DWDM Channels Research Articles

Bidirectional DPSK transmission of 16 × 10-Gb/s DWDM channels over 80-km SMF-28 using semiconductor optical amplifiers

A constant-intensity modulation format such as differential phase-shift-keying is in principle immune to XGM-induced crosstalk in SOAs. We report the reduction of crosstalk in a bidirectional system and successfully realize 16 × 10-Gb/s DWDM signals transmission over 80-km SMF-28 using a DPSK modulation format for the first time. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 525–527, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21036

C-band wavelength conversion in silicon photonic wire waveguides

We demonstrate C-band wavelength conversion in Si photonic-wire waveguides with submicron cross-section by means of nonresonant, nondegenerate four-wave mixing (FWM) using low-power, cw-laser sources. Our analysis shows that for these deeply scaled Si waveguides, FWM can be observed despite the large phase mismatch imposed by strong waveguide dispersion. The theoretical calculations agree well with proof-of-concept experiments. The nonresonant character of the FWM scheme employed allows to demonstrate frequency tuning of the idler from ~ 20 GHz to > 100 GHz thus covering several C-band DWDM channels.

Investigation of SOA Nonlinearities on the Amplification of DWDM Channels With Spectral Efficiency Up to 2.5 b/s/Hz

We have investigated and compared the effect of semiconductor optical amplifier (SOA) nonlinearities on the amplification of 14 dense wavelength-division-multiplexing channels using return-to-zero on-off keying [(RZ-OOK) 1 b/symbol], RZ differential quadrature phase-shift keying [(DQPSK) 2 b/symbol], and polarization (bit interleaved) multiplexed RZ-DQPSK (4 b/symbol) formats with aggregate data rates up to 50 Gb/s per channel. The channel spacing was 20 GHz with spectral efficiency from 0.625 up to 2.5 b/s/Hz. Our results have shown that while RZ-OOK format performs better at lower SOA input powers, RZ-DQPSK suffers less degradation from SOA nonlinearities at higher input powers. Overall, polarization-bit-interleaved RZ-DQPSK format was found to have the best tolerance to SOA nonlinearities.

S/S＋band에서 넓은 파장가변 영역을 가지고 50-GHz ITU-T격자에 맞는 채널을 생성하는 thulium이 첨가된 광섬유 레이저

S/S＋band에서 ITU-T의 50 ㎓격자에 맞는 채널을 가지는 광대역 파장가변 thulium첨가 광섬유레이저(TTDFL)를 개발하였다. 1.4<TEX>$\mu\textrm{m}$</TEX>및 <TEX>$1.5\mu\textrm{m}$</TEX>두 대역의 광원으로 펌핑되는 thulium첨가 광섬유(TDF)의 반전에 관한 분석을 통해, 대부분의 S/S＋band에서 파장을 가변할 수 있는 레이저를 구현하였다. 이 파장가변 레이저는 65.1nm의 넓은 3-㏈ 대역폭 내에서 6.7㏈m이상의 평탄한 출력 스펙트럼을 보여주었고, 생성된 DWDM채널 수는 178개에 달하였다. 또한 보조 펌프의 출력을 더 높일경우 66.2 nm까지도 대역폭을 넓힐 수 있었고, 공진기 내부 필터의 온도를 조절함으로써 레이저의 주파수를 더욱 안정화 할 수 있음도 보였다. 본 연구에서 개발된 이 레이저는 S/S＋band에서 기준 파장을 제공하는 유용한 광원으로 활용될 수 있다. We demonstrate an S/S＋band discretely tunable thulium doped fiber laser (TTDFL), anchored on a 50-㎓ ITU-T grid. Investigating the inversion analysis of the thulium doped fiber (TDF) in applying a dual wavelength (1.4 m and 1.5 m) pumping scheme, a laser whose tuning range covers most of the S/S＋band has been obtained. Within the wide 3-㏈ bandwidth of 65.1 nm, the output power of the tunable laser exceeds 6.1 ㏈m with very flat spectral profile and the number of DWDM channels generated is as large as 178. If we increase the subsidiary pump power to 22 ㎽, the bandwidth is expanded up to 66.2 nm. By controlling the temperature of the fine grid filter, we have also shown that the frequency locking capability of the laser can be improved. The laser developed in this work is expected to be utilized as a practical optical source providing reference wavelengths in the S/S＋band.

Crosstalk, noise, and stability analysis of DWDM channels generated by injection locking techniques

In this paper, theory and experimental results for wavelength-division-multiplexing (WDM) channel generation, formed by multi-line optical injection locking, is presented. A small-signal model to deal with wide-spectral-band optical injection problems has been developed. Based on this model, the crosstalk noise of an injection-locked laser in a coherent WDM system is assessed analytically. Experimental results on locking range, stability, and crosstalk noise confirms the modeling results, which indicate that stable and low-noise channels can be generated by this approach.

High extinction ratio performance of DWDM monolithic multichannel modulation circuit

A multichannel modulation circuit has been fabricated that monolithically integrates one 25 GHz-spacing AWG for both MUX and DEMUX, and eight channels of SOA and EAM. The compact circuit can generate individual optical signals for each DWDM channel with a high extinction ratio of >20 dB and loss compensation. The dynamic performances are also confirmed at 2.5 Gbit/s.

Long-haul 40 Gb/s DWDM transmission with aggregate capacities exceeding 1 Tb/s

We present an experimental investigation of 40 Gb/s transmission technology aimed at an aggregate capacity exceeding 1 Tb/s over multithousand kilometer transmission distances. These studies have been performed using a variety of dispersion management and modulation techniques. The transmission distances investigated range from a minimum of 2000 km, which is considered a regional undersea cable distance, up to a transatlantic distance of 6200 km. Our regional distance experiments were performed using both slope-matched and conventional dispersion maps where the accumulated dispersion becomes large for the edge channels. Dispersion map studies showed that slope-matched fiber performs better than nonslope-matched fiber (NZDSF) beyond 2000 km due to its larger effective area and lower accumulated dispersion slope. The demonstration of 38/spl times/40 Gb/s over 6200 km was the first transoceanic length experiment using 40 Gb/s DWDM channels. This was achieved with a relatively simple amplifier chain that uses only C-band EDFAs. Modulation format studies showed that RZ performs better over transoceanic distance, carrier-suppressed RZ performs better with nonslope-matched fiber at a distance of 2055 km, and prefiltered carrier-suppressed RZ is more suited for higher spectral efficiency. Experimental techniques for high bit-rate experiments are presented.

On the use of NRZ, RZ, and CSRZ modulation at 40 Gb/s with narrow DWDM channel spacing

The use of nonreturn-to-zero (NRZ), return-to-zero (RZ), and carrier-suppressed return-to-zero (CSRZ) modulation formats in an ultradense wavelength-division multiplexing (UDWDM) scenario at 40 Gb/s is investigated. The results of a simulative analysis on back-to-back setups are presented. Narrow optical filtering at the receiver and at the transmitter, as well as the orthogonal polarization launch of adjacent channels, is studied in order to improve spectral efficiency. We demonstrate that standard setups do not allow acceptable performances with 50-GHz channel spacing for all the considered modulation formats, while the use of a transmission optical filter may dramatically improve the performance of RZ and CSRZ modulation formats that become suitable for the use in UDWDM systems. We show that, due to the narrow transmission filtering, the RZ pulse becomes NRZ-like, and the CSRZ modulation is duobinary coded. Furthermore, we demonstrate that NRZ modulation does not benefit from the introduction of a transmission optical filter, while it takes advantage of the orthogonal polarization launch of adjacent channels, but its performance is still worse than the RZ and CSRZ performance in a UDWDM scenario.

8 x 10 Gb/s DWDM transmission over 240 km of standard fiber using a cascade of semiconductor optical amplifiers

Eight 10-Gb/s DWDM channels spaced 200 GHz around 1565 nm are transmitted over six 40-km spans of standard SMF using five inline semiconductor optical amplifiers (SOAs). SOAs are also used as booster and pre-amplifier in the transmitter and receiver, so that only SOAs are used in the experiment. For all channels, bit-error-rate penalties of 0.5-1.5 dB relative to baseline have been measured, with no evidence of error-rate floors.

Transmission of 8 DWDM channels at 20 Gb/s over 160 km of standard fiber using a cascade of semiconductor optical amplifiers

Eight DWDM channels in the wavelength region 1558-1570 nm, spaced at 200 GHz, are modulated at 20 Gb/s and transmitted over 160 km of SSMF (four 40-km spans) using four in-line SOA's. Transmitter booster-amplifiers and receiver preamplifiers are also SOA's, Q-factors better than 17 dB, corresponding to a BER of less than 3/spl middot/10/sup -13/, have been measured for all channels.

Zero frequency error DWDM channel synthesis usingoptical injection-lockedcomb line selection

The authors demonstrate for the first time the use of optical injection locking to synthesise exact frequency WDM channels from a broadband optical comb source. Unwanted channel outputs are suppressed by >30 dB relative to the selected channel.

Error-free transmission of 32 × 2.5 Gbit/sDWDM channels over 125 km usingcascaded in-line semiconductor optical amplifiers

By optimising the detector threshold and using an optical reservoir channel, error-free transmission of 32 × 2.5 Gbit/s DWDM channels has been obtained over 125 km of AllWave™ fibre using semiconductor optical amplifiers.