Abstract
New microwave photonic signal processing structures for generating in-phase and quadrature phase RF signals are presented. They are based on designing the bias angles of a dual-drive Mach Zehnder modulator (DDMZM) or a dual-parallel Mach Zehnder modulator (DPMZM) to introduce a specific phase shift to the optical carrier and using a wavelength division multiplexer to separate the lower and upper RF modulation sidebands. The optical carrier beat with the sidebands in a pair of photodetectors generate two output RF signals with a quadrature phase difference. The two proposed structures are simple, low cost and free of electrical components. The upper operating frequency of the two microwave photonic signal processors is only limited by the optical modulator bandwidth. Experimental results demonstrate the proposed microwave photonic signal processing structures have the ability to generate in-phase and quadrature phase signals with small phase and amplitude imbalance, over a wide frequency range.
Highlights
Processing radio frequency (RF) signals in an optical domain is attractive
Using the edge roll off of the two wavelength division multiplexer (WDM) channel magnitude responses shown in Fig. 9(b), ±0.3 GHz change in the tunable laser frequency causes less than 0.5 dB change in the carrier and sideband power at the two WDM channel outputs, which has negligible effect on the Microwave photonic Hilbert transformers (MPHTs) phase imbalance performance
The results indicate that the dual-parallel Mach Zehnder modulator (DPMZM) based MPHT has 10.4 dB improvement in the second order harmonic suppression compared to the dual-drive Mach Zehnder modulator (DDMZM) based MPHT
Summary
Processing radio frequency (RF) signals in an optical domain is attractive. This arises from the wideband capability of photonics, which overcomes the bandwidth limitation in conventional electronic signal processors [1], [2]. Microwave photonic Hilbert transformers (MPHTs) based on a multitap transversal filter have a complex structure as they require multiple laser sources with specific wavelengths and amplitudes, and a dispersive fibre [4], [5]. Their bandwidths are limited by the filter free spectral range. This MPHT can be integrated into a compact device It requires six DC voltages for biasing the two DPol-DDMZMs. Note that a ring resonator [9], [10], a nonuniformly spaced delay line filter [11] and a -phase shifted fibre Bragg grating (FBG) [12] can be used to implement a Hilbert transformer. Experimental results are presented that demonstrate in-phase and quadrature phase RF signal generation using the two proposed MPHT structures
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