Wavelength Semiconductor Lasers Research Articles

Advance of optoelectronic devices for long wavelength optical fiber communication in china

Abstract The advance of optoelectronic devices for long wavelength optical fiber communication in China is reviewed. The main features of the long wavelength semiconductor lasers and photodetectors are presented.

Longitudinal-mode stabilization in semiconductor lasers with wavelength-selective feedback

In optical communication systems operating near the zero-dispersion wavelength of the fiber, the wavelength of semiconductor lasers should remain stabilized to minimize the effects of fiber dispersion. We analyze theoretically the requirements for mode stabilization when external dispersive feedback is used to select a longitudinal mode. The feedback bandwidth should be less than the external-cavity mode spacing to avoid the excitation of side modes corresponding to the longitudinal modes of the external cavity. By a suitable choice of laser parameters, a multimode laser can remain stabilized in the vicinity of the feedback-selected wavelength even when the free-running wavelength has drifted by more than 10 nm.

Effect of nonlinear gain reduction on semiconductor laser wavelength chirping

A simple wavelength chirping formula is presented which includes small nonlinearities in the net gain such as spectral hole burning. The two dominant terms are a laser-structure-independent derivative or ‘‘transient’’ chirp and a structure-dependent ‘‘adiabatic’’ chirp, each with distinctly different lightwave system consequences. The two chirp contributions are indirectly related through their mutual association with relaxation oscillations. Time-resolved spectral measurements on a number of different laser structures support the results.

Grating lenses for the semiconductor laser wavelength

Off-axis grating lenses and astigmatic grating lenses, designed for semiconductor laser wavelengths, have been fabricated by an electron-beam (EB) exposure system. High N.A. off-axis grating lenses with near-diffraction-limited operation were obtained. Grating lenses with a complex function, such as astigmatic lenses, are also available by EB lithography.

Enhancement of Kerr rotation with amorphous Si film

The enhancemant of the Kerr rotation angle with amorphous silicon film was investigated. Doping oxygen, nitrogen and carbon as impurity in a-Si films, the absorptance at the semiconductor laser wavelength becomes almost zero keeping high refractive index. With the a-Si film containing the impurities on magnetic film, large enhancement effect is achieved than that of dielectric film. With a-Si:24at%O films, θk becomes a large value of 80 min comparing with 25 min of Gd-Tb-Fe-Co single layer film. The \sqrt{R} \cdot \thetak was improved 2 times higher than that of single layer film.

Growth and device characteristics of short wavelength GaAs multiple quantum well lasers

There is widespread interest in the use of the quantum size effect to modify the operating wavelength of semiconductor lasers, particularly in the AlGaAs/GaAs system where there is the possibility of producing short wavelength devices suitable for optical information systems. High quality current injection quantum well lasers grown by molecular beam epitaxy (MBE) have been reported with well widths as thin as 60 Å producing emission down to about 820 nm. Further reductions in wavelength have only been achieved by the addition of Al to relatively wide wells in which the wavelength shortening due to the quantum size effect is small. In this paper we report on the growth and characteristics of AlGaAs/GaAs multiple quantum well (MQW) injection lasers with thin (≤55 Å) GaAs wells utilizing the quantum size effect alone to obtain emission in the visible region of the spectrum. Growth of these multiple layer structures was carried out in a laboratory designed MBE system with rapid automatic beam shuttering in order to obtain abrupt interfaces and good periodicity. High speed substrate rotation was used to ensure uniformity across the wafer. Accurate determination of well widths is essential for meaningful comparisons between calculated and measured wavelengths, especially when well widths are reduced to a few monolayers. The well widths were determined both from growth rate, calibrated by RHEED oscillations, and by electrochemical profiling of the cladding layers. The structures were processed into oxide stripe lasers to study 300 K emission wavelengths and threshold currents as a function of well width. Laser operation at 300 K has been obtained in all devices, and a device with 13 Å wells gave the shortest wavelength (704 nm) reported for an MQW injection device with GaAs wells. The 300 K emission spectra were compared with both the calculated n=1(e‐hh) transition for each device and the wavelength of this transition obtained directly by photovoltage spectra on some devices. We have found that the lasing wavelength differs from both the calculated and measured n=1(e‐hh) transition wavelengths by about 20 nm over the whole range of well widths studied. A strong dependence of threshold currents on number of wells has been observed.

Wavelength-change characteristics of semiconductor lasers and their application to holographic contouring

The dependence of double-heterostructure AlGaAs semiconductor laser wavelength on injection current and temperature was investigated by means of a Michelson interferometer. The lasers operated in a single longitudinal mode at 790 nm, permitting them to be applied to two-wavelength holographic contouring. Continuous change and discontinuous change by mode hopping were observed. The wavelength was continuously tunable by variation of injection current and temperature at rates of 0.0045 nm/mA and 0.070 mm/ degrees C, respectively. Discontinuties in wavelength change were observed to be integer multiples of the longitudinal mode spacing. Holographic contour fringes were interpreted given the measured variation in wavelength.

Long Wavelength Semiconductor Lasers for Optical Communications

Long Wavelength Semiconductor Lasers for Optical Communications

New low-loss liquid-core fibre waveguide

Low-loss liquid-core fibre-optical waveguides having a transmission loss of 10 dB/km has been made using commercially available glass tubing. The loss is less than 20 dB/km over a wavelength range of greater than 0.8–1.1 μm, and, at the semiconductor laser wavelength of 0.9 μm, has a value of 14 dB/km. This is the first low-loss fibre to be made using glass.