6–34 GHz offset phase-locking of Nd:YAG 1319 nm nonplanar ring lasers

Optical Comb Sources and High-Resolution Optical Filtering for Measurement of Photodiode Harmonic Distortion

“…The output of the optical filter is combined with the output of a second laser (80 mW distributed feedback laser, EM4 Inc., nm) using another 50/50 coupler and the composite signal is directed onto the photodiode under test. As in other techniques [16], [19], the second laser is sufficiently offset in wavelength from the first that there is no beating between the two at the photodiode. Therefore, the second laser acts only as a source of average photocurrent allowing the output RF power and DC photocurrent to be varied independently.…”

“…For comparison we also measure the same photodiode using a pair of offset phase-locked Nd:YAG lasers at approximately 1320 nm [16]. The experimental parameters remain fixed-the fundamental excitation is at GHz, the average photocurrent is held at 10 mA and the measurements are made for both V and V. Table II summarizes the results of our measurements.…”

“…This is why a simple analog photonic link may not be used to characterize PD nonlinearity-for typical photodiodes and MZMs, the MZM distortion is significantly larger than that of the PD. Several techniques have been devised to provide pure optical excitation signals; the purest excitation is achieved through heterodyning a pair of offset phase-locked lasers [16]. This two optical-tone technique produces a single RF tone at the offset frequency and is ideally suited to characterize PD nonlinearity through measurements of harmonic distortion levels.…”

Millimeter-Wave Radio over Fiber System for Broadband Wireless Communication

“…The main drawback of optical self-heterodyning is the strong influence of laser phase noise and optical frequency variation on the purity and stability of the generated mm-wave signal. The optical phase-locked loop (OPLL) has been used to reduce the phase noise (Williams et al, 1989;Gliese et al, 1992). Hence the optical self-heterodyning is a costly solution for photonic generation of mm-wave signal because it needs a special laser system.…”

Coherent Optical Generation of a 6 GHz Microwave Signal with Directly Phase Locked Semiconductor DFB Lasers

“…Naturally, the hereby generated carriers must comply with the noise requirements of the microwave systems, in which they are to be used. Such carriers can be generated with a narrow band heterodyne optical phase locked loop (OPLL) based on either solid state lasers, such as the Nd:YAG [2], or semiconductor lasers with external cavities [3], [4] or with negative electrical feedback [5]. The use of semiconductor lasers without external linewidth narrowing arrangements would, however, be much more attractive due to compactness and potential for monolithic opto-electronic integration.…”