Showing papers on "Semiconductor optical gain published in 1979"

Lateral transverse mode instability and its stabilization in stripe geometry injection lasers

Abstract: A numerical analysis has been carried out on the behavior of semiconductor injection lasers with a stripe geometry double-heterostructure, taking into account spatial hole-burning and its effect on the waveguiding. It is shown that spatial hole-burning, the negative dependence of refractive index eta on the excited carrier density n (d_{eta}/ dn , and the lack of complete symmetry in any real laser structure are the three critical factors responsible for the lateral mode instability leading to such anomalous behaviors these lasers exhibit as a "kink" in the light output versus current relation and the lateral shift in the emission spot. Effects of rigid refractive index and gain-loss profiles built into the laser crystal on the mode stability have been examined, and conditions for kink-free, single lateral mode oscillations have been investigated.

Lateral mode behavior in narrow stripe lasers

Abstract: A theoretical and experimental description of the lateral mode behavior in oxide-insulated stripe geometry lasers with stripe width below 8 μm is given. The analysis is based on the waveguiding effects of carriers injected into the active region, and includes accurate, self-consistent solutions to the waveguide and carrier distribution equations. In agreement with experiment, wide ( \geq12 \mu m) near-field patterns and non-Gaussian far-field patterns are found for the fundamental mode. As the current is increased above threshold, the near fields become progressively wider and the far fields develop a twin peak structure. The optical properties of the output are dominated by a one-dimensional analog of spherical aberration. It is shown that high pulsed output power may be obtained in fundamental lateral mode without incurring catastrophic facet damage.

Nonplanar large optical cavity GaAs/GaAlAs semiconductor laser

Abstract: We report pulsed room‐temperature operation of a nonplanar large optical cavity semiconductor laser. As a result of a single LPE growth in an etched channeled substrate, a curved cavity is created which guides the laser light in both transverse dimensions. Representative lasers exhibit 50‐mA thresholds, 40% differential quantum efficiency, 25‐mW power output without kinks, and stable near‐ and far‐field optical patterns.

10 000-h continuous CW operation of In 1-x Ga x As y P 1-y InP DH lasers at room temperature

Abstract: Life tests of In1-xGaxAsyP1-y/InP DH lasers fabricated from

Optical gain spectra of InGaAsP/InP double heterostructures

Abstract: We report the first optical gain measurements on InGaAsP/ InP double heterostructures with composition corresponding to an emission wavelength of about 1.3 μm at 300 K. At optical pumping levels of about 1 MW/cm2the maximum gain values of the best samples available are 800 cm-1at 2 K, 500 cm-1at 77 K, and 200 cm-1at 300 K. We conclude from low-intensity luminescence and absorption spectra, that the laser transition corresponds to free-carrier recombination between band-tail states, which are present even in not intentionally doped material. Although these tail states result in rather broad low-intensity luminescence, narrow gain spectra comparable to those of GaAs/GaAlAs double heterostructures are obtained.

Near-threshold behavior of the intrinsic resonant frequency in a semiconductor laser

Abstract: The excitation-dependence of the resonant frequency intrinsic to a semiconductor laser is analyzed in terms of a spatially uniform laser model which takes into account radiative and nonradiative recombination as well as spontaneous emission into the lasing modes. The analysis reveals that the frequency of the resonance excited by internal quantum noise approaches a minimum value as the excitation level approaches threshold in contradiction to the behavior expected from a small-signal analysis of the external modulation spectrum or the relaxation oscillations. This distinctly different behavior of the noise-excited resonance is shown to result from the presence of noise fluctuations in the optical field, which are sensed only by the noise-excited spectrum. Experimental observations made with a stripe-geometry (AlGa)As double-heterostructure laser confirm the predicted behavior of the noise-excited resonant frequency in the near-threshold regime.

Electrooptically tuned external-cavity CW semiconductor laser and FM optical communications

Abstract: We report the operation of an external-cavity CW double-heterojunction GaAs injection laser that can be electrooptically tuned rapidly over a large spectral range (∼ 50 A) and experiments demonstrating the feasibility of FM optical communications using electronically tunable semiconductor lasers and CW and mode-locked dye lasers. An experiment on binary pulse-code FM optical communication is also reported and discussed.

Optical switching and bistability in tunable lasers

Abstract: We report the observation of optical switching and bistability, and such related effects as hysteresis, optical memory, multistability, and differential gain, in an electro‐optically tuned cw dye laser. Similar effects should be observable in other tunable lasers.

Simplified theory for mode locking in injection lasers

Abstract: Mode locking of semiconductor injection lasers is considered theoretically through the use of rate equations. The laser losses, rather than the material gain bandwidth, are found to limit the pulse width. Estimates for power output and the effects of spontaneous emission can be made

Spectral band homogeneous broadening and narrow-band emission of AlGaAs/GaAs injection lasers

Abstract: The influence of double-grating and single-grating external cavities on the spontaneous and stimulated emission of an injection laser has been investigated. The experiments show that homogeneous broadening is evident in semiconductor lasers. High resolution spectroscopic measurements indicate that single frequency emission is possible.

Influence of Structure Parameters on Lasing Characteristics of Semiconductor Lasers

Abstract: The influence of laser length l, stripe width w and facet reflectivity R on various lasing characteristics of AlGaAs–GaAs double hetero-structure semiconductor lasers is discussed experimentally, and the results are theoretically considered on the basis of the rate equations. It becomes clear that short cavity lasers with the high reflective facets are suitable for single longitudinal mode oscillation.

The phase shift of the light output in sinusoidally modulated semiconductor lasers

Abstract: The dependence of the phase shift of the light output from sinusoidally modulated semiconductor lasers was investigated as a function of the modulation current. This measurement is effective in accurately determining the short damping time constant associated with the relaxation oscillation. The frequency half width of this phase shift \Delta f was found to be inversely proportional to the damping time constant. For narrow stripe lasers, the phase shift occurs more gradually, which corresponds to the fact that the narrow stripe lasers have shorter damping time constants. To analyze the narrow stripe effect, the recently developed time-dependent self-consistent theory was applied, considering the transverse distribution of both optical field and carrier density and including the carrier diffusion term. This theory can explain the shorter damping time constant for narrow stripe lasers compared with broader stripe lasers.

Lateral waveguiding in stripe-geometry double-heterostructure lasers below the lasing threshold

Abstract: Structure in the far-field pattern of current-confined stripe-geometry double-heterostructure lasers in the angle range \pm 20\deg is observed at current levels of less than \frac{1}{4} of threshold value. The behavior is explained by leaky-mode guiding due to a gain maximum under the stripe and to a negative refractive index step on the order of -0.01.

Semiconductor luminous element

Abstract: PURPOSE: To obtain the composite semiconductor luminous element which is manufactured in high production yield and empolyed as a light source for modulation at high speed by modulating semiconductor laser by using an FET integrated and formed on the same substrate as the semiconductor laser. CONSTITUTION: The first∼third semiconductor layers 22∼24 are laminated on a semiconductor substrate 21 for growth. The first and third semiconductor layers 22, 24 have small refractive indices relatively and large prohibited band width relatively as compared to the second semiconductor layer 23. The both layers 22, 24 mutually form opposite conductive type laser oscillation semiconductor laminated regions and two pairs switch elements (FET); one side supplies said laser oscillation semiconductor regions with currents near laser oscillation threshold value, and the other side modulates laser rays by external input. Said switch elements are made up to the fifth semiconductor layer 26 forming the channels of FET sections through the fourth semiconductor layer 25 with high specific resistance on a semiconductor substrate. COPYRIGHT: (C)1981,JPO&Japio

3. Solid State Lasers

Abstract: Publisher Summary This chapter describes the energy levels and transition probabilities of solid-state lasers. The spectral range of solid-state lasers extends from approximately 0.5 to 3.0 pm, a wavelength factor of six. It is observed that for solid-state lasers, population inversion is achieved by optical pumping and is dependent upon the absorption spectrum of the laser ion in the host, the spectral match of this spectrum with the spectrum of the pumping source, the lifetime of the upper laser level, which determines the pumping rate required, and the quantum efficiency. The threshold for laser action involving vibronic transitions depends on the transition probability and the thermal Boltzman population in the terminal level. Optical transitions between electronic states of laser ions in solids, either that used for pumping or for stimulated emission, are predominantly of electric-dipole nature. Paramagnetic ions from several transition groups have been used for solid-state lasers. It is found that solid-state laser hosts include both ordered and disordered materials.

Semiconductor injection laser having a movable laser beam

Abstract: A semiconductor injection laser includes two contact regions on two oppositely-located major surfaces of the semiconductor body. One of these contact regions is divided into two sub-contact regions which are separated by a gap, and the active zone of the laser can be moved in a direction transverse to that of the laser beam by controlling the current distribution between the two sub-contact regions in order to move the laser beam.

Thermal properties of semiconductor lasers, and the interpretation of thermal-resistance measurements

Abstract: Conventional models of junction heating in semiconductor lasers have been considered, and are found to be inconsistent with the experimental observations on stripe-geometry double-heterojunction lasers. In particular, the onset of the thermal runaway of c.w. threshold current, induced either by increasing the heat-sink temperature or by degradation processes, is found to occur at a current much less than predicted theoretically. Part of the reason for these inconsistencies is that at high temperatures there is a departure from the commonly assumed exponential dependence of pulsed threshold on junction temperature. However, it is the observation that the temperature rise of the active region is not directly proportional to the input power which explains why the experimental results are so different from the theoretical predictions. The results are discussed with reference to a model of multiple heat sources, with sources assuming different relative importance as the input power increases.

Longitudinal mode competition in a pulse modulated AlGaAs DH semiconductor laser

Abstract: Mode competition in pulsed AlGaAs lasers, which oscillate in a few longitudinal modes, is studied by time resolved spectrum measurement. Only a single mode oscillates at a time; other modes are suppressed. Mode transition time is 30 ns which coincides with theoretical evaluation.

Mirror Reflectivity Dependence of Transverse-Modes in Semiconductor Lasers

Abstract: A new device construction of GaAs semiconductor lasers for optical transverse-mode control is reported. An antireflective coating is deposited partially on the right and left outer regions of the front facet of a laser in order to confine laser oscillation to the central narrow portion of the active layer, and to obtain a single transverse-mode. The laser oscillation in the coated regions was suppressed at currents up to 1.09 times of the threshold in the case of a photoresist coating, and up to 1.20 times in the case of a ZnO coating. An optimum reflectivity distribution in the front facet for transverse-modes is discussed.

Gain and optical extraction measurements in a pulser-sustained CO 2 laser

Abstract: Operational data on small-signal gain, gain profile, and optical power extraction is presented for a photoinitiated impulse-enhanced electrically excited (PIE) CO 2 laser. The measurements taken as a function of gas composition, input power loading, and flow velocity reveal a strong similarity to electron beam-sustained machines. The relatively simple construction and operational characteristics exhibited by the device may render it industrially viable.

Interpretation of frequency self-modulation of semiconductor laser radiation

Abstract: A physical model is used to explain deviation of the frequencies of longitudinal semiconductor laser modes observed in the case of amplitude self-modulation. The essence of the effect is that amplitude fluctuations are accompanied by synchronous fluctuations of the excess electron density and the latter influence the optical length of the resonator and longitudinal mode frequencies. It is shown that fluctuations of the electron density by 10–20% can give rise to a deviation comparable with the intermode separation in the radiation emitted from AlGaAs heterolasers at room temperature.

Optically coupling tunable diode lasers

Abstract: Proposed opticle coupling, using lenses and mirrors that replace complex mechanical systems, can combine separate tunable diode laser outputs and expand wavelength range. Method uses single cooler housing and requires no moving parts within cooler assembly.

Optical repeater using PFM at 1 GHz

Abstract: We report the first realization of PFM optical communication with a repeater station, using double heterostructure GaAs/GaAlAs semiconductor lasers. The system uses the property of semiconductor lasers for which the optical pulse rate can be locked by an external modulation of the injection current in the vicinity of the resonance frequency of the laser. This modulation scheme has the advantages of a high information rate capability by using the "spiking" resonance of the laser and, more importantly, of a simple repeater station in which another pulsing laser acts as a regenerative pulse amplifier.

Semiconductor laser with a holographic selector

Abstract: A study was made of a semiconductor laser with a holographic selector in an external resonator. The influence of the strength of feedback on the threshold characteristics , on the tuning range in the process of emission of a narrow spectral line, and on the coherence of the radiation was observed. The presence of a selector reduced the threshold current of a heterostructure laser by 26% without an antireflection coating on the end, a spectral line 0.015 nm wide was emitted for currents exceeding the threshold value by a factor of about 2.5, and the tuning range was 15 nm.

Observation of a dip in the spontaneous emission spectrum and a saturation of generation in single-mode semiconductor lasers

Abstract: We observed a dip in the spontaneous emission spectrum near the generation frequency. Threshold power for the dip occurrence, its width and dependence of width on intensity all permit us to interpret the effect as the formation of a gap in the electron energy spectrum. Saturation of single-mode generation is observed prior to threshold for occurrence of the second mode. Magnitude of threshold power and its quadratic dependence on photon lifetime in a cavity are in agreement with the kinetic laser theory.

Use of semiconductor lasers in geodesic interference measurements of distances

Abstract: A study was made of the use of semiconductor lasers in geodesic interference measurements of distances. Prototype experiments were carried out using a pulsed semiconductor laser operating at room temperature. The interferometer arms were equalized by determining the contrast maximum of the interference pattern on gradual reduction of the coherence length of the laser light source. The results indicated that it should be possible to simplify considerably the method and increase the precision of measurements of distances compared with the procedures employed at present.