H.F. Liu

Locking characteristics of a passively mode-locked monolithic DBR laser stabilized by optical injection

We demonstrate the generation of ultrastable millimeter-wave carriers from a passively mode-locked monolithic InGaAs MQW DBR laser injection locked by a double sideband suppressed carrier modulated optical signal. We investigate the effect of the optical power and the wavelength of the injection signal on the phase noise of the generated millimeter-wave carrier. Once locked, the laser can track the variations in the beat frequency of the injected millimeter-wave signal over an RF frequency range of approximately 172 MHz.

THz optical beat frequency generation from a single mode locked semiconductor laser

We demonstrate ultrahigh repetition rate beat signal generation by filtering two modes from the optical spectrum of a 110 GHz pulse train produced by a 1.56 μm wavelength, subharmonic hybrid mode locked monolithic semiconductor distributed Bragg reflector laser. The beat signal repetition rate can be tuned to any higher harmonic of the 110 GHz frequency up to 1.34 THz. Furthermore, the filtering technique facilitates low phase noise and synchronization with these signals.

Novel technique for reduction of amplitude modulation of pulse trains generated by subharmonic synchronous mode-locked laser

Subharmonically synchronous mode-locked and hybrid mode-locked lasers suffer from strong amplitude modulation at frequencies corresponding to injection signal frequency. In this paper, we demonstrate for the first time, significant reduction of amplitude modulation of pulse trains generated by a subharmonic synchronous mode-locked laser at 38 GHz using a nonlinear optical loop mirror. Experimental results as well as a theoretical analysis for the scheme are presented.

Subharmonic synchronous and hybrid mode-locking of a monolithic DBR laser operating at millimeter-wave frequencies

A detailed comparison of subharmonic synchronous and subharmonic hybrid mode-locking of a monolithic distributed Bragg reflector (DBR) laser operating at 33 GHz is presented. Optical injection at the 20th subharmonic frequency (1.65 GHz) has produced a locking range of 10 MHz with negligible amplitude modulation. In comparison, electrical injection at the 4th subharmonic frequency (5.83 GHz) has shown higher levels of amplitude modulation and a narrower locking range (4 MHz). While subharmonic hybrid mode-locking remains a simple and cost effective solution for the generation of low timing jitter high-repetition rate optical pulse trains, subharmonic synchronous mode-locking shows superior performance with regard to reduced amplitude modulation and larger locking range.

Multichannel dual-mode-based optical pulse source from a single laser diode

Generation of multichannel optical pulse trains by spectral slicing of two adjacent optical modes from a single subharmonically synchronous mode-locked laser diode is demonstrated in this letter. The obtained pulse source exhibits high extinction ratio (> 15 dB), low amplitude modulation (<-24.8 dB) and low timing jitter (< 0.5 ps) over all the channels from 1550 to 1564 nm. The resulting pulse trains can be used for the generation of carrier suppressed return-to-zero data in dense wavelength-division-multiplexed systems and optical generation of millimeter-wave signals required for future multiple channel fiber wireless systems.

Amplitude noise of 40-GHz pulses from a subharmonically synchronous mode-locked semiconductor laser

The broad-band amplitude noise of 40-GHz pulses from a subharmonically synchronous mode-locked (SSML) semiconductor laser is investigated. Experiments show that the amplitude noise of pulses generated from a SSML laser depends on the amplitude noise and pulsewidth of injected pulses, frequency detuning and subharmonic numbers.

Robust all-optical harmonic clock signal generation through optical injection into passively mode-locked semiconductor lasers

In this paper, we demonstrate all-optical harmonic clock signal generation, in a passively mode-locked semiconductor laser, through optical injection of pseudorandom optical pulses, with a repetition rate at a subharmonic of the lasers cavity frequency. The locking dynamics are characterized in terms of injected bit patterns. It is shown that the laser is a very robust clock signal generator at 38 GHz (timing jitter of less than 0.4 ps with 2/sup 31/-1 pseudorandom binary sequence (PRES) injection at the 20th subharmonic). It also can withstand extreme injection conditions (PRES mark ratio as low as 1/8) at the 20th subharmonic at an injection power of -3 dBm.

Suppression of amplitude modulation of pulses generated from a subharmonically mode-locked semiconductor laser

A feedforward modulation technique is used to suppress amplitude modulation associated with 40-GHz pulses generated from a subharmonically mode-locked semiconductor laser. It is shown that the amplitude modulation can be suppressed by as much as 20 dB. The improvement of amplitude modulation is shown for different subharmonic numbers.

Injection signal wavelength dependence of a subharmonically synchronous mode-locked monolithic semiconductor laser

Subharmonic synchronous mode-locking (SSML) has been shown to be a very attractive scheme for achieving high repetition rate optical pulses at mm-wave frequencies, and beyond. In this paper, we report the dependence of the injected signal wavelength on the performance of SSML lasers around its lasing wavelengths. In particular, the effect of coherent interaction will be addressed.

Multichannel dual-mode pulse generation for DWDM and fiber-wireless system application

In this paper we propose a novel technique for the generation of wideband dual-mode pulses from a single subharmonically synchronous mode-locked laser diode (LD). The obtained pulse source exhibits high extinction ratio (>15 dB) and low timing jitter (<0.5 ps) over all the channels from 1550 to 1564 nm. The proposed scheme is cost-effective and a promising candidate as a pulse source for generation of carrier suppressed return-to-zero (CSRZ) modulation format in dense wavelength division multiplexed (DWDM) systems and optical generation of millimeter-wave frequency signals in multiple channel fiber wireless systems.