台大光电所所讯

Synthesizer-free 28-GHz MMW Fiber-wireless Link with Orthogonally Polarized Dual-mode VCSEL

Professor Gong-Ru Lin’s Laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所林恭如教授

A synthesizer-free 28-GHz is proposed for fifth-generation (5G) millimeter wave over fiber (MMWoF) link by using orthogonally polarized dual-mode vertical-cavity surface-emitting laser (VCSEL) as the frontend transmitter, and the power envelope detection is employed for self-heterodyne down-conversion of the generalized frequency division multiplexing (GFDM) data stream. The demonstrated MMWoF link exhibits superior immunity to the residual frequency and phase noises as well as the inter-carrier interference induced by the free-running dual-mode carrier. After equalizing the dual modes with an extremely weak power as low as -26 dBm at TM-mode polarization, the dual-mode power extinction of only 5.4 dB is achieved for optimizing the remote-node optical heterodyne of 28-GHz MMW carrier with a peak power of -59.8 dBm before antenna propagation with remaining similar relative intensity noise (RIN) as compared to the free-running case. Moreover, the mode partition noise (MPN) is increased less than 2 dBc/Hz after mode-power equalization.

Fig. 1 Schematic diagram of 5G MMWoF link based on 2-l VCSEL transmitter with novel QAM-GFDM. (a) The photograph and (b) the optical spectrum of 2-l VCSEL without package.


Fig. 2 (a) The free-running polarization characteristic and (b) the P-I curves without and with master controlling of the dual-mode VCSEL.	Fig. 3 The RIN and MPN of the dual-mode VCSEL at (a) free-running operation with different bias current and (b) TE- (c) TM-mode injection controlling.

For back-to-back optical downstream wireline transmission, the receiving GFDM data optimizes its BER to 2.2´10^-4 by adjusting the bias current of the dual-mode VCSEL to 8 mA (3 I_th), and by grouping the GFDM data matrix with total symbols of N=K´M with K=2 subcarriers and M=24 timeslots. After long-reach 50-km DM-SMF, the qualified receiving power sensitivity is -12 dBm, whereas the decoding GFDM data reveals improved receiving sensitivity with extremely low power penalty of only 0.3 dB. After wireless delivering over 2 m in free space, the self-heterodyne down-conversion by power envelope detection guarantees the down-converted QAM-GFDM data stream with an average power of -48.4 dBm after optimizing the impedance matching by selecting appropriate frequency response of the power envelope detector. As a result, the wireless MMW transmission of 8-Gbit/s 4-QAM GFDM data stream is qualified with EVM of 16.9%, SNR of 8.5 dB and BER of 3.8´10^-3.


Fig. 4 The constellation plots and decoded SNR spectra of the modulated 30-Gbit/s 64-QAM GFDM data by the dual-mode VCSEL after BtB, 25-/50-km SMF and 50-km DM-SMF transmissions.	Fig. 5 The constellation plot, RF and SNR spectrum of the delivered 4-QAM GFMD data after 2-m free-space transmission and self-heterodyne down-conversion.

Reference:

[1] C.-Y. Lin, Y.-C. Chi, C.-T. Tsai, H.-Y. Wang and G.-R. Lin, “39-GHz millimeter-wave carrier generation in dual-mode colorless laser diode for OFDM-MMWoF transmission,” IEEE J. Sel. Top. Quantum Electron.,vol. 21, no. 6, pp. 609-618, 2015.

[2] C.-T. Tsai, C.-H. Lin, C.-T. Lin, Y.-C. Chi and G.-R. Lin, “60-GHz millimeter-wave over fiber with directly modulated dual-mode laser diode,” Sci Rep, vol. 6, no. 27919, pp. 1-12, 2016.

[3] C.-Y. Lin, Y.-C. Chi, C.-T. Tsai, H.-Y. Wang, H.-Y. Chen, M. Xu, G.-K. Chang and G.-R. Lin, “Millimeter-wave carrier embedded dual-color laser diode for 5G MMW of link,” J. Light. Technol., vol. 35, no. 12, pp. 2409-2420, 2017.

[4] C.-Y. Lin, Y.-C. Chi, C.-T. Tsai, H.-Y. Chen and G.-R. Lin, “Two-color laser diode for 54-Gb/s fiber-wired and 16-Gb/s MMW wireless OFDM transmissions,” Photonics Res., vol. 5, no. 4, pp. 271-279, 2017.

[5] Z.-K. Weng, Y.-C. Chi, H.-Y. Kao, C.-T. Tsai, H.-Y. Wang and G.-R. Lin, “Quasi-color-free LD-based long-reach 28-GHz MMWoF With 512-QAM OFDM,” J. Light. Technol., vol. 36, no. 19, pp. 4282-4297, 2018.

A New Fitting Method for Ambipolar Diffusion Length Extraction in Thin Film Structures Using Photoluminescence Measurement with Scanning Excitation

Professor Ming-Hua Mao’s Laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所毛明华教授

A new simple method is proposed to extract the ambipolar diffusion length for two-dimensional (2D) electronic transport in thin film structures using a scanning photoluminescence microscopy (SPLM) setup. No spatially-resolved photoluminescence detection methods are required. By measuring the excitation-position-dependent PL intensity across the edge of a semiconductor, ambipolar diffusion length can be extracted from the SPLM profile through a simple analytic fitting function. Numerical simulation was first used to verify the fitting method. Then the fitting method was applied to extract the ambipolar diffusion length from the measured SPLM profile of a GaAs thin film structure. Carrier lifetime was obtained in an accompanying time-resolved photoluminescence measurement under the same excitation condition, and thus the ambipolar diffusion coefficient can be determined simultaneously. The new fitting method provides a simple way to evaluate carrier transport properties in 2D electronic transport structures such as thin films or quantum wells. This work has been published in Scientific Reports: Chu, C. H., Mao, M.-H., Lin, R. Y. & Lin, H. H. A New Fitting Method for Ambipolar Diffusion Length Extraction in Thin Film Structures Using Photoluminescence Measurement with Scanning Excitation. Scientific Reports 10, 5200, doi:10.1038/s41598-020-62093-w (2020).

Fig. 1 (a) 2D photocarrier distribution mappings under CW excitation with varied excitation position (x,y) = (x_pump,0). (b) Cross-sections of the above mappings at y = 0 & scanning profile for the normalized total photocarrier number δN under pulse excitation. The result without Auger recombination is also shown for comparison.