J. Decobert

Transverse magnetic mode nonreciprocal propagation in an amplifying AlGaInAs∕InP optical waveguide isolator

The design, fabrication, and characterization of an amplifying transverse magnetic (TM)-mode optical waveguide isolator operating at a wavelength of 1300nm are presented. The magneto-optical Kerr effect induces nonreciprocal modal absorption in a semiconductor optical amplifier with a laterally magnetized ferromagnetic metal contact. Current injection in the active structure compensates for the loss in the forward propagation direction. Monolithic integration of this optical isolator configuration with active InP-based photonic devices is straightforward. The combination of AlGaInAs∕InP active material and the metal alloy Co50Fe50 results in greatly improved performance. 99dB∕cm TM mode isolation and significantly reduced insertion loss are demonstrated.

Transmission electron microscopy study of the InP/InGaAs and InGaAs/InP heterointerfaces grown by metalorganic vapor-phase epitaxy

InP/InGaAs and InGaAs/InP interfaces in heterostructures grown by metalorganic vapor-phase epitaxy (MOVPE) have been studied by transmission electron microscopy (TEM). Cross-sectional TEM 002 dark field images of the direct (InP–InGaAs) and inverted (InGaAs–InP) interfaces revealed a great difference in abruptness. Whereas the direct interface is always well defined and flat, the inverted one is compositionally graded and shows surface undulations. InP–InGaAs heterostructures were studied for different layer thicknesses and phosphine flow rates. The results indicate that this effect originates more from the substitution of arsenic by phosphorus atoms in subsurface InGaAs monolayers rather than from As carryover to the InP layer. The strong As–P exchange observed over several InGaAs monolayers is related to the large difference in chemical bond strength between Ga–As and Ga–P. This is supported by comparison with InP/InAlAs/InP and InP/In1−xGaxAsyP1−y/InP (0.1

Evanescently coupled photodiodes integrating a double-stage taper for 40-Gb/s applications-compared performance with side-illuminated photodiodes

The design, fabrication, and performance of double-stage taper photodiodes (DSTPs) are reported. The objective of this work is to develop devices compatible with 40-Gb/s applications. Such devices require high efficiency, ultrawide band, high optical power handling capability, and compatibility with low-cost module fabrication. The integration of mode size converters improves both the coupling efficiency and the responsivity with a large fiber mode diameter. Responsivity of 0.6 A/W and 0.45 A/W are achieved with a 6-/spl mu/m fiber mode diameter and cleaved fiber, respectively, providing relaxed alignment tolerances (/spl plusmn/1.6 /spl mu/m and /spl plusmn/2 /spl mu/m, respectively), compatible with cost-effective packaging techniques. DSTPs also offer a wide bandwidth greater than 40 GHz and transverse-electric/transverse-magnetic polarization dependence lower than 0.2 dB. Furthermore, a DSTP saturation current as high as 11 mA results in optical power handling greater than +10 dBm and a high output voltage of 0.8 V. These capabilities allow the photodiode to drive the decision circuit without the need of a broad-band electrical amplifier. The DSTP devices presented here demonstrate higher responsivities with large fiber mode diameter and better optical power handling capabilities and are compared with classical side-illuminated photodiodes.

High Gain

This letter demonstrates a planar junction GalnAs-AlInAs avalanche photodiode using back-side illumination through thinned InP substrate covered with chemical vapor deposition SiNx antireflection coating. The combined properties of very low dark current (I dark(M = 0) = 17 nA), low excess noise factor (f(M = 10) = 3.5), and high gain x bandwidth product over 140 GHz were simultaneously achieved with a high primary responsivity of 0.95 A/W at 1.55 mum.

\times

A vertical-access passive all-optical gate has been used to improve the extinction ratio of a 160 GHz picosecond pulse train at 1555 nm. An extinction ratio enhancement of 6 dB is observed within an 8 nm bandwidth. Such a device is a promising candidate for low-cost all optical reamplication and reshaping (2R) regeneration at 160 Gbits/s.

Bandwidth Product Over 140-GHz Planar Junction AlInAs Avalanche Photodiodes

The limitations owing to device heating and thermo-optic effects in high-speed quantum-well microcavity saturable absorber devices are investigated both theoretically and experimentally. A simplified theoretical description of the device electronic, thermal, and optical properties is developed and applied to the modeling of the device switching characteristics for reamplification + reshaping step (2R) all-optical regeneration. These predictions are compared to nonlinear optical measurements performed with switching pulses of fixed duration and variable repetition rate on two devices with significantly different thermal properties. It is shown that proper optimization of the device thermal properties is crucial to avoid the degradation of device performance at high bit rate. It is also shown that the negative effects of optically induced heating on the switching contrast may be compensated to some extent by operating the device on the long wavelength side of the microcavity resonance

All-optical extinction-ratio enhancement of a 160 GHz pulse train by a saturable-absorber vertical microcavity

We describe the design, optimization and fabrication of side-illuminated p-i-n photodetectors, grown on InP substrate, suitable for surface hybrid integration in low-cost modules. The targeted functionalities of these photodetectors were a very high responsivity at 1.3- and 1.55-/spl mu/m wavelengths and quasi-independent on the optical polarization, and had a high alignment tolerance. Moreover, in order to avoid any reliability problem, the principle of evanescent coupling was adopted. Two photodetectors were optimized, fabricated, and tested; the first was for classical cleaved fiber, and the second was for lensed fiber. Because the considered epitaxial structures were complicated to optimize, the method of the genetic algorithm was used, associated with a beam propagation method (BPM). The photodetectors are based on multimode diluted waveguides, which are promising structures in the field of optoelectronics and integrated optics. Starting from the presented comparisons between experimental and theoretical results, the interest of the design method is discussed and the complete performances of newly fabricated devices are presented. The aspect of the cutoff frequency is also considered.

Analysis of thermal limitations in high-speed microcavity saturable absorber all-optical switching gates

A 2.2 ps full-width-at-half-maximum impulse response is measured for ion-irradiated InGaAs photoconductive switches triggered by ultrashort 1.55 μm laser pulses. Correspondingly, the −3 dB bandwidth is estimated to be ∼120 GHz. Measurements of the electrical signals delivered by photoconductive switches are performed using an electro-optic sampling technique. As is shown, the ion irradiation reduces the carrier lifetime to less than 1 ps. The sheet resistance is 0.6×105 Ω/square. The photoconductive switch responsivity is found to exhibit a nonlinear dependence with optical power. The results are qualitatively interpreted.

Design, optimization, and fabrication of side-illuminated p-i-n photodetectors with high responsivity and high alignment tolerance for 1.3and 1.55-/spl mu/m wavelength use

We demonstrate an AlInAs-InGaAs separate absorption, grading, and multiplication avalanche photodiode (APD) with a very thin avalanche layer operating at 1550 nm for 10-Gb/s optical transmission achieving simultaneously high responsivity (0.9 A/W at M = 1), very low excess noise factor (F(M=10) = 3), and very high gain-bandwidth product of 240 GHz. To our knowledge, this is the first time that a back-side illuminated planar junction AlInAs-InGaAs APD achieved such performances.

Ultrafast response (∼2.2 ps) of ion-irradiated InGaAs photoconductive switch at 1.55 μm

Several all-optical switching devices based on quantum well microcavity structures have been studied in view of their possible use for all-optical regeneration of telecommunication signals. Experiments and modeling show that the saturation energy is inversely proportional to a scaling factor describing the enhancement of the intracavity intensity at the Fabry-Perot resonance. As a result the saturation energy is approximately proportional to the number of quantum wells in the device and can be kept small by a proper cavity design.