Circuits and methods for photonic wavelength division multiplexers

Abstract

Photonics has become a dominant or continuously developing technical solution for communication to meet the ever-increasing bandwidth demand. Wavelength division multiplexing (WDM) enables an optical fiber to support multiple and emit light signals, each signal having a different wavelength. However, manufacturing tolerances may affect the performance of these WDM multiplexers and demultiplexers. However, active deployment with WDM active thermal control may result in increased power consumption, thereby increasing initial deployment and lifecycle operating costs. Thus, this will be beneficial if a control method and circuit that reduces the thermal control power demand can be established.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims priority to U.S. Provisional Patent Application No. 63 / 571,651, filed on March 29, 2024.

[0002] This patent application claims priority to U.S. Provisional Patent Application No. 63 / 657,253, filed on June 7, 2024. Technical Field

[0003] The present invention relates to photonic circuits for optical networks, and more particularly to methods and apparatus structures for tuning coarse wavelength division multiplexer-demultiplexers. Background Art

[0004] Photonics has become the dominant or growing technology solution in a wide range of applications, including sensing, biomedical sensing, quantum computing, quantum sensing, and telecommunications. In the communications streaming sector, mobile data traffic and cloud computing continue to drive the ever-increasing demand for bandwidth at low costs, both in terms of the initial cost of the system and its installation, as well as the subsequent lifecycle operating costs.

[0005] Among established and emerging technologies, silicon photonics is a promising technology for adding integrated optical functions to integrated circuits or for discretely implementing photonic circuits by leveraging the economies of scale of the CMOS microelectronics industry. Some variants of silicon photonics can use other materials as waveguide cores, such as silicon nitride (SixNy) and silicon oxynitride (SiOxN1-x). In addition to utilizing CMOS-based silicon manufacturing processes, silicon photonics allows the integration of control and drive CMOS electronics, either alone or in combination with microelectromechanical systems (MEMS) elements, to provide micro-opto-electromechanical systems (MOEMS).

[0006] Furthermore, wavelength division multiplexing (WDM) allows optical fibers to support multiple, concurrently transmitted signals, each with a different wavelength. For example, coarse wavelength division multiplexing (CWDM) networks support up to 18 wavelengths with a 20nm channel spacing, ranging from 1271nm to 1611nm, and can achieve transmission distances of approximately 150km. However, manufacturing tolerances can affect the performance of multiplexers and demultiplexers in these CWDM networks, resulting in lower yields and increased component costs in passive deployments (without CWDM's active thermal control); while in active deployments (with CWDM's active thermal control), this can lead to increased power consumption, offsetting the reduction in initial deployment costs and increasing lifecycle operating costs. Therefore, it is beneficial to establish control methods and circuits that minimize the power requirements for thermal control.

[0007] Those skilled in the art will understand other aspects and features of the present invention by reading the following description of specific embodiments of the present invention in conjunction with the accompanying drawings. Summary of the Invention

[0008] The present invention aims to alleviate the limitations of the prior art relating to photonic circuits for optical networks, and more particularly to methods and apparatus structures for tuning coarse wavelength division multiplexer-demultiplexers.

[0009] According to an embodiment of the present invention, there is provided a device comprising: a plurality of circulating optical wavelength filters (COWFs) arranged in series in a plurality of stages; wherein each COWF of each of the plurality of stages, except for a last stage in the plurality of stages, coupled to a pair of COWFs in a next stage in the plurality of stages; A first stage of the plurality of stages is coupled to a port for receiving a plurality of wavelength division multiplexed signals on a defined wavelength grid; Within a stage in the plurality of stages, each COWF in the plurality of COWFs has a free spectral range (FSR) equal to a predetermined fraction of the FSR of those COWFs in a next stage in the plurality of stages; a subset of the plurality of stages including at least a first stage of the plurality of stages comprising a phase shift element (PSE) for adjusting characteristics of the COWF within the subset of the plurality of stages; and The COWFs in the plurality of COWFs in the subsequent ones of the plurality of stages to the first one of the plurality of stages are independent of the PSE configuration for adjusting characteristics of the COWFs in the subsequent ones of the plurality of stages to the first one of the plurality of stages.

[0010] According to an embodiment of the present invention, a method is provided, comprising: A plurality of circulating optical wavelength filters (COWFs) are provided, arranged in series in a plurality of stages; wherein each COWF of each of the plurality of stages, except for a last stage in the plurality of stages, coupled to a pair of COWFs in a next stage in the plurality of stages; A first stage of the plurality of stages is coupled to a port for receiving a plurality of wavelength division multiplexed signals on a defined wavelength grid; Within a stage in the plurality of stages, each COWF in the plurality of COWFs has a free spectral range (FSR) equal to a predetermined fraction of the FSR of those COWFs in a next stage in the plurality of stages; a subset of the plurality of stages including at least a first stage of the plurality of stages comprising a phase shift element (PSE) for adjusting characteristics of the COWF within the subset of the plurality of stages; and The COWFs in the plurality of COWFs in the subsequent ones of the plurality of stages to the first one of the plurality of stages are independent of the PSE configuration for adjusting characteristics of the COWFs in the subsequent ones of the plurality of stages to the first one of the plurality of stages.

[0011] Those skilled in the art will understand other aspects and features of the present invention by reading the following description of specific embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0013] Figure 1 A wavelength demultiplexer (WDMUX) design is described that utilizes cascaded wavelength filters, where the wavelength demultiplexer has a different free spectral range in each state;

[0014] Figure 2 A WDMUX utilizing a bandpass flattening wavelength filter utilizing cascaded Mach-Zehnder interferometer (MZI) elements is described;

[0015] Figure 3 A WDMUX utilizing bandpass flattening wavelength filters utilizing cascaded Mach-Zehnder interferometer (MZI) elements is described, wherein each stage comprises a WDMUX with an additional wavelength filter at each output;

[0016] Figure 4 Describes the Figure 3 The wavelength output of the designed WDMUX with nominal design parameters is Figure 5 Describes the wavelength output results of the WDMUX when the width and thickness deviate from the nominal design parameters;

[0017] Figure 6A Describes a design method according to an embodiment of the present invention, wherein only Figure 3 The initial stage of the designed WDMUX is temperature controlled, along with a schematic diagram showing the circuit design of the electrical and optical layers;

[0018] Figure 6B Describes the electrical control and heater configuration of the cascaded MZIs employed within embodiments of the present invention, and a design route for low electrical power consumption of silicon waveguides; and

[0019] Figure 7A and Figure 7B An electrical control path is described, along with a phase shifter element that is actuated in two different activation states. DETAILED DESCRIPTION

[0020] The present invention relates to photonic circuits for optical networks, and more particularly to methods and apparatus structures for tuning coarse wavelength division multiplexer-demultiplexers.

[0021] The subsequent description provides representative embodiments only and is not intended to limit the scope, applicability or configuration of the present disclosure. More specifically, the subsequent description of the embodiments will provide those skilled in the art with a feasible description for implementing one or more embodiments of the present invention. It should be understood by those skilled in the art that various changes may be made to the function and arrangement of the elements without departing from the scope of the present invention as set forth in the claims. Therefore, the embodiments are examples or implementations of the present invention, rather than the only implementations. The various appearances of "one embodiment," "embodiment," or "some embodiments" do not necessarily represent the same embodiment. Although the various features of the present invention may be described in the context of a single embodiment, these features may also be provided individually or in any suitable combination. On the contrary, for clarity, although the present invention may be described in the context of a single embodiment, the present invention may also be implemented in a single embodiment or in any combination of embodiments.

[0022] Reference in this specification to "one embodiment," "an embodiment," "some embodiments," or "other embodiments" means that a particular feature, structure, or characteristic associated with the embodiment is included in at least one embodiment, but not necessarily in all embodiments. The words and terminology used herein should not be construed as limiting and are for descriptive purposes only. It should be understood that when a claim or specification refers to "a" or "an" element, such reference should not be interpreted as meaning that there is only one of that element. It should be understood that when the specification states that a component feature, structure, or characteristic "may," "might," "could," or "can" include, that particular component, feature, structure, or characteristic is not required to be included.

[0023] References to terms such as "left," "right," "top," "bottom," "front," and "back" are intended to describe the orientation of a particular feature, structure, or component in the figures describing embodiments of the present invention. Obviously, such directional terms have no specific meaning with respect to actual use of the device, as the device can be employed in a variety of orientations by one or more users.

[0024] References to the terms "including," "comprising," "consisting of," and their grammatical variations do not preclude the addition of one or more components, features, steps, integers, or combinations thereof, and these terms should not be interpreted as referring to specific components, features, steps, or integers. Similarly, the phrase "consisting essentially of," and its grammatical variations, when used herein, should not be interpreted as excluding additional components, steps, features, integers, or combinations thereof, but rather as meaning that these additional features, integers, steps, components, or combinations thereof do not materially alter the basic and novel characteristics of the claimed composition, apparatus, or method. If the specification or claims refer to "additional" elements, this does not preclude the presence of more than one additional element.

[0025] As used herein, a "two-dimensional" waveguide, also referred to as a 2D waveguide or planar waveguide, may refer to, but is not limited to, an optical waveguide that supports propagation of optical signals within a predetermined wavelength range but does not guide the optical signals in a direction transverse to the direction of propagation of the optical signals.

[0026] As used herein, a "three-dimensional" waveguide, also referred to as a 3D waveguide, a channel waveguide, or simply a waveguide, may refer to, but is not limited to, an optical waveguide that supports propagation of optical signals within a predetermined wavelength range and guides the optical signals in a direction transverse to the propagation direction of the optical signals.

[0027] As used herein, a "photonic integrated circuit" (PIC) may refer to, but is not limited to, the monolithic integration of multiple integrated optical devices into a circuit formed on a common substrate to provide optical routing and processing capabilities. PICs are fabricated using wafer-level processing techniques, such as CMOS fabrication flows, MEMS fabrication flows, and the like.

[0028] As used herein, an "adiabatic coupler" may refer to, but is not limited to, an optical coupler that adiabatically converts a mode of an input optical waveguide into an even mode or an odd mode of two or more optical waveguides separated by a small gap. Thus, an adiabatic coupler may be, for example, a non-zero gap symmetrical directional coupler or a non-zero gap asymmetrical directional coupler.

[0029] In embodiments of the present invention, the inventors may refer to the term "hybridly integrated". In certain embodiments of the present invention, "hybridly integrated" may refer to, but is not limited to, "integrating" an optical element into a substrate by attaching the optical element or other elements physically integrated with the optical element to the substrate (platform) so that the optical element remains in place. Such attachment methods may include, but are not limited to, welding, epoxy resin, van der Waals forces, electrostatic attachment, magnetic attachment, physical interlocking, and friction. Therefore, in these embodiments of the present invention, the hybrid integrated optical element may be considered to be implemented in a manufacturing process parallel to other optical elements before being assembled together. The parallel manufacturing process may adopt one or more of the following combinations, including but not limited to liquid phase epitaxy (LPE), metal organic chemical vapor deposition (MOCVD), organometallic vapor phase epitaxy (OMVPE), selective area epitaxy, additive manufacturing processes, non-additive manufacturing processes, crystal growth, doping, induced damage, etching, doping, and deposition.

[0030] In other embodiments of the present invention, this approach may refer to, but is not limited to, "integrating" an optical element onto a substrate using a manufacturing method and / or technique that is different from the manufacturing method and / or technique used to form other optical components on the substrate. For example, this may utilize an LPE process to form another optical element on a substrate, wherein the optical element on the substrate is formed by MOCVD, or vice versa. Alternatively, the optical component and the other optical components may be formed using the same manufacturing method or a combination of manufacturing methods. These manufacturing methods may utilize one or more processes selected from the following combinations, including but not limited to LPE, MOCVD, OMVPE, selective area epitaxy, additive manufacturing processes, subtractive manufacturing processes, non-additive manufacturing processes, crystal growth, doping, induced damage, etching, doping and deposition.

[0031] In embodiments of the present invention, the inventors refer to the terms "hybridly integrated" and "hybrid integration". In some embodiments of the present invention, "hybrid integration" may refer to, but is not limited to, "integrating" optical elements into a substrate by attaching optical elements or other elements physically integrated with the optical elements to a substrate (platform) so that the optical elements remain in place. Such attachment methods may include, but are not limited to, welding, epoxy resin, van der Waals forces, electrostatic attachment, magnetic attachment, physical interlocking, and friction. Therefore, in these embodiments of the present invention, the hybrid integrated optical elements may be considered to be implemented in a manufacturing process parallel to other optical elements before being assembled together. The parallel manufacturing process may adopt one or more of the following combinations, including but not limited to liquid phase epitaxy (LPE), metal organic chemical vapor deposition (MOCVD), organometallic vapor phase epitaxy (OMVPE), selective area epitaxy, additive manufacturing processes, non-additive manufacturing processes, crystal growth, doping, induced damage, etching, doping, and deposition.

[0032] In the embodiments of the present invention, the inventors refer to the terms "monolithically integrated" and "monolithically integrated". In some embodiments of the present invention, this approach may refer to, but is not limited to, "integrating" optical elements onto a substrate by directly forming optical elements on the substrate (platform). The optical element may be one of a series of optical elements formed on the substrate to form an optical assembly or optical circuit. These optical elements may be optical waveguides themselves, may be interconnected by optical waveguides, may be interconnected by other optical elements formed on the substrate in subsequent processing steps or stages, or may be interconnected by other hybrid optical elements integrated onto the substrate. Therefore, these monolithically integrated optical elements, such as in these embodiments of the present invention, optical waveguides may be manufactured using one or more processes selected from the following combinations, including but not limited to liquid phase epitaxy (LPE), metal organic chemical vapor deposition (MOCVD), organometallic vapor phase epitaxy (OMVPE), selective area epitaxy, photolithography, direct write, ion beam milling, additive manufacturing processes, non-additive manufacturing processes, crystal growth, doping, induced damage, chemical etching, reactive ion etching (RIE), plasma etching, sputter etching, ion beam assisted etching, reactive ion beam etching, lift-off, and deposition.

[0033] As used herein, "ceramic" may refer to, but is not limited to, an inorganic, non-metallic solid material comprising metal, non-metal, or metalloid atoms primarily bound by ionic and covalent bonds. Such ceramics may be crystalline materials, such as oxides, nitrides, or carbides; may be elements, such as carbon or silicon; or amorphous materials. Exemplary ceramics may include high-temperature ceramics or high-temperature co-fired ceramics, such as aluminum oxide (Al2O3), zirconium oxide (ZrO2), and aluminum nitride (AlN), or low-temperature co-fired ceramics (LTCC). LTCCs may be formed from glass-ceramic combinations.

[0034] As used herein, the term "metal" or "alloy" may refer to, but is not limited to, materials with good electrical and thermal conductivity. Metals are generally malleable, fusible, and ductile. As used herein, metals may refer to elements such as gold, silver, copper, aluminum, and iron, while alloys, as used herein, refer to combinations of metals such as bronze, stainless steel, and steel.

[0035] As used herein, "polymer" may refer to, but is not limited to, a macromolecule or high molecule composed of many repeating subunits. Such polymers may be natural or synthetic and are typically produced by the polymerization of multiple monomers. Polymers can provide unique physical properties through their large molecular weight, including toughness, viscoelasticity, and a tendency to form glassy and semi-crystalline structures rather than crystals.

[0036] As used herein, "glass" may refer to, but is not limited to, an amorphous solid in a non-crystalline state. Glass may be, for example, fused quartz, silica, soda-lime glass, borosilicate glass, lead glass, aluminosilicate glass. Glass may include other inorganic and organic materials, including metals, aluminates, phosphates, borates, chalcogenides, fluorides, germanates (glasses based on GeO2), tellurites (glasses based on TeO2), antimonates (glasses based on Sb2O3), arsenates (glasses based on As2O3), titanates (glasses based on TiO2), tantalates (glasses based on Ta2O5), nitrates, carbonates, plastics, and acrylics.

[0037] As used herein, a "cyclic" wavelength division multiplexer (WMUX) may refer to, but is not limited to, a WMUX having a free spectral range (FSR), such that the filtering characteristics of the cyclic WMUX are repeated over a wavelength range having the FSR. For example, for a dense wavelength division multiplexing (WDM) system, the FSR may be 50 GHz, 100 GHz, 200 GHz, etc., or for a coarse WDM system, the FSR may be 10 nm, 20 nm, 40 nm, etc. A cyclic WMUX combines optical signals on multiple inputs into a common output. A cyclic wavelength division multiplexer (WDMUX) is a WMUX that operates in reverse, dividing a signal on a common input into multiple outputs.

[0038] Embodiments of the present invention may be implemented in one or more semiconductor materials (semiconductors) grown, for example, by LPE, MOCVD, or OMVPE. The one or more semiconductors may include, but are not limited to, III-V semiconductors, II-VI semiconductors, IV semiconductors, and IV-V-VI semiconductors. Examples of III-V semiconductors may include AlP, AlN, AlGaSb, AlGaAs, AlGaInP, AlGaN, AlGaP, GaSb, GaAsP, GaAs, GaN, GaP, InAlAs, InAlP, InSb, InGaSb, InGaN, GaInAlAs, GaInAlN, GaInAsN, GaInAsP, GaInAs, GaInP, InN, InP, InAs, InAsSb, InGaAsP, and AlInN. Examples of II-VI semiconductors may include ZnSe, HgCdTe, ZnO, ZnS, and CdO. Examples of IV semiconductors may include Si, Ge, and strained silicon. IV-V-VI semiconductors may include GeSbTe.

[0039] In many cases, this type of semiconductor can achieve monolithic integration of passive optical waveguides with active optical components, such as light-emitting diodes, semiconductor optical amplifiers, laser diodes (LDs), distributed feedback LDs, external cavity laser diodes (ECLs), photodetectors (PDs), and avalanche photodetectors (APDs). For example, InGaAsP semiconductors support PDs, LDs, ECLs, etc. operating in the conventional infrared communication windows, including the S-band (1460–1530 nm), C-band (1530–1565 nm), and L-band (1565–1625 nm).

[0040] In an embodiment of the present invention, the platform or substrate for epitaxial growth and processing of semiconductors may itself be a semiconductor material, such as GaAs or InP; in other embodiments of the present invention, it may also be other materials, such as silicon, germanium, ceramics, glass or polymers.

[0041] In embodiments of the present invention, the platform or substrate for integration can be a silicon substrate, wherein one or more optical waveguides on the substrate utilize silicon nitride as a core and have silicon oxide as upper and lower cladding layers to form a waveguide structure. Alternatively, one or more optical waveguides can utilize a silicon core with silicon nitride upper and lower cladding layers. Optionally, in other embodiments of the present invention, the upper cladding layer can be omitted.

[0042] Embodiments of the present invention may be implemented using one or more silicon-on-insulator (SOI) waveguides, such as air-encapsulated Si3N4-SiO2, SiO2-Si3N4-SiO2, SiO2-Ge:SiO2-SiO2, or Si-SiO2. Embodiments of the present invention may also be implemented using one or more waveguides, such as ion-exchanged glass waveguides, ion-implanted glass waveguides, polymer-on-silicon waveguides, doped silicon waveguides, and polymer waveguides. While not necessarily utilizing the advantages of photonic integration, embodiments of the present invention may also be implemented using optical fibers, free-space optics, and the like.

[0043] When passive optical waveguides are hybrid-integrated with active photonic components (such as LDs, ECLs, and PDs), they can be directly butt-coupled or use intermediate coupling optics such as ball lenses, spherical lenses, and gradient-index (GRIN) lenses for free-space coupling and / or photonic wire bonding. Other waveguide structures can also be used, including vertical and / or lateral waveguide tapered structures, as well as forming microsphere lenses at the end of the waveguide by melting the waveguide tip with a laser and / or arc.

[0044] Embodiments of the present invention that employ optical waveguides may employ waveguide cores embedded within upper and lower claddings, so-called buried waveguides, air-clad waveguides (i.e., a core with a lower cladding and air elsewhere), rib waveguides, diffused waveguides, ridge waveguides or line waveguides, strip waveguides, slot waveguides, antiresonant reflective optical waveguides (ARROW waveguides), photonic crystal waveguides, suspended waveguides, alternating layer stack geometries, subwavelength grating (SWG) waveguides, or enhanced waveguides (e.g., Si-SiO2-Polymer). Embodiments of the present invention may utilize step-index waveguides, graded-index waveguides, or hybrid-index waveguides (such as a combination of inverse step-index and graded-index).

[0045] Figure 1 The present invention describes a schematic diagram of a first and second wavelength demultiplexer (WDMUX) 100A and 100B, which adopt cascaded wavelength filters, wherein the wavelength demultiplexer has a different free spectral range in each state. In the first WDMUX 100A, the input optical streams represented as λ1; λ2; λ3; λ4 are coupled to a first loop WDMUX 110 having a first filtering characteristic FSR (1), so that the signals λ1; λ2 are coupled to the first second loop WDMUX 120 (1), and the other signals λ3; λ4 are coupled to the second second loop WDMUX 120 (2). Each of the first second loop WDMUX 120 (1) and the second second loop WDMUX 120 (2) has an FSR (2), so that the signals λ1; λ2 coupled to the first loop WDMUX 120 (1) are split to λ1 and λ2 on different output ports, while the signals λ3; λ4 coupled to the second loop WDMUX 120 (2) are split to λ3 and λ4 on different output ports. Therefore, in a typical embodiment FSR(1)=2*FSR(2).

[0046] In the second WDMUX 100B, the input optical streams denoted as λ1;λ2;λ3;λ4 are coupled to the first loop WDMUX 130 having the first filtering characteristic FSR(2), such that the signals λ1;λ3 are coupled to the first second loop WDMUX 140(1), and the other signals λ2;λ4 are coupled to the second second loop WDMUX 140(2). Each of the first second loop WDMUX 140(1) and the second second loop WDMUX 140(2) has FSR(1), such that the signals λ1;λ3 coupled to the first loop WDMUX 140(1) are split to λ1 and λ3 on different output ports, while the signals λ2;λ4 coupled to the second loop WDMUX 140(2) are split to λ2 and λ4 on different output ports. Therefore, in a typical embodiment, FSR(1)=0.5*FSR(1).

[0047] Although the output sequence of the second WDMUX 100B is now non-sequential, the circuit has the significant advantage of employing a reduced number of cyclic WDMUX components with smaller FSRs relative to WDMUX 100A. As shown, the number of FSR(2) components is reduced from 2 to 1, and this advantage increases with the size of the WDMUX. As a result, the number of components with smaller FSRs and tighter manufacturing tolerances is reduced.

[0048] In an embodiment of the present invention, each cyclic DMUX can be a simple Mach-Zehnder interferometer (MZI) that produces a sinusoidal wavelength filtering characteristic. However, this results in a large frequency variation in insertion loss from the peak, so the filter insertion loss specification is high for a wide range of input wavelengths. In addition, since the selection of lasers reduces yield and increases cost, the cost driver within the system is a wider passband, so the loss variation of the simple MZI is significant. Therefore, the simple single-stage MZI is replaced by a multi-stage MZI, resulting in a flatter passband characteristic, known as passband flattening. Although this design can reduce the loss that varies with wavelength, it comes at the cost of increased complexity and overall insertion loss.

[0049] Therefore, reference Figure 2 , describes a WDMUX 200 utilizing a bandpass flattening wavelength filter, which employs cascaded Mach-Zehnder interferometer (MZI) elements. As shown, the first loop WDMUX 210 is a three-stage MZI cascade having first to third MZIs 230-250, whose path length imbalances are ΔL, 2ΔL; 2ΔL+π, respectively, where L is established according to the FSR of the first loop WDMUX 210. The outputs from the first loop WDMUX 210 are coupled to the first second loop WDMUX 220 (1) and the second second loop WDMUX 220 (2), respectively. Each of these is a two-stage MZI cascade having a fourth MZI 260 and a fifth MZI 270, whose path length imbalances are ΔL; 2ΔL, respectively, where L is established according to the FSR of the first second loop WDMUX 220 (1) and the second second loop WDMUX 220 (2), respectively.

[0050] Although the passband flattening cycle WDMUX improves the passband characteristic manufacturing deviation and has little impact on the passband peak, it still affects the crosstalk performance of the WDMUX component. Figure 3As described above, the inventors design each stage by using cascaded Mach-Zehnder interferometer (MZI) elements within a multi-stage WDMUX while utilizing a passband flattening wavelength filter, so that it includes a WDMUX with an additional wavelength filter at each output. Therefore, the WDMUX 300 includes a first stage 300 (1) and a second stage 300 (2). The first stage 300 (1) includes a first cycle WDMUX 310, which is equivalent to Figure 2 The first loop WDMUX 210 in FIG. 210, wherein each output is then coupled to one of an equivalent first first filter 320(1) and a second first filter 320(2), which are designed to be identical to the first loop WDMUX 310 and Figure 2 Therefore, the first loop WDMUX 310 and each of the first first filter 320(1) and the second first filter 320(2) have the following characteristics: Figure 1 The FSR (2) is shown in the second WDMUX 100B.

[0051] The second stage 300(2) includes a first second-cycle WDMUX 330(1) and a second second-cycle WDMUX 330(2), which is equivalent to Figure 2 a first second-loop WDMUX 220(1) and a second second-loop WDMUX 220(2) in the circuit, wherein each output is then coupled to one of first to fourth second filters 340(1) to 340(4), which are identical in design to the first second-loop WDMUX 330(1) and the second second-loop WDMUX 330(2), and Figure 2 Therefore, each of the first second loop WDMUX 330(1) and the second second loop WDMUX 330(2) and the first to fourth second filters 330(1) to 340(4) has the following configurations: Figure 1 The FSR(1) described in the second WDMUX 100B in FIG. 1 , wherein FSR(1)=0.5*FSR(1).

[0052] Although the design and manufacturing complexity increases, the combination of WDMUX and subsequent filtering at each stage improves the overall crosstalk performance of the WDDMUX300.

[0053] Obviously, by adding additional stages, the Figures 1 to 3 The design concept in enables the device to demultiplex 8, 16, 32 channels when fully configured, or other numbers of channels when partially configured (channel planning).

[0054] Obviously, Figure 3 In the design concept, the first first filter 320(1) and the second first filter 320(2) as well as the first to fourth second filters 340(1) to 340(4) are illustrated as 2x2 MZIs, but may also be 1x2 or 1x1 MZIs without departing from the scope of the present invention.

[0055] Obviously, Figure 3 In the design concept, the first stage 300(1) includes additional filtering via a first first filter 320(1) and a second first filter 320(2), respectively, and the second stage 300(2) via first to fourth second filters 340(1) to 340(4). In other embodiments of the present invention, only some stages may include additional filtering, such as those with the lowest FSR or those with the highest FSR, depending on the modeling and simulation results of the WDDMUX, to reduce the complexity and footprint of the WDDMUX without compromising performance within manufacturing tolerances.

[0056] according to Figure 3 The design shown in Figure 4 The analog wavelength output of a WDMUX with a nominal design is described, with the wavelengths of the four channels at 1271 nm, 1291 nm, 1311 nm, and 1331 nm, respectively. Figure 5 The wavelength output of a WDMUX is depicted as the width and thickness deviate from the nominal design parameters. The waveguide thickness is reduced by 10nm, and the waveguide width is reduced by 20nm. The result is a wavelength response shift toward the blue by approximately 3.7nm. Therefore, it is clear that the design no longer meets the target performance parameters. This can be addressed by adding thermal tuning to realign the wavelength of the WDMUX components to the design target wavelength.

[0057] In the prior art, DMUX designs either adjust the entire substrate temperature or control all components within the DMUX. However, the inventors have determined that by controlling only the first stage, i.e. Figure 3 The first stage 300(1) (with the lowest FSR) can re-tune the WDMUX to the correct wavelength. Figure 6A The result shown in the first image 600 in FIG is that only the first stage 600A is controlled, which includes the first loop WDMUX 310 and the first and second first filters 320(1) and 320(2). The thermal heater directly heating the waveguide requires less electrical power than the thermal tuning required to heat the substrate.

[0058] The actual design of the heater implemented will vary depending on the waveguide technology employed, and for some waveguide technologies, different heater geometries can be implemented on a common waveguide technology. For example, for silicon-on-insulator waveguides, such as Figure 6B As shown in the second image 6500 in FIG. 1 , the heater element of the MZI may be implemented or embodied as follows: Increased thermal isolation of the waveguide portion with heater from the substrate by undercut 690, where the silicon substrate is etched beneath the buried oxide (insulator for silicon-on-insulator waveguide geometries), thereby reducing heater power; Insulation trenches 670 to improve thermal isolation between components; Doped silicon waveguide 672 portion; A waveguide 674 having an embedded conductor 676 embedded thereon, the conductor being embedded in the upper cladding layer, such as a tungsten element for the embedded conductor 676; Silicon waveguide with Ni-Silicide 678; and • A back-end stack 680 with metallization (eg copper) and passivation, where the current flows transversely to the waveguide, rather than longitudinally to the waveguide.

[0059] Figure 7A and Figure 7B The electrical control path is described, along with the phase shifter elements being excited in two different activation states. Figure 7A , the first to third electrode pads 710-730 are configured as signal (1), floating, and ground for the first activation, and as floating, signal (2), and ground for the second activation, respectively. Thus, through interconnection, a group of phase adjuster elements of each MZI is activated, for example, the first MZI 610 (equivalent to Figure 2 The first MZI 230 in the ), the second MZI 630 (equivalent to Figure 2 The second MZI 240) and the third MZI 650 (equivalent to Figure 2 The third MZI 250) in Figure 7A The first activation of the MZI is activated by applying Signal (1); and the other set of phase regulator elements of each MZI is activated in Figure 7B The second activation of the MZI is performed by applying Signal (2). One activation is equivalent to applying a blue shift to the MZI by applying a phase shift to one defined arm of each MZI, while the other activation is equivalent to applying a red shift to the MZI by applying a phase shift to the other arm of each MZI. Thus, simplified control is provided.

[0060] Obviously, Figure 6BThe design described in

[15] describes a single heater design for each arm of each MZI. However, in other embodiments of the present invention, the heater design of some MZIs may differ from that of other MZIs in the WDDMUX, such that, for example, the heater design for an MZI with FSR(X) is extended relative to the heater design for an MZI with FSR(Y), such that a larger effective phase shift is applied to the MZI with FSR(X) than FSR(Y), where, for example, FSR(X) > FSR(Y). The heater design for an MZI in embodiments of the present invention may be established based on the FSR of the WDDMUX stage of which the MZI forms a part.

[0061] It will be apparent to those skilled in the art that in other embodiments of the present invention, alternative techniques may be employed to achieve phase shifting discretely or in combination with other effects, which may include thermo-optical effects via heaters. In this specification, such elements are generally referred to as phase shifting elements (PSEs). Such techniques may utilize, but are not limited to, mechanical adjustment of the optical path via microelectromechanical system actuators, such as electro-optic effects, including but not limited to the Pockels effect (linear electro-optic effect), the Kerr effect (quadratic electro-optic effect), and current injection. In other embodiments of the present invention, optical nonlinearity may be utilized to provide optical control of the phase shift, either discretely or in combination with electrical control.

[0062] It is obvious to those skilled in the art that Figures 1 to 7B The wavelength division multiplexer described and illustrated in this connection can be operated in reverse and used as a wavelength multiplexer.

[0063] It is obvious to those skilled in the art that although Figures 1 to 7B The photonic circuits described and depicted employ MZI elements, but other wavelength-dependent optical splitters providing recurrent filtering may be employed without departing from the scope of the present invention.

[0064] Obviously, although Figures 2 to 7B The design depicted in utilizes the cascade geometry depicted in the second image 100B, but the principle can also be applied to the cascade geometry depicted in the first image 100A, where the heater is mounted on the loop WDMUX with the lowest FSR, i.e., on the last stage WDMUX before the output.

[0065] Specific details are provided in the above description to provide a thorough understanding of the embodiments. However, it should be understood that the embodiments may be practiced without these specific details. For example, circuits may be shown in block diagram form to avoid obscuring the embodiments in unnecessary detail. In other cases, well-known circuits, processes, algorithms, structures, and techniques may be shown in unnecessary detail to avoid obscuring the embodiments.

[0066] The foregoing disclosure of exemplary embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. In light of the foregoing disclosure, numerous variations and modifications of the embodiments described herein will be apparent to those of ordinary skill in the art. The scope of the present invention is defined solely by the appended claims and their equivalents.

[0067] In addition, when describing representative embodiments of the present invention, the description may present the method and / or process of the present invention as a specific sequence of steps. However, the method or process is not dependent on the specific order of steps described herein, and the method or process should not be limited to the specific order of steps described. As will be understood by those of ordinary skill in the art, other order of steps is also possible. Therefore, the specific order of the steps set forth in the description should not be interpreted as a limitation on the claims. In addition, the claims for the method and / or process of the present invention should not be limited to performing their steps in the order written, and those of ordinary skill in the art can readily understand that the order of these steps can be changed and still conform to the spirit and scope of the present invention.

Claims

1. A device comprising: a plurality of circulating optical wavelength filters (COWFs) arranged in series in a plurality of stages; in each COWF of each of the plurality of stages, except for a last stage of the plurality of stages, coupled to a pair of COWFs within a next stage of the plurality of stages; said first of said plurality of stages coupled to a port for receiving a plurality of wavelength division multiplexed signals on a defined wavelength grid; within a stage in the plurality of stages, each COWF in the plurality of COWFs has a free spectral range (FSR) that is equal to a predetermined fraction of the FSR of the COWF in a next stage in the plurality of stages; a subset of the plurality of stages including at least the first of the plurality of stages comprising a phase shift element (PSE) for adjusting characteristics of the COWF within the subset of the plurality of stages; as well as A COWF in the plurality of COWFs in a subsequent one of the plurality of stages to a first one of the plurality of stages is configured independently of a PSE for adjusting characteristics of the COWF in the subsequent one of the plurality of stages to the first one of the plurality of stages.

2. The device according to claim 1, wherein Each of the plurality of COWFs comprises: a first passband-flattened Mach-Zehnder interferometer (MZI) having an FSR defined by the stage of the plurality of stages associated with the COWF of the plurality of COWFs; and A pair of second passband flat MZIs each having a FSR defined by the stage of the plurality of stages associated with the COWF of the plurality of COWFs, wherein each second passband flat MZI of the pair of second passband flat MZIs is coupled to an output of the first passband flat MZI.

3. The device according to claim 1, wherein Each COWF of the plurality of COWFs having a subset of the plurality of stages comprises: a first passband-flattened Mach-Zehnder interferometer (MZI) having an FSR defined by the stage of the plurality of stages associated with the COWF of the plurality of COWFs; and a pair of second passband-flattened MZIs, each having an FSR defined by the stage of the plurality of stages associated with the COWF of the plurality of COWFs, wherein each second passband-flattened MZI of the pair of second passband-flattened MZIs is coupled to an output of the first passband-flattened MZI; and The subset of the plurality of stages are those stages having a FSR below a defined value or above a defined value.

4. The device according to claim 1, wherein each COWF within said subset of said plurality of stages comprises a Mach-Zehnder interferometer (MZI); and the PSE for adjusting characteristics of the COWF within the subset of the plurality of stages, comprising a first PSE on an arm of the MZI and a second PSE on another arm of the MZI; within each COWF of the subset of the plurality of stages, the first PSE and the second PSE are identical; as well as Within each COWF having each stage of the subset of the plurality of stages, the first PSE and the second PSE are identical.

5. The apparatus according to claim 1, wherein each COWF within said subset of said plurality of stages comprises a Mach-Zehnder interferometer (MZI); and the PSE for adjusting characteristics of the COWF within the subset of the plurality of stages, comprising a first PSE on an arm of the MZI and a second PSE on another arm of the MZI; within each COWF of a stage of the subset of the plurality of stages, the first PSE and the second PSE are identical; Within each COWF within a stage of the subset of the plurality of stages, the first PSE and the second PSE are established according to the FSR of the stage of the plurality of stages.

6. A method comprising: providing a plurality of circulating optical wavelength filters (COWFs) arranged in series in a plurality of stages; in each COWF of each of the plurality of stages, except for a last stage of the plurality of stages, coupled to a pair of COWFs within a next stage of the plurality of stages; A first stage of the plurality of stages is coupled to a port for receiving a plurality of wavelength division multiplexed signals on a defined wavelength grid; within a stage in the plurality of stages, each COWF in the plurality of COWFs has a free spectral range (FSR) that is equal to a predetermined fraction of the FSR of those COWFs in a next stage in the plurality of stages; a subset of the plurality of stages including at least the first of the plurality of stages comprising a phase shift element (PSE) for adjusting characteristics of the COWF within the subset of the plurality of stages; as well as The COWFs of the plurality of COWFs within the subsequent one of the plurality of stages to the first one of the plurality of stages are independent of a PSE configuration for adjusting characteristics of the COWFs within the subsequent one of the plurality of stages to the first one of the plurality of stages.

7. The method according to claim 6, wherein: Each of the plurality of COWFs comprises: a first passband-flattened Mach-Zehnder interferometer (MZI) having an FSR defined by the stage of the plurality of stages associated with the COWF of the plurality of COWFs; and A pair of second passband flat MZIs each having a FSR defined by the stage of the plurality of stages associated with the COWF of the plurality of COWFs, wherein each second passband flat MZI of the pair of second passband flat MZIs is coupled to an output of the first passband flat MZI.

8. The method according to claim 6, wherein: Each COWF of the plurality of COWFs having a subset of the plurality of stages comprises: a first passband-flattened Mach-Zehnder interferometer (MZI) having an FSR defined by the stage of the plurality of stages associated with the COWF of the plurality of COWFs; and a pair of second passband-flattened MZIs, each having an FSR defined by the stage of the plurality of stages associated with the COWF of the plurality of COWFs, wherein each second passband-flattened MZI of the pair of second passband-flattened MZIs is coupled to an output of the first passband-flattened MZI; and The subset of the plurality of stages are those stages having a FSR below a defined value or above a defined value.

9. The method according to claim 6, wherein: each COWF within said subset of said plurality of stages comprises a Mach-Zehnder interferometer (MZI); and the PSE for adjusting characteristics of the COWF within the subset of the plurality of stages, comprising a first PSE on an arm of the MZI and a second PSE on another arm of the MZI; within each COWF of the subset of the plurality of stages, the first PSE and the second PSE are identical; as well as Within each COWF having each stage of the subset of the plurality of stages, the first PSE and the second PSE are identical.

10. The method according to claim 6, wherein: each COWF within the subset of the plurality of stages comprises a Mach-Zehnder interferometer (MZI); and the PSEs for adjusting characteristics of the COWFs in the subset of the plurality of stages comprise a first PSE on an arm of the MZI and a second PSE on another arm of the MZI; within each COWF of a stage of the subset of the plurality of stages, the first PSE and the second PSE are identical; Within each COWF within a stage of the subset of the plurality of stages, the first PSE and the second PSE are established according to the FSR of the stage of the plurality of stages.

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