and a first contact110a, which may be substantially similar to the structure112, depicted inFIG. 1C. The structure200also includes a second film104bhaving second nanoapertures106b, a second semiconductor layer104b, and a second contact110b, which also may be substantially similar to the structure100. Therefore, the structure200may be, essentially, the structure100arranged in series with another structure100. WhileFIG. 2depicts two arrows pointing to the nanoapertures106aand106b, it is to be understood thatFIG. 2shows three apertures and that a third arrow is omitted for simplicity. Furthermore, the light depicted inFIG. 2may be applied to the entire surface of the film102to contact each of the nanoapertures and the film102may contain less than three nanoapertures or more nanoapertures than the three shown inFIG. 2. The first contact110ais depicted as being smaller than the second contact110b, such that the first contact110adoes not obstruct light, such as the λ1108from passing through the second film102b. However, the first and second contacts110aand110bmay be any reasonably suitable size so long as the first contact110adoes not obstruct the second nanoapertures106b. For instance, either or both of the first and second contacts110aand110bmay extend the entire length of the structure200and be formed of a transparent ITO, as set forth above with respect toFIG. 1C. The first contact110ais shown inFIG. 2as embedded in the first semiconductor layer104a. In this example, the first semiconductor layer104amay contain vias to allow a measuring device to access the first contact110a. In other examples, the first contact110amay not be embedded in the first semiconductor layer104a, but may be connected to an outer region of the first semiconductor layer104a.

The use of multiple films arranged in series, as shown inFIG. 2, allows light to be not only detected and modulated, but also analyzed. For instance, light is applied to the first film102aand the first nanoapertures106aare configured to allow predetermined subwavelengths of the light, such as λ1108, to be transmitted through the first film102a. The transmitted λ1108may pass through the first semiconductor layer104aand into the second film102b.

In one embodiment, the first nanoapertures106aof the first film102aare configured to transmit different subwavelengths of light than the second nanoapertures106bof the second film102a. For example, the first nanoapertures106amay be configured to transmit λ1108, which may be approximately 436 nm, while the second nanoapertures106bare configured to transmit a light of approximately 538 nm. The first semiconductor layer104aand the second semiconductor layer104bmay have different bandgaps. Thus, the structure200may be configured to detect different subwavelengths of the light108.

In the example described above, λ1108of 436 nm would normally not be detected at the second semiconductor layer104b, because the first and second nanoapertures106aand106bare configured to transmit different subwavelengths of light. That is, a 436 nm light is transmitted through the first film102avia the first nanoapertures106a, but cannot pass through the second nanoapertures106bof the second film102bbecause the second nanoapertures106bare configured to pass a 538 nm subwavelength. Therefore, the 436 nm subwavelength is blocked by the second film102b.

However, the first film102amay be associated with a contaminant, such as a biological or chemical substance. For example, an organic molecule may bind to the metallic surface of the first film102a. This interaction between the organic molecule and the first film102amay modify the resonance and refractive index of the first film102a, leading to a shift in the transmission subwavelength of the first nanoapertures106a. For instance, the organic molecule may modify the resonance of the first film102aby altering the dimensions of the first nanoapertures106a. This shift may cause the first nanoapertures106ato allow transmission of a different subwavelength of light than the first nanoapertures106awere originally configured to allow transmission of. Thus, if the first nanoapertures106awere originally configured to allow transmission of λ1108of approximately 436 nm, the contaminant interacting with the first film102amay cause the first nanoapertures106ato allow transmission of a subwavelength of 538 nm. Therefore, in this example, the 536 nm subwavelength of light is transmitted through both the first and second films102aand102b. Detection of the light at the second semiconductor layer104bprovides a determination that a contaminant is interacting with the first film102a.

In this manner, the first film102afunctions as a detector, while the second film102bfunctions as an analytical filter. The first film102adetects the presence of the contaminant by either blocking the transmission of the 536 nm subwavelength of light, described in the example above, or transmitting a shifted subwavelength of the 536 nm light. The second film102bmay analyze the shift in the light by allowing for the transmission of the shifted light to the second semiconductor layer104b, thereby providing a determination of what the subwavelength of the light has been shifted to. Knowing the shifted light may provide for the identification of the contaminant. For example, a shift from 436 nm to 538 nm may suggest that the organic molecule causing the shift is a particular [e.g. DNA] molecule. Alternatively, if the 538 nm light is not detected at the second semiconductor layer104b, then a determination is provided that the contaminant is not associated with the first film102a. Thus, the structure200operates as a detector operable to detect a contaminant associated with a film.

The structure200may also act as a tandem push-pull modulator. That is, the structure200may be two modulators placed in series and photons impinging on the structure200will have energy less than the bandgap of the semiconductor layers104aand104b. The structure200may then be forward-biased to generate carriers at the film102-semiconductor layer104interface when the film102is a metal or a p-type semiconductor material and the semiconductor layer104is an n-type semiconductor material. The structure200may operate in a push-pull mode to reduce the operating current/voltage necessary to modulate the incident photons at an acceptable modulation depth of better than 10 dB. In the push-pull mode, one modulator, such as the first film102aand first semiconductor layer104a, may be in depletion mode while the other modulator, such as the second film102band the second semiconductor layer104b, is in accumulation mode such that applying forward and reverse bias respectively will bring the two modulators to maximum transmission.

A person having ordinary skill in the art will appreciate that while examples of specific subwavelengths are recited above to describe various embodiments, that the first and second nanoapertures106aand106bmay be configured to allow transmission of any light. Similarly, differently configured nanoapertures may be used in any combination in the first and second films102aand102b. For instance, the first nanoapertures106amay be configured to transmit a specific narrow band of subwavelengths, while the second nanoapertures106bare configured to transmit multiple different narrow bands of subwavelengths.

FIG. 3illustrates a cross-sectional view of a structure300, according to an embodiment. The structure300includes a first film102ahaving first nanoapertures106aand a first semiconductor layer104a, which may be substantially similar to the film102and the semiconductor layer104of the structure100, depicted inFIG. 1. The structure300also includes a second film104bhaving second nanoapertures106band a second semiconductor layer104b, which also may be substantially similar to the structure100. In fact, the structure300may be a single integrated device, such as an elongated version of the structure100. That is, the first and second films102aand102bmay be virtually identical, while the first and second semiconductor layers104aand104bmay also be virtually identical. Therefore, the structure300may also be, essentially, the structure100arranged in parallel with another structure100. The structure300may be two structures100joined together, rather than an elongated version of the structure100, because joining the two structures may be a more efficient manufacturing process than fabricating an elongated version of the structure100. Although not illustrated, the structure300may also contain first and second contacts110aand110b, substantially similar to the first and second contacts110aand110bdepicted inFIG. 2.

The use of multiple films arranged in parallel in the structure300allows for the capture of a broader range of spectral information. For example, the spacing and configurations of the first and second nanoapertures106aand106bmay be altered to allow different wavelengths to pass through the structure300. For instance, the diameter of the first nanoapertures106amay be increased, reduced, and/or changed in shape to allow for the transmission of a first predetermined subwavelength of light, such as λ1108, while the configuration of the second nanoapertures106bmay be increased, reduced, and/or changed in shape to allow for the transmission of a different predetermined subwavelengths of light, such as λ2109. Altering the spacing and configuration of the first and second nanoapertures106aand106ballows for more spectral information to be obtained, because the structure300is operable to modulate multiple different subwavelengths.

Although not illustrated, the structure300may also include additional films and semiconductor layers arranged in series with the structure300. For instance, in an embodiment, the structure300may resemble the structure200, depicted inFIG. 2. That is, the structure300may have multiple films arranged in series, where the multiple films act as detectors and analyzers, as set forth above. Moreover, the structures200and300may contain the quantum well103and/or the Bragg mirror105, described above with respect toFIG. 1D.

FIG. 4illustrates a flow chart of a method400for modulating a subwavelength of light, according to an embodiment. For example, the method400may be used in conjunction with the structures100-113, illustrated inFIGS. 1A-Dto modulate a predetermined subwavelength of light. The method400is described with respect toFIGS. 1-3, by way of example and not of limitation. A person having ordinary skill in the art will appreciate that additional steps may be added to the method400and, similarly, that some of the steps outlined inFIG. 4may be omitted, changed, or rearranged without departing from a scope of the method400.

At step401, the method400includes receiving light at a film102having a plurality of nanoapertures106. The film102may have any number of nanoapertures106configured to detect any different number of subwavelengths of the light, including a single subwavelength or a range of subwavelengths. The film102may also include multiple films arranged either in series or in parallel, as depicted inFIGS. 2 and 3, respectively. The film102may be associated with a semiconductor layer104.

At step402, a refractive index of the semiconductor layer104is altered to modulate the predetermined subwavelength of light. The refractive index may be altered by inducing carrier generation through any of the methods described above, including, but not limited to, optically, electrically, thermally, chemically, and biologically. For example, a modulating beam of light109may be applied to the film102or a carrier generator115, such as a voltage source, may be used to induce carrier generation.

At step403, the modulated predetermined subwavelength of light, such as λ1108, is transmitted into the semiconductor layer connected to the film102. The modulated predetermined subwavelength of light may be transmitted through the film102via at least one of the plurality of nanoapertures106. In further steps, not illustrated inFIG. 4, the modulated predetermined subwavelength of light may be detected. When light is detected, the wavelength of the light may be automatically determined, as described above. The method400may be practiced with a structure having a contact110, such as the structure112depicted inFIG. 1C. The contact110may be an ohmic contact, for example, and may create a Schottky junction between the semiconductor-contact interface. The creation of the Schottky junction may facilitate detection of the predetermined wavelength of light transmitted through the film102, because transmission of the light may cause a photocurrent to flow from the semiconductor layer104to the contact110. This photocurrent may be detected, thereby providing a determination that the predetermined wavelength of light has been transmitted through the nanoapertures106.

The structures described herein may be useful in a variety of different applications. For instance, the structures may be used in information processing, sensors, and in laser data transmission applications. In one embodiment, the structures may function as a transistor by modulating and controlling the flow of information represented by different subwavelengths of light. In another embodiment, the methods and structures described herein may be used in a laser application.

While the embodiments have been described with reference to examples, those skilled in the art will be able to make various modifications to the described embodiments. The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. In particular, although the methods have been described by examples, steps of the methods may be performed in different orders than illustrated or simultaneously. Those skilled in the art will recognize that these and other variations are possible within the spirit and scope as defined in the following claims and their equivalents.