Phase modulator apparatus and method

Abstract

Embodiments of the present disclosure relate to a phase modulator device and method, the method comprising the steps of: a) forming a waveguide from a first material, the waveguide being configured to guide an optical signal; b) forming a layer made of a second material, the second material being electrically conductive and transparent to the wavelength of the optical signal, steps a) and b) being implemented such that the layer made of the second material is in contact with at least one of the faces of the waveguide, or such that the layer made of the second material is separated from at least one of the faces by a distance which is less than half, preferably less than a quarter, of the wavelength of the optical signal. The present application further relates to a phase modulator, in particular obtained by such a method.

Description

[0001] Cross Reference to Related Applications

[0002] This application claims the benefit of French application No. 1909284, filed on August 19, 2019, which is incorporated by reference herein. TECHNICAL FIELD

[0003] The present disclosure relates generally to photonic integrated circuits and methods, and more particularly to phase modulator devices and methods. BACKGROUND

[0004] Known photonic integrated circuits comprise a phase modulator provided with a waveguide and a heating element. The heating element, which is usually a metal layer portion, is configured to modify the temperature of the material of the waveguide in a controlled manner and thus to change the effective optical index of the signal propagating in the waveguide. When a control current circulates in the portion of the metal layer constituting the heating element, this causes a corresponding increase of its temperature due to the Joule effect and thus a corresponding increase of the temperature of the waveguide located in the vicinity of the heating element. The article entitled “SiN integrated photonics for near-infrared LIDAR” by Tyler et al. published in IEEE CPMT Symposium Japan (ICSJ) 2018, pages 1-4, discloses a phase modulator comprising a waveguide and a heating element configured to modify the temperature of the waveguide. The heating element is a metal layer portion. The waveguide is made of silicon nitride. The heating element is configured to modify the temperature of the waveguide in a controlled manner and thus to change the effective optical index of the signal propagating in the waveguide. When a control current circulates in the portion of the metal layer constituting the heating element, this causes a corresponding increase of its temperature due to the Joule effect and thus a corresponding increase of the temperature of the waveguide located in the vicinity of the heating element. Figure 2 One example of such a modulator is shown. SUMMARY

[0005] There is a need to solve all or some of the drawbacks of known phase modulators comprising a waveguide and a heating element configured to modify the temperature of the waveguide.

[0006] One embodiment solves all or some of the drawbacks of known phase modulators comprising a waveguide and a heating element configured to modify the temperature of the waveguide, in particular when the waveguide is made of silicon nitride.

[0007] Another embodiment provides a method for manufacturing a device, in particular a phase modulator, comprising a waveguide and a heating element configured to change the temperature of the waveguide, in particular when the waveguide is made of silicon nitride.

[0008] One embodiment provides a manufacturing method comprising the following steps:

[0009] a) forming a waveguide made of a first material, the waveguide being configured to guide an optical signal;

[0010] b) forming a layer made of a second material, the second material being electrically conductive and transparent to the wavelength of the optical signal,

[0011] Steps a) and b) are implemented so that the layer made of the second material is in contact with at least one of the faces of the waveguide, or the layer made of the second material is separated from at least one of the faces by a distance which is less than half the wavelength of the optical signal, preferably less than a quarter of the wavelength of the optical signal.

[0012] According to one embodiment, step a) is completed before step b).

[0013] According to one embodiment:

[0014] Step a) comprises the following successive steps:

[0015] a1) depositing a layer made of the first material on the first layer made of the third material, and

[0016] a2) etching the layer made of the first material to define the waveguide therein; and

[0017] In step b), the layer made of the second material is deposited on the exposed face of the waveguide and in contact with the exposed face, or the layer made of the second material is deposited on an intermediate layer and in contact with the intermediate layer, the thickness of the intermediate layer being equal to the distance mentioned above, and the intermediate layer having been previously deposited on the exposed face of the waveguide and in contact with the exposed face.

[0018] According to one embodiment:

[0019] Before step a), the method comprises a step of etching a cavity in the first layer made of the third material;

[0020] Step a) comprises the following successive steps:

[0021] a1) depositing a layer made of the first material so as to fill the cavity, and

[0022] a2) performing a mechanical chemical planarization until the layer made of the third material, a portion of the layer made of the first material being left in place in the cavity, forms the waveguide; and

[0023] In step b), the layer made of the second material is deposited on the exposed face of the waveguide and in contact with the exposed face, or the layer made of the second material is deposited on an intermediate layer and in contact with the intermediate layer, the thickness of the intermediate layer being equal to the distance mentioned above, and the intermediate layer having been previously deposited on the exposed face of the waveguide and in contact with the exposed face.

[0024] According to one embodiment:

[0025] Before step a), the method comprises a step of depositing another layer made of the second material; and

[0026] In step a1), a layer made of a first material is deposited on and in contact with another layer made of a second material, or a layer made of a first material is deposited on and in contact with another intermediate layer equal in thickness to the above-mentioned distance, and previously deposited on and in contact with another layer made of a second material.

[0027] According to one embodiment, the method further comprises, after step b), a step comprising depositing a second layer made of a third material, and a step comprising forming a conductive via through the second layer made of a third material, up to portions of the layer made of a second material.

[0028] According to one embodiment, step b) is completed before step a).

[0029] According to one embodiment:

[0030] In step b), a layer made of a second material is deposited on a first layer made of a third material; and

[0031] Step a) comprises the following successive steps:

[0032] a1) depositing a layer made of a first material on and in contact with a layer made of a second material, or depositing a layer made of a first material on and in contact with an intermediate layer equal in thickness to the above-mentioned distance, and previously deposited on and in contact with a layer made of a second material,

[0033] a2) etching the layer made of a first material to define a waveguide therein.

[0034] According to one embodiment:

[0035] Before step b), the method comprises a step comprising etching a cavity in the first layer made of a third material;

[0036] In step b), a layer made of a second material is deposited on the walls and the bottom of the cavity, and

[0037] Step a) comprises the following successive steps:

[0038] a1) filling the cavity by depositing a layer made of a first material on and in contact with a layer made of a second material, or depositing a layer made of a first material on and in contact with an intermediate layer having a thickness equal to the above-mentioned distance, and previously deposited on and in contact with a layer made of a second material; and

[0039] a2) performing mechanical chemical planarization at least until the layer made of the second material, a portion of the layer made of the first material being left in place in the cavity, forms a waveguide.

[0040] According to one embodiment, the method further comprises, after step a), a step of depositing another layer made of the second material on and in contact with the one or more exposed faces of the waveguide, or of depositing another layer made of the second material on and in contact with another intermediate layer having a thickness equal to the distance, the other intermediate layer being previously deposited on and in contact with the one or more exposed faces of the waveguide.

[0041] According to one embodiment, the method further comprises, after step a), a step of depositing a second layer made of a third material, and a step of forming a conductive via through the second layer made of the third material, up to the second material.

[0042] According to one embodiment, the first material is silicon nitride and the second material is indium tin oxide or amorphous carbon, the wavelength preferably being between 450 nm and 1 pm, for example substantially equal to 905 nm, preferably equal to 905 nm.

[0043] Another embodiment provides a phase modulator comprising:

[0044] a waveguide of a first material, the waveguide being configured to propagate an optical signal; and

[0045] a layer of a second material that is electrically conductive, the second material being transparent to the wavelength of the optical signal, the layer of the second material being in contact with at least one of the faces of the waveguide or being separated from at least one of the faces by a distance that is less than half the wavelength of the optical signal, preferably less than a quarter of the wavelength of the optical signal.

[0046] According to one embodiment, the first material is silicon nitride and the second material is indium tin oxide or amorphous carbon, the wavelength preferably being between 450 nm and 1 pm, for example substantially equal to 905 nm, preferably equal to 905 nm.

[0047] According to one embodiment, the modulator further comprises a layer of a thermally and electrically insulating material, preferably SiOC, the layer of the second material being interposed between the waveguide and the layer of the thermally and electrically insulating material.

[0048] According to one embodiment, the modulator is obtained by performing the method described herein above.

[0049] According to one embodiment, the layer of the second material comprises an upper portion and / or a lower portion, the upper portion resting on a top face of the waveguide and a bottom face of the waveguide resting on the lower portion.

[0050] According to one embodiment, the layer of second material further comprises, for each side of the waveguide, a side portion facing the side.

[0051] According to one embodiment, the layer of second material comprises a contact portion extending laterally on either side of the waveguide, each contact portion being configured to contact at least one conductive via.

[0052] Another embodiment provides a photonic integrated circuit comprising:

[0053] a semiconductor layer of the semiconductor-on-insulator (SOI) type, in and / or on which the components are defined;

[0054] an interconnection structure positioned above the semiconductor layer and configured to electrically connect the components; and

[0055] a modulator as described above, positioned in an insulating layer of the interconnection structure, the insulating layer comprising silicon oxide. BRIEF DESCRIPTION OF DRAWINGS

[0056] The above features and advantages, and other features and advantages, will be described in detail in the following description, given by way of example and not limitation, with reference to the accompanying drawings, in which:

[0057] Figure 1 a schematic cross-sectional view illustrating successive steps of one embodiment of a method for manufacturing a phase modulator is shown;

[0058] Figure 2 a schematic cross-sectional view illustrating successive steps of another embodiment of a method for manufacturing a phase modulator is shown;

[0059] Figure 3 a schematic cross-sectional view illustrating successive steps of one embodiment of a method for manufacturing a phase modulator is shown; Figure 3 a schematic cross-sectional view illustrating successive steps of one embodiment of a method for manufacturing a phase modulator is shown;

[0060] Figure 4 a schematic cross-sectional view illustrating successive steps of another embodiment of a method for manufacturing a phase modulator is shown;

[0061] Figure 5 a schematic cross-sectional view illustrating successive steps of another embodiment of a method for manufacturing a phase modulator is shown;

[0062] Figure 6 a schematic cross-sectional view illustrating successive steps of another embodiment of a method for manufacturing a phase modulator is shown;

[0063] Figure 7a schematic cross-sectional view illustrating successive steps of a method for manufacturing a phase modulator is shown; and

[0064] Figure 8 a schematic cross-sectional view illustrating one embodiment of a photonic integrated circuit comprising a phase modulator is shown. DETAILED DESCRIPTION

[0065] In the various drawings, like features have been designated by like reference numerals. In particular, structural and / or functional features that are common between various embodiments can have the same reference numerals and can be provided with the same structure, dimensions, and material properties.

[0066] For the sake of clarity, only the operations and elements that are useful for understanding the embodiments described herein have been illustrated and described. In particular, the operation of the photonic integrated circuits has not been described in detail, the described embodiments being compatible with the operation of typical photonic integrated circuits, in particular comprising a phase modulator. Moreover, various applications that can be provided with the photonic integrated circuits, in particular comprising a phase modulator, have not been described, the described embodiments being compatible with typical applications that provide such photonic integrated circuits. An exemplary circuit in which the modulator described below can be provided is an optical phased array (OPA).

[0067] Unless otherwise stated, when referring to two elements connected together, it is meant a direct connection without any intermediate element other than a conductor, and when referring to two elements coupled together, it is meant that the two elements can be connected or they can be coupled via one or more other elements.

[0068] In the following disclosure, unless otherwise stated, when referring to an absolute position qualifier (e.g. the terms “front”, “back”, “top”, “bottom”, “left”, “right”, etc.) or a relative position qualifier (e.g. the terms “above”, “below”, “upper”, “lower”, etc.) or an orientation qualifier (e.g. “horizontal”, “vertical”, etc.), reference is made to the orientation shown in the figures.

[0069] Unless otherwise stated, the expressions “about”, “approximately”, “substantially” and “in the order of” mean within 10%, preferably within 5%.

[0070] Here, the inventors propose to produce an apparatus comprising an optical waveguide of a first material and a heating element in the form of one or more portions of a layer of a second material, the heating element being in direct contact with the waveguide of the apparatus or at a small distance from the waveguide, for example at a distance smaller than half the wavelength of the optical signal, preferably smaller than a quarter of the wavelength of the optical signal, the waveguide being configured to propagate the optical signal. More particularly, the heating element covers at least one face of the waveguide.

[0071] In the rest of the present description, as a non-limiting example, the case is considered in which the phase modulator comprises a waveguide made of silicon nitride, configured to guide an optical signal having a wavelength comprised between 450 nm and 1 pm, for example substantially equal to 905 nm, preferably equal to 905 nm.

[0072] Figure 1 schematized cross-section views A, B and C illustrating successive steps of one embodiment of a method for manufacturing a phase modulator 1 Figure 1 schematized cross-section views A, B and C illustrating successive steps of one embodiment of a method for manufacturing a phase modulator 1

[0073] In the step illustrated in view A of the figure, a waveguide 100 made of a first material (for example, silicon nitride) has been formed on a first layer 102 made of a third material (for example, silicon oxide). In this example, the waveguide 100 is a strip waveguide, or in other words, it lacks lateral fins as in the case of a rib or ridge waveguide. Figure 1

[0074] In this embodiment, the waveguide 100 is formed by depositing a layer 104 made of the first material on the entire top surface of the layer 102, then the waveguide 100 is defined in the layer 104 by the successive steps of masking the layer portion 104 configured to form the waveguide 100, and removing the unmasked portions of the layer 104 by etching.

[0075] According to one embodiment, the layer 104 is formed directly on the layer 102. The waveguide 100 is then in contact with the layer 102, and more particularly, the bottom face of the waveguide 100 is in contact with the upper face of the layer 102.

[0076] In the step illustrated in view B of the figure, a layer 106 made of a second material has been deposited on and in contact with the exposed faces of the waveguide 100. More particularly, the layer 106 comprises a portion 106s covering the top face of the waveguide 100, the portion 106s being in contact with the top face of the waveguide, and two side portions 106l covering the two side faces of the waveguide 100, each portion 106l being in contact with a respective side face of the waveguide 100 and with the portion 106s. Figure 1

[0077] ​​In this embodiment, layer 106 further includes two portions 106c located on either side of waveguide 102, the two portions 106c resting on layer 102. In the transverse cross-sectional plane of waveguide 100 (i.e., in a cross-section orthogonal to the longitudinal direction of waveguide 100), each portion 106c extends laterally from the corresponding portion 106l.

[0078] Preferably, layer 106 is uniformly deposited on Figure 1 View A shows the entire exposed surface of the structure (solid plate deposition), and an etching mask is formed on the left-in-place portions 106s, 106l, and 106c of layer 106. The exposed (unmasked) portions of layer 106 are then removed by etching.

[0079] The material of layer 106, or the second material, is conductive. Furthermore, the second material is transparent to the wavelength of a signal configured to propagate in a guided manner within waveguide 100. Throughout this specification, it is considered, for example, that a material is transparent to a given wavelength if, at that given wavelength, the imaginary part of the material's refractive index is less than or equal to 0.01, preferably less than or equal to 0.005.

[0080] Preferably, the real part of the refractive index of the second material is less than or equal to the real part of the refractive index of the waveguide 100 material, and the material of the waveguide 100 participates in the guided propagation of the optical signal in the waveguide 100.

[0081] In this example, waveguide 100 is made of silicon nitride and configured to guide signals having wavelengths between 450 nm and 1 μm (e.g., substantially equal to 905 nm, preferably equal to 905 nm), and the second material is preferably indium tin oxide (ITO) or, for example, amorphous carbon.

[0082] exist Figure 1 In the step shown in view C, a second layer 108 made of a third material has been deposited to cover... Figure 1 The structure is illustrated in view B. Therefore, waveguide 100 and layer 106 are embedded in a layer of third material, which includes, and preferably consists of, a first layer 102 and a second layer 108 made of the third material.

[0083] Preferably, layer 108 is deposited on Figure 1 The entire structure shown in view B is deposited (solid plate deposition). Preferably, layer 108 is deposited with a thickness greater than the thickness of the stack of waveguide 100 and the portion 106s covering the top surface of waveguide 100. Preferably, the step of planarizing the top surface of layer 108 (e.g., by chemical mechanical polishing (CMP)) is provided after the deposition of layer 108.

[0084] In addition, Figure 1 In the steps illustrated in view C, after the deposition of layer 108 is the step of forming conductive vias 110 (e.g., metallic vias 110). Vias 110 are formed on either side of waveguide 100 considered along its length. In other words, in a cross-sectional plane transverse to waveguide 100, one via 110 is formed on one side of a first side of waveguide 100 (e.g., on the right side of view C), and another via 110 is formed on one side of another side of waveguide 100 (e.g., on the left side of view C). The vias 110 are formed through layer 108 up to a portion 106c of layer 106. More precisely, at least one via 110 contacts the portion 106c located on one side of waveguide 100 (e.g., on the right side of view C), and at least another via 110 contacts the portion 106c located on the other side of waveguide 100 (e.g., on the left side of view C).

[0085] During operation, when a voltage is applied between two vias 110 respectively located on either side of waveguide 100, current circulates in layer 106. This causes layer 106 to heat up, thus increasing the temperature of waveguide 100. This modulates the optical index of waveguide 100 and thus modulates the optical signal propagating therein. Preferably, the voltage is applied between one or more first vias 110 located at a first end of waveguide 100 along its length direction located in the modulator, and one or more second vias 110 located at a second end of waveguide 100 along its length direction located in the modulator.

[0086] In this embodiment, layer 106 thus forms the heating element of modulator 1. Furthermore, in this embodiment, three surfaces (side and top surfaces) of waveguide 100 are covered by and in contact with layer 106. In other words, in this embodiment, the heating element of modulator 1 includes: an upper portion 106s in contact with the top surface of waveguide 100, two side portions 106l in contact with corresponding side surfaces of waveguide 100, and two contact portions 106c that contact corresponding vias 110 configured to receive control voltage from the modulator.

[0087] With respect to the case of a modulator in which the heating element is metallic, the heating element 106 of the modulator 1 is transparent to the considered wavelength and can thus be positioned in direct contact with at least one face of the waveguide 100 of the modulator. As a result, for the same power supplied to the heating element, the modulator 1 allows a higher modulation efficiency, measured along the propagation direction of the optical signal in the waveguide, compared to a modulator having the same waveguide and having a metallic heating element which must be positioned at a distance from the waveguide so as not to destroy the signal propagating in the waveguide.

[0088] Moreover, the modulator 1 is more compact compared to a modulator having the same waveguide but a metallic heating element which must be positioned at a distance from the waveguide so as not to destroy the signal propagating in the waveguide. In particular, for a given modulation efficiency and a given power supplied to the heating element, the modulator 1 is not as long as a modulator having the same waveguide but a heating element which is positioned at a distance from the waveguide.

[0089] In an embodiment variant not illustrated, in the step of view B, a layer of fourth thermally and electrically insulating material (for example SiOC) is deposited on the layer 106. This makes it possible to limit or even eliminate the increase in temperature in the waveguide positioned in the vicinity of the modulator 1 during heating of the layer 106.

[0090] Figure 2 The schematic cross-sectional views A, B and C are shown which illustrate the successive steps of another embodiment of the method of Figure 1 view C) of the modulator 1. Figure 2 view C) of the modulator 1.

[0091] In this embodiment, the layer 106 made of a second material is not deposited after the waveguide 100 is defined in the layer 104, the layer 200 made of a second material is deposited before the deposition of the layer 104, then the layer 104 is formed on and in contact with this layer 200.

[0092] In the step of view A of the method of Figure 2 In the step of view A of the method of

[0093] According to one embodiment, the layer 200 is formed directly on the layer 102, then the layer 200 is in contact with the layer 102.

[0094] In the step of view A of the method of Figure 2The waveguide 100 is defined in the layer 104 in steps illustrated in view B of figure 1, for example by successive masking and etching steps of the layer 104, similar to the steps described with respect to Figure 1 The etching of the layer 104 here stops on the layer 200.

[0095] Furthermore, in the steps illustrated in view B of figure 1, portions of the layer 200 have been removed by etching. During this etching, a portion 200i of the layer 200 is left in place under the lower face of the waveguide 100, and two portions 200c of the layer 200 are left in place on either side of the waveguide 100. In a cross-sectional plane transverse to the waveguide 100, each portion 200c extends laterally on a different side of the waveguide 100, starting from the portion 200i. As an example, the etching mask for this step covers the waveguide 100 and overflows laterally on either side of the waveguide 100 on the layer 200. Figure 2

[0096] Figure 2 View C of figure 1 illustrates the structure obtained after the steps described with respect to view C of figure 1 have been implemented, from the structure illustrated in view B of figure 1, here the conductive via 110 being formed up to the portions 200c, instead of up to the portion 106c described with respect to view B of figure 1. Figure 1 Figure 2 View C of figure 1 illustrates the structure obtained after the steps described with respect to view C of figure 1 have been implemented, from the structure illustrated in view B of figure 1, here the conductive via 110 being formed up to the portions 200c, instead of up to the portion 106c described with respect to view B of figure 1. Figure 1

[0097] In this embodiment, the heating element comprises a lower portion 200i in contact with the lower face of the waveguide 100, and two contact portions 200c in contact with the via 110. In this embodiment, a single face (the lower face) of the waveguide 100 is covered by the heating element.

[0098] Figure 2 The operation of the modulator of figure 1 is similar to the operation of the modulator of figure 1. Furthermore, with respect to the modulator comprising a metallic heating element, Figure 1 The modulator 1 of view C of figure 1 benefits from the same advantages as the modulator 1 of view C of figure 1. Figure 2 Figure 1 In an embodiment variant not illustrated, a layer made of a fourth material is deposited on the layer 102 before the deposition of the layer 200, the layer 200 being deposited on and in contact with this layer made of the fourth material, and / or a layer of the fourth material is deposited on the portions 200c and on the waveguide 100 before the steps of view C. Similarly to before, this can limit or even eliminate the increase in temperature in the waveguide positioned in the vicinity of the modulator 1 when the electrical current circulates in the heating element of the modulator.

[0099] View C of figure 1 illustrates the structure obtained after the steps described with respect to view C of figure 1 have been implemented, from the structure illustrated in view B of figure 1, here the conductive via 110 being formed up to the portions 200c, instead of up to the portion 106c described with respect to view B of figure 1.

[0100] Figure 3 View C of figure 1 illustrates the structure obtained after the steps described with respect to view C of figure 1 have been implemented, from the structure illustrated in view B of figure 1, here the conductive via 110 being formed up to the portions 200c, instead of up to the portion 106c described with respect to view B of figure 1.​​​​Figure 2 the steps of the embodiment variant of the method of Fig. 1 1, and more specifically about the steps described with reference to the views A of Fig. 1 1. Figure 2 schematic cross-sectional views of the steps described with reference to the views A of Fig. 1 1. Figure 3 The cross-sectional views of Fig. 1 1 are taken in a cross-sectional plane orthogonal to the longitudinal direction of the modulator.

[0101] In this variant, the layer 200 is etched before the deposition of the layer 104, so as to leave only the portions 200i and 200c of the layer 200 in place.

[0102] The other steps of this variant are similar or identical to those described with reference to the embodiment of Fig. 1 1, and lead to obtaining the modulator 1 as illustrated in the view C of Fig. 1 1. Figure 2 Figure 2 The view C of Fig. 1 1 illustrates the structure obtained after the steps described with reference to the view C of Fig. 1 1.

[0103] Figure 4 schematic cross-sectional views A, B and C illustrating successive steps of another embodiment of the method for manufacturing the modulator 1 (view C of Fig. 1 1 ) are shown. The cross-sectional views A, B and C are taken in a cross-sectional plane orthogonal to the longitudinal direction of the modulator 1. Figure 4 This embodiment corresponds to a combination of the embodiment described with reference to the views A of Fig. 1 1 and the embodiment described with reference to the views B of Fig. 1 1.

[0104] Figure 1 In this embodiment, what is provided is that the layer 200 is deposited before the formation of the waveguide 100, and then the layer 106 is deposited after the formation of the waveguide 100. Figure 2 Figure 3 In the steps illustrated in the view A of Fig. 1 1, the steps described with reference to the views A and B of Fig. 1 1 have been implemented, with the difference that only the portion 200i of the layer 200 is left in place. As one example, the same etching mask is used to define the waveguide 100 in the layer 104 and to etch the layer 106.

[0105] In the steps illustrated in the view B of Fig. 1 1, the steps described with reference to the view B of Fig. 1 1 have been implemented, with the difference that only the portion 200i of the layer 200 is left in place. As one example, the same etching mask is used to define the waveguide 100 in the layer 104 and to etch the layer 106. Figure 4 Figure 2 The view B of Fig. 1 1 illustrates the structure obtained from the structure illustrated in the view A of Fig. 1 1 after the steps described with reference to the view B of Fig. 1 1 have been implemented.

[0106] Figure 4 The view C of Fig. 1 1 illustrates the structure obtained from the structure illustrated in the view B of Fig. 1 1 after the steps described with reference to the view C of Fig. 1 1 have been implemented. Figure 1 Figure 4 The view C of Fig. 1 1 illustrates the structure obtained from the structure illustrated in the view B of Fig. 1 1 after the steps described with reference to the view C of Fig. 1 1 have been implemented.

[0107] Figure 4 The view C of Fig. 1 1 illustrates the structure obtained from the structure illustrated in the view B of Fig. 1 1 after the steps described with reference to the view C of Fig. 1 1 have been implemented. Figure 1 Figure 4 The view C of Fig. 1 1 illustrates the structure obtained from the structure illustrated in the view B of Fig. 1 1 after the steps described with reference to the view C of Fig. 1 1 have been implemented.

[0108] ​​​​​​In this embodiment, the heating element of the modulator 1 comprises a lower portion 200i in contact with the bottom face of the waveguide 100, an upper portion 106s in contact with the top face of the waveguide 100, two lateral portions 106l in contact with the respective lateral faces of the waveguide 100, and two contact portions 106c in contact with the vias 110. The portions 106s and 200i are electrically linked in parallel through the portions 106l.

[0109] Figure 4 The operation of the modulator 1 is similar to the operation of the modulator of Figure 1 or Figure 2 However, compared to the modulator 1 of Figure 1 or Figure 2 the waveguide 100 of the modulator 1 of Figure 4 comprises more faces in contact with the heating element. Therefore, compared to the modulator 1 of Figure 1 or Figure 2 for the same voltage applied between the vias 110, the modulator 1 of Figure 4 allows a higher modulation efficiency. Moreover, compared to the temperature increase in the waveguide 100 of the modulator 1 of Figure 1 or Figure 2 the modulator 1 of Figure 4 allows a more uniform temperature increase in the waveguide 100.

[0110] Moreover, compared to a modulator comprising a metallic heating element, the modulator 1 of Figure 4 benefits from the same advantages as the modulator 1 of Figure 1 or Figure 2

[0111] In an embodiment variant not illustrated, the thickness of the layers 200 and 106 is configured to balance the electrical resistance of the electrically conductive path comprising the portions 106l, 106s of the layer 106 in contact with the waveguide 100, with the electrical resistance of the electrically conductive path comprising the portion 200i of the layer 200 in contact with the waveguide 100. This makes it possible to heat the waveguide 100 more uniformly.

[0112] In another embodiment variant not illustrated, a layer made of a fourth material is deposited on the layer 102, preferably on and in contact with the layer 200, before the deposition of the layer 200, and / or a layer made of a fourth material is deposited on, preferably in contact with, the layer 106. Similarly to before, this can limit or even eliminate the temperature increase in the waveguide positioned in the vicinity of the modulator 1 when the electric current circulates in the heating element of the modulator.

[0113] The modulator 1 of Figures 1-4 ​Embodiments and variations are described, wherein waveguide 100 is defined in layer 104 made of the material of waveguide 100, for example, by masking and etching steps. In these embodiments and variations, layer 200 is deposited prior to the formation of waveguide 100, and / or layer 106 is deposited after the formation of waveguide 100, thereby forming a heating element or heating layer in contact with at least one longitudinal surface of the waveguide by layers 106 and / or 200.

[0114] Other embodiments and variations will now be described, wherein waveguide 100 is formed by the following sequential steps: etching a cavity, depositing a layer made of waveguide material to fill the cavity, and CMP up to the top of the cavity. Similar to before, layer 200 is deposited before waveguide 100 is formed, and / or layer 106 is deposited after waveguide 100 is formed, thereby forming a heating element or heating layer by layers 106 and / or 200 that contacts at least one longitudinal surface (side, top, or bottom) of waveguide 100.

[0115] Figure 5 Schematic cross-sectional views A, B, C, and D are shown, illustrating the fabrication of phase modulator 1 ( Figure 5 The successive steps of another embodiment of the method (view D). Cross-sectional views A, B, C and D are taken in a cross-sectional plane orthogonal to the longitudinal direction of modulator 1.

[0116] exist Figure 5 In the step illustrated in view A, cavity 500 has been etched in layer 102. The dimensions of the cavity are determined by the waveguide 100 to be formed therein (in... Figure 5 The dimensions of the cavity 500 (which is not present in view A) are determined. Preferably, the dimensions of the cavity 500 are substantially equal to the dimensions of the waveguide 100.

[0117] Preferably, cavity 500 is etched from the top surface of layer 102 only on a portion of the thickness of layer 102, such that a portion of the thickness of layer 102 remains below the bottom of cavity 500.

[0118] exist Figure 5 In the steps illustrated in view B, layer 200, made of the second material, is preferably deposited uniformly over the entire exposed surface of layer 102 (solid plate deposition), thereby covering the bottom and walls of cavity 500. Then layer 104 is deposited to fill cavity 500. Layer 104 is deposited on and in contact with layer 200.

[0119] exist Figure 5In the step illustrated by view C, the portion of layer 104 located above the top level of cavity 500 (i.e. here the upper level of layer 200) has been removed by CMP until layer 200. The portion of layer 104 left in place in cavity 500 then forms waveguide 100 of the modulator. The bottom face and the lateral faces of waveguide 100 are then covered by the portion of layer 200 left in place in cavity 500. More specifically, the bottom face of waveguide 100 is in contact with portion 200i of layer 200, and the lateral faces of waveguide 100 are in contact with respective portions 20ol of layer 200. Portions 20ol are in contact with portion 200i.

[0120] Moreover, in the step illustrated by view C, the portion of layer 200 resting on layer 102 (i.e. layer 200 located outside cavity 500) has been removed by etching, leaving in place on layer 102 portions 200c of layer 200 positioned in a plane transverse to waveguide 100, respectively on either side of waveguide 100. Each portion 200c left in place is in contact with a corresponding portion 20ol, or in other words, each portion 200c extends laterally from a corresponding portion 20ol. Figure 5

[0121] As an example, this step for defining, by etching portions 200c in layer 200, is done using an etching mask covering the top face of waveguide 100 and extending laterally over layer 200, and more specifically over portions 200c of layer 200.

[0122] Figure 5 View D of the figure illustrates the structure obtained from the structure illustrated by view C of the figure after implementing the steps described with respect to the modulator of the figure. Figure 1 View C of the figure illustrates the structure obtained from the structure illustrated by view B of the figure after implementing the steps described with respect to the modulator of the figure. Figure 5 View C of the figure illustrates the structure obtained from the structure illustrated by view B of the figure after implementing the steps described with respect to the modulator of the figure.

[0123] In this embodiment, the heating element of modulator 1 comprises a lower portion 200i in contact with the bottom face of waveguide 100, two lateral portions 20ol in contact with respective lateral faces of waveguide 100, and two contact portions 200c in contact with vias 110. First portion 200c, first portion 20ol, portion 200i, second portion 20ol and second portion 200c are linked in series between vias 110.

[0124] Figure 5 The operation of the modulator of the figure is similar to the operation of the modulator of the figure. Figure 1 Moreover, with respect to the modulator comprising a metallic heating element,The modulator 1 of the figure benefits from the same advantages as the modulator 1 of the figure. Figure 5 Figure 1

[0125] ​​In an embodiment variant not illustrated, a layer made of a fourth material is deposited on the layer 102 before the deposition of the layer 200, the layer 200 is deposited on and in contact with this layer made of the fourth material, and / or between the step of view C and the step of view D, a layer of the fourth material is deposited on the portion 200c and the waveguide 100. Similarly to before, this makes it possible to limit or even eliminate the temperature rise in the waveguide located in the vicinity of the modulator 1 when the electrical current circulates in the heating element of the modulator.

[0126] Figure 6 The schematic cross-sectional views A and B are shown, which illustrate successive steps of a method for manufacturing the modulator 1 Figure 6 The cross-sectional views A and B are taken in a cross-sectional plane orthogonal to the longitudinal direction of the modulator 1.

[0127] In this embodiment, instead of depositing the layer 200 before the formation of the waveguide 100 in the cavity 500, a layer 106 made of a third material is deposited after the formation of the waveguide 100 in the cavity 500.

[0128] In the step illustrated by view A of Figure 6 , similarly to what is described with respect to view A of Figure 5 , the cavity 500 (not referenced in view A of Figure 6 ) has been etched in the layer 102, then similarly to what is described with respect to view B of Figure 5 , the layer 104 has been deposited to fill the cavity 500. The portion of the layer 104 located above the upper level of the cavity 500, i.e. here the top level of the layer 102, has been removed by CMP until the layer 102. Then, the portion of the layer 104 left in place in the cavity 500 forms the waveguide 100.

[0129] Moreover, in the step illustrated by view A of Figure 6 , the layer 106 has been deposited on the exposed faces of the structure, i.e. here on the top face of the waveguide 100 and on the exposed face of the layer 102.

[0130] The portions of the layer 106 have then been removed by etching. The etching is done so that the portions 106s of the layer 106 covering the top face of the waveguide 100, and the portions 106c of the layer 106 on either side of the waveguide 100 are left in place. The portions 106s are in contact with the top face of the waveguide. Each portion 106c extends laterally from the portion 106s.

[0131] Figure 6 View B of Figure 1 illustrates the structure obtained from the structure shown in view A of Figure 6 after implementing the steps described with respect to view C of

[0132] In this embodiment, the heating element of the modulator 1 comprises a contact portion 106c and an upper portion 106s. The first portion 106c, the portion 106s and the second portion 106c are linked in series between the vias 110.

[0133] Figure 6 The operation of the modulator is similar to the operation of the modulator Figure 1 . Moreover, with respect to the modulator comprising a metallic heating element, Figure 6 the modulator 1 benefits from the same advantages as the modulator 1 Figure 1 .

[0134] In an embodiment variant not illustrated, a layer made of a fourth material is deposited on the layer 106 before the deposition of the layer 108, and / or a layer made of a fourth material is deposited (solid plate) on the layer 102 between the etching of the cavity 500 and the deposition of the layer 104. In this latter case, after the deposition of the layer 104, a CMP step can be stopped on the layer of the fourth material deposited on the layer 102, or on the layer 102. Similarly to before, the deposition of one or two layers of the fourth material makes it possible to limit or even eliminate the temperature increase in the waveguide positioned in the vicinity of the modulator 1 when the electrical current circulates in the heating element of the modulator.

[0135] Figure 7 schematical cross-sectional views A, B, C and D are shown, which illustrate successive steps of another embodiment of a method for manufacturing the modulator 1 Figure 7 . The cross-sectional views A, B, C and D are taken in a cross-sectional plane orthogonal to the longitudinal direction of the modulator 1.

[0136] This embodiment corresponds to a combination of the embodiment described with respect to Figure 5 and the embodiment described with respect to Figure 6 . In other words, in this embodiment, what is provided is that the layer 200 is deposited before the waveguide 100 is formed, and then the layer 106 is deposited after the waveguide 100 is formed.

[0137] Figure 7 The views A and B of Figure 5 are identical to the corresponding views A and B of Figure 5 , and illustrate the same steps as described for the corresponding views A and B of

[0138] In the embodiment of Figure 7In the steps illustrated in view C, the portions of layers 200 and 104 positioned above the top level of cavity 500 (i.e., here above the top level of layer 102) have been removed by CMP down to layer 102. The portion of layer 104 remaining in situ in cavity 500 then forms the waveguide 100 of the modulator. The bottom and sides of waveguide 100 are then covered by the portion of layer 200 remaining in situ in cavity 500. More specifically, the bottom surface of waveguide 100 contacts portion 200i of layer 200, and the sides of waveguide 100 contact the corresponding portions 200l of layer 200. Portions 200l contact portions 200i.

[0139] It will be noted that, relative to about Figure 5 In the described embodiment, portion 200c of layer 200 is removed during the CMP step.

[0140] Still in Figure 7 In the step illustrated in view C, layer 106 is then formed on the entire exposed surface of the structure, i.e., on the top surface of waveguide 100 and the exposed surface of layer 102.

[0141] The portions of layer 106 are then removed by etching. The etching is performed such that the portion 106s of layer 106 covering the top surface of waveguide 100, and the portion 106c of layer 106 on either side of waveguide 100, remain in place. The portion 106s contacts the top surface of the waveguide. Each portion 106c extends laterally from the portion 106s. Furthermore, the top tip of each portion 200l of layer 200 contacts the corresponding portion 106c.

[0142] Figure 7 View D illustrates the implementation of... Figure 1 After the steps described in view C, from Figure 7 The structure obtained is shown in view C.

[0143] In this embodiment, the heating element of the modulator 1 includes: two side portions 200l covering corresponding sides of the waveguide 100, a lower portion 200i covering the bottom surface of the waveguide 100, an upper portion 106s covering the top surface of the waveguide 100, and two contact portions 106c contacting the vias 110. The portions 200i electrically connect the portions 200l to each other, and the portions 200l and 200i are connected in series. Furthermore, between the portions 106c, the collection of portions 200i and 200l is connected in parallel with the portion 106s, and each portion 106c is connected to a different via 110.

[0144] Figure 7 The operation of the modulator is similar to Figure 1 The operation of the modulator. Furthermore, compared to modulators that include metal heating elements, Figure 7 Modulator 1 benefits from withFigure 1 the modulator 1 of the same advantages.

[0145] In an embodiment variant not shown, a layer made of a fourth material is deposited on the layer 102, in particular in the cavity 500, before the deposition of the layer 200, and / or a layer made of a fourth material is deposited on the layer 106 before the deposition of the layer 108. Similarly to before, this can limit or even eliminate the temperature increase in the waveguide positioned in the vicinity of the modulator 1 when the electrical current circulates in the heating element of the modulator.

[0146] Figure 8 A cross-sectional view illustrating one embodiment of a photonic integrated circuit 8 comprising a modulator 1 as previously described is shown. More specifically, in this example, the modulator 1 is of the type shown in view C of Fig. 1. Figure 4

[0147] The circuit 8 comprises a substrate 800 covered by an insulating layer 802, which in turn is covered by a semiconductor layer 804, such as monocrystalline silicon. The layer 804 and the layer 802 form a structure of the SOI (Silicon On Insulator) type.

[0148] Various components 806 have been formed in the layer 804, for example by conventional masking, etching, epitaxy and / or doping steps. In other words, the components are formed in and / or on the layer 804. In the illustrated example, the circuit comprises a photodiode 806 (for example a photodiode made of germanium epitaxied from the layer 804, or a silicon photodiode formed in the silicon layer 804).

[0149] A waveguide 808 has also been defined in the layer 804, for example by conventional masking and etching steps of the layer 804.

[0150] In the illustrated example, the circuit 8 comprises, from left to right in Figure 8 : a strip waveguide 808, the photodiode 806, and a rib or ridge waveguide 808.

[0151] The components 806 and the waveguides 808 are covered by an insulating layer 810, such as silicon oxide.

[0152] The circuit 8 also comprises an interconnection structure 812 resting on the layer 810. The interconnection structure 812 comprises portions of a metal layer 814 separated from each other by insulating layers 816. The interconnection structure 812 also comprises vias 818 passing through the layers 816 in order to connect the portions of the metal layer 814 to each other, to contact pads 820 positioned at the top face of the interconnection structure 812 and / or to the components 806.

[0153] ​According to one embodiment, the modulator 1 is positioned in an insulating layer 816 of the interconnect structure 812, preferably positioned between layer 810 and a lower metal level of the interconnect structure 812. As an example, the lower metal level includes a metal layer portion 814 positioned at the same level and closest to layer 804.

[0154] The layer 816 where modulator 1 is located includes the aforementioned layers 102 and 108. Figure 8 (not shown in the image) or preferably composed of the aforementioned layers 102 and 108.

[0155] The interconnect structure 812 includes a via 110 for the modulator 1. The via 110 is electrically connected to a metal layer portion 814 of the interconnect structure 812 (e.g., a lower metal layer portion 814).

[0156] As an example, circuit 8 is obtained by performing the following steps:

[0157] -Component 806 and / or waveguide 808 are formed by SOI-type layer 804; and

[0158] - An interconnect structure 812 is formed above layer 804. Forming the interconnect structure 812 includes the following steps: forming layer 102 ( Figure 8 (not shown in the text); and perform the above regarding Figures 1-7 One of the methods described makes layers 102 and 108 ( Figure 8 (Not shown in the image) The insulating layer 816 corresponding to the interconnect structure 812, that is, the insulating layer 816 forming the interconnect structure.

[0159] According to one embodiment, circuit 8 is configured to perform light detection and ranging (LIDAR) functions.

[0160] refer to Figures 1-8 The embodiments and variations described above include a modulator 1 comprising a silicon nitride waveguide 100 embedded in insulating layers 102 and 108 (e.g., made of silicon oxide), and a heating element, such as ITO, in contact with at least one surface of the waveguide. These embodiments and variations can be adapted to cases where the modulator 1 comprises a waveguide of a different material by modifying the material of the heating element, provided that the material of the heating element remains conductive and transparent to the wavelength of the signal configured to propagate in the waveguide.

[0161] As an example, preferably by performing an action regarding Figure 1 The described method allows waveguide 100 to be made of monocrystalline silicon in an SOI-type layer, layer 102 to correspond, for example, to a silicon oxide layer, on which the SOI-type layer rests, and / or layer 106 to be made of, for example, ZnO, Cd2SnO4 or amorphous carbon.

[0162] Furthermore, although examples of embodiments and variants in which the waveguide 100 is a strip waveguide have been described, the person skilled in the art is able to adapt these embodiments and variants for the case in which the waveguide 100 is a rib or ridge waveguide.

[0163] Furthermore, embodiments and variants have been described in which the heating element is in direct contact with one or more faces of the waveguide. These embodiments and variants can be adapted for the case in which the heating element is not in direct contact with these faces of the waveguide, but is kept positioned at a distance from the waveguide which is less than half the wavelength of the signal propagated by the waveguide, preferably less than a quarter of this wavelength.

[0164] For example, it can be provided that the heating element is separated from one or more faces of the waveguide by an intermediate layer having a thickness which is less than half the wavelength of the optical signal propagated by the waveguide, preferably less than a quarter of this wavelength. In other words, the intermediate layer comprises a first face in contact with the waveguide and a second face in contact with the heating element and opposite the first face, the thickness of the intermediate layer being measured between its first and second faces. Providing such an intermediate layer can make the heating element less perturbing for the optical signal propagated in the waveguide, relative to the case in which the heating element is in contact with the waveguide. The intermediate layer preferably consists of a single layer. The intermediate layer is preferably made of a material having an optical index lower than the optical index of the first material (for example, of a third material).

[0165] The person skilled in the art is able to adapt the described embodiments and variants for the case in which such an intermediate layer is provided, in particular to provide steps for depositing this intermediate layer. In particular, the intermediate layer can be deposited on the waveguide and in contact with the waveguide before the layer of second material is deposited on the intermediate layer and in contact with the intermediate layer, and / or the intermediate layer can be deposited on the layer of second material and in contact with the layer of second material before the waveguide is formed on the intermediate layer and in contact with the intermediate layer.

[0166] Various embodiments and variants have been described. The person skilled in the art will understand that certain features of these embodiments can be combined, and that the person skilled in the art will easily think of other variants.

[0167] Finally, based on the functional description provided above, the actual implementation of the embodiments and variants described herein is within the capabilities of a person skilled in the art. In particular, a person skilled in the art is able to determine the length of each portion 106c and 200c, for example in a direction orthogonal to the side of the waveguide 100, measured for example from the side of the waveguide 100, and to determine the distance between the side of the waveguide 100 and the conductive via 110, measured for example in a direction orthogonal to these faces, so that the metal via 110 does not disturb the propagation of the optical signal in the waveguide 100. More generally, a person skilled in the art is able to determine the various dimensions of the modulator 1 according to the functional description given above, for example the dimensions of the cross section of the waveguide 100 as a function of the signal or the thicknesses of the layers 106 and 200 to be guided. To this end, a person skilled in the art can use computer-aided simulation software, for example the software designated under the trade name Lumerical.

Claims

1. A method for manufacturing a phase modulator, comprising the steps of: a) forming a waveguide from a first material, said waveguide being configured to guide an optical signal, said waveguide having a first side adjacent to an insulating layer, a second side perpendicular to said first side and a third side, and a fourth side parallel to said first side; and b) forming a layer made of a second material, said second material being electrically conductive and transparent to the wavelength of said optical signal, steps a) and b) being implemented so that said layer made of said second material is disposed on said first side, said second side, said third side and said fourth side of said waveguide, wherein said second material is in direct contact with said first side, said second side, said third side, said fourth side, or wherein said second material is separated from said first side, said second side, said third side, said fourth side by a distance smaller than half of said wavelength of said optical signal.

2. The method according to claim 1, wherein step a) is performed before step b).

3. The method according to claim 2, wherein: step a) comprises the following successive steps: al) on a first layer made of a third material, depositing a layer made of said first material, and a2) etching said layer made of said first material to define said waveguide therein; and in step b), said layer made of said second material is deposited on and in contact with an exposed face of said waveguide, or on and in contact with an intermediate layer having a thickness equal to said distance and previously deposited on and in contact with said exposed face of said waveguide.

4. The method according to claim 3, wherein: before step a), the method comprises a step comprising depositing a further layer made of said second material; and in step al), said layer made of said first material is deposited on and in contact with said further layer made of said second material, or said layer made of said first material is deposited on and in contact with a further intermediate layer having a thickness equal to said distance and previously deposited on and in contact with said further layer made of said second material.

5. The method of claim 3, further comprising: after step b), a step comprising depositing a second layer made of said third material, and a step comprising forming an electrically conductive via through said second layer made of said third material, up to a portion of said layer made of said second material.

6. The method according to claim 2, wherein: before step a), the method comprises a step comprising etching a cavity in a first layer made of a third material; step a) comprises the following successive steps: al) depositing a layer made of said first material so as to fill said cavity, and a2) etching said layer made of said first material to define said waveguide therein. a2) performing mechanical chemical planarization until the layer made of the third material, a portion of the layer made of the first material being left in place in the cavity, thereby forming the waveguide; and In step b) the layer made of the second material is deposited on the exposed face of the waveguide and in contact with the exposed face, or the layer made of the second material is deposited on an intermediate layer and in contact with the intermediate layer, the intermediate layer having a thickness equal to the distance and the intermediate layer having been previously deposited on the exposed face of the waveguide and in contact with the exposed face.

7. The method according to claim 6, wherein: Before step a) the method comprises a step comprising depositing further layers made of the second material; and In step al) the layer made of the first material is deposited on the further layers made of the second material and in contact with the further layers, or the layer made of the first material is deposited on a further intermediate layer and in contact with the further intermediate layer, the further intermediate layer having a thickness equal to the distance and the further intermediate layer having been previously deposited on the further layers made of the second material and in contact with the further layers made of the second material.

8. The method of claim 6, further comprising: After step b) a step comprising depositing a second layer made of the third material and a step comprising forming a conductive via through the second layer made of the third material up to the portion of the layer made of the second material.

9. The method according to claim 1, wherein step b) is performed before step a).

10. The method according to claim 9, wherein: In step b) the layer made of the second material is deposited on a first layer made of a third material; and Step a) comprises the following successive steps: al) depositing a layer made of the first material on the layer made of the second material and in contact with the layer made of the second material, or depositing a layer made of the first material on an intermediate layer and in contact with the intermediate layer, the intermediate layer having a thickness equal to the distance, the intermediate layer having been previously deposited on the layer made of the second material and in contact with the layer made of the second material, a2) etching the layer made of the first material to define the waveguide therein.

11. The method of claim 10, wherein the method further comprises: After step a) a step comprising depositing a further layer made of the second material on the exposed face of the waveguide and in contact with the exposed face, or depositing a further layer made of the second material on a further intermediate layer and in contact with the further intermediate layer, the further intermediate layer having a thickness equal to the distance and the further intermediate layer having been previously deposited on the exposed face of the waveguide and in contact with the exposed face.

12. The method of claim 10, further comprising: After step a), a step comprising depositing a second layer made of a third material, and a step comprising forming a conductive via through the second layer made of the third material, up to the second material.

13. The method of claim 9, wherein: Before step b), the method comprises a step comprising etching a cavity in a first layer made of a third material; In step b), the layer made of the second material is deposited on the walls and the bottom of the cavity; and Step a) comprises the following successive steps: al) filling the cavity by depositing a layer made of the first material on the layer made of the second material, in contact with the layer made of the second material, or on an intermediate layer, in contact with the intermediate layer, the intermediate layer having a thickness equal to the distance, and previously deposited on the layer made of the second material, in contact with the layer made of the second material; and a2) performing a mechanical chemical planarization at least up to the layer made of the second material, a portion of the layer made of the first material being left in place in the cavity, thereby forming the waveguide.

14. The method of claim 13, wherein the method further comprises: After step a), a step comprising depositing a second layer made of a third material, and a step comprising forming a conductive via through the second layer made of the third material, up to the second material.

15. The method of claim 13, further comprising:

16. The method of claim 1, wherein the first material is silicon nitride and the second material is indium tin oxide or amorphous carbon, the wavelength being between 450 nm and 1 pm.

17. The method of claim 1, wherein the layer made of the second material is separated from at least one of the first side, the second side, the third side, and the fourth side by a distance, the distance being less than one quarter of a wavelength of the optical signal.

18. A phase modulator comprising: a waveguide of a first material, wherein the waveguide is configured to propagate an optical signal, the waveguide having a first side adjacent to an insulating layer, a second side and a third side perpendicular to the first side, and a fourth side parallel to the first side; and a layer of a second material that is electrically conductive, the second material being transparent to a wavelength of the optical signal, wherein the layer of the second material is disposed over the first side, the second side, the third side, and the fourth side of the waveguide, wherein the second material that is electrically conductive is in direct contact with the first side, the second side, the third side, the fourth side, or ​ wherein said second material is electrically conductive and transparent to a wavelength of said optical signal, and wherein said layer of said second material is disposed on said first side, said second side, said third side, and said fourth side of said waveguide, 19. The modulator of claim 18, wherein said first material is silicon nitride and said second material is indium tin oxide or amorphous carbon, and wherein said wavelength is between 450 nm and 1 pm.

20. The modulator of claim 18, further comprising: a layer of thermally and electrically insulating material, wherein said layer of said second material is disposed between said waveguide and said layer of thermally and electrically insulating material.

21. The modulator of claim 18, wherein said layer of said second material comprises an upper portion resting on a top surface of said waveguide, and / or a lower portion on which a bottom surface of said waveguide rests.

22. The modulator of claim 21, wherein the layer of the second material further comprises: a side portion facing each side of said waveguide.

23. The modulator of claim 18, wherein said layer of said second material comprises contact portions extending laterally on either side of said waveguide, and each contact portion is configured to contact at least one conductive via.

24. The modulator of claim 18, wherein said layer of said second material is separated from at least one of said first side, said second side, said third side, and said fourth side by a distance that is less than one fourth of said wavelength of said optical signal.

25. A photonic integrated circuit, comprising: a semiconductor layer of a semiconductor-on-insulator (SOI) type; electronic components disposed in or on said semiconductor layer; an interconnect structure disposed above said semiconductor layer and electrically connecting said electronic components; and a phase modulator disposed in an insulating layer of said interconnect structure, said phase modulator comprising: a waveguide of a first material, wherein said waveguide is configured to propagate an optical signal, said waveguide having a first side adjacent to said insulating layer, a second side and a third side perpendicular to said first side, and a fourth side parallel to said first side, said first side being closer to said insulating layer than said fourth side; and a layer of a second material that is electrically conductive and transparent to a wavelength of said optical signal, wherein said layer of said second material is disposed on said first side, said second side, said third side, and said fourth side of said waveguide, wherein said second material is in direct contact with said first side, said second side, said third side, said fourth side, or wherein said second material is separated from said first side, said second side, said third side, said fourth side by a distance that is less than one half of said wavelength of said optical signal.

26. The photonic integrated circuit of claim 25, wherein said insulating layer comprises silicon oxide. ​

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