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We describe integration of lasers and optical amplifiers at 1.3 μm wavelength. The effects of the residual mirror reflectivity at the amplifier front facet are discussed. Using photonic integration techniques very high coupling efficiency of light from the laser to the amplifier sections was observed, with current transfer efficiency (ratio of photocurrent to drive current) as high as 33%. The output light current characteristics of the laser have a slope efficiency higher than 2 mW/mA. This device may be used for digital modulation with very low rf power drive requirements. Modulation at 2 Gbit/s has been demonstrated.

We observe saturation in the electroabsorption of InGaAs/InP multiple quantum wells (MQWs) at high optical intensity. Contrary to the mechanism for zero‐field MQWs, we find that saturation occurs due to the presence of trapped photogenerated holes that screen the MQWs from the applied electric field. By carefully measuring the absorption coefficient of the wells and the emission time for holes, we are able to fit the observed electroabsorption saturation with no adjustable parameters.

Using bulk InGaAsP as a saturable absorber we have passively mode locked a NaCl color center laser to produce transform‐limited, pedestal‐free pulses near 1.6 μm as short as 197 fs with up to 4.2 kW peak power. Our results simplify the saturable absorber material requirements and prove that excitons are not required for generating subpicosecond pulses. By comparing a dozen samples we find that a minimum band‐edge absorbance of 40% is required to generate subpicosecond pulses, although details of the band edge are not critical. In addition, we find stable mode locking always occurs on the long‐wavelength side of the laser gain peak.

High quality long‐wavelength InGaAsP/InP lasers were grown by atmospheric organometallic vapor phase epitaxy using tertiarybutylarsine (TBA) as a substitute for AsH3. Electrical and photoluminescence measurements on InGaAs and InGaAsP showed that TBA‐grown material was at least as good as AsH3 material in terms of suitability for lasers. From two wafers grown by TBA, current thresholds Ith as low as 11 mA were obtained for a 2‐μm‐wide semi‐insulating blocking planar buried heterostructure laser lasing near 1.3 μm wavelength. The differential quantum efficiencies ηD were as high as 21%/facet with a low internal loss α=21 cm−1. In addition Ith as low as 18 mA and ηD as high as 18% have been obtained for multiplequantum well lasers at 1.54 μm wavelength. These results show that TBA might be used to replace AsH3 without compromising on laser performance.

We report large‐ and small‐signal gain characteristics of 1.5 μm multiple quantum well optical amplifiers. We demonstrate a 350‐μm‐long amplifier with a peak gain of 15 dB. At a wavelength where the small‐signal gain is 13.5 dB, the 3 dB saturation output power is as large as 45 mW. The 3 dB saturation output energy is 5.1 pJ and the calculated gain recovery time is 57 ps. We also demonstrate a 625‐μm‐long device with a gain of 19 dB and a saturation output power of 42 mW.

The use of ultrathin etch-stop techniques to expand the vertical optical mode size adiabatically in 1.5- mu m InGaAs/InGaAsP MQW lasers using a tapered-core passive intracavity waveguide structure is discussed. 30% differential quantum efficiency out the tapered facet, far-field FWHM of approximately 12 degrees and a butt-coupling efficiency into a cleaved fiber of -4.2 dB, with -1-dB alignment tolerances of approximately +or-3 mu m, were achieved. >

The first interferometric wavelength converter with an integrated CW source is shown to operate with 0.5–0.8 dB penalty at 2.5 Gb/s for wavelength conversion and same-wavelength operation. Fiber coupled conversion gain of up to 7.5 dB is achieved. The chirp parameter α is measured to be 2.

A semiconductor optical 9mplifier array with 4 channels is presented. This SOA array was coupled to uncoated, flat end, single mode fibers using integrated adiabatic beam expanders, optical index matching gel, and specifically tailored TiO2 anti-reflection coatings. The TiO2 AR coating overcomes the indices misinatching of fiber glass and InP based device, and reduce optical reflection to 0.002% at 1.55 μm. The average coupling loss is 4.3 dB per facet for the devices measured. Fiber coupled small signal gain for the amplifiers is typically 11.6 dB and a saturation output power of 3.0 dBm. The method of characterization and optimization of the TiO2 coating is discussed.

A rhenium solar-thermal receiver/absorber propulsion (STRAP) device has been designed and fabricated. Its uniqueness lies in its simplicity of design and fabrication, consisting of just three components electron beam welded together: a rhenium foam heat exchanger between inner and outer rhenium structural shells, with the thrust chamber integral to the outer shell. Plans have been developed for testing this device at the Air Force Phillips Laboratory.

Anticoagulant andanti-platelet effectsare maintained following coadministration of otamixaban, adirect factor Xa inhibitor, with tirofiban in healthy volunteers

As optical access to the loop becomes more advanced, using emerging fiber to the loop (FTTL) architectures, and with the possible use of wavelength division multiplexing (WDM) to enhance transmission capacity and networking flexibility, it is important to consider new components that may be useful as building blocks for the upcoming local access networks. Obviously, for FTTL applications, low cost is an important prerequisite for components that are not widely shared. This may require uncooled operation, ease of packaging, and perhaps integration of opto-electronic devices. One of the new FTTL- WDM architectures that was recently demonstrated is RITE-Net [1,2], which is based on a WDM signals from a central office sent downstream to a remote node, and then to the local optical network unit (ONU). The carrier wavelength is modulated at the ONU using an on site optical modulator and returned upstream to the central office. One parameter that effects the performance is the insertion loss of the modulator. To improve the power budget of the system, it might be useful to employ a component that has integrated modulators and a semiconductor optical amplifier (SOA) resulting in a modest fiber to fiber gain rather than a large insertion loss. The proposed component can also enable WDM networks where frequency conversion and/or signal equalization over a large dynamic input range is required. It may be useful to integrate two modulators, so that one can be used for data encoding and the other for power level equalization.

Nondegenerate four-wave mixing in semiconductor optical amplifiers was studied both as a spectroscopic tool for probing semiconductor dynamics and as a wavelength conversion technique. Four-wave mixing spectra were measured at detuning frequencies ranging from GHz to THz rates and ultrasfast intraband mechanisms having relaxation time constants of 650 fs and less than 100 fs were revealed in the measurements. Cross-polarization four-wave mixing was also measured to study the inter quantum-well carrier transport process in quantum-well amplifiers. In addition, broadband wavelength conversion using four-wave mixing in semiconductor optical amplifiers was investigated. Results concerning the conversion efficiency over spans up to 65 nm, as well as a demonstration of wavelength conversion with gain are presented. The issue of converted signal-to-background noise in this process is also addressed.

Trans-oceanic soliton transmission systems employing optical amplifiers and ‘sliding-frequency guiding filters’ have the potential to reach capacities of 100 Gbit/s through extensive wavelength division multiplexing [1]. The sliding-frequency filter transmission line lends itself to wavelength multiplexing because of the periodic nature of the Fabry Perot filter. Each wavelength can be guided along the transmission fiber without interactions with neighboring solitons, excessive timing jitter or noise accumulation. However, practical application of soliton systems has been slowed by lack of a reliable pulse source.

Interwell carrier transport in a semiconductor optical amplifier having a structure of alternating tensile and compressively strained quantum wells was studied by four‐wave mixing at detuning frequencies up to 1 THz. A calculation of transbarrier transport efficiency is also presented to qualitatively explain the measured signal spectra.

The efficiency of broadband optical wavelength conversion by four-wave mixing in semiconductor traveling-wave amplifiers is measured for wavelength shifts up to 65 nm using a tandem amplifier geometry. A quantity we call the relative conversion efficiency function, which determines the strength of the four-wave mixing nonlinearity, was extracted from the data. Using this quantity, gain requirements for lossless four-wave mixing wavelength conversion are calculated and discussed. Signal to background noise ratio is also measured and discussed in this study. >

The integration of distributed-Bragg-reflector (DBR) lasers or distributed-feedback (DFB) lasers with semiconductor modulators has proven to be a successful approach for providing a compact, low-chirp source for long-haul optical-communication systems at multigigabit-per-second rates.1 Recently, a tunable DBR laser, combined with a bulk electroabsorption (EA) modulator operating at a 2.5 Gbit/s, showed the capability for error-free transmission over 674 km of conventional singlemode fiber.2

Wavelength conversion is recognized as an important function in future broadband multichannel lightwave systems [1], and several types of wavelength converters have been demonstrated, which can be broadly classified into those which use cross-saturation of gain and those which employ four-wave mixing (FWM) [2]-[7]. Various limitations, however, are inherent with most of these wavelength conversion techniques. Cross-saturation techniques are limited to strong input signals that employ ASK modulation at rates within the spontaneous rate. Among FWM based techniques, cavity-enhanced FWM in semiconductor lasers requires matching of input channels to the laser cavity resonances and speed is limited to a few Gb/s, corresponding to the resonance bandwidth. Wavelength converters based on FWM in dispersion-shifted fiber require long fiber lengths (10 km) to achieve sufficient conversion efficiencies.

We demonstrate greater than 90% quantum efficiency in an In/sub 0.53/Ga/sub 0.47/As photodetector with a thin (900 /spl Aring/) absorbing layer. This was achieved by inserting the In/sub 0.53/Ga/sub 0.47/As/InP epitaxial layer into a microcavity composed of a GaAs/AlAs quarter-wavelength stack (QWS) and a Si/SiO/sub 2/ dielectric mirror. The 900-/spl Aring/-thick In/sub 0.53/Ga/sub 0.47/As layer was wafer fused to a GaAs/AlAs mirror, having nearly 100% power reflectivity. A Si/SiO/sub 2/ dielectric mirror was subsequently deposited onto the wafer-fused photodiode to form an asymmetric Fabry-Perot cavity. The external quantum efficiency and absorption bandwidth for the wafer-fused RCE photodiodes were measured to be 94/spl plusmn/3% and 14 nm, respectively. To our knowledge, these wafer-fused RCE photodetectors have the highest external quantum efficiency and narrowest absorption bandwidth ever reported on the long-wavelength resonant-cavity-enhanced photodetectors. >

The generation of short optical pulses at 1.5 /spl mu/m is a key issue in future communications systems. Recently, a new approach to pulse generation has been reported in which the output ofa CW laser is converted to nearly transform limited pulses by a sinusoidally driven electro-absorption modulator. This simple technique is readily integrated and provides flexibility in both operating frequency and wavelength, an important asset for soliton and optical time division multiplexing (OTDM) applications.

Wavelength division multiplexing (WDM) is capable of tremendously increasing the throughput capacity of fiber transmission lines. It can also be used to build all-optical networks (1). To receive the individual channels, these systems employ WDM receivers, which optically demultiplex the different channels before detecting them with photodetectors. Together with an electronic switch array, such a device could also be used as a fast tunable receiver in an all-optical network (2).

The integrated laser-modulator has become a very attractive, compact source for future applications in high bit rate optical communication systems which require single frequency, low chirp performance. Recently, picosecond soliton pulse generation using sinusoidally driven electroabsorption modulators has been reported using both discrete [1,2] and integrated modulators [3,4], This technique provides flexible repetition rate operation and reduced complexity when compared with mode-locked fiber ring lasers or external cavity semiconductor lasers. Additional functionality is attained if the source is wavelength tunable, leading to potential application in wavelength division multiplexed (WDM) systems or single channel systems designed to operate at an optimum wavelength. Integrating a distributed Bragg reflector (DBR) laser with the semiconductor modulator enables electrical wavelength tuning to be achieved [5]. Here, we report an integrated DBR laser and bulk electroabsorption modulator which produces 25 ps transform-limited pulses at a repetition rate of 10 GHz over a 6.5 nm wavelength range near 1.55 μm.

We present a theoretical analysis and experimental measurements of broadband optical wavelength conversion by four-wave mixing in semiconductor traveling-wave amplifiers. In the theoretical analysis, we obtain an analytical expression for the conversion efficiency. In the experiments, both up and down-conversion efficiencies are measured as a function of wavelength shift for shifts up to 27 nm. The experimental data are well explained by the theoretical calculation. The observed higher conversion efficiency for wavelength down-conversion is believed to be caused by phase interferences that exist between various mechanisms contributing to the four-wave mixing process. >

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Ultrafast dynamics in a 1.5‐μm tensile‐strained quantum‐well optical amplifier has been studied by highly nondegenerate four‐wave mixing at detuning frequencies up to 1.7 THz. Frequency response data indicate the presence of two ultrafast physical processes with characteristic relaxation lifetimes of 650 fs and

A dual back-illuminated photodetector for balanced coherent receivers applications is presented. The photodetectors have an InP/InGaAs/InP p-i-n structure. Several additional semiconductor layers have been added to fabricate the structure by selective wet etching. The material was grown by metalorganic vapor phase epitaxy (MOVPE) on a semiinsulating, Fe doped, InP substrate. The passivation and the insulation between contacts were obtained using polyimide. The contact structure is intended to connect the photodetector to the package by flip-chip. The measured photodetector capacitance was around 0.2 pF for a single photodetector (without series connection), the series resistance under 20 ohms, and the dark current under 10 nA.

Active, passive, and hybrid mode-locking have been demonstrated in a monolithic extended-cavity semiconductor laser with an integrated saturable absorber. A 45-µm long reverse-biased segment of multiple quantum wells acts as the saturable absorber. Active and hybrid mode-locking at a repetition rate of 8.6 GHz, resulted in 6.2-ps and 4.4-ps pulses. The extended-cavity laser also exhibits self-starting passive mode-locking at a repetition rate of 8.57 GHz with 5.5 ps pulses. Wavelength selectivity over a range of 15 nm with little change in the pulse width is facilitated by a broad spectrum.

Semiconductor-laser amplifiers (SLA’s) can perform many optical-signal-processing functions. In addition to loss compensation and switching, a SLA can simultaneously amplify and detect an optical signal.1 Recently, two-contact amplifiers have demonstrated improved detection responsivi ty.23 Here, we show that a three-section SLA can further be used to monitor amplifier gain.

Semiconductor laser arrays are being realized for wavelength-division-multiplexed (WDM) lightwave communication systems. Such arrays can increase the amount of transmitted information through a fiber link, or can be used for optical switching applications. By combining the signals on chip, the alignment of fibers to individual lasers is eliminated.

Monolithic mode-locked semiconductor lasers are compact and reliable pulse sources for optical communication systems employing short pulses such as optical time division multiplexed systems and long distance soliton transmission [1]. These sources offer the advantage and flexibility for integration with filters, amplifiers, modulators, saturable absorbers, or other photonic components which can enhance the versatility and reliability of the transmission source [2,3]. However, the repetition rate at which the mode-locked laser operates is inversely proportional to the cavity length. Therefore, very long cavity lengths are required for operation at frequencies which are of practical interest for systems deployed today, such as those designed for the Sonet standard rate, OC-48 (2.488 Gbit/s). Maturing growth and processing techniques of III-V materials have enabled fabrication of very long 1.55 μm laser devices, that are suitable for mode-locking at repetition rates below 10 GHz [4]. Recent results indicate a trend toward lower, more practical operating frequencies and increased integration. Here, we report a semiconductor laser with a length twice that of any previously reported monolithic mode-locked laser. The resultant fundamental repetition rate is 2.2 GHz. Active mode-locking at the fundamental frequency, and at higher harmonics, yields optical pulses with widths ranging from 9.0-12.0 ps.

A photonic integrated circuit implementing a receiver with an optical preamplifier and a wavelength filter for dense WDM systems has been fabricated. The integrated filter is based on planar optics and formed by a waveguide lens and Bragg grating combination. This arrangement provides a narrow filtering response of 0.4 nm and a high sidemode rejection ratio of 20 dB. A monolithically integrated preamplifier and photodetector are also incorporated to allow for high-sensitivity and high-speed operation.

A tensile/compressive MQW amplifier shows good polarization insensitivity over a 100 nm bandwidth at 1.5 µm. This amplifer can be integrated in photonic circuits which require polarization-independent gain. @@Summary

The practical deployment of wavelength division multiplexed (WDM) systems will require integrated multi-wavelength laser sources using gratings with several different pitches in close proximity on a single chip. At present there is no technique for fabricating such arrays suitable for manufacturing. Holographic exposure has become the standard grating fabrication technique for guided-wave optoelectronic devices such as DFB or DBR lasers. While offering rapid, large area processing of the entire wafer, this method has severe limitations when more complex grating configurations are required. Electron-beam lithography has proven to be a powerful tool, but the long writing time required to create these patterns raises serious questions about the manufacturability of devices when several inch wafer processing is contemplated.

I suspect that I am not alone in being concerned about the opinions of Dr Des Spence in his recent article revisiting pain and its treatment.1 2 I take issue with six of his most recent assertions.1 This figure is well recognised—for example, a recent report claimed 19% on the basis of interviews with 46 000 people across Europe.3 The standard definition is a pain occurring more than twice a week for more than 6 months and of a severity of more than 5/10. It is a point prevalence, and will include people whose duration of pain is limited, but it clearly describes an …

The behavior of semiconductor-based, light-activated microelectrodes in redox electrolytes has been examined theoretically using commercial software to self-consistently solve the transport equations for solid-state and solution-phase species and the electrostatic potential within the semiconductor phase, subject to the appropriate boundary conditions under steady state. The lightlimited currents for such spatially localized microelectrodes, observed for a high voltage bias, bias, under normal irradiation and a strict axisymmetric geometry, were proportional to the photon flux intensity. The results of these simulations afforded strong evidence that under high bias, holes generated by the light on an n-type semiconductor escape beyond the edge of the illuminated disk, leading to a net increase in the predicted current and thus in the effective area of the light-activated microelectrode.

System demonstrations employing soliton transmission and/or optical time division multiplexing have emphasized the need for stable and reliable pulse sources with repetition rates in the 1 GHz to 10 GHz range. For these applications, we have fabricated several photonic integrated laser devices that through gain-switching or mode-locking generate optical pulses with durations between 20 ps and 50 ps. In this talk, we will discuss gain-switched DBR laser integrated with high-power optical amplifiers or electro-absorption modulators and laser devices with long low-loss passive waveguides for active mode-locking.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Semiconductor ring lasers are attractive, by the nature of their geometry, for short pulse generation through active mode-locking and colliding pulse mode-locking (CPM). However, to date, only CW operation of small diameter ring lasers in GaAs has been demonstrated. Recent advances in InP fabrication technology have enabled the realization of complex photonic integrated circuits using multiple quantum well (MQW) active regions and low-loss passive waveguides. Using these techniques, we have fabricated an 3.0-mm diameter InGaAsP MQW ring laser which is actively mode-locked at 9.0 GHz producing nearly transform limited 27 ps optical pulses.

Widely tunable semiconductor lasers are critical components for future wavelength division multiplexed networks and switching systems. Indeed, the total capacity of such systems is presently limited by the laser tuning range. The electrical tuning range of DFB and DBR lasers is limited to less than ~15nm. This limitation results from the fact that the fractional tuning range, Δλ/λ, of the fine-pitch Bragg grating wavelength-selective reflector is simply proportional to the normalized effective index change, ΔN/N. However, we have recently demonstrated that the grating-assisted vertical coupler provides an attractive bandpass filter that can be electrically tuned over a range substantially greater than a grating reflector for the same induced refractive index change [1,2]. Indeed, very recently a tunable twin guide laser that includes a vertical coupler structure between two nearly-synchronous guides exhibited evidence of extended, but irregular tuning [3]. Here we report a novel monolithic extended cavity laser with an integrated grating-assisted vertical coupler as a tunable intracavity filter. This laser has measured tuning range of 57nm and a tuning response that depends monotonically on the filter tuning current.

Propagation of solitons over several thousand kilometers has been reported in recirculating fiber loop experiments [1,2]. However, a major obstacle for commercial use of soliton transmission systems has been the lack of a stable and reliable soliton source. Laboratory experiments have used either actively mode-locked external cavity lasers or gain-switched DFB lasers followed by pulse compression and optical filtering to produce soliton pulses. Neither of these sources are likely to be viable for commercial use. In this paper, we demonstrate transmission over distances up to 15000 km of solitons generated by a 5.5-mm long monolithic extended-cavity laser. Actively mode-locked, the laser provides a train of transform-limited pulses at a repetition rate of 8.2 GHz. The 106 km long recirculating fiber loop uses three low-noise Er+3-doped fiber amplifiers pumped by laser diodes at a wavelength of 980 nm.

An InP based 1×16 optical switch is demonstrated. The output ports are spaced 250 microns apart, and the total device length is 5.9 mm. Optical amplifiers are used to both gate the optical signals and to provide optical gain. The total net loss of the device, excluding coupling, is 0-2.5 dB with extinction ratios in excess of 18 dB. The uniformity spread of the 16 channels is better than 6.7 dB.

With the recent advances of erbium-doped fiber amplifiers (EDFAs) the total unrepeatered distance for fiber-optic transmission near 1.55 pm has increased dramatically. In conventional (nondispersion- shifted) fiber systems the primary limitation is now dispersion, requiring sources with low chirp. For these systems, the simplicity of direct modulation of single-mode lasers is an attractive alternative to external modulation. We have used nine directly modulated distributed-Bragg reflector (DBR) lasers for 1.7-Gbit/s transmission through 257 km of conventional fiber with

Historically lymphoepithelioma was a term used to describe an undifferentiated mucosal carcinoma with a lymphocytic component arising only from the nasopharynx, although recently, lymphoepithelioma-like carcinoma has been found to occur as a primary tumor of the lung. Thus far, five patients have been documented as having this rare anatomical presentation. The patient that is being presented is the latest case of lymphoepithelioma-like carcinoma of the lung and will be compared clinically and histologically with the other four cases. The case is presented in order to discuss optimal methods of diagnoses and treatment for this condition.

Room-temperature pulsed operation of InGaAsP (1.3 mu m)/InP vertical cavity surface emitting lasers has been achieved with threshold current as low as 50 mA using a constricted-mesa structure with dielectric mirrors. Above-room-temperature operation has also been realized with a maximum operation temperature of 66 degrees C. Pulsed and continuous-wave threshold currents at 77 K are 1.5 and 3.9 mA, respectively. >