Photonic switching, when integrated with the optoelectronic circuit elements required for routing control and optical signal conditioning, is of interest for network reconfiguration, high-speed LANs, and optical cross-connects. The adiabatic modal evolution, asymmetric digital optical switch is a promising candidate for an efficient optical space switch for these applications. Its advantages include wavelength and polarization independent operation, complete switching for sufficient induced asymmetry, and since it is fabricated in a semiconductor, integration with other active devices. This switch is compact when fabricated with large opening angles and is suitable for application in WDM networks. We report on the fabrication and performance of the first InP digital optical switches with extinction ratios exceeding 20 dB at both 1.3 μm and 1.5 μm in the same switch for both polarizations

Record polarization-independent extinction ratios are reported for ridge waveguide digital optical switches in InP/InGaAsP. Wavelength insensitivity is demonstrated for the first time, with extinction ratios that exceed 20 dB at both 1.3 and 1.5 mum for the same switch. The switch's total opening angle of 0.5-degrees is more than a factor of two larger than other digital optical switches demonstrated at any wavelength.

Photonic switching is of interest for network reconfiguration, high-speed LANs, and optical cross connects.1-3 The adiabatic- modal-evolution, asymmetric digital optical switch (DOS) is a promising candidate for these applications. It can operate independent of light polarization, it is less sensitive to wavelength and fabrication uncertainties than are conventional directional couplers, it switches completely for sufficient induced asymmetry, and because it is a semiconductor, it may be integrated with other active devices. But for the DOS to achieve this potential, two deficiencies must be overcome. Its size must be reduced by increasing the opening angle, and to allow for cascading of switches, high extinction ratios must be achieved.

A high-sensitivity, wide-bandwidth, optical preamplifier is demonstrated in the form of a monolithically integrated semiconductor optical amplifier and waveguide photodetector. By fabricating the same device with a shorter photodetector section, part of the signal is passed through to an output fiber, forming an optical tap. Amplifier gains are sufficient to overcome the fiber-coupling and detector loss, and exhibit zero-insertion-loss operation. A lossless tap with an electrical bandwidth of 7 GHz, a responsivity of 26 A/W, and a fiber-to-fiber gain of 3 dB is shown to have a receiver sensitivity of -22 dBm at 3 Gb/s.

Photonic switching, when integrated with the optoelectronic circuit elements required for routing control and optical signal conditioning, is of interest for network reconfiguration, highspeed LANs, and optical cross-connects [l]-[4]. The adiabatic modal evolution, asymmetric Digital Optical Switch is a promising candidate for an efficient optical space switch for these applications. It can operate independently of light polarization, it is less sensitive to wavelength and fabrication uncertainties than conventional directional couplers, it switches completely for sufficient induced asymmetry, and because it is a semiconductor it may be integrated with other active devices.

The authors report the first monolithically integrated wide-bandwidth lossless tap-that is, an optical semiconductor amplifier followed by a colinear reverse-biased waveguiding photodetector with fiber-coupled input and output. The integration was achieved by using off-axis selective epitaxial growth of ridge waveguides on a patterned dielectric layer. The tilted facets produced by the off-axis growth, along with photodetector absorption, serve to reduce the effective facet reflectivity to -36 dB without any antireflection coating. By adjusting the length of the absorbing photodetector section, part or all of the amplified light may be absorbed, allowing the device to function respectively as a lossless tap or an optical preamplifier. A lossless tap with an electrical bandwidth of 7 GHz, a responsivity of 26 A/W, and a fiber-to-fiber gain of 3 dB is shown to have a receiver sensitivity of -22 dB at 3 Gb/s.<>

Optical fiber systems with a large number of parallel channels, such as those needed for fiber distribution to the home and computer interconnects, require the integration of many optoelectronic devices, fibers, and electronic circuits. Cost is the most significant issue in determining the feasibility of these systems. Packaging is the dominant cost for optoelectronic components, particularly in the case of diode lasers, which require active alignment of a fiber pigtail.

Record performance high frequency (3 dB bandwidth = 24.5 GHz) 1.3 pm wavelength lasers have recently been reported [I]. These results are due to a new fabrication sequence which controls dimensional tolerances to 0.1 pm [2]. At the core of this sequence is an anisotropic plasma etching process which provides deep (1-3 pm) channels to form mesas with smooth, vertical sidewalls. BH lasers with narrow (0.6-1.0 p) active layers and 0.1-0.2 pm per side of lateral InP cladding have resulted. These feature sizes are responsible for the low electrical parasitics and high photon densities necessary for achieving high modulation bandwidth performance. This paper describes the plasma etching process module in detail.

Optical preamplification has been shown to significantly improve the sensitivity of receivers for wideband lightwave systems when compared with conventional electronic postamplification. However, the large size and relatively fragile nature of optical preamplifiers assembled from discrete optoelectronic components (i.e., hybrid assemblies) has discouraged the use of optical preamplifiers for system applications. This paper discusses the technology required for integrating a semiconductor optical amplifier with a high-speed photodetector on the same chip, [1] and the expected performance of such a device. The monolithically Integrated Optical Preamplifier (lOP) is expected to combine the performance of hybrid receivers with the functionality of a single optoelectronic component. In addition, this integrated device can be used as a lossless optical tap for network monitoring and/or system reconfiguration, functions that are highly desirable for advanced network architectures.

Record high gains of 20-21 dB have been reproducibly obtained using a new type of semiconductor optical amplifier package incorporating a 1.3-mu-m tilted-facet ridge amplifier. The package uses a novel two-temperature-zone design to achieve independent soldering of the input and output fibres.

A process that permits the controllable fabrication of buried heterostructure (BH) lasers with <1.0 mu m wide active layers and 0.1-0.2 mu m of lateral cladding and achieves the high photon densities and low parasitics necessary for high resonance frequency and modulation bandwidth lasers is described. The process may be used with bulk heterostructure, quantum well, and distributed feedback (DFB) grated structures. Control of critical dimensions to +or-0.1 mu m can be realized using the process. The process development for fabrication of a 1.3 mu m or 1.5 mu m wavelength high frequency laser is discussed.<>

The intrinsic frequency response and the maximum modulation bandwidths of lasers with extremely large intrinsic resonance frequencies and thus with very high 3 dB modulation bandwidth potential are discussed. It is shown that in the absence of electrical parasitics. the modulation bandwidths approach 50 GHz and that the lasers, characterized by a large differential gain, are capable of achieving very high bandwidths at relatively low operating powers

This paper reports a practical technique for making a high-performance semiconductor optical amplifier by combining tilted-cavity and a simple anti-reflective facet coating. Gains of up to 29 dB are reported at a gain ripple of 3 dB.

High-performance, GaInAsP/InP tilted stripe ridge waveguide semiconductor optical amplifiers which require no antireflection coating to achieve reflectivities of less than -40 dB are demonstrated. This very low reflectivity is found to be both largely independent of polarisation and wavelength, and also easily reproducible from wafer to wafer.<>

1.3 μm InGaAsP lasers with 3 dB bandwidths of 24 GHz and intrinsic resonance frequencies in excess of 22 GHz have been successfully fabricated. This is the highest bandwidth ever reported for a semiconductor laser, and the highest resonant frequency for InGaAsP lasers. Excellent modulation efficiencies are observed to high frequencies.

The spontaneous noise spectrum of high-gain semiconductor optical amplifiers is normally assumed to be dominated by spontaneous-spontaneous and signal-spontaneous beat noise, which is white over the frequency range important to fiber-optic systems. Recent measurements have shown that a strong resonance peak in the spontaneous noise spectrum appears well below the threshold current, indicating the existence of relative intensity noise. This noise term has important implications for system design, and its effect on several transmission systems is described. Relative intensity noise in semiconductor optical amplifiers is compared to the similar relative intensity noise found in semiconductor lasers.< >

An extremely versatile technique for the fabrication of semiconductor light sources is described. The technique, which is based on the halide vapor phase regrowth (VPR) of InP on channeled and selectively etched InGaAsP/InP double heterostructure material, results in an buried heterostructure (BH) index-guided VPR-BH diode laser structure which can be optimized for a number of different types of semiconductor light sources. The conditions and parameters associated with the halide VPR process are given, and the properties of the regrown InP are reported. The processing and characterization of high-frequency lasers with 18-GHz bandwidths and high-power lasers with cw single-spatial-mode powers of 60 mW are described. Additionally, the fabrication and characterization of superluminescent LEDs based on this basic VPR-BH structure are described. These LEDs are capable of coupling more than 80 μW of optical power into a single-mode fiber at 100 mA, and can couple as much as 8µW of optical power into a single-mode fiber at drive currents as low as 20 mA.

A small-signal modulation bandwidth of 12.5 GHz is reported for vapor phase regrown 1.3-μm InGaAsP buried heterostructure (BH) lasers operated at a bias optical power of only 6.9 mW/facet. The bandwidth per square root of bias optical power is a factor of 1.6 higher than previous best results. In addition, the optical modulation amplitude remains flat to 12 GHz in sharp contrast to other types of BH lasers which exhibit signal roll-off at frequencies below the resonance frequency. The wide modulation bandwidth is attained by increasing the p-doping level in the active region and by the choice of short cavity length. The device is grown on a conductive substrate, indicating that it is unnecessary to use a semi-insulating substrate to obtain flat optical response in vapor phase regrown BH lasers.

Very high-frequency direct modulation of AlGaAs and InGaAsP diode lasers has been reported.1,2 An intrinsic modulation bandwidth of 12.5 GHz of 1.3-μm InGaAsP vapor phase regrown buried hetero-structure lasers (VPR-BH) under pulse bias operation was demonstrated.2 A small-signal modulation bandwidth of a 15-GHz record is reported for the VPR-BH lasers operated at a pulse bias optical power of only 7.5 mW/facet.

The letter describes 1.3 µm InGaAsP edge-emitting LEDs which couple 40 to 60 µW into a single-mode fibre. The 1.0 ns rise times and 30 to 45 nm spectral widths of these LEDs make suitable for optical communication systems operating at data rates as high as 400 Mbit/s.