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Advanced Photonics Nexus, Volume. 3, Issue 3, 036007(2024)

Beyond 200-Gb/s O-band intensity modulation and direct detection optics with joint look-up-table-based predistortion and digital resolution enhancement for low-cost data center interconnects

Qi Wu1,2,3, Zhaopeng Xu1、*, Yixiao Zhu2、*, Tonghui Ji1, Honglin Ji1, Yu Yang1, Junpeng Liang1, Chen Cheng1, Gang Qiao1, Zhixue He1, Jinlong Wei1, Qunbi Zhuge2, and Weisheng Hu1,2
Author Affiliations
  • 1Peng Cheng Laboratory, Shenzhen, China
  • 2Shanghai Jiao Tong University, State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Electronic Engineering, Shanghai, China
  • 3University of L’Aquila, Department of Physical and Chemical Sciences, L’Aquila, Italy
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    (a) Schematic of generation and predistortion procedures of LUT. XT(k−M:k+M), transmitted training symbols; Y(k−M:k+M), recovered training symbols; E(k), the difference between the known transmitted symbols and the recovered symbols; C(i), the counter; LUTe(i), averaged error; S(k−n:k:k+n), transmitted payload symbols; SLUT(k), the predistorted symbols. (b) Schematic block diagram of DRE. x(n), input signal needed to be converted to analog; xq(n), quantized version of x(n); qeff(n), effective quantization error; qro(n), the round-off error; u(n), an integer control sequence; DQ, dynamic quantization; Δ, DAC output step size; qdq(n), the dynamic quantization error; h(n), the combined frequency response of the channel and the matched filtering.

    Fig. 1. (a) Schematic of generation and predistortion procedures of LUT. XT(k−M:k+M), transmitted training symbols; Y(k−M:k+M), recovered training symbols; E(k), the difference between the known transmitted symbols and the recovered symbols; C(i), the counter; LUTe(i), averaged error; S(k−n:k:k+n), transmitted payload symbols; SLUT(k), the predistorted symbols. (b) Schematic block diagram of DRE. x(n), input signal needed to be converted to analog; xq(n), quantized version of x(n); qeff(n), effective quantization error; qro(n), the round-off error; u(n), an integer control sequence; DQ, dynamic quantization; Δ, DAC output step size; qdq(n), the dynamic quantization error; h(n), the combined frequency response of the channel and the matched filtering.

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    Pattern error versus pattern index for PAM-4 signal in the following experiment.

    Fig. 2. Pattern error versus pattern index for PAM-4 signal in the following experiment.

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    (a) Combined response of the channel and the matched filtering. (b) Electrical spectra of quantized signals for 124-GBd PAM-4 modulation with and without DRE.

    Fig. 3. (a) Combined response of the channel and the matched filtering. (b) Electrical spectra of quantized signals for 124-GBd PAM-4 modulation with and without DRE.

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    (a) Experimental setup. DFB, distributed feedback; AWG, arbitrary waveform generator; MZM, Mach–Zehnder modulator; SSMF, standard single-mode fiber; SOA, semiconductor optical amplifier; VOA, variable optical attenuator; PD, photodiode; RTO, real-time oscilloscope. (b) DSP procedures implemented at the transmitter and receiver sides. RRC, root-raised cosine; LUT, look-up-table; DRE, digital resolution enhancer. (c) Optical spectrum of 124-GBd PAM-4 signal. (d) Received electrical spectrum of 124-GBd PAM-4 signal.

    Fig. 4. (a) Experimental setup. DFB, distributed feedback; AWG, arbitrary waveform generator; MZM, Mach–Zehnder modulator; SSMF, standard single-mode fiber; SOA, semiconductor optical amplifier; VOA, variable optical attenuator; PD, photodiode; RTO, real-time oscilloscope. (b) DSP procedures implemented at the transmitter and receiver sides. RRC, root-raised cosine; LUT, look-up-table; DRE, digital resolution enhancer. (c) Optical spectrum of 124-GBd PAM-4 signal. (d) Received electrical spectrum of 124-GBd PAM-4 signal.

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    Measured BERs versus ROP in the case of 2-km SSMF transmission for (a) 124-GBd PAM-4, (e) 124-GBd PAM-6, and (i) 112-GBd PAM-8 signals. Measured BERs versus PNoB in the case of 2-km SSMF transmission for (b) 124-GBd PAM-4, (f) 124-GBd PAM-6, and (j) 112-GBd PAM-8 signals. Electrical spectra with and without DRE of (c) 124-GBd PAM-4 signal using a 3-bit DAC, (g) 124-GBd PAM-6 signal using a 3.5-bit DRE, and (k) 112-GBd PAM-8 signal using a 4-bit DRE. Temporary amplitudes versus sample index of (d) 124-GBd PAM-4 signal with a 3-bit DAC and DRE, (h) 124-GBd PAM-6 signal with a 3.5-bit DAC and DRE, and (l) 112-GBd PAM-8 signal with a 4-bit DAC and DRE.

    Fig. 5. Measured BERs versus ROP in the case of 2-km SSMF transmission for (a) 124-GBd PAM-4, (e) 124-GBd PAM-6, and (i) 112-GBd PAM-8 signals. Measured BERs versus PNoB in the case of 2-km SSMF transmission for (b) 124-GBd PAM-4, (f) 124-GBd PAM-6, and (j) 112-GBd PAM-8 signals. Electrical spectra with and without DRE of (c) 124-GBd PAM-4 signal using a 3-bit DAC, (g) 124-GBd PAM-6 signal using a 3.5-bit DRE, and (k) 112-GBd PAM-8 signal using a 4-bit DRE. Temporary amplitudes versus sample index of (d) 124-GBd PAM-4 signal with a 3-bit DAC and DRE, (h) 124-GBd PAM-6 signal with a 3.5-bit DAC and DRE, and (l) 112-GBd PAM-8 signal with a 4-bit DAC and DRE.

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    Measured BERs versus PNoB in the 40-km SSMF transmission for (a) 124-GBd OOK, (e) 124-GBd PAM-3, and (i) 124-GBd PAM-4 signals. Measured BERs versus ROP in the 40-km SSMF transmission for (b) 124-GBd OOK, (f) 124-GBd PAM-3, and (j) 124-GBd PAM-4 signals. Electrical spectra with and without DRE of (c) 124-GBd OOK with a 1.5-bit DAC, (g) 124-GBd PAM-3 with a 2-bit DAC, and (k) 124-GBd PAM-4 with a 3-bit DAC signals. Temporal amplitudes versus (d) 124-GBd OOK signal with a 1.5-bit DAC and DRE, (h) 124-GBd PAM-3 signal with a 2-bit DAC and DRE, and sample index (l) 124-GBd PAM-4 signal with a 3-bit DAC and DRE.

    Fig. 6. Measured BERs versus PNoB in the 40-km SSMF transmission for (a) 124-GBd OOK, (e) 124-GBd PAM-3, and (i) 124-GBd PAM-4 signals. Measured BERs versus ROP in the 40-km SSMF transmission for (b) 124-GBd OOK, (f) 124-GBd PAM-3, and (j) 124-GBd PAM-4 signals. Electrical spectra with and without DRE of (c) 124-GBd OOK with a 1.5-bit DAC, (g) 124-GBd PAM-3 with a 2-bit DAC, and (k) 124-GBd PAM-4 with a 3-bit DAC signals. Temporal amplitudes versus (d) 124-GBd OOK signal with a 1.5-bit DAC and DRE, (h) 124-GBd PAM-3 signal with a 2-bit DAC and DRE, and sample index (l) 124-GBd PAM-4 signal with a 3-bit DAC and DRE.

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    • Table 1. Comparison of high-speed IM-DD optics with low-resolution DAC.

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      Table 1. Comparison of high-speed IM-DD optics with low-resolution DAC.

      ReferenceBaud rate (GBd)Modulation formatNet data rate (Gb/s)BandDistance (km)Resolution of DAC (bit)DSP methodFEC
      Ref. 2828PAM-452.3C804EDC, TQNS7% HD-FEC
      Ref. 3232PAM-459.8C103Preequalization, EFNS7% HD-FEC
      Ref. 3340PS-PAM-474.1C33Preequalization, EFNS7% HD-FEC
      Ref. 315016/32/64-QAM-DMT91.7/114/137.5C24/5/6Preequalization, TQNS7% HD-FEC
      Ref. 4550PAM-493.5N/A03Preequalization, DREBER = 5×10−4, <7% HD-FEC
      Ref. 3650DFT-S-32-QAM-DMT93.5C25Preequalization, TQNS7% HD-FEC
      Ref. 2950DMT93.5C23Preequalization, CRD-NS7% HD-FEC
      Ref. 3755PAM-4102.8C23Preequalization, CRD-NS7% HD-FEC
      Ref. 4456PAM-4104.7C404THP, DRE7% HD-FEC
      Ref. 3056PAM-4104.7C803CDPC, Clipping, DRE7% HD-FEC
      Ref. 3560PAM-4112.1O404Preequalization, TQNS7% HD-FEC
      This work124PAM-4235.3O23DREKP4-FEC
      This work124PAM-6289.7O23.5DRE7% HD-FEC
      This work112PAM-8294.7O24DRE14% HD-FEC
      This work124PAM-2117.6O401.5LUT predistortion, DREKP4-FEC
      This work124PAM-3173.8O402LUT predistortion, DRE7% HD-FEC
      This work124PAM-4231.8O403LUT predistortion, DRE7% HD-FEC
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    Qi Wu, Zhaopeng Xu, Yixiao Zhu, Tonghui Ji, Honglin Ji, Yu Yang, Junpeng Liang, Chen Cheng, Gang Qiao, Zhixue He, Jinlong Wei, Qunbi Zhuge, Weisheng Hu. Beyond 200-Gb/s O-band intensity modulation and direct detection optics with joint look-up-table-based predistortion and digital resolution enhancement for low-cost data center interconnects[J]. Advanced Photonics Nexus, 2024, 3(3): 036007

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    Paper Information

    Category: Research Articles

    Received: Dec. 29, 2023

    Accepted: Apr. 3, 2024

    Published Online: Apr. 25, 2024

    The Author Email: Xu Zhaopeng (xuzhp@pcl.ac.cn), Zhu Yixiao (yixiaozhu@sjtu.edu.cn)

    DOI:10.1117/1.APN.3.3.036007

    Topics

    laser devices and laser physics
    Lasers and Laser Optics
    Laser physics
    laser manufacturing
    Instrumentation, Measurement and Metrology