CN101251627A - Photon crystal wave-guide polarization beam splitter - Google Patents

Abstract

The invention discloses a photonic crystal waveguide polarizing beam splitter which introduces a line defect to form a structure of a coupled waveguide in a two-dimensional tellurium dielectric rod photonic crystal, and implements beam splitting for TE beam and TM beam by using different coupled lengths of waveguides of the TE beam and the TM beam. The characteristics of the implementation of the polarizing beam splitter by adopting a two-dimensional photonic crystal waveguide are as follows: firstly, compared with the prior various polarizing beam splitter devices, the polarizing beam splitter adopting the two-dimensional photonic crystal waveguide can implement a polarizing beam splitting with high degree of polarization and high extinction ratio; secondly, the device can be provided with a smaller size, and can be structurally compatible with the prior photonic crystal device to meet a requirement of integration ratio; thirdly, the polarizing beam splitter adopting the two-dimensional photonic crystal waveguide has a very flexible structure, and can implement the polarizing beam splitting of any wavelength in a range from 3.5 to 35mu m for wavelengths through adjusting a length of a coupling region or a lattice constant. The invention also discloses a designing idea and a particular structural design of the polarizing beam splitter, an optical performance, etc. of the polarizing beam splitter acquired from the designing idea.

Description

Photon crystal wave-guide polarization beam splitter

Technical field

The present invention relates to optical element, specifically be meant a kind of based on the polarization beam apparatus of using in the formed waveguide of photon crystal structure.

Background technology

Photonic crystal is to introduce periodically specific inductive capacity modulation, a kind of microstructure that the cycle of its medium dielectric constant microwave medium can be compared with optical wavelength by the whole bag of tricks artificially.The cyclical variation of dielectric function can be modulated the state model of photon in the material, and photon band gap is occurred, and when light frequency is positioned at the photon band gap scope, it can not any direction in photonic crystal be propagated.Photonic crystal has important application prospects.Because its characteristic, can make brand-new principle or in the past the high performance device that can not make.At present, in theory and the photonic crystal polarization beam splitter of experimentally being realized mainly be the principle of utilizing the polarization dependence of forbidden photon band, wherein reflected light and refract light utilize at most.These polarization beam apparatus not only structurally can not be compatible mutually with the device that existing employing waveguide-coupled method realizes, and owing to adopted reflected light and refract light, its light path is more restive.

Summary of the invention

The purpose of this invention is to provide a kind of photon crystal wave-guide polarization beam splitter, solve the problem of the device compatibility that existing polarization beam apparatus structurally can not realize with existing employing waveguide-coupled method.

Photon crystal wave-guide polarization beam splitter of the present invention is the beam split that realizes TE light and TM light according to the principle of optical waveguide directional coupler.When two identical waveguides of structure are leaned on very closely, because the coupling between the waveguide, when light during by a waveguide incident, the phenomenon that light can presentation space be coupled periodically and propagates forward between two waveguides.If TE light has different coupling lengths with TM light, just can utilize their coupling length difference that they are coupled to respectively in the different waveguides and go, thereby realize the beam split of TE light and TM light.As, the coupling length of supposing TE light is LE, the coupling length of TM light is LM.If we select the length of coupling regime between two waveguides is L=even number * LE, L=odd number * LM, get back to again in the original waveguide after TE light is coupled through even number so and propagate, and TM light is propagated in the another one waveguide through odd number time coupling back, thereby realizes the beam split of TE light and TM light.Because photon crystal wave-guide compared a lot of advantages with conventional waveguide: for example bending loss very low, help with other photonic crystal element integratedly etc., the present invention adopts photon crystal wave-guide to realize polarization beam apparatus.

Based on above-mentioned mentality of designing, technical solution of the present invention is: introduce the beam split that the waveguide-coupled structure realizes TE light and TM light in the photonic crystal of two-dimentional dielectric column type square lattice.We adopt with other photon crystal devices (as, wavelength division multiplexer, directional coupler) compatible fully structure so that can form integrated optical circuit, as shown in Figure 1 with these devices.Incident light is by the port one incident of waveguide 4, in the coupled zone, TE light through twice coupling after final echo lead 4, draw by port 2; TM is drawn by port 3 through once being coupled to waveguide 5.The dielectric post material of photonic crystal is a tellurium single-crystal, and the characteristics of this material are anisotropic material, wavelength be 3.5 μ m in the scope of 35 μ m, the refractive index n of its ordinary light _o=4.8, the refractive index n of unusual light _e=6.2.

When the design device, make the direction of unusual optical axis be parallel to the direction of dielectric cylinder, device architecture is determined as follows:

Grating constant is that a and coupling regime length are L ₂, can regulate according to the needs of minute light wavelength lambda, its magnitude is a micron, wherein:

a＝0.3894×λ (1)

L ₂=even number * LE=odd number * LM (2)

In the formula: LE, LM can obtain by plane wave expansion method as shown in Figure 2.

The width of waveguide (waveguide is the distance between the two row dielectric cylinders up and down):

W＝2×a (3)

The incident port one arrives the length at edge, coupled zone:

L ₁≥3a (4)

The diameter of dielectric cylinder:

D＝0.4×a (5)

By the length of coupled zone to the transition of non-coupled zone:

L ₃＝4×a (6)

As deleting a dielectric post at 6 places, the protruding right angle of crook, right angle waveguide in the accompanying drawing 1, a dielectric post is mended at 7 places, the recessed right angle of waveguide.

Edge, non-coupled zone is to the length of exit ports:

L ₄≥3a (7)

The distance of coboundary is arrived in waveguide 4:

L ₇≥3a (8)

The distance of waveguide 4 to 5:

L ₆≥3a (9)

The distance of lower boundary is arrived in waveguide 5:

L ₅≥3a (10)

The advantage of the polarization beam apparatus that the present invention realized embodies a concentrated expression of it and can directly be integrated in photon crystal wave-guide, this is that all polarization beam apparatus are difficult to realize at present, also is to adopt photonic crystal constantly indispensable basic device in the microminiaturization of light integrated system in integrated optics.

Description of drawings

Fig. 1 is a device architecture synoptic diagram of the present invention;

Among the figure: 1---the light incident side mouth;

2---TE light exit side mouth;

3---TM light exit side mouth;

4---the incident waveguide;

5---coupled waveguide;

6---the protruding right angle at waveguide turning;

7---recessed right angle, waveguide turning.

Fig. 2 is the TE light of device of the present invention and the coupling length of TM light.

Fig. 3 is the FDTD analog result (normalized frequency is 0.3893 (a/ λ)) of TE light of the present invention.

Fig. 4 is the FDTD analog result (normalized frequency is 0.3893 (a/ λ)) of TM light of the present invention.

Fig. 5 is the TE transmittance spectrum of device of the present invention.

Fig. 6 is the TM transmittance spectrum of device of the present invention.

Fig. 7 is the extinction ratio curve map of device of the present invention.

Embodiment

According to technical solution of the present invention, we are that the polarization beam apparatus of λ=5.13 μ m is an example with the operation wavelength, in conjunction with the accompanying drawings the implementation method of 1 funerary objects spare.

The main design of Structural Parameters of device is as follows:

The grating constant of device (distances between the two column type dielectric post): a=0.3894 * λ=2um.

The diameter of dielectric cylinder: D=0.4 * a=0.8um.

The width of waveguide (waveguide is the distance between the two row dielectric cylinders up and down): W=2 * a=4um.

The incident port one is to the length at edge, coupled zone: L ₁Get L among the 〉=3a embodiment ₁=4 * a=8um.

Coupled zone length: L ₂=23 * a=46um.

By the length of coupled zone to the transition of non-coupled zone: L ₃=4 * a=8um.(annotate, in dielectric post of 6 places, the protruding right angle of crook, right angle waveguide deletion, a dielectric post has been mended at 7 places, the recessed right angle of waveguide).

Non-coupled zone is to the length of exit ports: L ₄〉=3a gets L among the embodiment ₄=7 * a=14um.

Waveguide 4 is to the distance of coboundary: L ₇〉=3a gets L among the embodiment ₇=3 * a=6um.

The distance of waveguide 4 to 5: L ₆〉=3a gets L among the embodiment ₆=4 * a=8um.

Waveguide 5 is to the distance of lower boundary: L ₅〉=3a gets L among the embodiment ₅=3 * a=6um.

System performance is as follows:

The transmission spectrum of device: TE light and TM light corresponding respectively transmissivity shown in accompanying drawing 5,6, as can be seen from the figure, near λ=5.13 μ m optical wavelength, the transmitance of 2 pairs of TE light of port reaches 84%, port 3 for the transmitance of TM light more up to 98%.That is: about 84% TE light is from port 2 outgoing, and 98% TM light is from port 3 outgoing.Accompanying drawing the 3, the 4th, optical wavelength respectively to TE light and TM light Simulation result, has as can be seen from the figure realized good beam split on this frequency when λ=5.13um.The extinction ratio of device: at the exit ports 2 of TE light, its extinction ratio is defined as:

$\mathrm{Ratio}=10\×{\log }_{10}\left(\frac{P_{\mathrm{TE}}}{p_{\mathrm{TM}}}\right)$

Wherein, P _TEBe the output intensity of TE light at port 2; p _TMBe the output intensity of TM light at port 2; The unit of Ratio is a decibel.At the exit ports 3 of TM light, its extinction ratio is defined as equally:

$\mathrm{Ratio}=10\×{\log }_{10}\left(\frac{P_{\mathrm{TM}}}{p_{\mathrm{TE}}}\right)$

Wherein, p _TMBe the transmitted light intensity of TM light at port 3; P _TEBe the transmitted light intensity of TE light at port 3; The unit of Ratio is a decibel.The extinction ratio of device is the important parameter that the emergent light degree of polarization is weighed, what times that its physical meaning is is another kind of polarization light intensity at a kind of polarization light intensity of the exit ports of light.Our extinction ratio spectrum of resultant device as shown in Figure 7.As can be seen from the figure near optical wavelength was λ=5.13 μ m, the extinction ratio of TE light exit side mouth 2 and TM light exit side mouth 3 had reached 19dB and 20dB respectively.This result shows from the TE light of port 2 outgoing with from the TM light of port 3 outgoing very high degree of polarization.

We can be by trim the value of grating constant a obtain to work in the device of other wavelength.For example, we need obtain to work in the device that wavelength is 8 μ m, the grating constant a=3.12 μ m that we can needing in the technology obtain by reduction formula a=0.3894 * λ.Go fabricate devices according to this parameter, can obtain the polarization beam apparatus that the work centre wavelength is 8 μ m.

Claims (2)

1. photon crystal wave-guide polarization beam splitter, it is characterized in that: it is the structure that the inlead defective forms coupled waveguide in two-dimentional tellurium dielectric post photonic crystal, utilize the beam split of TE light TE light of different realization with TM optical waveguide coupling length and TM light, beam splitting device structural parameters are determined as follows:

Grating constant a and coupling regime length L ₂:

a＝0.3894×λ (1)

L ₂=even number * LE=odd number * LM (2)

In the formula: LE, LM are respectively the coupling length of TE light and TM light, can obtain by the plane wave expansion method;

The width W of waveguide:

W＝2×a (3)

The incident port one is to the length L at edge, coupled zone ₁:

L ₁≥3a (4)

The diameter D of dielectric cylinder:

D＝0.4×a (5)

By the length L of coupled zone to the transition of non-coupled zone ₃:

L ₃＝4×a (6)

And locate to delete a dielectric post at the protruding right angle of crook, right angle waveguide (6), a dielectric post is located to mend in the recessed right angle of waveguide (7);

Edge, non-coupled zone is to the length L of exit ports ₄:

L ₄≥3a (7)

Waveguide 4 is to the distance L of coboundary ₇:

L ₇≥3a (8)

The distance L of waveguide 4 to 5 ₆:

L ₆≥3a (9)

Waveguide 5 is to the distance L of lower boundary ₅:

L ₅≥3a (10)

2. a kind of photon crystal wave-guide polarization beam splitter according to claim 1 is characterized in that: said polarization beam apparatus adopts the tellurium single-crystal material to make.

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