Enhanced optical frequency comb generation by pulsed gain-switching of optically injected semiconductor lasers

Abstract

We report on the experimental generation of broad and flat optical frequency combs (OFC) in a 1550 nm laser diode using gain switching with pulsed electrical excitation together with optical injection. The combination of both techniques allows the generation of high-quality OFCs at a repetition frequency of 500 MHz, showing a low-noise optical spectrum with unprecedent features in terms of width (108 tones within 10 dB) and flatness (56 tones within 3 dB) in comparison with those previously reported for this modulation frequency. The influence of the injection conditions on the OFC quality is studied. Using these two techniques, it has been possible to reduce the separation between tones, generating high spectral performance OFCs with a repetition rate of 100 MHz.

Gain-switched semiconductor lasers with pulsed excitation and optical injection for dual-comb spectroscopy

“…The measurement procedure includes the selection of the master laser wavelength at 1,549.63 nm, which is close to, but not equal to the center of the H 13 CN absorption line (12.5 GHz of detuning), because the combs show instabilities at the injection frequency. The injected power in the slaves is adjusted to ensure injection locking while maintaining broad and flat OFCs [17]. The emission frequencies of the two slave lasers are slightly tuned by temperature in order to have the master laser injection at the blue side of the combs.…”

“…Below the gigahertz range, the highest frequency resolution achieved with DCS based on GS and OI reported so far is 500 MHz [16]. However, we have recently demonstrated [17] that the limitation on the line spacing is overcome by a combination of OI and GS with pulsed electrical excitation. In that work, we reported on the generation of flat low-noise combs in the C-band with an optical bandwidth of 85 GHz and a line spacing of 100 MHz.…”

“…In [17] we investigated the optimal conditions for the generation of OFCs with repetition frequencies of 100 MHz by pulse-driven GS of optically injected laser diodes. Following that analysis, here we generate a couple of OFCs to perform DCS.…”

“…In parallel to the search for innovative applications, many efforts have been devoted to develop alternatives to mode-locked OFCs, with the aim of providing tunable, cost-efficient and field-deployable comb generators [9][10][11]. Among these comb platforms, OFCs generated from semiconductor lasers by gain-switching (GS) have attracted considerable attention in recent years [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Besides benefiting from the usual advantages of semiconductor sources (high efficiency, low cost and small footprint), the comb generation by GS also offers low losses, flexible comb line spacing and, outstandingly, suitability for photonic integration [20].…”

Self-starting VCSEL-based optical frequency comb generator

“…The GS technique consists of large-signal modulation of a semiconductor laser at a specific repetition frequency to ensure that only the first spike of the transient relaxation oscillations is excited [11]. Although edge-emitting lasers such as distributed feedback (DFB) [12] and discrete mode lasers (DML) [13] are preferred for their large modulation bandwidths, vertical-cavity surface-emitting lasers (VCSELs) have also been used for gain-switched OFC generation owing to their low threshold currents, low cost and single-mode transverse emission [14]. VCSEL-based OFCs produce energy-efficient and high mode coherence combs [15].…”