Μm InGaAsP Laser Research Articles

Dependence of semiconductor laser linewidth on measurement time: evidence of predominance of 1/f noise

Linewidths of 1.3 µm InGaAsP lasers were measured by using delayed self-heterodyne set-ups with two different delay-line lengths, i.e. with two equivalent measurement times. It has been found that in high-power operation the linewidth increases as the measurement time becomes longer, and that this dependence is explained well by a calculation assuming that the 1/f noise in the FM noise spectrum is the predominant cause of the spectral broadening. The significance of this fact in coherent optical communications is discussed.

Measurement of nonlinear gain from FM modulation index of InGaAsP lasers

The contribution of nonlinear gain to the FM modulation index and relaxation oscillation damping factor for a multi-mode laser is calculated and measured. The nonlinear gain term obtained from the measured FM modulation index of a 1.3 μm InGaAsP laser is used to predict the optical intensity modulation response. Excellent agreement between prediction and observation are obtained.

1.55 μm InGaAsP low-threshold buried-crescent injection laser

Fabrication of 1.55 μm InGaAsP buried-crescent (BC) injection lasers with a p-n-p-n blocking structure is described. The BC lasers exhibit a threshold current as low as 14 mA at 25°C, very high yield, output power more than 10 mW and high-temperature operation up to 80°C. These BC lasers have continued to operate in stable CW mode at 50°C for more than 1000 h. The lifetime of the 1.55 μm InGaAsP lasers at 50°C is estimated to exceed about 2.5 × 104 h.

Intermodulation and harmonic distortion in InGaAsP lasers

A theoretical and experimental study is presented of intermodulation and harmonic distortion in high-speed 1.3 and 1.5 μm InGaAsP lasers modulated at frequencies up to 8 GHz. It is found that all lasers measured, including Fabry-Perot and distributed feedback lasers, generate approximately the same distortion levels for a given modulation depth and relaxation resonance frequency. There are minor differences between lasers, which result from differences in the damping of the small-signal resonance peak.

Improved high-temperature performance of 1.52 (μm InGaAsP laser diodes fabricated by two-step VPE and LPE

Continuous-wave operation up to 115°C has been achieved in 1.52 μm InGaAsP double-channel planar-buried-heterostructure laser diodes using two-step VPE and LPE. The high-temperature operation has been found attributable to the reduction in the leakage current bypassing the active region.

Measurement of radiative and nonradiative recombination rates in InGaAsP and AlGaAs light sources

A small signal method is used to measure the carrier lifetime as a function of injected carrier density, and the results are used to determine the radiative and nonradiative recombination rates for AlGaAs LED's and 1.3 μm InGaAsP lasers. For AlGaAs LED's the radiative recombination constant decreases with injected carrier density and the rate equation contains a small nonradiative Cn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> term. The low internal efficiency of 1.3 μm InGaAsP lasers is found to be primarily caused by two factors: a radiative coefficient <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B(n)</tex> which strongly decreases with the injected carrier density, and CHHS Auger recombination having a recombination coefficient of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-2 \times 10^{-29}</tex> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> /s. A recombination term representing carrier leakage is observed in some devices, but it is not the principal cause of low internal efficiency.

Exact Calculation of the Reflection Coefficient for Coated Optical Waveguide Devices

We derive an exact solution to the problem of the reflection coefficient for a coated slab waveguide. A series of computer calculations apply these results to a λ = 1.3 μm InGaAsP laser with an active area of 0.2 micron, an active area index of refraction of 3.51, and a cladding index of refraction of 3.22. Our results show that the correction due to the index step is a few percent for an uncoated laser. For antireflection coatings (reflectivity less than 1 percent), the correction due to the index step is significant. These results are important in choosing coating indices and thicknesses when minimum reflectivities are desired (e.g., for a superluminescent diode). The results, calculated over a range of indices of refraction of the coating, show that the TE and TM reflectivities are minimized at about the same value of the index, 1.84. However, the coating thicknesses at which the reflectivity is minimized are different for the TE and TM case. For example, when the TE reflectivity is minimized, the TM reflectivity exceeds the TE reflectivity by over two orders of magnitude.

Am quantum noise in 1.3 μm InGaAsP lasers

Intensity fluctuations for two types of 1.3 μm InGaAsP laser are measured and calculated based on device structural and material parameters and are found to be in good agreement with the quantum-noise-limited level.

Measurement of linewidth and FM-noise spectrum of 1.52 μm InGaAsP lasers

The linewidth of 1.52 μm InGaAsP lasers was measured as a function of the output power. The result shows that the linewidth is about 15 MHz when the output power is 1 mW. The FM-noise spectrum was also measured in the frequency range from 10 Hz to 100 MHz. The measured spectrum consists of the 1/f-noise and white-noise components. The linewidth calculated from the FM-noise spectrum is in good agreement with the measured value.

High-temperature operation of 1.55 μm InGaAsP double-channel buried-heterostructure lasers grown by LPE

High-temperature operation of InGaAsP double-channel buried-heterostructure (DCBH) lasers emitting at 1.55 μm is reported. The 1.55 μm InGaAsP DCBH lasers have threshold currents as low as 18 mA at 20°C. The threshold current temperature sensitivity between 10°C and 75°C is characterised by a T0 value of 55–66 K. Electro-optical derivative measurements show that the 1.55 μm InGaAsP DCBH laser does not have substantial above-threshold leakage current for junction temperatures as high as 75°C. Finally, these devices were operated at temperatures as high as 110°C, the highest CW operating temperature obtained to date for a 1.55 μm InGaAsP laser.

Semiconductor laser lineshape and parameter determination from fringe visibility measurements

The field autocorrelation function of single-mode 1.3 μm InGaAsP lasers has been measured using a Michelson interferometer. Comparison with theory for semiconductor laser line broadening yields the relaxation oscillation frequency, its damping rate and the linewidth broadening factor. A comparison with other techniques for lineshape measurement is presented.

Spectral hole burnings at high energy tails in spontaneous emission and hot carrier relaxation in InGaAsP lasers

Spectral hole burnings in spontaneous emission spectra from 1.3 μm InGaAsP lasers were found. The results are understood on the basis of population burnings of holes associated with the saturation of intervalence-band absorption. Theoretical results on hot carrier relaxation are shown to explain the population burnings, pointing out an importance of nonequilibrium optical phonon populations in the active layers of long wavelength InGaAsP lasers and light emitting diodes (LED's).

Saturable Inter-Valence-Band Absorptions in 1.3 µm-InGaAsP Lasers

Theoretical values of inter-valence-band absorption coefficients in long wavelength InGaAsP/InP lasers and their saturation characteristics obtained from acoustic measurements are shown. Spectral hole burning in spontaneous emission spectra from the 1.3 µm-InGaAsP lasers was found. The results are understood on the basis of population-burning of holes associated with the saturation of the inter-valence-band absorption.

Radiative and nonradiative recombination law in lightly doped InGaAsP lasers

We analyse data relating to radiative and nonradiative recombination in a 1.3 μm InGaAsP laser operating below threshold. The results show that with a lightly doped active region the radiative recombination coefficient decreases with increasing carrier concentration in accordance with previous theoretical results. Further, they indicate that the Auger nonradiative recombination is relatively small.

Measurement of radiative recombination coefficient and carrier leakage in 1.3 μm InGaAsP lasers with lightly doped active layers

Carrier lifetime and spontaneous emission data for InGaAsP lasers with lightly doped active layers are used to measure the carrier-dependent radiative coefficient B(n) and the leakage current due to electron drift. The Auger recombination coefficient is less than 0.1 × 10−28 cm6/s.

Gain measurements in 1.3 µm InGaAsP-InP double heterostructure lasers

The net gain per unit length ( G ) versus current ( I ) is measured at various temperatures for 1.3 μm InGaAsP-InP double heterostructure lasers. G is found to vary linearly with the current I at a given temperature. The gain bandwidth is found to decrease with decreasing temperature. The lasing photon energy decreases at 0.325 meV/K with increasing temperature. Also, the slope dG/dI at the lasing photon energies decreases with increasing temperature. This decrease is more rapid for T > \sim210 K. This faster decrease is consistent with the observed higher temperature dependence of threshold (low T 0 at high temperatures) of 1.3 μm InGaAsP lasers. A carrier loss mechanism, due to Auger recombination, also predicts that dG/dI should decrease much faster with increasing temperature at high temperatures. We also find that the slope dG/dI decreases slowly with increasing temperature for a GaAs laser, which is consistent with the observed temperature dependence of threshold of these lasers.

IIIA-4 a comparison of temperature dependence of lasing characteristics of 1.3 µm InGaAsP and GaAs DH lasers

IIIA-4 a comparison of temperature dependence of lasing characteristics of 1.3 µm InGaAsP and GaAs DH lasers

Band-to-band Auger recombination effect on InGaAsP laser threshold

The band-to-band Auger recombination effect on the threshold current in an InGaAsP laser is studied theoretically. An approximation method for the calculation is derived and the Auger lifetime is obtained numerically in the framework of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k-p</tex> perturbation method for band structure calculation. Gain factor and radiative lifetime are calculated by using Stern's method, which involves the band tailing caused by injected carriers. Calculated carder lifetime, quantum efficiency, and threshold current density for the 1.27 μm InGaAsP laser agree well with reported experimental values. The calculated characteristic temperature T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> and the break point temperature T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</inf> are compared with experimental values for InGaAsP lasers with a variety of compositions. The comparison shows that the Auger recombination is one of the dominant effects in determining the threshold current of InGaAsP lasers.

1.6 Gbit/s optical receiver at 1.3 μm with SAW timing retrieval circuit

The performance of a 1.6 Gbit/s optical receiver employing a s.a.w. filter as a timing tank is reported. The error-rate characteristics in a p.c.m. transmission system using a 1.3 μm In-GaAsP laser and single-mode fibres were studied. The average received optical power at a 10-9 error rate was -28 dBm. In a 15 km transmission experiment, the receiving level was degraded by 2 dB owing to fibre dispersion. Timing phase margin of 75 degrees after 12 km transmission was confined with the self-timed receiver.