Silicon oxide-planarized single-mode 850-nm VCSELs with TO package for 10 Gb/s data transmission

In this letter, we report on an alternative method to fabricate a high-efficiency planar-type oxide-confined 850-nm vertical-cavity surface-emitting lasers (VCSELs). The planarized process of VCSELs was to use the silicon oxide as the buried layer. As a result, these devices with an oxidized aperture of 3 /spl mu/m in diameter exhibit a single-transverse mode behavior throughout the operation current range. In addition, the static characteristics of VCSELs at 300 K include a threshold current of 0.52mA corresponding to a threshold voltage of 2.2 V, a maximum single transverse-mode light output power of 1.13 mW at 4.5 mA, and an external differential quantum efficiency of 35%. On the other hand, this TO-packaged planar-type 850-nm VCSEL for back-to-back test shows a wide open along with symmetric eye diagram and could also pass the 10 Gb/s mask as operating at 10.3 Gb/s and 4 mA. Furthermore, the VCSEL can still keep the eye diagram open and symmetric after the 66-m multi-mode fiber transmission and has a power penalty of 6.6 dB because of fiber dispersion for 10.3 Gb/s data rate at a bit error rate of 10/sup -11/. These results confirm the excellent high-speed performance of SiO/sub x/-planarized VCSELs as compared to the polyimide-planarized VCSELs.     

High-speed Modulation of InGaAs: Sb-GaAs-GaAsP quantum-well vertical-cavity surface-emitting lasers with 1.27-/spl mu/m emission wavelength

1.27-/spl mu/m InGaAs: Sb-GaAs-GaAsP vertical-cavity surface-emitting lasers (VCSELs) were grown by metal-organic chemical vapor deposition and exhibited excellent performance and temperature stability. The threshold current changes from 1.8 to 1.1 mA and the slope efficiency falls less than /spl sim/35% as the temperature raised from room temperature to 70/spl deg/C. With a bias current of only 5 mA, the 3-dB modulation frequency response was measured to be 8.36 GHz, which is appropriate for 10-Gb/s operation. The maximal bandwidth is measured to be 10.7 GHz with modulation current efficiency factor (MCEF) of /spl sim/5.25 GHz/(mA)/sup 1/2/. These VCSELs also demonstrate high-speed modulation up to 10 Gb/s from 25/spl deg/C to 70/spl deg/C.     

Fabrication and Characteristics of high-speed oxide-confined VCSELs using InGaAsP-InGaP strain-compensated MQWs

This paper presents the fabrication and characteristics of high-performance 850-nm InGaAsP-InGaP strain-compensated multiple-quantum-well (MQW) vertical-cavity surface-emitting lasers (VCSELs). The InGaAsP-InGaP MQW's composition was optimized through theoretical calculations, and the growth condition was optimized using photoluminescence. These VCSELs exhibit superior performance with characteristics threshold currents /spl sim/0.4 mA and slope efficiencies /spl sim/0.6 mW/mA. The threshold current change with temperature is less than 0.2 mA, and the slope efficiency drops less than /spl sim/30% when the substrate temperature is raised from room temperature to 85/spl deg/C. A high modulation bandwidth of 14.5 GHz and a modulation current efficiency factor of 11.6 GHz/(mA)/sup 1/2/ are demonstrated. The authors have accumulated life test data up to 1000 h at 70/spl deg/C/8 mA.     

As/sup +/-implanted AlGaAs oxide-confined VCSEL with enhanced oxidation rate and high performance uniformity

We report the utilization of an As/sup +/-implanted AlGaAs region and regrowth method to enhance and control the wet thermal oxidation rate for 850-nm oxide-confined vertical-cavity surface-emitting laser (VCSEL). The oxidation rate of the As/sup +/-implanted device showed a four-fold increase over the nonimplanted one at the As/sup +/ dosage of 1/spl times/10/sup 16/ cm/sup -3/ and the oxidation temperature of 400/spl deg/C. 50 side-by-side As/sup +/-implanted oxide-confined VCSELs fabricated using the method achieved very uniform performance with a deviation in threshold current of /spl Delta/I/sub th//spl sim/0.2 mA and slope-efficiency of /spl Delta/S.E./spl sim/3%.     

Performance and Reliability of 12.5-Gb/s Oxide-Free 850-nm Mesa VCSELs

Oxide-free mesa vertical-cavity surface-emitting lasers (VCSELs) emitting at 850 nm have been designed for short reach datacom applications at data rates up to 12.5 Gb/s. The top distributed Bragg reflector is etched away creating a mesa that provides both current and photon confinement. The devices exhibit low threshold current and a donut-shaped far-field profile that is suited for transmission on both legacy and laser-optimized multimode fibers. Open eye diagrams with high margin are observed in on-wafer testing of 8-10 mum VCSELs at 10.3125 Gb/s over 5degC-95degC. Accelerated aging tests indicate a long device lifetime, with the time for a cumulative failure of 1% estimated to be 15 million h at 40degC for 12-mum VCSELs.     

High-Power and High-Speed Zn-Diffusion Single Fundamental-Mode Vertical-Cavity Surface-Emitting Lasers at 850-nm Wavelength

We demonstrate a high-performance Zn-diffusion single-mode 850-nm vertical-cavity surface-emitting laser, which has a low threshold current (0.5 mA), high differential efficiency (80%), high modulation current efficiency (8.2 GHz/mA), and can sustain the single fundamental-mode output with a maximum output power of 7.3 mW under the full range of bias currents. With this device we can achieve 10 Gb/s eye-opening at a low bias current (1.8 mA) and a peak-to-peak driving-voltage of 0.5 V, which corresponds to a very high data-rate/power-dissipation ratio of 6.5 Gps/mW.     

1.3-μm GaInAsN Vertical-Cavity Surface-Emitting Lasers by Oxide-Planarized and Surface-Relief Processes for Single-Mode Operation

In this letter, we investigate and characterize the 1.3-mum single-mode vertical-cavity surface-emitting lasers (VCSELs) with two GaInAsN strained multiple quantum wells as the active region. Surface relief technique and a thick silicon oxide were used for the spatial mode filtering and the planarization processing, respectively. The VCSELs with a 5-mum-diameter surface-relief aperture and a 12-mum-diameter oxide-confined aperture at room temperature exhibit a threshold current of 3 mA, a slope efficiency of 0.14 mW/mA, a maximum operation temperature of 90 degC, and a single-mode behavior. These VCSELs show a maximum light output power of 1 mW for the single fundamental mode with a transverse-mode suppression of more than 30 dB and also show a clear eye-opening feature operated at 2.488 Gb/s and 12.6 mA     

High-speed monolithically integrated silicon photoreceivers fabricated in 130-nm CMOS technology

A complementary metal-oxide-semiconductor (CMOS) monolithically integrated photoreceiver is presented. The circuit was fabricated in a 130-nm unmodified CMOS process flow on 2-/spl mu/m-thick silicon-on-insulator substrates. The receiver operated at 8 Gb/s with 2-dBm average input optical power and a bit error rate of less than 10/sup -9/. The integrated lateral p-i-n photodetector was simultaneously realized with the amplifier and had a responsivity of 0.07 A/W at 850 nm. The measured receiver sensitivities at 5, 3.125, 2, and 1 Gb/s, were -10.9, -15.4, -16.5, and -19 dBm, respectively. A 3-V single-supply operation was possible at bit rates up to 3.125 Gb/s. The transimpedance gain of the receivers was in the range 53.4-31 dB/spl Omega/. The circuit dissipated total power between 10 mW and 35 mW, depending on the design.     

High-speed digital modulation characteristics of oxide-confined vertical-cavity surface-emitting lasers-numerical simulations consistent with experimental results

The vertical-cavity surface-emitting laser (VCSEL) is a preferred light source for short-distance high-speed fiber-optic communication links. We simulate the digital modulation behavior of typical oxide-confined VCSELs under realistic working conditions with a comprehensive model that includes the detailed geometry when calculating the optical fields and that accurately accounts for the dynamic effects of carrier density and temperature on the modal distributions. The intrinsic output characteristics of single- and multimode VCSELs were studied as functions of bias and modulation depth under a 2/sup 7/-1 pseudorandom bit sequence current modulation at 2 and 10 Gb/s. The data were used to create numerical eye diagrams that show, e.g., the significant impact of the bit pattern history and the noise on the timing jitter in both single- and multimode VCSELs. For the single-mode VCSEL, the choice of the bias current and modulation depth was less critical due to its higher damping of the relaxation oscillations. The simulated VCSELs were fabricated and experimentally evaluated. The measured eye diagrams showed the same characteristic features as those in the simulations.     

1-Gb/s modulation characteristics of a vertical-cavity surface-emitting laser array module

Vertical-cavity surface-emitting lasers (VCSELs) are promising devices for low-cost optical data communications. We fabricated an 8-channel VCSEL array module that is easily push/pull-connected to a mechanically transferable (MT) fiber connector. Modal noise had little adverse effect on bit-error-rate (BER) performance. A BER measurement of 8-channel VCSELs recorded a sensitivity of less than -23.7 dBm at 1 Gb/s and BER=10/sup -11/.     

High performance selectively oxidized VCSELs and arrays forparallel high-speed optical interconnects

High-bandwidth single-mode selectively oxidized vertical-cavity surface-emitting laser (VCSEL) arrays operate at 980 nm or 850 nm emission wavelength for substrate or epitaxial side emission. Coplanar feeding lines and polyimide passivation are used to reduce electrical parasitics in top-emitting GaAs and bottom-emitting InGaAs VCSELs. To enhance fundamental single-mode emission for larger devices of reduced series resistance a surface relief transverse mode filter is employed. Fabricated VCSELs are applied in various interconnect schemes. InGaAs quantum-well based VCSELs at 935 nm emission wavelength are investigated for use in perfluorinated graded-index plastic-optical fiber (GI-POF) links. We obtain a 7 Gb/s pseudo random bit sequence (PRBS) nonreturn-to-zero (NRZ) data transmission over 80 m long 155 μm diameter GI-POF. We investigate data transmission over standard 1300 nm, 9 μm core diameter single-mode fiber with selectively oxidized single-mode GaAs and InGaAs VCSELs. We achieve biased 3 Gb/s and bias-free 1 Gb/s pseudo-random data transmission over 4.3 km at 830 nm emission wavelength where a simple fiber mode filter is used to suppress intermodal dispersion caused by the second order fiber mode. For the first time, we demonstrate 12.5 Gb/s data rate transmission of PRBS signals over 100 m graded-index multimode fiber or 1 km single-mode fiber using high performance single-mode GaAs VCSELs of 12.3 GHz modulation bandwidth emitting at λ=850 nm     

MOVPE-grown GaInNAs VCSELs at 1.3 /spl mu/m with conventional mirror design approach

1.3 /spl mu/m oxide confined GaInNAs VCSELs designed using the same design philosophy used for standard 850 nm VCSELs is presented. The VCSELs have doped mirrors, with graded and highly doped interfaces, and are fabricated using production-friendly procedures. Multimode VCSELs (11 /spl mu/m oxide aperture) with an emission wavelength of 1287 nm have a threshold current of 3 mA and produce 1 mW of output power at 20/spl deg/C. The maximum operating temperature is 95/spl deg/C. Emission at 1303 nm with 1 mW of output power and a threshold current of 7 mA has been observed from VCSELs with a larger detuning between the gain peak and the cavity resonance.     

Three-stage burst-mode transimpedance amplifier in deep-sub-/spl mu/m CMOS technology

A transimpedance amplifier, designed in a digital 120-nm CMOS technology, used as preamplifier for optical burst-mode receivers in passive optical networks is presented. A wide optical input power range of 27 dB can be handled with a variable transimpedance without stability problems by varying the open-loop gain by a factor of 115. Noise and stability analysis of the optical receiver are presented. Sensitivities of - 31.3 dBm at 622 Mb/s and - 28.6 dBm at 1.25 Gb/s with a bit error ratio of 10/sup -10/ and a pseudorandom bit stream of 2/sup 31/-1 are achieved with a power consumption of 88.5 mW.     

A high-speed 850-nm optical receiver front-end in 0.18-/spl mu/m CMOS

A high-speed optical interface circuit for 850-nm optical communication is presented. Photodetector, transimpedance amplifier (TIA), and post-amplifier are integrated in a standard 0.18-/spl mu/m 1.8-V CMOS technology. To eliminate the slow substrate carriers, a differential n-well diode topology is used. Device simulations clarify the speed advantage of the proposed diode topology compared to other topologies, but also demonstrate the speed-responsivity tradeoff. Due to the lower responsivity, a very sensitive transimpedance amplifier is needed. At 500 Mb/s, an input power of -8 dBm is sufficient to have a bit error rate of 3/spl middot/10/sup -10/. Next, the design of a broadband post-amplifier is discussed. The small-signal frequency dependent gain of the traditional and modified Cherry-Hooper stage is analyzed. To achieve broadband operation in the output buffer, so-called "f/sub T/ doublers" are used. For a differential 10 mV/sub pp/ 2/sup 31/-1 pseudo random bit sequence, a bit error rate of 5/spl middot/10/sup -12/ at 3.5 Gb/s has been measured. At lower bit-rates, the bit error rate is even lower: a 1-Gb/s 10-mV/sub pp/ input signal results in a bit error rate of 7/spl middot/10/sup -14/. The TIA consumes 17mW, while the post-amplifier circuit consumes 34 mW.     

Performance comparison of 850-nm and 1550-nm VCSELs exploiting OOK,OFDM, and 4-PAM over SMF/MMF links for low-cost optical interconnects

We experimentally compare the performance of two commercially available vertical-cavity surface-emitting laser diodes (VCSELs), a multi-mode 850-nm and a single-mode 1550-nm, exploiting on–off keying/direct detection (OOK/DD), and orthogonal frequency division multiplexed (OFDM) quadrature phase-shift keying (QPSK)/16-ary quadrature amplitude modulation (16QAM) with direct detection, over SMF (100 m and 5 km) and MMF (100 m and 1 km) short-range links, for their potential application in low-cost rack-to-rack optical interconnects. Moreover, we assess the performance of quaternary-pulse amplitude modulation (4-PAM), for the 1550-nm transmitter over SMF and MMF links and we compare it to the data-rate equivalent NRZ-OOK. The extensive performance comparison under various transmission scenarios shows the superiority of 1550-nm single-mode VCSEL compared to its multi-mode 850-nm counterpart. Moreover, OFDM/DD and 4-PAM in conjunction with low-cost, inexpensive VCSELs as transmitters prove to be an enabling technology for next-generation WDM, point-to-point, short-reach, SMF/MMF optical interconnects and potential candidates to substitute NRZ-OOK. Nevertheless, the sensitivity requirements are higher in that case, whereas these advanced, spectrally-efficient modulation formats become severely degraded when transmitted over MMF links, especially, when employing the inexpensive 850-nm VCSELs as transmitter. Finally, we compare the performance of the point-to-point links under investigation to the performance of a semiconductor optical amplifier (SOA)- based, scalable permutation switch fabric, the Optical Shared MemOry Supercomputer Interconnect System (OSMOSIS).     

Highly uniform and reproducible vertical-cavity surface-emitting lasers grown by metalorganic vapor phase epitaxy with in situ reflectometry

Vertical-cavity surface-emitting lasers (VCSELs) were grown by metalorganic vapor phase epitaxy. Excellent uniformity of Fabry-Perot cavity wavelength for VCSEL materials of /spl plusmn/0.2% across a 3-in diameter wafer was achieved. This results in excellent uniformity of the lasing wavelength and threshold current of VCSEL devices. Employing pregrowth calibrations on growth rates periodically with an in situ reflectometer, we obtained a run-to-run wavelength reproducibility for 770- and 850-nm VCSELs of /spl plusmn/0.3% over the course of more than a hundred runs.     

Degradation-robust 850-nm vertical-cavity surface-emitting lasers for 25Gb/s optical data transmission

Highly efficient fast vertical-cavity surface-emitting lasers (VCSELs) for the 850-nm spectral range, promising for the development of optical interconnections with a data transmission rate of 25 Gbit/s per channel, are fabricated and studied. Lasers with a selectively oxidized current aperture 6 μm in diameter demonstrate multimode lasing with a quantum efficiency of 35–45% and a threshold current of 0.5–0.7 mA in the temperature range 20–85°C. According to the results of small-signal frequency analysis, the maximum modulation frequency of the lasers exceeds 17 GHz, with the rate of its increase with current exceeding 9 GHz/mA^1/2, which provides VCSEL operation at a rate of 25 Gbit/s in the entire working temperature range. Endurance tests for 3000 h did not reveal any sudden degradation of the lasers. The optical power at working point and the threshold current changed relative to that at the beginning of the tests by no more than 5 and 10%, respectively.     

Low-cost, high-efficiency, and high-speed SiGe phototransistors in commercial BiCMOS

We present a new approach to obtain low-cost and high-performance SiGe phototransistors in a commercial BiCMOS process. Photoresponsivity of 2.7 A/W was obtained for 850-nm detection due to the transistor gain, corresponding to 393% quantum efficiency. Responsivities of 0.13 A/W and 0.07mA/W were achieved for 1060 and 1310 nm with SiGe absorption. With V/sub ce/=2 V, we measure a -3-dB bandwidth of up to 5.3 GHz for phototransistors with a 4-/spl mu/m/sup 2/ active area and 2.0 GHz for phototransistors with 60-/spl mu/m/sup 2/ active area and finger contacts. This high-efficiency and high-speed phototransistor is an enabling device for monolithic receiver integration.     

10-Gb/s limiting amplifier and laser/modulator driver in 0.18-/spl mu/m CMOS technology

A limiting amplifier incorporates active feedback, inductive peaking, and negative Miller capacitance to achieve a voltage gain of 50 dB, a bandwidth of 9.4 GHz, and a sensitivity of 4.6 mV/sub pp/ for a bit-error rate of 10/sup -12/ while consuming 150 mW. A driver employs T-coil peaking and negative impedance conversion to achieve operation at 10 Gb/s while delivering a current of 100 mA to 25-/spl Omega/ lasers or a voltage swing of 2 V/sub pp/ to 50-/spl Omega/ modulators with a power dissipation of 675 mW. Fabricated in 0.18-/spl mu/m CMOS technology, both prototypes operate with a 1.8-V supply.     

A 3-Gb/s optical detector in standard CMOS for 850-nm optical communication

This paper presents a monolithic optical detector, consisting of an integrated photodiode and a preamplifier in a standard 0.18-/spl mu/m CMOS technology. A data rate of 3 Gb/s at BER <10/sup -11/ was achieved for /spl lambda/=850 nm with 25-/spl mu/W peak-peak optical power. This data rate is more than four times than that of current state-of-the-art optical detectors in standard CMOS reported so far. High-speed operation is achieved without reducing circuit responsivity by using an inherently robust analog equalizer that compensates (in gain and phase) for the photodiode roll-off over more than three decades. The presented solution is applicable to various photodiode structures, wavelengths, and CMOS generations.