Shyh-Lin Tsao

Progress in laboratory R & D for fundamental physics space missions - weak light phase-locking, fibre-linked heterodyne interferometry, fibre delay line and picometre real-time motion control

Since 1992, we have engaged in laboratory studies for astrodynamical missions to test relativistic gravity in the solar system. The techniques developed are also relevant to other fundamental space missions such as LISA and the space interferometer for astrometry. Here we report our progress in weak light phase-locking, long fibre-linked heterodyne interferometry, fibre delay line and picometre real-time motion control during the last year. We demonstrated that for two lasers with offset locking up to 2.5 GHz, the heterodyne linewidth after travelling through a 26.27 km fibre-linked interferometer is less than 1 mHz. For weak light phase-locking, we achieved 4.3 nW locking with a 3.4 mW local oscillator. We improved our side-polishing technique to polish more than eight fibres simultaneously and reached a tunable sensitivity as high as 85 - 90 dB in liquid-drop tests. Using these side-polished fibres, we are currently in the process of making tunable directional couplers and fibre delay lines. For laser metrology, we use mid-point cyclic averaging to reduce the nonlinearity error, and use a fitting method to cancel the drift, and have reached 1.5 pm linearity. Currently, with modulation and real-time cyclic averaging, we reach a real-time measuring precision of 560 pm and real-time motion-control precision of 700 pm.

Design of a self-routing frequency division multiple access (SR-FDMA) network using an optical ring filter with or without gain as a router

Self-routing frequency division multiple access (SR-FDMA) network with ASK coherent detection and dual ring topology is proposed. The router, which employs the optical ring filter, is used as a means for selecting the desired channel carrier and at the same time as a bypass of the other channel carriers. The channel capacity and the carrier-to-noise ratio are investigated with the consideration of cross talk and power budget penalty. We find that there exists an optimum coupling coefficient of the transceiver coupler and a trade-off in selecting channel number and data rate. The results show that the router with gain can suppress the cross talk, compensate the power budget penalty, and largely increase the channel number. Therefore, with this router, a self-routing, high-density FDMA network is feasible.

High-resolution neural temperature sensor using fiber Bragg gratings

We demonstrate a novel high-resolution neural temperature sensor using two fiber Bragg gratings (FBGs) and a modular artificial neural network which is used to learn the mapping relation among frequency, temperature, and the normalized transmission power spectrum. Because of the fast computational ability of the modular artificial neural network and the sensitivity of FBGs, the sensor can make high-resolution temperature and frequency measurements in real time. The experimental results show that the temperature resolution of this sensor can reach 0.005/spl deg/C.

Multimode interference-based heterostructure photonic crystal waveguide power splitter

A novel power splitter based on self-imaging phenomena in multimode heterostructure is designed and analyzed. Such a photonic crystal waveguide is a hybrid structure combining square and hexagonal photonic crystal lattices. The size of our designed new power splitter is much smaller in comparison with the conventional MMI power splitter. The devices can be applied to optical communication systems and be integrated easily with other optical devices. The plane-wave expansion (PWE) method is used to calculate the bandgap structure of photonic crystals. The finite-difference time-domain (FDTD) method is adopted for the numerical simulation of related structure. This approach can be extended to novel design of MMI device based on photonic crystals.

Tunable subcarrier comb generator using phase modulator with high modulation index

Recently, subcarrier multiplexing method combined with the conventional microwave techniques provides high capacity multichannel optical fiber communication. But as the microwave frequency gets higher, the carrier generation and carrier recovery circuits are more difficult to implement by using traditional microwave technology. This paper proposes a way to generate many subcarriers using only a single reference tone by deep phase modulation method. Tunabilities of operating band and carrier spacing are presented in experimental results. It is found that the optimum phase modulation index is 3.1 for minimum power deviation to generate 7 carriers. Those generated subcarriers can operate from dc to K-band that can be used in transmitting end or receiving end.

New active device design: routing wavelength switch based on 2x2 micro-ring resonators

We propose an active routing wavelength switch by applying Micro-Ring Resonators (MRR). In this paper, this device is designed that the optical signals can be switched by electric signals. The electric signals modulate free carrier concentration that can change the refractive index of MRR. We can control the condition of light coupling so that one can switch light way or one wish. Therefore, we utilize the Schottky diode that can be tuned the refractive index of MRR by dc voltage. With combining MRR artfully, we can design a novel n x n switch active device based on switch architecture. Firstly, we build a 2 x 2 routing wavelength switch by MRR. Then, we use the frame of 2 x 2 routing wavelength switch to develop the 4 x 4 routing wavelength switch. The 30μm×75μm 4×4 silicon-on-insulator (SOI) wavelength switch can switch 4 wavelengths following ITU grid. With launching light from different inputs and see the output channels, the output power were simulated by Finite Difference Time Domain (FDTD) method. The simulation results illustrates the feasibility to achieve full function of optical cross connect routing wavelength switch.

Pulse Amplitude Equalization of RHMLFL with Nonlinear Parameter Consideration

We design a high repetition rate tunable rational harmonic mode-locked fiber laser (RHMLFL). The gain media in the laser ring cavity is provided by an erbium-doped fiber amplifier. The output power of the EDFA can be adjusted to 17dBm. There are two isolators incorporated in the erbium-doped fiber amplifier to ensure the unidirectional operation of the ring laser. We modulated the high repetition rate to get the higher modulation frequency. We achieve a pulse level equalized tunable rational harmonic mode-locked fiber laser (RHMLFL). The pulse amplitude of pulse train is equalized by operating at nonlinear modulation transfer function region of active modulator in RHMLFL. Without adding any other additional predistortion components, amplitude equalized short pulses up to the fourth order rational harmonic mode-locking are successfully demonstrated for 10 GHz. One can extend such a method for various mode-locked lasers even with much higher repetition rates. In this paper, we successfully to renew the systematic structure to generate the high frequency laser output pulse train of 50GHz. Then optical pulse compressing by sixth order solitonic effect is simulated. Pulsewidth variation versus compressor length for high order solitonic effect compression is analyzed. In our previous work, the output pulse is 28 ps with repetition rate 10 GHz. The shortest pulsewidth can be demonstrated compressed below 1.53 ps using solitonic technique.

Review of quantum optical communications and future device evaluations

In this paper, some devices were reviewed to be used in quantum communications. We presented a low density of Quantum Dots, which could be used to get single quantum dot as light emitting source for generating single photons. An analytical model to study the thermal behavior of a solid media in interaction with one, two or three laser beams was developed using the classical heat equation. Integrated optic micro-ring resonators and its simulated result also are presented. Development of active micro-ring in silicon is at an early stage, where both vertical and horizontal techniques are feasible. With the epitaxy growth techniques, a possibility for achieving controllable QD density, size and good uniformity are proposed. A low density of QDs in range of 108 cm-2 has demonstrated through successive adjustment of the growth parameters. Details among the devices are presented and discussed.

A CPW-fed broadband two-way electro-optic probe

A broadband microwave frequency division diplexer using photonic bandgap structure to improve the isolation and enhance output power level for tow-way electro-optic probe is presented. The microwave frequency division diplexer, where the lower pass-band is from 384 MHz to 2.58GHz and the upper pass-band is from 2.78 GHz to 8.55 GHz, is realized to connect two microwave circulators operated in different frequency band. Because of the compact size and easy to use for electrical probe, only four microwave circulators operated in different bands and three frequency division diplexer are considered to implement a planar electrical probe. Considering the ease of fabrication for wider ranges of realizable impedance values, easy to integrate with lumped-elements, small dispersion, and simple realization of series and shunt circuit elements, the coplanar waveguide structure is utilized to design and implement the proposed microwave frequency division diplexer. The simulated results of proposed microwave frequency division diplexer and experimental data of the wideband microwave frequency division diplexer with the circulators are presented and discussed in this paper.

A novel two-way wavelength-division-multiplexed fiber laser

We use the fiber loop mirror to form a cavity in our laser system, and two 1.5 μm semiconductor optical amplifier (SOA) also be used as a gain material in the cavity. We analyze the lasing power, SMSR, L-I curve and the stability of our designed symmetric resonator laser with various driving current of the SOA. According to our measured results, we can find that the polarization states of our lasers are stable and the output side-mode suppression ration (SMSR) of our laser is large. We successfully designed a symmetric two-way multi-wavelength wavelength-division-multiplexed (WDM) resonator laser system. The multi-wavelength continuous-wave(CW) fiber laser by utilizing the Fabry-Perot resonance can be applied to PolSK fiber-optic communication systems.