Optical electromagnetic wave generator

• US 20010014106A1
• Filed: 01/11/2001
• Published: 08/16/2001
• Est. Priority Date: 01/11/2000
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Nilsson, Mattias, Karlsson, Mats, Een, Joakim, Larsson, Anders, Gevorgian, Spartak, Calander, Nils
• Granted Patent: US 6,614,816 B2
• Time in Patent Office: Days
• US Class Current: 372/20
• CPC Class Codes: H01S 5/0623 using the beating between two closely spaced optical frequencies, i.e. heterodyne mixing
• CPC Class Codes: H01S 5/0656 Seeding, i.e. an additional light input is provided for controlling the laser modes, for example by back-reflecting light from an external optical component H01S5/14, H01S5/4062 and H01S5/4006 take precedence
• CPC Class Codes: H01S 5/4068 with lateral coupling by axially offset or by merging waveguides, e.g. Y-couplers
• CPC Class Codes: H01S 5/423 having a vertical cavity
• CPC Class Codes: H03B 28/00 Generation of oscillations by methods not covered by groups H03B5/00 - H03B27/00, including modification of the waveform to produce sinusoidal oscillations analogue function generators for performing computing operations G06G7/26; use of transformers for conversion of waveform in ac-ac converters H02M5/18

Abstract

Microwaves are generated by heterodyning the outputs of two or more optical lasers which have differing central frequencies to produce beat frequencies in the microwave range. One of the beat frequencies is used to modulate the output of at least one of the lasers so as to produce sidebands which differ from the central frequency by an integral number of the sideband frequency. Each laser is connected to one of the other lasers by a weak optical link to optically injection lock the laser to the sideband of the other laser.

Claims

1. A method of generating a frequency tunable electromagnetic signal, comprising heterodyning at least a part of the optical outputs of two or more lasers, of which at least one laser is frequency tunable and which have optical frequencies that produce at least one beat frequency, modulating the outputs of the lasers by one or more of said beat frequencies to produce one or more sidebands to said central frequency, and optically injection-locking at least one of said lasers to a sideband of another of said lasers.

2. A method according to

claim 1

, characterized by optically injection-locking the said other of said lasers to a sideband of the said one laser.

3. A method according to

claim 1

, characterized by combining at least a part of the optical outputs of each of the lasers and extracting from the combined signal at least one beat frequency signal as an electrical signal.

4. A method according to

claim 3

, characterized by extracting a part of said beat frequency signal and filtering said part of the said beat frequency signal or signals to allow only one of the beat frequencies to pass.

5. A method according to

claim 3

, characterized by feeding a part of the beat frequency signal extracted from the combined signal into an output for the beat frequency signal or signals.

6. A method according to

claim 3

, characterized by dividing the combined signal before the beat frequency is extracted from the combined signal.

7. A method according to

claim 1

, characterized by providing a reference signal which modulates the output of each of said lasers.

8. A method according to

claim 1

, characterized by changing the central frequencies of two or more of said lasers simultaneously and by the same amount so as to maintain the same beat frequency or frequencies.

9. A method according to

claim 1

, characterized by changing the difference in the central frequencies of two or more of said lasers so as to change the beat frequency or frequencies.

10. A method according to

claim 1

, characterized in that at least one of the beat frequencies is in the range of 1 to 300 Gigahertz.

11. An apparatus for generating a frequency tunable electromagnetic signal, comprising two or more lasers of which at least one laser is frequency tunable, means for producing a combined signal from the optical outputs of at least two of the said lasers, means for extracting as signals from the combined signal any beat frequencies produced by any difference in the optical central frequencies of the said lasers, characterized by means for feeding at least one of the said beat frequency signals into at least one of said lasers to modulate the output of said laser to produce one or more sidebands to said central frequency, and means optically cornecting the output of one of said lasers to another of said lasers so as to optically injection-lock the said other laser to a sideband of the central frequency of the said one laser.

12. An apparatus according

claim 11

, characterized in that the means optically connecting the output of one of said lasers to another of said lasers also optically connects the output of the said other laser to the said one laser so as to injection-lock the said one laser to a sideband of the central frequency of the said other laser.

13. An apparatus according to

claim 11

, characterized by means arranged to provide an output for one or more of said beat frequency signals.

14. An apparatus according to

claim 11

, characterized in that the apparatus is arranged to feed one or more of said beat frequency signals into one or more of said lasers to produce said sidebands.

15. An apparatus according to

claim 11

, characterized by means for varying the central frequency of one said laser relative to another said laser.

16. An apparatus according to

claim 11

, characterized by means for varying the central frequencies of two or more lasers by the same amount and simultaneously.

17. An apparatus according to

claim 11

, characterized by means for dividing out an part of the combined optical signal of said lasers before the signal is fed into said means for extracting beat frequency signals.

18. An apparatus according to

claim 11

, characterized in that the lasers are vertical cavity surface emitting lasers arranged on a semiconductor chip.

19. An apparatus according to

claim 18

, characterized in that the means for optically connecting comprise a thin optically transparent film optically connected to the optical outputs of each laser.

20. An apparatus according to

claim 18

, characterized in that the means for producing a combined signal comprise a thin film beam combiner.

21. An apparatus according to

claim 11

, characterized in that there are more than two lasers and the means for extracting beat frequency signals extracts signals of two or more beat frequencies.

22. An apparatus according to

claim 11

, characterized in that the apparatus is arranged to produce at least one beat frequency in the range 1 to 300 Gigahertz.