CN113900177B - Optical beam combiner and preparation method thereof - Google Patents
Optical beam combiner and preparation method thereof Download PDFInfo
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- CN113900177B CN113900177B CN202111162753.9A CN202111162753A CN113900177B CN 113900177 B CN113900177 B CN 113900177B CN 202111162753 A CN202111162753 A CN 202111162753A CN 113900177 B CN113900177 B CN 113900177B
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29346—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by wave or beam interference
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
- G02B6/2938—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/35—Optical coupling means having switching means
- G02B6/354—Switching arrangements, i.e. number of input/output ports and interconnection types
- G02B6/3544—2D constellations, i.e. with switching elements and switched beams located in a plane
- G02B6/3546—NxM switch, i.e. a regular array of switches elements of matrix type constellation
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12133—Functions
- G02B2006/1215—Splitter
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- Optical Integrated Circuits (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
Abstract
The invention relates to the technical field of optical communication, and provides an optical beam combiner and a preparation method thereof, wherein the optical beam combiner comprises the following components: a first input waveguide, a second input waveguide, a central output waveguide, and 2n bypass output waveguides; the 2n bypass output waveguides are symmetrically distributed on two sides of the central output waveguide; wherein n is a natural number greater than or equal to 1; compared with a 2-input 1-output structure beam combiner, the optical beam combiner provided by the invention has the advantages that the leaked signal light is led out of the beam combiner in a specific path, so that the influence of light reflection and light leakage on the overall performance of other devices or integrated optical chips is avoided, and the device and system performance is improved.
Description
Technical Field
The invention relates to the technical field of optical communication, in particular to an optical beam combiner and a preparation method thereof.
Background
With the development of optical communication technology, the communication capacity is gradually increased, and the integration level of optical devices is also higher and higher. The integrated optical device has the advantages of low energy consumption, high bandwidth, ultrahigh frequency spectrum utilization rate and the like, so that various electric devices such as optical interconnection, optical sensing, optical communication, quantum communication and the like are replaced in various fields. A Mach-Zehnder Modulator, abbreviated as MZ modulator, is one of the core devices for loading an electrical signal onto an optical wave, i.e., modulating light. MZ modulators are typically composed of beam splitters, waveguides, phase shifters, traveling wave electrodes, beam combiners, etc., which can be used to effect intensity modulation and phase modulation of light.
The beam combiner in the existing MZ modulator generally adopts a 2-input-1-output structure, such as a 2x1 multimode interferometer (Multimode Interference, MMI for short). When the amplitude of the radio frequency signal is smaller, the MZ modulator has larger modulation loss, and most of the lost light energy is dispersed to the core layer of the integrated optical chip through the beam combiner. The light leakage generated by the beam combiner will have an effect on other structures in the integrated optical chip. For example, noise is introduced, so that the signal-to-noise ratio of a rear-end Photodetector (PD) of the MZ modulator is reduced, and subsequent signal processing is interfered; and reflection is introduced into the input end of the beam combiner, even the input end of the whole integrated optical chip, so that return loss is reduced, and the overall performance of the optical chip is influenced. On the system level, the optical leakage causes great performance degradation to the application of the integrated optical chip in a coherent optical communication system, including degradation of light output power, degradation of optical signal to noise ratio and the like.
For the existing 2-input 1-output beam combiner, when the MZ modulator (QPSK, 16QAM, etc.) is used for phase modulation, as shown in FIG. 1, only when two arms of the Mach-Zehnder interferometer (Mach-Zehnder Interferometer, abbreviated as MZI) are in phase, namely the phase difference (two-input phase difference of the beam combiner) of the two arms of the MZI is 0 DEG, the optical beam combiner does not have output light leakage and input light reflection; that is, once the two arms of the MZI have different phases, there is output light leakage and input light reflection; as shown in fig. 2, for an intensity modulated MZ modulator, there is still some degree of light leakage and light reflection when operating at the quad point, i.e., the MZI arms are 90 degrees out of phase (the two input phase difference of the combiner); as shown in fig. 3, the MZ modulator works at null point, that is, the phase difference between two arms of the MZI (the phase difference between two inputs of the beam combiner) is 180 degrees, and the coherence cancellation at the output port of the beam combiner affects the performance of the optical chip and the whole system; the dashed boxes in fig. 1,2 and 3 are multimode interference regions and are not of particular interest, but only the energy levels of light in the left two input waveguides and the right one output waveguide of the figure at different phase differences.
In view of this, overcoming the drawbacks of the prior art is a problem to be solved in the art.
Disclosure of Invention
The invention aims to solve the technical problems that:
in the existing 2-input 1-output structure beam combiner, once the phases of two arms of the MZI are different, output light leakage and input light reflection exist, the output light leakage can affect other structures in the integrated optical chip, the input light reflection can reduce return loss, and the overall performance of the optical chip is affected.
In order to achieve the above purpose, the invention adopts the following technical scheme:
in one aspect, the present invention provides an optical combiner comprising: a first input waveguide, a second input waveguide, a central output waveguide, and 2n bypass output waveguides;
the 2n bypass output waveguides are symmetrically distributed on two sides of the central output waveguide; a first bypass output waveguide and a second bypass output waveguide exist in the 2n bypass output waveguides, the central line of the first bypass output waveguide is coaxial with the central line of the first input waveguide, and the central line of the second bypass output waveguide is coaxial with the central line of the second input waveguide;
of the 2n bypass output waveguides, 2n-2 bypass output waveguides except the first bypass output waveguide and the second bypass output waveguide are symmetrically arranged on two sides of the central output waveguide;
wherein n is a natural number greater than or equal to 1.
Preferably, the distance between the edge of the first bypass output waveguide and the edge of the second bypass output waveguide and the edge of the central output waveguide is larger than a first preset distance.
Preferably, the optical combiner further comprises: the first input back taper, the second input back taper, the multimode interference area, the central output back taper and 2n bypass output back tapers;
the first input waveguide is connected with the multimode interference area through the first input back taper, the second input waveguide is connected with the multimode interference area through the second input back taper, the central output waveguide is connected with the multimode interference area through the central output back taper, and the 2n bypass output waveguides are connected with the multimode interference area through the 2n bypass output back tapers.
Preferably, the optical combiner further comprises: 2n light absorbing structures; the 2n light absorbing structures are connected with the 2n bypass output waveguides, and the 2n light absorbing structures are used for absorbing light output from the 2n bypass output waveguides.
Preferably, the 2n light absorbing structures are metallic material absorbing structures or semiconductor material absorbing structures.
Preferably, the first input waveguide, the second input waveguide, the central output waveguide, and the 2n bypass output waveguides are all single-mode waveguides.
Preferably, the center position of the first input back taper is shifted upwards by a preset shift amount relative to the upper quarter of the width of the multimode interference zone, and the center position of the second input back taper is shifted downwards by a preset shift amount relative to the lower quarter of the width of the multimode interference zone; or alternatively, the process may be performed,
the center position of the first input back taper is offset downwards by a preset offset relative to the upper quarter of the width of the multimode interference zone, and the center position of the second input back taper is offset upwards by a preset offset relative to the lower quarter of the width of the multimode interference zone.
Preferably, the distance between the edge of the first bypass output back taper and the edge of the second bypass output back taper and the edge of the center output back taper is larger than a second preset distance.
Preferably, the shape of the multimode interference zone comprises a rectangular, polygonal or sub-wavelength structure.
In another aspect, the present invention provides a method of making an optical combiner, comprising: uniformly coating photoresist on a substrate; transferring the pattern of the optical beam combiner from the mask plate to the photoresist coated on the substrate through a photoetching development technology; transferring the pattern of the optical combiner from the photoresist coated on the substrate to the substrate by etching; and removing the photoresist coated on the substrate and etching residues on the substrate by cleaning.
Compared with the prior art, the invention has the beneficial effects that:
compared with a 2-input 1-output structure beam combiner, the optical beam combiner provided by the invention has the advantages that the leaked signal light is led out of the beam combiner in a specific path, so that the influence of light reflection and light leakage on the overall performance of other devices or integrated optical chips is avoided, and the device and system performance is improved.
Drawings
In order to more clearly illustrate the technical solution of the embodiments of the present invention, the drawings that are required to be used in the embodiments of the present invention will be briefly described below. It is evident that the drawings described below are only some embodiments of the present invention and that other drawings may be obtained from these drawings without inventive effort for a person of ordinary skill in the art.
FIG. 1 is a diagram showing the optical field distribution of an optical combiner of the prior art when the two inputs have a phase difference of 0 degrees;
FIG. 2 is a diagram showing the optical field distribution of the optical combiner of the prior art when the two inputs have a phase difference of 90 degrees;
FIG. 3 is a diagram showing the optical field distribution of an optical combiner of the prior art with a phase difference of 180 degrees between two inputs;
FIG. 4 is a top view of an optical combiner according to an embodiment of the present invention;
FIG. 5 is a top view of an optical combiner according to an embodiment of the present invention;
FIG. 6 is a cross-sectional view of an optical combiner provided by an embodiment of the present invention;
FIG. 7 is a cross-sectional view of an optical combiner provided by an embodiment of the present invention;
FIG. 8 is a top view of another optical combiner provided in an embodiment of the present invention;
FIG. 9 is a top view of another optical combiner provided in an embodiment of the present invention;
FIG. 10 is a top view of an optical combiner having a light absorbing structure provided by an embodiment of the present invention;
FIG. 11 is a top view of an optical combiner with offset design according to an embodiment of the present invention;
FIG. 12 is a graph showing the variation of the output insertion loss of the optical combiner according to the embodiment of the present invention along with the preset offset;
FIG. 13 is a top view of an optical combiner provided by an embodiment of the present invention, wherein the distances between the edge of the bypass output back taper and the edge of the center output back taper are both greater than a predetermined distance;
FIG. 14 is a top view of an optical combiner having differently shaped multimode interference zones provided by an embodiment of the invention;
FIG. 15 is a schematic diagram of light field distribution when two input phase differences of an optical combiner provided by an embodiment of the present invention are 180 degrees;
FIG. 16 is a graph showing the light leakage ratio with the offset distance when the two-input phase difference of the optical combiner is 180 degrees according to the embodiment of the present invention;
FIG. 17 is a graph showing the light leakage ratio according to the phase difference when the phase difference between two inputs of the optical combiner is 180 degrees according to the embodiment of the present invention;
FIG. 18 is a graph showing the light leakage ratio according to the phase difference when the two input phase difference of the optical combiner is 180 degrees;
FIG. 19 is a graph showing the variation of the output insertion loss of the optical combiner according to the phase difference according to the optical combiner of the prior art and the embodiment of the present invention;
FIG. 20 is a top view of an MZ type optical intensity modulator using an optical combiner provided by an embodiment of the invention;
fig. 21 is a top view of an MZ-type optical IQ modulator using an optical combiner according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
In the description of the present invention, the terms "inner", "outer", "longitudinal", "transverse", "upper", "lower", "top", "bottom", etc. refer to an orientation or positional relationship based on that shown in the drawings, merely for convenience of describing the present invention and do not require that the present invention must be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.
In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
The amplitude of the optical field of the upper arm and the lower arm of the MZ type optical modulator is A, the phase difference is theta, and for the optical beam combiner in the prior art, the output expression under the ideal condition is as follows:
E out the optical field expression is output for the signal of the optical beam combiner in the prior art, E out ' is a non-signal output light field expression of the optical combiner in the prior art; j is an imaginary unit; the optical combiner of the prior art has only one output port, E when the phase difference θ is not 0 out ' not 0, i.e. there is some optical energy in the optical combiner that cannot be output, this will cause some reflection of the input, while E out ' will diffuse to the core layer of the integrated optical chip in some unknown path, interfering with the proper operation of other devices.
Example 1:
an embodiment of the present invention provides an optical combiner, as shown in fig. 4, including: a first input waveguide 1, a second input waveguide 2, a central output waveguide 3 and 2n bypass output waveguides 4, where n is a natural number greater than or equal to 1.
The 2n bypass output waveguides 4 are symmetrically distributed on two sides of the central output waveguide 3, as shown in fig. 5, a first bypass output waveguide 41 and a second bypass output waveguide 42 exist in the 2n bypass output waveguides 4, the central line of the first bypass output waveguide 41 is coaxial with the central line of the first input waveguide 1, and the central line of the second bypass output waveguide 42 is coaxial with the central line of the second input waveguide 2.
Of the 2n bypass output waveguides 4, 2n-2 bypass output waveguides other than the first bypass output waveguide 41 and the second bypass output waveguide 42 are symmetrically disposed on both sides of the center output waveguide 3.
The following description will be given with reference to fig. 6 and 7, in which the 2n bypass output waveguides 4 are symmetrically distributed on both sides of the central output waveguide 3; fig. 6 is a sectional view at a broken line A-A 'in the case of n=1 in fig. 4, and fig. 7 is a sectional view at a broken line A-A' in the case of n=2 in fig. 4.
When n=1, as shown in fig. 6, two bypass output waveguides are the first bypass output waveguide 41 and the second bypass output waveguide 42, and the first bypass output waveguide 41 and the second bypass output waveguide 42 are respectively located at two sides of the central output waveguide 3 and respectively opposite to the first input waveguide 1 and the second input waveguide 2.
When n >1, taking fig. 7 as an example for illustration, the positions of the remaining 2n-2 bypass output waveguides among the 2n bypass output waveguides 4 except for the first bypass output waveguide 41 and the second bypass output waveguide 42 are: the 2n-2 bypass output waveguides are symmetrically arranged at two sides of the central output waveguide 3, and n-1 bypass output waveguides in the 2n-2 bypass output waveguides are arranged in the direction that the first bypass output waveguide 41 is far away from the central output waveguide 3, namely, the right side of the first bypass output waveguide 41 in fig. 7; the remaining n-1 of the 2n-2 bypass output waveguides are arranged in a direction of the second bypass output waveguide 42 away from the central output waveguide 3, i.e. to the left of the second bypass output waveguide 42 in fig. 7.
In the case where n >1, the leaked signal light is mainly led out through the first bypass output waveguide 41 and the second bypass output waveguide 42, and the other output waveguides are used for guiding out the leaked signal light that does not enter the first bypass output waveguide 41 and the second bypass output waveguide 42, so as to maximally guide out the leaked signal light from the optical combiner.
In the embodiment of the present invention, in order to avoid coupling between the first bypass output waveguide 41 and the second bypass output waveguide 42 and the central output waveguide 3, the distances between the edges of the first bypass output waveguide 41 and the second bypass output waveguide 42 and the edges of the central output waveguide 3 are both greater than a first preset distance; wherein the first preset distance is preferably 0.5um.
In order to avoid coupling of the 2n-2 bypass output waveguides with the central output waveguide 3, n-1 bypass output waveguides among the 2n-2 bypass output waveguides are arranged in a direction in which the first bypass output waveguide 41 is away from the central output waveguide 3, and n-1 bypass output waveguides are arranged in a direction in which the second bypass output waveguide 42 is away from the central output waveguide 3.
Further, in order to avoid that other bypass output waveguides than the first bypass output waveguide 41 and the second bypass output waveguide 42 are coupled with the center output waveguide 3, the distance between the other bypass output waveguides and the center output waveguide 3 is larger than the distance between the first bypass output waveguide 41 and the second bypass output waveguide 42 and the center output waveguide 3; that is, half of the other bypass output waveguides are disposed in a direction in which the first bypass output waveguide 41 is away from the center output waveguide 3, and the other half of the other bypass output waveguides are disposed in a direction in which the second bypass output waveguide 42 is away from the center output waveguide 3.
The first input waveguide 1, the second input waveguide 2, the central output waveguide 3 and the 2n bypass output waveguides 4 are all formed on the integrated optical chip by photolithography, and after the photolithography, the remaining portions are the first input waveguide 1, the second input waveguide 2, the central output waveguide 3 and the 2n bypass output waveguides 4, and in fig. 6, the first bypass output waveguide 41, the second bypass output waveguide 42 and the central output waveguide 3 are all core portions left after the photolithography, and the remaining portions are spaces formed by photolithography, and by coating the core portions left after the photolithography, the light can propagate only in the core portions left after the photolithography.
The first input waveguide 1 and the second input waveguide 2 are used for inputting optical signals; the central output waveguide 3 is used for outputting a signal light signal; the bypass output waveguide 6 is used for guiding out the leaked signal light.
By symmetrically arranging the 2n bypass output waveguides 4 on two sides of the central output waveguide 3, setting the central line of the first bypass output waveguide 41 to be coaxial with the central line of the first input waveguide 1, and setting the central line of the second bypass output waveguide 42 to be coaxial with the central line of the second input waveguide 2, the leaked signal light is led out of the optical beam combiner in a specific path, so that the signal light is prevented from being reflected into the input waveguide or the light is prevented from leaking into the core layer of the integrated optical chip to the greatest extent.
The optical beam combiner provided by the invention adopts an optical beam combiner with a 2-input 2n+1 output structure, wherein a central output waveguide 3 is used as in-phase light output inphase optical output, and 2n bypass output waveguides 4 are used as opposite-phase light output outphase optical output; when the modulator works at a null point, the port optical power of the central output waveguide 3 is 0, and most of the optical power is collected through the ports of the 2n bypass output waveguides 4, so that dispersion to a core layer is avoided; the optical beam combiner with the 2 input 2n+1 output structure provided by the invention has the advantages that the output structure adopts a symmetrical structure, the loss is lower, and the balance and the process error resistance are improved.
In an embodiment of the present invention, as shown in fig. 8, the optical combiner further includes: a multimode interference region 7, a first input back taper 5, a second input back taper 6, a central output back taper 8 and 2n bypass output back tapers 9.
The first input waveguide 1 is connected to the multimode interference zone 7 by the first input back taper 5, and the center line of the first input waveguide 1 is coaxial with the center line of the first input back taper 5.
The second input waveguide 2 is connected to the multimode interference zone 7 by the second input back taper 6, the centre line of the second input waveguide 2 being coaxial with the centre line of the second input back taper 6.
The central output waveguide 3 is connected with the multimode interference zone 7 through the central output back taper 8, and the central line of the central output waveguide 3 is coaxial with the central line of the central output back taper 8.
The 2n bypass output waveguides 4 are connected to the multimode interference region 7 through the 2n bypass output back tapers 9, as shown in fig. 9, a first bypass output back taper 91 and a second bypass output back taper 92 are present in the 2n bypass output back tapers 9, a center line of the first bypass output back taper 91 is coaxial with a center line of the first bypass output waveguide 41, and a center line of the second bypass output back taper 92 is coaxial with a center line of the second bypass output waveguide 42.
Wherein the first input waveguide 1 and the second input waveguide 2 are connected to one side of the multimode interference zone 7 through a first input back taper 5 and a second input back taper 6, respectively; the central output waveguide 3, the first bypass output waveguide 41 and the second bypass output waveguide 42 are connected to the other side of the multimode interference zone 7 through a central output back taper 8, a first bypass output back taper 91 and a second bypass output back taper 92, respectively.
In an embodiment of the present invention, in order to prevent leakage light from entering the core layer of the integrated optical chip and prevent reflected light from entering the first input waveguide 1 and the second input waveguide 2 to form a standing wave phenomenon, as shown in fig. 10, the optical combiner further includes: 2n light absorbing structures 10; the 2n light absorbing structures 10 are for absorbing light output from the bypass output waveguides 6; 2n bypass output waveguides 4 are connected to 2n light absorbing structures 10, specifically, each bypass output waveguide is connected to one light absorbing structure; by increasing the lengths of the 2n light absorbing structures 10 in the light propagation direction or adopting light absorbing materials of different light absorption coefficients, leaked signal light of the low order mode to the high order mode can be completely absorbed by the 2n light absorbing structures 10.
When the two input phase differences are 180 degrees, the signal light energy in the central output waveguide 3 is very weak, most of the light leaks outside the central output waveguide 3, the leaked signal light is led out of the optical beam combiner through the bypass output waveguide 6, and the leaked signal light is absorbed by introducing 2n light absorbing structures 10, so that the light leakage and light reflection can be reduced.
After the 2n light absorbing structures 10 absorb the portion of the leaked signal light, the portion of the leaked signal light absorbed by the 2n light absorbing structures 10 may be processed by using the photoelectric characteristics of an absorbing material, for example, a semiconductor germanium material, and an optical signal may be converted into an electrical signal for processing.
In the embodiment of the present invention, the 2n light absorbing structures 10 are metal material absorbing structures or semiconductor material absorbing structures, and specifically, different kinds of the 2n light absorbing structures 10 may be selected according to the operating band aimed by the optical beam combiner and the absorption coefficient of the absorbing material, for example, the operating band aimed by the optical beam combiner is a C band, that is, about 1550nm, the metal material absorbing structure may be selected to be aluminum, and the semiconductor material absorbing structure may be selected to be germanium.
In the embodiment of the present invention, in order to avoid light dispersion introduced by using multimode waveguides, the first input waveguide 1, the second input waveguide 2, the central output waveguide 3, and the 2n bypass output waveguides 6 are all single-mode waveguides.
In the embodiment of the present invention, the single-mode waveguide includes a straight waveguide or a curved waveguide, that is, the first input waveguide 1, the second input waveguide 2, the central output waveguide 3, and the 2n bypass output waveguides 6 may be all straight waveguides; can be curved waveguides; the waveguide can also be partly a straight waveguide and partly a curved waveguide, and the specific how of the waveguide is matched with the waveguide can be selected according to actual requirements.
The mode of light in the waveguide is not perfectly constrained in the waveguide, and has a certain extension outside the edge of the waveguide, so the width for theoretical calculation is larger than the physical width of the actual multimode interference zone 7, so the actual position is not the position of the upper quarter or the lower quarter of the width of the multimode interference zone 7, but has a certain offset; in order to reduce light leakage and reflection, ensure that more light of an input waveguide enters a central output waveguide 3 and minimize insertion loss from the input waveguide to the central output waveguide 3, the optical combiner provided by the invention performs offset design on the first input back taper 5 and the second input back taper 6, and specifically comprises: the center position of the first input back taper 5 is shifted upwards by a preset offset relative to the upper quarter of the width of the multimode interference zone 7, and the center position of the second input back taper 6 is shifted downwards by a preset offset relative to the lower quarter of the width of the multimode interference zone 7; alternatively, the center position of the first input back taper 5 is shifted downward by a preset shift amount with respect to the upper quarter of the width of the multimode interference zone 7, and the center position of the second input back taper 6 is shifted upward by a preset shift amount with respect to the lower quarter of the width of the multimode interference zone 7.
Taking n equal to 1 as an example, according to the principle of self-mapping in multimode waveguides, where multiple guided modes interfere with each other, one or more replicas of the input field occur at periodic intervals along the propagation direction of the wave, the positions x of the input and output ends of the multimode interference region along the width direction of the multimode interference region can be calculated in,r And x out,s And the light field intensity with r input port and s serial number of r output portAnd phase->
Wherein N represents the number of the output end self-images of the multimode interference zone 7; m represents the number of cycles in which N images appear in the multimode interference zone 7; w is the width of the multimode interference zone 7; r represents the input terminal number, r=1, 2 …, N-1; s represents the output sequence number, s=1, 2 …, N-1; b is the phase shift produced by the different inputs, b=1 for the symmetrical mode input; for the antisymmetric mode input, b=0.
In this embodiment, consider that the single-mode input is a symmetric-mode input, i.e., b=1; considering device size minimization, M takes a minimum value, i.e., m=1.
The positions of the input and output waveguides are calculated to satisfy equation 12, i.e., theoretically, the signal output optical energy |E out | 2 The ratio is 50%, and the optical field of the input signal at the signal output port is in phase, namely the phase difference is 0 DEG, and the input signal is called in-phase light; the optical field phase of the input signal at the non-signal output port is opposite, i.e. 180 deg. out of phase, referred to as inverted light.
The light field intensity r with the corresponding input port r and the output port serial number s can be calculated according to the formula 5 rs 2 The method comprises the steps of carrying out a first treatment on the surface of the For example, when n=8, r=2, s=2, r 22 2 =0.25; fixed input port r=2, changing output port serial number, calculating to obtain optical field intensities r of output ports with output port serial numbers of 2,4 and 6 respectively 22 2 ＝0.25，r 24 2 ＝0.5，r 26 2 =0.25; when the input port number is 6, the light field intensities of the output ports number 2,4 and 6 are r respectively 62 2 ＝0.25，r 64 2 ＝0.5，r 66 2 =0.25. The input port r=2 and the input port r=6 are the upper quarter input position and the lower quarter input position, and the output port s=4 is the position of the central output inverted cone. Thus, the upper and lower quarter input positions and the center-symmetrical output position may satisfy a signal output light energy ratio of 50%.
The relative phase of the optical field with the input port r and the output port serial number s can be calculated by the formula 6; when the input port r=2 is obtained,and input port r=6, +.> Thus, the input light is input from the input ports with the serial numbers of 2 and 6, and the phase difference of the optical field output from the output port with the serial number of 2 isInput light is input from input ports with serial numbers 2 and 6, and the phase difference of the optical field output from output port with serial number 4 is +.>Input light is input from input ports with serial numbers 2 and 6, and the phase difference of the optical field output from output port with serial number 6 is +.>Therefore, the upper quarter input position, the lower quarter input position and the central symmetry output position can meet the condition that the phase difference of the light field at the central symmetry output port is 0 DEG after the input light passes through the beam combiner, and the phase difference of the light field at the bypass output port is 180 deg.
That is, when the center position of the first input back taper 5 is at the upper quarter of the width of the multimode interference zone 7 and the center position of the second input back taper 6 is at the lower quarter of the width of the multimode interference zone 7, the center output waveguide 3 is satisfied as an in-phase light output, the bypass output waveguide 6 is an inverted light output, and the in-phase light output and the inverted light output are equal in energy.
Wherein W is the width of the multimode interference region, because of the Goos-Hahnchen effect, there is a widening, so that the actual input position will deviate, generally, the first input back taper 5 and the second input back taper 6 are designed to deviate, after the positions of the first input back taper 5 and the second input back taper 6 are determined, the positions of the first bypass output back taper 91 and the second bypass output back taper 92 are adjusted, so that the center line of the first bypass output back taper 91 is coaxial with the center line of the first input back taper 5, and the center line of the second bypass output back taper 92 is coaxial with the center line of the second input back taper 6.
As described in connection with fig. 11, the upper quarter of the width of the multimode interference zone 7 is identified at the junction of the first input back taper 5 and the multimode interference zone 7, and the lower quarter of the width of the multimode interference zone 7 is identified at the junction of the second input back taper 6 and the multimode interference zone 7, this position being relative to the width of the multimode interference zone 7, the length direction of the multimode interference zone 7 being the propagation direction of light.
Wherein the central position of the first input back taper 5 is upwards offset by a preset offset relative to the upper quarter of the width of the multimode interference zone 7; the center position of the second input back taper 6 is offset downwards by a preset offset relative to the lower quarter of the width of the multimode interference zone 7; in order to avoid excessive output insertion loss of the device, the preset offset is less than 2% of the width of the multimode interference zone 7.
Fig. 12 is a graph showing the variation of the output insertion loss of the optical combiner according to the embodiment of the present invention along with the preset offset, where it can be seen from the graph that the device insertion loss is the lowest when the preset offset is 0.51% of the width of the multimode interference region 7; when the preset offset is within 2% of the width of the multimode interference zone 7, the insertion loss can be ensured to be within 0.5dB, and thus, in order to avoid excessive output insertion loss of the device, the preset offset can be set to be less than 2% of the width of the multimode interference zone 7.
In the embodiment of the present invention, in order to avoid the coupling between the first bypass output back taper 91 and the second bypass output back taper 92 and the central output back taper 8, the distances between the edges of the first bypass output back taper 91 and the second bypass output back taper 92 and the edges of the central output back taper 8 are both greater than a second preset distance.
The second preset distance is preferably 0.2um, and the distance between the edge of the first bypass output back taper 91 and the edge of the second bypass output back taper 92 and the edge of the center output back taper 8 is the distance indicated by the double-headed arrow in fig. 13.
In the embodiment of the present invention, as shown in fig. 14, the shape of the multimode interference zone 7 includes a rectangular, polygonal or sub-wavelength structure.
Example 2:
by performing performance test on the optical beam combiner provided by the embodiment of the invention and the optical beam combiner in the prior art, the technical effect of the optical beam combiner provided by the invention compared with the optical beam combiner in the prior art is illustrated by the performance test result.
FIG. 15 is a schematic diagram of the optical beam combiner shown in FIG. 4 operating at null, i.e. the optical field distribution when the two inputs are 180 degrees out of phase, and as can be seen from FIG. 15, the optical energy in the central output waveguide is very weak when the two inputs are 180 degrees out of phase, and most of the light is output through the first bypass output waveguide and the second bypass output waveguide; when the phase difference of two inputs of the optical beam combiner in the prior art is 180 degrees, as shown in fig. 3, the light energy in the output waveguide is very weak, and most of light is dispersed out of the optical beam combiner; part of light leaks into a core layer of the integrated optical chip, so that the performance of the integrated optical chip is affected; the other part of light is reflected into the first input waveguide and the second input waveguide to form a strong standing wave; therefore, the optical combiner provided by the invention has the advantages that the first bypass output back taper and the second bypass output back taper are symmetrically arranged at two sides of the central output back taper, the central line of the first bypass output back taper and the central line of the first input back taper are coaxial, and the central line of the second bypass output back taper and the central line of the second input back taper are coaxial, so that leaked signal light is led out of the optical combiner in a specific path, standing waves formed in an input waveguide by non-signal light reflection or entering a core layer of an integrated optical chip by light leakage are avoided, and the performances of optical devices and systems are improved; the dashed box in fig. 15 is a multimode interference region and is not focused on the energy level of light in the two input waveguides on the left and one central output waveguide and two bypass output waveguides on the right in the figure.
FIG. 16 is a graph showing the light leakage ratio with offset distance when the two input phase difference of the optical combiner is 180 degrees, wherein the light leakage ratio is the ratio of the energy of the leaked light to the total energy of the input light; the offset distance comprises a displacement distance of the first bypass output back taper relative to the first input back taper in the width direction of the multimode interference zone and a displacement distance of the second bypass output back taper relative to the second input back taper in the width direction of the multimode interference zone; when the offset distance is 0, that is, the center line of the first bypass output back taper is coaxial with the center line of the first input back taper, the center line of the second bypass output back taper is coaxial with the center line of the second input back taper, the energy of the leaked light is minimum, the light which would leak is led out from the first bypass output waveguide through the first bypass output back taper, and the light is led out from the second bypass output waveguide through the second bypass output back taper, so that the light is prevented from dispersing into the core layer of the integrated optical chip, and the light is reflected into the first input waveguide and the second input waveguide to form standing waves.
FIG. 17 is a graph showing the light leakage ratio changing with the phase difference, which is the phase difference of the input light of the two input waveguides of the optical combiner, when the phase difference of the two inputs of the optical combiner is 180 degrees; as shown in fig. 17, although the light leakage ratio increases with an increase in the phase difference, the light leakage ratio is very low as a whole, and even when the phase difference is 180 degrees, the light leakage ratio is lower than 3%.
FIG. 18 is a graph showing the light leakage ratio changing with the phase difference when the two input phase difference between the optical beam combiner in the prior art and the optical beam combiner provided by the embodiment of the invention is 180 degrees, referring to FIG. 17, under the condition of different phase differences, the suppression effect of the optical beam combiner provided by the embodiment of the invention on the leakage light is very obvious, especially the phase difference is 180 degrees, and the light leakage ratio is reduced from nearly 100% to below 3%; when the phase difference is 0, the light leakage ratio is reduced from 2.4% to 2.3%.
Fig. 19 is a graph showing the change of the output insertion loss of the optical combiner according to the prior art and the optical combiner according to the embodiment of the present invention, and as can be seen from fig. 19, the performance of the optical combiner according to the embodiment of the present invention in the aspect of the output insertion loss is equivalent to that of the optical combiner according to the prior art, and is very close to the theoretical value.
Fig. 20 is a schematic structural diagram of an MZ optical intensity modulator using the optical combiner with a light absorbing structure according to an embodiment of the present invention, and the MZ optical intensity modulator using the optical combiner with a light absorbing structure according to an embodiment of the present invention further includes: an input waveguide 101 of the modulator and a beam splitter 102, wherein the beam splitter 102 equally divides light of the input waveguide 101 of the modulator, half of the light enters a first input waveguide 1 of the optical beam combiner through an upper phase-shifting arm 103 of the modulator, the upper phase-shifting arm 103 of the modulator and the first input waveguide 1 of the optical beam combiner form the upper arm of the modulator, half of the light enters a second input waveguide 2 of the optical beam combiner through a lower phase-shifting arm 104 of the modulator, and the lower phase-shifting arm 104 of the modulator and the second input waveguide 2 of the optical beam combiner form the lower arm of the modulator; the MZ type optical intensity modulator of the optical beam combiner provided by the embodiment of the invention can solve the technical problem of strong light leakage when the phase difference of two inputs of the beam combiner in the prior art is 90 degrees.
Fig. 21 is a schematic structural diagram of an MZ optical IQ modulator using an optical combiner with an optical absorption structure according to an embodiment of the present invention, where a dashed box 100, a dashed box 200 and a dashed box 300 are respectively a first optical combiner, a second optical combiner and a third optical combiner with an optical absorption structure according to an embodiment of the present invention, where 1021, 1023 and 1025 are multimode interference regions of the first optical combiner, the second optical combiner and the third optical combiner, respectively, and 1041 and 1042 are optical absorption structures of the first optical combiner; 1043 and 1044 are light absorbing structures of the second optical combiner; 1045 and 1046 are light absorbing structures of the third optical combiner.
The dashed box 400 and the dashed box 500 are respectively the sub-MZI of the MZ optical IQ modulator provided by the embodiment of the present invention, i.e. the I-path MZ modulator and the Q-path MZ modulator; the first optical beam combiner and the second optical beam combiner are respectively applied to the I-path MZ modulator and the Q-path MZ modulator; the third optical combiner is applied to the mother MZI of the IQ modulator.
The MZ optical IQ modulator with the optical beam combiner with the light absorption structure can solve the technical problems of strongest light leakage and light reflection when the two-input phase difference of the beam combiner in the prior art is 180 degrees.
Example 3:
the embodiment of the invention provides a preparation method of an optical beam combiner, which is used for preparing the optical beam combiner in the embodiment 1, and comprises the following steps:
uniformly coating photoresist on a substrate; wherein, the substrate can adopt an SOI substrate or an InP substrate; transferring the pattern of the optical beam combiner from the mask plate to the photoresist coated on the substrate through a photoetching development technology; transferring the pattern of the optical combiner from the photoresist coated on the substrate to the substrate by etching; and removing the photoresist coated on the substrate and etching residues on the substrate by cleaning.
In an embodiment of the present invention, the method for manufacturing an optical combiner further includes: after the cleaning is completed, the light absorbing structure is prepared by a growth process or a sputtering process.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.
Claims (8)
1. An optical combiner, comprising: a first input waveguide (1), a second input waveguide (2), a central output waveguide (3) and 2n bypass output waveguides (4);
the 2n bypass output waveguides (4) are symmetrically distributed on two sides of the central output waveguide (3); -there are a first bypass output waveguide (41) and a second bypass output waveguide (42) in the 2n bypass output waveguides (4), the centre line of the first bypass output waveguide (41) being coaxial with the centre line of the first input waveguide (1), the centre line of the second bypass output waveguide (42) being coaxial with the centre line of the second input waveguide (2);
of the 2n bypass output waveguides (4), 2n-2 bypass output waveguides other than the first bypass output waveguide (41) and the second bypass output waveguide (42) are symmetrically arranged on both sides of the central output waveguide (3);
wherein n is a natural number greater than or equal to 1;
the first input waveguide (1) is connected with the multimode interference zone (7) through a first input back taper (5), the second input waveguide (2) is connected with the multimode interference zone (7) through a second input back taper (6), the central output waveguide (3) is connected with the multimode interference zone (7) through a central output back taper (8), and the 2n bypass output waveguides (4) are connected with the multimode interference zone (7) through 2n bypass output back tapers (9);
the central position of the first input back taper (5) is offset upwards by a preset offset relative to the upper quarter of the width of the multimode interference zone (7), and the central position of the second input back taper (6) is offset downwards by a preset offset relative to the lower quarter of the width of the multimode interference zone (7); wherein the preset offset is less than 2% of the width of the multimode interference zone (7);
the first input back taper (5) and the second input back taper (6) are designed in an offset mode, after the positions of the first input back taper (5) and the second input back taper (6) are determined, the positions of the first bypass output back taper (91) and the second bypass output back taper (92) are adjusted, so that the center line of the first bypass output back taper (91) is coaxial with the center line of the first input back taper (5), and the center line of the second bypass output back taper (92) is coaxial with the center line of the second input back taper (6).
2. Optical combiner according to claim 1, characterized in that the edges of the first bypass output waveguide (41) and the edges of the second bypass output waveguide (42) are each more than a first preset distance from the edges of the central output waveguide (3).
3. The optical combiner as recited in claim 1, further comprising: 2n light absorbing structures (10); the 2n light absorbing structures (10) are connected to the 2n bypass output waveguides (4), the 2n light absorbing structures (10) being arranged to absorb light output from the 2n bypass output waveguides (4).
4. An optical combiner according to claim 3, wherein the 2n light absorbing structures (10) are metallic or semiconductor material absorbing structures.
5. The optical combiner according to claim 1, characterized in that the first input waveguide (1), the second input waveguide (2), the central output waveguide (3) and the 2n bypass output waveguides (4) are all single-mode waveguides.
6. The optical combiner according to claim 1, characterized in that the distance of the edges of the first bypass output back taper (91) and the second bypass output back taper (92) from the edge of the central output back taper (8) is both larger than a second preset distance.
7. Optical combiner according to claim 6, characterized in that the shape of the multimode interference zone (7) comprises a rectangular, polygonal or sub-wavelength structure.
8. A method for preparing an optical combiner, wherein the method comprises:
uniformly coating photoresist on a substrate; transferring the pattern of the optical beam combiner from the mask plate to the photoresist coated on the substrate through a photoetching development technology; transferring the pattern of the optical combiner from the photoresist coated on the substrate to the substrate by etching; and removing the photoresist coated on the substrate and etching residues on the substrate by cleaning.
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