Roger Helkey

A down-conversion optical link with RF gain

A down-conversion optical link with a radio frequency (RF) conversion gain of 33 dB was demonstrated at 450 MHz. The gain was increased to 17 dB using photodetector impedance matching. Limitations due to each link element are examined and down-conversion gain up to the millimeter-wave (mm-wave) frequency band is predicted.

Broadband, directly modulated analog fiber link with positive intrinsic gain and reduced noise figure

We report the concept and first demonstration of a broadband amplifierless, directly modulated analog fiberoptic link with an intrinsic gain of +3.8 dB, based on a series connection of diode lasers and a pin photodiode.

Effect of optical feedback on high-dynamic-range Fabry-Perot laser optical links

The effect of optical backreflection is measured on a 450-MHz optical link using a commercial Fabry-Perot laser without an isolator. With a low backreflection photodetector, the dynamic range of the Fabry-Perot link is comparable to a link with a high-linearity distributed feedback laser. With a standard photodetector, the dynamic range is 13 dB lower.

Relative-intensity-noise cancellation in bandpass external-modulation links

A new method of optically summing time-shifted complementary signals to cancel relative intensity noise (RIN) in narrow-band external-modulation optical links is proposed and demonstrated. Differential-link noise figure and dynamic-range improvement are compared to the conventional low-biased modulator configuration for suboctave applications. RIN suppression of 12 dB at 4 GHz is demonstrated.

Narrow-band optical A/D converter with suppressed second-order distortion

A high dynamic range narrow-band optical analog-to-digital converter configuration is proposed and demonstrated in which a narrow-band electrical input signal is converted to a baseband digitized signal while suppressing second-order modulator distortion products. Operation is demonstrated at 439 MHz, resulting in 72 dB of intermodulation suppression for a 0.8-ms sampling time.

Fabry-Perot laser high linearity analog optical links

High dynamic range analog optical links are demonstrated using a variety of Fabry-Perot lasers, including commercial and custom devices. All of the devices demonstrate a dynamic range and noise figure close to that of an analog DFB laser for short (<2 km) links. The best devices have performance which rivals that of a typical DFB laser.

Octave Bandwidth Analog Link with a Monolithic Laser/Electroabsorption Modulator

High linearity RF analog links are of great interest for remoting cellular radio and personal communications systems base stations. Electroabsorption modulators have been demonstrated to give high linearity when used in external modulation analog optical links1. Monolithically integrated laser/electroabsorption modulators have been demonstrated to be useful for long-haul multi-gigabit digital communications2,3. Integrated laser/modulators have been demonstrated for analog applications up to 10MHz4. In this paper, we demonstrate a monolithically integrated laser/electroabsorption modulator for high-frequency analog link applications. The monolithic laser/modulator is shown to offer good linearity with considerably reduced size and weight compared to an external electroabsorption modulator with a Nd:YAG pump laser.