CN103424893B - Optical polarization converter and preparation method thereof - Google Patents

Abstract

The invention discloses an optical polarization converter and a manufacturing method thereof. The optical polarization converter of the invention includes a polarization beam splitter, a first half-wave plate, a second half-wave plate, and a polarization beam combiner. The device is A thermo-optic polarization converter, which introduces a phase delay unit by changing the temperature of the silica optical waveguide, and distributes the light intensity of the two polarized lights in any proportion through the combination of an adjustable coupler and a phase shifter, Then the polarization state of the light can be precisely transformed in real time. The manufacturing method of the optical polarization converter of the present invention includes: (1) cutting the silicon wafer; (2) cleaning the silicon wafer; (3) thermally oxidizing the silicon wafer; (4) direct writing optical waveguide and micro-photonic devices; (5) making Microfilm heating electrodes. The invention has the advantages of small loss, simple and precise manufacture, high integration degree, low driving voltage and low power consumption, and can be used for real-time and precise transformation of the polarization state of light.

Description

Optical polarization converter and manufacturing method thereof

technical field

The invention belongs to the field of electronic technology, and further relates to an optical polarization converter and a manufacturing method thereof in the optical element manufacturing technology in the field of microelectronics. The optical polarization converter provided by the invention can be used for real-time and precise transformation of the optical polarization state. The manufacturing method of the present invention is for the integration of polarization converters and other optoelectronic devices, and provides a simple method of using femtosecond pulses to directly write in silicon-based silicon dioxide photonic waveguides and realize the waveguides and micro-optical devices required by polarization converters. , fast, low cost, high production precision method.

Background technique

The accumulation of polarization-dependent losses in multiple optical devices and polarization-dependent gains in multi-stage Erbium-doped amplifiers in fiber-optic communication systems creates a severe power penalty. In long-distance wavelength division multiplexing optical fiber transmission systems and reconfigurable optical time division multiplexing systems, when the transmission speed of optical signals exceeds 40Gb/S, polarization mode dispersion becomes one of the bottlenecks that limit the quality of optical signal transmission. Most of the traditional optical polarization converters achieve polarization conversion by modulating the refractive index of the material through the electro-optic effect, elastic-optic effect, magneto-optic effect and thermo-optic effect of the optical medium.

The patent application "A Polarization Controller" (Application No. 201110262016.4 Application Publication No. CN1023140042A) filed by the University of Electronic Science and Technology of China discloses a polarization controller, including a light importing device, a polarizer, a light exporting device, a rotating magneto-optical fiber structure and a magnetic control device. The polarization controller uses a rotating optical fiber structure made of magneto-optical materials, and uses a magnetron device to control the rotating optical fiber structure, and can adjust the change of the ellipticity and azimuth angle of incident light. The disadvantages of this device are: firstly, the changing magnetic field in the polarization controller will cause a large scattering loss to the polarized light passing through the magnetic field; secondly, the degree of integration is low.

In the paper "Reset-FreeIntegratedPolarizationControllerUsingPhaseShifters" (IEEEJOURNALOFSELECTEDTOPICSINQUANTUMELECTRONICS, VOLUME11, NUMER2, MARCH/APRIL2005), C.K.Madsen et al. proposed a reset-free integrated polarization converter made of phase shifters. The device is composed of a polarization beam splitter, a half-wave plate, and a fundamental path polarization mode converter. The device is a thermo-optic polarization converter, which introduces a phase delay unit by changing the temperature, and then controls the polarization state of light. The shortcomings of this device are: firstly, the device uses germanium doped in silicon to realize the optical waveguide, which requires complex technical process; secondly, doping germanium in silicon will cause light scattering effect, increasing The insertion loss of the device; third, the components of the polarization mode converter of the basic path are complex, which will cause a large insertion loss and low integration;

Contents of the invention

The object of the present invention is to overcome the shortcomings of the above-mentioned prior art, and provide an optical polarization converter and a manufacturing method thereof.

The idea of realizing the object of the present invention is that the optical polarization converter of the present invention is a thermo-optic polarization converter, and the phase delay unit is introduced by changing the temperature of the silica optical waveguide, and the adjustable coupler and phase shifter The combined device distributes the light intensity of the two polarized lights in any proportion, and then accurately transforms the polarization state of the light in real time.

The optical polarization converter of the present invention includes a combination device made of a silicon-based silicon dioxide material, a three-dimensional 2×2 polarization beam splitter, the first half-wave plate, an adjustable coupler and a phase shifter , the second half-wave plate, and the polarization beam combiner.

The polarization beam splitter is located at the leftmost end of the optical polarization converter, and is used to decompose the incident light of any polarization state into two linearly polarized lights whose polarization directions include an angle of 90°.

The first half-wave plate is connected with the polarization beam splitter through an optical waveguide, and is used for converting two beams of linearly polarized light output by the polarization beam splitter into two beams of linearly polarized light with the same polarization direction.

The combined device of the tunable coupler and the phase shifter is respectively connected with the polarization beam splitter and the first half-wave plate through the optical waveguide, so as to distribute the light intensity of two beams of linearly polarized light with the same polarization direction in an arbitrary ratio.

The second half-wave plate is connected to the combined device of the tunable coupler and the phase shifter through an optical waveguide to rotate the polarization direction of the linearly polarized light incident on the second half-wave plate by 90°, and the second half-wave plate The polarization angle between the linearly polarized light output by the plate and the linearly polarized light output by the first half-wave plate is 90°.

The polarization beam combiner is located at the far right end of the optical polarization converter, and the polarization beam combiner is respectively connected with the combined device of the tunable coupler and the phase shifter and the second half-wave plate through the optical waveguide, so as to convert the second half-wave plate The two beams of linearly polarized light output by the combined device of the wave plate, the tunable coupler and the phase shifter synthesize a beam of light with any desired polarization state.

The preparation method of the present invention comprises the steps of:

(1) Cutting silicon wafers:

Using laser cutting technology, the silicon wafer is cut to the size required to make the optical polarizer.

(2) Clean the silicon wafer:

The method of chemical cleaning is used to clean the dirt on the surface of the cut silicon wafer.

(3) Thermally oxidized silicon wafer:

Using thermal oxidation technology, one side of the cleaned silicon wafer is partially thermally oxidized in a silica tube furnace to obtain silicon-based silicon dioxide.

(4) Direct writing optical waveguide and micro-photonic devices:

4a) Fixing the thermally oxidized silicon wafer on a three-dimensional electric translation stage, with the thermally oxidized side of the silicon wafer facing up;

4b) adjusting the microscope objective lens so that the femtosecond laser pulse is vertically focused on the interior of the silicon dioxide layer in the silicon-based silicon dioxide;

4c) setting the built-in driver parameters in the computer;

4d) adjusting the variable attenuator to attenuate the energy of the femtosecond laser pulse to an optimal energy range;

4e) The computer controls the movement of the three-dimensional electric translation stage, so that the three-dimensional electric translation stage moves in the plane perpendicular to the propagation direction of the focused beam with the parameters set in step 4c), and completes the direct writing optical waveguide, adjustable coupler, and polarization beam splitting. device, the first half-wave plate, the second half-wave plate, and the polarization beam combiner.

(5) Making micro-thin film heating electrodes:

5a) calculate the length of the microfilm heating electrode;

5b) Directly above any transmission waveguide in the adjustable coupler, use the method of sputter coating to make a micro-thin film heating electrode to obtain a combined device of the adjustable coupler and the phase shifter.

Compared with the prior art, the present invention has the following advantages:

First, because the present invention uses femtosecond laser pulse direct writing technology to make optical waveguides in silicon dioxide, it overcomes the complex manufacturing process and the inconvenience of making optical waveguides in the prior art by using germanium-doped elements to change the refractive index of the medium. The disadvantage of large scattering loss makes the present invention have the advantages of small loss, simple manufacturing process and high manufacturing precision.

Second, since the present invention uses femtosecond laser pulse direct writing technology to make polarization converters in silicon-based silicon dioxide, it overcomes the disadvantages of complex structure, large insertion loss, and low integration in the prior art, making the present invention have integrated It has the advantages of high strength, simple structure and low loss.

Description of drawings

Fig. 1 is the structural representation of polarization converter of the present invention;

Fig. 2 is a flow chart of the manufacturing method of the optical polarization converter of the present invention.

detailed description

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

Referring to accompanying drawing 1, the optical polarization converter of the present invention includes a three-dimensional 2×2 polarization beam splitter 1, a first half-wave plate 2, and an adjustable coupler made of silicon-based silicon dioxide materials. Combination device 3 with phase shifter, second half-wave plate 4, polarization beam combiner 5.

The polarization beam splitter 1 is located at the leftmost end of the optical polarization converter, and the incident light of any polarization state is decomposed into two beams of linearly polarized light whose polarization directions have an included angle of 90° through the polarization beam splitter 1 .

The first half-wave plate 2 is connected to the polarization beam splitter 1 through an optical waveguide, and any one of the two beams of linearly polarized light output from the polarization beam splitter 1 is incident on the first half-wave plate through the optical waveguide, The polarization direction of the linearly polarized light output from the first half-wave plate 2 is the same as that of another beam of linearly polarized light.

The combined device 3 of the adjustable coupler and the phase shifter is respectively connected to the polarization beam splitter 1 and the first half-wave plate 2 through the optical waveguide, and the two beams of linearly polarized light with the same polarization direction are incident to the adjustable coupler and the first half-wave plate 2 through the optical waveguide. In the combined device 3 of the phase shifter, the light intensity of the two beams of linearly polarized light is distributed in any proportion through coherent interference and relative phase modulation.

The second half-wave plate 4 is connected with the combined device 3 of the adjustable coupler and the phase shifter through the optical waveguide, and one beam of linearly polarized light is output from the combined device 3 of the adjustable coupler and the phase shifter Into the second half-wave plate 4 through the light waveguide, the angle between the polarization direction of the beam linearly polarized light and the polarization direction of the linearly polarized light incident in the first half-wave plate 2 is 90°, the second half-wave plate 2 The wave plate 4 rotates the polarization direction of the incident linearly polarized light by 90°, and the included angle between the polarization state of the linearly polarized light output from the second half-wave plate 4 and the polarization direction of another beam is 90°.

The polarization beam combiner 5 is located at the far right end of the optical polarization converter, and is connected to the combined device 3 of the tunable coupler and the phase shifter and the second half-wave plate 4 through an optical waveguide, so as to convert the second half-wave The two beams of linearly polarized light output by the plate 4 and the combined device 3 of the tunable coupler and phase shifter are synthesized into a beam of light with any desired polarization state.

Referring to accompanying drawing 2, the implementation method of the present invention is further described.

Step 1, cutting the silicon wafer.

Use laser cutting technology to cut silicon wafers to obtain silicon wafers with a size of 1×1cm ² and a thickness of 2mm;

Step 2, cleaning the silicon wafer.

Use chemical cleaning method to clean the dirt on the surface of the cut silicon wafer;

Step 3, thermally oxidizing the silicon wafer.

One side of the cleaned silicon wafer is partially thermally oxidized in a silica tube furnace to obtain silicon-based silica; the thickness of silicon dioxide is approximately linear in the oxidation time, and the two can be judged by the oxidation time. silicon oxide thickness.

Step 4, direct writing of optical waveguides and micro-photonic devices.

The thermally oxidized silicon wafer is fixed on a three-dimensional electric translation stage, with the thermally oxidized side of the silicon wafer facing up; the three-dimensional micromachining platform is automatically controlled by a computer to move precisely in the X, Y and Z directions, and its movement accuracy can reach 500nm/ s; use a variable attenuator to attenuate the high-energy femtosecond laser pulse output by the Ti:Sapphire amplifier with a maximum single pulse energy of 1mJ, a pulse width of 50fs, and a repetition rate of 1kHz to obtain a pulse energy of 200nJ; use a numerical aperture of 0.5 The attenuated high-energy femtosecond laser pulse is focused at a depth of 10 μm below the surface of the silicon dioxide layer in silicon-based silicon dioxide by a microscope objective lens with a magnification of 50×, and the three-dimensional mobile platform is controlled by a driver program built into the computer Speed, direction, length of movement, direct write optical waveguide, adjustable coupler, polarization beam splitter, first half-wave plate, second half-wave plate, polarization beam combiner.

Step 5, making micro-thin film heating electrodes.

Directly above any transmission waveguide in the adjustable coupler, a micro-thin film heating electrode made of chromium or aluminum is fabricated by sputtering coating method to obtain a combined device of the adjustable coupler and the phase shifter. The length of the microfilm heating electrode is calculated by the following formula:

$\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&lambda;\&Delta;\&phi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;\&Delta;T</span>}}{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; dn</span>}}{\mathrm{<span\; class="notranslate">\; dT</span>}}<span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}$

Among them, L represents the length of the microfilm heating electrode, λ represents the working wavelength of the optical polarization converter, and its size is 1500nm, Δφ represents the phase difference between the two paths of light in the combined device of the tunable coupler and phase shifter, ΔT Indicates the temperature increase obtained by heating the optical waveguide in the phase shifter with the microfilm heating electrode, Indicates that the refractive index n of silicon dioxide is derived from the temperature T of silicon dioxide, and its value is the thermo-optic coefficient of silicon dioxide, which is 1×10 ^-5 K ^-1 .

Claims (5)

1. An optical polarization converter, including a three-dimensional 2×2 polarization beam splitter (1), a first half-wave plate (2), and an adjustable coupling made of silicon-based silicon dioxide materials. A combined device (3) of a device and a phase shifter, a second half-wave plate (4), and a polarization beam combiner (5); where: The polarization beam splitter (1) is located at the leftmost end of the optical polarization converter, and is used to decompose the incident light of any polarization state into two beams of linearly polarized light whose polarization directions include an angle of 90°; The first half-wave plate (2) is connected to the polarizing beam splitter (1) through an optical waveguide to convert the two beams output by the polarizing beam splitter (1) into linearly polarized light whose polarization direction angle is 90° are two beams of linearly polarized light with the same polarization direction; The combined device (3) of the adjustable coupler and the phase shifter is respectively connected with the polarization beam splitter (1) and the first half-wave plate (2) through the optical waveguide, so as to pair the two beams with the same polarization direction The light intensity of polarized light is distributed in any proportion; The combined device (3) of the adjustable coupler and phase shifter of the second half-wave plate (4) is connected through an optical waveguide, so as to polarize the linearly polarized light incident into the second half-wave plate (4). The direction is rotated by 90°, and the polarization direction angle between the linearly polarized light output by the second half-wave plate (4) and the linearly polarized light output by the first half-wave plate (2) is 90°; The polarization beam combiner (5) is located at the far right end of the optical polarization converter, and the polarization beam combiner (5) is respectively combined with an adjustable coupler and a phase shifter (3) and the second half-wave through the optical waveguide The plate (4) is connected to combine the two beams of linearly polarized light output from the second half-wave plate (4) and the combined device (3) of the adjustable coupler and phase shifter into one beam of light with any desired polarization state . 2. A manufacturing method of the optical polarization converter of the optical polarization converter according to claim 1, comprising the steps of: (1) Cutting silicon wafers: Use laser cutting technology to cut silicon wafers according to the size required for making optical polarizers; (2) Clean the silicon wafer: Use chemical cleaning method to clean the dirt on the surface of the cut silicon wafer; (3) Thermally oxidized silicon wafer: Using thermal oxidation technology, the single side of the cleaned silicon wafer is partially thermally oxidized in a silica tube furnace to obtain silicon-based silica; (4) Direct writing optical waveguides and microphotonic devices: 4a) Fixing the thermally oxidized silicon wafer on a three-dimensional electric translation stage, with the thermally oxidized side of the silicon wafer facing up; 4b) adjusting the variable attenuator to attenuate the energy of the femtosecond laser pulse to an optimal energy range; 4c) adjusting the microscope objective lens so that the femtosecond laser pulse is vertically focused on the interior of the silicon dioxide layer in the silicon-based silicon dioxide; 4d) setting the built-in driver parameters in the computer; 4e) The computer controls the movement of the three-dimensional electric translation stage, so that the three-dimensional electric translation stage moves in the plane perpendicular to the propagation direction of the focused beam with the parameters set in step 4c), and completes the direct writing optical waveguide, adjustable coupler, and polarization beam splitting. device, the first half-wave plate, the second half-wave plate, polarization beam combiner; (5) Making micro-thin film heating electrodes: 5a) calculate the length of the microfilm heating electrode; 5b) Directly above any transmission waveguide in the adjustable coupler, use the method of sputter coating to make a micro-thin film heating electrode to obtain a combined device of the adjustable coupler and the phase shifter. 3. A kind of optical polarization converter manufacturing method according to claim 2, is characterized in that, the femtosecond laser pulse described in step 4c) focuses vertically on the inner part of the silicon dioxide layer in silicon-based silicon dioxide. The depth is 10-100 μm. 4 . The manufacturing method of an optical polarization converter according to claim 2 , wherein the optimal energy range in step 4 b) is 200-400 nJ. 5. a kind of optical polarization converter manufacturing method according to claim 2 is characterized in that, the length of the microfilm heating electrode described in step 5a) is calculated according to the following formula: $\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; \&phi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}$ Among them, L represents the length of the microfilm heating electrode, λ represents the working wavelength of the optical polarization converter, Δφ represents the phase difference between the two light paths in the combined device of the adjustable coupler and phase shifter, and ΔT represents the microfilm heating The temperature rise obtained by electrodes heating the optical waveguide in the phase shifter, Indicates that the refractive index n of silicon dioxide is derived from the temperature T of silicon dioxide, and its value is the thermo-optic coefficient of silicon dioxide.