System and modulation method for controlling KTN cladding waveguide transmission mode using temperature

Abstract

The present invention relates to a system and a modulation method for controlling the transmission mode of a KTN cladding waveguide by using temperature, and the technical characteristics thereof are: comprising a helium-neon laser light source A, a Glan-Taylor prism B, a focusing objective lens C, a cladding waveguide mode modulator D, an imaging objective lens E, a beam quality analyzer F and a temperature controller G; the helium-neon laser light source is connected to the Glan-Taylor prism, the other end of the Glan-Taylor prism is connected to the cladding waveguide mode modulator through the focusing objective lens, and the other end of the cladding waveguide mode modulator is connected to the beam quality analyzer through the imaging objective lens. The present invention realizes the control of the light field mode distribution at the output end of the KTN cladding waveguide.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical functional devices and systems, and relates to a system and a modulation method for realizing the change of the transmission light mode in a KTN cladding waveguide, in particular to a system and a modulation method for controlling the transmission mode of a KTN cladding waveguide by using temperature. Background Art

[0002] With the development of optical communication, optical information processing and laser technology, traditional optical systems can no longer meet the needs of the development of optoelectronic technology due to their large size and slow information processing speed. In 1969, Dr. Miller of Bell Laboratory in the United States proposed the concept of "integrated optics", using a method similar to semiconductor integrated circuits to integrate various optical components on the same "chip" to achieve the integration, miniaturization and all-optical signal processing of optical information processing systems. Optical waveguides are the basic components of integrated optical circuits, and their quality directly affects the performance of the entire integrated optical circuit. Therefore, the development of optical waveguide technology plays a vital role in the development of integrated optics.

[0003] In integrated photonics, optical waveguides can be generated in various optical materials by direct writing of ultrafast laser pulses. For example, lithium niobate, yttrium aluminum garnet, vanadates, sapphire crystals, potassium titanyl phosphate, barium metaborate, etc. Depending on the laser parameters, the waveguides formed will also have different structures: the waveguides can be formed by the refractive index changes in the area directly written by the femtosecond laser, or by the stress changes of the materials around the direct writing area. This processing method can be used to prepare electro-optic modulators, frequency converters, and generate waveguide lasers.

[0004] The cladding waveguide is a columnar structure of arbitrary shape surrounded by multiple parallel etching marks. If the interval between the etching marks is close enough, about 3 to 4 μm, a low refractive index light wall can be formed, and the middle part surrounded by the light wall can form an optical waveguide. This kind of waveguide is a barrel-shaped structure, and the end face shape and size can be arbitrarily designed. It has good light guiding effect, is easy to couple, and has good matching with optical fiber. Common cladding waveguides include circular cladding waveguides, square cladding waveguides and hexagonal cladding waveguides.

[0005] KTN crystal is an excellent relaxor ferroelectric material. In recent years, many potential applications have been studied, including the ability to make high-speed deflectors, temperature modulators, photorefractive light needles, and scale-free optics and diffraction-free light wave transmission.

[0006] KTN crystals have great potential applications in the field of optics, but there is no report on processing cladding waveguides in KTN crystals. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and propose a system and a modulation method for controlling the transmission mode of a KTN cladding waveguide using temperature, and to utilize the temperature change of the KTN crystal to achieve regulation of the mode distribution of the light field in the crystal cladding waveguide.

[0008] The present invention solves the practical problem by adopting the following technical solutions:

[0009] A system for controlling a KTN cladding waveguide transmission mode by temperature comprises a He-Ne laser light source A, a Glan Taylor prism B, a focusing objective lens C, a cladding waveguide mode modulator D, an imaging objective lens E, a beam quality analyzer F and a temperature controller G; the He-Ne laser light source is connected to the Glan Taylor prism, and is used for outputting the circularly polarized light laser beam generated by the He-Ne laser light source to the Glan Taylor prism and then converting the circularly polarized light laser beam generated by the He-Ne laser light source into a linearly polarized light in a TE mode polarized along an X-axis; the other end of the Glan Taylor prism is connected to the cladding waveguide mode modulator through the focusing objective lens, and is used for focusing the linearly polarized light in the TE mode polarized along the X-axis on the cladding waveguide end face of the cladding waveguide mode modulator, and transmitting and mode modulating the conductable light in the cladding waveguide through the cladding waveguide mode modulator; the other end of the cladding waveguide mode modulator is connected to the beam quality analyzer through the imaging objective lens, and is used for imaging the light modulated by the cladding waveguide mode modulator on the beam analyzer, and receiving and recording the light field mode distribution information of the outgoing light beam by the beam analyzer.

[0010] Moreover, the cladding waveguide mode modulator includes a KTN crystal and a cooling plate arranged thereunder; the KTN crystal includes a KTN cladding waveguide for transmitting and modulating linearly polarized light in the TE mode polarized along the X-axis; the cooling plate is connected to the potassium tantalate niobate crystal and a temperature controller, and is used to change the temperature of the potassium tantalate niobate crystal and its KTN cladding waveguide.

[0011] A method for modulating a system for controlling a KTN cladding waveguide transmission mode by temperature, comprising the following steps:

[0012] Step 1. Turn on the temperature controller and set the temperature of the potassium tantalate niobate crystal to 20°C. After the temperature displayed by the temperature controller becomes stable, that is, the temperature fluctuation range does not exceed 0.03°C, proceed with the following steps;

[0013] Step 2: adjusting the cladding waveguide mode modulator based on potassium tantalate niobate crystal, and using the detection of the beam quality analyzer to make the mode at the waveguide output end a stable fundamental mode;

[0014] Step 3, increase the temperature T applied to the cladding waveguide mode modulator based on potassium tantalate niobate crystal, the temperature step is 5°C, adjust the cladding waveguide mode modulator until the beam quality analyzer can detect a stable fundamental mode, and record the corresponding temperature and light field mode information;

[0015] Step 4: Continue to increase the temperature until the beam quality analyzer can detect a stable TEM 11 Second-order light field mode, recording the temperature value and light field mode information. When the temperature value increases to 50°C, a complete modulation process ends;

[0016] Step 5. Repeat steps 2 to 4 multiple times. If the same result is obtained, the recorded temperature values ​​and light field mode distributions are sorted and matched. When the temperature is between 20 and 35 °C, the light field mode at the waveguide output end is the TE fundamental mode. When the temperature is between 40 and 50 °C, the light field mode at the waveguide output end is the TEM fundamental mode. 11 model.

[0017] Advantages and beneficial effects of the present invention:

[0018] 1. The present invention proposes for the first time a cladding waveguide structure in a KTN crystal and explores its optical properties. In the present invention, by simply controlling the temperature of the KTN crystal, and then controlling the size and distribution of the polar micro-nano regions in the KTN crystal, the conductive light mode in the KTN cladding waveguide is modulated, thereby achieving control of the light field mode distribution at the output end of the KTN cladding waveguide.

[0019] 2. The present invention can achieve modulation from single-mode waveguide output to multi-mode output by using end-face coupling technology at a wavelength of 500-650nm, simply by controlling the crystal temperature to change between 20℃ and 50℃. When the crystal temperature is between 20℃ and 35℃, the waveguide output end mode is the TE fundamental mode; when the crystal temperature is between 40℃ and 50℃, the waveguide output end mode is the TEM fundamental mode. 11 Multi-mode, and the output modes are relatively stable.

[0020] 3. The present invention can achieve stable single-mode and multi-mode output, and the waveguide coupling effect is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the system principle diagram of the present invention;

[0022] Figure 2 The end face structure diagram of the cladding waveguide of the present invention;

[0023] Figure 3 The light field mode distribution diagram of the output end of the waveguide at 20-35°C detected by the beam quality analyzer in the present invention;

[0024] Figure 4 This is the light field mode distribution diagram of the output end of the waveguide at 40-50°C detected by the beam quality analyzer in the present invention;

[0025] Figure 5 Schematic diagram for the theoretical explanation of the change in waveguide output mode in the present invention. DETAILED DESCRIPTION

[0026] The embodiments of the present invention are further described in detail below with reference to the accompanying drawings:

[0027] A system for controlling the transmission mode of a KTN (potassium tantalate niobate) cladding waveguide using temperature, such as Figure 1 As shown, it includes a He-Ne laser light source A, a Glan Taylor prism B, a focusing objective lens C, a cladding waveguide mode modulator D, an imaging objective lens E, a beam quality analyzer F and a temperature controller G; the He-Ne laser light source is connected to the Glan Taylor prism, and is used to output the circularly polarized light laser beam generated by it to the Glan Taylor prism and then convert it into a linearly polarized light in the TE mode polarized along the X-axis; the other end of the Glan Taylor prism is connected to the cladding waveguide mode modulator through the focusing objective lens, and is used to focus the linearly polarized light in the TE mode polarized along the X-axis on the cladding waveguide end face of the cladding waveguide mode modulator, and transmit and mode-modulate the conductible light in the cladding waveguide through the cladding waveguide mode modulator; the other end of the cladding waveguide mode modulator is connected to the beam quality analyzer through the imaging objective lens, and is used to image the light modulated by the cladding waveguide mode modulator on the beam analyzer, and the light field mode distribution information of the outgoing light beam is received and recorded by the beam analyzer.

[0028] In this embodiment, the cladding waveguide mode modulator includes a KTN crystal and a cooling plate arranged thereunder; the KTN crystal includes a KTN cladding waveguide for transmitting and modulating linearly polarized light in a TE mode polarized along the X-axis; the cooling plate is connected to a potassium tantalate niobate crystal and a temperature controller to change the temperature of the potassium tantalate niobate crystal and its KTN cladding waveguide.

[0029] The working process of the system of the present invention for controlling the transmission mode of KTN (potassium tantalate niobate) cladding waveguide by temperature is as follows:

[0030] First, a helium-neon laser generates a 632.8nm laser beam (circularly polarized light), which then enters a Glan-Taylor prism and becomes a linearly polarized light polarized along the X-axis. Then, the light beam emitted from the Glan-Taylor prism passes through a focusing objective lens and is incident on a cladding waveguide mode modulator. The light beam coming out of the cladding waveguide mode modulator passes through an imaging lens and is then incident on a beam quality analyzer, which records the light field mode distribution information of the outgoing light beam.

[0031] The functions of the various components of the system for controlling the KTN cladding waveguide transmission mode by temperature of the present invention are further described below:

[0032] A. Helium-neon laser (HNR-IHT-2.0-P, 632.8nm, ≥2mW), used to generate the laser required in the experiment;

[0033] B. Glan Taylor prism (Daheng, GCL-070213), used to convert the circularly polarized light generated by the HeNe laser into linearly polarized light in TE mode;

[0034] C. Focusing objective lens, used to focus the light beam on the end face of the cladding waveguide;

[0035] D. A cladding waveguide mode modulator based on a potassium tantalate niobate crystal placed on a cooling plate. The potassium tantalate niobate crystal contains the cladding waveguide required for the experiment of femtosecond laser writing. When the crystal temperature changes, the beam mode conducted by the waveguide will also change. The cooling plate is connected to a temperature controller to control the temperature of the potassium tantalate niobate crystal and its cladding waveguide.

[0036] E. an imaging objective lens, used to image the light guided out from the waveguide onto a beam analyzer;

[0037] F. Beam quality analyzer (WinCamD TM Series) for analyzing the conduction modes of the optical field in the cladding waveguide;

[0038] G. Temperature controller (Arroyo Instruments, 5305, 5A / 12V), used to change the temperature of the KTN crystal;

[0039] The operation process of the transmission light mode modulation in the KTN cladding waveguide of the present invention is as follows:

[0040] First, turn on the temperature controller G, set the temperature of the cladding waveguide mode modulator based on the potassium tantalate niobate crystal connected to the temperature controller to 20°C, and after the temperature tends to be stable (the temperature fluctuation range is within 0.03°C), turn on the helium-neon laser A, and the helium-neon laser A generates a 632.8nm laser beam (circularly polarized light), which enters the Glan-Taylor prism B, and B converts the circularly polarized light into linearly polarized light with the polarization direction in the X-axis direction. Secondly, the linearly polarized laser beam emitted by the Glan-Taylor prism B is incident on the cladding waveguide mode modulator D based on the potassium tantalate niobate crystal after passing through the focusing objective lens C;

[0041] Secondly, the light beam coming out of D passes through the imaging objective lens C, and then the light beam is incident on the beam quality analyzer F connected to the PC end, and the beam quality analyzer F receives the light field mode information passing through the cladding waveguide mode modulator D;

[0042] Secondly, the potassium tantalate niobate crystal in the cladding waveguide mode modulator D is a relaxor ferroelectric material. When the temperature of the crystal changes, the size and distribution of the polar micro-nano regions inside the crystal will also change, affecting the refractive index distribution of the potassium tantalate niobate crystal, thereby causing the refractive index distribution inside the cladding waveguide to change accordingly. At the same time, the optical field mode conducted by the waveguide also changes.

[0043] Finally, when the temperature change applied to the cladding waveguide mode modulator D is controlled by the temperature controller G, the beam quality analyzer F detects and records the change in the electric field mode of the cladding waveguide in the cladding waveguide mode modulator D.

[0044] The present invention proposes a modulation method of a system for controlling a KTN cladding waveguide transmission mode by temperature, comprising the following steps:

[0045] Step 1. Turn on the temperature controller and set the temperature of the potassium tantalate niobate crystal to 20°C. After the temperature displayed by the temperature controller becomes stable, that is, the temperature fluctuation range does not exceed 0.03°C, proceed with the following steps;

[0046] Step 2: adjusting the cladding waveguide mode modulator based on potassium tantalate niobate crystal, and using the detection of the beam quality analyzer to make the mode at the waveguide output end a stable fundamental mode;

[0047] Step 3, increase the temperature T applied to the cladding waveguide mode modulator based on potassium tantalate niobate crystal, the temperature step is 5°C, adjust the cladding waveguide mode modulator until the beam quality analyzer can detect a stable fundamental mode, and record the corresponding temperature and light field mode information;

[0048] Step 4: Continue to increase the temperature until the beam quality analyzer can detect a stable TEM 11 Second-order light field mode, recording the temperature value and light field mode information. When the temperature value increases to 50°C, a complete modulation process ends;

[0049] Step 5. Repeat steps 2 to 4 multiple times. If the same result is obtained, the recorded temperature values ​​and light field mode distributions are sorted and matched. When the temperature is between 20 and 35 °C, the light field mode at the waveguide output end is the TE fundamental mode. When the temperature is between 40 and 50 °C, the light field mode at the waveguide output end is the TEM fundamental mode. 11 model.

[0050] Figure 2 This is the end view of the KTN cladding waveguide actually processed in the experiment. Figure 2 As shown, the cladding waveguide type in this experiment is a hexagonal cladding waveguide.

[0051] Figure 3 This is the light field mode distribution diagram of the waveguide output end at 20-35°C detected by the beam quality analyzer in the present invention. Within this temperature range, the light field mode is the TE fundamental mode.

[0052] Figure 4 This is the light field mode distribution diagram of the waveguide output end at 40-50°C detected by the beam quality analyzer in the present invention. In this temperature range, the light field mode is TEM 11 model.

[0053] Figure 5 Schematic diagram for the theoretical explanation of the change in waveguide output mode in the present invention.

[0054] The working principle of the present invention is:

[0055] The system that uses temperature control to change the transmission light mode in the KTN cladding waveguide is designed based on the characteristics of the polar micro-nano region in the KTN crystal that changes with temperature. The polar micro-nano region appears near the Curie temperature TC. The TC of the KTN crystal used in this experiment is 15℃. It can be said that all the excellent properties of the KTN crystal are inseparable from the existence of the polar micro-nano region. KTN crystal is a typical relaxor ferroelectric material. When it is below TC, the crystal is in the ferroelectric phase; when it is above TC, the crystal is in the paraelectric phase. Within the temperature range of the experiment, the crystal is always in the paraelectric phase.

[0056] When processing the cladding waveguide in potassium tantalate niobate crystal with femtosecond laser, the refractive index of the laser ablated area becomes smaller, which causes the lattice expansion in the nearby area and the corresponding increase in refractive index. Therefore, the refractive index of the intermediate waveguide area surrounded by the processed multiple lines becomes larger, which can well confine the light in this area and realize the information transmission of light. When the temperature of KTN is low (20-35℃), it can be regarded as an optical fiber system with polarization-maintaining function. After the incident light of TE polarization passes through the waveguide, its polarization direction can be well maintained. When the crystal temperature is high (40-50℃), the waveguide loses its polarization-maintaining function, and the polarization state of the incident light of TE polarization changes after passing through the waveguide.

[0057] The effect of temperature changing the output light field mode involved in the present invention is caused by the change of polar micro-nano region in the crystal with temperature. The higher the temperature, the smaller the size of the polar micro-nano region. The size of the polar micro-nano region and the temperature of the crystal show the following relationship:

[0058]

[0059] Among them, L is the size of the polar micro-nano region in the crystal, C is the Curie Weiss constant, T0 is the Curie Weiss temperature, κ is a constant, and T is the crystal temperature. It can be seen that the higher the temperature of the crystal, the smaller the size of the polar micro-nano region.

[0060] like Figure 5 As shown in the figure, when the KTN crystal temperature is between 20 and 35°C, according to equation (1), due to the low temperature, the polar micro-nano region is large in size, and the gap between adjacent polar micro-nano regions is small. Affected by the long spot of the surrounding laser ablation area, the polar micro-nano region in the waveguide waveguide area is mostly aligned with the long spot, along the y direction, and only a small amount is along the x direction. At this time, when light propagates in the waveguide, it is mainly restricted by the polar micro-nano region. The role of the polar micro-nano region is similar to that of a polarizer. When the incident light is TE polarized light, the outgoing light is still the fundamental mode of TE polarization.

[0061] When the crystal temperature is between 40 and 50°C, the size of the polar micro-nano region decreases, and the gap between adjacent polar micro-nano regions increases. At this time, the light-guiding effect of the gap can no longer be ignored. When TE polarized light is incident, part of it is transmitted through the polar micro-nano region in the x direction, and the other part is scattered by the polar micro-nano region and conducted through the gap. The polarization direction of the scattered light also changes to a certain extent. Therefore, TEM light appears at the output end. 11 mode, realizing the regulation of the light field mode by temperature.

[0062] The present invention can change the cladding waveguide transmission mode from the TE fundamental mode to a stable TEM mode by temperature control near the wavelength of 632.8nm. 11 The second-order mode realizes the control of the light field mode in the cladding waveguide. We use pure potassium tantalate niobate crystal (the crystal is connected to a semiconductor refrigerator and has a cladding waveguide processed by a femtosecond laser inside) as the core material of the cladding waveguide mode modulator. By changing the temperature of the cladding waveguide mode modulator, the size of the polarization micro-nano region and the gap between the polarization micro-nano regions inside the waveguide are changed. When the size of the polarization micro-nano region is large and its gap is small, the waveguide is similar to a polarizer and has a polarization-maintaining effect; when the size of the polarization micro-nano region is small and its gap is large, the waveguide no longer has a polarization-maintaining effect. Therefore, when the crystal temperature increases, the mode of light guided inside the waveguide will change from the TE fundamental mode to a TEM fundamental mode. 11 The second-order mode transition realizes the temperature regulation of the light field mode.

[0063] The present invention can realize the conversion and stable transmission between different modes of the cladding waveguide. When the crystal temperature is 20-35°C, the cladding waveguide transmission light mode is the fundamental mode of the TE mode. When the temperature is raised to 40-50°C, a stable TEM mode appears in the output end mode. 11 The second-order mode realizes the temperature modulation of the light guided in the KTN crystal cladding waveguide.

[0064] It should be emphasized that the embodiments of the present invention are illustrative rather than restrictive. Therefore, the present invention includes but is not limited to the embodiments described in the specific implementation modes. Any other implementation modes derived by those skilled in the art based on the technical solutions of the present invention also fall within the scope of protection of the present invention.

Claims

1. A method for modulating a system for controlling a KTN cladding waveguide transmission mode by temperature, characterized in that: A system for controlling a KTN cladding waveguide transmission mode by temperature comprises a He-Ne laser light source A, a Glan Taylor prism B, a focusing objective lens C, a cladding waveguide mode modulator D, an imaging objective lens E, a beam quality analyzer F and a temperature controller G; the He-Ne laser light source is connected to the Glan Taylor prism, and is used to output the circularly polarized light laser beam generated by the He-Ne laser light source to the Glan Taylor prism and then convert it into a linearly polarized light of a TE mode polarized along an X-axis; the other end of the Glan Taylor prism is connected to the cladding waveguide mode modulator through the focusing objective lens, and is used to focus the linearly polarized light of the TE mode polarized along the X-axis on the cladding waveguide end face of the cladding waveguide mode modulator, and transmit and mode-modulate the conductable light in the cladding waveguide through the cladding waveguide mode modulator; the other end of the cladding waveguide mode modulator is connected to the beam quality analyzer through the imaging objective lens, and is used to image the light modulated by the cladding waveguide mode modulator on the beam analyzer, and the light field mode distribution information of the outgoing light beam is received and recorded by the beam analyzer; The modulation method comprises the following steps: Step 1. Turn on the temperature controller and set the temperature of the potassium tantalate niobate crystal to 20°C. After the temperature displayed by the temperature controller becomes stable, that is, the temperature fluctuation range does not exceed 0.03°C, proceed with the following steps; Step 2: adjusting the cladding waveguide mode modulator based on potassium tantalate niobate crystal, and using the detection of the beam quality analyzer to make the waveguide output end mode a stable fundamental mode; Step 3, increase the temperature T applied to the cladding waveguide mode modulator based on potassium tantalate niobate crystal, the temperature step is 5°C, adjust the cladding waveguide mode modulator until the beam quality analyzer can detect a stable fundamental mode, and record the corresponding temperature and light field mode information; Step 4: Continue to increase the temperature until the beam quality analyzer can detect a stable TEM 11 Second-order light field mode, recording temperature value and light field mode information. When the temperature value increases to 50°C, a complete modulation process ends; Step 5. Repeat steps 2 to 4 multiple times. If the same result is obtained, the recorded temperature values ​​and light field mode distributions are sorted and matched. When the temperature is between 20 and 35 °C, the light field mode at the waveguide output end is the TE fundamental mode. When the temperature is between 40 and 50 °C, the light field mode at the waveguide output end is the TEM fundamental mode. 11 model.

2. The modulation method of a system for controlling the transmission mode of a KTN cladding waveguide by temperature according to claim 1, characterized in that: The cladding waveguide mode modulator includes a KTN crystal and a cooling plate arranged thereunder; the KTN crystal includes a KTN cladding waveguide for transmitting and modulating linearly polarized light in a TE mode polarized along the X-axis; the cooling plate is connected to a potassium tantalate niobate crystal and a temperature controller, and is used to change the temperature of the potassium tantalate niobate crystal and its KTN cladding waveguide.

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