Haymen Shams

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.

100 Gb/s Multicarrier THz Wireless Transmission System With High Frequency Stability Based on A Gain-Switched Laser Comb Source

We propose and experimentally demonstrate a photonic multichannel terahertz (THz) wireless system with up to four optical subcarriers and total capacity as high as 100 Gb/s by employing an externally injected gain-switched laser comb source. Highly coherent multiple optical carriers with different spacing are produced using the gain switching technique. Single- and multichannel Terahertz (THz) wireless signals are generated using heterodyne mixing of modulated single or multiple carriers with one unmodulated optical tone spaced by about 200 GHz. The frequency stability and the phase noise of the gain switched comb laser are evaluated against free-running lasers. Wireless transmission is demonstrated for single and three optical subcarriers modulated with 8 or 10 GBd quadrature phase-shift keying (QPSK) (48 or 60 Gb/s, respectively) or for four optical subcarriers modulated with 12.5 GBd QPSK (100 Gb/s). The system performance was evaluated for single- and multicarrier wireless THz transmissions at around 200 GHz, with and without 40 km fiber transmission. The system is also modeled to study the effect of the cross talk between neighboring subcarriers for correlated and decorrelated data. This system reduces digital signal processing requirements due to the high-frequency stability of the gain-switched comb source, increases the overall transmission rate, and relaxes the optoelectronic bandwidth requirements.

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 12.5 Gbaud QPSK (75 Gbps total) without and with 40 km fibre transmission. The proposed system enhances the capacity of high-speed THz wireless transmission by using spectrally efficient modulated subcarriers spaced at the baud rate. This approach increases the overall transmission capacity and reduces the bandwidth requirement for electronic devices.

Electro-Optical Generation and Distribution of Ultrawideband Signals Based on the Gain Switching Technique

We demonstrate and compare the generation and distribution of pulse position modulation (PPM) ultrawideband (UWB) signals, based on two different techniques using a gain-switched laser (GSL). One uses a GSL followed by two external modulators, while the second technique employs two laser diodes gain switched (GS) using a combined signal from a pattern generator and an RF signal generator. Bit-error-rate (BER) measurements and eye diagrams for UWB signals have been measured experimentally by using the different GS transmitter configurations and various fiber transmission distances. The simulation of both systems also has been carried out to verify our obtained results, which show the suitability of employing gain switching in a UWB over fiber (UWBoF) system to develop a reliable, simple, and low-cost technique for distributing the impulse-radio UWB (IR-UWB) pulses to the receiver destination.

An IR-UWB Photonic Distribution System

Experimental results are presented for a novel distribution system for an impulse radio ultra-wideband (UWB) radio signals employing a gain-switched laser. The pulse position modulated short optical pulses with a bit rate of 1.25 Gb/s are transmitted over fiber to a remote antenna unit, where the signal is converted to the electrical domain and undergoes spectral shaping to remove unwanted components according to UWB requirements. An experimental radio terminal has also been constructed to enable bit-error-rate measurements to be carried out. These experiments show that the optical distribution system will be capable of supporting the radio part of the system.

Phase Noise Investigation of Multicarrier Sub-THz Wireless Transmission System Based on an Injection-Locked Gain-Switched Laser

In this paper, we propose a multi-carrier THz wireless communication system using an injection-locked gain-switched laser as an optical comb source. The phase noise of the 192 GHz signal resulting from the beating of two optical comb lines is theoretically analyzed and experimentally examined. Moreover, a three channel, 10 Gbaud QPSK THz signal is generated, and transmission over 40 km standard single mode fiber (SSMF) is experimentally demonstrated.

Demonstration and optimization of an optical impulse radio ultrawideband distribution system using a gain-switched laser transmitter

What we believe to be a novel system for the distribution of high-definition video streams in a residential environment is demonstrated. The system utilizes impulse radio ultrawideband (IR-UWB) technology integrated with a fiber-based distribution network. The pulses are directly generated in the optical domain, and the receiver is implemented with a carrier recovery system for the demodulation. The system was built and tested to demonstrate error-free operation of the distribution network and the receiver. Spectrum shaping by varying the pulse position within the bit slot to optimize system performance is also examined.

Sub-THz Wireless Over Fiber for Frequency Band 220–280 GHz

Higher capacity wireless access networks are required to serve the growing demands for mobile traffic and multimedia services. The use of sub-THz carrier frequencies is a potential solution for the increased data demands. This paper proposes and demonstrates experimentally the photonic generation of a multiband signal for sub-THz wireless-over-fiber transmission at up to 100 Gbit/s (20 Gbit/s in each band) using the full spectrum 220- 280 GHz for downlink wireless transmission and an uplink with 10 Gbit/s on-off keying. By using an optical frequency comb generator (OFCG), five optical tones spaced by 15 GHz are selected and split into odd and even optical subcarriers modulated separately using 10 Gbaud quadrature phase shift keying with Nyquist bandwidth achieved by using root raised cosine filtering with 0.01 roll off factor. These optical subcarriers are combined and transmitted over 10 km of fiber to the remote antenna unit (RAU). The optical bands are then filtered and transmitted separately at the RAU in a wireless channel. The received sub-THz band is down-converted to the intermediate frequency and digital signal processing (DSP) is employed at the receiver to measure the bit error ratio (BER). The performance is also evaluated to investigate the impact of the uplink on the downlink optical transmission. The receiver link budget and wireless distance for acceptable BER are also explored. The proposed system aims to distribute sub-band THz signals for short range indoor mobile units. The overall transmission capacity is increased by transmitting it as a multiband, which also reduces the bandwidth requirements on opto-electronic devices.

Optical generation, fiber distribution and air transmission for Ultra Wide Band over fiber system

A system for all-optical generation and distribution of Impulse Radio UWB signals has been implemented and demonstrated experimentally. Bit error rate measurements at 1.625Gbps and “over the air” performance is presented.

Modulated Millimeter-Wave Generation by External Injection of a Gain Switched Laser

We propose and experimentally demonstrate a novel technique for optical generation of modulated millimeter-wave (mm-wave) by using a gain switched laser (GSL) that is externally injected with a modulated light source. The GSL generates a stream of optical pulses, and these pulses exhibit a small shift in the time domain when the GSL is injected with an on-off keyed (OOK) optical data signal. This time shift can produce a phase modulated mm-wave signal at 60 GHz by suitable optical filtering of the GSL laser output. The system performance was analyzed for data streams at 1.25 Gb/s by using bit-error-rate (BER) measurements for back-to-back (BTB) and 3-km fiber transmission.