Electrical and Optical Gain Lever Effects in InGaAs Double Quantum Well Diode Lasers Page: 3 of 12
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Electrical and Optical Gain Lever Effects in
InGaAs Double Quantum Well Diode Lasers
Michael D. Pocha, Senior Member, IEEE, Lynford L. Goddard, Member, IEEE, Tiziana C. Bond,
Member, IEEE, Rebecca J. Nikolid, Member, IEEE, Stephen P. Vernon, Jeffrey S. Kallman, and
Elaine M. Behymer
Abstract- In multisection laser diodes, the amplitude or
frequency modulation (AM or FM) efficiency can be improved
using the gain lever effect. To study gain lever, InGaAs double
quantum well (DQW) edge emitting lasers have been fabricated
with integrated passive waveguides and dual sections providing a
range of split ratios from 1:1 to 9:1. Both the electrical and the
optical gain lever have been examined. An electrical gain lever
with greater than 7 dB enhancement of AM efficiency was
achieved within the range of appropriate DC biasing currents,
but this gain dropped rapidly outside this range. We observed a 4
dB gain in the optical AM efficiency under non-ideal biasing
conditions. This value agreed with the measured gain for the
electrical AM efficiency under similar conditions. We also
examined the gain lever effect under large signal modulation for
digital logic switching applications. To get a useful gain lever for
optical gain quenched logic, a long control section is needed to
preserve the gain lever strength and a long interaction length
between the input optical signal and the lasing field of the diode
must be provided. The gain lever parameter space has been fully
characterized and validated against numerical simulations of a
semi-3D hybrid beam propagation method (BPM) model for the
coupled electron-photon rate equation. We find that the optical
gain lever can be treated using the electrical injection model,
once the absorption in the sample is known.
Index Terms- amplitude modulation, gain lever, photonic
integrated circuits, semiconductor device measurement,
semiconductor device simulation, semiconductor lasers
G AIN competition in lasers offers the potential of
integrating several digital logic functions on the same
chip and with many applications for all-optical, high-speed
switching. Lasers with optical gain control, capable of routing
and logic functions ,  via the gain quench effect , 
have been demonstrated. All-optical photonic integrated
circuits where, edge emitting lasers and laser-logic (gain-
quenched inverters & nor-gates) will be interconnected by
passive waveguides in a monolithic integrated circuit are
Manuscript received February 23, 2007. This work was performed under
the auspices of the U.S. Department of Energy by University of California,
Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.
All authors are with the Lawrence Livermore National Laboratory, P.O.
Box 808, L-222, Livermore, CA 94551-0808 USA (phone: 925-422-8664;
fax: 925-422-2783; e-mail: email@example.com).
under investigation at LLNL. Gain in the active devices will
be useful to overcome coupling and transmission losses in the
passive waveguides. We are, therefore, investigating the gain
lever effect to enhance the modulation efficiency of our active
devices. Our test structures are InGaAs double quantum well
(DQW) graded index separate confinement heterostructure
(GRINSCH) lasers. The gain lever effect is illustrated in Fig.
1, where a cross-sectional schematic diagram of a split-
electrode laser is shown, along with a representative gain
curve. Lasing occurs when gain overcomes losses. The overall
modal gain in a laser is clamped, in steady-state,
approximately by the cavity losses. At the lasing threshold, an
increase in gain in one section of the laser allows an equal
decrease in gain of the other section (AG, = AGb in the figure)
and vice-versa. We call the shorter section a and the longer
section b, the respective drive currents I, and Ib and the
respective current densities Ja and Jb. In the literature sections
a and b are also referred to as control and slave sections,
respectively. Section b is biased to a higher carrier density
than section a. A small decrease in Ia reduces the carrier
density in the section, reducing the total gain below the total
loss. The circulating optical power decreases, which causes
the carrier density of section b to increase. The carrier density
continues increasing until the gain equal loss condition is re-
established. However, due to the sub-linear gain versus carrier
density relationship shown in the figure, the carrier density
increase in section b is enhanced compared to the decrease in
section a. The net result is an increase in the amplitude
modulation (AM) efficiency, i.e. the slope efficiency of the
The gain-lever effect has been extensively studied -,
especially in the context of electrical amplitude modulation in
split electrode lasers. Vahala, Newkirk, and Chen  also
show an optical gain lever in GRINSCH lasers. Most of these
papers concentrate on the small signal behavior. Here, in
addition to small signal behavior, we also study large signal
modulation because our application is digital logic switching.
We have conducted experiments and modeling to understand
and optimize the gain lever effect. While ultimately interested
in optical input, we began with electrical input to quickly
verify our models before pursuing the more complex optical
input study. Our numerical models  use a beam
propagation method (BPM) that in combination with the
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Pocha, M D; Goddard, L L; Bond, T C; Nikolic, R J; Vernon, S P; Kallman, J S et al. Electrical and Optical Gain Lever Effects in InGaAs Double Quantum Well Diode Lasers, article, January 3, 2007; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc895436/m1/3/: accessed January 21, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.