How to change spacing between caption numbering and text?

Question

Like in an IEEE paper, after the figure caption numbering, there are two letters spacing:

Fig. 1.  Bla bla

Not like

Fig. 1. Bla bla

I would like to have the former.

Answer 1

With caption package, this is how it can be done.

\usepackage{caption}
\DeclareCaptionLabelFormat{mylabel}{#1 #2.\hspace{1.5ex}}
\captionsetup[figure]{labelformat=mylabel,labelsep=none,name=Fig.}

Change 1.5ex to whatever you want.

Code:

\documentclass{article}

\usepackage{caption}
\DeclareCaptionLabelFormat{mylabel}{#1 #2.\hspace{1.5ex}}
\captionsetup[figure]{labelformat=mylabel,labelsep=none,name=Fig.}
\usepackage{graphicx}
\begin{document}
\begin{figure}[htb]
  \centering
  \includegraphics[width=4cm]{example-image-a}
  \caption{This is my figure}
\end{figure}
\end{document}

Change

Answer 2

Actually, this may only be an optical illusion, as IEEEtran inserts a single \nobreakspace (or tie ~) between both the caption label/number and the number/title. However, if you want to mimic (or adjust) caption-related content, it's best to use the caption package.

The caption package provides the key labelsep that defines your separation between the caption label and title. For illustration, below are some of the default options, together with some ones created:

\documentclass{article}
\usepackage{caption}% http://ctan.org/pkg/caption
\DeclareCaptionLabelSeparator{qquad}{\qquad}
\DeclareCaptionLabelSeparator{bigspace}{.\hspace*{4em}}
\begin{document}
\captionof{figure}{A figure}
\captionsetup{labelsep=space}
\captionof{figure}{A figure}
\captionsetup{labelsep=quad}
\captionof{figure}{A figure}
\captionsetup{labelsep=qquad}
\captionof{figure}{A figure}
\captionsetup{labelsep=bigspace}
\captionof{figure}{A figure}
\end{document}