A high-speed and high-power InGaAsP semi-insulating buried crescent (SIBC) laser operating at 1.3-μm wavelength is described. The laser is fabricated with two epitaxial growth steps. A 3-dB direct modulation bandwidth of 11 GHz and a maximum cw output power of 42 mW have been achieved. A model based on rate equations is used to analyze these laser diodes. The effects of packaging and device parasitics on high-speed modulation are incorporated through a simple circuit configuration. The calculated frequency response is in good agreement with the measured response. The model is then used to predict the maximum obtainable modulation bandwidth. Finally, the measured relative intensity noise performance of the SIBC laser is presented.

Recent progress in the development of high power("37 mW) and high speed ("11.5 GHz) p-substrate GaInAsP buried crescent lasers is summarized. Their modulation characteristics, such as signal to noise ratio and two-tone intermodulation distortion, are described. In addition, preliminary results for buried crescent lasers fabricated on semi-insulating InP substrates are presented.

Operation of a microwave system involve generation, manipulation and most importantly, transportation of signals throughout the system. A well known example in which signal transportation plays a crucial role is a phased array radar system, in which hundreds or even thousands of individual emitting elements must be synchronized and appropriately phased for proper operation. Optical fiber is an excellent medium for transportation of high speed signals. Microwave signals can be imposed on an optical carrier by direct modulation of a laser diode[1]. Present state of the art high speed laser diodes have direct modulation bandwidths of beyond 20GHz, with the potential of reaching the 30GHz range by using quantum well laser structures[2]. At the present moment it does not seem probable to extend the direct modulation bandwidth to the millimeter wave range of approximately 100GHz using established approaches.

A push-pull Mach-Zehnder configuration for III -V waveguide modulators which doubles the single-sided Bandwidth/voltage ratio is described. At 1.15w wavelength a 6.25 GHz bandwidth (unterminated drive) has been achieved in GaAs/AlGaAs for a V, of 9 volts.

The concept of using a low dielectric medium in a parallel-plate H-guide to obtain velocity-matching between optical and microwave signals for the LiNb0₃ modulator is analyzed in detail. From solutions of the wave equations, we have obtained characteristics of the fundamental mode and the design parameters which lead to velocity-matching. The mode is guided by the electrooptic substrate and decays exponentially outside the LiNb01 substrate. The parameter which determines itsproperties is 2a/A , i.e., width of the LiNbO₃ substrate divided by the wavelength of the modulation signal. The phase velocity is dispersive, therefore, for a specific substrate width, velocity matching occurs only at a specific modulation frequency. A modulator built with such a velocity-matched electrode is expected to have only a finite bandwidth centered around the design frequency. Details of the analysis and characteristics of the H-guide are discussed in this paper.

Practical methods to generate high power, optical intensity modulation, from a laser diode, at mm wave frequencies may be useful for a number of optical transmission, radar, signal processing, or component testing applications. While source bandwidths exceeding 20 GHz have been achieved by direct modulation of diode lasers[1], or by using external waveguide modulators[2], in general these devices fall short of the region between 30 and 100 GHz, which is of some interest. In this paper we discuss an interferometric method, the FM sideband technique, which has the following important features: 1 - intensity modulation from a laser diode is generated at frequencies which are much greater than the direct modulation bandwidth of the laser diode, 2 - the maximum frequency response is limited by detector rather than source bandwidth and, 3 - this technique is extremely efficient (in may cases, it is more efficient than direct modulation of a laser diode), and thus can generate signals with high power. Using the FM sideband technique a 40 GHz optical carrier signal has been generated by direct modulation of a laser diode at 13 GHz. While the maximum frequency we could observe was limited by the availability of high frequency measurement electronics, frequencies on the order of 100 GHz should be obtainable using suitable detectors[3,4]. We have also demonstrated upconversion of a narrow band baseband information channel to a 11 GHz carrier, and high frequency detector characterization using the FM sideband technique[5].

Fiber-coupled diode laser and photodiode microwave packages with performance extending to 20 GHz have been developed. A microwave transmission loss of 32 dB and relative intensity noise of less than -140 dB/Hz were measured at 1.3 μm wavelength.

We have developed planar InGaAs/InP avalanche photodiodes based on trichloride YPE material. Gain-bandwidth-products greater than 70 GHz and bandwidths above 5 GHz at a gain of 10 make these devices attractive for high frequency digital and analog communication. This paper discusses the effects that limit the bandwidth of heterostructure APDs and the design, fabrication, measurement and performance of our devices.

High speed GaInAs/InP photodiodes have been developed for applications to 40 GHz with monomode fibre pigtail or window optical access. The design is based on a substrate illuminated photodiode chip which is flip-chip bonded onto a coplanar microwave transmission line which contains the necessary bias decoupling. This approach offers the optimum design for minimising the parasitic impedances and maintaining the line impedance up to the active component. Results of modelling the transient performance of the photodiode chip as a function of the device diameter and epi-layer thickness will be presented for frequencies up to 40 GHz. This shows an optimum thickness for any given diameter to maintain maximum device area for efficient coupling. Using this approach a device of 30 ern diameter will have a predicted -3dB frequency response of 38 GHz. Fully packaged devices have been characterised by a laser heterodyning technique using two DFB lasers to generate microwave optical frequencies up to 16 GHz. 30 µm and 40μm diameter devices have been measured to have an essentially flat response up to 16 GHz.

A high-speed high-sensitivity planar GaAs/AL_0.3GA_0.7AS heterostructure Schottky barrier photodiode has been de-signed, fabricated, and characterized. A highly doped A1_0.3GA_0.7AS buffer layer is used to reduce the series resistance and the undesired diffusion tailing. Furthermore, surface passivation and antireflection coating, with various dielectric films, are performed to reduce the reverse-bias dark current and the reflection loss of the incident light, thereby significantly improves the sensitivity of the photodiode. The measured external quantum efficiency and responsivity are 60% to 77% and 0.47 A/W to 0.6 A/W, respectively, for the wavelength range of 0.5 μm to 0.84 μm. A risetime of 8.5 ps and a 3-dB cutoff frequency of 50 GHz have been measured.

High-speed In_0.53Ga_0.47As and GaAs photodiodes with varying absorption region thicknesses were grown by molecular beam epitaxy on semi-insulating InP and GaAs substrates, respectively. The fabricated devices exhibit measured impulse response characteristics which are close to the simulated ones. An Ino.53Gao.47As photodiode having 0.75 μm thick absorption region and 20 x 25 μm² area is characterized by a leakage current 1 nA and responsivity of 0.35 A/W. The temporal response characteristics of this diode is characterized by a risetime of 21 ps and a FWHM of 27 psec. A GaAs photodiode which has a 1µm absorption region and 20 x 25 μm² is characterized by a laser-limited rise time of 45 psec. and FWHM 55 psec. with a leakage current less than 1 nA and a responsivity of 0.65 A/W. A similar GaAs photodiode with a 0.5 μm absorption region and a 12 μm diameter active area is characterized by a risetime of 20 psec. and FWHM of 35 psec. with a leakage current much less than 1 nA and responsivity of 0.4 A/W. To our knowledge these performances are amongst the best reported for PIN photodiodes. Techniques for enhancing the device characteristics further will be described and discussed.

This paper reviews the design and performance of wideband microwave-multiplexed lightwave systems. Results are reported for systems transmitting 120 FM video channels, 20 100 Mb/s FSK channels, and a hybrid system carrying 100 Mb/s at baseband plus 60 FM channels.

The heterodyne laser microwave fiberoptic link configuration takes advantage of the undesirable laser diode nonlinearities to operate the semiconductor laser as an optical source and a microwave mixer simultaneously. A cost-effective microwave heterodyne laser fiberoptic link using low-cost multimode optical fiber and components will be described. The experimental results of several microwave heterodyne laser fiberoptic links are also to be presented. For example, a system signal-to-noise ratio of 115 dB/Hz has been obtained, without any special system/circuit optimization, for a 1 km X-band fiberoptic link using a multimode fiber cable, an inexpensive 1.4 GHz laser diode, a low frequency photo-detector, and an IF post-detector amplifier.

We describe the analysis of the performance of coherent fiber optic links used to carry analog information. Optical AM, FM, and PM coherent systems are considered and compared with the direct detection link implementation using AM. We report for the first time results on the analysis of the effects of laser phase noise on AM, PM and FM analog coherent system performance and indicate the potentially highly stringent laser linewidth require-ments for such systems. The theoretical limits of performance and that practically achievable using realisable components is analysed and assessed.

Very high signal to noise ratio transmission through a fiber optic link has been demonstrated for frequencies up to 18 GHz. To achieve this required good laser and photodiode frequency response, high laser and photodiode efficiency, low optical reflections, and a laser with good low frequency noise characteristics. Fiber optic links offer many features which make them attractive for microwave signal transmission. Among these are extremely low transmission loss, small size and weight of components, and immunity of optic fibers from EMI_1-3 In recent years, tremendous progress has been made in developing high speed lasers and photodiodes . In addition, many applications require high signal to noise transmission capability. In this paper, the dominant noise sources of fiber optic links will be reviewed and experimental results will be presented for a link with components selected for high signal to noise transmission at frequencies up to 18 GHz.

This paper describes a novel high speed, commercially available laser module incorporating a mass transport buried heterostructure laser diode (MTBH) with a MTTF in excess of 25 years and high stability of the package design meeting stringent MIL-STD requirements for fiber optic components. This paper presents data on frequency response, input impedance matching, linearity and noise, where a frequency response of over 10GHz, at a bias current of less than 100mA is obtained. This paper further describes a small signal model of the laser chip and module which accurately predicts many of the measured results.

Microwave and millimeter-wave (M/MMW) communications, radars, and electronic warfare systems demand fiber optic links for improving system flexibility, mobility, wide instan-taneous bandwidth, deployment speed/simplicity, reducing system cost, immunity of EMI/EMP, increasing interconnect or remoting distance, and upgrading system performance. Both direct modulation and external modulation approaches of laser diode are feasible for M/MMW fiber optics. Performance tradeoff of these two approaches is analyzed for various system applications in this paper. System level parameters analyses, design/optimization techniques, and hardware fabrication/selection of M/MMW analog fiber optic links are presented. Different schemes of coherent optic detection (including heterodyne and homodyne) using integrated optics (10) can improve system performance considerably. 21 GHz, 30 GHz, and 12 GHz fiber optic systems with 1 km link distance designs, construction methods, and experimental data will be discussed. For example, the preliminary test results of the 21 GHz link, using a RF power enhanced LiNbO₃ electro-optic modu-lator (EOM) and an InGaAs PIN photodetector, provides a signal-to-noise ratio (SNR) of 105 dB/Hz without any fine adjustment. A 30 GHz link achieves an SNR of 84 dB/Hz at EOM driving power of +2 dBm.

Single optical fiber can be used as a delay line to perform signal processing functions in the microwave frequency range. In this paper, we present a novel architecture which overcomes fundamental bending loss limitations prevalent in recirculating type delay lines. Design examples for a band pass filter, coded sequence generator and matrix multiplier are presented.

Fiberoptic links are becoming increasingly popular in both long-haul and short-haul applications. Losses in short-haul broadband fiberoptic links are primarily due to many characteristics of electrooptic devices. In particular, electrical mismatch at the electrical/optical interfaces of fiberoptic links have been the dominant source of loss. Fiberoptic link losses can be significantly reduced and link performance enhanced, by reactive matching of the laser and detector modules. The steps in the design of low loss fiber optic links are presented, which are on the basis of two tier de-embedding of laser and photodiodes from test fixtures, and reactively matched them to standard 50 Ω system. These concepts are demonstrated by design of a fiberoptic link operating at 0.5 to 1 GHz using reactively matched optical transmitter and receiver modules. Performance of these modules are also discussed.

Suppression of in-band intermodulation products in microwave frequency fiberoptic links has been achieved by the application of a strong out-of-band tone. In the measurements reported on in this paper, the desired signal frequency band extended from 3880 to 3920 MHz and the suppression tone frequency was 2000 MHz. The effect was measured using both a commercial diode laser transmitter and a research model diode laser, both operating at 1.3 µm.

A waveguide Mach-Zehnder electro-optic modulator and an interdigitated photoconductive detector designed to operate at 820 nm, fabricated on different GaAlAs/GaAs heterostructure materials, are being investigated for use in optical interconnects in phased array antenna systems. Measured optical attenuation effects in the modulator are discussed and the observed modulation performance up to 1 GHz is presented. Measurements of detector frequency response are described and results of these measurements are presented.

This paper reports on the optical gain and phase control of a GaAs MMIC transmit-receive module with applications for active phased array antennas. Amplifier gain control of 15 dB and phase shifts of 45 degrees were obtained using an LED output power 250 [t.w and 50 pm respectively. The experimental results were used as an input to a simulation program to demonstrate the effect of amplitude and phase tapering to control the radiating beam of a linear active phased array antenna.

A simple method using polarization multiplexing to double the number of channel capacity of a wavelength-multiplexed fiber-optic link is demonstrated. In this paper, we describe a four-channel double multiplexed fiber-optic link combining both wavelength-division-multiplexing and polarization multiplexing techniques. Singlemode polarization maintaining fibers, a pair of dual-channel integrated-optical waveguide Ti:LiNb0₃ wavelength multiplexer/demultiplexer, and bulk-optics broadband polarization beam splitter/combiner cubes are used in the demonstration.