160-gb/s adaptive dispersion equalization using an asynchronous dispersion-induced chirp monitor

This paper describes an adaptive dispersion equalizer (ADE) that uses an asynchronous dispersion-induced chirp monitor and the detailed study of the first demonstration of 160-Gb/s adaptive dispersion equalization. The device successfully equalized the dispersion change over a 40/spl deg/C temperature range (from 5/spl deg/C to 45/spl deg/C) and the dispersion slope of an 80-km dispersion-shifted fiber (DSF). The ADE will enhance the feasibility of 160-Gb/s optical transmission systems.     

Low insertion loss and low dispersion penalty InGaAsP quantum-well high-speed electroabsorption modulator for 40-Gb/s very-short-reach, long-reach, and long-haul applications

We present a metal-organic-chemical-vapor-deposition-grown low-optical-insertion-loss InGaAsP/InP multiple-quantum-well electroabsorption modulator (EAM), suitable for both nonreturn-to-zero (NRZ) and return-to-zero (RZ) applications. The EAM exhibits a dynamic (RF) extinction ratio of 11.5 dB at 1550 nm for 3 Vp-p drive under 40-Gb/s modulation. The optical insertion loss of the modulator in the on-state is -5.2 dB at 1550 nm. In addition, the EAM also exhibits a 3-dB small-signal response (S21) of greater than 38 GHz, allowing it to be used in both 40-Gb/s NRZ and 10-Gb/s RZ applications. The dispersion penalty at 40 Gb/s is measured to be 1.2 dB over /spl plusmn/40 ps/nm of chromatic dispersion. Finally, we demonstrate 40-Gb/s transmission performance over 85 km and 700 km.     

40-Gb/s WDM transmission with virtually imaged phased array (VIPA) variable dispersion compensators

We have demonstrated variable dispersion compensation by using a virtually imaged phased array (VIPA) to overcome the small dispersion tolerance in 40-Gb/s dense wavelength-division multiplexing (WDM) transmission systems. By utilizing the periodical characteristics of VIPA compensators, we performed simultaneous dispersion compensation in a 1.28-Tb/s (40-Gb/s/spl times/32 ch; C band) short-haul transmission and confirmed that only two VIPA compensators and one fixed dispersion-compensating fiber are required for a large transmission range of 80 km. This performance can greatly reduce the cost, size, and number of compensator menus in a 40-Gb/s WDM short-haul transmission system. In addition, we achieved 3.5-Tb/s (43-Gb/s/spl times/88 ch; C and L bands) transmission over a 600-km nonzero dispersion-shifted fiber by using VIPA compensators. Although channel-by-channel dispersion compensation is required due to the larger residual dispersion slope in long-haul transmission, the periodical characteristics of the VIPA compensators offer the advantage of considerably reducing the number of different modules required to cover the whole C (or L) band. An adequate optical signal-to-noise ratio, which was the same for all channels, was-obtained by using distributed Raman amplification, a gain equalizer, and a preemphasis technique. We achieved a Q-factor of more than 11.8 dB; (BER<10/sup -17/ with forward-error correction) for all 88 channels.     

Impact of dispersion fluctuations on 40-Gb/s dispersion-managed lightwave systems

We study numerically the impact of random dispersion fluctuations on the performance of 40-Gb/s dispersion-managed lightwave systems designed using either the chirped return-to-zero or the soliton format and employing backward-pumped distributed Raman amplification. We consider two-section dispersion maps with /spl beta//sub 2/=/spl plusmn/4 and /spl plusmn/8 ps/sup 2//km and show that the Q parameter decreases rapidly in both cases as the nonlinear effects become stronger. The impact of dispersion fluctuations can be reduced by lowering the average input power, but the system length is then limited by amplifier noise.     

Performance analysis of single-MZM APRZ transmitters

In this paper, an efficient single Mach-Zender modulator (MZM) implementation of alternate-phase return to zero (APRZ), which combines carrier-suppressed return to zero (CSRZ)'s ease of implementation with APRZ's nonlinear tolerance, is analyzed. In particular, the first numerical study of 67%-duty-cycle single-MZM APRZ over a 40-Gb/s 5 /spl times/ 100-km link, in terms of nonlinear, dispersion, and filtering tolerance, comparing it with 33% RZ, 33% APRZ, and standard 67% CSRZ, is presented. The results show that APRZ with phase shift close to /spl pi//2 is the optimum choice, independent of specific transmitter implementation. A new mechanism is also discovered, based on the interference of ghost pulses with the original pulse train, which improves the nonlinear tolerance of CSRZ in a 40-Gb/s transmission.     

Theoretical investigation of 8 /spl times/ 10-Gb/s WDM signal transmission performance based on gain-equalized SOAs using backward Raman pumping at DCF

We have theoretically investigated 8 /spl times/ 10-Gb/s wavelength-division multiplexing (WDM) signal transmission characteristics based on semiconductor optical amplifiers (SOAs) with equalized gain using discrete Raman amplification (DRA). Gain equalization and low noise figures have been obtained by adjusting the backward Raman pumping power and wavelength at a dispersion compensating fiber (DCF) for each span. Bit-error-rate characteristics were calculated for 8 /spl times/ 10-Gb/s WDM signal transmission over 6 /spl times/ 40-km single-mode fiber (SMF) + DCF links with gain-equalized SOAs using DRAs at DCF. Approximately a 2.5-dB improvement of the receiver sensitivity was achieved by using SOAs and DRAs with optimized Raman pumping. One can easily upgrade the transmission length of a link based on SOAs with an appropriate backward pump laser at each DCF.     

CSO/CTB performances improvement in a bi-directional DWDM CATV system

We proposed and demonstrated a four-wavelength bi-directional dense-wavelength-division-multiplexing (DWDM) CATV system that uses chirped fiber gratings (CFGs) as the dispersion compensation devices to reduce the fiber dispersion and cross-phase modulation (XPM)-induced crosstalk simultaneously. Our proposed system not only reduces the required number of fibers, but also offers the advantages of capacity doubling. Excellent performances of carrier-to-noise ratio (CNR) /spl ges/ 50 dB, composite second order (CSO) /spl ges/ 72 dB and composite triple beat (CTB) /spl ges/ 69 dB were obtained over a 50-km single-mode fiber (SMF) transport.     

Hybrid-Frequency Cutoffs in Gyrotropic Waveguides (Short Papers)

The behavior of the Brillouin diagram /spl omega/ versus /spl beta//sub z/ is analyzed for axially magnetized gyrotropic waveguides in the vicinity of the hybrid frequencies /spl omega//sub k/ and /spl omega//sub i/. Starting from the exact dispersion relation for the modes in the waveguides under consideration it is shown that 1) the dispersion curves terminate at discrete cutoff points located along the /spl omega/ = spl omega//sub k/, /spl omega//sub i/ line and 2) the group velocity at these points is zero. These results modify the behavior of the dispersion curves existing in the literature.     

Experimental demonstration of thin-film dispersion compensation for 50-GHz filters

Dispersion management is critical for next-generation high-bandwidth-utilization fiber-optical networks. Square-top thin-film bandpass filters for 50-GHz dense wavelength-division multiplexing inherently have high chromatic dispersion (CD) in transmission. The imparted dispersion power penalty on the network is undesirable. However, a second thin-film filter, operating in reflection, can be designed to compensate the CD of the bandpass filter. In this paper we demonstrate experimentally the reduction of the intrinsic CD of a 50-GHz thin-film coupler from /spl plusmn/170 ps/nm to /spl plusmn/50 ps/nm over a 30-GHz passband, through the use of such a cascaded thin-film compensator. Network simulations based on filter performance confirm the reduced dispersion power penalty of the cascade over the individual filter.     

Tunable dispersion compensation at 40-Gb/s using a multicavity etalon all-pass filter with NRZ, RZ, and CS-RZ modulation

We present a multichannel tunable dispersion compensator (TDC) based on multicavity all-pass etalons that is capable of operation at 40 Gb/s. The device has a tuning range of +200/-220 ps/nm with a group delay ripple < /spl plusmn/5 ps over a channel bandwidth of 80 GHz, an overall loss of < 5.2 dB, very low insertion loss ripple, and can operate on any channel on a 200-GHz grid over the C-band. In addition, we present system performance results at 40 Gb/s using NRZ, RZ, and CS-RZ modulation, compensating up to 45 km of nonzero dispersion shifted fiber (NZDSF). Our results show that this device introduces very little excess system penalty with signal frequency drifts of up to 20 GHz when operated near the center of its tuning range. For single channel experiments with fiber, the system penalty increase versus signal detuning is more significant, but can be reduced by dynamically optimizing the device dispersion during detuning. Finally, we demonstrate simultaneous compensation of 4 channels across the C-band over 25 km of NZDSF.     

An approach to determine small-signal model parameters for InP-based heterojunction bipolar transistors

A new method for the extraction of the small-signal model parameters of InP-based heterojunction bipolar transistors (HBT) is proposed. The approach is based on the combination of the analytical and optimization technology. The initial values of the parasitic pad capacitances are extracted by using a set of closed-form expressions derived from cutoff mode S-parameters without any test structure, and the intrinsic elements determined by using the analytical method are described as functions of the parasitic elements. An advanced design system is then used to optimize only the parasitic parameters with very small dispersion of initial values. Good agreement is obtained between simulated and measured results for an InP HBT with 5/spl times/5 /spl mu/m/sup 2/ emitter area over a wide range of bias points up to 40 GHz.     

Investigation of system upgradability over installed fiber-optic cable using 40-Gb/s WDM signals toward multiterabit optical networks

An investigation of system upgradability of installed fiber-optic cable was conducted using 40-Gb/s wavelength-division-multiplexing (WDM) signals toward multiterabit optical networks. A field trial of 63-channel 40-Gb/s dispersion-managed soliton WDM signal transmission was successfully demonstrated over 320-km (4 /spl times/ 80-km) installed nonzero-dispersion-shifted fibers. The average Q factor of 15.4 dB was obtained, and very stable long-term bit-error-ratio performance was confirmed without polarization-mode dispersion compensation. This system upgradability investigation in the field environment provided the confidence to introduce 40-Gb/s technologies and effectively to construct multiterabit optical networks following the demand increase in the future.     

All-Raman ultralong-haul single-wideband DWDM transmission systems with OADM capability

In this paper, we present a comprehensive experimental investigation of an all-Raman ultrawide single-band transmission system for both 10 and 40 Gb/s line rates. Enabling technologies include forward-Raman pumping of the transmission fiber, counter-Raman pumping of the fiber spans and dispersion compensation modules, wideband dispersion, and dispersion-slope compensation, and modulation formats resistant to both linear and nonlinear impairments. Ultralong-haul (ULH) 128/spl times/10 Gb/s return-to-zero (RZ) and ultrahigh-capacity (UHC) 64/spl times/40 Gb/s carrier-suppressed (CS) RZ transmission are demonstrated for commercially deployed fiber types, including both standard single-mode fiber (SSMF) and nonzero dispersion shifted fibers (NZDSF). The span losses of 23 dB (NZDSF) and 20 dB (SSMF) are consistent with those encountered in terrestrial networks. The optical reaches for 10 Gb/s rate are 4000 km (NZDSF) and 3200 km (SSMF). Using the same distributed Raman amplification (DRA) scheme, UHC over 2.5 Tb/s at a 40-Gb/s per channel rate is also demonstrated for all of the tested fiber types and for optical reaches exceeding 1300 km. We then study the impact of including optical add/drop modules (OADMs) in the transmission system for both 10 and 40 Gb/s channel rates. System performance is characterized by the system margin and the transmission penalty. For all of the experiments shown in this paper, industrial margins and small transmission penalties consistent with operation in commercially deployable networks are demonstrated, showing the feasibility of practical implementation of all-Raman amplified systems for ULH and UHC optical backbones. Attractive features of single-wideband transmission enabled by DRA include simplicity of design, flexible gain and gain-ripple control, good noise performance, and a small system footprint.     

RZ-DPSK field trial over 13 100 km of installed non-slope-matched submarine fibers

This work presents the first field trial using the return-to-zero differential-phase-shift-keying (RZ-DPSK) modulation format. A 96/spl times/10-Gb/s RZ-DPSK field trial was conducted over a 13 100-km optical undersea path by double passing the installed 6550-km underwater link which was deployed with non-slope-matched submarine fibers. All channels performed with more than a 3-dB forward-error correction margin, including channels that accumulated over /spl plusmn/13 000ps/nm of dispersion. It is also shown that the RZ-DPSK format has similar residual dispersion and channel power tolerance for both slope-matched and non-slope-matched fibers. Furthermore, it is demonstrated that the chirped RZ-DPSK format could further improve system performance by 1-2 dB.     

2R regeneration based on dispersion-imbalanced loop mirror and its applications in WDM systems

2R regeneration based on dispersion-imbalanced loop mirror is investigated including the characteristics of transfer function, output extinction ratio, initial chirp, predispersion, and WDM signals transfer functions. Theoretical results show that the input peak power is a critical parameter for the dispersion-imbalanced loop mirror (DILM) and furthermore, to guarantee the multiwavelength operation of the DILM, limitations due to accumulated dispersion and dispersion slope have to be considered. Our experiment demonstrates that 6/spl times/10 Gb/s WDM signals can be successfully regenerated by a novel 2R regenerator based on a DILM consisting of a single mode fiber (SMF) and a highly nonlinear dispersion-shifted fiber (DSF) after WDM transmission over 40 km SMF of the WDM signals.     

Single-frequency, single-spatial-mode ROW-DFB diode laser arrays

Single-frequency, stable single-spatial-mode operation from large-aperture (40-60 /spl mu/m) index-guided devices is demonstrated from resonant antiguided phase-locked InGaAs-InGaP-GaAs diode-laser arrays incorporating 2nd-order distributed-feedback gratings (i.e., ROW-DFB arrays). The devices operate in a single-spatial-mode up to 3.6/spl times/threshold, and truly single-mode (i.e., single-spatial-mode and single-frequency) up to 2/spl times/threshold, For 40 (60)-/spl mu/m-aperture 10-element arrays, the beam pattern is in-phase and diffraction-limited with 70% (75%) of the power residing in the main lobe. Single-frequency operation is obtained from 9640-9652 /spl Aring/, over a temperature range of approximately 20/spl deg/C, side-mode suppression ratios /spl ges/20 dB are recorded up to 2/spl times/threshold.     

Transparent ultra-long-haul DWDM networks with "broadcast-and-select" OADM/OXC architecture

We describe an experimental realization of ultra-long-haul (ULH) networks with dynamically reconfigurable transparent optical add-drop multiplexers (OADMs) and optical cross-connects (OXCs). A simple new approach to dispersion management in ULH dense-wavelength-division-multiplexing (DWDM) transparent optical networks is proposed and implemented, which enables excellent transmission performance while avoiding dispersion compensation on a connection-by-connection basis. We demonstrate "broadcast-and-select" node architectures that take full advantage of this method. Our implementation of signal leveling ensures minimum variations of path-averaged power among the wavelength-division-multiplexing (WDM) channels between the dynamic gain-equalizing nodes and results in uniform nonlinear and spontaneous-emission penalties across the WDM spectrum. We achieve 80/spl times/10.7-Gb/s DWDM networking over 4160 km (52 spans/spl times/80 km each) of all-Raman-amplified symmetric dispersion-managed fiber and 13 concatenated OADMs or 320/spl times/320 wavelength-port OXCs with 320-km node spacing. The WDM channels use 50-GHz grid in C band and the simple nonreturn-to-zero (NRZ) modulation format. The measured Q values exhibit more than a 1.8-dB margin over the forward-error correction threshold for 10/sup -15/ bit-error-rate operation. We compare these results with point-to-point transmission of 80/spl times/10-Gb/s NRZ WDM signals over 4160 km without OADM/OXC and provide detailed characterization of penalties due to optical signal-to-noise-ratio degradation, filter concatenation, and crosstalk.     

Propagation in Ferrite-Filled Coaxial Transmission Lines

The dispersion relations (/spl omega/-/spl beta/diagrams) for propagation of the quasi-TEM mode and higher-order symmetric modes in longitudinally magnetized ferrite-filled coaxial waveguide are presented. The dispersion relations for ferrite-filled coaxial cavity resonators are analyzed and presented graphically. The performance and operation of an X-band tunable ferrite filter is evaluated in light of the /spl omega/-/spl beta/diagrams     

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

1.3-/spl mu/m 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.     

Novel fiber design for flat gain Raman amplification using single pump and dispersion compensation in S band

This paper reports on a novel fiber design that has an inherently flattened effective Raman gain spectrum. Simulations show that gain-flattened broad-band Raman amplification, using a single pump, can be achieved in any wavelength band by suitably choosing the fiber parameters and the pump wavelength. The fiber also has a high negative dispersion coefficient-(380-515) ps/km/spl middot/nm over the operating range of wavelengths-and the shape of the dispersion curve is such that the total link dispersion can be not only compensated but also flattened. Hence, the designed fiber can serve as a lossless, broad-band, dispersion-flattening, and dispersion-compensating module for the S band, wherein lossless operation is achieved using inherently gain-flattened single-pump Raman amplification. The performance characteristics of such a module was modeled taking into account wavelength-dependent splice loss as well as background loss, and it has been shown through simulations that lossless operation with /spl plusmn/0.2-dB gain ripple is achievable over (1480-1511) nm using a single pump. Moreover, dispersion compensation for five spans of transmission in a 10-Gb/s system, over this 32-nm bandwidth in the S band, should be attainable using the proposed design.