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Low-noise high-performance current controllers for quantum cascade lasers
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Image of FIG. 1.
FIG. 1.

Block diagram of the PNNL current controllers. The shaded items are the focus of this article.

Image of FIG. 2.
FIG. 2.

Schematic showing voltage source, voltage noise source (NS), QCL, and simplified classic opamp-based current regulator.

Image of FIG. 3.
FIG. 3.

Plot of magnitudes of open loop gain G(s), suppression S(s), and noise functions N(s) and M(s) for current regulator using values typical of PNNL controllers.

Image of FIG. 4.
FIG. 4.

Power filters for PNNL current controllers. The zeners are 1N5242 500 mW; all other diodes are 1N4004 or equivalent. Electrolytic capacitors marked with an asterisk rather than a plus sign are tantalums.

Image of FIG. 5.
FIG. 5.

Noise performance of positive rail power conditioning chain in QCL7. Current controller loaded at 500 mA, positive rail current 230 mA.

Image of FIG. 6.
FIG. 6.

Schematic of a regulator block typical of the PNNL controllers. The sense resistor is 5 Ω for the QCL5 and 2.5 Ω for the QCL7. The series pass transistor Q is an IRFZ14 for the QCL5 and an IRFZ24 for the QCL7. Inductor L is typically 100 μH. Amplifier A r is an AD743 in a non-inverting unity gain configuration. Quantities starting with δ represent voltage and current noise, and are discussed in Sec. VI.

Image of FIG. 7.
FIG. 7.

Current noise spectral density traces for the QCL5 and QCL7 operating at 500 mA. The measurement noise floor is also shown. The peaking at 1 MHz and subsequent roll-off is the response of the SR560 voltage amplifier.

Image of FIG. 8.
FIG. 8.

Response of QCL5 to 100 kHz square wave.


Generic image for table
Table I.

Significant noise terms and their output contributions for the QCL5 operating at 500 mA, and internal case temperature T = 313°K.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Low-noise high-performance current controllers for quantum cascade lasers