Nondispersion-shifted Fiber Research Articles

Optimum bandwidth limitation method to overcome GVD-based effect in practical fibre-optic transmission systems

The paper describes an optical duobinary modulation scheme that reduces the waveform distortion caused by the effect of group velocity dispersion (GVD) and the combined self-phase modulation (SPM)–GVD effect as generated in non-dispersion shifted fibre (NDSF) with a length of over 300 km at 5 Gbit/s. Measured and simulated eye-opening penalties are used to compare the optical duobinary modulation scheme to the conventional non-return-to-zero (NRZ) intensity modulation scheme. A comparison of duobinary modulation with a duobinary filter against NRZ intensity modulation with a full-cosine roll-off filter shows that the former yields a compact spectrum even in the case of a single pulse, which needs the broadest bandwidth. NDSF repeaterless transmission at 5 Gbit/s and 363 km without dispersion compensation is established to confirm the effectiveness of the optical duobinary modulation scheme.

High-temperature and high-speed operation of a 1.3-/spl mu/m uncooled InGaAsP-InP DFB laser

1.3-μm uncooled InGaAsP-InP loss-coupled distributed feedback lasers operating over 10 Gb/s and at 85/spl deg/C were successfully fabricated. In order to achieve high-speed and high-temperature operation simultaneously, the following are thoroughly investigated: modulation-doped and strain-compensated multiple-quantum-well active layers, Fe-doped buried-heterostructure, coupling coefficient of loss-coupled grating, detuning lasing wavelength from the gain peak, and facet coatings. The authors also demonstrate 10 Gb/s transmission with negligible dispersion power penalty over 20 km of nondispersion-shifted fiber at 10 Gb/s for temperatures ranging from 25/spl deg/C to 85/spl deg/C.

Pump to signal RIN transfer in Raman fiber amplifiers

We present an analytical model and measurements of the pump to signal relative intensity noise (RIN) transfer characteristics of copumped and counterpumped Raman amplifiers. We give a quantitative analysis of noise averaging from chromatic dispersion in copumped systems and from different propagation directions in counterpumped systems. It is shown that nondispersion-shifted fibers and other fibers with high dispersion between the signal and pump wavelengths give a greater potential for use in copumped Raman amplified systems.

A low-cost WDM source with an ASE injected Fabry-Perot semiconductor laser

We propose and demonstrate a novel wavelength-division-multiplexing (WDM) source employing an uncooled and unisolated Fabry-Perot semiconductor laser diode (F-P SLD). The output wavelength of F-P SLD is locked to the externally injected narrow-band amplified spontaneous emission (ASE). The measured side-mode suppression ratio of the wavelength-locked F-P SLD is larger than 29 dB, when the extinction ratio of the directly modulated light output is above 13 dB. We achieved error-free transmission of 155-Mb/s data over 120 km of nondispersion-shifted fiber. We also propose a cost-effective WDM passive optical network architecture based on the proposed light sources.

Improved transmission of chirped signals from semiconductor optical devices by pulse reshaping using a fiber Bragg grating filter

Spectral filtering of chirped signals with an edge of a fiber grating filter improves propagation in nondispersion-shifted fiber. The improvement is due to a temporal shift of the frequency modulation with respect to the amplitude modulation. By filtering the chirped output of a semiconductor optical amplifier (SOA) wavelength converter with a fiber grating edge we obtain error-free transmission of converted data through 100 km of nondispersion-shifted fiber at 5 Gb/s.

Compact asymmetric strongly gain-coupled DFB laser array with integrated BFM array for simultaneous 4-λ 2.5 Gb/s 100 km WDM transmission

A low-cost and high-performance 4-/spl lambda/ wavelength division multiplexing distributed feedback (WDM-DFB) laser array (or WDM4), employing a newly developed asymmetric strongly gain-coupled (A-SGC) laser structure, and a novel compact packaging approach was developed for optical network applications. The WDM4 laser array is capable of simultaneous 4-/spl lambda/ 100 km transmission through a standard nondispersion-shifted fiber, with a simultaneous and independent direct modulation at 2.5 Gb/s for each of the four WDM channels spaced by 200 GHz.

Enhanced wavelength tuning range in two-section complex-coupled DFB lasers by alternating gain and loss coupling

A novel tunable two-section complex-coupled distributed feedback (DFB) lasers were demonstrated which exhibited an enhanced wavelength tuning range beyond 7 nm by current injection only. By a simple master-and-slave type of injection current control, either in-phase gain-coupling or antiphase loss-coupling mechanism can be activated, in such a way that one of the two Bragg modes around DFB stopband will become the lasing mode, and its wavelength can be simply and independently tuned by corresponding injection current. More then 45 dB side-mode suppression ratio (SMSR) over entire tuning range were obtained. Good system performance for 375 km transmission with butt-coupled III-V Mach-Zehnder (MZ) modulator at 2.5 Gb/s over nondispersion-shifted fiber was also demonstrated.

Scale of WDM transport network using different types of fibers

This paper describes a statistical calculation method for transmission limits taking into consideration dispersion-shifted fiber (DSF) zero-dispersion wavelength deviation for wavelength division multiplexing (WDM) systems employing unequal channel spacing. For example, the upper limit of fiber input power achieving a bit error rate (BER) less than 10/sup -12/ shows a 3 dB improvement when the standard deviation is increased from 1 to 8 nm when the transmission distance with a 80 km repeater spacing is 640 km. Furthermore, the network scales employing 1.55 /spl mu/m DSF, nondispersion-shifted fiber (N-DSF) and conventional single-mode fiber (SMF) are shown. Finally, a method for estimating the transmission limit for a receiver with different sensitivity, different node architecture, and different bit rates is described.

Effect of self-phase modulation on a dispersion compensated link employing a dispersion-compensating fiber

A study of the effect of self phase modulation (SPM) on a fiber link consisting of a non-dispersion shifted fiber (NDSF) and a dispersion compensating fiber (DCF) operating at 1550 nm has been carried out. The characteristics of signal pulse transmission through the fiber combination of NDSF followed by DCF (post-compensation) and DCF followed by NDSF (pre-compensation) are obtained by numerical simulation. It is found that though in the linear regime there can be exact compensation of dispersion for either combinations of NDSF + DCF and DCF + NDSF, in the nonlinear regime of transmission the two combinations behave very differently. For the case of NDSF + DCF the pulse width increases and attains a maximum value before decreasing with the input signal power, whereas for the combination of DCF + NDSF the pulse undergoes compression. It is also shown that when the linear dispersion in NDSF is slightly under compensated by DCF, the pulse width in the DCF + NDSF combination does not change appreciably for a large range of input signal power.

Resistance to External Optical Feedback of Low-Chirp Strained-Quantum-Well Complex-Coupled Distributed-Feedback Laser

Resistance to the optical feedback of complex-coupled DFB lasers with current blocking grating was studied experimentally. The measured relative intensity noise of the lasers was as low as -160 dB/Hz even in the presence of an external feedback level of -15 dB. The modulation chirping of the device was quite small with a linewidth enhancement factor α of 1.9 measured using a fiber-response peaks method. A transmission experiment was performed over a 235 Km standard nondispersion-shifted fiber at 2.488 Gbps by direct modulation without using an optical isolator, and the power penalty was only 1.55 dB at a bit error rate of 10-12.

40 Gbit/s 1.55 [micro sign]m RZ transmission over 109 km of non-dispersion shifted fibre with long continuously chirped fibre gratings

Chirped fibre gratings are compact and potentially cheap and have become an attractive alternative to technologies such as dispersion compensating fibres for the upgrade of the installed non-dispersion shifted fibre (NDSF) base. In particular the recent demonstrations of 10 Gbit/s transmission over 700 km of NDSF and 40 cm broadband (4 nm) linearly chirped gratings for much-increased source wavelength and operating condition tolerance confirm this potential. These long gratings have essentially flat reflectivity over their usable bandwidth with raised cosine apodisation at both ends of the spectrum. The delay characteristic can be controlled to be linear with less than 2% error with a dispersion slope as high as ~1700 ps/nm (enough for 100 km of standard fibre). At the same time, the broad bandwidth available from the long linearly chirped gratings makes it possible for the first time to achieve dispersion compensation over a significant length of NDSF at several tens of Gbit/s data rates. To date 40 Gbit/s transmission over a significant length of NDSF at 1.55µm has only been demonstrated using dispersion compensating fibres. The best result to our knowledge is an error-free transmission over 150 km of standard fibre. Without any means of dispersion management, the maximum transmission distance is ~4 km for this bit-rate. In this paper we report the first demonstration of 40 Gbit/s transmission over 109 km of NDSF at 1.55µm by employing two continuously-chirped 40 cm long, 4 nm-bandwidth gratings. In addition, a continuously-chirped 5.2 nm bandwidth 1 metre grating is demonstrated

Transmission of directly modulated 2.5-Gb/s signals over 250-km of nondispersion-shifted fiber by using a spectral filtering method

We demonstrate 250-km nondispersion-shifted fiber transmission of directly modulated 2.5-Gb/s signals. The chirping-induced power penalty is reduced by using a spectral filter whose transmission peak is tuned to "mark" wavelength of the modulated laser output. A well-known intensity modulation with a sufficiently high extinction ratio is used to suppress the intersymbol interference induced by nonuniform frequency modulation response of semiconductor lasers. The observed results are explained theoretically by using eye closure penalty.

Dependence of frequency chirping on bias current in LD wavelength conversion

Chirping influence is experimentally studied in wavelength conversion using a light injected DFB-LD. It is shown that signal degradation due to frequency chirping is small when the bias current is large and the relaxation oscillation frequency is high. An experiment demonstrates that 5-Gb/s wavelength converted light at 1.55 /spl mu/m is transmitted through 160-km nondispersion-shifted fiber with 2-dB penalty, which is only 0.5 dB larger than that in transmission using a LiNbO/sub 3/ Mach-Zehnder modulator.

5 Gbit/s unrepeatered transmission over 360 km of non-dispersion shifted fibre without dispersion compensation

5 Gbit/s unrepeatered transmission is successfully carried out over 360 km of non-dispersion shifted fibre (NDSF) without dispersion compensation, for the first time. Degradation caused by fibre nonlinearity and dispersion is overcome by reducing optical signal bandwidth.

Transmission of eight 20-Gb/s channels over 232 km of conventional single-mode fiber

As a demonstration of the upgradeability of conventional single-mode fiber systems, we demonstrate the transmission of eight 20-Gb/s channels over 232 km of nondispersion-shifted fiber using dispersion-compensating fiber with negative dispersion-slope. All channels were received without discernible transmission penalties. Due to fiber nonlinearity, differences were observed in system performance depending on the arrangement of the fibers. >

210 km repeaterless 10 Gb/s transmission experiment through nondispersion-shifted fiber using partial response scheme

In order to increase the dispersion-limited propagation distance at 10 Gb/s through nondispersion-shifted fiber, a chromatic dispersion tolerant signalling technique is used, based upon a reduced optical signal bandwidth. We have achieved a 210 km repeaterless transmission distance at 10 Gb/s over nondispersion-shifted fiber with a measured bit error ratio lower than 10/sup -12/. At this distance, a receiver penalty of 1.7 dB was obtained at 10/sup -10/ bit-error ratio, while an almost penalty-free transmission has been performed through 189 km. The technique relaxes the bandwidth requirements for the optoelectronic components at the transmitter level and involves a standard 10 Gb/s receiver at the output end of the transmission link.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

2.5-Gbit/s Repeaterless Transmission Systems over Non-Dispersion-Shifted Fiber Using Directly Modulated DFB Laser and Dispersion Compensating Fiber

Feasibility of repeaterless transmission systems over non-dispersion-shifted fiber (NDSF) using directly modulated DFB lasers and dispersion compensating fiber (DCF) was examined. The transmission characteristics were investigated by simulations, considering the effects of the laser chirping, fiber chromatic dispersion, and the self-phase-modulation (SPM) occurring in both NDSF and DCF. As a result, it was revealed that the post-compensation scheme is the most suitable and that the SPM in DCF dominantly deteriorates the transmission characteristics in this scheme. Following the predictions by the simulations, 2.5 Gbit/s repeaterless transmission over 306-km pure-silica-core fiber has been demonstrated with no power penalty, using a directly modulated DFB laser with a bulk active layer and dispersion compensating fibers.

A 50-channel externally modulated AM-VSB video distribution system with three cascaded EDFA's providing 50-dB power budget over 30 km of standard single-mode fiber

Presents an externally modulated 50-channel AM-VSB video lightwave system, employing three cascaded EDFAs. For system specifications of SNR=46 dB, CSO<-66 dBc and CTB<-55 dBc, up to 40 000 ONUs can be connected to a single transmitter unit at distances larger than 30 km with standard nondispersion-shifted fiber. Interferometric noise and SBS are suppressed using single-tone phase modulation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dispersion-supported transmission at 20 Gbit/s over 53 km standard singlemode fibre

The optical transmission of 20 Gbit/s signals over a record distance of 53 km standard nondispersion-shifted singlemode fibre (SMF) without optical dispersion compensation has been demonstrated successfully using a directly modulated MQW DFB laser operating at 1544 nm.

481 km, 2.5 Gbit/s and 501 km, 622 Mbit/s unrepeatered transmission using forward error correction and remotely pumped postamplifiers and preamplifiers

Using forward error correction, a remotely pumped postamplifier and a remotely pumped preamplifier, error-free unrepeatered transmission on nondispersion-shifted fibre is demonstrated over record distances of 481 km at 2.5 Gbit/s and 501 km at 622 Mbit/s.