A dual output semiconductor optical amplifier-based tunable fiber laser is provided that can be switched from low to high power and vice versa. The laser system uses bidirectional semiconductor optical amplifier (SOA) for amplification and hence is able to introduce a unique feature of adjustable dual/single output ports.

An optical fiber configured to improve the pump conversion efficiency of an L-band fiber amplifier which uses the multimode pump source. By directly absorbing multimode light including 915 nm, an active fiber core region co-doped with both erbium and ytterbium can provide gain to the L-band signals via stimulated emission. The unwanted C-band amplified spontaneous emission (ASE) light generate from this active fiber core region can be absorbed by another active fiber core region doped with erbium, then provides additional gain to the L-band signals. Active regions and cladding can be configured to match a given spatial mode of the optical signal. Signal-pump combiners with end-coupling or side coupling can be used.

A dual output laser diode may include first and second end facets and an active section. The first and second end facets have low reflectivity. The active section is positioned between the first end facet and the second end facet. The active section is configured to generate light that propagates toward each of the first and second end facets. The first end facet is configured to transmit a majority of the light that reaches the first end facet through the first end facet. The second end facet is configured to transmit a majority of the light that reaches the second end facet through the second end facet.

A pulsed laser device includes: a semiconductor laser device that outputs laser light having a single wavelength; a semiconductor optical amplifier that receives the laser light output from the semiconductor laser device and amplifies the laser light to output; and a semiconductor-optical-amplifier driver that supplies a pulse-modulated semiconductor-optical-amplifier driving current to the semiconductor optical amplifier.

A fiber amplifier that is particularly configured to provide gain across a large extent of the C-band spectral range (i.e., a gain bandwidth of at least 42 nm, preferably within the range of 46-48 nm) utilizes a specially-designed discrete Raman amplifier in combination with a high inversion level EDFA to extend the gain bandwidth of a conventional EDFA C-band optical amplifier, while maintaining the gain ripple below an acceptable value. The EDFA provides operation at a highly-inverted level and the specialized discrete Raman amplifier (sDRA) element has particular parameters (dispersion, length, effective area) selected to maintain operation within a small gain regime while also extending the long wavelength edge of the gain bandwidth and reducing the gain ripple attributed to the EDFA component.

An optical amplifier may comprise a first gain stage and a second gain stage. Each of the first and second gain stages may comprise a laser pump and an active fiber. A liquid crystal device may be coupled between an output of the first gain stage and an input of the second gain stage. A control unit may be coupled to the first and second gain stages, liquid crystal device and configured to control the first and second gain stages, and the liquid crystal device to provide a switchable gain. Light may pass through the first and second gain stages and be amplified by the first and second gain stages. The light amplified by the first gain stage may pass through the liquid crystal device and may be filtered by the liquid crystal device.

A broadband optical amplifier is configured to optically amplify an optical signal which is received at an amplifier input port and which includes first spectral components lying within a predetermined first optical band and second spectral components lying within a predetermined second optical band, and to output the amplified optical signal to an amplifier output port. Also provided is a method for designing a broadband optical amplifier including the steps of creating a mathematical model of the broadband optical amplifier, determining the efficiency-optimized design of the reference broadband optical amplifier, determining a maximum value of the wavelength-dependent noise figure of the reference broadband optical amplifier, determining a modified design and using the modified design for setting up a corresponding physical broadband optical amplifier.

A dual output laser diode may include first and second end facets and an active section. The first and second end facets have low reflectivity. The active section is positioned between the first end facet and the second end facet. The active section is configured to generate light that propagates toward each of the first and second end facets. The first end facet is configured to transmit a majority of the light that reaches the first end facet through the first end facet. The second end facet is configured to transmit a majority of the light that reaches the second end facet through the second end facet.

An optical fiber for amplification includes a core having an inner core and an outer core surrounding the outer circumferential surface of the inner core. The relative refractive index difference of the inner core to a cladding is smaller than the relative refractive index difference of the outer core to the cladding. The outer core is entirely doped with erbium. The theoretical cutoff wavelength of an LP.sub.11 mode light beam is a wavelength of 1,565 nm or more. The theoretical cutoff wavelength of an LP.sub.21 mode light beam is a wavelength of 1,530 nm or less. The theoretical cutoff wavelength of the LP.sub.02 mode light beam is a wavelength of 980 nm or less.

An amplification optical fiber operable to propagate light beams in a plurality of modes in a predetermined wavelength range through a core doped with a rare earth element, wherein Expression (1) is satisfied, where a cutoff wavelength of a propagated highest mode light beam is defined as max, under conditions in which the cutoff wavelength of the highest mode light beam is defined as c, a shortest wavelength of the wavelength range is defined as min, and a cutoff wavelength of a second-highest mode light beam to the highest mode light beam is min.
c>0.5 min+0.5 max(1).