WPF utiliser les variables d'une fenêtre dans une autre fenêtre

<Window x:Class="Test_WPF.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:def="Definition"
        Title="MainWindow" Height="350" Width="525">

    <Grid DataContext="{Binding .}">
        <TextBox Text="{Binding Nom, UpdateSourceTrigger=PropertyChanged}" Margin="10,10,371,275"/>
        <Button x:Name="MyButton" HorizontalAlignment="Left" Margin="308,120,0,0" VerticalAlignment="Top" Width="75">
            <TextBlock Text="Ciquer ici"/>
        </Button>
    </Grid>
</Window>

using System.Windows;


namespace Test_WPF
{
    /// <summary>
    /// Logique d'interaction pour MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {

        private Creator createur;


        public MainWindow()
        {
            InitializeComponent();

            createur = new Creator();
            this.DataContext = createur;

            DeuxiemeFenetre autrePage = new DeuxiemeFenetre();
            autrePage.DataContext = createur;
            autrePage.Show();
         }

    }
}

<Window x:Class="Test_WPF.DeuxiemeFenetre"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Test_WPF"
        mc:Ignorable="d"
        Title="DeuxiemeFenetre" Height="300" Width="300">
    <Grid DataContext="{Binding .}">
        <TextBox Text="{Binding Nom, UpdateSourceTrigger=PropertyChanged}" Margin="10,10,179,233"/>
    </Grid>
</Window>

using System.ComponentModel;

namespace Test_WPF
{
    public class Creator:INotifyPropertyChanged
    {
        private string nom;
        public string Nom
        {
            get { return nom; }
            set
            {
                if (value == nom)
                    return;

                nom = value;
                GenererPropertyChanged("Nom");
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        private void GenererPropertyChanged(string Propriete)
        {
            if (this.PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(Propriete));

        }
    }
}