Spectral Hole-burning Crystal Research Articles

High time-bandwidth product and high repetition rate period signal generation based on spectral hole burning crystal.

This paper proposes an approach for the generation of high time-bandwidth product (TBP) and high repetition rate pulse compression period signal. The complex spectral grating is created through a reference pulse and multiple programming pulses with different start frequencies. As the multiple probe chirped pulses with different start frequencies interact with the complex spectral gratings, a high TBP and repetition rate period signal is thus generated. This technique has the potential to generate a time-bandwidth product of 10⁵ when the repetition rate reaches up to tens of GHz. At the end of this paper, two simulation results of pulse compression period signal with 4×10⁵ TBP and 20 GHz repetition rate are presented.

Frequency-Doubled Fiber Lasers for RF Spectrum Analysis in Spectral-Hole-Burning Media

We demonstrate an RF spectrum analyzer based on spectral-hole burning (SHB) that operates with unity probability of intercept and resolution under 100 kHz. An SHB crystal, which consists of rare-earth ions doped into a crystal host, records the power spectrum of an RF signal modulated onto an optical carrier as a series of spectral holes that persist for about 10 ms. While the crystal's homogeneous and inhomogeneous linewidths place the fundamental limits on resolution and bandwidth, respectively, the practical limits depend on the lasers used to interrogate the record stored in the crystal's absorption profile. Up to now, SHB spectrum analyzers have used chirped beams from externally modulated, stabilized lasers, which have linewidths of under 10 kHz but cannot chirp over much more than octave bandwidths, or directly modulated diode lasers, which can chirp over more than 20GHz but have linewidths of about 1 MHz. Switching to chirped fiber lasers, which have natural linewidths of under 2 kHz and chirping linewidths on the order of 10 kHz, produces a measurement with fine resolution without any laser stabilization. In addition, by chirping the fiber laser with a sufficiently fast piezo, the resulting chirp could extend over tens of gigahertz in under 10 ms, yielding both fine resolution and broad bandwidth without extraordinary stabilization schemes.

Squint-Free Fourier-Optical RF Beamforming Using a SHB Crystal as an Imaging Detector

We describe and demonstrate a Fourier-optical beamformer that modulates RF energy from an antenna array onto a corresponding array of coherent optical beams and forms RF-frequency-scaled (or beam-squinted), far-field images through a single-lens optical Fourier transform. The squinted image is formed into a cryogenically cooled spectral hole burning (SHB) crystal, where it writes spatially-localized spectral images as holes in the crystal's spatial-spectral absorption profile. The spectral-hole images at each resolvable spectral bin (10 MHz at 4.2 K) integrate during the population lifetime ( 1 ms) for frequencies within the inhomogeneous crystal bandwidth ( 20 GHz). A chirped laser diffracts from the holes, producing a sequence of spectrally resolved RF images. The diffracted light passes through a swept-zoom lens synchronized to the chirped laser readout. This zoom lens compensates for beam squint during readout and forms the squint-free images onto a charge-coupled device (CCD), where they are coherently detected. We demonstrate experimental squinted images from a 5 element array across a 350 MHz bandwidth that are recorded into and read from a Er:Eu:YSiO SHB crystal before a digital zoom compensates for beam squint. This system can be scaled up to form images from 2-D arrays with 1000s of elements across 20 GHz bandwidths.

Spectral hole burning for pulse repetition frequency analysis

We demonstrate an optical processor based on spectral hole burning (SHB) that maps the carrier frequency into the time domain and the pulse repetition frequency (PRF) into the spatial domain by illuminating an SHB crystal with a signal beam that is scanned by a tilting mirror across a slice of the crystal. This time-to-space mapping makes it possible to measure signal envelopes with a resolution of 1 / T 1 = 100 Hz . A signal with a pulsed envelope engraves a vertical absorption grating with a spatial periodicity given by the product of the PRF and the scan velocity. Reading the grating, which the crystal stores for up to T 1 , with a collimated beam yields orders diffracted at angles proportional to the PRF, which are Fourier-transformed to produce spots displaced from the DC position by distances proportional to the PRF. Increasing the PRF increases the grating periodicity, causing the diffracted spots to move away from the DC position.

Demonstration of a radio-frequency spectrum analyzer based on spectral hole burning

Spectral hole-burning (SHB) technology is considered for >10-GHz instantaneous bandwidth signal-processing applications. In this context we report on what is believed to be the first demonstration of a SHB microwave spectrometer. A set of gratings engraved in a SHB crystal is used to filter one sideband of the optically carried microwave signal. The setup is confined to narrow-bandwidth operation, over a 35-MHz-wide interval. The first findings confirm the validity of the architecture in terms of spectral resolution, angular channel separation, and simultaneous detection of multiple spectral lines.

Enhanced nondegenerate four-wave mixing owing to electromagnetically induced transparency in a spectral hole-burning crystal

We have demonstrated electromagnetically induced transparency (EIT) in an inhomogeneously broadened spectral hole-burning system of Pr(3+)-doped Y(2)SiO(5) at 6 K. We have also shown enhancement of four-wave mixing under conditions of reduced absorption. This demonstration opens the possibilities of pursuing EIT applications such as high-resolution optical image processing and optical data storage in solids.