Apparatus for and method of generating millimeter waves

Abstract

Provided are an apparatus for and a method of generating millimeter waves, in which millimeter-wave generation and frequency up-conversion can be achieved at the same time using a single device. The apparatus includes a mode-locking laser diode (LD) which has a distributed feedback (DFB) sector and a gain sector and generates high-frequency optical pulses through a passive mode locking process, a modulator which modulates an external optical signal using an electric signal and injects the modulated optical signal to the mode-locking LD to lock the optical pulses, and a radio frequency (RF) locking signaling unit which injects the electric signal to the modulator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:

FIG. 1 is a schematic block diagram of an apparatus for generating millimeter waves according to an embodiment of the present invention;

FIG. 2 is an as-cleaved facet (AC) of a mode-locking laser diode (LD) of the apparatus of FIG. 1;

FIGS. 3A and 3B are graphs illustrating a radio frequency (RF) spectrum and an optical spectrum, respectively, of a free-running pulse generated in the mode-locking LD;

FIGS. 4A and 4B are graphs illustrating RF powers of a fundamental signal and a fourth harmonic signal, respectively, that are locked by an external optical signal according to frequencies;

FIG. 5 is a graph illustrating phase noises of a fundamental signal and a fourth harmonic signal; and

FIG. 6 is a graph illustrating a quadrature phase shift keying (QPSK) digital signal that is up-converted in millimeter waves generated according to an embodiment of the present invention.

Claims

1. An apparatus for generating millimeter waves, the apparatus comprising: a mode-locking LD (laser diode) which has a DFB (distributed feedback) sector and a gain sector and generates high-frequency optical pulses through a passive mode locking;a modulator which modulates an external optical signal using an electric signal and injects the modulated optical signal to the mode-locking LD to lock the optical pulses; andan RF (radio frequency) locking signaling unit which injects the electric signal to the modulator.

2. The apparatus of claim 1, wherein the passive mode locking process is performed by applying a current that is lower than a threshold current of the mode-locking LD to the DFB sector.

3. The apparatus of claim 1, wherein the millimeter waves are generated using a high-order harmonic pulse among the optical pulses generated in the mode-locking LD.

4. The apparatus of claim 3, further comprising a band pass filter which extracts the millimeter waves using the high-order harmonic pulse.

5. The apparatus of claim 3, wherein the high-order harmonic pulse is a fourth harmonic pulse.

6. The apparatus of claim 1, further comprising a TLS (tunable laser source) which generates the external optical signal.

7. The apparatus of claim 1, further comprising: a data signaling unit which generates a data signal to be transmitted; anda combiner which combines the data signal and the electric signal to be simultaneously injected to the modulator.

8. The apparatus of claim 7, wherein the data signal generated by the data signaling unit is a QPSK (quadrature phase shift keying) signal.

9. The apparatus of claim 7, wherein the high-order harmonic pulse among the optical pulses generated in the mode-locking LD is used to generate the millimeter waves, and the data signal is carried around the high-order harmonic pulse, whereby the frequency of the data signal is up-converted.

10. The apparatus of claim 1, further comprising a polarizer which controls the polarization state of the external optical signal modulated by the modulator.

11. The apparatus of claim 1, wherein the mode-locking LD comprises a phase control sector between the DFB sector and the gain sector.

12. The apparatus of claim 11, wherein the gain sector of the mode-locking LD is divided into at least two sub-sectors to uniformly supply a current to the gain sector.

13. The apparatus of claim 12, wherein the gain sector is divided into a first gain sub-sector and a second gain sub-sector, and the DFB sector, the phase control sector, the first gain sub-sector, andthe second gain sub-sector of the mode-locking LD have lengths of 0.5, 0.5, 1, and 1 mm, respectively.

14. The apparatus of claim 13, wherein the threshold current of the mode-locking LD is 40 mA, and currents of 30 mA, 10 mA, 100 mA, and 77 mA are applied to the DFB sector, the phase control sector, the first gain sub-sector, and the second gain sub-sector of the mode-locking LD, respectively.

15. An apparatus for generating millimeter waves, the apparatus comprising: a mode-locking LD (laser diode) which has a DFB (distributed feedback) sector and a gain sector and generates high-frequency optical pulses through a passive mode locking;a modulator which locks the optical pulses, modulates an external optical signal using an electric signal including a data signal, and injects the modulated optical signal to the mode-locking LD to lock the optical pulses;a TLS (tunable laser source) which injects the external optical signal to the modulator; anda signaling unit which injects the electric signal to the modulator.

16. The apparatus of claim 15, wherein the passive mode locking process is performed by applying a current that is lower than a threshold current of the mode-locking LD to the DFB sector.

17. The apparatus of claim 15, wherein the signaling unit comprises: an RF (radio frequency) locking signaling unit which generates an RF locking signal for locking the optical pulses;a data signaling unit which generates a data signal to be transmitted; anda combiner which combines the data signal and the electric signal to be simultaneously injected to the modulator.

18. The apparatus of claim 17, wherein the mode-locking LD comprises a phase control sector between the DFB sector and the gain sector.

19. The apparatus of claim 18, wherein millimeter waves are generated using a high-order harmonic pulse among the optical pulses generated in the mode-locking LD, and the data signal is carried around the high-order harmonic pulse, whereby the frequency of the data signal is up-converted.

20. The apparatus of claim 19, wherein the frequency of the RF locking signal is 14.835 GHz, the carrier frequency of the data signal is 150 MHz, andthe high-order harmonic pulse is a fourth harmonic pulse.

21. A method of generating millimeter waves, the method comprising: generating high-frequency optical pulses through a passive mode locking by supplying a current that is lower than a threshold current of a mode-locking LD (laser diode) having a DFB (distributed feedback) sector and a gain sector to the mode-locking LD;modulating an external optical signal with an electric signal using a modulator and injecting the modulated optical signal to the mode-locking LD to lock the optical pulses; andgenerating the millimeter waves using the optical pulses locked through the injection of the modulated external optical signal.

22. The method of claim 21, wherein the modulating of the external optical signal comprises injecting the electric signal to the modulator.

23. The method of claim 22, wherein the electric signal comprises an RF locking signal for locking the optical pulses and a data signal to be carried in the optical pulses.

24. The method of claim 23, further comprising, combining the RF locking signal and the data signal before injecting the electric signal to the modulator.

25. The method of claim 21, wherein the millimeter waves are generated using a high-order harmonic pulse among the locked optical pulses.

26. The method of claim 25, wherein the electric signal comprises a data signal and the data signal is carried in the high-order harmonic pulse, whereby the frequency of the data signal is up-converted.

27. The method of claim 21, wherein the mode-locking LD further comprises a phase control sector between the DFB sector and the gain sector, the gain sector is divided into a first gain sub-sector and a second gain sub-sector,the DFB sector, the phase control sector, the first gain sub-sector, and the second gain sub-sector of the mode-locking LD have lengths of 0.5, 0.5, 1, and 1 mm, respectively, andthe threshold current of the mode-locking LD is 40 mA.

28. The method of claim 27, wherein the millimeter waves are generated by applying currents of 30 mA, 10 mA, 100 mA, and 77 mA to the DFB sector, the phase control sector, the first gain sub-sector, and the second gain sub-sector, respectively.

29. The method of claim 28, wherein the electric signal comprises an RF locking signal for locking the optical pulses and a data signal to be carried in the optical pulses, the frequency of the RF locking signal is 14.835 GHz,the carrier frequency of the data signal is 150 MHz,the millimeter waves are generated using a fourth harmonic pulse among the locked optical pulses, andthe data signal is carried in the millimeter waves, whereby the frequency of the data signal is up-converted.