Wavelength tuning of fiber lasers using multimode interference effects

We report on a novel scheme to fabricate a simple, cheap, and compact tunable fiber laser. The tuning is realized by splicing a piece of single-mode fiber to one end of an active double-clad fiber, while the other end of the single-mode fiber is spliced to a 15 mm long section of 105/125 multimode fiber. The fluorescence signal entering into the multimode fiber will be reproduced as single images at periodic intervals along the propagation direction of the fiber. The length of the multimode fiber is chosen to be slightly shorter than the first re-imaging point, such that the signal coming out from the single mode fiber is obtained in free space, where a broadband mirror retroreflects the fluorescence signal. Since the position of the re-imaging point is wavelength dependent, different wavelengths will be imaged at different positions. Therefore, wavelength tuning is easily obtained by adjusting the distance between the broadband mirror and the multimode fiber facet end. Using this principle, the tunable fiber laser revealed a tunability of 8 nm, ranging from 1088-1097 nm, and an output power of 500 mW. The simplicity of the setup makes this a very cost-effective tunable fiber laser

Widely tunable erbium-doped fiber laser based on multimode interference effect

A widely tunable erbium-doped all-fiber laser has been demonstrated. The tunable mechanism is based on a novel tunable filter using multimode interference effects (MMI). The tunable MMI filter was applied to fabricate a tunable erbium-doped fiber laser via a standard ring cavity. A tuning range of 60 nm was obtained, ranging from 1549 nm to 1609 nm, with a signal to noise ratio of 40 dB. The tunable MMI filter mechanism is very simple and inexpensive, but also quite efficient as a wavelength tunable filter

Tunable Multimode Interference Devices

A tunable multimode interference (MMI) coupler that operates by modifying the phase of the multiple images that are formed around the midpoint of the MMI section is demonstrated. The phase change is achieved by current injection, and therefore minimizing current spreading is crucial for optimal operation. A zinc in-diffusion process has been implemented to selectively define p-i-n regions and effectively regulate the current spreading by controlling the depth of the zinc doping. Using this process a tunable 3-dB MMI coupler has been fabricated. Our initial results show that the device can be easily tuned all the way from a 90:10 to a 30:70 splitting ratio of the optical power transmitted through the two output ports. We believe that further improvement on the device fabrication will lead to a more symmetric tuning response of the device. Nevertheless, the initial results are very encouraging since, to our knowledge, this degree of tuning has never been experimentally demonstrated in similar MMI devices. Furthermore, this device processing technique can easily be applied to a wide variety of semiconductor photonic switches that operate on MMI effects

Integrated Electro-Optic Mach-Zehnder Switch Realized By Zinc In-Diffusion

We demonstrate the use of an area selective zinc in-diffusion technique to fabricate an integrated InP/InGaAsP Mach-Zehnder optical switch. The zinc in-diffusion process using a semi-sealed open-tube diffusion furnace was characterized to enable the creation of p-n junctions at a precise depth in selected areas of the device sample. The method is simple, yet highly controllable and reproducible; with the crystal quality remaining intact after the diffusion process is complete. Using this technique an integrated 1×2 Mach-Zehnder optical switch has been fabricated. Our preliminary devices show a switch contrast ratio of 12 dB with a voltage swing of ±2.5 volts. Improving our fabrication process will further optimize the performance of the switch. Nevertheless, very good electrical isolation is obtained between the contacts, which demonstrates the potential of the technique for the fabrication of Photonic Integrated Circuits

An Integrated 1x3 InP Photonic Switch

An integrated 1×3 optical switch that operates using the principle of carrier-induced refractive index change in InGaAsP multiple quantum wells is demonstrated. The device is very simple, only requiring currents to be applied to two electrodes for complete operational control. An area-selective zinc in-diffusion process is used to channel the currents into the multiple quantum wells, thereby enhancing the efficiency of the carrier-induced effects. This results in a low electrical power consumption, allowing the switch to be operated uncooled and under d.c. current conditions. The crosstalk between channels is better than -17 dB over a range of 50 nm centered at 1565 nm. © 2006 IEEE

Reconfigurable 1×4 Inp-Based Optical Switch

An integrated 1×4 InP-based optical switch is reported. The device is quite simple and full device operation is achieved by injecting electrical currents to two electrodes. Since the operation of the switch relies on current spreading, using the carrier-induced refractive index change in InGaAsP multiple quantum wells, an area-selective zinc in-diffusion process is used to regulate the current spreading and optimize device performance. As a result, the fabricated 1×4 switch exhibits a -14 dB crosstalk between channels over a wavelength range of 30 nm, while maintaining low electrical power consumption and allowing the switch to be operated uncooled and under d.c. current conditions. © 2007 Elsevier Ltd. All rights reserved

An Integrated 1×3 Inp Photonic Switch

An integrated 1×3 optical switch that operates using the principle of carrier-induced refractive index change in InGaAsP multiple quantum wells is demonstrated. The device is very simple, only requiring currents to be applied to two electrodes for complete operational control. An area-selective zinc in-diffusion process is used to channel the currents into the multiple quantum wells, thereby enhancing the efficiency of the carrier-induced effects. This results in a low electrical power consumption, allowing the switch to be operated uncooled and under d.c. current conditions. The crosstalk between channels is better than -17 dB over a range of 50 nm centered at 1565 nm. © 2006 IEEE

Reconfigurable 3-dB MMI splitter

A tunable multimode interference (MMI) coupler is demonstrated. The device operates by modifying the phase of the multiple images that are formed around the midpoint of the MMI. Current spreading is controlled using a zinc in-diffusion process to selectively define p-i-n regions and effectively regulate the current spreading by controlling the depth of the zinc doping. A tunable MMI coupler has been fabricated. Our initial results show that the device can be easily tuned all the way from a 90:10 to a 30:70 splitting ratio of the optical power transmitted through the two output ports. Further improvement on the device fabrication will lead to a more symmetric tuning response of the device. Nevertheless, the initial results are very encouraging since, to our knowledge, this degree of tuning has never been experimentally demonstrated in similar MMI devices. © 2008 IEEE

Integrated Beam-Steered Optical Switch

We report an optical switch that is based on the beam steering of an optical waveguide formed by injection of electrons in a p-i-n slab waveguide structure. The structure consists of an undoped InGaAsP multiple quantum well (MQW) layer, with a total thickness of 0.28 μm that is sandwiched between n-doped InP cladding layers. Zinc is diffused into the top cladding layer through a silicon nitride mask to form the p-regions on top of which a pair of 10 μm wide parallel titanium-zinc-gold contact stripes are deposited by evaporation and lift-off. The gap between the stripes is 20 μm wide and the device is cleaved to a length of 800 μm. Electrical currents are injected through the electrodes and a laser beam is launched into the middle of the gap region. The injected electrons accumulate in the MQW layer and spread sideways by diffusion. The regions that are saturated with electrons experience a decrease in refractive index and surround a narrow high index region effectively forming a channel waveguide. By carefully controlling the current ratio through the two parallel stripes, the waveguide can be shifted, thereby steering the guided laser beam

Integrated 1X4 Photonic Switch

We demonstrate a 1x4 optical switch fabricated from InGaAsP multiple quantum wells. The device operates via carrier injection, employing a beam steering subunit which guides the optical beam to each of the output waveguides. © 2005 Optical Society of America