1. Date of download: 7/5/2016 Copyright © 2016 SPIE. All rights reserved. Basic principle of the proposed circuit. The lower portion of the figure contains a schematic representation of the optical and microwave spectra. Figure Legend: From: Highly tunable microwave and millimeter wave filtering using photonic technology Opt. Eng. 2015;54(5):057102. doi:10.1117/1.OE.54.5.057102

2. Date of download: 7/5/2016 Copyright © 2016 SPIE. All rights reserved. Basic principle being proposed for adjusting the width of the tunable filter. The temperature, or some other adjustment parameter, is used to vary the center frequency of each grating, as depicted in subplots (a) to (c). Note that the arrow labeled “RF beat note” can represent the instantaneous frequency in an RF sweep, or a narrow slice from a much larger RF spectrum. Figure Legend: From: Highly tunable microwave and millimeter wave filtering using photonic technology Opt. Eng. 2015;54(5):057102. doi:10.1117/1.OE.54.5.057102

3. Date of download: 7/5/2016 Copyright © 2016 SPIE. All rights reserved. Typical modeling results for a multiphase-shift grating. The upper trace is the overall response showing the narrow central passband and side lobes. The lower trace is a detail of the central band showing both the transmission (solid) and reflection characteristics of the grating. Figure Legend: From: Highly tunable microwave and millimeter wave filtering using photonic technology Opt. Eng. 2015;54(5):057102. doi:10.1117/1.OE.54.5.057102

4. Date of download: 7/5/2016 Copyright © 2016 SPIE. All rights reserved. Electrical-domain measurements of the grating characteristics, as described in the text. Figure Legend: From: Highly tunable microwave and millimeter wave filtering using photonic technology Opt. Eng. 2015;54(5):057102. doi:10.1117/1.OE.54.5.057102

5. Date of download: 7/5/2016 Copyright © 2016 SPIE. All rights reserved. Response of two 120-mm FBG samples and the corresponding simulation result with the spectrum measured in (a) the optical domain using a tunable laser source and an optical power meter, and (b) the electrical domain. Figure Legend: From: Highly tunable microwave and millimeter wave filtering using photonic technology Opt. Eng. 2015;54(5):057102. doi:10.1117/1.OE.54.5.057102

6. Date of download: 7/5/2016 Copyright © 2016 SPIE. All rights reserved. Experimental setup for the electrical measurement of an FBG. Figure Legend: From: Highly tunable microwave and millimeter wave filtering using photonic technology Opt. Eng. 2015;54(5):057102. doi:10.1117/1.OE.54.5.057102

7. Date of download: 7/5/2016 Copyright © 2016 SPIE. All rights reserved. Filter performance measured in optical domain with sketches for carrier and sidebands. Note that the dynamic range of the gratings is typically 60 to 65 dB and is not accurately represented in the figure. The upper side band is attenuated by the blocking grating as it scans from 10 to 30 GHz (as shown by the arrows), while the lower side band traces out the shape of the filter grating. Figure Legend: From: Highly tunable microwave and millimeter wave filtering using photonic technology Opt. Eng. 2015;54(5):057102. doi:10.1117/1.OE.54.5.057102

8. Date of download: 7/5/2016 Copyright © 2016 SPIE. All rights reserved. Demonstration of variable width microwave filter as described in the text. The temperature of the second grating (0210B) is altered between 39.5 and 42.5°C in 1°C increments in subplots (a) to (d), respectively. Figure Legend: From: Highly tunable microwave and millimeter wave filtering using photonic technology Opt. Eng. 2015;54(5):057102. doi:10.1117/1.OE.54.5.057102

9. Date of download: 7/5/2016 Copyright © 2016 SPIE. All rights reserved. Temperature response of the blocking grating (other gratings have a similar response). The tuning rate is approximately 10.2 pm/°C or 1.25 GHz/°C. Figure Legend: From: Highly tunable microwave and millimeter wave filtering using photonic technology Opt. Eng. 2015;54(5):057102. doi:10.1117/1.OE.54.5.057102

10. Date of download: 7/5/2016 Copyright © 2016 SPIE. All rights reserved. Schematic description of the filter translation (each division is 10 GHz). The upper plot depicts the filter operating at around 20 GHz, while the lower is at 30 GHz. In both cases, the bandwidth of the filter will be the same (only one filter grating is shown for simplicity). Figure Legend: From: Highly tunable microwave and millimeter wave filtering using photonic technology Opt. Eng. 2015;54(5):057102. doi:10.1117/1.OE.54.5.057102

11. Date of download: 7/5/2016 Copyright © 2016 SPIE. All rights reserved. Central operating frequency of the grating can be tuned over a very large range, as described in the text. Figure Legend: From: Highly tunable microwave and millimeter wave filtering using photonic technology Opt. Eng. 2015;54(5):057102. doi:10.1117/1.OE.54.5.057102