Current (mA)
Optical power (m W)
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0123
85°C
60°C
40°C
25°C
22°C
0.5 mA
0.7 mA 1.0 mA
1. 3 mA
2. 1 mA
4 5 0 2 4 6 8 10 12 14 16
Frequency (GHz)
Normalized S21
2.0
1. 8
1. 6
1. 4
1. 2
1.0
0.8
0.6
0.4
0.2
Angewandte Physik & Elektronik GmbH
ape@ape-berlin.de
www.ape-berlin.com
picoEmerald 2
•
Intrinsically jitter-free and low noise
•
Coverage of entire Raman ;ngerprint region 700 ... 9000 cm- 1
•
Perfect pulse overlap in space and time with internal sensors
•
Up to 20 MHz modulation possible for video rate imaging
• Fully remote controlled
The Hands-Free All-In-One-Box Light Source
for CARS / SRS Microscopy
• Picosecond pulses for best resolution with line width < 10 cm- 1
• Wavelength sweep function
Software&Computing
33 Laser Focus World www.laserfocusworld.com September 2013
extract model parameters and accurately reproduce device
performance within OptSim.
The process of extracting model parameters from measured
data is well known and typically consists of the following elements (this same procedure is used for extracting model parameters from device simulation or datasheets). First, you obtain a set of measured device characteristics that you want to
replicate in simulation. You then define error functions that
quantify the differences between these device characteristics
and their equivalent simulation results as a function of the
model parameters. Finally, you optimize the model parameters such that these errors, and hence the differences between
simulation and experiment, are minimized.
As an example, consider a multiple quantum well (MQW)
laser. OptSim has a custom model that implements a MQW laser via a set of coupled rate equations, the parameters of which
are automatically obtained by fitting file-based measurement
data for the laser being used in the optical transmitter design. 7
Measured curves that can help OptSim extract rate-equation
parameters include the power-vs.-current (P-I) curve, small-signal amplitude modulation (AM) curves, small-signal frequency modulation curves, relative intensity noise curves, fiber transfer-function curves (AM curves with dispersive fiber),
and a laser-linewidth curve. For an accurate model of a laser,
measured P-I and AM data are essential; other curves from the
above list are helpful but not absolutely mandatory.
In comparison, VCSELs are more complicated devices due
to their thermal and spatial characteristics. The VCSEL model implemented within OptSim consists of a set of rate equations that take into account thermally dependent gain and
carrier leakage, the spatial dependence of the carrier distribution, and self-heating. 8 The model also includes expressions for the cavity current-voltage (I-V) relationship as well
as electrical parasitics.
Because of its thermal behavior, extraction of the VCSEL
model parameters requires measured data at different am-
bient temperatures. P-I curves at different temperatures
allow for the modeling of the threshold current’s temper-
ature sensitivity as well as thermal rollover, while the la-
ser’s S-parameter small-signal modulation response (S21) at
FIGURE 3. Parameter extraction can achieve good agreement between measured and modeled behavior, as shown here for two different
VCSELs (solid lines show OptSim; symbols show measurement; P-I curves are shown at left; S21 curves are shown at right).
