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The Generation of microwave signals by heterodyning two optical signals has been demonstrated in the past. However, so far this approach is limited in bandwidth, power and efficiency. In this paper we present an analysis of optical heterodyning in the uni-traveling carrier traveling wave photo detector taking into account the effect of ballistic electrons. The analysis is validated by comparison to measurement of an existing device made at the University of California, San Diego. Based on the above analysis a new photodiode design is made, which is expected to have a bandwidth well into the sub-MM wave region. The device exploiting the ballistic electrons effect can reach a bandwidth 2-3 times larger compared to device using velocity-saturated electrons.

Schottky contacts of Al/Si1−x−yGexCy were fabricated using conventional Si technology. Effects of thermal processing of the alloys on the electrical properties of the Al/Si1−x−yGexCy Schottky diodes were investigated. Current–voltage (I–V), capacitance–voltage (C–V), and x‐ray diffraction measurements were performed. These thick alloy films (100–150 nm) experienced strain relaxation upon annealing at 700 °C. Nearly ideal I–V and C–V behaviors were obtained for strain‐compensated samples. I–V and C–Vcharacteristics show evidence of dislocation‐related traps for strain‐relaxed samples. Carbon incorporation improves the I–V and C–V characteristics by lessening the extent of lattice relaxation due to thermal processing.

A Franz-Keldysh effect InGaAsP electroabsorption waveguide device is utilized as a high-frequency, high-linear dynamic range modulator and photodetector. The dual-function modulator/photodetector can be useful in compact transmit/receive front end antenna architectures. Adjusting the electrical bias to the reverse-biased p-i-n diode, either efficient optical modulation or detection is demonstrated. As an electroabsorption modulator, a fiber optic link with a -17.4-dB RF loss and a 124-dB-Hz/sup 4/5/ suboctave spurious-free dynamic range is obtained with electrical biases in the 2 to 3 V range. As a waveguide photodetector, a 0.45-A/W fiber coupled responsivity, photocurrents up to 20 mA, and an output second-order intercept of +34.5 dBm are achieved at 7-V electrical bias.

A numerical modeling approach based on the microwave transmission (ABCD) matrix theory is developed for analyzing the frequency response of segmented traveling-wave electroabsorption modulators (STEAM). It is found that for 300 /spl mu/m long exemplary modulation length, the STEAM can provide much wider bandwidth (73 GHz) than the lumped-element (26 GHz) and the continuous traveling-wave (47 GHz) counter-parts, with a small penalty of E/O conversion gain if low-loss passive optical waveguide is available.

An up-converting microwave photonic link which enables high dynamic range over a multioctave information bandwidth is demonstrated. The improvement in spurious-free dynamic range (SFDR) as compared to conventional links is experimentally demonstrated. The link consists of two heterodyned lasers with one optical carrier modulated by a LiNbO/sub 3/ Mach-Zehnder modulator biased at the null point. This results in strong optical sidebands, minimum even order distortion, and more than /spl sim/40-dB suppression of the optical carrier. The first carrier's two optical sidebands are heterodyned with the second unmodulated optical carrier. The modulated optical carrier is suppressed reducing noise power and enhancing SFDR. An SFDR of 115 dB/Hz/sup 2/3/ was measured. The detected local oscillator power is also suppressed, easing output filtering requirements.

A novel, compact, and tunable lithium niobate (LN) planar waveguide loop structure composed of two Y junction reflectors is proposed for optical and radio frequency signal processing applications. The preliminary device shows a high quality factor of 6.5/spl times/10/sup 4/, due to the low propagation loss of the titanium-diffused LN waveguide. The tunability of the loop by electric field is estimated.

Recent advances in component technology for microwave photonics networks are discussed. Different transmitter technologies are compared in term of analog link performance. The development of high power and wide bandwidth photodiodes for analog fiber-optic link is discussed.

Design for high efficiency, high power traveling wave electroabsorption modulator using Intra-Step-Barrier Quantum Well (IQW) and Peripheral Coupled waveguide (PCW) designs are presented. Both of these designs have separately yielded EAMs with high optical power handling and low Vp properties, in an analog fiber link configuration. The IQW EAM has low Vp (~0.73 V) and high power handling (100 mW). The lumped element IQW EAM has achieved a link gain of -16 dB, a multi-octave SFDR of 110 dB-Hz2/3 and a single-octave SFDR of 121dB-Hz4/5 at the 1543 nm wavelength. The PCW MQW EAM with lumped element configuration can achieve a low link low, a high multi-octave SFDR at the same wavelength. The traveling wave properties of these EAMs are under investigation.

High power electroabsorption modulator using intra-step-barrier quantum well and peripheral coupled waveguide are designed and tested for analog fiber link applications. The resulting device has demonstrated high optical power handling and low V/sup /spl pi// properties.

This paper presents a comparison of three different types of CPW fed slot antennas integrated with a photodetector. The antennas are driven by optical power converted into microwave power using the photodetector which is directly attached to the antennas without the use of any amplifying devices. The operating frequency of these antennas is around 18.5 GHz. This paper presents the approach for matching a photodetector to a single element or to an array of elements. Measured data and simulations for various antenna/photodetector configurations are compared and discussed.

The paper presents a set of issues and solutions for the integration of a WGPD (wave guide photo detector) and a CPW (coplanar waveguide) fed three element slot antenna. Novel designs for band pass filters and low loss transmission lines are also described. The operating frequency of the antenna is around 18.5 GHz and is connected directly with the photodetector without the use of amplifier or any active elements. Measured data and simulations for various antenna/photodetector configurations are compared and discussed.

The spurious-free dynamic range (SFDR) of an InGaAsP-InP Franz-Keldysh effect (FKE) waveguide modulator is studied. Low-biasing the FKE modulator is shown to enhance the SFDR by 22 dB with a 3-dB optical power penalty. Polarization-independent RF operation is also obtained with low bias. At 2 mA photocurrent, the simulated narrowband and broadband SFDR are, respectively, 127 dB and 104 dB in a 1-Hz bandwidth. The measured result projects a narrowband SFDR of 129 dB-Hz/sup 4/5/ at this photocurrent. >

The electrodes of a microwave coplanar waveguide (CPW) on planar p‐InP epitaxial layers are electrically isolated by helium implantation. Impedance, attenuation, and relative effective dielectric permittivity of implanted and unimplanted samples are compared over a frequency range of 0.13–20 GHz. The results show that coplanar waveguides on 4He+ implanted materials exhibit very low loss (

Summary form only given. Significant progress has been achieved towards the demonstration of direct wafer bonded photodetectors. This device design approach offers the freedom to combine dissimilar materials in order to fabricate novel device structures not obtainable using standard techniques. Significant device performance advantages have been demonstrated in specific device applications using wafer bonding. The results summarized here demonstrate additional progress towards defining wafer bonding as a mature technology - a manufacturable and cost-effective process applied to APDs that portends commercial application.

We review the design and fabrication of the traveling wave (TW) electrode for the EAM for high speed and high power operation. In one approach, EAMs with improved saturation properties have been demonstrated via the lowering of the hole barrier by applying appropriate strain at the well/barrier interface. An alternate approach to enhance the saturation power of the quantum well modulator is via the use of a barrier step inside the well to suppress the onset of the red shift in the quantum-confined Stark effect to a higher electric field. In these approaches, however, the saturation power is optimized without incorporating the modulation frequency considerations.

A uni-traveling carrier waveguide integrated photodiode (UTC-WIP) combining the advantages of a coupled waveguide integrated photodiode (WIP) and a uni-traveling carrier photodiode (UTC-PD) is investigated. Preliminary measurement results show that the DC responsivity is 0.4 A/W without an anti-reflection coating, and the peak pulse response can reach 94 mA (4.7 V across a 50 /spl Omega/ load) when the bias voltage is -9 V. The resulting device is capable of operating at 20 GHz. The IP/sub 3/ at 1 GHz and 18 GHz are 24 dBm and 8 dBm, respectively.

We present the design and preliminary analysis of an efficient and wide bandwidth peripheral coupled waveguide traveling-wave electroabsorption modulator (PCW-TW-EAM), which aims to decouple the optical waveguide and the microwave transmission line. The optical waveguide mode of this device is designed to closely match to a single mode fiber mode for the ease of coupling. The waveguide has presently shown an optical propagation loss of /spl sim/2dB/mm at the modulation wavelength which is essential for wide bandwidth and high modulation efficiency to be achieved in the same design. Simulations indicate that equivalent V/sub /spl pi// less than 1V over a very large bandwidth can be obtained.

For an analog-to-digital converter (ADC), it is important to have precise sampling time control to avoid resolution degradation. At high sampling rates, this precise sampling time control becomes increasingly difficult to achieve. To relax the stringent timing requirement of an ADC quantizer, a track-and-hold (T&H) circuit is implemented in many ADC architectures. In this work, a high power, high speed waveguide integrated photodiode (WIP) is tested as an optoelectronic switch for the T&H function. The photodiode operates with light launched into a passive waveguide before being coupled into the absorber. Using a matching layer between the passive waveguide and the absorber, the absorption profile along the absorber waveguide is modified to give small peak absorption. This reduces the effect of the charge screening effect and also the heating effect, so that the saturation power of the photodiode can be increased. Pulse measurement of an optical WIP switch is presented. The results show the peak current reaches 50 mA and the rise time is approximately 18.2 ps. These results show this switch can potentially be used for clocking an electronic T&H circuit.

Electroabsorption modulators (EAM) have been widely used in externally modulated RF link. In the conventional intensity modulation format, the RF efficiency of such link is critically dependent on the optical saturation of the EAM and the fiber dispersion. In an effort to minimize the dependence on these two factors, we have conducted an experimental study of an optical mixer that employs two heterodyned lasers to generate an optical local oscillator (LO). In contrast to the conventional schemes where both laser beams are launched into the same EAM, the EAM in the present scheme modulates only one of the laser beams. In this way, improvement in RF gain is obtained since it is not limited by the optical saturation of the EAM. The resulting optical spectrum shows that this scheme is equivalent to the optical single side band transmission. For sub-octave bandwidth applications, the dispersion effect in the fiber can be ignored.

A Radio-over-Fiber system with simplified Base Station (BS) is proposed in which a single chip DBR Reflective Electro-absorption Modulator (REAM) serves both as an optical transceiver and as a mixer at the BS. It enables full duplex optical transmission for base band and RF band services simultaneously due to good isolation between uplink and downlink at the same chip. Grating structure is incorporated into the EA modulator for the sake of system design. It also improves yield and efficiency of high-speed devices.

We present analysis and preliminary experimental results of intra-step-barrier quantum wells for high-saturation-optical-power electroabsorption modulators. We have shown that the intra-step-barrier delays the onset of red shift in the quantum-confined Stark effect to a higher field.

A high speed electroabsorption modulator (EAM) with high saturation optical power is desirable for analog fiber link applications, as the link gain increases quadratically with the optical power. EAMs with multiple-quantum-well (MQW) active layers are popular photonic applications. In this paper we also discuss the design and fabrication of the traveling wave (TW) electrode for the InGaAs QW EAM for high speed (>40 GHz) operation.

Photocurrent in semiconductor electroabsorption modulator (EAM) can potentially affect its microwave properties. In this work, we found that at high optical power, the modulation bandwidth can be increased at large photocurrent. Based on photocurrent effects on EAM harmonics, a new approach is proposed for modulator bias control for maximum RF link gain in analog fiber optic link. Photocurrent effects on the microwave properties of ultra-wide bandwidth traveling wave EAM waveguide are also examined.

The IMD3 of a p-i-n waveguide photodiode is characterized up to 18 GHz. The observed frequency dependence of the IP3 closely agrees with that obtained from an equivalent circuit analysis of the photodiode.

We report a simple and nondestructive photocurrent method for characterizing the bonding interface between two hydrophobically bonded Si wafers. The relationship of photocurrent versus wavelength was measured and analyzed. The direction of the photocurrent indicates the band-bending direction, and thus, the donor or acceptor nature of the interface states. The photocurrent is proportional to the electric field at the interface induced by band bending. Our results showed that the Si pairs bonded in air have much larger band bending at the interface than those bonded in dry nitrogen, and that both have donor-like interface states.

Design and performance of traveling-wave electroabsorption waveguide modulator for high speed and long haul applications are presented. Combining inner step-barrier quantum wells as medium for electroabsorption modulation and peripheral coupled waveguide for optical waveguiding in the same device, we have obtained enhancement in both optical power handling and efficiency.

We report metalorganic vapor phase epitaxy growth of InAs0.66P0.34/InP/In0.74Ga0.26P strain compensated multiple quantum wells (MQWs) at 1.5 μm wavelength. A composite InP/InGaP/InP barrier structure is used to tune the net strain of the MQWs. Compared with InAs0.66P0.34/InP strained MQWs grown under similar conditions, the InAs0.66P0.34/InP/In0.74Ga0.26P strain compensated MQWs show improvement in crystalline and optical quality.

Antifuse samples with very thin insulating oxide were fabricated using a technique of two-step PECVD oxide deposition. Dielectric strength as high as 13 MV/cm was obtained for our samples. Defect density and uniformity have been improved in this way. The on-state resistance of the programmed antifuses shows a stronger dependence on the oxide thickness when it was programmed at the lower current than when it was programmed at the higher current. >

The characteristic voltage V/sub f/ of different programmed metal-to-metal antifuses was measured and found to be nearly independent of the electrode materials. An electrothermal model, used previously to predict programmed silicon-electrode antifuse resistance, was extended to explain the above phenomenon. The metal-to-metal antifuse resistance vs. the programming current is governed by the Wiedeman-Franz Law. >

The critical role of the optical source spectral linewidth in semiconductor low loss waveguide measurements using the Fabry–Perot resonance method is analyzed. For 5‐mm‐long GaAs/AlGaAs waveguides with losses in the 1 dB/cm range, a frequency stabilized single mode laser with a linewidth of less than 0.01 A is required to obtain a loss value accurate to within 5%.

In this paper, the fabrication, frequency response, and saturation characteristics of a waveguide pin photodiode made from double heterostructure InGaAs/InP materials are presented. The detector is designed for operation at optical wavelengths ranging from 1.3 to 1.5 /spl mu/m. The materials are grown using a low pressure, organo-metallic vapor phase epitaxial reactor. Due to the use of a vent-run manifold and growth interruption at the heterointerface, high quality detector material is obtained. >

Laser mode-locking is an effective modulation technique which can be used in fiberoptic link applications. In a semiconductor laser, active mode-locking can be achieved through the direct modulation of the laser at the cavity resonant frequency. If the modulation frequency is detuned from this condition, large optical intensity fluctuations can occur, which can cause a significant degradation in the noise figure of the laser, and consequently in the noise figure of the overall link. In this paper, we investigate the consequence of frequency detuning an actively mode-locked external-cavity semiconductor laser. We experimentally demonstrate the existence of chaos in a mode-locked laser upon frequency detuning. To our knowledge, chaotic instability in an actively mode-locked semiconductor laser has not been reported. >

Guided-wave components are essential elements in optical fiber communication and signal processing systems. For 1.3-1.5 /spl mu/m wavelength applications, it is of interest to develop low loss optical waveguides on InP substrate. In this work, low-loss InGaAs-InP planar photoelastic waveguides using metal stresser stripes have been demonstrated for the first time. >

We study a new type of waveguide structures-two-dimensional photonic crystals sandwiched between two metal conductors. In the structures, not only the electromagnetic propagation, but also the radiation spectra can be controlled. Radiation from microwave dipole antennas can be completely suppressed in band gaps and enormously enhanced at specific pass bands frequencies.

For analog fiber optic links using electroabsorption modulators, the correlation between the RF link gain and the modulator photocurrent is investigated both theoretically and experimentally. Based on this correlation, a self-bias control scheme of the electroabsorption modulator for maximum RF link gain is proposed. This scheme can simplify the bias control of modulator arrays.

In the present work, two new approaches are investigated to simultaneously improve the saturation power and linearity: a) using a three layer waveguide structure with an InGaAsP (/spl lambda//sub g/ = 1.24 /spl mu/m) active layer, that operates through the Franz-Keldysh effect (FKE), and b) using a four-layer large optical cavity (LOG) asymmetric waveguide with InGaAs absorber and a passive InGaAsP layer.

Summary form only given. We have constructed a fast statistical time-division packet multiplexer (MLTX) based on the cascaded optical delay (GOD) architecture. The COD uses 2x2 lithium niobate photonic crossbar switches and lengths of fiber delay line to buffer contentious packets. The routing control of the COD is performed electronically on a packet-by-packet basis.

In this paper, we analyze numerically and compare the performance of the optical IGBT and the conventional IGBT. With optical excitation of the device, very high current switching can be achieved. Same dimensions and geometry are used in both devices: and scaling of dimensions and circuit parameter values is employed to simulate the high power performance of the optical IGBT. Our results show that, with sufficient optical power illuminating the channel of the optical IGBT, the switch can be closed quickly. In addition, with the gate controlled by light and not by voltage, the conduction channel can be much wider and hence it can carry more carriers for high current operation. The wider channel has the additional advantage of a smaller current density and this can relieve the thermal problem.

Mesa type fused InGaAs/Si separated absorption and multiplication APDs with a diameter of 130 /spl mu/m have been fabricated on n-type Si substrate. Substantial dark current reduction has been achieved compared with the published data for fused InGaAs/Si APDs. Dark current densities as low as 0.23 mA/cm/sup 2/ at -5 V and 3 mA/cm/sup 2/ at a gain of 10 are reported. Our improved dark current even though is still 2 orders larger than the conventional mesa-structure InGaAs/InP APD lower excess noise level is expected due to the larger difference between the electron and hole ionization coefficients of Si.

Traveling wave electroabsorption modulators (TW-EAMs) can provide large modulation bandwidth and high efficiency features for both analog and digital fiber-optic links. Here, high efficiency TW-EAMs with modulation bandwidths in excess of 40 GHz have been demonstrated. Observing the predicted bandwidth reduction for counter-propagating optical and microwave fields along the waveguide has validated the traveling-wave nature of the modulator.

The double-locked laser configuration used for these measurements is fiber coupled and consists of an optically isolated, dc-biased master laser that optically injects a slave laser through an optical circulator. The lasers operate at a wavelength of approximately 1557 nm. A modulation signal from a microwave frequency synthesizer is added to the dc bias of the slave laser. After passing through the optical circulator, the output of the slave laser is detected by a fast photodiode. The photodiode signal is amplified, split and routed to a microwave spectrum analyzer, a microwave phase noise test set, and a microwave mixer. At the mixer, the signal is compared with the output of the microwave frequency synthesizer.

Analogue to digital convertors (ADCs) operating at unprecedented speeds and resolutions are investigated using photonics and electronics techniques, with stringent constraints placed on receiver linearity and noise. This paper presents design and performance considerations of photodetectors and associated preamplifiers.

We have demonstrated avalanche gain in InGaAs-Si fused PIN photodiode at low bias range. Simulation from a theory based upon the interface states introduced by the fusion process appears to explain the observed gain behavior of the photodiode.

Previous works have shown that InGaAs/Si heterostructures fabricated using wafer fusion technology have resulted in PIN and APD detectors of high quantum efficiency and bandwidth. At least two bonding processes have been reported by different laboratories so far. One method directly fuses InGaAs/Si material first and then removes the InP substrate by wet etch; and the other method removes the InP substrate first from temporarily bonded InGaAs/Si wafers and then uses thermal annealing to achieve covalent bonding. The first part of the talk includes discussions on the pros and cons of both methods based on our own experience. For practical concerns, we finally chose the former method to make the heterostructure for interface characterization and photodetectors. The variable temperature I-V and PL characteristics show that the properties of the heterojunction are sensitive to the interface oxygen concentration as well as the properties of misfit dislocations. Making use of the bonding interface and tailoring the electric field profiles in InGaAs and Si, we have proposed and demonstrated new PIN and APD structures. The preliminary results showed that the internal quantum efficiency was greater than 60% at low bias voltage for the PIN structure. The estimated frequency response was about 12 GHz, limited by the RC delay. For nearly the same device structure, avalanche gain was observed at very low bias voltage (about 10 to 15 V). APD of low operating voltage is attractive because it simplifies the bias circuit and as a result, reduces the cost of the receiver. The low operating voltage is obtained by using heavily n-doped Si substrate as the anode and the InGaAs/Si heterojunction itself as an equivalent of a delta-doped p-region. It can be shown from the simulation results that both the injection efficiency and the multiplication factor can be enhanced using such a structure. One key remaining issue is the noise characteristics of the APD. Different designs will be discussed for the purpose of dark current reduction to improve the noise figure of the device.

We report here on wafer-bonded InGaAs/Si avalanche photodiodes (APDs) demonstrating very low excess noise factors that were fabricated using a high-yield, wafer-scale bonding process. The bonding interface quality was evaluated using high-resolution x-ray diffraction and dark current measurements. Measured dark currents on 20 μm diameter mesas are 25 nA and 170 nA at gains of 10 and 50, respectively. Low excess noise factors, which are predicted due to the superior noise properties of Si as a multiplication layer, were measured to be more than 3 times lower than commercial InGaAs/InP APDs at a gain of 10, and more than 9 times lower at a gain of 50. The corresponding electron/hole ionization coefficient ratio k in these devices is as low as 0.02.

This paper proposes the integration of an antenna with a photodetector for high capacity wireless communications. The side-illuminated waveguide photodetector (WGPD) is used to convert the RF-modulated optical power into a microwave signal, which in turn is fed to an antenna. The WGPD is a standard p-i-n device grown on a semi-insulating InP substrate and fabricated using conventional techniques. The performance of this RF/photonic antenna in the frequency range 17-20 GHz is studied theoretically and experimentally. An equivalent circuit model for the WGPD is developed to estimate the photodetector impedance as a function of frequency to assist in the impedance matching between the photodetector and the antenna. The agreement between measurement and circuit model results for the WGPD impedance is very good. It is envisioned that a large number of such RF/Photonic antenna elements could be networked together into a star configuration, feeding in and out of a radio hub.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Wafer-bonded avalanche photodiodes (APDs) combining InGaAs for the absorption layer and silicon for the multiplication layer have been fabricated. The reported APDs have a very low room-temperature dark current density of only 0.7 mA/cm2 at a gain of 10. The dark current level is as low as that of conventional InGaAs/InP APDs. High avalanche gains in excess of 100 are presented. The photodiode responsivity at a wavelength of 1.31 micrometers is 0.64 A/W, achieved without the use of an anti-reflection coating. The RC-limited bandwidth is 1.45 GHz and the gain-bandwidth product is 290 GHz. The excess noise factor F is much lower than that of conventional InP-based APDs, with values of 2.2 at a gain of 10 and 2.3 at a gain of 20. This corresponds to an effective ionization rate ratio keff as low as 0.02. The expected receiver sensitivity for 2.5 Gb/s operation at (lambda) = 1.31 um using our InGaAs/silicon APD is -41 dBm at an optimal gain of M = 80.

A Low Thermal Stress (LTS) process, involving the removal of most of the InGaAs(P) material, was used to allow for wafer-fusion of InGaAs(P) samples to Si. The formation and behavior of bubbles of trapped gas between the thinned layer of InGaAs(P) material and the thick Si substrate were studied due to the yield problems such bubbles represent. Observations revealed a low temperature regime

AlGaAs/GaAs double heterostructure transverse‐electric (TE) waveguide polarizers, 5 mm long, with extinction ratios exceeding 20 dB and excess losses of

The fabrication of low‐loss photoelastic waveguides in GaAs/AlGaAs layered structures by thin film reactions is investigated. The waveguides are formed by opening a narrow window stripe, a few microns wide, in an otherwise continuous Ni layer under tension deposited on a semiconductor structure. The local tensile stress induced by the Ni layer in the semiconductor causes the local refractive index to increase, thus providing the guiding mechanism. Annealing the sample at 250 °C for 1 h induced an interfacial reaction between the Ni film and the substrate to form Ni3GaAs. The formation of an interfacial compound stabilizes the stresses, making the stress state independent of the deposition system and technique. Single‐mode waveguide propagation losses as low as 1.4 dB/cm at 1.53 μm wavelength have been obtained on annealed waveguides. Further annealing up to 600 °C did not cause degradation in the optical confinement, thus indicating a thermally stable planar waveguide fabricated by this process. Other pho...