Transverse electric (TE) polarization mode AlGaInP/GaAs red laser diodes, especially with self-pulsating operation

Abstract

An AlGaInP / GaAs laser diode is disclosed in which the active region is made up of quantum wells that are sufficiently thin (less than 5 nm thick) that the transition energy increase due to quantum confinement of the carriers becomes significant. This allows the quantum well material composition to be selected for compressive strain so that the laser operates in the TE polarization mode, while still obtaining a transition energy of from 1.9-2.0 eV for 620-650 nm laser emission. Quantum barriers have sufficient thickness to confine carriers to the quantum wells. Self-pulsation may be obtained in a heterostructure that also includes a saturable absorption layer proximate to the active region and a ridge structure transversely confining absorption produced carriers in the central section of the absorber layer, while allowing lateral carrier diffusion to side regions where carriers are allowed to leave the absorber layer.

Description

Statement as to Rights to Inventions Made Under Federally-Sponsored Research and DevelopmentThis invention was made with government support under Contract No. 70NANB2H1241 awarded by the National Institute of Standards and Technology, Department of Commerce. The government has certain rights in the invention.TECHNICAL FIELDThe present invention relates to semiconductor diode lasers of the AlGaInP / GaAs material system which produce red (620-690 nm) laser emission, and also relates to laser diodes with compressively strained or lattice-matched active regions that operate in a transverse electric (TE) polarization mode. The present invention is especially directed to such laser diodes that have one or more saturable absorbing layers proximate to the laser active region to provide rapidly time-varying absorption of the light generated by the active region so as to exhibit a sustained, high frequency, self-pulsating mode of operation under a constant (dc) bias.BACKGROUND ARTSemiconductor...

AI Technical Summary

Benefits of technology

Because the increased effective bandgap energy of the quantum wells is obtained primarily through a decrease in well thickness to the point at which the contribution to the carrier energy states from quantum confinement of the carriers becomes significant, the material composition of the quantum wells can be selected to minimize or eliminate tensile strain of the quantum wells, and thereby achieve a TE mode of laser operation.

As a result of the increased quantum confinement energy and elimination of tensile strain in the active region's quantum wells, self-pulsating laser diodes with 620-650 nm wavelength, TE emission are obtained with significantly increased output power, and with self-pulsation operation up to higher operating temperatures compared to prior self-pulsating laser diodes in this wavelength range.

Problems solved by technology

Unfortunately, for the AlGaInP / GaAs material system it has been found that prior laser diodes of this type operate in the TE polarization mode only for the longer 650-690 nm emission wavelengths and that only the TM polarization mode is available for the shorter 620-650 nm wavelengths.

However, in such data storage systems, external reflective feedback typically occurs, in which some fraction of the emitted laser light is coupled back into the laser diode.

These phase variations in the feedback cause modal instabilities in the laser cavity, resulting in random fluctuations (i.e., noise) in the laser's output power.

Although this feedback sensitivity of the laser is also dependent to some extent upon the amplitude of the optical feedback, such that the noise in the emitted output of the laser could be reduced by using an optical design that minimizes the amount of reflected light coupling back into the laser, such a design normally requires completely separate illumination and collection optics, thereby leading to a much larger and heavier (and hence mechanically slower) read head containing such optics.

The high speed modulation renders the laser insensitive to feedback by destroying phase coherence between the reflected beam and the oscillating modes of the laser.

Unfortunately, the additional circuitry needed to bias and modulate the laser diode at high frequency considerably complicates the overall system and makes it much more expensive.

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