Martyn J. Fice

TeraHertz Photonics for Wireless Communications

Optical fibre transmission has enabled greatly increased transmission rates with 10 Gb/s common in local area networks. End users find wireless access highly convenient for mobile communication. However, limited spectrum availability at microwave frequencies results in per-user transmission rates limited to much lower values, e.g., 500 Mb/s for 5-GHz band IEEE 802.11ac. Extending the high data-rate capacity of optical fiber transmission to wireless devices requires greatly increased carrier frequencies. This paper will describe how photonic techniques can enable ultrahigh capacity wireless data distribution and transmission using signals at millimeter-wave and TeraHertz (THz) frequencies.

The static and dynamic characteristics of single and multiple phase-shifted DFB laser structures

The influence of longitudinal mode spatial hole burning (LMSHB) on the performance of distributed feedback (DFB) laser structures is examined in detail. A comprehensive model has been used to interpret the experimental results and to construct a theoretical framework that was utilized to develop more advanced device designs. An increasing side mode intensity with output power, movement of the lasing mode relative to the stopband, and curvature of the light-current characteristic at low power can all be manifestations of the influence of LMSHB on the static device performance. The dynamic behavior can also be affected, with extended wavelength chirp and amplitude patterning effects on the timescale of the effective carrier recombination time being particularly important. >

Hybrid Integrated Optical Phase-Lock Loops for Photonic Terahertz Sources

We present the first hybrid-integrated optical phase-lock loop (OPLL) for use in high spectral purity photonic terahertz sources. We have achieved the necessary short loop delay to lock a 1-MHz linewidth slave laser by hybrid integration of the slave laser and photodetector on a silicon motherboard with silica optical waveguides and combining this with a custom-designed low-delay electronic loop filter circuit. The laser and photodetectors are InP-based and are flip chip bonded to silicon daughter boards, which are in turn attached to the motherboard. Delay between the slave laser and photodiode was approximately 50 ps. The heterodyne between slave and master sources has a linewidth of less than 1 kHz and achieved phase noise less than -80 dBc/Hz at an offset of 10 kHz. The slave laser can be offset from the master source by 2-7 GHz, using a microwave oscillator. This integrated OPLL circuit was used with an optical comb source and an injection-locked laser comb filter to generate high spectral purity signals at frequencies up to 300 GHz with linewidths <;1 kHz and powers of about -20 dBm, while the two integrated lasers could deliver a tunable heterodyne signal at frequencies up to 1.8 THz.

146-GHz millimeter-wave radio-over-fiber photonic wireless transmission system

The broadband penetration and continuing growth of Internet traffic among residential and business customers are driving the migration of todays end users network access from cable to optical fiber and superbroadband wireless systems The integration of optical and wireless systems operating at much higher carrier frequencies in the millimeter-wave (mm-wave) range is considered to be one of the most promising solutions for increasing the existing capacity and mobility, as well as decreasing the costs in next-generation optical access networks. In this paper, several key enabling technologies for very high throughput wireless-over-fiber networks are reviewed, including photonic mm-wave generation based on external modulation or nonlinear effects, spectrum-efficient multicarrier orthogonal frequency-division multiplexing and single-carrier multilevel signal modulation. We also demonstrated some applications in wireless-over-fiber trials using these enabling techniques. The results show that the integrated systems are practical solutions to offer very high throughput wireless to end users in optically enabled wireless access networks.We report the experimental implementation of a wireless transmission system with a 146-GHz carrier frequency which is generated by optical heterodyning the two modes from a monolithically integrated quantum dash dual-DFB source. The monolithic structure of the device and the inherent low noise characteristics of quantum dash gain material allow us to demonstrate the transmission of a 1 Gbps ON-OFF keyed data signal with the two wavelengths in a free-running state at 146-GHz carrier wave frequency. The tuning range of the device fully covers the W-band (75 - 110 GHz) and the F-band (90 - 140 GHz).

Homodyne Coherent Optical Receiver Using an Optical Injection Phase-Lock Loop

We describe the operating principle, practical implementation, and experimental evaluation of a synchronous homodyne coherent optical receiver based on an optical phase-locking scheme that combines optical injection locking of the semiconductor laser local oscillator (LO) with low-speed electronic feedback to give both a large locking bandwidth and a wide tracking range. We demonstrate phase-error variance as low as 0.002 rad2 in 10-GHz bandwidth for locking to a continuous-wave (CW) signal for a combined signal and LO linewidth of 1.5 MHz (full-width at half-maximum), and robust phase locking to a 10-Gb/s binary amplitude-shift-keyed (ASK) signal, enabling synchronous back-to-back demodulation of the signal with low bit error ratio (BER <; 10- 10) and improved performance compared to direct detection at low optical SNR (OSNR). By locking to a low-power CW pilot carrier in the polarization orthogonal to the data signal, demodulation of binary phase-shift-keyed (BPSK) data has been achieved, with the required OSNR at BER = 10-3 reduced by 3 dB compared to demodulation of ASK data under the same conditions. The OSNR penalty after transmission of the ASK and BPSK signals over 40 km of standard single-mode fiber was 1-2 dB at BER = 10-3, indicating that the chromatic dispersion sensitivity of the coherent receiver is similar to that for direct detection, and verifying that the scheme for locking to the orthogonal pilot is applicable to transmission systems, provided that optical polarization tracking is employed. In addition, we demonstrate frequency-selective operation of the coherent receiver, demultiplexing and demodulating one of a pair of equal power, 10 Gb/s, ASK channels separated by 17.5 GHz, with OSNR penalty at BER = 10- 3 of 1.5 dB compared to single-channel operation.

Microwave Photonic Integrated Circuits for Millimeter-Wave Wireless Communications

This paper describes the advantages that the introduction of photonic integration technologies can bring to the development of photonic-enabled wireless communications systems operating in the millimeter wave frequency range. We present two approaches for the development of dual wavelength sources for heterodyne-based millimeter wave generation realized using active/passive photonic integration technology. One approach integrates monolithically two distributed feedback semiconductor lasers along with semiconductor optical amplifiers, wavelength combiners, electro-optic modulators and broad bandwidth photodiodes. The other uses a generic photonic integration platform, developing narrow linewidth dual wavelength lasers based on arrayed waveguide gratings. Moreover, data transmission over a wireless link at a carrier wave frequency above 100 GHz is presented, in which the two lasers are free-running, and the modulation is directly applied to the single photonic chip without the requirement of any additional component.

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. To demonstrate how photonics-enabled THz systems can be realized, we review the performance of key components, show recent demonstrations of integrated platforms, and give examples of applications.

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. To the best of our knowledge, this is the narrowest RF linewidth generated from a free-running dual-wavelength semiconductor laser. The device is realized as a photonic integrated circuit using active-passive integration technology, and fabricated on a multiproject wafer run, constituting a novel approach for a compact, low-cost dual-wavelength heterodyne source.

High-speed photodiodes for InP-based photonic integrated circuits

We demonstrate the feasibility of monolithic integration of evanescently coupled Uni-Traveling Carrier Photodiodes (UTC-PDs) having a bandwidth exceeding 100 GHz with Multimode Interference (MMI) couplers. This platform is suitable for active-passive, butt-joint monolithic integration with various Multiple Quantum Well (MQW) devices for narrow linewidth millimeter-wave photomixing sources. The fabricated devices achieved a high 3-dB bandwidth of up to 110 GHz and a generated output power of more than 0 dBm (1 mW) at 120 GHz with a flat frequency response over the microwave F-band (90-140 GHz).

Integrated InP Heterodyne Millimeter Wave Transmitter

A monolithically integrated tunable heterodyne source designed for the generation and modulation of sub-terahertz signals is demonstrated. Distributed feedback lasers, semiconductor optical amplifier amplifiers, passive waveguides, beam combiners, electro-optic modulators, and high-speed photodetectors have been monolithically integrated on the same InP-based platform. Millimeter wave generation at up to 105 GHz based on heterodyning the optical tones from two integrated lasers in the integrated high bandwidth unitraveling-carrier photodetector has been demonstrated. This photonic integrated chip was used in a 100-Mb/s OOK wireless transmission experiment using the integrated amplitude modulator.