1.

Numerical Modelling Software for Teaching

Educational institutions are continually asked to make courses more relevant to current industrial practice, yet also have to provide students with a thorough understanding of fundamental concepts, so that students are ‘future proofed’. As technology progresses, the gap between these requirements widens, or one side becomes ignored completely.

A common compromise is to teach theory (usually analytical solutions) in the lecture theatre, and leave practical aspects to laboratories and design projects. Unfortunately, this often means that lectures are ‘dry’, as real-world solutions often go beyond the mathematical prowess of undergraduates, and often beyond the reach of analytical solutions altogether. The other problem is that real-world laboratories are equipped with millions of dollars of equipment, which universities can never emulate, and also carry safety hazards and high maintenance costs.

Fortunately, numerical models can help bridge the gap between analytical solutions and realistic engineering design. This is because a numerical model is based on fundamental mathematics (such as differential equations), but can extrapolate to extremely complex situations. Thus, students can test that a numerical model agrees with analytical solutions in simple cases, and then extrapolate to complex designs using the model. Ideally, they will gain some understanding of how the algorithm works.

Industry has embraced commercial numerical modelling software, as it supports creativity beyond analytical solutions, and also captures the design details during use [1]. It also supports collaborative design amongst teams and between vendors and customers (‘design chains’) [2]. It is also essential for verifying designs, and optimizing production yields.

There are a number of software packages aimed at education and training, many of them developed in-house. However, using commercial software for teaching gives several benefits for the students:

Commercial software also has several benefits for the educational institution:

The main disadvantage, addressed here, is that commercial-grade software cannot be given away for free to the students for use off-campus. This is for the simple reason that the free software will undermine the commercial market, so eventually all development and support of the software will cease because it becomes unprofitable. One option is to provide cut-down simulation tools, with a limited range of models. Unfortunately, this means that the more interesting effects and phenomena cannot be explained.

2.

Free Take-Home Virtual Laboratories

To address this problem, VPI has developed VPIplayer™. This has the full simulation capabilities of the commercial tools VPItransmissionMaker™ and VPIcomponentMaker™, including exactly the same numerical models. Thus students get realistic results without compromise. VPIplayer can be downloaded from http://www.vpiphotonics.com/VPIplayer

VPIplayer is shown in Fig. 1. This GUI appears if a dynamicDataSheet™ is opened, say from an email, server or webpage. A dynamicDataSheet is a term coined for the commercial market, where vendors what to promote components and sub-systems to equipment manufacturers. For the purposes of the article a dynamicDataSheet is synonymous with a Virtual Laboratory. The top of the GUI shows the schematic of the system being simulated, including instrumentation. This uses Adobe’s SVG vector graphics format that can be zoomed into without losing detail. This allows annotations and parameter values to be seen, even of very complex schematics.

Fig. 1:

VPIplayer after a dynamicDataSheet for a mode-locked laser has been opened.

The buttons at the bottom-left allow (1) new dynamicDataSheets to be opened, (2) simulations to be run, and (3) emails sent to the originator, or the originator’s web-page to be accessed. This feature is useful when submitting questions to the course coordinator, or looking for updated tasks.

Above these buttons is an attachment area. This can show information relevant to a particular schematic, like course notes, spreadsheets with analytical solutions, mathematical modeling programs, or presentations.

To the right of the buttons is an area for controls. These controls allow certain parameters of the simulation to be changed before each simulation run. In the case of Fig. 1, the delay of the external cavity can be adjusted. This allows students to investigate harmonic mode-locking and unstable pulse generation. These controls can also be lists, such as lists of component choices or preferred values.

Running a simulation produces results presented within sophisticated visualization tools. The tools allow data to be examined and post processed after a simulation. For example the WDM Channel Analyzer (Fig. 2) can:

Fig. 2:

The WDM Channel Analyzer provides a wealth of functionality in one visualizer

Other visualizers include:

A range of applications demos also shows the operation of laboratory equipment and common test and measurement techniques [3], including the imitations of these techniques.

3.

Generating dynamicDataSheets (Virtual Laboratories) for distribution

Over 150 universities have purchased the full versions of VPIsystems’ simulation software, VPItransmissionMaker™ and VPIcomponentMaker™. These share a common interface, and allow almost any experiment to be assembled from over 700 generic photonic and electronic modules. Also, there are over 350 readymade demos, which can be modified if desired.

Schematics created in VPItransmissionMaker/VPIcomponentMaker can be exported as a dynamicDataSheet for free distribution and use with VPIplayer, as shown in Fig. 3. This is a simple process:

Fig. 3:

Creating, distributing and playing dynamicDataSheets.

The completed dynamicDataSheets are very compact (10-40 kB) so can be distributed electronically using email or web-page downloads. If desired, they can be locked with a password. This could be useful if a start-date is specified for an assignment: the password should be distributed on that start data.

4.

Full Versions of the Simulator

VPItransmissionMaker/VPIcomponentMaker share a graphical design environment, so that new components, subsystems, systems and networks can be defined by wiring modules together in a schematic. This design environment is shown in Figure 4. The modules are selected from a library on the left, and placed onto a schematic. Different parameter values can be set for each instance of a module on a schematic, or parameters values may be linked to common ‘global’ parameter settings (say to set the bandwidths of all optical filters at once).

Fig. 4:

Graphical Design Environment of VPItransmissionMaker/VPIcomponentMaker showing component libraries (left) and Interactive Controls (lower-right window)

Once the schematic has been created, simulations can be run and visualizers will appear, just as in VPIplayer. However, design process tools are provided to speed the design process, such as:

Table 1 compares the features of VPIplayer and the full simulation tools. One important point is that the simulation engine within VPIplayer is identical to that within the full tools. This means that VPIplayer will generate exactly the same results as the full tool.

Table 1:

Comparison of features in VPIplayer and the full simulation tools.

5.

Applications Coverage

VPIplayer dynamicDataSheets can be created from scratch using the almost infinite number of combination of the 700 photonic and electronic modules in VPItransmissionMaker and VPIcomponentMaker. However, it is easier to start from the existing demo set, of which there are more than 350. These demos cover the following categories:

6.

Ready-made VPIplayer dynamicDataSheets for educational use

A set of VPIplayer dynamicDataSheets have been created especially for the popular undergraduate and graduate textbook by Gerd Keiser “Optical Fiber Communications”, McGraw Hill, Boston, 2000. The downloads are available from http://www.mhhe.com/engcs/electrical/keiser/.

7.

Conclusions

VPIplayer provides free take-home laboratories and is based on the full capabilities of professional photonic simulation tools. This combination gives students to ‘industrial’ simulation power at no cost. The downside, if it can be called that, is that the experiments have fixed topologies, and a few variable parameters. However, this may actually be an advantage, as it focuses students on a prescribed parameter space. For postgraduate students, who wish to create new topologies and component libraries, VPIphotonics offers discounted versions of its full professional tools VPIcomponentMaker and VPItransmissionMaker.