A master oscillator-power amplifier (MOPA) device, comprising: a monolithic MOPA chip comprising a semiconductor substrate and at least one MOPA structure formed in or upon the semiconductor substrate, the at least one MOPA structure comprising: a master oscillator section comprising a single spatial mode DFB laser structure for generating laser light, the single spatial mode DFB laser structure comprising a Bragg grating for providing a distributed optical feedback therein and for defining a laser wavelength; and, a power amplifier section comprising a semiconductor amplifier structure optically following the single spatial mode DFB laser structure and integrally coupled thereto for amplifying the laser light and for providing output light in a single spatial mode; wherein the MO section comprises a first electrical contact and the PA section comprises a second electrical contact, wherein the first and second electrical contacts (111, 112) are electrically separate from each other for separately pumping the MO and PA sections (120, 130) of the MOPA device with first and second electrical currents; and, a MOPA driver (200, 420, 520) electrically connected to the first and second electrical contacts (111, 112) for driving the first electrical current through the MO section and the second electrical current through the PA section to initiate lasing in the MO section at the laser wavelength while providing optical amplification in the PA section, wherein the MOPA driver (200, 420, 520) comprises a controller configured to vary simultaneously the first and second electrical currents in opposite directions so that when the second electrical current through the PA section is increased for increasing an optical power of the output light, the first electrical current through the MO section is decreased so as to maintain a laser wavelength constant. a monolithic MOPA chip comprising a semiconductor substrate and at least one MOPA structure formed in or upon the semiconductor substrate, the at least one MOPA structure comprising: a master oscillator section comprising a single spatial mode DFB laser structure for generating laser light, the single spatial mode DFB laser structure comprising a Bragg grating for providing a distributed optical feedback therein and for defining a laser wavelength; and, a power amplifier section comprising a semiconductor amplifier structure optically following the single spatial mode DFB laser structure and integrally coupled thereto for amplifying the laser light and for providing output light in a single spatial mode; wherein the MO section comprises a first electrical contact and the PA section comprises a second electrical contact, wherein the first and second electrical contacts (111, 112) are electrically separate from each other for separately pumping the MO and PA sections (120, 130) of the MOPA device with first and second electrical currents; and, a master oscillator section comprising a single spatial mode DFB laser structure for generating laser light, the single spatial mode DFB laser structure comprising a Bragg grating for providing a distributed optical feedback therein and for defining a laser wavelength; and, a power amplifier section comprising a semiconductor amplifier structure optically following the single spatial mode DFB laser structure and integrally coupled thereto for amplifying the laser light and for providing output light in a single spatial mode; wherein the MO section comprises a first electrical contact and the PA section comprises a second electrical contact, wherein the first and second electrical contacts (111, 112) are electrically separate from each other for separately pumping the MO and PA sections (120, 130) of the MOPA device with first and second electrical currents; and, a MOPA driver (200, 420, 520) electrically connected to the first and second electrical contacts (111, 112) for driving the first electrical current through the MO section and the second electrical current through the PA section to initiate lasing in the MO section at the laser wavelength while providing optical amplification in the PA section, wherein the MOPA driver (200, 420, 520) comprises a controller configured to vary simultaneously the first and second electrical currents in opposite directions so that when the second electrical current through the PA section is increased for increasing an optical power of the output light, the first electrical current through the MO section is decreased so as to maintain a laser wavelength constant.