Title: Photoconductive switch module
Abstract: The present invention is directed to a photoconductive switch module. The photoconductive switch module comprises a first substrate having light-emitting elements, and a second substrate having photoconductive switch elements, whose number is equal to that of the light-emitting elements. The light-emitting elements face the photoconductive switch elements, so that the photoconductive switch elements are turned on/off in accordance with lighting/extinction of the light-emitting elements. The photoconductive switch module further comprises a third substrate arranged between the first substrate and the second substrate. The third substrate has through holes, whose number is equal to that of the light-emitting elements. Each through hole is positioned between a light-emitting element and a photoconductive switch element facing each other. Drive light emitted from each light-emitting element travels to the photoconductive switch element via the through hole.
Patent Number: 7,009,195 Issued on 03/07/2006 to Nakano, et al.
| Inventors:
|
Nakano; Junichi (Hachioji, JP);
Miyajima; Hiroshi (Hachioji, JP);
Matsuo; Daisuke (Hachioji, JP);
Murakami; Kenzi (Hino, JP);
Saito; Mitsuchika (Kawasaki, JP);
Kondoh; You (Yamato, JP);
Takenaka; Tsutomu (Hachioji, JP);
Kaneko; Yasuhisa (Kawasaki, JP)
|
| Assignee:
|
Olympus Corporation (Tokyo, JP)
|
| Appl. No.:
|
616258 |
| Filed:
|
July 9, 2003 |
Foreign Application Priority Data
| Jul 09, 2002[JP] | 2002-200209 |
| Current U.S. Class: |
250/551; 250/239; 257/82 |
| Current Intern'l Class: |
G02B 27/00 (20060101) |
| Field of Search: |
250/551,214.LS,214.SW,227.11,227.24,239
257/80-84,431-435
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Sohn; Seung C.
Attorney, Agent or Firm: Scully, Scott, Murphy & Presser
Claims
What is claimed is:
1. A photoconductive switch module comprising:
a first substrate having light-emitting elements;
a second substrate having photoconductive switch elements, whose number is equal
to that of the light-emitting elements, the light-emitting elements and the photoconductive
switch elements being arranged to face each other, the photoconductive switch elements
being turned on/off in accordance with lighting/extinction of the light-emitting
elements; and
a third substrate arranged between the first substrate and the second substrate,
the third substrate having through holes, whose number is equal to that of the
light-emitting elements, each through hole being arranged between the light-emitting
element and the photoconductive switch element facing each other, drive light emitted
from each light-emitting element traveling to the photoconductive switch element
via the through hole;
wherein the second substrate has a circuit wiring connected to the photoconductive
switch elements on the side facing the third substrate, the third substrate has
a concave portion extending along the circuit wiring, such that the through holes
terminate on the bottom surface of the concave portion, and the third substrate
has conductivity at least in the vicinity of the surface of the concave portion
and the circuit wiring and the concave portion are arranged to face each other.
2. The photoconductive switch module according to claim 1, wherein the third
substrate further has a convex portion protruding from the bottom surface of the
concave portion, and the convex portion has a height equal to or smaller than a
depth of the concave portion.
3. The photoconductive switch module according to claim 2, wherein the convex
portion is positioned between the photoconductive switch elements to be reversely
turned on/off.
4. The photoconductive switch module according to claim 2, wherein the convex
portion and the second substrate are spaced with a gap equal to or smaller than
100 μm, and the convex portion has a thickness (dimension in a direction
along which the concave portion extends) equal to or smaller than 100 μm.
5. The photoconductive switch module according to claim 2, wherein a height of
the convex portion is equal to a depth of the concave portion.
6. The photoconductive switch module according to claim 2, wherein a height of
the convex portion is smaller than a depth of the concave portion.
7. The photoconductive switch module according to claim 2, wherein the convex
portion surrounds the through hole.
8. A photoconductive switch module comprising:
a first substrate having light-emitting elements;
a second substrate having photoconductive switch elements, whose number is equal
to that of the light-emitting elements, the light-emitting elements and the photoconductive
switch elements being arranged to face each other, the photoconductive switch elements
being turned on/off in accordance with lighting/extinction of the light-emitting
elements; and
light isolation means for isolating the light between a pair of the light-emitting
element and the photoconductive switch element from the light between another pair
of the light-emitting element and the photoconductive switch element;
wherein the light isolation means comprises a third substrate arranged between
the first substrate and the second substrate, the third substrate has through holes,
whose number is equal to that of the light-emitting elements, each through hole
is arranged between the light-emitting element and the photoconductive switch element
facing each other, and drive light emitted from the light-emitting element travels
to the photoconductive switch element via the through hole; and
wherein the second substrate has a circuit wiring connected to the photoconductive
switch elements on the side facing the third substrate, and the photoconductive
switch module further comprises electromagnetic shield means for the circuit wiring,
the electromagnetic shield means being disposed on the third substrate on the side
facing the second substrate and arranged to face the circuit wiring.
9. The photoconductive switch module according to claim 8, wherein the third
substrate has a concave portion extending along the circuit wiring, such that the
through holes terminate on the bottom surface of the concave portion, the third
substrate has conductivity at least in the vicinity of the surface of the concave
portion, and the conductive part in the vicinity of the surface of the concave
portion constitutes the electromagnetic shield means.
10. A photoconductive switch module comprising:
a first substrate having light-emitting elements;
a second substrate having photoconductive switch elements, whose number is equal
to that of the light-emitting elements, the light-emitting elements and the photoconductive
switch elements being arranged to face each other, the photoconductive switch elements
being turned on/off in accordance with lighting/extinction of the light-emitting
elements; and
a third substrate arranged between the first substrate and the second substrate,
the third substrate having through holes, whose number is equal to that of the
light-emitting elements, each through hole being arranged between the light-emitting
element and the photoconductive switch element facing each other, drive light emitted
from each light-emitting element traveling to the photoconductive switch element
via the through hole;
wherein the second substrate has a circuit wiring connected to the photoconductive
switch elements on the side facing the third substrate, the third substrate has
a concave portion extending along the circuit wiring, such that the through holes
terminate on the bottom surface of the concave portion, and the third substrate
has conductivity at least in the vicinity of the surface of the concave portion
and the third substrate further has a convex portion protruding from the bottom
surface of the concave portion, and the convex portion has a height equal to or
smaller than a depth of the concave portion.
11. The photoconductive switch module according to claim 10, wherein the convex
portion is positioned between the photoconductive switch elements to be reversely
turned on/off.
12. The photoconductive switch module according to claim 10, wherein the convex
portion and the second substrate are spaced with a gap equal to or smaller than
100 μm, and the convex portion has a thickness (dimension in a direction
along which the concave portion extends) equal to or smaller than 100 μm.
13. The photoconductive switch module according to claim 10, wherein a height
of the convex portion is equal to a depth of the concave portion.
14. The photoconductive switch module according to claim 10, wherein a height
of the convex portion is smaller than a depth of the concave portion.
15. The photoconductive switch module according to claim 10, wherein the convex
portion surrounds the through hole.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior
Japanese Patent Application No. 2002-200209, filed Jul. 9, 2002, the entire contents
of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photoconductive switch module, which is realized
by a combination of light-emitting elements and photoconductive switch elements,
and more particularly to a small photoconductive switch module in which photoconductive
switch elements are integrated.
2. Description of the Related Art
U.S. Pat. No. 6,407,401B1 discloses a small high-frequency/high-performance
photoconductive relay. The photoconductive relay, which realizes a small high-frequency
switch, includes a photoconductive switch element, whose resistance varies according
to the intensity of incident light, and a light-emitting element, which emits light
to illuminate the photoconductive switch element, the photoconductive switch element
and the light-emitting element being closely positioned to face each other. This
photoconductive relay provides a minimum unit of a switch that can take the on
state and the off state.
The photoconductive switch element is an element which is important to realize
a photoconductive relay (photoconductive switch), and an example of such an element
is disclosed in, e.g., U.S. Pat. No. 6,252,221B1.
In order to realize a sophisticated switch module, photoconductive switch elements
must be used to constitute a switch circuit.
The circuit must be designed in such a manner that the layout becomes very compact,
i.e., the wiring becomes short in order to obtain the good performance in a high
frequency. That is, the photoconductive switch elements must be arranged in close
proximity to each other.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to a photoconductive switch module. The photoconductive
switch module comprises a first substrate having light-emitting elements, and a
second substrate having photoconductive switch elements, whose number is equal
to that of the light-emitting elements. The light-emitting elements face the photoconductive
switch elements, so that the photoconductive switch elements are turned on/off
in accordance with lighting/extinction of the light-emitting elements. The photoconductive
switch module further comprises a third substrate arranged between the first substrate
and the second substrate. The third substrate has through holes, whose number is
equal to that of the light-emitting elements. Each through hole is positioned between
a light-emitting element and a photoconductive switch element facing each other.
Drive light emitted from each light-emitting element travels to the photoconductive
switch element via the through hole.
Advantages of the invention will be set forth in the description which
follows, and in part will be obvious from the description, or may be learned by
practice of the invention. The objects and advantages of the invention may be realized
and obtained by means of the instrumentalities and combinations particularly pointed
out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
The accompanying drawings, which are incorporated in and constitute a part of
the specification, illustrate embodiments of the invention, and together with the
general description given above and the detailed description of the embodiments
given below, serve to explain the principles of the invention.
FIG. 1 shows a cross section of a photoconductive switch module according to
a first embodiment of the present invention;
FIG. 2 shows one layout of the photoconductive switch elements and a circuit
wiring illustrated in FIG. 1;
FIG. 3 shows an equivalent circuit of the photoconductive switch elements and
the circuit wiring according to the layout of FIG. 2;
FIG. 4 shows a further preferable layout of the photoconductive switch elements
and the circuit wiring depicted in FIG. 1;
FIG. 5 shows an equivalent circuit of the photoconductive switch elements and
the circuit wiring according to the layout of FIG. 4;
FIG. 6 shows a cross section of a photoconductive switch module according to
a second embodiment of the present invention;
FIG. 7 is a perspective view showing the side of a spacer facing a switch element
substrate depicted in FIG. 6;
FIG. 8 is a front view showing the side of the spacer facing the switch element
substrate depicted in FIG. 6;
FIG. 9 shows a cross section of a photoconductive switch module according to
a third embodiment of the present invention;
FIG. 10 is a perspective view showing the side of a spacer facing a switch element
substrate depicted in FIG. 9;
FIG. 11 is a front view showing the side of the spacer facing the switch element
substrate depicted in FIG. 9;
FIG. 12 is a perspective view showing the lower surface side of another spacer
having a convex portion whose height is different from that of the spacer depicted
in FIGS. 9 to 11; and
FIG. 13 is a perspective view showing the side of a spacer facing a switch element
substrate according to a fourth embodiment of the present invention which can be
applied in place of the spacer of the photoconductive switch module according to
the third embodiment depicted in FIGS. 9 to 11.
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments according to the present invention will be described
hereinafter with reference to the accompanying drawings.
First Embodiment
A photoconductive switch module according to the first embodiment will now be
described
with reference to FIGS. 1 to 5.
As shown in FIG. 1, a photoconductive switch module
100 has a light-emitting
element substrate
110 as a first substrate having light-emitting elements
112, a switch element substrate
120 as a second substrate having
photoconductive switch elements
122, whose number is equal to that of the
light-emitting elements
112, and a spacer
140 as a third substrate
arranged between the light-emitting element substrate
110 and the switch
element substrate
120.
The light-emitting elements
112 and the photoconductive switch elements
122 are arranged to face each other. The spacer
140 has through holes
142 whose number is equal to that of the light-emitting elements
112,
i.e., equal to that of the photoconductive switch elements
122. Each through
hole
142, which has a size substantially equal to a size of the photoconductive
switch element
122, e.g., a diameter of 20-100 μm, is arranged between
the light-emitting element
112 and the photoconductive switch element
122
facing each other. That is, the light-emitting element
112 and the photoconductive
switch element
122 face each other via the through hole
142. In other
words, the light-emitting element
112 and the photoconductive switch element
122 facing each other are optically coupled with each other via the through
hole
142.
Further, the switch element substrate
120 has a circuit wiring
130
connected to the photoconductive switch elements
122 on the side facing
the spacer
140. The photoconductive switch elements
122 and the circuit
wiring
130 constitute an electric circuit suitable for an application of
the photoconductive switch module
100. The circuit wiring
130 is
connected with an external electric circuit through wires
132.
The light-emitting element
112 is, but is not limited to, e.g., a VCSEL
(vertical cavity surface emitting laser). The photoconductive switch element
122,
which is a photoconductive switch disclosed in, e.g., U.S. Pat. No. 6,252,221B1,
is turned on/off in accordance with lighting/extinction of the light-emitting element
112. The document is incorporated in the present specification by reference.
In this specification, a term "photoconductive switch element" means a minimum
unit that performs the electrical on/off operation of a line connected to this
element by a change in resistance in response to illumination, and a term "photoconductive
switch module" means a switch circuit constituted by a combination of the photoconductive
switch elements.
The photoconductive switch element
122 has a characteristic that, when
it is not illuminated, has a high resistance, and while being illuminated, the
resistance is reduced in accordance with the intensity of the incident light.
Therefore, the photoconductive switch element
122 demonstrates
a high resistance when the corresponding light-emitting element
112 is off
to take the off state (i.e., insulation state or open state).
When the light-emitting element
112 is lighted, drive light
114
emitted from the light-emitting element travels through the through hole
142
to illuminate the photoconductive switch element
122. As a result, the photoconductive
switch element
122 has the resistance lowered, and is switched to the on
state (conductive state).
When the light-emitting element
112 is switched off, the resistance of
the photoconductive switch element
122 is increased to an initial value,
and the photoconductive switch element
122 returns to the off state (insulation
state, open state).
For example, the photoconductive switch elements
122 and the circuit wiring
130 are laid out as shown in FIG. 2. In FIG. 2, the switch element substrate
120 has a size of approximately 0.5 mm×1.0 mm, and the distance between
the photoconductive switch elements
122 is approximately 200-500 μm.
As apparent from FIG. 3 showing its equivalent circuit, the photoconductive switch
elements
122 and the circuit wiring
130 constitute a single-pole
double-throw switch circuit (1:2 switch circuit). Of course, the photoconductive
switch element
122 that is illuminated with the drive light is turned on,
and the photoconductive switch element
122 that is not illuminated with
the drive light is turned off.
More preferably, the photoconductive switch elements
122 and the circuit
wiring
130 are laid out as shown in FIG. 4. As apparent from FIG. 5 showing
its equivalent circuit, the photoconductive switch elements
122 and the
circuit wiring
130 constitute a single-pole double-throw switch circuit,
which avoids the influence of parasitic capacitances of the switch elements and
whose performance is further improved.
Since the photoconductive switch element has the characteristic that the intensity
of the drive light is substantially in inverse proportion to the resistance, if
the leakage light of the drive light that is directed to the photoconductive switch
element to be turned on enters the photoconductive switch element to be turned
off, the photoconductive switch element to be turned off, whose resistance is lowered,
fails to take the complete off state.
A beam of light projected from the light-emitting element such as a VCSEL is
diverging.
Further, as apparent from FIGS. 2 and 4, when one of the photoconductive switch
elements adjacent to each other is turned on, the other one is turned off in many cases.
Therefore, in the photoconductive switch module constituted without providing
the spacer
140 having the through holes
142, the light directed to
the photoconductive switch element
122 to be turned on easily leaks into
the photoconductive switch element
122 to be turned off. As a result, the
resistance of the photoconductive switch element
122 to be turned off is
lowered, resulting in deterioration in the transmission performance (insertion
loss or return loss) and the isolation performance as the switch circuit.
As shown in FIG. 1, however, in the photoconductive switch module
100
according
to this embodiment that includes the spacer
140 having the through holes
142 between the light-emitting element substrate
110 and the switch
element substrate
120, the beam of drive light
114 projected from
the light-emitting element
112 is diverging, but its spread is restricted
in the corresponding through hole
142. That is, the drive light
114
from the light-emitting element
112 is guided within the through hole
142
to travel to the photoconductive switch element
122 facing the light-emitting
element
112.
In other words, the spacer
140 having the through holes
142 constitutes
a light isolator that isolates the light between a pair of the light-emitting element
112 and the photoconductive switch element
122 from the light between
another pair of the light-emitting element
112 and the photoconductive switch
element
122.
As a result, generation of the leakage light or incidence on another photoconductive
switch element can be suppressed. That is, the resistance of the photoconductive
switch element
122 to be turned off is kept sufficiently high.
Therefore, although the photoconductive switch module
100 according
to this embodiment has a compact circuit design, degradation of the performance
due to the leakage light is suppressed.
That is, the photoconductive switch module
100 according to this embodiment
is sophisticated since the circuit is constituted by using the photoconductive
switch elements is small, since the photoconductive switch elements are arranged
in close proximity to each other, and has the good performance with suppression
of generation of the undesired leakage light.
Second Embodiment
A photoconductive switch module according to a second embodiment will now be
described
hereinafter with reference to FIGS. 6 to 8. In the drawings, like reference numerals
denote members equivalent to those in the photoconductive switch module according
to the first embodiment. In the following, detailed explanation of those members
will be eliminated in order to avoid tautological description.
As shown in FIG. 6, a photoconductive switch module
200 has a light-emitting
element substrate
110 having light-emitting elements
112, a switch
element substrate
120 having photoconductive switch elements
122,
whose number is equal to that of the light-emitting elements
112, and a
spacer
240 arranged between the light-emitting element substrate
110
and the switch element substrate
120.
The spacer
240 has through holes
242 arranged between the light-emitting
elements
112 and the photoconductive switch elements
122 and a groove,
i.e., a concave portion
244 formed on the side facing the switch element
substrate
120. The concave portion
244 extends along a circuit wiring
130 provided on the switch element substrate
120. Therefore, the
concave portion
244 cuts across the through holes
242, and each through
hole
242 terminates on the bottom surface of the concave portion
244
as shown in FIGS. 6 to 8.
For example, the circuit wiring
130 extends in the T form as shown in
FIG. 2, and the concave portion
244 extends in the T form in accordance
with this as shown in FIGS. 7 and 8.
The spacer
240 has conductivity at least near the surface of the concave
portion
244. That is, the spacer
240 has a conductive part at least
near the concave portion
244.
Therefore, the spacer
240 has a conductive film
246 provided
on the surface of the inner side of the concave portion
244 as shown in,
e.g., FIG. 6. The conductive film
246 may be formed on the entire lower
surface of the spacer
240 as well as the surface of the inner side of the
concave portion
244. Alternatively, the spacer
240 itself may be
formed of a conductive material in place of having the conductive film
246.
The conductive film
246 does not have to be exposed, and it may be covered
with a very thin insulating film, e.g., an oxide film although not shown.
The concave portion
244 has, e.g., a width of approximately 300 μm
and a depth of approximately 100 μm. The conductive film
246 is constituted
by, e.g., a metal film having sufficiently high conductivity such as aluminum (Al).
Preferably, the conductive film
246 is connected to a GND potential portion
of the switch element substrate
120 by a non-illustrated conductive member
(conductive adhesive or bump).
The switch operation in the photoconductive switch module
200 according
to this embodiment is completely the same as that of the photoconductive switch
module
100 according to the first embodiment, and its explanation will be
eliminated here.
In the photoconductive switch module
200 according to this embodiment,
the conductive part of the spacer
240 near the surface of the concave portion
244, e.g., the conductive film
246 extends along the circuit wiring
130 of the switch element substrate
120, and functions as an electromagnetic
shield with respect to the circuit wiring
130. As a result, the high-frequency
performance of the transmission line in the photoconductive switch module can be assured.
In other words, the photoconductive switch module
200 according to this
embodiment has a structure that the function of the electromagnetic shield is added
to the conductive switch module
100 according to the first embodiment. Therefore,
the photoconductive switch module
200 has the good performance in high frequency
in addition to the advantages of the photoconductive switch module
100 according
to the first embodiment.
Third Embodiment
A photoconductive switch module according to a third embodiment will now be described
hereinafter with reference to FIGS. 9 to 11. In the drawings, like reference numerals
denote members equivalent to those in the photoconductive switch module according
to the first embodiment. In the following, detailed explanation of these members
will be eliminated in order to avoid tautological description.
As shown in FIG. 9, a photoconductive switch module
300 has a light-emitting
element substrate
110 having light-emitting elements
112, a switch
element substrate
120 having photoconductive switch elements
122,
whose number is equal to that of the light-emitting elements
112, and a
spacer
340 arranged between the light-emitting element substrate
110
and the switch element substrate
120.
The spacer
340 has through holes
342 arranged between the light-emitting
elements
112 and the photoconductive switch elements
122, and a groove
344, i.e., a concave portion
344 formed on the side facing the switch
element substrate
120. The concave portion
344 extends along the
circuit wiring
130 provided to the switch element substrate
120.
Therefore, each through hole
342 terminates on the bottom surface of the
concave portion
344 as shown in FIGS. 9 to 11. For example, the concave
portion
244 extends in the T shape like the second embodiment.
The spacer
340 further has convex portions
348 protruding from
the bottom surface of the concave portion
344. Each convex portion
348
extends cutting across the concave portion
344 and has a height equal to
the depth of the concave portion
344. Therefore, the concave portion
344
is divided into three portions
344a,
344b and
344c
by the two convex portions
348 as shown in FIG. 11.
Such convex portions
348 are readily formed without applying to a base
material of the spacer
340 the processing to form the concave portion
344.
That is, the spacer
340 having such convex portions
348 is relatively
readily manufactured.
The two adjacent photoconductive switch elements
122 are reversely turned
on/off in many cases like the circuit configuration shown in FIGS. 2 to 4, for
example. Each convex portion
348 is positioned between the photoconductive
switch elements
122 that are reversely turned on/off in this manner.
The switch operation of the photoconductive switch module
300 according
to this embodiment is carried out in completely the same way as the photoconductive
switch module
100 according to the first embodiment.
In the photoconductive switch module
300 according to this embodiment,
of the light emitted from the light-emitting element
112 corresponding to
the photoconductive switch element
122 to be turned on, the majority of
the light directed toward the adjacent photoconductive switch element
122
while being diffusely reflected on the inner side of the concave portion
344
is reflected or absorbed by the convex portions
348. That is, the undesired
leakage light existing on the inner side of the concave portion
344 is greatly
attenuated by the convex portions
348. Therefore, the leakage light that
reaches the photoconductive switch element
122 to be turned off can be sufficiently attenuated.
Like the second embodiment, the spacer
340 preferably has a conductive
part at least near the surface of the concave portion
344, i.e., the portions
344a,
344b and
344c. This conductive
part is constituted by, e.g., a conductive film provided on the surface of the
inner side of the concave portion
344 and connected to a GND potential portion
of the switch element substrate
120 like the second embodiment.
The spacer
340 and the switch element substrate
120 are arranged
with a slight gap therebetween in order to avoid the electrical contact between
the convex portions
348 and the circuit wiring
130. Furthermore,
in order to fix and mount the switch element substrate
120 and the spacer
340, a space for a conductive adhesive or bump is required, and hence a
gap exists between the convex portions
348 and the switch element substrate
120.
Although the light that enters into this gap exists to a certain extent,
since this light is attenuated in the narrow gap between the convex portions
348
and the switch element substrate
120 during multiple reflection, the intensity
of the leakage light which enters the adjacent photoconductive switch element
122
to be turned off is sufficiently small.
As apparent from the above description, in view of attenuation of the leakage
light, it is preferable to set a thickness of each convex portion
348 (dimension
in the direction along which the circuit wiring
130 or the concave portion
344 extends) as large as possible and set the gap between the convex portion
348 and the switch element substrate
120 smaller.
However, since each convex portion
348 affects the concave portion
structure for the electromagnetic shield, it is preferable to set the thickness
of the convex portion
348 as small as possible and set the gap between each
convex portion
348 and the switch element substrate
120 larger in
view of the circuit performance.
Considering the balance of the thickness and the gap, it is good to set
the thickness of the convex portion
348 to approximately 10-100 μm,
preferably, approximately 20-50 μm and the gap between each convex portion
348 and the photoconductive switch element
122 to approximately 5-100
μm, preferably, approximately 10-50 μm.
The photoconductive switch module
300 according to this embodiment has
the convex portions
348 protruding from the bottom surface of the concave
portion
344 between the photoconductive switch elements
122 that
are reversely turned on/off, and the undesired leakage light directed toward the
photoconductive switch element
122 to be turned off is greatly attenuated
by the convex portions
348. Therefore, the leakage light that reaches the
photoconductive switch element
122 to be turned off can be sufficiently attenuated.
In the spacer
340 shown in FIGS. 9 to 11, although each convex portion
348 has a height equal to a depth of the concave portion
344, the
height of the convex portion
348 does not have to be equal to the depth
of the concave portion
344. For example, like a spacer
340A shown
in FIG. 12, the height of the convex portion
348 may be set smaller than
the depth of the concave portion
344. That is, in the photoconductive switch
module
300 according to this embodiment, the convex portion
348 may
have a height that is equal to or smaller than the depth of the concave portion
344.
Although such a spacer
340A has a demerit that its processing is
slightly complicated, the contact between each convex portion
348 and the
circuit wiring
130 can be assuredly avoided, and hence it has a merit that
the difficulty of connection/mounting of the spacer
340A and the switch
element substrate
120 can be lowered.
Fourth Embodiment
This embodiment is directed to another spacer, which may be applied in place
of the spacer
340 in the photoconductive switch module according to the
third embodiment. The spacer according to this embodiment will now be described
with reference to FIG. 13.
Like the third embodiment, a spacer
440 has through holes
442,
a groove, i.e., a concave portion
444 formed on the side facing the switch
element substrate
120, and a plate-like convex portion
448 protruding
from the bottom surface of the concave portion
444. The convex portion
448
extends cutting across the convex portion
444 and has a height equal to
a depth of the concave portion
444.
The spacer
440 has a tubular convex portion
450 protruding from
the bottom surface of the concave portion
444. Although the tubular convex
portion
450 is not restricted to one in the drawing, it has, e.g., a cylindrical
shape and surrounds a through hole
442. Therefore, the through hole
442
terminates on the end surface of the tubular convex portion
450. The tubular
convex portion
450 has a height equal to a depth of the concave portion
444.
The plate-like convex portion
448 and the tubular convex portion
450
are formed by eliminating the processing to form the concave portion
444
with respect to a base material of the spacer
440.
In the photoconductive switch module using the spacer
440 according to
this embodiment, the end of each through hole
442 is arranged in the close
proximity to the photoconductive switch element. That is, the through hole
442
is defined by the tubular convex portion
450 and extends to the vicinity
of the photoconductive switch element. Therefore, drive light from the light-emitting
element is contained in the through hole
442 immediately before reaching
the photoconductive element. Moreover, the light exiting from the through hole
442 hardly spreads, and reaches the photoconductive switch element.
As a result, the intensity of the drive light that reaches the photoconductive
switch element
122 to be turned on is further increased as compared with
the photoconductive switch module according to the third embodiment. That is, the
utilization efficiency of the drive light is further improved. Additionally, the
leakage light that reaches the photoconductive switch element
122 to be
turned off is further attenuated.
Therefore, the photoconductive switch module using the spacer
440
according to this embodiment has a structure that the utilization efficiency of
the drive light and generation of the undesired leakage light are improved in the
photoconductive switch module according to the third embodiment.
The photoconductive switch module using the spacer
440 according to this
embodiment has the further improved good performance as compared with the photoconductive
switch module according to the third embodiment.
Although the spacer
440 shown in FIG. 13 has the convex portion
448
and the tubular portion
450, the plate-like convex portion
448 may
be eliminated if the tubular convex portion
450 alone can obtain the sufficient
performance that satisfies the design requirement.
Although the embodiments according to the present invention have been described
above with reference to the accompanying drawings, the present invention is not
restricted to these embodiments, and various modifications or variations may be
carried out without departing from the scope of the present invention.
Additional advantages and modifications will readily occur to those skilled
in the art. Therefore, the invention in its broader aspects is not limited to the
specific details and representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit or scope of
the general invention concept as defined by the appended claims and their equivalents.
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