We discuss the Multi-stripe Array Grating Integrated Cavity (MAGIC) Laser: a multi-wavelength laser formed by monolithically integrating a diffraction grating and an array of active stripes in a planar semiconductor waveguide cavity. Recent results will be presented

Bhat, R.

Caneau, C.

Koza, M. A.

LeBlanc, H. P.

Poguntke, K. R.

Scherer, A.

SooIe, J. B. D.

Caltech Authors - Main

The MAGIC Laser: 
a MonolithicWDM Source 
K.R.Poguntke *, J.B.D.SooIe, A.Scherer, H.P.LeBlanc, 
C.Caneau, R.Bhat, and M.A.Koza 
Bellcore, 33 1 Newman Springs Road, Red Bank, N.J 07701 
* Dept. of Physics, University of Surrey, Guildfond, U.K. 
Abstract 
We discuss the Multi-stripe Array Grating Integrated Cavity (MAGIC) Laser: a 
multi-wavelength laser formed by monolithically integrating a diffraction grating and an array of 
active stripes in a planar semiconductor waveguide cavity. Recent results will be presented. 
Introduction 
There is currently considerable interest in the telecommunications arid computing industries at 
developing networks that use many different wavelengths. Not only for increasing the capacity of 
point-to-point links, but also for broadcast systems and, most interestingly, in multi-wavelength 
optical networks where wavelength is effectively used as an effective extra "dimension". 
Whatever the ultimate network envisaged, multi-wavelength systems will only become widely 
deployed if sources and wavelength-demultiplexing detectors can be developed that have precise 
factory-defined wavelengths and high field-reliability, and can also be: manufactured at low cost. 
This talk discusses a new type of multi-wavelength source - the MAGIC, or Multi-stripe Array 
Grating Integrated Cavity Laser - that we believe has the potential to fiilfill these criteria. 
The MAGIC Laser 
The device structure is illustrated schematically in Figure 1. It is based on a planar 
WAnGaAsPAnP waveguide. At one end a number of active laser stripes have been integrated, 
and at the other a fbcussing vertical-walled diffraction grating has beem etched through the guide 
layers [ 11. 
If one stripe is injection pumped, the spontaneous radiation emitted into the planar waveguide 
at one end is reflected at one wavelength by the grating and lasing occurs at the wavelength. 
different stripes cause lasing at different wavelengths. The integratedl laser is acting in a similar 
fashion to a conventional extemal cavity laser, with the bulk optic 1e:ns and grating of the latter 
replaced by the etched grating. 
h -  
( h -  
I I 
Active Stripes Etched Grating 
p-inP s.i. InP InGaAsP 
MQW 3 
active layer / 
A u  n+ -InP 
Figure 1. Schematic of the MAGIC laser. 
The interesting mode of operation of the MAGIC laser comes, however, when two stripes are 
pumped simultaneously. This is illustrated schematically in Figure 1. If these stripes are each 
selected so that, individualiy, they receive feedback from the grating towards (or beyond) at 
wavelengths at the opposite extreme ends of the gain curve of the active material, neither stripe is 
inclined to lase on its own. However, when both are pumped simultaneously a cavity is formed 
between them - via the gmting - at a wavelength midway between, i.e. towards the peak of the gain 
curve, and consequently lasing occurs at this wavelength. If one denotes one stripe the "output" 
and takes the radiation from its extemal facet, by then simply selecting different stripes for the 
"second" pumped element allows us to select different laser wavelengths without realigning the 
pick-up fiber. We now have a single-port wavelength-switchable laser. 
a -  . I  - 
1510 1520 1530 
Wavelength I nm 
Figure 2. h e r  emission at different wavelengths. 
Figure 2 gives a compilation of emissions from a MAGIC laser obtained from a single "output 
stripe" on selecting different "second stripes" to pump. 
One of the attractive features of the MAGIC laser is its wavelength accuracy. The emission 
wavelengths are determined only by the device geometery ;and the conrposition and thicknesses of 
the planar waveguide layers. These can all be held to fairly precise tolerances, which leads to 
precise wavelength control. 
Sigma = 01.02nm 
0 10 c c 
5 0.05 1 , 
0 1 2 3 4  5 6 7 8 9  
Laser Number 
Figure 3. Linearity of the wavelength spcing. 
We have demonstrated wavelength spacing accuracieis of k0.02nm; values on the order of 
kO.01 should be attainable. This is more than an order of magnitude greater precision than is 
currently attainable with DFB arrays. The comb of laser wavelengths can be raised or lowered by 
adjusting the device temperature. An absolute pre-determined accuracy of <-+lnm is possible with 
well-controlled wafer growth. This then requires < 10°C temperature tuning for complete alignment 
of the lasing wavelengths to required network values. Figure 3 shows the linearity obtained from 
one MAGIC laser. 
1510 1520 1530 
Wavelength (nm) 
Figure 4. Simultaneous k i n g  at four wavelengths. 
Several wavelength may be emitted simultaneously by pumping different ”second stripes” at 
the same time. Each stripe sets up its own lasing resonance with the output stripe and lasing 
occurs at each wavelength. Figure 4 shows the simultaneous emission of the MAGIC laser at four 
wavelengths. 
[ 1 ] J.B.D.Soole, K.Poguntke, A.Scherer, H.P.LeBlanc, C.Chang-Hasnain, J.R.Hayes, 
R.Bhat, C-Caneau, and M.A.Koza, Appl. Php. Lett., 61, 2750, 1992. 


The MAGIC Laser: a Monolithic WDM Source

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The MAGIC Laser: a Monolithic WDM Source

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