Gain-coupled DFB lasers with truncated quantum well second-ordergratings

Static and dynamic properties of in-phase gain-coupled multiple quantum well distributed feedback (DFB) lasers with second-order gratings have been measured at 1.55 μm. Devices with both facets antireflection coated and with a κL product between 4 and 5 have achieved a sidemode suppression ratio of over 63 dB. Relative intensity noise measurements have confirmed that the dynamic properties of second-order truncated well gain-coupled (GC)-DFB lasers are comparable to those with first-order truncated-well gratings     

Gain-coupled distributed feedback semiconductor lasers with anabsorptive conduction-type inverted grating

A gain-coupled (GC) distributed feedback (DFB) semiconductor laser with an absorptive conduction-type-inverted grating is proposed. Devices based on GaAlAs/GaAs materials are fabricated using two-step OMVPE. By inverting the conduction type of the absorptive region, threshold current is lowered by 10 mA, which is to compensate for the threshold increase due to extra absorption. In addition, nonlinear output property associated with the saturable nature of the absorption is eliminated. An ultralow chirping capability under gain switching high speed modulation and the narrow linewidth nature of this laser are experimentally studied     

Single-mode behavior of a circular grating for potentialdisk-shaped DFB lasers

The reflectivity and the resonance condition of a circular grating for a disk-shaped distributed-feedback (DFB) laser are calculated. The periodicity and the position of the grating are so chosen that all of the reflections from each refractive index step are superimposed in-phase so as to be consistent with the resonant behavior of the fundamental mode wave. The calculated wave impedance (E/H ) is almost purely imaginary in the central region of the grating for the higher modes     

Injection locking of broad-area angled grating DFB lasers

The injection locking properties of an angled-grating distributed feedback laser have been measured experimentally. Fringe visibility measurements were used to ascertain the quality of the phase lock between the master and slave laser as a function of master coupling level and frequency detuning. Experimental results show an asymmetric lockband with the stable lock region increasing in width as the coupling is increased     

Optically pumped surface-emitting DFB GaInAsP/InP lasers with circular grating

The lasing action in surface-emitting DFB lasers with circular grating (SE-CG DFB) is reported for the first time. 1.283 mu m laser oscillation is demonstrated by optical pumping. The threshold pumping power density is estimated to be 16.2 kW/cm/sup 2/. The pulsed output power is more than 25 mW.<>     

Gain-coupled DFB lasers versus index-coupled and phase shifted DFBlasers: a comparison based on spatial hole burning corrected yield

A statistical yield analysis is presented for gain- and index-coupled distributed feedback (DFB) laser structures, allowing a comparison of their single longitudinal mode (SLM) yield capabilities. For the yield calculations, the threshold gain difference and the longitudinal spatial hole burning (SHB) are taken into account. By comparing the experimental and theoretical yield of index-coupled DFB lasers, the significance of SHB for correct yield predictions is illustrated. For the purpose of comparison, yield calculations for various λ/4-shifted DFB lasers (with low facet reflectivities) are presented. The most emphasis, however, is on partly gain-coupled DFB lasers. Estimations of practical gain coupling coefficient values for gain and for loss gratings are discussed     

High device yield and performance of InGaAsP MQW DFB lasers with absorptive grating

AR/HR-coated, loss-coupled, InGaAsP multiple quantum well distributed feedback lasers emitting at 1.55 mum are reported, indicating a high device yield of ~66% for the quarter of a two-inch wafer and a good reliability as long as 5000 h operation at 85degC with a constant power of 5 mW. The high device yield was achieved by the automatically buried InAsP absorptive grating formed during the heat-up process on InP corrugations and the uniform surface-facing upward wet chemical etching process.     

Design and analysis of widely tunable sampled grating DFB laser diode integrated with sampled grating distributed Bragg reflector

A new widely tunable laser diode structure that requires only two tuning currents is proposed. The laser diode consists of a sampled grating distributed feedback (SGDFB) laser diode monolithically integrated with a sampled grating distributed Bragg reflector (SGDBR). The phase control sections are properly inserted between the grating bursts of the SGDBR and SGDFB sections for the discrete and continuous tuning. To confirm the feasibility of the new structure, the split-step time domain model is used. The simulation result for a particular design shows that the tuning range as wide as 27 nm is possible with side-mode suppression ratio exceeding 35 dB. Furthermore, the output power is larger than that from SGDBR laser diodes with similar parameters.     

基于SESAM的被动调Q光纤光栅掺铒光纤激光器

提出并研究了一种线性腔结构的基于 SESAM(半导体可饱和吸收镜)的被动调 Q光纤光栅掺铒光纤激光器,该激光器无需采用偏振控制器控制激光偏振态,简化了调 Q 激光器的结构。该激光器的中心波长为1549.975 nm,阈值功率为143 mW,斜效率为1.2%。当泵浦功率从149 mW增加到180 mW时,脉冲重复频率从5.431 kHz增加到9.778 kHz。当泵浦功率为155 mW时,激光脉冲的能量为5.6 nJ,重复频率为6.538 kHz,脉冲宽度为40μs。     

A tunable dual-wavelength fiber Bragg grating laser using an external-injected DFB laser

A tunable dual-wavelength fiber Bragg grating (FBG) laser based on a distributed feedback (DFB) laser injection is proposed and experimentally demonstrated. The wavelength spacing can be tuned by adjusting the operation temperature of the DFB laser. When the DFB works at 25 ℃, a dual-wavelength simultaneous oscillation at 1 549.67 nm and 1 553.44 nm with wavelength spacing of 3.77 nm is achieved. Our experimental results demonstrate the new concept of dual-wavelength lasing with a DFB laser injection and the technical feasibility.     

Analysis of surface-emitting λ/4-shifted DFB lasers with adistributed Bragg reflector

Threshold current density and differential quantum efficiency are analyzed for a surface emitting (SE) λ/4-shifted distributed feedback (DFB) laser consisting of alternating active and passive layers with a distributed Bragg reflector (DBR). It is shown that the threshold current density can be reduced by using the DFB action induced by alternating active and passive layers in the active region of the SE DFB laser structure, as compared to SE DBR lasers with a homogeneous active region. It is also shown that the differential quantum efficiency of the DFB laser with a DBR can be higher than that of conventional DBR lasers without increasing the threshold current density     

Sampled grating conventional DFB lasers with fabricability and high immunity to the spatial-hole burning

Sampled grating has been used to enlarge the allowed range of coupling coefficient for high spatial hole-burning corrected single-frequency yield in conventional index-coupled DFB lasers with 1%-80% mirror combination. Theoretical calculation using an effective-index transfer matrix method shows that the allowed range of coupling coefficient increases approximately by 20% in the proposed sampled grating distributed-feedback lasers (DFB) lasers compared with conventional ones. Thus, the tolerance to the coupling coefficient variation improves to the level typically achieved in grating fabrication. The improvement is attributed to the flattened axial photon distribution of gap modes, and therefore stability in other lasing characteristics can be expected.     

Narrow-stripe distributed reflector lasers with first-order vertical grating and distributed Bragg reflectors

Narrow-stripe 1.55-/spl mu/m wavelength distributed reflector lasers consisting of both distributed Bragg reflectors and vertical grating of the first Bragg order were fabricated. A low threshold current I/sub th/ of 2.8 mA, a differential quantum efficiency /spl eta//sub d/ of 28% from the front facet, and a submode suppression ratio of 44 dB were obtained for structures with a stripe width of 1.3 /spl mu/m and a cavity length of 150 /spl mu/m.     

Analysis of grating surface emitting lasers

An approach to the analysis of grating-coupled semiconductor lasers is presented. It is shown that there are only two resonant solutions when the grating has infinite extent. The solutions are either symmetric or antisymmetric about the center of the longitudinal coordinate system where the antisymmetric solution is nonradiating. The field in the grating layer is expressed in terms of grating eigenfunctions and rigorously matched to the boundary conditions at the waveguide interface. Solutions to the finite-length grating problem are expressed as linear combinations of the infinite-length solutions. It is shown that the two diffraction parameters in the coupled-wave equations are composed of sums and differences of the eigenvalues from the infinite-length problem     

Complex-coupled DFB lasers: advantages and drawbacks of gain andradiation loss grating

Two types of InGaAs-GaAs-AlGaAs complex-coupled distributed feedback laser structures grown by molecular beam epitaxy are compared. The first structure uses interrupted quantum wells (QW's) grown over a grating. Its properties strongly depend on the interface cleaning resulting in nonreproducible threshold current densities. The second structure includes three uniform QW's, the gain coupling being induced by the vertical radiation of the second order grating. This last structure has reproducible, low continuous wave threshold current densities (jth=300 A/cm²). The coupling strength and its origin are described for the two structures. Both structures have high mono-mode yield (>75%) and side-mode suppression ratios larger than 40 dB     

New diffraction grating profiles in InP for DFB lasers and integrated optics

A bilevel processing technique has been used to obtain sub-micrometer-period InP diffraction gratings. Novel cross-sectional grating profiles with depths of up to 4000 ? have been obtained which should facilitate the fabrication of more efficient Bragg devices.     

Modulation bandwidth of planar circular grating distributed Bragg reflector lasers

This paper presents an analysis of the 3-dB-modulation bandwidth in planar circular grating distributed Bragg reflector lasers. The theoretical model takes into account both the spatial hole burning effect and the transverse and longitudinal field distribution. That model allows the study of the influence of real structure parameters on the 3-dB-modulation bandwidth.     

DFB semiconductor diode laser frequency stabilization employingelectronic feedback and Bragg grating Fabry-Perot interferometer

A method for stabilizing the center frequency drift of a diode laser is described. The method employs electronic feedback of the frequency error signal and utilizes an in-fiber Bragg grating Fabry-Perot interferometer as a frequency discriminator. The measured standard deviation of the frequency drift of the heterodyne beat signal of two lasers was less than 16 MHz in a time of 2.5 h     

1.55 mu m index/gain coupled DFB lasers with strained layer multiquantum-well active grating

The fabrication and characterisation results of a novel 1.55 mu m index/gain coupled DFB laser with a strained-layer multiquantum-well active grating are reported. The laser exhibits very clear spectral features due to gain-coupling effects.<>     

Optimization of grating duty factor in gain-coupled DFB lasers withabsorptive grating-analysis and fabrication

Grating duty factor strongly affects the performance of gain-coupled (GC) distributed feedback (DFB) laser diodes with an absorptive grating. Through numerical analysis the authors have found an optimum value in the duty factor for their low threshold operation. The minimum threshold gain achievable at this optimum duty factor is found to be almost independent of the order of the grating. According to this prediction, the authors have fabricated GaAlAs/GaAs GC DFB lasers with a third-order absorptive grating where the grating duty factor has been made close to the theoretical optimum value. In 200-μm-long devices with both facets as-cleaved, low CW threshold current of 25 mA, external efficiency of 0.5 mW/mA, and SMSR as high as 45 dB have been obtained, which is qualitatively consistent with the analysis. High yield of single mode oscillation seems to be the result of the gain coupling