SOA-Integrated Dual-Mode Laser and a PIN-Photodiode for Compact CW Terahertz System

Abstract

We designed and fabricated a semiconductor optical amplifier‐integrated dual‐mode laser (SOA‐DML) as a compact and widely tunable continuous‐wave terahertz (CW THz) beat source, and a pin‐photodiode (pin‐PD) integrated with a log‐periodic planar antenna as a CW THz emitter. The SOA‐DML chip consists of two distributed feedback lasers, a phase section for a tunable beat source, an amplifier, and a tapered spot‐size converter for high output power and fiber‐coupling efficiency. The SOA‐DML module exhibits an output power of more than 15 dBm and clear four‐wave mixing throughout the entire tuning range. Using integrated micro‐heaters, we were able to tune the optical beat frequency from 380 GHz to 1,120 GHz. In addition, the effect of benzocyclobutene polymer in the antenna design of a pin‐PD was considered. Furthermore, a dual active photodiode (PD) for high output power was designed, resulting in a 1.7‐fold increase in efficiency compared with a single active PD at 220 GHz. Finally, herein we successfully show the feasibility of the CW THz system by demonstrating THz frequency‐domain spectroscopy of an α‐lactose pellet using the modularized SOA‐DML and a PD emitter.

Split‐step time‐domain modeling of dual‐mode DFB laser diode for terahertz wave generation

“…Power spectra of the generated THz wave from the dual‐mode DFB‐LD is also shown in Figure for various tuning conditions. The simulation results illustrate that the THz wave generation from 163 to 1,378 GHz is possible by proper thermo‐optic tuning and initial detuning combination, which is qualitatively analogous to the experimental results . In the above simulations, it is assumed that the facet of the dual‐mode DFB LD is perfectly anti‐reflection coated.…”

“…The simulation results illustrate that the THz wave generation from 163 to 1,378 GHz is possible by proper thermo-optic tuning and initial detuning combination, which is qualitatively analogous to the experimental results. 16 In the above simulations, it is assumed that the facet of the dual-mode DFB LD is perfectly anti-reflection coated. The variation of dual-mode lasing characteristics versus the facet reflectivity increase is shown in Figure 5.…”

“…16 The dual-mode LD is composed of two DFB LDs which are separated by a phase section, which can be used to suppress the compound cavity modes. 16 The cavity losses of the compound cavity modes can be increased by a reverse bias onto the phase section. With the aid of the micro-heaters on top of the DFB LDs the wavelength of each DFB LD can be tuned independently.…”

“…The device configuration of the dual‐mode DFB LD is shown in Figure . The dual‐mode LD is composed of two DFB LDs which are separated by a phase section, which can be used to suppress the compound cavity modes . The cavity losses of the compound cavity modes can be increased by a reverse bias onto the phase section.…”

Sub‐THz wave generation based on a dual wavelength microsquare laser

“…For example, two singlemode lasers such as distributed feedback lasers are used together with optical amplifiers and a high-speed photodiode mixer, and the laser outputs with two different wavelengths are fed into a mixer photodiode for extracting the beat signal with a difference frequency as THz wave output. This approach has been adopted in prior works using hybrid [3][4][5][6][7] and monolithic integration techniques [8,9]. However, this kind of device has a drawback of complicated structure requiring two lasers and therefore the total fabrication process becomes difficult and costly.…”