Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Reexamination Certificate
2000-01-12
2001-05-22
Mack, Ricky (Department: 2873)
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
C359S618000, C359S619000
Reexamination Certificate
active
06236477
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical transmission and receiving module usable for an optical communication system for transmitting and receiving optical signals through an optical fiber, and specifically to an optical transmission and receiving module for realizing high speed transfer based on, for example, IEEE1394 and USB2.
2. Description of the Related Art
Japanese Laid-Open Publication No. 7-248429 discloses an optical transmission and receiving module
1000
as shown in FIG.
30
. The optical transmission and receiving module
1000
operates in the following manner.
Transmission signal light which is emitted by a light emitting element
1001
is transmitted through a cover glass
1060
attached to a package and branched into two light components by a Foucault prism
1003
. The light components are collected to point A and point B by a lens
1004
. That is, only one of the light components is incident on an optical fiber
1007
.
Receiving signal light which is output by the optical fiber
1007
is collected by the lens
1004
and then incident on the Foucault prism
1003
. The light is branched into two light components by the Foucault prism
1003
and then transmitted through the cover glass
1060
. One of the two light components is incident on a light receiving element
1002
.
Japanese Laid-Open Publication No. 8-15582 discloses another optical transmission and receiving module
2000
as shown in FIG.
31
. The optical transmission and receiving module
2000
operates in the following manner.
Transmission signal light which is emitted by a semiconductor laser
2002
is collimated by a lens
2004
. The light is then incident on a holographic diffraction grating
2005
to be branched into a zeroth-order light component and a first-order light component. Only the zeroth-order light component, which is collected, is incident on an optical fiber
2006
.
Receiving signal light which is output by the optical fiber
2006
is incident on the holographic diffraction grating
2005
and branched into a zeroth-order light component and a first-order light component. Both light components are collimated. Only the first-order light component, which is collected by the lens
2004
, is incident on a light receiving element
2003
.
The optical transmission and receiving module
1000
shown in
FIG. 30
has the following problems.
(1) Since the vertex angle of the Foucault prism
1003
is as small as 2° to 3°, the light emitting element
1001
and the light receiving element
1002
are inevitably located close to each other. Accordingly, the light receiving element
1002
needs to be located far from a focal point
1008
of the receiving signal light. Therefore, the receiving signal light needs to be detected in an expanded state. This requires the light receiving element
1002
to be larger. Such a large light receiving element
1002
has a capacitance which is too large to perform high speed transmission.
Although it is conceivable to increase the vertex angle of the Foucault prism
1003
in order to extend the distance between the light emitting element
1001
and the light receiving element
1002
, such an arrangement requires the Foucault prism
1003
to be thicker. This makes difficult the size reduction of the optical transmission and receiving module
1000
.
(2) The Foucault prism
1003
needs to be located at a high precision since when the Foucault prism
1003
is not on an optical axis of the optical fiber
1007
, the branching ratio of the Foucault prism
1003
is changed from the designed ratio.
(3) When an RCLED (resonant cavity light emission diode) is used for the light emitting element
1001
, the light utilization factor is reduced since the peak radiation angle of the light generated at the high efficiency RCLED is not 0°.
The optical transmission and receiving module
2000
shown in
FIG. 31
has the following problems.
(1) The wavelength of the light changes in accordance with the temperature of the semiconductor laser
2002
. When the wavelength of the light incident on the holographic diffraction grating
2005
changes, the collection position of the light and the diameter of the light spot incident on the light receiving element
2003
change. Thus, the light receiving sensitivity of the optical transmission and receiving module
2000
is reduced.
(2) Since the diffracted light from the holographic diffraction grating
2005
includes a high-order diffracted light component, which is unusable for communication, the light utilization factor of the optical transmission and receiving module
2000
is reduced.
(3) Production of a sawtooth-shaped diffraction grating, which is required to suppress the high-order diffracted light component, is difficult due to the microscopic pitch of the grating.
(4) When an RCLED is used for the light emitting element instead of the semiconductor laser
2002
, the light utilization factor is reduced since the peak radiation angle of the light generated at the high efficiency RCLED is not 0°.
SUMMARY OF THE INVENTION
According to one aspect of the invention, an optical transmission and receiving module includes a light source; a light receiving element; and a light branching element for causing signal light from the light source to be incident on an optical fiber and causing signal light output from the optical fiber to be incident on the light receiving element. The light branching element includes a prism array including a plurality of triangular prisms arranged at substantially an identical pitch on a plane extending substantially perpendicular to an imaginary line connecting the light source and the light receiving element.
In one embodiment of the invention, the optical transmission and receiving module fulfills d/2>P>>&lgr;/sin&thgr; where d is a diameter of the optical fiber, &lgr; is a wavelength of light from the light source, P is a pitch of the plurality of triangular prisms, and &thgr; is a deflection angle of the plurality of triangular prisms.
In one embodiment of the invention, each of the plurality of triangular prisms has an isosceles triangular cross-section.
In one embodiment of the invention, each of the plurality of triangular prisms has a vertex angle in the range of about −20° to 60°.
In one embodiment of the invention, the optical transmission and receiving module fulfills:
1/tan(1
/&agr;tx
)=1/tan(1
/&agr;rx
)+tan(&agr;
rx
-arcsin(&agr;
rx
))
where &agr;tx is one vertex angle, &agr;rx is another vertex angle, and n is the refractive index of each of the plurality of triangular prisms.
In one embodiment of the invention, the optical transmission and receiving module fulfills &PHgr;>B where &PHgr; is the diameter of the signal light output from the optical fiber to the prism array, and B is the length of a base of each of the plurality of triangular prisms.
In one embodiment of the invention, the prism array is formed of acrylic.
In one embodiment of the invention, the light source includes a light emitting element which is formed a semiconductor laser element.
In one embodiment of the invention, the light source includes a light emitting element which is formed of a resonant cavity light emission diode.
In one embodiment of the invention, the light source includes a light emitting element, and a deflection angle of the light branching element and a peak radiation angle of radiation light from the light emitting element are substantially equal to each other.
In one embodiment of the invention, the light source includes a light emitting element, the light emitting element includes a first collection lens, the light receiving element includes a second collection lens, and the optical transmission and receiving module further includes at least one collimator lens provided between the prism array, and the first collection lens and the second collection lens, the at least one collection lens being parallel to the prism array.
In one embodiment of the invention, the prism array and the collimator lens are integrally formed.
In on
Ishihara Takehisa
Miyuki Hideki
Nagura Kazuhito
Nakatsu Hiroshi
Terashioma Kentaro
Conlin David G.
Dike Bronstein, Roberts & Cushman LLP
Hartnell, III George W.
Mack Ricky
Sharp Kabushiki Kaisha
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