Analog external cavity laser

Abstract

The present invention relates to the analog external cavity lasers (ECLs) including designs, materials, methods of manufacturing and methods of use for such ECLs and packages for such ECLS. Numerous criteria are presented that lead to improved cost / performance for ECLs and for systems incorporating such ECLs.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority from provisional patent application Ser. No. 60 / 558,927 filed Apr. 2, 2004, and provisional patent application Ser. No. 60 / 562,762, filed Apr. 16, 2004, and provisional patent application Ser. No. 60 / 638,679 filed Dec. 23, 2004, pursuant to one or more of 35 U.S.C. § 119, § 120, § 365. The entire contents of all cited provisional patent applications are incorporated herein by reference for all purposes.BACKGROUND OF THE INVENTION [0002] 1. Field of Invention [0003] This invention relates generally to the field of laser light sources and, more particularly, to external cavity laser light sources. [0004] 2. Description of the Prior Art [0005] Directly modulated distributed feedback (DFB) laser diodes are widely used in many applications, including the transmission of multiple channels of analog modulated signals as typically used for analog broadcast, digital simulcast and narrowcast (QAM-format) in cable ...

AI Technical Summary

Benefits of technology

"The present invention is about improving the cost-performance ratio of direct-modulated analog external cavity lasers (ECLs) for transmitting analog and semi-analog signals, particularly for broadcast, digital simulcast, and narrowcast applications. The invention achieves this by controlling chirp, low intermodulation distortions, and low Relative Intensity Noise (RIN) in the 1550 wavelength range. The invention also includes packaging design and methods for increasing the coupling efficiency between the fiber Bragg grating element and the FP chip, reducing unwanted reflectivity, and suppressing reflected optical energy from coupling back into the cavity. The invention also enhances the use of the distortion dip in analog ECLs, suppresses Stimulated Brillouin Scattering (SBS), and designs and implements techniques for tuning and stabilizing the emission wavelength of the analog ECL's output power, reducing frequency tilt, and incorporating known predistortion and Electronic Dispersion Compensation (EDC) technologies to further improve the distortion and reach performance of transmitters utilizing these analog ECLs. The invention achieves these technical effects by incorporating various optical fibers and utilizing Bragg gratings created inside the cores of these fibers."

Problems solved by technology

However, widespread deployment of 1550 nm networks for CATV and wireless distribution has been hampered by several factors, including the chirp produced by direct-modulated DFB lasers.

In addition, the deployment of new and more efficient modulation schemes has been delayed due to as yet unmet requirements for higher performing, lower cost optical transmitters.

However, utilizing QPSK techniques typically requires low cost laser sources having narrower linewidth than typical DFBs that are currently commercially available (see, for example, S. Norimatsu, et al.

Among the major barriers to the wider use of direct-modulated DFBs around the 1550 nm band is the high chirp and the relatively high intrinsic distortion of the solitary DFB laser.

Another limitation of direct-modulated DFBs operating near the 1550 nm band is the relatively large linewidth, of the order of 1 MHz.

Such effects lead to limited transmission performance under high channel loadings and for longer transmission distances.

Multiple approaches have been proposed to address these issues, but they generally have technical and / or cost drawbacks.

These solutions include (a) The use of dispersion compensators, which are usually expensive, complex, and cumbersome, typically requiring customization of each fiber span.

This combination can exhibit practically zero chirp in some circumstances, but the high cost makes this solution over-engineered and too expensive for all but a few specialized, typically low volume, applications.

(c) The use of electro-absorption modulated lasers (EMLs) which suffer from narrow operating margins, the requirement for complex predistortion circuitry to reduce the relatively large intrinsic harmonic distortion, and the low carrier-to-noise ratio (CNR) (due to the relatively low optical output power).

The main drawbacks of such techniques include the added expense and the need for customization in manufacturing to accommodate different levels of distortion correction.

However, this method has had very limited commercial success because of its high cost and complexity (for example, see H. Sung et al., “Dependence of Semiconductor Laser Intermodulation Distortions on Fiber Length and its Reduction by Optical Injection Locking,” Conference Proceedings, Paper WE2 10, p.

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