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(a) Diagram of a three-ridge surface-emitting DFB array. (b) Computed surface losses vs eigenfrequencies from three-dimensional finite-element method simulations on the same array. For the particular length of the phase sector used in the simulation, the in-phase mode (a) has the lowest surface loss. Adjacent mode (b) and out-of-phase mode (c) are also labeled. The insets show the far-field beam-patterns along the array direction for in-phase and out-of-phase modes. (c) Computed transverse magnetic fields for different spatial modes and their corresponding H-field magnitude diagrams along direction.
Pulsed curves from a single ridge DFB laser (solid line, near bottom) and a six-ridge DFB array (solid line, near top). The scaled curve of the single-ridge device (dotted line) is also shown. The of six-ridge device is as compared with of the single-ridge device. The emission spectra from the six-ridge device are single-mode at all biases. The scanning electron microscope (SEM) picture of a similar array device is also shown in the inset. The main laser ridges and the phase sectors have different bonding pads (labeled as A and B in the picture, respectively).
Far-field (20 cm) beam-patterns along array direction (solid circles) and simple point source simulation using measured emission frequencies and the distance between ridges (solid line) for different laser arrays. For single-ridge device, the simulated curve is the diffraction pattern of a single slit with the width of ridge. From top to bottom: single-ridge laser, a double-ridge array operated in the out-of-phase mode, another double-ridge array operated in the in-phase mode, and the six-ridge array (as shown in Fig. 2). The THz emission image from the six-ridge array taken by the microbolometer camera used in Ref. 19 is shown in the inset. The one-dimensional beam-pattern was measured along the dotted line.
Frequency shift of the emission from a seven-ridge array vs dc biases on the phase sectors. Pulsed measurements of main laser ridges (inset) and a closer look of the phase sectors (SEM picture).
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