C.A. Millar

Exposed-core single-mode-fiber channel-dropping filter using a high-index overlay waveguide

Using the coupling between a standard single-mode fiber and single higher-order modes in a high-index overlay waveguide, we demonstrate a wavelength-filtering device with a channel-dropping response. Two types of filter are described. One uses a thin overlay waveguide, giving a single tunable dropped band response in the 1.2-1.6-microm wavelength region with rejection greater than 20 dB and an insertion loss of about 0.5 dB. The other uses a thick overlay waveguide and gives a comb-filter response with a dropped channel spacing of 13 nm with 20-dB rejection and an insertion loss of between 1 and 4 dB.

A Nd 3+ -doped cw fiber laser using all-fiber reflectors

We demonstrate a novel all-fiber resonant optical cavity which uses two-fiber reflectors, each formed by a single loop of fiber between the output ports of a fiber directional coupler. The reflectivities of the fiber mirrors are each determined by the coupling ratio and the insertion loss of the fused couplers. When the cavity is formed in this way using a continuous length of Nd(3+)-doped fiber and pumped using a GaAs laser diode, lasing occurs at a wavelength of 1064 nm. Both theoretical and practical descriptions of the device are given.

Fibre reflection mach-zehnder interferometer

Abstract A novel design of two-port, all-fibre reflection Mach-Zehnder interferometer is demonstrated. We calculate the theoretical frequency variation of output power and demonstrate close agreement with experimental observations. The device has potential application as a reflective modulator for a fibre laser and as a fibre sensor.

Single transverse mode operation at 1345 nm wavelength of a diode-laser pumped neodymium:ZBLAN multimode fiber laser

A diode-laser pumped multitransverse-mode neodymium-doped fluoride fiber laser is shown to oscillate in the lowest-order transverse mode when the cavity conditions are optimized. The combination of good pump coupling efficiency, laser operating efficiency, and good overlap of the HE/sub 11/ mode to that of a single-mode fiber, allows up to 12 mW of continuous wave (CW) power to be coupled into a standard single-mode fiber at a 1345-nm wavelength. Improved lens design should significantly increase the power injected into the single-mode fiber from the multimode fiber laser.<<ETX>>

Laser diode pumped Er/sup 3+/-doped fiber amplifier in a 565 Mbit/s DPSK coherent transmission experiment

A laser-diode-pumped erbium-doped fiber amplifier, exhibiting 9-dB gain, has been operated as an in-line optical repeater in a 565-Mb/s coherent optical communications system. A sensitivity penalty of 0.4 dB was observed when the amplifier was positioned 35 dB away from the receiver, thus indicating a system improvement of 8.6 dB. By progressively reducing the coupling loss between amplifier and receiver, the noise figure of the contradirectionally pumped amplifier was calculated to be 5.4 dB, a value which is consistent with simple noise theory.<<ETX>>

The effect of pump and signal field overlap with the ion distribution on the efficiency of an Er3+-doped fibre amplifier

Abstract We report the use of a far-field scanning system to measure the pump and signal fields within erbium doped fibre amplifiers. Measurements were carried out on fibres with both uniform dopant throughout the core and dopant confined to the central region of the core. We have demonstrated that the improvement in amplifier performance associated with ion confinement is consistent with the change in overlap between pump and signal fields and the radial ion distribution. It is shown that most of the improvement available through the process of confinement can be obtained through restricting the dopant to the inner 40% of the pump mode field radius. The effects of radial ion confinement on the small-signal gain performance of amplifiers exhibiting pump excited states absorption are discussed and compared to the effects on amplifiers free from pump ESA. We conclude that the process of confinement is only of benefit in amplifiers free from the parasitic effects of pump excited state absorption.

A fiber-based crosspoint switch using high-refractive index interlay materials

A switch principle is described which relies on the coupling between two polished fiber coupler blocks through a high-index interlay waveguide whose refractive index is higher than the effective mode index of the fibers. Switching is effected by the input radiation coupling through the interlay waveguide into the second fiber (cross-coupled state) or recoupling into the first fiber (straight-through state). The half-coupler blocks were constructed with a nominal radius of curvature of 25 cm and the top surfaces polished close to the edge of the fiber core. Accurate glass and polymer ribbon spacers were used to separate the two blocks by from 5-20 mu m and align them in parallel. The interstice was filled with a film of transparent high-index oil to form a slab waveguide. >

Cladding alignment of butted optical fibers using a diffraction alignment device (DAD) and its application to mode-spot concentricity-error measurement

A novel technique which uses the interference of diffraction patterns to establish the mechanical alignment of butted optical fibers is described, and its application to mode-spot concentricity-error measurement is demonstrated. Complete spatial alignment to within 0.2 μm of relative offset and about 7-min of arc of relative tilt is achieved. In conjunction with a straightforward optical transmission loss apparatus, the method, when applied to mode-spot concentricity-error measurements, provides good agreement with alternative techniques. Accuracies are estimated and improvements suggested.

Rare-earth-doped fluoride fibers for optical amplification (Invited Paper)

Rare earth-doped fluorozirconate fibres show potential as optical amplifiers from the visible to the mid IR. This paper reviews the current status of their application in telecommunications, concentrating on Tm and Er-dopants for the 1st window and Nd and Pr-dopants for the 2nd window. A 1300 nm system operating at 2.5 Gbits/s using a Pr-doped fibre amplifier is described.

Rare-Earth Doped Fibre Lasers And Amplifiers For Optical Communications

Recently, the widespread use of single-mode fibres has demonstrated the need for a range of optical components which perform useful optical functions such as routeing, modulation, amplification, and carrier generation. The benefits of achieving these in all-fibre form are considerable. Interest in the latter functions was generated by the pioneering work at SouthamptonVniversity on the fabrication (1) and demonstration of efficient fibre lasers using Pr3+, Nd3+ and Erif as the rare-earth dopants (2), pumped using a variety of sources including inexpensive GaAs semiconductor lasers. Line-narrowed, tuned, mode-locked and Q-switched operation have been reported in these fibre lasers.