An overview of analog microwave photonics will be presented. The performance requirements for externally-modulated analog microwave photonic links will be reviewed with specific emphasis placed on modulator efficiency, laser noise, detected photocurrent, and link linearity.

http://ieeexplore.ieee.org/iel5/6387506/6403300/06403360.pdf

Microwave photonics

The low-loss wide bandwidth capability of opto-electronic systems makes them attractive for the transmission and processing of microwave signals, while the development of high-capacity optical communication systems has required the use of microwave techniques in optical transmitters and receivers. These two strands have led to the development of the research area of microwave photonics. This paper reviews the development status of microwave photonic devices, describes their systems applications, and suggests some likely areas for future development

Microwave Photonics

This paper is divided into two major parts. Following a brief introduction that establishes some definitions and assumptions, Section II updates our earlier study on the limits of the RF performance of optical links. Section III reviews progress since our 1997 review paper in the development of devices enabling link performance closer to these limits, including (but not limited to): 1) cascade lasers that permit broad-band direct modulation links with gain >0 dB; 2) injection-locked edge- and surface-emitting lasers at 1300 and 1550 nm with modulation frequency responses as great as 40 GHz; 3) modulators with improved performance, especially electroabsorption modulators that now have switching voltages as low as 0.36 V, or handle optical powers as great as 60 mW, or have bandwidths as great as 50 GHz (but not all three of these in one device yet); and 4) high-speed photodetectors with high saturation currents, e.g., a 20-GHz device with a saturation current of 90 mA and a 55-GHz device with saturation at 50 mA. We conclude in Section IV by summarizing the component developments necessary for higher performance RF-over-fiber links, i.e.: 1) semiconductor lasers (for direct modulation) that have higher slope efficiency and bandwidth and lower relative intensity noise (RIN) at reasonable bias current levels; 2) continuous wave (CW) lasers (for external modulation) with higher fiber-coupled power and lower RIN; 3) higher frequency lower loss external modulators with more linear transfer functions and lower V/sub /spl pi// that can withstand larger CW optical powers; and 4) photodetectors with higher responsivity and bandwidth that respond linearly even when illuminated by greater average optical powers.

Limits on the performance of RF-over-fiber links and their impact on device design

The authors correct an error in their original article (see ibid., vol.54, no.2, p.906-20, Feb. 2006).

Corrections to "Limits on the Performance of RF-Over-Fiber Links and Their Impact on Device Design"

A new ultrafast photodiode, uni-traveling-carrier photodiode (UTC-PD) is proposed, and its photoresponse characterization on fabricated devices is presented. The prime feature of this PD is much higher output saturation current than that in a conventional pin-PD. This is achieved by reducing the space charge effect by utilizing electron velocity overshoot in the carrier collecting layer. A 20 μm2-area UTC-PD fabricated with MOVPE-grown InP/InGaAs heterostructure generated an output voltage as high as 2 V for a 25 Ω load while maintaining an f3dB of 80 GHz. Proper device operations at high photocurrent densities up to 400 kA/cm2 were observed.

Uni-traveling-carrier photodiodes

We present novel (InGa)As photodetectors which exhibit 150 mA continuous photocurrent at 2 W power dissipation. A responsivity of 0.97 A/W at 1319 nm is achieved with greater than 60% external quantum efficiency from 920 to 1650 mm. Measured dark currents are below 1 nA and bandwidths of 295 MHz are achieved. These low dark-current devices have utility to applications requiring large output current and large dynamic range.

A 920-1650-nm high-current photodetector

A two-phase, 2DEG-CCD intended for signal acquisition and delay with sample rates in the 1 to 20 GHz range is described. Signal delay versus clock frequency has been measured from 1 MHz to 13 GHz, verifying CCD operation. The input-to-output transfer function is linear for input powers ranging from -25 dBm to +2 dBm, with a 1 dB compression point at 4.5 dBm. The lower bound on CTE is 0.995 at 10 MHz and 4.02 GHz. CTE characterization results for clock frequencies between 4.02 GHz to 16.4 GHz qualitatively agree with those of two-dimensional transient simulations, which show that the charge packet transfers at saturation velocity. Simulations of a device incorporating an InGaAs channel predict that CTE greater than 0.9999 is attainable for clock frequencies up to 50 GHz. >

A microwave 2DEG-CCD for high speed signal acquisition

A two-phase, InGaAs channel 2DEG-CCD (charge coupled device) intended for millimeter-wave signal acquisition and delay is presented. Signal delay versus clock frequency has been measured from 1 MHz to 14 GHz, verifying CCD operation. The input-to-output transfer function is linear with a 1 dB compression point at 2 dBm and a 3rd harmonic intercept at 35 dBm. A charge transfer efficiency (CTE) of 0.99 has been measured at 4.73 GHz. Two-dimensional transient simulations show that the charge packet transfers at saturation velocity, and that CTE degradation results primarily from charge trapping in interelectrode parasitic wells. The simulations predict that CTE greater than 0.9999 is achievable at clock frequencies up to 50 GHz. >

Millimeter wave AlGaAs/InGaAs 2DEG-CCDs

Summary form only given. In this paper we describe an InGaAs-based photodiode, which has demonstrated continuous 140-mA output current at 2-W power dissipation with 0.97-A/W conversion efficiency at 1320 nm.

R.A. LaRue

Papers

A 920-1650-nm high-current photodetector

A microwave 2DEG-CCD for high speed signal acquisition

Millimeter wave AlGaAs/InGaAs 2DEG-CCDs

A 920-1650-nm high-current photodiode