Optical phased arrays represent an enabling new technology that makes possible simple affordable, lightweight, optical sensors offering very precise stabilization, random-access pointing programmable multiple simultaneous beams, a dynamic focus/defocus capability, and moderate to excellent optical power handling capability. These new arrays steer or otherwise operate on an already formed beam. A phase profile is imposed on an optical beam as it is either transmitted through or reflected from the phase shifter array. The imposed phase profile steers, focuses, fans out, or corrects phase aberrations on the beam. The array of optical phase shifters is realized through lithographic patterning of an electrical addressing network on the superstrate of a liquid crystal waveplate. Refractive index changes sufficiently large to realize full-wave differential phase shifts can be effected using low (<10 V) voltages applied to the liquid crystal phase plate electrodes. High efficiency large-angle steering with phased arrays requires phase shifter spacing on the order of a wavelength or less; consequently addressing issues make 1-D optical arrays much more practical than 2-D arrays. Orthogonal oriented 1-D phased arrays are used to deflect a beam in both dimensions. Optical phased arrays with apertures on the order of 4 cm by 4 cm have been fabricated for steering green, red, 1.06 /spl mu/m, and 10.6 /spl mu/m radiation. System concepts that include a passive acquisition sensor as well as a laser radar are presented.

Optical phased array technology

Nonmechanical steering of optical beams will enable revolutionary systems with random access pointing, similar to microwave radar phased arrays. An early approach was birefringent liquid crystals writing a sawtooth phase profile in one polarization, using 2pi resets. Liquid crystals were used because of high birefringence. Fringing fields associated with voltage control required to implement the 2pi resets have limited the efficiency and steering angle of this beam steering approach. Because of steering angle limitations, this conventional liquid crystal steering approach is usually combined with a large angle step-steering approach. Volume holograms, birefringent prisms or sawtooth-profile birefringent phase gratings, and circular-type polarization gratings are the large angle step steering approaches that will be reviewed in this paper. Alternate steering approaches to the combined liquid crystal and step-steering approach exist. Microelectromechanical system mirrors, lenslet arrays, electrowetting, and a variable birefringent grating approach will be reviewed and compared against the conventional liquid crystal and step-steering approaches. Step-steering approaches can also be combined with these approaches. Multiple nonmechanical steering approaches are developing that will allow high-efficiency steering, excellent steering accuracy, and wide fields of view.

A Review of Phased Array Steering for Narrow-Band Electrooptical Systems

Nonmechanical steering of optical beams will enable revolutionary systems with random access pointing, similar to microwave radar phased arrays. An early approach was birefringent liquid crystals writing a sawtooth phase profile in one polarization, using 2� resets. Liquid crystals were used because of high birefringence. Fringing fields associated with voltage control required to implement the 2� resets have limited the efficiency and steering angle of this beam steering approach. Because of steering angle limitations, this conventional liquid crystal steering approach is usually combined with a large angle step-steering approach. Volume holograms, birefringent prisms orsawtooth-profile birefringentphase gratings, andcircular-type polarizationgratingsarethelargeanglestepsteeringapproaches that will be reviewed in this paper. Alternate steering approaches to the combined liquid crystal and step-steering approach exist. Microelectromechanical system mirrors, lenslet arrays, electro- wetting, and a variable birefringent grating approach will be reviewed and compared against the conventional liquid crystal and step-steering approaches. Step-steering approaches can also be combined with these approaches. Multiple nonmechan- ical steering approaches are developing that will allow high- efficiency steering, excellent steering accuracy, and wide fields of view.

A Review of Phased Array Steering for Narrow-Band Electrooptical Systems Rapid, accurate, non-mechanical techniques for steering optical beams can provide the kind of efficient random access pointing offered by microwave radars.

In accordance with the invention, light is coupled from a plurality of semiconductor emitters to a cladding-pumped fiber via tapered fiber bundles fusion spliced to the cladding-pumped fiber. Individual semiconductor broad stripe emitters can be coupled to individual multimode fibers. The individual fibers can be bundled together in a close-packed formation, heated to melting temperature, drawn into a taper and then fusion spliced to the cladding-pumped fiber. Advantageously, the taper is then overcoated with cladding material such as low index polymer. In addition, a fiber containing a single-mode core can be included in the fiber bundle. This single-mode core can be used to couple light into or out of the single-mode core of the cladding-pumped fiber.

Tapered fiber bundles for coupling light into and out of cladding-pumped fiber devices

The invention relates to: An optical coupler for coupling light from at least two input fibres into one output fibre. The invention further relates to a method of fabricating and to the use of an optical coupler. The object of the present invention is to provide an optical coupler, which is relatively easy to manufacture. The problem is solved in that the coupler comprises a) an input section comprising at least two input fibres, which are bundled over a bundling-length and having an output end face at one end of the bundling-length; and b) an output section comprising an output fibre comprising a confining region for confining light propagated in said input fibres and a surrounding cladding region and having an input end face; wherein said output end face of said input section is optically coupled to said input end face of said output section and at least said confining region of said output fibre is tapered down from a first cross sectional area at said input end face to a second, smaller cross sectional area over a tapering-length of said output fibre. This has the advantage that the output section comprises an optical fibre which can be made in easy to handle, appropriate lengths and which can be easily tapered. The invention may e.g. be used in fibre lasers or amplifiers, where efficient coupling of light from a number of pump sources to a single (e.g. double clad) output fibre is needed.

An optical coupler, a method of its fabrication and use

A lens system for use with a linearly arrayed light beam including a first optical element for receiving and redirecting different portions of the linearly arrayed light beam to different locations on an imaginary plane so as to generate a two-dimensional pattern of light beams on the imaginary plane; and a second optical element located at the imaginary plane and aligned with the two-dimensional pattern of light beams for redirecting each of the light beams of the two-dimensional pattern of light beams to any arbitrary direction.

Method and apparatus for efficient concentration of light from laser diode arrays

Agile steering of a helium-neon laser beam (X = 632.8 nm) has been demonstrated using a complementary pair of 5-cm-aperture binary optic microlens arrays in the Galilean telescope geometry. Segmentation of a collimated input beam by illuminating approximately 60,000 /5 microlenses of 200-jim diameter and parabolic phase profile results in nearly aberration free beam steering over an 1 1° field of view for 100-
pm lateral displacements of one array relative to the other. Wavefront quality and steering efficiency of the deflected beam has been measured as a function of steering angle and is compared to a simple theoretical
model.

Agile beam steering using binary optics microlens arrays

Apparatus and method for scaling solid-state devices to higher power using multiple sources each of which are separately collimated, followed by focusing of the pump radiation into gain medium colinear to laser mode using a moderated focus. A modularized system is also described.

Multiple-laser pump optical system

The individual outputs of a large laser diode array are combined using an optical transformer of diffractive optics. To allow for the tolerances in the laser array and combining optics required for mass production, the system further includes corrector optics. The corrector optics includes individual lens elements which are fabricated to provide specific correction of faults in the individual lasers and associated combining optics resulting from manufacturing tolerances. The preferred corrector lenses include diffractive lenses fabricated by laser milling.

Fault tolerant optical system using diode laser array

A Laser Writer system for recording centro-symmetric patterns in photoresist has been
developed as an alternative method for binary optics mask and component fabrica.-
tion.This system is capable of generating binary amplitude patterns with linewidths
below 1 tm and with a positional accuracy of less than 0.ljim on up to 3 in. diameter
planar substrates. The measured wavefront error and diffraction efficiency of a directwrite
two-phase-level F/10 lens confirm that high quality components can be fabricated
quickly, easily, and at low cost.

William C. Goltsos

Papers

Method and apparatus for efficient concentration of light from laser diode arrays

Agile beam steering using binary optics microlens arrays

Multiple-laser pump optical system

Fault tolerant optical system using diode laser array

Polar-coordinate laser writer for binary optics fabrication