# US 5,703,897 A · Semiconductor laser with integral spatial mode filter

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- Number: US 5,703,897 A
- Document ID: US5703897A
- Status: Granted
- Kind: A
- Application number: 08/707,022
- Filed: 1996-09-10
- Granted: 1997-12-30
- Earliest claimed: 1993-01-07
- Assignees: SDL, Inc.
- Inventors: David F. Welch; David G. Mehuys; Donald R. Scifres
- Web page: https://patentgrep.com/patent/US5703897A

## CPC

- H01S 5/1014: {Tapered waveguide, e.g. spotsize converter (H01S5/1064 takes precedence)}
- G02B 6/305: {and having an integrated mode-size expanding section, e.g. tapered waveguide}
- H01S 5/026: Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers (stabilisation of output H01S5/06)
- H01S 5/065: Mode locking; Mode suppression; Mode selection {; Self pulsating}
- H01S 5/10: Construction or shape of the optical resonator {, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region (H01S5/20 takes precedence)}
- H01S 5/141: {using a wavelength selective device, e.g. a grating or etalon (H01S5/146 takes precedence)}
- H01S 5/185: having only horizontal cavities, e.g. horizontal cavity surface-emitting lasers [HCSEL] (comprising a photonic bandgap structure H01S5/11)
- H01S 5/20: Structure or shape of the semiconductor body to guide the optical wave {; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers}
- G02B 6/12004: {Combinations of two or more optical elements}
- H01S 3/0818: {Unstable resonators}
- H01S 3/113: using intracavity saturable absorbers
- H01S 5/0286: {Coatings with a reflectivity that is not constant over the facets, e.g. apertures}
- H01S 5/04256: {characterised by the configuration}
- H01S 5/0625: in multi-section lasers
- H01S 5/06256: {with DBR-structure}
- H01S 5/0655: {Single transverse or lateral mode emission}
- H01S 5/1003: {Waveguide having a modified shape along the axis, e.g. branched, curved, tapered, voids}
- H01S 5/1064: {varying width along the optical axis}
- H01S 5/1082: {with a special facet structure, e.g. structured, non planar, oblique}
- H01S 5/1085: {Oblique facets}
- H01S 5/1215: {Multiplicity of periods}
- H01S 5/125: Distributed Bragg reflector [DBR] lasers
- H01S 5/14: External cavity lasers (H01S5/18 takes precedence; mode locking H01S5/065)
- H01S 5/146: {using a fiber as external cavity}
- H01S 5/187: using Bragg reflection
- H01S 5/2036: {Broad area lasers}
- H01S 5/2063: {obtained by particle bombardment}
- H01S 5/4025: {Array arrangements, e.g. constituted by discrete laser diodes or laser bar (H01S5/42 takes precedence)}
- H01S 5/4062: {with an external cavity or using internal filters, e.g. Talbot filters}
- H01S 5/4087: {emitting more than one wavelength}
- H01S 5/50: Amplifier structures not provided for in groups H01S5/02 - H01S5/30
- H01S 2301/166: Single transverse or lateral mode
- 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
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A semiconductor laser having a light amplifying diode heterostructure body having a single spatial mode aperture region or waveguide and a flared or tapered gain region having a narrow input end and wider output end provided in a resonant cavity, a portion of which cavity may be external of the body. The flared gain region has a narrow aperture end and a wide output end with narrow aperture end optically coupled to a single mode waveguide. A saturable aborbing region is formed as part of the single mode waveguide region and not between it and the flared gain section, and is reverse biased to provide for mode locked operation. The flared gain region and waveguide may be differentially pumped or modulated with current provided by separate contacts, and the flared gain region may be divided into one or more flared gain sections which may be differentially or separately pumped.

## Claims

### Claim 1

A semiconductor laser source comprising:
a longitudinally extending body of semiconductor material having an optical cavity,
a diverging gain region included in a portion of the body longitudinal extent and having a narrow input end and wider output end for achieving higher power output,
a single spatial mode aperture region included in another portion of the body longitudinal extent optically coupled to said diverging gain region narrow input end,
a portion of said single spatial mode aperture region for mode-locking the operation of said laser source, and
means to modulate said portion of said single spatial mode aperture region independent of electrical operation of said diverging gain region to achieve mode lock operation of said laser source.

### Claim 2 (depends on 1)

The laser source of claim 1 wherein at least a portion of said diverging gain region is modulated independently of and in lieu of electrical operation of said single spatial mode aperture region to achieve mode lock operation of said laser source.

### Claim 3 (depends on 1)

The laser source of claim 1 wherein said mode lock operation is achieved by modulation of at least a portion of said single spatial mode aperture region with a current at a frequency of c/2 NL where c/n is the speed of light in said optical cavity and L is optical cavity length.

### Claim 4

A semiconductor laser source comprising:
a longitudinally extending body of semiconductor material having an optical cavity,
a diverging gain region included in a portion of the body longitudinal extent and having a narrow input end and wider output end for achieving higher power output,
a single spatial mode aperture region included in another portion of the body longitudinal extent optically coupled to said diverging gain region narrow input end,
means to independently pump said diverging gain and single spatial mode aperture regions,
a saturable absorbing region formed within a portion of said single spatial mode aperture region for mode-locking the operation of said laser source, and
means to apply a reverse bias to said saturable absorbing region independently of said other regions.

### Claim 5 (depends on 1, 4)

The laser source as in claim 1 or 4 wherein said semiconductor source is an unstable resonator.

### Claim 6 (depends on 1, 4)

The laser source as in claim 1 or 4, wherein said semiconductor source is a stable resonator.

### Claim 7 (depends on 4)

The laser source of claim 4 wherein said gain region, single mode waveguide region and saturable absorbing region comprise at least a portion of an optical cavity of said laser, feedback means is included in said optical cavity comprising a mirror facet on a side of said single mode waveguide region opposite to said coupled gain region narrow aperture.

### Claim 8 (depends on 4)

The laser source of claim 4 wherein said gain region, single mode waveguide region and saturable absorbing region comprise at least a portion of said optical cavity of said laser, feedback means is included in said optical cavity comprising an external mirror adjacent to an antireflecting coated facet on a side of said single mode waveguide region opposite to said coupled gain region narrow aperture.

### Claim 9

A semiconductor laser source comprising:
a longitudinally extending body of semiconductor material,
a diverging gain region included in a portion of the body longitudinal extent and having a narrow input end and wider output end for achieving higher power output,
a single spatial aperture region included in another portion of the body longitudinal extent optically coupled to said diverging gain region narrow input end, and
means within said single spatial mode aperture region to mode lock the operation of said laser source,
said diverging gain region comprising adjacently disposed diverging gain sections, means to electrically isolate and independently pump said adjacently disposed diverging sections.

### Claim 10 (depends on 9)

The laser source of claim 9 wherein said electrically isolated diverging gain sections are current pumped, said diverging gain section including said gain region narrow input end pumped with a pumping current lower than the pumping current for another of said diverging gain sections.

### Claim 11

A semiconductor laser source comprising:
a longitudinally extending body of semiconductor material,
a diverging gain region included in a portion of the body longitudinal extent and having a narrow input end and wider output end for achieving higher power output,
a single spatial mode aperture region included in another portion of the body longitudinal extent optically coupled to said diverging gain region narrow input end,
means to independently drive said single spatial mode aperture region to provide an optical oscillator and said diverging gain region to provide high power output,
an optical cavity formed longitudinally in said coupled gain region and single spatial mode aperture region and extending externally of said semiconductor body to optical feedback means for said optical oscillator, and
saturable absorber independent of said semiconductor body positioned within a portion of said optical cavity which is external of said semiconductor body, operation of said saturable absorber for mode locking operation of said laser source via pumping of either at least a portion of said diverging gain region or said single spatial mode aperture region at a period coinciding with the round trip transit time of light pulses in said optical cavity.

### Claim 12 (depends on 11)

The laser source of claim 11 means to reverse biased said saturable absorbing region.

### Claim 13 (depends on 11)

The laser source as in claim 11, wherein said semiconductor source is an unstable resonator.

### Claim 14 (depends on 11)

The laser source as in claim 11, wherein said semiconductor source is a stable resonator.

### Claim 15 (depends on 11)

The laser source of claim 11 wherein said mode lock operation is achieved by modulation of at least a portion of said single spatial mode aperture region with a current at a frequency of c/2 nL where c/n is the speed of light in said optical cavity and L is optical cavity length.