Nortel Networks Corporation

Northern Telecom Limited

Bookham Technology Limited

Jin Hong

Hyung B Kim

Toshihiko Makino

Maurice M O'Sullivan

Rongqing Hui

Toshi Makino

A compact source capable of generating continuously tunable high frequency microwave radiation and short optical pulses in the picosecond/sub-picosecond range is invented. It includes a laser structure having two lasers formed on the same substrate which simultaneously operate at different longitudinal modes. Each laser has a complex coupled (gain-coupled or loss-coupled) grating which is formed by deep etching through a multi-quantum well structure, either of the active medium or of the additional lossy quantum-well layers, thus ensuring no substantial interaction between lasers. The lasers have a common active medium and shared optical path and provide mutual light injection into each other which results in generation of a beat signal at a difference frequency of two lasers. The beat frequency is defined by spacing between the laser modes and may be continuously tuned by current injection and/or temperature variation. Thus, the beat signal provides a continuously tunable microwave radiation. To form a train of short optical pulses, the beat signal is either further sent to a saturable absorber followed by a semiconductor optical amplifier, or sent directly into an optical compressor which includes a dispersion fiber. As a result, a duration of each impulse is compressed, and a train of short optical pulses is formed.

Generation of short optical pulses using strongly complex coupled DFB lasers

A two-dimensional matrix of complex coupled (gain or loss coupled) semiconductor DFB lasers is disclosed. The matrix includes several parallel branches of series lasers, each series having a plurality of lasers which are grown on the same wafer. The parallel branches are combined at either one end or both ends with either an integrated on-chip optical combiner or an external coupler to obtain a single optical output port. Each laser in the series comprises a multiple quantum well active region and a complex coupled grating having corrugations along a cavity length direction formed by periodic etching grooves through either the active region or the lossy QW region. The depth of etching is defined so as to provide a substantial insensitivity of each laser to the external feedback and random facet variations and to thereby ensure no substantial interaction between lasers in the series. Bragg wavelengths of lasers from different series interleave with each other or differ incrementally along a cavity length direction. The sub tuning wavelength range covered by one laser in the matrix falls outside of the stopbands of all other lasers which are not only in the same series but also physically close to the designated output port. The laser structure is capable of simultaneous multi-wavelength generation, and/or tunable selectable single wavelength operation, and/or reliable wavelength switching.

Strongly complex coupled DFB laser series

A one dimensional series of complex coupled (gain or loss coupled) DFB semiconductor lasers is disclosed. Each laser comprises a multiple quantum well active region and a complex coupled grating having corrugations along a cavity length direction formed by periodically etching grooves through the active region. The grating has a period comprising a first section and a second section, wherein substantially all quantum wells are etched away from the second section providing no substantial photon generation in the second section. The depth of etching is defined so as to provide a substantial insensitivity of each laser to the external feedback and random facet variations and to ensure no substantial interaction between lasers in the series. The lasers in the series may further comprise means for tuning laser wavelengths around corresponding lasing modes and/or means for switching between the lasing modes. The series of lasers is also capable of simultaneous multi-wavelength generation, with the number of generated wavelengths being equal to a number of lasers in the series excited above threshold levels.

Series of strongly complex coupled DFB lasers

A complex coupled (gain coupled or loss coupled) distributed feedback (DFB) semiconductor laser, having two sections axially distinct along a cavity length direction, and two excitation means for independent pumping of corresponding sections of the laser in a master and slave type of pumping control, is provided. An extended continuous wavelength tuning range of the laser is obtained by selectively activating a left Bragg mode or a right Bragg mode across the stop band of the laser as a dominant lasing mode by the master and slave type of current injection control into different sections of the laser to alternate gain coupling and loss coupling mechanisms of laser operation, and further tuning a wavelength around the activated Bragg mode. Methods of operating the laser, enhancing a tuning range, and fabricating thereof are provided.

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Nepean, Canada

Jin Hong