P.J.A. Thijs

High-performance 1.5 mu m wavelength InGaAs-InGaAsP strained quantum well lasers and amplifiers

Improved performance of 1.5- mu m wavelength lasers and laser amplifiers using strained In/sub x/Ga/sub 1-x/As-InGaAsP quantum well devices is reported. The device structures fabricated to study the effects of strained quantum wells on their performance are described. These devices showed TM mode gain, demonstrating the strain-induced heavy-hole-light hole reversal in the valence band. Lasers using these tensile strained quantum wells show higher and narrower gain spectra and laser amplifiers have a higher differential gain compared to compressively strained quantum well devices. Consequently, the tensile strained quantum well lasers show the smallest linewidth enhancement factor alpha =1.5 (compression alpha =2.5) and the lowest K-factor of 0.22 ns (compression K=0.58 ns), resulting in an estimated intrinsic 3 dB modulation bandwidth of 40 GHz (compression 15 GHz). >

Polarization insensitive multiple quantum well laser amplifiers for the 1300 nm window

A polarization insensitive (less than 1 dB gain difference over the 3 dB gain bandwidth) multiple quantum well laser amplifier for the 1300 nm window is reported for the first time. The amplifiers employ a single active layer containing three tensile strained and four compressively strained quantum wells and show a fiber to fiber gain of 16 dB at 1310 nm and 200 mA driving current. Furthermore at the same wavelength these devices have a record low fiber coupled noise figure of 6.5 dB and a conveniently high fiber coupled saturation output power of 13 dBm for both polarizations.

Reduced intermodulation distortion in 1300 nm gain-clamped MQW laser amplifiers

A 1300 nm gain-clamped DFB multiple quantum well laser amplifier with negligible pass band ripple, 20 dB fiber to fiber gain, and 10 dB reduction in gain saturation is demonstrated. The remaining gain saturation is attributed to longitudinal hole burning. After some modifications the reduction in gain saturation is improved to more than 30 dB for an input signal having the same polarization state as the lasing mode. From these experiments and a theoretical analysis it is concluded that there is a potential for realizing highly linear 1300 nm CATV semiconductor laser amplifiers using gain-clamping with less intermodulation distortion than todays directly modulated linear semiconductor lasers.<<ETX>>

High-performance /spl lambda/=1.3 /spl mu/m InGaAsP-InP strained-layer quantum well lasers

Compressively and tensile strained InGaAsP-InP MQW Fabry-Perot and distributed feedback lasers emitting at 1.3-/spl mu/m wavelength are reported. For both signs of the strain, improved device performance over bulk InGaAsP and lattice-matched InGaAsP-InP MQW lasers was observed. Tensile strained MQW lasers show TM polarized emission, and with one facet high reflectivity (HR) coated the threshold currents are 6.4 and 12 mA at 20 and 60/spl deg/C, respectively. At 100/spl deg/C, over 20-mW output power is obtained from 250-/spl mu/m-cavity length lasers, and HR-coated lasers show minimum thresholds as low as 6.8 mA. Compressively strained InGaAsP-InP MQW lasers show improved differential efficiencies, CW threshold currents as low as 1.3 and 2.5 mA for HR-coated single- and multiple quantum well active layers, respectively, and record CW output powers as high as 380 mW for HR-AR coated devices. For both signs of the strain, strain-compensation applied by oppositely strained barrier and separate confinement layers, results in higher intensity, narrower-linewidth photoluminescence emissions, and reduced threshold currents. Furthermore, the strain compensation is shown to be effective for improving the reliability of strained MQW structures with the quantum wells grown near the critical thickness. Linewidth enhancement factors as low as 2 at the lasing wavelength were measured for both types of strain. Distributed feedback lasers employing either compressively or tensile strained InGaAsP-InP MQW active layers both emit single-mode output powers of over 80 mW and show narrow linewidths of 500 kHz. >

Improved performance of compressively as well as tensile strained quantum‐well lasers

The results of a theoretical study together with an experimental verification of the effects of strain on the laser characteristics of InxGa1−xAs/InGaAsP quantum‐well lasers are reported. It is shown that tensile strained quantum‐well lasers can perform as well as compressively strained lasers with respect to the threshold current density. Both show an improved performance when compared to the unstrained case. The origin of this improved performance is discussed.

Passive FM locking in InGaAsP semiconductor lasers

Passive FM locking of the longitudinal modes in MOVPE (metalorganic vapor-phase epitaxy)-grown InGaAsP semiconductor lasers due to four-wave mixing is discussed. Due to the locking, the lasing field closely resembles a single-frequency modulated wave with a modulation frequency equal to the cavity mode spacing of about 160 GHz, when the lasers are well above threshold. The existence of this FM wave is demonstrated by comparing the fundamental and the second-harmonic spectrum. A simplified analysis of the FM operation which explains the experimental data rather well is presented. >

Polarization resolved, complete characterization of 1310 nm fiber pigtailed multiple-quantum-well optical amplifiers

A new method allowing an automated, polarization resolved, complete characterization of fiber pigtailed semiconductor optical amplifiers is presented and discussed. The method is applied to a high performance, polarization insensitive 1310 nm strained layer multiple-quantum-well semiconductor optical amplifier. For this amplifier 36 dB fiber to fiber gain, a 3 dB gain saturation output power of 15 dBm and a noise figure of 6.5 dB are demonstrated and the polarization dependence of these key performance figures is clarified. The result is presented in a form which should enable the end-user to derive realistic performance figures which will be obtained for a fluctuating random input signal state of polarization.

Effect of free carriers on the linewidth enhancement factor of InGaAs/InP (strained-layer) multiple quantum well lasers

In this letter the linewidth enhancement factor measured from a tensile strained, a compressively strained, and a lattice matched InGaAs/InP multiple quantum well laser is analyzed taking free‐ carrier effects into account. We find that the free carriers in the wells of compressively strained and lattice matched structures degrade the linewidth enhancement factor by about 40% due to the plasma effect. In tensile strained TM polarized lasers however, carrier movement parallel to the E vector is inhibited due to the quantum confinement, allowing a linewidth enhancement factor as low as 1.6 at the peak wavelength. Heterobarrier carrier leakage must be prevented using sufficiently large band‐gap barrier and separate confinement layers, otherwise the free carriers in these layers result in an additional degradation of the linewidth enhancement factor.

High-gain 1310 nm semiconductor optical amplifier modules with a built-in amplified signal monitor for optical gain control

A compact high-gain 1310-nm semiconductor optical amplifier (SOA) module incorporating two photodiodes to detect radiation emitted from the two opposite facets of the amplifier chip is reported. By subtracting their signals, a measure of the amplified signal is obtained without the need for optical filtering, Using this, amplified signals can be stabilized within 0.5 dB over a 25-dB range of input signals.

27-dB gain unidirectional 1300-nm polarization-insensitive multiple quantum well laser amplifier module

An unidirectional polarization-insensitive multiple quantum well laser amplifier module for the 1300-nm window with a record high gain of 27 dB and a 3-dB saturation output power of 13 dBm is demonstrated. The module gain has a 3-dB width exceeding 60 nm and shows a typical polarization sensitivity and gain ripple as low as 0.3 dB. To provide immunity for backscattered or reflected light, polarization independent optical isolators were inserted in the input and output coupling optics of the package. A practical optical amplifier module for the 1300-nm window is very desirable, because most of the presently installed fiber has its zero dispersion wavelength around 1310 mm, while much of the older fiber often only can be operated around this wavelength.<<ETX>>