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

Publisher Summary The pseudo–linear transmission is a method for the transmission of high-speed time-division multiplexed (TDM) signals where fast variations of each channel waveform with cumulative dispersion allows important averaging of the intrachannel effects of fiber nonlinearity. The pseudo–linear transmission involves complex optimization of modulation format, dispersion mapping, and nonlinearity. These transmissions occupy a space somewhere between dispersion-mapped linear transmission and nonlinear soliton transmission. The pseudo-linear regime of transmission is characterized by a rapid pulse broadening, which results in a dramatic reduction of the solitonic effect on each pulse. As a result, full dispersion compensation can be used in this regime. Extensive analysis of pseudo-linear transmission and reviews of the TDM transmission experiments at 40 and 160 Gb/s have been provided in the chapter. Two new forms of nonlinear interactions between rapidly dispersing pulses namely intrachannel cross–phase modulation (IXPM) and intrachannel four–wave mixing (IFWM) are also presented. These two intrachannel effects are the most important nonlinear interactions in pseudo-linear transmission and determine the dispersion mapping even for the wavelength–division multiplexed (WDM) systems. Further, the chapter describes the semiconductor–based technologies that enable the development of stable and reliable high–speed transmitters and receivers.

Pseudo-Linear Transmission of High-Speed TDM Signals: 40 and 160 Gb/s

In this letter, we have developed a tandem electroabsorption modulator with an integrated semiconductor optical amplifier that is capable of both nonreturn-to-zero and return-to-zero (RZ) data transmission at 40 Gb/s. The tandem modulator consists of a broad-band data encoder and a narrow-band pulse carver. The pulse carver is able to produce 5-ps pulses with more than 20 dB of extinction. The on-chip semiconductor optical amplifier provides up to 8.5 dB of fiber-to-fiber gain and enables the modulator to be operated with zero insertion loss. Devices have been realized with greater than 40-GHz bandwidth, and 13-dB dynamic extinction for a 2.5-V swing. For optimized designs bandwidths of nearly 60 GHz: have been realized. Using these devices penalty free RZ data transmission over a 100-kin dispersion compensated fiber link has been demonstrated with a received power sensitivity of -29 dBm.

40-Gb/s tandem electroabsorption modulator

Monolithically integrated single frequency lasers and electroabsorption modulators are attracting considerable interest as optical sources for long-haul and high-bit-rate fiber-optic links. Their frequency chirpless nature has indeed allowed nonreturn-to-zero (NRZ) transmission beyond the chromatic dispersion limit. They also offer a great potential as soliton pulse generators. This paper discusses the many integration schemes devised for their realization with particular emphasis on the identical active layer (IAL) approach. Recent progress in their high-speed applications is reported.

Monolithic integration of multiple-quantum-well lasers and modulators for high-speed transmission

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. >

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

20 Gbit/s soliton transmission over large distances (150000 km) is demonstrated in a recirculating loop with a record amplifier span of 105 km. For the first time, an electroabsorption modulator is used to provide the necessary in-line modulation control.

20 Gbit/s soliton transmission over transoceanic distances with a 105 km amplifier span

We report on the integration of two InGaAsP-InGaAsP MQW electroabsorption ridge modulators and an amplifier on the same active layer. The two modulators are separated by a 500-/spl mu/m ridge waveguide optical amplifier, in order to prevent electrical crosstalk, and to compensate for optical losses. The first modulator is used as a soliton generator, and the second codes the generated pulses. The amplifier showed 8.2-dB gain for 120-mA injected current. This allowed a low fiber to fiber insertion loss of 9 dB for the tandem. We present here for the first time to our knowledge, a 20 Gbit/s operation for a tandem-amplifier device, together with transmission experiments. >

20 Gbit/s high-performance integrated MQW TANDEM modulators and amplifier for soliton generation and coding

As a consequence of the growing interest for 1.55-μm optical-soliton transmission, many laboratories are investigating how to generate and code these optical pulses in a stable and reliable manner. Electroabsorption (EA) modulators have been demonstrated as zero-jitter, stable, and frequency-flexible high-speed soliton sources,1 by simply driving them with a sinusoidal signal.2 The integration of a second modulator allows the coding of the pulses. In our case we have also integrated on the same active layer an optical amplifier between the modulators to reduce electrical cross talk (<40 dB) and fiber-to-fiber losses (<9 dB).

E. Jeanney

Papers

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

20 Gbit/s soliton transmission over transoceanic distances with a 105 km amplifier span

20 Gbit/s high-performance integrated MQW TANDEM modulators and amplifier for soliton generation and coding

20-Gbit/s high-performance MQW TANDEM for soliton generation and coding