In this article, we report on energy efficient (6.2 mW/Gbit/s) transmitter and receiver assemblies capable of NRZ 80 Gbit/s and 72 Gbit/s fiber data transmission through 2 and 50 m of MMF, ...respectively. The optical link studied consisted of a 130 nm BiCMOS driver and transimpedance amplifier, ~30 GHz VCSEL, and ~27 GHz PD.
High Speed VCSEL Technology and Applications Ledentsov, Nikolay N.; Makarov, O. Yu; Shchukin, V. A. ...
Journal of lightwave technology,
03/2022, Letnik:
40, Številka:
6
Journal Article
Recenzirano
Historically optical links up to 100-300m distances are served by light emitting devices in the 850 nm spectral range in combination with multimode glass fibers (MMF). As the silicon scaling ...continues, a single channel data rate is to double each 24 months. Light-emitting diodes had to be replaced by vertical cavity surface emitting lasers (VCSELs) and the data rate increased from 100 Mb/s to 10 Gb/s. At higher data rates problems with further scaling evolved. To avoid the collapse an anti-waveguiding VCSEL cavity design was invented, applied, and presently serves data links operating up to 50-100 Gb/s per channel. Another requirement in data communication is the bandwidth density scaling, with the number of channels per link increasing approximately 5-fold each 10 years, while keeping a similar space for connectors. A coarse short-wavelength division multiplexing allowing 850 nm, 880 nm, 910 nm, and 940 nm wavelengths in a single MMF is introduced. The bandwidth density increase is also possible by using multicore fiber (MCF) coupled to on-chip VCSEL arrays. The data rates up to 224 Gb/s are already reached by 850nm VCSELs. At such data rates significant transmission distance over MMF is only possible by applying ultra-narrow spectrum VCSELs minimizing the chromatic dispersion effects. On-chip mini-arrays of oxide-confined VCSELs allow a high coupling efficiency to MMFs, a narrow spectrum, a high power, a significant transmission distance at high data rates. Coherent lasing in such arrays allow photon-photon resonance engineering aimed at modulation bandwidths ∼50-100 GHz.
Properly designed oxide-confined vertical cavity surface emitting laser (VCSEL) allows leakage of the optical modes from the all-semiconductor core region to the selectively oxidized periphery if the ...orthogonality between the core mode and the modes on the periphery is broken by the oxidation-induced optical field redistribution. The leakage losses are stronger for high-order transverse modes, which have a higher field intensity close to the oxidized region. Single mode lasing in the fundamental mode can thus proceed up to large aperture diameters. The 850-nm GaAlAs thick oxide aperture VCSEL based on this concept is designed, modeled, and fabricated, showing single-mode lasing with the aperture diameters up to 5 μm. Side mode suppression ratio >20 dB is realized at the current density of ~10KA/Cm 2 in devices with the series resistance of 90 Ω.
We present a comprehensive description of electric properties of vertical-cavity surface-emitting lasers (VCSELs). A complete drift-diffusion model is developed and applied for carrier transport in a ...multilayer semiconductor laser heterostructure with a p-n junction. We address the impact of interface grading in distributed Bragg reflectors (DBRs), modulation doping of the DBRs and surrounding layers of the quantum well as well as drastically material-dependent carrier mobilities and recombination constants. Solution of the drift-diffusion model yields spatial profiles of the nonequilibrium carrier concentrations and current. The focus is made on oxide-confined GaAs/AlGaAs VCSELs. We evaluate both depletion and diffusion capacitance of the device and show that both contributions to the capacitance as well as the differential series resistance critically depend on the injection current and VCSEL chip design such that, in general, VCSEL cannot be properly modeled by an equivalent circuit approximation. Solution for the current profile demonstrates significant enhancement of the current density at the edges of the oxide-confined aperture (current crowding). We show that, as long as the mesa diameter is small, the effective RC-product can be kept low at small aperture diameters.
We demonstrate 940-nm vertical-cavity surface-emitting lasers (VCSELs) with record-high -3 dB electrical-to-optical bandwidths of 40 and 32 GHz under room-temperature and 85 °C operations, ...respectively. The combination of Zn-diffusion with oxide-relief apertures inside the VCSEL cavity structure can greatly reduce the differential resistance and parasitic capacitance, which leads to an enhancement in the resistance-capacitance (RC)-limited bandwidth. Devices with different sizes of oxide-relief apertures are analyzed by use of the measured S 21 and S 11 two-port scattering parameters and equivalent circuit modeling techniques. For a device with a 3-μm diameter oxide-relief aperture, the extracted intrinsic bandwidth can be as high as 46.3 GHz. By using this novel device as the transmitter, we can achieve 60 Gbps error-free bit-error-ratio (BER) <;1 × 10 -12 ON-OFF keying transmission over a 1-m OM5 fiber under room temperature (RT) operation, without using any signal processing. In addition, invariant 50-Gbps transmission performance from RT to 85 °C operations, over a 100-m OM5 fiber has also been successfully demonstrated (with a BER <; 1 × 10 -7 ).
In this work we investigate the ultrabroadband dynamics of transverse coupled cavity VCSELs. This study is based on a multimode rate equation model, whose parameters are directly provided by a ...full-wave vectorial electromagnetic solver. This approach sets a step towards the comprehensive physics-based modeling of transverse-coupled cavity VCSELs, providing a relation between the features of the optical supermodes and the enhancements of the intensity modulation response. The approach emphasizes how the bandwidth enhancement, ascribable to a photon-photon resonance picture, can be triggered by forcing asymmetries in the bias and modulation contacting scheme of the device, and the importance of collecting the fields from each single cavity, providing an interpretation of recent experimental observations and paving the way towards more systematic design strategies.
Using the Zn-diffusion and oxide-relief techniques with the optimized aperture sizes, we demonstrate a novel single-mode 940 nm vertical-cavity surface-emitting laser (VCSEL) with high brightness ...performance. The highly single-mode (SM) output optical spectra (SMSR>50 dB) can be sustained under a full range of bias currents and from room temperature (RT) to 85°C operation. Under RT operation, the maximum SM power can be as high as 7.1 mW with a moderate threshold current (<inline-formula> <tex-math notation="LaTeX">\text{I}_{\mathrm {th}} </tex-math></inline-formula>: 1.1mA) and narrow divergence angles in the far-field pattern (FWHM: 5°, 1/e 2 : 7-8°). Furthermore, the maximum 3-dB E-O modulation bandwidth of this high-power SM VCSEL can reach 15 GHz without the low-frequency roll-off induced by spatial hole burning effect. By using this novel device as the transmitter, we can achieve 25 Gbit/sec error-free (bit-error-ratio (BER) <inline-formula> <tex-math notation="LaTeX"> < 1\times 10^{-12} </tex-math></inline-formula>) transmission over a 400 meter OM5 fiber without using any signal processing technique. This novel high-speed and high-brightness SM 940 nm VCSEL can serve as a light source in single-mode fiber for medium-reach (>0.3 km) data communications as well as in free-space optical communication.
High-speed transmission in multimode fibers (MMF) is becoming attractive for the realization of high-capacity transmission systems at low cost. This paper discusses the theoretical background of MMF ...transmission and gives an overview on system characterization and existing standards. The authors review latest achievements in component development for highest-speed MMF systems and discuss the challenges on reach, speed, and capacity-extension techniques for next generations of MMF systems.
High power single mode wafer-fused 1300-nm VCSELs with a gain region based on InGaAs/InAlGaAs short period superlattice are fabricated. An InP-based optical cavity and two AlGaAs/GaAs distributed ...Bragg reflector heterostructures were grown by molecular beam epitaõy. The current and optical confinement is provided by a lateral-structured buried tunnel junction with etching depth of <inline-formula> <tex-math notation="LaTeX">\sim 25 </tex-math></inline-formula> nm. It is shown that optimal diameter of the buried tunnel junction for high-power single mode emission is <inline-formula> <tex-math notation="LaTeX">\sim 5 </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">6~\mu \text{m} </tex-math></inline-formula>. The VCSEL demonstrates more than 6 mW single mode continuous-wave power and a threshold current less than 1.5 mA at 20 °C. The output optical power exceeds 1 mW at 85 °C. A -3dB modulation bandwidth up to 8 GHz and 6 GHz is obtained at 20 °C and 85 °C, respectively. The gain coefficient of <inline-formula> <tex-math notation="LaTeX">\sim 650 </tex-math></inline-formula> cm −1 and the transparency current density of <inline-formula> <tex-math notation="LaTeX">\sim 630 </tex-math></inline-formula> A/cm 2 are estimated at zero gain-to-cavity detuning (\sim 60 °C). The ultimate low internal optical losses about 0.08 % per round-trip (distributed losses ~3.2 cm −1 ) at 20 °C and 0.13 % per round-trip (distributed losses ~5.5 cm −1 ) at 100 °C were obtained.
We report the observation of narrow tilted lobes in the far-field emission pattern of leaky oxide-confined vertical-cavity surface-emitting lasers (VCSELs). The VCSEL cavity is surrounded by two ...selectively oxidized aperture layers, which are intentionally designed to produce a high lateral leakage of the high-order transverse modes of the vertical cavity. The device operates in the fundamental transverse mode at oxide aperture diameters below 5~\mu \text{m} and currents up to 4 and 5 mA. At higher currents or larger aperture diameters, an additional high-order transverse optical mode evolves. This mode is revealed by the appearance of a shorter wavelength emission line in the electroluminescence spectra of the device, resulting in multi-mode lasing and in the related changes in the near- and far-field patterns. In the far-field pattern, the evolution of the high-order mode is revealed by the evolution of the two overlapping emission lobes at moderate (~5°) tilt angles with respect to the normal to the surface and by the appearance of a multi-spot or a ring pattern in the CCD camera images. Most importantly, the appearance of this high-order transverse mode is accompanied by an observation of much narrower lobes in the far-field pattern observed at significantly larger tilt angles (~35°). The tilt angle and the narrow angular width of these emission lobes in the far-field spectrum are in agreement with those calculated in the 3-D cold cavity modeling of the optical modes of the device. These narrow tilted lobes revealed in this paper are the fingerprints of the leakage effect in specially designed oxide-confined VCSELs with their intensity being proportional to the optical power leaving the aperture region in the direction parallel to the surface and propagating into the oxidized region. The effect can be applied for engineering of single-mode VCSELs, coherently-coupled 2-D VCSEL arrays, laterally integrated VCSEL-photodetector chips, and VCSELs integrated to slow light waveguides, for coupled optical gates for optical computers and other types of photonic integrated circuits.
PDF