1. A passive, coupled multi-core fiber comprising:
multiple cores each supporting a spatial mode, the cores being positioned close enough to cause coupling between their modes that generates supermodes that are capable of transmitting data, the cores excluding a material that enables them to acquire gain; and
an outer cladding surrounding the cores.
2. The passive, coupled multi-core fiber of claim 1, wherein the fiber has a pitch-to-core ratio of approximately 2 to 10.
3. The passive, coupled multi-core fiber of claim 2, wherein each core and the cladding have an index difference of approximately 0.4%.
4. The passive, coupled multi-core fiber of claim 1, wherein the fiber has a coupling length less than 7 km.
5. The passive, coupled multi-core fiber of claim 1, wherein the fiber has a coupling coefficient larger than 0.2 km\u22121.
6. The passive, coupled multi-core fiber of claim 1, wherein the fiber has a crosstalk larger than \u221230 dBkm.
7. The passive, coupled multi-core fiber of claim 1, wherein the cores are single-mode cores that support only a single spatial mode.
8. The passive, coupled multi-core fiber of claim 1, wherein the cores are multi-mode cores that support multiple spatial modes.
9. The passive, coupled multi-core fiber of claim 8, wherein the cores are few-mode cores that support no more than seven spatial modes.
10. The passive, coupled multi-core fiber of claim 1, wherein at least one of the cores has an index of refraction that radially varies.
11. The passive, coupled multi-core fiber of claim 1, wherein the fiber comprises an inner cladding that is surrounded by the outer cladding, the inner cladding having an index of refraction that is different from the index of refraction of the outer cladding.
12. An optical transmission system, comprising:
one or both of a transmitter and a receiver; and
a coupled multi-core fiber including multiple cores each supporting a spatial mode, the cores being positioned close enough to cause coupling between their modes that generates supermodes that are available for transmitting data over the system.
13. The optical transmission system of claim 12, wherein the coupled multi-core fiber has a pitch-to-core ratio of approximately 2 to 10.
14. The optical transmission system of claim 12, wherein each core and cladding have an index difference of approximately 0.4%.
15. The optical transmission system of claim 12, wherein the coupled multi-core fiber has a coupling length less than 7 km.
16. The optical transmission system of claim 12, wherein the coupled multi-core fiber has a coupling coefficient larger than 0.2 km\u22121.
17. The optical transmission system of claim 12, wherein the coupled multi-core fiber has a crosstalk larger than \u221230 dBkm.
18. The optical transmission system of claim 12, wherein the cores are single-mode cores that support only a single spatial mode.
19. The optical transmission system of claim 12, wherein the cores are multi-mode cores that support multiple spatial modes.
20. The optical transmission system of claim 12, wherein the cores are few-mode cores that support no more than seven spatial modes.
21. A method of transmitting data using coupled multi-core fiber, the method comprising:
encoding data to be transmitted on an optical carrier;
exciting a supermode of the coupled multi-core fiber with the with the data-encoded optical carrier, the supermode being generated due to mode coupling between the cores of the coupled multi-core fiber; and
optically transmitting the supermode along the coupled multi-core fiber.
22. The method of claim 21, wherein the coupled multi-core fiber supports multiple supermodes but only one supermode is excited so as to transmit data in a single-mode operation scheme.
23. The method of claim 22, wherein the excited supermode is the fundamental supermode of the coupled multi-core fiber.
24. The method of claim 21, wherein the coupled multi-core fiber supports multiple supermodes and multiple supermodes are excited so as to transmit data in mode-division multiplexing scheme.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A particle-optical apparatus which includes
a particle source for producing a primary beam (22) of electrically charged particles that travel along an optical axis (4) of the apparatus,
a specimen carrier for a specimen (18) to be irradiated by means of the apparatus,
a focusing device (14, 16) for forming a focus of the primary beam in the vicinity of the specimen carrier by means of electrostatic electrodes, and
a detector (6, 8) that has a detector surface (9) for detecting electrically charged particles that emanate from the specimen in response to the incidence of the primary beam, which detector is arranged ahead of the focusing device, viewed in the propagation direction of the primary beam, and which detector surface is provided with a central bore (11) for the passage of the primary beam,
characterized in that
the detector (6, 8) is provided with a central electrode (35) at the area of the central bore (11), and
that the particle-optical apparatus is provided with power supply means for adjusting such a voltage across the central electrode that at the area of the detector surface (9) the central electrode exerts a repulsive force on the particles that emanate from the specimen.
2. A particle-optical apparatus as claimed in claim 1, wherein the central electrode (35) is rotationally symmetrical around the optical axis (4).
3. A particle-optical apparatus as claimed in claim 1 or 2, wherein the detector (6, 8) is constructed as a semiconductor detector.
4. A particle-optical apparatus as claimed in one of the preceding claims, wherein the voltage of the power supply means can be adjusted by the user of the apparatus.