PTB at Innovation '98 in Leipzig

At Europe's most modern exhibition centre in Leipzig, from November 3 to 6, 1998, innovative ideas, developments and procedures are the centre of interest at the "Innovation '98" Fair.

Under the motto: "The fair at which ideas learn to walk", about 500 exhibitors present novel technologies, innovative products and procedures, submit technology transfer offers, present financing concepts and broker cooperations. Besides these presentations, the extended framework program with special shows on photovoltaics and regenerative raw materials, the cooperation market as well as the 1st German Capital Exchange "Founders & Innovation" attract the interest of the visitors and help the fair to achieve its objective of becoming a supraregional forum of international importance.

At the same time, the BIK '98 - the specialist exhibition for telecommunication and computers - takes place at Leipzig's new exhibition centre and supplements the innovation fair. Both exhibitions take place under the patronage of Professor Dr. Roman Herzog, the President of the Federal Republic of Germany.

The Federal Ministry of Economics which supports the innovation efforts by providing the boundary conditions and strengthening the infrastructure necessary for innovation and by furthering industrial research and development, has requested its subordinate cooperation partners - among these the PTB - to participate in the Innovation '98 Fair, to present novel developments and to inform about their scientific and technical services for economy and science.

Members of the PTB are present to answer questions about all subjects concerning the PTB, such as calibration, accreditation, technical problems of the supervision of testing means, etc. As an example of the results of its current research activities, the PTB presents a DSP-controlled rubidium-stabilized diode laser for length measuring technology.

DSP-controlled rubidium-stabilized diode laser for length measuring technology

Digital signal processing which has increasingly become part of everyday life offers some advantages over the analog technique, for example flexibility as a result of software changes, exact reproducibility and high accuracy. A drawback is the quantizing noise. Furthermore, the frequency range in which digital signal processors (DSP) can be used is limited but the DSPs become ever more efficient. Thus the present-day communication technology is not imaginable without digital signal processors. The diode laser as a light source has advantages as regards miniaturization, useful life, costs, efficiency, radiant power, modulation capability, high-voltage-free operation, etc. Drawbacks of diode lasers are the scattering of the emitted wavelength, their relatively strong dependence on the diode parameters, injection current and temperature, and their temporal variation even if the diode parameters are kept constant. These disadvantages can be compensated by stabilization of the wavelength by link-up with an atomic absorption line, for example rubidium (Rb). The diode laser thus is an interesting alternative to the He-Ne gas lasers which are mostly used in length measuring technique.

A portable DSP-controlled Rb-stabilized diode laser has been developed, set up and tested in cooperation between the PTB in Braunschweig and the Braunschweig-Wolfenbüttel Technical College for use in precision length measuring technology. A DSP ensures the control and stabilization of a diode laser to an Rb absorption line so that the lay public could also operate this device. After the diode laser has been switched on, its wavelength is automatically stabilized to an Rb absorption maximum. The diode laser developed as a length standard emits a wavelength of 780,243 830 nm with a relative uncertainty of measurement of ±2 · 10^-8.