Apparatus and method for optical frequency conversion

Abstract

Apparatus and methods are provided for an optical frequency converter configured to double an input optical signal or have a carrier frequency of the input optical signal. The input optical signal provided to the optical frequency converter is in a higher order mode than a mode of the output optical signal. The optical frequency converter includes a core, a cladding material, and a substrate. The core includes a first core portion of a non-centrosymmetric nonlinear crystalline material, and second and third core portions of a centrosymmetric nonlinear crystalline material. The first core portion, the second core portion, and the third core portion are coplanar and adjacent to the first core portion between the second core portion and the third core portion.

Description

[0001] Statement Regarding Federally Sponsored Research or Development

[0002] This invention was made with government support. The government has certain rights in this invention. Background Art

[0003] Optical frequency converters are used in various technical systems including communication systems and measurement systems. Optical frequency converters can be made from waveguides using periodic poling or ion diffusion waveguides. https: / / en.wikipedia.org / wiki / Periodic_poling (October 11, 2023); Parfenov, M. et al. “Simulation of Ti-indiffused lithium niobate waveguides and analysis of their mode structure”, Journal of Physics: Conference Series, Volume 741, Issue 1, Institute of Physics Publishing, 2016. The references cited above are hereby incorporated by reference into this text. Waveguides made with periodic poling are complex and costly to manufacture. Ion diffusion waveguides are larger than waveguides using periodic poling and have lower conversion efficiency. Summary of the Invention

[0004] In some aspects, the technology described herein relates to an optical frequency converter configured to perform at least one of the following: doubling the carrier frequency of an input optical signal and halving the carrier frequency of the input optical signal, the optical frequency converter comprising: a substrate comprising a surface; a cladding on or above the surface of the substrate; a core comprising a non-centrosymmetric nonlinear crystal material, a first portion of a centrosymmetric nonlinear crystal material, and a second portion of the centrosymmetric nonlinear crystal material; wherein the core is above the surface of the substrate; wherein the non-centrosymmetric nonlinear crystal material is located between the first portion of the centrosymmetric nonlinear crystal material and the second portion of the centrosymmetric nonlinear crystal material; wherein the non-centrosymmetric nonlinear crystal material, the first portion of the centrosymmetric nonlinear crystal material, and the second portion of the centrosymmetric nonlinear crystal material are in a plane; wherein the plane is parallel to the surface; wherein the core is in the cladding; and wherein the cladding has a refractive index lower than the refractive index of the core.

[0005] In some aspects, the techniques described herein relate to a method of fabricating an optical frequency converter configured to perform at least one of the following: doubling and / or halving the carrier frequency of an input optical signal. The method includes: forming a first insulator on a substrate; forming a patterned non-centrosymmetric nonlinear crystal material over a portion of the surface of the first insulator; forming a first centrosymmetric nonlinear crystal material and a second centrosymmetric nonlinear crystal material from portions of the patterned non-centrosymmetric nonlinear crystal material, wherein each of the first centrosymmetric nonlinear crystal material and the second centrosymmetric nonlinear crystal material is adjacent to a different side of the remaining portion of the patterned non-centrosymmetric nonlinear crystal material; and forming a second insulator over the exposed surfaces of the first insulator, the first centrosymmetric nonlinear crystal material, the second centrosymmetric nonlinear crystal material, and the remaining portion of the patterned non-centrosymmetric nonlinear crystal material.

[0006] In some aspects, the techniques described herein relate to a method of operating an optical frequency converter cladding, a core including a non-centrosymmetric nonlinear crystal material, a first portion of a centrosymmetric nonlinear crystal material, and a second portion of a centrosymmetric nonlinear crystal material, wherein the non-centrosymmetric nonlinear crystal material is between the first portion and the second portion, wherein the core is within the cladding, and wherein the cladding has a lower refractive index than the refractive index of the core. The method includes: receiving an input optical signal at a first port of the optical frequency converter that is in a transverse electric or magnetic mode and has a first carrier frequency; and generating an output optical signal from the input optical signal and only within the non-centrosymmetric nonlinear crystal material, the output optical signal being in a transverse electric or magnetic mode and including at least one signal component having a second carrier frequency that is half or twice the first carrier frequency; wherein the order of the transverse electric or magnetic mode of the input optical signal is higher than the order of the transverse electric or magnetic mode of the output optical signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] It should be understood that the drawings depict only exemplary embodiments and should not be considered as limiting the scope of the invention. Exemplary embodiments will be described with additional features and details by use of the drawings, wherein:

[0008] Figure 1A A cross-sectional view of an embodiment of an optical frequency converter configured as an optical frequency doubler and / or an optical frequency divider is shown;

[0009] Figure 1B A cross-sectional view of an embodiment of an optical waveguide configured to be used with an optical frequency converter is shown;

[0010] Figure 1CA figure showing a plan view of an embodiment of an optical frequency converter having an optional first optical waveguide adjacent to a first port of the optical frequency converter and an optional second optical waveguide adjacent to a second port of the optical frequency converter;

[0011] Figure 2 A flowchart showing an exemplary method of generating at least one component of an output optical signal from an input optical signal, the output optical signal having a carrier frequency that is half or twice the carrier frequency of the input optical signal; and

[0012] Figure 3 A flowchart showing an exemplary method of fabricating an optical frequency converter that functions as an optical frequency doubler and / or an optical frequency divider.

[0013] By convention, the various features described are not necessarily drawn to scale but are used to emphasize specific features relevant to the exemplary embodiments. Reference characters represent like elements throughout the figures and the text. Detailed Description

[0014] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration specific exemplary embodiments. However, it is to be understood that other embodiments may be utilized and structural, mechanical, and electrical changes may be made. Additionally, the order in which each method presented in the drawings and the specification may be performed should not be construed as limiting. The following detailed description should not be regarded as limiting in nature.

[0015] Disclosed herein is an optical frequency converter formed of an optical waveguide and functioning as an optical frequency doubler and / or an optical frequency divider. The optical frequency divider is configured to reduce the frequency by half.

[0016] The input optical signal and the output optical signal described herein may be, respectively, a transverse electric (TE) mode optical signal or a transverse magnetic (TM) mode optical signal. For teaching purposes, the input optical signal and the output optical signal may be shown as transverse electric mode optical signals. The input optical signal provided to the optical frequency converter is a higher order transverse electric or magnetic mode than the corresponding transverse electric or magnetic mode of the output optical signal. Optionally, the mode of the input optical signal is the TE2 mode and the mode of the output electrical signal is the TE0 mode.

[0017] The optical frequency converter includes a core, a cladding material, and a substrate. The core is surrounded by the cladding material. The cladding material has a refractive index lower than that of the core. At least one surface of the cladding material is on the substrate, e.g., supported by the substrate.

[0018] The core includes a first core portion of a non-centrosymmetric nonlinear crystal material, and second and third core portions of centrosymmetric nonlinear crystal materials. The first, second, and third core portions are coplanar with the first core portion between the second and third core portions. A first sidewall of the first core portion is adjacent to a sidewall of the second core portion. A second core sidewall of the first core portion (opposite the first sidewall) is adjacent to a sidewall of the third core portion. Each of the sidewalls is substantially perpendicular (or orthogonal) to the surface 113 of the substrate 101.

[0019] Centrosymmetry means symmetry about a center point. A centrosymmetric nonlinear crystal material does not have second-order nonlinearity and thus is not configured to generate an output optical signal from an input optical signal that includes at least one signal component having a carrier frequency that is half or twice the carrier frequency of the input optical signal.

[0020] If the second and third core portions are formed of a non-centrosymmetric nonlinear crystal material, higher-order optical modes will be generated in the second and third core portions, which will destructively interfere with the frequency halving and / or doubling generated in the first core portion. This destructive interference will undesirably reduce the conversion efficiency of the optical frequency converter. The conversion efficiency is the power of the optical output signal provided by the optical frequency converter divided by the power of the optical input signal received by the optical frequency converter. To improve the optical frequency converter efficiency, only the central region, e.g., the first core portion, may be made of a non-centrosymmetric nonlinear crystal material. The other regions surrounding the first portion of the core must be made of a non-centrosymmetric material.

[0021] The first, second, and third portions of the core are shown herein as initially formed of one type of material. Alternatively, the centrosymmetric portions may be initially formed of a material different from the centrosymmetric portions; however, the material forming each portion must have a refractive index greater than that of the cladding.

[0022] Optionally, the second and third core portions are formed of a centrosymmetric nonlinear crystal material, e.g., by converting a non-centrosymmetric nonlinear crystal material into a centrosymmetric nonlinear crystal material. The resulting frequency converter (exemplary embodiments of which are disclosed herein) is more compact and has a higher conversion efficiency than an ion-diffused waveguide and is more cost-effective than a waveguide using periodic poling.

[0023] Figure 1AA cross-sectional view of an embodiment of an optical frequency converter 110A that functions as an optical frequency doubler and / or an optical frequency divider is shown. The optical frequency converter is formed as an optical waveguide including a cladding 106 on or above a substrate 101 and a core 104A in the cladding. Optionally, the cladding 106 is formed by, for example, a first or lower cladding portion 102 on or above the surface 113 of the substrate 101 and a second or upper cladding portion 107 on or above the first or lower cladding portion 102.

[0024] The substrate 101 can be an insulator such as glass and / or sapphire, or a semiconductor such as silicon and / or lithium niobate. The cladding 106 (and its portions) can be any material having a refractive index lower than that of the core 104A. Optionally, the cladding 106 can be formed by two or more portions of the cladding; optionally, each portion of the cladding can be formed of a different material. For teaching purposes, the cladding 106 is shown as being formed by a first cladding portion 102 formed on or above the substrate 101 and a second cladding portion 107 formed on or above the core 104A and the first cladding portion 102, for example, on or above the exposed surface of the first cladding portion 102 where the core 104 is not located on or above it. Optionally, the cladding 106 can be silica.

[0025] The core 104A is in the cladding 106. Optionally, the core 104A is on or above the first cladding portion 102 and below the second cladding portion 107.

[0026] The core 104A includes: (a) a first core portion 103 of the core 104A, which is a non-centrosymmetric nonlinear crystal material; and (b) a second core portion 105 and a third core portion 109, each of these core portions being a centrosymmetric nonlinear crystal material. The first core portion 103 of the core 104A including the non-centrosymmetric nonlinear crystal material has a first side 118 opposite to a second side 119; the first side 118 and the second side 119 are orthogonal to the surface 113 of the substrate 101, and the cladding 106, for example, the lower cladding portion 102, is located on or above the surface. The first core portion 103, the second core portion 15, and the third core portion 109 are coplanar, that is, in the same plane. Optionally, each of the first core portion 103, the second core portion 105, and the third core portion is composed of one of lithium niobate, lithium tantalate, and potassium niobate.

[0027] Optionally, the width WC of each of the second core portion 105 and the third core portion 109 is equal to the width WN of the first core portion 103. For teaching purposes, the width WC of each of the second core portion 105 and the third core portion 109 is shown to be equal herein. Alternatively, the widths of the second core portion 105 and the third core portion 109 may be different. The width of each core portion is along an axis 108 parallel to the surface 113 of the substrate. Optionally, the width T2 of the optical frequency converter (e.g., cladding) is approximately three times or more the height T0 of the optical frequency converter (e.g., cladding and core), e.g., the height of the cladding 106.

[0028] If both the second core portion 105 and the third core portion 109 are non-centrosymmetric nonlinear crystal materials, the side lobes of the higher-order TE mode optical input signal in the second core portion 105 and the third core portion 109 will destructively interfere with the main lobe of the higher-order TE mode optical input signal in the first core portion 103 and reduce the optical frequency conversion efficiency. This destructive interference is mitigated by converting the non-centrosymmetric nonlinear crystal materials of the second core portion and the third core portion into centrosymmetric nonlinear crystal materials.

[0029] Figure 1B A cross-sectional view of an embodiment of an optical waveguide 110B configured to be used with an optical frequency converter is shown. It can be utilized as shown subsequently in Figure 1C The optical waveguide 110B is similar to the optical frequency converter 110A, except that the core 104B of the optical waveguide 110B is formed only of centrosymmetric nonlinear crystal material. The core 104B of the optical waveguide 110B has a width WC1. Optionally, the first optical waveguide and the second optical waveguide are used to couple an input optical signal to the optical frequency converter 110A, and the second optical waveguide is used to couple the output optical signal from the optical frequency converter 110A (or vice versa) and may have other structures. Optionally, the width T2 of the optical waveguide (e.g., cladding) is approximately three times the height T0 of the optical waveguide (e.g., core and cladding). For teaching purposes, the height of the optical frequency converter and the height of the optical waveguide are shown to be equal; however, these two heights do not have to be equal. The refractive index of the cladding 106 is lower than the refractive index of the core 104B.

[0030] Figure 1C A diagram showing a plan view of an embodiment of an optical frequency converter 110C having an optional first optical waveguide 112A adjacent to the first port 114 of the optical frequency converter 110C and an optional second optical waveguide 112B adjacent to the second port 116 of the optical frequency converter 110C. The first port 114 or the second port 116 is configured to receive an input optical signal 115, e.g., a higher-order TE mode, e.g., the TE2 mode.

[0031] The optical frequency converters 110A, 110C are reciprocal optical devices. The first port 114 can be the input or output of the optical frequency converter 110C. The second port 116 can be the output or input of the optical frequency converter 110C, respectively. Optionally, the carrier wavelength of the input optical signal can be 775 nm, and the carrier wavelength of the output optical signal can be 1550 nm. Optionally, the carrier wavelength of the input optical signal can be 1550 nm, and the carrier wavelength of the output optical signal can be 775 nm.

[0032] Optionally, the optical frequency converter 110C is implemented according to Figure 1A the embodiments and descriptions shown. In this case, Figure 1A the cross-section shown in will be found at the cross-section at, for example, line AA-AA'. The optical frequency converter 110C has a width W1, which can be the width at one end of each of the first transition portion TP1 at the first port 114 and the second transition portion at the second port 116, as described elsewhere herein. The optical frequency converter 110C has a length L.

[0033] The non-centrosymmetric nonlinear crystal material of the optical frequency converter 110C is configured to generate an output optical signal 117 provided at the second port 116 or the first port 114, respectively. The output optical signal includes components having a carrier frequency that is half or twice the carrier frequency of the input optical signal.

[0034] The optional first optical waveguide 112A and the optional second optical waveguide 112B can optionally be implemented according to Figure 1B the embodiments shown. In this case, Figure 1A the cross-section shown in will be found at the cross-section at, for example, line BB-BB'. Portions 112A', 112B' of each of the optional first optical waveguide 112A and the second optical waveguide 112B are connected to the corresponding transition portions TP1, TP2.

[0035] Optionally, each of a portion 112A' of the optional first optical waveguide 112A, e.g., the cladding of the portion 112A', and a portion 112B' of the optional second optical waveguide 112B, e.g., the cladding of the portion 112B', has a width W2. For illustrative purposes, the widths of each of the portions 112A', 112B' of the optional first optical waveguide 112A and the second optical waveguide 112B are shown to be equal. However, the widths of each of the portions 112A', 112B' of each of the optional first optical waveguide and the second optical waveguide may be different. Optionally, the width W2 of each of the portions 112A', 112B', e.g., the cladding of each portion, is different from, e.g., smaller than, the width W1 of the optical frequency converter 110C, e.g., the cladding of the optical frequency converter.

[0036] Optionally, the first transition portion TP1 and / or the second transition portion TP2 can be used to avoid discontinuities when connecting the optional first optical waveguide 112A to the first port 114 and the second optical waveguide 112B to the second port 116, respectively. Accordingly, the illustrated optional first optical waveguide 112A and second optical waveguide 112B each include transition portions TP1, TP2 having a tapered width such that the width of the cladding of the optional first optical waveguide 112A at the first port 114 is equal to the width of the cladding of the optical frequency converter 110C at the first port 114, and the width of the cladding of the optional second optical waveguide 112B at the second port 116 is equal to the width of the cladding of the optical frequency converter 110C at the second port 116. Each of the transition portions TP1, TP2 can be formed of only centrosymmetric nonlinear crystal material having a cross-section similar to that Figure 1B shown therein. The sidewall taper of each of the transition portions TP1, TP2 can be linear or nonlinear.

[0037] Figure 2 A flowchart of an exemplary method 220 for generating at least one component of an output optical signal from an input optical signal is shown, where the output optical signal has a carrier frequency that is half or twice the carrier frequency of the input optical signal. The methods described herein are described in terms of being implemented with one or more of the devices Figures 1A through 1C shown therein; it should be understood that other implementations may be possible in other ways. For ease of explanation, the blocks of the flowchart are arranged in a generally sequential manner; however, it should be understood that this arrangement is merely exemplary and it should be recognized that the processing associated with the method (and the blocks shown in the figure) can occur in a different order (e.g., where at least some of the processing associated with the blocks is performed in parallel and / or in an event-driven manner). Optionally, method 220 is implemented using one or more of the devices Figures 1A through 1C shown therein or a portion of one or more of the devices.

[0038] In block 222, an input optical signal in a mode (e.g., TE or TM mode) and having a first carrier frequency is received at a first port of the optical frequency converter. Optionally, the input optical signal is received from a first optical waveguide.

[0039] In block 224, an output optical signal in another mode (e.g., another TE or TM mode respectively) is generated from the input optical signal. The output optical signal includes at least one signal component having a second carrier frequency that is half or twice the carrier frequency of the input optical signal. The order of the mode of the input optical signal (e.g., TE2) is higher than the order of the mode of the output optical signal (e.g., TE0). The output optical signal is generated only in a non-centrosymmetric nonlinear crystal material (e.g., a first core portion) of the optical frequency converter, which is coplanar and adjacent to (a) a first centrosymmetric nonlinear crystal material (e.g., a second core portion) on a first side of the non-centrosymmetric nonlinear crystal material and (b) a second centrosymmetric nonlinear crystal material (e.g., a third core portion) on a second side of the non-centrosymmetric nonlinear crystal material. Optionally, the output optical signal is provided to a second optical waveguide.

[0040] Figure 3 A flowchart of an exemplary method 330 for fabricating an optical frequency converter that functions as an optical frequency doubler and / or an optical frequency divider is shown. In block 332, a first insulator, i.e., a lower cladding portion 102, is formed above a substrate 101. Optionally, the insulator can be formed by deposition or growth.

[0041] In block 334, a patterned non-centrosymmetric nonlinear crystal material 335 is formed above a portion of a surface 333 of the first insulator, the surface being parallel to a surface 113 of the substrate 101, on or above which the first insulator is formed. Optionally, such formation can be performed by bonding the non-centrosymmetric nonlinear crystal material to the surface 333 of the first insulator and patterning the bonded non-centrosymmetric nonlinear crystal material (e.g., using photoresist, lithography, and etching); thus, the patterned non-centrosymmetric nonlinear crystal material is only above a portion of the surface of the first insulator.

[0042] In block 336, a first centrosymmetric nonlinear crystal material (e.g., a second core portion 105) and a second centrosymmetric nonlinear crystal material (e.g., a third core portion 109) are formed from portions of the patterned non-centrosymmetric nonlinear crystal material 335. As described elsewhere herein, each of the first centrosymmetric material and the second centrosymmetric nonlinear crystal material is adjacent to a different side of the remaining portion 103 of the patterned non-centrosymmetric nonlinear crystal material. The remaining portion 103, the first centrosymmetric material, and the second centrosymmetric nonlinear crystal material are also referred to herein as the first core portion 103, the second core portion, and the third core portion 109, respectively. Optionally, the first centrosymmetric material and the second centrosymmetric nonlinear crystal material are formed by the steps of: patterning a photoresist (e.g., using photolithography) on the surface 337 of the patterned non-centrosymmetric material nonlinear crystal material 335, and subjecting two exposed portions of the surface 337 not covered by the photoresist (i.e., not covered by the photoresist to proton exchange and / or ion bombardment, e.g., to replace lithium ions with hydrogen ions (the photoresist or a material formed using the photoresist (e.g., a metal or metal alloy) can be used to protect the non-centrosymmetric nonlinear crystal material from ion bombardment and / or proton exchange)); the portion of the patterned non-centrosymmetric material nonlinear crystal material 335 exposed to proton exchange and / or ion bombardment becomes a centrosymmetric material nonlinear crystal material. After completion of the proton exchange and / or ion bombardment, the photoresist is removed. The portion of the patterned non-centrosymmetric material nonlinear crystal material 335 whose surface is covered by the photoresist remains unaffected by proton exchange and / or ion bombardment and is thus non-centrosymmetric.

[0043] In block 338, a second insulator (e.g., a second or upper cladding portion 107) is formed over the exposed surface 339 of the first insulator, the exposed surfaces 337a, 337b of the first centrosymmetric nonlinear crystal material and the second centrosymmetric nonlinear crystal material (e.g., the second core portion 105 and the third core portion 109), and the exposed surface 337c of the remaining portion of the patterned centrosymmetric nonlinear crystal material (e.g., the first core portion 103). Optionally, the second insulator can be formed by growth or deposition.

[0044] Although the present teachings have been shown with respect to one or more specific embodiments, changes and / or modifications may be made to the shown embodiments without departing from the scope of the appended claims. Additionally, although a particular feature of the present disclosure may be described with respect to only one of several specific embodiments, such feature may be combined with one or more other features of other specific embodiments as may be desired or advantageous for any given or particular function. Further, to the extent that the terms “comprises,” “comprising,” “has,” “having,” “with,” or variants thereof are used in the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “including.” The term “at least one of” is used to denote that one or more of the listed items may be selected. As used herein, the term “one or more of” with respect to a series of items such as, for example, A and B or A and / or B, refers to either A alone, B alone, or A and B. The term “at least one” is used to denote that one or more of the listed items may be selected.

[0045] As used in this application, terms of relative position are defined based on a plane parallel to the normal plane or working surface of the material (e.g., a layer or substrate), regardless of orientation. Terms such as “on,” “higher,” “lower,” “above,” “top,” and “below” are defined with respect to the normal plane or working surface located on the top surface of the layer or substrate, regardless of orientation. The term “about” or “substantially” means that the specified value or parameter may be slightly changed, so long as the change does not cause the process or structure to be inconsistent with the shown embodiments. Finally, “exemplary” means that the description is used as an example and does not imply that it is an ideal situation. Although specific embodiments have been shown and described herein, those of ordinary skill in the art will recognize that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. It is, therefore, evident that the present invention is limited only by the claims and their equivalents.

[0046] Exemplary embodiments

[0047] Embodiment 1 includes an optical frequency converter configured to perform at least one of doubling the carrier frequency of an input optical signal and halving the carrier frequency of the input optical signal. The optical frequency converter includes: a substrate including a surface; a cladding on or above the surface of the substrate; a core including a non-centrosymmetric nonlinear crystal material, a first portion of a centrosymmetric nonlinear crystal material, and a second portion of the centrosymmetric nonlinear crystal material; wherein the core is above the surface of the substrate; wherein the non-centrosymmetric nonlinear crystal material is located between the first portion of the centrosymmetric nonlinear crystal material and the second portion of the centrosymmetric nonlinear crystal material; wherein the non-centrosymmetric nonlinear crystal material, the first portion of the centrosymmetric nonlinear crystal material, and the second portion of the centrosymmetric nonlinear crystal material are in a plane; wherein the plane is parallel to the surface; wherein the core is in the cladding; and wherein the cladding has a refractive index lower than that of the core.

[0048] Embodiment 2 includes the optical frequency converter of Embodiment 1. The optical frequency converter further includes: a first port configured to receive the input optical signal; a second port configured to provide an output optical signal including at least one signal component having a carrier frequency that is half or twice the carrier frequency of the input optical signal; a first optical waveguide optically coupled to the first port and configured to provide the input optical signal to the first port; and a second optical waveguide optically coupled to the second port and configured to provide the output optical signal from the second port.

[0049] Embodiment 3 includes the optical frequency converter of Embodiment 2, wherein each of the first optical waveguide and the second optical waveguide includes: a substrate; a cladding on or above the surface of the substrate; and another core composed of the centrosymmetric nonlinear crystal material, wherein the another core is above the surface of the substrate; wherein the another core is in the cladding; and wherein the cladding has a refractive index lower than that of the another core.

[0050] Embodiment 4 includes the optical frequency converter of Embodiment 3, wherein the centrosymmetric nonlinear crystal material of the another core is composed of one of the following materials: lithium niobate, lithium tantalate, and potassium niobate.

[0051] Example 5 includes the optical frequency converter described in any one of Examples 2 to 4, wherein each of the first optical waveguide and the second optical waveguide includes a transition portion having a tapered width such that the width of the cladding of the first optical waveguide at the first port is equal to the width of the cladding of the optical frequency converter at the first port, and the width of the cladding of the second optical waveguide at the second port is equal to the width of the cladding of the optical frequency converter at the second port.

[0052] Example 6 includes the optical frequency converter described in Example 5, wherein the taper of the tapered width is linear or non-linear.

[0053] Example 7 includes the optical frequency converter described in any one of Examples 1 to 6, wherein each of the non-centrosymmetric non-linear crystal material, the first portion of the centrosymmetric non-linear crystal material, and the second portion of the centrosymmetric non-linear crystal material has an equal width, and each width is along an axis parallel to the surface of the substrate.

[0054] Example 8 includes the optical frequency converter described in any one of Examples 1 to 7, wherein each of the non-centrosymmetric non-linear crystal material, the first portion of the centrosymmetric non-linear crystal material, and the second portion of the centrosymmetric non-linear crystal material is composed of one of lithium niobate, lithium tantalate, and potassium niobate.

[0055] Example 9 includes the optical frequency converter described in any one of Examples 1 to 8, wherein the substrate is composed of an insulator.

[0056] Example 10 includes the optical frequency converter described in any one of Examples 1 to 9, wherein the cladding includes: a first cladding portion located on or above the surface of the substrate; and a second cladding portion located on or above the core and the first cladding portion.

[0057] Example 11 includes the optical frequency converter described in any one of Examples 1 to 10, wherein the cladding contains silica.

[0058] Example 12 includes the optical frequency converter described in any one of Examples 1 to 11, wherein the width of the cladding is at least three times the height of the cladding.

[0059] Example 13 includes a method of manufacturing an optical frequency converter configured to perform at least one of the following: doubling and / or halving the carrier frequency of an input optical signal, the method including: forming a first insulator on a substrate; forming a patterned non-centrosymmetric nonlinear crystal material over a portion of the surface of the first insulator; forming a first centrosymmetric nonlinear crystal material and a second centrosymmetric nonlinear crystal material from portions of the patterned non-centrosymmetric nonlinear crystal material, wherein each of the first centrosymmetric nonlinear crystal material and the second centrosymmetric nonlinear crystal material is adjacent to a different side of the remaining portion of the patterned non-centrosymmetric nonlinear crystal material; and forming a second insulator over the exposed surfaces of the first insulator, the first centrosymmetric nonlinear crystal material, the second centrosymmetric nonlinear crystal material, and the remaining portion of the patterned non-centrosymmetric nonlinear crystal material.

[0060] Example 14 includes the method of Example 13, wherein forming the first insulator on the substrate includes depositing the first insulator on the substrate or growing the first insulator on the substrate.

[0061] Example 15 includes the method of any one of Examples 13 to 14, wherein forming the patterned non-centrosymmetric nonlinear crystal material over the portion of the surface of the first insulator includes: bonding a non-centrosymmetric nonlinear crystal material to the surface of the first insulator; and patterning the bonded non-centrosymmetric nonlinear crystal material such that the patterned non-centrosymmetric nonlinear crystal material is only over a portion of the surface of the first insulator.

[0062] Example 16 includes the method of any one of Examples 13 to 15, wherein forming the first centrosymmetric nonlinear crystal material and the second centrosymmetric nonlinear crystal material from portions of the patterned non-centrosymmetric nonlinear crystal material includes: subjecting two exposed portions of the surface of the patterned non-centrosymmetric nonlinear crystal material to at least one of the following: proton exchange and ion bombardment.

[0063] Example 17 includes the method according to any one of Examples 13 to 16, wherein forming the second insulator above the exposed surfaces of the first insulator, the first centrosymmetric nonlinear crystal material, the second centrosymmetric nonlinear crystal material, and the remaining portion of the patterned non-centrosymmetric nonlinear crystal material includes: depositing the second insulator on the exposed surfaces of the first insulator, the first centrosymmetric nonlinear crystal material, the second centrosymmetric nonlinear crystal material, and the remaining portion of the patterned non-centrosymmetric nonlinear crystal material, or growing the second insulator on the exposed surfaces of the first insulator, the first centrosymmetric nonlinear crystal material, the second centrosymmetric nonlinear crystal material, and the remaining portion of the patterned non-centrosymmetric nonlinear crystal material.

[0064] Example 18 includes an optical frequency converter cladding, a core including a non-centrosymmetric nonlinear crystal material, a first portion of a centrosymmetric nonlinear crystal material, and a second portion of a centrosymmetric nonlinear crystal material, wherein the non-centrosymmetric nonlinear crystal material is between the first portion and the second portion, wherein the core is in the cladding, and wherein the cladding has a refractive index lower than that of the core. The method includes: receiving an input optical signal at a first port of the optical frequency converter that is in a transverse electric or magnetic mode and has a first carrier frequency; and generating an output optical signal from the input optical signal and only in the non-centrosymmetric nonlinear crystal material, the output optical signal being in a transverse electric or magnetic mode respectively and including at least one signal component, the at least one signal component having a second carrier frequency that is half or twice the first carrier frequency; wherein the order of the transverse electric or magnetic mode of the input optical signal is higher than the order of the transverse electric or magnetic mode of the output optical signal respectively.

[0065] Example 19 includes the method according to Example 18, wherein the transverse electric (TE) or magnetic mode of the input optical signal is a TE2 mode, and the corresponding transverse electric or magnetic mode of the output optical signal is a TE0 mode.

[0066] Example 20 includes the method according to Example 19, wherein the input optical signal is received from a first optical waveguide; wherein the output optical signal is provided to a second optical waveguide; wherein each of the input optical waveguide and the output optical waveguide includes: the cladding; another core composed of the centrosymmetric nonlinear crystal material; wherein the another core is in the cladding; and wherein the cladding has a refractive index lower than that of the another core.

[0067] Although specific embodiments have been shown and described herein, those of ordinary skill in the art will recognize that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. It is, therefore, evident that the invention is limited only by the claims and their equivalents.

Claims

1. An optical frequency converter, the optical frequency converter being configured to perform at least one of the following: doubling a carrier frequency of an input optical signal and halving the carrier frequency of the input optical signal, the optical frequency converter comprising: a substrate, the substrate comprising a surface; a cladding layer on or over the surface of the substrate; a core comprising a non-centrosymmetric nonlinear crystal material, a first portion of a centrosymmetric nonlinear crystal material, and a second portion of the centrosymmetric nonlinear crystal material; wherein the core is above the surface of the substrate; wherein the non-centrosymmetric nonlinear crystal material is located between the first portion of the centrosymmetric nonlinear crystal material and the second portion of the centrosymmetric nonlinear crystal material; wherein the non-centrosymmetric nonlinear crystal material, the first portion of the centrosymmetric nonlinear crystal material and the second portion of the centrosymmetric nonlinear crystal material are in a plane; wherein the plane is parallel to the surface; wherein said core is within said cladding; wherein the cladding has a lower refractive index than the refractive index of the core.

2. The optical frequency converter according to claim 1, further comprising: a first port configured to receive the input optical signal; a second port configured to provide an output optical signal comprising at least one signal component having a carrier frequency that is half or twice the carrier frequency of the input optical signal; a first optical waveguide optically coupled to the first port and configured to provide the input optical signal to the first port; and A second optical waveguide is optically coupled to the second port and is configured to provide the output optical signal from the second port.

3. The optical frequency converter of claim 1 , wherein each of the non-centrosymmetric nonlinear crystal material, the first portion of the centrosymmetric nonlinear crystal material, and the second portion of the centrosymmetric nonlinear crystal material has an equal width, wherein each width is along an axis parallel to the surface of the substrate.

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