Read data from an array that is inside another array

I have an associative array (data) that contains data and another associative array (other values) within it, the problem is that I can only read the data contained before the array (other values) throwing the error Catchable fatal error: Object of class stdClass could not be converted to string this in php, if I print it by console everything is correct, what I want is to be able to access the values of the array (other values);
Jquery

    var otrosValores={
        val1:"valor 1",
        val2:"valor 2",
        val3:"valor 3"
    }
    var dato={
        nombre:"aqui el nombre",
        apellido:"aqui el apellido",
        rut:"aqui el rut",
        otros:otrosValores,
    }
    console.dir(dato)
    $.ajax({
        url : 'admin/controlador.php',
        type : 'POST',
        cache : false,
        data : "op=saveFicha&datos="+JSON.stringify(dato),
        success: function(resultado){
            $(".resultado").html(resultado)                 
        }
    })

Php

$datos=json_decode($_POST["datos"]);

foreach ($datos as $key => $value) {
    echo $key," => ",$value,"<br>";
    if($key=="otros"){
        foreach ($key as $key2 => $value2) {
            echo $key2," => ",$value2;
        }
    }
}