We report a novel method to measure two important parameters for optical fiber intensity modulated transmission systems: dispersion of optical fibers and chirp parameter of modulated light emitters. The method is easy, quick, and accurate for chirp parameter in the -10-to-10 range. >

Simple measurement of fiber dispersion and of chirp parameter of intensity modulated light emitter

The past few years a lot of effort has been put in the development and fabrication of III-V semiconductor waveguiding devices with monolithic integrated mode size converters (tapers). By integrating a taper with a waveguide device, the coupling losses and the packaging cost of OEICs in future fiber-optical networks can be much reduced. This paper gives an overview of different taper designs, the possible fabrication technologies and performances of tapered devices.

A review on fabrication technologies for the monolithic integration of tapers with III-V semiconductor devices

The fabrication and basic characteristics of a InGaAs/InGaAsP multi-quantum-well (MQW) electroabsorption modulator with a novel structure integrated with a distributed-feedback (DFB) laser are presented. A fundamental study was performed on the applicability of the InGaAs/InGaAsP MQW structure to an electroabsorption-type modulator. Efficient attenuation small hole pileup and small chirp characteristics of a discrete modulator based on this MQW structure were demonstrated experimentally. A study of the controllability of in-plane band-gap energy by the use of selective-area metal-organic chemical vapor deposition (MOCVD) was also demonstrated. The modulator was monolithically integrated with a MQW DFB laser of the same material. Using a low-capacitance semi-insulating buried heterostructure, over 14 GHz modulation under high-light-output operations up to +10 dBm was achieved. Modulation at 10 Gb/s with a modulation voltage swing of only 1 V/sub pp/ demonstrates the potential value of this system for 1.55- mu m lightwave communications. >

InGaAs/InGaAsP MQW electroabsorption modulator integrated with a DFB laser fabricated by band-gap energy control selective area MOCVD

In this paper, a fiber-optic millimeter-wave (mm-wave) downlink system using 60 GHz-band external modulation is investigated. We prepare the fiber-optic 60 GHz-band mm-wave downlink testbed. It consists of an optical modulation section with a mm-wave signal generator, an optical single sideband (SSB) filter, a standard single-mode fiber (SMF), an optical detection section with a 60 GHz-band radio transmitter and a 60 GHz-band radio receiver. To modulate the laser output with 60 GHz-band mm-wave signals directly, a specially designed electro-absorption modulator with high-efficiency at around 60 GHz is used. The use of this modulator makes the simpler system configuration possible. Using the downlink testbed, the 5 m-long free-space propagation of subcarrier multiplexed 156 Mb/s-DPSK 60 GHz-band mm-wave signals recovered by optical direct detection is successfully demonstrated. The transmission of the mm-wave signals over 85 km-long standard SMF is also successfully demonstrated, using an optical SSB filtering technique to overcome the fiber dispersion. The BER of 10/sup -9/ is achievable at the optical received power of -7.0 dBm.

Fiber-optic millimeter-wave downlink system using 60 GHz-band external modulation

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

A single-mode modulator was realized from an AP-MOCVD grown structure. The multiple-quantum-well electroabsorptive material is made of shallow InGaAsP wells separated by InGaAsP barriers. It exhibits at 1.54 mu m (TE) a 17 dB extinction ratio for a 3 V drive voltage, a 2.7 dB on-state loss and a small-signal bandwidth over 20 GHz with 1-2 mW of coupled optical power. >

Ingaasp/ingaasp multiple-quantum-well modulator with improved saturation intensity and bandwidth over 20 ghz

The simple fabrication technology of an active waveguide for polarization insensitive optical amplifiers, integrated with tapers and a passive waveguide for fiber coupling, is presented. The spot size transformation along the taper, yielding a mode expansion factor of more than 9 in horizontal direction and about 2 in vertical direction, is experimentally verified and the results are compared to theoretical computations. Using a cleaved single mode fiber, the coupling loss is as low as 2.6 dB with -1-dB positional tolerances of 2.2 /spl mu/m and 1.5 /spl mu/m in vertical and horizontal directions. Besides relaxing on fiber coupling, the large spot size transformation in horizontal direction allows for a drastic reduction of the reflection coefficient to less than 10/sup -3/ at a facet tilted by 4/spl deg/ with respect to the waveguide axis. >

Theoretical and experimental studies of a spot-size transformer with integrated waveguide for polarization insensitive optical amplifiers

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

The authors report the simple integration of a 1.55 µm optical amplifier taper with a coupling waveguide yielding a lateral beam divergence of 7.5°, a lateral spot size expansion factor of 9.5 and a coupling loss to a cleaved standard fibre of 2.6 dB.

Taper-waveguide integration for polarisation insensitive InP/InGaAsP based optical amplifiers

Efficient electroabsorption in an InGaAsP/InGaAsP MQW optical waveguide modulator structure is reported. A 17 dB extinction ratio is obtained by applying a 3.5 V drive voltage to a 78 μm long waveguide operating at 1.54 μm under TE-polarisation mode. The on-state attenuation is only 2 dB.

A. Carenco

Papers

Ingaasp/ingaasp multiple-quantum-well modulator with improved saturation intensity and bandwidth over 20 ghz

Theoretical and experimental studies of a spot-size transformer with integrated waveguide for polarization insensitive optical amplifiers

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

Taper-waveguide integration for polarisation insensitive InP/InGaAsP based optical amplifiers

Efficient electroabsorption in InGaAsP/InGaAsP MQW optical waveguide