CN102540332A - Light polarization splitter based on lithium-niobate photon rays - Google Patents

Abstract

The invention discloses a polarization splitter based on lithium-niobate photon rays, which comprises a lithium-niobate substrate, a silicon-dioxide coating layer and two parallel lithium-niobate light waveguides, wherein the heights of the two parallel lithium-niobate light waveguides are both 0.73mum, and the widths of the tops of the waveguides are both 0.5mum; and the shaft distance Sc of the two parallel light waveguides forming the polarization splitter is equal to 0.74mum, and the coupling length Lc is equal to 49.28mum. The waveguide parameters suitable for the polarization splitter are as follows: the working waveguide is 1.55mum; the refractive index nLN of a liquid nitrogen (LN) waveguide is equal to 2.2; the refractive index nSiO2 of an SiO2 area is equal to 1.44; and the polarization splitter based on the lithium-niobate photon rays can be used for a light path with high integration degree based on the lithium-niobate photon rays. The distribution graphs of the electric field and the magnetic field of the polarization splitter are simulated by utilizing OptiFDTD business software. The light orientation coupler not only has the advantage of high transmissivity on the working wavelength but also has a supercompact structure.

Description

Optical polarization splitter based on lithium niobate photonic wire

technical field

The invention belongs to one of the key components in the technical field of photonics, specifically, an ultra-compact optical polarization splitter based on lithium niobate photon wire (abbreviated as LN).

Background technique

LN photonic wires (i.e., lithium niobate optical waveguides) ^[1-8] are becoming candidates for future integrated photonics due to their small size and structure, excellent electro-optic, acousto-optic, and nonlinear optical properties ^[9] , susceptible to doping with rare earth ions to give laser-active materials ^[10] , particularly promising for high-efficiency devices (possible even at modest optical power values). Obviously, the optical polarization splitter based on LN photonic wire is a key component of the integrated optical circuit composed of LN photonic wire. However, according to the data retrieval conducted by the applicant, so far, there is no relevant research report on the optical directional coupler based on the LN photonic wire.

The following are relevant documents retrieved by the inventor:

[1] P.Rabiei, and W.H.Steier, "Lithium niobate ridge waveguides and modulators fabricated using smart guide," Appl.Phys.Lett.Vol.86, no.16, pp.161115-161118, Apr 2005.

【2】D.Djukic, G.Cerda-Pons, R.M.Roth, R.M.Osgood, Jr., S.Bakhru, and H.Bakhru,"Electro-optically tunable second-harmonic-generation gratingsin ion-exfoliated thin films of periodically poled lithium niobate," Appl. Phys. Lett. Vol. 90, no. 17, pp. 171116-171119, April 2007.

[3] A.Guarino, G.Poberaj, D.Rezzonico, R.Degl'innocenti, and P.Günter, "Electro-optically tunable microring resonators in lithium niobate," Nat.Photonics Vol.1, no.7, pp .407-410, May 2007.

E.B.Kley，A.Tünnermann，and W.Wesch，“Ultrathin membranes in x-cut lithium niobate，”Opt.Lett.Vol.34，no.9，pp.1426-1428，April 2009。【4】F. Schrempel, T. Gischkat, H. Hartung, T.

EB Kley, A. Tünnermann, and W. Wesch, "Ultrathin membranes in x-cut lithium niobate," Opt. Lett. Vol. 34, no. 9, pp. 1426-1428, April 2009.

【5】T.Takaoka, M.Fujimura, and T.Suhara, "Fabrication of ridgewaveguides in LiNbO3 thin film crystal by proton-exchange acceleratedetching," Electron.Lett.Vol.45, no.18, pp.940-941( 2009).

[6] G.Poberaj, M.Koechlin, F.Sulser, A.Guarino, J.Hajfler, and P.Günter, "Ion-sliced lithium niobate thin films for active photonic devices," Opt.Mater.Vol.31, no .7, pp. 1054-1058 (2009).

[7] G.W.Burr, S.Diziain, and M.-P.Bernal, "Theoretical study of lithium niobate slab waveguides for integrated optics applications," Opt.Mater.Vol.31, no.10, pp.1492-1497(2009 ).

[8] H. Hu, R. Ricken, and W. Sohler, "Lithium niobate photonicwires," Opt. Express, Vol.17, no.26, pp.2426-242681, December 2009.

[9] R.S.Weis, and T.K.Gaylord, "Lithium niobate: summary of physical properties and crystal structure," Appl. Phys., A Mater. Sci. Process. Vol.37, no.4, pp.191-203, March 1985 .

[10] W. Sohler, B. Das, D. Dey, S. Reza, H. Suche, and R. Ricken, "Erbium-doped lithium niobate waveguides lasers," in 2005 IEICE Trans.Electron.E88(C), pp. 990-997.

【11】H.Hu, R.Ricken, and W.Sohler, Large area, crystal-bonded LiNbO3thin films and ridge waveguides of high reactive index contrast, Topical Meeting "Photorefractive Materials, Effects, and Devices-Control of Light and Matter" (PR 09), Bad Honnef, Germany 2009. On the poster, presented to PR 09, a photograph of a 3 inch LNOI wafer was shown. A manuscript to describe the LNOI-technology developed is in preparation.

Contents of the invention

The purpose of the present invention is to provide an optical polarization splitter based on LN photonic wires, which can be used in highly integrated optical circuits based on lithium niobate photonic wires, so as to adapt to the increasing development of optical communication and transmission in the contemporary era. The urgent need for sensing technology.

In order to achieve the above tasks. The present invention takes following technical solution to realize:

An optical polarization splitter based on LN photon lines, characterized in that it consists of a lithium niobate substrate, a silicon dioxide coating and two parallel lithium niobate optical waveguides, wherein, wherein, two parallel niobate The height of the lithium optical waveguide is 0.73 μm, and the top width of the waveguide is 0.5 μm; the axial distance S _c =0.74 μm and the coupling length L _c =49.28 μm of the two parallel optical waveguides constituting the polarization splitter.

The method for preparing the optical polarization splitter based on the above-mentioned LN photon line is characterized in that the method first makes a lithium niobate sample based on an insulator (abbreviated as LNOI), and the LNOI includes silicon dioxide (SiO ₂ ) a 730 nanometer thick single crystal LN layer (i.e. LN film) on the layer, the silicon dioxide layer is coated on the Z surface of the congruent Z-cut lithium niobate substrate through plasma enhanced chemical vapor deposition, i.e. The LN film and the LN substrate with a thickness of 1um have congruent crystal orientation; the surface of the LN film is treated with a chemical mechanical polishing process (CMP) to reach an rms roughness of 0.5 nm; The strips are used as etch masks. The photoresist was annealed at 120°C for 1 hour, then, in the Oxford Plasmalab System100, 100W RF power was used to induce plasma coupling, and 70W RF power was coupled to the sample surface, etched by argon milling for 60 minutes, and the end face was polished , that is.

The optical directional coupler based on the LN photon line of the present invention brings the following technical effects:

1. Under the conditions of the above given waveguide size parameters and optical parameters (suitable for transmission of quasi-TE (qTE) and quasi-TM (qTM) single-mode), in the case of working wavelength λ=1.55μm, for quasi- For TE (qTE) single-mode input light waves, a transmittance of 97.31% can be obtained at the shorter straight waveguide output end; for quasi-TM (qTM) single-mode input light waves, 97.25% can be obtained at the longer straight waveguide output end % transmittance. When both quasi-TE (qTE) and quasi-TM (qTM) single-mode input light waves are included, the quasi-TE (qTE) wave can be obtained at the output end of the shorter straight waveguide through the optical polarization splitter, and its transmittance It is 97.31%. At the same time, quasi-TM (qTM) waves can be obtained at the output end of the longer straight waveguide, and its transmittance is 97.25%.

2. The optical polarization splitter has a compact structure.

The applicant's simulation and analysis prove that the optical polarization splitter based on LN photonic wire can be used in a highly integrated optical circuit based on lithium niobate photonic wire to adapt to the increasing development of optical communication technology and optical sensing technology. urgent need.

Description of drawings

Fig. 1-1 is the transversal sectional view of the input end of the optical polarization splitter based on the LN photon line of the present invention;

Figure 1-2 is a transverse cross-sectional view of the output end of the LN photonic line-based optical polarization splitter corresponding to Figure 1-1;

Figure 1-3 is a top view of the optical polarization splitter corresponding to Figure 1-1 and Figure 1-2;

Figure 2 is the magnetic field distribution diagram obtained by using the commercial software OptiFDTD when the quasi-TE (qTE) single-mode light wave is input under the above-mentioned given size parameters and optical parameters (input power: 0.7178W, output power: 0.6985W, passed Rate: 97.31%);

Figure 3 is the electric field distribution diagram obtained by using the commercial software OptiFDTD (input power: 0.727W, output power: 0.707W, by Rate: 97.25%);

Figure 4-1(a, b) and Figure 4-2(a, b) are schematic diagrams of the manufacturing process, in which Figure 4-1a is the input end of the optical polarization splitter based on the lithium niobate sample of insulator (LNOI) , Figure 4-2a is the output of a photopolarization splitter based on an insulator lithium niobate sample (LNOI); while Figure 4-1b, Figure 4-2b and 4-3 represent the final sample.

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

Detailed ways

1. Simulation results

The optical polarization splitter structure based on the LN photonic wire given in this embodiment, as shown in FIG. 1 , consists of a lithium niobate substrate, a silicon dioxide coating and two parallel lithium niobate waveguides. The height of two parallel lithium niobate optical waveguides is 0.73 μm, and the width of the top of the waveguide is 0.5 _μm ; _c = 49.28 μm.

The thickness of the lithium niobate substrate is 1 μm, and the thickness of the silicon dioxide coating is 1.3 μm.

The waveguide parameters suitable for this optical polarization splitter are: the refractive index n _LN of the LN waveguide =2.2; the refractive index n _SiO2 of the _SiO2 region =1.44; the height h of the waveguide = 0.73 μm, the top width w = 0.5 μm, and so on Select to ensure single-mode transmission. The axial distance S _c of two parallel optical waveguides (ie, photon wires) constituting the polarization splitter is 0.74 μm, and the coupling length L _c is 49.28 μm. Working wavelength λ=1.55 μ m, the bottom surface of _SiO2 layer is connected with the Z-face of Z-cut LN substrate, LN waveguide (being LN photon line) is connected with _SiO2 layer top surface, and LN substrate and LN photon line have Omnidirectional crystal orientation.

The results of the simulation of the structure shown in Figure 1 using the commercial software OptiFDTD show that the polarization splitter can obtain 97.31% transmission at the output end of the short straight waveguide for quasi-TE (qTE) single-mode input light waves rate; for quasi-TM (qTM) single-mode input light waves, a transmittance of 97.25% can be obtained at the output end of the longer straight waveguide. When both quasi-TE (qTE) and quasi-TM (qTM) single-mode input light waves are included, the quasi-TE (qTE) wave can be obtained at the output end of the shorter straight waveguide through the optical polarization splitter, and its transmittance It is 97.31%. At the same time, quasi-TM (qTM) waves can be obtained at the output end of the longer straight waveguide, and its transmittance is 97.25%. Figure 2 and Figure 3 show the corresponding magnetic field and electric field distribution diagrams obtained by simulation.

2. Manufacturing process

In order to make a lithium niobate (LN) photonic wire directional coupler, it is necessary to make an insulator-based lithium niobate sample LNOI (shown in Figure 4-1-a and Figure 4-2-a). This sample consisted of a 730 nm thick single crystal LN layer (LN thin film) adhered directly on a 1.3 µm thick layer of silicon dioxide (SiO ₂ ) deposited by plasma-enhanced chemical vapor deposition (PECVD) _. Coated on the Z surface of a congruent Z-cut lithium niobate substrate (thickness 1um), that is, the LN film and the LN substrate with a thickness of 1um have congruent crystal orientation; the surface of the LN film must be chemically mechanically polished (CMP) After processing, the rms roughness of 0.5 nm is achieved.

Due to the large difference in refractive index (n _LN =2.2, n _SiO =1.44), the LNOI sample is a planar waveguide with strong light guiding performance, so it is very suitable for making lithium niobate photonic wires.

Photolithography requirements: 1.7μm thick and 0.5μm wide strips of photoresist (OIR 907-17) are used as etch masks. In order to improve the selectivity of the mask, the photoresist was annealed at 120°C for 1 hour. Then, in Oxford Plasmalab System100, 100W RF power is used to induce plasma (ICP) coupling, and 70W RF power is coupled to the surface of the sample. The sample thus treated is etched by argon milling for 60 minutes. The result is shown in Figure 4-1- b and Figure 4-2-b.

Finally, the end faces of the samples are carefully polished to allow efficient endfire light coupling.

3. Conclusion

An ultra-compact structure optical polarization splitter suitable for 1.55μm wavelength based on LN photonic wire is proposed for the first time. The field distribution diagram of the optical polarization splitter is simulated by using the commercial software OptiFDTD, and the manufacturing process is given. The optical polarization splitter has the characteristics of high transmittance and ultra-compact structure.

The present invention has been funded by the National Natural Science Foundation of China (fund number: 61040064).

Claims (3)

1. A light polarization splitter based on LN photon lines, characterized in that it consists of a lithium niobate substrate, a silicon dioxide coating and two parallel lithium niobate optical waveguides, wherein the two parallel niobate The height of the lithium optical waveguide is 0.73 μm, and the top width of the waveguide is 0.5 μm; the axial distance S _c =0.74 μm and the coupling length L _c =49.28 μm of the two parallel optical waveguides constituting the polarization splitter. 2 . The optical polarization splitter based on LN photonic lines according to claim 1 , wherein the thickness of the lithium niobate substrate is 1 μm, and the thickness of the silicon dioxide coating is 1.3 μm. 3 . 3. the preparation method of the optical polarization splitter based on LN photon wire according to claim 1, is characterized in that, this method first makes the lithium niobate sample based on insulator, and sample comprises the silicon dioxide that directly adheres to 1.3 microns thick The 730nm-thick single crystal LN layer on the layer, the silicon dioxide layer is coated on the Z surface of the congruent Z-cut lithium niobate substrate by plasma enhanced chemical vapor deposition, that is, the LN film and the thickness of 1um The LN substrate has congruent crystal orientation; the surface of the LN film is treated with a chemical mechanical polishing process to reach an rms roughness of 0.5 nm; The resistance was annealed at 120°C for 1 hour, then, in Oxford Plasmalab System100, 100W RF power was used to induce plasma coupling, and 70W RF power was coupled to the sample surface, etched by argon milling for 60 minutes, and the end face was polished. Instantly.

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