Spectral characteristics of 1.3 micrometers DFB lasers with different wavelength detunings are investigated at various temperatures ranging from 20 to 80 degree(s)C. DFB lasers have different amounts of detuning at RT: almost no detuning, a positive detuning of 5 nm and a negative detuning of 25 nm. AR-HR coated 300 micrometers long DFB lasers have typical CW threshold currents of 9 mA, slope efficiencies of 0.27 mW/mA, and coupling coefficients (K) of 60 cm-1. For the DFB LD with a positive detuning, the detuning of +5 nm at 20 degree(s)C is changed to -15 nm at 80 degree(s)C with the SMSR of 38 dB maintained. Whereas, at 80 degree(s)C Fabry-Perot modes appear from the DFB LD with a negative detuning and a smaller SMSR of 35 dB is obtained from the DFB LD with almost no detuning. These results indicate that a DFB LD with a positive detuning shows better spectral characteristics than others.
It is well known that gratings with high spatial frequency (spacings <EQ (lambda) /2) show form birefringence. Therefore, gratings formed in dielectric materials can act as a wave plate when the grating spacing is smaller than, or near to, half of the incident beam wavelength. Previous researchers used high frequency surface relief structures or sinusoidal gratings formed in photoresists to produce this effect. In this paper we show the performance of a volume holographic quarterwave plate formed in DCG operating at 632.8 nm. To our knowledge this is the first demonstration of a retardation plate exhibiting this magnitude of phase delay in a volume material. The fabrication techniques required to realize this element are also presented.
Optical interconnects have potential advantage over electrical methods at the backplane level. In this paper we present a free-space optical connection cube for backplane interconnect applications. The connection cube has a symmetric structure which reduces skew between boards. It can be expanded into a 3-dimensional configuration for parallel communication using vertical-cavity surface-emitting laser (VCSEL) and receiver arrays. Fan-out and fan-in of propagation beams for the connection cube are realized using volume holographic optical elements formed in dichromated gelatin (DCG) emulsion. A four-port communication system has been demonstrated using the connection cube and tested at 500 MHz. In this paper, advantages and detailed implementation of the free-space optical connection cube are presented. Design considerations for fan-out/in holographic gratings and alignment tolerances for the connection cube are discussed. Characteristics of the connection cube are also presented.
The rigorous coupled-wave model is used to determine the polarization of diffracted waves from two superimposed volume gratings with their grating vectors in the same plane. The phase relations used in computing the phase shift of diffracted beams are derived. The relative phase difference between orthogonal components of the + 1 diffracted order is computed for a single grating and two superimposed gratings. The level of induced ellipticity in polarization is greater for light diffracted from a multiplexed grating than from a single grating. Experimental and theoretical results show that the phase shift of a beam diffracted from two superimposed gratings has both positive and negative values.
Magneto-optic data storage is an emerging read/write storage technology with many potential applications in consumer computer systems. One of the limitations to this development is the cost of the read/write head. This device must provide high optical power during the write phase, and sense a small change in the polarization of the beam reflected from an MO disk during the read operation. Typically the head consists of many individual optical components which must be aligned and accurately assembled, and contributes significantly to system cost. Two important elements in the head are a leaky beamsplitter and a polarization beamsplitter. In this presentation we discuss the design parameters and performance characteristics for these beamsplitters formed in dichromated gelatin. Experimental grating performance is also given.
The refractive index of holographic emulsions is an important parameter needed for designing holographic optical elements (HOEs). In this paper theoretical calculations of the accuracy required for the refractive index and thickness of emulsions needed to meet predetermined Bragg angle conditions are presented. A modified interferometric method is used to find average refractive index of the unexposed and the developed dichromated gelatin holographic films. Slanted transmission HOEs are designed considering the index and thickness variations, and used to verify the index measurement results. The Brewster angle method is used to measure surface index of the unexposed and the developed films. The differences between average index and surface index are discussed. Theoretical calculation of the effects of index variation on diffraction efficiency, and experimental results for index modulation variation caused by process changes are also presented.
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