 Integrated circuit memory with column voltage holding circuit |
| An object of the present invention is to make an integrated circuit memory comprising a circuit ... |
|
| Standby current detecting circuit for use in a semiconductor memory device and method thereof |
| Therefore, it is an object of the present invention to provide a standby current detecting circuit ... |
|
| Process and device for checking substrate wafers |
| Since a defect counting process, particularly a counting process carried out by an operator, is ... |
|
| Synchro-to-digital converter |
| Accordingly, a primary object of the present invention is to provide a synchro-to-digital converter ... |
|
| Duty cycle control apparatus |
| What is claimed is: 1. Apparatus for controlling the duty cycle of an input signal having a period, ... |
|
| Signal level comparing circuit |
| It is accordingly an object of this invention to provide a signal level comparing circuit which can ... |
|
| Circuit arrangement for correcting slip errors in pcm receivers |
| I claim: 1. In a receiver for binary code words including information bits and redundancy bits to ... |
|
| Redundant clock system utilizing nonsynchronous oscillators |
| In accordance with the present invention, there is provided a clock system with two nonsynchronized ... |
|
|
Photonic cross-connect switch
| Details |
Inventors: Fatehi, Mohammad T.; Srinivasan, Nattu V.;
Assignee: AT&T Bell Laboratories (Murray Hill, NJ)
Primary Examiner: Coles, Sr.; Edward L.
Assistant Examiner: Negash; Kinfe-Michael
Attorney, Agent or Firm: Weiss; E.
This invention relates to an optical cross-connect switch which is substantially loss-less and is transparent to signal bit rate, format and modulation scheme. The optical cross-connect switch can be comprised of at least two stages of chips coupled in tandem via optical fibers. Each chip can be of lithium niobate having a plurality of digital switch elements or directional couplers which, by means of an electric field, can selectively switch optical energy from one waveguide to another. The chips are coupled together via optical fiber amplifiers and the optical fiber amplifiers are pumped by optical pumps, e.g., 1.48 .mu.m CW, laser pumps, coupled to appropriate nodes within either one or both of the chips. In operation, the pump energy is switched through the chips along with the optical data signals to pump only those optical fiber amplifiers which are in the optical data signal path. |
|
DETAILED DESCRIPTION Lithium niobate switches permit rapid switching of optical signals without reconversion to electrical form.
By diffusing strips of titanium into a LiNbO.
sub.
3 substrate, single mode waveguides with high refractive indices are produced.
When a voltage is applied across these guides, a refractive index change occurs due to the high electrooptic coefficient of LiNbO.
sub.
3.
This results in a change in the cross-coupling between guides and allows optical power to be switched from one guide to the other.
Two types of lithium niobate switches are commercially available.
One type is normally identified as being a "directional coupler" and the other is identified as being a "digital switch".
Referring to FIG.
1, there is illustrated a prior art 4.
times.
4 lithium niobate cross-connect switch 10 using switches which are identified as being directional couplers.
The cross-connect switch normally comprises a plurality of embedded waveguides 12, 14, 16, 18 fabricated in a crystal of dielectric material, such as LiNbO.
sub.
3, or of a semi-insulating material, such as Fe-doped InGaAs P/InP.
Single-mode Ti:LiNbO.
sub.
3 waveguide devices have mode spot sizes which closely match the mode spot sizes of typical single-mode fibers.
A p-n, p-i-n, or Schottky junction 17 is employed to attain an electric field in the waveguide volume of the semiconducting material to effect switching of optical energy from one optical fiber to another, for example, from 12 to 14 by means of an electric field which selectively changes the electrooptic index of the material.
The input ports of the waveguide 12, 14, 16, 18 are normally coupled to receive optical signals from optical transmission paths or optical fibers 20, 22, 24, 26; and the output ports of the waveguides are coupled to transmit the switched optical signals to optical transmission paths or optical fibers 28, 30, 32, 34.
Briefly, by applying an appropriate control voltage to corresponding electrodes of the directional coupler, each directional coupler 17 in the chip operates as a 2
|
|
Fault Detection 
