D. L. Crawford

Ultrafast graded double‐heterostructure GaInAs/InP photodiode

Ultrafast graded double‐heterostructure GaInAs/InP p‐i‐n photodiodes grown by gas source molecular beam epitaxy have been fabricated on an InP semi‐insulating substrate. The graded band‐gap layers and the double heterostructure reduce carrier trapping effects and diffusion current and the resulting response of a 5 μm×5 μm device was measured by electro‐optic sampling to be 5 ps full width at half maximum (FWHM). The deconvolved impulse response is 3.8 ps FWHM.

Temperature dependence of the properties of DBR mirrors used in surface normal optoelectronic devices

The variation in the center wavelength of distributed Bragg reflectors used in optoelectronic devices, such as surface emitting lasers and Fabry-Perot modulators, is measured as the temperature of the mirrors changes over the range 25 degrees C to 105 degrees C. An analytic expression for the shift in center wavelength with temperature is presented. The mirrors measured are made of InP/InGaAsP ( lambda /sub gap/=1.15 mu m), GaAs/AlAs, and Si/SiN/sub x/. The linear shifts in center wavelength are 0.110+or-0.003 nm/ degrees C, 0.087+or-0.003 nm/ degrees C, and 0.067+or-0.007 nm/ degrees C for the InP/InGaAsP, GaAs/AlAs, and Si/SiN mirrors, respectively. Based on these data, the change in penetration depth with temperature is calculated.<<ETX>>

Comparison of bulk and quantum wire photodetectors

A theoretical comparison of the operating characteristics of p‐i‐n GaAs/AlGaAs photodetectors incorporating either bulk or quantum wire absorbing regions is presented in an effort to realistically compare both the bandwidth and the quantum efficiency of these devices. Devices utilizing quantum wire absorbing regions may have enhanced operating characteristics assuming increased absorption and saturated carrier drift velocities can be realized in these quantized structures.

High speed InGaAs/InP p-i-n photodiodes fabricated on a semi-insulating substrate

High speed, mass-produced InGaAs-InP p-i-n photodiodes have been fabricated on a semi-insulating substrate. The FWHM (full width at half maximum) impulse response of a 25- mu m/sup 2/ device has been measured to be under 16 ps, entirely limited by the measurement system. The high speed of this structure was achieved by scaling the area down to 25 mu m/sup 2/ and the intrinsic layer thickness down to 0.3 mu m. Further scaling of this structure is possible, and bandwidths in excess of 200 GHz should be achievable. This structure is also useful for integration with bias tees, matching networks, and optical and electronic preamplifiers.<<ETX>>

Design of 1.3-μm GaInAsP surface-emitting lasers for high-bandwidth operation

Important design considerations for high-speed GaInAsP 1.3-μm surface-emitting lasers are described. Modified rate equations for surface-emitting lasers and a small-signal analysis are used to calculate the frequency response versus the mirror reflectivity. For the structure analyzed, the results predict optimum reflectivities of 98% for high-frequency operation and maximum quantum efficiency. Strong gain-saturation effects are predicted owing to the high photon densities that occur in these devices. As the mirror thickness increases, the frequency response of the laser reduces greatly. The effect of heating is found to be important and is included in the analysis.

Ultrawide bandwidth 1.55-um lasers

This paper describes the essential elements for creating a practical wide bandwidth directly modulated laser source. This includes considerations of the intrinsic limitations of the laser structure, due to the resonant frequency and damping of the laser output, together with carrier transport issues to allow carriers in the device active region to be efficiently modulated at high speeds. the use of a P-doped compressively strained multiple-quantum well active region to provide high intrinsic speed and remove transport limitations is described, together with record setting results of 25 GHz modulation bandwidth for a 1.55 micrometer Fabry-Perot laser and 26 GHz bandwidth for a 1.55 micrometer DFB laser. The challenges of providing high bandwidth electrical connections to the laser on a suitable submount, together with fiber attachment and microwave packaging, are discussed. Results of fully packaged 1.55 micrometer DFB lasers with 25 Ghz modulation bandwidth are shown. Digital modulation of the packaged 1.55 micrometer DFB including impedance matching is described, and the transient wavelength chirp is presented. This low chirp is reduced further using an optical filter, to provide a 10 GBit/s source with chirp similar to that of an external electroabsorption modulator.

High speed photodetectors

High speed photodetectors are required for use in high speed optical interconnects. Recent results on high speed photodetectors are reviewed, and devices with important implications for future high speed photodetector operation are considered.

Temperature dependence and material properties of InGaAsP/InP mirrors

The authors have measured and modeled the temperature characteristics and material properties of quarter wavelength mirrors made using InP and InGaAsP. The center wavelength of the mirror moves at 0.110 nm/ degrees C, in good agreement with the theory. This is an important result for the thermal design of such devices as VCSELs. This result can be used to find the shift in the resonant mode of the cavity or the change in penetration depth of the mirror with temperature. The authors have also characterized the reflectivity and bandwidth of this mirror as a function of the number of layers. Using selective wet chemical etchants, they removed one layer at a time and then measured the spectrum of the mirror. From this structural analysis, it was found that the center wavelength is much more sensitive than the bandwidth or peak reflectivity in detecting drift in layer thicknesses. This technique can be used to find the actual reflectivity for different numbers of layers without resorting to several expensive, time-consuming mirror growths. The measured reflectivity and bandwidth are in good agreement with theory.<<ETX>>

Design of high speed GaInAs/InP p-i-n photodetectors

The material and design constraints for high speed InGaAs/InP p-i-n photodetectors and the operation of such devices are discussed. The photodetector wafer was grown on

GaInAs PIN photodetectors on semi-insulating substrates

An InGaAs/InP PIN photodiode integrated with 50 ohms coplanar waveguides has been fabricated on a semi-insulating substrate for high-speed operation. This photodetector exhibits a system limited impulse response of 16 ps, which is considered to be the fastest measured impulse response reported to date for these devices.