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We propose and demonstrate a long-reach wavelength-division-multiplexed passive optical network (WDM PON) capable of providing 100-Gb/s service to each subscriber, for the first time to the best of our knowledge. For cost-effectiveness, this network is implemented in loopback configuration by using directly modulated reflective semiconductor optical amplifiers (RSOAs) at 25.78 Gb/s. For the modulation of the RSOA at such a high-speed, we have to minimize the electrical parasitics by using the butterfly package. Also, to overcome the limited bandwidth of the RSOA, we utilize the electronic equalization technique at the receiver. We use four RSOAs at each optical network unit for the 103-Gb/s upstream transmission. The operating wavelengths of these RSOAs are separated by the free-spectral range of the cyclic arrayed waveguide gratings used at the central office and remote node (RN) for (de)multiplexing the WDM channels. We extend the maximum reach of this WDM PON to be >; 120 km by using Erbium-doped fiber amplifiers at the RN. The results show that the error-free transmission can be achieved for all WDM channels in the wavelength range of >; 35 nm with sufficient power margins.

We report the 25.78-Gb/s operation of the reflective semiconductor optical amplifier (RSOA) for the next-generation optical access network. For this purpose, we develop a butterfly-packaged RSOA and minimize the electrical parasitics. As a result, the modulation bandwidth of RSOA is improved from 2.2 to 3.2 GHz (which is the fundamental limit imposed by the carrier lifetime). In addition, the slope of the RSOA's frequency response curve is enhanced from -40 to -20 dB/decade. Using this butterfly-packaged RSOA, we have demonstrated the 25.78-Gb/s operation. The receiver sensitivity is measured to be -11 dBm with the help of the electronic equalization and forward-error-correction (FEC) techniques. To evaluate the possibility of implementing the 100-Gb/s passive optical network (PON) by using this RSOA and the coarse wavelength-division-multiplexing (CWDM) technique, we evaluate the BER performance at four different wavelengths in the C-band. The results show that the error-free transmission can be achieved in the wavelength range of 20 nm with a penalty less than 2 dB. Thus, we can realize the 100-Gb/s PON cost-effectively by utilizing the directly modulated RSOAs operating at 25 Gb/s.

We investigate the performance of the forward-error correction (FEC) code for the 10-Gb/s wavelength-division-multiplexed passive optical network (WDM PON) implemented by using reflective semiconductor optical amplifiers (RSOAs) with extremely limited modulation bandwidth and the electronic equalizers to compensate for the degradations resulting from the use of such RSOAs. We show that the error occurrences in this network strongly depend on the bit pattern and the burst errors are likely to occur. Thus, it is important to use the FEC code capable of correcting the burst errors such as Reed-Solomon (RS) code. In addition, since a significant penalty can be induced by the increased line rate resulting from the use of the FEC code, it is necessary to find the optimum redundancy required to minimize the bit-error rate. We also evaluate the tolerance to the chromatic dispersion of the proposed 10-Gb/s WDM PON implemented by using the RS code with the optimum redundancy.

The bit-error-rate performance of a multilevel phase-shift-keying (PSK) signal can be easily degraded by a slight phase distortion induced by the setting errors of the modulator such as the offsets of bias voltages. To solve this problem, we examine the possibility of using the data-aided phase noise estimation (DAPNE) algorithm, which has been originally proposed for the reduction of differential phase noise. The experimental results show that DAPNE can enhance the tolerance to the setting errors of differential quadrature PSK and 8-ary PSK modulators.

In this letter, we demonstrate the wavelength- and polarization-independent operation of a receiver for differential quadrature phase-shift-keying and 8-ary phase-shift-keying signals, which utilizes a single delay interferometer made of a 3 times 3 optical coupler. We show that the phase distortion, which occurred in the proposed receiver, can be reduced to less than 2deg without any adjustments. This feature enabled us to achieve nearly quantum-limited sensitivities.

We describe a new method for quantitative evaluation of the quality of multilevel differential phase-shift-keyed (DxPSK) signals by using a differential phasor monitor. This method measures the phase deviation of the symbols in the differential phasor diagram and estimates the bit-error rate (BER) by using a simple relation based on the Q -factor defined for multilevel DxPSK signals. We demonstrate that the proposed method can accurately estimate the BER of differential quadrature PSK and 8-ary PSK signals.

A hybrid wavelength-division-multiplexing/ time-division multiple access-passive optical network system using self-homodyne scheme and differential coding was proposed. The laser seed light injected reflective semiconductor optical amplifier was used as the colorless transmitter. It was shown that the proposed scheme can increase the power loss budget of optical distribution network significantly by complete suppression of the reflection noise.

We report on the operable ranges of temperature and wavelength for a 1.25-Gb/s wavelength-division-multiplexed passive optical network (WDM PON) implemented by using uncooled reflective semiconductor optical amplifiers (RSOAs). Both the gain and modulation bandwidth of the RSOA are substantially reduced at high temperatures. As a result, it is difficult to achieve the error- free operation at temperatures above 40degC. In order to mitigate this limitation, we implement a simple bias-control circuit, in which the bias current is controlled stepwise according to the operating temperature of the RSOA. Using this circuit, we extend the operable wavelength range of the RSOA-based WDM PON to ~55 nm in the temperature range of -20degC to 60degC.

We report on the 1O-Gb/s operation of the reflective semiconductor optical amplifier (RSOA) for the next-generation wavelength-division-multiplexed passive optical network (WDM PON). The bandwidth of the RSOA used in this experiment is merely 2.2 GHz. Nevertheless, a clear eye opening is obtained at 10 Gb/s by using the electronic equalizer processed offline. We investigate the impacts of the network's operating conditions (such as the injection power to the RSOA and the fiber length) on the performances of these equalizers. The results show that the RSOA-based WDM PON is operable at 10 Gb/s and the maximum reach can be extended to >20 km with the help of the forward error correction codes.

We describe a new method for monitoring the ldquoin-bandrdquo optical signal-to-noise ratio (OSNR) of differential phase-shift-keying (DPSK) and differential quadrature phase-shift-keying (DQPSK) signals. This technique estimates the OSNR by analyzing the radio frequency spectrum obtained by the self-heterodyne detection. The results show that the performance of the proposed technique is not sensitive to the effects of chromatic dispersion and polarization-mode dispersion. In addition, this technique can be used for monitoring the polarization-scrambled signals. For a demonstration, we measure the OSNR of the polarization-scrambled 10-Gb/s DPSK and 20-Gb/s DQPSK signals in a 640-km-long transmission link.

We propose and demonstrate a novel scheme of the all-optical, high-speed add-drop multiplexer (ADM) for the optical time-division multiplexed signal. The ADM employs a single nonlinear optical loop mirror (NOLM) composed of an optical fiber. The key technical point of this scheme is the simultaneous use of the reflection mode (add function) and the transmission mode (drop function) of the NOLM, which results in significant simplification of the overall ADM configuration. Experimental results show that simultaneous add-drop operation at 80 Gb/s can be successfully achieved without bit errors.

We demonstrate a broad-band wavelength-tunable Bismuth Oxide-based Erbium-doped fiber (Bi-EDF) laser covering both the conventional wavelength band and the long wavelength band. It features single frequency and single polarization oscillation; the former is obtained by making the cavity length short and incorporating an intracavity narrow-band fiber Fabry-Pe/spl acute/rot filter, and the latter is achieved with a sigma laser configuration using nonpolarization maintaining fibers. Tuning over 90 nm (1520-1610 nm) is achieved by utilizing the broad gain bandwidth of Bi-EDF amplifier.

We demonstrate the in-service dispersion monitor in a 16 /spl times/ 10.6 Gb/s 960-km wavelength-division-multiplexing transmission system. We use the optical frequency method for the dispersion monitor, and modify it so as to be able to detect the sign of the dispersion without the loss of simplicity. The accuracy of the dispersion monitoring and the influence on the bit-error-rate performance are experimentally evaluated.

We experimentally investigate the validity of the Gaussian approximation model of intraband crosstalk from multiple channels, which can degrade system performance significantly in wavelength-division multiplexed (WDM) networks. A recirculating fiber loop is employed for the first time to generate multiple crosstalk elements up to 20. The power penalties predicted by the Gaussian approximation model match well with the experimental results as the number of crosstalk elements is increased. This is because the probability distribution of the signal power mixed with intraband crosstalk approaches the Gaussian distribution with growing number of crosstalk elements in accordance with the central limit theorem.

We demonstrate a multiwavelength pulse source which utilizes the super-continuum generated in a normal group-velocity dispersion fiber and an arrayed-waveguide grating filter. Over 20-channels of pulse train with a repetition rate of 10 GHz are realized, and each channel has almost the same pulsewidth. This uniformity originates from the fact that the super-continuum pulse generated in a normal-dispersion fiber has a rectangular waveform and a linear chirp.

We experimentally investigate the gain spectrum of erbium-doped fiber amplifiers whose gain is clamped by internal laser oscillation. The gain is ideally clamped and immune to the input signal power in the wavelength range of 17 nm. The clamped gain spectrum is equalized by a Mach-Zehnder interferometer, and we achieve the 17-nm-wide uniform gain, which is not dependent on input optical power levels.

We propose a novel configuration of Fabry-Perot fiber lasers for achieving single-frequency and polarization-stable oscillation. The laser consists of a nonpolarization-maintaining active fiber, Faraday rotator mirrors, and a specially designed intracavity frequency-selective element. An erbium-doped fiber laser is actually constructed according to the cavity design, and we can observe stable single longitudinal-mode oscillation.