Cascaded arrangement of dual-mode Bragg gratings for multiplexing applications

Abstract

Various aspects described herein include an optical device comprising an input port configured to receive an optical signal comprising a plurality of wavelengths and a plurality of output ports. Each output port is configured to output a respective wavelength from the plurality of wavelengths. The optical device further comprises a first plurality of dual-mode Bragg gratings arranged in cascade. Each grating in the first plurality of dual-mode Bragg gratings is configured to reflect a respective wavelength from the plurality of wavelengths toward a respective output port from the plurality of output ports and transmit any remaining wavelengths from the plurality of wavelengths.

Description

Technical Field

[0001] The embodiments presented in this disclosure relate generally to optical multiplexing, and more particularly to wavelength division multiplexing (WDM) using a cascaded arrangement of dual-mode Bragg gratings. Background Art

[0002] WDM schemes support multiple channels via a light-carrying medium (e.g., optical waveguides or optical fibers). WDM schemes are typically distinguished by the spacing between wavelengths. For example, a "normal" WDM system supports two channels spaced 240 nanometers (nm), a coarse wavelength division multiplexing (CWDM) system supports up to eighteen (18) channels spaced 20 nm, and a dense WDM (DWDM) system supports up to eighty (80) channels spaced 0.4 nm. Because of the wavelength spacing, CWDM systems tend to be more fault-tolerant than DWDM systems and do not require a high-precision controlled laser source. Consequently, CWDM systems tend to be less expensive and consume less power. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] In order that the above-recited features of the present disclosure may be understood in detail, a more particular description of the present disclosure, briefly summarized above, may be given by reference to embodiments, some of which are shown in the accompanying drawings. It should be noted, however, that the drawings illustrate typical embodiments and are therefore not to be considered limiting; other equally effective embodiments are contemplated.

[0004] Figure 1 is an illustration of an exemplary optical device according to one or more embodiments.

[0005] Figure 2 and Figure 3 is an illustration of an exemplary silicon-on-insulator (SOI) based optical waveguide according to one or more embodiments.

[0006] Figure 4 is a diagram illustrating exemplary implementations of dual-mode Bragg gratings having different sidewall corrugation shapes in accordance with one or more embodiments.

[0007] Figure 5 and Figure 6 is an illustration of an exemplary implementation of a demultiplexer having a cascaded arrangement of dual-mode Bragg gratings in accordance with one or more embodiments.

[0008] Figure 7 and Figure 8 is an illustration of an exemplary implementation of a demultiplexer with mitigated crosstalk in accordance with one or more embodiments.

[0009] Figure 9is a graph illustrating the operation of a dual-mode Bragg grating as a bandpass filter according to one or more embodiments.

[0010] Figure 10 is a graph illustrating the operation of a dual-mode Bragg grating as a low-pass filter according to one or more embodiments.

[0011] Figure 11 is a graph illustrating the operation of a dual-mode Bragg grating as a bandpass filter with partially overlapping passbands, according to one or more embodiments.

[0012] Figure 12 A method of demultiplexing using a cascaded arrangement of dual-mode Bragg gratings is shown in accordance with one or more embodiments.

[0013] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. DETAILED DESCRIPTION

[0014] Overview

[0015] In one embodiment, an optical device includes an input port configured to receive an optical signal including multiple wavelengths and a plurality of output ports. Each output port is configured to output a corresponding wavelength from the multiple wavelengths. The optical device also includes a first plurality of dual-mode Bragg gratings arranged in cascade. Each grating in the first plurality of dual-mode Bragg gratings is configured to reflect a corresponding wavelength from the multiple wavelengths toward a corresponding output port from the multiple output ports and transmit any remaining wavelengths from the multiple wavelengths.

[0016] In another embodiment, an optical device includes a plurality of receivers and a demultiplexer, the demultiplexer including an input port configured to receive an optical signal including a plurality of wavelengths and a plurality of output ports. Each output port is configured to output a corresponding wavelength of the plurality of wavelengths to a corresponding receiver of the plurality of receivers. The demultiplexer also includes a first plurality of dual-mode Bragg gratings arranged in cascade. Each grating of the first plurality of dual-mode Bragg gratings is configured to reflect a corresponding wavelength of the plurality of wavelengths toward a corresponding output port of the plurality of output ports and transmit any remaining wavelengths of the plurality of wavelengths.

[0017] Example Embodiments

[0018] To achieve compact WDM-based optical transceiver modules, the optical multiplexing and demultiplexing (mux / demux) functions can be implemented (or integrated) within the transceiver module's photonic integrated circuit (IC). The low optical loss of optical mux / demux is particularly well-suited for supporting low-power optical communication systems. Furthermore, optical mux / demux with a flat-top passband eliminates the need for laser temperature control and reduces the overall power consumption of optical communication systems.

[0019] According to embodiments described herein, an optical device includes an input port configured to receive an optical signal comprising multiple wavelengths and multiple output ports. Each output port is configured to output a corresponding wavelength from the multiple wavelengths. The optical device also includes multiple dual-mode Bragg gratings arranged in cascade. Each grating is configured to reflect a corresponding wavelength from the multiple wavelengths toward a corresponding output port and transmit any remaining wavelengths from the multiple wavelengths. In some embodiments, a dual-mode Bragg grating is formed in an optical waveguide of a silicon photonic chip. The dual-mode Bragg grating can have a sidewall corrugation shape, for example, a rectangular shape, a sine shape, or a cosine shape.

[0020] Advantageously, the use of a cascaded arrangement of dual-mode Bragg gratings provides a relatively flat passband for a multiplexer and / or demultiplexer, and the use of dual-mode Bragg gratings based on silicon nitride or silicon oxynitride can eliminate the need for temperature control of the laser source and / or reduce the power consumption of the optical device. Furthermore, the dual-mode Bragg gratings can achieve very low insertion loss, enabling multiplexers and / or demultiplexers to have low insertion loss, for example, less than 1-2 decibels (dB). Furthermore, the dual-mode Bragg gratings can have a wider passband and greater manufacturing tolerances.

[0021] Figure 1 is a diagram 100 of an exemplary optical device according to one or more embodiments. In some embodiments, the optical device represents an optical transceiver module integrated into a silicon photonic chip. Other implementations of the receiving optical device are also contemplated.

[0022] The optical device includes a plurality of transmitters (TX) 105-1, 105-2, 105-3, ..., 105-M (collectively, transmitters 105), which provide optical signals to a multiplexer (MUX) 115 via a corresponding plurality of optical links 110-1, 110-2, 110-3, ..., 110-M (collectively, optical links 110). In some embodiments, each transmitter 105 includes a laser source that generates a corresponding optical signal having a corresponding wavelength (e.g., an unmodulated continuous wave (CW) optical signal). The wavelength of the optical signal can be selected according to a predefined multiplexing scheme (e.g., WDM, DWDM, or CWDM). Each transmitter 105 may also include an optical modulator configured to modulate the corresponding optical signal and may also include circuitry for further processing the corresponding optical signal. In some embodiments, the optical link 110 is an optical waveguide formed in a silicon photonic chip. In other embodiments, the optical link 110 is an optical fiber.

[0023] Multiplexer 115 combines several optical signals into a multiplexed optical signal, which is output onto optical link 120. In some embodiments, multiplexer 115 comprises a CWDM multiplexer, although implementations using other WDM schemes are also contemplated. In some embodiments, optical link 120 is an optical waveguide formed in a silicon photonic chip. In other embodiments, optical link 120 is an optical fiber.

[0024] Demultiplexer (DEMUX) 125 is communicatively coupled to multiplexer 115 via optical link 120. Demultiplexer 125 demultiplexes the multiplexed optical signal transmitted by optical link 120 into multiple optical signals. In some embodiments, demultiplexer 125 comprises a CWDM demultiplexer, but other implementations are also contemplated. Multiple optical signals are provided from demultiplexer 125 to multiple receivers (RX) 135-1, 135-2, 135-3, ..., 135-N (collectively, receivers 135) via corresponding multiple optical links 130-1, 130-2, 130-3, ..., 130-N (collectively, optical links 130). In some embodiments, optical link 130 is an optical waveguide formed in a silicon photonic chip. In other embodiments, optical link 130 is an optical fiber. In some embodiments, each receiver 135 includes an optical demodulator for demodulating the corresponding optical signal and may also include circuitry for further processing the corresponding optical signal.

[0025] In some embodiments, and as will be discussed in greater detail, the multiplexer 115 and / or the demultiplexer 125 include dual-mode Bragg gratings in a cascade arrangement. Advantageously, the use of a cascade arrangement of dual-mode Bragg gratings provides a relatively flat passband for the multiplexer 115 and / or the demultiplexer 125 and can be used to eliminate temperature control of the laser source of the transmitter 105 and / or reduce power consumption of the optical device. Furthermore, the dual-mode Bragg gratings can achieve very low insertion loss, such that the multiplexer 115 and / or the demultiplexer 125 has an insertion loss of less than 1-2 dB.

[0026] Figure 2 and Figure 3 FIG200 and FIG300 are exemplary diagrams of optical waveguides based on silicon on insulator (SOI) according to one or more embodiments. Features of FIG200 and FIG300 can be used in combination with other embodiments. For example, Figure 1 The multiplexer 115 and / or the demultiplexer 125 may be implemented in a silicon photonic chip using the SOI structure shown in diagrams 200 and 300 .

[0027] In some embodiments, silicon substrate 205 comprises a bulk silicon (Si) substrate in which one or more features or materials of the active optical device(s) to be produced (e.g., lasers, detectors, modulators, absorbers) are pre-processed. The thickness of silicon substrate 205 can vary depending on the specific application. For example, silicon substrate 205 can be the thickness of a typical semiconductor wafer (e.g., 100-700 microns), or can be thinned and mounted on another substrate.

[0028] Diagrams 200 and 300 each depict a silicon substrate 205, an insulator layer 210 (disposed above the silicon substrate 205), and an optical waveguide 215 (formed in a waveguide layer 220 disposed above the insulator layer 210). In some embodiments, the insulator layer 210 comprises a buried oxide (BOX) layer formed of silicon dioxide. The thickness of the insulator layer 210 can vary depending on the desired application. In some embodiments, the thickness of the insulator layer 210 can range from less than one micron to tens of microns. In some embodiments, the waveguide layer 220 is formed of elemental Si (e.g., single crystal Si or polycrystalline Si). In other embodiments, the waveguide layer 220 can be formed of other suitable semiconductor materials, such as silicon nitride or silicon oxynitride deposited on the insulator layer 210. The thickness of the waveguide layer 220 can range from less than 100 nm to greater than one micron. More specifically, the thickness of the waveguide layer 220 can be between 100 nm and 300 nm.

[0029] In diagram 300, optical waveguide 215 is formed as a ridge waveguide including a ridge 310 protruding from a base 305. The ridge waveguide generally confines a propagating optical signal to a portion of the waveguide layer 220. In some embodiments, the waveguide layer 220 has a thickness between 3 and 5 microns. In some embodiments, the width of the ridge 310 (as viewed from left to right) is between 3 and 5 microns. With these dimensions, the diameter of the optical mode can be 4 to 5 microns.

[0030] As described above, a grating pattern may be etched along the sidewalls of the optical waveguide 215 to form a dual-mode Bragg grating for the multiplexer 115 and / or the demultiplexer 125 . Figure 4 FIG4 is a diagram 400 illustrating an exemplary implementation of dual-mode Bragg gratings having different sidewall corrugation shapes according to one or more embodiments. Features of diagram 400 can be used in conjunction with other embodiments. For example, a dual-mode Bragg grating can use sidewall gratings to transmit one wavelength of light propagating through optical waveguide 215 and reflect another wavelength.

[0031] Diagram 400 depicts a mode multiplexer 405 and a dual-mode Bragg grating 410. A first arm 415 of the mode multiplexer 405 propagates a fundamental mode 425 (e.g., a fundamental transverse electric (TE) mode), which is propagated to the dual-mode Bragg grating 410. The dual-mode Bragg grating 410 includes sidewalls 435-1, 435-2 having a grating pattern with a corrugation period Λ1 and a depth d1. While the corrugation shape of the sidewalls 435-1, 435-2 is shown as a rectangular shape, alternative shapes are contemplated, such as a sinusoidal shape (as in the grating pattern 440), a cosine shape, etc.

[0032] The grating pattern can be formed, for example, by deep etching into the edge of the optical waveguide to produce a periodic grating pattern along the length of the optical waveguide. As shown, the dual-mode Bragg grating 410 transmits a first mode (e.g., fundamental mode 425) and reflects a second mode (e.g., second-order mode 430) to the mode multiplexer 405. The second arm 420 of the mode multiplexer 405 propagates the second-order mode. Other implementations of the mode multiplexer 405 are also contemplated, such as an asymmetric Y-junction mode multiplexer.

[0033] In some embodiments, the grating pattern is formed from silicon nitride or silicon oxynitride material. For example, the silicon nitride or silicon oxynitride material can be deposited on top of a silicon oxide layer and a dry etching process is used to form the optical waveguide. Both silicon nitride and silicon oxynitride have a smaller thermo-optical coefficient than elemental silicon, which results in the dual-mode Bragg grating (and associated optical device) being less sensitive to temperature changes during operation. In some cases, the lower temperature sensitivity means that thermal tuning of the optical device is not required during operation.

[0034] The grating pattern may have any suitable alternative implementation. For example, a buried grating layer may be used to form one or more grating patterns. Furthermore, in cases where the length of the dual-mode Bragg grating is sufficiently long (e.g., implemented within an optical fiber), the sidewall gratings may be spaced apart from each other (e.g., at different locations along the length of the first Bragg grating).

[0035] Figure 5 and Figure 6 FIG500 and FIG600 are diagrams of exemplary implementations of demultiplexers 505 and 605 having a cascade arrangement of dual-mode Bragg gratings according to one or more embodiments. The features shown in FIG500 and FIG600 can be used in combination with other embodiments. For example, the mode multiplexer and dual-mode Bragg grating included in the demultiplexer 505 and 605 can be as shown in FIG500 and FIG600. Figure 4 Configure as shown.

[0036] In diagram 500, demultiplexer 505 includes an input port 510 and a plurality of dual-mode Bragg gratings 515-0, 515-1, 515-2 (also referred to herein as "gratings" or "Bragg gratings") arranged in cascade (also referred to as a "series" arrangement). Each grating 515-0, 515-1, 515-2 reflects a corresponding wavelength and transmits any remaining wavelengths. For example, grating 515-0 reflects a first wavelength through a drop port and transmits at least one wavelength through an output port to gratings 515-1, 515-2 downstream of grating 515-0.

[0037] The gratings (515-0, 515-1, 515-2) can have any suitable filter response to separate the respective wavelengths for reflection. In some embodiments, the gratings 510-0, 515-1, 515-2 are bandpass filters, which can have non-overlapping or partially overlapping passbands. For example, the gratings 515-0, 515-1, 515-2 can have partially overlapping passbands, with the center wavelengths and roll-off wavelengths of the partially overlapping passbands selected so that the range of respective wavelengths reflected by the gratings 510-0, 515-1, 515-2 is completely included between the center wavelength and the roll-off wavelength. In other embodiments, the gratings 515-0, 515-1, 515-2 are low-pass filters and can have successively larger roll-off wavelengths.

[0038] In some embodiments, the demultiplexer 505 further includes a plurality of mode multiplexers 520-0, 520-1, 520-2. Each of the plurality of mode multiplexers 520-0, 520-1, 520-2 receives a wavelength reflected by a corresponding grating 515-0, 515-1, 515-2. Each mode multiplexer converts the mode of the reflected wavelength (e.g., a first-order TE mode) into a fundamental TE mode. The plurality of mode multiplexers 520-0, 520-1, 520-2 can have any suitable implementation, for example, using an open-resonance and an off-resonance switch ring. Each mode multiplexer 520-0, 520-1, 520-2 has an output that is coupled to a corresponding output port 525-0, 525-1, 525-2 of the plurality of output ports 525-0, 525-1, 525-2, 525-3 of the demultiplexer 505. In other embodiments, the plurality of mode multiplexers 520-0, 520-1, 520-2 may be omitted such that the gratings 515-0, 515-1, 515-2 provide reflected wavelengths (eg, as first-order or higher-order modes) directly to the output ports 525-0, 525-1, 525-2.

[0039] Thus, in response to receiving an optical signal 530 comprising a plurality of wavelengths λ0, λ1, λ2, and λ3 at input port 510, grating 515-0 reflects wavelength λ0 and transmits the remaining wavelengths λ1, λ2, and λ3. Mode multiplexer 520-0 receives wavelength λ0 and provides wavelength λ0 (with the mode converted to the fundamental mode) as optical signal 535-0 to output port 525-0. Grating 515-1 receives wavelengths λ1, λ2, and λ3, reflects wavelength λ1, and transmits the remaining wavelengths λ2 and λ3. Mode multiplexer 520-1 receives wavelength λ1 and provides wavelength λ1 (with the mode converted to the fundamental mode) as optical signal 535-1 to output port 525-1.

[0040] Grating 515-2 receives wavelengths λ2 and λ3, reflects wavelength λ2, and transmits the remaining wavelength λ3. Mode multiplexer 520-2 receives wavelength λ2 and provides wavelength λ2 (with the mode converted to the fundamental mode) as optical signal 535-2 to output port 525-2. The remaining wavelength λ3 is provided from grating 515-2 to output port 525-3 as optical signal 535-3.

[0041] In demultiplexer 505, grating 515-2 represents the "last" grating in the cascaded arrangement of gratings 515-0, 515-1, and 515-2. Here, grating 515-2 reflects the "second-to-last" wavelength (i.e., wavelength λ2) of the plurality of wavelengths λ0, λ1, λ2, and λ3 toward output port 525-2, and transmits the "last" wavelength (i.e., wavelength λ3) to output port 525-3.

[0042] In diagram 600, demultiplexer 605 includes input port 510, multiple output ports 525-0, 525-1, 525-2, 525-3, and a cascaded arrangement of gratings 515-0, 515-1, 515-2, and grating 515-3. The operation of demultiplexer 605 is generally similar to that of demultiplexer 505. However, grating 515-3 receives wavelength λ3 from grating 515-2 and reflects wavelength λ3. Demultiplexer 605 also includes mode multiplexer 520-3, which receives wavelength λ3 and provides wavelength λ3 (with the mode converted to the fundamental mode) as optical signal 535-3 to output port 525-3. In another embodiment, mode multiplexer 520-3 can be omitted.

[0043] In some embodiments, the output (e.g., transmit port) of the grating 515-3 is coupled to a light absorber 610. In some embodiments, the light absorber 610 comprises a heavily doped silicon waveguide. Advantageously, the light absorber 610 reduces reflection of the optical signal, which can further improve the signal-to-noise ratio (SNR) of the optical signal 535-3.

[0044] In demultiplexer 605, grating 515-3 represents the "last" grating in the cascaded arrangement of gratings 515-0, 515-0, 515-1, 515-2, 515-3. Here, grating 515-3 reflects the "last" wavelength (i.e., wavelength λ3) among the plurality of wavelengths λ0, λ1, λ2, λ3 toward output port 525-3.

[0045] Figure 7 and Figure 8 FIG700 and FIG800 are diagrams of exemplary implementations of demultiplexers 705 and 805 with reduced crosstalk according to one or more embodiments. The features shown in FIG700 and FIG800 can be used in combination with other embodiments. For example, the mode multiplexer and dual-mode Bragg grating included in the demultiplexer 705 and 805 can be as shown in FIG700 and FIG800. Figure 4 Configure as shown.

[0046] In diagram 700, demultiplexer 705 includes input port 510, a plurality of output ports 525-0, 525-1, 525-2, 525-3, a cascaded arrangement of gratings 515-0, 515-1, 515-2, and a plurality of mode multiplexers 520-0, 520-1, 520-2. The operation of demultiplexer 705 is generally similar to the operation of demultiplexer 505 discussed above.

[0047] The demultiplexer 705 also includes a second plurality of dual-mode Bragg gratings 710-0, 710-1, 710-2. Each grating 710-0, 710-1, 710-2 receives a wavelength reflected by a corresponding grating 515-0, 515-1, 515-2 and reflects the wavelength toward a corresponding output port 525-0, 525-1, 525-2. The demultiplexer 705 also includes a plurality of mode multiplexers 715-0, 715-1, 715-2. Each of the plurality of mode multiplexers 715-0, 715-1, 715-2 receives a wavelength reflected by a corresponding grating 710-0, 710-1, 710-2. Each mode multiplexer 715-0, 715-1, 715-2 has an output coupled to a corresponding output port 525-0, 525-1, 525-2. The demultiplexer 705 also includes a plurality of optical absorbers 720-0, 720-1, 720-2. Each grating 710-0, 710-1, 710-2 has an output coupled to a corresponding optical absorber 720-0, 720-1, 720-2, each of which can be configured similarly to the optical absorber 610.

[0048] In diagram 800, demultiplexer 805 includes input port 510, a plurality of output ports 525-0, 525-1, 525-2, 525-3, a cascaded arrangement of gratings 515-0, 515-1, 515-2, 515-3, and a plurality of mode multiplexers 520-0, 520-1, 520-2, 520-3. The operation of demultiplexer 805 is generally similar to the operation of demultiplexer 605 discussed above.

[0049] The demultiplexer 805 also includes a second plurality of dual-mode Bragg gratings 710-0, 710-1, 710-2, 710-3. Each grating 710-0, 710-1, 710-2, 710-3 receives a wavelength reflected by a corresponding grating 515-0, 515-1, 515-2, 515-3 and reflects the wavelength toward a corresponding output port 525-0, 525-1, 525-2, 525-3. The demultiplexer 805 also includes a plurality of mode multiplexers 715-0, 715-1, 715-2, 715-3. Each of the plurality of mode multiplexers 715-0, 715-1, 715-2, 715-3 receives a wavelength reflected by a corresponding grating 710-0, 710-1, 710-2, 710-3. Each mode multiplexer 715-0, 715-1, 715-2, 715-3 has an output coupled to a corresponding output port 525-0, 525-1, 525-2, 525-3. The demultiplexer 705 also includes a plurality of optical absorbers 720-0, 720-1, 720-2, 720-3. Each grating 710-0, 710-1, 710-2, 710-3 has an output coupled to a corresponding optical absorber 720-0, 720-1, 720-2, 720-3.

[0050] like Figure 4 As shown, although the combination of the mode multiplexer 405 and the dual-mode Bragg grating 410 is used to perform the demultiplexing function in the implementation of the demultiplexers 505, 605, 705, and 805, it should be noted that the combination of the mode multiplexer 405 and the dual-mode Bragg grating 410 can be used to perform the multiplexing function. Therefore, the combination of the mode multiplexer 405 and the dual-mode Bragg grating 410 can be used to implement a multiplexer including multiple dual-mode Bragg gratings arranged in cascade.

[0051] Figure 9 Graphs 900-0, 900-1, 900-2, and 900-3 illustrate the operation of a dual-mode Bragg grating operating as a bandpass filter, according to one or more embodiments. The features illustrated in graphs 900-0, 900-1, 900-2, and 900-3 can be used in conjunction with other embodiments. For example, a cascaded arrangement in any of the demultiplexers 505, 605, 705, and 805 can include a grating configured as a bandpass filter. As described above, the gratings can have non-overlapping or partially overlapping passbands.

[0052] In graph 900-0, a first grating in a cascade arrangement receives an optical signal comprising a plurality of signal components 905-0, 905-1, 905-2, 905-3 at a corresponding plurality of wavelengths λ0, λ1, λ2, λ3. A filter response 910-0 of the first grating comprises a first passband 915-0 such that signal component 905-0 (at wavelength λ0) is reflected by the first grating. The remaining wavelengths λ1, λ2, λ3 (shown as group 920-0 of signal components 905-1, 905-2, 905-3) are transmitted by the first grating to a second grating in the cascade arrangement.

[0053] In graph 900-1, a second grating receives signal components 905-1, 905-2, 905-3 at respective wavelengths λ1, λ2, λ3. The filter response 910-1 of the second grating includes a second passband 915-1 such that signal component 905-1 (at wavelength λ1) is reflected by the second grating. The remaining wavelengths λ2, λ3 (shown as a group 920-1 of signal components 905-2, 905-3) are transmitted by the second grating to a third grating in a cascade arrangement.

[0054] In graph 900-2, a third grating receives signal components 905-2 and 905-3 at respective wavelengths λ2 and λ3. The filter response 910-2 of the third grating includes a third passband 915-1 such that signal component 905-2 (at wavelength λ2) is reflected by the third grating. The remaining wavelength λ3 (shown as group 920-2 of signal component 905-3) is transmitted by the third grating.

[0055] In graph 900-3, signal component 905-3 (at wavelength λ3) is shown. In some embodiments, signal component 905-3 is transmitted by the third grating to the output port. In other embodiments, signal component 905-3 is reflected by the fourth grating toward the output port. While graphs 900-0, 900-1, 900-2, 900-3 illustrate one sequence of filtering signal components 905-0, 905-1, 905-2, 905-3 using a cascade arrangement, other embodiments may have alternative sequences for filtering signal components 905-0, 905-1, 905-2, 905-3.

[0056] Figure 10Graphs 1000-0, 1000-1, 1000-2, and 1000-3 illustrate the operation of a dual-mode Bragg grating operating as a low-pass filter, according to one or more embodiments. The features illustrated in graphs 1000-0, 1000-1, 1000-2, and 1000-3 can be used in conjunction with other embodiments. For example, a cascaded arrangement in any of the demultiplexers 505, 605, 705, and 805 can include a grating configured as a low-pass filter.

[0057] In graph 1000-0, a first grating in a cascade arrangement receives an optical signal comprising a plurality of signal components 905-0, 905-1, 905-2, and 905-3. The filter response 1005-0 of the first grating comprises a first passband 1010-0 such that signal component 905-0 (at wavelength λ0) is reflected by the first grating. The remaining wavelengths λ1, λ2, and λ3 are transmitted by the first grating to the second grating in the cascade arrangement.

[0058] In graph 1000-1, the second grating receives signal components 905-1, 905-2, and 905-3. The filter response 1005-1 of the second grating includes a second passband 1010-1, such that signal component 905-1 (at wavelength λ1) is reflected by the second grating. The remaining wavelengths λ2 and λ3 are transmitted by the second grating to the third grating in the cascade arrangement.

[0059] In graph 1000-2, the third grating receives signal components 905-2, 905-3. The filter response 1005-2 of the third grating includes a third passband 1010-1 such that signal component 905-2 (at wavelength λ2) is reflected by the third grating. The remaining wavelength λ3 is transmitted by the third grating.

[0060] Signal component 905-3 (at wavelength λ3) is shown in graph 1000-3. In some embodiments, signal component 905-3 is transmitted by the third grating to the output port. In other embodiments, signal component 905-3 is reflected by the fourth grating toward the output port.

[0061] As shown, passbands 1010-0, 1010-1, 1010-2, and 1010-3 partially overlap. However, other embodiments may include different combinations of passbands, including some non-overlapping passbands. For example, a cascaded arrangement may include a combination of one or more gratings configured as low-pass filters and one or more gratings configured as band-pass filters. Furthermore, gratings configured as high-pass filters are also contemplated, either alone or in combination with other types of filters.

[0062] Figure 111100 is a graph illustrating the operation of a dual-mode Bragg grating operating as a bandpass filter with partially overlapping passbands, according to one or more embodiments. The features illustrated in graph 1100 can be used in conjunction with other embodiments. For example, a cascaded arrangement in any of demultiplexers 505, 605, 705, 805 can have a grating configured as a bandpass filter.

[0063] Graph 1100 shows the filter responses 910-0, 910-1, 910-2, 910-3 of each grating. The filter responses 910-0, 910-1, 910-2, 910-3 include partially overlapping passbands 915-0, 915-1, 915-2, 915-3. Each passband 915-0, 915-1, 915-2, 915-3 has a corresponding center wavelength λ C0 ,λ C1 ,λ C2 ,λ C3 and the corresponding roll-off wavelength λ R0 ,λ R1 ,λ R2 ,λ R3 . Center wavelength λ C0 ,λ C1 ,λ C2 ,λ C3 and the roll-off wavelength λ R0 ,λ R1 ,λ R2 ,λ R3 is selected so that the ranges 1105-0, 1105-1, 1105-2, 1105-3 around the respective wavelengths λ0, λ1, λ2, λ3 are completely included in the center wavelength λ C0 ,λ C1 ,λ C2 ,λ C3 and the roll-off wavelength λ R0 ,λ R1 ,λ R2 ,λ R3 In other words, the first grating is designed so that the range 1105-0 around the first wavelength λ0 is completely included in the center wavelength λ C0 and the roll-off wavelength λ R0 The second grating is designed so that the range 1105-1 around the second wavelength λ1 is completely included in the central wavelength λ C1 and the roll-off wavelength λ R1By adapting the ranges 1105-0, 1105-1, 1105-2, 1105-3 in this manner, the partially overlapping passbands 915-0, 915-1, 915-2, 915-3 can be spaced more closely together to have a greater amount of overlap while maintaining appropriate selectivity of the gratings in the cascaded arrangement (i.e., reflecting one wavelength but not an adjacent wavelength).

[0064] In one non-limiting example of a CWDM scheme, four (4) channels are defined such that wavelength λ0 = 1271 nm, wavelength λ1 = 1291 nm, wavelength λ2 = 1311 nm, and wavelength λ3 = 1331 nm. Each of ranges 1105-0, 1105-1, 1105-2, 1105-3 is ±6.5 nm of the corresponding wavelength λ0, λ1, λ2, λ3, such that range 1105-0 is 1264.5 nm to 1277.5 nm (corresponding to a total range of 13 nm), range 1105-1 is 1284.5 nm to 1297.5 nm, range 1105-2 is 1304.5 nm to 1317.5 nm, and range 1105-3 is 1324.5 nm to 1337.5 nm.

[0065] Assuming the central wavelength λ C0 =1264nm, center wavelength λ C1 =1284nm, center wavelength λ C2 =1304nm, center wavelength λ C3 = 1324 nm (corresponding to a channel pitch of 20 nm). Since each grating has a passband of 32 nm, the upper roll-off wavelength λ R0 =1280nm, upper roll-off wavelength λ R1 =1300nm, upper roll-off wavelength λ R2 =1320nm, upper roll-off wavelength λ R3 =1340nm.

[0066] Thus, the range 1105-0 (1264.5 nm to 1277.5 nm) is completely included in the central wavelength λ of the first grating. C0 (1264nm) and upper nm wavelength λ R0 (1280nm), the range 1105-1 (1284.5nm to 1297.5nm) is completely included in the central wavelength λ of the second grating C1 (1284nm) and upper roll-off wavelength λ R1 (1300nm), etc.

[0067] Advantageously, by configuring the grating to provide passbands 915-0, 915-1, 915-2, 915-3 ( Figure 9 、 Figure 11 ), passband 1010-0, 1010-1, 1010-2, 1010-3 ( Figure 10 ) are configured with a relatively wide passband and a flat top with a steeply edged spectral response. Demultiplexers tend to be more tolerant to manufacturing variations, variations in material layer thickness, and / or temperature changes. Using silicon nitride or silicon oxynitride as the grating material can further increase tolerance to these variations.

[0068] While the above examples are discussed in terms of partially overlapping passbands 915-0, 915-1, 915-2, 915-3 for bandpass filters, similar techniques can be used to space the passbands of lowpass filters more closely while maintaining suitable selectivity. For example, the cutoff wavelength of the lowpass filter can be selected so that there is a minimum margin (e.g., 2 nm) between the cutoff wavelength of the grating and the range around the specific wavelength of the optical signal that will be reflected by the grating.

[0069] Furthermore, while the demultiplexers 505, 605, 705, 805 have been described as one-to-four (1:4) demultiplexers having three (3) or four (4) dual-mode Bragg gratings in a cascade arrangement, other configurations of the demultiplexers 505, 605, 705, 805 are also contemplated. For example, the demultiplexer 125 may include a greater or lesser number of Bragg gratings in a cascade arrangement, different filter responses for the gratings, and so forth.

[0070] Figure 12 A method 1200 of demultiplexing using a cascaded arrangement of dual-mode Bragg gratings according to one or more embodiments is shown. The method 1200 can be used in conjunction with other embodiments, for example, performed using any of the demultiplexers 505, 605, 705, 805 described above.

[0071] Method 1200 begins at block 1205, where a demultiplexer receives an optical signal comprising multiple wavelengths at an input port. At block 1215, the corresponding wavelengths are reflected using a cascaded dual-mode Bragg grating. At block 1225, the mode of the reflected wavelength is converted to a fundamental mode. In some embodiments, the conversion is performed using a mode multiplexer disposed at a tap port of the dual-mode Bragg grating.

[0072] At block 1235, any remaining wavelengths are transmitted using a dual-mode Bragg grating. From block 1235, method 1200 returns to block 1215 for each dual-mode Bragg grating in the cascaded arrangement. In some embodiments, the last wavelength is reflected by the last grating in the cascaded arrangement. In other embodiments, the last grating reflects the second-to-last wavelength and transmits the last wavelength. At block 1245, the single wavelength is output at the corresponding output port. After completion of block 1245, method 1200 ends.

[0073] In the foregoing, reference has been made to the embodiments presented in this disclosure. However, the scope of this disclosure is not limited to the specifically described embodiments. Rather, any combination of the described features and elements, whether or not related to different embodiments, is contemplated for use in implementing and practicing the contemplated embodiments. Furthermore, while the embodiments disclosed herein may achieve advantages over other possible solutions or over the prior art, whether or not a particular advantage is achieved by a given embodiment does not limit the scope of this disclosure. Therefore, unless expressly recited in claim(s), the foregoing aspects, features, embodiments, and advantages are merely illustrative and are not considered to be elements or limitations of the appended claims.

[0074] Various aspects of the present disclosure are described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments presented in the present disclosure. It should be understood that each block in the flowchart illustrations and / or block diagrams, as well as combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device create a module for implementing the functions / actions specified in one or more blocks of the flowchart and / or block diagram.

[0075] These computer program instructions may also be stored in a computer-readable medium, which can direct a computer, other programmable data processing apparatus or other device to function in a specific manner so that the instructions stored in the computer-readable medium produce an article of manufacture, which includes instructions for implementing the functions / actions specified in one or more blocks of the flowchart and / or block diagram.

[0076] The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device, so that a series of operational steps are performed on the computer, other programmable apparatus, or other device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable apparatus provide a process for implementing the functions / actions detailed in one or more blocks of the flowchart and / or block diagram.

[0077] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of the systems, methods, and computer program products according to various embodiments. In this regard, each block in the flowchart or block diagram can represent a portion of a module, fragment, or code that contains one or more executable instructions for implementing (one or more) specific logical functions. It should also be noted that in some alternative implementations, the functions mentioned in the blocks may appear in an order different from that mentioned in the accompanying drawings. For example, depending on the functions involved, two blocks shown in succession may actually be executed substantially simultaneously, or blocks may sometimes be executed in reverse order. It should also be noted that each block in the block diagram and / or flowchart illustration, as well as the combination of blocks in the block diagram and / or flowchart illustration, may be implemented by a dedicated hardware-based system that performs a specific function or action, or by a combination of dedicated hardware and computer instructions.

[0078] In view of the foregoing, the scope of the present disclosure is determined by the following claims.

Claims

1. An optical device comprising: an input port configured to receive an optical signal, the optical signal comprising a plurality of wavelengths; a plurality of output ports, wherein each output port is configured to output a respective wavelength of the plurality of wavelengths; and a first plurality of dual-mode Bragg gratings arranged in cascade, wherein each grating of the first plurality of dual-mode Bragg gratings is configured as: transmitting a first mode of a corresponding wavelength of the plurality of wavelengths; reflecting the second mode of the corresponding wavelength toward a corresponding output port among the plurality of output ports; and Any remaining wavelengths in the plurality of wavelengths are transmitted.

2. The optical device according to claim 1, wherein Each grating of the first plurality of dual-mode Bragg gratings comprises silicon nitride or silicon oxynitride material.

3. The optical device according to any one of claims 1 to 2, further comprising: a plurality of mode multiplexers, wherein each mode multiplexer of the plurality of mode multiplexers is configured to receive a respective wavelength reflected by a respective grating of the first plurality of dual-mode Bragg gratings, Each of the plurality of output ports is coupled to an output of a corresponding mode multiplexer in the plurality of mode multiplexers.

4. The optical device according to claim 3, wherein Each mode multiplexer is configured to propagate a fundamental mode along the first arm and a reflected second order mode along the second arm.

5. The optical device according to claim 1, wherein The last grating of the cascade arrangement is configured as: reflecting a second to last wavelength of the plurality of wavelengths toward a first output port of the plurality of output ports; and A last wavelength of the plurality of wavelengths is transmitted to a second output port of the plurality of output ports.

6. The optical device according to claim 1, wherein The last grating of the cascade arrangement is configured as: A last wavelength of the plurality of wavelengths is reflected to a first output port of the plurality of output ports.

7. The optical device according to claim 1, further comprising: a second plurality of dual-mode Bragg gratings, wherein each grating in the second plurality of dual-mode Bragg gratings is configured as: receiving a respective wavelength reflected by a respective grating of the first plurality of dual-mode Bragg gratings; and The corresponding wavelength is reflected toward a corresponding output port of the plurality of output ports.

8. The optical device according to claim 7, further comprising: A plurality of light absorbers, wherein each grating of the second plurality of dual-mode Bragg gratings has an output coupled to a corresponding light absorber of the plurality of light absorbers.

9. The optical device according to claim 1, wherein The first plurality of dual-mode Bragg gratings have non-overlapping passbands.

10. The optical device according to claim 1, wherein The first plurality of dual-mode Bragg gratings have partially overlapping passbands.

11. The optical device according to claim 10, wherein Each of the partially overlapping passbands has a center wavelength and an upper roll-off wavelength selected such that a range of corresponding wavelengths reflected by a corresponding grating is completely comprised between the center wavelength and the upper roll-off wavelength.

12. The optical device according to claim 1, wherein The first plurality of dual-mode Bragg gratings are low-pass filters.

13. An optical device comprising: multiple receivers; and Demultiplexer, including: an input port configured to receive an optical signal, the optical signal comprising a plurality of wavelengths; a plurality of output ports, wherein each output port is configured to output a corresponding wavelength of the plurality of wavelengths to a corresponding receiver of the plurality of receivers; and a first plurality of dual-mode Bragg gratings arranged in cascade, wherein each grating of the first plurality of dual-mode Bragg gratings is configured as: transmitting a first mode of a corresponding wavelength of the plurality of wavelengths; reflecting the second mode of the corresponding wavelength toward a corresponding output port among the plurality of output ports; and Any remaining wavelengths in the plurality of wavelengths are transmitted.

14. The optical device according to claim 13, wherein The demultiplexer is a coarse wavelength division multiplexing (CWDM) demultiplexer.

15. The optical device according to any one of claims 13 to 14, wherein: Each grating of the first plurality of dual-mode Bragg gratings comprises silicon nitride or silicon oxynitride material.

16. The optical device according to claim 13, wherein: The demultiplexer further comprises: a plurality of mode multiplexers, wherein each mode multiplexer of the plurality of mode multiplexers is configured to receive a respective wavelength reflected by a respective grating of the first plurality of dual-mode Bragg gratings, wherein each of the plurality of output ports is coupled to an output of a corresponding mode multiplexer in the plurality of mode multiplexers, and Each mode multiplexer is configured to propagate a fundamental mode along a first arm and a reflected second-order mode along a second arm.

17. The optical device according to claim 13, wherein The demultiplexer further comprises: a second plurality of dual-mode Bragg gratings, wherein each grating in the second plurality of dual-mode Bragg gratings is configured as: receiving respective wavelengths reflected by respective ones of the first plurality of dual-mode Bragg gratings; and The corresponding wavelength is reflected toward a corresponding output port of the plurality of output ports.

18. The optical device according to claim 17, further comprising: A plurality of light absorbers, wherein each grating of the second plurality of dual-mode Bragg gratings has an output coupled to a corresponding light absorber of the plurality of light absorbers.

19. The optical device according to claim 13, wherein The first plurality of dual-mode Bragg gratings are bandpass filters.

20. The optical device according to claim 13, wherein The first plurality of dual-mode Bragg gratings are low-pass filters.

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