E. Zielinski

Polarization-independent and ultra-high bandwidth electroabsorption modulator in multiquantum-well deep-ridge waveguide technology

Electroabsorption modulators with polarization-independence of transmission (TE/TM sensitivity <0.4 dB at 1550 nm) over a wide wavelength range from 1540-1560 nm have been realized using tensile-strained InGaAs and InGaAsP quantum wells. Both designs show 42-GHz modulation bandwidth with a high bandwidth-to-drive-voltage ratio of >23 GHz/V. Polarization insensitivity of modulator transmission and chirp is demonstrated. Technical realization has been done in ridge waveguide technology with low-pressure MOVPE, reactive ion etching (RIE) for semiconductor etching and polyimide for planarization.

MOVPE of In(GaAs)P/InGaAs MQW structures

Abstract We report on MOVPE growth of In(GaAs)P/InGaAs multi-quantum-well (MQW) structures. The growth was carried out at a reactor pressure of 20 hPa in an horizontal lamp heated cold wall reactor with rectangular inner liner tube using as group III elements TMIn and TMGa and as group V elements 100% AsH3 and PH3. Wedge transmission electron microscopy (WTEM), photoluminescence (PL) measurements at 2K and 300 K, and X-ray double crystal diffractometry (DCD) were used for characterization. WTEM technique demonstrates monolayer interfaces and an excellent periodicity of the structures. This is in addition proven by DCD measurements with satellite peaks up to the 8th order. Separate confinement MQW (SCMQW) laser structures with InGaAsP barriers were grown and fabricated to Broad Area (BA) lasers. As a best value we measured threshold current densities of 800 A/cm2. A graded refractive index separate confinement heterostructure (GRINSCH) MQW laser structure with 7 InGaAsP grading layers was also grown and showed very homogeneous laser results with a 20% increased quantum efficiency as compared to SCMQW structures.

Low-chirp highly linear 1.55 mu m strained-layer MQW DFB lasers for optical analog TV distribution systems

The design and realization of highly linear 1.5- mu m distributed-feedback (DFB) lasers for optical analog TV distribution systems based on dispersive single-mode fibers are reported. A simple and comprehensive model relating grating characteristics to laser chirp was developed and used for optimization of the DFB grating. The model predicts that lasers emitting at wavelengths located in the positive slope sections of the DFB-reflectivity-wavelength characteristic have higher resonance frequencies and reduced chirp. The lasers were realized by using strained-layer multiple quantum wells for high differential gain and low alpha factor, antireflection (AR) coating of one laser facet for reduction of internal photon density, and a special grating design for low spatial hole burning and chirp reduction. >

1.55 μm strained layer multiple quantum well DFB-lasers with low chirp and low distortions for optical analog CATV distribution systems

Abstract Strained layer multiple quantum-well 1.55 μm DFB-lasers with extremely low chirp and low intermodulation distortions were made. System experiments with transmission of more than 35 analog modulated TV and Radio carriers over 32 km of standard fiber were performed.

Mode-locked laser realized by selective area growth for short pulse generation and optical clock recovery in TDM systems

We report on monolithically integrated active/passive coupled cavity mode locked lasers for 1.55 micrometer realized by selective area growth technology of InGaAs(P) quantum wells. Mode locked FP or DBR lasers are fabricated with an integrated cavity comprising up to three different band gaps. The devices emit short light pulses at around 10 GHz repetition rate with pulse width down to 8.7 ps. A time-bandwidth product of 0.5 is achieved for mode locked DBR lasers. Active/passive integrated mode locked laser is used for generation of optical 10 GHz clock signal from optical 10 Gb/s PRBS RZ data stream injected into the laser cavity.

The sizes of coherent band states in semiconductors, derived from the Franz - Keldysh effect

Electroabsorption spectroscopy with small modulation voltages has been used to study coherent states above the gap of . At very low fields only excitonic effects are observed which disappear in fields as small as to become part of the Franz - Keldysh oscillations, the response of the continuum states. Different sets are observed for the three valence bands which vary with field in perfect accordance with theory. The range of oscillations, which at moderate fields extends over 0.5 eV, increases linearly with field and is directly related to the coherence length of the continuum states. The coherence length in the ternary sample is 160 nm, more than twice as large as in a quaternary sample and larger than the value derived from Stark ladder transitions in superlattices.

Monolithic mode locked DBR laser with multiple-bandgap MQW structure realized by selective area growth

The realization of novel monolithically integrated multiple-segment pulse laser sources in InGaAsP MQW technology is reported. The MQW layers for all functional sections of these devices, the modulator, the active (gain) and the passive waveguide, as well as the Bragg section were grown in a single selective area growth (SAG) step by LP-MOVPE on SiO/sub 2/ patterned 2 inch InP substrates. Due to a properly selected pattern geometry 3 different bandgap regions with smooth interfaces are thereby formed along the laser cavity. The more than 4 mm long DBR lasers which exhibit a threshold current as low as 30 mA were mode locked by an intra-cavity electroabsorption modulator applying a sinusoidal voltage at around 10 GHz. In this way an optical pulse train with pulse widths <13 ps (measured with a streak camera) and high extinction ratio was generated. A time-bandwidth product of 0.5 close to the Fourier limit is obtained. This device is very attractive for signal generation in 40 Gb/s OTDM transmission systems at 1.55 /spl mu/m wavelength.

Modelocking of interferometric Y-lasers in an external cavity

The first report on active modelocking of interferometric Y-lasers in an external cavity are reported. Pulse widths between 20 and 30 ps for 1.3- mu m and 1.55- mu m devices were achieved by modulation of the injection current synchronously to the external cavity roundtrip frequency. A time-bandwidth-product of 0.97 was determined for 1.55- mu m devices.<<ETX>>

Strained MQW DFB lasers for high speed digital and analog transmission

The advantages of SLMQW (strained-layer multiquantum well) lasers as compared to MQW and bulk lasers are shown. The successful application of SLMQW DFB (distributed feedback) structures to 10-Gb/s digital as well as to high-speed analog applications is reported.<<ETX>>

Highly linear 1.55/spl mu/m strained-layer MQW DFB Lasers for Optical Analog TV Distribution Systems

We have realized highly linear 1.55/spl mu/m DFB lasers with CSO as low as -67dBc, CM below -71dBc (BK450FO German TELEKOM), and low FM-response down to 70MHz/MAL by using strained-layer MQWs and an improved grating structure.