Unbalanced Polarization Research Articles

Dual-ring parity-time symmetric brillouin fiber laser with an unbalanced polarization Mach-Zehnder interferometer.

A dual-ring parity-time (PT) symmetric Brillouin fiber laser (BFL) with an unbalanced polarization Mach-Zehnder interferometer (UP-MZI) is proposed and experimentally investigated. An UP-MZI consisting of optical coupler, polarization beam combiner (PBC) and two asymmetric length arms with 10 km and 100 m single-mode fiber, is used to achieve Vernier effect and PT symmetry. Due to the orthogonally polarized lights created in the PBC, the dual-ring PT symmetry BFL with an UP-MZI implements two unbalanced length feedback rings that are connected to one another, one long length ring with a Brillouin gain and the other short length ring with a loss of the same magnitude, to break a PT symmetric and maintain the Vernier effect. By contrast with existing PT symmetry BFL studies, this design does not require same lengths of the gain and loss loops, but can manipulate freely PT symmetry status in accordance with a rational scaling factor between them. Experimental results reveal that the 3-dB linewidth of dual-ring PT symmetry BFL with an UP-MZI is about 4.85 Hz with the threshold input power of 9.5 mW, in accordance with the 97 Hz measured linewidth at the -20 dB power point. Within 60 mins of the stability experiment, the power and frequency stability fluctuation are ±0.02 dB and ±0.137 kHz, respectively. Thanks to the two asymmetric ring lengths, the sidemode suppression ratio (SMSR) is optimized by 54 dB compared to that with the only long ring structure, 26 dB when using only the Vernier effect or 12 dB for existing PT symmetry BFL. This BFL design with single longitudinal mode and high SMSR output can be applied to high coherent communication and Brillouin-based microwave photonics systems with low phase noise.

Faithful Transmission of Single-Photon Qubits Using Error-Rejection Coding

Here, we experimentally demonstrate a faithful single-photon qubits transmission using error-rejecting coding, resorting to neither ancillary photons nor entangled photon resources. Using unbalanced polarization interferometer, the polarization qubits are transferred into the state on time-bin degree of freedom. Additionally, the deterministic transmission of single photon quantum states can be achieved with high fidelity. The immunity of time-bin encoded qubits against collective noise paves the way to practical quantum error-correction and error-rejection in quantum information science.

Faithful qubit transmission against collective noise without ancillary qubits

We present a faithful qubit transmission scheme with linear optics against collective noise, not resorting to ancillary qubits. Its setup is composed of three unbalanced polarization interferometers, based on a polarizing beam splitter, a beam splitter, and a half wave plate, which makes this scheme more feasible than others with present technology. The fidelity of successful transmission is 1, independent of the parameters of the collective noise, and the success probability for obtaining an uncorrupted state can be improved to 100% with some time delayers. Moreover, this scheme has some good applications in one-way quantum communication for rejecting the errors caused by the collective noise in quantum channel.

40 Gbit/s Metropolitan networks using power unbalanced polarization division multiplexing

The feasibility of a 40 Gbit/s wavelength division multiplexed system using a power unbalanced polarization division multiplexing (PUPDM) scheme has been explored for metropolitan distances using the standard single mode fiber and erbium doped fiber amplifiers. PUPDM is a quaternary communication scheme in which two subchannels, each carrying 20 Gbit/s information data, are combined on the same wavelength to effectively communicate 40 Gbits/s using only binary transmitters and binary receivers. PUPDM not only reduces the cost of the optics and electronics in metropolitan networks but also reduces the degrading effect of polarization mode dispersion (PMD) by actually transmitting at half of the effective data rate. The effects of fiber nonlinearity and PMD are extensively analyzed for each of two 20 Gbit/s subchannels for an aggregate 40 Gbit/s capacity per wavelength channel. The analysis suggests that a 40 Gbit/s PUPDM system with 50 GHz channel spacing is feasible for up to 600 km of transmission distance on single mode fiber, using 7% Reed-Solomon forward error correction and 20 Gbit/s electronics.