CN114553319A - Method for filtering partial coherent noise in light beam by using double-beam interferometer - Google Patents
Method for filtering partial coherent noise in light beam by using double-beam interferometer Download PDFInfo
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Abstract
The invention discloses a method for filtering partial coherent noise in a light beam by using a double-light-beam interferometer, wherein the light beam containing signal light and noise light is incident to the double-light-beam interferometer, and the light beam for filtering partial coherent noise is output; the distance between the mirror bodies in the double-beam interferometer is adjusted to enable the propagation path difference of the signal light and the noise light in the double-beam interferometer to meet a certain condition; the dual-beam interferometer is one or more cascaded michelson interferometers or mach-zehnder interferometers. The method disclosed by the invention not only can filter out-of-band noise, but also can filter out in-band partial coherent noise, and the loss of signal light is very small.
Description
Technical Field
The invention relates to the field of noise filtering, in particular to a method for filtering partial coherent noise in a light beam by using a dual-beam interferometer.
Background
With the development of internet technology, the requirements of optical communication systems for receiver sensitivity are higher and higher. The sensitivity of the optical receiver is a comprehensive reflection of the system performance, and the main influencing factors of the sensitivity are noise, including thermal noise, shot noise, spontaneous radiation noise of an optical amplifier and the like in an optical communication system. These noises can each be considered as partially coherent noises with different coherence times.
In order to reduce the above noise effect, a filter is usually added to the optical receiver. The common filter is a band-pass filter, but no matter the filter is a band-pass filter or a low-pass, high-pass, band-stop filter, etc., the filters are all based on the spectrum filtering action, i.e., the signals are only screened on the wavelength level, the signals of the required wave band are left, the signals of the unnecessary wave band are filtered, and then the effect of inhibiting the wide-spectrum noise is achieved. The spectrum filtering mode has certain limitation, and can only filter out-of-band noise, and cannot distinguish signals from in-band noise. In order to filter noise as much as possible, a filter of a spectral filtering method requires a narrow pass band width and good pass band characteristics, but even if the pass band is narrow enough, in-band noise cannot be avoided, and an excessively narrow pass band may cause distortion of a signal.
Disclosure of Invention
In order to solve the above technical problems, the present invention provides a method for filtering out partial coherent noise in a light beam by using a dual-beam interferometer, so as to achieve the purpose of filtering out-of-band noise and in-band partial coherent noise.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a method for filtering partial coherent noise in light beam by using double-light beam interferometer is to make light beam containing signal light and noise light incident into double-light beam interferometer and output light beam with partial coherent noise filtered; the distance between the mirrors in the double-beam interferometer is adjusted to ensure that the propagation path difference of the signal light and the noise light in the double-beam interferometer meets the following condition:
where Δ D is the propagation path difference of the signal light and the noise light in the dual-beam interferometer, ceil () represents rounding the number in parentheses, and Δ L2λ is the center wavelength of the incident beam, which is the coherence length of the noisy light.
In the above scheme, the dual-beam interferometer is one or more cascaded michelson interferometers.
In a further technical scheme, isolators are arranged among the plurality of cascaded michelson interferometers.
In a further technical solution, the propagation path difference of the signal light and the noise light in the michelson interferometer is adjusted by changing the distance between a half-mirror and two mirrors in the michelson interferometer.
In the above scheme, the dual-beam interferometer is one or more cascaded mach-zehnder interferometers.
In a further technical scheme, the propagation optical path difference of the signal light and the noise light in the mach-zehnder interferometer is adjusted by changing the distance between two half mirrors and two reflecting mirrors in the mach-zehnder interferometer.
Through the technical scheme, the method for filtering partial coherent noise in the light beam by using the double-beam interferometer has the following beneficial effects:
1. the invention filters out the out-band and in-band partial coherent noise by utilizing the difference of the time coherence of the signal light and the noise light, particularly, the signal light and the partial coherent noise light pass through the same double-beam interferometer, the signal light has no loss or very little loss, the bandwidth is very large, the signal light has almost no distortion, and the in-band partial coherent noise has very large loss when passing through the double-beam interferometer.
2. The invention can further reduce the coherent noise of the in-band part by cascading a plurality of double-beam interferometers, thereby greatly improving the signal-to-noise ratio in the band.
3. The invention adopts the double-beam interferometer, and because the interference structure is sensitive to the wavelength generally, the light which is not in the passband can not reach the signal output end, so that the signal with the out-of-band noise filtered can be obtained at the signal output end, and therefore, the method can simultaneously filter the out-of-band noise and the in-band partial coherent noise.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.
FIG. 1 is a schematic diagram of a single Michelson interferometer disclosed in accordance with an embodiment of the present invention;
FIG. 2 is a simulation result of transmittance change of signal light at an exit port of a Michelson interferometer;
FIG. 3 is a simulation result of transmittance change of noise light at an exit port of a Michelson interferometer;
FIG. 4 is a noise figure NF of a Michelson interferometer;
FIG. 5 is a schematic diagram of a Michelson interferometer cascade structure;
FIG. 6 is a schematic diagram of a single Mach-Zehnder interferometer configuration;
FIG. 7 is a schematic diagram of a Mach-Zehnder interferometer cascade structure.
In the figure, 1, a half-transmitting half-reflecting mirror I; 2. a first reflecting mirror; 3. a second reflecting mirror; 4. an isolator; 5. a first Michelson interferometer; 6. a second Michelson interferometer; 7. a second half-transmitting half-reflecting mirror; 8. a third reflector; 9. a fourth reflecting mirror; 10. a third half-transmitting half-reflecting mirror; 11. a semi-transparent semi-reflecting mirror IV; 12. a fifth reflecting mirror; 13. a sixth reflector; 14. a first Mach-Zehnder interferometer; 15. and a second Mach-Zehnder interferometer.
Detailed Description
The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.
Example 1
The invention provides a method for filtering partial coherent noise in a light beam by using a double-beam interferometer, which is characterized in that the light beam containing signal light and noise light is incident to a Michelson interferometer, and the light beam with the partial coherent noise filtered is output. The distance between the mirrors in the double-beam interferometer is adjusted to ensure that the propagation path difference of the signal light and the noise light in the double-beam interferometer meets the following condition:
wherein D is1And D2The propagation optical paths of the signal light and the noise light in the dual-beam interferometer are respectively, ceil () represents that the number in the parentheses is rounded up, Δ L2λ is the center wavelength of the incident beam, which is the coherence length of the noisy light.
As shown in fig. 1, the michelson interferometer is composed of a half mirror 1, a mirror 2 and a mirror 3. Wherein, the first half mirror 1 and the horizontal direction are arranged at an included angle of 45 degrees, the first reflector 2 is horizontally arranged, and the second reflector 3 is vertically arranged. The line with the arrow represents the direction of transmission of the light path, D1The optical path of light back and forth between the half mirror 1 and the reflector 2, D2The light path is the light path between the half mirror 1 and the reflecting mirror 3. D1And D2The optical path difference can be adjusted by changing the distance between the half mirror I1 and the mirror I2 or the mirror II 3.
To more clearly show the conditions required for a michelson interferometer to achieve optimal filtering of in-band partially coherent noise, table 1 gives the simulation conditions:
TABLE 1 simulation conditions for Michelson interferometer
| Parameter/symbol | Numerical value/Unit |
| Center wavelength λ | 1.5μm |
| Signal light coherence length Δ L1 | 3mm |
| Noise light coherence length Δ L2 | 40μm |
| Optical path difference between two |
0 to 4mm |
The simulation results obtained under the above simulation conditions are shown in fig. 2 to 4, in which | D |, is2-D1When | ═ 40.5 μm, that is, when the optical path length difference satisfies the condition shown in equation (1), the noise index NF of the michelson interferometer is minimum, about NF ═ 3dB, and the signal light transmittance is 99%, that is, a signal containing only in-band partial coherent noise passes through the michelson interferometer, and then the signal-to-noise ratio is improved by 3dB, and the signal light loss is almost negligible.
A single michelson interferometer has a limited effect of filtering out the in-band partially coherent noise, and in order to further filter out the in-band partially coherent noise, N michelson interferometers may be cascaded in the manner shown in fig. 5. Since the noise filtered by the michelson interferometers will be output from the input end in the opposite direction (shown by the dotted line), an isolator 4 is also required to be introduced between each michelson interferometer. The method specifically comprises the following steps: emergent light of the first Michelson interferometer 5 passes through the isolator 4 and then is incident into the second Michelson interferometer 6. Wherein, the second michelson interferometer 6 and the first michelson interferometer 5 are in 180-degree mirror image relation with respect to the isolator 4, namely the second half-transmitting mirror 7 is arranged at an included angle of 45 degrees with the horizontal direction, the third reflector 8 is vertically arranged, and the fourth reflector 9 is horizontally arranged.
Total noise figure NF of the systemtIs composed of
NFt＝N×NF (2)
Where NF is the noise figure of a single michelson interferometer.
Example 2
The invention provides a method for filtering partial coherent noise in a light beam by using a double-beam interferometer, which is characterized in that the light beam containing signal light and noise light is incident to a Mach-Zehnder interferometer, as shown in figure 6, the Mach-Zehnder interferometer comprises a semi-transparent semi-reflective mirror three 10, a semi-transparent semi-reflective mirror four 11, a reflecting mirror five 12 and a reflecting mirror six 13, wherein the inclination directions of the semi-transparent semi-reflective mirror three 10 and the reflecting mirror five 12 are consistent and are both 135 degrees, the inclination directions of the semi-transparent semi-reflective mirror four 11 and the reflecting mirror six 13 are consistent and are both 45 degrees, and the semi-transparent semi-reflective mirror three 10, the semi-transparent semi-reflective mirror four 11, the reflecting mirror five 12 and the reflecting mirror six 13 are positioned on four vertexes of a rectangle.
After the light beam passes through the Mach-Zehnder interferometer, outputting a light beam with partial coherent noise filtered; the propagation path difference of the signal light and the noise light in the dual-beam interferometer satisfies the following conditions:
wherein, Δ L2λ is the center wavelength of the incident beam, ceil () represents the number rounded up in parentheses, L1,L2,L3And L4The optical distances from the third half mirror 10 to the fifth mirror 12, from the fifth mirror 12 to the sixth mirror 13, from the sixth mirror 13 to the fourth half mirror 11, and from the third half mirror 10 to the fourth half mirror 11 in the mach-zehnder interferometer are respectively.
The propagation path difference of the signal light and the noise light in the Mach-Zehnder interferometer is adjusted by changing the distance between two half mirrors and two reflecting mirrors in the Mach-Zehnder interferometer.
Under the simulation conditions shown in table 1, the simulation results of the mach-zehnder interferometer are identical to those of the michelson interferometer, and are not repeated here.
A single mach-zehnder interferometer has a limited filtering effect on the in-band partially coherent noise, and in order to further filter the in-band partially coherent noise, N mach-zehnder interferometers may be cascaded in the manner shown in fig. 7. Since the input end of each Mach-Zehnder interferometer does not have reverse output light, and noise light is output from the side of the half-mirror four 11 (shown by a dotted line in the figure), no isolator needs to be introduced between each Mach-Zehnder interferometer. The arrangement modes of the Mach-Zehnder interferometers are completely the same, and an isolator is not required to be introduced, namely emergent light of the first Mach-Zehnder interferometer 14 directly enters the second Mach-Zehnder interferometer 15.
The dual beam interferometer of the present invention may also be other dual beam interferometers, such as one or more cascaded rayleigh interferometers, one or more cascaded mach-zehnder interferometers constructed based on 3dB fiber couplers, or in the case of cascaded dual beam interferometers of different configurations.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (6)
1. A method for filtering partial coherent noise in light beam by using double-light beam interferometer is characterized in that the light beam containing signal light and noise light is incident to the double-light beam interferometer, and the light beam with partial coherent noise filtered is output; the distance between the mirrors in the double-beam interferometer is adjusted to ensure that the propagation path difference of the signal light and the noise light in the double-beam interferometer meets the following condition:
where Δ D is the propagation path difference of the signal light and the noise light in the dual-beam interferometer, ceil () represents rounding the number in parentheses, and Δ L2λ is the center wavelength of the incident beam, which is the coherence length of the noisy light.
2. The method of claim 1, wherein the dual-beam interferometer is one or more cascaded michelson interferometers.
3. The method of claim 2, wherein an isolator is disposed between the plurality of cascaded michelson interferometers.
4. The method of claim 2, wherein the propagation path difference between the signal light and the noise light in the michelson interferometer is adjusted by changing the distance between the half mirror and the two mirrors in the michelson interferometer.
5. The method of claim 1, wherein the dual-beam interferometer is one or more cascaded mach-zehnder interferometers.
6. The method of claim 5, wherein the propagation path difference between the signal light and the noise light in the Mach-Zehnder interferometer is adjusted by changing the distance between two half mirrors and two reflecting mirrors in the Mach-Zehnder interferometer.
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| CN102980601A (en) * | 2012-12-07 | 2013-03-20 | 天津大学 | Demodulating device and method for optical fiber Young interference optical path difference based on low coherent interference |
| CN203016921U (en) * | 2013-01-18 | 2013-06-26 | 杭州电子科技大学 | Spectral phase calibration system based on cascaded mach-zehnder interferometer |
| CN107144537A (en) * | 2016-06-13 | 2017-09-08 | 中国海洋大学 | A kind of visible optical Fourier transform absorption spectrum measuring method and system |
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