Method and apparatus of color mixing in a laser diode system

• US 6,606,332 B1
• Filed: 11/01/2000
• Issued: 08/12/2003
• Est. Priority Date: 11/01/2000
• Status: Expired due to Fees

• Current Assignee: Bogie Boscha
• Original Assignee: Bogie Boscha
• Inventors: Boscha, Bogie
• Primary Examiner(s): Ip, Paul
• Assistant Examiner(s): NGUYEN, TUAN M
• Application Number:
  US09/702,605
• Time in Patent Office: 1,014 Days
• Field of Search: 372/42, 372/31, 372/9, 348/750
• US Class Current: 372/42
• CPC Class Codes: G02F 1/37 for second-harmonic generation G02F1/3532 takes precedence
• CPC Class Codes: H01S 3/0826 using a diffraction grating
• CPC Class Codes: H01S 5/02251 using optical fibres
• CPC Class Codes: H01S 5/02325 Mechanically integrated components on mount members or optical micro-benches
• CPC Class Codes: H01S 5/02415 by using a thermo-electric cooler [TEC], e.g. Peltier element
• CPC Class Codes: H01S 5/02438 Characterized by cooling of elements other than the laser chip, e.g. an optical element being part of an external cavity or a collimating lens
• CPC Class Codes: H01S 5/02446 Cooling being separate from the laser chip cooling
• CPC Class Codes: H01S 5/146 using a fiber as external cavity
• CPC Class Codes: H01S 5/4012 Beam combining, e.g. by the use of fibres, gratings, polarisers, prisms
• CPC Class Codes: H01S 5/4093 Red, green and blue [RGB] generated directly by laser action or by a combination of laser action with nonlinear frequency conversion
• CPC Class Codes: H04N 9/3129 scanning a light beam on the display screen scanning a light beam on a screen in displays other than projection devices G09G3/02; scanning systems in general G02B26/10; projectors using laser light sources in general H04N9/3161

Abstract

A color mixing system is proposed for use in an optical-fiber laser-diode assembly comprising at least two semiconductor laser diodes, optical fiber light input and output couples, a system of spatial superposition of laser beams of different wavelength with at least one semi-transparent mirror, and a system for electronic control of light power in monochromatic light components to be mixed. The electronic control system makes it possible to produce a plurality of different colors. The basic colors, i.e., blue, green, and red, are produced by respective laser diode assemblies provided with means for adjusting output light power on each individual assembly. The electronic system contains a microprocessor connected to a pulse width modulation unit capable of modulating the duration and shape of the light pulse emitted from the laser diode. This allows for selecting a required ratio of energetic brightnesses of light beams produced by individual laser diode assemblies. The electronic system contains a microprocessor connected to a pulse width modulation unit capable of modulating the duration of the light pulse emitted from the laser diode for controlling chromaticity of the color and to a current source for controlling the luminescence, i.e., the light power. The aforementioned control of chromaticity and light power is carried out simultaneously in real time with reproduction of perfect colors based on the use of single-mode pure stabilized and frequency double wavelengths with narrow linewidths of the light spectra.

Claims

1. A method of color mixing in a laser diode system comprising the steps of:

generating laser beams of at least two different wavelengths by at least two single mode laser diode assemblies;

supplying the laser beams of at least two different wavelengths into two single mode fibers so that a laser beam of one of said at least two wavelengths is supplied into corresponding one of said single mode fibers;

combining the laser beams of different wavelengths outputting from said at least two single mode fibers into at least one laser beam;

supplying said at least one laser beam into a further single mode fiber;

controlling each of said at least two single fiber laser diode assemblies by an electronic control system having ratio control means for controlling a ratio of energetic brightnesses of said laser beams;

selecting said ratio in compliance predetermined value;

energizing said laser diode assemblies for emitting said laser beams of at least two different wavelengths toward said laser beam combining means;

adjusting said ratio to said predetermined value with the use of said means for controlling a ratio of energetic brightnesses to form adjusted laser beams.

2. The method of claim 1, further comprising the step of providing said electronic control system with temperature control means and controlling the temperature individually in each of said laser diode assemblies with the use of said temperature control means.

3. The method of claim 1, further comprising the step of providing said apparatus with a feedback circuit from said ratio control means to said electronic control system, and constantly maintaining said ratio at said value by sending a signal from said ratio control means to said electronic control system via said feedback control circuit.

4. The method of claim 1, wherein each said laser diode assembly comprises a laser diode and a pulse-width modulating means between said laser diode and said electronic control system, said laser diode generating a light signal, and said step of adjusting said ratio being carries out by adjusting the shape and duration of said signal.

9. The method of claim 1, wherein each said laser diode assembly comprises a laser diode and a pulse-width modulating means between said laser diode and said electronic control system, said laser diode generating a laser beam in a pulse mode, and said step of adjusting said ratio being carries out by adjusting the shape and duration of said pulse.

5. A method of color mixing in a laser diode system comprising the steps of:

generating laser beams of three different colors which are a red laser beam, green laser beam, and blue laser beam, respectively by three single mode laser diode assemblies;

supplying outputs of said single mode laser diode assemblies to three single mode fibers so that the output of each of said three single mode laser diode assemblies is supplied into respective one of said single mode fibers;

combining the laser beams of different colors outputting from said single mode fibers into a combined laser beam;

supplying said combined laser beam to a further single mode fiber;

controlling each of said laser diode assemblies by an electronic control system having ratio control means for controlling a ratio of energetic brightnesses of said laser beams;

selecting said ratio in compliance with a predetermined standard;

energizing said laser diode assemblies for emitting said laser beams of three different colors toward said laser beam combining means;

adjusting said ratio to said standard value with the use of said means for controlling a ratio of energetic brightnesses to form adjusted laser beams.

6. The method of claim 5, wherein said red laser beam has a wavelength of 700 nm, said green laser beam has a wavelength of 546.1 nm, and said blue laser beam has a wavelengths of 435.8 nm, said ratio of energetic brightnesses of said red, green, and blue being equal to 72.1:

1.4;

1.0.

7. The method of claim 6, further comprising the step of providing said electronic control system with temperature control means and controlling the temperature individually in each of said laser diode assemblies with the use of said temperature control means.

8. The method of claim 5, further comprising the step of providing said apparatus with a feedback circuit for feedback from said ratio control means to said electronic control system, and constantly maintaining said ratio at said value by sending a signal from said ratio control means to said electronic control system via said feedback circuit.

10. An apparatus of color mixing in a laser diode system comprising:

a support means;

at least two single mode laser diode assemblies installed on said support means and generating laser beams of at least two different wavelengths;

at least two single mode fibers arranged so that said laser beams of at least two different labelings are supplied into said at least two single mode fibers so that a laser beam of one of said two different wavelengths is supplied into a corresponding one of said at least two single mode fibers;

at least one laser beam combining means installed on said support means and intended for combining said laser beams of different wavelengths outputted from said at least two single mode fibers;

a further single mode fiber arranged so that the combined laser beams of different wavelengths is supplied from said at least one laser beam combining means into said further fiber; and

an electronic control system for each of said at least two laser diode assemblies having means for controlling a ratio of energetic brightnesses of said laser beams.

11. The apparatus of claim 10, wherein each said laser diode assembly being composed of optical components and comprises:

a laser diode assembly housing;

a semiconductor laser diode which is installed on said laser diode assembly housing and radiates a light of a given wavelength band;

an input optical fiber;

a laser cavity formed by a part of said optical components and comprising said input optical fiber, and at least a first reflecting mirror essentially with 100% reflection of light, a second reflecting mirror that passes only a selected portion of said light of a predetermined frequency, and a frequency selection means formed in said input optical fiber for selecting a light of a predetermined frequency in said given wavelength band;

a first coupling means for coupling said semiconductor laser diode to said input optical fiber;

an output optical fiber; and

a second coupling means for coupling said input optical fiber to said output optical fiber.

12. The apparatus of claim 11, wherein each said laser diode has a direction of propagation of light, said at least one laser beam combining means comprises a semitransparent mirror plate having a front side and a rear side, said semitransparent plate being arranged at an angle to said direction of propagation of light emitted from one of said laser diodes and at an angle to said direction of propagation of light emitted from another of said at least two laser diodes, one of said at least two laser diodes having said direction of propagation of light directed toward said rear side of said semitransparent mirror plate, and another of said at least two laser diodes having said direction of propagation of light directed toward said front side of said semitransparent mirror plate, said rear side being coated with a first mirror coating which ensures maximum possible passage of the light emitted from said one of said at least two laser diodes, and said front side being coated with a second coating which ensures maximum possible reflection of the light emitted from said another of said at least two laser diodes.

13. The apparatus of claim 12, wherein said frequency selection means is a Bragg grating.

14. The apparatus of claim 13, wherein said electronic control system further comprises a microprocessor and a feedback circuit between said output optical fiber and said microprocessor for sending a light signal from said output optical fiber to said microprocessor, said microprocessor being connected to said ratio control means for constantly maintaining said ratio at a selected value in response to said light signal.

15. The apparatus of claim 14, wherein said feedback circuit comprises a photodiode and an analog/digital converter connected in series in said feedback circuit.

16. The apparatus of claim 14, wherein said laser diode has switching means for operating said laser diode in a pulse mode for generating pulsed light signals, said ratio control means comprises:

a digital/analog converter and a power supply unit that are connected in series between said microprocessor and said laser diode;

a pulse width modulation unit connected to said laser diode via said switching means for controlling duration of said pulse and thus the level of optical power of light generated by said laser diode.

17. The apparatus of claim 14, wherein said laser diode assembly has a temperature control means connected to said microprocessor, and said housing has cooling means connected to said temperature control means.

18. An apparatus of color mixing in a laser diode system comprising:

a support means;

three single mode laser diode assemblies installed on said support means and generating laser beams of three different colors;

three single mode fibers arranged so that said laser beams of three different colors are supplied into said three single mode fibers individually so that one of said laser beams is supplied into a corresponding one of said single mode fibers;

a first laser beam combining means installed on said support means and intended for combining two of said laser beams of three different colors outputted from two of said three single mode fibers for forming a two-component beam;

a second laser beam combining means installed on said support means and intended for combining the third one of said three laser beams outputted from the third one of said single mode fibers with said two-component beam outputting from said first laser beam combining means a further single mode fiber receiving a three-component beam from said second laser beam combining means; and

an electronic controls system for each of said three laser diode assemblies having means for controlling a ratio of energetic brightness of said laser beams.

19. The apparatus of claim 18, wherein each said laser diode assembly being composed of optical components and comprises:

a laser diode assembly housing;

a semiconductor laser diode which is installed on said laser diode assembly housing and radiates a light of a given wavelength band;

an input optical fiber;

a laser cavity formed by a part of said optical components and comprising said input optical fiber, and at least a first reflecting mirror essentially with 100% reflection of light, a second reflecting mirror that passes only a selected portion of said light of a predetermined frequency, and a frequency selection means formed in said input optical fiber for selecting a light of a predetermined frequency in said given wavelength band;

a first coupling means for coupling said semiconductor laser diode to said input optical fiber;

an output optical fiber; and

a second coupling means for coupling said input optical fiber to said output optical fiber.

20. The apparatus of claim 19, wherein each said laser diode has a direction of propagation of light, each said laser beam combining means comprises a semitransparent mirror plate having a front side and a rear side, said semitransparent plate being arranged at an angle to said direction of propagation of light emitted from one of said laser diodes and at an angle to said direction of propagation of light emitted from two other of said three laser diodes, one of said at least two laser diodes having said direction of propagation of light directed toward said rear sides of said semitransparent mirror plates, a second of said three laser diodes having said direction of propagation of light directed toward said front side of said first laser beam combining means, and a third of said three laser diodes having said direction of propagation of light directed toward said front side of said second laser beam combining means, said rear side of each of said semitransparent mirror plates being coated with a first mirror coating which ensures maximum possible passage of the light incident onto said rear side, and said front side of each of said semitransparent mirror plates being coated with a second coating which ensures maximum possible reflection of the light incident onto said front side.

21. The apparatus of claim 19, wherein said electronic control system further comprises a microprocessor and a feedback circuit between said output optical fiber and said microprocessor for sending a light signal from said output optical fiber to said microprocessor, said microprocessor being connected to said ratio control means for constantly maintaining said ratio at a selected value in response to said light signal.

22. The apparatus of claim 21, wherein said feedback circuit comprises a photodiode and an analog/digital converter connected in series in said feedback circuit.

23. The apparatus of claim 21, wherein said laser diode has switching means for operating said laser diode in a pulse mode for generating pulsed light signals, said ratio control means comprises:

a digital/analog converter and a power supply unit that are connected in series between said microprocessor and said laser diode;

a pulse width modulation unit connected to said laser diode via said switching means for controlling duration of said pulse and thus the level of optical power of light generated by said laser diode.

24. The apparatus of claim 21, wherein said laser diode assembly has a temperature control means connected to said microprocessor, and said housing has cooling means connected to said temperature control means.

25. The apparatus of claim 19, wherein said electronic control system further comprises a microprocessor and a feedback circuit between said output optical fiber and said microprocessor for sending a light signal from said output optical fiber to said microprocessor, said microprocessor being connected to said ratio control means for constantly maintaining said ratio at a selected value in response to said light signal.

26. The apparatus of claim 20, wherein said feedback circuit comprises a photodiode and an analog/digital converter connected in series in said feedback circuit.

27. The apparatus of claim 26, wherein said laser diode has switching means for operating said laser diode in a pulse mode for generating pulsed light signals, said ratio control means comprises:

a digital/analog converter and a current control unit that are connected in series between said microprocessor and said laser diode;

a pulse width modulation unit connected to said laser diode via said switching means for controlling duration of said pulse and thus the level of optical power of light generated by said laser diode.

28. The apparatus of claim 27, wherein said laser diode assembly has a temperature control means connected to said microprocessor, and said housing has cooling means connected to said temperature control means.

29. The apparatus of claim 25, wherein said three laser diodes are a red-light laser diode, a green light laser diode, and a blue light laser diode, said housings of said blue and green laser diodes consisting each of two parts, each of said two parts having said temperature control means and said cooling means for individual controlling temperature of said parts.

30. A method of color mixing in a laser diode system comprising the steps of:

generating laser beams of at least two different wavelengths by at least two single mode laser diode assemblies;

supplying the laser beam to at least two different wavelengths into at least two single mode fibers so that a laser beam of one of said two different wavelengths if supplied into a corresponding one of said single mode fibers;

combining the laser beams of different wavelengths outputted from said single mode fibers in a selected ratio;

supplying the combined laser beam into further single mode fiber; and

controlling by an electronic control system comprising at least current control means current in each of said at least two laser diode assemblies and light pulse modulation width control means for controlling duration of light pulse in each of said at least two laser diode assemblies, each said laser diode assembly having frequency stabilization means and linewidth narrowing means;

energizing said laser diode assemblies for emitting said laser beams of at least two different wavelengths toward said laser beam combining means;

stabilizing the frequency of the light of a selected wavelength with said frequency stabilization means;

narrowing the linewidth of the light spectrum produced by each of said laser beam assemblies;

obtaining light beams of colors close to perfect colors in each of said laser beam assemblies by simultaneously controlling light power with the use of said current control means and chromaticity of light with the use of said light pulse modulation control means; and

mixing said light beams of colors close to perfect colors with the use of said at least one laser beam combining means.

31. An apparatus of color mixing in a laser diode system comprising:

at least two single mode laser diode assemblies that generate laser beams at least two different wavelengths, at least two single mode fibers arranged so that said laser beams of at least two different wavelengths are supplied into said at least two single mode fibers so that a laser beam of one of said two different wavelengths is supplied into corresponding one of said at least two further fibers, at least one laser beam combining means for combining said laser beams of different wavelengths outputted from said at least two single mode fibers;

a further single mode fiber arranged so that the combined laser beams of different wavelengths outputted from said at least one laser beam combining means is supplied into said further single mode fiber means for controlling duration of light pulse in each of said at least two laser diode assemblies, each said laser diode assembly having frequency stabilization means and linewidth narrowing means, and an electronic control system comprising at least a current control means for controlling light power in each of said at least two laser diode assemblies, and light pulse modulation width control means for controlling chromaticity of light generated by each of said at least two laser diode assemblies.