Nicholas J. Frigo

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>>

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.

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>>

112 channel split-band WDM lightwave CATV system

The authors demonstrate a 1.3/1.55 mu m wavelength-division-multiplexed analog lightwave system which transports 112 channels (55.25-751.25 MHz) over 10 km of standard single-mode fiber. The lower 60 channels are transmitted by externally modulating a 1.55- mu m DFB laser diode. The signal is amplified using an erbium-doped fiber amplifier which allows broadcasting to 8 hubs. Fifty-two higher-frequency narrowcast channels are added by direct modulation at 1.3 mu m using wavelength-division-multiplexing.<<ETX>>

On a method for calculating the strength of intermodulation distortion and products

Frigos recent method for approximately calculating intermodulation distortion products for nonlinear systems is clarified, and a derivation from first principle is provided. >

Noise reduction in long-haul lightwave all-amplifier systems

The overall gain of a chain of erbium-doped fiber amplifiers in a long-haul all-amplifier system would be automatically stabilized if each amplifier were operated slightly into saturation. However, with the required low level of amplifier output power which is imposed by nonlinearity in the transmission fiber, the resulting pump power becomes too low to effectively invert the gain medium of the amplifiers. Consequently, the amplifier output noise level becomes too high for proper system operation. This problem is solved by pumping the amplifiers harder so that a higher gain and higher output power are achieved. The excess gain is then counteracted by an appropriate value of post-amplifier loss. Because of the higher pump power in this case, the amplifier noise is reduced significantly. This technique is investigated theoretically, and experimental work that verifies it is reported. >

Thermal characteristics of light-emitting diodes and their effect on passive optical networks

LEDs have been demonstrated in several new passive optical networks (PON) architectures which capitalize on their wide spectral emission. We show that, due to thermal properties, LEDs exhibit higher than expected output powers under RF subcarrier modulation and baseband packet modulation, leading to advantageous power budgets in PON applications.