# US 5,345,454 A · Antiresonant Fabry-Perot p-i-n modulator

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- Number: US 5,345,454 A
- Document ID: US5345454A
- Status: Granted
- Kind: A
- Application number: 08/010,029
- Filed: 1993-01-27
- Granted: 1994-09-06
- Earliest claimed: 1991-11-06
- Assignees: AT&T Bell Laboratories
- Inventors: Ursula Keller
- Web page: https://patentgrep.com/patent/US5345454A

## CPC

- H01S 3/1109: Active mode locking
- G02F 1/218: {using semi-conducting materials}
- G02F 1/3523: {Non-linear absorption changing by light, e.g. bleaching}
- H01S 3/1118: Semiconductor saturable absorbers, e.g. semiconductor saturable absorber mirrors [SESAMs]; Solid-state saturable absorbers, e.g. carbon nanotube [CNT] based
- G02F 2203/26: Pulse shaping; Apparatus or methods therefor
- H01S 3/0817: {having 5 reflectors, e.g. W-shaped resonators}
- H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS

## Abstract

The advantages of both active and passive modelocking techniques are realized within a single device by providing a p-i-n modulator formed at antiresonance within a Fabry-Perot etalon. The p-i-n modulator actively modulates light within the laser cavity by introducing periodic loss in response to changing voltages applied to the modulator. The p-i-n modulator includes an intrinsic region that is disposed between a p-doped region and an n-doped region. The modelocking performance of the p-i-n modulator is enhanced by the saturable absorber action of the intrinsic region.

## Claims

### Claim 1

Optical apparatus comprising:
first and second reflective elements being spaced apart to form a Fabry-Perot etalon therebetween, the Fabry-Perot etalon being characterized by a plurality of optical frequencies each frequency corresponding to a resonant condition; and
semiconductor material having a nonlinear optical absorption that can be varied with an applied voltage substantially at a predetermined optical frequency and being positioned between the first and second reflective elements, the predetermined optical frequency being between any two adjacent optical frequencies in the plurality of optical frequencies so that the predetermined optical frequency occurs substantially at an optical frequency corresponding to an anti-resonant condition for the Fabry-Perot etalon, the semiconductor material comprising a p-i-n modulator having a p-doped region, an intrinsic region, and an n-doped region, the intrinsic region being disposed between the p-doped and n-doped regions.

### Claim 2 (depends on 1)

The invention as defined in claim 1 wherein the first and second reflective elements are monolithically integrated with the semiconductor material.

### Claim 3 (depends on 1)

The invention as defined in claim 1 wherein the intrinsic region comprises:
first layers of material having a first bandgap energy; and
second layers of material having a second bandgap energy, the first bandgap energy being larger than the second bandgap energy, the first layers alternated with the second layers to form a multiple quantum well structure.

### Claim 4 (depends on 3)

The invention as defined in claim 3 wherein the first layers comprise a composition of InGaAs and the second layers comprise a composition of GaAsP.

### Claim 5 (depends on 3)

The invention as defined in claim 3 wherein the n-doped region and the second reflective element are integrated as a single element which comprises:
third layers of semiconductor material having an optical thickness of one-quarter wavelength at the predetermined optical frequency; and
fourth layers of semiconductor material having an optical thickness of one-quarter wavelength at the predetermined optical frequency, the third and fourth layers being alternated with each other.

### Claim 6 (depends on 5)

The invention as defined in claim 5 wherein the third layers include GaAs and the fourth layers include AlAs.

### Claim 7 (depends on 5)

The invention as defined in claim 5 wherein the p-region is a fifth layer comprising p-type GaAs.

### Claim 8 (depends on 7)

The invention as defined in claim 7 wherein the first reflective element includes a sixth layer comprising SiO.sub.2 and a seventh layer comprising TiO.sub.2, the sixth layer being adjacent to the fifth layer.

### Claim 9

Optical apparatus comprising:
first and second reflective elements being spaced apart to form a Fabry-Perot etalon therebetween, the Fabry-Perot etalon being characterized by a plurality of optical frequencies each frequency corresponding to a resonant condition; and
a integrated modulator positioned between the first and second reflective elements and having a nonlinear optical absorption, that can be varied with an applied voltage, substantially at a predetermined optical frequency and the predetermined optical frequency being between any two adjacent optical frequencies in the plurality of optical frequencies so that the predetermined optical frequency occurs substantially at an optical frequency corresponding to an anti-resonant condition for the Fabry-Perot etalon.

### Claim 10 (depends on 9)

The invention of claim 9 wherein the integrated modulator is a p-i-n modulator having a p-doped region, an intrinsic region, and an n-doped region, the intrinsic region being disposed between the p-doped and n-doped regions.