A.J. Seeds

Optical control of microwave semiconductor devices

The use of optically controlled devices to perform a range of circuit functions is reviewed. The optical control of amplifier performance is discussed. The optical control of two- and three-terminal oscillators and optically pumped mixers is discussed. Among the active devices treated are Gunn and IMPATT oscillators; MESFET and HEMT amplifiers, oscillators, and mixtures; and diode mixers. Future directions for research in this area are discussed. >

High-performance phase locking of wide linewidth semiconductor lasers by combined use of optical injection locking and optical phase-lock loop

The requirement for narrow linewidth lasers or short-loop propagation delay makes the realization of optical phase-lock loops using semiconductor lasers difficult. Although optical injection locking can provide low phase error variance for wide linewidth lasers, the locking range is restricted by stability considerations. Theoretical and experimental results for a system which combines both techniques so as to overcome these limitations, the optical injection phase-lock loop (OIPLL), are reported. Phase error variance values as low as 0.006 rad/sup 2/ (500 MHz bandwidth) and locking ranges exceeding 26 GHz were achieved in homodyne OIPLL systems using DFB lasers of summed linewidth 36 MHz, loop propagation delay of 15 ns and injection ratio less than -30 dB. Phase error variance values as low as 0.003 rad/sup 2/ in a bandwidth of 100 MHz, a mean time to cycle slip of 3/spl times/10/sup 10/ s and SSB noise density of -94 dBc/Hz at 10 kHz offset were obtained for the same lasers in an heterodyne OIPLL configuration with loop propagation delay of 20 ns and injection ratio of -30 dB.

Optically generated true-time delay in phased-array antennas

This tutorial review paper deals with various methods for solving a basic problem of wideband phased arrays, i.e. beam squinting, using optical technologies. The problem of beam squinting in phased arrays is analyzed and the concept of true-time delay is introduced. The advantages of realizing variable delay lines by optical rather than by microwave means are reviewed, together with principles of operation. Among the techniques described are switched-path length delay lines, fiber stretchers, tunable lasers with highly dispersive fiber, and coherent techniques incorporating dispersive delay. Recent experimental results are discussed in the light of practical system requirements. >

1.3-μm InAs/GaAs quantum-dot lasers monolithically grown on Si substrates

III-V semiconductors monolithically grown on Si substrates are expected to be an ideal solution to integrate highly efficient light-emitting devices on a Si platform. However, the lattice mismatch between III-V and Si generates a high density of threading dislocations (TDs) at the interface between III-V and Si. Some of these TD will propagate into the III-V active region and lead to device degradation. By introducing defect filter layers (DFLs), the density of TDs propagating into the III-V layers can be significantly reduced. In this paper, we present an investigation on the development of InGaAs/GaAs strained-layer superlattices as DFLs for 1.3-μm InAs/GaAs quantum-dot lasers monolithically grown on a Si substrate. We compare two broad-area InAs/GaAs quantum-dot lasers with non-optimized and optimized InGaAs/GaAs DFLs. The laser device with optimal DFLs has a lower room-temperature threshold current density of 99 A/cm2 and higher maximum operation temperature of 88 °C, compared with 174 A/cm2 and 68 °C for the reference laser.

Packaged semiconductor laser optical phase-locked loop (OPLL) for photonic generation, processing and transmission of microwave signals

In this paper, we present the first fully packaged semiconductor laser optical phase-locked loop (OPLL) microwave photonic transmitter. The transmitter is based on semiconductor lasers that are directly phase locked without the use of any other phase noise-reduction mechanisms. In this transmitter, the lasers have a free-running summed linewidth of 6 MHz and the OPLL has a feedback bandwidth of 70 MHz. A state-of-the-art performance is obtained, with a total phase-error variance of 0.05 rad/sup 2/ (1-GHz bandwidth) and a carrier phase-error variance of 7/spl times/10/sup -4/ rad/sup 2/ in a 15-MHz bandwidth. Carriers are generated in the range of 7-14 GHz. The OPLL transmitter has been fully packaged for practical use in field trials. This is the first time this type of transmitter has been fabricated in a packaged state which is a significant advance on the route to practical application.

Millimeter-wave modulated optical signal generation with high spectral purity and wide-locking bandwidth using a fiber-integrated optical injection phase-lock loop

We report the first experimental demonstration of millimeter-wave modulated optical signal generation by an optical injection phase-lock loop. A 36-GHz signal was generated by combining optical sideband injection locking with optical phase-lock loop techniques for two fiber-coupled DFB lasers. Single sideband noise spectral density of -92 dBc/Hz at 10 kHz offset, and phase-error variance lower than 0.005 rad/sup 2/ in a 100 MHz bandwidth were measured. The locking bandwidth exceeded 30 GHz.

Millimeter-Wave Photonic Components for Broadband Wireless Systems

We report on advanced millimeter-wave (mm-wave) photonic components for broadband radio transmission. We have developed self-pulsating 60-GHz range quantum-dash Fabry-Perot mode-locked laser diodes (MLLD) for passive, i.e., unlocked, photonic mm-wave generation with comparably low-phase noise level of -76 dBc/Hz @ 100-kHz offset from a 58.8-GHz carrier. We further report on high-frequency 1.55-μm waveguide photodiodes (PD) with partially p-doped absorber for broadband operation (f3dB ~70-110 GHz) and peak output power levels up to +4.5 dBm @ 110 GHz as well as wideband antenna integrated photomixers for operation within 30-300 GHz and peak output power levels of -11 dBm @ 100 GHz and 6-mA photocurrent. We further present compact 60-GHz wireless transmitter and receiver modules for wireless transmission of uncompressed 1080p (2.97 Gb/s) HDTV signals utilizing the developed MLLD and mm-wave PD. Error-free (BER = 10-9, 231 - 1 PRBS, NRZ) outdoor wireless transmission of 3 Gb/s over 25 m is demonstrated, as well as wireless transmission of uncompressed HDTV signals in the 60-GHz band. Finally, an advanced 60-GHz photonic wireless system offering record data throughputs and spectral efficiencies is presented. For the first time, we demonstrate photonic wireless transmission of data throughputs up to 27.04 Gb/s (EVM 17.6%) using a 16-QAM OFDM modulation format resulting in a spectral efficiency as high as 3.86 b/s/Hz. Wireless experiments were carried out within the regulated 57-64-GHz band in a lab environment with a maximum transmit power of - 1 dBm and 23 dBi gain antennas for a wireless span of 2.5 m. This span can be extended to some 100 m when using high-gain antennas and higher transmit power levels.

1.8-THz bandwidth, zero-frequency error, tunable optical comb generator for DWDM applications

We report on the experimental realization of a simple optical comb generator, based on phase modulation within an amplified fiber loop, which offers exact referencing to an arbitrary supplied reference frequency and tunable comb-line spacing. At a reference wavelength of 1529 nm up to 103 comb lines within a 40-dB power envelope were generated with spacings adjustable from 1 to 25 GHz, limited only by the bandwidth of the phase modulator.

Generation and transmission of millimeter-wave data-modulated optical signals using an optical injection phase-lock loop

Generation and transmission of millimeter-wave data-modulated optical signals is presented using an optical injection phase-lock loop (OIPLL). Millimeter-wave signal generation is demonstrated with wide locking range, 30-GHz low phase noise level, -93 dBc/Hz, and a wide frequency tuning range, 4-60 GHz generation demonstrated using optical injection locking only, verified by using OIPLL in the 26-40 GHz range. The OIPLL is also used to transmit error-free 140-Mb/s amplitude shift keying and 68-Mb/s differential phase-shift keying (DPSK) modulated millimeter-wave signals over up to 65 km of uncompensated standard singlemode fiber. The DPSK system uses reference frequency modulation, eliminating the need for optical amplification.

Continuous-wave InAs/GaAs quantum-dot laser diodes monolithically grown on Si substrate with low threshold current densities

We report the first room-temperature continuous-wave operation of III-V quantum-dot laser diodes monolithically grown on a Si substrate. Long-wavelength InAs/GaAs quantum-dot structures were fabricated on Ge-on-Si substrates. Room-temperature lasing at a wavelength of 1.28 μm has been achieved with threshold current densities of 163 A/cm(2) and 64.3 A/cm(2) under continuous-wave and pulsed conditions for ridge-waveguide lasers with as cleaved facets, respectively. The value of 64.3 A/cm(2) represents the lowest room-temperature threshold current density for any kind of laser on Si to date.