Optical apparatus

Details Optical apparatus Optical apparatus

2002-03-18

2003-02-18

Sikder, Mohammad (Department: 2872)

Optical: systems and elements

Prism

With reflecting surface

C359S834000, C359S835000, C359S837000

Reexamination Certificate

active

06522487

ABSTRACT:

TECHNICAL FIELD
This invention relates to an optical apparatus suitable for transmission/reception of e.g., signal light for optical communication.
BACKGROUND ART
In these years, in keeping up with information diversification, thus is with the tendency towards multi-media, development of a small-sized, high-performance low-cost communication apparatus has become a desideratum. The optical communication by a two-core optical fiber, having a glass optical fiber for transmission and a glass optical fiber for reception, has already been put to practical use because it permits high transmission rate and long-distance transmission and also because it is strong against electromagnetic noise. However, in the optical communication employing the two-core optical fiber, the optical fiber and the communication apparatus are both expensive, such that it is not used extensively in households and finding only limited practical application. Thus, the recent tendency is towards communication employing a sole inexpensive plastic optical fiber, such that preparations are being made for a communication environment by a uni-core optical fiber.
FIGS. 37 and 38
mainly show the schematic structure of optical components of a conventional optical communication apparatus employing a uni-core optical fiber.
FIGS. 37 and 38
show an optical path L
11
of the transmitting light along with the schematic structure of an optical system of the optical communication apparatus and an optical path L
12
of the transmitting light along with the schematic structure of the optical system of the optical communication apparatus.
As shown in these figures, the optical system of the communication apparatus includes a light source
101
constructed by e.g., a semiconductor laser for radiating a transmitting laser light beam, and a collimator lens
102
for converting the light from the light source
101
into collimated light and for radiating a collimated light beam. The optical system also includes a polarization beam splitter
103
for reflecting the S-polarized component of the incident light substantially by total reflection and transmitting a P-polarized component of the incident light substantially by total transmission. The optical system also includes a coupling lens
104
for converging the transmitting light radiated from the polarization beam splitter
103
on an end face
105
a
of a uni-core optical fiber
105
and for radiating the received light radiated from the end face
105
a
of the optical fiber
105
as a collimated light beam. The optical system also includes a converging lens
106
for converging the collimated light beam radiated from the coupling lens
104
, and a photodetector
107
for detecting the received light converged by the converging lens
106
. The polarization beam splitter
103
includes an inclined surface
103
a
on the surface of which a dielectric multilayer film is formed for imparting a polarization beam splitter function, that is for reflecting an S-polarized light component of the incident light substantially by total reflection and for transmitting a P-polarized light component thereof substantially by total transmission. In the transmitting/reception device, the light source
101
and the polarization beam splitter
103
are arranged so that the plane of polarization of light radiated from the light source
101
to fall on the inclined surface
103
a
will the S-polarization plane. Thus, the light from the light source
101
(S-polarized light) undergoes substantially total reflection on the inclined surface
103
a.
In the above-described circuit apparatus, employing the polarization beam splitter
103
, bidirectional optical communication, that is transmission and reception employing the laser light, becomes possible with the use of a sole device.
The optical communication in the transmission apparatus capable of bidirectional optical communication occurs as follows:
Referring first to
FIG. 37
, when light is transmitted from the circuit apparatus, the transmitting light is radiated from a light source
101
and collimated by the collimator lens
102
to fall on the polarization beam splitter
103
. Since the light source
101
and the polarization beam splitter
103
are arranged relative to each other so that the plane of polarization of the light radiated from the light source
101
to fall on the inclined surface
103
a
will be the P-polarized light, the light radiated from the light source
101
is reflected substantially by total reflection by the inclined surface
103
a
. The light beam reflected by total reflection by the inclined surface
103
a
falls on the end face
105
a
of the optical fiber
105
via the coupling lens
104
. The light incident on the optical fiber
105
is transmitted through the optical fiber
105
to the destination of communication as the signal light for communication.
Referring to
FIG. 38
, the signal light transmitted through the optical fiber
105
at the time of light reception by the communication apparatus is radiated from the end face
105
a
of the optical fiber
105
. The light beam of the signal light radiated from the end face
105
a
is collimated by the coupling lens
104
of the communication apparatus so as to fall on the polarization beam splitter
103
. The light beam incident on the polarization beam splitter
103
has a random plane of polarization (light of random polarization). Of the light beam incident on the polarization beam splitter
103
, the S-polarized light component is reflected substantially by total reflection by the inclined surface
103
a
so as to be radiated towards the light source
101
as the so-called feedback light. On the other hand, of the light beam incident on the polarization beam splitter
103
, the P-polarized light is transmitted through the inclined surface
103
a
substantially by total transmission to exit the polarization beam splitter
103
. The light radiated from the polarization beam splitter
103
is converged by the converging lens
106
on the photodetector
107
, which then detects the light converged by the converging lens
106
on photoelectric conversion as a reception signal.
Thus, with the communication apparatus shown in
FIGS. 37 and 38
, employing the polarization beam splitter
103
, bidirectional optical communication employing the laser light becomes possible even though no other device is used.
The polarization beam splitting function of the above-described polarization beam splitter is realized by forming a film structure described below on an optical component.
As the technique of adding an optical function, such as the above-mentioned polarization beam splitter function, to an optical element, the operation of optical interference, as occurs when setting the film thickness of a transparent thin film to a value of the number of orders of light wavelength, is frequently used.
It is noted that the condition of interference when the light falls on the sole layer film in a perpendicular direction is shown by the following equation:
n×d=m
(¼)×&lgr;
where &lgr; is the light wavelength, n the refractive index of a monolayer film, m an number of orders of interference and d is a physical film thickness. In general, in the above equation, n×d is termed the optical film thickness, while the number of orders of interference m is termed the phase thickness of a quarter wave optical thickness (QWOT). For example, in the case of a thin film in which the wavelength &lgr; of the light used is 550 nm, the refractive index of the monolayer of 2.3 and the physical film thickness d of 59.78 nm, the optical film thickness (n×d) is 137.5 nm, with the optical film thickness, that is the number of orders of interference m, being 1.
Meanwhile, if a single coating or a monolayer is formed on a substrate as an optical element, there are two boundary surfaces having different refractive indexes between the air and the film, that is a boundary surface between the air and the film (first boundary surface), and a boundary surface between the film and

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