Optimization of DFB lasers integrated with Franz-Keldysh absorptionmodulators

The influence of the residual facet reflectance on electroabsorption modulators monolithically integrated with DFB lasers is analyzed, for both index- and partly loss-coupled lasers. The optimum laser design is discussed from the standpoint of system requirements in long-distance 10 Gb/s transmission systems, requiring a minimum of chirp. The integrated device's performance will depend as much on the laser design as on the modulator. The DFB laser should be long (L>500 μm) with a coupling strength of about κ·L=2-3 and should have a high relaxation oscillation frequency. The residual reflectance should be less than 1·10^-4     

Continuous-wave operation of 1.5 ?m distributed-feedback ridge-waveguide lasers

CW operation of 1.5 ?m ridge-waveguide DFB lasers is reported for the first time. The ridge-waveguide DFB laser structure offers the prospect of high modulation speeds due to the absence of parasitic capacitances associated with reverse-biased current-blocking layers. These devices also represent the first report of CW operation of DFB lasers fabricated using the hybrid LPE/MOCVD crystal-growth technique and also of DFB lasers with gratings produced by electron-beam lithography.     

Broad-band continuously tunable all-fiber DFB lasers

Up to 27-nm continuous tuning is demonstrated from Er/Yb all-fiber distributed-feedback (DFB) lasers using a simple tuning technique for axial extension and compression. The demonstrated devices operate with powers up to 10 dBm and remain operating in single mode over the full tuning range. Our results represents the broadest tuning-range previously reported in any DFB laser configuration and demonstrate that uniform compression tuning of long Bragg gratings is possible with high reliability     

1.3-/spl mu/m continuously tunable distributed feedback laser with constant power output based on GaInNAs-GaAs

We have investigated tunable distributed-feedback (DFB) lasers based on GaInNAs quantum wells grown by molecular-beam epitaxy. Three-section tunable DFB lasers were fabricated by patterning laterally gain coupled binary superimposed gratings perpendicular to a ridge waveguide. The discrete tuning range covers 24 nm with sidemode suppression ratios of about 35 dB. The lasers were tuned continuously over a range of over 10 nm with a constant power output of 15 mW per facet.     

Realization and wafer test of InGaAsP/InP DFB laser/monitor OEICs

Wafer-testable distributed feedback (DFB) lasers and monolithically integrated monitor diodes are realized to replace the time consuming and expensive single-chip test procedure in semiconductor laser fabrication process. Laser-end facets and integrated monitor diodes are defined on 1.5-μm InGaAsP/InP multiple quantum well (MQW) DFB laser wafers by reactive ion beam etching (RIBE). Using terminal electrical noise (TEN) measurement, the lasers are characterized directly on the wafer with respect to threshold current and single mode operation. Threshold currents down to 10 mA have been achieved for the integrated devices     

InAs-InAlGaAs quantum dot DFB lasers based on InP [001]

The InAs-InAlGaAs quantum dot (QD) lasers with the InAlGaAs-InAlAs material system were fabricated on distributed feedback (DFB) grating structures on InP [001]. The single-mode operation of InAs-InAlGaAs QD DFB lasers in continuous-wave mode was successfully achieved at the emission wavelength of 1.564 /spl mu/m at room temperature. This is the first observation on the InP-based QD lasers operating around the emission wavelength window of 1.55 /spl mu/m. The threshold current density of the InAs-InAlGaAs QD DFB laser with a cavity length of 1 mm and a ridge width of 3 /spl mu/m, in which one of the cleaved facets was coated with 95% high-reflection, was 1.23 kA/cm/sup 2/ (176 A/cm/sup 2/ for single QD layer). The sidemode suppression ratio value of the QD DFB laser was as high as 42 dB at the driving current of 100 mA.     

High-speed 1.5-μm compressively strained multi-quantum wellself-aligned constricted mesa DFB lasers

A great improvement in the high-speed characteristics for compressively strained multi-quantum-well (MQW) distributed-feedback (DFB) lasers with self-aligned constricted mesa structures is described. Negative wavelength detuning is an important factor in making possible the extraction of potential advantages for the compressively strained MQW DFB lasers. A 17-GHz bandwidth, which is the highest among the 1.5-μm MQW DFB lasers, is demonstrated. A wavelength chirp width of 0.42 nm at 10 Gb/s is obtained due to a reduced linewidth enhancement factor that has a magnitude of less than 2. Nonlinear damping K factor in a DFB laser with 45-nm negative detuning has drastically decreased to 0.13 ns, about half of that for unstrained MQW lasers. This is mainly due to an enhanced differential gain as large as 6.9×10 ^-12 m³/s. The estimated intrinsic maximum bandwidth is 68 GHz     

Static and dynamic simulation for ridge-waveguide MQW DFB lasers

An efficient and versatile computer-aided simulator for the design and analysis of ridge-waveguide (RWG) multiple-quantum-well (MQW) distributed-feedback (DFB) lasers has been developed and is presented. This simulator combines spectral index method and Green's function-based transfer-matrix method (TMM) to deal with the transverse RWG MQW structure and longitudinal DFB structure, respectively. It is capable of simulating both static and dynamic behaviors for a variety of RWG MQW DFB lasers. The major difference from most of the existing models and analyses is that this simulator is capable of linking important device characteristics with practical material and geometrical parameters directly and self-consistently. For instance, the effects of lateral ridge width, vertical MQW layers and longitudinal nonuniformity are all explicitly included in the simulator. important laser characteristics, such as L-I curve, effective linewidth enchancement factor, static lasing wavelength shift, spectral linewidth, facet-power spectrum, AM and FM modulation responses, dynamic-wavelength chirping, as well as longitudinal photon and carrier distribution, can be predicted based on material and waveguide parameters. Therefore, this simulator may be used as an efficient and versatile tool for the systematic exploitation and optimization of a wide range of practical RWG MQW DFB lasers. Analysis of a λ/4 shifted SCH RWG MQW DFB laser is performed to illustrate the capability of this simulator     

Distributed feedback InGaAsP/InP lasers with window region emitting at 1.5 µm range

Distributed feedback (DFB) InGaAsP/InP lasers with a window region formed at an end of the corrugated DFB region were made in order to overcome the problems inherent in the previous structures of DFB lasers with cleaved, sawed, etched, or AR-coated facets, or with an unexcited corrugation region. The window structure DFB lasers showed linear current versus output (I-L) curves, in contrast to those with a hysteresis or a kink appearing in a DFB laser with an unexcited region. Suppression of Fabry-Perot (F-P) resonances due to the two facets were sufficient enough to keep a single longitudinal mode property by DFB up to high excitation level. CW operation up to 65°C was achieved at the 1.5 μm wavelength range. Axial modes concerning the corrugated resonator were measured at about the threshold current. A stop band of a DFB laser was clearly observed with two dominant modes and much smaller submodes, which almost agreed with the axial modes predicted from a basic DFB theory.     

Laterally coupled strained MQW ridge waveguide distributed-feedbacklaser diode fabricated by wet-dry hybrid etching process

The fabrication and the characteristics of the laterally coupled GaInAsP-InP quantum-well ridge waveguide distributed-feedback (DFB) lasers are presented. The electron beam (EB) lithography and the wet and dry hybrid etching technique have been used to fabricate the deep grating structures for the DFB lasers on and beside the sidewalls of the narrow ridge waveguide. The threshold current was 18.5 mA at 20°C, and the sidemode suppression ratios (SMSRs) were ensured to be more than 40 dB for as-cleaved devices with various cavity lengths. The continuous-wave output powers of over 15 mW/facet have been observed, while transverse and longitudinal modes have remained in single mode at this output level     

Wavelength trimming by photoabsorption-included disordering for multiple-wavelength distributed-feedback laser arrays

In this letter, we describe a simple method to adjust the oscillation wavelength of distributed-feedback (DFB) lasers after the device fabrication without using any external active tuning. The method utilizes a permanent change of refractive index in the quantum well active layer induced by external laser beam irradiation. We have demonstrated 0.36 nm adjustment in a 1.55-/spl mu/m ridge waveguide DFB laser.     

GaInAsSb-AlGaAsSb distributed feedback lasers emitting near 2.4 /spl mu/m

We have investigated fabrication and characteristics of continuous wave (cw) GaInAsSb-AlGaAsSb distributed feedback (DFB) lasers in the 2.4-/spl mu/m range. Single-mode DFB emission is obtained without overgrowth by first order Cr-Bragg gratings on both sides of a laser ridge. The cw threshold currents for a cavity with a length of 800 /spl mu/m and a width of 4 /spl mu/m are around 30 mA. At 20/spl deg/C and at an injection current of 190 mA output powers of 8.5 mW were realized. Monomode emission with a side-mode suppression ratio (SMSR) of 33 dB has been obtained.     

Chirp reduction of directly modulated semiconductor lasers at 10Gb/s by strong CW light injection

The influence of strong light injection on the reduction of the dynamical linewidth broadening of directly current-modulated semiconductor lasers at high bit rates is theoretically investigated and experimentally verified for 10 Gb/s NRZ pseudorandom modulation with a large current swing of 40 mA pp. Significant chirp reduction and single-mode operation are observed for bulk DFB, quantum well DFB lasers at 10 Gb/s and a weakly coupled bulk DFB laser at 8 Gb/s, so that an improvement of the transmission performance using standard monomode fibers in the 1.55 μm low-loss wavelength region can be achieved for all these laser types, where dispersion otherwise causes severe penalties for long-haul transmission. The properties of injection-locked bulk DFB and quantum well DFB lasers with respect to high bit rate modulation have been systematically studied by the use of the rate equation formalism. A dynamically stable locking range of more than 30 GHz under modulation has been found for both laser types with injection ratios higher than 0.5     

Monolithic integration of multiple quantum well DFB lasers and electroabsorption modulators

Advanced fibre optics telecommunication systems rely on high performance components amongst which photonic integrated circuits (PICs) play a major role. In particular, there has been a growing need for low chirp optical sources, such as externally modulated distributed feedback (DFB) lasers. In this paper, the various monolithic integration schemes of multiple quantum well DFB lasers and electro-absorption modulators are reviewed and typical applications of these devices are briefly presented.     

Fabrication approach for antiphase narrow linewidth complex coupled 1.55 /spl mu/m DFB lasers

A new method for fabricating narrow linewidth antiphase complex coupled MQW DFB lasers by periodically etching the active layer and quarternary InGaAsP overgrowth is reported. The minimum linewidth for a 375 /spl mu/m long ridge waveguide laser is only 250 kHz at an optical output power of 4 mW.     

Low dispersion penalty and wide temperature range operation over120 K with 1.55 μm strained MQW-DFB laser module

STM 16 (2.488 Gbit/s) system operation over a wide DFB chip temperature range of more than 120 K (from -25°C to +95°C) is presented with dispersion penalty below 1 dB after transmission across 100 km standard fibre. DFB operation at 1.55 μm with a high sidemode suppression ratio of 40 dB is achieved within -40°C to +95°C. The lasers were realised using a BRS lateral structure and a quaternary InGaAsP MQW stack with six compressively strained quantum wells and a highly detuned DFB grating     

Effect of p-doping on the temperature dependence of differentialgain in FP and DFB 1.3-μm InGaAsP-InP multiple-quantum-well lasers

The temperature dependence of differential gain dG/dn for 1.3-μm InGaAsP-InP FP and DFB lasers with two profiles of p-doping was obtained from RIN measurements within the temperature range of 25°C-65°C. Experiments showed that the change of the active region doping level from 3·10¹⁷ cm^-3 to 3·10¹⁸ cm^-3 leads to a 50% increase of the differential gain for FP lasers at 25°C. Heavily doped devices also exhibit more rapid reduction of the differential gain with increasing temperature. The effect of active region doping on the energy separation between the electron Fermi level and electronic states coupled into the laser mode explains the observations. The temperature dependence of differential gain for DFB devices strongly depends on the detuning of the lasing wavelength from the gain peak     

The properties of MOVPE grown 1.3 μm DFB MQW lasers infilled with semi-insulating InP fabricated on semi-insulating substrates

The use of optoelectronic integrated circuits (OEICs) is now emerging as a practical technology for a variety of applications, particularly in advanced telecommunications. OEICs consist of a range of devices such as lasers, waveguides, modulators, amplifiers, transistors, detectors, etc. fabricated on the same substrate. When a semi-insulating substrate is used, these devices can be electrically isolated by channel etching, resulting in a low capacitance structure with reduced electrical interference between the subcomponents. One of the devices which is particularly advantageous for this type of integration scheme is the distributed feedback (DFB) laser. The laser can be made to function more efficiently by minimizing the current flowing outside the active region. This can be achieved by surrounding the active region with semi-insulating iron doped InP. This work describes for the first time, the MOVPE growth, fabrication, and device characterization of 1.3 um buried heterostructure DFB MQW lasers, which combine the advantages of using both a semi-insulating substrate and a semi-insulating infill region in the same device structure. The potential advantage of this design scheme is improved OEIC performance as a result of, reduced capacitance and electrical crosstalk, enhanced laser output power, higher speed, increased efficiency, wider operating temperature and reduced threshold current. The laser active region consists of 8 x 140 Å quantum wells of GalnAsP (λ = 1.3 μm) and 110 Åbarriers of GalnAsP (λ= 1.07 μm). Single mode 1.3 urn devices of length 250 μm operating at room temperature produced threshold currents of 8 mA, efficiencies of up to 25%, output powers of 18 mW at 80 mA (pulsed), and a frequency response greater than 12GHz. The parasitic capacitance was estimated to be less than 3 pF.     

Optical frequency spacing tunable four-channel integrated 1.55 mu m multielectrode distributed-feedback laser array

A four-channel integrated 1.55- mu m multielectrode distributed-feedback (DFB) laser array was fabricated using the metallorganic vapor-phase deposition/liquid-phase epitaxy (MOVPE/LPE) hybrid method. Simultaneous single-longitudinal mode operation was achieved in each multielectrode DFB laser on a single chip. Utilizing the frequency tunability of multielectrode DFB lasers, optical frequency spacings were controlled and set to within a few gigahertz. The drift of frequency spacings due to temperature fluctuation was in the range of +or-50 MHz for temperature control of +or-0.1 degrees .<>     

Long wavelength quantum well lasers: Synopsis of the RACE “AQUA” project: MOVPE/MBE/GSMBE for InGaAsP/InP and InGaAlAs/InP high speed MQW DFB lasers

The technological limits for ultra high speed devices are now rapidly expanding due to the use of quantum well (QW) materials. This new class of materials gives the opportunity of tailoring materials parameters by controlling geometries on an atomic scale. They look very promising as materials for lasers, detectors and transistors suitable even above 10 Gb/s. It will be demonstrated that state of the art MQW structures can be realized in both material systems, InGaAsP/InP and InGaAlAs/InP. Parallel lateral laser structures (e.g. SIBH, BRS and TBH) have been designed to take full benefit of QW technology. Ultimate reduction of parasitics, whilst using potential low cost fabrication technologies is the basis for achieving high bitrate (10 Gb/s) MQW lasers, even with the stronger damping in QW material. Using the DFB-SIBH laser structure 10 Gb/s large signal experiments are successfully performed with bulk, MQW and SLMQW lasers. Extremely low fall times of 44 ps are achieved. Additional MQW based improvements are observed such as: −3 times higher differential gain, increased output power (>110 mW), 2.5 times lower chirp (Δλ_−20dB = 0.40 nm at 10 Gb/s modulation), and 2 dB gain in power budget at 10 Gb/s digital transmission.