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The use of strained layer multiple quantum well optical amplifiers for high frequency modulation and switching of a laser diode output is described. Modulation bandwidth of 1.8 GHz and digital modulation at 2 Gbit/s have been demonstrated.

The authors demonstrate a polarisation insensitive tunable reflective filter, with an integrated in-line optical amplifier providing a net fibre coupled gain for the device. The filter has a spectral width of 10 A FWHM, with 1 A deviation between the TE and TM input polarisations. The filter can be tuned over a spectral range of 95 A. Tunable filter-amplifier devices can be useful for low noise WDM receivers, and for channel selection in WDM networks.

A six-wavelength laser array with an integrated amplifier and modulator designed for transmission of a single selectable wavelength is demonstrated. The lasers have thresholds of ~20 mA, and the single-step printed gratings yield an average channel spacing of 200 GHz. Output powers through the modulator of several milliwatts are obtained from all six lasers when 75 mA is applied to the amplifier.

A novel scheme for a digitally tunable laser requiring only P+Q+1 optical amplifiers for a device with in total P×Q wavelength channels is presented. A 32-channel InP/InGaAsP based device is fabricated. An optimised active layer and low on-chip losses result in a high optical output power.

An electroabsorption modulator integrated with a DBR laser and driven with a dual gate FET forms a transform-limited, wavelength-tunable soliton transmitter. Back-to-back bit error rate measurements at 2.5 Gbit/s are reported.

The authors demonstrate an electroabsorption modulator operating at 1.55 mu m wavelength, which is integrated with passive waveguide gradually tapered spotsize transformers allowing a low loss coupling to cleaved flat optical fibres. The modulator has 10.1 dB total fibre to fibre insertion loss with 15 dB extinction ratio and 300 AA spectral range. The modulator polarisation sensitivity is lower than 0.5 dB. >

Transmission over 192 km of conventional singlemode fibre is achieved using a packaged 1.56 mu m DBR laser-electroabsorption modulator transmitter operating at 5.0 Gbit/s. In an optically amplified system experiment, a dispersion penalty less than 0.5 dB at a bit error rate of 10/sup -9/ is measured. >

The authors have demonstrated a compact (70 µm free-space radiation length), potentially robust, broadband (1.53–1.56 µm), polarisation-insensitive 3 dB optical power splitter based on InP using free-space radiative input-output coupling. This passive, 3 dB splitter is compatible with photonic integrated circuits.

Broadly tunable, narrowband wavelength filters that can be integrated with other photonic devices are important elements for WDM multi/demultiplexing systems. Recently, we have demonstrated a broadly tunable, narrowband wavelength selective grating assisted vertical directional coupler with a 215 A tuning range. In the Letter, an improved version of the vertically stacked buried rib InGaAsP/InP integrable wavelength filter that has a tuning range greater than 370 A is reported.

The authors report all-optical 100 Gbit/s wavelength conversion employing cross-phase modulation for the first time.

An integrated high-speed 1 × 4 switch array on InP-substrate using 8 GHz Y-branch switch elements is described. This switch array is suitable for optical time division multiplexing (OTDM) and demultiplexing data at 10 Gbit/s over a wide optical bandwidth. The channel-channel isolation and insertion loss are 18 and 15 dB, respectively, which may be improved by optimisation of the switch design and fabrication techniques.

A 1 × 2 digital optical switch in InGaAsP multiple-quantum-wells with an 8 GHz bandwidth is demonstrated, which may also be operated as a wavelength-, polarisation-, and drive-voltage insensitive modulator. The total length of the switch/modulator device is 3 mm which includes passive fan-outs for fibre interconnection. The on-chip insertion loss is 3 dB out of which the Y-branch excess loss is only 0.7 dB. The measured switch crosstalk is –18 dB for a 4 V push-pull bias. Further crosstalk reduction is expected from a more optimised design and improved fabrication processes.

The effective threshold for stimulated Brillouin scattering for a data-encoded signal is increased from 11.0 to 23.4 dBm by using a temperature-tunable laser diode. A 5 kHz sinusoid is applied to a Ti/Pt thin film resistor located along the laser contact on top of the device, resulting in a 10 kHz dithering of the wavelength. The residual amplitude modulation index at 10 kHz is only 1.2/spl times/10/sup -4/.

The authors demonstrate a 1.55 /spl mu/m wavelength multiquantum well semiconductor optical amplifier, integrated with bulk layer electroabsorption modulators and passive waveguide beam expanders at the input and output ports. The device has a fibre to fibre gain of 9 dB, an extinction ratio of 15 dB per modulator, a spectral range >35 nm, and polarisation sensitivity

The authors demonstrate for the first time broadband wavelength conversion with amplification by four-wave mixing in semiconductor travelling-wave optical amplifiers and verify the cubic dependence of wavelength conversion efficiency on the amplifier's single-pass optical gain.

The Letter demonstrates a 1.55μm multiquantum well amplifier on an extended InGaAsP passive waveguide with only ±0.14 dB gain. Reflectivity

An electroabsorption modulator has been monolithically integrated with an extended-cavity laser, which incorporates a Bragg reflector. Actively modelocked at the fundamental cavity resonance frequency of 4.5 GHz, the laser provides a train of 6.3 ps pulses with a centre wavelength of 1544 nm onto which data is encoded by the modulator. This 4.5 Gbit/s single-chip transmitter is suitable for systems employing short optical pulses.

A tuning range of 48 nm has been achieved with a tuning current of only 40 mA in a 1.55 mu m InGaAsP/InP multiquantum-well laser based on a grating-assisted vertical coupler intracavity filter. Using a combination of current and voltage tuning a 55 nm tuning range was demonstrated.

Multiwavelength transmission over 217 km of nondispersion shifted fibre is demonstrated at 1.7 Gbit/s using an integrated 16×1 laser/modulator array. Bit error rate performance is reported for single channel transmission using seven of the laser/modulators at discrete wavelengths from 1.545 to 1.555 μm. Additionally, electrical and optical crosstalk penalties are measured in a two channel WDM experiment.

The first monolithically integrated laser/interferometric modulator is reported. The total chip length of 2.5 mm includes a 970 μm-long strained InGaAs/InGaAsP quantum well gain section, a 230 μm-long wavelength tuning section containing a distributed Bragg reflector grating, and an 800 μm-long active length Mach-Zehnder modulator based on electrorefractive InGaAsP/InP quantum wells. 4 V pushpull drive voltage produces 12.5 dB modulation depth with −9 dBm optical power coupled into a cleaved fibre.

A photonic integrated transmitter for RZ transmission provides 50 ps optical pulses on-off modulated at a bit rate of 3Gbit/s. BER performance is measured in a back-to-back transmission experiment and compared to NRZ transmission using the same photonic circuit with the laser operated CW. A 2.8 dB improvement in receiver sensitivity is obtained for the RZ case.

A 1.0 cm long, two contact, monolithic extended-cavity laser has been fabricated and actively mode-locked at a repetition rate of 4.4 GHz to produce 9.0 ps optical pulses. Doubling of the optical pulse repetition rate of 8.8 GHz without changing the sinusoidal drive frequency is achieved by synchronously modulating two separate active regions.

Formation of buried InGaAsP/InP quantum well waveguides by means of phosphorus ion implantation and thermal annealing during regrowth is demonstrated. Absorption spectra of implanted and unimplanted regions are used to estimate the induced index difference, which is of the order of 1% at 1.55 μm. Calculated mode intensities are in good agreement with the observed near field intensity patterns. With this etchless implant technique, we achieve a significant reduction in propagation loss for singlemode pin waveguides relative to etched semi-insulating planar buried heterostructure waveguides fabricated from the same quantum well structure. In addition to reduced scattering loss, buried quantum well waveguides produced by ion implantation are more manufacturable because fewer and less-critical processing steps are involved.

Gain-switching a strained-layer multiple quantum well laser-amplifier photonic integrated circuit has produced optical pulses with durations of 28 ps and peak powers of 590 mW (i.e. pulse energies of 21 pJ). The device was gain-switched at frequencies from 2 to 8 GHz. Such monolithic high-power pulse sources are of great importance for nonlinear fibre device applications.

Low threshold and high efficiency operation of strained layer multiple quantum well InGaAs/InGaAsP lasers at 1.5 micrometres wavelength is demonstrated. Current thresholds as low as 2.2 mA with threshold current densities of 440 A/cm2 have been obtained. With 7.3 mA threshold current, quantum efficiency was 65%/front facet. At 20 mW CW output power the drive current was as low as 53 mA.

The DC and microwave performance of modulation doped GaInAs/InP HFETs (heterostructure FET), grown by atmospheric pressure organometallic vapour phase epitaxy is reported. An extrinsic transconductance of 300 mS/mm and a best value of the cutoff frequency, F/sub r/=14.1 GHz in a 1.5 mu m gate device was measured at room temperature. Improved performance of the Schottky gate device is obtained using an Au gate on the InP/GaInAs heterostructure layers. A low access resistance of 3 Omega mm is obtained using a self-aligned technique with high conductivity n/sup +/-GaInAs top layers.

We report active mode locking in a monolithic long-cavity semiconductor laser, operating at 1.5 µm wavelength. Pulses with durations of 4 ps at repetition rates up to 40 GHz have been achieved, with a modulation depth of 97%. This is the first report of active mode locking in a monolithic device, and the highest repetition rate achieved with an actively mode locked laser.

We demonstrate improved performance in tunable distributed-Bragg-reflector lasers using GaInAs/GaInAsP multiple-quantum-well active layers. We observe linewidths as low as 1.9 MHz, differential quantum efficiencies as large as 33%/front facet at 1.5μm, and rapid electronic access to all frequencies throughout a 1000GHz range.

GaInAs/InP planar buried heterostructure (PBH) lasers with semi-insulating blocking layers were grown in an `all? atmospheric OMVPE system. These layers had current thresholds as low as 35 mA and differential quantum efficiencies of ?16% at a wavelength of 1.64 ?m. The maximum power output was 80 mW pulsed and 8mWCW.

CW and high-speed (100 ps pulse) single-longitudinal-mode operation has been achieved with a short-coupled-cavity (SCC) InGaAsP injection laser (in the 1.3 ?m to 1.55 ?m spectral range) consisting of a short (50?80 ?m) cleaved laser and a short (30?80 ?m) external air resonator with a high-reflectivity mirror. The SCC laser resonator combines the advantages of both a short-cavity laser and a coupled-cavity laser for effective mode selection. Single-mode operation has been maintained at modulation rates of 2 Gbit/s.

The spectral behaviour of monolithic two-section GaInAsP/InP lasers is studied. Single-longitudinal-mode light pulses of less than 750 ps length are produced by driving the long section of the laser only or by prebiasing the long cavity and modulating the short section with a current pulse of 1 ns halfwidth. The wavelength of the output light can be changed by varying the operation temperature or the prebias level.

A new 1.55 μm wavelength GaInAsP laser is described: the multisection ridge laser. Pulsed thresholds were typically 40–80 mA. CW thresholds were comparable. The lowest measured CW threshold was 38 mA at 12°C. The laser operated stably in a single longitudinal mode (spurious modes down by −16 dB) under fast pulse modulation with a prebias below threshold. Theoretical results based on a waveguide scattering theory are in qualitative agreement with the experimental results.

Monolithic fabrication of a GaInAsP/InP laser with an etched mirror and monitoring detector is reported. Stripegeometry lasers operating at wavelengths of ~1.3 ?m with threshold current of only 300 mA have been obtained. The monitoring detector on the same InP substrate was confirmed to operate with high sensitivity, comparable with that of an external Ge photodiode.

Using angled reactive ion etching (RIE) and wet chemical etching (WCE), planar (011) facets have been exposed on (100) GaInAsP/InP double heterostructures for the first time. Positively sloped wall profiles observed previously for this orientation are eliminated by an initial RIE that cuts through the stop-etching (111)A plane. These (011) mirror facets are preferred over (011) for most state-of-the-art low-threshold lasers.

A high-power, high-speed GaInAsP/InP laser operating at a 1.3μm wavelength is described. The laser is obtained with three epitaxial growth steps and has semi-insulating InP blocking layers resulting in low parasitic capacitance. A 3 dB bandwidth of 14.7 GHz together with 38 mW output power has been achieved.

We propose an efficient and simple optical interconnection between active semiconductor components by deposition and spin coating. The demonstration shows a low-threshold (2.0 kA/cm2) and high-coupling (81%) operation of a laser-polyimide/SiO2 slab waveguide integrated on a GaInAsP/InP chip.

Fundamental-transverse-mode ridge waveguide lasers have been operated at 1.55 μm with threshold current as low as 42 mA. The threshold of fabrication and performance are similar to that of 1.3 μm ridge lasers, including the large modulation bandwidth.

We present the undercutting rate of an indium phosphide crystal as a function of angle within the (100) plane. We use concentrated HC1 as the etchant and epitaxial InGaAsP as an etch mask. Undercutting behaviour including wall profile is determined as a function of etch time. The resulting description can be used to design crystallographic structures with a variety of orientations.

We report the first absolute measurement of electric-fieldinduced changes in refractive index in GalnAs quantum well heterostructures. Even for wavelengths as far as 40meV below the absorption edge, excitonic effects dominate electro-optic phase modulation. This effect close to resonance yields index changes two orders of magnitude larger than in bulk material. We find that the size of the index change, its dependence on applied voltage, and its behaviour with wavelength are well described in terms of the quantum confined Stark effect on excitonic absorption.

A high-contrast, three port optical AND gate based on the photoconductive effect in Ga/sub 0.47/In/sub 0.53/As:Fe and operating in the lambda =1.3-5 mu m wavelength range is demonstrated. A 250:1 optical power contrast ratio (or 48 dB in electrical power after detection) is obtained in an optical-to-optical time division demultiplexing of a 100 MHz pulse train by a 6.25 MHz clock, both at lambda =1.3 mu m, with the demultiplexed output pulses at lambda =1.5 mu m.

We describe planar buried heterostructure lasers which have low capacitance (lpF), large bandwidth (19GHz), high power (>20mW/facet) and high temperature operation (100°C). These lasers are very suitable for long-distance, highspeed digital and analogue signal transmission.

We describe the structure and performance characteristics of an InGaAs/InP multiple-quantum-well (MQW) electro-absorption buried-mesa optical modulator. The device is fabricated with two metal-organic chemical-vapour-deposition (MOCVD) growth steps, wherein small-area circular (40μm diameter) PIN diodes are buried with Fe-doped semiinsulating (SI) InP regrowth. The modulator has a relatively low insertion loss (4.5 dB) with 25% modulation depth and very high modulation bandwith (5.3 GHz) operating at 1.62μm wavelength.

We describe the fabrication and performance of the first integrated heterodyne receiver capable of actual heterodyne data reception. Integrating a continuously tunable 1.5 μm MQW-DBR laser with a single-mode directional coupler/switch and zero-bias MQW waveguide photodetectors, we have achieved error-free reception of FSK-modulated pseudorandom digital code at 105 Mbit/s.

The first c.w. operation of a GaInAsP/InP stripe laser (??1.3 ?m) having a chemically etched mirror has been achieved at room temperature. One of the cavity facets was monolithically formed by a wet chemical etch and passivated with a Si3N4 film to simplify bonding the chip on a heat sink. Threshold currents for 10 ?m-stripe lasers were as low as 190 mA and the differential quantum efficiencies from the cleaved facet were ~18% (27°C, pulsed). C.W. operation was obtained up to 35°C.

To make short, high-speed electroabsorption modulators, it is necessary to use a material and device structure that displays a large change in absorption coefficient, Δα. We report a device with Δα= 7800 cm−1, which provides an on/off ratio of 44:1 at λ= 1.6μm with a drive voltage of 10 V.