Selective-area MOCVD growth for distributed feedback lasers integrated with vertically tapered self-aligned waveguide

The growth pressure and mask width dependent thickness enhancement factors of selective-area MOCVD. grow th were investigated in this article. A, high enhancement of 5.8 was obtained at 130 mbar with the mask width of 70 mum. Mismatched InGaAsP (-0.5%) at the maskless region which could ensure the material at butt-joint region to be matched to InP was successively grown by controlling the composition and mismatch modulation in the selective-area growth. The upper optical confinement layer and the butt-coupled tapered thickness waveguide were regrown simultaneously in separated confined heterostructure 1.55 gm distributed feedback laser, which not only offered the separated optimization of the active region and the integrated spotsize converter, but also reduced the difficulty of the butt-joint selective regrowth. A narrow beam of 9degrees and 12degrees in the vertical and horizontal directions, a low threshold current of 6.5 mA was fabricated by using this technique. (C) 2003 Elsevier Science B.V. All rights reserved.

Experimental and numerical study on AlGaInAs/AlGaAs distributed feedback lasers with GaInP gratings

Ridge-waveguide AlGaInAs/AlGaAs distributed feedback lasers with lattice-matched GaInP gratings were fabricated and their light-current characteristics, spectrum and far-field characteristics were measured. On the basis of our experimental results we analyze the effect of the electron stopper layer on light-current performance using the commercial laser simulation software PICS3D. The simulator is based on the self-consistent solution of drift diffusion equations, the Schrodinger equation, and the photon rate equation. The simulation results suggest that, with the use of a 80 nm-width p-doped Al0.6GaAs electron stopper layer, the slope efficiency can be increased and the threshold current can be reduced by more than 10 mA.

Grating optimization and experiment on high-power distributed feedback lasers

Coupling coefficient is an important parameter for distributed feedback lasers. Modified coupled-wave equations are used to calculate the effect of grating shape on coupling coefficient of the second-order gratings. Corresponding devices demonstrate that the maximum kink-free power per facet reaches 50 mW and the sidemode suppression ratio is 36 dB.

Material growth and device fabrication of highly strained InGaAs/InGaAsP long wavelength distributed feedback lasers

1.6-1.7 mu m highly strained InGaAs/InGaAsP distributed feedback lasers was grown and fabricated by low pressure mentalorganic chemical vapor deposition. High quality highly strained InGaAs/InP materials were obtained by using strain buffer layer. Four pairs of highly strained quantum wells were used in the devices and carrier blocking layer was used to improve the temperature characteristics of the devices. The uncoated 1.66 mu m and 1.74 mu m lasers with ridge wave guide 3 mu m wide have low threshold current (< 15mA) and high output power (> 14mW at 100mA). In the temperature range from 10 degrees C to 40 degrees C, the characteristic temperature T-0 of the 1.74 mu m laser is 57K, which is comparable to that of the 1.55 mu m-wavelength InGaAsP/InP-DFB laser.

Coupling coefficients of gain-coupled distributed feedback lasers with absorptive grating

An effective coupling efficient is introduced for gain-coupled distributed feedback lasers with absorptive grating. When radiation and other partial wave coupling effects are considered, the effective coupling coefficient will change significantly. In some cases, it will become real, although both loss and index coupling are presented.

Offset quantum-well method for tunable distributed Bragg reflector lasers and electro-absorption modulated distributed feedback lasers

A two-section offset quantum-well structure tunable laser with a tuning range of 7 nm was fabricated using offset quantum-well inethod. The distributed Bragg reflector （DBR） was realized just by selectively wet etching the multiquantum-well （MQW） layer above the quaternary lower waveguide. A threshold current of 32 mA and an output power of 9 mW at 100 mA were achieved. Furthermore, with this offset structure method, a distributed feedback （DFB） laser was integrated with an electro-absorption modulator （EAM）, which was capable of producing 20 dB of optical extinction.

Low-threshold conjugated polymer distributed feedback lasers on InP substrate

We demonstrate a low threshold polymer solid state thin-film distributed feedback (DFB) laser on an InP substrate with the DFB structure. The used gain medium is conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV) doped polystyrene (PS) and formed by drop-coating method. The second order Bragg scattering region on the InP substrate gave rise to strong feedback, thus a lasing emission at 638.9nm with a line width of 1.2nm is realized when pumped by a 532nm frequency-doubled Nd: YAG pulsed laser. The devices show a laser threshold as low as 7 nJ/pulse.

Room temperature operation of photonic-crystal distributed-feedback quantum cascade lasers with single longitudinal and lateral mode performance

We demonstrate room temperature operation of photonic-crystal distributed-feedback quantum cascade lasers emitting at 4.7 mu m. A rectangular photonic crystal lattice perpendicular to the cleaved facet was defined using holographic lithography. The anticrossing of the index- and Bragg-guided dispersions of rectangular lattice forms the band-edge mode with extended mode volume and reduced group velocity. Utilizing this coupling mechanism, single mode operation with a near-diffractive-limited divergence angle of 12 degrees is obtained for 33 mu m wide devices in a temperature range of 85-300 K. The reduced threshold current densities and improved heat dissipation management contribute to the realization of devices' room temperature operation.

Design of surface emitting distributed feedback quantum cascade laser with single-lobe far-field pattern and high outcoupling efficiency

A 7.8-mu m surface emitting second-order distributed feedback quantum cascade laser (DFB QCL) structure with metallized surface grating is studied. The modal property of this structure is described by utilizing coupled-mode theory where the coupling coefficients are derived from exact Floquet-Bloch solutions of infinite periodic structure. Based on this theory, the influence of waveguide structure and grating topography as well as device length on the laser performance is numerically investigated. The optimized surface emitting second-order DFB QCL structure design exhibits a high surface outcoupling efficiency of 22% and a low threshold gain of 10 cm(-1). Using a pi phase-shift in the centre of the grating, a high-quality single-lobe far-field radiation pattern is obtained.

CONTINUOUSLY CHIRPED DFB GRATINGS BY SPECIALLY BENT WAVE-GUIDES FOR TUNABLE LASERS

We have implemented and studied a new type of tunable multiple-section semiconductor distributed feedback (DFB) laser using tailored chirped DFB gratings. Arbitrarily and continuously chirped DFB gratings are defined by bent waveguides on homogeneous grating fields with ultrahigh spatial precision, The mathematical bending functions are optimized in this case to provide enlarged wavelength tuning ranges. We present the results of model calculations, the technological device realization and experimental results of the DFB laser characterization e.g. a tuning range of 5.5 mm without wavelength gaps and high side mode suppression ratio.

1.3 mu m InGaAsP/InP strained layer multi-quantum-well complex-coupled distributed feedback laser

1.3 mu m strained-layer multi-quantum wells complex-coupled distributed feedback lasers with a wide temperature range of 20 to 100 degrees C are reported. The low threshold current of 10mA and high single-facet slope efficiency of 0.3mW/mA were obtained for an as cleaved device. The single mode yield was as high as 80%.

Control of the lasing wavelength by a sampled grating in a complex-coupled DFB laser

The lasing wavelength of a complex-coupled DFB laser is controlled by a sampled grating. The key concepts of the approach are to utilize the -1st order (negative first order) reflection of a sampled grating for laser single mode operation, and use conventional holographic exposure combined with the usual photolithography to fabricate the sampled grating. The typical threshold current of the sampled grating based DFB laser is 32 mA, and the optical output is about 10 mW at an injected current of 100 mA. The lasing wavelength of the device is 1.5356 mu m, which is the -1st order wavelength of the sampled grating.

Two-dimensional simulation of high-order laterally-coupled GaAs-AlGaAs DFB laser diodes

Laterally-coupled distributed feedback (LC-DFB) laser diodes made without an epitaxial re-growth process have the advantage of a simple fabrication process. In this paper, two-dimensional optical field distribution of the fundamental quasi TE (transverse electric) mode is calculated by means of a semivectorial finite-difference method (SV-FDM). The dependence of the effective coupling coefficient (kappa(eff)) on the dutycycle of first-, second- and third-order LC-DFB LDs is investigated using modified coupled wave equations.

Coupling coefficients of gratings with graded refractive index waveguides

In this paper, the effective coupling coefficient k(eff) and the self-coupling coefficient zeta(1) are introduced to describe the characteristic of gratings in a resonant situation when the effects of radiation and other partial waves coupling are considered. The dependence of these two coupling coefficients on grating tooth shapes and depths and the dimensions of graded refractive index (GRIN) waveguides is numerically analysed. The results show that the gratings with linear GRIN waveguides have the largest \k(eff)\. The possibility of realizing a complex-coupled DFB laser, even a pure gain or loss coupled DFB laser, employing only a real refractive index coupled grating is also discussed.

Single mode and multimodes lasing emission from MEH-PPV doped polystyrene thin films with surface ripples formed by vapour-induced phase separation

We report single mode and multimodes lasing emission from conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) doped polystyrene ( PS) thin films with surface ripples. Surface ripples were formed by water vapour-induced phase separation. A single mode lasing emission at 606 nm with a line-width of less than 0.4 nm was obtained. The laser threshold was as low as 3.5 mu J pulse(-1). The side mode suppression ratio was 5.76 dB. The periodic changes of the refraction index in the MEH-PPV : PS blending film due to the phase separation should be attributed to the lasing actions.