Narrow-band tunable optical filter

Abstract

The invention provides a narrow-band adjustable optical filter, which relates to the technical field of optical fiber communication, combines an optical waveguide technology with a free space optical system, and utilizes a multi-port optical waveguide chip to guide an optical signal to repeatedly transmit back and forth in a free space optical path so as to realize multiple cyclic filtering, so that the filtering line width can be effectively compressed; tuning and narrow-band filtering of incident target signal light are achieved in a wide tuning range, an extremely narrow filtering line width is obtained, the filtering line width and the wavelength tuning range can be considered, meanwhile, the narrow-band filtering characteristic and the ultra-wide tuning range are achieved, the constraint problem between the tuning range and the filtering line width is solved, and the spectral resolution of the filter is improved. Moreover, the filter highly integrates the optical fiber array, the optical waveguide chip and the free space optical system, and is simple and compact in structure. The optical waveguide chip in the filter serves as a core device, the size and complexity of the filter are reduced, and the stability and reliability of the filter are improved.

Description

Technical Field

[0001] This invention relates to the field of optical fiber communication technology, and in particular to a narrowband tunable optical filter. Background Technology

[0002] Optical fiber communication technology can transmit tens to over a hundred wavelengths in a single optical fiber, a technique known as dense wavelength division multiplexing (DWDM). DWDM transmission systems require optical performance monitoring (OPM) equipment to monitor the optical signal-to-noise ratio (OSNR) in the fiber optic link in real time. As the demand for bandwidth in optical fiber communication networks grows, DWDM technology, previously used in backbone optical networks, is being extended to metropolitan area optical networks. With the expansion of DWDM applications, the demand for OPM is rapidly increasing.

[0003] There are two main technical solutions for Optical Probe Mining (OPM). The first involves using a narrowband tunable optical filter (TOF) to sequentially filter out each wavelength and then measuring the optical power to obtain the OSNR. The second involves mixing a tunable laser with the signal light and using heterodyne detection technology to obtain the power of each wavelength, thus obtaining the OSNR. Because the second solution is very expensive, the industry typically uses the first solution. The TOF in the first solution usually employs a free-space optical system, using micromirrors in a micro-electro-mechanical system (MEMS) to tune the transmission wavelength.

[0004] However, Time-of-Flight (TOF) free-space optical systems based on MEMS micromirrors are limited by the mirror size and deflection angle of the MEMS micromirrors, resulting in a trade-off between wavelength tuning range and filter linewidth. For example, in the C-band of fiber optic communication, if a wavelength tuning range of 1525-1567 nm is required, the filter linewidth can only reach about 0.2 nm. To further reduce the filter linewidth, the requirement for wavelength tuning range must be reduced, making it impossible to simultaneously achieve both filter linewidth and wavelength tuning range. Summary of the Invention

[0005] This invention provides a narrowband tunable optical filter to address the shortcomings of related technologies.

[0006] This invention provides a narrowband tunable optical filter, comprising: an optical fiber array, an optical waveguide chip, and a free-space optical system. The first side of the optical fiber array includes an input end and an output end. The second side of the optical fiber array is connected to the first side of the optical waveguide chip, and the second side of the optical waveguide chip is connected to the free-space optical system. The optical waveguide chip includes two first-type optical waveguides and multiple second-type optical waveguides. The first-type optical waveguides each have a port on the first side and the second side of the optical waveguide chip, and the second-type optical waveguides each have two ports on the second side of the optical waveguide chip. The target optical signal enters the fiber array and the optical waveguide chip sequentially through the input terminal, and is incident on the free space optical system through the port on the second side of the optical waveguide chip for filtering. Based on the free space optical system and each of the second type of optical waveguides, the signal is transmitted back and forth multiple times between the optical waveguide chip and the free space optical system to achieve multiple filtering before being output through the output terminal.

[0007] According to the present invention, a narrowband adjustable optical filter is provided, wherein the free-space optical system includes a collimating lens, a grating, and a microelectromechanical system (MEMS) micromirror, and the deflection angle of the MEMS micromirror is adjustable; The collimating lens is used to collimate the light signal incident on the free space optical system. The grating is used to split the aligned optical signal; The micromirror of the microelectromechanical system is used to reflect a specific wavelength of light signal from the split light signal, and the reflected light signal is output after passing through the grating and the collimating lens in sequence.

[0008] According to the present invention, a narrowband adjustable optical filter is provided, wherein the optical waveguide chip is located on the front focal plane of the collimating lens, and the micromirror of the microelectromechanical system is located at one focal length of the collimating lens.

[0009] According to the present invention, a narrowband adjustable optical filter is provided, wherein the micromirror of the microelectromechanical system is driven by a motor to adjust the deflection angle.

[0010] According to the present invention, a narrowband adjustable optical filter is provided, wherein the collimating lens includes one of a spherical lens, an aspherical lens, and a cemented doublet lens.

[0011] According to the present invention, in a narrowband tunable optical filter, the number of ports on the second side of the optical waveguide chip is twice the number of times the target optical signal is filtered.

[0012] According to the present invention, a narrowband tunable optical filter is provided, wherein the second type of optical waveguide is an arc-shaped optical waveguide, and the bending radius of the second type of optical waveguide is greater than the minimum bending radius, wherein the minimum bending radius is determined based on the refractive index difference between the core layer and the non-core layer of the second type of optical waveguide.

[0013] According to the present invention, a narrowband tunable optical filter is provided in which the cross angle between the waveguides inside the optical waveguide chip is greater than 10°.

[0014] According to the present invention, a narrowband tunable optical filter is provided in which the port spacing on the second side of the optical waveguide chip is greater than twice the waveguide width.

[0015] According to the present invention, in a narrowband tunable optical filter, the ports on the first and second sides of the optical waveguide chip are both tapered.

[0016] The narrowband tunable optical filter provided by this invention combines optical waveguide technology with a free-space optical system. It utilizes a multi-port optical waveguide chip to guide the optical signal through multiple round trips in a free-space optical path to achieve multiple cyclic filtering. This effectively compresses the filter linewidth, enabling tuning and narrowband filtering of the incident target signal light within a wide tuning range. It achieves an extremely narrow filter linewidth, balancing both linewidth and wavelength tuning range, and simultaneously possesses narrowband filtering characteristics and an ultra-wide tuning range. This solves the constraint problem between tuning range and filter linewidth, improving the filter's spectral resolution. Furthermore, this filter highly integrates the fiber array, optical waveguide chip, and free-space optical system, resulting in a simple and compact structure. The optical waveguide chip, as the core component, replaces the complex spatial optical path in traditional multiple filtering systems, reducing the filter's size and complexity, improving its stability and reliability, and meeting the requirements for small filter size. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this invention or related technologies, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is one of the structural schematic diagrams of a traditional free-space broadband tunable optical filter.

[0019] Figure 2 This is a schematic diagram showing the variation of the 3dB linewidth of a traditional free-space wide-spectrum tunable optical filter with the radius of the spot on the diffraction grating.

[0020] Figure 3This is the second schematic diagram of a traditional free-space broadband tunable optical filter.

[0021] Figure 4 This is one of the structural schematic diagrams of the narrowband tunable optical filter provided by the present invention.

[0022] Figure 5 This is a schematic diagram of the structure of an optical waveguide chip with 2×10 ports in the narrowband tunable optical filter provided by the present invention.

[0023] Figure 6 This is the second schematic diagram of the narrowband tunable optical filter provided by the present invention.

[0024] Figure 7 This is a schematic diagram of the shape of the two ports on both sides of the optical waveguide chip in the narrowband tunable optical filter provided by the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0026] In the prior art, a traditional free-space broadband tunable optical filter, such as Figure 1 As shown, the system includes a dual-fiber collimator 011, a diffraction grating 014, and a MEMS micromirror 015. During operation, the broadband optical signal input to the input fiber of the dual-fiber collimator 011 is spatially wavelength-separated by the diffraction grating 014; a specific wavelength is selected from the separated spectrum using the MEMS micromirror 015; and the selected wavelength is reflected back to the output fiber of the dual-fiber collimator 011, achieving tunable narrowband filtering. The dual-fiber collimator 011 includes dual-fiber ferrules 012 and a collimating lens 013.

[0027] The filter linewidth depends on the spot size on the diffraction grating 014, and the relationship between the two is as follows: Figure 2 As shown. Figure 2 The horizontal axis represents the spot radius on the diffraction grating 014, in millimeters (mm), and the vertical axis represents the 3dB bandwidth, in nanometers (nm).

[0028] from Figure 2It can be seen that to obtain a narrow filter linewidth, the beam needs to form a sufficiently large spot on the grating; therefore, the light exiting from the input fiber must first be beam-expanded. However, due to process limitations, the mirror size of the MEMS micromirror is finite, and the beam diffracted by the diffraction grating must be compressed before reaching the MEMS micromirror. Therefore, a beam-expanding and compression system is needed, which will increase the size of the filter. Due to the size limitation of the filter, Figure 1 The filter can only achieve a 3dB linewidth of 1~2nm, and the spectral resolution of the filter is low.

[0029] In the prior art, another type of conventional free-space broadband tunable optical filter, such as Figure 3 As shown, the system includes dual fiber optic ferrules 021, a mirror 022, a first lens 023, a diffraction grating 024, a second lens 025, a third lens 026, and a MEMS micromirror 027. Among these, the first lens 023, the second lens 025, and the third lens 026 are all telephoto lenses. Based on the principle, a larger spot size helps improve the spectral resolution of the filter, thereby obtaining a narrower filter linewidth. To couple the optical signal to the finite-sized MEMS micromirror 027, Figure 3 The filter employs a telephoto lens to increase the size of the light spot on the diffraction grating 024, and compresses the spot size through beam transformation to match the mirror surface of the MEMS micromirror 027. However, while compressing the spot size, the lens also increases the angular dispersion generated by the diffraction grating 024, resulting in a more significant spatial broadening of different wavelengths of light signals on the MEMS micromirror 027. Since the deflection angle of the MEMS micromirror 027 itself is limited, it cannot cover the wider wavelength range resulting from the increased angular dispersion, ultimately limiting the effective tuning range of the filter.

[0030] To balance the filter linewidth and wavelength tuning range, this embodiment of the invention provides a narrowband tunable optical filter. Figure 4 This is a schematic diagram of the structure of a narrowband tunable optical filter provided in an embodiment of the present invention, as shown below. Figure 4 As shown, the narrowband tunable optical filter includes: an optical fiber array 1, an optical waveguide chip 2, and a free-space optical system 3. The first side of the optical fiber array 1 includes an input end and an output end. The second side of the optical fiber array 1 is connected to the first side of the optical waveguide chip 2, and the second side of the optical waveguide chip 2 is connected to the free-space optical system 3. The optical waveguide chip 2 includes two first-type optical waveguides and multiple second-type optical waveguides. The first-type optical waveguides each have one port on the first side and the second side of the optical waveguide chip 2, and the second-type optical waveguides each have two ports on the second side of the optical waveguide chip 2. The target optical signal enters the fiber array 1 and the optical waveguide chip 2 sequentially through the input end. It is then incident on the free space optical system 3 through the port on the second side of the optical waveguide chip 2 for filtering. Based on the free space optical system 3 and each type II optical waveguide, the signal undergoes multiple round trips between the optical waveguide chip 2 and the free space optical system 3 to achieve multiple filterings before being output through the output end.

[0031] Specifically, in this embodiment of the invention, the fiber array 1 is an array composed of multiple optical fibers. The first side of the fiber array 1 is the input end of a narrowband tunable optical filter. The second side of the fiber array 1 is connected to the first side of the optical waveguide chip 2. For example, the connection can be achieved by coupling and bonding, or by fiber fusion splicing. No specific limitation is made here.

[0032] The input target optical signal can be coupled to the optical waveguide chip 2 via the fiber optic array 1, thus enabling the transmission of the target optical signal. Here, the first side of the fiber optic array 1 includes at least one input end and one output end, meaning the fiber optic array 1 contains at least two optical fibers. The target optical signal is the input optical signal of a narrowband tunable optical filter, and can be a broadband optical signal.

[0033] The optical waveguide chip 2 can be a planar optical waveguide or an integrated optical waveguide; no specific limitation is made here. The optical waveguide chip 2 can be made of materials such as silicon-based silicon dioxide or indium phosphide.

[0034] The optical waveguide chip 2 contains multiple optical waveguides. The number of optical waveguides can be determined based on the number of filters achieved by the narrowband tunable optical filter. The cross-section of each optical waveguide can be flexibly selected according to packaging requirements, such as rectangular, square, circular, or elliptical shapes.

[0035] The internal structure of the optical waveguide chip 2 may include two first-type optical waveguides and multiple second-type optical waveguides. The first-type optical waveguides are those that penetrate the optical waveguide chip 2, meaning that each first-type optical waveguide has a port on both the first and second sides of the optical waveguide chip 2. The second-type optical waveguides are those whose ports are all located on the second side of the optical waveguide chip 2, meaning that each second-type optical waveguide has two ports on the second side of the optical waveguide chip 2.

[0036] One of the two type-1 optical waveguides serves as the input waveguide, and the other as the output waveguide. The target optical signal is incident on the input waveguide via fiber array 1, and then enters the free-space optical system for filtering via the port on the second side of the input waveguide chip 2. The transmission direction of the filtered signal of the specified wavelength can be controlled by the free-space optical system, exiting from the free-space optical system and entering the type-2 optical waveguide on the second side of the optical waveguide chip 2. After multiple round trips between the optical waveguide chip 2 and the free-space optical system 3 to achieve multiple filtering operations, the signal is output through the output terminal on the first side of fiber array 1. At this point, the output optical signal is the optical signal obtained after multiple filtering operations.

[0037] In this embodiment of the invention, the free-space optical system can achieve narrowband filtering characteristics and may include a filtering component. The filtering component performs wavelength selection and filtering on the incident light signal to obtain a filtered signal of a specific wavelength within the target tuning band and controls the transmission direction of the filtered signal.

[0038] Understandably, in the process of multiple filtering steps, the optical waveguide chip provides the physical structure for the implementation of multiple filtering steps, while the free-space optical system provides the optical path conversion and filtering operations. Therefore, by combining the optical waveguide chip and the free-space optical system, the bandwidth of the target signal light can be further compressed, resulting in narrower filtering characteristics.

[0039] Taking a narrowband tunable optical filter with a filtering order of N=5 as an example, the second side of the optical waveguide chip 2 can be configured with 10 ports, such as... Figure 5 As shown, the left side is the first side of the optical waveguide chip 2, and the right side is the second side of the optical waveguide chip 2. The internal structure of the optical waveguide chip includes two first-type optical waveguides and four second-type optical waveguides. The first-type optical waveguides are the input optical waveguide 21 and the output optical waveguide 22, and the second-type optical waveguides are the first optical waveguide 23, the second optical waveguide 24, the third optical waveguide 25, and the fourth optical waveguide 26.

[0040] The first side of the optical waveguide chip 2 may include a first port 211 of the input optical waveguide 21 and a first port 212 of the output optical waveguide 22. After the target optical signal is input to the input end of the fiber array 1, it is transmitted through the fiber array 1 and then incident on the first port 211 of the input optical waveguide 21, and is first incident on the free space optical system 3 from the second port 225 of the input optical waveguide 21.

[0041] The free-space optical system 3 performs a first filtering on the first incident light signal and controls the transmission angle of the first filtered signal so that the first filtered signal enters the first optical waveguide 23 from the first port 226 and is incident on the free-space optical system 3 for the second time from the second port 221 of the first optical waveguide 23.

[0042] The free-space optical system 3 performs a second filtering on the second incident light signal and controls the transmission angle of the second filtered signal so that the second filtered signal enters the second optical waveguide 24 from the first port 230 and is incident on the free-space optical system 3 for the third time from the second port 223 of the second optical waveguide 24.

[0043] The free-space optical system 3 performs a third filtering on the third incident light signal and controls the transmission angle of the third filtered signal so that the third filtered signal enters the third optical waveguide 25 from the first port 228 and is incident on the free-space optical system 3 for the fourth time from the second port 222 of the third optical waveguide 25.

[0044] The free-space optical system 3 performs a fourth filtering on the fourth incident optical signal and controls the transmission angle of the fourth filtered signal so that the fourth filtered signal enters the fourth optical waveguide 26 from the first port 229 and is incident on the free-space optical system 3 for the fifth time from the second port 224 of the fourth optical waveguide 26.

[0045] The free-space optical system 3 performs a fifth filtering on the fifth incident light signal and controls the transmission angle of the fifth filtered signal so that the fifth filtered signal enters the output optical waveguide 22 from the second port 227 and exits from the first port 212 of the output optical waveguide 22.

[0046] The narrowband tunable optical filter provided in this embodiment of the invention includes an optical fiber array, an optical waveguide chip, and a free-space optical system connected in sequence. This filter combines optical waveguide technology with a free-space optical system, utilizing a multi-port optical waveguide chip to guide the optical signal through multiple round trips in the free-space optical path to achieve multiple cyclic filtering. This effectively compresses the filter linewidth, achieving tuning and narrowband filtering of the incident target signal light within a wide tuning range, resulting in an extremely narrow filter linewidth. It balances filter linewidth and wavelength tuning range, possessing both narrowband filtering characteristics and an ultra-wide tuning range, thus solving the constraint problem between tuning range and filter linewidth and improving the filter's spectral resolution. Furthermore, this filter highly integrates the optical fiber array, optical waveguide chip, and free-space optical system, resulting in a simple and compact structure. The optical waveguide chip, as the core component, replaces the complex spatial optical path in traditional multiple filtering systems, reducing the filter's size and complexity, improving its stability and reliability, and meeting the small-size requirements of the filter.

[0047] Based on the above embodiments, such as Figure 6 As shown, the free space optical system 3 includes a collimating lens 31, a grating 32, and a MEMS micromirror 33, the deflection angle of which is adjustable.

[0048] Collimating lens 31 is used to collimate the light signal incident on the free space optical system 3; The grating 32 is used to split the aligned optical signal; MEMS micromirror 33 is used to reflect a specific wavelength of light signal in the split light signal, and the reflected light signal is output after passing through grating 32 and collimating lens 31 in sequence.

[0049] Specifically, the collimating lens 31 is used to collimate the divergent light signal incident on the free space optical system 3 into parallel light, so as to ensure that the beam can accurately pass through the subsequent grating 32 and MEMS micromirror 33.

[0050] The filtering components in the free-space optical system may include a grating 32 and a MEMS micromirror 33. The grating 32 may be a transmission phase diffraction grating, and its grating density may be selected according to the working wavelength. For example, the grating grating grating density may be selected as 940 lines / mm.

[0051] It is used to disperse and separate light signals incident on or collimated into a free-space optical system, spreading light signals of different wavelengths at different diffraction angles. In addition, grating 32 can also combine the light emitted from the free-space optical system.

[0052] According to the diffraction characteristics of the grating, the optical signals from each port on the second side of the optical waveguide chip 2 have different diffraction angle distribution ranges. Only the diffraction angle of a certain sub-band of the beam is distributed within the tuning range of the MEMS micromirror 33. This sub-band is called the target tuning band.

[0053] Among the diffracted beams dispersed by the grating 32, the beam directly incident on the MEMS micromirror 33 exhibits the highest coupling efficiency. In other beams dispersed differently from those directly incident, the coupling efficiency decreases because the reflection direction deviates from the optimal reception direction at the output port. Therefore, the narrowband filtering characteristic curve of the narrowband tunable optical filter in this embodiment will exhibit a curve with high transmittance at the center wavelength, and symmetrically distributed transmittance on both sides gradually decreasing with increasing distance from the center wavelength.

[0054] The MEMS micromirror 33 can reflect a specific wavelength of light within the target tuning band of the split light signal as a filtered signal to the grating 32, and then output it to the second type of optical waveguide in the optical waveguide chip 2 after passing through the collimating lens 31. Multiple round trips can be made between the optical waveguide chip 2 and the free-space optical system 3 via the second type of optical waveguide, thereby achieving narrowband filtering characteristics.

[0055] The linewidth of the tunable optical filter is related to the diameter of the light spot incident on the grating 32; the larger the diameter of the light spot incident on the grating 32, the narrower the linewidth. Theoretical analysis and experimental verification show that in order to compress the linewidth to below 0.2 nm, the diameter of the light spot incident on the grating 32 must be greater than 3 mm. In this embodiment of the invention, by using the optical waveguides in the optical waveguide chip 2 to allow the optical signal to be transmitted multiple times in free space, narrow linewidth filtering below 0.2 mm can be achieved.

[0056] The deflection angle of the MEMS micromirror 33 can be controlled by changing the voltage or current through an external driving circuit, thereby altering the angle of reflected light and achieving wavelength selection. By precisely controlling the deflection angle of the MEMS micromirror 33, it can be made to reflect only light signals of a specific wavelength at a specific reflection angle.

[0057] In this embodiment of the invention, by using gratings and MEMS micromirrors as filtering components, not only can the narrowband filtering characteristics of the filter be realized, but also the wavelength can be continuously and accurately selected over an ultra-wide spectral range based on the adjustable deflection angle of the MEMS micromirrors.

[0058] Based on the above embodiment, the optical waveguide chip 2 is located on the front focal plane of the collimating lens 31, so that the optical signal output from the optical waveguide chip 2 is collimated by the collimating lens 31 and incident on the grating 32 at a fixed angle to undergo diffraction. The MEMS micromirror 33 is located on the rear focal plane of the collimating lens 31, for example, at one focal length of the collimating lens 31. The optical signal of a specified wavelength in the diffracted light obtained by the grating 32 is reflected by the MEMS micromirror 33 and can return to the optical waveguide chip 2 on the grating 32 at another fixed diffraction angle. Thus, by controlling the deflection angle of the MEMS micromirror 33, the feasibility of achieving fast and accurate continuous wavelength selection in a narrowband tunable optical filter can be ensured.

[0059] Based on the above embodiments, the MEMS micromirror 33 is driven by a motor to adjust the deflection angle. The motor can be controlled by changing the voltage, current and other methods through the drive circuit.

[0060] Based on the above embodiments, the number of ports on the second side of the optical waveguide chip 2 is twice the number of times the target optical signal is filtered. For example, if the number of times the narrowband tunable optical filter is N, then the number of ports on the second side of the optical waveguide chip 2 can be 2N. Therefore, the number of times the filter applies to the input target optical signal can be flexibly designed by the number of optical waveguides integrated on the optical waveguide chip. According to the specific requirements of the filter for line filtering width and insertion loss, the number of filtering times can be set to achieve the optimal balance between performance and loss.

[0061] Based on the above embodiments, the second type of optical waveguide is an arc-shaped optical waveguide, and the bending radius of the second type of optical waveguide is greater than the minimum bending radius, which is determined based on the refractive index difference between the core layer and the non-core layer of the second type of optical waveguide.

[0062] Specifically, such as Figure 5 As shown, each type of second-class optical waveguide can be an arc-shaped optical waveguide, that is, each type of second-class optical waveguide has an arc shape, and the bending radius of each type of second-class optical waveguide is greater than the minimum bending radius required by the waveguide characteristics.

[0063] Here, the minimum bending radius can be determined by the refractive index difference between the core layer and the non-core layer of the type-II optical waveguide. The core layer of the type-II optical waveguide refers to the region where optical signals are transmitted using the principle of total internal reflection. The non-core layer of the type-II optical waveguide can be a region with a lower refractive index than the core layer, such as the cladding or substrate outside the core layer. The refractive index difference is the difference between the refractive index of the core layer and the refractive index of the non-core layer of the type-II optical waveguide.

[0064] For example, if the refractive index difference between the core layer and the non-core layer of a type II optical waveguide is 2%, then the minimum bending radius needs to be greater than 1.5 mm.

[0065] In this embodiment of the invention, by limiting the bending radius between the core layer and the non-core layer of the second type of optical waveguide, the bending loss of the second type of optical waveguide can be reduced.

[0066] Based on the above embodiments, the cross angle between the waveguides inside the optical waveguide chip 2 should be as large as possible, for example, greater than 10°, in order to reduce loss and reduce crosstalk.

[0067] Based on the above embodiments, the port spacing between any two adjacent ports on the second side of the optical waveguide chip 2 is the same. The port spacing should be minimized as much as possible while ensuring low crosstalk, in order to reduce the off-axis aberration of each port relative to the collimating lens in the free-space optical system and reduce filter loss. For example, the port spacing on the second side of the optical waveguide chip 2 needs to be greater than twice the waveguide width.

[0068] In this embodiment of the invention, the standard for low crosstalk is crosstalk below -20dB.

[0069] Meanwhile, the spacing between the input and output ends on the first side of the fiber array also needs to ensure low crosstalk. For example, it can be 5 times the port spacing between two adjacent ports on the second side of the optical waveguide chip 2, or other values ​​can be used. No specific limitation is made here.

[0070] Based on the above embodiments, such as Figure 7 As shown, the ports on both the first and second sides of the optical waveguide chip 2 adopt a gradually tapered design. Here, Figure 7 The diagram only shows that the first side of the optical waveguide chip 2 has 2 ports and the second side has 4 ports.

[0071] The first port of the optical waveguide chip 2 adopts a tapered design, which can increase the mode field diameter, thereby better matching the mode field of the fiber array and significantly reducing the coupling loss with the fiber array. Similarly, the second port of the optical waveguide chip 2 also adopts a tapered design, which can increase the mode field size of the beam, allowing the use of collimating lenses with longer focal lengths in free-space optical systems, reducing losses caused by aberrations, and further reducing the overall insertion loss of the filter.

[0072] Based on the above embodiments, the collimating lens 31 includes one of a single spherical lens, an aspherical lens, and a cemented doublet. Among them, the aspherical lens or the cemented doublet can better correct spherical aberration and chromatic aberration, and improve beam quality; by selecting a lens with a longer focal length, a large-aperture collimated beam can be directly output, which meets the linewidth requirements of narrowband filtering.

[0073] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0074] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the parts that contribute to the related technology, can be embodied in the form of software products. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A narrowband tunable optical filter, characterized in that, include: The fiber array, the optical waveguide chip, and the free-space optical system are provided. The first side of the fiber array includes an input end and an output end. The second side of the fiber array is connected to the first side of the optical waveguide chip, and the second side of the optical waveguide chip is connected to the free-space optical system. The optical waveguide chip includes two first-type optical waveguides and multiple second-type optical waveguides. The first-type optical waveguides each have a port on the first side and the second side of the optical waveguide chip, and the second-type optical waveguides each have two ports on the second side of the optical waveguide chip. The target optical signal enters the fiber array and the optical waveguide chip sequentially through the input terminal, and is incident on the free space optical system through the port on the second side of the optical waveguide chip for filtering. Based on the free space optical system and each of the second type of optical waveguides, the signal is transmitted back and forth multiple times between the optical waveguide chip and the free space optical system to achieve multiple filtering before being output through the output terminal.

2. The narrowband tunable optical filter according to claim 1, characterized in that, The free-space optical system includes a collimating lens, a grating, and a microelectromechanical system (MEMS) micromirror, the deflection angle of which is adjustable. The collimating lens is used to collimate the light signal incident on the free space optical system. The grating is used to split the aligned optical signal; The micromirror of the microelectromechanical system is used to reflect a specific wavelength of light signal from the split light signal, and the reflected light signal is output after passing through the grating and the collimating lens in sequence.

3. The narrowband tunable optical filter according to claim 2, characterized in that, The optical waveguide chip is located on the front focal plane of the collimating lens, and the micromirror of the microelectromechanical system is located at one focal length of the collimating lens.

4. The narrowband tunable optical filter according to claim 2, characterized in that, The micromirrors in the microelectromechanical system are driven by a motor to adjust their deflection angle.

5. The narrowband tunable optical filter according to claim 2, characterized in that, The collimating lens includes one of a spherical lens, an aspherical lens, and a cemented doublet lens.

6. The narrowband tunable optical filter according to any one of claims 1-5, characterized in that, The number of ports on the second side of the optical waveguide chip is twice the number of times the target optical signal is filtered.

7. The narrowband tunable optical filter according to any one of claims 1-5, characterized in that, The second type of optical waveguide is an arc-shaped optical waveguide, and the bending radius of the second type of optical waveguide is greater than the minimum bending radius, which is determined based on the refractive index difference between the core layer and the non-core layer of the second type of optical waveguide.

8. The narrowband tunable optical filter according to any one of claims 1-5, characterized in that, The cross angle between the waveguides inside the optical waveguide chip is greater than 10°.

9. The narrowband tunable optical filter according to any one of claims 1-5, characterized in that, The port spacing on the second side of the optical waveguide chip is greater than twice the waveguide width.

10. The narrowband tunable optical filter according to any one of claims 1-5, characterized in that, The ports on both the first and second sides of the optical waveguide chip are tapered.

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