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1.5µm PHASE SHIFTED DISTRIBUTED FEEDBACK LASER
M. Gilleron, J. Charil, D. Lesterlin, P. Correc, J. Bouley
To cite this version:
M. Gilleron, J. Charil, D. Lesterlin, P. Correc, J. Bouley. 1.5µm PHASE SHIFTED DIS- TRIBUTED FEEDBACK LASER. Journal de Physique Colloques, 1988, 49 (C4), pp.C4-337-C4-339.
�10.1051/jphyscol:1988471�. �jpa-00227969�
JOURNAL DE PHYSIQUE
Colloque C4, suppl6ment au n09, Tome 49, septembre 1988
1.5wm PHASE SHIFTED DISTRIBUTED FEEDBACK LASER
M. GILLERON, J. CHARIL, D. LESTERLIN, P. CORREC and J.C. BOULEY
Centre National dd'Etudes des TBlBcommunications, Laboratoire de Bagneux,
1 9 6 ,Av. Henri Ravera,
F-92220Bagneux, France
RCsumd
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Nous p r e s e n t o n s l a c o n c e p t i o n , l a technologic d e f a b r i c a t i o n e t l e s p r o p r i d t d s d'Cmission d e l a s e r s ii c o n t r e - r C a c t i o n d i s t r i b u d e d 6 p h a s 0 e . L'utilisation d ' u n r u b a n d e l a r g e u r non u n i f o r m e c o n d u i t B u n p o u r c e n t a g e p l u s dlevd d e f o n c t i o n n e m e n t monomodal.A b s t r a c t
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We p r e s e n t t h e d e s i g n , t e c h n o l o g y a n d l a s i n g p r o p e r t i e s of p h a s e - s h i f t e d d i s t r i b u t e d f e e d b a c k l a s e r s . T h e u s e of a non-uniform w i d t h s t r i p e l e a d s t o a h i g h e r p e r c e n t a g e of s i n g l e - l o n g i t u d i n a l - m o d e o p e r a t i o n .GaInAsP/InP d i s t r i b u t e d f e e d b a c k (DFB) l a s e r s a r e a t t r a c t i v e l i g h t s o u r c e s f o r l o n g - h a u l , h i g h b i t - r a t e o p t i c a l f i b r e t r a n s m i s s i o n s y s t e m s . I n o r d e r t o i m p r o v e t h e s i n g l e - mode o p e r a t i o n y i e l d , many s t r u c t u r e s h a v e b e e n p r o p o s e d /1,2,3/ t o i n t r o d u c e a n o p t i c a l p h a s e - s h i f t i n s i d e t h e c a v i t y t o r e m o v e t h e w a v e l e n g t h d e g e n e r a c y a n d s u p p r e s s t h e w a v e l e n g t h d e p e n d e n c e o n t h e f a c e t p o s i t i o n s u s u a l l y o b s e r v e d i n t h e c o n v e n t i o n a l DFB l a s e r s . I n t h i s p a p e r , we p r e s e n t t h e t e c h n o l o g y a n d p r o p e r t i e s of a 1.55pm P h a s e - S h i f t e d B u r i e d Ridge S t r i p e (PS-BRS) l a s e r e a s i l y o b t a i n e d b y a d j u s t i n g t h e o p t i c a l wave p r o p a g a t i o n c o n s t a n t with a l o n g i t u d i n a l l y non-uniform s t r i p e width.
PHASE SHIFT REGION
Fig. 1: S c h e m a t i c view of t h e 1 . 5 ~ m Fig. 2: SEM p h o t o g r a p h of t h e p h a s e s h i f t e r P h a s e - S h i f t e d B u r i e d Ridge S t r i p e l a s e r . b e f o r e t h e s e c o n d e p i t a x y .
T h e PS-BRS l a s e r , d e r i v e d from t h e BRS s t r u c t u r e / 4 / , i s s c h e m a t i c a l l y s h o w n i n Fig. 1. The l a s e r r e p o r t e d h e r e h a s b e e n e n t i r e l y g r o w n b y Liquid P h a s e E p i t a x y (LPE).
F i r s t , a n - I n P b u f f e r l a y e r , a 1.5ym GaInAsP a c t i v e l a y e r a n d a 1 . 3 7 ~ m GaInAsP g u i d e l a y e r w e r e s u c c e s s i v e l y g r o w n b y t w o - p h a s e LPE. T h e n , a Znd o r d e r g r a t i n g was chemically e t c h e d i n t o t h e g u i d e l a y e r a n d a non-uniform w i d t h s t r i p e s e l e c t i v e l y e t c h e d i n t o t h e a c t i v e a n d g u i d e l a y e r s (Fig. 2). Finally, s i n g l e - p h a s e , l o w - t e m p e r a t u r e LPE was u s e d t o o v e r g r o w t h e
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1988471
JOURNAL
DE
PHYSIQUEb u r y i n g p-InP a n d .the c o n t a c t p + - q u a t e r n a r y l a y e r s . GaAs p r o t e c t i o n c o v e r was u s e d r e d u c e t h e g r a t i n g d e f o r m a t i o n l i k e l y t o o c c u r d u r i n g t h e h e a t i n g p e r i o d p r i o r o v e r g r o w t h . C l a s s i c a l t e c h n o l o g i e s w e r e u s e d t o o b t a i n 300pm-long l a s e r c h i p s .
I I I I I
1
0 1.0 2.0
AW = Wp
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Wp ( prnFig. 3: Calculated r e l a t i o n s h i p b e t w e e n t h e p h a s e s h i f t e r l e n g t h L p a n d t h e s t r i p e width w i d e n i n g ( n a r r o w i n g ) of t h e s t r i p e A W .
T h e w i d e r s t r i p e r e g i o n of w i d t h W e a n d l e n g t h L ~ 5 0 p m a c t s a s a p h a s e s h i f t e r a n d h a s b e e n d e s i g n e d t o p r o d u c e a n / 2 - p h a s e s h i f t /1,3/. T h e nominal s t r i p e width of t h e mask i s 2pm b u t , b e c a u s e of u n d e r e t c h i n g , t h e a c t u a l uniform s t r i p e w i d t h W g is 1.8pm. To a v o i d p a r a s i t i c r e f l e c t i o n s a t t h e e n d s of t h e p h a s e s h i f t e r , t a p e r e d r e g i o n s w e r e i n t r o d u c e d t o c o n n e c t it s m o o t h l y t o t h e uniform r e g i o n s a n d t h e w i d e n i n g of t h e s t r i p e A W = W p
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W g was s e t t o lpm. Fig. 3 s h o w s t h e c a l c u l a t e d r e l a t i o n s h i p b e t w e e n t h e p h a s e s h i f t e r l e n g t h L p a n d t h e w i d e n i n g ( n a r r o w i n g ) of t h e s t r i p e AW. We n o t i c e t h a t L p is r a t h e r s e n s i t i v e t o W g.
F o rexample, if, b e c a u s e of e x c e s s i v e e t c h i n g , W g d e c r e a s e s from 1.8 t o 1.5pm, t h e optimum p h a s e s h i f t e r l e n g t h d e c r e a s e s from 50 t o 35 pm a n d a 5Oym-long p h a s e s h i f t e r d e s i g n e d f o r W61.8pm a n d A W = l o r n w i l l p r o d u c e a t o t a l p h a s e - s h i f t of 0 . 7 n . Hence, t h e l a s i n g p r o p e r t i e s of t h e r e s u l t i n g l a s e r s w i l l b e s e v e r e l y d e g r a d e d .
3-LASING CHARACTERISTICS
0 50 100
CURRENT ImA) 14950A WAVELENGTH 15050i
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Fig. 4: T y p i c a l l i g h t - c u r r e n t c h a r a c t e r i s t i c s Fig. 5: S u b - a n d a b o v e - t h r e s h o l d s p e c t r a of a
of a PS-BRS. PS-BRS l a s e r with a n a n t i - r e f l e c t i o n c o a t e d
f r o n t f a c e t
isoo&A - -
- I = 0.96 I,,
>
.- 0
2
0 YI
Fig. 4 s h o w s t h e l i g h t - c u r r e n t c h a r a c t e r i s t i c s of 12 u n s e l e c t e d l a s e r s m e a s u r e d from t h e same c l e a v e d b a r . T h r e s h o l d c u r r e n t s r a n g e b e t w e e n 40 a n d 50 m A . Almost 90% of t h e mounted l a s e r s e x h i b i t e d CW s i n g l e l o n g i t u d i n a l mode (SLM) o p e r a t i o n with a s i d e mode s u p p r e s s i o n r a t i o g r e a t e r t h a n 30 dB.
Fig. 5 s h o w s t y p i c a l s u b - a n d a b o v e - t h r e s h o l d s p e c t r a of a PS-BRS l a s e r with a n a n t i - r e f l e c t i o n c o a t e d f r o n t f a c e t . Above t h r e s h o l d , t h e l a s e r e x h i b i t s mode h o p p i n g f r e e SLM o p e r a t i o n u p t o t h e o p t i c a l power s a t u r a t i o n d u e t o t h e c u r r e n t l e a k a g e of t h e BRS s t r u c t u r e . SLM o p e r a t i o n is a l s o o b s e r v e d with a main mode a n d s i d e modes l o c a t e d s y m m e t r i c a l l y t o t h e main mode. T h i s s y m m e t r y d e m o n s t r a t e s t h e e f f e c t of t h e p h a s e s h i f t e r on mode s e l e c t i o n a n d v a l i d a t e s t h e s t r i p e d e s i g n .
We h a v e r e p o r t e d o n t h e d e s i g n , t e c h n o l o g y a n d l a s i n g c h a r a c t e r i s t i c s of PS-BRS l a s e r s . We h a v e e x p e r i m e n t a l l y o b s e r v e d t h a t t h e p e r c e n t a g e of SLM o p e r a t i o n is h i g h e r f o r s u c h l a s e r s t h a t f o r c o n v e n t i o n a l l a s e r s with uniform w i d t h s t r i p e s .
/ I / H. Soda, Y. Kotaki, H. S u d o , H. I s h i k a w a , S. Yamakoshi a n d H. Imai, IEEE J. Q u a n t u m Electron.,
4E-23
(1987) 804./2/ K. L'taka, S. Akiba, K. S a k a i a n d Y. Matsushima, IEEE J. Q u a n t u m Electron., QE-22 (1986) 1042.
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67
(1985) 4./4/ D. L e s t e r l i n , J. Charil, B. Rose, M. Gilleron, P. C o r r e c a n d J.C. Bouley, Proc. ESSDERC'87 ( S e p t . 1987) 803.
