Variable reflectance mirrors and windows

#The present invention generally pertains to a rearview mirror assembly for a vehicle and to windows (both architectural and vehicular). More particularly, the present invention pertains to a rearview mirror assembly incorporating an electronic device such as a display, light source, and/or light sensor, and to windows having a variable transmittance.

#It is desirable to provide electronic devices such as displays, sensors, signal lights, and indicator lights in a rearview mirror assembly of a vehicle. There are several issues with designing a rearview mirror assembly incorporating such an electronic device, particularly when the rearview mirror assembly is an inside mirror assembly. If the electronic device is disposed adjacent the mirror element, it causes the inside rearview mirror assembly to have a larger area, which disadvantageously blocks more of the driver's view through the windshield. To address this problem, electronic devices are provided behind the mirror element so as to transmit or receive light through the mirror element. To allow for light to be transmitted through the mirror element, a portion of the reflective layer of the mirror element is removed to define a window in front of the electronic device. This solution, however, reduces the reflective viewing area of the mirror assembly. Such a window also provides further problems when the reflective layer serves as an electrode for an electro-optic mirror element, such as an electrochromic mirror element. Thus, the window acts to eliminate the electrode across a portion of the electrochromic mirror element thereby causing an objectionable non-uniform coloration of the mirror element when dimmed.

#Commonly-assigned U.S. Pat. No. 6,700,692 discloses several solutions for incorporating electronic devices behind an electro-optic mirror element. In particular, this patent discloses the use of a “transflective” layer, which is partially reflective, partially transmissive. Although such a transflective layer is very effective for most forms of electronic devices, the transflective layer tends to block a large percentage of light (passing about 10% of incident light). As a result, the light from a display or light source behind the mirror element is not efficiently transmitted through the transflective layer. This becomes more problematic when a display is provided that displays images of variable brightness during periods of bright daylight. This is because the reflectivity of the transflective layer is still rather high, and therefore, there is large light loss going through transflective layer producing poorer contrast. The above '692 patent further discloses an embodiment whereby slit-like, parallel apertures are etched in the reflective layer in front of a compass display and/or in front of turn signal indicator lights. Such apertures are often relatively large and few in number.

#In the drawings:

#FIG. 1 is a front elevational view schematically illustrating a rearview mirror system constructed in accordance with the present invention;

#FIG. 2 is a front elevational view schematically illustrating an inside rearview mirror assembly constructed in accordance with one embodiment of the present invention;

#The present invention pertains to various structures for variable reflectance rearview mirrors and variable transmittance windows. One embodiment pertains to the provision of a polarized reflector in a rearview mirror. Another embodiment pertains to the provision of a switchable cholesteric liquid crystal element in a window. Yet another embodiment pertains to the provision of a plurality of apertures in a reflector layer of a rearview mirror where the apertures are sized and positioned in alignment with light emitting areas of a display positioned behind the reflector layer. In another embodiment, a moveable display or mirror element is attached to a rearview mirror housing.

#According to one of the above embodiments, the present invention may generally include a rearview mirror assembly comprising a variable reflectance mirror element and an electronic device positioned behind the mirror element so as to transmit or receive light through the mirror element. Unlike prior rearview variable reflectance mirror elements, however, the mirror element used in the present invention, may utilize a polarized reflector that transmits light having a first polarization, while reflecting light having a second polarization opposite the first polarization. The electronic device emits light or receives light having the first polarization such that the light passes very efficiently through the mirror element with almost no loss. Approximately half of the ambient light, on the other hand, is reflected so that the mirror element acts as an effective rearview mirror. The polarized reflector may function as one of the electrodes of the variable reflectance mirror element.

#The reflective polarizer may be a “wire grid” type of polarizer that reflects (specularly) one plane of light polarization and transmits the other. A display or other light source that emits polarized light would not suffer a large drop in brightness if it is oriented such that its polarized light is transmitted through the mirror element and not reflected. If a light source or light emitting display that does not emit polarized light is used behind a “wire polarizer” mirror element, a portion of the light is transmitted and a portion of the light is reflected. Both the transmitted and reflected light is polarized. The polarized reflected light could be de-polarized by reflective scattering and part of that light will then be transmitted by the mirror element or the plane of polarization of the light could be rotated 90 degrees and reflected back through the “wire grid” polarizer. This will enhance the display brightness. Similar techniques could be used to utilize ambient light that is transmitted through the wire grid polarizer into the display/reflector assembly.