Continuous-phase frequency-shift keying with external modulation

Takahide Sakamoto*, Tetsuya Kawanishi, Masayuki Izutsu

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

24 Citations (Scopus)


A high-speed external modulation scheme for optical continuous-phase frequency-shift keying (CPFSK) is presented. In external frequency-shift keying (FSK) modulation using singlesideband modulation technology, an optical upper/lower sideband (USB/LSB) component with respect to a carrier frequency is selectively generated. However, the FSK-modulated signal has phase discontinuities at the timings of frequency shifts. To overcome the problem, we propose a synchronous control technique that enables continuous phase modulation. In the external CPFSK modulation, the USB/LSB is allowed to shift to the other state when their phases coincide with each other. It is shown that CPFSK with a zero-topeak frequency deviation of 0.5 × (bit rate) is achieved with this synchronous control. Occupant bandwidth is less than half that of the externally modulated incoherent FSK with phase discontinuities. At a modulation speed of 10 Gb/s, higher order sidelobes are highly suppressed by more than 20 dB at the 20-GHz offset, comparing to a conventional binary phase-shift keying (BPSK). By the use of a Mach-Zehnder interferometer with balanced photodetection, receiver sensitivity is 3-dB greater than that of an on-off keying, as well as a BPSK. In this paper, we report on the experimental demonstration of CPFSK modulation/demodulation. A six-channel wavelength-division-multiplexed, 10-Gb/s CPFSK modulation/demodulation was successfully demonstrated.

Original languageEnglish
Article number1668100
Pages (from-to)589-594
Number of pages6
JournalIEEE Journal on Selected Topics in Quantum Electronics
Issue number4
Publication statusPublished - 2006 Jul
Externally publishedYes


  • Continuous-phase frequency-shift keying (CPFSK)
  • External modulation
  • Modulation formats
  • Optical fiber communication

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Electrical and Electronic Engineering


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