WO2023077834A1 - Multi-band acousto-optic tuned filter - Google Patents

Abstract

Disclosed is a multi-band acousto-optic tuned filter. The acousto-optic filter consists of an acousto-optic waveguide and an optical mode beam splitter. In the acousto-optic waveguide part, a reconfigurable multimode waveguide grating is formed by means of exciting one or more acoustic modes, causing an input optical mode to be converted into another optical mode in a same direction or in a reverse direction in a phase-matched wave band; the two optical modes are then separated by the optical mode beam splitter, thereby achieving band-pass or band-stop filtering. The method has advantages such as low power consumption, high tuning speed, and an ultra-large tuning range. A synthesized time-varying waveguide grating can be formed by means of exciting propagation of multiple sound waves having different frequencies, thereby achieving independent switching of multiple common-path wave bands and filtering spectral type modulation.

Description

Multiband Acousto-Optic Tunable Filter technical field

The invention belongs to the fields of optical communication, optical interconnection, optical sensing technology, etc., and is suitable for tunable filters in systems such as wavelength division multiplexing optical communication, optical interconnection, spectral analysis, and adjustable light sources, and especially relates to multi-band acoustic Optical tuning filter.

Background technique

Tunable photonic filters are extremely important reconfigurable photonic devices, which can be widely used in wavelength division multiplexing optical communication and optical interconnection, spectral analysis, tunable light source, etc. In particular, the large-capacity wavelength division multiplexing optical communication network is one of the basic structures of the Internet and the Internet of Things. Tunable photonic integrated filters are the key to flexible reconfiguration of wavelength division multiplexing optical networks, and the physical basis of elastic optical networks that realize real-time dynamic optimization of network structure and bandwidth allocation. How to achieve a larger tuning range and adjustable filter spectrum etc. are facing important challenges and have very important research significance.

At present, thermo-optic modulation is a common implementation scheme of tunable photonic integrated filters, and its device structure mainly includes arrayed waveguide gratings, Mach-Zehnder interferometers, microring resonators, and waveguide gratings. Although great progress has been made in recent years, the mechanism of thermo-optic regulation determines that the tuning range of a single device is generally only 10–20 nm at reasonable device power consumption and operating temperature. The actual dense WDM system occupies the bands of C (1530–1565nm) and L (1565–1625nm), while the sparse WDM system can occupy the band of hundreds of nanometers (1270–1610nm). A range that is unattainable with thermo-optical tuned filters. In addition, key indicators such as tuning speed (a few microseconds) and power consumption (tens of milliwatts and above) of existing typical thermo-optical devices still need to be fully broken through.

The guided wave acousto-optic device provides a new idea to break through this problem. From the point of view of classical physics, the essence of guided wave acousto-optic modulation is to form a reconfigurable multimode waveguide grating by exciting one or more acoustic modes to achieve flexible modulation of light wave modes. Electro-optic, thermo-optic, and magneto-optical control methods are completely different, and they have very unique advantages in realizing a variety of reconfigurable photonic integrated devices.

Contents of the invention

In view of the problems existing in the background technology, the object of the present invention is to provide a multi-band acousto-optic tuning filter, which can realize band-pass or band-stop filtering, and has the advantages of low power consumption, high tuning speed, and super large tuning range. And it can form a synthetic time-varying waveguide grating by exciting multiple sound waves of different frequencies to propagate together, so as to realize independent switching of multiple common-channel wavebands and filter spectrum control.

The technical scheme adopted in the present invention is:

A multi-band acousto-optic tuning filter, including an acousto-optic waveguide and an optical mode beam splitter, the optical mode A is input into the acousto-optic waveguide, and the acoustic mode is excited at the same time, and a reconfigurable multi-mode is formed by exciting one or more acoustic modes. The mode waveguide grating makes the input optical mode A convert in the same direction or in the opposite direction in the optical band of the acousto-optic phase matching. After being split by the optical mode beam splitter, the output band-stop filtered optical mode A and band-pass filter Optical Mode B.

Another multi-band acousto-optic tuning filter includes an acousto-optic waveguide and an optical mode beam splitter. The optical mode A is output to the acousto-optic waveguide through the optical mode beam splitter to excite the acoustic mode, and by exciting one or more acoustic modes A reconfigurable multimode waveguide grating is formed, so that the input optical mode A is reversely converted in the optical band of the acousto-optic phase matching, and the output band-stop filtered optical mode A is output through the optical mode beam splitter. Optical Mode B.

The acoustic mode is a single frequency or multiple different frequencies. When multiple acoustic modes of different frequencies propagate together in the acousto-optic waveguide, a synthetic time-varying waveguide grating is formed, thereby realizing independent switching of multiple common-channel wavebands And filter spectrum control.

The acousto-optic waveguides and optical mode beam splitters may be based on piezoelectric or non-piezoelectric materials.

The optical mode A is converted in the same direction or in the opposite direction in the optical waveband of the acousto-optic phase matching, and the conversion of different polarization modes or modes of different orders is used. The efficiency of optical mode conversion is the same as that excited in the acousto-optic waveguide. related to the type of acoustic mode.

SV ₁ acoustic mode has high conversion efficiency to TE ₀ /TM ₀ , and SH ₀ acoustic mode has high conversion efficiency to TE ₀ /TE ₁ .

The length of the acousto-optic waveguide decreases with the increase of the acoustic wave power, and increases with the increase of the acoustic wave loss.

When multiple acoustic modes of different frequencies propagate together in the acousto-optic waveguide, the acoustic modes are at equal or non-equal frequency intervals to synthesize periodic or aperiodic sound waves.

The control of the filter spectrum type adjusts the frequency interval of the acoustic mode to realize the adjustment of the wavelength interval of the filter band, and can generate a flat-top filter spectrum type.

The linewidth of the bandpass filter can be narrowed by cascading the input end of the acousto-optic waveguide and the output end of the optical mode beam splitter multiple times, wherein the output end of the odd-numbered level unit is the output of the optical mode B, and the even-numbered level unit The output terminal is the optical mode A output.

The beneficial effects that the present invention has are:

The invention has simple process and low cost. The multi-waveband acousto-optic tuning filter of the present invention can realize band-pass or band-stop filtering, and has the advantages of low power consumption, high tuning speed, super-large tuning range, etc.; and can transmit together by exciting multiple sound waves of different frequencies to form a composite time Variable waveguide grating, so as to realize the independent switching of multiple common channel bands and filter spectrum control.

Description of drawings

Figure 1 is a schematic diagram of the transmission of the action of a single-frequency acoustic mode using a multi-band acousto-optic tuning filter in the present invention, in which the input optical mode A in the figure is converted into another optical mode B in the same direction.

Fig. 2 is a schematic diagram of the transmission of the action of the single-frequency acoustic mode using a multi-band acousto-optic tuning filter in the present invention, in which the input optical mode A is reversely converted into another optical mode B.

Fig. 3 is a schematic diagram of the transmission of multi-frequency acoustic modes using multi-band acousto-optic tuning filters according to the present invention. In the figure, the input optical mode A is transformed into another optical mode B in the same direction.

Fig. 4 is the optical mode TE ₀ in the lithium niobate suspended waveguide in the embodiment of the present invention.

Fig. 5 is the optical mode TM ₀ in the lithium niobate suspended waveguide in the embodiment of the present invention.

Fig. 6 is the optical mode TE ₁ in the lithium niobate suspended waveguide in the embodiment of the present invention.

Fig. 7 is the acoustic mode SV ₁ in the lithium niobate suspended waveguide in the embodiment of the present invention.

Fig. 8 is the acoustic mode SH ₀ in the lithium niobate suspended waveguide in the embodiment of the present invention.

Fig. 9 is a single-band filter spectrum pattern of TE ₀ /TM ₀ co-transformation in an embodiment of the present invention.

Fig. 10 is a dual-frequency acoustic power waveform of co-transformed TE ₀ /TM ₀ in an embodiment of the present invention.

Fig. 11 is a dual-band filter spectrum pattern of TE ₀ /TM ₀ co-transformed in an embodiment of the present invention.

Fig. 12 is a three-frequency acoustic power waveform of co-transformed TE ₀ /TM ₀ in an embodiment of the present invention.

Fig. 13 is a three-band filter spectrum pattern of co-transformation of TE ₀ /TM ₀ in the embodiment of the present invention.

Fig. 14 is the power waveform at the midpoint of the five-frequency sound wave period transformed in the same direction by TE ₀ /TM ₀ in the embodiment of the present invention.

Fig. 15 is a five-band synthesized flat-top filter spectrum pattern of TE ₀ /TM ₀ co-transformed in an embodiment of the present invention.

Fig. 16 is the power waveform at the first and last moments of the five-frequency sound wave period transformed in the same direction by TE ₀ /TM ₀ in the embodiment of the present invention.

Fig. 17 is a five-band filter spectrum pattern of co-transformation of TE ₀ /TM ₀ in the embodiment of the present invention.

Fig. 18 is a single-band general filter spectrum pattern of reverse conversion of TE ₀ /TE ₁ in the embodiment of the present invention.

Detailed ways

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

As shown in Figures 1 and 3, a multi-band acousto-optic tuning filter includes an acousto-optic waveguide and an optical mode beam splitter. The optical mode A is input into the acousto-optic waveguide, and the acoustic mode is excited at the same time. By exciting one or more Two acoustic modes form a reconfigurable multimode waveguide grating, so that the input optical mode A is converted in the same direction in the optical band of the acousto-optic phase matching. After being split by the optical mode beam splitter, the output band-stop filtered optical mode A and bandpass filtered optical mode B. Among them, Figure 1 shows a single frequency, and Figure 3 shows a multi-frequency acoustic mode.

As shown in Figure 2, another multi-band acousto-optic tuning filter includes an acousto-optic waveguide and an optical mode beam splitter. The optical mode A is output to the acousto-optic waveguide through the optical mode beam splitter to excite the acoustic mode. One or more acoustic modes form a reconfigurable multimode waveguide grating, so that the input optical mode A is reversely converted in the optical band of the acousto-optic phase matching, and the output band-stop filtered optical mode A is split by the optical mode tor output bandpass filtered optical mode B.

Acousto-optic waveguides and optical mode beam splitters can be based on 400nm thickness x-cut thin-film lithium niobate wafers. The width of the waveguide is 0.8μm. Due to the characteristics of the existing lithium niobate etching process, there is a 30° angle between the side of the waveguide and the vertical direction. . The transmission direction of the waveguide is z. In order to enhance the acousto-optic interaction and reduce the acoustic loss, the acousto-optic waveguide is suspended in the air.

There are three optical modes in the acousto-optic waveguide, namely TE ₀ (Fig. 4), TM ₀ (Fig. 5), and TE ₁ (Fig. 6). In this embodiment, two examples are given for the way of realizing the mode conversion in the same direction through the acousto-optic interaction, and one example is given for the way of realizing the reverse mode conversion through the acousto-optic interaction, but the actual optional way is not limited to this. As shown in Figure 1, the first is the mutual conversion of TE ₀ and TM ₀ , and the corresponding acoustic mode is SV ₁ (Figure 7), and the optical mode beam splitter is used to separate TE ₀ and TM ₀ ; The two are the mutual transformation of TE ₀ and TE ₁ , and the corresponding acoustic mode is SH ₀ (Figure 8), and the optical mode beam splitter is used to separate TE ₀ and TE ₁ . By calculation, when the acoustic power is 0.1 mW, the length of complete conversion of TE ₀ and TM ₀ is about 389 μm, and the length of complete conversion of TE ₀ and TE ₁ is about 1063 μm. As shown in Figure 2, the mutual conversion of TE ₀ and TE ₁ is given, and the corresponding acoustic mode is SH ₀ (Figure 8). The conversion efficiency increases with the length of the acousto-optic waveguide, and the optical attenuation constant is about is 200m ^-1 .

Taking the co-directional conversion of TE ₀ /TM ₀ as an example, the specific calculation results of the filter spectrum type are given below.

As shown in Figure 1, the acoustic mode is a single frequency, TE ₀ is used as the input of optical mode A, SV ₁ is used as the excitation of the acoustic mode, the acoustic wave wavelength is 4.55 μm, assuming that the acoustic wave loss is negligible, the acoustic wave power is a constant value of 0.1 mW, after With a common transmission distance of 389μm, TE ₀ at the central wavelength of 1550nm is completely converted to TM ₀ , and then through the optical mode beam splitter, the output of TE ₀ realizes band-stop filtering, and the output of TM ₀ realizes band-pass filtering, and the band-pass filtering spectral type As shown in Figure 9. There is no additional loss at the center wavelength, the filter bandwidth is 16nm, and the sidelobe suppression ratio is about 10dB.

As shown in Figure 3, if the acoustic mode is set to multi-frequency, multi-band filter spectrum control can be realized. When the sound wave has dual frequencies at 76.5MHz intervals, the change of the sound wave power with the transmission distance is shown in Figure 10, which is a periodic change, and the filter spectrum type is shown in Figure 11, which is a dual-band filter; when the sound wave is

and

For the three frequencies at intervals, the change of the acoustic power with the transmission distance is shown in Figure 12, which is an aperiodic change, and the filter spectrum type is shown in Figure 13, which is a three-band filter. In particular, when the sound wave has five frequencies at intervals of 7 MHz, the transmission period of the sound wave is longer than the transmission length, and the filter spectrum has time-varying characteristics. For example, at the midpoint of the cycle, the acoustic spectrum type is shown in Figure 14, and the filter spectrum type is shown in Figure 15, which produces a five-band synthetic flat-top filter spectrum type; while at the beginning and end of the cycle, the acoustic wave spectrum type is shown in Figure 16. As shown, the filter spectrum type is shown in Figure 17, which produces a five-band general filter spectrum type.

Taking the inverse conversion of TE ₀ /TE ₁ as an example, the specific calculation results of the filter spectrum type are given below.

As shown in Figure 2, the acoustic mode is a single frequency, with TE ₀ as the input of optical mode A, SH ₀ as the excitation of the acoustic mode, the acoustic wave wavelength is 0.577μm, assuming that the acoustic wave loss is negligible, the acoustic wave power is a constant value of 1mW, after 10mm About 95% of the TE ₀ at the center wavelength of 1550nm is converted into TE ₁ , and the output of TE 0 realizes band-stop filtering, and the reflected _{TE 1 realizes} band-pass filtering through the output of the optical mode beam splitter, and the band-pass filtering spectrum The type is shown in Figure 18. The loss at the central wavelength is -0.25dB, and the filtering bandwidth is 3nm.

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention. Should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (10)

1. A multi-band acousto-optic tuning filter is characterized in that: it includes an acousto-optic waveguide and an optical mode beam splitter, the optical mode A is input into the acousto-optic waveguide, and the acoustic mode is excited at the same time, and is formed by exciting one or more acoustic modes The reconfigurable multimode waveguide grating enables the input optical mode A to be converted in the same direction in the optical band of the acousto-optic phase matching. After being split by the optical mode beam splitter, the output band-stop filtered optical mode A and the band-pass Filtered Optical Mode B.
2. A multi-band acousto-optic tuning filter is characterized in that it includes an acousto-optic waveguide and an optical mode beam splitter, the optical mode A is output to the acousto-optic waveguide through the optical mode beam splitter, and the acoustic mode is excited, and by exciting one or more Two acoustic modes form a reconfigurable multimode waveguide grating, so that the input optical mode A is reversely converted in the optical band of the acousto-optic phase matching, and the output band-stop filtered optical mode A passes through the optical mode beam splitter output band Pass-filtered optical mode B.
3. A multi-band acousto-optic tuning filter according to claim 1 or 2, characterized in that: the acoustic mode is a single frequency or a plurality of different frequencies, when the acoustic modes of a plurality of different frequencies are in the acousto-optic When co-propagating in the waveguide, a synthetic time-varying waveguide grating is formed, thereby realizing the independent switching of multiple co-channel wavebands and the control of the filter spectrum.
4. A multi-band acousto-optic tuning filter according to claim 1 or 2, characterized in that:

   The acousto-optic waveguides and optical mode beam splitters may be based on piezoelectric or non-piezoelectric materials.
5. A multi-band acousto-optic tuning filter according to claim 1 or 2, characterized in that:

   The optical mode A is converted in the same direction or in the opposite direction in the optical waveband of the acousto-optic phase matching, and the conversion of different polarization modes or modes of different orders is used. The efficiency of optical mode conversion is the same as that excited in the acousto-optic waveguide. related to the type of acoustic mode.
6. A multi-band acousto-optic tuning filter according to claim 5, characterized in that:

   SV ₁ acoustic mode has high conversion efficiency to TE ₀ /TM ₀ , and SH ₀ acoustic mode has high conversion efficiency to TE ₀ /TE ₁ .
7. A multi-band acousto-optic tuning filter according to claim 1 or 2, characterized in that:

   The length of the acousto-optic waveguide decreases with the increase of the acoustic wave power, and increases with the increase of the acoustic wave loss.
8. A multi-band acousto-optic tuning filter according to claim 3, characterized in that:

   When multiple acoustic modes of different frequencies propagate together in the acousto-optic waveguide, the acoustic modes are at equal or non-equal frequency intervals to synthesize periodic or aperiodic sound waves.
9. A multi-band acousto-optic tuning filter according to claim 8, characterized in that:

   The control of the filter spectrum type adjusts the frequency interval of the acoustic mode to realize the adjustment of the wavelength interval of the filter band, and can generate a flat-top filter spectrum type.
10. A multi-band acousto-optic tuning filter according to claim 1 or 2, characterized in that: the line width of the band-pass filter can be adjusted by the input end of the acousto-optic waveguide and the output end of the optical mode beam splitter Multiple cascading to narrow, where the output of the odd-numbered units is the optical mode B output, and the output of the even-numbered units is the optical mode A output.

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