David Bryan Mortimore

Fiber loop reflectors

The theory and application of fiber loop reflectors, fabricated by forming a fiber loop between the output ports of a directional coupler, is described. The reflectivity of the loop is shown to depend upon the coupling characteristics of the coupler and on the degree of birefringence in the fiber loop. Measured loop reflectivities, in terms of wavelength response, coupling ratio, and loop birefringence are shown to agree very well with theory. Two applications of the fiber reflector are briefly discussed; an all fiber laser and a duplex optical communications link using a single light source. >

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.

Monolithic wavelength-flattened 1 × 7 single-mode fused fiber couplers: theory, fabrication, and analysis

The basic theory of monolithic 1 x 7 couplers is presented. The results of fabricating eighty-two devices are described, and the steady improvement in achieved device performance is shown leading to the fabrication of a controlled batch of eleven devices. These devices have excess losses of <0.1 dB together with good coupling uniformity to the seven output fibers. Maximum insertion losses are all around 10 dB or less, which is seen to compare favorably with devices obtained by concatenating 2 x 2 couplers. It is shown that to obtain an equal power split between the center and outer fibers it is necessary to control carefully the degree of fusion of the structure. An analysis of this coupling behavior is presented.

Theory and fabrication of 4×4 single-mode fused optical fiber couplers

The theory, fabrication, and performance of monolithic 4 x 4 single-mode fused couplers is reported. The field coupling matrix is derived and used to show that a device having equal coupling between the four fibers may be obtained. The fabrication of such a device is described, and measurements show that the device exhibits excellent coupling uniformity and low excess loss. The wavelength response of a device designed for equal coupling at 1.53 microm is shown between 1.2 and 1.6 microm.

Theory and fabrication of wavelength flattened 1 X N single-mode couplers

By using a theoretical model to describe coupling between an array of cores, it is shown that a range of monolithic wavelength flattened 1 x N couplers may be fabricated. Graphs of coupled power with coupling length are shown and the procedure for obtaining wavelength flattened devices is discussed for values of N ranging from 2 to 7. The fabrication and performance of a 1 x 7 coupler is described. The device has low excess loss (<0.3 dB) together with good coupling uniformity of <1% standard deviation at both 1.3 microm and 1.53 microm.

New all-fiber laser

We describe a Nd3+-doped fiber laser which uses all-fiber reflectors to form the resonant cavity. The mirrors, each made using a loop of doped single-mode fiber between the output ports of a fused tapered coupler1 (Fig. 1), are used in series with a length of doped fiber to form a structure which resembles an all-fiber Fabry-Perot laser (Fig. 2). A continuous length of doped fiber may be used to make the device.

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.