[Tex/LaTex] Problem With Capital Greek Letters

Question

I am writing an article in the Journal of the Optical Society of America B (JOSA B) and I have used the journal's LaTeX template.

Unfortunately, I have a problem with the output PDF. Instead of capital Greek letters I get a black square and I cannot figure out what the problem is. This problem is exclusively for capital Greek letters. Other letters and mathematical signs are shown properly. I only use the amsmath package.

\documentclass[9pt,twocolumn,twoside]{osajnl} % http://www.opticsinfobase.org/josab/submit/templates/pc/osajnl_2015.zip (*.zip-file, 581 kB) ‎
\usepackage{amsmath}
\usepackage{breqn}
\usepackage{subfigure} 
\journal{josab} % Choose journal (ao‎, ‎josaa‎, ‎josab)‎ 
\setboolean{shortarticle}{false} % true = letter‎, ‎false = research article‎ ‎

\begin{document}
\begin{subequations}
\begin{equation}
\left[\tilde{V}^{-^{(n)}}\right]=\left[\Gamma^{(n)}\right]\left[\tilde{V}^{+^{(n)}}\right],
\end{equation}
\begin{align}
‎\left[V_m^{(n)}(z) \right]=\left[ P^{(n)} \right]‎
 ‎\left( \left[ \exp \left(‎ -‎j k ^{(n)} \left( z-z_n \right) \right) \right] \left[ \tilde{V}^{+^{(n)}} \right]‎ + \\
 ‎\left[ \exp \left(‎ +‎j k ^{(n)} \left( z-z_{n+1} \right) \right) \right] \left[ \tilde{V}^{-^{(n)}} \right] \right)
\end{align}
\end{subequations}
\end{document}

Answer 1

Remove the call of the breqn package.

After the operation I get

Note that subfigure has been obsolete for several years. The official replacement is subfig. Alternatively, use subcaption. Note that the class already loads caption, so subcaption should probably be chosen.

I add a version without \left and right, which don't seem necessary (they rarely are in cases like this) and where the superscripts (n) are similar to the one for Gamma. More importantly, the two consecutive equations are together in a gather environment: two equation environments should never appear immediately after one another.

\begin{subequations}
\begin{gather}
[ \tilde{V}^{-^{(n)}} ] = [ \Gamma^{(n)} ] [ \tilde{V}^{+^{(n)}} ],
\\
[ \tilde{V}^{-\,(n)} ] = [ \Gamma^{(n)} ] [ \tilde{V}^{+\,(n)} ],
\end{gather}
\end{subequations}

In order to accommodate the split formula where you use \left and \right across lines, just remove all of them; for better clarity, some of the fences can be made \big, but not more than that. Note that multline is the environment of choice for this.

\begin{multline}
[V_m^{(n)}(z)]=[ P^{(n)} ]
 \bigl( \bigl[ \exp \bigl( -j k ^{(n)} ( z-z_n) \bigr) \bigr] [ \tilde{V}^{+^{(n)}}] + \\
\bigl[ \exp \bigl( +j k ^{(n)} ( z-z_{n+1} ) \bigr) \bigr] [ \tilde{V}^{-^{(n)}} ]\bigr)
\end{multline}