Showing papers on "Dispersion-shifted fiber published in 1989"

Soliton trapping in birefringent optical fibers

Abstract: We show experimentally the trapping of orthogonally polarized solitons in birefringent optical fibers with polarization dispersions as high as 90 psec/km. Solitons along two axes of a fiber compensate for the polarization dispersion by shifting their frequencies, and we observe frequency splitting up to 1.03 THz for a polarization dispersion of 80 psec/km. For a 20-m fiber the energy required to compensate for the polarization dispersion is ~84 pJ, and for a 76-m fiber the energy required reduces to ~64 pJ.

Efficient Er3+‐doped optical fiber amplifier pumped by a 1.48 μm InGaAsP laser diode

Abstract: Optical gain characteristics of an Er3+ ‐doped silica fiber have been studied by end pumping with a 1.48 μm InGaAsP high‐power laser diode. A gain as high as 12.5 dB was obtained for an absorbed pump power of 16 mW with a 3‐m‐long fiber. By constructing an Er3+ fiber ring cavity with a 3 dB single‐mode fiber coupler, we have obtained continuous wave laser oscillation at a wavelength of 1.553 μm.

Single mode bend insensitive fiber for use in fiber optic guidance applications

Abstract: A double-clad single mode optical fiber with a depressed inner cladding exhibits increased resistance to attenuation increases resulting from small radius bends and lower attenuation sensitivity to temperature changes when the mode field diameter is less than 7 um and the ratio of the radius of the inner cladding to the radius of the core is at least 6.5 to one.

Resistance of solitons to the effects of polarization dispersion in optical fibers.

Abstract: Using numerical simulation, we show that solitons of any pulse width can avoid splitting or excessive broadening in response to birefringence of randomly varying orientation as long as the fiber’s polarization-dispersion parameter (in psec/km1/2) is less than ~0.3D1/2, where D is the dispersion parameter (in psec nm−1 km−1). Nevertheless, we also find that polarization dispersion tends to produce a significant amount of dispersive wave radiation from the soliton.

Analysis of transient gain saturation and recovery in erbium-doped fiber amplifiers

Abstract: An analysis of transient gain dynamics in erbium-doped fiber amplifiers is presented to provide a qualitative explanation of its time constants. The theory yields analytical solutions at the fiber amplifier input end, making it convenient to study the time dependence of gain saturation and recovery under changing input signal conditions. It is shown that, independently of the pump wavelength, gain saturation and recovery effects have long characteristic times (0.2-10.0 ms) which advantageously reduce saturation-induced crosstalk in the amplifier. The effect of saturation-induced gain modulation is found to vanish at signal frequencies above F=1 kHz, which is in good agreement with observed experimental results. >

Fiber optic sensors

Abstract: Serveral improvements in fiber optic sensing systems are disclosed. One improvement incorporates a dielectric filter applied directly to the sensing end of an optical fiber detector which has the characteristic that it reflects back a reference light beam of one wavelength while passing a sensing signal of a different wavelength which is modulated in some predetermined fashion beyond the filter. Both light signals are reflected back through the fiber and are, accordingly, attenuated in the identical or nearly identical fashion in response to various noise sources. The ratio of the intensity of the two signals is proportional to the sensed parameter and renders the system essentially self-compensating. The dielectric filter is preferably directly coated onto the exit end of the fiber through vapor deposition techniques. Time division multiplexing is used to sequentially fire plural light sources and a single photodetector is used for measuring the intensity of the reflected back signals of the various wavelengths. Another improvement encompasses the detection unit in which the input and reflected signals are separated using an off-axis parabolic mirror which provides excellent separation efficiency. According to another principal feature of this invention, a concave surface is formed at the fiber end which increases the numerical aperture of the fiber which provides greater sensitivity to the deflection of a pressure sensitive diaphragm spaced from the confronting the fiber end.

Investigation of coupling between a fiber and an infinite slab

Abstract: An optical waveguide system consisting of an unclad fiber core suspended at a constant distance parallel to the surface of an infinite extended dielectric slab is investigated. Fiber and slab are both embedded in a homogeneous dielectric medium. The fate of light initially launched into the fiber depends on the relationship between the refractive index values of the slab and fiber. When the refractive index of the fiber is considerably larger than that of the slab, the latter exerts little influence on the wave, so that almost no power is transferred out of the fiber. When the refractive indexes of fiber and slab are more nearly the same, a beating phenomena is observed, that is, light is exchanged periodically between the fiber and the slab. However, after some distance the beating dies out. Some of the light energy remains in the combined system of fiber and slab, which can be regarded as a ridge waveguide, while the remaining light spreads out laterally in the slab. If the refractive index of the slab is considerably larger than that of the fiber, the slab acts as a drain on the light initially launched into the fiber. The light power in the fiber decreases exponentially with the distance along the fiber axis as it is transferred to the slab where it is carried away. >

Superfluorescent broadband fiber laser source

Abstract: A superfluorescent broadband fiber laser source comprises a fiber doped with laser material coupled to a multiplexing coupler. In the preferred embodiment, a source of pumping illumination provides pumping light to the doped fiber, and the coupler is adjusted to have a 0% coupling efficiency at the wavelength of the source. The pumping light is sufficiently intense to produce amplified spontaneous emission within the doped fiber, and gives rise to a forward signal and a backward signal. One of the superfluorescent signals is reflected back to the doped fiber by a reflector cemented to one end of the doped fiber or to one end of another fiber through the coupling function of the coupler. The coupler is adjusted to provide complete coupling at the frequency of the lasing light. The temperature dependence of the coupler can be selected to reduce or cancel the temperature dependence of the superfluorescent signal. Other arrangements utilizing the multiplexing properties of the coupler are also described. An all-fiber reflector can also be used.

Optical fiber switch employing a Sagnac interferometer

Abstract: Switching in less than 1 ns of an optical signal at 632 nm is demonstrated in a 1 m optical fiber Sagnac interferometer. Full signal modulation was obtained with a pump power of 24 W at a wavelength of 532 nm.

An apparatus for optically connecting a single-mode optical fiber to a multi-mode optical fiber

Abstract: An apparatus connects a single-mode optical fiber (2) in a transmitting side to a multi-mode optical fiber (4) in a receiving side without a deterioration of baseband transmission characteristics. The apparatus optically connects the single-mode fiber (2) to the multi-mode fiber (4) with an optical axes displacement therebetween, so that an optical signal to a multi-mode optical fiber (4) from a single mode optical fiber (2) is incident in a steady state mode including not only lower mode, but higher mode. In one embodiment, the optical axes displacement is achieved by axial displacement (d) between the single-mode fiber (2) and multimode fiber (4). In another embodiment, the optical axes displacement is achieved by an angle displacement between the single-mode fiber and multi-mode fiber.

Modulation instability-based fiber interferometric switch

Abstract: High incremental gain and ultrafast switching operation are achieved in a fiber interferometer switch by employing a control optical signal in one arm of the interferometer and a pump optical signal split between both arms of the interferometer wherein signal frequencies are in the anomalous group velocity dispersion region of only one arm of the fiber interferometer to cause modulation instability to occur. Net gain in excess of 10 4 has been observed where net gain is the ratio of device output peak power to control signal input power. In a preferred embodiment of the invention, the interferometer is a balanced Mach-Zehnder interferometer utilizing a single mode, dispersion shifted, polarization-preserving optical fiber.

Optical fiber transmission path with dispersion compensation

Abstract: An optical fiber transmission path wherein total dispersion of the system is compensated by use of fibers composed of glasses with total dispersion of opposite signs at the operating wavelength for the system. With silica-based fibers, CdF 2 --LiF--AlF 3 --PbF 2 --KF--YF 3 fluoride glass-based fibers may be used for a system with 1.55 μm operating wavelength.

Observation of ultrafast nonlinear polarization switching induced by polarization instability in a birefringent fiber rocking filter

Abstract: Ultrafast all-optical switching between two orthogonal linear polarizations in a periodically twisted fiber filter is discussed. The dependence of the switching characteristics on the input power and operating wavelength is considered. >

Erbium-doped fiber amplifier coupling device

Abstract: This invention is directed toward reducing substantially the loss incurred when two optical fibers of different mode diameters are coupled together. In this invention, the coupling of one fiber to that of another where the fibers are of different mode diameters is not with a tapered fusion, core-to-core splice, but with an evanescent field fiber coupler. Briefly, to achieve amplification of a weak optical signal, an amplifying fiber is inserted into the system at one or a plurality of locations. More specifically, at a desired location, the transmission fiber is severed to provide two sections and the severed sections are transversely coupled to the amplifying fiber. The weak signal from the first section of the transmission fiber is coupled into the amplifying fiber via a first evanescent field type of fiber coupler; and the amplified signal is coupled from the amplifying fiber to the second section of the transmission fiber via a second evanescent field type of fiber coupler. The first evanescent field type of fiber coupler is designed to couple substantially all of the signal energy from the first section of the transmission fiber to the amplifying fiber and to couple substantially none of the laser diode pump signal or energy from the amplifying fiber to the transmission fiber. The second evanescent field type of fiber coupler is designed to couple substantially all of the signal energy in the amplifying fiber to the transmitting fiber and substantially no laser diode pump energy is transferred from the amplifying fiber to the transmission fiber. Either or both cut ends of the transmission fiber can be coupled to monitor devices to detect and determine the value of the signal being coupled into and/or out of the amplifying fiber to control, for example, the gain of the amplifying fiber.

Broadband optical fiber laser

Abstract: An optical fiber laser includes a single-mode optical fiber doped with a lasing material such as Neodymium. The optical fiber is pumped with a pump optical signal having a pump wavelength selected to cause spontaneous emission of an optical signal at a second wavelength different from the pump wavelength. The optical fiber is formed into a laser cavity such as by including a suitable reflector at each of the two ends of a suitable length of the optical fiber so that the emitted optical signal oscillates therein. One of the reflectors has a reflectivity at the wavelength of the emitted light so that most (e.g., approximately 95%) of the emitted light is reflected back into the laser cavity and a smaller portion (e.g, approximately 5%) is transmitted through the mirror as a laser output signal. Alternatively, the optical fiber can be formed into a ring laser structure using an optical coupler that couples a substantial portion (e.g., approximately 95%) of the emitted light back into the ring for recirculation therein and provides a smaller portion of the emitted light (e.g., approximately 5%) as a laser output signal. The wavelength of the pump optical signal is selected to be outside the pump variable tuning range of the Neodymium-doped optical fiber (i.e., the range of pump wavelengths which stimulate emitted wavelengths having a average wavelengths with a generally one-to-one correspondence to the pump wavelength). Pumping with a pump signal outside the pump variable tuning ranges causes the emitted light to have a broad spectral envelope of longitudinal modes having emission wavelengths corresponding to substantially all the pump variable tuning range. Thus, by pumping the optical fiber with a single pump wavelength, a broadband laser output signal is generated.

Transmission of AM-VSB video signals over an optical fiber

Abstract: The use of a doped optical fiber amplifier enables the transmission of multi-channel AM-VSB television signals. An Erbium doped fiber amplifier is disclosed. The amplifier is also useful for reducing second order distortion products produced in an amplitude modulated subcarrier optical communication system. The amplifier may be used in a tree and branch structure optical fiber television network.

Doped optical fiber laser amplifier

Abstract: An erbium-doped fiber laser amplifier (1), characterized by the fact that said fiber (3) is doped to a concentration lying in the range 5 ppm to 50 ppm, that the length of said fiber lies in the range 250 m to 30 m depending on the selected concentration of doping, and that the radial position of the doped zone substantially coincides with the energy maximum of the set of propagation modes in said fiber at the pumping wavelength.

A carrier injection type optical switch in GaAs using free carrier plasma dispersion with wavelength range from 1.06 to 1.55 mu m

Abstract: The switching current for the device is about 90 mA at all in-range wavelengths. Its broad wavelength range is suitable for optical signal-processing applications in wavelength-division multiplexing transmission systems. High coupling efficiency to a single-mode fiber is achieved by using a small- Delta waveguide structure with carrier blocking layers. The effective refractive index change in the waveguide per unit of the injected current density is doubled by the carrier blocking layers without reducing coupling efficiency. >

A new single-polarization optical fiber

Abstract: In the single-polarization optical fiber, two isolated stress-applying parts contribute to radiate one of the two orthogonal polarization modes due to the asymmetrical geometric-index effect in addition to a stress-induced birefringence effect without bending the fiber. The loss spectra for x- and y-polarizations and the length dependence of the crosstalk show that the present fiber exhibits single-polarization characteristics. >

Applications of ultra-stable fiber optic distribution systems

Abstract: Present and future applications of fiber-optic frequency distribution systems are discussed and it is noted that for applications requiring distribution stability greater than one part in 10/sup 15/ at 1000 s averaging times, a stabilized fiber optic link is the only choice presently available. A stabilized fiber optic system that can improve distribution stability by more than 100 times is also described. It uses a cable delay compensator. >

Er-doped optical fiber laser device

Abstract: An Er-doped optical fiber laser device adapted for pumping by light from a pumping light source in an erbium (Er)-doped optical fiber which enters a single mode at the wavelength of amplified light. In accordance with the present invention, the Er-doped optical fiber is further doped with at least one of holmium (Ho), thulium (Tm) and dysprosium (Dy). The pumping light source emits light in a 1.1 to 1.4 μm band. The output light from the pumping light source and signal light incident to the Er-doped optical fiber are combined by a combining optical fiber coupler.

Broadband all‐fiber filters for wavelength division multiplexing application

Abstract: In‐line spectral filters are designed and realized using the tapering technique to provide additional isolation to the demultiplexing fused fiber couplers. The typical performances obtained are less than 1 dB loss with more than 15 dB isolation in a 40 nm range around the desired wavelengths.

Nonlinear propagation and self-switching of ultrashort optical pulses in fiber nonlinear directional couplers: the normal dispersion regime

Abstract: The propagation of short optical pulses in a nonlinear directional coupler operating in the normal dispersion regime is investigated. The specific example of a birefringent periodically rocked fiber filter where coupling occurs between the two orthogonally polarized modes that are aligned with the birefringence axes of the fiber is considered. In the simulations, a bell-shaped input pulse is injected into one polarization mode: for different input peak powers, the energy present in the same mode at the output of a coupler, which is one or two coupling lengths long, is calculated. The nonlinear temporal broadening, due to the combined effect of group velocity dispersion and self-phase modulation, sets a fundamental lower limit to the time width of the input pulses. When pulses shorter than this critical value are used, the power-dependent energy switching characteristics of a device one coupling length long gets substantially spoiled. Effects related to the finite spectral bandwidth of the fiber filter are discussed. Numerical simulations are compared to recent experimental results on the self-switching of picosecond pulses in the visible (615 nm) with a birefringent rocking fiber. >

Laser-to-fiber coupling via optical fiber up-tapers

Abstract: A method for coupling single-mode fiber to laser diodes with high efficiency and greatly reduced alignment sensitivities is discussed. It consists of a spherical ruby lens and a single-mode optical fiber up-taper. Using a double-channel planar buried heterostructure (DCPBH) laser, more than 60% of the light from the lens is coupled into a single-mode fiber via the taper. The lateral and axial tolerances of the lens-taper arrangement are reduced by factors of 20 and 1000 times, respectively, compared with laser coupling to a lensed single-mode fiber. These relaxed alignment tolerances have the potential to allow the taper to interface with a hermetically-sealed laser-lens package via a window and a connector on the package exterior. >

Mode-locked fiber laser with a fiber phase modulator.

Abstract: FM mode-locked operation of a single-mode Nd3+-doped fiber laser has been achieved with an integrated fiber phase modulator. The technique permits a low-loss cavity configuration, resulting in low threshold and high slope efficiency. Pulses of ~200psec duration are observed at a repetition rate of 417 MHz with an average output power of 15 mW.

Ionization-induced nonequivalent absorption in a birefringent silica fiber

Abstract: The response of a single-mode highly birefringent fiber, operating at a wavelength of 1.3 mu m and irradiated by a source of 200 MeV pulsed protons, is presented. The fiber fast and slow axes of birefringence were optically excited and observed to exhibit transient absorption at different rates which scaled linearly over the pulsed exposure range of 2.6-17.4 krad (Si). Mechanisms possibly affecting the fiber birefringence are discussed including the introduction of transient electric and magnetic fields arising from the ionizing radiation. >