Phase locking of an Optical Injection Phase-lock Loop coherent receiver under emulated atmospheric fading conditions

An Optical Injection Phase-Lock Loop coherent receiver has been tested against various levels of deep atmospheric fading to experimentally evaluate its feasibility in a ground-to-satellite optical communications application

Low-power-consumption coherent receiver architecture for satellite optical links

As the demand for satellite data transmission increases, higher capacity optical links need to be developed to allow satellites to be connected directly to ground stations (GST). The advantages of Low Earth Orbit (LEO) direct-to-Earth links are smaller latency when compared to relay systems using Geostationary Orbit (GEO) satellites, i.e. LEO-to-GEO and GEO-to-GST, and an increased available bandwidth offered by the optical spectrum with respect to radio frequency (RF) which allows for much higher link capacity. The increase in data rate of optical satellite to ground links towards 100 Gbps will require implementing optical coherent transceivers with capability to compensate for Doppler shift and atmospheric channel impairments. An important figure of merit which needs to be carefully considered in a satellite system is the equipment power consumption. The power consumption of coherent receivers used for terrestrial applications is closely related to the bit rate, with a receiver back-end digital signal processing being responsible for the vast majority of the power consumed. In this paper we propose a hybrid approach to signal processing consisting of simplified digital and analogue elements allowing for significant power reduction. Moreover, one of the attractive aspects of the proposed approach is that it does not require an increased complexity for an increase in baud rate. It will be discussed that the analogue approach to the frequency and phase recovery would allow a saving of approximately 40% to 50% of power on the overall DSP block at baud rates between 10 Gbaud and 100 Gbaud

Integrated Semiconductor Laser Optical Phase Lock Loops

An Optical Phase Lock Loop (OPLL) is a feedback control system that allows the phase stabilization of a laser to a reference laser with absolute but adjustable frequency offset. Such phase and frequency locked optical oscillators are of great interest for sensing, spectroscopy, and optical communication applications, where coherent detection offers advantages of higher sensitivity and spectral efficiency than can be achieved with direct detection. As explained in this paper, the fundamental difficulty in realising an OPLL is related to the limitations on loop bandwidth and propagation delay as a function of laser linewidth. In particular, the relatively wide linewidth of semiconductor lasers requires short delay, which can only be achieved through shortening of the feedback path, which is greatly facilitated through photonic integration. This paper reviews the advances in the development of semiconductor laser-based OPLLs and describes how improvements in performance have been enabled by improvements in photonic integration technology. We also describe the first OPLL created using foundry fabricated photonic integrated circuits and off-the-shelf electronic components. Stable locking has been achieved for offset frequencies between 4 and 12 GHz with a heterodyne phase noise below -100 dBc/Hz at 10 kHz offset. This is the highest performance yet reported for a monolithically integrated OPLL and demonstrates the attractiveness of the foundry fabrication approach

Monolithically integrated optical phase lock loop with 1 THz tuneability

We have demonstrated a monolithically integrated optical phase lock loop based on a foundry fabricated photonic integrated circuit. The InP chip contains PIN photodiodes integrated with a 1.5 μm DBR laser which can be phase stabilised with respect to an external optical reference tone at all wavelengths throughout its 1 THz (8 nm) tuning range. The frequency offset between the two lasers can be set to any value between 4 GHz and 12 GHz. The phase noise of the heterodyne signal is also reported. Such an OPLL, together with an optical frequency comb and broad-bandwidth photodetector, could be used for high purity, tuneable mm-wave / THz signal generation

5 Gbps wireless transmission link with an optically pumped uni-traveling carrier photodiode mixer at the receiver

We report the first demonstration of a uni-traveling carrier photodiode (UTC-PD) used as a 5 Gbps wireless receiver. In this experiment, a 35.1 GHz carrier was electrically modulated with 5 Gbps non-return with zero on-off keying (NRZ–OOK) data and transmitted wirelessly over a distance of 1.3 m. At the receiver, a UTC-PD was used as an optically pumped mixer (OPM) to down-convert the received radio frequency (RF) signal to an intermediate frequency (IF) of 11.7 GHz, before it was down-converted to the baseband using an electronic mixer. The recovered data show a clear eye diagram, and a bit error rate (BER) of less than 10 −8 was measured. The conversion loss of the UTC-PD optoelectronic mixer has been measured at 22 dB. The frequency of the local oscillator (LO) used for the UTC-PD is defined by the frequency spacing between the two optical tones, which can be broadly tuneable offering the frequency agility of this photodiode-based receiver

Integrated Photonics for Wireless and Satellite Applications

The concept of using Photonic Integrated Circuits for generation of tunable mm-wave signals for wireless and satellite communication application is presented. The paper outlines the requirements for frequency stabilization and power consumption of semiconductor lasers when implemented in terrestrial wireless and satellite communication applications

InP Photonic Integrated Circuit for 6.7GHz Spaced Optical Frequency Comb Generator

We have demonstrated a novel approach to photonically integrated optical frequency comb generation on Indium Phosphide (InP) using generic foundry platforms. The optical comb utilized a recirculating loop technique to generate 59 comb lines (within a 20 dB power envelope) which are separated by 6.7 GHz frequency spacing. All comb lines exhibit strong phase coherence as characterized by low phase noise measurements of -105 dBc/Hz at 100 kHz. The choice of InP as an integration platform allowed for an immediate optical amplification of the modulated sideband tones. This approach reduced the requirement for external high-power RF amplifiers and therefore made the entire system more compact and power efficient. The amplified recirculating loop comb occupied 6 x 0.7 mm2 area of InP chip and consisted of electro-optic phase modulator (EOPM) and semiconductor optical amplifier (SOA) components embedded within a short (12 mm long) waveguide loop, such that the round-trip loop frequency corresponding to the loop optical length equated to 6.7 GHz. Modulation frequencies equal to the round-trip loop frequency were used to generate broad comb spans

Photonically-driven Schottky diode based 0.3 THz heterodyne receiver

Photonics-based technologies are key players in a number of emerging applications in the terahertz (THz) field. These solutions exploit the well-known advantages of optical devices, such as ultra-wide tuneability and direct integration with fiber networks. However, THz receivers are mainly implemented by fully electronic solutions, where Schottky barrier diodes (SBD) are the preferred option as detectors and mixers due to their excellent response within the THz range at room temperature, and technological maturity. Here, we demonstrate an SBD-based subharmonic mixer (SHM) at 300 GHz pumped with a photonic local oscillator. The Schottky mixer is a prototype designed and manufactured by ACST GmbH, operating at 270-320 GHz. The local oscillator is generated by photomixing on a high-frequency and high-power uni-travelling-carrier photodiode (UTC-PD), providing enough power to saturate conversion loss. Minimum single-side-band conversion loss of 14.4 dB and a peak dynamic range of 130 dB have been measured. Finally, as a proof of concept we realize an all-photonics-based 5 Gbps wireless bridge, utilizing the optically-pumped SBD mixer. With this work, we prove the feasibility of high-performance hybrid Schottky-photonic THz receivers, incorporating the best of both worlds

Demonstration of Photonic Integrated RAU for Millimetre-wave Gigabit Wireless Transmission

This work reports the performance of a wireless transmission link based on a radio access unit (RAU) implemented in photonic integrated circuit (PIC) form. The PIC contains a high speed photodiode for direct optical to RF conversion, monolithically integrated with a semiconductor laser, used as an optical local oscillator for up-conversion of the incoming 16-QAM-OFDM signal through heterodyning. Wireless transmission was demonstrated with a spectral efficiency as high as 3 bits/s/Hz at 60 GHz carrier and with 1.2 Gb/s transmission rate. Moreover, the RAU based on a broad bandwidth photodiode integrated with a tuneable laser allowed for a compact unit that could operate at carrier frequencies up to 100 GHz