J. Halonen

Analog modulation properties of oxide confined VCSELs at microwave frequencies

Motivated by the need for affordable, high-performance fiber-optic microwave links in fiber-fed microcellular networks and radar systems, we have performed a comprehensive experimental evaluation of the microwave modulation characteristics of high-speed oxide-confined vertical cavity surface emitting lasers (VCSELs) emitting at 840 nm. VCSELs with different oxide aperture diameters, including both single- and multimode lasers, have been used to track the dependence on modal behavior. The study includes both static and dynamic characteristics, with an emphasis on those of major importance for analog modulation. This includes the small-signal modulation response (S/sub 11/ and S/sub 21/), the relative intensity noise (RIN), and the intermodulation distortion. From this, we determine the spurious free dynamic range, the impedance characteristics, and the speed limitations.

Ultralow-Power Cryogenic InP HEMT With Minimum Noise Temperature of 1 K at 6 GHz

We present in this letter an InGaAs/InAlAs/InP high-electron-mobility transistor (InP HEMT) with record noise temperature at very low dc power dissipation. By minimizing parasitic contact and sheet resistances and the gate current, a 130-nm-gate-length InP HEMT was optimized for cryogenic low-noise operation. When integrated in a 4- to 8-GHz three-stage hybrid low-noise amplifier operating at 10 K, a noise temperature of 1.2 K ± 1.3 K at 5.2 GHz was measured. The gain of the amplifier across the entire band was 44 dB, consuming only 4.2 mW of dc power. The extracted minimum noise temperature of the InP HEMT was 1 K at 6 GHz.

Epitaxially regrown GaAs/AlGaAs laser mesas with semi-insulating GaInP: Fe and GaAs: Fe

Selective regrowth of semi-insulating iron-doped Ga0.51In0.49P (SI-GaInP:Fe) and SI-GaAs:Fe around GaAs/AlGaAs mesas by hydride vapor phase epitaxy (HVPE) has been achieved. A HCl based in-situ cleaning procedure has been used to remove aluminum oxide from the etched walls of the mesas. Regrowth conducted without proper cleaning results in an irregular interface with voids. Regrowth morphology aspects are also presented. Our cleaning and regrowth methods have been used for fabricating GaAs/AlGaAs buried heterostructure in-plane lasers and vertical-cavity surface-emitting lasers.

Nonlinear distortion and dynamic range of red (670 nm) oxide confined VCSELs

The analog modulation properties of oxide confined InGaAlP vertical cavity surface emitting lasers (VCSELs) emitting in the visible region (670 nm) are investigated. Two VCSELs with different oxide aperture sizes (10 and 18 /spl mu/m) were measured. The larger VCSEL exhibits a spurious free dynamic range as high as 92-100 dB/spl middot/Hz/sup 2/3/ in the frequency range 0.1-3 GHz while the smaller VCSEL exhibits a dynamic range of 88-94 dB/spl middot/Hz/sup 2/3/ in the same frequency range.

Performance characteristics of buried heterostructure VCSELs using semi-insulating GaInP:Fe regrowth

We have fabricated GaAs-AlGaAs buried heterostructure vertical cavity surface emitting lasers, emitting at 850 mm, using semi-insulating GaInP:Fe regrowth and investigated their static properties. Lasers of different size (10-21 /spl mu/m) have threshold currents in the range 2.8-7.0 mA, and produce a maximum output power of 1.7-6.0 mW at room temperature. The variation of threshold current with device size shows that the leakage current at the regrowth interface accounts for a significant part of the injection current. In spite of this, a differential quantum efficiency in the range 20%-30% is obtained which indicates that the regrowth interface is smooth and does not introduce any significant scattering loss. Studies of the transverse mode properties suggest that the GaInP provides weak guiding, resulting in single mode operation up to an output power of 0.7 mW and a beam divergence of only 60 for lasers as large as 10 /spl mu/m.

Nonlinear distortion reduction in transverse mode stabilized oxide-confined VCSELs

Fundamental mode operation has been achieved in a large area oxide-confined vertical-cavity surface-emitting laser (VCSEL) by etching a shallow surface relief in the top mirror. The nonlinear distortion during analog modulation has been measured and compared to the distortion in a planar multimode VCSEL. The distortion was quantified by conventional two-tone measurements from which the spurious free dynamic range was determined. Several decibels improvement in dynamic range was observed in the low frequency range (0.1-2 GHz) for the single-mode VCSEL. This is primarily due to a higher relaxation frequency and an absence of mode competition and mode partition noise in the single-mode VCSEL, indicating the advantages of using single-mode VCSELs for high-performance analog modulation.

Comparative study of the high-speed digital modulation performance of single- and multimode oxide confined VCSELs for free space optical interconnects

We have performed an extensive experimental study of the high-speed digital modulation characteristics of BCB-planarized oxide confined 850 nm VCSELs. In particular, we have compared the performance of single- and multimode VCSELs intended for high capacity free space optical interconnects. The digital modulation characteristics were evaluated by recording eye diagrams from 2 to 12 Gbit/s and measuring bit-error-rates (BER) at 10 Gbit/s. The single-mode VCSELs produce open and symmetric eyes at all bit rates and this behavior is maintained under large variations in bias current and modulation depth. For the multimode VCSELs, symmetric eyes can only be achieved under certain bias and modulation conditions. Both VCSELs allow for error free transmission at 10 Gbit/s. The receiver sensitivity at a BER of 1-9 under optimum bias and modulation conditions was -12.9 and -13.4 dBm for the single-mode and multimode VCSELs, respectively. The single-mode VCSELs produce near Gaussian beams ideal for free space optical interconnects where well defined and stable beams are needed for high efficiency and low cross-talk. The multimode VCSELs, on the other hand, have beam characteristics that are unpredictable and dependent on bias current, and are therefore less favorable for free space optical interconnects.

Cryogenic 0.5–13 GHz low noise amplifier with 3 K mid-band noise temperature

A 0.5–13 GHz cryogenic MMIC low-noise amplifier (LNA) was designed and fabricated using a 130 nm InP HEMT process. A packaged LNA has been measured at both 300 K and 15 K. At 300 K the measured minimum noise temperature was 48 K at 7 GHz. At 15 K the measured minimum noise temperature was 3 K at 7 GHz and below 7 K within the entire 0.5–13 GHz band. The gain was between 34 dB and 40 dB at 300 K and between 38 dB and 44 dB at 4 K.

Cryogenic low-noise InP HEMTs: A source-drain distance study

The scaling effect of the source-drain distance was investigated in order to improve the performance of low-noise InP HEMTs at cryogenic temperatures 4-15 K. The highest dc transconductance at an operating temperature of 4.8 K and low bias power was achieved at a source-drain distance of 1.4 μm. The extracted HEMT minimum noise temperature was 0.9 K at 5.8 GHz for a 3-stage 4-8 GHz hybrid low-noise amplifier at 10 K.

GaAs/AlGaAs buried-heterostructure laser diodes with semi-insulating GaInP:Fe regrowth

GaAs/AlGaAs buried-heterostructure in-plane lasers and vertical-cavity surface-emitting lasers using GaInP:Fe as the burying layer have been fabricated and investigated. Regrowth of GaInP:Fe around etched laser mesas was achieved by hydride vapor phase epitaxy. The lasers exhibit good performance under CW operation and show promising high-speed characteristics.