Scott S.-H. Yam

SUCCESS: a next-generation hybrid WDM/TDM optical access network architecture

In this paper, the authors propose a next-generation hybrid WDM/TDM optical access network architecture called Stanford University aCCESS or SUCCESS. This architecture provides practical migration steps from current-generation time-division multiplexing (TDM)-passive optical network (PONs) to future WDM optical access networks. The architecture is backward compatible for users on existing TDM-PONs, while simultaneously capable of providing upgraded high-bandwidth services to new users on DWDM-PONs through advanced WDM techniques. The SUCCESS architecture is based on a collector ring and several distribution stars connecting the CO and the users. A semipassive configuration of the Remote Nodes (RNs) enables protection and restoration, making the network resilient to power failures. A novel design of the OLT and DWDM-PON ONUs minimizes the system cost considerably: 1) tunable lasers and receivers at the OLT are shared by all ONUs on the network to reduce the transceiver count and 2) the fast tunable lasers not only generate downstream data traffic but also provide DWDM-PON ONUs with optical CW bursts for their upstream data transmission. Results from an experimental system testbed support the feasibility of the proposed SUCCESS architecture. Also, simulation results of the first SUCCESS DWDM-PON MAC protocol verify that it can efficiently provide bidirectional transmission between the OLT and ONUs over multiple wavelengths with a small number of tunable transmitters and receivers.

Refractive index sensor based on an abrupt taper Michelson interferometer in a single-mode fiber

A simple refractive index sensor based on a Michelson interferometer in a single-mode fiber is constructed and demonstrated. The sensor consists of a single symmetrically abrupt taper region in a short piece of single-mode fiber that is terminated by approximately 500 nm thick gold coating. The sensitivity of the new sensor is similar to that of a long-period-grating-type sensor, and its ease of fabrication offers a low-cost alternative to current sensing applications.

Refractive Index Sensing With Mach–Zehnder Interferometer Based on Concatenating Two Single-Mode Fiber Tapers

A novel refractive index (RI) sensor based on a fiber Mach-Zehnder interferometer was realized by concatenating two single-mode fiber tapers separated by a middle section. The proposed device had a minimum insertion loss of 3 dB and maximum interferometric extinction ratio over 20 dB. The resolution (0.171 nm) of the two-taper sensor to its surrounding RI change (0.01) was found to be comparable to that (0.252 nm) of similar structures made from an identical long-period gratings pair, and its ease of fabrication makes it a low-cost alternative to existing sensing applications.

Single-Mode Fiber Refractive Index Sensor Based on Core-Offset Attenuators

Mach-Zehnder and Michelson interferometers using core-offset attenuators were demonstrated. As the relative offset direction of the two attenuators in the Mach-Zehnder interferometer can significantly affect the extinction ratio of the interference pattern, single core-offset attenuator-based sensors appear more robust and repeatable. A novel fiber Michelson interferometer refractive index (RI) sensor was subsequently realized by a single core-offset attenuator and a layer of ~ 500-nm gold coating. The device had a minimum insertion loss of 0.01 dB and maximum extinction ratio over 9 dB. The sensitivity (0.333 nm) of the new sensor to its surrounding RI change (0.01) was found to be comparable to that (0.252 nm) of an identical long period gratings pair Mach-Zehnder interferometric sensor, and its ease of fabrication makes it a low-cost alternative to existing sensing applications.

In-Line Abrupt Taper Optical Fiber Mach–Zehnder Interferometric Strain Sensor

A Mach-Zehnder interferometer with two abrupt single-mode fiber tapers is simulated, constructed, and demonstrated. The interferometer has an insertion loss of 5 dB and an extinction ratio over 15 dB. The interferometer is tested as a strain sensor based on the maximum attenuation wavelength shift with a comparable sensitivity (slope: 2000 nm/ epsiv, R 2 = 0.996) with long-period-grating-type sensor and promises low fabrication cost.

In-Line Single-Mode Optical Fiber Interferometric Refractive Index Sensors

Novel in-line single-mode fiber interferometers- Mach-Zehnder and Michelson-have been designed, fabricated, and tested as refractive index (RI) sensors. Abrupt tapers and connector-offset attenuators are proposed as alternatives to long period gratings (LPGs) as mode-coupling mechanisms to transfer optical power between core and cladding modes in optical fiber. The coupling coefficients between core and cladding modes in the proposed designs were calculated using numerical packages and the devices were subsequently implemented using commercially available fusion splicer. For an abrupt taper, most coupling occurs between the LP01 and LP0 m modes, with the first ten modes accounting for 98% of the incident mode energy. For a connector-offset attenuator, coupling mainly occurs between the LP01 and LP1 m modes, with the first ten LP0 m modes and first ten LP1 m modes accounting for 92% of the incident mode energy. In particular, in the case of connector-offset attenuator, the relative direction between the two connector-offsets was found to be very important to the interference performance. Interference patterns were realized in simulation for the interferometers using both mode-coupling mechanisms. Three interferometers were realized in the experiment using abrupt taper-Mach-Zehnder and Michelson-and connector-offset attenuator-Michelson. They showed large extinction ratios (up to 23 dB) and small insertion losses (smaller than 3 dB). Although it is difficult to make Mach-Zehnder interferometers using connector-offset attenuator pair due to the lack of polarization control in the fusion splicer, some evidence of constructive interference was observed in the experiment. The interferometers were tested as RI sensors using the maximum attenuation wavelength shift. Given that the minimum resolution of optical spectrum analyzer is 10 pm, ~ 10-4 difference of RI can be detected by the proposed interferometric sensors, providing similar performance as LPG-based interferometers at a lower cost and simpler fabrication process.

Performance demonstration of a fast-tunable transmitter and burst-mode packet receiver for HORNET

We demonstrate error-free packet-over-WDM transmission using a fast-tunable transmitter and novel packet receiver. The transmitter tunes fine (0.8 nm) and. wide (/spl sim/30 nm) within 15 ns, while the receiver receives unframed packets by bit-synchronizing in 40 ns.

Reducing the complexity of perturbation based nonlinearity pre-compensation using symmetric EDC and pulse shaping

Perturbation based nonlinearity pre-compensation has been performed for a 128 Gbit/s single-carrier dual-polarization 16-ary quadrature-amplitude-modulation (DP 16-QAM) signal. Without any performance degradation, a complexity reduction factor of 6.8 has been demonstrated for a transmission distance of 3600 km by combining symmetric electronic dispersion compensation and root-raised-cosine pulse shaping with a roll-off factor of 0.1. Transmission over 4200 km of standard single-mode fiber with EDFA amplification was achieved for the 128 Gbit/s DP 16-QAM signals with a forward error correction (FEC) threshold of 2 × 10(-2).

Laser beam shaping using a single-mode fiber abrupt taper

A new beam-shaping device was realized by an abrupt taper with a length of approximately 700 microm and a waist of approximately 40 microm. The insertion loss of the device is less than 3%. The diameter of the flat beam top can be up to approximately 900 microm with a small intensity variation (4%) and a small half-divergence angle (2.5 degrees). The conversion efficiency of the new device from a Gaussian-shaped to a flat-top profile is comparable with that of a long-period-gratings-based device, while keeping the fabrication cost low. The new device requires only a fusion splicer and standard SMF-28 fiber, eliminating the need for photolithographic procedures. The new device also has no obvious incident light polarization dependence.

Loss determination in microsphere resonators by phase-shift cavity ring-down measurements

The optical loss of whispering gallery modes of resonantly excited microresonator spheres is determined by optical lifetime measurements. The phase-shift cavity ring-down technique is used to extract ring-down times and optical loss from the difference in amplitude modulation phase between the light entering the microresonator and light scattered from the microresonator. In addition, the phase lag of the light exiting the waveguide, which was used to couple light into the resonator, was measured. The intensity and phase measurements were fully described by a model that assumed interference of the cavity modes with the light propagating in the waveguide.