The integration of a double barrier resonant tunneling diode within a unipolar optical waveguide provides electrical gain over a wide bandwidth. Due to the non-linearities introduced by the double barrier resonant tunneling diode an unipolar InGaAlAs/InP optical waveguide can be employed both as optical modulator and optical detector. The modeling results of a device operating as optical modulator agree with preliminary experimental data, foreseeing for an optimized device modulation depths up to 23 dB with chirp parameter between -1 and 0 in the wavelength range analyzed (1520 nm - 1600 nm).

In 1901 the third Conference Generale des Poids et Mesures (CGPM) defined the weight of a body as ``the product of its mass and the acceleration due to gravity". In practical terms the weight force corresponds to the gravitational force. However, this gravitational definition of the weight lacks logic from the perspective of present knowledge and can be misleading. In a space traveling time, weight associated concepts such as "true weight", "apparent weight", "weightlessness", "zero gravity", "microgravity", are ambiguous and strong deceptive. The superfluousness or ambiguousness of these concept would be removed if an operational definition of the weight of a body as the force the body exerts on its support or suspender is adopted. In this definition the weight force does not act on the body and it is not necessary to describe the body's sate of motion. This avoids the imprecision of the concepts such as "true weight" and "apparent weight" of a body, for example. This paper discusses the need of the weight force of a body concept in Physics, and asks for a re-exame of the CGPM definition to improve the physics teaching and learning.

In the spirit of the International Year of Physics 2005 the author advices the replacement of the teaching methods based on verbal explanations and to perform a number of tasks following a given recipe by procedures that actively involve the students in the physics discovery process.

The basic mechanism underlying electric field switching produced by a resonant tunnelling diode (RTD) is analysed and the theory compared with experimental results; agreement to within 12% is achieved. The electro-absorption modulator (EAM) device potential of this effect is explored in an optical waveguide configuration. It is shown that a RTD-EAM can provide significant absorption coefficient change, via the Franz-Keldysh effect, at appropriate optical communication wavelengths around 1550 nm and can achieve up to 28 dB optical modulation in a 200 um active length device. The advantage of the RTD-EAM, over the conventional reversed biased pn junction EAM, is that the RTD-EAM has in essence an integrated electronic amplifier and therefore requires considerably less switching power.

With rare exceptions, in high school and college/university physics courses literature and in journals of physics, the weight is defined as a gravitational force or an exclusive consequence of it. These definitions lack logic from the perspective of present knowledge and can be misleading. The operational definition of weight of a body as the force the body exerts on its support or suspender can eliminate the ambiguities associated to "true weight", "apparent weight", "state of weightlessness", "zero weight", "zero gravity", "microgravity", "vertical", "up" and "down". Nevertheless, the concept of weight of a body is not fundamental in Physics and its exclusion from the physics vocabulary will eliminate some of former concepts or their ambiguousness with evident benefit for physics teaching and learning. This paper discusses weight of a body concepts and presents several examples that show the advantages of avoiding its use or adopting the above-mentioned operational definition. It is believed that this will eliminates the frequent identification with the body's mass and will boost student's understanding associated subjects.