THIN FILM LITHIUM NIOBATE OPTICAL DEVICE HAVING AN ENGINEERED SUBSTRATE FOR HETEROGENEOUS INTEGRATION

An electro-optic device is described. The electro-optic device includes a substrate, an insulator on the substrate, an optical structure on the insulator and an electrode proximate to at least a portion of the optical structure. The substrate includes a trench region having a plurality of trenches therein. The trench region has an effective microwave index based on a substrate material and the plurality of trenches. The insulator is on the substrate. The optical structure is on the insulator. The optical structure has a thin film electro-optic layer including lithium. The electrode is proximate to a portion of the optical structure.

BACKGROUND OF THE INVENTION

Electro-optic devices may utilize thin film electro-optic (TFEO) materials that contain lithium, such as thin film lithium niobate (TFLN) and thin film lithium tantalate (TFLT). In optical modulators, for example, the optical signal carried by a waveguide is modulated by a microwave signal carried in electrodes in proximity to the waveguide. Lithium-containing TFEO materials are desirable for use in photonics devices such as optical modulators because of their large change in index of refraction in response to a given applied electric field. Electro-optic devices including lithium-containing TFEO materials are also desired to be integrated with photonics devices using other materials. For example, lithium-containing TFEO devices may be desired to be integrated with silicon photonics (SiPh) devices to form heterogeneous devices.

Integration of electro-optic devices using lithium-containing TFEO materials with other photonics devices encounters significant obstacles. This is particularly true for integration of lithium-containing TFEO devices with SiPh devices. For example, TFLN and/or TFLT devices utilize a thick buried oxide (BOX) layer that is typically formed of SiO2. The BOX layer is between the lithium-containing TFEO component (e.g. waveguide) and an underlying silicon substrate. These BOX layers are generally at least five micrometers to ten micrometers thick. The thick BOX layers allow the microwave mode for microwave signals carried by the electrodes to be within the BOX layer and not extend to the underlying silicon substrate. As a result, the thick BOX layer improves the matching between the speed of the optical signal in the lithium-containing TFEO waveguide and the speed of the microwave signal carried by electrodes. However, SiPh devices utilize a thinner BOX layer. For example, the BOX layer may be as thin as one micrometer. The use of such thin BOX layers in an integrated device including both SiPh and lithium-containing TFEO can adversely affect performance of lithium-containing TFEO component(s). Accordingly, a mechanism for improving the ability of TFEO materials, such as TFLN and/or TFLT, to be integrated with devices such as SiPh devices is desired.

DETAILED DESCRIPTION

Electro-optic devices may utilize thin film electro-optic (TFEO) materials. Lithium-containing TFEO materials include thin film lithium niobate (TFLN) and thin film lithium tantalate (TFLT). The optical signal carried by the lithium-containing TFEO waveguide can be modulated by a microwave signal carried in electrodes that are in proximity to the TFEO waveguide. TFLN and/or TFLT have a large modulation in the index of refraction for a given electric field. Thus, such materials are desirable for use in photonics devices such as optical modulators.

Integration of electro-optic devices using lithium-containing TFEO materials such as TFLN and/or TFLT may face challenges. This is particularly true when such lithium-containing electro-optic materials are combined with materials such as silicon. For example, for TFLN and/or TFLT devices, a thick buried oxide (BOX) layer is generally desired. The thick BOX layer is typically formed of SiO2. Such layers are generally desired to be at least five micrometers thick for TFLN and/or TFLT devices. For example, five to ten micrometers of SiO2may frequently be used as the BOX layer. In some cases, the BOX layer is desired to have a thickness of ten micrometers or more. Such thick BOX layers allow the microwave mode for microwave signals carried by the electrodes to be within the BOX layer and not extend significantly (or at all) to the underlying silicon substrate. Thus, the index of refraction (i.e. the microwave index) for the microwave mode includes the microwave index of the BOX layer, rather than the underlying silicon substrate. Such thick BOX layers thus improve the ability of the speed of the optical signal in the TFLN and/or TFLT waveguide to be matched with the speed of the microwave signal carried by electrodes. However, silicon photonics (SiPh) devices generally utilize a thinner BOX layer. For example, the BOX layer may be three micrometers or less. In some cases, the BOX layer may be as thin as one micrometer. The use of such thin BOX layers can adversely affect performance of TFEO devices. For example, a mismatch between the optical signal carried by the waveguide formed of lithium-containing TFEO materials and the microwave signal may result. Thus, the desired modulation may not be obtained. Accordingly, a mechanism for improving the ability of TFEO materials, such as TFLN and/or TFLT, to be integrated with devices such as SiPh devices.

An electro-optic device is described. The electro-optic device includes a substrate, an insulator on the substrate, an optical structure on the insulator, and an electrode proximate to at least a portion of the optical structure. The substrate includes a trench region having trenches therein. The trench region has an effective microwave index based on a substrate material and the plurality of trenches. In some embodiments, the effective microwave index is less than 2.5. The optical structure is on the insulator. In some embodiments, the insulator does not exceed three micrometers in thickness. The optical structure has a thin film electro-optic layer including lithium. The electrode is proximate to a portion of the optical structure. In some embodiments, a photonics structure, such as a silicon photonic waveguide, is between the optical structure and the trenches.

In some embodiments, the electrode is configured to carry an electrode signal having a microwave frequency. In such embodiments, the trenches have a periodicity smaller than half of a wavelength corresponding to the microwave frequency. In some embodiments, the trenches have a periodicity not exceeding fifty micrometers. Each trench may have a width not exceeding twenty micrometers. Each trench may have a height not exceeding twenty micrometers and not less than three micrometers. In some embodiments, the trenches have a fill therein. The fill may be vacuum and/or an insulating cladding. Thus, the effective microwave index for such embodiments corresponds to the substrate material and the fill. In some embodiments, a portion of the plurality of trenches are under a portion of the electrode. In some embodiments, the trenches extend through at least a portion of the insulator.

An integrated electro-optic device is described. The integrated electro-optic device includes a substrate, an insulator on the substrate, a first optical structure, and a second optical structure. The substrate includes a trench region having trenches therein. The trench region has an effective microwave index based on a substrate material and the trenches. The first and second optical structures are on the substrate. The first optical structure includes a first photonics material. The second optical structure includes a thin film electro-optic layer including lithium. In some embodiments, the first optical structure is a silicon photonics optical structure such as a silicon photonics waveguide. For example, a silicon photonics optical structure may be on the insulator and between the second optical structure and the insulator. In some embodiments, the insulator has a thickness not exceeding three micrometers.

A method for providing an optical device is described. The method includes providing trenches in a trench region of a substrate. Thus, the trench region has an effective microwave index corresponding to a substrate material and the plurality of trenches. An insulator is provided on the substrate. An optical structure is provided on the insulator. The optical structure has a thin film electro-optic layer including lithium. An electrode is provided proximate to a portion of the optical structure. The electrode may be configured to carry an electrode signal having a microwave frequency. In such embodiments, the trenches have a periodicity smaller than half of a wavelength corresponding to the microwave frequency.

In some embodiments, providing the trenches includes etching the trenches into the substrate. Providing the insulator may include cladding the substrate with an insulating layer and planarizing the insulating layer. In some embodiments, the cladding is performed before the etching of the plurality of trenches. Thus, the trenches may extend through the insulator. Providing the trenches may also include at least partially filling the plurality of trenches using a fill. In some embodiments, the fill includes a vacuum and/or an insulating cladding. Thus, the effective microwave index corresponds to the substrate material and the fill. In some embodiments, the effective microwave index is less than 2.5.

FIG.1depicts a cross-sectional view of a portion of an embodiment of electro-optic device100.FIG.1is not to scale. Electro-optic device100includes substrate101, insulator102(e.g. BOX layer102in the embodiment shown), and optical structure112(i.e. waveguide112in the embodiment shown). In the embodiment shown, waveguide112is formed from thin film electro-optic (TFEO) materials that may contain lithium. Lithium-containing TFEO layer110has been formed into ridge waveguide112and slab114. In some embodiments, optical structure112may have another function and/or a different geometry. Cladding (not shown) is typically present and covers waveguide112as well as other structures that are not shown. For example electro-optic device100may include electrodes and/or other structures. Further, waveguide112may have other features including but not limited to tapers and/or mode converters.

Substrate101may include or consist of one or more materials such as silicon. In other embodiments, other materials may be used. BOX layer102may be or include a material such as SiO2. Although various structures are described herein as “layers” in some embodiments, a layer may include sublayers. In some embodiments, BOX layer102is relatively thin. For example, in some embodiments, BOX layer102is less than five micrometers thick. In some embodiments, BOX layer102is not more than three micrometers thick (e.g. may be less than three micrometers thick). In some embodiments, BOX layer102is not more than two micrometers thick. In some embodiments, BOX layer102is at least one micrometer thick. In some embodiments, BOX layer102is at least eight hundred nanometers thick. BOX layer102may be sufficiently thick to electrically isolate waveguide112from substrate101and/or structures (e.g. CMOS components) that are formed on or in substrate101. However, BOX layer102may not be sufficiently thick to substantially prevent a microwave mode from a microwave signal carried by electrodes (not shown) at or near BOX layer102from penetrating substrate101.

Waveguide112is used to transmit an optical signal. In the embodiment shown, waveguide112is a ridge waveguide. However, in some embodiments, waveguide112is a channel waveguide. For example, slab114of TFEO material be removed. Waveguide112may include one or more lithium-containing electro-optic materials and is a thin film waveguide. In some embodiments, the waveguide112is a Si waveguide. In such embodiments, waveguide112may be a channel waveguide and slab114omitted. In some embodiments, the waveguide112is TFEO waveguide that includes or consists of thin film lithium niobate (TFLN) and/or thin film lithium tantalate (TFLT). TFEO layer (e.g. TFLN and/or TFLT)110may have a thickness not exceeding ten micrometers in electro-optic devices. In some embodiments, TFEO layer110has a thickness of not more than one micrometer. In some embodiments, the thickness of TFEO layer110may be not more than seven hundred nanometers. In some such embodiments, the thickness may be not more than four hundred nanometers. Other thicknesses are possible. When used in electro-optic devices, TFEO layer110forms optical structures such as ridge waveguide112and/or channel waveguides used in optical modulators, mode converters, polarization beam rotators, and/or other optical devices.

To fabricate waveguide112, the lithium-containing TFEO layer110may undergo a physical etch, for example using dry etching, reactive ion etching (ME), inductively coupled plasma RIE. In some embodiments, a chemical etch and/or electron beam etch may be used. Waveguide112may thus have improved surface roughness. For example, the sidewall(s) of ridge112may have reduced surface roughness. For example, the short range root mean square surface roughness of a sidewall of ridge waveguide112is less than ten nanometers. In some embodiments, this root mean square surface roughness is not more than five nanometers. In some cases, the short range root mean square surface roughness does not exceed two nanometers. Waveguide112may have the optical losses in the range described above. In some embodiments, the height of ridge112is selected to provide a confinement of the optical mode such that there is a 10 dB reduction in intensity from the intensity at the center of ridge112at ten micrometers from the center of ridge112. For example, the height of ridge112is on the order of a few hundred nanometers in some cases. However, other heights are possible in other embodiments.

Trenches120are formed in substrate101. For clarity, only two trenches are labeled inFIG.1. In the embodiment shown, trenches120are also formed in BOX layer102. In some embodiments, trenches120are lithographically formed (e.g. via etching). In some such embodiments, the sidewalls of trench120may be substantially vertical or sloped so that the bottom of trench120is narrower than the top of trench120. Thus, trenches120may not undercut the remaining substrate material (e.g., the remaining silicon substrate101or the remaining BOX layer102). In the embodiment shown, trenches120have a constant spacing (i.e. a constant pitch). In some embodiments, the pitch is not constant. A set of trenches120extends over a length1. In some embodiments, the periodicity of trenches120(e.g. the distance from a wall of one trench120across the trench to the wall of the next trench) is smaller than half the microwave wavelength for the electrical (e.g. microwave) signal carried by the electrodes (not shown). In some embodiments, the periodicity is not more than three hundred micrometers (e.g. for a wavelength of six hundred micrometers or more). In some embodiments the periodicity is not more than one hundred micrometers (e.g. for a wavelength of six hundred micrometers or more). In some embodiments, the periodicity is not more than fifty micrometers. In some embodiments, the periodicity is not more than thirty micrometers. In some embodiments, the periodicity is not more than twenty micrometers. In some embodiments, the periodicity is at least five micrometers. Other periodicities are possible.

Trenches120have a height, h, and a width, w. In some embodiments, different trenches120may have different heights and/or widths. The aspect ratio (h/w) of trenches120may be larger than 1, and high in some embodiments. For example, the aspect ratio may be at least two. In some embodiments, the aspect ratio may be greater than 3 and greater than 5 in some such embodiments). For example, trench120may be five to ten micrometers wide and five to twenty micrometers deep in some embodiments. The width of trench120may be not more than ten micrometers. In some embodiments, the width of trench120does not exceed five micrometers. In some embodiments, trench120does not exceed one micrometer in width. Each of trenches120may have a height not exceeding fifteen micrometers. For example, in some embodiments, trench120may be at least five micrometers thick and not more than fifteen micrometers thick. In some such embodiments, the height of trench120may not be more than ten micrometers. The trench height may be at least three micrometers, and at least five micrometers in some embodiments. In some embodiments, the trench height is at least the distance a microwave mode for a microwave signal carried in the electrodes is expected to penetrate into the substrate. Other widths and/or heights are possible. The density of trenches120, distribution of trenches120, height and/or width of trenches, periodicity of the trenches120, and footprint of the trench region may also be tailored. Various configurations are possible depending upon the desired effective microwave index.

In some embodiments, trenches120are empty (e.g. may have a vacuum or air filling). If a vacuum fill is desired, the tops of trenches120are generally closed off. In other embodiments, trenches have another fill such as an insulator. In some embodiments, the fill for trenches120is insulating cladding. For example, the fill may be or include SiO2. In some embodiments, trenches120are completely filled, while in other embodiments trenches are not completely filled. For example, trench120may be partially filled with SiO2and partially filled with air or vacuum. Thus, in the region of the trenches120, the substrate has an effective microwave index. The effective microwave index corresponds to the substrate material (e.g. silicon and BOX layer102material) and the fill of trenches120(e.g. vacuum or cladding). For example, the effective microwave index for the region of trenches120may be a combination of the substrate microwave index and the trench microwave index (e.g. the microwave index for the fill of the trenches). In some embodiments, the effective microwave index is less than 3. In some such embodiments, the effective microwave index is not more than 2.5. In some embodiments, the effective microwave index is not more than 2.4. In some embodiments, the effective microwave index is not more than 2.3 and/or at least 2.1. Further, although indicating as extending only under a region adjacent to the sides of waveguide112, trenches120may extend a different distance. For example, additional trenches further from waveguide112and/or under waveguide112may be provided.

The use of trenches120(e.g. how trenches120are configured and laid out) as well as the fill (e.g. SiO2) allows the effective microwave index of the trench region to be tailored to be different than the microwave index of the substrate. Use of the effective index of refraction may improve performance of the device. In some configurations, substrates that may otherwise be unusable in the electro-optic device because of the substrate microwave index, may be incorporated into the electro-optic device. For example, silicon has a high microwave index. In some cases, the microwave index is close to 3.4. Use of a thick BOX layer (e.g. five through fifteen micrometers) allows the microwave mode to remain mostly or completely in the BOX layer. However, thinner BOX layers may be desired in some electro-optic devices. If BOX layer102is thin (e.g. approximately one micrometer thick) and no trench region is incorporated, a significant portion of the microwave mode experiences the microwave index of the silicon substrate. This may make velocity matching between the optical mode of TFLN and/or TFLT waveguide112(which may have an optical group index between 2 and 2.5, often approximately 2.2) and the microwave mode (which experiences a substrate microwave index of 3.4) of a signal carried by electrodes (not shown) challenging. In contrast, use of the trench region may provide an effective microwave index that may be in the ranges described herein. For example, the effective microwave index of the trench region may be determined by the fraction of the volume of the area of the trench region occupied by trenches120multiplied by the index of refraction of the fill (e.g. SiO2and/or vacuum) added to the fraction of the trench region occupied by substrate101multiplied by the index of refraction of substrate101added to the fraction of the trench region occupied by BOX layer102(if any) multiplied by the index of refraction of BOX layer102. The size of individual trenches, aspect ratio of individual trenches, and periodicity of trenches provides a density of trenches and, therefore, the fill. This provides the effective microwave index of the material (substrate material combined with the fill material). The aspect ratio and density (and/or other aspects of the trenches) in combination with the fill material may provide an effective microwave index that is (for example) not more than 2.3 for a straight electrode. In some embodiments, a smaller effective microwave index may be attained. This lower effective index may allow for other designs, such as the use of electrodes having extensions (or segments), which may slow the microwave down. In some embodiments, the effective trench region is configured to allow for a velocity mismatch between optical modes in the waveguide and microwave modes in the electrodes of not more than three percent. For example, waveguide112may have an optical mode index of at least 2.2 and not more than 2.3. In such embodiments, the trench region may have an effective index of not more than 3.37 and greater than 2.13.

Electro-optic device100ofFIG.1may have improved performance. The microwave index experienced by the microwave mode (not shown) includes the effective microwave index. The effective microwave index can be tailored to improve operation of the electro-optic device. For example, velocity matching between the optical signal carried by the waveguide and the microwave signal carried by the electrodes (not shown) may be improved. This may be achieved by configuring the size, density, and number of trenches120as well as the microwave index and amount of the fill used for trenches120. For example, a velocity mismatch of not more than three percent may be achieved. Further, the thickness of BOX layer120may be tailored (e.g.) based on considerations other than and/or in addition to the microwave mode. For example, BOX layer102may be thinner. Thus, performance may be improved.

FIG.2depicts a cross-sectional view of a portion of an embodiment of electro-optic device200including substrate201, insulator202(e.g. a BOX layer in the embodiment shown), and optical structure212(i.e. waveguide212in the embodiment shown).FIG.2is not to scale. The electro-optic device shown inFIG.2and the components therein are analogous to those shown inFIG.1. Thus, substrate201, BOX layer202, lithium-containing TFEO (or other) layer210, waveguide212, slab214(if present), and trenches220(including any fill) are analogous to substrate101, BOX layer102, lithium-containing TFEO (or other) layer110, waveguide112, slab114(if present), and trenches120(including any fill). However, the width of trenches220has been increased. Thus, trenches220having other widths may be used. Although the number of trenches220has been reduced, in some embodiments, more trenches may be present. Further, the height of trenches220may be changed.

Electro-optic device200ofFIG.2may share the benefits of electro-optic device100ofFIG.1. The microwave index experienced by the microwave mode (not shown) includes the effective microwave index. The effective microwave index can be tailored to improve operation of electro-optic device200by configuring trenches220and their fill (not shown). For example, velocity matching between the optical signal carried by the waveguide and the microwave signal carried by the electrodes (not shown) may be improved. Further, the thickness of the BOX layer may be tailored based on considerations other than and/or in addition to the microwave mode. Thus, performance may be improved.

FIG.3depicts a cross-sectional view of a portion of an embodiment of electro-optic device300including substrate301, insulator302(e.g. BOX layer302in the embodiment shown), and optical structure312(i.e. waveguide312in the embodiment shown).FIG.3is not to scale. Electro-optic device300shown inFIG.3and the components therein are analogous to those shown inFIGS.1-2. Thus, substrate301, BOX layer302, lithium-containing TFEO (or other) layer310, waveguide312, slab314(if present), and trenches320(including any fill) are analogous to substrate101and201, BOX layer102and202, lithium-containing TFEO (or other) layer110and210, waveguide112and212, slab114and214(if present), and trenches120and220(including any fill). In addition, fill340that partially fills trenches320has also been shown. Although shown as extending from the bottom of trenches320upward, fill340may extend inward from the sides of the trench320. This may occur when fill340is conformally deposited. Although depicted as partially filling trenches320, in some embodiments, fill340may entirely fill trenches320. In some embodiment, fill340may close the top of trenches320, but leave void(s) within one or more of trenches320. The fill may be insulating. The fill may be selected to have index(es) of refraction that provide the desired effective microwave index for the trench region and/or the substrate. Cladding (not shown) is typically present.

Electro-optic device300ofFIG.3may share the benefits of electro-optic device100and/or200ofFIGS.1-2. The microwave index experienced by the microwave mode (not shown) includes the effective microwave index. The effective microwave index can be tailored to improve operation of electro-optic device300. Further, the thickness of BOX layer302may be tailored (e.g.) based on considerations other than and/or in addition to the microwave mode. Thus, performance may be improved.

FIG.4depicts a cross-sectional view of a portion of an embodiment of electro-optic device400including substrate401, insulator402(e.g. BOX layer402in the embodiment shown), and optical structure412(i.e. waveguide412in the embodiment shown).FIG.4is not to scale. Electro-optic device400shown inFIG.4and the components therein are analogous to those shown inFIGS.1-3. Thus, substrate401, BOX layer402, waveguide412, and trenches420and420′ (including any fill) are analogous to substrate101,201, and301, BOX layer102,202, and302, waveguide112,212, and312, and trenches120,220, and320(including any fill). Waveguide412is shown as a channel waveguide, but may have another form (e.g. a ridge waveguide) in some embodiments, Electrode450are also explicitly shown. Although not explicitly depicted, trenches420and420′ may be partially or completely filled. In addition, in the embodiment shown, trenches420and420″ may have different heights, h and h′. In other embodiments, trenches420and420′ may have the same height. Although shown as having the same width, in some embodiments, trenches420and420′ may have different widths. Trenches420and420′ are shown as being not only between electrodes450and waveguide412, but also extending under electrodes450and being further from waveguide412than electrodes450are. In some embodiments, trenches420and420′ may extend under waveguide412. Other configurations of trenches420and420′ are possible. Waveguide412may be a TFLN and/or a TFLT waveguide. For a TFLN and/or TFLT waveguide, the trenches420may be desired to be completely filled to improve the adherence of the LN and/or LT layer to BOX layer402. In some embodiments, waveguide412may be a Si waveguide. Further, as discussed above, although depicted as a channel waveguide, the waveguide may be a ridge waveguide. Cladding (not shown) is typically present.

Also shown in the device ofFIG.4are electrodes450. For example, electro-optic device400may be an optical modulator. Electrodes450are configured to carry an electrical signal, typically in the microwave range. In some embodiments, electrodes450may include extensions and/or other structures. The extent of the microwave mode in substrate401and BOX layer402for one of electrodes450is shown. As can be seen inFIG.4, some or all of the microwave mode in substrate401may be in the same region as the trenches420and420′. As a result, some or all of the microwave mode in the substrate experiences an effective microwave index that is a combination of the microwave index due to the trenches (e.g. the fill in the trenches) and the substrate.

Electro-optic device400ofFIG.4may share the benefits of the electro-optic device(s)100,200, and/or300ofFIGS.1-3. The microwave index experienced by the microwave mode includes the effective microwave index due to a combination of trenches420and420′ and substrate401. The characteristics of trenches420and420′, the fill, and substrate401can be selected such that the effective microwave index enhances performance. Further, the thickness of BOX layer402may be tailored (e.g.) based on considerations other than and/or in addition to the microwave mode. Thus, performance may be improved.

FIG.5depicts a cross-sectional view of a portion of an embodiment of electro-optic device500including substrate501, an insulator502(e.g. BOX layer502in the embodiment shown), and optical structure512(i.e. waveguide512in the embodiment shown).FIG.5is not to scale. The electro-optic device500shown inFIG.5and the components therein are analogous to those shown inFIGS.1-4. Although not explicitly indicated, trenches520may be partially or completely filled. Waveguide512may be a TFLN and/or a TFLT waveguide. For a TFLN and/or TFLT waveguide, trenches520may be desired to be completely filled to improve the adherence of the LN and/or LT layer to BOX layer502. In some embodiments, waveguide512may be a Si waveguide. Further, as discussed above, although depicted as a channel waveguide, waveguide502may be a ridge waveguide. Cladding (not shown) is typically present.

Trenches520inFIG.5do not extend through BOX layer502. In some embodiments, trenches520may be formed prior to BOX layer502. In other embodiments, the trenches520may be formed after the BOX layer502and apertures (not shown) in BOX layer502refilled.

Electro-optic device500ofFIG.5may share the benefits of electro-optic device(s)100,200,300, and400ofFIGS.1-4. The microwave index experienced by the microwave mode includes the effective microwave index due to a combination of trenches520and substrate501. The characteristics of trenches520, the fill (not shown), and substrate501can be selected such that the effective microwave index enhances performance. For example, velocity matching between the optical signal carried by waveguide512and the microwave signal carried by the electrodes (not shown) may be improved. Further, the thickness of BOX layer502may be tailored (e.g.) based on considerations other than and/or in addition to the microwave mode. Thus, performance may be improved.

FIG.6depicts a cross-sectional view of a portion of an embodiment of heterogeneous integrated electro-optic device600.FIG.6is not to scale. Heterogeneous integrated electro-optic device includes substrate601, insulator602(e.g. BOX layer602in the embodiment shown), and an optical structure612(i.e. waveguide680directly on BOX layer602in the embodiment shown) that are analogous to those shown inFIGS.1-5. Waveguide680residing directly on BOX layer602is a Si waveguide in the embodiment shown. The heterogeneous integrated electro-optic device600also includes additional insulator670on BOX layer602and Si waveguide680, electrodes650, and a TFLN and/or TFLT waveguide612. Cladding (not shown) is typically present and covers the TFLN/TFLT waveguide612and electrodes650. Also indicated is the microwave mode for the electrodes.

Trenches620, BOX layer602, and waveguide are formed680. After formation of the Si waveguide680, the additional insulator670may be provided on BOX layer602. Additional insulator670may also be SiO2. In some embodiments, the combination of BOX layer602and additional insulator670have a thickness in the ranges described for BOX layer102,202,302,402, and502. Other thicknesses are possible. To form TFLN/TFLT waveguide612, a layer of LN (and/or LT) may be provided on the insulator670. The TFLN and/or TFLT are etched to form optical structures such as the TFLN/TFLT waveguide612. Electrodes650and cladding are also provided. Thus, a heterogeneous integrated Si and TFLN/TFLT electro-optic device600may be formed.

Electro-optic device600ofFIG.6may share the benefits of the electro-optic device ofFIGS.1-5. The microwave index experienced by the microwave mode includes the effective microwave index due to a combination of trenches620and substrate601. The characteristics of trenches620, the fill, and substrate601can be selected such that the effective microwave index enhances performance. For example, velocity matching between the optical signal carried by the waveguide612and the microwave signal carried by the electrodes650may be improved. Further, the thickness of BOX layer602may be tailored (e.g.) based on considerations other than and/or in addition to the microwave mode. Moreover, a SiPh device and a TFLN/TFLT electro-optic device may be integrated. Thus, performance may be improved.

FIGS.7A and7Bdepict cross-sectional views of portions of embodiments of electro-optic devices700and700′, respectively. Electro-optic devices700and700′ each include substrate701, insulator702(e.g. BOX layer702in the embodiment shown), and optical structures712or712′ (i.e. waveguides712and712′ in the embodiment shown). Cladding (not shown) is typically present.FIGS.7A-7Bare not to scale. The electro-optic devices700and700′ shown inFIGS.7A-7Band the components therein are analogous to those shown inFIGS.1-6. Although not explicitly depicted, trenches720may be partially or completely filled. Additional insulator770on the BOX layer and under waveguide712and adjacent to waveguide712′ is also shown.

In the embodiment shown, trenches720are shown as being not only between the electrodes750and the waveguides712and712′, but also extending under the waveguide(s)712or712′. Trenches720may also have height (or a depth) of at least five micrometers and not more than fifteen micrometers. Other heights are possible. Other configurations of the trenches720(e.g. heights, widths, number, and/or location) are possible. The waveguide(s)712and/or723′ may be TFLN and/or TFLT waveguides. The additional insulator may improve the adherence of the LN and/or LT layer to BOX layer702. In some embodiments, the waveguide712and/or712′ are channel waveguides. In other embodiments, the waveguide712and/or712′ may be a ridge waveguide. Also shown in the device ofFIG.7are electrodes750. For example, electro-optic devices700and700′ may be TFLN/TFLT optical modulators. Electrodes730are configured to carry an electrical signal, typically in the microwave range. In some embodiments, electrodes750may include extensions and/or other structures.

Electro-optic devices700and700′ ofFIGS.7A and7Bmay share the benefits of the electro-optic device100,200,300,400,500, and/or600ofFIGS.1-6. The microwave index experienced by the microwave mode includes the effective microwave index due to a combination of trenches720and substrate701. The characteristics of trenches720, the fill, and substrate701can be selected such that the effective microwave index enhances performance. Further, the thickness of BOX layer702may be tailored (e.g.) based on considerations other than and/or in addition to the microwave mode. Thus, performance may be improved.

FIG.8depicts a plan view of a portion of an embodiment of electro-optic device800including a substrate (not explicitly shown), an insulator (not explicitly shown), optical structure812(i.e. waveguide812in the embodiment shown), and electrodes850including extensions852. Cladding (not shown) is typically present.FIG.8is not to scale. The electro-optic device800shown inFIG.8and the components therein are analogous to those shown inFIGS.1-7. Although not explicitly depicted, trenches820may be partially or completely filled. Trenches820are depicted as being between extensions852and having a circular footprint. Other configurations of trenches820are possible. Waveguide812may be a TFLN and/or a TFLT waveguide. For a TFLN and/or TFLT waveguide, trenches820may be desired to be completely filled to improve the adherence of the LN and/or LT layer to the BOX layer. As discussed above, although depicted as a channel waveguide, waveguide812may be a ridge waveguide.

Electro-optic device800ofFIG.8may share the benefits of the electro-optic devices100,200,300,400,500,600,700, and/or700′ ofFIGS.1-7B. The microwave index experienced by the microwave mode includes the effective microwave index due to a combination of trenches820and the substrate. The characteristics of trenches820, the fill, and the substrate can be selected such that the effective microwave index enhances performance. For example, velocity matching between the optical signal carried by waveguide812and the microwave signal carried by electrodes850may be improved. Velocity matching may be further improved through the use of extensions852on electrode850. The thickness of the BOX layer may be tailored (e.g.) based on considerations other than the microwave mode. Thus, performance may be improved.

FIG.9depicts a plan view of a portion of an embodiment of electro-optic device900including a substrate (not explicitly shown), an insulator (not explicitly shown), optical structure912(i.e. a waveguide in the embodiment shown), and electrodes950including extensions952and channel regions954. Cladding (not shown) is typically present.FIG.9is not to scale. The electro-optic device900shown inFIG.9and the components therein are analogous to those shown inFIGS.1-8. Although not explicitly depicted, trenches920may be partially or completely filled. Trenches are depicted as having a circular footprint. Trenches920also extend under the channel region954of electrodes950as well as under extensions952. Other configurations of trenches920are possible. Waveguide912may be a TFLN and/or a TFLT waveguide. For a TFLN and/or TFLT waveguide, trenches920may be desired to be completely filled to improve the adherence of the LN and/or LT layer to the BOX layer. As discussed above, although depicted as a channel waveguide, waveguide912may be a ridge waveguide.

The electro-optic device900ofFIG.9may share the benefits of the electro-optic device(s) ofFIGS.1-8. The microwave index experienced by the microwave mode includes the effective microwave index due to a combination of trenches920and the substrate. The characteristics of trenches920, the fill, and the substrate can be selected such that the effective microwave index enhances performance. The thickness of the BOX layer may be tailored (e.g.) based on considerations other than and/or in addition to the microwave mode. Thus, performance may be improved.

FIG.10depicts a plan view of a portion of an embodiment of electro-optic device1000including a substrate (not explicitly shown), an insulator (not explicitly shown), optical structure1012(i.e. waveguide1012in the embodiment shown), and electrodes1050including extensions1052. Cladding (not shown) is typically present.FIG.10is not to scale. The electro-optic device1000shown inFIG.10and the components therein are analogous to those shown inFIGS.1-9. Although not explicitly depicted, trenches1020may be partially or completely filled. Trenches1020are depicted as having circular or oval footprint. Thus, in addition to trenches1020having varying heights, widths, and locations, the footprint(s) of trenches1020may vary. Thus, other configurations of trenches1020are possible. Waveguide1012may be a TFLN and/or a TFLT waveguide. For a TFLN and/or TFLT waveguide, trenches1020may be desired to be completely filled to improve the adherence of the LN and/or LT layer to the BOX layer. As discussed above, although depicted as a channel waveguide, waveguide1012may be a ridge waveguide.

The electro-optic device1000ofFIG.10may share the benefits of the electro-optic devices100,200,300,400,500,600,700,700′,800, and900ofFIGS.1-9. The microwave index experienced by the microwave mode includes the effective microwave index due to a combination of trenches1020and the substrate. The characteristics of trenches1020, the fill, and the substrate can be selected such that the effective microwave index enhances performance. For example, velocity matching between the optical signal carried by waveguide1012and the microwave signal carried by electrodes1050may be improved. Velocity matching may be further improved through the use of extensions1052on electrodes950. The thickness of the BOX layer may be tailored (e.g.) based on considerations other than the microwave mode. Thus, performance may be improved.

FIG.11is a flow-chart depicting method1100for providing an optical device. Method1100is described in the context of processes that may have sub-processes. Although described in a particular order, another order not inconsistent with the description herein may be utilized.

Trenches are provided in a substrate, at1102. In some embodiments,1102may be performed photolithographically. For example, providing the trenches may include masking the substrate and etching the trenches into the substrate. The trenches may optionally be filled, at1104. In some embodiments,1104may be skipped. The filling at1104may partially or completely fill the trench. In some embodiments, the fill is conformally grown on the trench (e.g. at least partially from the walls of the trench inward). Thus, even if filled, the trench may have voids therein.

An insulator is provided In the substrate, at1106. The insulator is used for the BOX layer. Providing the insulator at1106may include cladding the substrate with an insulating layer and planarizing the insulating layer. In some embodiments,1106is performed before the etching of the trenches at1102. In such embodiments, the trenches may extend through the insulator. One or more optical structures are provided, at1108. For example, a lithium-containing TFEO waveguide may be formed. In some embodiments, another structure such as a SiPh waveguide might be fabricated. Electrodes for the waveguide may be formed at1110. Additional structures may also be provided, at1112. For example, if a SiPh waveguide is formed at1108,1112may include providing an insulating layer on the SiPh waveguide and fabricating a lithium containing TFEO layer therein.

Using method1100, an electro-optic device having a tailored microwave index of refraction may be provided. Thus, electro-optic device(s)100,200,300,400,500,600,700,700′,800,900,1000, and/or some combination of feature(s) thereof may be formed. The electro-optic devices so formed may share the benefits of the electro-optic devices described herein. The microwave index experienced by the microwave mode includes the effective microwave index due to a combination of trenches formed at1102and the substrate. The characteristics of trenches, the fill provided at1104(if any), and the substrate can be selected such that the effective microwave index enhances performance. For example, velocity matching between the optical signal carried by the waveguides and the microwave signal carried by the electrodes may be improved. Velocity matching may be further improved through the use of extensions on the electrodes. The thickness of the BOX layer may be tailored (e.g.) based on considerations other than the microwave mode. Thus, performance of the optical devices may be improved.