WPF Binding problem

<UserControl x:Class="myControl.UserControl1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <Grid>
        <TextBlock Name="_innerCaption" > Hello</TextBlock>
    </Grid>
</UserControl>

namespace myControl
{
    /// <summary>
    /// Interaction logic for UserControl1.xaml
    /// </summary>
    public partial class UserControl1 : UserControl
    {
        public UserControl1()
        {
            InitializeComponent();
        }

        public TextBlock InnerCaption
        {
        get { return (TextBlock)this.GetValue(InnerCaptionProperty); }
        set { this.SetValue(InnerCaptionProperty, value); }
        }
        public static readonly DependencyProperty InnerCaptionProperty = DependencyProperty.Register(
        "InnerCaption", typeof(TextBlock), typeof(UserControl1),new PropertyMetadata(false));
        }
}