Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2002-04-23
2004-10-26
Wong, Don (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S020000, C372S043010, C372S044010, C372S045013, C372S046012, C372S049010, C372S049010, C372S049010, C372S099000, C372S102000
Reexamination Certificate
active
06810058
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to lasers, and in particular to high-power semiconductor lasers having transversal and longitudinal mode stability.
BACKGROUND OF THE INVENTION
Semiconductor lasers have great utility for a wide variety of applications, particularly optical communications. There are a variety of semiconductor laser structures (e.g., double heterostructure, buried heterostructure, ridge waveguide, etc.), as well as a variety of semiconductor laser geometries, such as distributed feedback or “DFB,” distributed Bragg reflector or “DBR,” grooved coupled-cavity or “GCC,” and “grating coupler sampled reflector” or “GCSR.” Fundamental to such lasers structures and geometries is that lasing is made possible by a solid-state gain medium being arranged within a resonant cavity.
Semiconductor lasers can lase in multiple cavity modes in both the transverse and longitudinal directions with frequencies where the gain medium has gain larger than the losses. A spectral filter that selects a single frequency (or narrow frequency band) can be used to ensure single-mode lasing. For example, in a DBR laser, the spectral filter includes a Bragg grating tuned to reflect the desired frequency. In a grating coupler sampled reflector (GCSR) laser, the spectral filter is made up of two elements: a sampled reflector that produces a series of reflector peaks, and a coupler that selects one of the peaks.
It is often preferred that a semiconductor laser provide the highest output power possible. However, this can result in high power densities in the gain medium that can induce non-linear effects (e.g., four-wave mixing), which in turn can induce lasing in longitudinal (i.e., spatial) modes other than the preferred longitudinal mode. This tends to limit the amount of power obtainable from the laser, particularly from a single transverse mode laser, which needs to have a small waveguide width to maintain transversal stability. The small waveguide width makes the power density high even for rather modest output powers, which induces the non-linear effects.
Accordingly, what is needed is a semiconductor laser that provides high output power in a single lateral mode without creating large power densities in the gain medium to ensure longitudinal and transverse mode stability of the laser.
SUMMARY OF THE INVENTION
A high-power semiconductor laser with a gain waveguide layer tailored to provide transverse and lateral mode stability is disclosed. Narrow sections of the gain waveguide layer provide transversal stability by filtering out higher-order modes, while the wide sections reduce the average four-wave mixing and the resultant longitudinal modal instabilities. Thus, the whole laser does not need to be narrow to avoid transversal instability.
In one example embodiment of the invention, the semiconductor laser includes a tuning section with a waveguide layer having a first width. The laser also includes a gain section with a gain waveguide layer. The gain waveguide layer has a front facet and a rear end that define a laser cavity. The gain section is coupled to the waveguide layer of the tuning section at the rear end to form a joint to the tuning section. The gain waveguide layer is formed on a mesa between a layer of n-doped indium phosphide (n-InP) and a layer of p-doped indium phosphide (p-InP). The gain waveguide layer has a varying power distribution, and the width of the gain waveguide layer varies in correspondence with the varying distribution. The gain waveguide layer matches the width of the tuning section waveguide layer at the joint to the tuning section, and has a select width at the front facet.
Another example embodiment of the invention is a laser module. The laser module includes a semiconductor laser having a tuning section coupled to a gain section. The tuning section includes a phase section and a reflector section, and a waveguide layer having a first width. The gain section has a gain layer with front facet and a rear end that define a laser cavity. The gain layer is coupled to the waveguide layer of the tuning section at the rear end to form a joint to the tuning section. In an example embodiment, the gain layer is formed on a mesa between a layer of n-doped indium phosphide (n-InP) and a layer of p-doped indium phosphide (p-InP). The gain layer supports a varying power distribution. The width of the gain waveguide layer varies in correspondence with the distribution of power, and matches the width of the tuning section waveguide layer at the joint to the tuning section. The module further includes first, second and third current sources electrically connected to the gain section, phase section and reflector section, respectively. A programmable controller is connected to the first, second and third current sources and is programmed to control the current sources to deliver select amounts of current to the respective sections of the laser.
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ADC Telecommunications Inc.
Flores Ruiz Delma R.
Schwegman Lundberg Woessner & Kluth P.A.
Wong Don
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