# US 10,122,445 B2 · Method for enhancing optical signal-to-noise ratio measuring precision by correcting spectral resolution

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- Number: US 10,122,445 B2
- Document ID: US10122445B2
- Status: Granted
- Kind: B2
- Application number: 15/314,014
- Filed: 2016-09-20
- Published: 2018-06-28
- Granted: 2018-11-06
- Earliest claimed: 2016-09-09
- Assignees: Huazhong University of Science and Technology
- Applicants: Huazhong University of Science and Technology
- Inventors: Changjian Ke; Deming Liu; Guo Yin; Chen Xing
- Web page: https://patentgrep.com/patent/US10122445B2

## CPC

- H04B 10/07953: {Monitoring or measuring OSNR, BER or Q}
- H04B 10/079: using measurements of the data signal
- H04B 10/07955: {Monitoring or measuring power}
- H04B 10/07957: {Monitoring or measuring wavelength}
- H04B: TRANSMISSION

## Abstract

A method for enhancing optical signal-to-noise ratio measuring precision by correcting spectral resolution is provided, which can obtain optical signal-to-noise ratio with enhanced measuring precision, by measuring actual power of broad spectrum signals in a certain bandwidth, determining the sum of the power of the sampling points for the broad spectrum signals in the bandwidth by using an optical spectrum analyzer, obtaining the corrected resolution of the optical spectrum analyzer, and replacing the setting resolution of the optical spectrum analyzer with the corrected resolution. The method can effectively solve the problem of large OSNR measuring error resulted from the difference between the setting resolution and the actual resolution of optical spectrum analyzer. The method is applicable to correct resolution for all optical spectrum analyzers, and also applicable to enhance the measuring precision for all OSNR measuring methods based on spectrum analysis, and has the advantages of easiness to handle and implement.

## Claims

### Claim 1

A method for enhancing optical signal-to-noise ratio (OSNR) measuring precision by correcting spectral resolution, the method comprising steps of:
(1) obtaining actual powers PAi of a series of broad spectrum signals which have a central wavelength of λ, a bandwidth of Δλ1, a power interval of ΔPz, and a power range of (Pmin-Pmax), wherein, i=1, 2, . . . , n; z=1; Pmin is the minimal power of the broad spectrum signals; and Pmax is the maximum power of the broad spectrum signals;
(2) measuring a calibration spectrum of each signal for the series of broad spectrum signals by using optical spectrum analyzer (OSA), adding up powers of sampling points which fall into spectrum range having the central wavelength of λ, the bandwidth of Δλ1, to obtain a sum of powers of the sampling points, to obtain a series of sums PBi for the series of broad spectrum signals, wherein, i=1, 2, . . . , n;
(3) obtaining corrected resolutions Resi=PBi·Δλ2/PAi according to the actual powers PAi of the series of broad spectrum signals, the series of sums PBi of powers of the sampling points, and a wavelength interval Δλ2 between adjacent sampling points;
(4) obtaining a fitting expression according to the corrected resolutions Resi and the series of sums PBi of powers of the sampling points by a least squares method;
(5) obtaining a series of corrected resolutions RES′i after being fitted according to the series of sums PBi of powers of sampling points and the fitting expression; obtaining measured powers of the series of broad spectrum signals P′Ai=PBi·Δλ2/RES′i according to the series of corrected resolutions RES′i after being fitted, the series of sums PBi of powers of the sampling points, and the wavelength interval Δλ2;
(6) according to the actual powers PAi and the measured powers P′Ai of the broad spectrum signals, obtaining relative errors

P
Ai
-
P
Ai
′
P
Ai

;
and determining whether the following formula

P
Ai
-
P
Ai
′
P
Ai

<
ɛ
is satisfied; if yes, performing step (7); or else, making ΔPz=ΔPz/2, z=z+1, and repeating steps (1)-(5), wherein, 0<ε<1; and
(7) measuring a spectrum of a signal under test, so as to obtain the corrected resolutions corresponding to the sampling points required by calculating OSNR in the spectrum; and obtaining OSNR based on the corrected resolution.

### Claim 2 (depends on 1)

The method for enhancing the OSNR measuring precision by correcting spectral resolution according to claim 1, in which the step (7) comprises sub steps of:
(7.1) measuring the spectrum of the signal under test which have the central wavelength of λ and a bandwidth of Δλ3 by using the OSA; substituting PBi=Paj·Δλ1/Δλ2 into the fitting expression, to obtain the corrected resolutions Resaj corresponding to the sampling points required by calculating the OSNR in the spectrum, wherein, Paj are the powers of the sampling points required by calculating the OSNR in the spectrum, j=1, 2, . . . , m, and Δλ3≤Δλ4;
(7.2) obtaining a total power of the signal under test
P
⁡
(
Δλ
3
)
=
∑
k
=
1
l
⁢
⁢
P
bk
·
Δλ
2
Res
bk
,
wherein, Pbk are the powers of sampling points which fall into the spectrum range having the central wavelength of λ and the bandwidth of Δλ3, k=1, 2, . . . , l; Resbk are the corrected resolutions corresponding to the powers Pbk of the sampling points;
(7.3) obtaining a total power of noise
N
⁡
(
Δλ
3
)
=
f
⁡
[
∑
t
=
1
S
⁢
⁢
P
ct
·
Δλ
2
Res
ct
,
∑
p
=
1
q
⁢
⁢
P
dp
·
Δλ
2
Res
dp
]
,
wherein, Pct and Pdp are the powers of the sampling points, t=1, 2, . . . , s, p=1, 2, . . . , q; and Resct and Resdp are corrected resolutions corresponding to the powers Pct and Pdp of the sampling points, respectively;
(7.4) obtaining the optical signal to noise ratio
OSNR
=
10
⁢
⁢
log
⁢
P
⁡
(
Δλ
3
)
-
N
⁡
(
Δλ
3
)
N
⁡
(
Δλ
3
)
·
λ
r
/
Δλ
3
according to the total power of the signal under test and the total power of noise, wherein, A, is a reference bandwidth.

### Claim 3

A method for enhancing optical signal-to-noise ratio (OSNR) measuring precision by correcting spectral resolution, the method comprising steps of:
(1) obtaining actual power PA of a broad spectrum signal which has a central wavelength of λ and a bandwidth of Δλ1;
(2) measuring a calibration spectrum of the broad spectrum signal by using volume grating optical spectrum analyzer (OSA), adding up powers of sampling points which fall into spectrum range having the central wavelength of λ and the bandwidth of Δλ1, to obtain a sum PB of the powers of the sampling points;
(3) obtaining a corrected resolution Res=PB·Δλ2/PA, according to the actual power PA of the broad spectrum signal, the sum PB of the powers of the sampling points, and a wavelength interval Δλ2 between adjacent sampling points;
(4) measuring a spectrum of a signal under test by using the volume grating OSA, and obtaining the OSNR based on the corrected resolution.

### Claim 4 (depends on 3)

The method for enhancing the OSNR measuring precision by correcting spectral resolution according to claim 3, in which the step (4) comprises:
(4.1) measuring the spectrum of the signal under test which has the central wavelength of λ and a bandwidth of Δλ3 by using the volume grating OSA, wherein, Δλ3≤Δλ1;
(4.2) obtaining a total power of the signal under test
P
⁡
(
Δλ
3
)
=
∑
k
=
1
l
⁢
⁢
P
k
·
Δλ
2
Res
,
wherein, Pk are the powers of the sampling points which fall into the spectrum range having the central wavelength of λ and the bandwidth of Δλ3, k=1, 2, . . . , l;
(4.3) obtaining a total power of noise
N
⁡
(
Δλ
3
)
=
(
P
⁡
(
λ
-
Δλ
)
Res
+
P
⁡
(
λ
+
Δλ
)
Res
)
·
Δλ
3
2
,
wherein, P(λ−Δλ) and P(λ+Δλ) are the powers of the sampling points at wavelengths of λ−Δλ and λ+Δλ, respectively, wherein, λ indicates the central wavelength; and
(4.4) obtaining the optical signal to noise ratio
OSNR
=
10
⁢
⁢
log
⁢
P
⁡
(
Δλ
3
)
-
N
⁡
(
Δλ
3
)
N
⁡
(
Δλ
3
)
·
λ
r
/
Δλ
3
,
wherein, λr is a reference bandwidth.