CN114553319B - 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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- CN114553319B CN114553319B CN202210118579.6A CN202210118579A CN114553319B CN 114553319 B CN114553319 B CN 114553319B CN 202210118579 A CN202210118579 A CN 202210118579A CN 114553319 B CN114553319 B CN 114553319B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
- H04B10/61—Coherent receivers
- H04B10/615—Arrangements affecting the optical part of the receiver
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Abstract
The invention discloses a method for filtering partial coherent noise in light beams by utilizing a double-beam interferometer, wherein the light beams containing signal light and noise light are incident into the double-beam interferometer, and the light beams for filtering the partial coherent noise are output; the propagation optical path difference of the signal light and the noise light in the double-beam interferometer meets a certain condition by adjusting the distance between the lens bodies in the double-beam interferometer; 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 partial coherent noise in the band, and the loss of signal light is 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 double-beam interferometer.
Background
With the development of internet technology, the requirements of the optical communication system on the sensitivity of the receiver are increasing. The sensitivity of an optical receiver is a comprehensive reflection of the performance of the system, and the main influencing factors are noise, including thermal noise, shot noise, spontaneous emission noise of an optical amplifier and the like in an optical communication system. These noises can be regarded as partially coherent noises having different coherence times.
In order to reduce the effect of the above noise, a filter is typically added to the optical receiver. Common filters are bandpass filters, but both bandpass filters and lowpass, highpass and bandstop filters are based on spectral filtering, i.e. signals are screened only on the wavelength level, signals of a required wave band are left, signals of an unnecessary wave band are filtered, and further the effect of suppressing wide-spectrum noise is achieved. The spectrum filtering mode has a certain limitation, and can only filter out-of-band noise, and can not distinguish signals from in-band noise. In order to filter out noise as much as possible, a filter of the spectral filtering method requires a narrow passband width and good passband characteristics, but even if the passband is sufficiently narrow, in-band noise is unavoidable, and an excessively narrow passband may cause distortion of the signal.
Disclosure of Invention
In order to solve the technical problems, the invention provides a method for filtering partial coherent noise in a light beam by using a double-beam interferometer, so as to achieve the purpose of filtering out-of-band noise and filtering out in-band partial coherent noise.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
A method for filtering partial coherent noise in light beam by using double-beam interferometer includes such steps as making light beam containing signal light and noise light incident on double-beam interferometer, and outputting the light beam with partial coherent noise filtered out; the propagation path difference of the signal light and the noise light in the dual-beam interferometer can meet the following conditions by adjusting the distance between the mirrors in the dual-beam interferometer:
where Δd is the propagation path difference of the signal light and the noise light in the dual beam interferometer, ceil () represents the upward rounding of the numbers in brackets, Δl 2 is the coherence length of the noise light, and λ is the center wavelength of the incident beam.
In the above scheme, the dual beam interferometer is one or more cascaded michelson interferometers.
In a further technical scheme, an isolator is arranged between the plurality of cascaded Michelson interferometers.
In a further technical scheme, the propagation path difference of 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.
In the above scheme, the dual beam interferometer is one or more cascaded mach-zehnder interferometers.
In a further technical solution, 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 reflectors in the mach-zehnder interferometer.
Through the technical scheme, the method for filtering the partial coherent noise in the light beam by using the double-beam interferometer has the following beneficial effects:
1. The invention utilizes the time coherence difference of the signal light and the noise light to filter out the out-of-band and in-band split-phase interference noise, in particular, the signal light and the partial coherent noise light pass through the same double-beam interferometer, the signal light passes through the double-beam interferometer without loss or with little loss, the bandwidth is large, the signal light is almost undistorted, and the in-band split-phase interference noise has great loss when passing through the double-beam interferometer.
2. The invention can further reduce in-band split-phase interference noise by cascading a plurality of double-beam interferometers, thereby greatly improving in-band signal-to-noise ratio.
3. The invention adopts the double-beam interferometer, because the interference structure is generally sensitive to the wavelength, the light which is not in the passband can not reach the signal output end, so that the signal which can filter out-of-band noise can be obtained at the signal output end, and therefore, the method can filter out-of-band noise and in-band split-phase dry noise simultaneously.
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 an embodiment of the present invention;
FIG. 2 is a graph showing simulation results of transmittance variation of signal light at an exit port of a Michelson interferometer;
FIG. 3 is a simulation result of the transmittance change of noise light at the exit port of the 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 structure;
FIG. 7 is a schematic diagram of a Mach-Zehnder interferometer cascade structure.
In the figure, 1, a half mirror I; 2. a first reflecting mirror; 3. a second reflecting mirror; 4. an isolator; 5. michelson interferometer one; 6. michelson interferometer two; 7. a half-mirror II; 8. a third reflecting mirror; 9. a reflection mirror IV; 10. a semi-transparent semi-reflective mirror III; 11. a half-mirror IV; 12. a fifth reflecting mirror; 13. a reflection mirror six; 14. Mach-Zehnder interferometer one; 15. Mach-Zehnder interferometers two.
Detailed Description
The technical solutions 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 utilizing a double-beam interferometer. The propagation path difference of the signal light and the noise light in the dual-beam interferometer can meet the following conditions by adjusting the distance between the mirrors in the dual-beam interferometer:
Where D 1 and D 2 are propagation paths of signal light and noise light in the dual-beam interferometer, respectively, ceil () represents rounding up numbers in brackets, Δl 2 is a coherence length of the noise light, and λ is a center wavelength of an incident beam.
As shown in fig. 1, the michelson interferometer is composed of a half mirror 1, a mirror 2, and a mirror 3. Wherein, semi-transparent half mirror 1 is 45 contained angles with the horizontal direction and is placed, and speculum 2 level is placed, and speculum two 3 are vertical to be placed. The line with an arrow represents the optical path transmission direction, D 1 is the optical path of light to and fro between the half mirror 1 and the mirror 2, and D 2 is the optical path of light to and fro between the half mirror 1 and the mirror 3. The optical path difference between D 1 and D 2 can be adjusted by changing the distance between half mirror 1 and mirror one 2 or mirror two 3.
To more clearly show the conditions required for the michelson interferometer to reach the best filtering of the in-band split-phase dry noise, the simulation conditions are given in table 1:
TABLE 1 simulation conditions for Michelson interferometer
| Parameters/symbols | Numerical value/unit |
| Center wavelength lambda | 1.5μm |
| Signal light coherence length DeltaL 1 | 3mm |
| Noise optical coherence length DeltaL 2 | 40μm |
| Optical path difference of two arms | 0 To 4mm |
The simulation results obtained under the above simulation conditions are shown in fig. 2 to 4, wherein when |d 2-D1 |=40.5 μm, that is, when the optical path difference satisfies the condition shown in the formula (1), the noise figure NF of the michelson interferometer is minimum, about nf= -3dB, and the signal light transmittance is 99%, that is, after only the signal containing the internal phase-separated dry noise passes through the michelson interferometer, the signal-to-noise ratio increase of 3dB can be obtained, and the signal light loss is almost negligible.
The single michelson interferometer has limited filtering effect on the in-band split-phase noise, and N michelson interferometers can be cascaded in the manner shown in fig. 5 in order to further filter out the in-band split-phase noise. Since the noise filtered by the michelson interferometers will be output back from its input (shown in dashed lines), an isolator 4 is also introduced between the michelson interferometers. The method comprises the following steps: the outgoing light of the first Michelson interferometer 5 passes through one isolator 4 and then enters the second Michelson interferometer 6. The Michelson interferometer II 6 and the Michelson interferometer I5 are in a 180-degree mirror image relationship with respect to the isolator 4, namely, the half-mirror II 7 is placed at an included angle of 45 degrees with the horizontal direction, the reflector III 8 is placed vertically, and the reflector IV 9 is placed horizontally.
The total noise figure NF t of the system is
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 light beams by utilizing a double-beam interferometer, which is characterized in that the light beams containing signal light and noise light are incident into a Mach-Zehnder interferometer, as shown in fig. 6, the method comprises a half mirror three 10, a half mirror four 11, a half mirror five 12 and a mirror six 13, wherein the inclination directions of the half mirror three 10 and the mirror five 12 are consistent and are 135 degrees, the inclination directions of the half mirror four 11 and the mirror six 13 are consistent and are 45 degrees, and the half mirror three 10, the half mirror four 11, the mirror five 12 and the mirror six 13 are positioned on four vertexes of a rectangle.
Outputting a light beam with partial coherent noise filtered after the light beam passes through a Mach-Zehnder interferometer; the propagation path difference of the signal light and the noise light in the dual-beam interferometer satisfies the following conditions:
Where Δl 2 is the coherence length of noise light, λ is the center wavelength of the incident beam, ceil () represents the upward rounding of numbers in brackets, and L 1,L2,L3 and L 4 are the optical paths between half mirror three 10 to half mirror five 12, half mirror five 12 to half mirror six 13, half mirror six 13 to half mirror four 11, half mirror three 10 to half mirror four 11, respectively, in the mach-zehnder interferometer.
The propagation path difference of the signal light and the noise light in the mach-zehnder interferometer is adjusted by changing the distance between the two half mirrors and the two mirrors in the mach-zehnder interferometer.
Under the simulation conditions shown in table 1, the simulation results of the mach-zehnder interferometer are exactly the same as those of the michelson interferometer, and will not be repeated here.
The single mach-zehnder interferometer has limited filtering effect on the in-band split-phase noise, and N mach-zehnder interferometers may be cascaded in the manner shown in fig. 7 in order to further filter out the in-band split-phase noise. Since the input end of the Mach-Zehnder interferometer has no 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), an isolator is not required to be introduced between the Mach-Zehnder interferometers. The arrangement of each mach-zehnder interferometer is identical and no isolator is required to be introduced, i.e. the outgoing light of the first mach-zehnder interferometer 14 is directly incident into 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 based on 3dB fiber couplers, or a cascade of 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 beams by utilizing a double-beam interferometer is characterized in that light beams containing signal light and noise light are incident into the double-beam interferometer, and the light beams for filtering the partial coherent noise are output; the propagation path difference of the signal light and the noise light in the dual-beam interferometer can meet the following conditions by adjusting the distance between the mirrors in the dual-beam interferometer:
where Δd is the propagation path difference of the signal light and the noise light in the dual beam interferometer, ceil () represents the upward rounding of the numbers in brackets, Δl 2 is the coherence length of the noise light, and λ is the center wavelength of the incident beam.
2. A method of filtering out partially coherent noise in a beam of light using a dual beam interferometer according to claim 1, wherein the dual beam interferometer is one or more cascaded michelson interferometers.
3. A method of filtering out partially coherent noise in a beam using a dual beam interferometer according to claim 2, wherein an isolator is provided between the plurality of cascaded michelson interferometers.
4. A method of filtering out partially coherent noise in a beam using a dual beam interferometer according to claim 2, wherein the propagation path difference of the signal light and the noise light in the michelson interferometer is adjusted by varying the distance between the half mirror and the two mirrors in the michelson interferometer.
5. A method of filtering out partially coherent noise in a beam of light using a dual beam interferometer according to claim 1, wherein the dual beam interferometer is one or more cascaded mach-zehnder interferometers.
6. A method of filtering out partially coherent noise in a beam using a dual beam interferometer according to claim 5, wherein the propagation path difference of the signal light and the noise light in the mach-zehnder interferometer is adjusted by varying the distance between two half mirrors and two 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 |
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| 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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