Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-04-08
2002-10-01
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
Reexamination Certificate
active
06459519
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an optical transmitter-receiver, and more particularly, to an optical transmitter-receiver in which an optical transmitter and an optical receiver are interconnected such that optical transmission is possible.
2. Description of the Background Art
Optical transmission for transmitting information with light modulated by the information has been expected to be widely used for a future high speed communication network due to low-loss and wideband properties. For example, an optical transmitter-receiver for optically transmitting an electrical signal having a high-frequency (hereinafter referred to as a first optical transmitter-receiver), and an optical transmitter-receiver for optically transmitting a baseband signal (hereinafter referred to as a second optical transmitter-receiver), have been proposed. The two optical transmitter-receivers will be specifically described referring to the drawings.
Description is now made of the first optical transmitter-receiver. In recent years, a wireless service such as a portable telephone or a PHS (Personal Handyphone System) has been rapidly enlarged. Therefore, utilization of still higher frequencies has been examined. A mirco-cell system or a pico-cell system utilizing a millimeter-wave band of approximately 30 GHz to 300 GHz has been examined. In such a cell system, a signal having a high frequency such as a millimeter-wave band is radiated from a lot of base stations connected to a control station, so that a wireless service is provided. The cell system has various advantages. First, the signal having the millimeter-wave band does not easily adversely affect next cells due to a propagation loss in a space. Second, the signal having the millimeter-wave band has a short wavelength, so that an antenna or the like set in the control station or the like is miniaturized. Third, the signal having the millimeter-wave band has a high frequency, so that the transmission capacity can be increased. Consequently, it may be possible to provide a high speed transmission service which is difficult to realize in a conventional wireless service.
In a wireless communication system to which such a cell system is applied, however, a lot of base stations are set throughout a town. Therefore, the base station must be small in size and low in cost. A first optical transmitter-receiver employing a so-called subcarrier optical transmission system which has been tremendously researched and developed in recent years may, in some cases, be applied to the wireless communication system. The subcarrier optical transmission system is described in detail in “Microwave and millimeter-wave fiber, optic technologies for subcarrier transmission systems” (Hiroyo Ogawa, IEICE Transactions on Communications, Vol. E76-B, No. 9, pp. 1078-1090, September, 1993), for example.
In the subcarrier transmission system, the intensity of a main carrier, which is typically unmodulated light, is modulated by a modulated signal so that an optical signal is obtained. In the modulated signal a subcarrier is modulated by information, which is a voice signal and/or an image signal. The change in the intensity of the optical signal uniquely corresponds to the change in the amplitude, the change in the frequency or the change in the phase of the modulated signal. In the subcarrier optical transmission system, an optical fiber, which is very low in loss, is used. When the modulated signal has a millimeter-wave band, therefore, the modulated signal can be transmitted to a remote location as it is.
FIG. 17
is a block diagram showing the structure of a typical first optical transmitter-receiver. In
FIG. 17
, the first optical transmitter-receiver comprises a light source
110
, an external optical modulating portion
120
, an optical fiber
140
, an optical/electrical converting portion
150
, a frequency converting portion
1710
, and a demodulating portion
1720
. The light source
110
and the external optical modulating portion
120
constitute an optical transmitter
101
, and are set in a base station, while the optical/electrical converting portion
150
, the frequency converting portion
1710
, and the demodulating portion
1720
constitute an optical receiver
102
, and are set in a control station.
FIG. 17
shows only signal path in the one direction, that is, the signal path transmitted from the base station to the control station.
In the first optical transmitter-receiver, an electrical signal to be transmitted from the base station to the control station is typically a modulated electrical signal Smod having a millimeter-wave band in which a subcarrier is modulated by a baseband signal such as a voice signal and/or an image signal. The modulated electrical signal Smod is inputted to the external optical modulating portion
120
in the light transmitter
101
through an antenna or an amplifier (not shown) from a portable telephone, a PHS terminal, or the like which is moved outside the base station. The light source
110
oscillates using unmodulated light as a main carrier Mc. The main carrier Mc is also inputted to the external optical modulating portion
120
. The external optical modulating portion
120
performs external light-intensity modulation, to modulate the intensity of the inputted main carrier MC on the basis of the change in the amplitude of the inputted modulated electrical signal Smod, thereby obtaining an optical signal OSmod. The optical signal OSmod itself outputted from the external optical modulating portion
120
to the optical fiber
140
is changed into a carrier, and is incident on the optical/electrical converting portion
150
in the optical receiver
102
while the modulated electrical signal Smod is being conveyed through the optical fiber
140
as it is. The optical/electrical converting portion
150
performs optical/electrical conversion, to convert the incident optical signal OSmod into an electrical signal including its intensity modulation component. The frequency converting portion
1710
down-coverts the electrical signal inputted from the optical/electrical converting portion
150
into an electrical signal having an intermediate frequency band. The demodulating portion
1720
demodulates the information of the baseband signal such as the voice signal and/or the image signal on the basis of the electrical signal having the intermediate frequency band inputted from the frequency converting portion
1710
.
Description is now made of the second optical transmitter-receiver for merely optically transmitting a baseband signal.
FIG. 18
is a block diagram showing the structure of a typical second optical transmitter-receiver. In
FIG. 18
, the second optical transmitter-receiver comprises a light source driving portion
1810
, a light source
110
, an optical fiber
140
, and an optical/electrical converting portion
150
. The light source driving portion
1810
and the light source
110
constitute an optical transmitter
101
, while the optical/electrical converting portion
150
constitutes an optical receiver
102
. In the second optical transmitter-receiver, it is assumed that a baseband signal SBB to be transmitted from the optical transmitter
101
to the optical receiver
102
is digital information, which is a voice signal and/or an image signal, for example. The baseband signal SBB is inputted to the light source driving portion
1810
. The light source driving portion
1810
drives the light source
110
, and modulates the intensity of an optical signal outputted from the light source
110
on the basis of the inputted baseband signal SBB (a direct optical modulation system). The optical signal is transmitted through the optical fiber
140
, and is then optical/electrical-converted in the optical/electrical converting portion
150
, so that the original baseband signal SBB is obtained. Such a light transmission technique is general, and is described in Chapter 2 “Practice of Optical Communication System” of “Hikari Tsushin Gijyutsu Dokuhon (Opt
Maeda Kazuki
Sasai Hiroyuki
Utsumi Kuniaki
Matsushita Electric - Industrial Co., Ltd.
Pascal Leslie
Singh Dalzid
Wenderoth , Lind & Ponack, L.L.P.
LandOfFree
Optical transmitter-receiver does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical transmitter-receiver, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical transmitter-receiver will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2951559