Abstract
A microwave photonic link (MPL) with simultaneous suppression of the even-order and third-order distortions using a polarization modulator (PolM), an optical bandpass filter (OBPF), and a balanced photodetector (BPD) is proposed and experimentally demonstrated. The even-order distortions are suppressed by utilizing orthogonal polarization modulation based on the PolM and balanced differential detection based on the BPD. The third-order distortions (IMD3) are suppressed by optimizing the spectral response of the OBPF with an optimal power ratio between the optical carrier and the sidebands of the phase-modulated signals from the PolM. Since the suppression of the IMD3 is achieved when the MPL is optimized for even-order distortion suppression, the proposed MPL can operate with simultaneous suppression of the even-order and third-order distortions. The proposed MPL is analyzed theoretically and is verified by an experiment. For a two-tone RF signal of f1 = 10 GHz and f2 = 19.95 GHz, the spurious-free dynamic range (SFDR2) is enhanced by 23.4 dB for the second harmonic (2f1), and 29.1 and 27.6 dB for the second intermodulation (f2-f1 and f1 + f2), as compared with a conventional MPL. For a two-tone RF signal of f1 = 9.95 GHz and f2 = 10 GHz, the SFDR3 is increased by 13.1 dB as compared with a conventional MPL.
Highlights
Microwave photonic links (MPLs) have been used for various applications such as antenna remoting, phased array beamforming, and wireless access networks, due to the advantages such as very low insertion loss, ultra-broad bandwidth, and high immunity to EMI [1,2,3]
We have recently proposed a simplified solution using a single polarization modulator (PolM) [16,17,18] that could operate equivalently as two Mach-Zehnder modulators (MZMs), which greatly decrease the complexity and cost
To verify that the proposed MPL is effective in the suppression of the even-order and the third-order distortions, a proof-of-concept experiment based on the system shown in Fig. 1 is implemented
Summary
Microwave photonic links (MPLs) have been used for various applications such as antenna remoting, phased array beamforming, and wireless access networks, due to the advantages such as very low insertion loss, ultra-broad bandwidth, and high immunity to EMI [1,2,3]. All the MPLs reported in [6,7,8,9] are able to operate with significantly reduced evenorder distortions, but the odd-order distortions are still there which will affect the microwave signal power accommodating capacity of the MPLs. To eliminate the odd-order distortions, primarily the IMD3, several techniques have been proposed, including those implemented in the electrical domain and the optical domain. In [19], an MPL using two optical sources with a large wavelength difference and a single MZM was proposed, in which the MZM was biased at the opposite transmission points due to the wavelength-dependent transmission function of the MZM Both the second-order and third-order distortions were minimized by a precise control of the bias points and the ratio between the optical powers of the two wavelengths.
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