GB2237469A - Optical transmission process and system - Google Patents
Optical transmission process and system Download PDFInfo
- Publication number
- GB2237469A GB2237469A GB8923879A GB8923879A GB2237469A GB 2237469 A GB2237469 A GB 2237469A GB 8923879 A GB8923879 A GB 8923879A GB 8923879 A GB8923879 A GB 8923879A GB 2237469 A GB2237469 A GB 2237469A
- Authority
- GB
- United Kingdom
- Prior art keywords
- frequency
- carrier
- optical
- intensity
- frequency part
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 230000003287 optical effect Effects 0.000 title claims abstract description 29
- 230000005540 biological transmission Effects 0.000 title claims abstract description 20
- 238000000034 method Methods 0.000 claims abstract description 11
- 239000004065 semiconductor Substances 0.000 claims abstract description 4
- 238000002347 injection Methods 0.000 claims abstract description 3
- 239000007924 injection Substances 0.000 claims abstract description 3
- 238000011084 recovery Methods 0.000 claims abstract 2
- 230000000694 effects Effects 0.000 claims description 3
- 238000001514 detection method Methods 0.000 abstract description 3
- 239000000835 fiber Substances 0.000 description 4
- 238000001228 spectrum Methods 0.000 description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 230000008878 coupling Effects 0.000 description 2
- 238000010168 coupling process Methods 0.000 description 2
- 238000005859 coupling reaction Methods 0.000 description 2
- 239000000969 carrier Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 230000008054 signal transmission Effects 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
- H04B10/54—Intensity modulation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/501—Structural aspects
- H04B10/503—Laser transmitters
- H04B10/504—Laser transmitters using direct modulation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
- H04B10/548—Phase or frequency modulation
Landscapes
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Optics & Photonics (AREA)
- Optical Communication System (AREA)
Abstract
In a frequency shift keyed direct detection (FSKDD) optical transmission system, an optical carrier 14 is frequency modulated with a higher frequency part 16 of an input signal. The frequency modulation is converted in an optical frequency discriminator 18 (eg Mach Zehnder or Fabry Perot interferometer) to an intensity modulation and the carrier is further intensity modulated with a lower frequency part 17 of the input signal, eg by phase modulating the discriminator. The doubly modulated carrier is then transmitted to a receiver station for demodulation and recovery of the original signal. The technique overcomes the problem of poor low frequency response of semiconductor injection lasers. <IMAGE>
Description
OPTICAL TRANSMISSION
PROCESS AND SYSTEM
This invention relates to the transmission of signals on an optical carrier, and in particular to transmission via frequency shift keying (FSK) modulation of the carrier. Conveniently, the modulated carrier may be transmitted via a fibre optic transmission path.
Frequency shift keying is a form of frequency modulation in which the modulating wave shifts a carrier frequency between predetermined values. The technique is finding increasing use in fibre optic transmission systems, particularly in submarine applications. A preferred form of frequency shift keying is that using direct detection of the modulation to regenerate an intensity modulated carrier. Such a technique is described for example in our UK specification No. 2 107 147B. In a frequency shift keying direct detection (FSKDD) system, signals are transmitted on a carrier by frequency modulation of that carrier. A frequency discriminator is then used to convert the frequency modulation to a corresponding intensity modulated signal which is then demodulated to recover the transmitted signal.Conventionally, the frequency modulated signal is generated via a solid state laser whose output spectrum is determined by the level of the signal drive applied thereto. Problems have been experienced with many semiconductor lasers as their low frequency FM response is unstable. This has restricted transmission of the lower frequency part of the information spectrum.
The object of the present invention is to minimise or to overcome this disadvantage,
According to one aspect of the invention there is provided an optical frequency shift keying (FSK) transmission system, including a transmitter having a light source for generating an optical carrier, a receiver, a transmission path between the transmitter and receiver, optical frequency discrimination means disposed in the path betweeen the transmitter and the receiver, means for frequency modulating the carrier with a higher frequency part of an input signal, and means associated with the frequency discriminator for intensity modulating the carrier with a lower frequency part of the input signal whereby to provide, at said receiver, the carrier intensity modulated with both the lower frequency and higher frequency paths of the input signal.
According to another aspect of the invention there is provided a method of transmitting on an optical carrier an information signal having a higher frequency part and a lower frequency part, the method including frequency modulating the optical carrier with said higher frequency part, converting said frequency modulation of the carrier to intensity modulation, and further intensity modulating the carrier with said lower frequency part of the signal.
As the lower frequency part of the signal is intensity modulated on the carrier, the problem of low frequency FM response is overcome.
Reference is directed to our co-pending application No. (R.E. Epworth 47) of even date which relates to a system and method in which a first light source is frequency modulated with the higher frequency part of an input signal and a second light source is intensity modulated with a lower frequency part. The two modulated carriers are transmitted over a common channel to a receiver, the frequency modulation being converted to phase modulation prior to reception by the receiver.
It will be understood that the term 'light source' includes devices operating in the visible and infra-red regions of the spectrum
An embodiment of the invention will now be described with reference to the accompanying drawing in which the single Figure is a schematic diagram of an optical transmission system employing both frequency shift keying and intensity modulation of a common optical carrier.
Referring to the drawing, the optical transmission system includes a transmitter 11, a receiver 12 and a transmission path comprising e.g. a fibre optic link 13 therebetween. The transmitter 11 includes, light source 14, typically a semiconductor injection laser, and launch optics 15 for coupling the light source 14 to the transmission path 13. The transmitter 11 further includes a high pass filter 16 and a low pass filter 17 to which an input information signal to be transmitted is fed in parallel. The output of the high pass filter comprising the higher frequency part of the input signal, is coupled to the light source 14 to effect frequency modulation of the light source.
Typically, in a 1GHz bandwidth system, the cut-off between the higher and lower frequencies is at about 1MHz.
Advantageously, the light source operates in the infra-red region of the spectrum where silica optical fibres exhibit minimum dispersion.
Prior to launch into the transmission path, the frequency modulated optical carrier is converted to a intensity modulated carrier by a frequency discriminator 18. This may comprise e.g. a Mach Zehnder interferometer or a Fabry Perot interferometer tuned to pass light at the source frequency. The output of the low pass filter 17 is coupled to the frequency discriminator whereby to effect phase modulation of the frequency modulated carrier with the lower frequency part of the input signal. This intensity modulates the carrier with the lower frequency signal part. At the same time the frequency modulation representing the higher frequency signal part is converted by the discriminator to intensity modulation. The output for the frequency modulation is thus an optical carrier which is intensity modulated with both the higher and lower frequency components of the input signal.
In some applications the transmitter station including the frequency discriminator may be provided as a self-contained unit for coupling to an existing fibre optic system.
The doubly modulated carrier is transmitted via the transmission path to the receiver where the carrier is demodulated to recover the original information signal.
The transfer function for the FSK component of the signal is linear, whilst that of intensity modulated low frequency component is sinusoidal but monotonic.
However, linearity is easily recovered by the use of a non-linear network and/or by the use of feedback control.
Claims (7)
1. A method of transmitting on an optical carrier an information signal having a higher frequency part and a lower frequency part, the method including frequency modulating the optical carrier with said higher frequency part, converting said frequency modulation of the carrier to intensity modulation, and further intensity modulating the carrier with said lower frequency part of the signal.
2. A method of transmitting on an optical carrier an information signal having a higher frequency part and a lower frequency part, the method including frequency modulating an optical carrier with the higher frequency part of the information signal, directing said optical carrier through an optical frequency discriminator whereby to convert the frequency modulation to intensity modulation, phase modulating the frequency discriminator with the lower frequency part of the information signal whereby to further intensity modulate the carrier with said lower frequency part, and transmitting the intensity modulated carrier to a receiver station whereby to effect demodulation of the carrier and recovery of the information signal.
3. A method of transmitting an information signal substantially as described herein with reference to and as shown in the accompanying drawings.
4. An optical frequency shift keying (FSK) transmission system, including a transmitter having a light source for generating an optical carrier, a receiver, a transmission path between the transmitter and receiver, optical frequency discrimination means disposed in the path betweeen the transmitter and the receiver, means for frequency modulating the carrier with a higher frequency part of an input signal, and means associated with the frequency discriminator for intensity modulating the carrier with a lower frequency part of the input signal whereby to provide, at said receiver, the carrier intensity modulater with both the lower frequency and higher frequency paths of the input signal.
5. An optical transmission system as described in claim 4, wherein said light source comprises a semiconductor injection laser.
6. An optical transmission system as claimed in claim 4 or 5, wherein the frequency discriminator comprises a Mach-Zehnder or a Fabry-Perot interferometer tuned to the frequency of the light source.
7. An optical transmission system substantially as described herein with reference to and as shown in the accompanying drawing.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8923879A GB2237469B (en) | 1989-10-24 | 1989-10-24 | Optical transmission process and system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8923879A GB2237469B (en) | 1989-10-24 | 1989-10-24 | Optical transmission process and system |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8923879D0 GB8923879D0 (en) | 1989-12-13 |
| GB2237469A true GB2237469A (en) | 1991-05-01 |
| GB2237469B GB2237469B (en) | 1993-10-20 |
Family
ID=10665043
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8923879A Expired - Fee Related GB2237469B (en) | 1989-10-24 | 1989-10-24 | Optical transmission process and system |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2237469B (en) |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2254746A (en) * | 1991-04-12 | 1992-10-14 | Northern Telecom Europ Ltd | Optical transmitter |
| EP0523921A1 (en) * | 1991-07-18 | 1993-01-20 | Nortel Networks Corporation | Polarisation state insensitive optical discriminator |
| US5361155A (en) * | 1992-03-26 | 1994-11-01 | Alcatel Cit | Optical filter tuned by rotation and comprising a Fabry-Perot interferometer |
| US5373383A (en) * | 1993-03-02 | 1994-12-13 | The Boeing Company | Optical carrier filtering for signal/noise and dynamic range improvement |
| GB2303984A (en) * | 1995-08-01 | 1997-03-05 | Fujitsu Ltd | Wavelength division multiplexing optical transmission system |
| WO2005084268A2 (en) | 2004-02-27 | 2005-09-15 | Azna Llc | Fm source and spectral reshaping element |
| WO2007099165A3 (en) * | 2006-03-03 | 2007-11-15 | Siemens Ag | Modulator device for generating an optical transfer signal modulated by means of a binary signal |
-
1989
- 1989-10-24 GB GB8923879A patent/GB2237469B/en not_active Expired - Fee Related
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2254746A (en) * | 1991-04-12 | 1992-10-14 | Northern Telecom Europ Ltd | Optical transmitter |
| GB2254746B (en) * | 1991-04-12 | 1995-03-29 | Northern Telecom Europ Ltd | Optical transmitter |
| EP0523921A1 (en) * | 1991-07-18 | 1993-01-20 | Nortel Networks Corporation | Polarisation state insensitive optical discriminator |
| US5361155A (en) * | 1992-03-26 | 1994-11-01 | Alcatel Cit | Optical filter tuned by rotation and comprising a Fabry-Perot interferometer |
| US5373383A (en) * | 1993-03-02 | 1994-12-13 | The Boeing Company | Optical carrier filtering for signal/noise and dynamic range improvement |
| GB2303984A (en) * | 1995-08-01 | 1997-03-05 | Fujitsu Ltd | Wavelength division multiplexing optical transmission system |
| US5877879A (en) * | 1995-08-01 | 1999-03-02 | Fujitsu Limited | Wavelength division multiplexing optical transmission system and optical transmitting device used in the transmission system |
| GB2303984B (en) * | 1995-08-01 | 2000-07-12 | Fujitsu Ltd | Wavelength division multiplexing optical transmission system and optical transmitting device used in the transmission system |
| WO2005084268A2 (en) | 2004-02-27 | 2005-09-15 | Azna Llc | Fm source and spectral reshaping element |
| EP1738504A4 (en) * | 2004-02-27 | 2017-04-19 | Finisar Corporation | Optical system comprising an fm source and a spectral reshaping element |
| WO2007099165A3 (en) * | 2006-03-03 | 2007-11-15 | Siemens Ag | Modulator device for generating an optical transfer signal modulated by means of a binary signal |
| US7876852B2 (en) | 2006-03-03 | 2011-01-25 | Nokia Siemens Networks Gmbh & Co. Kg | Modulator device for generating an optical transfer signal modulated by binary signal |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8923879D0 (en) | 1989-12-13 |
| GB2237469B (en) | 1993-10-20 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732E | Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977) | ||
| 732E | Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20041024 |