Roberto Paoletti

SPICE simulation for analysis and design of fast 1.55 /spl mu/m MQW laser diodes

A rate equation model for static and dynamic behavior of 1.55 /spl mu/m InGaAsP multiquantum-well (MQW) semiconductor lasers has been developed. A three level scheme for the rate equations has been chosen in order to model carrier transport effects. The introduction of quasi-two dimensional (quasi-2-D) gateway states between unbound and confined states has been used to calculate, for each well independently, carrier density and gain, allowing to take nonuniform injection into account. Starting from the formal identity between a rate equation and a Kirchoff current balance equation at a capacitor node, the model has been implemented on a SPICE circuit emulator, SPICE has granted an easy handling of parasitics and opens the possibility of integration with electrical components. The models parameters have been directly derived from a complete set of measurements on real devices. Thanks to this characterization and the model accuracy, we have obtained good agreement between simulations and experimental data. The model was finally used to improve both static and dynamic properties of MQW devices. Based on this optimization, compressive strained InGaAsP-InP MQW Fabry-Perot lasers were realized, achieving low threshold current, high efficiency, and more than 10 GHz of direct modulation bandwidth.

Highly reliable and high-yield 1300-nm InGaAlAs directly modulated ridge fabry-Perot lasers, operating at 10-gb/s, up to 110/spl deg/C, with constant current swing

Transceivers for 300 m multimode links, based on a serial 10 Gb laser source and incorporating receiver based electronic dispersion compensation (EDC) are creating the first high volume application for 10 Gb FP (Fabry Perot). A highly reliable and high yield uncooled ridge FP laser is presented. The device shows excellent power characteristics in the 25-150/spl deg/C temperature range with very high T0 (95 K in the temperature range 0-85/spl deg/C and still 78 K at 150/spl deg/C). Outstanding dynamic performances are also shown: 6 dB of extinction ratio can be achieved up to 110/spl deg/C, by using a constant current swing of 50 mA.

Comparison of optical and electrical modulation bandwidths in three different 1.55-μm InGaAsP buried laser structures

Static and dynamic characteristics of three different laser structures, by using the same active structure, have been investigated: (1) conventional BRS (Buried Ridge Structure), (2) p-n multi-junctions (MJ) blocking layers and (3) Fe-doped semi-insulating (SI) InP blocking layer. Good blocking properties in MJ and SI laser structures have been showed by measuring the DC leakage current and the linearity of the power versus current (P-I) curve, also at high operating temperature; SI laser, respect to BRS and MJ structures, has shown a large reduction in parasitic capacitance and a considerable improvement in modulation bandwidth, limited only by dynamic characteristic of active region.

High reliability, high-yield, high modulation bandwidth, low threshold current 1.55 /spl mu/m MQW laser by new in-situ etching technique

For the first time to our knowledge, an InP based Fabry-Perot MQW semiconductor laser is obtained by using an in-situ etching technique. Good static and dynamic laser characteristics together with high process yield and reliability confirm the validity of this new technological process.

Uncooled high-speed DFB lasers for gigabit ethernet applications

Uncooled DFB lasers directly modulated at 10 Gbit/s are a key devices for Optical communication systems operating at 10 Gbit/s, such as 10 Gbit Ethernet, since their effective use in optical transceivers to reduce cost, size and power consumption. The paper describe the current status of these sources (including well assessed InGaAsP MQW and recent progress for AlGaInAs MQW active layers), as well as the Agilents very recent results. Combining an optimized active region based on InGaAsP strained MQW (Multi Quantum Well) and a low parasitic lateral confinement region, we have fabricated 10 Gb directly modulated uncooled DFB lasers which represent, we believe, the state of art. Our DFB lasers work up to 100 degree(s)C (chip temperature), with eye diagram perfectly open (showing an extinction ratio > 5 dB), and with Bit Error Rate over 10 km without error floor. Up to 90 degree(s)C our DFBs show threshold current as low as 29 mA, optical power as high as 13 mW and meet perfectly 10 Gb scaled Ethernet mask with extinction ratio > 6 dB.

ADS equivalent circuit of direct-modulated high-speed DFB lasers

A rate equation-based model of MQW semiconductor lasers, has been developed describing power and chirp dynamics. The equations are implemented using an equivalent circuit approach, exploiting the analogy between rate equations and a Kirchoff current balance equation at a capacitor node. Current and voltages across the circuit components are equivalent to the main elements of the rate equations. This solution offers different advantages like the possibility to study the parasitic effects and the opportunity to integrate an high-speed laser model with an IC driver model in the same simulation environment. The model can be easily implemented in any circuit simulator (SPICE, Cadence, Agilent EESoft ADS). All parameters have been derived from measurements on real DFB devices. The model was used to improve static and dynamic performances of InGaAsP MQW-DFB laser 10Gb/s operations, as well as to study the problem of interfacing laser and IC driver. This optimization gave contributions to the realization of uncooled (up to 95°C chip temperature) DFB lasers directly modulated at 10 Gb/s for optical transceivers in 10Gb-Ethernet networks.

HDBR (hybrid distributed Bragg reflector) for WDM and OTDM applications

HDBR (Hybrid Distributed Bragg Reflector) laser (also called FGL - Fiber Grating Laser), has been recently demonstrated as low-chirp and potentially low cost lasers emitting at predetermined (ITU-T grid) wavelengths, as well as high quality picosecond pulses laser source. WDM transmission of three densely spaced directly modulated HDBR lasers at 2.6 Gbit/s over 117 km of standard fiber and the direct modulation at 10 Gbit/s have been demonstrated. By using appropriate cavity and grating design, we have realized, for DWDM applications, an HDBR laser that can be directly modulated at 10Gbit/s, while for OTDM systems, we have recently demonstrated a Mode-Locked HDBR laser source, for picosecond optical pulse generation at 10 GHz repetition rate.

Wavelength stabilized DBR high power diode laser using EBL optical confining grating technology

This paper reports a DBR High Power Diode Laser (DBR-HPDL) realization, emitting up to 10W in the 920 nm range. High spectral purity (90% power in about 0.5 nm), and wavelength stability versus injected current (about 5 times more than standard FP laser) candidates DBR-HPDL as a suitable device for wavelength stabilized pump source, and high brightness applications exploiting Wavelength Division Multiplexing. Key design aspect is a multiple-orders Electron Beam Lithography (EBL) optical confining grating, stabilizing on same wafer multiple wavelengths by a manufacturable and reliable technology. Present paper shows preliminary demonstration of wafer with 3 pitches, generating DBRHPDLs 2.5 nm spaced.

Optimization of InGaAsP/InP buried heterostructure DFB lasers for 10-Gbit/s operation up to 100°C

The optimization of a 1300nm buried heterostructure(BH)InGaAsP/InP DFB laser for uncooled directly modulated 10Gbit/s operation is described. The development process as well as the key process parameters are discussed and results are presented on an optimized structure. Bandwidths in excess of 10GHz were measured at 90C chip base temperature. Clean open eye diagrams were recorded over the full temperature range, resulting in error free transmission over 40km. To our knowledge the results represent the current state of the art for uncooled BH DFB lasers operating at 1300nm.

High stability package for hybrid distributed Bragg reflector laser source

We show the aspects that rule the design of a Hybrid Distributed Bragg Reflector (HDBR) package and a possible low cost solution with adhesives. We ensure single-mode behaviour in a operative range of 10/spl deg/C (17-27/spl deg/C) bending and fixing a tapered fiber to a very stable ceramic structure. The source at 1.55 /spl mu/m, suitable for direct modulation at 2.5 Gbit/s, exhibits a temperature dependence of 0.013 nm//spl deg/C (nearly one order of magnitude less than a typical DFB laser) and a static linewidth lower than 40 kHz at 1.5 mW output power, with Side Mode Suppression Ratio (SMSR) of 43 dB.