Continuous Tunable Terahertz Wave Generation via a Novel CW Optical Beat Laser Source (original) (raw)
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Optics Express, 2010
We propose a widely tunable dual-wavelength Erbium-doped fiber laser that uses two micro-heater-integrated Fabry-Perot laser diodes (FP-LDs) and two fiber Bragg gratings (FBGs) for tunable continuous-wave (CW) terahertz (THz) radiation. Each wavelength can be independently tuned by using an FP-LD and an FBG. The wavelength fine tuning is achieved by simultaneously applying current to the micro-heater on the FP-LD and strain to the FBG. The side-mode suppression ratio is more than 35 dB for both wavelengths. The wavelength spacing of the dual wavelength can be continuously tuned from 3.2 nm to 9.6 nm. Continuous frequency tuning of the CW THz radiation is also successfully achieved using an InGaAs-based photomixer with our dual-wavelength fiber laser as the optical beat source. The emitted CW THz radiation is continuously tuned from 0.3 to 0.8 THz.
Measurement …, 2008
We present a tunable continuous-wave terahertz radiation source based on photomixing of a tunable dual-mode semiconductor laser on a log-periodic antenna. The discontinuously tunable dual-mode emission of the laser is achieved by spectrally filtered feedback in a double-external-cavity configuration. Two different two-frequency lasing regimes have been identified: pure dual-mode and dual-mode-comb emission. We spectrally investigate the laser emission in these two regimes and study the consequences for the generation of terahertz radiation. Under pure dual-mode emission, we achieve higher power, higher coherence and good tunability of the THz radiation. We demonstrate by detecting absorption lines of water vapor and hydrochloric acid gas that our concept for a tunable continuous-wave terahertz radiation source offers attractive properties for spectroscopic applications.
Scientific reports, 2015
We propose and systematically investigate a novel tunable, compact room temperature terahertz (THz) source based on difference frequency generation in a hybrid optical and THz micro-ring resonator. We describe detailed design steps of the source capable of generating THz wave in 0.5-10 THz with a tunability resolution of 0.05 THz by using high second order optical susceptibility (χ((2))) in crystals and polymers. In order to enhance THz generation compared to bulk nonlinear material, we employ a nonlinear optical micro-ring resonator with high-Q resonant modes for infrared input waves. Another ring oscillator with the same outer radius underneath the nonlinear ring with an insulation of SiO2 layer supports the generated THz with resonant modes and out-couples them into a THz waveguide. The phase matching condition is satisfied by engineering both the optical and THz resonators with appropriate effective indices. We analytically estimate THz output power of the device by using practi...
Nonlinear optical resonators for tunable THz emission
Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications VII, 2014
We designed and theoretically investigated nonlinear optical micro-ring resonators for tunable terahertz (THz) emission in 1-10 THz range by using difference frequency generation (DFG) phenomenon with large second order optical nonlinearity (χ (2) ). Our design consists of a nonlinear ring resonator and another ring underneath capable of sustaining high-Q resonant modes for infrared pump beams and the generated THz radiation, respectively. The nonlinear ring resonator generates THz through DFG by mixing the input waves carried by a pair of waveguides. The proposed device can be a viable platform for tunable, compact THz emitters and on-chip integrated spectrometers. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/18/2015 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 8985 898505-3 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/18/2015 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 8985 898505-5 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/18/2015 Terms of Use: http://spiedl.org/terms
Optics Express, 2012
We propose and demonstrate a simple compact, inexpensive, SOA-based, dual-wavelength tunable fiber laser, that can potentially be used for photoconductive mixing and generation of waves in the microwave and THz regions. A C-band semiconductor optical amplifier (SOA) is placed inside a linear cavity with two Sagnac loop mirrors at its either ends, which act as both reflectors and output ports. The selectivity of dual wavelengths and the tunability of the wavelength difference (Δλ) between them is accomplished by placing a narrow bandwidth (e.g., 0.3 nm) tunable thin film-based filter and a fiber Bragg grating (with bandwidth 0.28 nm) inside the loop mirror that operates as the output port. A total output power of + 6.9 dBm for the two wavelengths is measured and the potential for higher output powers is discussed. Optical power and wavelength stability are measured at 0.33 dB and 0.014 nm, respectively.
Optics Express, 2011
We demonstrate a tunable continuous-wave (CW) terahertz (THz) homodyne system with a novel detuned dual-mode laser diode (DML) and low-temperature-grown (LTG) InGaAs photomixers. The optical beat source with the detuned DML showed a beat frequency tuning range of 0.26 to over 1.07 THz. Log-spiral antenna integrated LTG InGaAs photomixers are used as THz wave generators and detectors. The CW THz radiation frequency was continuously tuned to over 1 THz. Our results clearly show the feasibility of a compact and fast scanning CW THz spectrometer consisting of a fiber-coupled detuned DML and photomixers operating in the 1.55-μm range.
A tunable cavity-locked diode laser source for terahertz photomixing
IEEE Transactions on Microwave Theory and Techniques, 2000
An all solid-state approach to the precise frequency synthesis and control of widely tunable terahertz radiation by differencing continuous-wave diode lasers at 850 nm is reported in this paper. The difference frequency is synthesized by three fiber-coupled external-cavity laser diodes. Two of the lasers are Pound-Drever-Hall locked to different orders of a Fabry-Perot (FP) cavity, and the third is offset-frequency locked to the second of the cavity-locked lasers using a tunable microwave oscillator. The first cavity-locked laser and the offset-locked laser produce the difference frequency, whose value is accurately determined by the sum of an integer multiple of the free spectral range of the FP cavity and the offset frequency. The dual-frequency 850-nm output of the three laser system is amplified to 500 mW through two-frequency injection seeding of a single semiconductor tapered optical amplifier. As proof of precision frequency synthesis and control of tunability, the difference frequency is converted into a terahertz wave by optical-heterodyne photomixing in low-temperature-grown GaAs and used for the spectroscopy of simple molecules. The 3-dB spectral power bandwidth of the terahertz radiation is routinely observed to be 1 MHz. A simple, but highly accurate, method of obtaining an absolute frequency calibration is proposed and an absolute calibration of 10 7 demonstrated using the known frequencies of carbon monoxide lines between 0.23-1.27 THz.
Highly tunable fiber-coupled photomixers with coherent terahertz output power
IEEE Transactions on Microwave Theory and Techniques, 1997
Low-temperature-grown (LTG) GaAs is used as an optical-heterodyne converter or photomixer, to generate coherent continuous-wave (CW) output radiation at frequencies up to 5 THz. Photomixers consist of an epitaxial LTG-GaAs layer that is patterned with interdigitated metal electrodes, on which two laser beams are focused with their frequencies offset by the desired difference frequency. The difference-frequency power is coupled out of the photomixer using coplanar waveguide at low frequencies and using log-spiral, dipole, and slot antennas at higher frequencies. Difference-frequency power is limited by the maximum optical-pump power that the photomixer can withstand. Fiber-coupled photomixers were operated at 77 K-a configuration in which they exhibited improved heatsinking and, therefore, withstood higher pump power. Progress has been made in the development of photomixer local oscillators (LO's) for space-based receivers that use superconducting tunnel junctions and hot-electron bolometers as heterodyne detectors.
Miniature self-aligned external cavity tunable single frequency laser for THz generation
Terahertz Technology and Applications V, 2012
We report on the unique highly-configurable wavelength tuning and switching properties of a tunable external cavity laser based on multiplexed volume holographic gratings (VHGs) and a micromirror device. The ultra-compact laser has a 3 THz bandwidth and exhibits single mode operation in either single or multiple wavelengths with narrow linewidth (<7.5MHz), and a switching rate of 0.66KHz per wavelength. A prototype laser exhibited 40 mW of output power for wavelengths from 776-783 nm. The unique discrete-wavelength-switching features and low power consumption of this laser make it well suited as a source for continuous-wave (cw) terahertz signal generation in portable photomixing systems.