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2 × 40 Gbit / s RZ-DQPSK transmission over 263 km of fiber with tunable chromatic dispersion compensator
| Content Provider | Semantic Scholar |
|---|---|
| Author | Sandel, David Bhandare, Suhas Ismail, A. Fauzi Abas Wuest, Frank Milivojevic, Biljana Hidayat, Ariya Noé, Reinhold Guy, Martin Lapointe, Martin |
| Copyright Year | 2004 |
| Abstract | We report on 2×40 Gbit/s RZ-DQPSK transmission over a 263 km fiber link. Sufficient resilience against nonlinear phase noise and band limitation in a 40Gbit/s WDM DEMUX is achieved with a Q factor of 17.5 dB. The back-to-back Q factor is > 20 dB, and the receiver sensitivity of –27.5 dBm is 0.2 dB better than for RZ-ASK even though the data rate is twice as high. Introduction With demands to increase capacity, increase reach and reduce cost, there has been growing interest in developing alternative modulation formats for high bit rate optical transmission systems [1-5]. A simple alternative to double the existing transmission capacity wit hout optical bandwidth increase is to use Differential Quadrature Phase Shift Keying (DQPSK). Combined with RZ coding its robustness against XPM is also large because the intensity is not modulated by the data. The theoretically possible receiver sensitivity of DQPSK receiver is better than for intensity modulation. Here we report on 2×40 Gbit/s (40 Gbaud) RZ-DQPSK transmission over 263 km with a Q factor > 20 dB. Transmission setup Fig. 1 shows the RZ -DQPSK 40 Gbaud transmission setup. The transmitter employs a 16:1 Infineon multiplexer that processes 16 2.5 Gbit/s data streams, mutually delayed by multiples of 8 bits, SHF modulator drivers for a Triquint dual drive DPSK modulator. It is followed by an in-house developed all-fiber temperature-stabilized Mach-Zehnder interferometer with a differential delay of 3 symbol durations. The polarization dependent phase shift is < 500 MHz and the extinction ratio is ~24 dB. A piezo fiber stretcher is included in one of the arms for an active phase control. A quadrature control loop based on a 10 kHz lock-in scheme stabilizes the interferometer phase. As its input signal we use the RF power which occurs in the photodetected signal at one of the interferometer outputs. The photoreceiver bandwidth is about 8 GHz and does therefore not cover the clock signal. Only when the two optical signals are superimposed in quadrature there is no interference and hence no RF power. The 10 kHz phase modulation has a depth of ~0.01 rad (rms). A Triquint dual drive pulse carver driven at half the clock rate generates the RZ-DQPSK signal for transmission. The optical frequency is 192.5 THz (1557.366 nm). The receiver employs optical preamplifiers, a flat-top C band DWDM DEMUX (Optun) and an integrated-optical MachZehnder demodulator with a delay of 4 symbol durations. For proper reception of in-phase and quadrature data channels, the phase difference of delay demodulator is set to 45° or 135° using microheaters. The demodulator outputs are connected to two high-speed photodetectors from u2t, which in turn are connected to differential inputs of a 1:16 Infineon demultiplexer that uses standard clock and data recovery circuits. An advantage here is that we do not need an extra high-speed photodiode to recover the clock from 40 GHz intensity modulation. A 2-1 PRBS was transmitted. Note that the demodulated bit patterns in in-phase and quadrature data channels differ from the transmitted ones. The half rate clock sign als in transmitter and receiver are generated by VCOs from WORK Microwave GmbH. 100 ps 20 GHz RZ 75 ps 10 kHz lock-in 10 GHz PIN-TIA DQPSK DCF DCF DFB laser DPSK 5 MHz FM&AM 40 Gbit/s data out clock and data recovery loop filter clock VCO tunable CD compensator 90 km 84 km 89 km RF power detector Fig. 1: 40 Gbaud RZ-DQPSK transmission setup Experiment The aim of this transmission experiment is to demonstrate 2×40 Gbit/s RZ -DQPSK transmission and compare its performance to that of the RZ -ASK and RZ -DPSK modulation formats in terms of receiver sensitivity and OSNR. For RZ-DPSK operation, the all-fiber Mach-Zehnder interferometer at the TX is left out. For RZ-ASK operation, both interferometers and one photodiode are left out. The optical signal is transmitted over 3 fiber spans with a total length of 263 km. These are 170 km of SSMF, 60 km of NZDSF, and 33 km of DSF. DCF with a total dispersion of –2713 ps/nm was inserted between first and second stages of the two inline EDFAs. The residual dispersion was compensated by a thermally tunable dispersion compensator. It was set to –470 ps/nm, while the total tuning range is –300 to –700 ps/nm. Fig. 2 shows measured BERs vs. optical preamplifier input power for RZ-DQPSK, RZ -ASK, and RZ -DPSK modulation formats. The back-to-back Q factors for these modulation formats are 20.9 dB (for both I and Q data channels), 26.6 dB, and 29.5 dB, respectively. The corresponding back-to-back receiver sensitivities are –27.5 dBm (for both I and Q data channels), –27.3 dBm, and –33.6 dBm. They are equivalent to OSNRs of 29.7, 27.7, and 23.8 dB/0.1nm, respectively. With the 263 km fiber link in place, the Q factors are reduced to 17.5 dB (for I and Q data channels), 19.6, and 20.4 dB, respectively. As can be seen from Figure 2, the DQPSK receiver sensitivity is almost the same as for ASK. However, DQPSK transports 80 Gbit/s whereas ASK transports only 40 Gbit/s. When the sensitivities are compared on the basis of photons/bit (not photons/symbol) then DQPSK is 3.2 dB better than ASK, and 3.1 dB worse than DPSK. All 2.5 Gbit/s subchannels are bit error free, with almost identical sensitivities. -40 -38 -36 -34 -32 -30 -28 -26 10 10 10 10 10 |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://ei.uni-paderborn.de/fileadmin/elektrotechnik/fg/ont/docs/auto/publication/221540_Gbits_RZDQPSK_transmission_over_263_km_of_fiber_with_tunable_chromatic_dispersion_compensator.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
