Zhaosong Li

InP-based monolithically integrated few-mode devices

Mode-division multiplexing (MDM) has become an increasingly important technology to further increase the transmission capacity of both optical-fiber-based communication networks, data centers and waveguide-based on-chip optical interconnects. Mode manipulation devices are indispensable in MDM system and have been widely studied in fiber, planar lightwave circuits, and silicon and InP based platforms. InP-based integration technology provides the easiest accessibility to bring together the functions of laser sources, modulators, and mode manipulation devices into a single chip, making it a promising solution for fully integrated few-mode transmitters in the MDM system. This paper reviews the recent progress in InP-based mode manipulation devices, including the few-mode converters, multiplexers, demultiplexers, and transmitters. The working principle, structures, and performance of InP-based few-mode devices are discussed.

A waveguide loss measurement method based on the reflected interferometric pattern of a Fabry-Perot cavity

We propose a new waveguide loss measurement method based on the reflected interferometric pattern from the waveguide. The loss of the waveguide is obtained by analyzing the fineness of the reflected interferometric pattern from the Fabry-Perot (F-P) cavity formed by the facets of a single-mode waveguide. In this method, a single mode lensed fiber and a circulator is used to direct the tunable laser into the waveguide under test and collect the reflected spectrum pattern through a photodetector. Comparing to the traditional transmission F-P interferometric method relying on double end fiber coupling, the proposed method requires only a single end coupling, considerably simplifying the coupling difficulty and the measurement system complexity. The fineness measurement is also free from the influence of background noise level, and reduces the coupling accuracy requirement. This method is low-cost, easy-to-operate and reliable, which can serve as an alternative method to measure the waveguide loss.

Electrically and Optically Bistable Operation in an Integration of a 1310nm DFB Laser and a Tunneling Diode

We experimentally demonstrate an InP-based hybrid integration of a single-mode DFB laser emitting at around 1310nm and a tunneling diode. The evident negative differential resistance regions are obtained in both electrical and optical output characteristics. The electrical and optical bistabilities controlled by the voltage through the tunneling diode are also measured. When the voltage changes between 1.46V and 1.66 V, a 200-mV-wide hysteresis loop and an optical power ON/OFF ratio of 17 dB are obtained. A side-mode suppression ratio of the integrated device in the ON state is up to 43 dB. The tunneling diode can switch on/off the laser within a very small voltage range compared with that directly controlled by a voltage source.

Asymmetric quantum well broadband thyristor laser

A broadband thyristor laser based on InGaAs/GaAs asymmetric quantum well (AQW) is fabricated by metal organic chemical vapor deposition (MOCVD). The 3- μ m-wide Fabry–Perot (FP) ridge-waveguide laser shows an S-shape I − V characteristic and exhibits a flat-topped broadband optical spectrum coverage of ~27 nm (Δ −10 dB) at a center wavelength of ~1090 nm with a total output power of 137 mW under pulsed operation. The AQW structure was carefully designed to establish multiple energy states within, in order to broaden the gain spectrum. An obvious blue shift emission, which is not generally acquired in QW laser diodes, is observed in the broadening process of the optical spectrum as the injection current increases. This blue shift spectrum broadening is considered to result from the prominent band-filling effect enhanced by the multiple energy states of the AQW structure, as well as the optical feedback effect contributed by the thyristor laser structure.

An InP-based two-mode converter/(de)multiplexer with 100% mode conversion efficiency by using multimode interference couplers as the building blocks

A two-mode converter/(de)multiplexer with 100% mode conversion efficiency is designed and demonstrated on InP substrate by using multimode interference couplers as the building blocks to realize the functions of mode conversion, multiplexing and phase shifting.

Proposal of an InP-based few-mode transmitter based on multimode interference couplers for wavelength division multiplexing and mode division multiplexing applications

An InP-based monolithically integrated few-mode transmitter aiming at the combination of wavelength division multiplexing (WDM) and mode division multiplexing (MDM) technologies is proposed. The core elements of the proposed transmitter are mode converters and a wavelength-mode division multiplexer that are all based on multimode interference (MMI) couplers. Simulations show that the wavelength-mode division multiplexer has a large fabrication tolerance of 30 and 0.5 μm for the length and the width of the device, respectively. A low loss below 0.26 dB for the passive parts of the transmitter is obtained in the whole C-band wavelength range.

A Monolithically Integrated InP-based Few-mode Laser

A monolithically integrated InP-based few-mode laser comprising of a distributed feedback laser (DFB) and a multimode interference coupler (MMI) based mode converter is designed and manufactured. TE0 and TE1 laser modes generation are demonstrated.

Proposal of an InP-based monolithically integrated few mode transmitter based on multimode interference coupler

We propose an InP-based monolithically integrated few mode transmitter structure based on multimode interference coupler (MMI), and demonstrate an integrated mode converter and multiplexer (converter-multiplexer). This converter-multiplexer can convert the TE0 mode to either TE0 or TE1 mode and multiplex the two modes into a common output port. The device can be potentially used in mode division multiplexing system.