We report a simple method to obtain a p-i-n photodiode’s harmonic distortion levels at different frequencies from the microwave reflection coefficient S11 of the photodiode under dc illumination. This approach is based upon the tracking of the photodiode’s microwave impedance with S11 at different incident optical powers before severe saturation occurs at low bias or at high optical power. The second-harmonic distortions measured from a waveguide photodiode agree closely with those predicted from the S11 data.

Peripheral coupled waveguide (PCW) design has been deployed in InGaAsP multiple quantum-well (MQW) electroabsorption modulator (EAM) at 1.55-micrometer wavelength. PCW enhances the optical saturation power and reduces the optical insertion loss and the equivalent V(sub pi) simultaneously. A radio-frequency link using a 1.3-mm-long lumped-element PCW EAM has achieved experimentally a link gain of 3 dB, at 500 MHz and at input optical power of 80 mW. The corresponding two-tone multioctave spurious-free dynamic range (SFDR) at the same bias is measured at 118 dB Hz2/3. The single-octave SFDR at the third-order null bias is 132 dB Hz4/5.

Afused InGaAs–Si avalanche photodiode (APD) with a low excess noise factor of 2.3 at a gain of 20 is reported. This corresponds to a k factor of 0.02 for the silicon avalanche region. Dark current density as low as 0.04 mA/cm2 at 5 V and 0.6 mA/cm2 at a gain of 10 are measured; a small thermal coefficient, 0.09%/degree C, of the breakdown voltage is observed for this APD.

A novel approach is proposed for controlling the bias of an electroabsorption waveguide modulator for maximum radio-frequency (RF) gain in analog fiber-optic links. It is based upon the correlation between the RF gain and the modulator dc photocurrent. It is found that, under various operating conditions, the modulator bias at which the modulator dc photocurrent experiences the largest change with incremental bias, coincides with the bias for the maximum RF gain. This approach eliminates the need for an external tracking photodiode, and can be useful in bias controls of a modulator array.

Theoretical analysis and numerical calculations are presented for ultrahigh-speed (>50 GHz) traveling-wave electroabsorption modulators (TW-EAM’s), including effects of velocity mismatch, impedance mismatch, and microwave attenuation. A quasi-static equivalent circuit model is used to examine the TW-EAM microwave properties, including the effect of photocurrent. Due to the optical propagation loss of the waveguide, the TW-EAM waveguide length for maximum RF link gain is currently limited to 200–300 micrometer. The discussion indicates that the carrier transit time in the intrinsic layer may not severely limit the TW-EAM bandwidth. Three TW-EAM design approaches are discussed: low-impedance matching; reducing the waveguide capacitance; and distributing the modulation region.

A novel electroabsorption modulator (EAM) using intrastep quantum wells (IQWs) and a single-sided large optical cavity waveguide is demonstrated to operate at up to 100 mW of input optical power. When the IQW EAM with uncoated facets is tested in an analog fiber link, the radio-frequency link gain reaches 16.1 dB at 100-mW optical power. We have measured a single-octave spurious-free dynamic range (SFDR) of 121 dB Hz4/5 and multioctave SFDR of 110 dB Hz2/3 for this EAM.

In Hayes’s (1993) and Williams’s (1996) analyses, the photodiode nonlinearity is attributed to the space charge screening effect. In this paper, the third-order intermodulation distortions of a high frequency, large optical cavity p-i-n waveguide photodiode are characterized up to 18 GHz using a two-tone measurement. At high bias voltage, the third-order intercept point (IP3) of the waveguide photodiode is constant at low frequency and approximately f-3 at high frequency. This closely agrees with our model, which is based upon variation of the photodiode impedance. The measured IP3 of the same device at low bias voltages indicates the contribution of space charge screening under low bias voltage or severe saturation.

High-saturation power traveling-wave electroabsorption modulators (TW-EAMs) with modulation bandwidth greater than 40 GHz have been demonstrated. Microwave properties of the TW-EAM waveguide are extracted from the measured S-parameters using the equivalent circuit model in [4]. Excellent agreement is obtained between the predicted and the measured frequency responses.

We demonstrate a digitally tunable microwave-photonic notch filter based on a differential group-delay module which produces a relative delay between two orthogonal polarizations. A maximum rejection level greater than 60 dB is obtained. The tenability of the filter is achieved through real-time electronic control of the relative delay time.

We demonstrate for the first time an electroabsorption (EA) waveguide utilized as an integrated photodetector/mixer for frequency conversion of radio frequency signals, through field-controlled absorption. Using an InAsP–GaInP multiple- quantum-well EA waveguide, a conversion loss of 18.9 dB was obtained at 10-mW optical local oscillator (LO) power, and a suboctave, two-tone spur-free dynamic range of 120.0 dB-Hz4/5 was measured for an up-converted signal at 1.9 GHz. This scheme can be useful in antenna applications where optical LO signal distribution is used for frequency converting microwave signals.