Conventional Laser Diodes Research Articles

Trace gas detection with short-external-cavity InGaAsP diode laser transmitter modules operating at 158 μm

Detection of CO(2) and CO at 1.58 microm (6322 cm(-1)) using an InGaAsP diode laser and mode control is described.Mode control is a technique whereby a short cavity, external to the laser, is used to force the laser to operate in a single mode. By monitoring the voltage across the terminals of the laser and using electronic feedback it is possible to optimize continually the external cavity so that the laser operates reliably in the mode of choice for scans >3.5 cm(-1). This technique offers the possibility of high-sensitivity detection over a region of ~30 cm(-1) with continuous coverage in overlapping sections of ~3 cm(-1) with conventional (and hence inexpensive) multimode diode lasers.

Carrier-induced refractive-index change in quantum-well lasers

We investigated the loaded gain and the carrier-induced refractive-index change in quantum-well lasers. A quantum-well laser is found typically to have a higher gain and a smaller refractive-index change than a conventional diode laser. We also found that the gain and the refractive-index change for these two types of semiconductor lasers saturate similarly, with the refractive index being a much weaker function of laser intensity.

Ultrafast switching characteristics of a bistable surface-emitting multiple quantum well distributed Bragg reflector laser

We describe an ultrafast switching operation of a bistable surface-emitting distributed Bragg reflector laser. The rise time was as small as 12 ps and the fall time was 90 ps. Both are much smaller than those of conventional bistable laser diodes. Ths was realized by the effect of the multiple quantum well structure and a strong detuning.

Voltage-controlled optical bistability associated with two-dimensional exciton in GaAs-AlGaAs multiple quantum well lasers

Voltage-controlled optical bistable laser operation is demonstrated for the first time using nonlinear optical absorption of two-dimensional excitons in a GaAs-AlGaAs multiple quantum well (MQW) laser. The laser used here is the conventional MQW laser diode but with tandem electrode configuration. The L-I curve of light output as a function of current injected into one segment of electrodes can be changed by a bias voltage applied to the other segment of electrodes. At the onset of laser oscillation, a hysteresis loop appears, the shape of which depends strongly on the applied bias voltage. This bistability is ascribed to the nonlinear absorption of two-dimensional excitons.

Anomalous length dependence of threshold for thin quantum well AlGaAs diode lasers

The threshold current in conventional semiconductor diode lasers decreases linearly with decreasing cavity length. We have found that for AlGaAs diode lasers fabricated from very thin active layer material, the threshold current can be essentially constant over a wide range of cavity lengths. At short cavity lengths, threshold increases dramatically. This anaomalous behaviour is attributed to physical mechanisms which become important when active layer threshold gain requirements become unusually high.

Etched-mirror unstable-resonator semiconductor lasers

The operation and performance of the first etched-mirror high-loss (ray unstable) semiconductor diode lasers are reported and discussed. This is an alternate approach to conventional plane-parallel stripe geometry diode lasers or monolithic laser arrays for obtaining improved mode control and higher power.

Realisation of flat FM response by directly modulating a phase tunable DFB laser diode

Flat and efficient FM responses in a wide frequency range were obtained by directly modulating the injection current of a 1.3 μm phase-tunable DFB-DC-PBH laser diode. The FM response is flat between 1 kHz and 300 MHz, and the nor malised frequency deviation is 1–3 GHz/mA, which is 5–10 times larger than that of a conventional laser diode in the several hundred megahertz region.

A Consideration of an Optical Coupler for Optical Submarine Transmission Laser Redundancy Systems

Theoretical and experimental results are described for a new optical coupler which consists of two laser diodes, two GRIN spherical rod lenses, a polarizing filter, and a single-mode fiber, and which employs laser diode polarization characteristics for an optical submarine transmission laser redundancy system. This optical coupler has two channels at 1.3 μm wavelength. Optical coupler loss values, which include coupling loss, polarization loss, and assembly loss, are 4.9 dB for one laser diode and 5.2 dB for another laser diode. Such loss values are almost the same as the conventional laser diode module loss for a single-mode fiber. This paper describes in detail a laser redundancy system in an optical submarine transmission system, structure and characteristics of an optical coupler, and experimental results on a high bit rate long-haul transmission system using the proposed optical coupler.

Dynamic behaviour of a GaAs-AlGaAs MQW laser diode

A comparative study is given on the dynamic properties existing between a GaAs-AlGaAs multi-quantum-well (MQW) laser diode fabricated from an MBE-grown wafer and a conventional double-heterostructure laser diode. Spectral broadening and wavelength shift associated with deep injection current modulation were found to be much smaller in MQW laser diodes than in conventional DH laser diodes.

Diode laser array excited star coupler suitable for Fibernet II

18- and 100-port fibre-optic coupler systems are driven by 10 emitter laser arrays capable of CW output powers in excess of 500 mW/facet. This source has advantages over both LEDs and conventional laser diodes, including insensitivity to feedback, no modal noise, ease of coupling and a very high launched power per output fibre.

Single-mode operation of a modulated laser diode with a short external cavity

Single longitudinal mode operation of a conventional laser diode is obtained under high bit-rate modulation by installing a 100 μm long external cavity. Oscillating mode can be selected in the range of about 30 Å by adjusting the external cavity length.

Stripe-geometry Pb<inf>1-x</inf>Sn<inf>x</inf>Te diode lasers

In order to avoid parasitic modes that frequently occur in conventional rectangular lead-chalcogenide diode laser structures, stripe junction lasers emitting at about 11 μm at 4.2 K have been fabricated from vapor-grown Pb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.88</inf> Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.12</inf> Te. Measurements of spectra, polarization, mirror illumination patterns, and far-field patterns provide conclusive evidence that these lasers emit in a fundamental spatial transverse mode. The emission spectra of the stripe lasers consist of regularly spaced modes corresponding to the longitudinal cavity with an effective index of refraction of 7.1. The measured width of the emitting region closely corresponds to the junction width both for the 50- and 100- μm-wide stripe lasers used. The depth of the emitting region perpendicular to the junction plane was measured to be approximately 50 μm in all of the lasers. As <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> S <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> dielectric coatings of various optical thicknesses have been sequentially applied to one end face in order to evaluate the gain and loss parameters of the active region from the threshold variation with reflectivity. Loss parameter values of 12-54 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , gain parameter values of 0.084-0.24 cm/A, and internal quantum efficiencies of 0.013-0.055 are deduced from these measurements. In addition, the antireflection coating produced as much as a fourfold increase in output power at currents above threshold.

Microwave self-modulation of a diode laser coupled to an external cavity

An external cavity coupled to a conventional Fabry-Perot GaAs diode laser operating continuously has been found to cause modulation of the light output at a frequency within the range 0.5 to several GHz. The modulation depth is close to 100 percent and the linewidth can be made as narrow as 180 kHz. The modulation is thought to be stimulated by the intensity noise fluctuations, which peak at the well-known spiking frequency f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> . The oscillations are strongly enhanced by a frequency locking action of the external cavity, being efficient when the external cavity round-trip time <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2L/c</tex> , or a multiple thereof, corresponds to the inverse of the spiking frequency. Since the latter is dependent on both pump current and temperature, the system can simply be tuned by adjusting the pump current. For a fixed resonator length, the narrow-band oscillations occur in a small current range, in which an increase in frequency with increasing current at a rate of 400 kHz/mA is observed. A small-signal analysis based on simple rate equations shows the influence of the external cavity on the intrinsic resonance frequency f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> . It demonstrates that self-modulation can only occur for small values of the coupling coefficient ε between the laser diode and the external cavity.