A bandwidth tunable frequency converter and control method thereof

Abstract

The present application discloses a bandwidth tunable frequency converter and a control method thereof, wherein the bandwidth tunable frequency converter comprises a conical periodically polarized lithium niobate waveguide, and also comprises a substrate, a cover layer, a silica gel layer, a copper layer and a semiconductor refrigerator which are sequentially stacked, wherein the conical periodically polarized lithium niobate waveguide is located between the substrate and the cover layer. The core structure of the periodically polarized lithium niobate waveguide adopts a conical structure, and the temperature of the entire waveguide is controlled by two semiconductor refrigerators at the head and tail. The tunable wavelength range covers the C band, and the C band can be doubled, which will be effectively applied to biomedical research, environmental monitoring, optical precision measurement, material processing, national defense security and other fields.

Description

Technical Field

[0001] The present application relates to a bandwidth tunable frequency converter and a control method thereof, and belongs to the field of nonlinear optics. Background Art

[0002] Wavelength tunable lasers are usually used in DWDM where protection is required. Currently, DWDM technology is developing rapidly, and the number of wavelengths in the system has reached hundreds. If a fixed wavelength laser is used to back up each laser, the number of lasers will increase and the cost will rise. However, using tunable lasers as backup, due to their variable wavelengths, one laser can back up several wavelengths or even the entire wavelength band, thereby reducing costs.

[0003] The C band ranges from 1530nm to 1565nm, representing the conventional band. Optical fiber exhibits the lowest loss in the C band, and has a great advantage in long-distance transmission systems, and is usually used in many fields combined with WDM. Nonlinear frequency variation technology makes it possible to convert and expand wavelengths, especially based on quasi-phase matching technology, which can achieve arbitrary wavelength output in its light transmission window through flexible period design. Summary of the invention

[0004] The present application provides a waveguide structure with simultaneously tunable wavelength and temperature, which is composed of a silicon dioxide substrate, a conical periodically polarized lithium niobate waveguide, a cover layer, silica gel, metal copper and a semiconductor refrigerator. The core component is the conical periodically polarized lithium niobate waveguide. A bandwidth tunable frequency converter based on the periodically polarized lithium niobate waveguide is used to double the frequency of light waves in the conventional band, i.e., the C band.

[0005] In one aspect of the present application, a bandwidth tunable frequency converter is provided, which includes a substrate, a conical periodically poled lithium niobate waveguide, a covering layer, a silica gel layer, a copper layer and a semiconductor cooler which are sequentially stacked.

[0006] Optionally, the tapered periodically poled lithium niobate waveguide has a first tapered side surface and a second tapered side surface that are parallel to each other;

[0007] The first tapered side and the second tapered side each have a narrow end and a wide end;

[0008] Optionally, preferably, the narrow end width is d1, 7.5≤d1≤7.52μm;

[0009] The width of the wide end is d2, 12.7≤d2≤13μm;

[0010] 5.18≤d2-d1≤5.5;

[0011] Optionally, the narrow end width is independently selected from any value among 7.5 μm, 7.51 μm, 7.52 μm, or any value between any two of the above points.

[0012] Optionally, the width of the wide end is independently selected from any value of 12.7 μm, 12.8 μm, 13 μm, or any value between any two of the above points.

[0013] Optionally, a vertical distance between the first tapered side surface and the second tapered side surface is 9 to 9.5 μm;

[0014] Optionally, the vertical distance between the first tapered side surface and the second tapered side surface is independently selected from any value of 9 μm, 9.3 μm, 9.5 μm, or any value between any two of the above points.

[0015] Optionally, the polarization period of the tapered periodically poled lithium niobate waveguide is 18 to 18.2 μm, and the total length of the waveguide is 43 to 45 mm.

[0016] Optionally, the poling period of the tapered periodically poled lithium niobate waveguide is independently selected from any value of 18 μm, 18.1 μm, 18.2 μm or any value between any two of the above points.

[0017] Optionally, the total waveguide length of the tapered periodically poled lithium niobate waveguide is independently selected from any value among 43 mm, 44 mm, 45 mm or any value between any two of the above points.

[0018] Optionally, the semiconductor refrigerator comprises a first semiconductor refrigerator and a second semiconductor refrigerator;

[0019] The first semiconductor refrigerator is used to adjust the temperature of the narrow end of the tapered waveguide;

[0020] The second semiconductor refrigerator is used to adjust the temperature of the wide end of the tapered waveguide;

[0021] Optionally, the temperature tunable range of the semiconductor refrigerator is 30-150°C; that is, the temperature tunable bandwidth is 120°C.

[0022] Optionally, the substrate comprises a silicon dioxide layer I;

[0023] The tapered periodically poled lithium niobate waveguide is located between the silicon dioxide layer I and the cover layer;

[0024] Optionally, the substrate further comprises a lithium tantalate crystal layer;

[0025] The silicon dioxide layer I is located between the lithium tantalate crystal layer and the tapered periodically poled lithium niobate waveguide;

[0026] Optionally, the thickness of the silicon dioxide layer I is 0.5 to 1 μm;

[0027] The covering layer is a silicon dioxide layer II; the thickness of the silicon dioxide layer II is 1 to 10 μm.

[0028] The thickness of the silica gel layer is 1 to 20 μm, and the thickness of the copper layer is 1 to 30 μm.

[0029] Optionally, the thickness of the silicon dioxide layer I is independently selected from any value among 0.5 μm, 0.7 μm, 1 μm, or any value between any two of the above points.

[0030] Optionally, the thickness of the silicon dioxide layer II is independently selected from any value of 1 μm, 5 μm, 10 μm, or any value between any two of the above points.

[0031] Optionally, the thickness of the silica gel layer is independently selected from any value among 1 μm, 5 μm, 10 μm, 15 μm, 20 μm or any value between any two of the above points.

[0032] Optionally, the thickness of the copper layer is independently selected from any value of 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or any value between any two of the above points.

[0033] The bandwidth tunable frequency converter provided in the present application has a main principle that when the light wave propagates in the conical periodically polarized lithium niobate waveguide, frequency doubling occurs to generate second harmonics. By adjusting the temperature of the semiconductor refrigerator, the temperature at different positions of the waveguide can be adjusted to obtain the desired band. The tunable wavelength range is the C band.

[0034] As a specific implementation, the bandwidth tunable frequency converter includes a substrate lithium tantalate crystal (LT), a substrate silicon dioxide (SiO2) with a thickness of 0.5um, a tapered periodically poled lithium niobate waveguide (MgO:PPLN), a covering layer of silicon dioxide (SiO2), silica gel (Si), metal copper (Cu), and two semiconductor refrigerators (TEC). The tapered periodically poled lithium niobate waveguide has a width of 7.5μm at one end, a width of 13μm at the other end, a height of 9μm, a polarization period of 18μm, and a total length of 45mm.

[0035] Another aspect of the present application provides a control method for the above-mentioned bandwidth tunable frequency converter, comprising: propagating a light wave in the periodically poled lithium niobate waveguide, and outputting a desired wavelength by adjusting the temperature of the periodically poled lithium niobate waveguide.

[0036] Optionally, the wavelength band of the light wave is a conventional wavelength band C band;

[0037] The C band is 1530-1565 nm, that is, the wavelength tunable bandwidth is 35 nm.

[0038] Optionally, a light wave is incident on the periodically poled lithium niobate waveguide, and the temperature of the narrow end and the temperature of the wide end of the periodically poled lithium niobate waveguide are controlled by the semiconductor refrigerator to output the wavelength.

[0039] Optionally, the temperature of the narrow end is 30 to 150°C;

[0040] The temperature of the wide end is 30-150°C.

[0041] Optionally, the temperature of the narrow end is independently selected from any value of 30° C., 100° C., 150° C. or any value between any two of the above points.

[0042] Optionally, the temperature of the wide end is independently selected from any value of 30° C., 100° C., 150° C. or any value between any two of the above points.

[0043] Optionally, the bandwidth-tunable frequency converter based on periodically poled lithium niobate waveguide can obtain a desired band by adjusting the TEC temperature, and the tunable wavelength range covers the C band, which has high practical value.

[0044] Another aspect of the present application provides an application of the above-mentioned bandwidth tunable frequency converter or the above-mentioned control method in biomedical research, environmental monitoring, optical precision measurement, material processing, and national defense security.

[0045] The beneficial effects of this application include:

[0046] The present application provides a bandwidth-tunable frequency converter based on a periodically poled lithium niobate waveguide, wherein the core structure of the periodically poled lithium niobate waveguide adopts a conical structure, and the temperature of the entire waveguide is controlled by two semiconductor refrigerators at the head and tail. The tunable wavelength range covers the C-band, and the C-band can be doubled in frequency, which will be effectively applied to biomedical research, environmental monitoring, optical precision measurement, material processing, national defense security and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A front view of a bandwidth-tunable frequency converter based on a periodically poled lithium niobate waveguide provided in Example 1 of the present application;

[0048] Figure 2 A top view of a tapered periodically polarized lithium niobate waveguide provided in Example 1 of the present application;

[0049] Figure 3 A schematic diagram of the structure of a tapered periodically polarized lithium niobate waveguide provided in Example 1 of the present application;

[0050] Figure 4 The relationship between the wave vector mismatch and the waveguide width of Example 2 provided in this application (wavelength is 1530nm, T=30°C);

[0051] Figure 5 The relationship between the wave vector mismatch and the waveguide width of Example 2 provided in this application (wavelength is 1565nm, T=150°C);

[0052] Figure 6 The relationship between the wave vector mismatch and the waveguide width of Example 3 provided in this application (wavelength is 1546nm, T=30°C);

[0053] Figure 7 The relationship between the wave vector mismatch and the waveguide width of Example 3 provided in this application (wavelength is 1550nm, T=150°C);

[0054] Figure 8 The relationship between the wave vector mismatch and the waveguide width of Example 4 provided in this application (wavelength is 1540nm, T=100°C);

[0055] Fig. 9 The relationship between the wave vector mismatch and the waveguide width of Example 4 provided in the present application (wavelength is 1557nm, T=100°C).

[0056] in:

[0057] 1. Lithium tantalate crystal; 2. Silicon dioxide substrate; 3. Conical periodically poled lithium niobate waveguide (PPLN);

[0058] 4. Silicon dioxide layer; 5. Silicone gel; 6. Metal copper layer; 7. The first semiconductor refrigerator (TEC);

[0059] 8. The second semiconductor cooler (TEC); 9. The narrow end of the tapered periodically polarized lithium niobate waveguide;

[0060] 10. Wide end of a tapered periodically poled lithium niobate waveguide. DETAILED DESCRIPTION

[0061] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0062] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0063] Example 1

[0064] This embodiment provides a bandwidth tunable frequency converter based on a periodically poled lithium niobate waveguide, the structure of which is shown in FIG. Figure 1As shown, from bottom to top, they are respectively: lithium tantalate crystal 1, silicon dioxide substrate 2, tapered periodic poled lithium niobate waveguide (PPLN) 3, silicon dioxide layer 4, silica gel 5, and metal copper layer 6; a first semiconductor refrigerator (TEC) 7 and a second semiconductor refrigerator (TEC) 8 are respectively located on the upper layer of the metal copper layer, the first semiconductor refrigerator (TEC) 7 is located at the narrow end 9 of the tapered periodic poled lithium niobate waveguide, and the second semiconductor refrigerator (TEC) 8 is located at the wide end 10 of the tapered periodic poled lithium niobate waveguide; a top view of the narrow end 9 of the tapered periodic poled lithium niobate waveguide and the wide end 10 of the tapered periodic poled lithium niobate waveguide is shown in FIG. Figure 2 , the schematic diagram of the tapered periodically polarized lithium niobate waveguide is shown in Figure 3 .

[0065] The thickness of the silicon dioxide substrate 2 is 0.5um, the width of the narrow end 9 of the tapered periodically poled lithium niobate waveguide is 7.5um, the width of the wide end 10 of the tapered periodically poled lithium niobate waveguide is 13um, and the height is 9um. The polarization period of the tapered periodically poled lithium niobate waveguide is 18um, and the total waveguide length of the tapered periodically poled lithium niobate waveguide is 45mm.

[0066] Example 2

[0067] This embodiment proposes a bandwidth based on periodically poled lithium niobate waveguide, with a temperature tunable range of 30°C-150°C, a wavelength tunable range covering the C band 1530nm~1565nm, and an output spectrum range of 765nm~782.5nm. The details are as follows:

[0068] The C-band is incident on the tapered periodically poled lithium niobate waveguide (PPLN) 3 crystal in the bandwidth tunable frequency converter obtained in Example 1. The temperature of the first semiconductor refrigerator (TEC) 7 at the narrow end 9 of the tapered periodically poled lithium niobate waveguide is set to 150°C, and the temperature of the second semiconductor refrigerator (TEC) 8 at the wide end 10 of the tapered periodically poled lithium niobate waveguide is set to 30°C. Through the temperature control of the TEC at both ends of the waveguide, the temperature of the entire waveguide will present a gradient, and the temperature at each location of the waveguide will be different, ranging from 30°C to 150°C. Then, the 1530nm light wave will be frequency doubled at a location near the wide end 10 of the tapered periodically poled lithium niobate waveguide, and the 1565nm light wave will be frequency doubled at a location near the narrow end 9 of the tapered periodically poled lithium niobate waveguide. Light waves with wavelengths between 1530nm and 1565nm will be frequency doubled at different locations of the waveguide. That is, in this embodiment, the temperature bandwidth is 120°C and the wavelength bandwidth is 35nm. The relationship between the wave vector mismatch and the waveguide width is shown in Figure 4 , Figure 5 .

[0069] Example 3

[0070] This embodiment proposes a bandwidth tunable frequency converter based on periodically poled lithium niobate waveguide, with a temperature adjustable range of 30°C to 150°C, a wavelength tunable range of 1546nm to 1550nm, and an output spectrum range of 773nm to 775nm. The details are as follows:

[0071] The difference between this embodiment and embodiment 2 is that the temperature of embodiment 1 is reversed, that is, the TEC temperature at the narrow end 9 of the tapered periodic poled lithium niobate waveguide is 30°C, and the TEC temperature at the wide end 10 of the tapered periodic poled lithium niobate waveguide is 150°C, then the 1546nm~1550nm band can be doubled, and the tunable bandwidth is reduced. That is, in this embodiment, the temperature bandwidth is 120°C and the wavelength bandwidth is 4nm. The relationship between the wave vector mismatch and the waveguide width is shown in Figure 6 , Figure 7 .

[0072] Example 4

[0073] This embodiment proposes a bandwidth tunable frequency converter based on periodically poled lithium niobate waveguide. When the TEC temperature at both ends is the same, both are 100°C, the wavelength tunable range is 1541nm~1557nm, and the output spectrum range is 770.5nm~778.5nm. The details are as follows:

[0074] The difference between this embodiment and embodiment 2 is that the temperature at both ends of the waveguide is set to 100°C, that is, under constant temperature conditions, the light wave with a wavelength of 1541nm to 1557nm can be doubled, and the tunable bandwidth is 16nm. The relationship between the wave vector mismatch and the waveguide width is shown in Figure 8 , Fig. 9 .

[0075] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A bandwidth tunable frequency converter, characterized in that: The bandwidth tunable frequency converter comprises a substrate, a tapered periodically polarized lithium niobate waveguide, a cover layer, a silica gel layer, a copper layer and a semiconductor refrigerator which are sequentially stacked; The tapered periodically poled lithium niobate waveguide has a first tapered side surface and a second tapered side surface which are parallel to each other; The first tapered side and the second tapered side each have a narrow end and a wide end; The narrow end width is d1,7.5≤d1≤7.52μm; The width of the wide end is d2, 12.7≤d2≤13μm; 5.18≤d2-d1≤5.5; The semiconductor refrigerator comprises a first semiconductor refrigerator and a second semiconductor refrigerator; The first semiconductor refrigerator is used to adjust the temperature of the narrow end of the tapered waveguide; The second semiconductor refrigerator is used to adjust the temperature of the wide end of the tapered waveguide.

2. The bandwidth tunable frequency converter according to claim 1, characterized in that: A vertical distance between the first tapered side surface and the second tapered side surface is 9-9.5 μm.

3. The bandwidth tunable frequency converter according to claim 1, characterized in that: The polarization period of the tapered periodically poled lithium niobate waveguide is 18 to 18.2 μm, and the total length of the waveguide is 43 to 45 mm.

4. The bandwidth tunable frequency converter according to claim 1, characterized in that: The temperature of the semiconductor refrigerator can be adjusted within a range of 30 to 150°C.

5. The bandwidth tunable frequency converter according to claim 1, characterized in that: The substrate comprises a silicon dioxide layer I; The tapered periodically poled lithium niobate waveguide is located between the silicon dioxide layer I and the cover layer.

6. The bandwidth tunable frequency converter according to claim 5, characterized in that: The substrate also includes a lithium tantalate crystal layer; The silicon dioxide layer I is located between the lithium tantalate crystal layer and the tapered periodically poled lithium niobate waveguide.

7. The bandwidth tunable frequency converter according to claim 5, characterized in that: The thickness of the silicon dioxide layer I is 0.5 to 1 μm; The covering layer is a silicon dioxide layer II; the thickness of the silicon dioxide layer II is 1 to 10 μm; The thickness of the silica gel layer is 1 to 20 μm; The copper layer has a thickness of 1 to 30 μm.

8. A control method for a bandwidth tunable frequency converter according to any one of claims 1 to 7, characterized in that: The light wave propagates in the periodically poled lithium niobate waveguide, and the desired wavelength is output by adjusting the temperature of the periodically poled lithium niobate waveguide.

9. The control method according to claim 8, characterized in that: The wavelength band of the light wave is C-band.

10. The control method according to claim 8, characterized in that: The light wave is incident on the periodically poled lithium niobate waveguide, and the temperature of the narrow end and the temperature of the wide end of the periodically poled lithium niobate waveguide are controlled by the semiconductor refrigerator to output the wavelength.

11. The control method according to claim 10, characterized in that: The temperature of the narrow end is 30 to 150°C; The temperature of the wide end is 30-150°C.

12. Application of the bandwidth tunable frequency converter according to any one of claims 1 to 7 or the control method according to any one of claims 8 to 11 in biomedical research, environmental monitoring, optical precision measurement, material processing, and national defense security.

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