Simultaneous even- and third-order distortion suppression in a microwave photonic link based on orthogonal polarization modulation, balanced detection, and optical sideband filtering

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.

Advanced photonic signal processing and hybrid integrated microwave photonic systems

“…Therefore the noise oor in balanced detection can be much reduced compared to the case of direct detection with a single detector, as shown in Figure 2.6(b), where the RF output power using a single photodiode is compared to the RF output power when using balanced detection. Thus, using balanced detection can further improve the APL performance [16], [17].…”

“…In the noiseless ideal scenario the output SNR is the same as the input SNR, since there is no degradation. Instead, for the noisy case, the output SNR becomes 17) where P n,a is the additional noise power generated by the two-port device referred to the input. Practically, an easily measurable quantity which describes the reduction of the output SNR when compared to the input SNR, is the noise factor, F , dened as follows The APL can be inserted in Figure 2.8 as the two-port noisy device.…”

“…17 shows the impact of a 10% detuning for the phase of one ring (ϕ ur ) on the transmission response. This is just an example, and ou calculations show that a change in any parameter will aect the transmission as well as the phase response of the lter so much that the ltering functionality might be compromised.…”