Low power all-fibre intensity modulator at 2.7MHz

A monolithic single-mode fibre acousto-optic amplitude modulator is reported. Nearly 100% modulation is achieved at a modulation frequency of 2.7MHz for an electrical drive power of 2mW

All fibre polariser using a null coupler

We report a new fibre polariser based on a twisted null taper coupler. The best extinction ratio observed so far is 15dB

3x3 all-fibre routing switch

An all-fibre acousto-optic switch has been constructed from a 3x3 null fused coupler. The maximum drive power required is 4 mW, the switching time is 100µs and the insertion loss is less than 0.5 dB. The switch shares the advantages of an earlier 2x2 switch but with more fibre ports. and should permit the design of compound routing arrays with fewer switching elements per channel

All-fibre 3 x 3 acousto-optic switch

We report an all-fibre 3 x 3 acousto-optic switch. The maximum drive power required is 4 mW, the switching time is 100µs and the insertion loss is less than 0.5 dB

40-MHz all-fiber acoustooptic frequency shifter

We report the development of a 40 MHz four-port all-fibre frequency shifter operating at a wavelength of 1.55 µm. The device has a high conversion efficiency, low drive power requirement and is manufactured from standard telecommunications fibre

Low-power low-loss acousto-optic fibre switch

We have previously reported a new design of all-fibre acousto-optic frequency shifter. It is based on a special asymmetric fused taper coupler which in the passive state does not actually couple light at any wavelength: the null coupler. An appropriate flexural acoustic wave imposed on the coupler causes light to couple between the fibres. This device can equally well function as a 2x2 all-fibre optical routing switch: the switch is in the "cross" state when the acoustic wave is on, and is in the "bar" state when the acoustic wave is off. Of particular interest are the switching time, insertion loss, crosstalk and drive power

All-fibre polariser based on a null taper coupler

An entirely new type of single-mode all-fiber polarizer is reported. The polarizer is based on a narrow circularly fused null taper coupler, which was twisted through 45° after being made. The polarizing effect is due to the excitation of hybrid second modes in the coupler waist. An extinction ratio of 15 dB and an insertion loss of 0.2 dB have been obtained, with scope for further improvement

New early Eocene tapiromorph perissodactyls from the Ghazij Formation of Pakistan, with implications for mammalian biochronology in Asia

Early Eocene mammals from Indo-Pakistan have only recently come under study. Here we describe the first tapiromorph perissodactyls from the subcontinent. Gandheralophus minor n. gen. and n. sp. and G. robustus n. sp. are two species of Isectolophidae differing in size and in reduction of the anterior dentition. Gandheralophus is probably derived from a primitive isectolophid such as Orientolophus hengdongensis from the earliest Eocene of China, and may be part of a South Asian lineage that also contains Karagalax from the middle Eocene of Pakistan. Two specimens are referred to a new, unnamed species of Lophialetidae. Finally, a highly diagnostic M3 and a molar fragment are described as the new eomoropid chalicothere Litolophus ghazijensis sp. nov. The perissodactyls described here, in contrast to most other mammalian groups published from the early Eocene of Indo-Pakistan, are most closely related to forms known from East and Central Asia. Tapiromorpha are diverse and biochronologically important in the Eocene there and our results allow the first biochronological correlation between early Eocene mammal faunas in Indo-Pakistan and the rest of Asia. We suggest that the upper Ghazij Formation of Pakistan is best correlated with the middle or late part of the Bumbanian Asian Land-Mammal Age, while the Kuldana and Subathu Formations of Pakistan and India are best correlated with the Arshantan Asian Land-Mammal Age

High-performance four-port acousto-optic frequency shifter at 1.55µm using standard single-mode telecommunications fibre

If a four-port fused-taper coupler is constructed from dissimilar fibers, the maximum splitting ratio can be close to zero over a broad spectral band. As previously shown, such a null coupler can be used to form an effective four-port acousto-optic frequency shifter. In Ref. 1, two dissimilar nonstandard fibers were used. Here we report the successful construction of a null coupler made by using standard telecommunications fiber. The procedure involves pretapering one of an identical pair of fibers to provide the necessary dissimilarity. In this way the device can be constructed entirely from one fiber type with four identical ports, and it can be made compatible with any existing network. Our present device used standard 125µm single-mode telecommunications fiber throughout, for operation at a wavelength of 1.55µm