Analog transmitter using an external cavity laser (ECL)

• US 20050220458A1
• Filed: 04/01/2005
• Published: 10/06/2005
• Est. Priority Date: 04/02/2004
• Status: Active Grant

• Current Assignee: Emcore Corporation
• Original Assignee: K2 Optronics, Inc. (Emcore Corporation)
• Inventors: Kupershmidt, Vladimir, Major, John, Siala, Sabeur
• Granted Patent: US 7,548,567 B2
• Time in Patent Office: Days
• US Class Current: 398/196
• CPC Class Codes: H01S 2301/03 Suppression of nonlinear conversion, e.g. specific design to suppress for example stimulated brillouin scattering [SBS], mainly in optical fibres in combination with multimode pumping
• CPC Class Codes: H01S 3/1055 one of the reflectors being constituted by a diffraction grating
• CPC Class Codes: H01S 3/1398 by using a supplementary modulation of the output
• CPC Class Codes: H01S 5/0064 Anti-reflection components, e.g. optical isolators
• CPC Class Codes: H01S 5/0078 for frequency filtering
• CPC Class Codes: H01S 5/02216 Butterfly-type, i.e. with electrode pins extending horizontally from the housings
• 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 5/028 Coatings ; Treatment of the laser facets, e.g. etching, passivation layers or reflecting layers
• CPC Class Codes: H01S 5/0427 for applying modulation to the laser
• CPC Class Codes: H01S 5/06804 by monitoring an external parameter, e.g. temperature
• CPC Class Codes: H01S 5/0683 by monitoring the optical output parameters
• CPC Class Codes: H01S 5/0687 Stabilising the frequency of the laser
• CPC Class Codes: H01S 5/141 using a wavelength selective device, e.g. a grating or etalon H01S5/146 takes precedence
• CPC Class Codes: H01S 5/147 having specially shaped fibre, e.g. lensed or tapered end portion
• CPC Class Codes: H01S 5/4012 Beam combining, e.g. by the use of fibres, gratings, polarisers, prisms
• CPC Class Codes: H01S 5/4062 with an external cavity or using internal filters, e.g. Talbot filters
• CPC Class Codes: H01S 5/4087 emitting more than one wavelength

Abstract

The present invention relates to an analog transmitter using an external cavity laser (ECL) in which specific characteristics of the ECL are enhanced and exploited to improve 2nd and 3rd order distortion while increasing the threshold for the occurrence of deleterious stimulated Brillouin scattering (SBS). The performance of the ECL shows a substantial reduction in distortion occurring over certain narrow ranges of operating temperatures. Optical, electronic, thermal and/or mechanical methods are described that cause this “distortion dip” to be moved to, or created at, stable regions of ECL operation, away from mode hops. Methods are also described that allow the distortion dip to be moved to, or created at, ECL operating regions in which sufficiently high chirp occurs, thereby reducing SBS. Transmitters and other devices employing these and related techniques are also described.

Claims

1. A temperature-controlled external cavity laser comprising:

a laser and one or more temperature controllers wherein the operating temperature of said laser is such as to cause said laser to operate in or near the temperature region of the distortion dip of said laser.

2. An external cavity laser as in claim 1 wherein said laser has a temperature region of operation having predetermined chirp approximately at said temperature region of said distortion dip.

3. An external cavity laser as in claim 2 wherein said predetermined chirp is application-specific.

4. An external cavity laser as in claim 1 wherein mode hops of said laser are absent from said temperature region of said distortion dip.

5. An external cavity laser as in claim 1 wherein the emission wavelength of said laser at said temperature region of said distortion dip substantially coincides with at least one wavelength of the standard grid for wavelength division multiplexed systems.

6. An external cavity laser as in claim 1 further comprising one or more temperature sensors and a feedback loop connecting said sensors and said temperature controllers such that the temperature of said laser substantially remains in said temperature region of said distortion dip.

7. An analog transmitter comprising a temperature-controlled external cavity laser as in claim 1.

12. An external cavity laser as in claim 1 further comprising predistortion circuitry acting on said laser to reduce second order harmonic distortion, third order harmonic distortion or both.

13. An external cavity laser as in claim 1 further comprising circuitry providing electronic dispersion compensation acting on said laser so as to reduce signal degradation caused by the propagation of the optical signal generated by said laser inside an optical fiber.

14. An external cavity laser as in claim 1 further comprising an in-line optical isolator to suppress reflected optical power from coupling back into the cavity of said laser.

8. A method of controlling the width of the temperature region over which a distortion dip occurs in a temperature-controlled external cavity laser, said laser comprising a light source within an optical feedback cavity wherein one end of said optical feedback cavity is a partially-reflective grating, said method comprising at least one of:

a) applying stress to said grating wherein said stress is thermal stress, mechanical stress or both; and

,

b) employing a non-chirped grating having transmission bandwidth in the range from approximately 100 picometers to approximately 400 picometers full-width at half-maximum as said partially-reflective grating; and

,

c) employing a chirped grating as said partially-reflective grating; and

,

d) employing a grating having a knee-shaped reflectivity profile as said partially-reflective grating.

9. A method of distortion locking a temperature-controlled external cavity laser comprising:

a) applying two radio frequency pilot signals having different frequencies and a fixed phase difference to said external cavity laser, thereby producing in the optical output of said laser a distortion signal at the frequency difference of said pilot signals; and

,

b) extracting phase information from said distortion signal; and

,

c) generating an error signal from said phase information; and

,

d) adjusting the temperature of said temperature-controlled external cavity laser so as to reduce said error signal to a value near zero.

10. A method of distortion locking a temperature-controlled external cavity laser comprising:

using a thermal electrical cooler and a temperature sensor forming a thermal control loop whereby the operating temperature of the external cavity of said external cavity laser is maintained substantially at a value whereby the output signal of said laser is locked simultaneously at a distortion dip and at an emission wavelength substantially at a wavelength of the standard grid for wavelength division multiplexed systems.

11. An application-specific analog transmitter for broadcast and narrowcast transmission, said transmitter operating at a wavelength substantially at a wavelength of the standard grid for wavelength division multiplexed systems, said transmitter comprising:

a temperature-controlled external cavity laser locked to simultaneously operate substantially at a distortion dip and at a pre-determined chirp.