JP2013015678A - Terahertz wave generator and adjustment method thereof - Google Patents

Abstract

A method for adjusting a terahertz wave generator that maximizes the generation efficiency of terahertz waves.
SOLUTION: Array photodiodes PD1 to PD4 that receive an optical beam from an array optical waveguide 11, two adjustment photodiodes mPD1 and mPD2 installed at both ends of the array photodiode, and 2 Using a terahertz wave generator having two adjustment optical waveguides m11 and m12 connected to the adjustment optical beams mBeam1 and mBeam2 of each of the adjustment photodiodes, the output of one mPD1 is maximized. The arrayed optical waveguide 11 is moved in the horizontal and vertical directions with respect to the arrayed photodiode so that the maximum output of the mPD1 is maintained, and the output of the other mPD2 is equal to the output of one of the adjustment photodiodes. As such, an array type optical waveguide or array type photo with one mPD1 as an axis A method of adjusting by rotating an array of diodes.
[Selection] Figure 1

Description

  The present invention relates to a terahertz wave generator including an array type photodiode with an adjustment function and an adjustment method thereof.

  The terahertz wave band (0.1 to 10 THz) is expected to be applicable in many fields such as imaging, sensing, security, and communication (Non-Patent Document 1). Terahertz waves have light straightness and are permeable to materials such as plastic, paper, rubber, wood, and ceramic, and are expected to be used for safe nondestructive inspection. Thanks to dramatic advances in terahertz wave generation and detection technology, terahertz spectroscopy, which is the spectroscopic method, has attracted attention, and its potential as a new chemical sensing method is being explored. In addition, since there is a higher frequency resolution than radio waves in the gigahertz (GHz) band, it is possible to improve the spatial resolution of imaging and the communication speed of wireless communication. Applications include IT applications (such as wireless communications), agriculture / food applications, security applications (concealment inspection, postal nondestructive inspection, etc.), bio / medical applications, environmental measurement applications, space measurement applications, industrial applications (LSI failure analysis, New materials development).

  As a generation source of terahertz waves, particularly in the communication field, there are roughly classified electronic devices and photonic devices. Photonic devices have the advantages of a wide frequency band, tunability, and stability (Non-patent Document 1), and are further advantageous in that they can be easily connected to an optical fiber cable. As a typical device, there is a photodiode that operates in the near infrared (1.3 to 1.55 μm) and covers a millimeter wave band to a terahertz wave band. At higher frequencies than microwaves, the device capacitance (electrical capacity) increases, so the generation efficiency decreases at higher frequencies. In order to reduce the capacitance for higher output, it is necessary to reduce the device size of the photodiode. However, when the size of the photodiode is reduced, connection with the optical fiber becomes difficult. As another method, if the operating current is increased, it is possible to increase the output to some extent, but it is highly possible that the device of the photodiode is deteriorated due to heat.

  Taking these problems into consideration, as a technique to increase the output of terahertz waves, a power combiner (synthesizer) combines multiple signal sources output from an array-type device used in the millimeter wave band. (Non-Patent Documents 2 and 3).

  4 and 5 show an example of a terahertz wave generator 100 using a conventional combiner. An optical waveguide 101 that guides the optical beam, such as a planar lightwave circuit (PLC) or fiber, and one or more lenses Lens-1, Lens that are used to focus the optical beam and control the direction of the optical beam. -2, array type photodiodes PD1, PD2, PD3, PD4, power combining circuit 102, impedance matching network 103 between photodiodes PD1, PD2, PD3, PD4 and power combining circuit 102, and DC bias photo It is composed of other components for the diode, such as the bypass capacitor 106.

  In such a conventional terahertz wave generator 100, by combining outputs from 2N terahertz photodiodes PD1 to PD2N, the output can be increased up to 2N times. That is, 16 photodiodes PD1 to PD16 can increase the output by 16 times. By integrating the photodiode PDi, the power combining circuit 102, and the impedance matching network 103 between the photodiode PDi and the power combining circuit 102 into a single chip 105, the terahertz wave optical waveguide 101 and the impedance matching network are integrated. 103, the path loss in the power combining circuit 102 can be minimized, and the distances between the photodiodes can be defined equally. As a result, the power coupling efficiency can be maximized.

  However, in this configuration, there is a problem in the process of aligning the optical beam between the optical waveguide 101 (array type optical fiber or planar type light wave circuit PLD) and the array type photodiodes PD1 to PD4. That is, one electrode of the photodiode is electrically connected to the terahertz power combining circuit 102 that forms a short circuit in DC. From the output of the power combining circuit 102, only the total amount of photocurrent output from all the photodiodes PD1 to PD4 can be grasped. If the array type device is a terahertz wave device as small as several tens of micrometers compared to millimeter waves, it is estimated whether all devices are connected under proper irradiation and which devices are not irradiated Insufficient for For example, even when the optical beam Beam4 is coupled to one photodiode PD4 among the four optical beams Beam1 to Beam4 in FIG. 4, it is specified how many other photodiodes are under sufficient irradiation. Can not. If the bias network of all the photodiodes PD1 to PD4 is divided, the photocurrent of each device can be checked. However, in that case, 2N pads for wire bonding (eight in the example of FIG. 4) are required, which is much larger than the number of photodiodes, so that the total size of the array type photodiodes is increased. And the spatial efficiency of the photodiode array IC 105 is significantly reduced.

  Therefore, conventionally, when the array type photodiodes PD1 to PD4 are used as the terahertz wave generator, each photodiode device is smaller than the millimeter wave band, so that the optical waveguide 101 (array type optical fiber or planar type light wave circuit PLC) is surely provided. There has been a demand for a method for accurately confirming whether or not it is connected to the.

"Terahertz wave new industry", supervised by Masayoshi Tonouchi, CMC Publishing, 2011, P238-245, "Chapter 11 Terahertz wave information and communication use". IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 46, NO. 4, P541-545, 2010. JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 28, NO. 6, P965-971, March 15, 2010.

  The present invention has been made in view of the problems of the prior art, and it can be confirmed whether or not the connection between the array type photodiode and the optical waveguide is reliably performed, and the generation efficiency of the terahertz wave is maximized. It is an object of the present invention to provide a terahertz wave generator that can be used and a method for adjusting the terahertz wave generator.

  One aspect of the present invention is an array type optical waveguide that guides an optical beam, an array type photodiode that receives the optical beam from the array type optical waveguide, and an array type photodiode disposed at each end of the array type photodiode. Two adjustment photodiodes, and two adjustment optical waveguides coupled to the adjustment optical beams of the two adjustment photodiodes, respectively, the two adjustment optical waveguides, Separately from the array type optical waveguide, the adjustment type optical beam is guided to each of the two adjustment photodiodes, and the photocurrent and voltage of the adjustment photodiode are monitored, so that the array type photodiodes are reliably connected. It is a terahertz wave generator that checks whether or not

  Further, another feature of the present invention is that an array type optical waveguide that guides an optical beam, an array type photodiode that receives the optical beam from the array type optical waveguide, and an array photodiode at each end of the array type photodiode. A terahertz wave generator adjustment method comprising the two adjustment photodiodes and two adjustment optical waveguides coupled to the adjustment optical beams of the two adjustment photodiodes, respectively. Moving the arrayed optical waveguide in a horizontal direction and a vertical direction with respect to the arrayed photodiode so that one output of the two adjusting photodiodes is maximized; and While maintaining the output of the diode, the other output of the two adjustment photodiodes is the same as the output of the one adjustment photodiode. To be equal, a method of adjusting the terahertz wave generator and a step of rotating the array optical waveguides said one adjustment photodiode as an axis.

  According to the terahertz wave generator of the present invention, the step of moving the array type optical waveguide in the horizontal direction and the vertical direction with respect to the array type photodiode so that the output of one of the two adjustment photodiodes is maximized. While maintaining the output of one of the adjustment photodiodes, the other adjustment photodiode is used as an axis so that the other output of the two adjustment photodiodes is equivalent to the output of the one adjustment photodiode. It is possible to confirm whether or not the connection between the array type photodiode and the optical waveguide is reliably performed by the step of rotating the array type optical waveguide.

The element layout figure of the terahertz wave generator of one embodiment of this invention. Explanatory drawing of the adjustment method of the terahertz wave generator of the said embodiment. The measurement graph of the output of the two photodiodes for adjustment in each step of step 1-step 3 by the adjustment method of the terahertz wave generator of the said embodiment. The element layout figure of the conventional terahertz wave generator. The side view of the element layout of the conventional terahertz wave generator.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a terahertz wave generator 10 having an array type photodiode with an adjustment function according to one embodiment of the present invention. The terahertz wave generator 10 of this embodiment is an array type optical waveguide 11 that guides an optical beam, such as a planar lightwave circuit (PLC) or an optical fiber, and focuses the optical beam or controls the direction of the optical beam. One or a plurality of lenses Lens-1, Lens-2, array type photodiodes PD1, PD2, PD3, PD4, power combining circuit 12, array type photodiodes PD1, PD2, PD3, PD4 and power combining circuit 12 And an impedance matching network 13 between and other components for a DC biased photodiode, such as a bypass capacitor 14.

  As a feature of the present embodiment, two additional adjustment photodiodes mPD1 and mPD2 are added to both ends of the array type photodiodes PD1 to PD4, and the adjustment optics of these added adjustment photodiodes mPD1 and mPD2 are added. The adjustment optical waveguides m11 and m12 are also connected to the beams mBeam1 and mBeam2. The added adjustment optical waveguides m11 and m12 are set to guide an optical signal separately from the other optical waveguides 11 in the process of arrangement.

  In the case of this embodiment, in general, in the case of a one-dimensional array arrangement of 2N photodiodes PD1 to PD2N, only two photodiodes mPD1 and mPD2 and two added optical waveguides m11 and m12 are required. It is. Furthermore, without measuring the photocurrents of the array type photodiodes PD1 to PD4, the photocurrents Im1 and Im2 and the voltages Vm1 and Vm2 of the adjustment photodiodes mPD1 and mPD2 are monitored, so that the array type photodiodes PD1 to PD4 It is possible to confirm whether the connection is reliably performed, and to maximize the generation efficiency of the terahertz wave.

  Next, a method for adjusting the terahertz wave generator 10 according to the above embodiment will be described. A case where the one-dimensional array type photodiodes PD1 to PD4 are adjusted as shown in FIG. 2 will be described. Six photodiodes PD1 to PD4 and adjustment photodiodes mPD1 and mPD2 are arranged at intervals of 64 microns. The array type photodiode of this arrangement is manufactured using the InP process. The laser used was 1.5 microns in wavelength (manufactured by Suntech), and was emitted from both ends of a planar optical waveguide (the distance between the output laser beams was 127 microns) using a coupler.

  As in Step 1 of FIG. 2, the optical waveguide m11 of the adjustment photodiode mPD1 supplies light, and the optical waveguide holder and the lens set are controlled so that the photocurrent Im1 from the mPD1 reaches the maximum. At this stage, the optical beam is controlled only in the horizontal X direction and the vertical Y direction. In FIG. 2, the axis AX1 is the array axis of the array type photodiodes PD1 to PD4, and the axis AX2 is the array axis of the optical beam.

  Next, as in step 2 of FIG. 2, the optical waveguide m12 of the other adjustment photodiode mPD2 is also supplied with light, and the magnification of the lens and the angle of the optical beam are controlled so that the photocurrent Im1 of the mPD1 is always maximized. While holding, fine adjustment is made in the array axis AX2 direction (m) so that the photocurrent Im2 of mPD2 also reaches the maximum, and the rotation angle φ about one adjustment photodiode mPD1 is adjusted. When controlling the angle φ of the optical beam, the holder of the optical waveguide 11 may be rotated about the mPD1.

  The results are shown in FIG. It is important to observe the degree of balance between the photocurrents Im1 and Im2 of the adjustment photodiodes mPD1 and mPD2, and it is ideal that the two photocurrents Im1 and Im2 are equal to achieve the best adjustment. . In the graph of FIG. 3, timing tA indicates the timing at which the photocurrent reaches the maximum for the adjustment photodiode mPD1 and fine adjustment is started for the adjustment photodiode mPD2. The timing tB indicates the timing at which the photocurrent Im1 of the adjustment photodiode mPD1 is always kept at the maximum and the photocurrent Im2 of the other adjustment photodiode mPD2 is also finely adjusted.

  With this adjustment, it is assumed that all the optical beams coincide completely or substantially coincide with each other within the optimum frame of each photodiode as in step 3 of FIG. Therefore, at this stage, the optical beam is accurately tuned while observing the total photocurrent I (m1 + m2) of the photodiode array and the balance between the photocurrents Im1 and Im2 of mPD1 and mPD2 (step 3 in FIG. 3). ).

  With the adjustment method for the terahertz generator 10 described above, it is possible to confirm whether or not the array-type photodiodes PD1 to PD4 and the array-type optical waveguide 11 are securely connected.

DESCRIPTION OF SYMBOLS 10 Terahertz wave generator 11 Array type optical waveguide 12 Power synthesis circuit 13 Impedance matching network 13
14 is composed of a bypass capacitor 14.

15 Array type photodiode IC
PD1 to PD4 Array type photodiode mPD1, mPD2 Adjustment photodiode mBeam1, mBeam2 Adjustment optical beam m11, m12 Adjustment optical waveguide

Claims (2)

An arrayed optical waveguide for guiding an optical beam;
An array type photodiode that receives the optical beam from the array type optical waveguide; and
Two adjustment photodiodes installed at both ends of the array-type photodiode;
Two adjustment optical waveguides coupled to the adjustment optical beams of the two adjustment photodiodes,
From each of the two adjustment optical waveguides, an adjustment optical beam is led to each of the two adjustment photodiodes separately from the array type optical waveguide,
An array type photodiode with an adjustment function, wherein the photocurrent and voltage of the two adjustment photodiodes are monitored to confirm whether or not the array type photodiodes are reliably connected. An array-type optical waveguide for guiding an optical beam; an array-type photodiode for receiving the optical beam from the array-type optical waveguide; and two adjustment photodiodes installed at both ends of the array-type photodiode. A method of adjusting an array type photodiode with an adjustment function, comprising two adjustment optical waveguides coupled to the adjustment optical beams of the two adjustment photodiodes, respectively,
Moving the arrayed optical waveguide in a horizontal direction and a vertical direction with respect to the arrayed photodiode so that one output of the two adjusting photodiodes is maximized;
While maintaining the maximum output of the one adjustment photodiode, the other output of the two adjustment photodiodes is equal to the output of the one adjustment photodiode. A method for adjusting an array type photodiode with an adjustment function, comprising: rotating the array type optical waveguide around a diode.

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