T. Jung

Characterization of a coherent optical RF channelizer based on a diffraction grating

A coherent optical RF channelizer has been constructed and characterized. The optical channelizer is based on a free-space optical diffraction grating, and utilizes coherent optical heterodyne detection to translate all of the frequency channels to a common intermediate frequency (IF). The designed optical channelizer has a 1-GHz channel spacing, and a nominal 5-GHz IF and can offer an instantaneous bandwidth greater than 100 GHz. The channelizing receiver has been characterized for its frequency response, crosstalk, and spur-free dynamic range, and the results are in a good agreement with the theoretical values.

Experimental demonstration of a balanced electroabsorption modulated microwave photonic link

A novel balanced electroabsorption modulated photonic link for simultaneous suppression of even-order distortions, third-order distortions, laser relative intensity noise (RIN), and common amplified spontaneous emission noise at the same modulator bias point was experimentally demonstrated for the first time. By biasing the balanced electroabsorption modulator at the third-order null, the third-order distortions were suppressed, while the balanced link architecture suppressed all even-order distortions and common mode noises. The fabricated balanced electroabsorption modulator (B-EAM) showed well-matched dc characteristics in terms of I-V and transfer curve. System experiments were performed to compare single-EAM and B-EAM links. In the B-EAM link, 2-dB suppression of laser RIN and 20-dB improvement in spurious free dynamic range over the single-EAM link were observed.

CW injection locking of a mode-locked semiconductor laser as a local oscillator comb for channelizing broad-band RF signals

CW injection locking of mode-locked semiconductor lasers has been experimentally demonstrated. The phases of the mode-locked frequency comb are shown to be coherent with that of the master CW laser. The pulsewidth of the mode-locked laser remains almost unchanged (<2 ps) for a broad range of injection power (-28 to -12 dBm). Pulling of the entire mode-locked frequency comb by 400 MHz has been demonstrated. The coherent multifrequency source can be used as a local oscillator comb for coherent optical channelizers for ultrawide-band RF signals.

High power and highly linear monolithically integrated distributed balanced photodetectors

A distributed balanced photodetector with high saturation photocurrent and excellent linearity has been experimentally demonstrated. The maximum linear direct current (DC) photocurrent of 33 mA per branch is equivalent to 66 mA in single-ended photodetectors. A setup for investigating the alternating current (AC) linearity of the receiver is proposed and experimentally demonstrated. The receiver exhibits high AC linearity, even under high power operation. The bandwidth of the receiver remains unchanged when the effective do photocurrent is varied from 1 mA to 21 mA. The distribution of photocurrents was also measured. Device length for optimum radiofrequency performance is calculated and implemented in the design. A correlation between the dark current of the photodiodes and their failure mechanism has been established. Analyzing the failure mechanism, junction diodes are found to be more suitable for high power applications.

Modulation bandwidth enhancement and nonlinear distortion suppression in directly modulated monolithic injection-locked DFB lasers

We have experimentally investigated the dynamic performance and the suppression of nonlinear distortions of a monolithic optical injection-locked distributed feedback (DFB) laser. The master and the slave lasers are monolithically integrated in a single strip of strongly coupled DFB laser. Optical injection locking is achieved by current tuning. The resonant frequency of the laser is increased from 11 GHz to 23 GHz, and nonlinear distortions are suppressed by more than 15 dB.

A novel monolithic distributed traveling-wave photodetector with parallel optical feed

We report on a novel monolithic distributed traveling wave photodetector with parallel optical feed to an array of individual photodiodes using an integrated multimode interference (MMI) coupler to attain high saturation current. The parallel optical feed reduces the maximum photocurrent and photocurrent density seen by any single photodiode, thus increasing the maximum linear photocurrent of the detector. We have successfully fabricated a device with a maximum linear photocurrent of 20 mA and a responsivity of 0.13 A/W.

Generation of millimeter waves by photomixing at 1.55 /spl mu/m using InGaAs-InAlAs-InP velocity-matched distributed photodetectors

Millimeter-wave generation by photomixing at 1.55 /spl mu/m in long-wavelength velocity-matched distributed photodetector (VMDP) is experimentally demonstrated. The VMDP exhibits a dc responsivity of 0.25 A/W, a breakdown voltage of 7-9 V, and up to 15-mA dc photocurrent without damage. Millimeter-wave output powers of -21 dBm at 75 GHz and -24 dBm at 95 GHz were measured.

Optical injection-locked gain-lever distributed Bragg reflector lasers with enhanced RF performance

Directly modulated fiber-optic links offers significant advantages in system cost and complexity. However, they often suffer from high link loss and inferior RF performance compared with externally modulated links. In this paper, we have experimentally investigated the amplitude modulation (AM) efficiency, modulation bandwidth, and the nonlinear distortions of a directly-modulated gain-lever distributed Bragg reflector (DBR) laser under external light injection for the first time. By combining gain-lever modulation with optical injection locking, increased modulation efficiency (10 dB) and bandwidth (3 times) as well as suppressed third-order intermodulation distortion (15 dB) have been achieved simultaneously.

Optical generation of millimeter-waves using monolithic sideband injection locking of a two-section DFB laser

A novel optical millimeter-wave generation using sideband injection locking is demonstrated using monolithic two-section DFB lasers. The tunable millimeter-wave is generated by adjusting the RF-modulation frequency and bias currents.

Velocity-matched distributed photodetectors with p-i-n photodiodes

We report on the first demonstration of velocity-matched distributed p-i-n photodetectors. A record high linear DC photocurrent of 45 mA has been achieved without suffering from thermal damage, thanks to the superior power handling capability of p-i-n photodiodes. The frequency response is flat from 1 GHz to 35 GHz.