Transmitter for an Optical Free-Beam Communication System and Optical Free-Beam Communication System

Abstract

Disclosed is a transmitter for an optical free-beam communication system, in particular for a data uplink to a satellite, for emission of a light signal, including a number of m data channels. In some non-limiting embodiments or aspects, the data channels may each have a different wavelength WL. Further, a multiplexer is provided for superimposition of the m data channels into a sum signal. A number of n pulse devices form a pulse signal from the sum signal, the pulse signals being chronologically offset from each other. A respective transmission device is connected with a pulse device for emitting the respective pulse signal.

Claims

1. A transmitter for an optical free-beam communication system, in particular for a data uplink to a satellite, for emission of a light signal, comprising; a number of m data channels, the data channels each having a different wavelength, a multiplexer for superimposition of the m data channels into a sum signal, a number of n pulse devices, a pulse signal being formed from the sum signal by respective pulse devices, the pulse signals being offset in time from each other, and a number of n transmission devices, each transmission device being connected with a pulse device for emitting respective pulse signals.

2. The transmitter of claim 1, wherein the number m of the data channels is larger than 50.

3. The transmitter of claim 1, wherein the number n of the pulse devices and the number n of the transmission devices is at least 2.

4. The transmitter of claim 1, wherein an amplifier is provided for amplifying the pulse signal.

5. The transmitter of claim 1, wherein a sum of one or more lengths of the pulse signals equals a length of an original data bit.

6. The transmitter of claim 1, wherein a length of a respective pulse signal equals 1/n of a length of an original data bit.

7. The transmitter of claim 1, wherein a chronological offset between individual pulse signals is generated by optical waveguides of different lengths.

8. The transmitter of claim 1, wherein the transmission devices are spaced by a distance that is greater than a structural size of turbulence cells in an optical free-beam transmission, so that the light signal is transmitted via different atmospheric paths, the devices being spaced apart in particular by a distance of more than 20 cm.

9. A free-beam communication system for a data uplink to a satellite, comprising a transmitter according to claim 1, and a DWDM receiver.

10. The free-beam communication system claim 9, wherein the receiver has a receiving device for receiving the light signal emitted by the transmitter, a demultiplexer for wavelength-selective splitting of the received light signal, the demultiplexer being connected with the receiving device, and a number of m detectors for receiving the respective data channel, each detector receiving one wavelength of the light signal.

11. The free-beam communication system of claim 9, wherein the respective data channels are modulated using IM/DD, selfhomodyne DPSK, BPSK or ASK heterodyne.

Description

[0042] In the Figures:

[0043] FIG. 1 shows the basic functionality of a transmitter diversity,

[0044] FIG. 2 shows an exemplary received power vector received at the satellite,

[0045] FIG. 3 shows an embodiment of the transmitter according to the invention,

[0046] FIG. 4 shows a receiver of the free-beam communication system of the present invention,

[0047] FIG. 5 shows a spectrum of the light signal at the transmitter side, and

[0048] FIG. 6 shows a spectrum of the received light signal at the receiver side.

[0049] FIGS. 1 and 3 were already discussed in the context of prior art.

[0050] FIG. 3 shows an embodiment of the transmitter of the present invention which has three data channels (m=3) and four pulse devices (n=4). The device has three laser light sources 10 for generating laser light with a first wavelength WL 1, a second wavelength WL 2 and a third wavelength WL 3. Here, the wavelengths of the lasers 10 differ from each other. In a modulator 12, the respective laser light of the laser 10 is superimposed with a data channel 14. Here, the number of data channels corresponds to the number of wavelengths used. The data channel having the first wavelength WL 1, the data channel having the second wavelength WL 2 and the data channel having the third wavelength WL 3 are combined into a sum signal in a multiplexer 16, which sum signal is supplied to four pulse devices 18. Here, all pulse devices 18 receive the same sum signal. In the embodiment illustrated the pulse devices 18 are each modulators which are controlled via a pulse source 20 so as to form a pulse signal from the sum signal. Here, the pulse signals all have the same length and are offset in time with respect to each other, as illustrated by the indicated trigger pulse 22 in FIG. 3. The length of the pulses 22 corresponds to just 1/n= of the original bit length. Thus, the first quarter of the original bit is detected by the first pulse device 18, the second quarter of the original bit is detected by the second pulse device 18, etc.

[0051] The pulse signals are amplified in an amplifier 24. Subsequently, each pulse signal is emitted via a dedicated transmission telescope 26. The transmission telescopes 26 are spaced from each other by a distance that is greater than the structural size of the turbulence cells of the optical free-beam transmission, in particular the atmosphere. Here, each transmission telescope 26 emits the same signal, but at different times due to the offset in time of the pulse signals with respect to one another.

[0052] The pulse signals emitted via the transmission telescopes 26 become superimposed to form a light signal consisting of the three wavelengths WL 1, WL2 and WL3, and are received by a receiving telescope 28 at the receiver side, as illustrated in FIG. 4. The light signal received is pre-amplified in a pre-amplifier 30. Thereafter, the received light signal is split into the wavelengths WL 1, WL 2 and WL 3 in a demultiplexer 32. The first wavelength WL 1 is detected by a first detector 34, the second wavelength WL 2 is detected by a second detector 36 and the third wavelength WL 3 is detected by a third detector 38. Using the detectors 34, 36, 38, it is possible to extract the bit data sequence of the data channels 14 that was to be transmitted originally.

[0053] In FIG. 5 the spectra of the three wavelengths WL 1, WL 2 and WL 3 are plotted. Due to the generation of short pulses of the pulse signal by the pulse devices 18, the spectrum of a respective pulse 40 is widened, also illustrated in FIG. 5, but for the wavelength WL 2 only. During superimposition in the receiver, the pulses of the respective wavelengths are added (spectrum 42), the sum spectrum having a width that substantially corresponds to the width of the spectrum of the three wavelengths WL 1, WL 2 and WL 3. Thus, using transmitter diversity, a plurality of data channels can be efficiently transmitted. A restriction to merely two data channels does not exist.