John F. Diehl

Improvement in the Phase Noise of a 10 GHz Optoelectronic Oscillator Using All-Photonic Gain

We have investigated the improvement in the phase noise of a 10 GHz optoelectronic oscillator using all-photonic gain as compared to using an electronic amplifier in the cavity. The optoelectronic oscillator achieves the necessary RF gain for oscillation by using the carrier-suppression technique of a low-biased Mach-Zehnder modulator (MZM) followed by optical amplification. The measured RF gain due to this all-photonic technique is as high as 15 dB and matches well with theoretical predictions. The phase noise of the generated 10 GHz signal is at least 10 dB lower than the signal from the same oscillator using an electronic amplifier. The improvement in the phase noise is due to the lower RF noise figure of the all-photonic gain process as compared to the electronic amplifier configuration.

Wideband Analog Photonic Links: Some Performance Limits and Considerations for Multi-Octave Implementations

High-performance analog photonic links are discussed and the prevalent modulation formats are highlighted. Because of its multi-octave and millimeter-wave potential, special attention is given to intensity modulation with direct detection (IMDD) employing an external Mach-Zehnder modulator (MZM). The theory for IMDD is reviewed and some experimental results are discussed. Two limiting factors in multi-octave IMDD implementations are quantified. The MZM bias requirements in order to remain third-order limited are shown to be very stringent in high-performance links. Photodiode nonlinearities, perhaps the most inhibiting factor in present-day wideband analog photonics, are cast in terms of output intercept points and tied to the IMDD link performance.

Photodiode linearity requirements for radio-frequency photonics and demonstration of increased performance using photodiode arrays

The impact that photodiode nonlinearities have on intensity-modulation direct-detection analog photonic links is described. The second- and third-order linearity requirements for photodiodes, quantified in terms of output intercept points, are calculated. Measured data at 1 GHz for a high-current (60-mA) partially-depleted-absorber photodiode are presented. A four-photodiode 26-mA array at 5 MHz is demonstrated to achieve modulation-limited third-order performance and a second-harmonic output intercept point of 84 dBm.

Even-order harmonic cancellation for off-quadrature biased Mach-Zehnder modulator with improved RF metrics using dual wavelength inputs and dual outputs

We present a technique using a dual-output Mach-Zehnder modulator (MZM) with two wavelength inputs, one operating at low-bias and the other operating at high-bias, in order to cancel unwanted even-order harmonics in analog optical links. By using a dual-output MZM, this technique allows for two suppressed optical carriers to be transmitted to the receiver. Combined with optical amplification and balanced differential detection, the RF power of the fundamental is increased by 2 dB while the even-order harmonic is reduced by 47 dB, simultaneously. The RF noise figure and third-order spurious-free dynamic range (SFDR(3)) are improved by 5.4 dB and 3.6 dB, respectively. Using a wavelength sensitive, low V(pi) MZM allows the two wavelengths to be within 5.5 nm of each other for a frequency band from 10 MHz to 100 MHz and 10 nm for 1 GHz.

An Optical Technique for Radio Frequency Interference Mitigation

A new photonics-based approach for interference mitigation utilizing the nonlinear response of optical modulators is described. The technique is analyzed both theoretically and experimentally with excellent agreement. Proof-of-concept experiments demonstrate upward of 78-dB suppression of a large interfering signal, while degrading the response to small signals of interest by only 8 dB.

Equations for Two-Tone Analog Optical Phase Modulation With an Asymmetric Interferometer

Analytical research is presented for electro-optic phase modulation followed by an asymmetric interferometer that is used for phase-to-intensity conversion. The resulting closed-form equations quantify the performance for arbitrary interferometer bias and input radio-frequency power. Even-order distortions, very important for multi-octave applications, are analyzed. Measured data for a Mach-Zehnder interferometer (MZI) are demonstrated to agree well with the theoretical results. Photodiode-induced even-order distortion is identified as the limiting nonlinearity when the MZI is biased at quadrature.

Long-Reach Analog Photonics for Military Applications

In the increasingly digital world of electronic warfare, defense and signals intelligence, analog fiber optics and photonics still play a crucial enabling role.

Microwave photonic delay line signal processing.

This paper provides a path for the design of state-of-the-art fiber-optic delay lines for signal processing. The theoretical forms for various radio-frequency system performance metrics are derived for four modulation types: X- and Z-cut Mach-Zehnder modulators, a phase modulator with asymmetric Mach-Zehnder interferometer, and a polarization modulator with control waveplate and polarizing beam splitter. Each modulation type is considered to cover the current and future needs for ideal system designs. System gain, compression point, and third-order output intercept point are derived from the transfer matrices for each modulation type. A discussion of optical amplifier placement and fiber-effect mitigation is offered. The paper concludes by detailing two high-performance delay lines, built for unique applications, that exhibit performance levels an order of magnitude better than commercial delay lines. This paper should serve as a guide to maximizing the performance of future systems and offer a look into current and future research being done to further improve photonics technologies.

Tandem Electrooptic Modulation and Interferometric Detection: Theory and Application

This paper expands upon the RF photonic theory of electrooptic phase and intensity modulation detection as seen when coupled in tandem with an asymmetric Mach-Zehnder interferometer through the derivation of power transfer functions for such optical-microwave configurations. An inspection of the theory is presented and validated through experimental results. Several applications of a modulation/interferometric architecture are also reviewed, delineating the importance of a valid model for predicting the behavior of similar analog optical systems.

Fiber-optic links with all-photonic RF gain and low RF noise figure

State-of-the-art analog fiber-optic links exhibiting electronic power gain and/or electronic noise figure less than 20 dB at frequencies higher than 1 GHz are demonstrated and reviewed.