Nonlinear optical waveguide structures for light generation and conversion

An optical waveguide structure comprising a nonlinear optical waveguide, a central region, a first side region, and a second side region. The central region is located within the nonlinear optical waveguide, wherein the central region comprises a nonlinear optical material. The first side region is on a first side of the central region and the second side region is on a second side of the central region. The nonlinear optical material comprising the central region has a first nonlinear coefficient that is larger than a second nonlinear coefficient of a second material comprising the first side region and the second side region.

BACKGROUND INFORMATION

The present disclosure relates generally to optical waveguide structures and, in particular, to optical waveguides with nonlinear optical materials.

Optical waveguides are physical structures that guide electromagnetic waves in an optical spectrum. Optical waveguides can be used as components in integrated optical circuits. With respect to quantum communications and processing, nonlinear optical material structures can be used to create photon transmitters, repeaters, and other quantum devices for communications. Nonlinear optical structures can be used to change the light passing through them depending on factors such as orientation, temperature, wavelength of light, polarization of light, and other factors.

For example, a waveguide with light of a blue wavelength passing through the waveguide can generate one or more photons of light that has a longer wavelength, such as green or red, and a correspondingly lower photon energy. This type of conversion can be performed using waveguides that incorporate a nonlinear optical material having a second order or third order nonlinear optical susceptibility.

Current waveguides and structures that implement nonlinear optical processes are not as efficient as desired. Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues. For example, it would be desirable to have a method and apparatus that overcome a technical problem with increasing the efficiency of nonlinear optical processes using optical waveguides with nonlinear optical materials.

SUMMARY

An embodiment of the present disclosure provides an optical waveguide structure comprising a nonlinear optical waveguide, a central region, a first side region, and a second side region. The central region is located within the nonlinear optical waveguide, wherein the central region comprises a nonlinear optical material. The first side region is on a first side of the central region and the second side region is on a second side of the central region. The nonlinear optical material comprising the central region has a first nonlinear coefficient that is larger than a second nonlinear coefficient of a second material comprising the first side region and the second side region.

Another embodiment of the present disclosure provides method for moving a light through a nonlinear optical waveguide structure. A light at a pump wavelength is input into the nonlinear optical waveguide structure having a central region within a nonlinear optical waveguide in the nonlinear optical waveguide structure; a first side region of a first side of the central region; and a second side region on a second side of the central region. The central region comprises a nonlinear optical material and the central region has a first nonlinear coefficient that is larger than a second nonlinear coefficient of the first side region and the second side region. The light at the pump wavelength is propagated along a path in the optical waveguide structure, wherein light generation occurs in the nonlinear optical waveguide.

DETAILED DESCRIPTION

The illustrative embodiments recognize and take into account one or more different considerations. For example, the illustrative embodiments recognize and take into account that when light propagates through an optical waveguide, the light may have different wavelengths. The illustrative embodiments recognize and take into account that the light of the shortest wavelength, such as a pump light, can have a propagation mode such as a transverse electric (TE)31mode, which is a higher order mode. The illustrative embodiments recognize and take into account that the light of other wavelengths traveling through an optical waveguide can have a fundamental mode such as TE11. The illustrative embodiments recognize and take into account that the light of the other wavelengths can be a signal light or an idler light generated within the optical waveguide as a result of the pump light traveling through the optical waveguide.

The illustrative embodiments recognize and take into account that the configuration of a nonlinear optical waveguide can affect the efficiency of generating at least one of a signal light or an idler light. As used herein, the phrase “at least one of,” when used with a list of items, means different combinations of one or more of the listed items can be used, and only one of each item in the list may be needed. In other words, “at least one of” means any combination of items and number of items may be used from the list, but not all of the items in the list are required. The item can be a particular object, a thing, or a category.

The illustrative embodiments recognize and take into account that it is desirable to avoid light of a particular wavelength having a first sign and a second sign that are opposite of each other. The illustrative embodiments recognize and take into account that the sign is for the amplitude of an electric field component of the light. The illustrative embodiments recognize and take into account that this condition can result in the nonlinear optical interaction of the light of one or more wavelengths being canceled or partially canceled.

Thus, the illustrative embodiments provide a method, apparatus, and system for moving light in optical waveguides with a desired level of light generation. In one illustrative example, an optical waveguide structure comprises a nonlinear optical waveguide with a central region, a first side region, and a second side region located within the nonlinear optical waveguide. The central region comprises a nonlinear optical material. The first side region is located on a first side of the central region. The second side region is located on a second side of the central region. The central region has a first nonlinear coefficient that is larger than a second nonlinear coefficient of the first side region and the second side region.

With reference now to the figures and, in particular, with reference toFIG.1, an illustration of a block diagram of an optical waveguide structure is depicted in accordance with an illustrative embodiment. In this illustrative example, optical waveguide structure100comprises nonlinear optical waveguide102that comprises nonlinear optical material104.

In this illustrative example, a number of nonlinear optical processes106can occur within nonlinear optical waveguide102. As used herein, a “number of,” when used with reference, to items means one or more items. For example, a “number of nonlinear optical processes106” is one or more of nonlinear optical processes106. Different nonlinear optical processes in nonlinear optical processes106can occur in different locations or regions within nonlinear optical waveguide102.

The nonlinear optical processes106can be three-wave mixing and four-wave mixing processes that generate light. For example, nonlinear optical process106can include at least one of spontaneous parametric down conversion (SPDC) and spontaneous four-wave mixing (SFWM). These nonlinear optical processes can generate light. Nonlinear optical process106also can include second harmonic generation, third harmonic generation, sum frequency generation and difference frequency generation. For example, pump light108can be input into nonlinear optical waveguide102. Nonlinear optical processes106can generate at least one of signal light110or idler light112in response to pump light108propagating through nonlinear optical material104in nonlinear optical waveguide102.

In this illustrative example, pump light108, signal light110, and idler light112are lights of different wavelengths. In this illustrative example, pump light108can have a wavelength that is shorter than the wavelength of signal light110and idler light112.

In this illustrative example, the structure of nonlinear optical waveguide102can be configured to increase light generation by nonlinear optical processes106. As depicted, nonlinear optical waveguide102comprises central region114, first side region116, and second side region118.

In this example, first side region116is on first side120of central region114. Second side region118is on second side122of central region114. In this illustrative example, first side120is opposite of second side122. In other words, first side region116and second side region118are on opposite sides of central region114.

As depicted, central region114comprises nonlinear optical material104. For example, central region114can be comprised of at least one of lithium niobate (LiNbO3), silicon carbide, aluminum nitride, gallium nitride, gallium aluminum nitride, gallium phosphide, gallium aluminum phosphide, aluminum phosphide, gallium arsenide, gallium aluminum arsenide, aluminum arsenide, or some other suitable material.

First side region116, and second side region118comprise second material119. In this illustrative example, first side region116and second side region118can be comprised of second material119whose second-order nonlinear coefficient is smaller as compared to the second-order nonlinear coefficient of the nonlinear optical material104in central region114such that the nonlinear optical process is weaker and generates less light or does not generate light. In other words, nonlinear optical process in first side region116and second side region118does not generates less light or no light because the nonlinear optical process is weaker. For example, second material119in first side region116and second side region118can be selected from at least one of silicon nitride, titanium dioxide silicon, silicon oxynitride, hafnia, or other suitable materials.

Nonlinear optical material104in central region114and second material119in first side region116and second side region118can generate light through other processes, such as direct emission of light.

In this example, nonlinear optical material104comprising the central region has first nonlinear coefficient124that is larger than second nonlinear coefficient126of second material119comprising first side region116and the second side region118. In this illustrative example, second nonlinear coefficient126can be selected such that a nonlinear optical interaction is reduced to about zero in first side region116and second side region118. In other words, second nonlinear coefficient126can be selected such that first side region116and second side region118have a reduced contribution to light generation128.

For example, nonlinear optical material104can be a first nonlinear optical material that has first nonlinear coefficient124in the form of a first second-order nonlinear coefficient with a magnitude that is at least one picometer/volt. First side region116and second side region118can be a second nonlinear optical material that has second nonlinear coefficient126in the form of a second second-order nonlinear coefficient whose magnitude is equal to or less than one third the magnitude of the first second-order nonlinear coefficient for the first nonlinear optical material.

In this illustrative example, this configuration of regions extends through some or all of nonlinear optical waveguide102. This configuration of central region114, first side region116, and second side region118can provide a desired level of light generation128within nonlinear optical waveguide102.

As depicted, central region114has a set of dimensions130selected to increase light generation128in optical waveguide structure100. In this example, light generation128is increased in nonlinear optical waveguide102in optical waveguide structure100. In one illustrative example, the set of dimensions130can be selected from at least one of width132, height134, sidewall slope135, or some other dimension.

For example, width132can be for central region114. As another illustrative example, width132can be for first side region116, central region114, and second side region118. As yet another illustrative example, height134can be for central region114. In still another illustrative example, height134can be for first side region116, central region114, and second side region118. In another illustrative example, at least one of first side120or second side122for central region114can have a sidewall slope135, which can be defined as an angle.

As depicted, the set of dimensions130can be for the cross-section geometry131of nonlinear optical waveguide102. Cross-sectional geometry131includes a set of dimensions130that describe a set of cross-sections133in nonlinear optical waveguide102.

As used herein, a “set of,” when used with reference to items, means one or more items. For example, a “set of dimensions130” is one or more of dimensions130.

The set of dimensions130can be selected such that light generation128increases for at least one of a signal light110or idler light112when pump light108travels through nonlinear optical waveguide102. For example, in the set of dimensions130, width132can be selected to increase an overlap of an electromagnetic field for a light of interest with the central region such that light generation128is increased in nonlinear optical waveguide102. The light of interest can be pump light108, signal light110or idler light112.

For example, width132can selected to increase an overlap of the electromagnetic field that has a first sign for the light of interest within central region114and the electromagnetic field has a second sign for the light of interest in first side region116and second side region118such that light generation128is increased within nonlinear optical waveguide102. The light of interest can be at least one of pump light108, signal light110, or idler light112.

In this illustrative example, electric field amplitude of a first light traveling in nonlinear optical waveguide102has first sign136in nonlinear optical waveguide102in central region114while having second sign138in first side region116and second side region118. In other words, the sign is of the electric field amplitude of the light traveling through the different regions in nonlinear optical waveguide102.

In this illustrative example, the first light is the light that has the shortest wavelength of the lights of different wavelengths traveling through nonlinear optical waveguide102. For spontaneous parametric down conversion (SPDC), the first light is pump light108. For second harmonic generation, the first light can be the generated light such as signal light110and idler light112, which are both the second harmonic light. For spontaneous four-wave mixing (SFWM), the first light can be signal light110.

When first sign136is positive, second sign138is negative. When first sign136is negative, second sign138is positive. In this illustrative example, these signs are for the amplitude of the electric field. Nonlinear optical waveguide can be designed to reduce or avoid the amplitude of electric field of first light having both the first sign and the second sign in central region114.

In the illustrative example, the sign of the electric field component of first light in the central region114versus the sign the electric field component of first light in the side regions, first side region116and second side region118, affect light generation128. In other words, these two signs are opposite signs to each other.

By reducing second nonlinear coefficient126in first side region116and second side region118, the contribution to a nonlinear optical process from these side regions do not detract from the contribution to a nonlinear optical process from central region114. As a result, increased efficiency in light generation can occur using nonlinear optical waveguide102with central region114, first side region116, and second side region118.

For example, optical waveguide structure100include other components such as an optical coupler that couples nonlinear optical waveguide102to other optical waveguides. In another illustrative example, other structures can be present in nonlinear optical waveguide102in addition to central region114, first side region116, and second side region118. For example, a substrate in nonlinear optical waveguide102can be present on which these structures are formed.

Detailed embodiments of the claimed structures and methods are disclosed herein; however, it is to be understood that the disclosed embodiments are merely illustrative of the claimed structures and methods that may be embodied in various forms. In addition, each of the examples given in connection with the various embodiments is intended to be illustrative, and not restrictive.

Further, the figures are not necessarily to scale, some features may be exaggerated to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the methods and structures of the present disclosure.

For purposes of the description hereinafter, the terms “upper,” “lower,” “right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” and derivatives thereof shall relate to the embodiments of the disclosure, as it is oriented in the drawing figures. The terms “positioned on” means that a first element, such as a first structure, is present on a second element, such as a second structure, wherein intervening elements, such as an interface structure, such as an interface layer, may be present between the first element and the second element.

In this disclosure, when an element, such as a layer, region, or substrate is referred to as being “on” or “over” another element, the element can be directly on the other element or intervening elements can also be present. In contrast, when an element is referred to as being “directly on”, “directly over”, or “on and in direct contact with” another element, intervening elements are not present, and the element is in contact with the other element.

The processes, steps, and structures described below do not form a complete process flow for manufacturing integrated circuits. The disclosure can be practiced in conjunction with integrated circuit fabrication techniques currently used in the art, and only so much of the commonly practiced process steps are included as necessary for an understanding of the different examples of the present disclosure. The figures represent cross sections of a portion of an integrated circuit during fabrication and are not drawn to scale, but instead are drawn so as to illustrate different illustrative features of the disclosure.

Turning next toFIG.2, an illustration of a block diagram of a configuration for an optical waveguide structure is depicted in accordance with an illustrative embodiment. In the illustrative examples, the same reference numeral may be used in more than one figure. This reuse of a reference numeral in different figures represents the same element in the different figures.

As depicted in this example, nonlinear optical waveguide102comprises core region200and cladding region201. In this example, cladding region201is comprised of a dielectric material and core region200is located within cladding region201. The dielectric material can be selected to have a smaller refractive index relative to the refractive index of core region200. The dielectric material of cladding region201can be selected from at least one of a silicon dioxide, a polymer, air, or other suitable material.

As depicted, cladding region201can be comprised of lower cladding region204, and upper cladding region202. As depicted, core region200is located between lower cladding region204and upper cladding region202. In this depicted example, the terms “upper” and “lower” are used to indicate relative locations of components with respect to each other. In this example, “upper” and “lower” can be relative locations on a structure in a vertical position. In a cross-sectional configuration, “upper” and “lower” are relative vertical positions. Left side and right side are relative horizontal positions.

Core region200can comprise a single spatially-uniform material and have a single value of its refractive index for a given wavelength of light. In this example, core region200also can comprise a spatially non-uniform material that is better described by a “net refractive index” whose value can be determined by the spatially varied refractive index distribution of that material.

A number of different components can form core region200. In this illustrative example, central region114, first side region116, and second side region118are components that form core region200.

In this illustrative example, core region200has core region refractive index206, and upper cladding region202has upper cladding refractive index208that is lower than core region refractive index206. As depicted, lower cladding region404has lower cladding refractive index210that is lower than core region refractive index206.

In another illustrative example, upper cladding region202has height212that can be selected to compensate for a variation of the phase walk-off in the nonlinear optical waveguide. In this illustrative example, upper cladding region202can have height212selected to compensate for a variation in a set of dimensions214in core region200which can be one cause in the variation of the phase walk-off in the nonlinear optical waveguide.

For example, height212for upper cladding region202can be adjusted during fabrication to compensate for a variation in the set of dimensions214for core region200from an as-designed value for the set of dimensions214. In this illustrative example, the set of dimensions214can be, for example, a width or a height of core region200, the width or the height of central region114, or the width or the height of first side region116or second side region118. As depicted, height212of upper cladding region202can be sufficiently small that adjustments of height212can affect the effective refractive indices of the nonlinear waveguide modes.

In this illustrative example, lower cladding region204can be located on substrate216. Substrate216can be comprised of various materials depending on the implementation. For example, substrate216can comprise a set of materials selected from at least one of lithium niobate, silicon carbide, sapphire, quartz, alumina, silicon, germanium, or other suitable types of materials. Substrate216can be located on a wafer that is processed using fabrication equipment for semiconductor processing.

The illustration of structures for nonlinear optical waveguide102is provided to illustrate one manner in which nonlinear optical waveguide102can be implemented. This illustration is not meant to limit the manner in which nonlinear optical waveguide102can be configured in other illustrative examples. For example, cladding region201may be a single component rather than having upper cladding region202and lower cladding region204. Additionally, core region200is shown as a component located between upper cladding region202and lower cladding region204. In other illustrative examples, core region200can be located within upper cladding region202, lower cladding region204, or both of these regions in cladding region201.

In the illustrative example, a set of phase shifters240can be present in optical waveguide structure100and used with nonlinear optical waveguide102. The set of phase shifters240can be, for example, a set of electrodes242. The set of electrodes242can be used to affect the manner in which light propagates through the nonlinear optical waveguide102. For example, the set of electrodes242can be used to change the phase of a light of a particular wavelength propagating through nonlinear optical waveguide102or other types of optical waveguides.

Although in this illustrative example, the set of phase shifters240has been described as a set of electrodes242, other types of phase shifters may be used in addition to or in place of the set of electrodes242in other illustrative examples. For example, the set of phase shifters240can be a set of elements that is selected from at least one of a thermal element, shape memory alloy element, piezo electric element, or some other element that can emit energy to change the phase of a light of a particular wavelength propagating through nonlinear optical waveguide102. The elements can also have different shapes and configurations selected to provide a desired change the phase of a light of a particular wavelength propagating through nonlinear optical waveguide102or other types of optical waveguides.

The set of electrodes242or other elements can apply a set of activations244that can take a number of different forms. For example, the set of activations can be selected from at least one of a voltage, a current, a thermal energy, an electrically induced strain, or some other type of energy that can be applied to an optical waveguide to affect the manner in which light propagates through nonlinear optical waveguide102. In particular, the energy can be used to affect the phase of a light of the particular wavelength propagating through nonlinear optical waveguide102.

Further, core region200can be first core region249, and second core region250can be present within optical waveguide structure100. In this illustrative example, second core region250can have different configurations.

For example, second core region250can have the same configuration as core region200. In another example, second core region250may only have a central region that may be a nonlinear optical material or may not be a nonlinear optical material.

With reference now toFIG.3, an illustration of a cross-sectional view of a nonlinear optical waveguide in an optical waveguide structure is depicted in accordance with an illustrative embodiment. Nonlinear optical waveguide300is an example of an implementation for nonlinear optical waveguide102shown in block form inFIG.1and inFIG.2.

In this illustrative example, nonlinear optical waveguide300has core region302. In this illustrative example, core region302comprises a nonlinear optical material, such as x-cut lithium niobate (LiNbO3). As depicted, nonlinear optical waveguide300also has cladding regions.

Nonlinear optical waveguide300has lower cladding region306and upper cladding region308. In this depicted example, the cladding regions can comprise at least one of silicon dioxide, air, or other suitable materials.

In this example, lower cladding region306is comprised of silicon oxide (SiO2). As depicted, a first portion of upper cladding region308is comprised of silicon dioxide303and a second portion of upper cladding region308is comprised of air305. As depicted, silicon dioxide in upper cladding region308has upper cladding region height307.

Although upper cladding region308is depicted as being silicon dioxide303and air305, upper cladding region308can take other forms in other illustrative examples. For example, upper cladding region308can be comprised of just silicon dioxide or air instead of an air and silicon dioxide combination.

Further, as depicted in this cross-sectional view, nonlinear optical waveguide300has side regions on either side of central region304that form core region302. As depicted, these two side regions are located laterally adjacent to central region304. In this illustrative example, the side regions comprise first side region310and second side region312, which are comprised of silicon nitride (Si3N4).

As depicted, nonlinear optical waveguide300has strip width314. In this cross-sectional view of nonlinear optical waveguide300, the cross-section of central region304, first side region310, and second side region312has strip width314that is selected to cause a phase matching condition.

Additionally, central region304in nonlinear optical waveguide300has center region top width316. As depicted, center region top width316can be selected to increase an overlap of an electromagnetic field for a light of interest with central region304such that light generation is increased in nonlinear optical waveguide300. As another illustrative example, sidewall320and sidewall322for central region304can have a side slope defined by angle326and angle328.

In this illustrative example, silicon nitride can be a suitable material for first side region310and second side region312because silicon nitride has a minimal second-order optical nonlinearity and the refractive index of silicon nitride is slightly smaller than the refractive index of lithium niobate, the nonlinear optical material used in central region304. In this depicted example, the refractive index of silicon nitride can be less than 10% smaller than the refractive index of lithium niobate.

As depicted, nonlinear optical waveguide300can be especially suitable for modal phase matching in which the shortest wavelength of the light involved in the nonlinear optical process is in the TExy=TE31mode (or in the TMxy=TM31mode). For this nomenclature, the x-axis of the cross-section is in the horizontal direction and the y-axis of the cross-section is in the vertical direction. These axes are reference directions in a cross-sectional depiction and are not necessarily the same as the X, Y, and Z axes of a lithium niobate crystal. For a spontaneous parametric down conversion nonlinear optical process, a pump light has the shortest wavelength (highest energy) and is in the TE31mode.

The illustration of nonlinear optical waveguide300is provided as an example of one implementation for nonlinear optical waveguide102shown in block form inFIG.1andFIG.2. This illustration is not meant to limit the manner in which nonlinear optical waveguide300can be implemented in other illustrative examples. For example, a layer of a material comprising first side region310, second side region312, or some other material can be located over at least one of central region304, first side region310, or second side region312.

With reference now toFIG.4, an illustration of field profiles in a nonlinear optical waveguide is depicted in accordance with an illustrative embodiment. As depicted, field profiles400are for light in a nonlinear optical waveguide, such as nonlinear optical waveguide300inFIG.3. In this illustrative example, the pump light is in the TE31mode and the signal light and the idler light are in the TE11(or fundamental) mode.

As depicted in field profile402, the TE31pump mode in a cross-section of nonlinear optical waveguide102has 3 lobes, center lobe404, side lobe406, and side lobe408. The magnitude of the electric field amplitude is largest near the central portions of these lobes as seen in field profile402. For a higher-order mode of the waveguided light, such as the TE31pump mode, the amplitude of the electric field can have a positive value or a negative value, as seen in field profile402.

Also, the electric field amplitude distribution can have a large magnitude (having a value close to +1 or −1) or can have a small magnitude (having a value close to 0). The portions of the electric field amplitude distribution having a large magnitude can be called the lobes of the electric field distribution.

As depicted, field profile402is for an optical field within core region302, which is formed by central region304, first side region310, and second side region312inFIG.3. In this illustrative example, central region304is shown by outline401, first side region310is shown by outline403, and second side region312is shown by outline405.

In this depicted example profile, the center lobe404overlaps the nonlinear optical material in central region304in nonlinear optical waveguide300in which central region304is shown by outline401. Side lobe406overlaps first side region310as shown by outline403for first side region310. As depicted, lobe416overlaps second side region312as shown by outline405for second side region312.

In this illustrative example, center lobe404has an amplitude with a sign that is positive. In contrast, side lobe406and side lobe408, have amplitudes of the opposite sign, in which the signs are negative.

Electric field profile410for the signal light has lobe412, and electric field profile414for the idler light has lobe416. The electric field profiles or spatial distributions illustrate the waveguide modes for the signal and idler light in a given cross-section for nonlinear optical waveguide300. Field profile410and field profile414each have one peak, or lobe, for the electric field amplitudes. As depicted in field profile410and field profile414, peak amplitudes of signal and idler electric fields have a positive sign.

As depicted, field profile410is shown for a signal light optical field within core region302as shown by outline420. In this illustrative example, field profile414is shown for a signal light optical field within core region302as shown by outline422.

For purposes of illustration, the entire waveguide cross-section can be assumed to be comprised of a nonlinear optical material. For example, first side region310, second side region312, and central region304can all comprised of a nonlinear optical material. For example, nonlinear optical material can have dNL<0, i.e. dNLis a negative value.

In the illustrative example, equation (2) below can be considered for the spatial combination of the three electric field peaks in the pump mode shown in field profile402. These three electric field peaks are center lobe404, side lobe406, and side lobe408in field profile402for the pump light. The rate of generation of signal light contributed by the center lobe is positive using equation (2) below. Because the signal and idler modes have electric fields amplitude that peak in the center of nonlinear optical waveguide in this example, the central region will have the greatest contribution to the rate of signal generation.

Considering now the contributions to equation (2) below from the two side peaks of the pump mode, the rate of generation of signal light is negative in this example. The electric field amplitude of the pump mode has one sign in center lobe404, and opposite signs on side lobe406and side lobe408. In this illustrative example, the amplitude of the idler field has the same sign across all of nonlinear optical waveguide300. As a result, the contribution to the generation of a signal light and an idler light has one sign in the center of nonlinear optical waveguide300in central region304, and an opposite sign for the sides of nonlinear optical waveguide300in first side region310and second side region312.

Because the electric field amplitude of the pump mode has one sign in the center lobe, and opposite signs in the side lobes, but the amplitude of the lobe(s) of the electric field amplitude of the idler mode has the same sign across the entire structure, the contribution to the rate of generation of signal light will have one sign for the center of the structure, and the opposite sign for the sides of the structure. In the illustrative example, difference in the sign of the electric field amplitude in different regions of the nonlinear optical waveguide300results in the difference in the sign of the contribution those regions make to the rate of generation of signal light.

Thus, the light generation contributed by the side regions, first side region310and second side region312, versus central region304is a competitive process. Because the amplitudes of idler electric fields (and also of signal electric fields for the case of spontaneous parametric down conversion (SPDC)) are relatively weak in first side region310and second side region312, the magnitude of the contribution to light generation by these side regions is smaller than the magnitude of the contribution to light generation by central region304.

Next, when first side region310and second side region312are comprised of a material that has little-to-no nonlinearity in the depicted examples the rate of light generation of a signal light and an idler light contributed by the side regions is effectively zero, according to equation (2) below. In this illustrative example, deffNL≈0deffNL≈0 in the two side regions.

Thus, the rate of light generation of the signal light (and also of the idler light in the case of spontaneous parametric down conversion (SPDC)) in nonlinear optical waveguide300can be dominated by the rate of light generation of the signal light (and also of idler light in the case of spontaneous parametric down conversion (SPDC)) in central region304of nonlinear optical waveguide300. In this example, center lobe404of the pump light mode in field profile402most strongly overlaps with the idler modes in field profile414(and for the case of spontaneous parametric down conversion (SPDC), also with the signal modes in field profile410).

In this illustrative example, the side lobes in field profile402for the pump mode do not detract from the rate of light generation of signal light, and idler light, or both in nonlinear optical waveguide300because these side lobes, side lobe406and side lobe408, do not significantly overlap a material with a large nonlinear coefficient. Thus, the competition between contributions from different spatial regions to the nonlinear optical process can be significantly reduced, if not entirely eliminated.

In this example, using all 3 lobes of the pump mode shown in field profile402for the nonlinear process results in a cancellation of the contributions from different spatial regions to nonlinear optical processes. This cancellation can occur because of the differing signs of electric field amplitude in the differing pump mode lobes such as side lobe406and side lobe408versus center lobe404.

With nonlinear optical waveguide300, the side lobes of the pump mode in field profile402are located in a material that has low nonlinearity relative to the nonlinearity of central region304. As a result, the contribution of central region304in nonlinear optical waveguide300with high nonlinearity level is not cancelled by the contribution from the side lobes of the pump mode in field profile402, which would otherwise subtract from the contribution of central region304to the nonlinear optical process. The first nonlinear optical coefficient in central region304and second nonlinear optical coefficient in first side region310and second side region312can be selected to have relative values to provide a desired level of light generation or light generation rate in nonlinear optical waveguide300.

Turning next toFIG.5, an illustration of field profiles in central region of a nonlinear optical waveguide is depicted in accordance with an illustrative embodiment. As depicted, field profiles500are for a central region such as central region304in nonlinear optical waveguide300inFIG.3.

As depicted, field profile502is for a pump light optical field, field profile504is for a signal light optical field, field profile506is for an idler light optical field. In the illustrative example, these field profiles are for central region304as indicated outline508in field profiles500. The fields illustrative within outline508in the different field profiles are the portions of the optical fields that are involved in a nonlinear optical process that generates light in nonlinear optical waveguide300.

In nonlinear optical waveguide300inFIG.3, the rate of generation of signal light from pump light and idler light in an exemplary second-order nonlinear optical process of difference frequency generation can be described by the coupled-wave equation, given below for signal light:

dAsdz=deff⁢Ap⁢Ai*⁢i⁢⁢2⁢πns⁢λs⁢ei⁢⁢Δ⁢⁢kz(1)
where Asis the electric field amplitude of signal light110, Apis the electric field amplitude of pump light108, A*iis the complex conjugate of electric field amplitude of idler light112, deffis the effective nonlinear optical coefficient, λsis the vacuum wavelength of the signal light, nsis the effective refractive index of the signal light propagating in nonlinear optical waveguide300, Δk is the wavevector mismatch, z is the distance propagated by the optical fields, and i is imaginary unit (i2=−1).

In this example, nsis the effective refractive index for the signal light. The “effective” nonlinear optical coefficient deffis described by the values for first nonlinear coefficient in central region304and second nonlinear coefficient in first side region310and second side region312, as well as by the spatial distributions of the optical fields. In the illustrative example, “optical field” is the propagating electromagnetic field of the light.

In the depicted example, the dimensions describing the cross-section geometry for nonlinear optical waveguide300can be selected to meet a particular phase-matching condition, or value for

Δ⁢⁢k=2⁢π⁡(npλp-niλi-nsλs),
which depends on the particular implementation. The first three factors as well as the wave-vector mismatch in the exponential on the right-hand-side of equation (1) are terms of interest in light generation for nonlinear optical waveguide300. For any point along the longitudinal dimension z of the waveguide, the generation of the signal light will depend on the transverse or spatial variation of the nonlinear optical coefficient in the waveguide's cross-sectional structure and on the spatial variation of the electric fields for the pump light and the idler light. These spatial variations are described in the spatially integrated value for deff,

dAsdz∝deff=∫∫dNL⁢up⁢ui⁢dxdy(2)
In equation (2), dNLis the nonlinear optical coefficient of the material, and can have a different value different for different spatial regions of the waveguide; upis the normalized electric field distribution for the pump light and uiis the normalized electric field distribution for the idler light. The integration can be performed over the transverse or cross-sectional dimensions.

The electric field distributions shown inFIG.5are only those portions for which the waveguide material has a value for dNLthat is non zero. Only these portions of the electric field distributions contribute to the result of the integration done to obtain the value for deffas describe by equation (2).

Turning now toFIG.6, an illustration of a graph of an optical field overlap factor for different configurations of nonlinear optical waveguides is depicted in accordance with an illustrative embodiment. In this illustrative example, graph600illustrates an optical field overlap factor as a function of strip width. In this illustrative example, graph600, represents optical field overlap factors generated after performing the integration in equation (2) with a normalized value of 0 or 1 for the material nonlinear optical coefficient dNL. The normalized value is one when the optical field is within outline401or outline508and is 0 when the optical field is outside of this outline401or outline508as depicted inFIG.4andFIG.5.

In this example, y-axis602represents the optical field overlap factor, and x-axis604represents strip width in micrometers. The lines in graph600illustrate values of the optical field overlap factor obtained for various configurations of nonlinear optical waveguides.

The lines in section606are obtained using a material with a low value or normalized to 0 for material nonlinear optical coefficient dNL.

As depicted, the lines in section606depict optical field overlap factors for nonlinear optical waveguides that have a spatially uniform lithium niobate core region, whose normalized nonlinear optical coefficient has a value of 1. In section606, line652is for a waveguide with a spatially uniform lithium niobate core region and an upper cladding height of 0.50 μm, and line654is for a waveguide with a spatially uniform lithium niobate core region and an upper cladding height of 0.45 μm. In this example, the lines in section606result from a nonlinear optical waveguide whose core region comprises spatially uniform lithium niobate and does not have any side regions.

In this illustrative example, the lines in section608illustrate optical field overlap factors for nonlinear optical waveguides whose core region comprises a central region and two side regions. The lines in section608are obtained when the central region has a normalized nonlinear optical coefficient dhLequal to 1 and the two side regions have a normalized nonlinear optical coefficient dNLequal to 0.

Examples of these types of waveguides include nonlinear optical waveguide102inFIG.1, nonlinear optical waveguide300inFIG.3, nonlinear optical waveguide702inFIG.7, nonlinear optical waveguide902inFIG.9, and nonlinear optical waveguide1002inFIG.10. These nonlinear optical waveguides can have a lithium niobate center region and silicon nitride side regions.

In section608, line656is for a nonlinear optical waveguide with a center region width of 0.3 μm and an upper cladding height of 0.46 μm; and line658is for a nonlinear optical waveguide with a lithium niobate center region and silicon nitride side regions having a center region width of 0.3 μm and an upper cladding height of 0.47 μm.

In the illustrative examples, the generation of light in the nonlinear optical waveguides depends on the square of the optical field overlap factor. As a result, increasing the optical field overlap factor results in an increase in the generation of light such as at least one of a signal light or an idler light from a pump light propagating through the nonlinear optical waveguide.

The selection of values for the center width for a central region with side regions as depicted in the illustrative examples can result in an optical field overlap factor that provides greater performance in light generation as compared to current nonlinear optical waveguides as can be seen by the difference in the optical field overlap factor in section608and section606.

Turning now toFIG.7, an illustration of a cross-sectional view of an optical waveguide structure with electrodes is depicted in accordance with an illustrative embodiment. Optical waveguide structure700is an example of an implementation for optical waveguide structure100inFIG.1andFIG.2.

In this illustrative example, optical waveguide structure700comprises nonlinear optical waveguide702, electrode722, and electrode724. Nonlinear optical waveguide702is an example of an implementation for nonlinear optical waveguide102shown in block form inFIG.1and inFIG.2.

In this illustrative example, nonlinear optical waveguide702comprises core region704, upper cladding region706, and lower cladding region708. Lower cladding region708is formed on a silicon substrate710. As depicted, upper cladding region706and lower cladding region708are formed using an oxide (SiO2).

As depicted, core region704comprises central region712, first side region714, and second side region716. In this illustrative example, central region712is comprised of lithium niobate (LiNbO3). First side region714and second side region716are comprised of silicon nitride (Si3N4).

As depicted, core region704has strip width718, and central region712has center width720. Core region704also has strip height719.

These dimensions can be selected to obtain desired propagation of light through nonlinear optical waveguide702. For example, at least one of strip width718or strip height719can be selected to obtain a desired phase matching condition or a desired value for the wave-vector mismatch Δk. Center width720can be selected to increase an overlap of a first portion of an electromagnetic field having a first sign for a light of interest within central region712and such that a second portion of an electromagnetic field having the second sign is located in first side region714, and second side region716such that light generation is increased in nonlinear optical waveguide702.

In this illustrative example, optical waveguide structure700also includes electrode722and electrode724. As depicted, electrode722and electrode724form an optical waveguide structure that can function as an optical phase shifter that can shift the phases of the electromagnetic fields of light traveling through nonlinear optical waveguide702. The fields can be, for example, transverse electric (TE) fields or transverse magnetic (TM) fields. In other illustrative examples, a single electrode can be located in proximity to the waveguide core region. In yet other illustrative examples, a third electrode can be placed over core region704and upper cladding region706. In yet another illustrative example, electrode722or electrode724can be fabricated to extend over core region704.

Turning now toFIG.8, an illustration of a cross-sectional view of an optical waveguide structure is depicted in accordance with an illustrative embodiment. Optical waveguide structure800is an example of an implementation for optical waveguide structure100inFIG.1.

In this illustrative example, optical waveguide structure800comprises nonlinear optical waveguide802, electrode822, electrode824, and electrode825. Nonlinear optical waveguide802is an example of an implementation for nonlinear optical waveguide102shown in block form inFIG.1and inFIG.2.

In this illustrative example, nonlinear optical waveguide802comprises core region804, upper cladding region806, and lower cladding region808. Lower cladding region808is formed on silicon substrate810. As depicted, upper cladding region806and lower cladding region808are formed using an oxide (SiO2).

As depicted, core region804comprises central region812, first side region814, and second side region816. In this illustrative example, central region812is comprised of lithium niobate (LiNbO3). First side region814and second side region816are comprised of silicon nitride (Si3N4).

As depicted, core region804has strip width818and strip height819. In this example, central region812has center width820. These two dimensions can be selected to obtain desired propagation of light through nonlinear optical waveguide702. For example, at least one of strip width818or strip height819can be selected to obtain a desired phase matching condition. Center width820can be selected to increase an overlap of an electromagnetic field having a first sign for a light of interest within central region812while the electromagnetic signal has a second side in first side region814and second side region816such that light generation is increased in nonlinear optical waveguide702.

In this illustrative example, optical waveguide structure800also includes electrode822and electrode824. As depicted, electrode822, electrode724, and electrode825enable optical waveguide structure800to function as a phase shifter that can shift phases of the electromagnetic fields in light traveling through nonlinear optical waveguide802. The fields can be, for example, transverse electric (TE) fields or transverse magnetic (TM) fields. In other illustrative examples, a single electrode can be used.

InFIG.9, another illustration of a cross-sectional view of an optical waveguide structure with two core regions is depicted in accordance with an illustrative embodiment. Optical waveguide structure900is an example of an implementation for optical waveguide structure100inFIG.1andFIG.2. Optical waveguide structure900can function as optical coupler and can be a wavelength selective coupler.

In this illustrative example, optical waveguide structure900comprises nonlinear optical waveguide902and nonlinear optical waveguide904. Nonlinear optical waveguide902and nonlinear optical waveguide904are an example of an implementation for nonlinear optical waveguide102shown in block form inFIG.1and inFIG.2.

As depicted, optical waveguide structure900comprises nonlinear optical waveguide902and nonlinear optical waveguide904. In this illustrative example, nonlinear optical waveguide902and nonlinear optical waveguide904have upper cladding region908and lower cladding region910. Lower cladding region910is formed on silicon substrate912. Upper cladding region908and lower cladding region910are comprised of an oxide (SiO2).

In this illustrative example, nonlinear optical waveguide structure900has first core region914and second core region926that are separated from each other by gap906. This first core region914comprises central region916, first side region918, and second side region920. As depicted, central region916is comprised of lithium niobate (LiNbO3). First side region918and second side region920are comprised of silicon nitride (Si3N4).

As depicted, first core region914has strip width922. Central region916has center width924. These two dimensions can be selected to obtain desired propagation of light through nonlinear optical waveguide902and the coupling of light between first core region914and second core region926.

As depicted, nonlinear optical waveguide904has second core region926. In this example, second core region926comprises central region928and does not include side regions as compared to first core region914in nonlinear optical waveguide902. Central region928is comprised of lithium niobate (LiNbO3) in this depicted example.

Central region928has strip width930. This width can be selected to adjust optical properties in the propagation of light through optical waveguide structure900and the coupling of light between the two core regions914and926.

As depicted, first core region914has strip height932and second core region926has strip height934. These heights can also be adjusted to obtain desired optical transmission properties. Adjusting the strip height and the strip width can change the effective refractive index for the pump light (np), signal light (ns), and idler light (ni). These changes can affect the coupling of light between the core regions. These changes can also affect the phase shift contributed by the optical coupler to the phase match. For separate waveguides, these changes also affect the wave-vector mismatch and the phase matching, which in turn affects the efficiency of the nonlinear optical generation process.

Turning toFIG.10, yet another illustration of a cross-sectional view of an optical waveguide structure with two core regions is depicted in accordance with an illustrative embodiment. Optical waveguide structure1000is an example of an implementation for optical waveguide structure100inFIG.1andFIG.2. Optical waveguide structure1000can function as an optical coupler.

In this illustrative example, optical waveguide structure1000comprises nonlinear optical waveguide1002and optical waveguide1004. Nonlinear optical waveguide1002is an example of an implementation for nonlinear optical waveguide102shown in block form inFIG.1and inFIG.2. Optical waveguide structure1000is similar to optical waveguide structure900inFIG.9except that optical waveguide1004is present in place of nonlinear optical waveguide904inFIG.9.

In this illustrative example, nonlinear optical waveguide1002and optical waveguide1004have upper cladding region1008and lower cladding region1010. Lower cladding region1010is formed on silicon substrate1012. Upper cladding region1008and lower cladding region1010are comprised of an oxide (SiO2).

As depicted, optical waveguide structure1000comprises first core region1014and second core region1026that are separated from each other by gap1006. In this illustrative example, nonlinear optical waveguide1002has first core region1014. This first core region comprises central region1016, first side region1018, and second side region1020. As depicted, central region1016is comprised of lithium niobate (LiNbO3). First side region1018and second side region1020are comprised of comprised of silicon nitride (Si3N4).

As depicted, first core region1014has strip width1022. Central region1016has center width1024. These two dimensions can be selected to obtain desired propagation of light through nonlinear optical waveguide1002and the coupling of light between first core region1014and second core region1026.

As depicted, optical waveguide1004has second core region1026. In this example, second core region1026comprises central region1028. In this particular example, central region1028is not comprised of nonlinear optical material. As depicted, central region1028is comprised of silicon nitride (Si3N4).

Central region1028has strip width1030. This width can be selected to adjust optical properties in the propagation of light through optical waveguide1004and the coupling of light between first core region1014and second core region1026.

As depicted, first core region1014has strip height1032and second core region1026has strip height1034. These heights can also be adjusted to obtain desired optical transmission properties.

With reference toFIG.11, another illustration of a cross-sectional view of an optical waveguide structure with merged core regions that form a multimode interference coupler is depicted in accordance with an illustrative embodiment. Optical waveguide structure1100is an example of optical waveguide device that can be used in optical waveguide structure100inFIG.1andFIG.2. Optical waveguide structure1100can function as an optical coupler.

In this illustrative example, optical waveguide structure1100comprises a multimode interference coupler core1105that can be used in optical waveguide structure100shown in block form inFIG.1andFIG.2to couple nonlinear optical waveguide102to another optical waveguide that can be used in optical waveguide structure100.

As depicted, nonlinear optical waveguide structure1100has upper cladding region1108and lower cladding region1110. Lower cladding region1110is formed on silicon substrate1112. Upper cladding region1108and lower cladding region1110are comprised of an oxide (SiO2).

In this illustrative example, multimode interference coupler in optical waveguide1100has first core region1114that is an example of core region200inFIG.2. This core region comprises central region1116, first side region1118, and second side region1120. As depicted, central region1116is comprised of lithium niobate (LiNbO3). First side region1118and second side region1120are comprised of silicon nitride (Si3N4). As depicted, central region1116in first core region1114has center width1124.

As depicted, multimode interference coupler core1105in optical waveguide structure1100also has second core region1126with central region1128. In this example, central region1128in second core region1126has width1130and is comprised of lithium niobate (LiNbO3) in this depicted example. This width can be selected to adjust optical properties in the propagation of light through optical waveguide structure1100.

As depicted, first core region1114and second core region1128has strip height1134. This height can also be adjusted to obtain desired optical transmission properties.

InFIG.12, yet another illustration of a cross-sectional view of an optical waveguide structure with merged core regions that form a multimode interference coupler is depicted in accordance with an illustrative embodiment. Optical waveguide structure1200is an example of an optical waveguide component that can be used in optical waveguide structure100inFIG.1andFIG.2. Optical waveguide structure1200can function as an optical coupler.

In this illustrative example, optical waveguide structure1200comprises nonlinear optical waveguide1202that is an example of an implementation for nonlinear optical waveguide102shown in block form inFIG.1and inFIG.2. Optical waveguide structure1200is similar to optical waveguide structure1100inFIG.11.

In this illustrative example, has upper cladding region1208and lower cladding region1210. Lower cladding region1210is formed on silicon substrate1212. Upper cladding region1208and lower cladding region1210are comprised of an oxide (SiO2).

In this illustrative example, nonlinear optical waveguide1202has first core region1214that is an example of core region200inFIG.2. This first core region comprises central region1216, first side region1218, and second side region1220. As depicted, central region1216is comprised of lithium niobate (LiNbO3). First side region1218and second side region1220are comprised of comprised of silicon nitride (Si3N4).

As depicted, central region1216in first core region1214has center width1224. This width can be selected to obtain desired propagation of light through nonlinear optical waveguide1202.

As depicted, multimode interference coupler core1205has second core region1226. In this example, second core region1226is not comprised of nonlinear optical material. As depicted, second core region1226region1228is comprised of silicon nitride (Si3N4).

As depicted, first core region1214and second core region1226have strip height1234. This height can be adjusted to obtain desired optical transmission properties.

Turning now toFIG.13, an illustration of a cross-sectional view of an optical waveguide structure is depicted in accordance with an illustrative embodiment. Optical waveguide structure1300is an example of an implementation for optical waveguide structure100inFIG.1andFIG.2.

In this illustrative example, optical waveguide structure1300comprises nonlinear optical waveguide1302. Nonlinear optical waveguide1302is an example of an implementation for nonlinear optical waveguide102shown in block form inFIG.1and inFIG.2.

In this illustrative example, nonlinear optical waveguide1302comprises core region1304, upper cladding region1306, and lower cladding region1308. Lower cladding region1308is formed on a silicon substrate1310. As depicted, upper cladding region1306is a two-part cladding region comprises air1305and silicon oxide1307. As depicted, lower cladding region1308that is comprised of silicon oxide.

As depicted, core region1304comprises central region1312, first side region1314, second side region1316, and top region1317. In this illustrative example, central region1312is comprised of lithium niobate (LiNbO3). First side region1314, second side region1316, and top region1317are comprised of silicon nitride (Si3N4).

As depicted, first side region1314, second side region1316are on either side of central region1312, and top region1317is located over central region1312. Although first side region1314, second side region1316, and top region1317are described as separate elements, these elements can be a single structure formed at the same time during fabrication of nonlinear optical waveguide1302.

In this illustrative example, top region1317affects the electric field distributions for the pump light, signal light, and idler light. This top region can also affect the values for the effective refractive indices np, nsand niof the pump light, signal light, and idler light. Top region1317, when present in a phase shifter, can improve the efficiency of the phase shifter.

As depicted, core region1304has strip width1318, and central region1312has center width1320. These two dimensions can be selected to obtain a desired propagation of light through nonlinear optical waveguide1302.

As depicted, upper cladding1306has height1319. Height1319is measured based on the height of silicon oxide1307in upper cladding region1306.

The illustrations of the different cross-sections inFIGS.3and7-13are provided as a non-limiting examples of implementations for optical waveguide structure100inFIG.1andFIG.2. These illustrations provide illustrative examples of how different cross-sections can be implemented and are not meant to be limiting as to how other illustrative examples can be included.

For example, in other implementations, the sides of central region304, first side region310and second side region312in core region302of nonlinear optical waveguide300inFIG.3, can have sides that are perpendicular to lower cladding region306instead of angled sides as depicted inFIG.3. Examples of perpendicular sides are shown inFIGS.7-13. The angled sides are not meant to limit the other examples to particular angles. In yet similar illustrative examples, the central region can have perpendicular sides while the side regions have angled sides. In yet other depicted examples, the central region can have a perpendicular side while the side regions have angled sides.

As yet another example, other types of tuning elements may be used in addition to or in place of tuning electrodes that apply a voltage inFIG.7. For example, a tuning element can cause phase shifting of optical signals traveling through an optical waveguide using an activation such as a thermal energy, a strain, or some other type of energy that can be applied to the optical waveguide to affect the manner in which light propagates through the optical waveguide.

With reference now toFIG.14, an illustration of an optical waveguide structure is depicted in accordance with an illustrative embodiment. As depicted, optical waveguide structure1400comprises main nonlinear optical waveguide1402, first extension optical waveguide1404, and second extension optical waveguide1406. In this illustrative example, main nonlinear optical waveguide1402and first extension optical waveguide1404are comprised of nonlinear material.

As depicted, first extension optical waveguide1404can be an idler loop extension optical waveguide, and second extension optical waveguide1406can be a pump loop extension waveguide. Additionally, area1440can be an ending first extension wavelength selective coupler located in an ending first extension location in main nonlinear optical waveguide1402and first extension optical waveguide1404.

In this illustrative example, light can propagate through these optical waveguides. For example, light comprising a pump light, a signal light, and an idler light can propagate through one or more of main nonlinear optical waveguide1402, first extension optical waveguide1404, and second extension optical waveguide1406. In this illustrative example, optical waveguide structure1400incorporates one or more nonlinear optical processes that generate at least one of a signal light or an idler light using a pump light input into optical waveguide structure1400through pump input waveguide1408.

As depicted, optical waveguide structure1400also comprises signal output waveguide1410and idler output waveguide1412. In this illustrative example, pump input waveguide1408operates to input a pump light into second extension optical waveguide1406in optical waveguide structure1400. Signal output waveguide1410operates to output a signal light from main nonlinear optical waveguide1402. Idler output waveguide1412operates to output light from first extension optical waveguide1404.

Additionally, optical waveguide structure1400also includes electrode1414, electrode1416, and electrode1418. As depicted, electrode1414and electrode1416are adjacent to portions of main nonlinear optical waveguide1402. These electrodes can operate to shift the phases of one of optical signals propagating through main nonlinear optical waveguide1402. These optical signals can be, for example, selected from at least one of a pump light, a signal light, or an idler light.

In this illustrative example, electrode1418is located adjacent to a portion of first extension optical waveguide1404. This electrode operates to shift the phase of an idler light propagate through first extension optical waveguide1404.

Optical waveguide structure1400can be implemented using one or more of optical waveguide structures such as the optical waveguide structures depicted in cross-sectional form inFIG.3andFIGS.7-13. For example, area1420containing main nonlinear optical waveguide1402and second extension optical waveguide1406can have a cross-sectional structure as shown for optical waveguide structure1000inFIG.10or for optical waveguide structure1200inFIG.12. As another example, area1422contains main nonlinear optical waveguide1402and first extension optical waveguide1404. This area can have a cross-sectional structure as shown for optical waveguide structure900inFIG.9or for optical waveguide structure1100inFIG.11.

As depicted, area1422can be for a first extension wavelength selective coupler located at a first extension starting location in main nonlinear optical waveguide1402and the first extension optical waveguide1404.

In this depicted example, area1424includes main nonlinear optical waveguide1402and electrode1414. Additionally, area1426includes main nonlinear optical waveguide1402and electrode1416. These two areas can have a cross-sectional structure as shown for optical waveguide structure700inFIG.7in which a single tuning electrode is present. As yet another example, area1428includes main nonlinear optical waveguide1402. Area1428can have a cross-sectional structure as shown for nonlinear optical waveguide300inFIG.3.

As depicted, area1440is an optical coupler for coupling a signal light from main nonlinear optical waveguide1402to signal output waveguide1410. This area can have a cross-sectional structure as shown for optical waveguide structure1000inFIG.10.

In this example, light of different wavelengths can travel in different loops having different lengths within optical waveguide structure1400. For example, first light of a first wavelength can travel within a first loop within main nonlinear optical waveguide1402. The first light can be a signal light in this example. A second light of the second wavelength can travel in a second loop within main nonlinear optical waveguide1402and first extension optical waveguide1404in which the second loop has a second length for the second light of the second wavelength. In this example, the second light can be an idler light. A third light of a third wavelength travels in a third loop within main nonlinear optical waveguide1402and second extension optical waveguide1406in which the third loop has a third length for the third light of the third wavelength. In this example, the third light can be a pump light.

With reference toFIG.15, an illustration of an optical waveguide structure is depicted in accordance with an illustrative embodiment. As depicted, optical waveguide structure1500comprises main nonlinear optical waveguide1502, signal loop extension optical waveguide1504, and idler loop extension optical waveguide1506. In this illustrative example, main nonlinear optical waveguide1502, signal loop extension optical waveguide1504and idler loop extension optical waveguide1506are comprised of nonlinear material.

Light can propagate through the optical waveguides in optical waveguide structure1500. For example, light comprising a pump light, a signal light, and an idler light can propagate through one or more of main nonlinear optical waveguide1502, signal loop extension optical waveguide1504, and idler loop extension optical waveguide1506. In this illustrative example, optical waveguide structure1500incorporates one or more nonlinear optical processes that generate at least one of a signal light or an idler light using a pump light input into optical waveguide structure1500through pump input waveguide1508.

In this illustrative example, optical waveguide structure1500also has signal output waveguide1510and idler output waveguide1512. Pump input waveguide1508operates to input a pump light into main nonlinear optical waveguide1502. As depicted, signal output waveguide1510operates to output a signal light from signal loop extension optical waveguide1504, and idler output waveguide1512operates to output an idler light from idler loop extension optical waveguide1506.

In this illustrative example, optical waveguide structure1500also includes electrode1514, electrode1516, and electrode1518. These electrodes can operate to apply control signals in the form of voltages or currents to adjust the phases of one or more of the different wavelengths of light traveling through optical waveguide structure1500.

Optical waveguide structure1500can be implemented using one or more of the optical waveguide structures such as the optical waveguide structures depicted in cross-sectional form inFIG.3andFIGS.7-13. For example, area1520includes main nonlinear optical waveguide1502. In this example, area1520can have a cross-sectional structure as shown for nonlinear optical waveguide300inFIG.3.

As another example, area1522contains main nonlinear optical waveguide1502and signal loop extension optical waveguide1504. This area can have a cross-sectional structure as shown for optical waveguide structure900inFIG.9or for optical waveguide structure1100inFIG.11and can form a first wavelength selected coupler. Area1524contains main nonlinear optical waveguide1502and idler loop extension optical waveguide1506. As illustrated, area1524can also have a cross-sectional structure as shown for optical waveguide structure900inFIG.9or for optical waveguide structure1100inFIG.11and can form a second wavelength selected coupler.

In this depicted example, area1526includes main nonlinear optical waveguide1502and electrode1516. This area can have a cross-sectional structure as shown for optical waveguide structure700inFIG.7using a single tuning electrode.

As depicted, area1540is an optical coupler for coupling a signal light from main nonlinear optical waveguide1502to pump input waveguide1508. This area can have a cross-sectional structure as shown for optical waveguide structure1000inFIG.10.

With reference now toFIG.16, an illustration of a flowchart of a process for moving light through an optical waveguide structure is depicted in accordance with an illustrative embodiment. The process inFIG.16can be implemented in a physical waveguide structure such as nonlinear optical waveguide102inFIGS.1and2. This process can also be implemented using the different optical waveguides shown inFIG.3andFIGS.7-13in the different physical implementation shown in the different illustrative examples.

The process begins by inputting a light at a pump wavelength into a nonlinear optical waveguide structure having a central region within the nonlinear optical waveguide, wherein the central region comprises a nonlinear optical material, a first side region on a first side of the central region, and a second side region on a second side of the central region, wherein the central region has a first nonlinear coefficient that is larger than a second nonlinear coefficient of the first side region and the second side region (operation1600).

The process propagates the light at the pump wavelength along a path in the optical waveguide structure (operation1602). The process terminates thereafter. In operation1602, light generation occurs in the nonlinear optical waveguide.

Turning now toFIG.17, an illustration of a block diagram of a product management system is depicted in accordance with an illustrative embodiment. Product management system1700is a physical hardware system. In this illustrative example, product management system1700includes at least one of manufacturing system1702or maintenance system1704.

Manufacturing system1702is configured to manufacture products. As depicted, manufacturing system1702includes manufacturing equipment1706. Manufacturing equipment1706includes at least one of fabrication equipment1708or assembly equipment1710.

Fabrication equipment1708is equipment that used to fabricate the nonlinear optical waveguide structure. Multiple copies or multiple versions of nonlinear optical waveguide structures can be fabricated on a substrate wafer. For example, different structures in nonlinear optical waveguides can be fabricated on the same substrate wafer. The substrate wafer can comprise a material such as silicon or lithium niobate or quartz or sapphire or silicon carbide.

Fabrication equipment1708can be used to fabricate a number of different structures. For example, fabrication equipment1708can be used to fabricate at least one of optical waveguide structures, nonlinear optical waveguides, laser transmitters, ultraviolet transmission systems, point-to-point communication devices, laser infrared countermeasure sources, through water optical communication devices, or other suitable devices, antennas, or other suitable types of parts or devices.

Fabrication equipment1708can include machines and tools. With respect to fabricating semiconductor components and optical waveguide components, fabrication equipment1708can comprise at least one of an epitaxial reactor, an oxidation system, a diffusion system, an etching system, a cleaning system, a bonding machine, a dicing machine, a wafer saw, an ion implantation system, a physical vapor deposition system, a chemical vapor deposition system, a photolithography system, an electron-beam lithography system, a plasma etcher, a die attachment machine, a wire bonder, a die overcoat system, molding equipment, a hermetic sealer, an electrical tester, a burn-in oven, a retention bake oven, a UV erase system, or other suitable types of equipment that can be used to manufacture semiconductor structures.

Assembly equipment1710is equipment used to assemble parts to form a product such as a chip, an integrated circuit, a sensor, an optical transmitter, an optical receiver, a computer, an aircraft, or some other product. Assembly equipment1710also can include machines and tools. These machines and tools may be at least one of a robotic arm, a spinner system, a sprayer system, an elevator system, a rail-based system, or a robot.

In this illustrative example, maintenance system1704includes maintenance equipment1712. Maintenance equipment1712can include any equipment needed to perform maintenance on and evaluation of a product. Maintenance equipment1712may include tools for performing different operations on parts on a product. These operations can include at least one of disassembling parts, refurbishing parts, inspecting parts, reworking parts, manufacturing replacement parts, or other operations for performing maintenance on the product. These operations can be for routine maintenance, inspections, upgrades, refurbishment, or other types of maintenance operations.

In the illustrative example, maintenance equipment1712may include optical inspection devices, x-ray imaging systems, surface-profile measurement systems, drills, vacuum leak checkers, and other suitable devices. In some cases, maintenance equipment1712can include fabrication equipment1708, assembly equipment1710, or both to produce and assemble parts that needed for maintenance.

Product management system1700also includes control system1714. Control system1714is a hardware system and may also include software or other types of components. Control system1714is configured to control the operation of at least one of manufacturing system1702or maintenance system1704. In particular, control system1714can control the operation of at least one of fabrication equipment1708, assembly equipment1710, or maintenance equipment1712.

The hardware in control system1714can be implemented using hardware that may include computers, circuits, networks, and other types of equipment. The control may take the form of direct control of manufacturing equipment1706. For example, robots, computer-controlled machines, and other equipment can be controlled by control system1714. In other illustrative examples, control system1714can manage operations performed by human operators1716in manufacturing or performing maintenance on a product. For example, control system1714can assign tasks, provide instructions, display models, or perform other operations to manage operations performed by human operators1716. In these illustrative examples, the different processes for fabricating semiconductor structures, optical structures, nonlinear optical waveguides, laser transmitters, photon generators, photon transmitters, photon detectors, ultraviolet transmission systems, point-to-point communication devices, laser infrared countermeasure sources, through water optical communication devices, or other suitable devices can be manufactured using processes implemented in control system1714.

In the different illustrative examples, human operators1716can operate or interact with at least one of manufacturing equipment1706, maintenance equipment1712, or control system1714. This interaction can occur to manufacture semiconductor structures and other components for products such as semiconductor devices, optical waveguides, or other components for use in products such as aircraft, spacecraft, communications systems, computation systems, and sensor systems.

Further, control system1714can be used to adjust manufacturing of nonlinear optical waveguides, optical waveguides, optical couplers and terminations dynamically during the manufacturing process. For example, many points in the process of fabricating the optical waveguide structure including the nonlinear optical waveguide as well as other components are present at which adjustments can be made to control characteristics of components in an optical waveguide structure.

The dimensions of the fabricated core region can be measured, and optical waveguide design simulations can be performed to determine the values of the effective refractive indices that can be obtained for various candidate values of the upper cladding height. The upper cladding height that gives the desired value for the phase walk-off can be chosen accordingly. Upper cladding material can then be deposited that has the desired thickness or height.

Another point in the fabrication process is after the upper cladding material has been deposited to a value that is greater than what might be desired. Test devices such as asymmetric Mach-Zehnder interferometers and micro-ring resonators can be fabricated in addition to the nonlinear optical waveguide.

These test devices can be characterized to extract values for the effect refractive indices for the upper cladding height of those test devices. The upper cladding height can then be reduced by etching away some of the upper cladding material, possibly in an iterative manner accompanied by additional measurements of the test structures. In this way, the desired value for the upper cladding height can be approached and then achieved.

Thus, the illustrative embodiments provide a method, apparatus, and system for propagating light in an optical waveguide structure. In one illustrative example, an optical waveguide structure comprises a nonlinear optical waveguide, a central region, a first side region, and a second side region. The central region is located within the nonlinear optical waveguide, wherein the central region comprises a nonlinear optical material. The first side region is on a first side of the central region and the second side region is on a second side of the central region. The central region has a first nonlinear coefficient that is larger than a second nonlinear coefficient of the first side region and the second side region.

The configuration of the core region containing the central region and the two side regions can be made in a manner that increases the generation of light by the optical waveguide structure. The different dimensions can be selected to increase the efficiency and light generation in the different illustrative examples.

Thus, illustrative embodiments provide a method, apparatus, system for a cross-section in an optical waveguide has desired characteristics in at least one of light propagation or light generation. In one illustrative example, an optical waveguide structure comprises a nonlinear optical waveguide with a central region, a first side region, and a second side region located within the nonlinear optical waveguide. The central region comprises a nonlinear optical material. The first side region is located on a first side of the central region. The second side region is located on a second side of the central region. The central region has a first nonlinear coefficient that is larger than a second nonlinear coefficient of the first side region and the second side region. The central region, the first side region, and the second side region form a core region within the nonlinear optical waveguide.

In one illustrative example, the different structures in the core region can be designed in a manner that provides at least one of the design propagation or light generation within the nonlinear optical waveguide. The design can include a selection of at least one of a material or a dimension for the different components in the core region. As another example, the dimensions the core region as a whole can be selected. In yet another illustrative example, other structures can be included in the nonlinear optical waveguide such as a cladding, another core region, or other suitable components.

Some features of the illustrative examples are described in the following clauses. These clauses are examples of features not intended to limit other illustrative examples.

An optical waveguide structure comprising:a nonlinear optical waveguide;a central region within the nonlinear optical waveguide, wherein the central region comprises a nonlinear optical material having a first nonlinear coefficient;a first side region on a first side of the central region; anda second side region on a second side of the central region, wherein the nonlinear optical material comprising the central region has the first nonlinear coefficient that is larger than a second nonlinear coefficient of a second material comprising the first side region and the second side region.

The optical waveguide structure according to clause 1, wherein the central region has a set of dimensions selected to increase a light generation within the optical waveguide structure.

The optical waveguide structure according to clause 2, wherein the light generation increases for at least one of a signal light or an idler light when a pump light travels through the nonlinear optical waveguide.

The optical waveguide structure according to one of clause 2 or 3, wherein the set of dimensions is a width selected to increase an overlap of an electromagnetic field for a light of interest with the central region and the electromagnetic field for the light of interest has a second sign in the first side region and the second side region such that light generation is increased in the nonlinear optical waveguide.

The optical waveguide structure according to one of clause 2, 3, or 4, wherein the set of dimensions is selected from least one of a width, a height, or a sidewall slope.

The optical waveguide structure according to one of clause 1, 2, 3, 4, or 5, wherein the second nonlinear coefficient is selected such that the first side region and the second side region have a reduced contribution to light generation.

The optical waveguide structure according to one of clause 1, 2, 3, 4, 5, or 6, wherein the second nonlinear coefficient is selected such that a nonlinear optical interaction in the nonlinear optical waveguide is reduced to about zero.

The optical waveguide structure according to one of clause 1, 2, 3, 4, 5, 6, or 7, wherein a pump light traveling in the optical waveguide structure has an electromagnetic field that has a first sign in the central region while having a second sign in the first side region and the second side region.

The optical waveguide structure according to one of clause 1, 2, 3, 4, 5, 6, 7, or 8, wherein a cross-section of the central region, the first side region, and the second side region has at least one of a strip width or a strip height that is selected to cause a phase matching condition.

The optical waveguide structure according to one of clause 1, 2, 3, 4, 5, 6, 7, 8, or 9, wherein the central region, the first side region and the second side region form a core region, the optical waveguide structure further comprising:a cladding region comprising a dielectric material, wherein the core region is located within the cladding region.

The optical waveguide structure according to clause 10, wherein the dielectric material is selected from at least one of a silicon dioxide, a polymer, or air.

The optical waveguide structure according to one of clause 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11, wherein the nonlinear optical material is a first nonlinear optical material that has a first second order nonlinear coefficient with a magnitude that is at least one picometer/volt, and wherein the first side region and the second side region have a second nonlinear optical material that has a second second-order nonlinear coefficient whose magnitude is equal to or less than one third the magnitude of the first second order nonlinear coefficient for the first nonlinear optical material.

The optical waveguide structure according to one of clause 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, wherein the central region is comprised of at least one of lithium niobate (LiNbO2), silicon carbide, aluminum nitride, gallium nitride, gallium aluminum nitride, gallium phosphide, gallium aluminum phosphide, aluminum phosphide, gallium arsenide, gallium aluminum arsenide, or aluminum arsenide.

The optical waveguide structure according to one of clause 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13, wherein the second material in the first side region and the second side region are comprised of a material such that a nonlinear optical process in the first side region and the second side region does not generate light.

The optical waveguide structure according to one of clause 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14, wherein the first side region and the second side region are comprised of at least one of silicon nitride, titanium dioxide silicon, silicon oxynitride, or hafnia.

The optical waveguide structure according to one of clause 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15, wherein the nonlinear optical waveguide is a main nonlinear optical waveguide, the optical waveguide structure further comprising:a first extension optical waveguide;a second extension optical waveguide;a first wavelength selective coupler that couples the main nonlinear optical waveguide and the first extension optical waveguide to each other such that a second light of a second wavelength is coupled between the main nonlinear optical waveguide and the first extension optical waveguide; anda second wavelength selective coupler that couples the main nonlinear optical waveguide and the second extension optical waveguide to each other such a third light of a third wavelength is coupled between the main nonlinear optical waveguide and the second extension optical waveguide.

The optical waveguide structure according to clause 16, wherein the second light of the second wavelength travels in a second loop within the main nonlinear optical waveguide and the first extension optical waveguide in which the second loop has a second length for the second light of the second wavelength, and wherein the third light of the third wavelength travels in a third loop within the main nonlinear optical waveguide and the second extension optical waveguide in which the third loop has a third length for the third light of the third wavelength.

The optical waveguide structure according to clause 16, wherein the first wavelength selective coupler is a starting first extension wavelength selective coupler located at a first extension starting location in the main nonlinear optical waveguide and the first extension optical waveguide and the second wavelength selective coupler is a starting second extension wavelength selective coupler located at a second extension starting location in the main nonlinear optical waveguide and the second extension optical waveguide, the optical waveguide structure further comprising:an ending first extension wavelength selective coupler located in an ending first extension location in the main nonlinear optical waveguide and the first extension optical waveguide; andan ending second extension wavelength selective coupler located at an ending second extension location in the main nonlinear optical waveguide and the second extension optical waveguide.

The optical waveguide structure according to one of clause 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18 further comprising:a set of electrodes in a location selected from at least one of adjacent to the first side region, adjacent to the second side region, adjacent to the central region.

The optical waveguide structure according to one of clause 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or 19, wherein the central region, the first side region and the second side region form a first core region and further comprising:a second core region.

The optical waveguide structure according to clause 20, wherein a gap is present between the first core region and the second core region.

A method for moving a light through a nonlinear optical waveguide structure:inputting a light at a pump wavelength into the nonlinear optical waveguide structure having a central region within a nonlinear optical waveguide in nonlinear optical waveguide structure, wherein the central region comprises a nonlinear optical material, a first side region of a first side of the central region, and a second side region on a second side of the central region, wherein the central region has a first nonlinear coefficient that is larger than a second nonlinear coefficient of the first side region and the second side region; andpropagating the light at the pump wavelength along a path in the optical waveguide structure, wherein light generation occurs in the nonlinear optical waveguide.

The method of according to clause 22, wherein the central region has a set of dimensions selected to increase a light generation in the optical waveguide structure.

The method according to clause 23, wherein the light generation increases for at least one of a signal light or an idler light when a pump light overlaps the central region of the nonlinear optical waveguide.

The method according to clause 23, wherein the set of dimensions is a width selected to increase an overlap of an electromagnetic field has a first sign for a light of interest with the central region and the electromagnetic field for the light of interest has a second sign in the first side region and the second side region such that light generation is increased within the nonlinear optical waveguide.

The method according to one of clause 23, 24, or 25, wherein the set of dimensions is selected from least one of a width or a height.