In short-distance optical links, the development of driving circuits for vertical-cavity surface-emitting lasers (VCSELs) requires precise and computationally efficient VCSEL models. A small-signal model of a VCSEL is computationally efficient and simple to implement; however, it does not take into account the nonlinear output behavior of the VCSEL. In contrast, VCSEL models that are highly based on first principles cannot be implemented in standard circuit device simulators, because the simulation of eye diagrams becomes too time consuming. We present another approach using VCSEL models, which are based on the 1-D rate equations. Our analysis shows that they combine efficient extraction and short simulation time with an accurate calculation of eye diagrams over a wide range of ambient temperatures. As different implementations of the rate equations exist, tradeoffs between three different versions are presented and compared with measured GaAs oxide-confined VCSELs. The first model has a linear and the second a logarithmic function of the gain versus the carrier density. The third model considers the additional transport time for carriers to reach the active region with quantum wells. For parameter extraction, a minimum set of parameters is identified, which can be determined from fundamental measurements.
The temporal coupled mode theory is applied on the design of
filters and waveguide crossings that feature a resonator with
a high quality factor. To determine the transmission properties of the device we calculate the decay rate of the resonator. The analysis using the decay rates requires far less computational effort than conventional FDTD transmission calculations and therefore the
optimum device properties can be determined quickly.
Organic two-dimensional photonic bandgap structures (2D PBG) have been fabricated by spin-coating a thin polymer film onto a nano-patterned SiO2 circular-grating surface-emitting distributed Bragg reflectors (CG-SE-DBR). When optically pumped and for certain grating parameters, these structures exhibit a peak inside the stop band that
leads to lasing with a reduced threshold. An analytical model based on the transfer-matrix method has been developed to investigate the origin of this peak. The theoretical results are in excellent agreement with the experimental findings.
The development of optical interconnects in printed circuit boards (PCBs) is driven by the increasing bandwidth requirements in servers, supercomputers and switch routers. At higher data rates, electrical connections exhibit an increase in crosstalk and attenuation; which limits channel density and leads to high power dissipation. Optical interconnects may overcome these drawbacks, although open questions still need to be resolved. We have realized multimode acrylate-polymer-based waveguides on PCBs that have propagation losses below 0.04 dB/cm at a wavelength of 850 nm and 0.12 dB/cm at 980 nm. Transmission measurements at a data rate of 12.5 Gb/s over a 1-m-long waveguide show good eye openings, independent of the incoupling conditions. In the interconnect system, the transmitter and receiver arrays are flip-chip-positioned on the top of the board with turning mirrors to redirect the light. The coupling concept is based on the collimated-beam approach with microlenses in front of the waveguides and the optoelectronic components. As we aim for large two-dimensional waveguide arrays, optical crosstalk is an important parameter to be understood. Accordingly, we have measured optical crosstalk for a linear array of 12 optical channels at a pitch of 250 um. The influence of misalignment at the transmitter and the receiver side on optical crosstalk will be presented as a function of the distance between waveguide and transmitter/receiver.
This paper describes methods to control and manipulate birefringence in SiliconOxyNitride waveguides and devices.
Each method is demonstrated by measurements on example devices. The methods and devices that will be covered are:
Reduction of heater induced birefringence in a dynamic gain equalizer by heater design or etched trenches.
Reduction of polarization mode dispersion in a tunable dispersion compensator by UV trimming of residual
waveguide birefringence.
Polarization conversion using integrated optical half-wave-plates, fabricated by etching trenches at one side of
a waveguide.
Polarization splitting using waveguide sections with specified birefringence, obtained by etched trenches at
both sides of the waveguide.
Fast pulse-generating laser sources at 10 GHz are commercially available. For future communications system applications of these light sources at 40 GHz, we developed a passive, fully integrated optical 10 to 40 GHz time-domain multiplexer. This device is very compact (16×5 mm2) and robust, whereby its miniaturization and robustness are based on the high-index-contrast silicon-oxynitride (SiON) waveguide technology used. This 4X multiplexer consists of two cascaded asymmetric Mach-Zehnder structures. Thereby a total of three directional couplers and two delay lines of 50 ps and 25 ps, respectively, are cascaded. Because of the high SiO2-SiON index contrast of 3.8 % it was possible to realize a multiplexer device with bending radii of less than 1.0 mm in an ultra-compact double-folded design. The slightly unbalanced attenuation in the delay lines was pre-compensated by the directional coupler design, i.e. by detuning from 50 % : 50 % coupling ratio. We demonstrated experimentally that with a fundamentally mode-locked 10 GHz Er:Yb:glass laser source at the design wavelength of 1535 nm our 4X multiplexer produces a 40 GHz pulse train with < 0.22 dB pulse-to-pulse power variation and < 350 fs timing jitter. Although the current device is designed for 40 GHz, its principle can be applied to 160 GHz or higher, provided that suitable pulse sources are available.
The fabrication of etched mirrors for AlGaAs semiconductor lasers is described. The coating techniques for the passivation and reflectivity modification of the etched mirror surfaces are presented. Measurements on coated lasers show excellent beam quality, and satisfactory uniformity of laser characteristics across a wafer. Lasers which operate in a single transverse mode at output powers up to about 50 mW and have catastrophic optical damage (COD) thresholds greater than 120 mW have also been demonstrated.
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