J. Wallin

74 nm wavelength tuning range of an InGaAsP/InP vertical grating assisted codirectional coupler laser with rear sampled grating reflector

A vertical-grating-assisted codirectional coupler laser with rear sampled grating reflector (GCSR laser) combines single-mode operation over a very wide tuning range of 74 nm with a side-mode suppression of better than 30 dB over most of the wavelength span. The total tuning span is limited by the combined bandwidths of the active material gain curve and the envelope of the sampled grating reflection peak spectrum, while the tuning capacity of the directional coupler filter alone is estimated to be at least 140 nm.<<ETX>>

Long-wavelength quantum-well infrared detectors based on intersubband transitions in InGaAs/InP quantum wells

In0.53Ga0.47As/InP infrared detectors with peak absorption at a wavelength of 8.5 micrometers have been fabricated and tested. It is shown that very high current responsivities and high gain are obtained. It is found that gain increases drastically when approaching detector voltages close to -8.5 V, which is explained by carrier impact excitation of electrons from the QW ground state to the excited extended state. The detectivity D* is about 1.2(DOT)1010 cm Hz1/2 W-1 at 80 K for a 45 degree(s) polished edge detector assuming unpolarized radiation. Grating coupling is studied by etching crossed gratings into the upper part of the mesas. The increase in responsivity as compared to a polished edge detector is by a factor of 2.5 to 3, irrespective to mesa sizes 500 X 500 or 150 X 150 micrometers 2. This gives a corresponding detectivity of (3 - 3.5)(DOT)1010 cm Hz1/2 W-1 at 80 K for unpolarized radiation.

Access to 20 evenly distributed wavelengths over 100 nm using only a single current tuning in a four-electrode monolithic semiconductor laser

We report improved tuning regularity in a vertical grating assisted codirectional coupler laser with a super-structure grating distributed Bragg reflector (GCSR). Access to 20 wavelengths with SMSR better than 20 dB within a tuning range of 100 nn was obtained with a single current control in a GCSR laser. The total tuning behavior shows a potential of complete wavelength coverage over 100 nm by use of three tuning currents.<<ETX>>

High-frequency GaInAsP/InP laser mesas in (-110) direction with thick semi-insulating InP:Fe

Growth of thick semi-insulating InP:Fe (Si-InP:Fe) current-blocking layers to reduce parasitic capacitance around (-110) directional laser mesas has been demonstrated for the first time. The regrowth is found to be equivalent to that around the normally used

DFB laser with nonuniform coupling coefficient realized by double-layer buried grating

A technique for the realization of a nonuniform grating coupling coefficient kappa , and its implementation in distributed-feedback (DFB) lasers is presented. This technique, which is an extension of the buried-grating concept, offers precise control of the coupling coefficient and enables a kappa -ratio greater than 10. DFB lasers with an asymmetric kappa -variation have been fabricated using this method. A front-to-rear facet output power ratio close to five was obtained, qualitatively in agreement with simulations.<<ETX>>

Wide continuous wavelength tuning of a narrow linewidth DBR laser

A continuous wavelength tuning range of 5.4 nm is obtained for a three-section DBR (distributed Bragg reflector) laser by applying one control current in both forward and reverse bias directions. In the reverse direction no significant linewidth broadening is seen due to the absence of injection-recombination shot noise, and a linewidth of less than 3 MHz is obtained over a wavelength span of 1.8 nm. The minimum linewidth observed is 580 kHZ.<<ETX>>

Improved spectral characteristics of MQW-DFB lasers by incorporation of multiple phase-shifts

The single-mode stability of strained-layer MQW-DFB lasers with electron-beam written gratings containing zero, one and three phase-shifts, and with a relatively large coupling strength, has been investigated theoretically and experimentally. The fabricated lasers with the multiple phase-shifted (MPS) structure exhibited a higher degree of stability than the /spl lambda//4-shifted lasers, and a considerably improved stability for both categories with phase-shifts compared to the nonshifted lasers was obtained. These results were in good agreement with our simulations. An investigation of the linewidths of the phase-shifted lasers is also presented. The MPS lasers had a significantly lower linewidth floor (down to 600 kHz) than those with one phase-shift. There was no degradation of the side-mode suppression-ratio correlated to the linewidth floor or rebroadening. A possible explanation for the lower linewidth floors obtained for the MPS lasers is that this structure is less sensitive to inhomogeneous carrier fluctuations. Longitudinal fluctuations in the shape of the photon density distribution will thereby be suppressed. >

Increased modulation bandwidth up to 20 GHz of a detuned-loaded DBR laser

A small signal amplitude modulation bandwidth of 20 GHz has been obtained with a three-section tunable DBR laser fabricated with semi-insulating current blocking layers grown by hydride VPE. The modulation bandwidth and laser linewidth are strongly dependent on the position of the lasing mode relative to the Bragg reflection peak.<<ETX>>

Evaluation of an automatic method to extract the grating coupling coefficient in different types of fabricated DFB lasers

Distributed feedback (DFB) laser parameters such as grating coupling coefficient, effective indices, facet reflectances, and the phases of facet reflectances have been determined using a method based on least-square fitting of theoretical spectra to measured, subthreshold DFB laser emission spectra. The only inputs needed are geometrical parameters such as length, grating period, and internal grating phase shifts. A larger number of devices have been successfully characterized, and consistent results have been obtained in both 1.3-/spl mu/m multi-quantum-well (MQW) DFB lasers with both facets as-cleaved, and in 1.55-/spl mu/m MQW DFB lasers with no, one, or two facets as-cleaved.

Regrowth of semi-insulating iron doped InP around reactive ion etched laser mesas in [110] and [-110] directions by hydride vapour phase epitaxy

Hydride vapor phase epitaxy (HVPE) has been used for regrowth of semi-insulating iron doped InP around reactive ion etched laser mesas in [110] and [-110] directions. The regrowth morphology and the electrical properties are similar in both cases. It is also demonstrated that HVPE is a quick and easy technique to realize buried heterostructure (BH) lasers in both [110] and [-110] directions.<<ETX>>