INTEGRATED OPTICAL FILTER AND PHOTODETECTOR AND METHOD FOR MANUFACTURING THE SAME

Abstract

Integrated optical filter and photodetector (100), comprising: a substrate (102); an insulating layer (104) on the substrate; a semiconductor layer (106) on the insulating layer; an optical filter (108) comprising a ring resonator with a resonance cavity (110) formed in or on the semiconductor layer; a photodetector (115) comprising part of the ring resonator, one or more first metal fingers (112) on the semiconductor layer and a second metal finger (114) on the semiconductor layer, wherein one or more first metal fingers and the second metal finger are arranged above the part of the ring resonator and form Schottky barriers, and wherein one or more of the first metal fingers are made of a different metal than the second metal finger.

Description

BACKGROUND

[0001] Optoelectronic communication (e.g., using optical signals to transmit electronic data) is increasingly being used as a potential solution, at least in part, for the ever-growing demand for high-bandwidth, high-quality, and low-power data transmission in applications such as high-performance computer systems, high-capacity data storage servers, and network devices. Optoelectronic systems or devices, such as photonic integrated circuits (PICs), have a variety of electronic, optical, and optoelectronic components that can be used to convert, transmit, or process the optical signals or electronic data. For example, optical filters can be used to separate or filter individual wavelengths of a composite or multi-wavelength optical signal (e.g., demultiplexing).Photodetectors can then be used to detect the optical signals at each individual wavelength and convert them into electrical signals. Improved integrated optical filters and photodetectors capable of filtering, detecting, and converting optical signals, as well as methods for fabricating them, are described here. US 2014 / 0376851A1 describes an optical semiconductor device and a method for controlling an optical semiconductor device.

[0002] CN 1 04 303 315 A describes devices with independently controllable electric fields in absorption and multiplication regions.

[0003] The present invention is defined by independent claims 1, 13 and 15. Embodiments are the subject of the respective dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Specific examples are described in detail below with reference to the drawings, in which: Fig. 1A shows a top view of an example of an integrated optical filter and photodetector according to an implementation of the present disclosure; Fig. 1B a sectional view of part of the integrated optical filter and photodetector made of Fig. 1A shows; Fig. 1C a schematic representation of the integrated optical filter and photodetector made of Fig. 1A, which are coupled with ground-signal-ground (GSG) pads, according to an implementation of the present disclosure; Fig. 2A shows a band structure diagram of a Si-based Schottky photodetector with a blocking bias as described herein, according to an implementation of the present disclosure; Fig. 2B and Fig. 2C restricted optical modes within a closed silicon waveguide of the integrated optical filter and photodetector of Fig. 1A and Fig. 2A, surrounded by a copper metal finger or a platinum metal finger on a semiconductor layer, according to an implementation of the present disclosure; and Fig. Figure 3 schematically shows an optical system with an optical receiver comprising an arrangement of integrated optical filters and photodetectors as described herein, according to an implementation of the present disclosure. DETAILED DESCRIPTION OF SPECIFIC EXAMPLES

[0005] Photonic integrated circuits (PICs), and in particular silicon photonics (Si photonics) technology, have attracted increasing interest as a platform for cost-effective, high-speed optical links and data transport due to their ability to overcome the data density limitations of conventional electronic systems. A key application of Si photonics is in the context of fast, low-energy optical links using wavelength division multiplexing (WDM) or dense wavelength division multiplexing (DWDM), which can be deployed in data centers and high-performance computing (HPCs).

[0006] Optical WDM or DWDM links or systems include an optical receiver. Typically, the optical receiver generally has multiple optical filters and separate photodetectors, depending on the desired number of optical channels (e.g., a four-channel optical link has four optical filters to select or filter four specific wavelengths, which are then routed to four separate photodetectors). Each optical filter is coupled to an input waveguide of the receiver to filter a specific wavelength of light from a multi-wavelength optical signal propagating through the input waveguide. Each optical filter then delivers its respective filtered wavelength of light, via a separate waveguide from the input waveguide, to a separate photodetector for conversion into an electrical signal (e.g., for further processing).This consequently leads to an increased number of components, resulting in increased space requirements and increased complexity of such optical connections.

[0007] Additionally, due to the wide bandgap of silicon (e.g., ~1.12 eV) in silicon photonics platforms, heterogeneous integration of germanium (Ge) may be required for photodetection at telecommunications wavelengths (e.g., 1310 nm or 1550 nm) on certain silicon photonics platforms, increasing process time, complexity, and fabrication costs. For example, some conventional photodetectors on silicon photonics platforms are based on a silicon-Ge heterojunction (e.g., a Ge absorption layer, which may require selective epitaxy on the silicon ion insulator (SOI) wafer of such platforms). This Ge epitaxy may require several additional steps, increasing process complexity, time, and cost.

[0008] Therefore, several all-Si photodetectors and methods have been proposed, such as the use of a two-photon absorption mechanism, the insertion of mid-band gap defect states into a silicon lattice, or the deposition of an active polysilicon layer. Such devices and methods either exhibit very poor response sensitivity (e.g., ~10 mA / W) or introduce other complex fabrication or processing steps. Furthermore, many existing photodetectors cannot simultaneously achieve the required high bandwidth and good response sensitivity (e.g., for photodetection at telecommunications wavelengths).

[0009] Several embodiments described herein are directed toward an improved integrated optical filter and photodetector. The disclosed integrated optical filters and photodetectors are uniquely configured to provide both filtering and photodetection capabilities and are capable of simultaneously achieving the required high bandwidth and good response sensitivity for photodetection at telecommunications wavelengths (e.g., 1310 nm or 1550 nm). The integrated optical filter and photodetector can, for example, operate as a filter and photodetector in an optical receiver used in optical communication technologies such as WDM and DWDM. Because of the integration of optical filtering and photodetection functionality into a single component or device, its implementation in optical receivers can offer advantages over many other conventional receiver designs.

[0010] Furthermore, according to certain implementations of this disclosure, the improved integrated optical filter and photodetector, and methods for fabricating it as described herein, may include an optical filter with a resonant cavity. For example, an optical resonator with a microring or ring resonator structure (e.g., a silicon ring resonator) may be configured to function directly as an optical wavelength filter (e.g., to simplify the optical interconnect). The resonant cavity of the optical filter may improve the response sensitivity for photodetection, as further described below, and may also function as an optical wavelength filter, resulting in a cost-effective, fast, and responsive integrated optical filter and photodetector.

[0011] In some implementations, the integrated optical filter and photodetector comprises a Schottky photodetector on a resonant cavity of a ring resonator, operable for telecommunications wavelengths. As described in more detail below, in some implementations, instead of heterogeneous integration, Ge metal fingers are grown or deposited directly on a Si ring resonator (or other enhancement resonator) to form a Si ring resonator-based Schottky photodetector. By adjusting one or more dimensions of the metal fingers (e.g., width, thickness, or length), a surface plasmon-polariton (SPP) effect can be achieved to further improve light-matter interaction in addition to the increased response sensitivity of the ring resonator.As such, the integrated optical filter and photodetector described here can feature a metal-semiconductor-metal (MSM) photodetector structure with thin metal fingers grown directly on a silicon ring resonator or formed otherwise. Due to the absorption enhancement provided by a resonant cavity of the ring resonator and the SPP effect, the integrated optical filter and photodetector can offer a solution that meets the required speed and response sensitivity (e.g., high bandwidth and good sensitivity) for photodetection requirements at telecommunications wavelengths.

[0012] An “optical fiber”, as described here, can refer to a single optical fiber (e.g., with a core and a cladding) to enable unidirectional or bidirectional optical communication, can refer to a bidirectional pair of optical fibers (e.g., each with a core and a cladding) to enable both transmit and receive communication in an optical network, or can refer to a multicore fiber such that a single cladding can encapsulate a multitude of single-mode cores.When a first material or layer is arranged "over" a second material or layer, in the present application the first material or layer may be in direct contact with the second material or layer, or one or more materials or layers may be present between the first and second materials or between the first and second layers. When a first material or layer is arranged "on" a second material or layer, then the first material or layer is in direct contact with the second material or layer, or there is a bonding material or layer between the first and second materials or between the first and second layers.

[0013] The Fig. Figures 1A-1B show an example of an integrated optical filter and photodetector 100 according to the present disclosure. The integrated optical filter and photodetector 100 is a semiconductor-based device comprising a substrate 102 (e.g., an organic substrate layer), an insulating layer 104 on the substrate 102, and a semiconductor layer 106 on the insulating layer 104. An optical filter 108 with a resonant cavity 110 (e.g., a ring resonator) is formed in or on the semiconductor layer 106, as described in more detail below. Furthermore, the integrated optical filter and photodetector 100 has at least two metal fingers (e.g., a first metal finger 112 and a second metal finger 114) on the semiconductor layer 106, as described in more detail below.In the example shown, the integrated optical filter and photodetector 100 has, for example, two first metal fingers 112 and a second metal finger 114 interdigitated between the two first metal fingers 112, which are deposited on the semiconductor layer 106 or otherwise formed and form Schottky barriers (e.g. at corresponding transitions or interfaces of the metal fingers and the semiconductor layer).

[0014] In other examples, only a first metal finger 112 and a second metal finger 114 are included. In other examples, the integrated optical filter and photodetector 100 has more than three metal fingers (e.g., four, five, six, seven, eight, nine). There can be an equal number of first and second metal fingers, or a different number. Furthermore, the damping of the ring resonator can be tuned by changing the number of metal fingers (as described in more detail below). The first metal finger(s) 112 are constructed of a different metal than the second metal finger(s) 114 (e.g., to provide suitable electron and hole barrier heights, as described in more detail below). Additionally, the first and second metal fingers 112 and 114 can be coupled to ground and signal pads, as described in more detail below.

[0015] The substrate 102 can consist of one or more semiconductor materials, including, but not limited to, silicon (Si), indium phosphide (InP), germanium (Ge), gallium arsenide (GaAs), silicon carbide (SiC), or combinations thereof. In specific implementations, such as those described here, the substrate 102 is a Si substrate. For example, the optical filter and photodetector 100 is a silicon-on-insulator (SOI) in which the insulating layer 104 is positioned between a Si substrate and a Si semiconductor layer (e.g., the substrate 102 and the semiconductor layer 106). In other implementations, the optical filter and photodetector 100 has a silicon-on-glass structure.

[0016] In some implementations, the insulating layer 104 is a buried oxide layer (BOX) consisting of silicon dioxide or another insulating oxide material. In certain implementations, the insulating layer 104 can be formed by oxidizing the substrate 102. For example, if the substrate 102 consists of Si, the insulating layer 104 can consist of silicon dioxide (SiO2), which can be formed in the presence of oxygen at a temperature in the range of 900 °C to 1300 °C. In other embodiments, the insulating layer 104 can be a buried oxide layer, such that the silicon dioxide is buried within the substrate 102. In some examples, a layer of silicon dioxide acting as the insulating layer 104 can be buried within the substrate 102 at a depth of less than 100 nm to several micrometers from the substrate or wafer surface, depending on the application.In other implementations, the insulating layer 104 consists of a different insulating material such as sapphire, diamond, or glass.

[0017] As in the implementation of the Fig. As shown in Figures 1A-1B, the optical filter 108 of the integrated optical filter and photodetector 100 can be a ring resonator (e.g., a silicon ring resonator) with a resonant cavity 110. The ring resonator (e.g., a closed waveguide) filters or couples a resonant wavelength of light from a bus waveguide or other suitable output waveguide 116. The optical resonance in the resonant cavity 110 can greatly improve the length of the light-matter interaction and therefore reduce the amount or level of light absorption required at the interface or transition between the metal fingers 112 and 114 (e.g., directly at the ring resonator, as described in more detail below) and the semiconductor layer 106. Additionally, the quality factor (Q) of the ring resonator is strongly dependent on the loss coefficient of the ring resonator. Thus, the Q-factor of the ring resonator can be determined even though the absorption per circle (e.g.,Since the cycle value can be relatively low, a higher optical intensity in the ring resonator is possible (which can, for example, further compensate for the overall absorption coefficient), thereby increasing the response sensitivity. For example, the response sensitivity can be increased to a value of approximately 0.1 to 0.3 A / W.

[0018] As described above, the first and second metal fingers 112 and 114 are deposited directly onto the semiconductor layer 106 (e.g., the ring resonator formed in or on the semiconductor layer 106) or formed by other means. The semiconductor layer 106 or the ring resonator formed in or on the semiconductor layer 106 can be formed from an undoped or intrinsic semiconductor material (e.g., Si), since the metal fingers 112 and 114 lie directly on the ring resonator or the semiconductor layer 106 and form Schottky barriers (e.g., to form a Schottky photodetector) without any intervening doped layers, unlike a PIN photodiode (e.g., for the deposition of Ge on it). In other words, the integrated optical filter and photodetector 100 with Schottky barriers can absorb light of telecommunications wavelengths (e.g. with Si as semiconductor layer 106) without additional doping process or Ge epitaxy steps.Furthermore, the undoped semiconductor or silicon layer is beneficial for charge carrier transit. A low bias depletes the undoped region between the metal fingers, allowing the electric field to draw charge carriers through this depletion region, potentially leading to a higher bandwidth. Additionally, the undoped semiconductor layer can prevent the absorption of free charge carriers, thus reducing optical loss in the ring resonator. Finally, undoped silicon or another semiconductor material can simplify the process complexity described here (e.g., no additional doping processes are required, and problems with doping diffusion due to process heat are avoided).

[0019] The first and second metal fingers 112 and 114 are arranged on the ring resonator or the semiconductor layer 106 such that the photodetector has a metal-semiconductor-metal (MSM) structure. The first and second metal fingers 112 and 114 can be coupled to ground-signal-ground (GSG) pads, as shown in Fig. Figure 1C is shown. In some implementations, as shown, the first metal fingers 112 are coupled to ground pads and the second metal finger 114 is coupled to a signal pad and configured to be biased in the blocking direction to achieve a GSG configuration.

[0020] Metals with suitable work functions (e.g. Φ) MThe values ​​for the first and second metal fingers 112 and 114 are selected to achieve an effective barrier emission probability. In general, the quantum efficiency of a Schottky photodetector (e.g., the integrated optical filter and photodetector 100) increases with a lower barrier height. However, the dark current also typically increases with a lower barrier height. Therefore, a suitable Schottky barrier height is required to maximize the sensitivity of the integrated optical filter and photodetector 100 (e.g., the MSM photodetector). Various metal combinations (e.g. Cu / Al, Cu / Pt, Cu / Pd, Cu / Au or other suitable metal material combinations) for the first and second metal fingers 112 and 114 can be selected to form Schottky barriers (e.g. on a Si-based semiconductor layer 106 or a ring resonator) with suitable barrier heights (e.g. about 0.2 eV to 0.4 eV).

[0021] For example, in Fig. 2A a band structure diagram of a Si-based Schottky photodetector (e.g. the integrated optical filter and photodetector 100 from Fig. 1C) with a blocking bias. As shown, an image force effect can be seen or recognized at the corners, which can further improve the internal photoemission effect (IPE) or ΔΦ of the respective Schottky barriers (e.g., Cu and Pt metal fingers) and reduce the effective barrier heights, where Φ N and Φ P The electron and hole barrier heights of the respective metal fingers are represented (e.g., with suitable barrier heights of approximately 0.38 eV and 0.25 eV, respectively), and Eg is the energy gap of semiconductor layer 106. IPE increases with bias voltage. Therefore, when a voltage is applied to the metal fingers, the image force effect leads to an increased IPE and reduced effective barrier heights.

[0022] Referring to the example in Fig. In 2A, the Si-based semiconductor layer 106 or the ring resonator has an energy gap or band gap of approximately 1.12 eV. The metal fingers 112 and 114 are constructed from different metals (e.g., Pt and Cu) as described above and are coupled to ground pads and a signal pad, respectively. As shown, by selecting suitable different metals for the metal fingers, appropriate hole and electron barrier heights (e.g., 0.25 eV and 0.38 eV) as well as response sensitivities (e.g., for telecom wavelengths) can be achieved for the integrated optical filters and photodetectors described here.

[0023] Additionally, by configuring the metal fingers 112 and 114 of the MSM photodetector with suitable dimensions (e.g., thickness T, width W, and length L) and the distance S (e.g., edge-to-edge) between the metal fingers, a surface plasmon polariton (SPP) effect can be realized to further restrict the optical mode at the interface or transition between the metal fingers 112 and 114 and the semiconductor layer 106 (e.g., Si ring resonator). Such improved optical confinement enables a suitable loss coefficient (e.g., of the ring resonator) to achieve a high photon lifetime-limited bandwidth for the integrated optical filter and photodetector 100.Furthermore, the integrated optical filter and photodetector 100, due to its MSM structure, is capable of achieving a very high bandwidth (up to ~ THz) because of the small gaps or distances between the metal fingers and the width W, as well as the very small RC time constant (e.g., by adjusting the metal finger widths and distances). In some examples described here, W can be in the range of approximately 300 nm to 500 nm, T in the range of approximately 10 to 70 nm, S in the range of approximately 100 nm to 1000 nm, and L in the range of approximately -100 nm to several µm.

[0024] Furthermore, configuring the metal fingers with a thickness T sufficiently below the mean free path of the charge carriers can also improve the internal quantum efficiency. Fig. Figures 2B-2C show the restricted optical mode in the closed waveguide of a ring resonator of the integrated optical filter and photodetector 100 with Cu and Pt metal fingers (T=30 nm, W=450 nm, L=500 nm, S=500 nm) on a Si ring resonator and an optical signal with a wavelength of 1310 nm, respectively. With reference back to Fig. 2A The Cu fingers have a relatively low barrier height for electrons and the Pt finger has a relatively low barrier height for holes, so that the integrated optical filter and photodetector 100 has suitable barrier heights, as described herein, for both electrons and holes.

[0025] In asymmetric cladding layers (e.g., different dielectrics above and below the metal fingers), a bound TM-like mode (e.g., a quasi-TM mode) can be observed due to the SPP effect described above. While the depicted metal fingers are embedded between Si and air, in other examples the metal fingers may be embedded between other materials (such as Si and SiO2). The SPP effect is a coupled excitation involving electron oscillation in the metal (e.g., metal fingers 112 and 114) and an electromagnetic wave. This TM-like surface mode resulting from the SPP effect allows for increased confinement (e.g., of the light mode around the interface between the metal and Si) and a higher loss coefficient, so that the light has a higher probability of being absorbed by the integrated optical filter and photodetector 100, leading to better optical absorption per circuit.

[0026] With reference to Fig. Figure 3 comprises an optical system 300 with an optical transmitter 322 coupled to an optical receiver 330 via an optical fiber 332 (e.g., forming an optical WDM or DWDM link). The optical transmitter 322 includes an optical multi-wavelength source 324 (e.g., a comb laser) configured to emit an optical multi-wavelength signal. The optical transmitter 322 includes a waveguide 326, the first end of which is coupled to the optical multi-wavelength source 324 (e.g., via an input coupler 328) and configured to receive the optical multi-wavelength signal from the optical multi-wavelength source 324.

[0027] The optical transmitter 322 further comprises an array of two or more optical modulators 350 (e.g., four) coupled to the waveguide 326, wherein a first optical modulator is configured to filter and modulate data on the first wavelength of light (e.g., λ1) from the waveguide, and a second optical modulator is configured to filter and modulate data on the second wavelength of light (e.g., λ2) from the waveguide 326, and wherein the first and second modulated wavelengths of light are multiplexed together back into the waveguide 326 and transmitted via the optical fiber 332 to the optical receiver 330. A first end of the optical waveguide 332 can be coupled to an output coupler 352 of the optical transmitter 302, which is coupled to a second end of the waveguide 326. A second end of the optical waveguide 332 can be coupled to the optical receiver 330 (e.g.via an input coupler 338).

[0028] The light can then be transmitted from a chip or device on which the optical transmitter 302 is arranged via the optical fiber 332 and sent via the optical fiber 332 to be demultiplexed and converted from the optical domain to the electrical domain by the optical receiver 330. The optical receiver 330 can include the input coupler 338 to couple the optical fiber 332 to a waveguide 336.

[0029] The optical receiver 330 includes the waveguide 336, which is configured to receive the multi-wavelength optical signal from the optical transmitter with data signals modulated onto it. The optical receiver comprises an array of two or more integrated optical filters and photodetectors 354 (e.g., four) coupled to the waveguide 336. The integrated optical filters and photodetectors 354 can include any of the features of integrated optical filters and photodetectors described herein (e.g., integrated optical filters and photodetectors 100).A first integrated optical filter and photodetector is configured to filter the first wavelength of light from the multi-wavelength optical signal propagating through waveguide 336, and a second integrated optical filter and photodetector is configured to filter the second wavelength of light from the multi-wavelength optical signal propagating through waveguide 336, which differs from the first wavelength of light. As described above, each of the first and second integrated optical filters and photodetectors comprises a substrate, an insulating layer on the substrate, and a semiconductor layer on the insulating layer.

[0030] Each of the first and second integrated optical filters and photodetectors also includes an optical filter (e.g., optical filter 108) with a resonant cavity (e.g., cavity 110) formed in or on the semiconductor layer (e.g., a ring resonator 334 with a closed waveguide). Each of the ring resonators 334 (individually designated 334a-1, 334a-2, up to 334a-n, where n = 2, 4, 8, 16, 32, etc.) is configured to be tuned to different resonant wavelengths, each corresponding to different wavelengths of the light emitted by the optical transmitter 302.

[0031] The resonance characteristics of each ring resonator 334 can be precisely tuned to select the specific wavelength by adjusting the radius of each ring or the mantle index. Tuning can be achieved by thermal tuning (e.g., providing controllable microheating through each ring resonator), by bias tuning, or by a combination of both. Although ring resonators are specifically referenced, in other examples, ring resonators as described here can be replaced by microdiscs or other suitable traveling-wave resonators.

[0032] The ring resonators 334 act as filters to extract the respective resonant wavelengths from the waveguide 336. The array of ring resonators 334 receives the multi-wavelength optical signals from the optical transmitter 302. Resonant wavelengths specific to or corresponding to each ring resonator 334 are individually demultiplexed into separate integrated Schottky photodetectors to convert the optical signals into electrical signals (e.g., for further processing), as described here. Thus, each of the ring resonators 334 can "drop" or otherwise filter a single wavelength of the modulated light or of the signals from the multiplexed optical signals with multiple wavelengths of the light received via the optical fiber 332.

[0033] Each of the first and second integrated optical filters and photodetectors also includes two first metal fingers 312 and one second metal finger 314, which interlock between the two first metal fingers on the semiconductor layer or closed waveguide of each ring resonator and form Schottky barriers (e.g., forming a Schottky photodetector integrated on each ring resonator 334), the first metal fingers being constructed of a different metal than the second metal finger. Each of the Schottky photodetectors is integrated with the respective ring resonator 334 to form the array of wavelength-selective photodetectors (e.g., integrated optical filter and photodetector).

[0034] An example method for fabricating an integrated optical filter and photodetector, as described here, may include one or more of the following steps. The method includes providing a substrate, an insulating layer on the substrate, and a semiconductor layer on the insulating layer. The method includes forming an optical filter with a resonant cavity in or on the semiconductor layer and depositing first metal fingers and a second metal finger, interdigitated between the two first metal fingers, onto the semiconductor layer, forming Schottky barriers. The first metal fingers are made of a different metal than the second metal finger.

[0035] In some implementations, the step of forming an optical filter in or on the semiconductor layer includes forming a ring resonator (e.g., forming a ring resonator with a closed waveguide in the semiconductor layer). In some implementations, the step of depositing the first metal fingers and a second metal finger interdigitated between the two first metal fingers on the semiconductor layer includes depositing the first metal fingers and the second metal finger onto the ring resonator (e.g., the closed waveguide of the ring resonator). In still other implementations, as described here, the semiconductor layer, the insulator layer, and the substrate have a silicon-on-insulator (SOI) structure.

[0036] As described above, such an improved integrated optical filter and photodetector, along with methods for its fabrication, can simplify the assembly process and reduce assembly time and costs. This is because the IPE (Integrated Optical Equivalent) of Schottky barriers can overcome the limitations of certain semiconductor materials that cannot absorb light at telecommunications wavelengths without additional Ge epitaxy steps. Furthermore, since the photodetector components consist only of semiconductor material and metal fingers, no additional doping processes, as required for PIN photodiodes, are necessary. Integrating the photodetector and optical filter onto a single device, as described here, can save space and simplify the optical WDM interconnect of a Si photonics platform. The resonant nature of the microring or ring resonator and the mode confinement provided by the SPP (Single-Pulse Photon) effect can dramatically improve light-matter interaction.This improvement is helpful in achieving the response sensitivity necessary for photodetection of light at telecommunications wavelengths. Furthermore, the MSM structure of the photodetector enables a high transit-time-limited bandwidth and a high RC-time-limited bandwidth due to the flexibility to adapt metal finger material, widths, and gap or spacing widths.

[0037] It is acknowledged that the terms "comprehensive," "include," and "with," as used herein, are expressly to be understood as open technical terms. The term "or" in relation to a list of two or more elements covers all of the following interpretations of the word: each of the elements in the list, all the elements in the list, and any combination of the elements in the list. As used herein, the terms "connected," "coupled," or any variant thereof, mean any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements may be physical (e.g., mechanical), logical, electrical, optical, or a combination thereof.

[0038] In the figures, identical reference numbers denote identical or at least generally similar elements. To facilitate the explanation of a particular element, the most significant digit or digits of a reference number refer to the figure in which that element is first introduced. For example, element 110 is first described with reference to Fig. 1. presented and explained.

Claims

[1] Integrated optical filter and photodetector (100), comprising: a substrate (102); an insulating layer (104) on the substrate; a semiconductor layer (106) on the insulating layer; an optical filter (108) comprising a ring resonator with a resonance cavity (110) formed in or on the semiconductor layer; a photodetector (115) comprising part of the ring resonator, one or more first metal fingers (112) on the semiconductor layer and a second metal finger (114) on the semiconductor layer, wherein one or more first metal fingers and the second metal finger are arranged above the part of the ring resonator and form Schottky barriers, and wherein one or more of the first metal fingers are made of a different metal than the second metal finger. [2] Integrated optical filter and photodetector according to claim 1, wherein the one or more first metal fingers are spaced apart from the second metal finger by between 100 nm and 1000 nm. [3] Integrated optical filter and photodetector according to claim 1, wherein the one or more first metal fingers comprise two first metal fingers, wherein the second metal finger is interdigitated between the first metal fingers and wherein the first metal fingers and the second metal finger are formed on the ring resonator. [4] Integrated optical filter and photodetector according to claim 3, wherein the first metal fingers and the second metal finger interdigitated between the two first metal fingers have a ground-signal-ground, GSG, pad configuration (124). [5] Integrated optical filter and photodetector according to claim 1, wherein at least one of the first metal fingers forms a Schottky barrier with the semiconductor layer having a hole barrier height between 0.2 eV and 0.4 eV, and wherein the second metal finger forms a Schottky barrier with the semiconductor layer having an electron barrier height between 0.2 eV and 0.4 eV. [6] Integrated optical filter and photodetector according to claim 1, wherein one or more first metal fingers are made of one or more of the following materials: copper, aluminum, platinum, palladium or gold. [7] Integrated optical filter and photodetector according to claim 1, wherein the second metal finger is made of one or more of the following materials: copper, aluminum, platinum, palladium or gold. [8] Integrated optical filter and photodetector according to claim 1, wherein the semiconductor layer is not doped. [9] Integrated optical filter and photodetector according to claim 1, wherein the semiconductor layer, the insulator layer and the substrate have a silicon-on-insulator (SOI) structure. [10] Integrated optical filter and photodetector according to claim 1, wherein the integrated optical filter does not have a germanium layer formed in or on the semiconductor layer. [11] Integrated optical filter and photodetector according to claim 1, wherein the one or more first metal fingers have a thickness between 10 nm and 70 nm. [12] Integrated optical filter and photodetector according to claim 1, wherein the one or more first metal fingers have a width between 300 nm and 500 nm. [13] Method for manufacturing an integrated optical filter and photodetector (100), the method comprising: Providing a substrate (102), an insulating layer (104) on the substrate and a semiconductor layer (106) on the insulating layer; Forming an optical filter (108) comprising a ring resonator with a resonant cavity (110) in or on the semiconductor layer; Forming a photodetector (115) integrated with the optical filter by depositing one or more first metal fingers (112) and a second metal finger (114) on the semiconductor layer, which are arranged over a part of the ring resonator and form Schottky barriers, wherein the one or more first metal fingers are made of a different metal than the second metal finger. [14] Method according to claim 13, wherein the one or more first metal fingers comprise two first metal fingers and the application of the one or more first metal fingers and the second metal finger comprises the application of the second metal finger interdigitated between the two first metal fingers on the ring resonator. [15] Optical system (300) with: an optical receiver (330), comprising: a waveguide (336) configured to receive an optical signal with multiple wavelengths; an array of two or more integrated optical filters and photodetectors (354) coupled to the waveguide, wherein a first integrated optical filter and photodetector is configured to filter a first wavelength of light from the multi-wavelength optical signal propagating through the waveguide, and a second integrated optical filter and photodetector is configured to filter a second wavelength of light from the multi-wavelength optical signal propagating through the waveguide, which is different from the first wavelength of light, and wherein each of the first and second integrated optical filters and photodetectors comprises the following: a substrate; an insulating layer on the substrate; a semiconductor layer on the insulating layer; an optical filter (108) comprising a ring resonator with a resonance cavity (110) formed in or on the semiconductor layer; a photodetector comprising a part of the ring resonator and two first metal fingers (312) and a second metal finger (314) interdigitated between the two first metal fingers on the semiconductor layer, forming Schottky barriers, wherein the first metal fingers and the second metal finger are arranged over the part of the ring resonator and the first metal fingers are made of a different metal than the second metal finger. [16] Optical system according to claim 15, further comprising: an optical transmitter (322) coupled to the optical receiver via an optical fiber (332), which includes the optical transmitter: an optical multi-wavelength source (324) configured to emit the optical multi-wavelength signal; a waveguide (326) coupled to the optical multi-wavelength source and configured to receive the optical multi-wavelength signal from the optical multi-wavelength source; and an array of two or more optical modulators (350) coupled to the waveguide, wherein a first optical modulator is configured to filter and modulate data on the first wavelength of the light from the waveguide, and a second optical modulator is configured to filter and modulate data on the second wavelength of the light from the waveguide, and wherein the first and second modulated wavelengths of the light are multiplexed together back into the waveguide and transmitted via the optical fiber to the optical receiver. [17] Optical system according to claim 16, wherein each of the optical modulators comprises a ring resonator. [18] Optical system according to claim 15, wherein the optical receiver does not have waveguides coupling the respective optical filters of the integrated optical filters and photodetectors to the respective photodetectors of the integrated optical filters and photodetectors.

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