Abstract: Multiple-cavity fiber optic lasers are fabricated with high-gain fibers in low-loss, high-finesse fiber ferrule resonance cavity configurations supported in low-loss ferrule alignment fixtures developed for use in FFP filters. These lasers incorporate rare-earth doped, sensitized glass fiber as the active medium within FFP cavities. FFP lasers of this invention include those exhibiting single-frequency and/or single-polarization mode operation with wide mode separation. Lasers provided include those with short cavity lengths, where the longest of the cavities of can be less than or equal to about 10 mm in length. These FFP laser sources are fixed-frequency or discretely-tunable. Multiple-cavity configurations in which at least one of the cavities formed contains active fiber are readily formed in fiber ferrule assemblies. FFP lasers can be end-pumped using single- or double-pass pumping configuration or pump resonance cavity configurations.

Abstract: Passive, self-adjusting and tracking optical wavelength filters are described. The filters are absorptive and can be of either transmissive or reflective type. The filters comprise an unpumped doped optical waveguide configured so that signals of different wavelength are spatially decoupled to some extent. The self-adjustment of the filter centre wavelength is achieved by the combined effects of the power-dependent saturable absorption, provided by an appropriate dopant, and partial longitudinal hole burning provided by the spatial decoupling of the different wavelengths. External cavity lasers using this type of filter in the external cavity are also described. This external cavity configuration can provide stable single frequency operation of, for example, a semiconductor laser. By using a saturable absorber for the external cavity (e.g. an erbium doped fibre), longitudinal mode-hopping can be suppressed, ensuring single frequency operation.

Abstract: Compact, fixed-wavelength and tunable fiber optic lasers combine a sub-millimeter length of high-gain rare-earth-doped, sensitized glass fiber within a fiber Fabry-Perot (FFP) cavity. Tunable, single-frequency fiber lasers at 1535 nm employing high-gain erbium:ytterbium phosphate glass fiber are specifically provided. Single-frequency and/or single-polarization mode erbium:ytterbium glass fiber lasers, having cavity lengths less than about 200 .mu.m with continuous wavelength tuning range over several nanometers are provided. Amplified single-frequency lasers incorporating fiber rare-earth ion optical amplifiers are also provided. Single-frequency lasing employing sub-millimeter lengths of rare-earth doped sensitized fiber in a 3 mirror laser design is also demonstrated.

Abstract: An optical amplifier comprises first (22) and second (24) lengths of erbium-doped fibre connected in series via an isolator 20 which reduces the transmission of backward-travelling ASE from the second length to the first length when pump power in inputted in to the first length.

Abstract: The spectral-gain characteristics of an erbium-doped fibre amplifier have been tailored by incorporating a gain-shaping-filter within the amplifier. The filter is chosen to modify the natural gain spectrum of the amplifier so as to suppress the gain peak and thus flatten the overall spectral-gain profile. Because the amplifier is distributed, it is possible to insert one or more filters along the length of the fibre. It is shown that there are considerable advantages to locating the filter within the length of the amplifier, rather than at the end, which is the more obvious choice. Advantages are that the amplifier pump efficiency is almost unaffected and the output saturation power is similar to that of the unshaped amplifier. In addition, the flat spectral gain provides an amplifier ideally-suited for use at a number of signal wavelengths, as required for wavelength-division multiplexing (WDM).

Abstract: An active device (FIG. 1) comprising a length of doped fiber (1) and an end-coupled pump source (11). The fiber (1) is of single-mode geometry and incorporates rare-earth or transition metal dopant ions. These latter are incorporated at a low-level uniform concentration (.ltorsim.900 ppm). The fiber host (1) selected exhibits an inherently ultra low attentuation loss (.ltorsim.40 dB/km) at the emission wavelength. The fibers (1) are generally of long length (e.g. 5 m to 300 m) and may be coiled for compact packaging. The fiber (1) may be formed as part of a Fabry-Perot cavity (1, 7, 9); or, as a ring cavity (FIG. 8) using a doped fiber coupler (29) spliced to form a ring (27). Q-switch and mode-locking devices (19) and gratings (25) may be included as part of the Fabry-Perot cavity to allow pulse-mode operation and/or wavelength tuning, respectively. The fiber (1) may also be utilised as an amplifier.

Abstract: A sensor for sensing magnetic fields. A single mode optical fiber has a core which is wound into a helical shape. The fiber is formed with a former and a core, and the core is preferably attached to the inner surface of the former and wound into a helical shape tracing its inner periphery. The core is also offset from the central axis of the fiber former.

Abstract: A fibre laser (1) of the type comprising a doped single-mode optical fibre (3) arranged between reflectors (5,7), and which is coupled (11) to an optical pumping source (9). For the given reflection efficiency of the reflectors (5,7), the length of the optical fibre (3) is chosen such that it exceeds that affording saturation and provides at its end a region for absorption (FIG. 1). The resultant hysteretic behavior of this bistable device may be utilized for logic memory (bistable), and regenerative amplification applications. To this end a second source (9') can be coupled (11',19) to the laser fibre (3).

Abstract: A method of making a preform for drawing optical fibers includes the steps of depositing a dopant material 3 in a dopant carrier chamber 1, heating the dopant material to cause it to vaporise at a predetermined rate, depositing from a mixture of a source material (GeCl.sub.4, SiO.sub.4, O.sub.2) and said vaporised dopant a mixture of solid components 8 and fusing said solid components to form a doped glass.

Abstract: A frequency selective optical polarizer is formed by pressing a length of single mode polarization maintaining fiber 12 against a ribbed plate 10 in order to generate a distributed strain pattern with a periodicity which causes for a particular optical frequency one of the guided modes to couple into an unguided mode while the other guided mode remains substantially uncoupled.

Abstract: A detector comprises an optical radiation source (10) and a length of optic fibre (18) sensitive to local variations in a physical variable. Changes in radiation back-scattered by the fibre are received by a detector (24) which gives an output dependent on local changes in the physical variable.

Abstract: To determine the radial profile of the refractive index of a substantially cylindrical transparent object such as an optical fibre or optical fibre preform, the object is illuminated with a collimated beam of light incident at an angle to the axis of the cylindrical object differing substantially from 90 degrees and measuring the refraction angle at which light leaves a substantially plane endface as a function of the radial position on the endface.

Abstract: A method of sensing the optical deflection function of an approximately cylindrical object, such as an optical fibre preform, comprises illuminating the object with collimated light; focusing the transmitted light so that in the focal plane the distance of the light from the optical axis is linearly proportional to the angle through which light has been deviated by the object; optically modulating the focused light so that a property of the light varies as a function of said distance, and calculating the deflection function from the modulated light. The modulations may be spatial or temporal. The refractive index profile can also be calculated.

Abstract: A star coupler for distributing light from an input optical fibre to one or more output fibres comprises a glass mixer rod interfaced with an optical fibre array and provided with a coating of highly reflective material at the array/mixer rod interface. The coating is provided with apertures which correspond to the fibre core positions such that the coating masks the cladding and interstitial regions of the fibre array. The end face of the mixer rod remote from this interface can be either uniformly mirrored or can be coupled with a second fibre array by a similar reflecting array/mixer rod interface.

Abstract: An optical waveguide has a silica cladding and a phosphosilicate core. Additional components may be added to improve the match of physical properties between core and cladding. The waveguide is manufactured by passing a mixture of vapors of silicon tetrachloride and phosphorus oxychloride through the interior surface of a glass tube and heating to cause oxidation and simultaneous deposition of silica and phosphorus pentoxide. The interior coated tube is then collapsed to a rod and the rod is drawn into an optical fibre.