Abstract
We report a monolithic photonic integrated circuit (PIC) for THz communication applications. The PIC generates up to 4 optical frequency lines which can be mixed in a separate device to generate THz radiation, and each of the optical lines can be modulated individually to encode data. Physically, the PIC comprises an array of wavelength tunable distributed feedback lasers each with its own electro-absorption modulator. The lasers are designed with a long cavity to operate with a narrow linewidth, typically <4 MHz. The light from the lasers is coupled via an multimode interference (MMI) coupler into a semiconductor optical amplifier (SOA). By appropriate selection and biasing of pairs of lasers, the optical beat signal can be tuned continuously over the range from 0.254 THz to 2.723 THz. The EAM of each channel enables signal leveling balanced between the lasers and realizing data encoding, currently at data rates up to 6.5 Gb/s. The PIC is fabricated using regrowth-free techniques, making it economic for volume applications, such for use in data centers. The PIC also has a degree of redundancy, making it suitable for applications, such as inter-satellite communications, where high reliability is mandatory.
Highlights
A PIC-based optoelectronic multi-frequency pumping source for THz communication systems has been demonstrated for the first time
The PICs were fabricated using simple side-wall gratings and QWI technologies, which eliminate the multiple stages of crystal regrowth required in traditional approaches and so reduce cost
Along with developments in THz antennas, this PIC-based pumping source will be a significant enabler of THz wireless systems in the near future
Summary
An optical micrograph and the dimensions of the device are shown in Fig. 1(a), the fabrication processes being similar to those described in ref. The inherently wide gain spectrum exhibited by strained MQWs structures (~50 nm 3-dB gain bandwidth)[21] allows the DFB laser wavelengths to be detuned to longer wavelengths than the excitonic absorption bandedge of the EAMs, allowing flexibility in the design of insertion losses and the modulation depths. By biasing EAMs at property voltages, the intensity of each laser could be controlled individually, the intensity difference between the two lasers can be kept less than 2 dB At this stage, our emphasis is to analyze the tuning and redundancy frequency properties of the THz channels from our InP-PIC. The higher reverse bias voltages and reduced extinction ratios are the result of the relative differences between the EAM bandgap energy (which is the same for all of the devices) and the photon energy from the lasers (which is determined by the respective periods of the Bragg gratings). Along with developments in THz antennas, this PIC-based pumping source will be a significant enabler of THz wireless systems in the near future
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