Hewlett-packard Company

Harmonic Lightwaves, Inc.

Moshe Nazarathy

Yishai Kagan

Josef Berger

William R Trutna, Jr

David W Dolfi

Steven A Newton

Brian H Kolner

Doron Mick

Scott H Foster

Roger Lee Jungerman

Paul Zorabedian

Tirumala R Ranganath

William Richard

Anthony J Ley

Hans C Verhoeven

Yaron Simler

A temporal imaging system is presented consisting of a dispersive input path, a phase modulator producing a phase modulation substantially equal to A+Bt.sup.2, and an output dispersive path. This temporal imaging system can be combined with other temporal lenses to image input signals in the same manner that spatial lenses can be used to image light from spatial sources. In particular, this temporal imaging system can be used to expand, compress and or invert input temporal signals.

Temporal imaging with a time lens

This invention teaches new types of linearization circuits, exhibiting improved broadband suppression of nonlinear distortion. These realizations do not require the use of reactive elements such as capacitors, or of active elements such as transistors, eliminating the drawbacks of prior art realizations. The linearization circuits are particularly suitable for linearizing optical sources with odd wave voltage to light transfer characteristics, such as externally modulated CW lasers. The fundamental building blocks of the linearization circuits of this invention are novel nonlinear electrical one-ports with an expansive V-I characteristic, denoted as ENLOP (Expansive Nonlinear one-Ports). The ENLOP building blocks are further embedded in linear circuits.

Shunt-expansive predistortion linearizers for optical analog transmitters

An optical modulation system having cascade-coupled electro-optic modulator stages in either dual tandem or split tandem configurations. An electrical splitter derives multiple electrical drives for the multiple stages from a single modulating input signal. The multiple drive signals are linearly related in magnitude and preferably induce simultaneous antiphase (180.degree. out-of-phase) optical modulation in the tandem stages. While a double Mach-Zehnder cascade configuration could be used, at least one modulator stage might instead be a balanced-bridge interfometer-type modulator having at least one directional coupler. At least one directional coupler in such a configuration may be a .DELTA..beta. coupler. Application of bias voltages to the interferometer sections and to coupler sections by means of a parametric feedback loop is done in order to simultaneously enhance the linear modulation coefficient, minimize odd order distortions and null the even order distortions that are associated with biased .DELTA..beta. couplers.

Cascaded optical modulation system with high linearity

A novel optical system is taught including an optical source, an optical modulator having at least one optical input port for receiving the optical signal from the optical source, a modulation port for receiving the optical signal from the optical source, a modulation port for receiving a modulating signal, and complementary output port signals. The complementary modulated output signals are applied to one or more optical receivers at the other end of an optical transmission link. In one embodiment, the two complementary signals are provided to two separate optical receivers, thereby allowing distribution of optically modulated signals, for example, in a cable television or other type distribution system. In another embodiment, the two complementary modulated signals are applied to a single balanced receiver, thereby providing information content to the complementary receiver twice the power level available on either one channel alone. Furthermore, utilizing a balanced receiver, common mode error signals cancel, thereby increasing the signal to noise ratio of the system. In one embodiment of this invention, a single optical transmission channel is used, and the two optically modulated signals are separated in polarization so as to be capable of being separately detected on the receiving end of the link. In one embodiment feedback means is used to insure proper polarization states for the two complementary signals.

Optical distribution of analog and digital signals using optical

A laser generates a beam which is actively steered into an optical element having a waveguide which receives and transmits the beam. The waveguide is coupled to an optical fiber which is also actively steered. Both the beam steering and fiber steering mechanisms seek to align the beam from the laser to the fiber for maximum output. The beam steering mechanism features a pair of planar mirrors pivoted at right angles to each other. A precision force transducer will cause desired amounts of pivoting to adjust the beam. The fiber steering mechanism features a pair of flexures, arranged with bending moments of the flexures being at right angles. Electrical signals control the extent of bending in each flexure. The amount of light in the fiber is sensed downstream from both steering mechanisms and compared to an expected amount. The resulting error signal is sensed and used as feedback in a servo loop to iteratively correct the two steering mechanisms in order to achieve the best alignment and maximum light output.

Active alignment system for laser to fiber coupling

The invention discloses a general technique of taking advantage of the stability of the modulator transfer characteristic in order to correct for second and third order distortion. These objectives are achieved in a way compatible with the nature of the video distribution frequency formats. The method of this invention for linearizing the amplitude transfer characteristic of integrated optic devices for analog transmission is accomplished by injecting pilot signals, monitoring the harmonic and intermodulation distortion content of the optical output, and feeding back bias signals to parametrically tune the operating points of the integrated optic modulator and of a predistortion network. General principles for realizing suitable parametrically tunable predistortion networks are also presented.

Optical transmitters linearized by means of parametric feedback

Apparatus and method for determining dynamically the polarization vector direction, or polarization vector components and associated temporal phase angle, of a light beam. The apparatus includes a compact polarization beam splitter that receives a beam of light, separates the beam into two perpendicular polarization components and directs these components to a pair of optical detectors and associated circuits that form the sum and difference signals of the electrical signals produced by the optical detectors. This produces a projection of the polarization vector on a given direction. If the light is generally elliptically polarized, use of two such polarization beam splitters and four optical detectors allows reconstruction of the polarization ellipse for the light beam. Alternatively, use of one such polarization beam splitter, two optical detectors and a rotating wave plate in a multiplexed configuration allows reconstruction of the polarization ellipse. The polarization detector is very compact and may be housed in a container that is no more than a few cm. in diameter.

Light wave polarization determination using a hybrid system

An optical time domain reflectometer that injects at least two complementary code sequences into an optical fiber and detects the return signal produced by each of these code sequences. These return signals are processed to extract the function h.sub.k that is equal to the response function for the fiber when a single pulse is injected into the fiber. This processing utilizes a correlation scheme that has no sidelobe distortion. Various combinations of Golay codes are suitable for use as the complementary codes.

Spread spectrum optical time domain reflectometer

A grating tuned laser system having an anamorphic optical section (72) that produces a line image on the grating (73). This system is insensitive to tilt of the grating (73) about an axis (T) perpendicular to the rulings (74) of the grating (73). An embodiment that utilizes a degenerate external cavity is also insensitive to small lateral misalignment of the optical elements.

Misalignment-tolerant, grating-tuned external-cavity laser

A travelling wave modulator in which the phase velocity of a first wave is modulated by a second travelling wave. Means are provided to alter the polarity of the second wave in accordance with a pseudorandom code. Barker codes and Golay codes are particularly suitable for improving the bandwidth-to-voltage ratio of the modulator over a comparable conventional modulator.

Coded sequence travelling-wave optical modulator

A sampler that can be used to sample optical or electrical signals, having an improved sensitivity-resolution product compared to conventional samplers. A coded switched electrode modulator has electrodes that produce polarity reversals in an applied voltage signal in accordance with a pseudorandom code having small sidelobes. An optical signal is injected into an optical waveguide that is oriented parallel to the electrodes. When the optical signal is proportional to the coded electrode pattern, the device is used as an electrical sampler. When the applied voltage signal is proportional to the coded electrode pattern, the device is used as an optical sampler.

Distributed sampling of electrical and optical signals using coded

A method of dynamically changing the measurement window and operating parameters of the instrument, based on intermediate results, in order to minimize the total time required to make a complete measurement. Also, a method of combining partial results from subwindows into a final result to be displayed that has not been corrupted by variation in system response due to time-varying operating parameters.

Adaptive selection of OTDR test parameters and the fusion of data taken

A quasi-planar monolithic unidirectional ring laser is disclosed including an Nd:YAG crystal shaped so that a ring formed therein has an out-of-plane angle of about 1.degree.. The reflection opposite the output-coupling point on the front face is off the rear face. This arrangement provides for a very low pumping threshold and reduced magnetic field requirements. The disclosed laser can be pumped with a semiconductor laser and yield single mode 1.319 .mu.m and 1.338 .mu.m outputs suitable for fiber optic communications.

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Palo Alto, CA, United States of America

Moshe Nazarathy