Bell Telephone Laboratories

At&t Bell Laboratories

Ping K Tien

Albert Anthony Ballman

Rodney C Alferness

Uziel Koren

Robert G Swartz

Theodore H Geballe

Chandra K Patel

Bruce A Wooley

Gadi Eisenstein

Matthew S Whalen

Rodney S Tucker

Harold Brown

Raymond J Martin

Aly H Dayem

Thomas R Harrison

Wavelength tunability and single frequency output are achieved in a coherent light source employing an adjustably controllable reflector. The light source includes a gain medium coupled to a single-mode fiber having a partially reduced cladding region at a predetermined distance from the gain medium. A Bragg reflector is either formed on the reduced cladding region of the single-mode fiber or formed on an external element in close proximity to the reduced cladding region. A single resonant optical cavity is formed by placing another reflector on the side of the gain medium opposite the gain medium-to-fiber coupling. Wavelength tuning of the light source is accomplished by controllably adjusting the period or the Bragg reflector element.

Wavelength tunable composite cavity laser

A photodetector useful at long wavelengths where silicon normally is transparent. It includes a photodiode stage which comprises a silicide layer forming a Schottky-barrier junction with a silicon substrate and which is integrated with an amplification stage which uses a silicon transistor adapted to amplify the photovoltaic voltage derived by the photodiode stage. In the preferred embodiment, the silicide layer forms the grid of a permeable base transistor.

Phototransistor for long wavelength radiation

A plurality of semiconductor lasers (431-434) and a photodetector (120) are mounted on a silicon substrate (100) having an integrated circuit (101) fabricated therein. The integrated circuit includes a biasing circuit (405) for establishing a threshold current level that is dependent on the output of the photodetector and a modulator circuit (404) for providing a modulation current that is dependent on the digital values in an input signal. A semiconductor switch (406) selects only one of the plurality of semiconductor lasers for activation by the biasing and modulator circuits. The integrated circuit also includes a circuit (408) that operates the semiconductor switch so as to selectively activate a different one of the plurality of semiconductor lasers in response to either a predetermined output from said photodetector or in response to an external supervisory signal.

Semiconductor lasers with selective driving circuit

A stripe geometry is fabricated in a laser-diode structure having a plurality of epitaxial layers, including in tandem an undoped active semiconductor layer (3), a p-doped semiconductor layer (4), a moderately n-doped semiconductor layer (5) and a heavily p.sup.+ -doped layer (6) by focusing laser radiation on the n-doped semiconductor layer (5). The laser radiation is chosen to have a wavelength which passes through the p.sup.+ -doped layer (6) without absorption. When the laser radiation is absorbed in the n-doped layer, heat is generated which causes diffusion of p-dopant from the two adjacent layers to convert the exposed region to p-type. As the laser beam is scanned, a stripe having a forward pn junction for laser action is formed.

Heterojunction semiconductor laser fabrication utilizing laser radiation

Nb.sub.3 Ge, Nb.sub.3 Al and Nb.sub.3 Si are prepared in A15 structures at the exact stoichiometric ratio with epitaxial growth on selected substrates. The phase diagrams of the materials are altered by this technique and only the A15 phase is stable at the stoichiometric ratios thus permitting attainment of higher and sharper transition temperatures.

Epitaxial growth of superconductors such as Nb.sub.3 Ge superconductors

An apparatus is disclosed for making unchirped holographic diffraction gratings that are formed from curved lines in a thin film. The gratings so made focus as well as reflect light that is confined to the film incorporating the grating. SU

Forming focusing diffraction gratings for integrated optics

A method of epitaxial crystal growth is disclosed in which the lattice constants of adjacent layers are in the ratios of small integers other than one. This method permits the use of previously incompatible compounds, in particular the combination of magneto optic and electro optic elements on the same substrate.

Epitaxial growth of dissimilar materials

A process is described for making optical circuits on LiTaO.sub.3 substrates. The process involves putting down an epitaxial layer of LiNbO.sub.3 on the LiTaO.sub.3 substrates. Growth is preferably carried out on certain planes of the LiTaO.sub.3. These optical circuits are unique in that they are smooth, uniform in thickness and have a refractive index significantly larger than that of the substrate. This is advantageous in optical circuitry, since the optical modes in the circuits are quite distinct and can be coupled separately using such light sources as lasers and light emitting diodes.

Waveguiding epitaxial LiNbO.sub.3 films

A liquid phase epitaxial growth technique for growing lithium niobate films on lithium tantalate substrates involves growth from a flux system based on either lithium borate, lithium tungstate, tungsten oxide or potassium tungstate. Optical waveguiding occurs in films grown from the described flux systems.

Technique for growth of thin film lithium niobate by liquid phase epitaxy

The comprehensive large scale integration of thin-film optical circuits is made possible by a series of related developments. The key concept is the isolation of the high index substrate, necessary to active devices, wherever it is desired to have a passive device, by the interposition of an oxide layer such as SiO.sub.2. It is preferred that the passive devices and the SiO.sub.2 by amorphous. This new arrangement allows the use of discrete thin-film corner reflectors, instead of distributed feedback, in resonant active devices and wherever a reflector or beam-splitter is needed. Further, the active devices may be located photolithographically by etching windows in the SiO.sub.2 layer. All of the active devices share a common active layer, which forms the passive devices wherever it extends between windows and simultaneously is the light guiding layer throughout.

Growing community of inventors

Chatham Township, NJ, United States of America

Ping K Tien