We report electroabsorption modulation of light at around 1550 nm in a unipolar InGaAlAs optical waveguide containing an InGaAs/AlAs double-barrier resonant tunneling diode ͑RTD͒. The RTD peak-to-valley transition increases the electric field across the waveguide, which shifts the core material absorption band edge to longer wavelengths via the Franz-Keldysh effect, thus changing the light-guiding characteristics of the waveguide. Low-frequency characterization of a device shows modulation up to 28 dB at 1565 nm. When dc biased close to the negative differential conductance region, the RTD optical waveguide behaves as an electroabsorption modulator integrated with a wide bandwidth electrical amplifier, offering a potential advantage over conventional pn modulators. © 1999 American Institute of Physics. ͓S0003-6951͑99͒00748-2͔Because of their intrinsic high-speed response and potential for electrical gain over a wide bandwidth, resonant tunneling diodes ͑RTDs͒ have been proposed by several groups 1-3 for optoelectronic applications. Previously, we reported work on an GaAs/AlAs RTD that was successfully integrated in a unipolar GaAs-AlGaAs optical waveguide, 4 and high-speed optical modulation ͑up to 18 dB͒ combined with electrical gain was demonstrated. 5 This device operated around 900 nm. For devices functioning at the usual optical communication wavelengths, 1300 or 1550 nm, applications could include, for example, optical distribution of modulated millimeter-wave frequency carriers for mobile communication systems. In this letter we describe a resonant tunneling diode electroabsorption modulator ͑RTD-EAM͒ operating at wavelengths around 1550 nm.The operation of the device is based on a RTD within an optical waveguide which introduces a nonuniform electric field distribution across the waveguide core. The electric field becomes strongly dependent on the bias voltage, due to accumulation and depletion of electrons in the emitter and collector sides of the RTD, respectively. Depending on the dc bias operating point, a small high frequency ac signal ͑Ͻ1 V͒ can induce high-speed switching. This produces substantial high-speed modulation of the waveguide optical absorption coefficient at a given wavelength near the material band edge via the Franz-Keldysh effect 4 and, therefore, modulates light at photon energies lower than the waveguide core band-gap energy. The modulation depth can be considerable because, under certain conditions, the RTD operation point switches well into the two positive differential resistance portions of the current-voltage ͑I-V͒ characteristic, with a substantial part of the terminal voltage dropped across the depleted region in the collector side. 5,6 The advantage of the RTD-EAM compared to conventional pn modulators is that, when dc biased close to the negative differential conductance ͑NDC͒ region, the device behaves as an optical waveguide electroabsorption modulator integrated with a wide bandwidth electrical amplifier.The high-frequency and large modulation depth characteristics of ...

We report high-speed optical modulation in a resonant tunneling relaxation oscillator consisting of a resonant tunneling diode ͑RTD͒ integrated with a unipolar optical waveguide and incorporated in a package with a coplanar waveguide transmission line. When appropriately biased, the RTD can provide wide-bandwidth electrical gain. For wavelengths near the material band edge, small changes of the applied voltage give rise to large, high-speed electroabsorption modulation of the light. We have observed optical modulation at frequencies up to 14 GHz, associated with subharmonic injection locking of the RTD oscillation at the fundamental mode of the coplanar transmission line, as well as generation of 33 ps optical pulses due to relaxation oscillation.

No abstract

Hybrid sol-gel planar optics devices for astronomy are produced for the first time. This material system can operate from the visible (0.5 microm) up to the edge of astronomical J-band (1.4 microm). The design, fabrication and characterization results of a coaxial three beam combiner are given as an example. Fringe contrasts above 94% are obtained with a source with spectral bandwidth of 50 nm. These results demonstrate that hybrid sol-gel technology can produce devices with high quality, opening the possibility of rapid prototyping of new designs and concepts for astronomical applications.

Integrated optics coaxial two, three and four telescope beam combiners have been fabricated by hybrid sol-gel technology for astronomical applications. Temporal and spectral analyses of the output interferometric signal have been performed, and their results are in mutual good agreement. The results of the characterization method employed are cross-checked using contrast measurements obtained independently, demonstrating that the chromatic differential dispersion is the main contributer to contrast reduction. The mean visibility of the fabricated devices is always higher than 95 %, obtained using a source with spectral bandwidth of 50 nm. These results show the capability of hybrid sol-gel technology for fast prototyping of complex chip designs used in astronomical applications.