A simultaneous operation of a semiconductor laser at high power and high speed was demonstrated in a buried crescent laser on a P-InP substrate. In a cavity length of 300μm, a

maximum CW power of 130mW at room temperature was obtained in a junction-up mounting configuration. A 3dB bandwidth in excess of 12GHz at an output power of 52mW was observed

Bar-Chaim, N.

Blauvelt, H.

Chen, T. R.

Yariv, A.

Zhuang, Y. H.

English

Caltech Authors - Main

al.,’ who found that for the specific case of u)/h = 0.101 and 
t / h  = 0.011, the microstrip with a circular-edged strip will 
U - 1  1 IO 100 
microstrip width /substrate height 
ps”’ 
t = IOpm 
-0 -60 ”  - x - 3 0  
-A- 45” __ circular 
Fig. 3 Conductor power loss 
have 15% less conductor loss than the microstrip with rec- 
tangular edges. For the same configuration, the present tech- 
nique predicts a 10.7% decrease in loss for a circular 
cross-section. 
Conclusion: Microstrip conductor loss can be calculated 
quickly by a perturbation method which includes the effect of 
strip edge shape. The work of Lewin and Vainshtein has been 
extended here to implement the technique on microstrip. The 
required stopping points in the loss integrations have been 
found here for a variety of trapezoidal strip edges. Loss calcu- 
lations have been done for these and other edges, and it is 
apparent that the edge shape has a significant effect on the 
conductor loss. Although results here tend to overestimate the 
effect owing to breakdown of the approximations, conductor 
loss due to edge shape increases as the edge shape gets sharper 
and the strip gets narrower or thicker. 
E. L. BARSOTTI 
1. M. DUNN 
E. F. KUESTER 
University oJ Colorado 
Campus Box 425 
Boulder, CO 80309-0425. USA 
References 
10th May 1990 
LEWIN, L.: ‘A method of avoiding the edge current divergence in 
perturbation loss calculations’, I E E E  Trans., 1984, MlT-32, pp. 
7 17-7 19 
VAINSHTEIN, L. A.. and ZHVRAV, s. M.: ‘Strong skin effect at the 
edges of metal plates’ in Russian, Pis’ma Zh. Tekh. Fiz., 1986, 12, 
pp. 123 129; English translation in Sou. Tech. Phys. Lett., 1986, 
12, (6), pp. 298-299 
VON KOPPENFELS, w , and STALLMAN, F.: ‘Praxis Der Konformen 
Abbildung’ (Springer-Verlag, Berlin, 1959), pp. 207-209 
GRADSHTEYN, I. s., and RYZHIK, I. M.: ‘Table of integrals, series, and 
products’ (Academic Press, Inc., San Diego, 1980), p. 58 
BARSOTTI, E. L., KUESTER, E. K., and DUNN, 1. M.: ‘A simple method 
to account for edge shape in the conductor loss in microstrip’. 
MIMICAD Technical Rep. No. 2, University of Colorado, 
Boulder, Colorado, 1990 
BARSOTTI, E. L., KUESTER, E. K., and DUNN, I. M. ‘A simple method 
to account for edge shape in the conductor loss in microstrip’, to 
be published 
KOBAYASHI, M.: ‘Longitudinal and transverse current distributions 
on microstriplines and their closed-form expression’, I E E E  Trans., 
1985, MlT-33, pp. 78&788 
CHRVSSOMALLIS, M., SIAKAVARA, K., and SAHALOS, I. N.: ‘A study of 
open thick microstrip: the hybrid quasistatic approximation’, 
Canadian Journal oJPhysics, 1989,67, pp. 741-752 
COMBINED HIGH POWER AND HIGH 
FREQUENCY OPERATION OF InGaAsP/lnP 
LASERS AT 1.3ptm 
Indexing terms: Semiconductor lasers, Optical communications 
A simultaneous operation of a semiconductor laser at high 
power and high speed was demonstrated in a buried crescent 
laser on a P-InP substrate. In a cavity length of 300pm. a 
maximum CW power of 130mW at room temperature was 
obtained in a junction-up mounting configuration. A 3dB 
bandwidth in excess of 12GHz at an output power of 52mW 
was observed. 
A combination of high power and high speed operation of a 
1.3pm wavelength laser is very desirable in a number of appli- 
cations such as long-haul wide-hand optical fibre communica- 
tion. The very high power capability also offers increased 
reliability since usefully large amounts of power can be 
obtained with the laser ‘idling’ at a fraction of its maximum 
capability.’ It has been established that certain laser struc- 
tures such as buried crescent (BC) on P-InP substrate2~’ and 
double channel planar buried heterostructure (DCPBH) 
lasers4 are capable of delivering a CW optical power in excess 
of lOOmW and can be operated reliably over thousands of 
hours.’ The general approach for obtaining high output 
power is based on the following: the use of long laser cavity, 
the application of low reflectivity coating to the laser output 
facet and the adoption of junction-down mounting configu- 
ration and efficient heat sinking. A combination of all these 
techniques has led to a CW output power of 2001nW.~ 
Unfortunately, the techniques for high power operation are 
not always compatible with the conditions needed to obtain 
high frequency operation. These include the use of a short 
cavity to increase the corner frequency (at the same power 
level) and the formation of a narrow mesa to reduce the para- 
sitic capacitance contributed by the reverse-biased blocking 
junction. BC lasers with semi-insulating blocking layers are 
ELECTRONICS LETTERS 5th July 1990 Vo/. 26 No. 14 
expected to have high modulation bandwidth. A 3dB band- 
width of - 11 GHz was The maximum output 
powers of these lasers were 30mW or less. With vapour- 
phase-regrown type of lasers, even higher frequency response, 
22GHz at a power level of 15mW was reported.’ The laser 
structure was not specially designed for high power operation. 
Efforts to combine high power and high frequency oper- 
ation have been reported. A BC type laser with a Fe-doped 
semi-insulating (SI) current blocking layer demonstrated a 
3 dB bandwidth of 6 GHz at a power level of 8 The laser 
used was 700pm long and was capable of emitting 90mW 
light power in a junction-down mouting configuration. 
In this letter, we report on a different approach leading to a 
combined high power and high frequency operation of a BC 
laser on P-InP substrate. Medium (25C300pm) to short 
(-150pm) cavity lengths were employed to increase the 
corner frequency. Both narrow mesa and reduced bonding 
pads were employed to minimise the parasitic capacitance and 
junction-up mounting configuration was adopted to avoid 
further complication in fabrication and assembling (such as 
the use of polyimide). To obtain high output power, dielectric 
coatings were applied to the facet mirrors with specially tai- 
lored reflectivities. As a result, high power and high frequency 
operation were achieved simultaneously. A CW output power 
in excess of 130mW was obtained in a laser of -300pm 
cavity length. A 3dB bandwidth larger than 12GHz at a ‘safe’ 
output power level of 52 mW was demonstrated. 
The basic laser structure and fabrication process are similar 
to those described elsewhere.2,’0 A P-InP substrate was 
employed to facilitate high power ~ p e r a t i o n . ~  The laser 
parameters, such as the active layer width and thickness, the 
position of the active layer relative to the blocking layers and 
the doping level of the layers were designed for both high 
power and high speed performances. The typical values of the 
lasers’ parameters are as follows: the active layer width is 
1.5-2.0, the thickness of the active layer at the centre of the 
crescent is 0-124.22, the active layer is located at or slightly 
above the interface between the n-InP and p-InP blocking 
layers, the doping level of the active layer is estimated to be 
985 
0.34 .9  x 1018/cm'. A mesa of -8pm width was etched and a 
bonding pad of 100 x 100pm' was formed to reduce the 
parasitic capacitance. 
As we have chosen medium to short cavity lasers, in favour 
of high frequency operation, rather than the long cavity ones 
(-700pm) usually employed in high power operation, the key 
for a combined high power and high frequency operation is to 
obtain the maximum output power. In contrast to the conclu- 
sions drawn from long l a ~ e r s , ~ . ~  a high reflectivity coating on 
the rear facet and a low reflectivity coating on the front facet 
are equally important. It has been confirmed that the effect of 
mirror coating on the maximum output power depends 
strongly on the internal loss a,L of the laser (compared with 
mirror loss Ln(I/RiR2)). For high internal loss factor, a,, 
and/or long cavity length, L, the effective way to increase the 
maximum output power is the application of a low reflectivity 
(LR), coating on the front facet.'.' A high reflectivity (HR) 
coating on the rear mirror can only improve the output power 
by a small fraction (-10%). However, the HR coating 
becomes increasingly important when the product a, L is small 
which is usually the case for medium and short cavity lasers. 
In some cases of short cavity lasers, a low enough coating on 
the front mirror may even cause a decrease in maximum 
output power. Therefore, an optimising of mirror reflectivities 
with respect to the cavity length and internal loss is of crucial 
importance. 
In our medium cavity length (- 300pm) lasers, with LR/HR 
coatings on the front and rear facet, respectively, the typical 
room temperature CW output power is - 100mW. The best 
example is the following. A laser of 300pm cavity length 
emitted a CW optical power of Po = 58mW. When the rear 
facet mirror was coated to R, = 0.9, the maximum power was 
increased to 91 mW (1.57PJ. A further coating on the front 
facet mirror to R,  = 0.05 resulted in an optical power of 
130 mW (2.24P0). Light output against current characteristics 
of this laser with different coatings are plotted in Fig. 1. When 
cavity length increases further, the LR coating makes a major 
contribution to the power increase. However, for short cavity 
lasers (e.g., L - 150pm), HR coating plays a major role. A 
detailed theoretical and experimental study will he presented 
elsewhere. 
130- 
120- 
110- 
100- 
90 - 
z 
E. 80-  
7 0 -  
6 - 6 0 -  
50 - 
4 0  - 
30 
2 0  
L a 
L 
- 
- 
0 100 200 300 
current, mA 
Fig. 1 Light against current characteristics of a buried crescent laser 
with different mirror refectiuities 
L = 300pm 
986 
Fig. 2 shows the modulation characteristics of a 3Wpm 
long laser. A 3dB bandwidth of over 12GHz at an output 
power of 52mW was demonstrated. The maximum power of 
the laser was 101 mW. For short cavity lasers, the maximum 
power becomes smaller. The frequency response of a 150pm 
long laser is shown in Fig. 3. The laser was coated to RI = 
0.18 and R, = 0.9. The maximum output power was 54mW 
and a 3 dB cut-off frequency of 12GHz at an output power of 
33 mW was observed. 
Fig. 2 Frequency response OJ a medium cavity laser 
L = 300pm 
The mirror reflectivities are R, = 0.9, R, = 0.05, the threshold 
current is 28mA, the maximum power is 101 mW 
1 " " " " ' I  
0 2 4 6 8 10 12 14 16 18 20 
frequency, GHz 
Fig. 3 Frequency response o f a  short cavity laser 
L = 150pm 
The mirror reflectivities are R,  = 0.9 and R ,  = 0.18, the rhreshold 
current is l lmA,  the maximum power is 54mW 
In conclusion, for medium to short cavity BC lasers, an 
optimisation of laser parameters and mirror reflectivities leads 
to a combined high output power and high frequency capabil- 
ity. A maximum CW power of 130mW and a 3dB bandwidth 
of 12 GHz at a 52 mW optical power level were demonstrated 
in a junction-up mouting configuration. The idea is also 
applicable to other laser structures. 
The authors are grateful to D. Huff for his help in the 
modulation experiment. This work has been supported by the 
Defense Advanced Research Projects Agency and the Ofice of 
Naval Research. 
T. R. CHEN 
Y H. ZHUANG 
A. YARIV 
Applied Physics 128-95 
California Institute of Technology, Pasadena, C A  91125 
10th May 1990 
H. BLAUVELT 
N. BAR-CHAIM 
Ortel Corporation 
2015 W .  Chestnut Street, Alhambra, C A  91803 
ELECTRONICS LETTERS 5th July 1990 Vol. 26 No. 74 
References 
1 OSHIBA, s., MATOBA, A., HORIKAWA, H., KAWAI, Y., and SAKUTA, M.: 
‘Reliability of 1.3pm V-grooved inner-stripe laser diodes under 
high-power operation’, Electron. Lett., 1986, 22, (8), p. 428 
2 IMANAKA, ., HORIKAWA, H., MATOBA, A., KAWAI, Y., and SAKUTA, M.:
‘High power output, low threshold, inner stripe GaInAsP laser 
diode on a ptype InP substrate’, Appl. Phys. Lett., 1984, 45, (3), 
p. 282 
inner-stripe laser diodes on a p-type substrate operating over 
IOOmW at 1-5pm wavelength’, Appl. Phys. Lefters, 1987, 50, (7), 
3 HORIKAWA, H., OSHIBA, S., MATOBA, A., and KAWAI, Y.: ‘V-grooved 
p. 374 
4 KOSZI, L. A., TEMKIN, H., PRYZBYLEK, G. I., SEGNER, B. P., IVAPHOLTZ, 
s. G., BOGDANOWIZ, C. M., and DUTTA, N. K.: ‘High power operalion 
of InPflnGaAsP double-channel planar buried-heterostructure 
lasers with asymmetric facet coatings’, Appl. Phys. Lett., 1987, 51, 
(26). p. 2219 
A. Y.: ‘High power output over 200mW of GaInAsP/InP VIPS- 
LD. 10th IEEE Int. Semiconductor Laser Conf., Kanazawa, 
Tokyo, 1986, pp. 148-149 
6 ZAH, C. E., CANEAU, C., MENOCAL, S .  G., FAVIRE, F., and LEE, T. P: 
‘High-speed 1.3 pm GalnAsP p-substrate buried-crescent lasers 
with semi-insulating Fepi-doped InP current blocking layers’, 
Electron. Lett., 1988, 24, ( I I ) ,  p. 695 
BAUM, A.. WOLF, o., RENNER, D., HESS, K. L., and ZEHR. s. w.: ‘1.3pm 
InGaAsP buried crescent lasers with cobalt-doped semi-insulating 
current blocking layers grown by metalorganic chemical vapor 
deposition’, Appl. Phys. Lett., 1988, 53, (14), p. 1257 
8 OLSHANSKY, R., FQWAZINK, w., HILL, P., LANZISERA, v., and LAUER, 
R. B.: ’InGaAsP buried heterostructure laser with 22GHz band- 
width and high modulation efficiency’, Electron. Lett., 1987, 23, 
(Wt6), p. 839 
KAWAI, Y.: ‘High-power and high-speed semi-insulating blocked 
V-grooved inner-stnpe laser at 1.3 pm wavelength fabricated on 
p-InP substrates’, Appl. Phys. Lett., 1989,54, (12), p. 1077 
SUSAKI, w., IK~DA,  K., and NIIKAWA, K.: ‘InCaAsP/lnP buried 
crescent laser diode emitting at 1.3pm wavelength’, I E E E  J. 
Quantum Electronics, 1989, QE-20, (8), pp, 806-814 
5 OSHIBA, S., HORIKAWA. H., MATOBA, A., KAWAHARA, M., and KAWAI, 
7 CHENG, W. H., eOOLADDU, I., HUANG, S .  Y., BUEHRING, K. D., APPEL- 
9 HORIKAWA, H., WADA, H., MATWI, Y., YAMADA, T., OGAWA, Y., and 
10 OOMURA, E., HIGUCHI, H., SAKAKIBAKA, Y., HIRANO, R., NAMIZAKI, H., 
O N  THE CRAMER-RA0 BOUND OF 
FINITE-LENGTH CEPSTRUM SPECTRAL 
EST1 MATORS 
Indexing terms: Speech recognition, Spectral analysis 
Spectral estimators based on finite-length cepstrum model- 
ling are useful in several applications. The Cramer-Rao 
lower bound of the asymptotic variance of their logarithmic 
spectral estimates can be obtained in explicit form. This does 
not depend on the specific underlying spectrum. 
Introduction: Parametric modelling of stationary random 
process is widely used in many engineering and statistics 
applications. Especially popular are rational models as the 
all-pole or autoregressive (AR) model and the general pole- 
zero or autoregressive moving-average (ARMA) model.’ 
There also exist nonrational models of interest in a number of 
applications. Particularly, the model 
S(w) = 8‘”’ (1) 
where P(w) is a trigonometric polynomial of the angular fre- 
quency 4 - n  10 I n) 
M - 1  
P(w) = C c,e-jok 
k = - M + I  
appears in various fields, e.g., radar and sonar applications 
that make use of Gaussian spectra,’ or the absorption spectra 
encountered in interferometric ~pectroscopy.~ From a theo- 
retical point of view, this type of model arises from the maxi- 
ELECTRONICS LETTERS 5th July 1990 Vol. 26 No. 14 
misation of an entropy measure of the underlying random 
process assuming an accurate set of autocorrelation values is 
given.“ Since the coeficients ck of P(w) are the cepstral coefi- 
cients of S(w),’ this type of spectral model is equivalent to 
consider a finite-length cepstrum. 
Finite-length cepstrum spectral estimators obtained from 
AR (or LPC) modelling are very successful in speech pro- 
cessing whenever a distance between spectra has to be evalu- 
ated.6 Since the AR spectral modelling involves an infinite 
cepstral sequence, the model underlying these distances (of 
Euclidean type) is no longer of AR type. Actually, it is a 
finite-length cepstrum model, as indicated by eqn. 1. In fact, 
whenever a spectral estimator involves a cepstrum windowing, 
it will be based on this type of modelling (see Reference 7 for 
another example). 
In spite of the use that is being made of spectral estimators 
based on this type of model, the statistical eficiency of them 
can not be easily evaluated due to the lack of a theoretical 
explicit lower bound for the variance. In this letter a general 
expression for the asymptotic Cramer-Rao lower bound of 
the log spectrum is given. As will be shown, it does not 
depend on the specific underlying spectrum. Before finding 
this Cramer-Rao bound we will calculate the corresponding 
Fisher information matrix. 
Asymptotic Fisher information matrix of finite-length models: 
Let x(n) be a zero-mean Gaussian stationary time series. 
Assume that measurements are available in the range 
1 I n I N where N + 00, and the cepstral parameters cy, 
k = 0, 1, . . . , M - 1, are estimated from x(n). The Fisher infor- 
mation matrix associated with this estimation is given by 
Whittle’s formula (expression (3.3 in Reference 8): 
d w  (3) 
F,, = 5 j log S ( 4  a log S ( 4  
4n ac, ac, 
-I 
where Fij  are the elements of the Fisher matrix F, where 
i , j = O , l , _ . . ,  M -  1. 
According to the spectral model eqns. 1 and 2 
log s(w) = co + 1 ck(Ba’ + ,- jot) M -  I 
k = l  
so that the derivatives involved in eqn. 3 are 
d log S(W) 
8% 
~- - 1  
(4) 
The Fisher matrix takes the simple form 
F,,  = NS(i - j )  if i, j # 0 
N 
F,, = - 
2 
F = N ( :  1/2 0 0 
(7) 
which does not depend on the parameter values ck.  
C r a m e - R a o  lower_ bound of the asymptotic log spectrum 
variance: Assume C = [fo, fl, . . . , ZM - is an asymptotically 
unbiased estimator of the vector of M cepstral parameters of 
the model. The spectral estimate log g(w) obtained through 
eqns. 1 and 2 is also asymptotically unbiased and its asymp- 
totic variance is bounded by the corresponding Cramer-Rao 
bound? 
If the estimator is eficient, this variance will approach the 
Cramer-Rao lower bound as N, the number of data points, 
tends to infinity. If it is not efficient, then var {log &a)} will be 
strictly greater than the bound as N + 00. 
987 


Combined High Power and High Frequency Operation of InGaAsP/InP Lasers at 1.3μm

Reliability of 1.3pm V-grooved inner-stripe laser diodes under high-power

http://authors.library.caltech.edu/465/1/CHEel90.pdf

Combined High Power and High Frequency Operation of InGaAsP/InP Lasers at 1.3μm

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