DocumentCode :
1239421
Title :
Measurement of Differential Phasor Diagram of Multilevel DPSK Signals by Using an Adjustment-Free Delay Interferometer Composed of a 3 ,\\times, 3 Optical Coupler
Author :
Takushima, Y. ; Choi, H.Y. ; Chung, Y.C.
Author_Institution :
Dept. of Electr. Eng., Korea Adv. Inst. of Sci. & Technol., Daejeon
Volume :
27
Issue :
6
fYear :
2009
fDate :
3/15/2009 12:00:00 AM
Firstpage :
718
Lastpage :
730
Abstract :
We develop an adjustment-free differential-phase demodulator based on a delay-interferometer (DI) made of a 3 times 3 optical coupler, which is used as a 120-degree optical hybrid, and demonstrate the possibility of using it as a phasor monitor for the multilevel differential phase-shift keyed (DxPSK) signal. The key features of the proposed demodulator are twofold: (a) in-phase and quadrature (I-Q) components and the phasor diagram can be obtained only by using a single DI, and (b) the phase delay of the DI can be derived from the output power of the DI without the knowledge of the signal under test. These features enable us to demodulate the I-Q components of DxPSK signals without any adjustments. We formulate a theoretical model for deriving the differential phasor from the output signals of the 3 times 3 coupler regardless of unbalances in the phase retardations and the splitting ratios of the 3 times 3 coupler. Thus, the discrepancy from the ideal 120-degree optical hybrid is not a problem, and hence the requirements of the 3 times 3 couplers are greatly relaxed. For a demonstration, we implement the proposed demodulator by using a fiber Michelson interferometer with Faraday rotator mirrors and use it as a differential phasor monitor capable of the plug-and-play (wavelength- and polarization-independent) operation. We show that this phasor monitor can be used for diagnosis of differential phase-shift keyed (DPSK) and differential quadrature phase-shift keyed (DQPSK) transmitters by identifying the sources of impairments from the measured constellation diagram and phasor trajectories. The proposed phasor monitor can also be used for monitoring the optical signal-to-noise ratio (OSNR) of DPSK signal.
Keywords :
Faraday effect; Michelson interferometers; differential phase shift keying; mirrors; optical couplers; optical fibre communication; optical noise; optical retarders; optical transmitters; quadrature phase shift keying; DPSK; Faraday rotator mirrors; adjustment-free differential-phase demodulator; constellation diagram; delay-interferometer; differential phasor; differential phasor monitor; differential quadrature phase-shift keyed transmitters; fiber Michelson interferometer; multilevel differential phase-shift keyed signal; optical coupler; optical signal-to-noise ratio; phase retardations; phasor diagram; phasor monitor; plug-and-play operation; quadrature components; splitting ratios; Delay; Demodulation; Differential quadrature phase shift keying; Monitoring; Optical coupling; Optical fiber polarization; Optical interferometry; Optical transmitters; Power generation; Signal to noise ratio; Differential phase shift keying; optical fiber communication; optical interferometry; optical modulation;
fLanguage :
English
Journal_Title :
Lightwave Technology, Journal of
Publisher :
ieee
ISSN :
0733-8724
Type :
jour
DOI :
10.1109/JLT.2008.927777
Filename :
4814820
Link To Document :
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