Abstract:
An optoelectronic switch using millimeter wavelength (MMW) is provided. An r voltage pulse is applied to a device under test (DUT) for switching the photo-generated MMW power The DUT is operated under reverse bias. An optical light source with modulated MMW envelop is injected on to DUT for MMW power generation. Thus, based on change of the reverse bias, speed is violently changed and the MMW optoelectronic switch is thus obtained.

Description:
TECHNICAL FIELD OF THE DISCLOSURE 
     The present disclosure relates to an optoelectronic switch; more particularly, relates to operate a device under test (DUT) under a reverse bias for obtaining a millimeter wavelength (MMW) optoelectronic switch having great change in electron drift-velocity based on change of the reverse bias. 
     DESCRIPTION OF THE RELATED ARTS 
     In an MMW radio communication system, high-frequency switch is a very important component. On designing a high-frequency circuit, efficiency of the circuit is usually limited by the components. For a high-frequency switch using MMW, isolation of the switch under on/off states is limited by characteristics of the components. When a field effect transistor (FET) is in an off state under a high frequency, an equivalent capacitor is formed by drain and source of a transistor. Thus, a low resistance, not a high resistance, is formed, and so performance of the whole circuit is affected. Besides, in the high-frequency circuit, signals are often coupled between abiding lines and so performance of the whole circuit is further affected. Hence, resistance isolation is not good in high-frequency band of the switch. 
     Therefore, uni-traveling-carrier photodiode (UTC-PD) is introduced. However, its speed on isolation is not fast enough. When a device having this structure is switched and data signals are imported, a forward bias is required; but, repeated operations between forward bias and reverse bias are needed to make big change on current to operate the switch. In  FIG. 8 , change of a photocurrent is very obvious for switching. Devices are normally operated under reverse bias, but the UTC-PD is repeatedly operated between forward bias and reverse bias. As a result, the device becomes unstable in performance. 
     Another prior art shows in  FIG. 9 . A distance between its chip  81  and its antenna  82  is big, about 4 to 5 wavelength (λ); and so it can not be easily micro-scaled and its cost becomes high. Hence, the prior arts do not fulfill all users&#39; requests on actual use. 
     SUMMARY OF THE DISCLOSURE 
     The main purpose of the present disclosure is to operate a device under test (DUT) under a reverse bias for obtaining an MMW optoelectronic switch having great change in electron drift-velocity-based on change of the reverse bias. 
     To achieve the above purpose, the present disclosure is an optoelectronic switch transmitter using MMW, comprising an input device; a pulse pattern generator (PPG); a DUT; an antenna-signal processor; and an error detector (ED), where the DUT comprises an intermediate frequency (IF) input; a radio frequency (RF) choke connected with the IF Input; an optoelectronic switch connected with the RF choke; a fan-shaped broadband transition device connected with the optoelectronic switch; and a transmitter connected with the optoelectronic switch; where the DUT is positioned in a waveguide to be combined to a first horn antenna through the waveguide; where the optoelectronic switch has a structure of p-n-p-i-n epi-layers, comprising, from top to bottom, a first p-type doped layer; a first n-type doped layer; a second p-type doped layer; an undoped layer; and a second n-type doped layer; and where the epi-layers are grown on a doped semiconductor substrate or a semi-insulating semiconductor substrate. Accordingly, a novel optoelectronic switch transmitter using MMW is obtained. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
       The present disclosure will be better understood from the following detailed description of the preferred embodiment according to the present disclosure, taken in conjunction with the accompanying drawings, in which 
         FIG. 1  is the structural view showing the preferred embodiment according to the present disclosure; 
         FIG. 2  is the structural view showing the DUT; 
         FIG. 3  is the perspective view showing the DUT; 
         FIG. 4  is the view showing the optoelectronic switch; 
         FIG. 5  is the view sowing the relationship curves between power and photocurrent; 
         FIG. 6  is the view showing the frequency responses; 
         FIG. 7  is the view showing the output power curve of the changing photocurrents; 
         FIG. 8  is the view of the current curve of the prior art; and 
         FIG. 9  is the structural view of the prior art. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following description of the preferred embodiment is provided to understand the features and the structures of the present disclosure. 
     Please refer to  FIG. 1  to  FIG. 4 , which are a structural view showing the preferred embodiment according to the present disclosure; a structural view and a perspective view showing a DUT; and a view showing an optoelectronic switch. As shown in the figures, the present disclosure is an optoelectronic switch transmitter using millimeter wavelength (MMW), comprising an input device  1 , a pulse pattern generator (PPG)  2 , a device under test (DUT)  3 , an antenna-signal processor  4  and an error detector (ED)  5 , where a high-power pulse is applied to the DUT  3  to detect emitting of photon from the DUT through sensing light source. 
     The input device  1  comprises a single-mode fiber (SMF)  11  and a lensed fiber  12 , where the lensed fiber  12  is set at a side of the SMF  11  and is connected with a probe at a first end of the SMF  11 ; and, at another side, the SMF  11  is optically coupled with a light source (optical MMW source)  13 , a fiber amplifier  14  (erbium-doped fiber amplifier, EDFA) and an attenuator  15 . 
     The PPG  12  generates 12.5 Gbit/s pulse signals. 
     A part of the DUT  3  is set in a waveguide  36  and is combined with a first horn antenna  34  through the waveguide  36 . The DUT  3  comprises an intermediate frequency (IF) input  31 ; a radio frequency (RF) choke  32  connected with the IF input  31 ; an optoelectronic switch  33  connected with the RF choke  32 ; a fan-shaped broadband transition  34  connected with the optoelectronic switch  33 ; and a transmitter  35  connected with the optoelectronic switch  33 . Therein, there is a tiny wavelength (λ) between the optoelectronic switch  33  and the transmitter  35 ; the optoelectronic switch  33  has a structure of p-n-p-i-n epi-layers, comprising, from top to bottom, a first p-type doped layer  331 , a first n-type doped layer  332 , a second p-type doped layer  333 , an undoped layer  334  and a second n-type doped layer  335 ; the epi-layers are grown on a thoroughly-doped or semi-insulating semiconductor substrate; the semiconductor substrate is made of GaAs, InP, GaN, AlN, Si, or GaSb; the first p-type doped layer  331  is a light-absorbing layer made of a light-absorbing material and is graded doped to accelerate emission of electrons; the first n-type doped layer  332  is made of a non-light-absorbing material characterized with ballistic transport to accelerate transport of carriers and is n-type doped to increase a breakdown voltage and a greatest output current; the second p-type doped layer  333  and the undoped layer  334  are made of a non-light-absorbing alloy of a III group element or a IV group element and are doped to a certain degree with a certain thickness to operate the first n-type doped layer  332  at a peak drift velocity of carriers; the second p-type doped layer  333  is thus characterized with ballistic transport; the second n-type doped layer  335  is made of a heavy-doped semiconductor to obtain an ohmic contact; the epi-layers are made of a compound semiconductor and a compound alloy semiconductor; or, is made of a IV group semiconductor and a IV group alloy semiconductor; the compound semiconductor is GaAs, InP or GaN; the compound alloy semiconductor is AlGaN, InGaN, InGaAs, InGaAsP, InAlAs, InP, InAlGaAs, GaAs or AlGaAs; the IV group semiconductor is Si; and, the IV group alloy semiconductor is SiGe. 
     The antenna-signal processor  4  comprises a W-band low noise amplifier (LNA)  41 ; a W-band power detector  42  connected with the W-band LNA  41 ; and an IF amplifier  43  connected with the W-band power detector  42 , where the antenna-signal processor  4  is electrically connected with a second horn antenna  40  at a front end. 
     The ED  5  is electrically connected with the antenna-signal processor  4 . 
     Thus, a novel switch transmitting MMW is obtained. 
     Therein, the DUT  3  is operated under a reverse bias to intensely change its electron drift-velocity and response according to change of the reverse bias; the transmitter  35  is a Quasi-Yagi antenna; and the optoelectronic switch  33  is a near-ballistic uni-traveling carrier photodiode (NBUTC-PD) used as a side-illumination detector (as shown in  FIG. 3 ) or a vertical-illumination detector (as shown in  FIG. 3 ). 
     The present disclosure can further comprise a microwave probe to load the PPG  2 . As shown in  FIG. 1 , a signal path comprises an optical path and an electrical path  44 . On using the present disclosure, in the optical path  10 , the light source  13  of the input device  1  generates a 100 GHz carrier light source. After optical signals are magnified and attenuated through the fiber amplifier  14  and the attenuator  15 , light beam of the light source is expanded by the SMF  11  and is outputted as a collimated light beam to be focused through the lensed fiber  12 . Thus, the optical signals are efficiently moved from the SMF  11  to the lensed fiber  12  to be filled into the DUT  3  in a form of light spots  330  in the optoelectronic switch  33 . In the electrical path  44 , the PPG  2  generates 12.5 Gbit/s pulse signals imported into the DUT  3  from the IF input  31  through the microwave probe. 
     The optical signals from the input device  1  and the pulse signals from the PPG  2  are integrated in the optoelectronic switch  33  of the DUT  3 . Through low RF resistance generated by the RF choke  32 , a voltage difference between the source of pulse signals and the source of optical signals is weakened. Then, based on broadband signals generated by the fan-shaped broadband transition  34 , MMW signals transformed from the optical signals, which have IFs around 100 GHz, are outputted and transmitted to the waveguide  36  by the transmitter  35  to be emitted from the first horn antenna  37 . 
     The antenna-signal processor  4  receives and magnifies waveband of the MMW signals from the second horn antenna  40  to magnify W-band of the MMW signals for obtaining W-band MMW signals. Then, power check is processed to the W-band MMW signals to obtain a check result and the check result is transformed into voltage level signals. Then, base on the voltage level signals, intermediate voltages of the W-band MMW signals are magnified to be outputted to the ED  5  for checking to obtain an error rate of the W-band MMW signals. 
     Please refer to  FIG. 5  to  FIG. 7 , which are a view sowing relationship curves between power and photocurrent; a view showing frequency responses; and a view showing an output power curve of changing photocurrents. As shown in the figures, when the present disclosure is operated under a reverse bias with a power at 100 GHz and with different optical excited pulses, a 60 milli-watt (mW) power curve  6   a  with its first photocurrent curve  6   b  are compared to a 100 mW power curve  6   c  with its second photocurrent curve  6   d . The 100 mW power curve  6   c  with its second photocurrent curve  6   d  show that photocurrent is not changed when the reverse bias is increased. Hence, the present disclosure can change power based on change of the reverse bias; and, when the reverse bias is increased, the power of the related MMW signal is increased with a steady photocurrent. 
     In  FIG. 6 , with an area of 64 μm 2  and a photocurrent of 7.5 milli-ampere (mA) and a frequency of 100 GHz, relative response curves  7   a ,  7   b ,  7   c  are measured under bias voltages of 1V, −3V and −5V. In  FIG. 7 , with the same area and 25 ohms (Ω) of bias resistance under a −3V bias voltage at a 100 GHz frequency, an output power curve  7   d  for different photocurrents is obtained. It shows that change of reverse bias may cause great change of velocity on components of the present disclosure; and an MMW optoelectronic switch is thus obtained. 
     In NBUTC structure of the present disclosure, a second p-type doped layer and an undoped layer are added after a first n-type doped layer. Most electrons in an electrical field on the first n-type doped layer are drifted to two ends of the undoped layer and only few electrons in the electrical field are drifted to the first n-type doped layer. When the electrons are drifted, most of the time they are drifted in the first n-type doped layer with ballistic transport; yet only a short time they are drifted in the undoped layer at a low speed. In this way, effect of ballistic transport is obtained with a high bias voltage regardless of load resistance. Besides, because only few electrons in the electrical field are drifted in the first n-type doped layer, more doping is used to increase a greatest output current for enhancing electrical power output without decreasing breakdown voltage. 
     The present disclosure make most of the electrical field fall on the undoped layer, so that, even through a high bias voltage is used in operation, the first n-type doped layer still has a low electrical field while ballistic transport is kept. Furthermore, doping in the first n-type doped layer is increased to enhance power output without sacrificing breakdown voltage. Moreover, the present disclosure reduces trade-off of bandwidth and a ratio of greatest output power to efficiency on surface area. 
     To sum up, the present disclosure is an optoelectronic switch transmitter using MMW, where velocity is greatly changed based on change of reverse bias for obtaining an MMW optoelectronic switch. 
     The preferred embodiment herein disclosed is not intended to unnecessarily limit the scope of the disclosure. Therefore, simple modifications or variations belonging to the equivalent of the scope of the claims and the instructions disclosed herein for a patent are all within the scope of the present disclosure.