H. W. Yen

17‐GHz bandwidth electro‐optic modulator

A high‐speed integrated‐optic Ti:LiNbO3 Mach–Zehnder interferometric modulator for 0.83‐μm wavelength operation has been fabricated and characterized. The modulator exhibits smooth, resonance‐free frequency response with a 17‐GHz 3‐dB bandwidth. The modulator has a built‐in phase bias of π/2 for maximum linearity. Complete intensity modulation can be achieved with 120‐mW drive power. Optical modulation was measured up to 18 GHz directly by using a very high‐speed photodiode and indirectly using the swept frequency technique.

Switching of GaAs IMPATT diode oscillator by optical illumination

A study was made of the microwave oscillaton characteristics of GaAs IMPATT diodes under external optical illumination. It was found that depending on the diode’s bias condition, the frequency of oscillation and the intensity of illumination, the IMPATT microwave output power can be either enhanced or reduced.

Minimizing dc drift in LiNbO3 waveguide devices

Improved stability against electrical dc bias drift has been demonstrated in LiNbO3 electro‐optic modulators by replacing the commonly used SiO2 buffer layer with indium tin oxide (ITO), a transparent conductor. The long term drift of the modulators having an ITO buffer layer with a sheet resistivity of ∼20 Ω/⧠ is less than 0.3% in 8 h. The mechanism of the dc drift phenomenon is discussed using an electrical equivalent circuit model of the modulator.

Optical injection locking and switching of transistor oscillators

In this letter we describe a novel approach of achieving injection locking of solid‐state oscillators. This is done by taking an external driving signal to modulate a GaAlAs cw injection laser and then guiding the modulated light output in a fiber waveguide to illuminate the active solid‐state component in the oscillator circuit. Experiments were carried out with silicon transistor oscillators with frequency ranging from below 1 kHz up to 1.8 GHz. Optical injection locking was observed not only at fundamental frequencies, but also at various subharmonics with less tolerance in frequency deviation. It is also possible to achieve switching and locking simultaneously in these oscillators.

Fabrication and characterization of GaAs Schottky barrier photodetectors for microwave fiber optic links

High‐Speed GaAs Schottky barrier photodiodes have been fabricated and characterized. These detectors have 3‐dB bandwidths of 20 GHz and quantum efficiencies as high as 70%. The response of the detectors to light modulated at 1–18 GHz has been directly measured. Microwave modulated optical signals were obtained by using a LiNbO3 traveling wave modulator and by heterodyning two laser diodes.

Traveling-wave electrooptic modulator

An integrated-optics Mach-Zehnder interferometric modulator in LiNbO3 has been designed and fabricated. The electrodes are 3-μm thick asymmetric coplanar striplines formed by ion-beam etching techniques. The push–pull design and the r33 electrooptic coefficient of LiNbO3 are utilized for efficient modulation. Complete modulation is achieved with 6.5 V for the 6-mm long device at 0.83-μm wavelength and with 18 V at 1.3-μm wavelength. The 3-dB bandwidth of the modulator is 3.5 GHz, being limited by the excessive resistive loss of the stripline electrodes. Since this particular modulator retains a dc electrical bias, it performs either as an intensity modulator by applying a π/2 dc phase bias to achieve maximum linearity or as a frequency shifter by changing the dc bias point to π. In addition, we analyzed the principle of operation of the Y junction by observing both the in-phase and the out-of-phase modes of a multimode waveguide modulator.

High-Speed Optical Modulation Techniques

In this paper, transmitter and receiver components for microwave fiber optic links are reviewed. Present link signal to noise limitations imposed by the performance of these components are analyzed, and promising trends in component development are discussed.

Radar applications of X-band fiber optic links

High-speed fiber-optic delay lines for use in radar phase noise and repeater test sets are described. Both FM and AM signal-to-noise performance measurements of the X-band modulated (10-GHz) fiber-optic links for these applications are presented. Using long delay lines, improved measurement capability and flexibility was achieved with small components.<<ETX>>

10 GHz RF Fiber Optic Links

A 10-GHz direct laser modulation and an external modulation link were demonstrated. Signal-to-noise ratios of 130 dB/Hz and 115 dB/Hz have has been measured for the external modulation link at 1.3 µm wavelength and for the direct modulation link at 0.83 µm wavelength, respectively.

Radar measurement applications of fiber optic links

Novel applications of fiber-optic delay lines to improve the capability and performance of radar repeater and phase noise test sets are described. Using a 2.25-km-long fiber-optic link, the generation of an ideal target for a radar repeater test set and the measurement of phase noise within 100 Hz of a 9.6-GHz radar carrier signal is demonstrated using a delay line discriminator phase noise test set. FM and AM signal-to-noise measurements were made to determine the performance capability of the 10-GHz modulated fiber-optic links for radar applications.<<ETX>>