Rectangular QPSK for generation of optical eight-ary phase-shift keying

Area of Science:

• Optical communications
• Digital modulation techniques

Background:

• Conventional Quadrature Phase-Shift Keying (QPSK) uses balanced in-phase/quadrature (IQ) modulators, resulting in a square constellation (S-QPSK).
• Unbalanced driving conditions in IQ modulators can generate rectangular QPSK (R-QPSK), a novel concept.
• Advanced modulation formats are crucial for increasing data rates in optical networks.

Purpose of the Study:

• To propose and demonstrate a novel transmitter for synthesizing optical eight-ary phase-shift keying (8PSK) using cascaded IQ modulators.
• To introduce the concept of rectangular QPSK (R-QPSK) for optical signal generation.
• To highlight the transmitter's versatility for generating various multi-level modulation formats like Quadrature Amplitude Modulation (QAM).

Main Methods:

• Proposed a transmitter architecture based on two cascaded IQ modulators.
• Synthesized optical 8PSK by cascading an S-QPSK modulator with an R-QPSK modulator.
• Demonstrated the generation of other multi-level formats by adjusting driving and bias conditions.

Main Results:

• Successfully synthesized optical 8PSK using the proposed cascaded IQ modulator configuration.
• Experimentally demonstrated a 30-Gb/s optical 8PSK signal transmission.
• Confirmed the transmitter's capability to generate different modulation formats.

Conclusions:

• The proposed transmitter structure enables the synthesis of R-QPSK and optical 8PSK.
• The cascaded IQ modulator design offers a versatile platform for future dynamic optical networks.
• This approach facilitates the generation of various advanced modulation formats, enhancing spectral efficiency.