Plastic Fiber Communication Research Articles

Red and Near-Infrared III-Nitride Quantum Dot Lasers

InGaN/GaN self-organized quantum dots and similar dots in GaN nanowires are formed by strain relaxation and the luminescence from these nanostructures extends to longer wavelengths than generally obtained with quantum wells. We have exploited this advantage by incorporating these nanostructures in the gain region of edge-emitting diode lasers. Here, we describe the characteristics of 650 nm self-organized quantum dot lasers epitaxially grown on GaN and 1.3 μm dot-in-nanowire array lasers grown on (001) Si by molecular beam epitaxy. The devices are characterized by relatively low threshold currents, excellent temperature stability (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> > 200 K), and differential gain ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-16</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The highest measured small-signal modulation bandwidth of the dot-in-nanowire laser is 3.3 GHz. The experiments have been complemented by theoretical modeling of the self-organized quantum dots and lasers made with them. These new classes of devices open up new opportunities in applications such as displays, optical data storage, heads-up displays in automobiles, plastic fiber communication, and silicon photonics.

Small-signal modulation characteristics of a polariton laser

Use of large bandgap materials together with electrical injection makes the polariton laser an attractive low-power coherent light source for medical and biomedical applications or short distance plastic fiber communication at short wavelengths (violet and ultra-violet), where a conventional laser is difficult to realize. The dynamic properties of a polariton laser have not been investigated experimentally. We have measured, for the first time, the small signal modulation characteristics of a GaN-based electrically pumped polariton laser operating at room temperature. A maximum −3 dB modulation bandwidth of 1.18 GHz is measured. The experimental results have been analyzed with a theoretical model based on the Boltzmann kinetic equations and the agreement is very good. We have also investigated frequency chirping during such modulation. Gain compression phenomenon in a polariton laser is interpreted and a value is obtained for the gain compression factor.

Small signal modulation characteristics of red-emitting (λ = 610 nm) III-nitride nanowire array lasers on (001) silicon

The small signal modulation characteristics of an InGaN/GaN nanowire array edge- emitting laser on (001) silicon are reported. The emission wavelength is 610 nm. Lattice matched InAlN cladding layers were incorporated in the laser heterostructure for better mode confinement. The suitability of the nanowire lasers for use in plastic fiber communication systems with direct modulation is demonstrated through their modulation bandwidth of f-3dB,max = 3.1 GHz, very low values of chirp (0.8 Å) and α-parameter, and large differential gain (3.1 × 10−17 cm2).

Monolithic electrically injected nanowire array edge-emitting laser on (001) silicon.

A silicon-based laser, preferably electrically pumped, has long been a scientific and engineering goal. We demonstrate here, for the first time, an edge-emitting InGaN/GaN disk-in-nanowire array electrically pumped laser emitting in the green (λ = 533 nm) on (001) silicon substrate. The devices display excellent dc and dynamic characteristics with values of threshold current density, differential gain, T0 and small signal modulation bandwidth equal to 1.76 kA/cm(2), 3 × 10(-17) cm(2), 232 K, and 5.8 GHz respectively under continuous wave operation. Preliminary reliability measurements indicate a lifetime of 7000 h. The emission wavelength can be tuned by varying the alloy composition in the quantum disks. The monolithic nanowire laser on (001)Si can therefore address wide-ranging applications such as solid state lighting, displays, plastic fiber communication, medical diagnostics, and silicon photonics.

InGaN/GaN Quantum Dot Red $(\lambda=630~{\rm nm})$ Laser

Lasers emitting in the 600 nm wavelength range have gained attention for a number of important applications, including optical information processing, plastic fiber communication systems, optical storage, and full color (RGB) laser displays and laser projectors. Visible lasers are currently realized with GaN-based heterostructures having InGaN/GaN quantum wells as the gain media. The performance of these devices, particularly at longer wavelengths, is limited by materials inhomogeneity and effects related to a large strain-induced polarization in the quantum wells. A laser emitting in the red (λ ~ 630 nm) has not been realized. Here, we demonstrate lasers which emit at 630 nm, the longest wavelength achieved with the nitride system, by incorporating InGaN/GaN self-organized quantum dots as the gain media. Strain relaxation during dot formation results in reduced polarization fields and consequently low threshold current density, Jth=2.5 kA/cm2, small blue shift of the emission peak, very weak temperature dependenc eof Jth (T0=236 K), and linearly TE polarized output.

AlGaInP visible resonant cavity light-emitting diodes

Visible (670-nm) resonant cavity light-emitting diodes (RCLEDs) composed entirely of AlGaInP alloys are discussed. The devices consist of a strained quantum well optical cavity active region surrounded by AlInP/(AlGa)InP distributed Bragg reflectors (DBRs). The bottom DBR is a 60.5 period high reflector while the top partial reflector, which determines the emission linewidth, is a five-period output coupling DBR with a reflectance of about 57%. The devices exhibit linewidths of 4.8 nm (13.3 meV) at 300 K and are promising for plastic fiber communication systems and monochromatic displays. >

Visible (657 nm) InGaP/InAlGaP strained quantum well vertical-cavity surface-emitting laser

We report the first visible (657 nm) vertical-cavity surface-emitting laser. The photopumped undoped structure was grown using low-pressure metalorganic vapor-phase epitaxy in a single-growth sequence on misoriented GaAs substrates. The optical cavity consists of an In0.54Ga0.46P/In0.48(Al0.7Ga0.3)0.52 P strained quantum-well active region and a lattice-matched In0.48(AlyGa1−y)0.52 P (0.7≤y≤1.0) graded spacer region, while the distributed Bragg reflectors are composed of Al0.5Ga0.5As/AlAs quarter-wave stacks. Room-temperature optically pumped lasing was achieved with a very low-threshold power, clearly demonstrating the viability of this new technology. These results provide the foundation for visible semiconductor laser-diode arrays for a number of applications including laser projection displays, holographic memories, and plastic fiber communication.