A laser utilizes a cavity design which allows the stable generation of high peak power pulses from mode-locked multi-mode fiber lasers, greatly extending the peak power limits of conventional mode-locked single-mode fiber lasers. Mode-locking may be induced by insertion of a saturable absorber into the cavity and by inserting one or more mode-filters to ensure the oscillation of the fundamental mode in the multi-mode fiber. The probability of damage of the absorber may be minimized by the insertion of an additional semiconductor optical power limiter into the cavity.

Mode-locked multi-mode fiber laser pulse source

A sensing portion for an interferometric acousto-optic sensor and a sensor using that sensing fiber are disclosed. The sensor fiber has an outer coating of a material having a low bulk modulus. This coating greatly enhances the sensitivity of the sensor fiber. In a preferred embodiment, the material of low bulk modulus embeds the sensor fiber and any included reference fiber. Most preferably, the material having a low bulk modulus is a polymer such as polyurethane. The sensing portions made according to the present invention will usually be incorporated into sensors used for underwater exploration.

Planar fiber-optic interferometric acoustic sensor

Multi-mode fiber amplifier

An acousto-optic filter has a non-birefringent single mode optical fiber with a longitudinal axis, a core and a cladding in a surrounding relationship to the core. The optical fiber has multiple cladding modes and a single core mode that is guided along the core. An acoustic wave propagation member has a proximal end and a distal end coupled to the optical fiber. The acoustic wave propagation member propagates an acoustic wave from the proximal to the distal end and launches a flexural wave in the optical fiber. At least one acoustic wave generator is coupled to the proximal end of the acoustic wave propagation member.

Acousto-optic filter

An optical transmission system has an input light guide and N multipath modulators operated as frequency shifters connected in cascade to receive light from the input light guide and output light along N output light guides where N is 1 or more, wherein the light carried by each ith output light guide, where i=1, . . . , N, is shifted in frequency from light carried by the input light guide by iω m , and where each set of multipath modulators contributes a frequency translation of ω m and where the light from each output light guide is modulated and combined with all other modulated output light to form a multiwavelength transmission system. A receiver equipped with similar frequency shifters is configured to generate a number of optical reference signals of frequencies ω 0 +iω m , each reference sign to be added as a separate portion of the received signal so as to perform self-homodyne detection of the information signal associated with each respective modulated frequency.

Optical frequency shifter and transmission system

A birefringent single-mode optical fiber (200) which propagates light into orthogonal polarization modes is subjected to a series of second order traveling flexural waves for propagation within the fiber (200). An acoustic wave generator (202) applies a periodic lateral squeezing force to the fiber (200), thus causing a second order flexural wave to propagate within the fiber (200). The wavelength of the second order flexural wave is selected to cause light propagating in one polarization mode to be coupled to the orthogonal polarization mode. The optical signal in the second orthogonal propagation mode has a frequency which is equal to either the sum of or the difference between the frequency of the optical signal in the first propagation mode and the frequency of the traveling flexural wave. The frequency of the optical signal in the second orthogonal propagation mode is shifted upward of or downward from the frequency of the optical signal in the first propagation mode as determined by the direction of propagation of the first optical signal with respect to the direction of propagation of the traveling flexural wave, and as also determined by whether the phase propagation velocity of the optical signal in the first propagation mode is greater or less than the propagation velocity of the optical signal in the second propagation mode. The centripetal couple of squeezing forces is preferably oriented at an angle of substantially 45° with respect to the axes of birefringence of the fiber (200).

Fiber optic inter-mode coupling single-sideband frequency shifter

An optical fiber is subjected to a series of traveling flexural waves propagating along a length of the fiber. At least a portion of an optical signal propagating within the optical fiber in a first propagation mode is coupled to a second propagation mode. The optical signal in the second propagation mode has a frequency which is equal to either the sum of or the difference between the frequency of the optical signal in the first propagation mode and the frequency of the traveling flexural waves. The frequency of the optical signal in the second propagation mode is shifted upward or downward from the frequency of the optical signal in the first propagation mode as determined by the direction of propagation of the first optical signal with respect to the direction of propagation of the traveling flexural waves, and as also determined by whether the phase propagation velocity of the optical signal in the first propagation mode is greater than or less than the propagation velocity of the optical signal in the second propagation mode. An acoustic wave is induced in a generator having a gradual tapered cross-section. The generator preferably has the shape of a horn and is coaxially mounted with said optical fiber, so as to suppress the acoustic wave induced in the optical fiber in the reverse direction.

Helge E. Engan

Papers

Fiber optic inter-mode coupling single-sideband frequency shifter

Fiber optic intermode coupling single sideband frequency shifter