Fabrication-tolerant on-chip multiplexers and demultiplexers are provides via a lattice filter interleaver configured to receive an input signal including a plurality of individual signals and to produce a first interleaved signal with a first subset of the plurality of individual signals and a second interleaved signal with a second subset of the plurality of individual signals; a first Bragg interleaver configured to receive the first interleaved signal and produce a first output signal including a first individual signal of the plurality of individual signals and a second output signal including a second individual signal of the plurality of individual signals; and a second Bragg interleaver configured to receive the second interleaved signal and produce a third output signal including a third individual signal of the plurality of individual signals and a fourth output signal including a fourth individual signal of the plurality of individual signals.

TECHNICAL FIELD

Embodiments presented in this disclosure generally relate to multiplexers and demultiplexers for optical signal processing. More specifically, embodiments disclosed herein provide for greater fabrication tolerances, including temperature insensitivities, via a multi-stage design.

BACKGROUND

As optical signaling grows in use, users are demanding ever higher data throughput rates in ever smaller or more efficient optical signaling devices. One way to provide higher data rates is using wavelength division multiplexing (WDM) to send several different signals at different wavelengths over a shared optical transmission medium. Placing several optical signals onto a shared channel is referred to as multiplexing, while extracting or separating the individual optical signals from the shared channel once multiplexed is referred to as demultiplexing. A device used to multiplex signals together is referred to as a multiplexer or “MUX”, while a device used to demultiplex signals apart is referred to as a demultiplexer or “DeMUX”. To ensure that the signals can be properly placed onto and retrieved from the shared optical transmission medium, especially as the separation in wavelength between individual signals decreases, the MUXs and DeMUXs are often held to extremely tight manufacturing tolerances, are subject to active tuning (using electrical power), or are bulky.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Overview

One embodiment presented in this disclosure provides a demultiplexer, comprising: a lattice filter interleaver configured to receive an input signal including a plurality of individual signals and to produce a first interleaved signal with a first subset of the plurality of individual signals and a second interleaved signal with a second subset of the plurality of individual signals; a first Bragg interleaver configured to receive the first interleaved signal and produce a first output signal including a first individual signal of the plurality of individual signals and a second output signal including a second individual signal of the plurality of individual signals; and a second Bragg interleaver configured to receive the second interleaved signal and produce a third output signal including a third individual signal of the plurality of individual signals and a fourth output signal including a fourth individual signal of the plurality of individual signals.

One embodiment presented in this disclosure provides a multiplexer, comprising: a first Bragg interleaver configured to receive a first individual signal of a first wavelength and a second individual signal of a second wavelength and produce a first interleaved signal including the first individual signal and the second individual signal; a second Bragg interleaver configured to receive a third individual signal of a third wavelength and a fourth individual signal of a fourth wavelength and produce a second interleaved signal including the third individual signal and the fourth individual signal, wherein the third wavelength is between the first wavelength and the second wavelength and the fourth wavelength is greater than the first wavelength and the second wavelength; and a lattice filter interleaver configured to receive the first interleaved signal and the second interleaved signal to produce a multiplexed output signal including the first individual signal, the second individual signal, the third individual signal, and the fourth individual signal.

One embodiment presented in this disclosure provides a device, comprising: a lattice filter interleaver connected on a first side to a multiplexed signal port and connected on a second side to: a first Bragg interleaver that is connected to a first individual signal port and a second individual signal port; and a second Bragg interleaver connected to a third individual signal port and a fourth individual signal port.

EXAMPLE EMBODIMENTS

The present disclosure provides a design for multiplexers (MUX) and demultiplexers (DeMUX) on an integrated silicon photonic platform for various optoelectronic applications. The device uses a two-stage design using optical lattice filters (LF) in one stage, and Bragg gratings in the other stage. The design provides a compact and fully passive solution (e.g., not using external electrical power during operation) that is compatible with Complementary Metal Oxide Semiconductor (CMOS) fabrication processes.

The LFs in the first stage split the input signal into interleaved signals to multiple Bragg gratings in the second stage, with wide bandwidth spacing between the split signals, thus giving greater tolerance for the Bragg gratings to distinguish the signals. Although referred to generally as “signals” or “optical signals” in the present disclosure, the signal may include a single wavelength or multiple wavelengths within a wavelength band. When operated as a MUX, the devices described herein interleave individual wavelengths within a designated wavelength bands. Similarly, when operated as a DEMUX, the devices described herein de-interleave individual wavelengths within a designated wavelength bands. Depending on the standard used by the device, the wavelengths of the single wavelength signals are specified at known positions within the wavelength band. Accordingly, the wavelength bands and the pitch between the individual wavelengths for the single wavelength signals fixed), but the individual signals might not be located on a fixed wavelength pitch.

In various embodiments, the LFs include Mach-Zehnder Interferometer (MZI) lattice filters, made up of several broadband tap couplers (Btap) with different phase delay lines disposed between one another. By designing the width, length, and material composition of the delay lines to reduce the effect of fabrication process variations, the overall design can minimize spectral shift in operation, further providing for proper spacing of the output signals and the ability of the components to distinguish between the multiplexed signals.

FIGS.1A and1Billustrate layouts of a MUX/DeMUX100in DeMUX operation, according to embodiments of the present disclosure. Although examples given in the present disclosure are primarily given in relation to DeMUX operations, one of skill in the art will appreciate that the described devices may work in one direction as a MUX and in the opposite direction as a DeMUX. Stated differently, the direction of the light path through the described hardware defines whether a given device operates as a MUX or as a DeMUX, and the operation as a DeMUX can be understood mutatis mutandis to describe the operation as a MUX for the described hardware. Accordingly, examples given with reference to a multiplexed signal moving from left to right in the example figures in which the individual signals are split apart from one another (e.g., demultiplexing operation) can be understood in the reverse; where multiple individual signals move from right to left in the example figures to combine into a single multiplexed signal (e.g., multiplexing operation).

The MUX/DeMUX100includes a first lattice filter interleaver110a(generally or collectively, lattice filter interleaver110) that receives a plurality of individual signals130a-d(generally or collectively, individual signals130) that are carried in a multiplexed signal140to be divided onto separate transmission media for each individual signal130.

In each ofFIGS.1A and1B, one or more lattice filter interleavers110are provided as a first stage to separate adjacent individual signals130on a multiplexed signal140from one another. For example, a second individual signal130bis adjacent to a first individual signal130aand a third individual signal130c, and a fourth individual signal130dis adjacent to the third individual signal130dwithin the multiplexed signal140. The first lattice filter interleaver110atherefore outputs the second individual signal130band the fourth individual signal130don a different output path from the first individual signal130aand the third individual signal130c; demultiplexing the multiplexed signal140into two interleaved signals.

In various embodiments, such as inFIG.1A, the first lattice filter interleaver110areceives a Coarse Wavelength Division Multiplexed (CWDM) multiplexed signal140with four signals130a-dwith wavelengths nominally separated by, e.g., 20 nanometers (nm) from one another. In other embodiments, such as inFIG.1B, the first lattice filter110areceives a half of the signals130a-dof a partially processed CWDM multiplexed signal140with eight signals130a-hwith wavelengths nominally separated by 20 nm from one another that a second lattice filter110bsplits into a first subset for further demultiplexing by the first lattice filter interleaver110aand a second subset for further demultiplexing by a third lattice filter interleaver110c. Stated differently, the second lattice filter110breceives an origin signal with eight signals130a-hmultiplexed thereon, provides a first output signal with four signals130a-dmultiplexed thereon to the first lattice filter interleaver110a, and provides a second output signal with four signals130e-hmultiplexed thereon to the third lattice filter interleaver110c. Although generally described in relation to CWDM with nominal wavelength spacing of 20 nm, the present disclosure may be applied in multiplexing/demultiplexing scenarios using different nominal wavelength spacing values and numbers of individual signals130included in the respective multiplexed signals140.

Accordingly, each lattice filter interleaver110receives a set in individual signals130and divides the set into two parts; referred to generally as the “even” signals and the “odd” signals. Each lattice filter interleaver110effectively doubles the spacing between the individual signals130for the next stage of the MUX/DeMUX100. For example, the second lattice filter interleaver110binFIG.1Bthat receives a multiplexed signal140with individual signals130with wavelengths spaced 10 nm apart, provides outputs to the first lattice filter interleaver110aand the third lattice filter interleaver110cwith the wavelengths of the individual signals spaced 20 nm apart. In turn, as shown inFIGS.1A and1B, the first lattice filter interleaver110aprovides outputs to the first Bragg interleaver120a(generally or collectively, Bragg interleaver120) and the second Bragg interleaver120bspaced 40 nm apart. Similarly, the third lattice filter interleaver110cprovides outputs to the third Bragg interleaver120cand the fourth Bragg interleaver120dspaced 40 nm apart.

The Bragg interleavers120, similarly to the lattice filter interleavers110, receive a set in individual signals130and divides the set into an “even” signal and an “odd” signal on separate transmission media. For example, the first Bragg interleaver120areceives a first interleaved signal from the first lattice filter interleaver110athat includes the first individual signal130aand the third individual signal130c, and outputs the first individual signal130aand the third individual signal130con separate transmission media (or ports) for separate and individual processing. Similarly, the second Bragg interleaver120breceives a second interleaved signal from the first lattice filter interleaver110athat includes the second individual signal130band the fourth individual signal130d, and outputs the second individual signal130band the fourth individual signal130don separate transmission media (or ports) for separate and individual processing.

Although the lattice filter interleavers110and the Bragg interleavers120perform similar functions (e.g., demultiplexing signals into even/odd sets or multiplexing individual signals130into an interleaved signal) as one another, the underlying hardware of the interleavers are different. The hardware and construction of the lattice filter interleavers110is described in greater detail in regard toFIGS.2A-2B,3,4,5A-5B, and6A-6B, and the hardware and construction of the Bragg interleavers120is discussed in greater detail in regard toFIGS.7A-7D.

The different hardware components used in the described MUX/DeMUX100provides a hybrid design approach that offers the overall MUX/DeMUX100with greater tolerance to variations in the fabrication process and variations in temperature during operation and with improved resilience to cross-talk and deviations from nominal signal spacing than designs using just one of lattice filter interleavers110or Bragg interleavers120. Because Bragg gratings (e.g., included in the Bragg interleavers120) can be more sensitive to variations in the thickness of the underlying material used in the waveguides (e.g., Silicon Nitride (SiN)) compared to lattice filters (e.g., included in the lattice filter interleavers110), but provide greater resilience to cross-talk between individual signals130than lattice filters, the hybrid design offers the benefits of both hardware configurations while minimizing the downsides of the individual configurations.

FIGS.2A and2Billustrate operations of individual lattice filters210a-c(generally or collectively, lattice filter210) within a lattice filter interleaver110, according to embodiments of the present disclosure.

FIG.2Aillustrates operation of the lattice filter interleaver110in demultiplexing mode. When operated in demultiplexing mode, the lattice filter interleaver110receives a multiplexed signal140and output two sets of interleaved signals that each include half of the individual signals130included in the multiplexed signal140. For example, when receiving a multiplexed signal140including four individual signals130a-dat a first port of a first lattice filter210a, a second lattice filter210boutputs an interleaved signal including the first individual signal130aand the third individual signal130c(excluding the second individual signal130band the fourth individual signals130d). Similarly, a third lattice filter210coutputs an interleaved signal including the second individual signal130band the fourth individual signal130d(excluding the first individual signal130aand the third individual signals130c).

In various embodiments, the first lattice filter210aextinguishes the second individual signal130band the fourth individual signal130dto various extents (e.g., −X decibels (dB)) on the first interleaved signal provided to the second lattice filter210b. Similarly, the first lattice filter210aextinguishes the first individual signal130aand the third individual signal130cto various extents (e.g., −X dB) on the second interleaved signal provided to the third lattice filter210c. Accordingly, in some embodiments, the second lattice filter210band the third lattice filter210cmay further extinguish the undesired individual signals130(e.g., an additional −Y dB) to ensure the undesired individual signals are received by the respective Bragg interleavers120below a threshold amplitude. In other embodiments, when the first lattice filter210aprovides the undesired individual signals130to each of the second lattice filter210band the third lattice filter210calready below the threshold amplitude, the second lattice filter210band the third lattice filter may provide additional filtering and signal shaping for the desired individual signals130.

FIG.2Billustrates operation of the lattice filter interleaver110in multiplexing mode. When operated in multiplexing mode, the lattice filter interleaver110receives two interleaved signals that each include half of the individual signals130to multiplex together, and outputs one multiplexed signal140that includes the individual signals130. For example, a second lattice filter210breceives an input signal (e.g., from a Bragg interleaver120or an upstream lattice filter interleaver110) that includes the first individual signal130aand the third individual signal130c, while the third lattice filter210creceives an input signal (e.g., from a different Bragg interleaver120or upstream lattice filter interleaver110) that includes the second individual signal130band the fourth individual signal130d. The first lattice filter210areceives the interleaved signals from the second lattice filter210band the third lattice filter210c, and multiplexes the two inputs to produce one multiplexed signal140that includes the provided individual signals130.

FIG.3illustrates a construction of the individual lattice filters210in a lattice filter interleaver110, according to embodiments of the present disclosure. Each lattice filter210includes a series of broadband tap (btap) couplers310a-l(generally or collectively, btap couplers310) that are adiabatic couplers. A btap coupler310is an optical device that can be used in a fiber optic communication system intended for high bandwidth usage, and as such may operate over a broad range of signal wavelengths. Accordingly, each btap coupler310in the MUX/DeMUX100may be constructed with the same nominal characteristics to cover the bandwidth of the multiplexed signal140, despite (potentially) operating on a subset of the individual signals130depending on where a given btap coupler310is located in the optical path of the MUX/DeMUX100. By using a uniform design for the btap couplers310, a fabricator may simplify design and fabrication of the MUX/DeMUX100and provide for signal conditioning in the wavelengths between the individual signals130.

Each btap coupler310included in a given lattice filter210is linked to the next btap coupler310in that lattice filter210via a pair of phase delay lines320a-l(generally or collectively, phase delay line pairs320or pair of phase delay lines). The btap couplers included in different lattice filters210that are linked (e.g., the fourth btap coupler310dwith the fifth btap coupler310eand the ninth btap coupler310i) are linked via a single waveguide (e.g., not a pair with different delay characteristics).

The delay lines320induce phase delays to the signals carried between subsequent btap couplers310within a given lattice filter210, which allow the signals to constructively or destructively interfere with one another to extinguish some of the individual signals130. Accordingly, the first lattice filter210amay receive a multiplexed signal140including X individual signals130and each of the second lattice filter210band the third lattice filter210coutput X/2 individual signals. The signals output by the second lattice filter210band the third lattice filter210care interleaved with one another so that the individual signals130included in each output signal have twice the separation in bandwidth between one another compared to the input signal received by the first lattice filter210a.

In various embodiments, each initial pair of phase delay lines320in the respective lattice filter210(e.g., the first delay lines320a, the fourth delay lines320d, and the seventh delay lines320g) induce a phase delay using a different length in each arm of the delay lines320(e.g., ΔL between the arms; L1−L2=ΔL). The intermediate pair of phase delay lines320in the respective lattice filter210(e.g., the second delay lines320b, the fifth delay lines320e, and the eighth delay lines320h) also induce a phase difference of using a different length in each of the arms of the delay lines320(e.g. for a total offset of 2ΔL if both pairs use the same ΔL). The final pair of phase delay lines320in the respective lattice filter210(e.g., the third delay lines320c, the sixth delay lines320f, and the ninth delay lines320i) induce a phase difference on an opposite arm of from the initial and intermediate pairs of delay lines using a length equal to the total length used by the other phase delay lines320, plus additional length for π radians of phase shift in the carried signals (e.g., 2ΔL+π for a total offset of π radians). By using different lengths in the delay lines320, the lattice filters210may be used as passive devices (e.g., requiring no additional power to induce a phase shift). In various embodiments, different offsets than those given in the above example may be used in the various pairs of phase delays lines320.

In various embodiments, the tap strengths (k) used in the various lattice filters210have the same configuration for the first lattice filter210a, the second lattice filter210b, and the third lattice filter210c. For example, the tap strengths may be set as laid out in Table 1, where k1corresponds to the tap strength of the first btap coupler310a, k2corresponds to the tap strength of the second btap coupler310b, etc., so that the tap strengths are set to be equivalent to one another across the lattice filters210. As will be appreciated, due to manufacturing tolerances, the actual tap strengths may vary from the nominal values (e.g., by ±5%) while still being set to equivalent values across the corresponding btaps couplers310in each lattice filter210.

In other embodiments, the second lattice filter210band the third lattice filter210cuse the same tap strengths as one another, but different tap strengths from the first lattice filter210a. Using different configurations of tap strengths between the first lattice filter210aand the other lattice filters210b-ccan improve the roll-off for selective signal filtering, while maintaining low crosstalk between the signals (e.g., less than −25 dB). For example, the tap strengths may be set as laid out in Table 2, where k1corresponds to the tap strength of the first btap coupler310a, k2corresponds to the tap strength of the second btap coupler310b, etc.

Although generally discussed in relation to a signal flow moving from the first lattice filter210ato the second lattice filter210band the third lattice filter210cfor DEMUX operation, lattice filter interleavers110may operate in the opposite direction when used in MUX operation. Accordingly, the arms described as input arms in a DEMUX arrangement may be understood as output arms in a MUX arrangement, and vice versa. For example, in DEMUX operation, the second btap310breceives phase delayed signals from the first phase delay line pair320a(via input arms) and transmits output on the second phase delay line pair320b(via output arms). However, in MUX operation, the second btap310breceives phase delayed signals from the second phase delay line pair320b(via input arms) and transmits output on the first phase delay line pair320a(via output arms).

FIG.4illustrates an MZI400defined by a first btap coupler310aand a second btap coupler310bwith the intervening delay lines320, according to embodiments of the present disclosure. The phase delay line pairs320linking the first btap coupler310aand the second btap coupler310bare divided into a first leg410and a second leg420. To change the relative phases of signals carried in each of the legs, the phase delay line pairs320are constructed to include delay elements430a-d(generally or collectively delay element430) with one or more of a different length (L) or width (w) between opposing legs. For example, the first leg410has delay elements430a-bwith a width of w1and a total length of L1(e.g., L1/2 in each delay element430), whereas the second leg420has delay elements430c-dwith a width of w2and a total length of L2(e.g., L2/2 in each delay element430)

The variations in fabrication process affecting the thickness of the waveguide material layer can result in spectral shift (Δλ) that moves the individual signals130away from nominal wavelengths and potentially clustering adjacent individual signals130closer to one another or further from one another than intended, thus resulting in cross-talk or malformed signals lower ability for distinguishing between the individual signals130. The lattice filters210are therefore designed to guard against spectral shift when multiplexing or demultiplexing by configuring various aspects of the btap couplers310and delay lines320to have specific widths and lengths according to the materials used and the wavelengths to be carried in response to the known dominant factor(s) in manufacturing process variations. This proactive design process provides greater resilience in the lattice filter210to the process variations expected to occur in fabricating the described MUX/DeMUX100.

For example, when the process variations are dominated by variations in width and thickness, the spectral shift (Δλ) for an original wavelength λ0may be expressed according to Formula 1, where Δw is the change in width, Δh is the change in thickness, and ΔT is the change in temperature. Additionally, ng1and ng2are the group indices of the first leg410and the second leg420of the phase delay line pairs320, respectively; n1and n2are the effective indices of the first leg410and the second leg420, respectively; and L1and L2are the lengths of the first leg410and the second leg420, respectively.

The Free Spectral Range (FSR) of the design can similarly be understood according to Formula 2.

By choosing a waveguide material with a lower thermo-optic coefficient (TOC), such as SiN, a fabricator can reduce the effect of changes in temperature ΔT on spectral shift (Δλ) compared to materials with relatively higher TOCs, (e.g., Si).

Similarly, by using different widths in the different legs of the phase delay elements430of each leg, a fabricator can use shorter lengths in the corresponding phase delay elements430to create the same phase offset (relative to phase delay elements430that use the same widths), and thus reduce the effect of changes in width Δw on unintended spectral shift (Δλ) compared designs using longer or different lengths of delay lines320to create phase differences.

As used herein, the thickness of the waveguide measures the “height” of the illustrated components projecting into or out of the page. In a layered deposition fabrication process, the nominal thickness of the waveguide may vary, resulting in regions with greater or lesser thicknesses than the nominal thickness. Because waveguide thickness is expected to vary gradually over the surface of the chip, components that are located closer together are expected to observe more similar thickness values, and thus result in lower spectral shift (Δλ) than devices that include components spread over a greater area (and are thus subject to greater potential variation in thickness). The effect of changes in thickness of the waveguides can be minimized by various design choices, such as using smaller footprints and clustering various devices together. Several layouts for reducing the footprint of the MUX/DeMUX100are discussed in greater detail in regard toFIGS.5A-5B and6A-6B.

Accordingly, the present MUX/DeMUX100can reduce spectral variation using one or more techniques or design choices to minimize the effects of width, temperature, and thickness on spectral shift.

FIGS.5A and5Billustrate on-chip pathing for an individual lattice filter210, according to embodiments of the present disclosure. To reduce the spatial process variations on the lattice filters210, the footprint of the hardware components is kept compact so that localized variations equally affect all of the hardware components. Each of the optical paths are routed in the same direction from an original btap coupler310to a destination btap coupler310to allow the delay lines to lay in close proximity to one another, but with sufficient separation to avoid optical coupling between two paths. Accordingly, various approach regions510a-f(generally or collectively, approach regions510) may include regions where the delay lines are placed between X and Y nm of each other (e.g., according to a spacing range threshold) to reduce the effect of regionalized thickness variations on the lattice filters210while reducing the likelihood of cross-coupling.

To further reduce the overall footprint of the lattice filter210, the on-chip pathing uses a series of loops520a-c(generally or collectively, loop520) for the delay lines320to link the btaps310together.

As shown inFIG.5A, the first delay lines320aform a first loop520athat projects from one side of the first btap coupler310ato connect to the second btap coupler310bon the first side. The third delay lines320calso project from the first side of third btap coupler310cand the fourth btap coupler310dto form a third loop520cthat is encompassed by the first loop520a. The second delay lines320bform a second loop520bthat projects from the opposite side of the second btap coupler310band the third btap coupler310c(relative to the first loop520aand the third loop520c) to connect to the second btap coupler310bto the third btap coupler310c.

As shown inFIG.5B, the first delay lines320aform a first loop520athat projects from one side of the first btap coupler310ato connect to the second btap coupler310bon the first side. The third delay lines320calso project from the first side of third btap coupler310cand the fourth btap coupler310dto form a third loop520cthat encompasses the first loop520a. The second delay lines320bform a second loop520bthat projects from the opposite side of the second btap coupler310band the third btap coupler310c(relative to the first loop520aand the third loop520c) to connect to the second btap coupler310bto the third btap coupler310c.

The inputs and outputs of the first btap coupler310aand the fourth btap coupler310dare shown on the same side as the second loop520bprojects from the second btap coupler310band the third btap coupler310cwith the signal directions indicated from demultiplexing operation.

Although described with inputs and outputs for use in demultiplexing operation, the on-chip layouts shown inFIGS.5A and5Bmay additionally or alternatively be used in multiplexing operation. Accordingly, the first btap coupler310a, as the input for the demultiplexer (and output for the multiplexer) may include one leg that is unconnected to an input source (or output destination). The fourth btap coupler310d, as the output for the demultiplexer (and the input for the multiplexer) is connected to two destinations (or two sources), which may include other lattice filter interleavers110or Bragg interleavers120.

FIGS.6A and6Billustrates on-chip pathing for a lattice filter interleaver110, according to embodiments of the present disclosure. Similarly to the routing of the delay lines in the individual lattice filters210shown inFIGS.5A and5B, a fabricator can reduce the spatial process variations in the overall lattice filter interleaver110by positioning the several component lattice filters210closer to one another.FIGS.6A and6Btherefore show layouts of the components that allow for close proximity of the lattice filters210, which may reduce the potential variations in waveguide thickness compared to layouts with greater spacing between the components.

As is shown inFIGS.6A and6B, the first lattice filter210ais located centrally to the second lattice filter210band the third lattice filter210c. To help reduce the overall footprint of the lattice filter interleaver110, the second lattice filter210bis constructed with a reverse orientation of input/output btaps310compared to the first lattice filter210aand the third lattice filter210c, thus allowing for shorter inter-filter routing and a tighter overall grouping of the lattice filters210.FIG.6Aillustrates the on-chip pathing using the layout shown inFIG.5Afor the first lattice filter210a, andFIG.6Billustrates the on-chip pathing using the layout shown inFIG.5Bfor the first lattice filter210a. The second lattice filter210band the third lattice filter210cin both of theFIGS.6A and6Buse the layout shown inFIG.5A.

InFIG.6A, the first lattice filter210ais connected on a first side to a multiplexed signal port610, which may be a signal source for a multiplexed signal140(when operating as a demultiplexer) or a signal destination for a multiplexed signal140(when operating as a multiplexer). On a second side, the second lattice filter210bis connected to a first interleaved port620a(generally or collectively, interleaved port620) and the third lattice filter210cis connected to a second interleaved port620b. In some embodiments, the interleaved ports620are connected to Bragg interleavers120, while in other embodiments (using multiple stages150of lattice filter interleavers110like inFIG.1B), the interleaved ports620are connected to the multiplexed ports610of other lattice filter interleavers110.

InFIG.6B, the first lattice filter210ais connected on a first side to a multiplexed signal port610, which may be a signal source for a multiplexed signal140(when operating as a demultiplexer) or a signal destination for a multiplexed signal140(when operating as a multiplexer). Also on the first side, the second lattice filter210bis connected to a first interleaved port620aand the third lattice filter210cis connected to a second interleaved port620b. In some embodiments, the interleaved ports620are connected to Bragg interleavers120, while in other embodiments (using multiple stages150of lattice filter interleavers110like inFIG.1B), the interleaved ports620are connected to the multiplexed ports610of other lattice filter interleavers110.

FIGS.7A-7Dillustrate layouts of Bragg interleavers120, according to embodiments of the present disclosure. Each Bragg interleaver120includes a mode multiplexer710and a Bragg grating720tuned for the specific wavelengths of signals to be multiplexed or demultiplexed.

The Bragg grating720induces a periodic variation in the refractive index of the transmission medium to transmit certain wavelengths and reflect others. As illustrated inFIG.7A, the Bragg grating720for the first Bragg interleaver120areflects the wavelengths associated with the first individual signal130aand permits transmission of the wavelengths associated with the third individual signal130c.FIG.7Cillustrates an alternative construction where the Bragg grating720is instead designed to reflect the wavelengths associated with the third individual signal130cand permit transmission the wavelengths associated with the first individual signal130a; reversing the input/output of the individual signals130compared toFIG.7A.

Similarly, as illustrated inFIG.7B, the Bragg grating720for the second Bragg interleaver120breflects the wavelengths associated with the second individual signal130band permits transmission of the wavelengths associated with the fourth individual signal130d.FIG.7Dillustrates an alternative construction where the Bragg grating720is instead designed to reflect the wavelengths associated with the fourth individual signal130dand permit transmission the wavelengths associated with the second individual signal130b; reversing the input/output of the individual signals130compared toFIG.7B. Either arrangement shown inFIG.7B or7Dmay be paired with either arrangement shown inFIG.7A or7C.

When operated as a demultiplexer, the Bragg interleaver120receives an interleaved signal on a first signal arm730from an upstream lattice filter interleaver110that has removed half of the individual signals130(with the other half being sent to the mode multiplexer of the paired Bragg interleaver120). The Bragg grating720allows one of the individual signals130to pass through to a second signal arm740(connected to an associated individual signal port), and reflects the other individual signal back to the mode multiplexer710, which propagates the other individual signal130. The mode multiplexer710includes a third signal arm750, which receives the reflected individual signal130from the Bragg grating720and carries the reflected individual signal130to a separate individual signal port to process the two individual signals separately from one another.

For example, with reference toFIG.7A, the first Bragg interleaver120areceives a multiplexed signal that includes the first individual signal130aand the third individual signal130con the first signal arm730, where the second individual signal130band the fourth individual signal130dhave been routed to the second Bragg interleaver120b(as inFIG.7B or7D). The first signal arm730carries the two individual signals130to the Bragg grating720, which reflects the first individual signal130a, but permits the second individual signal130bto propagate to the second signal arm740. The first individual signal130ais reflected from the Bragg grating720onto the third signal arm750.

When operated as a multiplexer, the Bragg interleaver120receives individual signals130on the second signal arm740and third signal arm750, and combines the individual signals130onto the first signal arm730for a downstream lattice filter interleaver110. The multiplexing of the individual signals130in a given Bragg interleaver120leaves spacing for other individual signals130(handled by other Bragg interleavers120) for the downstream lattice filter interleavers110to handle for further multiplexing. The Bragg grating720allows the individual signal130received on the second signal arm740to pass through to the first signal arm740. The mode multiplexer710propagates the other individual signal130onto the first signal arm730to reflects off of the Bragg grating720and redirect the other individual signal130to the downstream lattice filter interleaver110.

For example, with reference toFIG.7A, the first Bragg interleaver120areceives a first individual signal130aon the third signal arm750and the third individual signal130con the second signal arm740, and multiplexes the two individual signals130together on the first signal arm730for receipt by a downstream lattice filter interleaver110(which receives the omitted second individual signal130band the fourth individual signal130dfrom a second Bragg interleaver120b(as inFIG.7B or7D)).

In various embodiments, the second signal arm740and the third signal arm750are connected to various signal destinations (when used as a demultiplexer) for further processing, or from various signal sources (when used as a multiplexer). These various destinations or sources may be on the same chip as the MUX/DeMUX100is fabricated on or a different chip, and are generally referred to as “ports”. Each port is associated with a corresponding wavelength of signal, and in various embodiments, some of the ports may remain unconnected or otherwise not send/receive optical signals without affecting the operation of the MUX/DeMUX100. For example, the third signal arm750may receive a corresponding individual signal130while the second signal arm740does not receive a corresponding individual signal130, and the resulting output would include a “null” or zero-amplitude space in the interleaved signal where the signal from the second signal arm740would have been received.