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A device quality of selective epitaxy growth of InGaAsP/InP multiple quantum well (MQW) structure using low-pressure metalorganic vapor phase epitaxy (MOVPE) technique is described. The technique is applied to a monolithically integrated electroabsorption modulator with distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers. Superior device characteristics such as efficient modulation, low threshold current and high efficiency operation of the integrated devices are obtained.

The authors report a mode-locked pulse source with extremely wide operating frequency range and very stable operation, through the use of a long, linearly chirped Bragg reflector as the output coupler integrated in a fiber external cavity. A 1.55 mu m strained MQW laser diode is used, with one facet high reflectivity (HR) coated for improved cavity Q, and the other antireflection (AR) coated to allow coupling to the external cavity and suppress Fabry-Perot modes. Near-transform-limited pulses are obtained over a frequency range of 700 MHz around a system operating frequency of 2.488 GHz, with pulsewidths of 50 ps, as required for a practical soliton transmission system. >

Novel MQW integrated passive waveguide (IPW) DFB lasers have been fabricated using a selective area MOVPE growth technique. Detailed measurements of the absorption loss of the passive waveguide in the structure as well as its influences on the laser linewidth are reported for the first time. A linewidth reduction factor of more than 3 is observed as compared to a simple DFB laser despite the high absorption loss. >

The first complete nonlinear optical-loop mirror demultiplexing experiments including error-rate measurements are reported. Broadband demultiplexing of 16-, 32-, and 64-Gb/s, 2/sup 15/-1 data was performed using only semiconductor lasers. The penalty for demultiplexing a 64-Gb/s time-division multiplexed data stream to the 4-Gb/s fundamental rate was 2.2 dB at an error rate of 10/sup -9/. The switching pulse energy was 1.1 pJ. >

The authors demonstrate error-free optical soliton transmission at 32 Gb/s over 90 km of dispersion-shifted fiber. Fiber loss was compensated for by using diode laser pumped Er/sup 3+/-doped fiber amplifiers located every 30 km and a 4 Gb/s data pattern was passively multiplexed to 32 Gb/s. Approximately 16-ps-wide, near transform-limited pulses were launched into the system and the output pulsewidth was about 14 ps. At the receiver, four-wave mixing was employed to perform all optical demultiplexing of the data down to the base data rate. At a 10/sup -9/ (2/sup 15/-1 word length) bit-error rate, the penalties from the demultiplexing and the 90-km soliton transmission were approximately 1.6 and 0.5 dB, respectively. >

We describe reproducible growth of multiple quantum well graded index separate confinement distributed feedback (MQW- GRIN-SCH-DFB) lasers by atmospheric pressure metalorganic vapor phase epitaxy (MOVPE). Epitaxial layers were grown directly on a first order grating prepared on a (100) n-InP substrate. The gratings were preserved by introducing a suitable mixture of AsH 3 and PH 3 into the reactor. The quality of epitaxial layers grown on preserved gratings was found to improve by deposition of a very thin quaternary layer (7 nm thick) at low temperature (500°C), before the growth of the waveguide and subsequent graded index layers at the normal growth temperature (625°C). With the cavity length varied from 0.5 to 2 mm, the corresponding threshold currents were 22 and 100 mA, respectively. A remarkable improvement in both laser linewidth and output power was observed with devices as long as 2–3 mm. With 2 mm long device we observed linewidth as narrow as 600 kHz at a power output of 35 mW.

Multiwavelength soliton interaction over 10000 km in an Er/sup 3+/-doped fiber amplifier based system is studied in a fiber loop configuration. Collisions that takes place over distances significantly longer than amplification period are found to produce nonpermanent shifts of the soliton carrier frequencies, thus acting as collisions in a lossless medium. The spectral shift is found to be inversely proportional to the wavelength separation and is reduced with increasing pulse width. The effects of these unavoidable collisions will impose a limit on the minimum channel spacing in ultra-long-haul soliton based communication systems. >

A report is presented on the growth and characterization of the first InGaAs-InP-based graded-index separate-confinement-heterostructure (GRIN-SCH) strained quantum-well lasers operating near 1.47 mu m. The structure features linearly graded InGaAsP waveguide layers for both optical and carrier confinement in a very narrow, strained quantum-well layers. The excellent structural quality of the active and waveguide regions has been confirmed by transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS) analysis results. Strained quantum-well lasers with well widths as narrow as 5-6 nm were fabricated with threshold current densities as low as 750 A/cm/sup 2/. Buried-heterostructure lasers based on strained quantum-well active lasers exhibit threshold currents as low as 10-15 mA with quantum efficiency of 70-80%. With antireflection coating on one side of the sample, the laser shows threshold current of 35 mA with highest output power of 160 mW. >

The first monolithically integrated DFB laser/Mach-Zehnder interferometric modulator fabricated by the selective area low pressure MOVPE growth technique is reported. A near 3-dB power divider at the Y-branches of the interferometer has been reproducibly achieved by a photolithographically defined dielectric mask used in the selective area growth technology and confirmed by an infrared near field imaging technique. A modulation depth of over 12 dB was achieved both in the forward and reverse bias to the arms of the phase modulator. >

A packaged hybrid soliton pulse source is used in a soliton transmission experiment employing sliding-frequency guiding filters. The source shows excellent stability and very clean tuning characteristics. Control of the operating frequency and wavelength are described. Error free transmission at 10 GBit/s is achieved over a distance of 27000 km. >

The authors investigate the dependence of the spectral linewidth of strained MQW-DFB (multiquantum-well distributed-feedback) lasers on device parameters, such as coupling strength and the number of quantum wells. The spectral linewidth of the MQW-DFB lasers is compared to that of a bulk active laser, as well as to that of a novel MQW-DFB laser with a monolithically integrated passive waveguide. The spectral linewidth of the strained MQW lasers was found to be less than that of the bulk active DFB lasers. Further reduction in the spectral linewidth was observed for MQW structures with a fewer number of wells and larger detuning of the Bragg wavelength. However, the monolithically integrated passive waveguide DFB structure was found to improve the spectral linewidth to a greater extent than conventional strained MQW-DFB lasers. >

25 GHz modulation bandwidth is achieved from a fully packaged 1.55 mu m DFB laser, using devices with p-doped compressively strained MQW active regions and large negative wavelength detuning. Devices on submounts show a record bandwidth of 26 GHz, limited by device and bonding parasitics. Resonance frequencies of over 26 GHz are measured. >

We describe hybrid lasers combining a semiconductor gain section and fiber cavity with integrated chirped Bragg reflector. These devices have produced output powers of 27.5 mW in a narrow linewidth (400 KHz) stable single longitudinal mode. The use of a chirped reflector to stabilize the single mode output, and correct grating orientation are described. The laser output has a side‐mode suppression ratio of over 55 dB at 27.5 mW output, and relative intensity noise (RIN) below 160 dB/Hz.

We describe a mode-locked hybrid pulse source which produces short (23 ps) mode locked pulses with an average power of 7.8 mW, high peak power of 137 mW, at a repetition rate of 2.51 GHz. The source uses a two section laser diode to allow high peak power, in an optical fiber cavity with an integrated Bragg reflector. The Bragg reflector controls the operating wavelength to sub nanometer precision, and also confines the bandwidth of the pulses to keep the time bandwidth product below one. >

Summary form only given. A fully packaged hybrid soliton pulse source is described. Excellent stability and tuning characteristics are shown. Error free soliton transmission at 10 Gbit/s is achieved over 27,000 km using sliding-frequency guiding filters.

Summary form only given. 2.5 Gbit/s transmission over 517 km of standard fiber is reported using a monolithically integrated InGaAsP MQW EA modulator/DFB laser by selective-area MOVPE. A low chirp of 0.13 /spl Aring/ peak-peak and good reliability are shown.

We have demonstrated the first monolithic integration of a DFB laser with a Mach-Zehnder type modulator fabricated by the selective area MOVPE growth technique and operating at 1.55 /spl mu/m. A spatially resolved micro photoluminescence setup was used to characterize the crystal quality. We have achieved a low loss and near 3 dB Y-branch power divider in the structure with the modulator achieving an attenuation up to 17 dB and a /spl pi/ phase shift voltage of 2 V.

1.3- mu m InGaAsP/InP buried heterostructure lasers were fabricated using Ch/sub 4//H/sub 2/ reactive ion etching (RIE) for mesa definition and metalorganic chemical vapor deposition for blocking laser growth. Results show that high-quality lasers can be made using RIE, with threshold current as low as 10 mA. It was also found that a slight chemical etching of the RIE mesas was necessary to obtain lasers with as high quality as those fabricated entirely by wet etching. >

A new approach to reduce the rates of threshold current increase and external quantum efficiency decrease with increasing temperature in a semiconductor laser is proposed and demonstrated. This is based on the realization that the total laser cavity loss, which is normally relatively independent of wavelength, can be made to decrease with increasing wavelength. Since the gain peak of the laser shifts towards longer wavelength as temperature is increased, the rate of threshold current increase is thus reduced with increasing temperature. To implement this, we proposed and demonstrated the broadband enhanced feedback (BEF) approach using multilayer coatings, very weak or chirp gratings with peak reflectivity centered at the lasing wavelength corresponding to the maximum operating temperature desired. It was shown that the threshold‐temperature coefficient T0 improved from the typical value of ∼45 K in long wavelength InGaAsP lasers (bulk active or MQW) to 85 K in BEF coated lasers. This scheme also simultan...

High performance InGaAsP/InP multiquantum well (MQW) buried heterostructure lasers emitting around 1.3 μm were prepared for the first time by chemical‐beam epitaxy. At 20 °C, continuous‐wave (cw) threshold currents were 5–8 mA and quantum efficiencies were 0.35–0.45 mW/mA for 250 μm long lasers having one facet ∼85% reflective coated. At 80 °C, the cw threshold currents remained low, 23 mA, quantum efficiency stayed high, 0.22 mW/mA, and output power of ∼10 mW was achieved. cw power output as high as 125 mW was achieved with 750 μm long lasers having AR–HR (∼5%–85%) coatings. Lasers with bulk active were also studied for comparison. Though they also have excellent device performance, in general, they are somewhat inferior to MQW lasers.

We demonstrated the first successful growth of 1.5 μm strained‐layer InGaAs/InGaAsP multi‐quantum‐well (MQW) distributed feedback (DFB) lasers by chemical beam epitaxy (CBE). In these DFB wafers, a quaternary grating is placed at the bottom of the MQW stack with an InP spacer layer. Studies by transmission electron microscopy show that defect‐free InP regrowth was achieved with no mass transport needed over the grating corrugations before regrowth. With CBE regrowth the shapes of the gratings were well preserved. The InP overlayer also very effectively smoothed out the quaternary surface corrugations resulting in very flat MQW structures. Buried‐heterostructure 6‐QW DFB lasers (250 μm long and as‐cleaved) operated at 1.55 μm with cw threshold currents 10–15 mA and slope efficiencies up to 0.35 mW/mA (both facets). Side‐mode suppression ratios (SMSR) as high as 49 dB was obtained. The laser operated in the same DFB mode with SMSR staying above 40 dB from threshold and throughout the entire current range even at high temperatures (70 °C checked).

The polarization-dependent gain spectra of both tensile and compressive strain multiple-quantum-well (MQW) In/sub x/Ga/sub 1-x/As-InP lasers in a relatively large strain regime are presented. The results show that MQW lasers with tensile strain and an In concentration as low as 43% in the wells lase in a pure transverse magnetic (TM) mode rather than a transverse electric (TE) mode with a gain difference of 60-70 cm/sup -1/ at all the injection currents investigated. The peak gain for the TE mode is shifted toward shorter wavelengths from that of the TM mode, indicating that the emission is principally due to light hole-electron transition. The differential gain of the TM mode is about 1.5 times higher than that of the TE mode operation. Opposite phenomena were observed in the compressive strained MQW lasers. >

A survey of graded‐index separate confinement multiple quantum well distributed feedback lasers comparing the effects of strain in the quantum well upon threshold, output power, and linewidth is reported. Lasers with either compressive or tensile strained quantum wells and a long cavity length (890 μm) show lower threshold current (10–20 mA) as well as lower linewdith power product than lasers with unstrained quantum wells and have a comparable minimum linewidth to the unstrained quantum well lasers. A minimum linewidth as narrow as 900 and 440 kHz for compressive strain and unstrained quantum well lasers, respectively, was obtained at output power of 30 mW. Single longitudinal mode operation with a maximum output power over 80 mW was observed in all the structures.

Solitons of different wavelengths are found to exhibit substantial spectral and temporal changes when collisions are centered in erbium‐doped fiber amplifiers. By using two soliton pulse trains, with ∼70‐ps‐wide pulses, spectrally separated by 1.8 A, and 106 km of non‐dispersion‐shifted fiber, we observe a spectral and temporal shift of as much as 0.35 A and 55 ps, respectively, for each soliton. Both soliton wavelengths shift the same amount, but in opposite directions and remain undisturbed in terms of shape and amplitude after the collision. This shift may impose limitations on multiple wavelength soliton based communication systems utilizing fiber amplifiers.

We describe InGaAs/InP multiquantum well distributed feedback (DFB) lasers with novel properties atrributable to the quantum well based active layer. The low internal loss waveguide and shallow gratings have allowed the fabrication of lasers with a cavity length varying from 0.5 to 2 mm, and corresponding threshold currents of 22 and 100 mA, respectively. A mode rejection ratio as high as 50 dB has been obtained in lasers with one antireflection‐coated facet. The long cavity devices exhibit linewidths as low as 600 kHz at a power output of 35 mW. Transmission experiments through 70 km of fiber, at 1.7 Gb/s, showed a dynamic chirp penalty of only 0.25 dB, a factor of 8–10 smaller than in conventional lasers.

A record high power output strained‐layer InGaAs/InP quantum well laser emitting at 1.48 to 1.51 μm is demonstrated. Maximum cw output as high as 206 mW is obtained from a sample with a cavity length of 890 μm and a facet reflectivity of ∼5 and 85% for the front and the rear facets, respectively. The laser has a threshold of 30 mA and a slope efficiency as high as 0.4 mW/mA.

A high continuous-wave (CW) output and high quantum efficiency of 1.5 mu m-wavelength InGaAs/InP graded-index separate-confinement multiple-quantum-well DFB lasers were demonstrated. A threshold current of 45 mA with a maximum output power close to 100 mW and a quantum efficiency of 0.33 mW/mA was obtained. Single-frequency light output with power as high as 16 dBm (40 mW) was launched into a single-mode fiber. >

Summary form only given. Here we report the first penalty-free transmission results over 48 km of nondispersion-shifted fiber using a 1.3-/spl mu/m wavelength integrated electroabsorption modulated MQW laser (EML) device at a bit rate of 10 Gbit/s.

Optical transmitters with monolithically integrated electroabsorption-modulator/DFB lasers (EMLs) are expected to be key components in future lightwave transmission systems. The low chirp of these devices makes them well suited for long-haul (500 km) 2.5-Gbit/s transmission systems that make use of existing standard fiber and erbium-doped fiber amplifiers (EDFAs).1 Recently, several groups have also reported transmission at 10 Gbit/s over 50 km of standard fiber,2 which is the theoretical dispersion limit, as well as over longer spans by using dispersion-shifted fiber3,4 or nonlinear dispersion compensation.2 However, many of these devices have a butt-joined waveguide structure and/or use polyimide dielectrics to reduce the parasitic capacitance of the modulator,2,3 both of which are serious concerns for manufacturability and long-term reliability.

We report on the generation of short optical pulses by utilizing the non-linear absorption characteristics of a multiple quantum well (MQW) electro-absorption modulator, which is monolithically integrated with a MQW wavelength-tunable distributed Bragg reflector (DBR) laser on a single chip. Optical pulses as short as 39 ps and 15 ps have been generated at a repetition rate of 3 GHz and 10 GHz, respectively, with a broad tuning range of 5.4 nm near 1554 nm lasing wavelength.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Lasers with integrated electroabsorption (EA) modulators are showing a lot of promise as low-chirp sources for long-haul transmission systems at multigigabit-per-second speeds.1,2 There are various structures and growth techniques for making such devices.3·4 Here we demonstrate a multiple-quantum-well (MQW) DBR-LD/EA modulator in a 495-km transmission system operating at 2.5 Gbit/s.

The realization of long distance soliton-based transmission systems requires a reliable, stable source of transform limited pulses at 1.55 μm with a pulsewidth of 30-60 ps, at repetition rates of 2.5-5.0 GHz. This requires a very narrow optical bandwidth. Wavelength-division multiplexing of solitons also requires accurate wavelength control. External cavity lasers utilizing air cavities require the alignment of bulk optics, together with a diffraction grating and etalon. Integrated structures provide an attractive alternative, with monolithic mode-locked lasers1-3 providing pulses at high repetition rates. The hybrid soliton pulse source (HSPS) is an ideal candidate for a practical source for soliton transmission systems (Fig. 1). Low-loss silica waveguides allow long cavity lengths and therefore low repetition rates, and a high level of fabrication control (silicon optical bench technology4) allows precise control of operating wavelength and extremely narrow Bragg reflectors.

We demonstrate the first complete loop mirror demultiplexing experiments including error-rate measurements. Narrowband demultiplexing of 16 Gb/s, 32 Gb/s and 64 Gb/s 215-1 data was performed with small penalties using semiconductor lasers.

Strained-layer quantum-well InGaAsP/InP lasers emitting at wavelengths between 1.47 and 1.55 mu m are reported. The lasing wavelength could be adjusted by introducing either tensile or compressive strain as well as by changing the layer thickness of the quantum wells. To obtain a lasing wavelength as short as 1.47 mu m, tensile strain is preferable due to the relaxed constraints in layer thickness of the quantum wells. Both tensile and compressive strain were found to improve the performance of the lasers as compared to the lattice-matched ones. A sample with compressive strain showed a CW threshold current as low as 4 mA. Maximum CW output power as high as 206 mW with a lasing wavelength of 1.47 mu m was obtained from a quantum-well active layer with tensile strain. >

Optical communication systems based upon solitons [1] have recently gained considerable interest as a possible scheme for very long-haul repeaterless communication links [2,3]. The implementation of such systems have become feasible due to the availability of efficient diode laser pumped erbium-doped fiber amplifiers (EDFA) [4,5]. Contrary to linear optical pulses, however, closely spaced soliton pulses may interact with each other [6,7]. In addition, solitons of unequal carrier wavelengths e.g. in a wavelength division multiplexing (WDM) system will, due to fiber dispersion, inevitably collide at some point in the system.

34, 17 and 14 ps pulses have been generated at repetition rates of 2.5, 5 and 10 GHz, respectively, from an integrated laser modulator at 1.5 µm. Pulse widths were significantly reduced by modulating at both the fundamental and the second harmonic frequencies.

Summary form only given. The authors report on the generation of short optical pulses by utilizing the nonlinear absorption characteristics of a multiple quantum well (MQW) electroabsorption (EA) modulator, which is monolithically integrated with an MQW wavelength-tunable distributed Bragg reflector (DBR) laser on a single chip. Preliminary measurements show that optical pulses as short as 39 ps have been generated at a repetition rate of 3 GHz with a broad tuning range of 5.4 nm near 1554-nm lasing wavelength. The bandgap energies of both the narrow-gap active MQW region and the wide-gap passive MQW region are controlled by the oxide width and grown at the same time using selective-area epitaxy by metal-organic vapor-phase epitaxy (MOVPE). >

The use of semiconductor-laser-pumped erbium-doped fiber amplifiers and an externally modulated mode-locked external-cavity semiconductor laser to obtain soliton data transmission at 4 Gb/s over 136 km of nondispersion shifted fiber is described. After 136 km of transmission and at low pulse powers, the approximately 80 ps fiber input pulse width was broadened to approximately 150 ps. At high pulse powers the output pulse width was maintained at 80 ps, as expected for N=1 solitons. N=3 solitons were also observed at lower data rates. >

A tuning range of 200 nm has been achieved with a step‐graded multiquantum well InGaAs/InP laser in an external‐cavity configuration. Continuous, single‐mode lasing could be observed from 1440 to 1640 nm. Depending on the current density, the laser can operate both at the n=1 and n=2 quantized states. At low current density, the n=1 state gives higher gain, whereas for higher carrier densities, the n=2 level dominates. This gives rise to a flat gain profile and an extended operating range, in fact, the widest tuning range reported so far for semiconductor lasers.

We describe a mode-locked hybrid pulse source with a two-section laser diode to obtain short mode-locked pulses (23 ps) with an average power of 7.8 mW, a high peak power of 137 mW, and a repetition rate of 2.51 GHz. The hybrid laser incorporates a two-section laser and an optical fiber cavity with an integrated Bragg reflector. The Bragg reflector controls the operating wavelength to subnanometer precision and also confines the bandwidth of the pulses so as to keep the time-bandwidth product below 1.

The first results of an actively mode-locked semiconductor laser diode using a fibre external cavity with integrated Bragg reflector are reported. The device produces transform limited pulses of 18-5ps FWHM at a repetition rate of 2-37GHz. High peak power of 49 mW in the output fibre is achieved.

Two wavelength division multiplexed soliton pulse trains (2*2 Gbit/s 0101. . .) have been propagated more than 9000 km with less than 10/sup -9/ bit error rate for both channels. Soliton collisions have no effect on the error rate for wavelength separations larger than 7 AA or for collisions centred inside the fibre. >

Stimulated Raman spectra were obtained from H2O, D2O, H2OD2O mixtures, and solutions of NaClO4 in H2O and D2O using picosecond pulse excitation at 530.0 nm. The stimulated emission peaks could be predicted from the spontaneous Raman contour shapes for the OD stretching vibrations, but exclusive stimulation of either hydrogen-bonded or of nonhydrogen-bonded components was observed for the OH stretching vibrations. The large widths of the stimulated spectra are discussed in relation to self-focusing and refractive index modulation.

A scheme for using semiconductor laser amplifiers for simultaneous compensation of both the fibre loss and the fibre dispersion in the 1.5 mu m region is proposed and demonstrated. Experimentally, the authors demonstrate propagation of 16 Gbit/s pulses over 70 km of non-dispersion-shifted fibre at 1.53 mu m wavelength. This distance is four times longer than the fundamental dispersion limit for transform-limited pulses. >