Wavelength tunable laser

Abstract

A wavelength tunable laser comprising a laser diode and a closed external cavity formed by one or more optical resonators either horizontally or vertically coupled to adjacent waveguides. The optical resonator primarily functions as a wavelength selector and may be in the form of disk, ring or other closed cavity geometries. The emission from one end of the laser diode is coupled into the first waveguide using optical lens or butt-joint method and transferred to the second waveguide through evanescent coupling between the waveguides and optical resonator. A mirror system or high reflection coating at the end of the second waveguide reflects the light backwards into the system resulting in a closed optical cavity. Lasing can be achieved when the optical gain overcomes the optical loss in this closed cavity for a certain resonance wavelength which is tunable by changing the resonance condition of the optical resonator through reversed biased voltage or current injection. Multiple optical resonators may be used to reduce the lasing threshold and provide higher power output. With monolithic integration, more optical devices can be integrated with the tunable laser into the same substrate to produce optical devices that are capable of more complex functions, such as tunable transmitters or waveguide buses.

Description

FIELD OF THE INVENTION The present invention relates to the field of optical communications and more particularly, to a light source with tunable wavelength for use in optical communications systems. BACKGROUND OF THE INVENTION The rapid growth of Internet data traffic has driven current fiber optic networks to a new stage where much broader bandwidth and higher capacity are required. Dense wavelength division multiplexed (DWDM) systems with narrow channel spacing and low crosstalk have proven to be a promising solution. Generally in a DWDM system, each channel is represented by a fixed wavelength from a wavelength-fixed laser source and all the different channels are sent into the same optical fiber and transmitted to a receiver end. In order to fully implement a DWDM system with thousands of channels under this wavelength-fixed scheme, service providers in the telecom industry face huge inventory, complexity, and cost problems because of the large number of laser sources and acc...

AI Technical Summary

Benefits of technology

The present invention is directed to an improved tunable wavelength light source for use in optical communications systems that facilitates high speed, broad band wavelength tuning, is mechanically simple, scaleable and reliable, and facilitates monolithic integration of optical components. The novel wavelength tunable light source of the present invention preferably comprises a semiconductor laser diode optically coupled to a tunable wavelength selective external cavity. Preferably, the external cavity comprises a waveguide-coupled optical resonator that includes an optical resonator, or multiple optical resonators, either horizontally or vertically coupled to adjacent semiconductor waveguides. The optical reso

Problems solved by technology

In order to fully implement a DWDM system with thousands of channels under this wavelength-fixed scheme, service providers in the telecom industry face huge inventory, complexity, and cost problems because of the large number of laser sources and accessories needed, as well as the need for backup lasers and spare parts.

Although DFB lasers are well behaved and very reliable, they have the disadvantages of low output power and very limited wavelength tuning range (i.e., a range of about 5.0 nm).

DBR lasers have some advantages such as fast tuning speed, relatively large tuning range (about 40 nm), but suffer drawbacks of wavelength instability, broad

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