Martin Stach

Multi-mode photonic crystal fibers for VCSEL based data transmission

Quasi error-free 10Gbit/s data transmission is demonstrated over a novel type of 50 microm core diameter photonic crystal fi ber with as much as 100m length. Combined with 850 nm VCSEL sources, this fi ber is an attractive alternative to graded-index multi-mode fi bers for datacom applications. A comparison to numerical simulations suggests that the high bit-rate may be partly explained by inter-modal diffusion.

Bidirectional Optical Interconnection at Gb/s Data Rates With Monolithically Integrated VCSEL-MSM Transceiver Chips

We present the operation characteristics of 850-nm wavelength GaAs-based monolithically integrated transceiver chips designed for low-cost short-distance bidirectional optical data transmission over a butt-coupled 200-mum core diameter polymer-clad silica fiber. The chips containing a vertical-cavity surface-emitting laser and a large-area metal-semiconductor-metal photodiode can well handle data rates of 2.5Gb/s in back-to-back mode and 0.5 Gb/s for 10-m fiber length

True bidirectional optical interconnects over multimode fiber

We report the fabrication and properties of 850nm wavelength AlGaAs/GaAs-based transceiver chips, in which vertical-cavity surface-emitting lasers (VCSELs) and photodiodes are monolithically integrated. Various types of devices allow half- and full-duplex bidirectional optical interconnection at multiple Gbit/s data rates over a single butt-coupled glass or polymer-clad silica optical fiber with core diameters of 100 or 200 μm. Whereas metal-semiconductor-metal (MSM) photodiodes are employed for these large-area fibers, we also investigate the integration of PIN-type photodiodes which appear more promising in combination with standard 62.5 or 50 μm core diameter graded-index multimode fibers. This interconnect solution based on two identical chips is attractive owing to lower volume, weight, and cost. Applications will be found in home, in-building, industrial, or automotive networks and potentially within computer clusters or central offices.

Monolithic integration of VCSELs and MSM photodiodes for bidirectional multimode fiber communications

The monolithic integration of 850 nm vertical-cavity surface-emitting laser diodes and GaAs-based metal-semiconductor-metal photodiodes is introduced as an approach to bidirectional optical data transmission in the Gbit/s range of data rates. Polymer-clad silica fibers and graded-index fibers with core diameters of 200 and 100 &mgr;m, respectively, serve as the transmission medium, covering link lengths relevant for in-car up to in-house communications and beyond.

Monolithically integrated optical transceiver chips at 850 nm wavelength consisting of VCSELs and MSM photodiodes

In this paper we report on a transceiver chip that is even suited for bidirectional Gbit/s transmission over a PCS fiber. The monolithic integration of a VCSEL and a metal-semiconductor-metal photodiode (MSM PD) as well as a design avoiding the use of external optics are expected to simultaneously save space, weight and module cost.

Monolithically integrated transceiver chips for bidirectional optical interconnection

We report on the design, fabrication and test results of monolithically integrated transceiver chips consisting of GaAs metal-semiconductor-metal photodiodes and 850nm wavelength vertical-cavity surface-emitting lasers. These chips are well suited for low-cost and compact bidirectional optical interconnection at Gbit/s data rates in mobile systems and industrial or home networks employing large core size multimode fibers.

Toward more efficient fabrication of high-density 2-D VCSEL arrays for spatial redundancy and/or multi-level signal communication

We present flip-chip attached high-speed VCSELs in 2-D arrays with record-high intra-cell packing densities. The advances of VCSEL array technology toward improved thermal performance and more efficient fabrication are reviewed, and the introduction of self-aligned features to these devices is pointed out. The structure of close-spaced wedge-shaped VCSELs is discussed and their static and dynamic characteristics are presented including an examination of the modal structure by near-field measurements. The lasers flip-chip bonded to a silicon-based test platform exhibit 3-dB and 10-dB bandwidths of 7.7 GHz and 9.8 GHz, respectively. Open 12.5 Gbit/s two-level eye patterns are demonstrated. We discuss the uses of high packing densities for the increase of the total amount of data throughput an array can deliver in the course of its life. One such approach is to provide up to two backup VCSELs per fiber channel that can extend the lifetimes of parallel transmitters through redundancy of light sources. Another is to increase the information density by using multiple VCSELs per 50 μm core diameter multimode fiber to generate more complex signals. A novel scheme using three butt-coupled VCSELs per fiber for the generation of four-level signals in the optical domain is proposed. First experiments are demonstrated using two VCSELs butt-coupled to the same standard glass fiber, each modulated with two-level signals to produce four-level signals at the photoreceiver. A four-level direct modulation of one VCSEL within a triple of devices produced first 20.6 Gbit/s (10.3 Gsymbols/s) four-level eyes, leaving two VCSELs as backup sources.

Design and communication applications of short-wavelength VCSELs

We report on recent progress in the design of short-wavelength vertical-cavity surface-emitting lasers (VCSELs) for 10 Gbit/s datacom applications. Topics of interest include differential mode delay characterizations of high-performance multimode fibers and their interplay with transverse single- and multimode VCSELs, flip-chip integrated two-dimensional arrays at 850 nm wavelength, as well as experiments toward the realization of optical backplanes. In the latter case, reliable 10 Gbit/s data transmission has been achieved over low-loss integrated polymer waveguides with up to 1 meter length. Moreover we present VCSELs with output powers in the 10 mW range that are employed in multi-beam transmitters for free-space optical data transmission with Gbit/s speed over distances of up to about 2 km.

Recent progress in short-wavelength VCSEL-based optical interconnections

We report on recent progress in the design and application of vertical-cavity surface-emitting lasers (VCSELs) for optical interconnect applications in the 850 nm emission wavelength regime. Ongoing work toward parallel optical interconnect modules with channel data rates of 10 Gbit/s is reviewed and performance results of flip-chip integrated two-dimensional VCSEL arrays are presented. 10 Gbit/s speed as well as low thermal resistance of the lasers has been achieved. As a possible alternative to graded-index multimode fibers, we show 10 Gbit/s data transmission over 100 m length of a novel, entirely undoped multimode photonic crystal fiber. The use of VCSELs with output powers in the 10 mW range is demonstrated in a 16-channel free-space optical (FSO) module and VCSELs with even higher output power are shown to provide possible FSO connectivity up to data rates of 2.5 Gbit/s.