• Chinese Optics Letters
  • Vol. 22, Issue 1, 013901 (2024)
Lihan Wang, Lingyun Ren, Xiangchuan Wang*, and Shilong Pan**
Author Affiliations
  • National Key Laboratory of Microwave Photonics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
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    DOI: 10.3788/COL202422.013901 Cite this Article Set citation alerts
    Lihan Wang, Lingyun Ren, Xiangchuan Wang, Shilong Pan. Time-resolution enhanced multi-path OTD measurement using an adaptive filter based incoherent OFDR[J]. Chinese Optics Letters, 2024, 22(1): 013901 Copy Citation Text show less

    Abstract

    High accuracy and time resolution optical transfer delay (OTD) measurement is highly desired in many multi-path applications, such as optical true-time-delay-based array systems and distributed optical sensors. However, the time resolution is usually limited by the frequency range of the probe signal in frequency-multiplexed OTD measurement techniques. Here, we proposed a time-resolution enhanced OTD measurement method based on incoherent optical frequency domain reflectometry (I-OFDR), where an adaptive filter is designed to suppress the spectral leakage from other paths to break the resolution limitation. A weighted least square (WLS) cost function is first established, and then an iteration approach is used to minimize the cost function. Finally, the appropriate filter parameter is obtained according to the convergence results. In a proof-of-concept experiment, the time-domain response of two optical links with a length difference of 900 ps is successfully estimated by applying a probe signal with a bandwidth of 400 MHz. The time resolution is improved by 2.78 times compared to the theoretical resolution limit of the inverse discrete Fourier transform (iDFT) algorithm. In addition, the OTD measurement error is below ±0.8 ps. The proposed algorithm provides a novel way to improve the measurement resolution without applying a probe signal with a large bandwidth, avoiding measurement errors induced by the dispersion effect.
    iPMD(fm)=l=1Lal2exp(j2πfmτl),

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    i=F(τ)ψ+e,

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    f(τk)=[exp(j2πf1τk),,exp(j2πfMτk)]T,

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    iiDFT=[FH(τ)i)][FH(τ)F(τ)],

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    Q(τk)=F(τ)PFH(τ)Pkf(τk)fH(τk),

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    C(ψk)=[if(τk)ψk]HQ1(τk)[if(τk)ψk].

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    ψ^k=fH(τk)Q1(τk)ifH(τk)Q1(τk)f(τk).

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    ψ^knew=fH(τk)Q1(τk)ifH(τk)Q1(τk)f(τk),k=1,2,,K,

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    Pnew=diag[|ψ^1new|2,|ψ^2new|2,,|ψ^Knew|2],

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    Q(τk)new=F(τ)PnewFH(τ)|ψ^knew|2f(τk)fH(τk).

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    Lihan Wang, Lingyun Ren, Xiangchuan Wang, Shilong Pan. Time-resolution enhanced multi-path OTD measurement using an adaptive filter based incoherent OFDR[J]. Chinese Optics Letters, 2024, 22(1): 013901
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