Optical generation of a precise microwave frequency comb by harmonic frequency locking

Abstract

A semiconductor laser under negative optoelectronic feedback is applied to the generation of a microwave frequency comb through the nonlinear dynamics. The laser system is operated in a harmonic frequency-locked pulsing state, where its power spectrum is a microwave frequency comb that consists of multiples of a locking frequency. Every frequency component of the comb can be simultaneously stabilized by simply injecting an external microwave modulation at any component of the comb. This phenomenon can be viewed as a kind of microwave injection locking of the laser dynamics.

Frequency locking in a semiconductor laser with double incoherent optical feedback

“…Moreover, as shown in Fig. 2(c), different orders of beating can also be found, and a broadband microwave frequency comb with 382 MHz interval is formed within 0-15 GHz range [7]. Fig.…”

“…Therefore, employing the similar approach used in Refs. [6][7][8], the FL state f lock ≈ 3 f loop1 ≈ 2 f loop2 could be defined and f lock ≈ 382 MHz can be obtained. Moreover, as shown in Fig.…”

“…The dynamics of a semiconductor laser (SL) has been widely studied by many researchers since SL has many applications in optical communications, optical sensors and microwave photonics [1][2][3][4][5][6][7][8][9]. By adjusting operation parameters, SL constructed system can display rich dynamical behaviors, such as periodic, quasiperiodic oscillations, frequency locking (FL) and chaos [2][3][4][5].…”

“…These dynamical states, whose intensities usually vary at a level of microwave frequency, can produce continuous or discrete broadband power spectrum signals. For example, continuous spectrum signals can be generated from the chaotic state [5], and discrete spectrum signals or microwave frequency comb can be produced from the FL state [6,7].…”

“…FL manifests itself when two oscillators are coupled together and entrain each other to some rational multiple of their natural frequencies, and oscillates periodically with a common frequency. FL phenomena have been reported in some SL systems such as optoelectronic feedback SLs [6,7], modulated external cavity injection SLs [8,9], and modulated self-pulsing SLs [10] ports show that the introduction of a second external cavity can increase complexity of a single external cavity SL or control its dynamics [11,12]. Recently, phase-locking phenomenon, which is similar to FL, was theoretically studied in a SL with double external cavities [13].…”