A novel design of two-mode (DE)MUX based on multimode interference (MMI) couplers on InP substrate is proposed. A phase shifting section based on the thickness variation of the core layer is introduced in the (DE)MUX to realize a 100% mode conversion efficiency and multiplexing. The total length of the structure is only 549 μm, much shorter than other InP based mode (DE)MUXs. Simulations show that, the device crosstalk is below -20 dB and the insertion loss is lower than 1 dB for both of the fundamental mode and the first order mode within the whole C band. This new structure can be potentially integrated with other devices based on InP substrate to serve as a monolithic few-mode transmitter/receiver.
Monolithically integrated electroabsorption modulated lasers (EML) are widely being used in the optical fiber communication systems, due to their low chip, compact size and good compatible with the current communication systems. In this paper, we investigated the effect of Zinc diffusion on extinction ratio of electroabsorption modulator (EAM) integrated with distributed feedback laser (DFB). EML was fabricated by selective area growth (SAG) technology. The MQW structure of different quantum energy levels was grown on n-type InP buffer layer with 150nm thick SiO2 parallel stripes mask by selective area metal-organic chemical vapor deposition (MOCVD). A 35nm photoluminescence wavelength variation was observed between the laser area (λ<sub>PL</sub>=1535nm) and modulator area (λ<sub>PL</sub>=1500nm) by adjusting the dimension of parallel stripes. The grating (λ=1550nm) was fabricated in the selective area. The device was mesa ridge structure, which was constituted of the DFB laser, isolation gap and modulator. The length of every part is 300μm, 50μm, and 150μm respectively. Two samples were fabricated with the same structure and different p-type Zn-doped concentration, the extinction ratio of heavy Zn-doped device is 12.5dB at -6V. In contrast, the extinction ratio of light Zn-doped device is 20dB at -6V, that was improved for approximate 60%. The different Zn diffusion depth into the MQW absorption layer was observed by Secondary ion mass spectrometer (SIMS). The heavy Zn-doped device diffused into absorption layer deeper than the light Zn-doped device, which caused the large non-uniformity of the electric field in the MQW layer. So the extinction ratio characteristics can be improved by optimizing the Zn-doped concentration of p-type layer.
We report systematic modelling of 1310 nm InGaAsP/InP electroabsorption modulators. The modulator is a reverse
biased p-i-n diode, in which the MQW structure is composed of several InGaAsP/InGaAsP quantum wells. By a 3D
finite element software PICS3D, we have comprehensively investigated the internal physical mechanism of the
modulator, which includes the red shift of the absorption edge with the reverse bias and the absorption intensity, which
could be derived from the normalized overlap integral between the energy levels for the electrons and the holes. The
absorption spectrum on wavelength and the reverse bias voltage is analyzed, which provide us with both the extinction
ratio and the transimision loss for a special operating wavelength. Key design parameters such as barrier height and
quantum well width are optimized for extinction ratio, and confirmed by parallel experimental studies. What’s more, the
RF performance has been investigated in detail. The junction capacitance, the series resistance and the parasitic
capacitance (mostly the bonding pad) are studied systematically. A ridge structure model is analyzed for high speed
performance, in which the important parameters, such as the ridge width, the cavity length, the area of the bonding pad
and the thickness of polyimide (or BCB) under the bonding pad, are optimized for over 20GHz 3dB bandwidth. The
cavity length is optimized by making compromise between the extinction ratio and the RF performance. In conclusion,
the design parameter space of the 1310nm InGaAsP/InP EAM have been systematically explored. Our work should
provide a firm basis for 1310nm InGaAsP/InP EAM device design optimization for optical datacom applications.