A highly reconfigurable photonic microwave frequency mixer

Abstract

Frequency mixers represent one of the most essential components of microwave and millimeter-wave systems. Compared to conventional electrical mixers, photonic microwave frequency mixers are of great interest for wideband, multifunctional, and reconfigurable radio frequency (RF) systems. This is due to a number of distinct features, including wide bandwidth, good isolation, and immunity to electromagnetic interference. However, despite great efforts being devoted to the development of high-performance photonic microwave frequency mixers over the past two decades, the two intrinsic challenges of photonic mixers-undesirable mixing spurs (unnecessary frequency components produced due to nonlinearities in the mixer), which restrict the operation bandwidth and reduce the signal-to-interference ratio, and limited mixing functions-have not yet been overcome. Most traditional photonic microwave mixers are equivalent to a single-ended mixer. Single-ended mixers suffer from large mixing spurs, DC leakages, phase-relevant operation, and relatively large mixing noise values. Other highperformance mixers that are widely used in microwave and millimeter-wave systems-e.g., the double-balanced mixer, which reduces spurious responses and suppresses DC components; the in-phase/quadrature (I/Q) mixer, which enables phase-irrelevant frequency conversion and produces two quadrature signals with equal amplitudes; and the image-reject mixer, which performs single-sideband downconversion, enabling interference from spurious signals to be avoided-have rarely been implemented in the optical domain.

Photonics-Based Microwave Image-Reject Mixer

“…Phase-cancellation technique is another way to realize photonics-based microwave IRMs [18][19][20][21][22][23][24][25][26][27][28][29][30], also known as Hartley architecture. Figure 5 shows the principle method.…”

“…The third class of photonic IRMs based on phase cancellation applies a 90 • optical hybrid to introduce a quadrature phase [25][26][27][28][29]. Benefiting from a simple structure and the small phase imbalance of the commercially available optical hybrid over a wide frequency range, a high image rejection ratio can be achieved in a large bandwidth.…”

“…One branch is modulated by an RF signal and the other is modulated by an LO signal, both with carrier-suppressed single-sideband (CS-SSB) modulation. The CS-SSB modulation can be realized by using either optical filters placed in each branch [25][26][27], or I/Q modulators operated at CS-SSB mode [28,29]. Signals from the two branches are sent to the signal port and the LO port of the 90 • optical hybrid, which typically has two in-phase output and two quadrature output ports.…”

“…It should be noted that if other outputs of the 90 • optical hybrid are directed to PDs, single-ended and balanced mixers can also be realized. Since parallel modulations, and/or parallel filterings, and parallel amplifications are required to obtain the independent RF and LO sidebands, the system performance will therefore be vulnerable to any path length difference between the two branches [26][27][28][29]. Therefore, environmental vibration, which cause path length variations, would be a challenge for practical application of such IRMs.…”

“…In this paper, we review recent developments in photonics-based microwave IRM with an emphasis on the pre-filtering method [12][13][14][15][16][17] and the phase cancellation method [18][19][20][21][22][23][24][25][26][27][28][29][30]. Applications of photonics-based microwave IRMs in electronic warfare, radars, satellite communications, and so on, are described [31][32][33][34][35][36][37][38][39][40][41][42][43], with challenges in implementing photonics-based microwave IRMs to meet the requirements of RF systems.…”