Haisong Jiang

All-optical flip-flop operation based on asymmetric active-multimode interferometer bi-stable laser diodes

We demonstrate fast and low energy all optical flip-flop devices based on asymmetric active-multimode interferometer using high-mesa waveguide structure. The implemented devices showed high speed all-optical flip-flop operation with 25 ps long pulses. The rising and falling times of the output signal were 121 ps and 25 ps, respectively. The required set and reset pulse energies were only 7.1 fJ and 3.4 fJ, respectively.

Active MMI devices: Concept, proof, and recent progress

Multi-mode interference (MMI) couplers (waveguides) are widely studied and developed as key components of photonic integrated circuits, including power coupler/dividers, and others. Furthermore, another possibility utilizing MMI has been investigated on active devices so far. Owing to the wider area of the multi-mode waveguide section compared with that of the regular single-mode waveguide, MMI may result in higher performance (high power, low power consumption, and others) rather than conventional active devices while maintaining regular single-mode output. Thus, active multi-mode interferometer (active-MMI) devices, including laser diodes (LDs), super-luminescent light emitting diodes (SLEDs), and semiconductor optical amplifiers (SOAs) have been studied. Moreover, they have been also exploited to bi-stable LDs and single wavelength emitters, and others using the interference inside the MMI section. In this paper, we review and summarize the recent progress in active MMI devices. We provide proof of MMI phenomena in active waveguides and discuss the results.

A novel active MMI bi-stable laser using cross-gain saturation between fundamental and first order modes

A novel MMI-based bi-stable laser is proposed for realizing compact size. Relatively low operation current of 100 mA (8 mA hysteresis), and high ON/OFF optical power-ratio of 15 dB were successfully achieved (@L=550 mum).

Electrically controlled optical-mode switch for fundamental mode and first order mode

We have proposed an optical mode switch, the principle of which is based on the partial phase shift of injected light; therefore, one important issue is to clarify the proper design criteria for the mode combiner section. We focused on the bending radius of the S-bend waveguide issue that is connected to the multi mode waveguide in the Y-junction section that acts as mode combiner. Long radius leads to undesired mode coupling before the Y-junction section, whereas a short radius causes radiation loss. Thus, we simulated this mode combiner by the beam-propagation method to obtain the proper radius. In addition, we used a trench pin structure to simplify the fabrication process into a single-step dry-etching process. As a result, we successfully fabricated an optical-mode switch with the bending radius R = 610 µm. It showed the successful electrical mode switching and the achieved mode crosstalk was approximately −10 dB for 1550 nm wavelength with the injection current of 60 mA (5.7 V).

Demonstration of photon-photon resonance peak enhancement by waveguide design modification on active multimode interferometer laser diode

Photon-photon resonance (PPR) peak enhancement on active multimode interferometer laser diode is demonstrated. 3.8 GHz enhancement of PPR peak that results in 3 dB-down frequency response of 17 GHz has been successfully achieved by waveguide geometry modification.

Mode crosstalk evaluation on optical mode switch

We show the mode crosstalk between the fundamental mode and the 1st order mode based on the optical mode switch to investigate the performance experimentally for the first time. In order to evaluate the mode crosstalk, we fabricated and integrated multimode interference (MMI) mode filter with the optical mode switch. The crosstalk of approximately -10 dB between modes has been evaluated by using this mode filter.

Low Hysteresis Threshold Current (39 mA) Active Multimode-Interferometer (MMI) Bistable Laser Diodes Using Lateral-Modes Bistability

We demonstrate low hysteresis threshold current (39 mA) bistable laser diodes (BLDs), with maintaining sufficient hysteresis window (7 mA, 18% of the hysteresis threshold), in active multimode-interferometer (MMI) using lateral-modes bistability. The sufficient cross-gain saturation effect, due to the lateral-modes bistability principle, enables wide hysteresis window. By using this principle, we could design the active-MMI BLDs with relatively short saturable-absorber length that has been one of the main causes of high hysteresis threshold current. In the actual design, we reduce the saturable-absorber region length to 25 μm, and thus, we could achieve a low hysteresis current of 39 mA in the active-MMI BLDs with maintaining sufficient hysteresis window for the first time.

Bandwidth enhancement scheme demonstration on direct modulation active-MMI laser diode using multiple photon photon resonance

By introducing properly designed multiple photo photon resonances (PPRs) on an active-Multimode Interferometer Laser Diode, the confirmed direct modulation bandwidth was enhanced from less than 5 GHz to at least 34 GHz. Multiple oscillating cavities that have slightly different free space ranges (FSRs) are integrated within a single device. The overlap between such FSRs contributes to multiple wavelength differences that are directly related to the PPR frequencies. Evaluated PPR frequencies from experimental data match with designed frequencies. The potential of the 100 GHz level bandwidth of the device has been proved.

Theoretical modelling of photon-photon resonance on active multimode interferometer laser diode toward 40Gbps

Theoretical modelling of photon-photon resonance is confirmed on active MMI LD for the first time. As a result, experimentally obtained resonance peak on active MMI LD of 15GHz is explained successfully.

Dry etching for Germanium waveguides by using CHF3 inductively coupled plasma

Dry etching for Ge waveguide has been researched by using inductively coupled plasma technique with CHF3 gas. It realizes a high selectivity of 5:1 against regular photoresist mask. Moreover, anisotropic etching without under-cut has been successfully realized with an etched siclewall angle of 85 degree with an etching rate of 190 nm/min.