# US 5,353,164 A · Objective lens for a free-space photonic switching system

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- Number: US 5,353,164 A
- Document ID: US5353164A
- Status: Granted
- Kind: A
- Application number: 07/969,495
- Filed: 1992-10-30
- Granted: 1994-10-04
- Earliest claimed: 1992-10-30
- Assignees: AT&T Bell Laboratories
- Inventors: Jose M. Sasian-Alvarado
- Web page: https://patentgrep.com/patent/US5353164A

## CPC

- G02B 13/22: Telecentric objectives or lens systems
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

An objective lens for a free-space photonic switching system is disclosed. The objective lens is utilized to change a collimated array of beams into an array of spots which will focus on the array of spatial light modulating elements (S-SEEDs, for example). The requirements for the lens (low f-number, field of view, etc.), result in a lens which includes an external stop, positive doublet, a positive (e.g., plano-convex) lens and a negative (e.g., field flattener) lens, the latter pair of lenses being separated by a predetermined distance d.

## Claims

### Claim 1

A free-space photonic switching system comprising
an optical source for producing as an output a collimated array of beams;
an array of spatial light modulating devices; and
an objective lens disposed between said optical source and said array of spatial light modulating devices, said objective lens positioned to receive as an input said collimated array of beams and utilized for focusing said array of collimated beams onto said array of spatial light modulating devices, the lens comprising
a positive doublet lens;
a positive lens disposed beyond said positive doublet lens;
a negative lens separated a predetermined distance d from said positive lens; and
an external stop located before the entrance of said positive doublet lens, wherein the collimated array passes through said external stop, enters the positive doublet lens and exits the negative lens, so as to provide a focused spot beam array on said array of spatial light modulating devices.

### Claim 2 (depends on 1)

In the system of claim 1, the positive lens being separated from the positive doublet lens.

### Claim 3 (depends on 1)

In the system of claim 1, the positive doublet lens comprising a first lens of a relatively low refractive index material and a second lens of a relatively high refractive index material.

### Claim 4 (depends on 1)

In the system of claim 1, the positive lens comprising a plano-convex lens.

### Claim 5 (depends on 4)

In the system of claim 4, the plano-convex lens comprising a relatively low refractive index material.

### Claim 6 (depends on 1)

In the system of claim 1, the negative lens comprising a field flattener lens.