Mounting assembly for modulators

A mounting assembly (50) for an electro-optic modulator array (10) is disclosed. Electro-optic modulator array (10) is mounted on a ledge (52) of wiring board (53). A recess (51) in wiring board (53) allows electrical connection of electrodes (14,15) from both a first surface of electro-optic modulator array (10) to a first side of wiring board (53), and from a second surface of electro-optic modulator array (10) to a second side of wiring board (53). A resilient adhesive (54) is used to attach electro-optic modulator array (10) to board (53). Wiring electro-optic modulator array (10) to both sides of wiring board (53) allows full utilization of the PLZT substrate and hence, higher light beam density per unit length.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a mounting assembly for electro-optic 
modulator arrays having electrical connections on both sides, for higher 
image density in the same modulator length. 
2. Description of the Prior Art 
An array of electro-optic modulators is often used to control transmission 
of beams of light used to print images. Electro-optic materials employed 
in individual modulators have properties which change in accordance with 
the strength of an electrical field established within the material. A 
material typically used is lanthanum doped lead zirconate titanate, 
referred to as PLZT. 
Electro-optic modulators are usually manufactured in a group or array. In 
these arrays, each electro-optic modulator must be spaced from the 
adjacent modulator in order to minimize electrical and optical cross talk. 
This leads to unused portions of the electro-optic material. PLZT is 
expensive, and unused portions add unnecessary cost. 
An improved modulator design is the ridge modulator, in which two grooves 
are cut into the PLZT material, and electrodes are metallized around these 
grooves to form a structure which resembles a capacitor. This provides an 
aperture, an area without surface electrodes, which transmits light. The 
ridge modulator can be readily extended to form a linear array of 
modulators. To minimize both electrical and optical cross-talk between 
adjacent light beams, a gap between the electrodes is still required. The 
solution to this problem led to the development of a double-sided ridge 
modulator. Use of a double-sided ridge modulator, however, led to 
additional problems because the electro-optic modulator array must be 
connected to both sides of a wiring board. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide a mounting assembly for an 
electro-optic modulator array in which both surfaces of the modulator 
array are electrically connected to both sides of a wiring board. The 
modulator array is mounted in a recess on a printed wiring board, open to 
both a first side and a second side of the wiring board, using a resilient 
adhesive. Electrical connections on a first surface of the modulator array 
are electrically connected to the first side of the printed wiring board, 
and electrical connections on a second surface of the modulator array are 
electrically connected to the second side of the wiring board.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows an electro-optic modulator array, referred to in general by 
the numeral 10. Electro-optic modulator array 10 is constructed on a PLZT 
substrate 12. 
A first surface 13 of substrate 12 has grooves 16 and 17, forming a first 
ridge 18. In a similar manner, second surface 43 of substrate 12 has 
grooves 46 and 47, forming a second ridge 48. 
First electrode pairs 14 are plated on the first surface of substrate 12 
and in grooves 16 and 17. Gaps 19 separate first electrode pairs. 
Electrodes may be aluminum, silver, gold, or other conductive materials. 
The electrodes may also be layers of these materials. To facilitate 
adhesion of the metal electrodes to the PLZT, other material such as 
chrome, tantalum and titanium may be used. The preferred embodiment uses 
layers of chrome, aluminum, titanium and gold, applied in that order. The 
layer of gold provides good reflectivity for near infrared radiation, 
which minimizes the power loss due to electrode blocking. Electrode 
blocking is incident light which is absorbed by the electrodes when the 
modulator array is used with a near infrared laser diode source. For an 
alternate embodiment using a visible light modulator, silver is used as a 
top layer. A single layer of one material, such as aluminum, may be used. 
For convenience, each electrode pair 14 is shown in the drawing as being a 
single layer of one metal. The thickness of electrode pairs 14, shown in 
more detail in FIG. 2, are on the order of 0.5 to 4.0 microns. 
First ridge 18 forms an area between electrode pairs 14. An electric field 
is established across ridge 18 by an electric circuit through first wires 
32 and 34 and first electrode pairs 14. Each first electrode pair 14 is 
individually connected to a wiring lead as discussed in more detail below. 
Although all electrode pairs are individually connected, only one 
connection is shown in FIGS. 1 and 2, for convenience. 
FIG. 3 shows in schematic how an electro-optic modulator array 10 would be 
used in a modulator assembly 21. A light beam 20 from a source strikes a 
first polarizer 26. In actual operation, a series of light beams, in 
parallel to each other, would strike first ridge 18, on the first surface 
of array 10. A laser diode array is used as a light source in the 
preferred embodiment. However, a tungsten halogen lamp or other suitable 
light sources may also be used. With electrodes off, that is without 
voltage applied across ridge 18, polarized light passes through the 
modulator array 10. Polarizer 28, which is oriented approximately 
90.degree. from polarizer 26, prevents transmission of light beam 20 
through modulator assembly 21. When the first electrode pairs 14 are 
energized, light beam 20 is phase shifted and aligned with the 
polarization axis of second polarizer 28, allowing the light beam to pass 
through modulator assembly 21. 
A second circuit, shown in FIG. 4, is established by second wires 36 and 38 
connected to a circuit on a wiring board, discussed in more detail below. 
Gaps 39, shown in FIG. 1, separate second electrode pairs 15. Second 
electrode pairs 15 are arranged in a staggered fashion with electrode 
pairs 14 on the first surface 13, so that light beams 25, shown 
schematically in FIG. 5, and controlled by second electrode pairs 15, are 
adjacent to light beams 24, controlled by electrode pairs 14. FIG. 5 shows 
a top plan view of modulator array 10 showing the staggered array of beams 
24 and 25. Thus, each area of the ridge 18 is used, cutting down on cost 
for excess, unused material. There are no gaps between light beams 24 and 
25. 
FIGS. 6A and 6B show a mounting assembly 50 for electro-optic modulator 
array 10. Array 10 is mounted on a ledge 52 of printed wiring board 53. In 
the preferred embodiment, wiring board 53 has printed circuits, but the 
scope of the invention is intended to cover various types of wiring 
boards. In the preferred embodiment, wiring board 53 is a composite of 
fiberglas and epoxy. Other material that may be used for wiring boards 
include polyamide, Mylar, ceramic, or co-fired ceramic. 
Wiring board 53 and array 10 are attached to each other using adhesive 54. 
Adhesive 54 is a resilient material, such as a silicone adhesive or 
flexible epoxy. These adhesives should have some elasticity since any 
mechanical strain on array 10 changes the optical properties of the PLZT 
substrate. Acceptable hardness values for adhesives, should be on the 
order of 25 to 100 Shore A. 
First wires 32 and 34 connect array 10 to a first electric circuit 57 on 
the first side of printed wiring board 53. In a similar manner, second 
wires 36 and 38 connect electro-optic modulator array 10 to second 
electric circuit 59 on a second side of printed wiring board 53. These 
wires are attached by ultrasonic wire bonding in the preferred embodiment. 
Recess 51, cut into wiring board 53, allows transmission of light between 
the first side and the second side of wiring board 53. Thus, light beams 
pass through mounting assembly 50 and wiring board 53. 
FIG. 8 shows an alternate embodiment 60 of a mounting assembly according to 
the present invention. In this embodiment, electro-optic modulator array 
10 is flush mounted in a opening 56 in wiring board 53. A resilient 
adhesive 54 is used to attach array 10 to wiring board 53. First wires 32 
and 34 connect to first circuit 57 and second wires 36 and 38 connect to 
second circuit 59, as described above. 
An advantage to a double-sided electro-optic modulator is that the adjacent 
electrodes are on opposite sides of the substrate. This essentially 
eliminates electrical cross talk between electrodes controlling adjacent 
light beams. The next nearest electrode on the same side of the substrate 
is separated by one light beam. There may be slight optical cross talk 
depending on the pitch. Any electrical cross talk will be less than that 
achieved by moving the light beams closer together on a single-sided 
modulator array, which is the only option to increase the fill factor of a 
single-side modulator array. A mounting assembly, as disclosed in the 
present invention, allows full utilization of a double-sided electro-optic 
modulator array.