In this paper, the basic principle of operation, design issues, limitations, recent developments and emerging research trends on wide-bandwidth lasers and modulators for radio-frequency photonic applications are reviewed. The topics covered are wide-bandwidth lasers, lumped and traveling-wave electroabsorption modulators, traveling-wave LiNbO/sub 3/, GaAs, and polymer modulators.

Wide-bandwidth lasers and modulators for RF photonics

An optical access network transceiver based on a reflective semiconductor optical amplifier operating as modulator and photodetector is demonstrated. Device characterization and modulation/detection tests show the system proper operation at 1.25 Gb/s to 30-km reach. This optical network unit design is a simple and capable solution for future fiber-to-the-home networks.

Optical network unit based on a bidirectional reflective semiconductor optical amplifier for fiber-to-the-home networks

This paper investigates the impact of backreflection lights on upstream transmission in wavelength division multiplexing (WDM) single-fiber loopback access networks, where a WDM light source is located at the central office (CO) and each optical network unit (ONU) includes an optical modulator with optical amplifiers. This study considers backreflection lights from two sources, the continuous wave (CW) light at the CO (Reflection-I) and the modulated signal at the ONU (Reflection-II). It is confirmed, for the first time, that the impact of Reflection-II increases strongly with ONU gain. To estimate the impact of these backreflection lights, a simple intensity noise estimation scheme is presented. This scheme clarifies that the acceptable transmission line losses is 10 dB for 1.25 Gb/s under the optical return loss (ORL) of -32 dB.

Impact of backreflection on upstream transmission in WDM single-fiber loopback access networks

Integrating the input and output waveguides with a multiple-quantum-well (MQW) electro-absorption (EA) optical modulator is shown to achieve ultra-high-speed modulation while keeping the total device length long enough for easy fabrication and packaging. Testing with fabricated modulators showed that a shorter modulation region results in a larger modulation bandwidth. The additional loss due to the waveguide integration was less than 1 dB. An optimized modulator showed a large modulation bandwidth of 50 GHz, a low driving voltage of less than 3 V, and a low insertion loss of 8 dB. A prototype module of this modulator had a bandwidth of greater than 40 GHz. Optimizing the MQW structure makes the modulator insensitive to polarization. These results demonstrate that MQW-EA modulators with integrated waveguides are advantageous in terms of fabrication, packaging, and ultra-high-speed modulation.

Ultra-high-speed multiple-quantum-well electro-absorption optical modulators with integrated waveguides

An analytical theory describing all-optical wavelength converters based on cross-gain modulation (XGM) in semiconductor-optical amplifiers is derived. Our theory consists of two parts: a large-signal analysis yielding the transmission function for the signal, and a small-signal analysis in order to describe the transformation of the signal and probe intensity noise. Both the large-signal as well as the small-signal theory reveal similar performance for the co- and the counterpropagating injection scheme for bit rates up to 2.5 Gb/s. This is confirmed by computer simulations. Consequently, the counterpropagating configuration is preferable because the implementation is simpler and conversion to the same wavelength is possible. In order to increase the conversion efficiency it is better to reduce the average signal power than to increase the probe power, which additionally reduces the output power range. However, there is a tradeoff between conversion efficiency and output extinction ratio. According to the small-signal analysis, the relative-intensity noise (RIN) due to the probe and due to the amplified spontaneous emission is negligible. Moreover, the converted signal has a lower RIN than the input signal.

Performance analysis of wavelength converters based on cross-gain modulation in semiconductor-optical amplifiers

We report on a MQW electroabsorption modulator with tensile-strained wells. The device transmission is shown to be fully polarization insensitive, i.e. both in amplitude and phase. The modulation efficiency is over 20 GHz/V (bandwidth higher than 20 GHz and 1 V drive voltage) which is the highest figure of merit reported for any kind of polarization insensitive modulator. Full polarization independence is further demonstrated by 2.5 Gb/s transmission at 1.55 /spl mu/m over 475 km of standard fiber without penalty at 10/sup -9/ BER whatever the polarization. >

Full polarization insensitivity of a 20 Gb/s strained-MQW electroabsorption modulator

Extinction ratio conservation, wide dynamic range, and large operating wavelength window are important features for all-optical wavelength converters. Practical converters may probably be multistage devices and have to be precisely modeled. We present an experimental analysis and phenomenological modeling of single- and multistage wavelength converters using cross-gain modulation in polarization insensitive multiquantum-well optical amplifiers. One of the studied double-stage converters is able to produce a large extinction ratio improvement with a regeneration factor higher than 1.5 for any conversion in the 1.53-1.56-/spl mu/m window. The phenomenological model yields a very good agreement with the experimental results.

Extinction ratio of cross-gain modulated multistage wavelength converters: model and experiments

One component for the reception and emission for the subscriber in the future WDM (FTTH) fibre to the home network is considered. A study of the performances of a modulator based on a semiconductor laser amplifier with a reflector is presented. It offers the prospect of a low-cost subscriber module.

A semiconductor laser amplifier-reflector for the future FTTH applications

Non-linear optical device for processing an optical signal, comprising an interferometer with multiple arms. This device comprises an optical interferometer comprising N arms (B 1 . . . BN) where N≧3n, N semiconductor optical amplifiers (A 1 . . . AN) each being inserted in the N arms, a first optical coupling means ( 28 ) that receives a control signal and distributes this control signal into the N arms and a second optical coupling means ( 32 ) that receives an input signal and distributes it in at least N-1 of the N arms and collects the light resulting from the distribution of the control signal in the N arms and supplies an output signal which is the resultant of interference of these two light sources. Application to optical telecommunications.

Non-linear optical device for processing an optical signal, comprising an interferometer with multiple arms

The device comprises an optical interferometer comprising two arms (8,10) to receive an optical signal to be processed Two semiconductor optical amplifiers (12,14) are inserted in the two arms in such a way as to be able to modify the refractive index of one of the amplifiers by the injection of a pumping signal into the corresponding arm The opto-geometric characteristics or structural characteristics of at least one of the two arms of the interferometer are tuned by the introduction of a phase shift of between the two arms The interferometer may either by a Michelson interferometer, or a symmetrical Mach-Zehnder interferometer The circuit also comprises provision to bias the optical amplifiers by the same electrical current

Sandrine Chelles

Papers

Full polarization insensitivity of a 20 Gb/s strained-MQW electroabsorption modulator

Extinction ratio of cross-gain modulated multistage wavelength converters: model and experiments

A semiconductor laser amplifier-reflector for the future FTTH applications

Non-linear optical device for processing an optical signal, comprising an interferometer with multiple arms

Nonlinear optical signal processing device