George E. Bodeep

A wavelength-division multiplexed passive optical network with cost-shared components

We demonstrate a passive optical network (PON), based on a wavelength-division multiplexing router, with modulators (instead of lasers) at the subscriber terminals. A single, cost-shared, tunable laser is time-division multiplexed to provide bidirectional switched WDM services for N subscribers with independent formats and bit-rates for each. Simultaneous support of telephony and compressed digital video are presented in which RF subcarrier multiplexing is used to provide service segregation and resolve upstream packet contention.<<ETX>>

Lightwave subcarrier CATV transmission systems

The design and performance of multichannel amplitude-modulated (AM) vestigial-sideband (VSB) lightwave cable television (CATV) systems are described. Requirements on linearity and noise are derived, and factors limiting the performance of the laser transmitters and receivers are discussed. For the high-performance lasers the carrier-to-noise ratio and composite second- and third-order distortions are acceptable for video trunk systems. Impairments because of fiber reflections and dispersion and mode partition fluctuations in the laser are discussed. Feedforward, feedback, and predistortion are discussed; difficulties with each prevent immediate application. The use of LiNbO/sub 3/ external modulators and high-power solid-state lasers is considered. The third-order distortion and insertion loss of the modulator more than counteract the high available laser power (100 mW), making this alternative unattractive unless a third-order linearizer can be implemented. >

Nonlinear distortion generated by dispersive transmission of chirped intensity-modulated signals

Transmission through dispersive and nonlinear optical fibers produces distortion in subcarrier intensity-modulated systems. Analytic expressions for second- and third-order distortion are derived using the time-domain form of the field envelope wave equation. The distortion predicted by these expressions agrees well with numerical simulation and reasonably well with experimental data. Significant composite second-order distortion is predicted in typical 1.55 mu m cable television systems.<<ETX>>

Clipping distortion in lightwave CATV systems: models, simulations, and measurements

We report theoretical, numerical, and experimental investigations of clipping distortions in CATV systems are reported. The applicability of A.A.M. Salehs (1989) calculation of the carrier-to-nonlinear-distortion ratio (CNLD) is extended by incorporating a more precise spectral analysis and further analytic results. An effective transfer function model which spectrally resolves the clipping distortion at intermodulation products (IMPs) of all orders and frequencies, and features closed-form analytic calculation of the second- and third-order distortions (CSO and CTB) from basic principles, as well as the CNLD, is introduced. It is found that Salehs model slightly overestimates the simulation results for the CNLD, while the new model is in essential agreement with the simulation for all three distortion measures. Experimental measurements of the CSO, CTB, and CNLD over a 50-dB range in distortion exhibited excellent agreement with the simulations and the new model over the entire range. The unified nature of the model allows standard CATV, CSO, and CTB measurements to be theoretically connected to the CNLD and clipping boundary.

Fiber-reflection-induced impairments in lightwave AM-VSB CATV systems

Impairments due to multiple fiber reflections are evaluated for amplitude-modulated (AM) vestigial-side-band (VSB) lightwave cable TV (CATV) systems using directly modulated distributed feedback (DFB) lasers or externally modulated diode-pumped YAG laser transmitters. For DFB lasers, the spectral broadening caused by laser chirp results in a Gaussian optical spectrum with a width near 5 GHz. Square-law detection of multipath signals from two -30-dB reflections results in an effective intensity noise near -150 dB/Hz. For externally modulated YAG lasers, the same multiple reflections result in interference that cannot be described by an effective RIN. Although the total interference power is comparable to that of the DFB lasers, the signal and interference are highly correlated. As a result of this correlation, multipath interference for YAG-based systems cannot be measured using the standard test procedure with unmodulated carriers. >

Brillouin scattering in externally modulated lightwave AM-VSB CATV transmission systems

The authors measure the stimulated Brillouin scattering threshold for a CW (continuous wave) laser externally modulated with an AM-VSB (amplitude modulation vestigial sideband) CATV (cable television) signal. The threshold is essentially unchanged from the unmodulated case. For injected powers above the threshold power, substantial degradation of the carrier to noise ratio is seen.<<ETX>>

Broad-band AM-VSB/64 QAM cable TV system over hybrid fiber/coax network

We demonstrate the first broad-band AM-VSB/64 QAM cable TV

Semiconductor lasers versus external modulators: a comparison of nonlinear distortion for lightwave subcarrier CATV applications

Second- and third-order distortion measurements performed on various buried-heterostructure InGaAsP DFB (distributed feedback) lasers and on LiNbO/sub 3/ external modulators are discussed. It is shown that by optimally biasing the external modulator, the second-order distortion can be eliminated but the third-order distortion is 25 dB greater than that of direct modulation. It is also shown that these discrete two-tone measurements can be used to predict the system performance of a 42-channel CATV trunk system. The increased composite-triple beat and lower carrier-to-noise ratio, due to modulator loss, are the disadvantages of the external modulator. If it is possible to improve third-order distortion by modifying the structure of the modulator or by electronic compensation without increasing the second-order distortion, then these modulators may be useful for CATV applications.<<ETX>>

Clipping-induced impulse noise and its effect on bit-error performance in AM-VSB/64QAM hybrid lightwave systems

We demonstrate that the impulse noise generated from clipping AM signals limits QAM bit-error performance in AM-VSB/M-QAM hybrid optical transmission systems. A new technique is developed to adequately predict QAM bit-error rate by defining a measurable parameter which can be obtained from impulse counting using a standard spectrum analyzer.<<ETX>>

Clipping distortion in AM-VSB CATV subcarrier multiplexed lightwave systems

The authors discuss theoretical and experimental investigations of clipping distortion in CATV systems. After reporting an exact form of an earlier clipping model, the authors present a new model which predicts the clipping distortion at each intermodulation product (IMP) frequency of a set of carriers as a function of their modulation depth for all orders. This allows the calculation of distortion ratios (CSO, CTB, and CNLD) from basic principles, expressed in closed form. Experiments were performed to test the models validity. The results of CSO, CTB, and CNLD measurements are presented and they are found to agree well with the predictions of the model.<<ETX>>