An optical conversion node scheme for direct detection of complex modulation format is proposed to bridge long-haul transmissions and short-reach interconnects. A noisy 10G Baud quadrature phase shift keying signal is converted into a 10G Baud normal 4-level pulse amplitude modulation (PAM4) signal by the node. The conversion node is realized mainly relies on four-wave mixing-based phase-sensitive amplifiers. The power ratio and constellation shape of the converted PAM4 both can be flexibly designed based on network demands and five kinds of uniform or non-uniform PAM4s are generated to verify the shaping functionality. With the input optical signal-to-noise ratio range of (10 dB∼30 dB), the key indicators of the signals went through every part are measured, includes constellations, eye diagrams, error vector magnitudes, bit error rates, normalized impact factors of phase and amplitude. The proposed node scheme has great application potential in intermediate nodes for bridging long-haul transmissions and short-reach interconnects, hierarchical modulation and flexible constellations design for advanced format signals.

In this paper, a phase-sensitive amplifier (PSA)-based two dimensional (2D)-to-one dimensional (1D) constellation reforming system is proposed and analyzed in detail. The proposed system theoretically realizes seven kinds of 10 GBaud quadrature amplitude modulation (QAM)-to-pulse amplitude modulation (PAM) conversions, including quadrature phase shift keying-to-PAM4 and 8QAM-to-PAM8 conversions. The constellation reforming system consists of a constellation squeezing PSA and a multi-level vector moving PSA. The operating principle and formula derivations of constellation squeezing and vector moving processes are fully explained, including the PSA transfer characteristics and PSA gain axis angle analytical solutions. When implementing QAM-to-PAM conversions, the constellations, spectra, eye diagrams, error vector magnitudes and bit error ratio (BER) performances of the QAM and PAM signals are measured. For 8QAM-to-PAM8 conversion, with the input OSNR of 25 dB and 30 dB, at the BER of 10⁻³, the converted PAM8 shows the receiver OSNR of 38.9 dB and 35.2 dB, respectively. The proposed and verified 2D-to-1D constellation reforming system builds an optical bridge connecting long-haul and short-reach networks, which can be employed in the format conversion, high-order format signal generation and shaping, and flexible information aggregation/de-aggregation.

Flexible conversion between modulation formats enables intelligent grooming techniques for an elastic optical network (EON) aimed at dynamical spectral efficiency allocation in optical fiber transmission. In this paper, we propose and demonstrate an all-optical modulation format conversion scheme between an 8-ary phase shift keying (8PSK) signal and two quadrature phase shift keying (QPSK) signals based on phase-sensitive amplification in highly nonlinear fiber. Benefiting from two simultaneous but different phase-squeezing processes, the two QPSK signals can be obtained simultaneously to avoid the loss of original information. The system transfer functions show the feasibility of the proposed scheme, and the system performance is evaluated by input–output constellations, calculated error vector magnitude (EVM), and bit error rate (BER) in numerical simulation. At BER of $3.8\times 10^{-3} $ , about 5-dB optical signal-to-noise-ratio (OSNR) improvement between the input 8PSK signal and output QPSK signals can be observed. Furthermore, several potential applications in optical fiber transmission can also be found based on the converter.

Optical format conversion technologies have attracted a lot of attention to bridge the different optical networks employing different formats. In this paper, the advances of optical format conversion technologies are introduced and reviewed. Through analyzing the optical network architecture and modulation technology development, we focus on the format conversions between the signals with one dimensional and two dimensional constellations. The important enabling technologies for flexible constellation manipulation are introduced in detail, including the linear and nonlinear optical effects-based functions. Then the key format conversion researches are reviewed in four categories: one-to-one conversions, optical aggregations, optical de-aggregations, and optical interconversions. Finally, the current issue and future trend of this research field is analyzed and discussed.

In this paper, a reconfigurable optical network intermediate node scheme with format conversion capacity and full-quadrature regeneration functionality is proposed. With a degraded input quadrature phase-shift keying (QPSK), the proposed network node can be dynamically reconfigured based on the network situation to output a QPSK or a four-level pulse amplitude modulation (PAM4), both full-quadrature regenerated. The input QPSK is first converted into the two full-quadrature regenerated binary phase-shift keying tributaries after phase sensitive amplifier-based quadrature de-multiplexing and selfphase modulation-based amplitude regeneration. Then the output regenerated QPSK or PAM4 are generated through vector addition by tuning the relative phase and amplitude between two tributaries. For an input 20 Gb/s QPSK with optical signal-to-noise ratio (OSNR) of 15 dB, the output regenerated QPSK gets 10.4% decrease in error vector magnitude (EVM), 2 dB receiver OSNR improvement at the bit error rate of 10 ^-3 , and regeneration factors of 6.4 dB and 3.7 dB in amplitude and phase, respectively. In the case with regenerated PAM4 as the output, compared with the input QPSK, it has 10.4% improvement in EVM and regeneration factors of 7.1 dB and 2.5 dB in amplitude and phase, respectively. The numerical simulation results reveal that the system effectively regenerates input signal in full-quadrature with format conversion capacity. The proposed node scheme can be applied as a fullquadrature QPSK regenerator between optical networks, which both employ QPSK to increase the transmission distance, or an alloptical interconnection node between different optical networks where different modulation formats are used individually.