Optics and Electronics Seminar

Over the Rainbow: The Other World Seen by Animals

Topic: 
OSA Special Seminar: Over the Rainbow: The Other World Seen by Animals
Abstract / Description: 

Much of what we understand about the world comes from our eyes, which sense the colors from red to violet that are expressed in the rainbow. Yet we know that this patch of colors is just a small island in the vast electromagnetic spectrum, which extends from radio waves to gamma rays. Two unseen regions of great importance to us are those just over and just under the rainbow - the infrared and ultraviolet, respectively. These were discovered about 200 years ago in inspired experiments that anyone can understand, originally conducted by Frederick William Herschel and Johann Wilhelm Ritter. Only recently has it come to be understood that a variety of animals live in a visual world totally unfamiliar to us, particularly in the ultraviolet.

I will discuss this from the perspective of measurement science, and demonstrate other influences of the ultraviolet in technology, astronomy and climate change.

This seminar is sponsored by Stanford OSA.

Date and Time: 
Tuesday, February 17, 2015 - 4:15pm to 5:15pm
Venue: 
Spilker 232

Stanford Optical Society Seminar: High-speed operation, wavelength, and mode control in vertical-cavity surface-emitting lasers

Topic: 
High-speed operation, wavelength, and mode control in vertical-cavity surface-emitting lasers
Abstract / Description: 

We address recent achievements in Vertical–Cavity Surface–Emitting Lasers for data communication. (i) Recent concepts for high speed VCSEL operation include anti–waveguiding cavity design with AlAs–rich core, further increased optical confinement factor, engineering of the density of states, thick oxide apertures and superlattice barriers aimed at prevention of the leakage of nonequilibrium carriers. Serial data transmission up to 50Gb/s is realized in laser modules without preemphasis and equalization. The expected lifetime of such VCSELs exceeds 10 years at 95oC. (ii) Electrooptically–modulated VCSELs allow optical modulation bandwidth beyond 35GHz and electrical bandwidth exceeding 60GHz. So far error-free digital data transmission at 10Gb/s is realized. With effort 100 Gb/s operation at a low current density and ultralow power consumption can become feasible. (iii) VCSEL design may allow uncooled wavelength multiplexing, for example within the narrow 840–860 nm spectral range of low modal dispersion of the standard multimode fiber. Complete temperature stability of the VCSEL is achieved due to the passive cavity concept. The gain medium is placed in the region of the bottom semiconductor distributed Bragg reflector (DBR) while the further part of the bottom DBR, the cavity region and the top DBR are made of dielectric materials. Due to the virtually no dependence of the refractive index on temperature at certain dielectric compositions, a temperature stabilized operation without cooling becomes possible. Furthermore, due to dielectric DBRs and a cavity offer a high optical confinement factor even for InP-based 1300nm - 1550nm VCSELs extending the range of VCSEL applications. (iv) Single mode VCSELs at moderate oxide diameters of the oxide aperture (5-6 µm), fully compatible to the standard technology, are feasible by the optical field engineering in the oxidized part. The leakage is engineered to suppress the high order transverse optical modes. The effect is achieved by a proper positioning of thick aperture oxide layers, inducing an optical mode suitable for the leakage. The mode engineering effect can be also used, as opposite, to create a 3D confinement of the optical modes in the microcavity allowing a long lifetime of the VCSEL modes in a broad spectral range allowing, for example, near field VCSEL. (v) Single mode operation allows to overcome effects related to significant spectral dispersion of the multimode fiber (MMF) in the 840–860 nm range. A 1000 m error–free transmission at 25Gb/s is realized in parallel MMF links using single mode VCSEL arrays in combination with commercially available array electronics and standard optical couplers assembled into parallel 12-channel transceiver and receiver boards.

This seminar is sponsored by Stanford OSA

Date and Time: 
Monday, February 2, 2015 - 2:00pm to 3:15pm
Venue: 
Y2E2 299

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