At&t Bell Laboratories

American Telephone and Telegraph, Co.

Tyco Telecommunications (us) Inc.

At+t Corp.

American Telephone & Telegraph Co., At&t Bell Laboratories

At&t Ipm Corp.

George T Harvey

Michael S Heutmaker

Linn F Mollenauer

Alan H Gnauck

Neal S Bergano

Martin C Nuss

Per Bang Hansen

Morten Nissov

Bo Pedersen

Ekaterina A Golovchenko

Franklin Webb Kerfoot, Iii

Stuart M Abbott

Gregory Raybon

Chinlon Lin

Stephen G Evangelides, Jr

Kenneth D Singer

Peter Roland Smith

Peter Hartpence Read

Ralph A Treder

Gregory M Wolter

Yanjie Chai

Joseph S Kovalchick

Mark G Kuzyk

Michael A Mills

Nan M Froberg

Laurence Shrapnell Watkins

An apparatus for measuring the noise figure in optical amplifiers employed for large bandwidth applications such as dense wavelength division multiplexing systems. A booster amplifier coupled to a light source increases the average power associated with a plurality of optical channels. A periodic filter is coupled to the booster amplifier to reflect noise between each of the optical channels across the predetermined bandwidth. An amplifier under test is coupled to the periodic filter and the noise figure associated with the amplifier under test is measured.

Method and apparatus for measuring noise figure in optical amplifiers

A WDM optical communication system is provided that includes a transmitter and a receiver. An optical fiber transmission path couples the transmitter to the receiver. The transmission path includes at least one repeater having an optical amplifier located therein. A dispersion compensator is disposed at an intermediate point along the transmission path. The intermediate point is located outside of the repeater. The compensator includes a wavelength routing device for dividing a signal having a prescribed bandwidth into a plurality of distinct sub-bands. A plurality of output paths is provided for respectively receiving the plurality of distinct sub-bands. The dispersion compensator also includes a dispersion compensating optical element coupled to each of the output paths. Each dispersion compensating optical element substantially compensates for dispersion at a prescribed wavelength within the bandpass of its respective sub-band. A coupler recombining the distinct sub-bands and couples them back onto the optical fiber transmission path.

Method and apparatus for providing chromatic dispersion compensation in a wavelength division multiplexed optical transmission system

The apparatus and method according to the present invention includes a semiconductor laser-modulator which is used to simultaneously generate optical pulses and encode data. The optical data output from the laser-modulator are soliton pulses in RZ format suitable for transmission in long distance optical communications.

Data encoded optical pulse generator

The parallelism of two nominally parallel surfaces is determined by placing a planar reflector (50) on one surface and a cube beam splitter (52) on the other surface. The reflector is placed to reflect light in a direction normal to the plane of the reflector. The cube beam splitter is placed to reflect part of the light striking a first face (54) back in the opposite direction. The cube beam splitter also reflects part of the incident light towards the reflector so that the reflector reflects the light back to the cube beam splitter, causing the light to exit the first cube beam splitter face. An autocollimator (10) is provided to direct a beam of light (24) into the first face (54) of the cube beam splitter (52) and to display the divergence between the first and second reflected beam portions, the divergence corresponding to the degree of non-parallelism between the two surfaces.

Method and apparatus for measuring the parallelism of two surfaces

In a harmonically mode-locked laser, first (33) and second (34) optical beams are derived from the laser optical path which are directed, respectively, through first and second optical filters (37) having optical pass-bands (40, 41) that are displaced in frequency but which intersect at approximately the center frequency (f.sub.c) of operation of the laser. The free spectral range of a Fabry-Perot optical resonator (24) in the laser ring is deviated from a frequency exactly equal to the pulse repetition rate of the laser by a frequency (df) sufficient to permit changes in the length of the optical path to be manifested as changes in the wavelength of light transmitted along the optical path. Apparatus (39, 40, 42) for detecting the difference of intensity of light passing through the first and second filters can then be used to generate a signal proportional to the difference of intensity of such light for the purpose of adjusting, by length adjusting apparatus (43), the length of the optical path to compensate for spurious temperature-induced length variations.

Harmonically mode-locked laser

The invention is an improvement of a harmonically mode-locked ring laser of the type comprising means (12) defining an optical path, an active laser medium (15) for emitting coherent light to be transmitted along the optical path, and means (18) included in the optical path for causing the light to propagate along the path as a train of pulses having a period which is substantially equal to the transit time of light pulses in the optical path divided by an integer. The improvement is characterized in that the optical path includes a Fabry-Perot optical resonator (24) having a free spectral range substantially equal to the pulse repetition rate of the optical pulses in the ring laser. Under this condition, the Fabry-Perot resonator tends to equalize the energy, shape and width of the individual pulses.

Substrates for supporting optical fibers in an optical coupler are made by, first, making grooves in a glass preform which are about ten times the desired size, and then using glass drawing techniques to draw from the preform a substrate of the proper size. Optical fibers are arranged in ribbon form and placed in a fixture which allows the ends to be cut and polished at the angle required for proper coupler operation. Fibers are stripped from the end of the ribbon that has been cut and polished and placed in the grooves for proper alignment with abutting fibers. The ends of the fibers that remain fixed to the ribbon prevent unwanted rotation of the fibers.

Optical coupler method

An integrated circuit device (11) is tested by directing a laser beam (19) onto an electrochromic member (17) in close proximity to a conductor (13) of the integrated circuit. Reflected laser light is directed to a detector (21) which converts it to an electrical signal for display by a lock-in amplifier (25). The display characterizes the voltage on the conductor (17) and thereby permits diagnosis of the operation of the integrated circuit (11).

Optical probing method and apparatus

An integrated circuit (11) is tested at a high microwave frequency through the use of a laser beam (19) having a repetition rate much lower than the test frequency. Electric fields of the test signal extend into an electro-optic material (12) that modulates part of the laser beam. Another part of the laser beam is converted to an electrical pulsed signal that is applied to a microwave mixer (33) along with part of the test frequency signal. A harmonic of the pulsed signal mixes with the test frequency to yield a difference frequency that can be used as a phase reference for analyzing the phase of the test signal. The component pulses (30) of the laser beam have a pulse width which is much shorter than the separation of the pulses, which make it inherently rich in higher harmonics of the fundamental pulse repetition rate.

Amplitude noise is dramatically reduced in an optically pumped modelocked laser arrangement by incorporating an intra-cavity or external cavity mode selection element with a continuous-wave pump laser coupled optically to a modelocked laser. The mode selection element causes a light beam generated from the pump laser to operate nominally at a single frequency, that is, substantially a single longitudinal mode. Mode selection may be realized with an air-spaced or solid material Fabry-Perot etalon.

Amplitude noise reduction for optically pumped modelocked lasers

Photomasks (11, 12) are aligned on opposite sides of a wafer by directing light beams through zone plates (13 A-C) in one photomask and through aligned transparent slits (14 A-C) on the other photomask. Simulantaneous detection of the beams by photodetectors (18 A-C) indicates alignment. A method for obtaining precise centering by scanning the slits with the beams, sampling light transmitted through the slits, and fitting the samples to a parabola by the use of a computer (27) is also described.

Method for aligning photomasks

Photomasks (11,12) are aligned on opposite sides of a wafer by directing light beams through zone plates (13 A-C) in one photomask and through aligned transparent slits (14 A-C) on the other photomask. Simultaneous detection of the beams by photodetectors (18 A-C) indicates alignment. A method for obtaining precise centering by scanning the slits with the beams, sampling light transmitted through the slits, and fitting the samples to a parabola by the use of a computer (27) is also described.

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Princeton, NJ, United States of America

George T Harvey