Fiber optic communication terminal, fiber optic communication system, and its wavelength setting method

• US 5,532,865 A
• Filed: 09/11/1995
• Issued: 07/02/1996
• Est. Priority Date: 10/09/1992
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Yamamoto, Hiroaki, Utsumi, Kuniaki, Fujito, Katsuyuki
• Primary Examiner(s): Boudreau, Leo
• Assistant Examiner(s): MEHTA, BHAVESH M
• Application Number:
  US08/526,578
• Time in Patent Office: 295 Days
• Field of Search: 359/110, 359/161, 359/173, 359/179, 359/189, 359/194, 359/180, 359/187, 359/190, 359/191
• US Class Current: 398/1
• CPC Class Codes: H04B 10/506 Multiwavelength transmitters
• CPC Class Codes: H04B 10/564 Power control
• CPC Class Codes: H04B 10/572 Wavelength control
• CPC Class Codes: H04J 14/02 Wavelength-division multiplex systems

Abstract

In a fiber optic communication terminal composed of a light mixing part for mixing an input light signal and a light signal from own station, a detecting part for picking up a part of the output of the light mixing part to detect its quality deterioration, and a light source part in which the wavelength of output light is variable, increase of noise level or occurrence of bit error due to beat interference caused by mixing of input light signal and light signal from the own station is detected as quality deterioration in the detecting part, and by controlling the wavelength of the light source part accordingly, generation of beat interference can be prevented, and moreover by using a fiber optic communication terminal capable of maintaining the wavelength so that the signal quality may be the set value, the output light wavelength can be arranged at high density on the whole as a fiber optic communication system.

Claims

1. A fiber optic communication terminal comprising:

light source means for producing an output light signal having a wavelength and a spectrum distribution of a specified shape,

light mixing means for mixing an input light and the output light signal from the light source means,

light branching means for separating the mixed light signal output from the light mixing means into a first light signal and a second light signal each having respective signal qualities, said second light signal having a noise level and a bit error rate,

detecting means for detecting deterioration of the signal quality of the second light signal from the light branching means by detecting one of the noise level and the bit error rate of the second light signal and producing a detection signal, and

control means for controlling the wavelength of the output light signal of the light source means in response to the detection signal to prevent deterioration of the signal quality of the first light signal regardless of the specified shape of the spectrum distribution of the output light signal emitted by the light source means.

2. A fiber optic communication terminal of claim 1, wherein the light mixing means and light branching means are included in a fusion type optical coupler.

3. A fiber optic communication terminal of claim 1, wherein the light mixing means and light branching means are included in one waveguide type optical coupler.

4. A fiber optic communication terminal of claim 1, wherein the light source means has a light source which is a semiconductor laser producing a semiconductor light having a semiconductor wavelength, said semiconductor laser having a temperature and a bias current, said semiconductor wavelength is controlled by controlling one of the temperature and the bias current of the semiconductor laser.

5. A fiber optic communication terminal of claim 1, wherein the light source means has a semiconductor laser having a wavelength variable function.

6. A fiber optic communication terminal of claim 1, wherein the detecting means produces the detection signal depending on the noise level.

7. A fiber optic communication terminal of claim 1, wherein the detecting means produces the detection signal depending on the bit error rate.

8. A fiber optic communication terminal of claim 7, wherein the light source means produces the output light signal by modulating the light signal with a frequency multiplexed signal, said light signal having at least one carrier which is digitally modulated, and the detecting means detects the bit error rate of the digitally modulated light signal having the highest frequency.

9. A fiber optic communication terminal of claim 7, wherein the light source means produces the output light signal by modulating the light signal with a modulating signal, said modulating signal combined with a bit error rate signal for detecting a higher frequency bit error rate, said bit error signal having a higher frequency than the output light signal, and the detecting means detects the bit error rate using the bit error rate signal for detection of bit error rate.

10. A fiber optic communication terminal of claim 1, wherein the wavelength of the output light signal of the light source means is changed by a preset value to maintain the output light signal in the same state when the detecting means detects deterioration of the signal quality of the second light signal.

11. A fiber optic communication terminal of claim 1, wherein when the detecting means detects deterioration of signal quality of the second light signal, the wavelength of output light signal of the light source means is changed using the control means which continues to operate for a preset time in order to decrease or maintain the deterioration of the signal quality, if the deterioration of the signal quality cannot be decreased or maintained, the wavelength of output light signal of the light source means is changed by a preset amount, and then the control means continues to change the wavelength of output light signal of the light source means.

12. A fiber optic communication system comprising:

a plurality of fiber optic communication terminals, each one of the plurality of fiber optic communication terminals comprising;

(a) light source means for producing an output light signal having a wavelength and a spectrum distribution of a specified shape,

(b) light mixing means for mixing an input light and the output light signal from the light source means,

(c) light branching means for separating the mixed light signal output from the light mixing means into a first light signal and a second light signal each having respective signal qualities, said second light signal having one of a noise level and a bit error rate,

(d) detecting means for detecting deterioration of the signal quality of the second light signal from the light branching means by detecting one of the noise level and the bit error rate of the second light signal and producing a detection signal, and

(e) control means for controlling the wavelength of the output light signal of the light source means in response to the detection signal to prevent deterioration of the signal quality of the first light signal regardless of the specified shape of the spectrum distribution of the output light signal emitted by the light source means, and

one center station, the plurality of fiber optic communication terminals and the one center station coupled in cascade through optical fibers where the one center station is at one end, the one center station receives light signals from all of the plurality of the fiber optic communication terminals.

13. A fiber optic communication system comprising:

a plurality of fiber optic communication terminals each one of the plurality of fiber optic communication terminals comprising;

(a) light source means for producing an output light signal having a wavelength and a spectrum distribution of a specified shade,

(b) light mixing means for mixing an input light and the output light signal from the light source means,

(c) light branching means for separating the mixed light signal output from the light mixing means into a first light signal and a second light signal each having respective signal qualities, said second light signal having one of a noise level and a bit error rate,

(d) detecting means for detecting deterioration of the signal quality of the second light signal from the light branching means by detecting one of the noise level and the bit error rate of the second light signal and producing a detection signal, and

(e) control means for controlling the wavelength of the output light signal of the light source means in response to the detection signal to prevent deterioration of the signal quality of the first light signal regardless of the specified shape of the spectrum distribution of the output light signal emitted by the light source means, and

one center station, the plurality of communication terminals and the one center coupled annularly in cascade through optical fibers, where the one center station receives light signals from all of the plurality of the fiber optic communication terminals, and the center station having a center station light signal which is provided to the plurality of fiber optic communication terminals.

14. A method of setting wavelengths for a fiber optic communication system comprising:

(a) a plurality of fiber optic communication terminals comprising;

(1) light source means for producing an output light signal having a wavelength and a spectrum distribution of a specified shape,

(2) light mixing means for mixing an input light signal and the output light signal from the light source means,

(3) light branching means for separating the mixed light signal output from the light mixing means into a first light signal and a second light signal each having respective signal qualities, said second light signal having one of a noise level and a bit error rate,

(4) detecting means for detecting deterioration of the signal quality of the second light signal from the light branching means by detecting one of the noise level and the bit error rate of the second light signal and producing a detection signal depending on one of the bit error rate and the noise level, and

(5) control means for controlling the wavelength of the output light signal of the light source means in response to the detection signal to maintain the signal quality of the first light signal,

(b) one center station, the plurality of fiber optic communication terminals and the one center station coupled in cascade through optical fibers, wherein the one center station is at one end, and the one center station receives light signals from all of the plurality of fiber optic communication terminals, and

(c) a remote communication terminal which is one of the plurality of communication terminals which is located at a most remote position on a furthest side from the one center station, said method comprising the steps of;

transmitting a remote output light signal from the remote communication terminal, said remote output light signal having a remote communication terminal wavelength; and

sequentially setting, with respect to the remote communication terminal wavelength, the wavelength of the output light signal of each one of the plurality of fiber optic communication terminals starting from the fiber optic communication terminal located at a next most remote position on the furthest side from the one center station;

wherein the wavelengths of the output light signals are set to prevent deterioration of the signal quality of the first light signal of each one of the plurality of fiber optic communication terminals regardless of the specified shape of the spectrum distribution of the output light signal emitted by the light source means of each one of the plurality of fiber optic communication terminals.

15. A method of setting wavelengths for a fiber optic communication system comprising:

(a) a plurality of fiber optic communication terminals comprising;

(1) light source means for producing an output light signal having a wavelength and a spectrum distribution of a specified shape,

(2) light mixing means for mixing an input light signal and the output light signal from the light source means,

(3) light branching means for separating the mixed light signal output from the light mixing means into a first light signal and a second light signal each having respective signal qualities,

(4) detecting means for detecting deterioration of the signal quality of the second light signal from the light branching means by detecting one of the noise level and the bit error rate of the second light signal and producing a detection signal depending on one of the bit error rate and the noise level, and

(5) control means for controlling the wavelength of the output light signal of the light source means in response to the detection signal to maintain the signal quality of the first light signal, and

(b) one center station having an output side, the plurality of communication terminals and the one center station connected annularly in cascade through optical fibers, wherein the light signals from all of the plurality of fiber optic communication terminals are received by the one center station, said one center station providing a center station light signal to the plurality of fiber optic communication terminals, said method comprising the steps of;

transmitting the center station light signal from the one center station, said center station light signal having a center station wavelength; and

sequentially setting, with respect to the center station wavelength, the wavelength of the output light signal of each one of the plurality of fiber optic communication terminals starting from one of the plurality of fiber optic communication terminals closest to the output side of the center station to the plurality of fiber optic communication terminals progressing gradually further from the output side of the center station;

wherein the wavelengths of the output light signals are set to prevent deterioration of the signal quality of the first light signal of each one of the plurality of fiber optic communication terminals regardless of the specified shape of the spectrum distribution of the output light signal emitted by the light source means of each one of the plurality of fiber optic communication terminals.