Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-08-19
2002-04-09
Negash, Knife-Michael (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C372S032000, C372S034000
Reexamination Certificate
active
06369926
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multichannel light source wavelength and strength stabilizing apparatus and a method thereof, and in particular, to an improved multichannel light source wavelength and strength stabilizing apparatus and a method thereof, which are capable of stabilizing a channel interval, and a center wavelength of a wavelength division multiplexing multichannel light source using a wavelength locker of each channel, as well as a wavelength and light strength of a multichannel light source in which a strength of an output light source is stabilized using an automatic light output controller.
2. Description of the Prior Art
Conventionally, a light multiplexing transmission apparatus is an apparatus for integrating several basic transmission signals to one single optical fiber by an optical method, not electrical method. The amount of the information is determined by the speed of a basic transmission signal speed and the number of signals and a multiplication based on the number of channels.
In addition, a transmission capacity may be exceeded in major transmission intervals due to a gradual increase of demand for a broadband service such as a multimedia, so that a new multiplexing method such as an optical frequency multiplexing method is needed.
The optical frequency multiplexing method is a method in which modulated optical signals outputted from various light sources in the transmitting side are received and then aligned based on a predetermined optical frequency slot for thereby integrating the signals, and the optical signals aligned in each frequency slot are separated and extracted using an optical filter in the receiving side.
The optical frequency multiplexing method is directed to transmitting a large amount of signals, is directed to maximizing the transmission speed per channel differently from the system for a subscriber and then increasing the number of multiplexing channels. The performance of the above-described multiplexing method is determined by the frequency slot which is used for the multiplexing operation.
In the conventional art, as an optical fiber filter, an oscillator is used for generating a frequency slot which is used for a multiplexing operation. Namely, the oscillation frequency is used as a slot.
However, in the above-described conventional art, a multichannel frequency is stabilized using a passing through light. The strength of the passing through light is increased as the number of multiplexing channels is increased. The photodetector which receives a multiplexed passing through light is saturated when receiving a predetermined amount of passing through light, so that a signal reliability is decreased, and it is impossible to obtain a stabilized feed back signal.
In addition, a low frequency signal is applied to a light source for overcoming the above-described problems, and the center frequency of the light source is dithered, and the frequency of each light source is aligned with the oscillation frequency having an optical fiber filter, and the variation level of the dithering is analyzed at each oscillating point by receiving a reflection output using a photodetector and is used as a stabilizing feed back signal. Therefore, an optical frequency multiplexing apparatus capable of implementing multiple channels is used.
FIG. 1
is a block diagram illustrating the construction of a conventional multichannel light source wavelength stabilizing apparatus. As shown therein, an error signal is extracted using a reflection output of an optical fiber filter
17
, not a reflection output thereof for thereby increasing a signal-to-noise ratio of an optical signal and maximizing the number of multiplexing light sources.
As shown in
FIG. 1
, a low frequency signal outputted from a low frequency oscillator
11
of a local oscillator
10
is applied to each light source
13
, and a center carrier frequency of the light source
13
is dithered, so that the light source
13
outputs an optical signal having a dithering.
The optical signal having a dithering outputted from the light source
13
is combined to form the n-number of signals by a light combining unit, and a 2×2 light combining unit
15
combines the optical signals outputted from the light source
13
, and one output is externally outputted through the optical fiber as the finally aligned (or multiplexed) output. The other output is applied to a 2×1 light combining unit
16
for extracting an error signal which is used for an alignment.
The optical signal applied to the 2×1 light combining unit
16
is applied to an optical fiber filter
17
formed of Fabri-Perot type, and the optical signal having a minimum value at the oscillation point is applied to the photodetector
18
through the 2×1 light combining unit
16
based on the oscillation characteristic of the optical fiber filter
17
.
The reflected optical signal applied to the photodetector
18
is converted into an electrical signal and then is applied to an optical frequency stabilizing controller
19
, and the stabilizing controller
19
detects an error signal corresponding to an escape at the oscillation point, and the thusly detected error signal is converted into a current value and is applied to the bias of the light source
13
.
The center carrier frequency of the light source
13
is aligned to coincide with the oscillation frequency determined by the oscillation length of the oscillator, so that it is possible to obtain an optical frequency-multiplexed output.
In addition, since the 2×1 light combining unit
16
is used for the front portion of the optical fiber filter
17
, it is possible to remove Fresennel reflection output which fed back from the output which is not used when using the 2×2 light combining unit
15
and thereby decrease noise.
In the method for controlling the center wavelength and interval of the multichannel light source is directed to maintaining a center wavelength and interval at a free spectral range (FSR) of an interference by locking the wavelength of the light source to various peak values among the oscillation characteristic of one Fabri-Perot type interference unit. When using one oscillator, the structure is simple irrespective of the number of channels. However, the above-described method uses a dithering method thereby causing a complicated electrical structure. In addition, if a failure occurs in the interference unit, it is impossible to maintain a predetermined wavelength for which all channels are set, so that an independent and maintenance characteristic of the channel is not implemented.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a multichannel light source wavelength and strength stabilizing apparatus and a method thereof which overcome the aforementioned problems encountered in the conventional art.
It is another object of the present invention to provide a multichannel light source wavelength and strength stabilizing apparatus and a method thereof which are capable of stabilizing a channel interval and a center wavelength of a wavelength division multiplexing multichannel light source using a wavelength locker of each channel and stabilizing the strength of an output light source using an automatic power controller for thereby stabilizing a wavelength of a multichannel light source and the strength of light.
It is another object of the present invention to provide a multichannel light source wavelength and strength stabilizing apparatus and a method thereof which provides a multichannel light transmitter used for a wavelength division multiplexing system for converting an electrical signal modulated to a set wavelength wherein a wavelength division multiplexing method is used, which is capable of transmitting a large amount of information without changing the existing optical line.
The wavelength variation of the multichannel transmission unit generates a predetermined variation in a light strength when the light passes through an o
Lee Hyun Jae
Lee Jong Hyun
Lyu Gap Youl
Park Seo Yeon
Cohen & Pontani, Lieberman & Pavane
Electronics and Telecommunications Research Institute
Negash Knife-Michael
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