Spatial modal control of two-dimensional photonic crystal Bragg lasers

Abstract

We investigate the modal losses and field distributions of different order transverse modes supported by the photonic crystal Bragg structure using a transfer matrix method. We find that only the fundamental transverse mode has a single-lobed near field and far field and there exists a trade-off between ensuring lasing in the fundamental transverse mode and reducing the threshold. Employing these design principles, we experimentally demonstrate a large-area, edge-emitting, and single-mode semiconductor photonic crystal Bragg laser with a single-lobed, diffraction-limited far field under continuous wave condition. We have shown that the single-mode lasing is obtained by satisfying both the longitudinal and transverse Bragg conditions and the PC Bragg lasers are efficient for practical applications. In [9], we showed the laser oscillated in a true single mode by using an optical heterodyne method, and the laser output power was about 5 mW with an injected current of 70 mA and the slope efficiency was about 0.15 W / A. However, the far-field profile shown in [8] has two side peaks, which are detrimental for most applications since the side peaks in the far field reduce the coupling efficiency to optical fibers and planar waveguides.In this Letter, we show that the side peaks inside the PC Bragg laser far field are associated with highorder transverse Bragg resonance (TBR) modes. We first use a transfer matrix model [10,11] to compare different order transverse modes of the PC Bragg laser and find that only the first-order (fundamental) TBR mode has a single-lobed near field and thus a single-lobed far field. We show that the transverse coupling coefficient determines the intermodal discrimination between the fundamental and high-order TBR modes and there exists a trade-off between ensuring lasing in the fundamental TBR mode and reducing the threshold. We fabricate the PC Bragg lasers with different transverse coupling coefficients by changing the etch depths, and we measure the thresholds, spectra, near fields, and far fields of these lasers. Both fundamental and high-order TBR lasing modes are obtained depending on the transverse coupling coefficient. The experimental results agree well with the theoretical predictions.Figure 1(a) shows a schematic diagram of our PC Bragg laser. The photonic crystal consists of a rectangular lattice array of polymer-filled holes each with a radius of 100 nm on the wafer surface. The transverse and longitudinal lattice constants are a and b, respectively. The cleaved facet is titled relative to the transverse lattice direction by an angle tilt . We use a first-order Bragg reflection ͑l =1͒ for the transverse direction with a lattice constant of a =1 m and a second-order Bragg reflection ͑j =2͒ for the longitudinal direction with a lattice constant of b = 470 nm. The design corresponds to a resonance wavelength of 1483 nm. (The effective index n eff is estimated to be 3.24.) The metal contact width is about 100 m and the facet tilt angle is 13.2°. Detailed fabrication procedures can...

Mode Selectivity in Bragg Reflection Waveguide Lasers

“…These peaks do not correspond to the different longitudinal modes due to their large wavelength separation. According to the field distribution of BRW modes [1], [15], we can recognize that the first lasing mode (976 nm) is the fundamental mode, i.e., TE mode. The two lobes shown in the NFP measured at 100 mA confirm that the mode at 984 nm is the TE mode.…”

“…In other words, the lasing of mode 992 nm does not change the shape of NFP significantly. This suggests that the third lasing mode is likely to be TE , the reason being that the field distribution of the TE mode is similar to that of TE plus TE [15]. The net modal gains are gotten from SES using Hakki-Paoli method [16] and plotted in Fig.…”

Mode stabilization of a laterally structured broad area diode laser using an external volume Bragg grating

“…Furthermore, mode selective elements can be implemented on the chip itself like lateral tapered structures for beam preserving power amplification [8] and Bragg gratings for longitudinal mode selection [9]. Another way to achieve spatial mode selection is transverse Bragg resonance (TBR) [10][11][12]. The internal TBR grating of the BAL defines a low loss transversal mode at a specific angle of incidence matching a certain wavelength.…”