InP integrated optical frequency comb generator using an amplified recirculating loop.

A novel realisation of photonically integrated optical frequency comb generation is demonstrated on indium phosphide (InP) using a generic foundry platform. The architecture, based on the amplified recirculating loop technique, consists of cascaded electro-optic phase modulators embedded within a short waveguide loop. While an injected continuous wave laser signal is recirculated by the loop, the modulators are driven with a modulation frequency corresponding to the round-trip loop length frequency.

High performance waveguide uni-travelling carrier photodiode grown by solid source molecular beam epitaxy.

The first waveguide coupled phosphide-based UTC photodiodes grown by Solid Source Molecular Beam Epitaxy (SSMBE) are reported in this paper. Metal Organic Vapour Phase Epitaxy (MOVPE) and Gas Source MBE (GSMBE) have long been the predominant growth techniques for the production of high quality InGaAsP materials. The use of SSMBE overcomes the major issue associated with the unintentional diffusion of zinc in MOVPE and gives the benefit of the superior control provided by MBE growth techniques without the costs and the risks of handling toxic gases of GSMBE.

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.

Foundry fabricated photonic integrated circuit optical phase lock loop.

This paper describes the first foundry-based InP photonic integrated circuit (PIC) designed to work within a heterodyne optical phase locked loop (OPLL). The PIC and an external electronic circuit were used to phase-lock a single-line semiconductor laser diode to an incoming reference laser, with tuneable frequency offset from 4 GHz to 12 GHz. The PIC contains 33 active and passive components monolithically integrated on a single chip, fully demonstrating the capability of a generic foundry PIC fabrication model.

Terahertz generation mechanism in nano-grating electrode photomixers on Fe-doped InGaAsP.

We report the generation mechanism associated with nano-grating electrode photomixers fabricated on Fe-doped InGaAsP substrates. Two different emitter designs incorporating nano-gratings coupled to the same broadband antenna were characterized in a continuous-wave terahertz (THz) frequency system employing telecommunications wavelength lasers for generation and coherent detection. The current-voltage characteristics and THz emission bandwidth of the emitters is compared for different bias polarities and optical polarisations.

Modelling and measurement of the absolute level of power radiated by antenna integrated THz UTC photodiodes.

We determine the output impedance of uni-travelling carrier (UTC) photodiodes at frequencies up to 400 GHz by performing, for the first time, 3D full-wave modelling of detailed UTC photodiode structures. In addition, we demonstrate the importance of the UTC impedance evaluation, by using it in the prediction of the absolute power radiated by an antenna integrated UTC, over a broad frequency range and confirming the predictions by experimental measurements up to 185 GHz. This is done by means of 3D full-wave modelling and is only possible since the source (UTC) to antenna impedance match is properly taken into account.

Accurate equivalent circuit model for millimetre-wave UTC photodiodes.

We present a comprehensive study of uni-travelling carrier photodiode impedance and frequency photo-response supported by measurements up to 110 GHz. The results of this investigation provide valuable new information for the optimisation of the coupling efficiency between UTC-PDs and THz antennas. We show that the measured impedance cannot be explained employing the standard junction-capacitance/series-resistance concept and propose a new model for the observed effects, which exhibits good agreement with the experimental data.

Optical injection locking to optical frequency combs for superchannel coherent detection.

Optical injection locking characteristics of a distributed feedback laser are experimentally investigated for multiple-wavelength injection. Using a three-wavelength source generated by intensity modulation as the injected signal, it was found that the presence of adjacent lines could cause disturbance to the locking if a minimum guard band between the respective locking limits of two adjacent lines was not observed. With a 21-line comb with 20 GHz line spacing as the injected signal, the injection locking range was observed to become asymmetrical in relation to the laser free-running frequency under high-power injection conditions and was found to be dependent on whether the laser was locked to lines located at centre and or edges of the comb.

Optical injection locking of monolithically integrated photonic source for generation of high purity signals above 100 GHz.

A monolithically integrated photonic source for tuneable mm-wave signal generation has been fabricated. The source consists of 14 active components, i.e.

Photonic generation for multichannel THz wireless communication.

We experimentally demonstrate photonic generation of a multichannel THz wireless signal at carrier frequency 200 GHz, with data rate up to 75 Gbps in QPSK modulation format, using an optical heterodyne technique and digital coherent detection. BER measurements were carried out for three subcarriers each modulated with 5 Gbaud QPSK or for two subcarriers modulated with 10 Gbaud QPSK, giving a total speed of 30 Gbps or 40 Gbps, respectively. The system evaluation was also performed with three subcarriers modulated with 12.

Coherent terahertz photonics.

We present a review of recent developments in THz coherent systems based on photonic local oscillators. We show that such techniques can enable the creation of highly coherent, thus highly sensitive, systems for frequencies ranging from 100 GHz to 5 THz, within an energy efficient integrated platform. We suggest that such systems could enable the THz spectrum to realize its full applications potential.

InGaAsP-based uni-travelling carrier photodiode structure grown by solid source molecular beam epitaxy.

We report the first InGaAsP-based uni-travelling carrier photodiode structure grown by Solid Source Molecular Beam Epitaxy; the material contains layers of InGaAsP as thick as 300 nm and a 120 nm thick InGaAs absorber. Large area vertically illuminated test devices have been fabricated and characterised; the devices exhibited 0.1 A/W responsivity at 1550 nm, 12.

95 GHz millimeter wave signal generation using an arrayed waveguide grating dual wavelength semiconductor laser.

We report the generation of a 95 GHz carrier frequency by optical heterodyning of two wavelengths from adjacent channels from an arrayed waveguide grating-based multiwavelength laser. The extended cavity structure of the device provides low phase noise and narrow optical linewidth, further enhanced by the intracavity filter effect of the arrayed waveguide grating. We demonstrate that the generated RF beat note, at 95 GHz, has a -3  dB linewidth of 250 kHz.

Modelling of surface waves on a THz antenna detected by a near-field probe.

We have modelled the experimental system based on the sub-wavelength aperture probe employed in our previous work for terahertz (THz) surface plasmon wave imaging on a bowtie antenna. For the first time we demonstrate the accuracy of the proposed interpretation of the images mapped by the probe. The very good agreement between numerical and experimental results proves that the physical quantity detected by the probe is the spatial derivative of the electric field normal component.

Terahertz probe for spectroscopy of sub-wavelength objects.

A system of two probes is designed for terahertz (THz) time-domain spectroscopy of sub-wavelength size objects. A twin-needle probe confines broadband THz pulses spatially by means of surface plasmon waves to a sub-wavelength spot smaller than 10 microns. The confined pulses are detected within the near-field zone of the twin-needle probe by a sub-wavelength aperture probe.

Monolithically integrated heterodyne optical phase-lock loop with RF XOR phase detector.

We present results for an heterodyne optical phase-lock loop (OPLL), monolithically integrated on InP with external phase detector and loop filter, which phase locks the integrated laser to an external source, for offset frequencies tuneable between 0.6 GHz and 6.1 GHz.

Optoelectronic detection of millimetre-wave signals with travelling-wave uni-travelling carrier photodiodes.

Optically pumped mixing in travelling-wave uni-travelling carrier photodiodes is proposed as a novel technique for detecting millimetre-wave signals. An experimental demonstration was performed at a frequency of 100 GHz. From DC measurements, an increase in the responsivity was found at high levels of optical power.

Effective homodyne optical phase locking to PSK signal by means of 8b10b line coding.

We demonstrate a novel technique that allows effective homodyne optical phase locking to a phase shift keying (PSK) signal with a residual carrier. We exploit 8b10b coding of the signal in order to reduce its low frequency spectral content, suppressing the data-to-phase crosstalk effect. In a transmission experiment on a 10 Gb/s binary PSK signal (8 Gb/s before coding), we achieved transmission over 215 km of dispersion-compensated, installed single-mode fibre, with no penalty compared to back-to-back at a bit error ratio of 10(-3).

Traveling-wave Uni-Traveling Carrier photodiodes for continuous wave THz generation.

The design, experimental evaluation and performance of a Traveling-Wave Uni-Traveling Carrier photodiode for Terahertz generation are described and its advantages in terms of frequency response are demonstrated. The device delivered 148 microW at 457 GHz, 24 microW at 914 GHz when integrated with resonant antennas and 105 microW at 255 GHz, 30 microW at 408 GHz, 16 microW at 510 GHz and 10 microW at 612 GHz. Record levels of Terahertz figure of merit (PTHz/Popt2 in W(-1)) were achieved ranging from 1 W(-1) at 110 GHz to 0.