In a two section laser which consists of gain and saturable absorber in which gain is connected to forward biased current and absorber is connected to the reversed biased voltage, mode locking will occur.
Is is possible to get mode locking if the absorber is forward biased?
Kindly explain this
You will usually observe the unlocked behaviour of a regular (Fabry-Perot) laser with random phase of the lines and therefore no pulsing. However several single-section lasers showed "intrinsic" mode locking behaviour, e.g. by four wave mixing. Then the MLL can still lock - even if the absorber is switched transparent.
So the summary: depends on your laser, QD or QW lasers sometimes have good FWM effects that enable mode locking without absorber.
Best wishes,
Johannes
The saturable absorber will be in fact transparent, so no phase control is performed, but the laser could still work in modelocked condition, locked in phase but not "aligned", so no pulses. The phase lag between all modes would be dependent on the dispersion within the cavity, which could be compensated externally with a long fiber with the correct GDD properties.
J.C. Balzer already gave the perfect answer: yes it may be possible, but it depends on your device (gain, losses, absorption, wavelength detuning...). I only want to add a note that the (typically) favorable short carrier recovery time is fastest at highest reverse voltages (see for instance the 20 years old paper: Karin et.al., Appl. Phys. Lett. 64[6], 676 (1994)), which favors modelocking against other parameters. But what is favorable depends on what you want to achieve with your device: highest average power, highest peak power, pulsed modelocking etc.? So it may be worth to look for that regime... but obvoiusly not if you are looking for the shortest possible pulses only.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Optics