Leif A. Johansson

Millimeter-wave modulated optical signal generation with high spectral purity and wide-locking bandwidth using a fiber-integrated optical injection phase-lock loop

We report the first experimental demonstration of millimeter-wave modulated optical signal generation by an optical injection phase-lock loop. A 36-GHz signal was generated by combining optical sideband injection locking with optical phase-lock loop techniques for two fiber-coupled DFB lasers. Single sideband noise spectral density of -92 dBc/Hz at 10 kHz offset, and phase-error variance lower than 0.005 rad/sup 2/ in a 100 MHz bandwidth were measured. The locking bandwidth exceeded 30 GHz.

High Performance InP-Based Photonic ICs—A Tutorial

The performance of relatively complex photonic integrated circuits (PICs) is now reaching such high levels that the long sought goal of realizing low-cost, -size, -weight, and -power chips to replace hybrid solutions seems to have been achieved for some applications. This tutorial traces some of the evolution of this technology that has led to an array of high-functionality InP-based PICs useful in optical sensing and communication applications. Examples of recent high-performance PICs that have arisen out of these developments are presented. Fundamental to much of this work was the development of integration strategies to compatibly combine a variety of components in a relatively simple fabrication process. For the UCSB work, this was initially based upon the creation of a single-chip widely tunable semiconductor laser that required the integration of gain, reflector, phase-tuning and absorber sections. As it provided most of the elements needed for many more complex PICs, their creation followed somewhat naturally by adding more of these same elements outside of the laser cavity using the same processing steps. Of course, additional elements were needed for some of the PICs to be discussed, but in most cases, these have been added without adding significant processing complexity. Generally, the integration philosophy has been to avoid patterned epitaxial growths, to use post-growth processing, such as quantum-well intermixing to provide multiple bandgaps, rather than multiple epitaxial regrowths, and to focus on processes that could be performed with vendor growth and implant facilities so that only basic clean room processing facilities are required.

An Optical Phase-Locked Loop Photonic Integrated Circuit

We present the design, fabrication, and results from the first monolithically integrated optical phase-locked loop (OPLL) photonic integrated circuit (PIC) suitable for a variety of homodyne and offset phase locking applications. This InP-based PIC contains two sampled-grating distributed reflector (SG-DBR) lasers, semiconductor optical amplifiers (SOAs), phase modulators, balanced photodetectors, and multimode interference (MMI)-couplers and splitters. The SG-DBR lasers have more than 5 THz of frequency tuning range and can generate a coherent beat for a wide spectrum of frequencies. In addition, the SG-DBR lasers have large tuning sensitivities and do not exhibit any phase inversion over the frequency modulation bandwidths making them ideal for use as current controlled oscillators in feedback loops. These SG-DBR lasers have wide linewidths and require high feedback loop bandwidths in order to be used in OPLLs. This is made possible using photonic integration which provides low cost, easy to package compact loops with low feedback latencies. In this paper, we present two experiments to demonstrate proof-of-concept operation of the OPLL-PIC: homodyne locking and offset locking of the SG-DBR lasers.

Generation and transmission of millimeter-wave data-modulated optical signals using an optical injection phase-lock loop

Generation and transmission of millimeter-wave data-modulated optical signals is presented using an optical injection phase-lock loop (OIPLL). Millimeter-wave signal generation is demonstrated with wide locking range, 30-GHz low phase noise level, -93 dBc/Hz, and a wide frequency tuning range, 4-60 GHz generation demonstrated using optical injection locking only, verified by using OIPLL in the 26-40 GHz range. The OIPLL is also used to transmit error-free 140-Mb/s amplitude shift keying and 68-Mb/s differential phase-shift keying (DPSK) modulated millimeter-wave signals over up to 65 km of uncompensated standard singlemode fiber. The DPSK system uses reference frequency modulation, eliminating the need for optical amplification.

Programmable Photonic Microwave Filters Monolithically Integrated in InP–InGaAsP

We demonstrate an integrated programmable photonic filter structure capable of producing bandpass filters with both tunable passband bandwidth and center frequency. Such filters could provide dynamic pre-filtering of very wide bandwidth analog microwave signals, essential to the next generation RF-front ends. The photonic filter is constructed from an array of uncoupled identical filter stages, each reconfigurable as a zero or a pole using an asymmetrical Mach-Zenhder Interferometer (MZI) structure with feedback. Integrated on a standard InP-InGaAsP material platform, semiconductor optical amplifiers (SOAs) and current injected phase modulators (PMs) are used to rapidly adjust the individual pole and zero locations, thereby reconfiguring the overall filter function. In this paper, we demonstrate cascaded filter structures with up to four filter stages, capable of producing a variety of higher order filters. Demonstrated filters have a free spectral range (FSR) of 23.5 or 47 GHz. A center frequency tunability over 28 GHz is demonstrated for a 2nd order bandpass filter, and a passband tunability of 1.9-5.4 GHz with stopband rejection >; 32 dB using 3rd and 4th order filters. Finally, the linearity of our active filters is investigated; a preliminary spurious-free dynamic range (SFDR) of 86.3 dB* Hz2/3 is obtained. However, we believe this number can be improved significantly by optimizing the design.

Integrated Coherent Receivers for High-Linearity Microwave Photonic Links

In this paper, we present a coherent receiver based on an optical phase-locked loop (PLL) for linear phase demodulation. The receiver concept is demonstrated at low frequency. For high-frequency operation, monolithic and hybrid integrated versions of the receiver have been developed and experimentally verified in an analog link. The receiver has a bandwidth of 1.45 GHz. At 300 MHz, a spurious free dynamic range (SFDR) of 125 dB ldr Hz2/3 is measured.

36-GHz 140-Mb/s radio-over-fiber transmission using an optical injection phase-lock loop source

We report the first millimeter-wave radio-over-fiber transmission demonstration using optical phase-lock loop techniques. A 36-GHz 140-Mb/s ASK modulated carrier was transmitted through 65 km of standard single-mode fiber with a bit-error rate (BER) of <10/sup -9/, using an optical injection phase-lock loop based on fiber-pigtailed commercially available components.

Highly integrated optical heterodyne phase-locked loop with phase/frequency detection.

A highly-integrated optical phase-locked loop with a phase/frequency detector and a single-sideband mixer (SSBM) has been proposed and demonstrated for the first time. A photonic integrated circuit (PIC) has been designed, fabricated and tested, together with an electronic IC (EIC). The PIC integrates a widely-tunable sampled-grating distributed-Bragg-reflector laser, an optical 90 degree hybrid and four high-speed photodetectors on the InGaAsP/InP platform. The EIC adds a single-sideband mixer, and a digital phase/frequency detector, to provide single-sideband heterodyne locking from -9 GHz to 7.5 GHz. The loop bandwith is 400 MHz.

Highly Linear Coherent Receiver With Feedback

We propose and demonstrate a novel coherent receiver with feedback for high-linearity analog photonic links. In the proposed feedback receiver, a local phase modulator tracks the phase change of the signal and reduces the effective swing across the phase demodulator without reducing the transmitted signal. The signal-to-noise-ratio is thus maintained while linearity is improved. Up to 20-dB improvement in spur-free dynamic range (SFDR) is achieved experimentally. At 3.13 mA of average photocurrent per photodiode, the measured SFDR is 124.3 dBmiddotHz2/3, which corresponds to an SFDR of 131.5 dBmiddotHz2/3 when the link is shot-noise-limited

High Output Saturation and High-Linearity Uni-Traveling-Carrier Waveguide Photodiodes

Waveguide uni-traveling-carrier photodiodes (UTC-PDs) have been fabricated and tested. Output saturation currents greater than 40 mA at 1 GHz are demonstrated for a 10 mumtimes150mum photodiode (PD). The third-order intermodulation distortion is also measured and exhibits a third-order output intercept point of 43 dBm at 20 mA and 34 dBm at 40 mA for this same PD. UTC-PDs with geometries of 5 mumtimes100 mum and 10 mumtimes100 mum are also compared and it is shown that a wider waveguide PD has improved saturation characteristics due to the lower optical power density which reduces the saturation at the front end of the device