2.488 Gb/s-318 km repeaterless transmission using erbium-dopedfiber amplifiers in a direct-detection system

The authors have achieved a 2.488 Gb/s, 318 km repeaterless transmission without any fiber dispersion penalty through a nondispersion-shifted fiber in a direct detection system. The system was loss limited with a T-R power budget of 57 dB. Three key components enabled the authors to achieve this result: (1) a Ti:LiNbO₃ external amplitude modulator enabling a dispersion-free transmission, (2) erbium-doped fiber amplifiers increasing the transmitting power to +16 dBm, and (3) an erbium-doped fiber preamplifier enabling a high-receiver sensitivity of -4.1 dBm for 10^-9 BER. To the author's knowledge, this result is the longest repeaterless transmission span length ever reported for direct detection at this bit rate. From the experimental results and a theoretical model, the authors identified the sources of the receiver sensitivity degradation from the quantum limit (-48.6 dBm) and estimated the practically achievable receiver sensitivity of ~-44 dBm (~-124 photons/bit) for 2.5 Gb/s optical preamplifier detection     

Duty cycle ratio dependence on the performance of a q-switched laser with an Er3+-Yb3+ codoped glass waveguide

We examine the performance of a hybrid Q-switched LiNbO(3) and Er(3+)-Yb(3+) doped glass waveguide laser as a modulation function of the duty cycle ratio. As the duty cycle ratio decreases, the laser operates at higher peak power and pulse width. At low duty cycle ratio (<1%), we observe variations in the Q-switched pulse shape; while the laser produces 59-W and 200-ns pulses to a 1-kHz repetition rate for a 50% duty cycle, it yields 27-W and 100-ns pulses to a 10-kHz repetition rate for a 0.01% duty cycle.     

Performance evaluation of waveguide phase modulators for coherent systems at 1.3 and 1.5 µm

This article describes the fabrication and performance evaluation ofX-cut andZ-cut Ti:LiNbO3traveling wave waveguide phase modulators designed for coherent systems applications at 1.3 and 1.5 μm. Details of device fabrication and measurements of phase shift as a function of optical wavelength, input polarization, modulation voltage, and modulation frequency are reported. Phase modulator performance in a 40-Mbit/s self-heterodyne coherent DPSK experiment is also discussed.     

Fundamental limitations in the performance of chirped grating lenses on planar optical waveguides

The fundamental limitations in the performance of chirped grating lenses on planar optical waveguides caused by diffraction and by fabrication tolerances have been analyzed based on the generalized coupled mode theory (GCMT). The two most crucial lens parameters that affect the performance have been identified as the minimum grating periodicity and the maximum coupling coefficient. They have a strong effect on both the higher orders of diffraction and the phase distortions that eventually reduce the efficiency, enlarge the spot size and restirct the angular field of view. Both etched and deposited linear and curved grating lenses have been fabricated and evaluated on single-mode glass waveguides. Their measured performance is in good agreement with the predictions of the GCMT. High throughput efficiency (in excess of 80 percent) combined with very large angle of view (larger than 0.1 rad), as well as the performance limitations caused by diffraction have been demonstrated experimentally.     

Amplifying four-wavelength combiner, based on erbium/ytterbium-doped waveguide amplifiers and integrated splitters

We report the successful system demonstration of a four-wavelength integrated-optics amplifying combiner. The arrangement consists of an all-connectorized 4/spl times/1 glass splitter followed by a 4.5-cm-long Er/Yb-doped waveguide amplifier. When injecting 120 mW of 975-nm laser diode pump, we record, in the amplifying section, 11.6 dB of net gain in the single pass configuration and 23 dB in the double pass as well as a noise figure of 4.5 dB. These results show the potentiality of ion-exchange technology for the fabrication of lossless telecommunication devices.     

10 Gb/s 120-km Bidirectional Repeaterless Transmission over Single-Mode Fiber

A successful repeaterless 10 Gb/s bidirectional transmission experiment is demonstrated at the 1550 nm wavelength through 120 km of single-mode fiber. Fiber chromatic dispersion compensation in both transmission directions is realized by insertion of the same dispersion compensating fiber in the transmission fiber span. Excellent long-term error rate performance (BER < 10-¹⁴) is achieved by suppression of the Rayleigh backscattered signal power with low loss narrow-band fiber grating reflection filters.     

Spontaneous and stimulated Brillouin scattering gain spectra in optical fibers

We study the Brillouin scattering behavior in several single-mode fibers with different waveguide characteristics in terms of their longitudinal mode structures in the gain spectrum, linewidth narrowing, and stimulated Brillouin scattering (SBS) threshold levels. Evolution from spontaneous to SBS is investigated by monitoring the Brillouin line-shape and the behavior of the longitudinal acoustooptic resonance modes that exist in the core. We compare our results with the current theory of Brillouin scattering generated from noise in the undepleted pump approximation. We also present experimentally Brillouin gain spectra in the highly depleted pump regime, where there is no analytical solution, by showing the evolution of the gain spectrum as a function of the injected laser intensity.     

High-performance integrated erbium/sup +3/-ytterbium/sup +3/ codoped glass waveguide laser

We report the design and characterization of an efficient erbium/sup +3/-ytterbium/sup +3/ codoped ion exchanged glass distributed Bragg reflector (DBR) laser pumped by a 980-nm pigtailed laser source. Laser oscillation at 1536 nm is demonstrated with a pump threshold of 35 mW and a slope efficiency of 10.6%. The dependence of lasing performance on pump wavelength detuning is examined for different cavity designs.     

Repeatered Bidirectional 10 Gb/s–240 km Fiber Transmission Experiment

We report the design and performance evaluation of a novel circulator-based bidirectional optical amplifier. Using this amplifier as a mid-span repeater, we have demonstrated successful bit error rate (BER<10⁻¹³) transmission at 10 Gb/s over 240 km of dispersion shifted fiber in both directions for channel wavelengths at 1557.5 and 1559 nm.