Ruikang Zhang

A 40-GHz Colliding Pulse Mode-Locked Semiconductor Laser

A monolithically active-passive integrated colliding pulse mode-locked semiconductor laser is demonstrated in the InGaAsP/InP material system. The device is mode locked at the second harmonic passive mode-locking regime with a wide mode-locking range. Pulse trains with the repetition rate of 40 GHz, 3-dB rf line width of 25 kHz, the pulse width of 2.5 ps, and a nearly transform-limited time-bandwidth product of 0.53 are obtained.

A Two-Mode (De)Multiplexer Based on Multimode Interferometer Coupler and Y-Junction on InP Substrate

A two-mode (de)multiplexer [(DE)MUX] based on a multimode interferometer coupler and a symmetric Y-junction coupler is proposed and demonstrated on an InP substrate. By introducing a phase shifter section with a thickness-detuned core layer, a miniature two-mode (DE)MUX with mode conversion of 100% is designed and demonstrated. Simulation shows that the total length of the device can be as small as 446 μm: much shorter than other mode (DE) MUX in InP materials. Within the entire C-band wavelength range, the calculated insertion loss of the device is less than 0.7 dB, and the crosstalk is below -24 dB. A mode (DE) MUX was fabricated in InP materials, and the mode conversion of the TE0 and TE1 modes were successfully demonstrated.

Loss-Reduction in Flexibly Vertical Coupled Ring Lasers Through Asymmetric Double Shallow Ridge and ICP/ICP Cascade Etching

Loss-reduction in flexibly vertical coupled ring lasers is demonstrated through asymmetric double shallow ridge in the main ring area and inductively coupled plasma (ICP)/ICP cascade etching. Compared with the previous counterpart, the reduced threshold current and enhanced output power are obtained; coupling ratio is tuned from 27% to 1.5% when threshold current is varied from 60 to 80 mA. Single-mode lasing with sidemode-suppression ratio of 27 dB and quality factor of 13120 is achieved when I c=15 mA, I d=58 mA, which are nearly twofolds of that in the previous one. Such strategies can be widely employed to reduce loss in other vertical coupled photonic circuits.

Synchronized 4 × 12 GHz hybrid harmonically mode-locked semiconductor laser based on AWG.

We report a monolithically integrated synchronized four wavelength channel mode-locked semiconductor laser chip based on arrayed waveguide grating and fabricated in the InP material system. Device fabrication was completed in a multiproject wafer foundry run on the Joint European Platform for Photonic Integration of Components and Circuits. The integrated photonic chip demonstrated 5th harmonic electrical hybrid mode-locking operation with four 400 GHz spacing wavelength channels and synchronized to a 12.7 GHz RF clock, for nearly transform-limited optical pulse trains from a single output waveguide. A low timing jitter of 0.349 ps, and RF frequency locking range of ~50 MHz were also achieved.

An MMI-Based Mode (DE)MUX by Varying the Waveguide Thickness of the Phase Shifter

A two-mode (de)multiplexer [(DE)MUX] based on multimode interference couplers on InP substrate is proposed and experimentally demonstrated. A phase shifting section with a variation of the waveguide thickness is introduced to precisely control the phase shift to realize 100% mode conversion efficiency and multiplexing. Performance analysis of the (DE)MUX is carried out numerically, showing excellent properties with insertion loss <;1.2 dB and crosstalk <;-18.4 dB for both the TE0 and TE1 mode within the whole C-band. The proposed device is also fabricated and demonstrated on InP substrate.

Bistable 1060-nm High-Power Single-Mode DFB Laser Diode

We report a novel high-power bistable distributed feedback (DFB) semiconductor laser diode operating near 1060 nm, which is realized by inserting a high-bandgap electron barrier layer and a grating layer in a super large optical cavity laser design. Optical and electrical bistable characteristics are both observed for this device. An on-state optical output power of 98 mW and an on-off extinction ratio of 22 dB were demonstrated between the bistable states. A qualitative physical model based on carrier population profile shift is used to explain the switching effect. Optical flip-flop operation was also demonstrated.

Fabrication of 32 Gb/s Electroabsorption Modulated Distributed Feedback Lasers by Selective Area Growth Technology

A 32 Gb/s monolithically integrated electroabsorption modulated laser is fabricated by selective area growth technology. The threshold current of the device is below 13 mA. The output power exceeds 10 mW at 0 V bias when the injection current of the distributed feedback laser is 100 mA at 25°C. The side mode suppression ratio is over 50 dB. A 32Gb/s eye diagram is measured with a 3.5Vpp nonreturn-to-zero pseudorandom modulation signal at −2.3 V bias. A clearly opening eyediagram with a dynamic extinction ratio of 8.01 dB is obtained.

High power 1060-nm super large vertical cavity semiconductor lasers

High power single-mode ridge waveguide 1060-nm semiconductor lasers are reported. The lasers consist of compressively strained double InGaAs/GaAs quantum wells and a GaAs/AlGaAs separate confinement vertical structure. A super large vertical optical cavity is employed to have a low internal loss, large optical spot size and low vertical optical divergence angle. The material composition and thickness of waveguide layers and claddings layer are optimized systematically. The active layer is detuned from center of the waveguide and thickness of cladding layers is optimized to guaranty single mode lasing of the large optical cavity. The large vertical cavity laser structure with thickness of 4 μm allows the lasers have a low internal loss of less than 0.6 /cm, a large optical spot size about 1μm and a vertical divergence angle about 20 degree. For lateral optical confinement, a double trench ridge waveguide is employed to maintain single-lateral-mode operation. Based on the optimization, 1.5 W continue wave optical power is achieved for broad area lasers with 1mm longitude cavity length. Narrow stripe ridge waveguide lasers of 1mm cavity length with single mode current and optical power of 700 mA and 340 mW is obtained. Suggestions for further improvements in terms of single mode power and applications of the high power semiconductors are discussed.

A MOCVD-Growth Multi-Wavelength Laser Monolithically Integrated on InP

We present an arrayed waveguide grating multi-wavelength laser (MWL). The device is operated with five wavelength channels of 194 GHz spacing around a central wavelength of 1.57 μm. A side mode suppression ratio of better than 35 dB for all channels is demonstrated. A very attractive feature of the MWL is that it has been realized by a novel one step regrowth approach to achieve a high quality active and passive interface.

Wide Temperature Range Operation of 1.3-um Directly Modulated High Speed DFB Lasers

We report the fabrication and systematic characterization of a high speed 1.3 μm DFB laser with excellent 10°C∼85°C performance: f<inf>3dB</inf> up to 26.1GHz, power up to 38 mW, SMSR beyond 50 dB.