Quasi‐analytic steady‐state solution of VCSEL rate equations including spatial hole burning and carrier diffusion losses

We propose a new set of equations describing a cylindrical vertical cavity surface emitting laser (VCSEL) cavity under CW operation, based on the rate equations including lateral carrier diffusion. The only numerical step in the calculation consists in finding the roots of a polynomial expression. This model enables a quasi‐instantaneous calculation of the laser's light‐current characteristic, including such effects as spatial hole burning, current spreading, inhomogeneous optical intensity distribution, and diffusion losses. An analysis of the VCSELs threshold current and differential quantum efficiency is proposed, which illustrates the interplay between injected current profile and diffusion coefficient. Copyright © 2003 John Wiley & Sons, Ltd.     

Single-chip 622-Mb/s SDH/SONET framer, digital cross-connect andadd/drop multiplexer solution

This paper presents a single-chip all-CMOS solution for 4×OC-3c, OC-12, and OC-12c synchronous digital hierarchy/synchronous optical network (SDH/SONET) framing with integrated serial line interfaces. Outstanding features of this chip are clock and data recovery and fulfillment of ITU-T and Bellcore jitter requirements for SDH/SONET systems, as well as the large range of functions offered. These functions include asynchronous transfer mode (ATM) and point-to-point protocol (PPP) support, as well as built-in native SDH/SONET functions such as digital cross-connect, add/drop multiplexing, and automatic protection switching. In addition, the chip is based on a new scalable modular architecture     

2-D VCSEL model for investigation of dynamic fiber coupling and spatially filtered noise

We propose a set of transformed two-dimensional (2-D) rate equations, which allow the computation of dynamic gain competition resulting from inhomogeneous field and carrier spatial distributions inside a vertical cavity surface-emitting laser cavity. Any explicit spatial dependency has been removed from the modified equations, reducing the computational time by several orders of magnitude. Resulting 2-D dynamic intensity profiles allow investigating effects related to improper fiber coupling due to transverse misalignment between laser beam and fiber. Although the expected increased relative intensity noise (RIN) levels associated with mode partition noise are observed, other effects might have larger contributions to the total noise under specific conditions. We show that the minimum RIN level is not necessarily reached for zero misalignment, but at positions where modes with broad far-field profiles and low power experience important filtering.     

Complementary Josephson-junction circuit: a fast flip-flop and logic gate

A logic circuit with Josephson junctions has been developed that operates as logic gate or as a flip-flop. Despite the latching-type characteristic of the Josephson tunnel junction, the complementary logic circuit is nonlatching. The test circuit has a power dissipation of 16.4 ?W and a signal risetime of approximately 60 ps has been measured.     

Cellular remote antenna feeding: optical fibre or coaxial cable?

Remote antennas in cellular telephone networks can be supplied by coaxial cable or optical fibre. It is useful to know which of the two technologies is more appropriate with respect to dynamic range and costs. Coaxial and optical fibre links are considered for GSM applications. The link length-dependent costs are compared for two reasonable values of the dynamic range     

X and Ku band GaAs m.e.s.f.e.t.

A GaAs Schottky-barrier f.e.t. (m.e.s.f.e.t.) with a 1 ?m gate has been built, which is suitable for X band and Ku band applications. The unilateral power gain over the X band is above 9 dB and the noise figure is only 5 dB at 10 GHz.