Polarisation switching in active devices

Claim 2

A bistable polarisation source comprising a semiconductor injection laser capable of providing optical gain in two distinguishable waveguiding paths, the waveguding paths extending substantially parallel to one another at a small enough separation to enable the fields of optical radiation in the two paths to overlap, the laser being switchable between first and second states in which the direct optical output of the laser is predominantly TE polarised and predominantly TM polarised respectively.

Claim 3

A polarisation source as claimed in Claim 1 wherein in both said first and second states the ratio of the dominant polarisation type to the subordinate polarisation type is greater than 10 to 1.

Claim 4

A polarisation source as claimed in Claim 1 wherein the ratio is greater than 15 to 1.

Claim 5

A polarisation source as claimed in Claim 3 wherein the ratio is greater than 20 to 1.

Claim 6

A polarisation source as claimed in any of the preceding claims wherein switching between said states is effected by adjusting the operating current of the laser.

Claim 7

A polarisation source as claimed in any one of Claims 1 to 4 wherein switching between said states is effected by injecting optical control signals.

Claim 8

A polarisation source as claimed in any one of the preceding Claims wherein said laser comprises a twin stripe laser.

Claim 9

A polarisation source as claimed in Claim 7 wherein said laser has an active layer which is 150 µm or more in length.

Claim 10

A polarisation source as claimed in Claim 8 wherein said active layer is 170µm or more in length.

Claim 11

A polarisation source as claimed in any one of claims 7 to 9 wherein the twin stripes are separated by a distance of between 5 and 20µm.

Claim 12

A polarisation source as claimed in any one of Claims 1 to 6 wherein the said laser comprises a twin ridge waveguide laser.

Claim 13

A polarisation source as claimed in Claim 11 wherein the ridge waveguides are separated by no more than 10µm.

Claim 14

A polarisation source as claimed in Claim 11 or Claim 12 wherein said laser has an active layer which is 170µm or more in length.

Claim 15

An optical logic element comprising a semiconductor injection laser capable of providing optical gain in two distinguishable waveguiding paths, the waveguiding paths extending substantially parallel to one another at a small enough separation to enable the fields of optical radiation in the two paths to overlap, the laser being switchable between first and second states in which the direct optical output of the laser is predominantly TE polarised and predominantly TM polarised respectively.

Claim 16

An optical logic element comprising a semiconductor injection laser capable of providing optical gain in two distinguishable waveguiding paths, the waveguiding paths extending substantially parallel to one another at a small enough separation to enable the fields of optical radiation in the two paths to overlap, the laser being switchable between first and second states in which the direct optical output of the laser is predominantly TE polarised and predominantly TM polarised respectively.

Claim 17

An optical clock arrangement for providing a regular stream of optical pulses comprising: laser means capable of providing optical gain in two distinguishable waveguiding paths, the waveguiding paths extending substantially parallel to one another at a small enough separation to enable the fields of optical radiation in the two paths to overlap, the laser means being switchable between first and second states in which the direct optical output of the laser is predominantly TE polarized and predominantly TM polarized respectively; feedback means providing an optical path by means of which an optical output from the laser means may be fed back into the laser means; and polarization modifying means in said optical path providing a substantially orthogonal polarization shift in said fed back optical output.

Claim 18

An optical clock arrangement for providing a regular stream of optical pulses comprising: laser means capable of providing optical gain in two distinguishable waveguiding paths, the waveguiding paths extending substantially parallel to one another at a small enough separation to enable the fields of optical radiation in the two paths to overlap, the laser means being switchable between first and second states in which the direct optical output of the laser is predominantly TE polarized and predominantly TM polarized respectively; feedback means providing an optical path by means of which an optical output from the laser means may be fed back into the laser means; and polarization modifying means in said optical path providing a substantially orthogonal polarization shift in said fed back optical output.

Claim 19

An optical clock arrangement as claimed in claim 15 wherein said feedback means consists essentially of a single mirror.

Claim 20

An optical clock arrangement as claimed in claim 15 wherein said feedback means comprises a ring resonator.

Claim 21

An optical clock arrangement as claimed in claim 17 wherein the ring resonator comprises a plurality of reflectors.