Disclosure of Invention
In view of this, the present disclosure provides an optical filter including an N + 1-order optical switch, an N-order second-order micro-ring optical filter unit, an input optical waveguide unit, an N-order first waveguide, an N-order second waveguide, and an output optical waveguide unit. Wherein:
n +1 stages of optical switches, each stage of the optical switch including a first input terminal, a second input terminal, a first output terminal and a second output terminal, wherein N is a positive integer;
an N-level second-order micro-ring optical filter unit, where each level of the second-order micro-ring optical filter unit includes two micro-ring resonators, and radii of the micro-ring resonators of the N-level second-order micro-ring optical filter unit are different, where a kth-level second-order micro-ring optical filter unit is connected to the first output terminal of a kth-level optical switch, and is configured to filter an input optical signal, where k is a positive integer less than or equal to N;
an input optical waveguide unit for inputting a received optical signal into the optical switch of the 1 st stage;
an N-th-stage first waveguide, wherein a kth-stage first waveguide is connected to an output terminal of the kth-stage second-order micro-ring optical filter unit and the first input terminal of the (k + 1) -th-stage optical switch;
an N-th-stage second waveguide, wherein a kth-stage second waveguide connects the second output terminal of the kth-stage optical switch and the second input terminal of the (k + 1) -th-stage optical switch; and
and the output optical waveguide unit is connected with the (N + 1) th-level optical switch and used for outputting the filtered optical signal.
According to an embodiment of the present disclosure, the optical switch includes a directional coupling type optical switch and an MZI type optical switch.
According to the embodiment of the present disclosure, the optical switch switches the optical signal transmission path by a thermo-optical effect or a photoelectric effect.
According to an embodiment of the present disclosure, each of the second-order micro-ring optical filter units further includes an input waveguide and an output waveguide, wherein the two micro-ring resonators are equidistant from the input waveguide and the output waveguide.
According to an embodiment of the present disclosure, the two micro-ring resonators of the second-order micro-ring optical filter unit have the same radius; the waveguide width and the waveguide thickness of the micro-ring resonant cavity of the second-order micro-ring optical filter unit of the N level are the same.
According to the embodiment of the disclosure, the micro-ring resonant cavity has a resonance wavelength, and a free spectral region is formed between two adjacent resonance wavelengths.
According to an embodiment of the present disclosure, a relationship between the resonant wavelength and the radius of the micro-ring resonator is as follows:
wherein m represents the number of resonance stages; λ represents the center wavelength of the current resonance order; n iscRepresenting the effective refractive index of the micro-ring resonant cavity; r represents the radius of the micro-ring resonant cavity;
the size of the free spectral region of each level of the second-order micro-ring optical filtering unit is calculated according to the following formula:
in the formula, FSR represents the size of the free spectral region.
According to the embodiment of the present disclosure, the adjustment of the free spectral range of the optical filter is realized by switching the optical switch.
According to an embodiment of the present disclosure, the first waveguide includes: a curved waveguide; the second waveguide includes: a straight waveguide.
According to the embodiment of the present disclosure, the optical filter is manufactured on a lithium niobate, silicon dioxide, indium phosphide or gallium arsenide platform by a semiconductor process.
According to the embodiment of the disclosure, the optical path comprises the micro-ring resonant cavities with different radiuses by switching the optical switch, so that the size of the free spectral region in the filtering curve of the optical filter is changed, the problem that the free spectral region is not tunable is solved, and the tunable filtering period and the tunable bandwidth of the optical filter are further realized.
Detailed Description
Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be understood that the description is illustrative only and is not intended to limit the scope of the present disclosure. In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the disclosure. It may be evident, however, that one or more embodiments may be practiced without these specific details. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present disclosure.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The terms "comprises," "comprising," and the like, as used herein, specify the presence of stated features, steps, operations, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, or components.
All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise defined. It is noted that the terms used herein should be interpreted as having a meaning that is consistent with the context of this specification and should not be interpreted in an idealized or overly formal sense.
Where a convention analogous to "at least one of A, B and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B and C" would include but not be limited to systems that have a alone, B alone, C alone, a and B together, a and C together, B and C together, and/or A, B, C together, etc.). Where a convention analogous to "A, B or at least one of C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B or C" would include but not be limited to systems that have a alone, B alone, C alone, a and B together, a and C together, B and C together, and/or A, B, C together, etc.).
The present disclosure provides an optical filter comprising: each stage of the optical switch comprises a first input end, a second input end, a first output end and a second output end, wherein N is a positive integer; the optical filter unit comprises an N-level second-order micro-ring optical filter unit, wherein each level of second-order micro-ring optical filter unit comprises two micro-ring resonant cavities, the radii of the micro-ring resonant cavities of the N-level second-order micro-ring optical filter unit are different, the kth-level second-order micro-ring optical filter unit is connected with the first output end of the kth-level optical switch and is used for filtering an input optical signal, and k is a positive integer less than or equal to N; an input optical waveguide unit for inputting the received optical signal into the 1 st-order optical switch; the first waveguide of the Nth level is connected with the output end of the second-order micro-ring optical filter unit of the kth level and the first input end of the optical switch of the (k + 1) th level; the kth-stage second waveguide is connected with the second output end of the kth-stage optical switch and the second input end of the (k + 1) th-stage optical switch; and the output optical waveguide unit is connected with the (N + 1) th-level optical switch and used for outputting the filtered optical signal.
Fig. 1 schematically illustrates a schematic diagram of an optical filter according to an embodiment of the disclosure.
As shown in fig. 1, the optical filter includes an optical switch 110, a second order micro-ring optical filter unit 120, an input optical waveguide unit 130, a first waveguide 140, a second waveguide 150, and an output optical waveguide unit 160. The optical switch 110, the second-order micro-ring optical filter unit 120, the first waveguide 140, and the second waveguide 150 constitute a filter structure of the optical filter, and the optical filter may be formed by cascading any number of filter structures, and in this embodiment, it is assumed that the number of the filter structures is N.
The optical switch 110 comprises at least a first input 111, a second input 112, a first output 113 and a second output 114. The optical signal has 4 transmission paths in the optical switch 110, and is input into the optical switch 110 from the first input terminal 111 or the second input terminal 112, and output from the first output terminal 113 or the second output terminal 114, respectively.
The input end of the second order micro-ring optical filter unit 120 is connected to the first output end 113 of the same-stage optical switch 110, and the output end of the second order micro-ring optical filter unit 120 is connected to the first waveguide 140 of the same stage. For example, for the kth-stage second-order micro-ring optical filter unit 120, an input terminal thereof is connected to the first output terminal 113 of the kth-stage optical switch 110, and an output terminal thereof is connected to the kth-stage first waveguide 140.
The second-order micro-ring optical filter unit 120 includes two micro-ring resonators 121, and the radii of the micro-ring resonators 121 in different second-order micro-ring optical filter units 120 are different. The micro-ring resonator 121 may be used to filter an input optical signal.
The input optical waveguide unit 130 includes two straight waveguides, which are respectively connected to the first input end 111 and the second input end 112 of the level 1 optical switch 110, and can be used for inputting the received optical signal into the level 1 optical switch.
In particular, in other embodiments of the present disclosure, the input optical waveguide unit 130 may include only one straight waveguide, and accordingly, the 1 st-order optical switch may include only one input end, and the number of output ends thereof remains unchanged.
The first waveguide 140 is connected to the optical switch 110 and the second order micro-ring optical filter 120, and specifically, the kth-stage first waveguide 140 connects the output of the kth-stage second order micro-ring optical filter unit 120 and the first input 111 of the (k + 1) -th-stage optical switch 110. Based on the difference in size of the second order micro-ring optical filter unit 120 and the optical switch 110, the first waveguide 140 may include a curved waveguide for convenience of structural design.
The second waveguide 150 is connected to two adjacent optical switches 110, and specifically, the kth-stage second waveguide 150 connects the second output terminal 114 of the kth-stage optical switch 110 and the second input terminal 112 of the (k + 1) th-stage optical switch. In order to reduce the optical signal loss due to the long optical path, the second waveguide 150 may preferably include a straight waveguide.
The output optical waveguide unit 160 includes two straight waveguides, which are respectively connected to the first output terminal 113 and the second output terminal 114 of the (N + 1) th-level optical switch 110, and can be configured to receive the optical signal transmitted by the (N + 1) th-level optical switch 110 and output the optical signal through the two straight waveguides.
In particular, in other embodiments of the present disclosure, the output optical waveguide unit 160 may only include one straight waveguide, and correspondingly, the N +1 th-level optical switch may only include one output terminal, and the number of input terminals thereof remains unchanged. In addition, the (N + 1) th-stage optical switch may be replaced by other devices having a function of combining optical paths, such as an optical fiber combiner.
The optical waveguides in the input optical waveguide unit 130, the first waveguide 140, the second waveguide 150, and the output optical waveguide unit 160 may be integrated optical waveguides represented by planar dielectric optical waveguides and strip dielectric optical waveguides, or may be cylindrical optical waveguides represented by optical fibers, and the type of the optical waveguides is not limited in the embodiments of the present disclosure.
According to the embodiment of the disclosure, the optical path comprises the micro-ring resonant cavities with different radiuses by switching the optical switch, so that the size of the free spectral region in the filtering curve of the optical filter is changed, the problem that the free spectral region is not tunable is solved, and the tunable filtering period and the tunable bandwidth of the optical filter are further realized.
The optical filter shown in fig. 1 is further described below with reference to fig. 2a, 2b and 3 in connection with specific embodiments.
Fig. 2a and 2b show schematic diagrams of an optical switch 110 in an optical filter according to an embodiment of the disclosure.
As shown in fig. 2a and 2b, the optical switch 110 can be selected according to the type of the optical switch that can be modulated, for example, in the case of modulating the optical switch by the electro-optical effect, the optical switch 110 can be selected from a directional coupling type optical switch, an MZI type optical switch, a Y-branch type optical switch, an SOA optical gate type optical switch, and the like; when the optical switch is modulated by the thermo-optical effect, the optical switch 110 may be selected from an MZI type optical switch, a 3dB directional coupling type optical switch, a thermo-optical digital Y-branch type optical switch, and the like. Preferably, in the embodiment of the present disclosure, the optical switch 110 may be a directional coupling type optical switch or an MZI type optical switch, and the function of the optical switch 110 may also be implemented by a thermo-optic effect or an electro-optic effect.
Fig. 3 schematically illustrates a schematic diagram of a second order micro-ring optical filter cell 120 according to an embodiment of the present disclosure.
As shown in fig. 3, the second order micro-ring optical filter unit 120 further includes an input waveguide 122 and an output waveguide 123. For each level of the second-order micro-ring optical filter unit 120, the two micro-ring cavities 121 form an integer with the same distance from the input waveguide 122 to the output waveguide 123.
The micro-ring resonator 121 has a resonance wavelength and a periodic download spectrum at the resonance wavelength, an interval between adjacent resonance wavelengths is called a free spectral range, and a bandwidth of a filter curve indicates a width between corresponding spectral lines at the resonance wavelength when an energy of the filter curve is half of a maximum intensity of an output.
The resonant wavelength of the micro-ring resonator 121 is related to the radius of the micro-ring resonator 121, and can be specifically expressed as:
in formula (1), m represents the number of resonance stages; λ represents the center wavelength of the current resonance order; n iscRepresenting the effective refractive index of the micro-ring resonator; r represents the radius of the micro-ring resonator.
The size of the free spectral range of the micro-ring resonator 121 can be calculated according to the formula (1), which can be specifically expressed as:
in the formula (2), FSR represents the size of the free spectral region, and the remaining parameters represent the same meanings as in the formula (1).
Meanwhile, the position of the resonant wavelength of the micro-ring resonator 121 can be finely adjusted by a thermo-optic effect or a photoelectric effect.
In the optical filter of the embodiment of the present disclosure, each of the second-order micro-ring optical filter units 120 includes two micro-ring resonators 121 having the same radius and having the same waveguide width and waveguide thickness. However, the radii of the micro-ring cavities 121 are different and the waveguide widths and waveguide thicknesses are the same between different second-order micro-ring optical filter units 120, which results in different filtering curves of the different second-order micro-ring optical filter units 120.
According to the embodiment of the present disclosure, based on consideration of enhancing controllability of the free spectral range of the optical filter, each second-order micro-ring optical filter unit 120 may be connected according to the radius of the micro-ring resonator 121 thereof, for example, the radius of the micro-ring resonator 121 of the 1 st-order second-order micro-ring optical filter unit 120 is the smallest, and the radius of the micro-ring resonator 121 of the nth-order second-order micro-ring optical filter unit 120 is the largest.
According to the embodiment of the present disclosure, the free spectral range of the optical filter is the least common multiple of the free spectral ranges of the second-order micro-ring optical filter units 120 in the optical path, and therefore, the combination of different second-order micro-ring filters passed by the optical path can be determined by adjusting the switch switching, and the tuning of the free spectral range and the bandwidth can be realized.
According to the embodiment of the present disclosure, the optical switch 110, the second-order micro-ring optical filter unit 120, and each optical waveguide in the optical filter may be fabricated and implemented on a lithium niobate, silicon dioxide, indium phosphide, or gallium arsenide platform by a semiconductor process, thereby providing the optical filter with characteristics of high stability, low loss, small volume, and the like.
According to the embodiment of the disclosure, paths are switched based on each stage of optical switches, and by selecting combinations among different second-order micro-ring filters through which optical paths pass and adjusting resonant wavelengths of the corresponding filters, a new filtering period is obtained, and the bandwidth is adjusted, so that the filtering function of the reconfigurable optical filter is completed.
The embodiments of the present disclosure have been described above. However, these examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Although the embodiments are described separately above, this does not mean that the measures in the embodiments cannot be used in advantageous combination. The scope of the disclosure is defined by the appended claims and equivalents thereof. Various alternatives and modifications can be devised by those skilled in the art without departing from the scope of the present disclosure, and such alternatives and modifications are intended to be within the scope of the present disclosure.