Waveguide photodetector for reducing retro-reflection and increasing bandwidth

Abstract

A waveguide photodetector for reducing retroreflection and increasing bandwidth is provided. The waveguide photodetector includes: a waveguide photodiode having: a main waveguide; an absorption waveguide integrated with the main waveguide; an input surface located on the absorption waveguide; and an input waveguide for transmitting light to the waveguide photodiode, an input angle between the input waveguide and the input face being an acute interface angle.

Description

Technical Field

[0001] The present invention relates to waveguide photodetectors, and in particular to waveguide photodetectors for reducing retro-reflection and increasing bandwidth. Background Art

[0002] A photodetector typically includes a photodiode, which includes a photosensitive semiconductor diode that generates an electric current in response to the absorption of photons. The photodetector and / or photodiode can be a discrete device or integrated as a waveguide into a photonic integrated circuit (PIC). A waveguide photodiode typically includes a main waveguide for guiding light into an absorption waveguide of the waveguide photodiode and can be physically located at the end of an input waveguide for delivering input light to the waveguide photodiode, which input light can be received from a transmitter in an optical communication system, for example. The main waveguide and absorption waveguide of the waveguide photodiode can typically be aligned with the input waveguide for guiding light into the absorption waveguide (e.g., which converts light into electrons and holes (e.g., electron-hole pairs) to generate an electric current). The input waveguide can be made of silicon or silicon nitride with a dielectric cladding. The main waveguide can be made of silicon with an attached, grown, and / or absorption waveguide, and the material of the absorption waveguide can include germanium.

[0003] The function of the absorbing waveguide is to convert the optical signal into an electrical signal. The absorbing waveguide is typically connected to positive and negative contacts. The electrical signal can then be transmitted to an amplifier on or off the PIC.

[0004] Absorbing waveguides are both transmissive and absorptive. In optical or electromagnetic terms, the material has a complex refractive index with both real and complex components.

[0005] Generally speaking, reflections occur in an optical path when the real part of the refractive index of the optical material carrying the incident light, such as in a waveguide, changes. Thus, returning to the waveguide photodetector and / or waveguide photodiode, when the respective optical axes of the main waveguide and the input waveguide coincide, and the input facet of the absorbing waveguide is perpendicular to the input waveguide, a significant amount of light may be reflected back through the input waveguide, with the magnitude of the reflected light being determined by the difference in refractive indices between the input and absorbing waveguides and the angle of incidence relative to the input facet (in this example, 90°). This reflected light may cause the waveguide photodetector and / or waveguide photodiode to malfunction (e.g., because the reflected light is not detected), and the reflected light may be transmitted back through the input waveguide and interfere with the transmission signal carried by the incident light. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] In order to better understand the various embodiments described herein and to more clearly show how they may be implemented, reference will now be made, by way of example only, wherein:

[0007] Figure 1 is a schematic illustration of a waveguide photodetector according to a non-limiting embodiment.

[0008] Figure 2 is a schematic illustration of a waveguide photodetector according to an alternative non-limiting embodiment.

[0009] Figure 3 is a schematic illustration of a waveguide photodetector according to yet another alternative non-limiting embodiment.

[0010] Figure 4 is a schematic illustration of a waveguide photodetector according to yet another alternative non-limiting embodiment.

[0011] Figure 5 is a schematic illustration of a waveguide photodetector according to yet another alternative non-limiting embodiment.

[0012] Figure 6 is a schematic illustration of a waveguide photodetector that refracts light toward a p-type doped semiconductor region according to yet another alternative non-limiting embodiment.

[0013] Figure 7 is a schematic illustration of a waveguide photodetector that refracts light toward a p-type doped semiconductor region according to yet another alternative non-limiting embodiment.

[0014] Figure 8 Plotted compared to an example bandwidth of a waveguide photodetector that refracts light toward an n-type doped semiconductor region. Figure 7 Example frequency response of a waveguide photodetector.

[0015] Figure 9 The corresponding responsivities of a waveguide photodetector that refracts light toward a p-type doped semiconductor region and a waveguide photodetector that does not refract light toward either the p-type doped semiconductor region or the n-type doped semiconductor region are depicted.

[0016] Figure 10 Depicts passing through Figure 1 Cross-section of the waveguide photodetector along line AA'.

[0017] Figure 11 is a schematic illustration of a waveguide photodetector according to yet another alternative non-limiting embodiment. DETAILED DESCRIPTION

[0018] This specification provides a waveguide photodetector comprising: a waveguide photodiode having: a main waveguide, an absorption waveguide integrated with the main waveguide, and an input facet located at the absorption waveguide; and an input waveguide for transmitting light to the waveguide photodiode, wherein the input angle between the input waveguide and the input facet comprises an acute interface angle. Such an arrangement is understood to prevent and / or reduce retro-reflection from the input facet back along the input waveguide.

[0019] The waveguide photodetector may further include: an n-type doped semiconductor region along a first side of the absorbing waveguide; and a p-type doped semiconductor region along a second side of the absorbing waveguide, the second side being opposite the first side. The input facet may further form an acute angle with the optical axis, and the interior of the input facet may be angled toward the p-type doped semiconductor region such that light input to the input facet is refracted toward the p-type doped semiconductor region. This arrangement may result in increased bandwidth capabilities of the waveguide photodetector.

[0020] The present specification further provides a waveguide photodiode comprising: a main waveguide; an absorption waveguide integrated with the main waveguide, one or more of the absorption waveguide and the main waveguide having an optical axis; an n-type doped semiconductor region along a first side of the absorption waveguide; a p-type doped semiconductor region along a second side of the absorption waveguide, the second side being opposite to the first side; and an input facet at the absorption waveguide, the input facet forming an acute angle with the optical axis, the interior of the input facet being angled toward the p-type doped semiconductor region such that light input to the input facet is refracted toward the p-type doped semiconductor region, and the input facet. Such an arrangement can result in an increased bandwidth capability of the waveguide photodiode.

[0021] Such a waveguide photodiode can be a component of a waveguide photodetector, comprising: a waveguide photodiode having: a main waveguide, an absorption waveguide integrated with the main waveguide, and an input facet located at the absorption waveguide; and an input waveguide for transmitting light to the waveguide photodiode; in such examples, the input angle between the input waveguide and the input facet typically comprises an acute interface angle. Such an arrangement is understood to prevent and / or reduce retro-reflection from the input facet back along the input waveguide.

[0022] Reference Figure 1, depicts a waveguide photodetector 100 comprising a waveguide photodiode 102 including a main waveguide 104, an absorption waveguide 106, and an input facet 108 located at the absorption waveguide 106. Waveguide photodetector 100 further comprises an input waveguide 110 for transmitting light 112 to waveguide photodiode 102. Light 112 is received at input facet 108 and guided and / or transmitted and / or refracted through main waveguide 104 into absorption waveguide 106, as indicated by transmitted light 114. A portion of light 112 may be reflected from input facet 108, as indicated by reflected light 116. For clarity, input facet 108 is represented as a line; however, input facet 108 is understood to include the end of absorption waveguide 106 that receives light 112. Furthermore, light 112 may be interchangeably referred to herein as incident light 112, e.g., incident on input facet 108.

[0023] Furthermore, it should be understood that the absorption waveguide 106 and the main waveguide 104 form an integrated structure. In other words, the absorption waveguide 106 is integrated with the main waveguide 104. For example, temporarily focusing on Figure 10 , which depicts the waveguide photodiode 102 passing through (e.g., Figure 1 ) line AA', and it shows that the absorption waveguide 106 can be formed into grooves and / or recesses and trenches (e.g., anisotropic etched features) of the main waveguide 104. Returning attention to Figure 1 It should be further understood that the main waveguide 104 can be positioned around the absorbing waveguide 106 such that the main waveguide 104 is also positioned at and / or around the input facet 108 of the absorbing waveguide 106. Thus, incident light 112 from the input waveguide 110 can enter the main waveguide 104 and be incident on the input facet 108 of the absorbing waveguide 106. Consequently, certain solutions for reducing reflections from the input facet 108 (e.g., anti-reflection coatings) are not possible in the integrated structure of the waveguide photodetector and / or waveguide photodiode as provided herein.

[0024] Thus, it should be further understood that the main waveguide 104 generally facilitates guiding incident light 112 into the absorption waveguide 106 via the input face 108, and further, the absorption waveguide 106 both transmits the transmitted light 114 (e.g., a waveguiding function) and converts the transmitted light 114 into electrical current (e.g., and / or electron-hole pairs). Thus, it should be understood that the absorption waveguide 106 is formed of any suitable photodiode material, including but not limited to germanium; however, any suitable type of photodiode material is within the scope of the present disclosure, including but not limited to gallium arsenide, indium gallium arsenide, etc. It should be further understood that the length of the absorption waveguide 106 (e.g., along the optical axis 122) can be selected such that the transmitted light 114 is substantially absorbed before reaching the end of the absorption waveguide 106 opposite the end of the input face 108.

[0025] Because the waveguide photodetector 100 can be used in optical communication systems, it should be understood that the incident light 112 can be at a wavelength compatible with such optical communication systems, such as approximately 1310 nm, although the waveguide photodetector 100 can be used with other wavelengths and / or in other types of systems.

[0026] Furthermore, because the waveguide photodetector 100 can be a component of a photonic integrated circuit (PIC), it should be understood that references herein to certain optical properties of materials used for certain components of the waveguide photodetector may be affected by being a component of a PIC. For example, in the context of an optical waveguide, the relevant refractive index of an optical material is referred to as the mode index. Therefore, any reference to the refractive index of a material, as used herein, is understood to be a reference to the mode index, and vice versa.

[0027] Although light 112, 114, 116 is depicted as discrete arrows for simplicity, it should be understood that light 112, 114, 116 may include modulated light and / or an optical signal having data encoded therein, and that the transmitted light 114 is detected by the absorbing waveguide 106 and converted into an electrical current by the absorbing waveguide 106. In practice, the input waveguide 110 may be the end of a longer waveguide (not depicted), and / or the input waveguide 110 may be in optical communication with such a longer waveguide. Regardless, in use, the input waveguide 110 may be in optical communication with a transmitter of an optical communication system, which transmits data in the form of modulated incident light 112 to the waveguide photodetector 100. In practice, the waveguide photodetector 100 may be a component of a receiver (e.g., a PIC receiver) in such an optical communication system. Although not depicted, the waveguide photodetector 100 is generally understood to include contacts (e.g., n-type doped semiconductor and p-type doped semiconductor, such as silicon, but any suitable semiconductor is within the scope of this description) for receiving the current generated by the waveguide photodetector 106. When the transmitted light 114 is understood to be modulated, the current generated by the absorbing waveguide 106 can also be modulated, so that data encoded in the incident light 112 can be determined by other components (not depicted) that receive the modulated current.

[0028] As depicted, the waveguide photodetector 100 can optionally include an output waveguide 118 extending from the main waveguide 104, and the output waveguide 118 can transmit reflected light 116 from the input facet 108. In general, the sum of the intensities of the transmitted light 114 (e.g., immediately upon entering the input facet 108) and the reflected light 116 is understood to be approximately the same as the intensity of the light 112.

[0029] To absorb reflected light 116 , and when such an output waveguide 118 is present, the waveguide photodetector 100 can optionally include a light collector 120 (e.g., a device for absorbing light), such as at an end of the output waveguide 118 opposite the corresponding end at the absorbing waveguide 106 .

[0030] However, the output waveguide 118 may include any suitable material and / or structure to one or more of scatter, disperse, and absorb the reflected light 116 so that the reflected light 116 does not return to the input waveguide 110 .

[0031] For clarity, and to facilitate discussion of the geometric relationships between components of the waveguide photodetector 100, respective optical axes 122, 124, 126 of the waveguides 104 (and / or waveguides 106), 110, 118 are also depicted, with it being understood that light carried by the waveguides 104, 106, 110, 118 may generally be centered on such optical axes 122, 124, 126 (e.g., unless refracted away from the optical axis 122, as described with respect to FIG. Figure 2 It should be further understood that the optical axes 122, 124, 126 can also define the respective longitudinal axes of the waveguides 104, 106, 110, 118.

[0032] In prior art waveguide photodetectors and / or waveguide photodiodes, the optical axes 122, 124 of the waveguides 104, 110 typically coincide, causing the incident light 112 to strike the input facet 108 at a perpendicular and / or 90° angle, and consequently, the reflected light 116 to reflect back along the input waveguide 110. This typically results in a reduction in the intensity of the transmitted light 114, which in turn may result in a reduction in the current generated by the absorbing waveguide 106 and may lead to errors in the detection of the data embedded in the incident light 112. Furthermore, when the reflected light 116 reflects back along the input waveguide 110, it travels through the optical communication system back toward the transmitter that emitted the incident light 112, and the reflected light 116 may typically interfere with the proper transmission of the communication signal and / or the data encoded in the incident light 112. In bulk optical components, solutions such as anti-reflective coatings can be used to reduce such reflections, for example, by applying them to the input surface of the absorbing photodiode medium to reduce reflections. However, in the case of the waveguide photodetectors and / or waveguide photodiodes provided herein, such antireflective coatings are not possible.

[0033] Therefore, to avoid this problem (e.g., and without using anti-reflection coatings as a solution), the sharp input interface angle 128 (also indicated as Figure 1The "Θ" in ) generally includes an acute interface angle (e.g., less than 90°), and more particularly, the acute input interface angle 128 (e.g., an acute interface angle) can be in the range of about 8° to about 65°.

[0034] Furthermore, it should be understood that an acute input interface angle 128 (eg, an acute interface angle) can be defined as being between the optical axis 124 of the input waveguide 110 and the normal 130 to the input face 108 .

[0035] In fact, if Figure 1 As depicted, the acute input interface angle 128 (e.g., an acute interface angle) can be located between the respective optical axes 122, 124 of the waveguides 104, 106 and the input waveguide 110, and it should be understood that the input facet 108 is approximately perpendicular to the optical axes 122 of the waveguides 104, 106 such that a normal 130 to the input facet 108 is coincident with the optical axes 122 of the waveguides 104, 106.

[0036] Same as Figure 1 As depicted, for example, based on the angle of incidence being equal to the angle of reflection, the respective optical axes 122, 126 of the main waveguide 104 and the output waveguide 118 are at an output angle 132 that is the same as the acute input interface angle 128 (e.g., an acute interface angle). Specifically, the output waveguide 118 is also at the same acute interface angle as the input waveguide 110, but in the direction of the reflected light 116. Furthermore, it should be understood that, similar to the acute input interface angle 128, the output angle 132 can be located between the optical axis 126 of the output waveguide 118 and the normal 130 to the input facet 108.

[0037] It should be further understood that the materials of the waveguides 104, 110, 118 and the absorption waveguide 106 have refractive indices that may affect the intensity of the transmitted light 114 and the reflected light 116. For example, the input waveguide 110 may comprise silicon and / or silicon nitride, e.g., with a dielectric cladding, and when made of silicon, the input waveguide 110 may have a mode index (e.g., a refractive index) of approximately 2.4 at a wavelength of 1310 nm for the incident light 112. The output waveguide 118 may similarly comprise silicon and / or silicon nitride, e.g., with a dielectric cladding, and when made of silicon, the input waveguide 110 may have a mode index (e.g., a refractive index) of approximately 2.4 at a wavelength of 1310 nm for the incident light 112. In general, the waveguides 110, 118 may comprise the same material and / or multiple materials and / or may be components of a PIC receiver.

[0038] The main waveguide 104 may comprise silicon and / or comprise the same material and / or materials as the waveguides 110, 118. In fact, all three waveguides 104, 110, 118 may comprise the same material and / or materials and / or may be components of a PIC receiver, such that all three waveguides 104, 110, 118 may comprise the same refractive index and / or mode index, so that no optical interfaces exist therebetween and / or light is refracted and / or reflected from interfaces between the waveguides 104, 110, 118. Furthermore, the waveguides 104, 110, 118 may be integrated with one another at the PIC.

[0039] However, the absorption waveguide 106 typically comprises a waveguide photodiode material, including but not limited to germanium, having a mode index (e.g., refractive index) of approximately 4.1 (e.g., the real part of the mode index) at a wavelength of 1310 nm of the incident light 112. The absorption waveguide 106 can be attached to and / or grown on and / or embedded in the main waveguide 104. Furthermore, the mode index of the absorption waveguide 106 is understood to have a significant complex part (e.g., less than approximately 0.1 at a wavelength of 1310 nm of the incident light 112).

[0040] Because the input waveguide 110 and the absorption waveguide 106 typically have different refractive indices and / or mode indices, when incident light 112 impinges on the input face 108, the incident light 112 will be refracted at least into the absorption waveguide 106 as transmitted light 114, and in some instances, depending on the acute input interface angle 128, a portion of the incident light 112 will be reflected from the input face 108 as reflected light 116.

[0041] In particular, the acute input interface angle 128 (e.g., an acute interface angle) can be selected such that the acute input interface angle 128 is a Brewster angle, e.g., to minimize and / or eliminate reflected light 116 and cause the transmitted light 114 to propagate along (e.g., parallel to) the optical axis 122 of the waveguides 104, 106.

[0042] For example, the input waveguide 110 (e.g., its material) can have a first refractive index and / or mode index "n1", and the absorption waveguide 106 (e.g., its material) can have a second refractive index and / or mode index "n2", and the acute input interface angle 128 (e.g., the acute interface angle) can be determined according to arctan(n2 / n1) or the formula for determining the Brewster angle. Such examples assume that the main waveguide 104 is integrated with the input waveguide 110, and that the two waveguides 104, 110 are made of the same material and therefore have the same and / or approximately the same refractive index and / or mode index "n1".

[0043] For example, using n1=2.4 for silicon (e.g., the input waveguide 110 and the main waveguide 104 comprise silicon), and n2=4.1 (e.g., the absorption waveguide 106 comprises germanium), the input interface acute angle 128 can be selected to be a Brewster angle of approximately 30° (e.g., arctan(2.4 / 4.1)).

[0044] In fact, the closer the acute input interface angle 128 is to the Brewster angle and / or the further it is from 90°, the more the reflected light 116 can be reduced. Thus, the waveguide photodetector 100 reduces retro-reflection from the input face 108, at least relative to prior art waveguide photodetectors, where light is incident on the input face of the waveguide photodiode at 90°.

[0045] While specific materials and / or specific refractive indices and / or specific mode indices are described herein, it should be understood that the various components of the waveguide photodetector 100 can be made of any suitable materials and have any suitable refractive indices and / or mode indices. Furthermore, it should be understood that the refractive index and / or mode index can vary depending on the materials used for the waveguide photodetector 100 and / or the wavelength of the incident light 112. Thus, the various angles described throughout this specification can vary depending on such factors. Thus, any suitable combination of materials, refractive indices, mode indices, wavelengths of light, and angles is within the scope of this specification. In other words, while the components of the waveguide photodetector 100 have been described with respect to certain materials and optical properties, the components of the waveguide photodetector 100 can include any suitable materials and associated optical properties.

[0046] Furthermore, the waveguide photodetector 100 can be fabricated in any suitable manner (e.g., using photolithographic methods), such as as a component of a PIC receiver, and at least the waveguides 104, 110 and the absorbing waveguide 106, as well as the acute input interface angle 128, can be positioned accordingly using the Brewster angle. In practice, when the acute input interface angle 128 comprises the Brewster angle, the output waveguide 118 (e.g., and / or the light collector 120) can be optional and / or omitted, assuming that reflected light 116 is minimized and / or eliminated. However, in some of these examples, because manufacturing techniques are understood to have tolerances that may result in the acute input interface angle 128 being close to (but not exactly) the Brewster angle, the output waveguide 118 (e.g., and / or the light collector 120) can be included to carry and / or absorb even a small amount of the resulting reflected light 116 away from the input face 108.

[0047] Furthermore, the presently provided waveguide photodiodes may have other geometric configurations.

[0048] For example, follow Figure 2, which depicts a waveguide photodetector 200 that is substantially similar to the waveguide photodetector 100, with like components having like component numbers, but the geometric arrangement of the components of the waveguide photodetector 200 is different from the geometric arrangement of the components of the waveguide photodetector 100, but achieves the same effect.

[0049] Specifically, the respective optical axes 122, 124 of the waveguides 104, 106 and the input waveguide 110 of the waveguide photodetector 100 are coincident, but the input face 108 forms an acute input interface angle 128 (e.g., an acute interface angle) with a line 202 that is approximately perpendicular to the optical axes 122 of the waveguides 104, 106. For clarity, a line 204 extending from the input face 108 and coincident with the input face 108 is also depicted to better illustrate the angle of the input face 108. Furthermore, while the angle of the input face 108 is depicted as being defined relative to the line 202 that is approximately perpendicular to the optical axes 122 of the waveguides 104, 106, the angle of the input face 108 may be defined in other ways, such as relative to the optical axes 122 of the waveguides 104, 106.

[0050] In other words, at the waveguide photodetector 200, the input waveguide 110 and the input facet 108 form an acute input interface angle 128 (e.g., the acute input interface angle 128 is located between the optical axis 124 of the input waveguide 110 and the normal 130 of the input facet 108), but the input facet 108 is angled relative to the optical axis 124 of the input waveguide 110 (e.g., rather than angling the input waveguide 110 as in the waveguide photodetector 100). As depicted, the transmitted light 114 is refracted, for example, at an angle to the optical axis 122, rather than along the optical axis 122 as in the waveguide photodetector 100. Specifically, the transmitted light 114 can be refracted toward a contact of the absorptive waveguide 106, such as an n-type doped semiconductor region or a p-type doped semiconductor region. It should be further understood that the width of the absorptive waveguide 106 (e.g., perpendicular to the optical axis 122) can be selected so that the transmitted light 114 is substantially absorbed before reaching the edge of the absorptive waveguide 106.

[0051] As will be referred to below Figure 6 、 Figure 7 、 Figure 8 and Figure 9 As described in further detail, the geometry of the waveguide photodetector 200 may be selected such that the transmitted light 114 is refracted toward the p-type doped semiconductor region containing the contacts of the absorbing waveguide 106 .

[0052] Can be combined Figure 1 and Figure 2 For example, let's focus on Figure 3, which depicts a waveguide photodetector 300 that is substantially similar to the waveguide photodetector 100 and / or the waveguide photodetector 200, wherein like components have like component numbers, but the geometric arrangement of the components of the waveguide photodetector 300 is a combination of the geometric arrangements of the components of the waveguide photodetector 100 and the waveguide photodetector 200, but achieves the same effect.

[0053] Specifically, angles 128 and 132 are also acute angles (e.g., also indicated as Figure 3 ” in ), and are generally the same at least with respect to the normal 130 of the input face 108, such as in terms of the angle of incidence being equal to the angle of reflection.

[0054] Furthermore, like the waveguide photodetector 100, the input waveguide 110 is angled relative to the optical axis 122 of the waveguides 104, 106, although such angle may be selected based on the values of the angles 128, 132 and the angle of the input facet 108 as explained next.

[0055] For example, like the waveguide photodetector 200, the input face 108 forms an angle 306 (e.g., also indicated as ) with a line 302 that is approximately perpendicular to the optical axis 122 of the waveguides 104, 106. Figure 3 For clarity, a line 304 extending from and coinciding with the input face 108 is also depicted to better illustrate the angle 306 of the input face 108 .

[0056] However, unlike the waveguide photodetector 200, the angle 306 is different from the angles 128 and 132. Conversely, the angle 306 is different from the angles 128 and 132. However, the angles 128, 132, and 306 can all still be selected so that the angle 128 includes the Brewster angle, so that the transmitted light 114 is refracted along the optical axis 122 of the waveguides 104 and 106. Alternatively, the angles 128, 132, and 306 can still be selected so that the transmitted light 114 is refracted toward a specific contact of the waveguide photodiode 102, such as an n-type doped semiconductor region or a p-type doped semiconductor region.

[0057] In other words, at the waveguide photodetector 300, the input waveguide 110 forms an acute input interface angle 128 with the input facet 108, and the input facet 108 forms an acute angle 306 with a line 302 that is approximately perpendicular to the optical axes 122 of the waveguides 104, 106, the acute angle 306 being different from the acute input interface angle 128, and further, the input waveguide 110 and the respective optical axes 124, 122 of the waveguides 104, 106 are non-coincident.

[0058] Indeed, the waveguide photodetector 300 illustrates the flexibility of the waveguide photodetectors provided herein. For example, for certain manufacturing techniques, a larger angle than the depicted "low" angle of the optical axis 124 of the input waveguide 110 relative to the line 304 (e.g., which may be between about 20° and about 35°) may be more appropriate, but any suitable angle is within the scope of the present disclosure.

[0059] As previously described, the waveguide photodetectors 100, 200, 300 may be fabricated using photolithographic methods, which may often result in rounded corners of components of the waveguide photodetectors 100, 200, 300. In such instances, when the corners are sufficiently rounded, such rounded corners may result in portions of one or more of the waveguides 104, 110, 118 being absent and / or may interfere with the light 112, 114, 116. To address this issue, during fabrication, photolithographic compensation structures may be placed at one or more corners to compensate for the rounding.

[0060] For example, follow Figure 4 and Figure 5 , which depict waveguide photodetectors 400, 500, respectively, which are substantially similar to waveguide photodetectors 100, 200, respectively, with like components having like reference numerals. Furthermore, it should be understood that although for simplicity, the light, angle, and optical axis of the waveguide photodetectors 100, 200 are not shown in FIG. Figure 4 and Figure 5 , but such light, angles, and optical axes may still exist at the waveguide photodetectors 400, 500.

[0061] In particular, the waveguide photodetectors 400, 500 are substantially similar to the waveguide photodetectors 100, 200, respectively, but use photolithographic compensation structures 402 to round and / or outwardly extend corresponding corners of the respective main waveguides 104 that are closest to the waveguides 110, 118 relative to corresponding corners of the respective main waveguides 104 of the waveguide photodetectors 100, 200. Such photolithographic compensation structures 402 can ensure that no light leaks from the waveguide photodetectors 400, 500 and / or such leakage is minimized, and / or that any rounding of such corners does not result in narrowing of the respective main waveguides 104 in the region of the input facet 108, and / or that any rounding of such corners does not interfere with the light 112, 114, 116.

[0062] Although no similar examples are provided with respect to the waveguide photodetector 300 , the waveguide photodetector 300 may be similarly adapted to include photolithographic compensation structures.

[0063] Furthermore, it should be understood that the waveguide photodiodes provided herein can have input faces angled in a particular direction, for example to refract incident light toward a p-type doped semiconductor region to improve bandwidth and / or responsivity, as described below.

[0064] For example, follow Figure 6 , which depicts something essentially similar to Figure 2 The waveguide photodiode 602 is a waveguide photodiode of the waveguide photodiode 102, wherein like components have like reference numerals, but in the "600" series rather than the "100" series. Specifically, the waveguide photodiode 602 is configured to refract transmitted light toward a p-type doped semiconductor region, as described next.

[0065] Furthermore, although the waveguide photodiode 602 is depicted without the remainder of the waveguide photodetector, the waveguide photodiode 602 may be Figure 2 Components of the waveguide photodetector 200, Figure 3 Components of the waveguide photodetector 300, and / or Figure 5 Components of the waveguide photodetector 500, and / or any of the waveguide photodetectors 200, 300, 500 can be adapted to include certain features of the waveguide photodiode 602, as described below. In particular, any of the waveguide photodetectors 200, 300, 500 can be adapted to refract transmitted light toward a p-type doped semiconductor region.

[0066] In particular, although not depicted, the waveguide photodiode 602 can be provided with an input waveguide, similar to Figure 2 The input waveguide 110 (eg, integrated with the main waveguide 604, similar to Figure 2 ), and / or output waveguides similar to Figure 2 The output waveguide 118 of FIG. 1 (and optionally with an optional light collector, similar to light collector 120, for example) may be further adapted to include photolithographic compensation structures such as Figure 5 Alternatively or additionally, a waveguide photodetector incorporating a waveguide photodiode 602 may have a similar geometry to the waveguide photodetector 300 .

[0067] As depicted, waveguide photodiode 602 includes: a main waveguide 604 and an absorptive waveguide 606. Furthermore, it should be understood that absorptive waveguide 606 includes an input facet 608 that is angled according to a particular configuration as described herein.

[0068] For clarity, incident light 612 and refracted (eg, transmitted) light 614 are also depicted, and although reflected light (eg, similar to Figure 2 612 ), although such reflected light may also be present (e.g., and not reflected in the direction of incident light 612). For clarity, the optical axis 622 of the main waveguide 604 and / or the absorption waveguide 606 is also depicted.

[0069] Figure 6 6. As depicted, contacts for the waveguide photodiode 602 are also depicted. For example, as depicted, such contacts include an n-type doped semiconductor region 625 along a first side 627 of the absorbing waveguide 606 and a p-type doped semiconductor region 629 along a second side 631 of the absorbing waveguide 606, the second side 631 being opposite the first side 627, e.g., relative to the optical axis 622.

[0070] As depicted, although optional, some overlap can exist between the doped semiconductor regions 625, 629 and the absorption waveguide 606; such overlap can depend on the width of the absorption waveguide 606 (e.g., perpendicular to the optical axis 622). In a specific example, and when the absorption waveguide 606 comprises Ge and the doped semiconductor regions 625, 629 can comprise n-type doped silicon and p-type doped silicon, respectively, the width of the absorption waveguide 606 can be between about 400 nm and about 900 nm, and the doped semiconductor regions 625, 629 can overlap the absorption waveguide 606 by about 50 nm to about 100 nm. However, it should be further understood that the depicted overlap can be optional, and the doped semiconductor regions 625, 629 can be adjacent to and contact the respective side surfaces 627, 631.

[0071] When a photon of refracted light 614 is absorbed by the absorption waveguide 606, the material of the absorption waveguide 606 (e.g., Ge) is excited, thereby generating electrons and holes (e.g., electron-hole pairs). Furthermore, the electrons are generally understood to migrate toward the n-type doped semiconductor region 625 and the holes are generally understood to migrate toward the p-type doped semiconductor region 629, and the resulting current is measured by a current measurement device (not depicted). The current flow can be assisted by placing a voltage bias across the absorption waveguide 606, for example, between the doped semiconductor regions 625 and 629, but such a voltage bias is optional. Furthermore, since the incident light 612 may be modulated due to the encoded data, the refracted light 614 may also be modulated, and thus the resulting current may also be modulated.

[0072] Focusing again on the input face 608, as depicted, the input face 608 forms an acute angle 633 (e.g., less than 90° and also indicated as Figure 6 in ). In addition, the inner side 635 of the input surface 608 is angled toward the p-type doped semiconductor region 629, so that the incident light 612 input to the input surface 608 is refracted toward the p-type doped semiconductor region 629, for example, Figure 6 , refracted light 614 is directed toward a p-type doped semiconductor region 629 as an example.

[0073] Although the geometry of the input face 608 is described with respect to an acute angle 633, the geometry of the input face 608 can be described in other ways, such as with respect to the angle between the input face 608 and a line (similar to lines 202, 302) perpendicular to the optical axis 622 of the waveguides 604, 606. In fact, such an angle is also understood to be an acute angle, with the inner side 635 of the input face 608 again angled toward the p-type doped semiconductor region 629.

[0074] It should be further understood that although Figure 6 In some embodiments, the input facet 608 spans the entire end of the absorbing waveguide 606 (e.g., the end of the absorbing waveguide 606 that receives the incident light 612), but in other embodiments, the input facet 608 may span only a portion of such end of the absorbing waveguide 606 that receives the incident light 612.

[0075] For example, follow Figure 7 , which is essentially similar to Figure 6 , like parts have like component numbers. In addition, it should be understood that although for the sake of clarity Figure 7 The acute angle 633 is not indicated in FIG, but the input face 608 is still angled at the acute angle 633, similar to the angle with respect to FIG. Figure 6 However, in Figure 7 In, with Figure 6 In contrast, the input facet 608 spans only a portion of the end of the absorbing waveguide 606 that receives the incident light 612, with the remaining portion 708 of the end being approximately perpendicular to the optical axis 622. Furthermore, the incident light 612 is arranged (e.g., using an input waveguide) to be incident near the center of the angled input facet 608; thus, while the incident light 612 remains parallel to the optical axis 622, the incident light 612 may not be along the optical axis 622.

[0076] Furthermore, it should be understood that the angled input facet 608 can be closer to the n-type doped semiconductor region 625 than the p-type doped semiconductor region 629, and / or that the remaining portion 708 can be closer to the p-type doped semiconductor region 629 than the n-type doped semiconductor region 625. In other words, as depicted, the remaining portion 708 is located between the angled input facet 608 and the p-type doped semiconductor region 629.

[0077] supply Figure 7The arrangement is intended to illustrate that various alternatives to the shape and / or position of the input face 608 are within the scope of this description, and indeed any of the waveguide photodetectors 200 , 300 , 500 may be similarly employed.

[0078] As the following will Figure 8 and Figure 9 As described, testing and / or modeling of the waveguide photodiode 602 (e.g., whether Figure 6 Configuration or Figure 7 configuration) has demonstrated that the waveguide photodiode 602 is larger than when the input face of the waveguide photodiode is in contact with Figure 6 (or Figure 7 ) is more effective when the refracted light is angled in the direction opposite to that depicted, so that the refracted light is directed toward the n-type doped semiconductor region. Similar testing and / or modeling of the waveguide photodiode 602 (e.g., whether Figure 6 Configuration or Figure 7 configuration) has shown that the waveguide photodiode 602 is more efficient than when the input facet 608 is at 90° to the optical axis of the main waveguide (e.g., such that the refracted light is guided along the optical axis of the main waveguide).

[0079] This effect can be understood in terms of the mobility of electrons and holes in the waveguide photodiode material. For example, using Ge as a specific example material for the absorbing waveguide 606, electrons are understood to have a higher mobility than holes in Ge (e.g., and such mobility is also generally a function of temperature). The time it takes for electrons and holes, such as from the location where electron-hole pairs are generated in the absorbing waveguide 606, to reach the corresponding doped semiconductor regions 625, 629 can be referred to as the transit time. Thus, in Figure 6 and / or Figure 7 In the depicted configuration, when the refracted light 614 is directed toward the p-type doped semiconductor region 629, holes and electrons can be generated closer to the p-type doped semiconductor region 629, for example, than when the refracted light 614 is directed toward the n-type doped semiconductor region 625 and / or than when the refracted light 614 is directed along the optical axis 622. Thus, the acute angle 633 can be selected so that the transit times of the electrons and holes generated at the absorption waveguide 606 via the refracted light 614 have approximately the same transit time. Doing so can result in the waveguide photodiode 602 having a higher bandwidth and higher responsivity than when the refracted light 614 is directed toward the n-type doped semiconductor region 625 or along the optical axis 622.

[0080] In other words, the refracted light 614 generates electron-hole pairs; because the mobility of electrons in Ge is much higher than the mobility of holes (e.g., holes move slower than electrons), the angle of the refracted light 614 toward the p-type region 629 that receives the holes may cause the holes to be formed closer to the p-type region 629. Therefore, the electrons and holes may arrive at their respective doped semiconductor regions 625, 629 at approximately the same time.

[0081] However, because measuring transit time can be challenging, testing and / or modeling of various values for acute angle 633 have shown that a value of approximately 45° can produce the greatest bandwidth. Such testing and / or modeling have shown that other values for acute angle 633 can result in higher bandwidth and higher responsivity than when refracted light 614 is directed toward n-type doped semiconductor region 625 or along optical axis 622. For example, acute angle 633 can be between approximately 30° and approximately 70°. In a specific example, acute angle 633 can be between approximately 45° and approximately 60°. However, any suitable angle is within the scope of the present disclosure and can be heuristically selected to balance the bandwidth requirements and manufacturing requirements of the waveguide photodetectors of the present disclosure.

[0082] In particular, it will be appreciated that data encoded into the incident light 612 carried by the input waveguide may have a particular bandwidth, and the waveguide photodiode 602 may detect such data in the form of a modulated current across the doped semiconductor regions 625 , 629 .

[0083] Next follow Figure 8 , which depicts the display Figure 7 FIG8 is a graph 800 of the frequency response of a waveguide photodetector, and in particular, signal intensities 802, 804 as a function of the bandwidth of the data encoded into the incident light (e.g., as indicated by the frequency of the data encoded into the incident light). The intensities 802, 804 are both defined relative to the S21 transmission coefficient. In particular, the intensity 802 is for a waveguide photodetector having Figure 7 800 . Intensity 802 and 804 are determined for a waveguide photodiode 602 having the configuration shown and having an acute angle 633 of 45°. Conversely, intensity 804 is determined for a waveguide photodiode having an input facet with an absorbing waveguide that directs refracted light toward an n-type doped semiconductor region and having the same configuration as waveguide photodiode 602 of graph 800 . It should be further understood that both intensities 802 and 804 were determined using a bias voltage of -1 V. Both waveguide photodiodes are fabricated on the PIC from silicon and germanium.

[0084] Graph 800 further includes a line 806 extending horizontally from -3 dB. It will be appreciated that below -3 dB, data encoded in the incident light may be difficult to detect. Therefore, it will be appreciated that when the strengths 802, 804 of the signals depicted in graph 800 drop below -3 dB, the corresponding waveguide photodiodes may become inoperative.

[0085] For example, vertical line 808 shows the intersection of intensity 804 and line 806 at -3 dB, illustrating that intensity 804 drops below -3 dB at a bandwidth of 12 GHz and remains below -3 dB above 12 GHz. Thus, a waveguide photodiode having an input facet of an absorbing waveguide that directs refracted light toward a doped semiconductor region typically does not function at approximately 12 GHz.

[0086] In contrast, the intensity 802 of the waveguide photodiode 602 is above -3 dB at least until approximately 40 GHz.

[0087] Thus, graph 800 clearly shows that the waveguide photodiode 602 that refracts light toward the p-type doped semiconductor region can detect data at a rate greater than about 40 GHz, while the waveguide photodiode that refracts light toward the n-type doped semiconductor region can stop detecting data at at least about 12 GHz. Although this is a specific example, with a specific configuration of the waveguide photodiode used to generate graph 800, it should be understood that graph 800 illustrates the relative advantage in bandwidth of the waveguide photodiode 602 that refracts light toward the p-type doped semiconductor region compared to the waveguide photodiode that refracts light toward the n-type doped semiconductor region.

[0088] It can also achieve advantages in terms of responsiveness. For example, the following Figure 9 , which depicts a graph 900 of the responsivity 902, 904 of a waveguide photodiode 602 and a waveguide photodiode with an input facet of the absorption region at 90° to the optical axis of the main waveguide, respectively. The waveguide photodiode 602 has Figure 7 The configuration shown has an acute angle 633 of 45°. Again, both waveguide photodiodes are made of silicon and germanium and are integrated into the PIC.

[0089] Specifically, the responsivity can be defined as a bandwidth of a certain intensity, such as 3 dB (e.g., as depicted by graph 900), as a function of the current generated by the waveguide photodiode. Comparing the responsivities 902, 904, it is apparent that the waveguide photodiode with Figure 7 The waveguide photodiode 602 in the configuration shown and having an acute angle 633 of 45° has much better responsivity than a waveguide photodiode in which the input facet of the absorption region is at 90° to the optical axis of the main waveguide. For example, at a comparable current of 1 mA (e.g., as indicated by line 906), a waveguide photodiode having an acute angle 633 of 45° has a much better responsivity than a waveguide photodiode in which the input facet of the absorption region is at 90° to the optical axis of the main waveguide. Figure 7 A waveguide photodiode 602 configured as shown in FIG. 5 and having an acute angle 633 of 45° achieves a bandwidth of approximately 50 GHz, whereas a waveguide photodiode with the input facet of the absorption region at 90° to the optical axis of the main waveguide only achieves a bandwidth of 20 GHz.

[0090] Other alternatives are within the scope of this specification. For example, the following focuses on Figure 11 , which depicts another example waveguide photodetector 1100 including a waveguide photodiode 1102 that is similar to the combination of the waveguide photodiode 102 and the waveguide photodiode 602 of the waveguide photodetector 300, wherein similar components have similar component numbers. For example, the waveguide photodiode 1102 includes a main waveguide 104 and an absorption waveguide 106 integrated with the main waveguide 104. However, in contrast to the waveguide photodiode 102 and / or the waveguide photodiode 602 of the waveguide photodetector 300, the waveguide photodiode 1102 includes two input facets 108-1, 108-2 at opposite ends of the waveguide photodiode 1102, for example, along its optical axis 122. Furthermore, the waveguide photodetector 1100 includes respective input waveguides 110-1, 110-2 located at opposite ends of a waveguide photodiode 1102, and respective output waveguides 118-1, 118-2 (and respective light collectors 120-1, 120-2) located at opposite ends of the waveguide photodiode 1102. While various angles between the respective input waveguides 110-1, 110-2 and the respective input facets 108-1, 108-2 are not depicted for simplicity, it should be understood that the respective input waveguides 110-1, 110-2 and the respective input facets 108-1, 108-2 have similar geometries as the waveguide photodetector 300 (and / or may be similar to the geometry of the waveguide photodiode 602).

[0091] As depicted, the waveguide photodetector 1100 further includes an n-type doped semiconductor region 625 and a p-type doped semiconductor region 629 of the waveguide photodiode 602. It should be further understood that the geometry of the respective input waveguides 110-1, 110-2 and the respective input facets 108-1, 108-2 directs the refracted light at the two input facets 108-1, 108-2 toward the p-type doped semiconductor region 629. For clarity, Figure 11 In FIG. 1 , the semiconductor regions 625 , 629 are drawn with dashed lines to distinguish the semiconductor regions 625 , 629 from other components of the waveguide photodetector 1100 .

[0092] At the waveguide photodetector 1100, one input waveguide 110-1 can carry light initially in a first polarization state (e.g., TE), while the other input waveguide 110-2 can carry light initially in a second polarization state (e.g., TM). For example, light transmitted to the waveguide photodetector 1100 can carry two polarization states of unknown ratio, and a polarization separation component (not depicted) can separate such light into the two polarization states and transmit such light of different polarization states to the respective input waveguides 110-1 and 110-2, but light from one of the polarization states (e.g., TM) can be converted to the other polarization state (e.g., TE, using any suitable polarization conversion component, not depicted) before inputting into the waveguide photodetector 1100. The length of the waveguide photodiode 1102 (e.g., along the optical axis 122) can be selected so that light refracted into the waveguide photodiode 1102 at one input facet 108 is substantially absorbed by the absorptive waveguide 106 and does not reach the other input facet 108.

[0093] It should be further understood that any waveguide photodetector and / or waveguide photodiode provided herein may be adapted in a similar manner as waveguide photodetector 1100 and / or waveguide photodiode 1102 .

[0094] Many features and advantages of the embodiments will be apparent from the description and, therefore, it is intended that the appended claims cover all such features. Furthermore, since numerous modifications and changes will readily occur to one skilled in the art, it is not desired to limit the embodiments to the exact construction and operation as illustrated and described and, therefore, all suitable modifications and equivalents falling within the scope of the invention may be resorted to.

[0095] It should be further understood that instances of the term "configured to," such as "a computing device configured to," "a processor configured to," "a controller configured to," etc., can be understood to include features of a computer-readable storage medium having program instructions stored thereon, which, when executed by a computing device and / or processor and / or controller, can cause the computing device and / or processor and / or controller to perform a set of operations, which can include the features that the computing device and / or processor and / or controller is configured to perform. Therefore, it should be understood that the term "configured to" is not unduly limited to means-plus-function interpretations, etc.

[0096] In addition, descriptions of a processor and / or controller and / or device and / or engine, etc. configured to perform a particular function should be understood to include but not be limited to more than one processor and / or more than one controller and / or more than one device and / or more than one engine, etc. performing such functions.

[0097] It should be understood that for the purposes of this specification, the language of "at least one of X, Y, and Z" and "one or more of X, Y, and Z" can be interpreted as only X, only Y, only Z, or any combination of two or more items X, Y, and Z (e.g., XYZ, XY, YZ, XZ, etc.). Similar logic can be applied to any two or more items that appear with the language of "at least one of..." and "one or more of..."

[0098] The terms "approximately," "substantially," "substantially," "approximately," and the like are defined as "close to," for example, as understood by one of ordinary skill in the art. In some instances, the terms are understood to mean "within 10%," in other instances "within 5%," in still other instances "within 1%," and in still other instances "within 0.5%."

[0099] Those skilled in the art will appreciate that there are still many more possible alternatives and modifications, and the above examples are only illustrations of one or more examples. Therefore, the scope is limited only by the appended claims.

Claims

1. A waveguide photodetector comprising: A waveguide photodiode comprising: a main waveguide, an absorption waveguide integrated with the main waveguide, and an input facet located on the absorption waveguide; as well as An input waveguide for transmitting light to a waveguide photodiode, wherein an input angle between the input waveguide and an input facet includes an acute interface angle.

2. The waveguide photodetector of claim 1, wherein the acute interface angle is between about 8° and about 65°.

3. The waveguide photodetector of claim 1, wherein the acute interface angle is a Brewster angle.

4. The waveguide photodetector of claim 1, wherein the input waveguide has a first refractive index n1 and the absorption waveguide has a second refractive index n2.

5. The waveguide photodetector of claim 1, further comprising an output waveguide, and an output angle between the output waveguide and the input facet comprises the acute interface angle.

6. The waveguide photodetector of claim 5, further comprising a light absorber located at an end of the output waveguide opposite to a corresponding end at the absorbing waveguide.

7. The waveguide photodetector of claim 1 , wherein the respective optical axes of the input waveguide and the main waveguide are at the acute interface angle, and the input facet is substantially perpendicular to the optical axis of one or more of the absorbing waveguide and the main waveguide.

8. The waveguide photodetector of claim 1 , wherein the respective optical axes of the input waveguide and the main waveguide coincide, and the input facet forms the acute interface angle with a line substantially perpendicular to the optical axis of one or more of the absorption waveguide and the main waveguide.

9. The waveguide photodetector of claim 1, wherein the input facet forms an acute angle with a line substantially perpendicular to the optical axis of one or more of the absorbing waveguide and the main waveguide, the acute angle being different from the acute interface angle.

10. The waveguide photodetector of claim 1, wherein the acute interface angle is between an optical axis of the input waveguide and a normal to the input facet.

11. The waveguide photodetector of claim 1 , wherein the input waveguide comprises silicon with a dielectric cladding.

12. The waveguide photodetector of claim 1, wherein the main waveguide comprises silicon.

13. The waveguide photodetector of claim 1, wherein the absorbing waveguide comprises germanium.

14. The waveguide photodetector of claim 1, wherein one or more corresponding corners of one or more of the input waveguide and the main waveguide include photolithographic compensation structures.

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