CN102141651A - Optical multiplexer/demultiplexer integrated based on surface plasmas and preparation method thereof - Google Patents

Abstract

The invention discloses an optical multiplexing/demultiplexing device based on surface plasmon integration, which belongs to the technical field of integrated optoelectronics. It includes a metal slot waveguide, and a plurality of resonant cavities and coupling areas formed in the metal slot waveguide. The metal slot waveguide includes a bus waveguide and a plurality of branch waveguides, and all the resonant cavities are connected to the The above-mentioned bus waveguide is coupled and connected, and each resonant cavity is also coupled and connected with a branch waveguide through another coupling region. The invention also provides a preparation method of the above product. The invention can greatly reduce the size of the optoelectronic device and improve its integration degree, and can be applied in the fields of photon integration, optical communication and the like.

Description

Optical multiplexer/demultiplexer based on surface plasmon integration and its preparation method

technical field

The invention relates to the technical field of integrated optoelectronics, in particular to an optical multiplexer/demultiplexer based on surface plasmon integration and a preparation method thereof.

Background technique

As we all know, the carrying and processing capacity of information in integrated circuits encounters an insurmountable bottleneck, and the speed of data exchange between various parts faces considerable restrictions, while the use of optical signals to transmit data can obtain a thousand times the bandwidth, so integrated photonics gives An effective way to solve this problem. Integrated optical devices include light sources, optical waveguides, photonic crystals, optical switches, optical signal filters, optical multiplexers/demultiplexers, optical modulators, and optical detectors. Among them, the optical multiplexer/demultiplexer realizes the function of combining or decomposing multiple wavelength signal lights, and is one of the important devices in the field of optical communication and optical signal processing. Most of the current integrated optical multiplexers/demultiplexers are composed of optical microring resonators or photonic crystals. However, due to the limitations of diffraction limit and bending loss, the optoelectronic device based on the traditional dielectric waveguide has complex structure and large size, which hinders the miniaturization and large-scale integration of the device.

Figure 1 is a schematic structural diagram of a traditional optical multiplexer/demultiplexer using an optical microring resonator structure, which is based on a dielectric waveguide (the structure of the dielectric waveguide is shown in Figure 2), and the size of this type of structure is generally large. For example, based on the current research level, the radius of a single microring resonator needs to be at least several microns. To realize the multiplexing/demultiplexing function of multiple wavelengths, multiple microrings need to be cascaded, so that the entire device The size is large and the structure is more complicated.

In recent years, with the continuous progress of nano-optoelectronics technology, a new waveguide structure—Surface Plasmon Polaritons (SPPs) waveguide has become an emerging research direction in the field of integrated optics. Surface plasmon exists near the interface between metal and medium, and its field strength reaches the maximum at the interface, and decays exponentially along the direction perpendicular to the interface on both sides of the interface. It has strong field confinement properties and can confine energy to a region whose spatial size is much smaller than its free-space wavelength. Especially the metal/dielectric/metal metal slit waveguide mode, which can realize the subwavelength confinement of the optical field, and control and confine the optical field at the nanoscale. In addition, some special resonant cavity structures can be well used to construct optical filters or optical multiplexing/demultiplexing devices by utilizing the natural reflective end faces of the metal/dielectric interface. Among them, the metal/dielectric/metal waveguide is also called the metal slot waveguide. The metal slot waveguide is a kind of surface plasmon waveguide, which is composed of two metal plates separated by a certain distance. The waveguide structure is shown in Figure 3. The width of the waveguide is w. In this waveguide structure, the optical field will be confined to the middle dielectric layer.

Contents of the invention

(1) Technical problems to be solved

Aiming at the defects of traditional optical multiplexer/demultiplexer with complex structure and large device size, the technical problem to be solved by the present invention is how to provide a novel optical multiplexer/demultiplexer based on surface plasmon integration and its preparation method , to greatly reduce the size of optoelectronic devices and improve their integration.

(2) Technical solution

In order to solve the above technical problems, the present invention provides an optical multiplexer/demultiplexer based on surface plasmon integration, including a metal slit waveguide, and multiple resonant cavities and coupling regions formed in the metal slit waveguide , the metal slot waveguide includes a bus waveguide and a plurality of branch waveguides, all resonators are coupled to the bus waveguide through a coupling region, and each resonator is also coupled to a branch waveguide through another coupling region.

Wherein, the coupling region is a coupling region formed by evanescent coupling or a coupling region formed by aperture coupling.

Wherein, the resonant cavity is perpendicular or parallel to the bus waveguide.

Wherein, the resonant cavity is a Fabry-Perot resonant cavity structure.

Wherein, all resonant cavities are located on one side of the bus waveguide or distributed on both sides of the bus waveguide.

Wherein, when the coupling region is formed by the evanescent coupling method, the coupling strength between the waveguide and the corresponding resonant cavity is determined by the coupling distance between the waveguide and the corresponding resonant cavity.

Wherein, when the coupling region is formed by aperture coupling, the coupling strength between the waveguide and the corresponding resonant cavity is determined by the width of the coupling aperture of the coupling region.

Wherein, when the resonant cavity is perpendicular to the bus waveguide, the coupling position between the branch waveguide and the corresponding resonant cavity is located on the end face or side of the resonant cavity; when the resonant cavity is parallel to the bus waveguide, the coupling position between the branch waveguide and the corresponding resonant cavity The coupling position is located on the end face or side of the resonator.

Wherein, the distance between adjacent resonant cavities is greater than 40nm.

The present invention also provides a method for preparing an optical multiplexer/demultiplexer based on surface plasmon integration, comprising the following steps:

S1, plating a layer of metal layer on the substrate;

S2. Etching the optical multiplexer/demultiplexer on the metal layer.

(3) Beneficial effects

The invention adopts the metal slit waveguide structure, which can greatly reduce the size of the optoelectronic device and improve its integration; through the design of the distance between the resonant cavities, the mutual interference between the mode fields of adjacent branch waveguides can be avoided; through the coupling The design of the zone structure can reduce the requirements for processing accuracy (the structure of aperture coupling can reduce the requirements for processing technology).

Description of drawings

Fig. 1 is the structural representation of traditional optical multiplexing/demultiplexing device;

Fig. 2 is a schematic structural diagram of the dielectric waveguide of Fig. 1;

Fig. 3 is a structural schematic diagram of a metal slot waveguide;

4 and 5 are top views of two optical multiplexing/demultiplexing device embodiments of the present invention;

Fig. 6 is a transmission spectrum diagram of a 1 * 6 optical multiplexing/demultiplexing device;

Fig. 7 is a top view of another embodiment of the present invention;

Fig. 8 is a flow chart of the method of the present invention;

FIG. 9 is a schematic diagram of a side coupling output structure.

Detailed ways

The specific implementation manners of the present invention will be described in further detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

As shown in Figures 4 and 5, they are structural schematic diagrams of a 1×N optical multiplexer/demultiplexer. It has two functions of multiplexing and demultiplexing. "1×N" indicates that it is an optical multiplexing/demultiplexing structure of N channels, "1" indicates that there is a bus waveguide in the structure, and "N" indicates that there are N branch waveguides (both the bus waveguide and the branch waveguide are made of metal/ dielectric/dielectric composition in metal waveguides). For example, during demultiplexing, the signal lights of N wavelengths (or the optical field containing N wavelength signals) are all input in the bus waveguide, and then the signal lights of N wavelengths can be output from the N branch waveguides respectively, so It is called "1×N optical multiplexing/demultiplexing device" (also refer to Figure 1).

The two structures in Figures 4 and 5 both include a metal slot waveguide, and a plurality of resonant cavities and coupling regions formed in the metal slot waveguide, the metal slot waveguide includes a bus waveguide and a plurality of branch waveguides, All resonators are coupled and connected to the bus waveguide through a coupling region (evanescent coupling region in FIG. 4, and aperture coupling region in FIG. 5), and each resonator also passes through another coupling region (in FIG. The metal between the branch waveguide and the corresponding resonant cavity, in FIG. 5 consists of the medium between each branch waveguide and the corresponding resonant cavity) is coupled and connected with one branch waveguide. The resonant cavities are all perpendicular to the bus waveguide, and the coupling position between the branch waveguide and the corresponding resonant cavity is located on the end face of the resonant cavity (or on the side of the resonant cavity, as shown in FIG. 9 ). The resonant cavity is a Fabry-Perot resonant cavity structure. All resonators are located on one side of the bus waveguide. The medium in the metal slot waveguide (ie metal/dielectric/metal waveguide) shown in Figures 4 and 5 is any general dielectric material (such as air).

The resonant cavity length and width can be of any size on the nanometer/micrometer scale. The optical multiplexing/demultiplexing function for specific wavelengths can be realized by rationally designing the length or width of the resonant cavity (the width of the resonant cavity is preferably between 0 and hundreds of nanometers, and the length is between 0 and several microns) . The distance between the resonant cavities of adjacent channels is any value larger than 40nm, so as to avoid the mutual interference between the mode fields of adjacent branch waveguides. One output port (branch waveguide) corresponds to one optical signal channel (that is, the "channel" in Figures 4 and 5).

Figure 4 is realized by evanescent coupling. At this time, the coupling strength between the waveguide (bus waveguide or branch waveguide) and the corresponding resonant cavity is determined by the coupling between the waveguide (respectively bus waveguide or branch waveguide) and the corresponding resonant cavity. Depending on the distance, the larger the coupling distance, the smaller the coupling strength between the waveguide and the resonant cavity, and the narrower the transmission spectrum bandwidth in each channel. For example: when the coupling region distance is further increased, the width of the 6 transmission lines in Figure 6 will be narrowed. The working principle is: the optical fields of different wavelengths propagating in the bus waveguide can be coupled into different resonant cavities in the form of evanescent waves, and output in different branch waveguides, so as to realize the demultiplexing function. Similarly, when the optical field is input from the branch waveguide, the multiplexing function can also be realized.

Figure 5 is realized by aperture coupling. At this time, the coupling strength between the waveguide (bus waveguide or branch waveguide) and the corresponding resonant cavity is determined by the width of the coupling aperture in the coupling area. The smaller the aperture width, the greater the gap between the waveguide and the resonant cavity. The smaller the coupling strength of , the narrower the transmission spectral bandwidth in each channel. The working principle is similar to the above, the difference is that the light fields of different wavelengths are coupled into the resonant cavity through the aperture and generate resonance in the cavity. The aperture coupling method is a special coupling method in the metal/dielectric/metal waveguide structure, which cannot be realized in the traditional dielectric waveguide shown in FIG. 2 .

Comparison of the structure of the above two coupling methods:

Evanescent coupling mode: Since the penetration (skin) depth of the SPPs mode electromagnetic field in the metal is less than 30nm, only when the coupling distance between the waveguide and the resonant cavity (t in Figure 5) is less than 30nm, it has a higher Only when the coupling strength is high, the electromagnetic field can be effectively evanescently coupled into the resonant cavity, which requires high processing precision in the manufacturing process.

Aperture coupling mode: The coupling strength has nothing to do with the coupling distance t, but is adjusted by changing the width of the coupling aperture, which is not limited by the penetration (skin) depth of 30nm, so it is easier to process.

FIG. 6 is a transmission spectrum diagram of an example of a 1×6 optical multiplexer/demultiplexer, 1 to 6 are channels 1 to 6, respectively. The demultiplexing function for specific wavelengths can be realized by selecting appropriate structural parameters of the resonant cavity (for example, length). The structure is shown in Figure 4. At this time, N=6, the width of the bus waveguide and the branch waveguide w=50nm, the width of the resonant cavity Wt=50nm, and the coupling distance t=15nm. For the transmission line of channel 6, the lengths of the six resonant cavities corresponding to channels 1 to 6 are 250nm, 285nm, 320nm, 355nm, 390nm and 425nm, respectively.

As shown in FIG. 7, the present invention also provides an optical multiplexer/demultiplexer with another structure. Wherein, the resonant cavity is parallel to the bus waveguide and distributed on both sides of the bus waveguide, and the coupling position between the branch waveguide and the corresponding resonant cavity is located on the side of the resonant cavity.

As shown in Figure 8, the present invention also provides a method for preparing an optical multiplexer/demultiplexer based on surface plasmon integration, comprising the following steps:

S1. Plating a metal layer on the substrate; the substrate is a non-absorbing material, such as silicon dioxide.

S2. Etching the optical multiplexer/demultiplexer on the metal layer.

As can be seen from the above embodiments, the present invention adopts a metal/medium/metal waveguide structure, which does not have a cut-off width of the guided wave mode (Fig. 1), so the waveguide width can be any size of nano/micron order, for example, The width of the waveguide can be as small as tens of nanometers or even several nanometers, while the size of the traditional dielectric waveguide (Fig. 2) is at least hundreds of nanometers or even microns, so the present invention can greatly reduce the size of the optoelectronic device and improve its The degree of integration can be applied to photonic integration, optical communication and other fields.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, some improvements and modifications can also be made, these improvements and modifications It should also be regarded as the protection scope of the present invention.

Claims (10)

1. one kind based on the integrated light multiplexing demultiplexing device of surface plasma, it is characterized in that, comprise the metal narrow slit wave-guide, and a plurality of resonator cavitys and the coupled zone that in described metal narrow slit wave-guide, form, described metal narrow slit wave-guide comprises a bus waveguide and many branch-waveguides, all resonator cavitys are of coupled connections by a coupled zone and described bus waveguide, and each resonator cavity also is of coupled connections by another coupled zone and a branch-waveguide.

2. smooth multiplexing demultiplexing device as claimed in claim 1 is characterized in that, described coupled zone is for adopting suddenly the die coupled zone of coupling scheme formation or the coupled zone of adopting aperture-coupled mode to form.

3. smooth multiplexing demultiplexing device as claimed in claim 1 is characterized in that described resonator cavity is vertical or parallel to bus waveguide.

4. smooth multiplexing demultiplexing device as claimed in claim 3 is characterized in that, described resonator cavity is the Fabry-Perot cavity structure.

5. smooth multiplexing demultiplexing device as claimed in claim 1 is characterized in that, all resonator cavitys are positioned at a side of bus waveguide or are distributed in the both sides of bus waveguide.

6. smooth multiplexing demultiplexing device as claimed in claim 2 is characterized in that, when adopting the coupling scheme that suddenly die to form the coupled zone, the stiffness of coupling between waveguide and the corresponding resonator cavity is determined by waveguide and coupling distance between the corresponding resonator cavity.

7. smooth multiplexing demultiplexing device as claimed in claim 2 is characterized in that, when adopting aperture-coupled mode to form the coupled zone, the stiffness of coupling between waveguide and the corresponding resonator cavity is decided by the width in the coupling aperture of coupled zone.

8. smooth multiplexing demultiplexing device as claimed in claim 3 is characterized in that, described resonator cavity is during perpendicular to bus waveguide, and branch-waveguide and the coupling position between the corresponding resonator cavity are positioned at the end face or the side of this resonator cavity; When described resonator cavity was parallel to bus waveguide, branch-waveguide and the coupling position between the corresponding resonator cavity were positioned at the end face or the side of this resonator cavity.

9. smooth multiplexing demultiplexing device as claimed in claim 1 is characterized in that the distance between the adjacent resonator cavity is greater than 40nm.

10. the preparation method based on the integrated light multiplexing demultiplexing device of surface plasma is characterized in that, may further comprise the steps:

S1, on substrate, plate the layer of metal layer;

S2, on described metal level each described smooth multiplexing demultiplexing device of etching claim 1～9.

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