A broadband optical amplifier for operation in the 2 μm visible wavelength band is based upon a single-clad Tm-doped fiber amplifier (TDFA). A compact pump source uses a combination of low-power laser diode with a fiber laser to provide a multi-watt pump beam without needing to include thermal management and/or pump wavelength stability components. The broadband optical amplifier is therefore able to be relatively compact device with fiber coupled output powers of >0.5 W CW, high small signal gain, low noise figure, and large OSNR, important for use as a versatile wideband preamplifier or power booster amplifier.

A broadband optical amplifier for operation in the 2 μm visible wavelength band is based upon a single-clad Ho-doped fiber amplifier (HDFA). A compact pump source uses a combination of discrete laser diode with a fiber laser (which may be a dual-stage fiber laser) to create a pump output beam at a wavelength associated with creating gain in the presence of Ho ions (an exemplary pump wavelength being 1940 nm). The broadband optical amplifier may take the form of a single stage amplifier or a multi-stage amplifier, and may utilize a co-propagating pump and/or a counter-propagating pump arrangement.

A fiber structure includes a covering part, the covering part having an optical fiber strand and a coating covering the optical fiber strand; a strand exposed part adjacent to the covering part, the strand exposed part including an exposed optical fiber strand, and a sealing part covering a boundary between the covering part and the strand exposed part. The sealing part including a fluororesin having a structure represented by formula (1):

##STR00001##

where R represents a divalent organic fluorine compound group, and n represents an integer of 1 or more.

A fiber laser apparatus includes: an amplification optical fiber that amplifies a laser beam; one or more pumping light sources that generate pumping light that is supplied to the amplification optical fiber; an output optical fiber including a first core that allows the laser beam amplified by the amplification optical fiber to propagate therethrough, and a first cladding having a refractive index lower than a refractive index of the first core and surrounding a circumference of the first core; a delivery fiber including a second core optically coupled to the first core of the output optical fiber, and a second cladding having a refractive index lower than a refractive index of the second core and surrounding a circumference of the second core; and a first housing unit that houses the amplification optical fiber and the output optical fiber therein.

A laser system for the generation of ultrashort optical pulses of light including an oscillator emitting low power and negatively chirped optical pulses with a spectral bandwidth W1, a dispersive connecting segment to maintain the sign of the chirp of the pulses of the oscillator, an optical amplifier for amplifying the optical light pulses and a negative group velocity dispersion segment for compensating phase contributions of the whole propagation process. During the propagation from the output of the oscillator to the end of the optical amplifier, the chirp of the light pulses will change once from negative to positive chirp. After a final compression stage ultrashort optical pulses can be generated.

The present invention benefits from the determination that pre-selected spectral bandwidths that avoid the spectrum of an electronic transition of a metal/alloy vapor allow for welds substantially free from detritus that may discolor the weld. Accordingly, the present invention provides analytical methods, welding methods and fiber lasers configured to provide high quality metal/alloy welds.

A method for reducing or eliminating bias instability in a SBS laser gyroscope comprises introducing a first pump signal propagating in a CW direction, and a second pump signal propagating in a CCW direction in a resonator; generating a CCW first-order SBS signal and a CW first-order SBS signal in the resonator; increasing a power level of the first pump signal above a threshold level such that the CW first-order SBS signal generates a CCW second-order SBS signal; and increasing a power level of the second pump signal above the threshold level such that the CCW first-order SBS signal generates a CW second-order SBS signal. Above the threshold level, an intensity fluctuation of the first-order SBS signals disappear and their DC power are clamped at substantially the same power level. A Kerr effect bias instability of the SBS laser gyroscope is reduced or eliminated by the clamped first-order SBS signals.

An optical fiber includes a core and a cladding. An effective area A.sub.eff of light of a fundamental mode, having a wavelength of 1070 nm and propagating through the core, is 500 μm.sup.2 or more. A numerical aperture NA of the core satisfies the following formula:

NA≥(1.3×10.sup.−11×a.sup.4/b.sup.6).sup.1/6

where a (m) is a radius of the core and b (m) is a radius of the cladding. A V value, that is a waveguide parameter of the optical fiber, satisfies the following formula:

V≤1.3583×b.sup.−0.2555.

A photonic device is configured with a photonic integrated circuit (PIC), a plurality of fiber-based gain mediums in optical communication with the PIC, and at least one optical pump outputting pump light coupled into two or more gain mediums. At least one of the fiber-based gain media and the PIC form a hybrid resonant optical cavity there between operative to lase light into the PIC. The gain media further include one or more fiber amplifiers amplifying light signals coupled into and decoupled from the PIC. The photonic device is integrated with Si photonic passive and active photonic elements, while ail fiber links between the gain media and PIC are free from these elements.

An EHz ultrafast modulated pulse scanning laser and a distributed fiber sensing system. A plurality of phase-shift gratings are engraved on a doped fiber, the phase-shift gratings having different central window wavelengths and a wavelength interval between the adjacent central window wavelengths being a preset fixed value. When a pump light emitted by a pump laser source is coupled by a wavelength division multiplexer and enters the doped fiber, a single-mode narrow-linewidth laser light having multiple wavelengths with a wavelength interval being a preset fixed value can be generated, by using the phase-shift gratings graved on the doped fiber. The ultrafast modulation is completed by using a time-domain control method based on an EOM. An internally frequency converted pulse light formed by splicing pulse lights whose frequencies linearly increase is obtained, thus forming the EHz ultrafast modulation of a distributed feedback fiber laser. In this way, a coherence length of an output laser light is increased while a frequency of the laser light is remained.