J. P. Turkiewicz

Impact of the sample modal composition of 850nm VCSELs on high speed data transmission over multimode fiber applying different modulation formats

Modern high speed multimode fibers exhibit very low modal dispersion but suffer from the chromatic dispersion in glass, which is rather high at 850nm. To increase the transmission capacity on multimode fibers tested two approaches are applied and evaluated. On the transmitter side we designed and fabricated novel types of Vertical Cavity Surface Emitting Lasers (VCSELs) with spectrally ultra-narrow lasing emission both through achieving simple transverse mode operation and the negligible chirp. For increasing the transmission efficiency high-order modulation formats capable to increase the transmission capacity per single transmitter are applied. We report on development of very fast optical VCSEL and photodiodes within the European Project ADDAPT and show our recent results on high speed transmission over multi-mode fiber using 850nm VCSELs and GaAs PIN photodiodes applying different modulation formats. We show that the transmission distance and the transmission capacity of a single lane can be improved by applying high speed single mode VCSELs which are modulated with 4-PAM, 8-PAM and DMT modulation.

High speed transmission with 850 nm SM and MM VCSELs

The ever growing data volumes in the IT infrastructure can only by carried by the optical transmission technologies. The key requirements for such transmission systems are the small footprint, high energy efficiency and the low cost of ownership. One of the most promising candidates to realize the energy efficient high speed transmission over the short distance is transmission with the multi-mode fibre and the 850 nm VCSELs. In this paper the transmission performance of the two types of the 850 nm VCSEL, namely single mode and multimode one is compared. Several key VCSEL transmission characteristics, like bandwidth of both VCSEL types were measured and evaluated. The transmission experiments in the various system configurations were performed at the bit rates up to 56 Gbit/s. The results demonstrate that the SM VCSEL outperforms MM VCSEL for longer distances and higher data rates.

Progress in design and development of anti-guiding vertical cavity surface emitting laser at 850 nm: Above 50 Gb/s and single mode

Design of the oxide-confined vertical cavity surface emitting laser (VCSEL) with anti-guiding AlAs-rich core has recently attracted a lot of attention. Lack of the waveguiding core increases the oscillator strength of the VCSEL mode, allows the ultimate optical confinement (“λ/2 design”) and reduces dramatically the optical power accumulated in the VCSEL mesa in the regions outside of the oxide aperture. We consider basic differences of conventional and antiwaveguiding VCSEL and address optical modes in the device. Both Joule heat and heat generated by the free carrier absorption of the optical mode in the doped semiconductor layers and their impact on the refractive index profile are considered. We show that for typical regimes of the VCSEL design and operation absorption-induced heat exceeds by several times the Joule heat while the shape of the generated heated domains strongly differ. Modeling shows that current increase results in an increase in spectral separation of the fundamental and high-order transverse optical modes. Selection of the fundamental mode persists upon increase in injection current up to 10 mA at 5 µm aperture diameter. We report on data transmission experiments up to 160 Gb/s using single mode antiwaveguiding VCSELs.

High speed data transmission over multimode fiber based on single mode 850 nm leaky VCSELs

To reach >50 Gb/s bit data rates using 850nm vertical cavity surface emitting laser (VCSEL) at distances up to a few hundred meters, narrow spectrum single mode VCSELs are used to avoid negative influence of the chromatic dispersion that can significantly limit performance beside the mode dispersion. Currently available single-mode VCSELs suffer from small oxide aperture diameter, and thus from higher resistances and lower powers. Oxide–confined apertures in VCSELs can be engineered such that the design promotes leakage of the high order transverse optical modes from the non–oxidized core region into the selectively oxidized periphery of the device. This novel leaky VCSEL approach may allow fabrication of single-mode VCSELs with significantly larger oxide apertures, improving the performance of the single-mode VCSELs. In this paper, we investigate the high speed transmission over long distance multimode fiber using single mode 850nm leaky VCSELs.

Remote Access Unit for optic-to-wireless conversion

In this paper we propose a design of a reconfigurable Remote Access Unit (RAU) interfacing optical dense wavelength division multiplexed (DWDM) networks with radio communication links. To generate a radio signal the device utilizes a principles of incoherent heterodyne signal upconversion. The proposed RAU is able to operate in a whole optical C-band with 100 GHz spaced channels and can generate radio signals in a wide frequency range limited only by used photodiode. Experimental tests of the RAU showed error free operation after 15km of fiber and 50m of radio link in W-band frequency range.