阅读说明：本技术 极化无关的宽带波导分束器 (Polarization independent broadband waveguide beam splitter ) 是由 金贤敏 王辞迂 于 2018-06-19 设计创作，主要内容包括：一种极化无关的宽带波导分束器,包括：两个波导组成的至少一个交叉耦合区域和一个平行耦合区域,具体包括：至少一个交叉耦合区域、至少一个平行耦合区域和第二个交叉耦合区域组成或一个交叉耦合区域和至少一个平行耦合区域。本发明能够实现大规模光量子计算的内核——实现多粒子量子随机行走网络的芯片。由于结构的极化无关特性支持不同极化编码的入射光,可实现更高维的量子计算。(A polarization independent broadband waveguide splitter comprising: at least one cross-coupling region and one parallel coupling region formed by two waveguides specifically comprise: at least one cross-coupling region, at least one parallel coupling region and a second cross-coupling region or one cross-coupling region and at least one parallel coupling region. The invention can realize the kernel of large-scale light quantum computation, namely a chip for realizing a multi-particle quantum random walking network. Because the polarization independent characteristic of the structure supports incident light of different polarization codes, higher-dimensional quantum computation can be realized.)

1. A polarization independent broadband waveguide beam splitter, comprising: at least one cross-coupling region and one parallel coupling region formed by two waveguides specifically comprise: at least one cross-coupling region, at least one parallel coupling region and a second cross-coupling region or one cross-coupling region and at least one parallel coupling region.

2. The broadband polarization independent beam splitter of claim 1 wherein the two waveguides are cross-coupled in an S-bend configuration, and are cross-coupled again after being parallel coupled.

3. The broadband polarization independent beam splitter of claim 2 wherein said S-bend is adapted to minimize radiation loss by joining two arcs of maximum radius of curvature with each other at a tangent.

4. The broadband polarization independent beam splitter of claim 1,the coupling is characterized in that the transmission of light in the waveguide satisfies the Helmholtz equation:

5. The broadband polarization independent beam splitter according to claim 1 or 2, wherein the two waveguides are all homowaveguides, and the coupling between the two waveguides is satisfied in consideration of the perturbation-free parallel single-mode coupling:

6. The broadband polarization independent beam splitter of claim 5, wherein the polarization independent broadband waveguide beam splitter is tunable for proportional splitting, and specifically comprises: because the coupling coefficient intensities of the H light and the V light are equal at the intersection point of the c-value curve of the coupling coefficient, when the coupling distance of the cross coupling of the waveguide is smaller than the coupling distance at the intersection point of the c-value curve, the synchronous transfer of the coupling energy of the H light and the V light can be realized by adjusting the structures of the two S-shaped bending arms; at the moment, after crossing, the positions of the first waveguide and the second waveguide are interchanged to carry out parallel coupling, so that the coupling distance of the parallel coupling region is equal to the coupling distance at the c-value curve crossing point of the H light and the V light, and the coupling length of the parallel region can be adjusted to realize the regulation and control of any beam splitting ratio.

7. The broadband polarization independent beam splitter of claim 6 wherein the energy is transferred between the two waveguides, and the first waveguide is further cross-coupled to the second waveguide and tuned to separate the two waveguides at a location where coupling is achieved near 50/50 beam splitting, such that a symmetrical structure with two cross-couplings and one parallel coupling can achieve very stable polarization independent beam splitting with any proportion of beam splitting, and consistent polarization dependent loss of light.

8. An optical quantum computing chip comprising a plurality of broadband polarization independent beam splitters according to any preceding claim.

9. Use of the optical quantum computing chip according to claim 8 for receiving arbitrary optical qubits that directly encode the degree of freedom of photon polarization.

Technical Field

The invention relates to a technology of optical information, in particular to a polarization-independent broadband waveguide beam splitter with passively adjustable beam splitting ratio.

Background

The polarization-independent beam splitter is an important basic element in the field of optical information and is widely applied to various fields such as optical communication, quantum computing and the like. However, when the waveguide type beam splitting device in the prior art is used for coupling and beam splitting, due to the double refraction effect of the waveguide, the coupling intensities of the optical signals incident in different polarizations are different, and perfect polarization-independent beam splitting cannot be performed, which brings influence on subsequent and overall experiments, which is difficult to measure.

The search of the prior art shows that Alexander Szaunit and the like disclose that the elliptical waveguide shows strong anisotropy in coupling in Control of directional evanescent coupling in fs laser writing waveguides, 19 February 2007/Vol.15 and No.4/OPTICS EXPRESS 1579, but the performance of the isotropic circular waveguide array related in the technology still cannot meet the requirements of the current optical communication field.

Disclosure of Invention

The invention overcomes the series problems caused by the existing birefringent waveguide, provides a broadband waveguide beam splitter irrelevant to polarization, and can provide basic support for wavelength division multiplexing.

The invention is realized by the following technical scheme:

the invention relates to a polarization independent broadband waveguide beam splitter comprising: at least one cross-coupling region and one parallel-coupling region of two waveguides, wherein:

one preferred structure of the broadband polarization independent beam splitter is as follows: at least one cross-coupling region, at least one parallel coupling region and a second cross-coupling region or one cross-coupling region and at least one parallel coupling region, wherein: the two waveguides are cross-coupled in an S-shaped bending mode, and are cross-coupled again after being parallel coupled.

The S-shaped bending adopts a connection mode that two arcs with the largest curvature radius are overlapped at the tangent position so as to realize the minimum radiation loss.

The coupling is such that the transmission of light in the waveguide is such that Helmh is satisfiedThe Hotz equation:wherein A (x, y) is the mode field diameter, n_effIs the effective refractive index of the transmission mode, x, y are defined according to the common general knowledge of the skilled person; .

The two waveguides are all the same waveguides, and the coupling between the two waveguides meets the following requirements under the condition of considering the perturbation-free parallel single-mode coupling in the same direction:

wherein: A. b is the normalized amplitude, and a (z) is the light injection port, i.e., a (0) is 1, B (0) is 0, corresponding to a (z) coscz, B (z) isincz, the energy will be transferred between the two waveguides, and the coupling coefficient will be changed

I.e. the coupling coefficient c varies non-linearly with the variation of the coupling pitch, z being defined according to the common general knowledge of a person skilled in the art.

The polarization-independent broadband waveguide beam splitter is adjustable in proportion beam splitting, and specifically comprises the following steps: because the coupling coefficient intensity of the H light and the V light at the intersection of the c-value curve of the coupling coefficient is equal, when the coupling interval of the cross coupling is smaller than the coupling interval at the intersection of the c-value curve, the coupling coefficient intensity of the H light is larger than that of the V light, and conversely, the V light is larger than the H light. Therefore, the structures of the two S-shaped bent arms can be adjusted always, and the equal energy transfer condition of the coupling of the H light and the V light is realized. At this time, the positions of the first waveguide and the second waveguide are exchanged after crossing, but this does not affect the energy transfer of the parallel coupling between them. In order to realize more stable polarization independence, the coupling distance of the parallel coupling region is equal to the coupling distance when the c value curves of the H light and the V light are the same, and then the adjustment and control of any beam splitting proportion can be realized by adjusting the coupling length of the parallel region.

Preferably, the energy is mutually transferred between the two waveguides, the first waveguide and the second waveguide are separated after being cross-coupled again at a position close to 50/50 beam splitting by coupling, so that polarization-independent beam splitting of beam splitting in any proportion and polarization-dependent loss of light can be adjusted to be consistent by a symmetrical structure which is subjected to twice cross-coupling and once parallel coupling, passive regulation and control of the structure are easy to realize, extra voltage and current modulation is not needed, and the structure is a good integrated optical passive device.

The invention relates to a light quantum computing chip which comprises a plurality of broadband polarization independent beam splitters with adjustable proportional beam splitting.

The invention relates to the application of the above-mentioned optical quantum computing chip, which is used for receiving any optical quantum bit directly coding the freedom degree of photon polarization.

Technical effects

Compared with the prior art, the invention realizes the broadband waveguide type polarization independent beam splitter, and belongs to on-chip passive devices. The invention has the same effect on symmetry of different injection ports, and the polarization dependent loss can be tuned to be consistent. The invention can be realized in the same plane, is convenient to be connected with other devices in series or in parallel, and is suitable for large-scale use of integrated printing, hybrid integration and the like. The invention is universal to each wavelength and can provide basic support for wavelength division multiplexing. The invention can realize the kernel of large-scale light quantum computation, namely a chip for realizing a multi-particle quantum random walking network. Because the polarization independent characteristic of the structure supports incident light of different polarization codes, higher-dimensional quantum computation can be realized.

Drawings

FIG. 1 is a schematic diagram of two cross-coupled and parallel-coupled structures according to the present invention;

in the figure: a is a top view; b is a schematic view in the direction A; c is a schematic view in the direction B;

FIG. 2 is a schematic diagram of a cross-coupling plus parallel coupling structure according to the present invention;

in the figure: a is a top view; b is a schematic view in the direction A; c is a schematic diagram in the direction B, and x, y and z are defined according to the common knowledge of the skilled person;

FIGS. 3a and 3b are schematic diagrams of a chip for implementing large-scale photon counting with a multi-stage serial structure according to the present invention, wherein the number of polarization-independent beam splitters included in the chip can be adjusted according to the situation;

FIG. 4 is a schematic view of an S-bend;

FIG. 5 is a graph illustrating the c-value curves for different polarization situations;

FIG. 6a is a schematic representation of the refractive index profile after crossing of a waveguide disposed on a substrate; FIG. 6b is a schematic diagram of the light intensity evolution in the waveguide obtained by a beam propagation method using transparent boundary conditions for simulation.

Detailed Description