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

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

The chirp parameter of a multiple-quantum-well (MQW) electroabsorption modulator was measured with accuracy for several operating wavelengths in the 1.5 /spl mu/m window. It varied strongly with applied bias. Effective chirp parameter, defined as the ratio of phase change to transmission change between modulator on and off states, is about zero, or even negative. However, experimental transmission length on standard fiber at 10 Gb/s NRZ is much smaller than what is expected for such a low chirp parameter. It is demonstrated that the effective chirp parameter should not be computed from changes between on and off states, but from the average of the chirp parameter values in a 3 dB region of the most transparent states of the modulator. This simple rule allows us to predict transmission performances based on measurements of the chirp parameter, and can be used to optimize optical components without actually experimenting on a transmission system. The effective chirp parameter of the MQW electroabsorption modulator is found positive. This should be intrinsic to red-shift electroabsorption effects, such as the quantum confined Stark effect. >

On the transmission performances and the chirp parameter of a multiple-quantum-well electroabsorption modulator

We demonstrate the improved modulation properties of a new strained InGaAs/InAlAs MQW electro-absorption modulator. This tensile strained MQW modulator shows low driving voltage (V/sub 15 dB/=1.2 V), large modulation bandwidth (f/sub 3 dB/>20 GHz), and a 10 Gbit/s eye pattern with a clear eye opening and high extinction ratio. The effective /spl alpha/ parameter determined from waveform deterioration is 0.6, which is low enough for multigigabit long-haul fiber transmission systems. >

Strained InGaAs/InAlAs MQW electroabsorption modulators with large bandwidth and low driving voltage

The quantum-confined Stark effect (QCSE) is an established optical modulation mechanism, yet top-performing modulators harnessing it rely on costly fabrication processes. Here, we present large modulation amplitudes for solution-processed layered hybrid perovskites and a modulation mechanism related to the orientational polarizability of dipolar cations confined within these self-assembled quantum wells. We report an anomalous (blue-shifting) QCSE for layers that contain methylammonium cations, in contrast with cesium-containing layers that show normal (red-shifting) behavior. We attribute the blue-shifts to an extraordinary diminution in the exciton binding energy that arises from an augmented separation of the electron and hole wavefunctions caused by the orientational response of the dipolar cations. The absorption coefficient changes, realized by either the red- or blue-shifts, are the strongest among solution-processed materials at room temperature and are comparable to those exhibited in the highest-performing epitaxial compound semiconductor heterostructures.

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The quantum-confined Stark effect in layered hybrid perovskites mediated by orientational polarizability of confined dipoles

The authors have fabricated a ridge waveguide electroabsorption modulator based on the quantum-confined Stark effect in InGaAsP/InGaAsP multiple quantum wells. The drive voltage for 12-dB extinction ratio is 1.2 V, and the frequency response is flat within 2 dB from DC to 20 GHz. Operation at 20 Gb/s is reported. Extensive data concerning the parasitic phase modulation (chirping) are obtained as a function of applied bias acid operating wavelength. >

F. Dorgeuille

Papers

20 Gbit/s operation of a high-efficiency InGaAsP/InGaAsP MQW electroabsorption modulator with 1.2-V drive voltage