C52_原責

High Power Semiconductor Laser Diode for Fiber Laser

Pumping

Yuji Yamagata,

Ryozaburo Nogawa,

Yoshikazu Kaifuchi,

Syunta Sato,

and Yumi Yamada

We report performance improvement of single emitter laser diodes based on Asymmetric

Decoupled Conﬁnement Heterostructure (ADCH). Laser design optimization in vertical layer

and lateral current injection structure enabled high power operation of 915 nm laser diodes up

to 17 W and high power conversion efﬁciency more than 60 %. Mean time to failure of random

mode is estimated to be over 600,000 hours for 17 W operation at room temperature. These

results prove high reliability of ADCH at high power.

1. Introduction

High power semiconductor laser diodes (LDs) with

9xx nm wavelength band have been widely used in in-

dustrial applications. Especially demand for pump

sources in ﬁber laser systems is increasing rapidly,

because ﬁber laser systems is replacing conventional

arc welding systems and Yttrium Aluminum Garnet

(YAG) laser systems in material processing

1) 2)

. Our

LD structure is based on Asymmetric Decoupled Con-

ﬁnement Heterostructure (ADCH)

3) 4)

. ADCH can re-

alize low internal loss and ultra-low optical conﬁne-

ment, which are essential features required for high

power, high efﬁciency and high reliability operation

without Catastrophic Optical Damage (COD). In this

paper, high power and high reliability characteristics

are demonstrated for single emitter LDs with 915 nm

wavelength. Future possibility of improvement in high

power operation is also discussed.

2. LD structure and design

Figure 1 and 2 show the cross-sectional structure

and the schematic lateral current blocking structure of

LDs. Vertical structure of the LDs consisting of In-

GaAs/AlGaAs material system is grown by Metal-Or-

ganic-Chemical-Vapor-Deposition (MOCVD). Self-

Aligned Stripe (SAS) structure is used so as to form

lateral current blocking structure as well as non-cur-

rent injection window of laser mirror facets. Front and

rear facets are anti-reﬂection and high-reﬂection coat-

ed and applied facet stringent process with our own

technology.

Refractive index and optical mode proﬁles of wave-

guide in 9xx nm-LDs are shown in Fig. 3. ADCH de-

sign can optimize optical conﬁnement to the active

layer (G

well) and the ratio of optical conﬁnement to p-

doped and n-doped layer (G

p/Gn), independently. The

well is a key parameter determining threshold current

and highly related to COD level. the G

p/Gn is a another

parameter related to internal loss thereby it should be

small value. Such a ﬂexible waveguide design realizes

highly reliable operation at high power and high efﬁ-

ciency.

1 Optical Device Research Department, Advanced Technology Laboratory

2 Optoenergy, Inc.

GaAs

p-Ohmic

electrode

p-contact

n-current block

p-clad layer

Active layer

n-wave guide

n-clad layer

n-substrate

n-Ohmic

electrode

GaAs

AlGaAs

InGaAs-SQW

Fig. 1. Cross section of laser diode.

Fig. 2. Current injection structure of laser diode.

Fujikura Technical Review, 2016

3. Performances of Laser Diode

Lasing characteristics and reliability were evaluated

for LDs with 4 mm-long cavity and 915 nm wavelegth

operation. Two different LDs with current injection

stripe widths (W

s) of 100 µm and 150 µm are fabricat-

ed for comparison. They are bonded on high thermal

conductive ceramic base submount for measurement.

Figure 4 shows measured results of light output ver-

sus drive current (L-I) characteristics under CW and

pulsed conditions. The maximum output power of

s=150 µm LDs reaches 28 W and 47 W for CW and

pulsed conditions, respectively. COD free operation

up to such high power levels reveals an advantage of

ADCH design in reliability. The maximum output pow-

er of W

s=100 µm LDs is slightly lower due to thermal

rollover. Figure 5 shows power conversion efﬁciency

(PCE) of LDs with different W

s of 100 and 150 µm.

WPE for both samples exceed 65 % in peak value and

wider stripe sample keeps over 60 % high efﬁciency up

to high output power of 18 W.

Beam properties of LDs are essential parameter

which dominates coupling efﬁciency to the output ﬁ-

ber in modules. Figure 6 compares beam parameter

product (BPP) of lateral beam properties for W

s =100

µm and 150 µm-LDs, as a function of output power.

Degradation of BPP from 100 µm to 150 µm stripe

width LDs is smaller than the expectation, because of

better heat dissipation by the ceramic base submount.

Wider stripe conﬁguration is considered to be one of

options to realize high power laser modules.

501052015 3025 40 45350

Operating current (A)

Light output (W)

915 nm, L=4 mm

Pulse

@RT

150 um

100 um

Fig. 4. CW and pulse L-I characteristics for 4 mm cavity LDs

with 100 µm and 150 µm stripe width.

Active layer (Quantum Well)

Optical mode profile

n-Sidep-Side

n-Clad

<< G

well

Index

p-Clad

Light lntensity

Index

n-Clad

p-Clad

Band diagram

Waveguide

Fig. 3. Schematic index guide structure, optical mode proﬁle

and band diagram of LD.

1842861210 16140

Operating current (A)

Light output (W)

Power conversion efficiency (%)

915 nm, L=4 mm

150 um

100 um

Fig. 5. L-I and WPE-I characteristics for 4 mm cavity LDs with

100 µm and 150 µm stripe width..

Panel 1. Abbreviations, Acronyms, and Terms.

–

Laser Diode

ADCH

–

Asymmetric Decoupled Confinement Het-

erostructure

COD

–

Catastrophic Optical Damage

GaAs

–

Gallium Arsenide

InGaAs

–

Indium Gallium Arsenide

AlGaAs

–

Aluminum Gallium Arsenide

SAS

–

Self-Aligned Stripe

–

Continuous Wave

PCE

–

Power Conversion Efficiency

BPP

–

Beam Parameter Product

MTTF

–

Mean Time To Failure