Abstract
Establishing parity-time (PT) symmetry in non-spatial space is a promising way to simplify the PT-symmetry system structure. In this paper, an implementation of PT symmetry in optical polarization space is reported. By utilizing the polarization multiplexing technology, PT symmetry is formed in overlapping spatial parameter space. The degeneracy of eigenmodes with two distinct PT phases in polarization space is demonstrated. In the PT-symmetric phase, the eigenmodes have real eigenfrequencies that respect PT symmetry, exhibiting broken degeneracy (mode splitting); in the PT-broken phase, the eigenmodes are degenerate with a pair of complex conjugate eigenfrequencies. The sharp-pointed peak filter response in the PT-broken phase due to the strong field localization is characterized, which explains the mode-selection mechanism of PT-symmetry breaking. The polarization-space PT symmetry is applied in a 7-km single-loop optoelectronic oscillator, and a stable single-mode oscillation signal is generated with a phase noise of −138 dBc/Hz at 10 kHz and side-mode suppression ratio of 49 dB. The approach expands the parameter spaces to carry out PT symmetry and could promote the integration of the PT-symmetry photon system.
Highlights
The polarization-space PT symmetry is applied in a 7-km single-loop optoelectronic oscillator, and a stable single-mode oscillation signal is generated with a phase noise of −138 dBc/Hz at 10 kHz and side-mode suppression ratio of 49 dB
PT symmetry has been demonstrated in the parameter space of polarization in microwave photonics
Two mutually coupled polarization-space resonators (PSRs) were implemented with anti-symmetric gain and loss coefficients in a single-loop optoelectronic oscillators (OEOs) by utilizing the polarization dependent modulation property of the LiNbO3 Mach–Zehnder modulator (MZM)
Summary
Zhang et al extended the PT symmetry from spatial space to wavelength space and proposed a PT-symmetric OEO with a special single-loop architecture, in which the gain and loss microwave modes are carried by two different optical wavelengths but still at the expense of two tunable laser sources (TLSs). We report an experimental implementation of PT symmetry in optical polarization space and propose a novel approach to realize single-mode oscillation in a common single-loop OEO with a long loop. A single-loop PT-symmetric OEO is proposed with a lower complexity, which greatly simplifies the implementation of OEOs for ultralow phase noise microwave generation and contributes to the full photonic integration of PT symmetry
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