KR100395425B1 - A voltage controlled optical attenuator and method of making it - Google Patents

Abstract

The present invention relates to a voltage controlled optiacal attenuator and a method of manufacturing the same.

The attenuator of the present invention includes a pair of optical link forming means attached to one end of two optical cables, respectively, to form a parallel optical link, and an attenuation filter for attenuating light passing between the optical cables and inserted between the parallel optical links. And attenuation amount control means for controlling a transfer mechanism for transferring the attenuation filter and controlling the transfer mechanism according to a set value to adjust the attenuation amount of light passing between the optical cables.

Therefore, the voltage adjusting type variable optical attenuator according to the present invention can maintain the light output at the set value by automatically transferring the attenuation filter located between two optical collimators using a motor when the set value and the measured value are different.

Description

Voltage-adjustable variable attenuator and its manufacturing method {A VOLTAGE CONTROLLED OPTICAL ATTENUATOR AND METHOD OF MAKING IT}

The present invention relates to an optical attenuator, and more particularly, to a voltage controlled optiacal attenuator and a method of manufacturing the same.

In general, an optical attenuator is a device that serves to attenuate the intensity of an input optical signal. A variable optical attenuator is an optical attenuator that can externally adjust the degree of attenuation of an optical signal in an electrical or mechanical manner. Such optical attenuators are widely used in the characteristics of optical systems or optical devices for light intensity, ranging from wavelength division multiplex (WDM) systems. For example, in a WDM-based optical transmission network, multiple wavelengths are multiplexed and transmitted, and thus, it is necessary to maintain the light intensity of each wavelength uniformly within a specific range. Since the amplification and loss characteristics of the devices are different for each wavelength, a variable optical attenuator is used. This needs to be adjusted. It is also used to adjust the intensity of the input light at the receiving end of the optical transmission and reception system or optical relay system.

The optical attenuator uses a fixed optical attenuator using attenuated optical fibers doped with germanium (Ge) and aluminum (Al) to optical fibers, a fixed optical attenuator fused and fused in a tapered form, and an air gap according to a method of operation. The fixed or variable light attenuator, the fixed or variable light attenuator using light absorption and scattering by the attenuated thin film, and the variable light attenuator for controlling the light intensity using the liquid crystal and polarizer.

However, among the variable optical attenuators, a variable optical attenuator using an air gap is used to receive an optical signal from a single mode in multiple modes. In this case, interference may occur and a large amount of reflected light may be received by the photodetector. In addition, in the case of the variable optical attenuator using the polarization of the light by the liquid crystal, there is a problem that the polarization loss is very large. On the other hand, in the case of the variable light attenuator using the attenuated thin film, light absorption is used and the interference and polarization loss of light are small.

The present invention can automatically adjust the attenuation level by the voltage, and an object thereof is to provide a voltage adjusting type variable optical attenuator using an attenuation thin film.

In addition, another object of the present invention is to provide a manufacturing method of manufacturing a voltage regulating variable optical attenuator as described above.

1 is a schematic diagram showing the concept of a voltage regulating variable attenuator according to the present invention;

2 is a schematic view showing the configuration of a voltage regulating variable optical attenuator according to the present invention;

3 is a block diagram showing the configuration of a damping control module according to the present invention;

4 is a flowchart illustrating a procedure performed by a CPU of the attenuation control module according to the present invention;

5 is a flowchart illustrating a procedure performed by a PC according to the present invention;

6 is a flow chart showing a procedure for manufacturing the optical attenuation module according to the present invention;

7 is a view of a fixing sleeve for fixing the optical collimator according to the present invention,

8 is a perspective view of an optical link structure manufactured according to the present invention;

9 is a view showing the structure of a damping filter according to the present invention;

10 is a view of a fixed block for fixing the damping filter according to the present invention;

11 is an internal configuration diagram of an optical attenuation module according to the present invention;

12 is a view showing a housing inner box according to the present invention,

13 shows a housing enclosure according to the invention.

* Explanation of symbols for main parts of the drawings

102a, 102b: optical cable 104a, 104b: optical collimator

106: attenuation filter 201: setting unit

204a, 204b: optical connector 206: connector

210: attenuation control module 220: optical attenuation module

221: housing enclosure 222: housing enclosure

223: transfer mechanism 224: motor

225: filter fixing block 226: worm gear

227: shaft 228: plate

In order to achieve the above object, the attenuator of the present invention comprises: a pair of optical link forming means attached to one end of two optical cables to form a parallel optical link; An attenuation filter inserted between the parallel optical links to attenuate light passing between the optical cables; Conveying means for conveying said damping filter; And attenuation amount control means for controlling the transfer means according to a set value to adjust an attenuation amount of light passing between the optical cables.

In order to achieve the other object as described above, the manufacturing method of the present invention comprises the steps of: aligning a pair of optical collimator; Soldering the aligned optical collimator to a fixed sleeve to create an optical link; Depositing the damped thin film on the glass substrate so that the thickness of the damped thin film increases or decreases linearly with the position on the glass substrate; Depositing a multilayer antireflective thin film on the glass substrate; Fixing the glass substrate on which the attenuated thin film and the antireflective thin film are deposited to a filter fixing block, and assembling and soldering to a housing inner box; And assembling and soldering the housing inner box, the optical link, and the housing outer box.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

According to the present invention, the variable optical attenuator using the attenuated thin film is a pair of optical collimators (Collimator: 104a, attached to the cut surface by cutting the optical fiber cables (hereinafter simply referred to as optical cables: 102a, 102b) as shown in Figure 1). 104b) and an attenuation filter 106 inserted between the optical collimators 104a and 104b. That is, the variable optical attenuator according to the present invention has a basic structure in which the attenuation filter 106 is inserted between the optical links after forming the optical link using the optical collimators 104a and 104b between the two optical fibers 102a and 102b. In this case, the configuration of the optical link is a very important parameter that determines the initial insertion loss of the variable optical attenuator.

The attenuating method of the variable optical attenuator based on the optical link composed of the two optical collimators 104a and 104b includes an optical path blocking method, an alignment mismatch method of the optical collimator, and a damping filter method. The optical path blocking method uses a component that can change a small distance to block parallel light between optical collimator links to give a change in the amount of received light, thereby attenuating the amount of light. The loss is large. The misalignment method of the optical collimator attenuates the amount of light received by rotating one optical collimator. The structure is simple and has a low initial attenuation value, but the attenuation amount is not linear with the rotational speed, Very large a small change in attenuation is difficult.

In the attenuation method using the attenuation filter applied to the present invention, the main characteristics of the variable optical attenuator are determined according to the characteristics of the attenuation filter 106 which is a core element. As described below, the attenuated thin film composed of the metal thin film may be inserted between the optical links and moved at a small distance, and the amount of light transmitted through the thin film on the substrate may be linearly reduced due to the progressively thick deposition. .

Referring to FIG. 1, in the damping filter 106 inserted between the optical collimators 104a and 104b, a damping thin film causing light attenuation on the glass substrate is gradually thickened downward. Therefore, as the damping filter 106 is conveyed upward, the amount of attenuation gradually increases, and if it is conveyed downward, the amount of damping decreases. That is, the desired amount of attenuation can be obtained by appropriately moving the damping filter 106 in the vertical direction.

2 is a schematic diagram showing the configuration of a voltage regulating variable optical attenuator according to the present invention. The voltage adjusting type variable optical attenuator of the present invention includes a setting unit 201 for largely setting the attenuation amount, and an attenuation control module 210 for controlling the attenuation amount of the optical attenuation module 220 according to the setting value of the setting unit 201. The optical attenuation module 220 performs the attenuation function by a predetermined amount according to the control of the attenuation control module 210.

In the embodiment of the present invention, the setting unit 201 is implemented as a personal computer (PC), and the attenuation control module 210 measures the output light of the light attenuation module 220 as described below, and compares it with the setting value. If different from each other, the control signal is output so that the output light becomes a set value.

The optical attenuation module 220 has a structure in which the attenuation filter 106 is inserted between two optical collimators 104a and 104b, and the attenuation filter 106 is the optical collimator 104a and 104b by the transfer mechanism 223. ) Up and down. In the embodiment of the present invention, the feed mechanism is the filter fixing block (225 of FIG. 11) for fixing the motor 224 and the damping filter 106, the shaft shaft filter fixing block 225 by the rotational movement of the motor 224 And a shaft 227 and a worm gear 226 for feeding in the direction. And the motor 224 is a step motor (step motor) to enable the precise control, the damping filter 106 by the worm gear 226 by rotating the shaft 227 in accordance with the control signal of the damping control module 210 Transfer it.

In order to maintain such a mechanical structure, the motor 224, the shaft 227, the filter fixing block 225, and the damping filter 106 are fixedly supported by the housing inner box 222, and the two optical collimators 104a. 104b is secured by the collimator fixing sleeve as shown in FIG. 7 to stably support the optical link, and the entire component is coupled to the housing enclosure 221 in a soldering manner to form a single optical attenuation module 220. Are formed. The optical attenuation module 220 is connected to the outside by two optical connectors 204 and 204b for connecting an optical cable to the optical collimators 104a and 104b and a connector 206 for transmitting electrical signals to the motor 224. do. At this time, a portion of the optical cable (102a, 102b) is introduced into the optical attenuation module 220, the boot (boot) is installed to seal and protect the cable.

As shown in FIG. 3, the attenuation control module 210 according to the present invention receives an optical signal in order to monitor the output light of the optical attenuation module 220 and outputs most of it as it is, and a part of the tap coupler 211 branches. ), An optical detector 212 for converting the monitoring optical signal of the tap coupler 211 into an electrical signal, an amplifier 213 for amplifying the output signal of the photodetector 212, and an analog output of the amplifier 213. It consists of an analog-to-digital converter 214, a microcontroller 215, and a motor driver 216 for converting the signal into a digital signal.

Referring to FIG. 3, the output light of the optical attenuation module 220 is input to a tap coupler 211 so that an optical signal of about 5% is output to the photodetector PD 212 for output monitoring. About 95% of the optical signal is transmitted as it is to the optical system or light beam. As such, the tap coupler 211 serves to branch a part of the output light to monitor the optical signal.

The photo detector 212 is an InGaAs PIN photodiode, which converts an optical signal into an electrical signal, and the amplifier 213 is composed of an OP AMP, which is required to control a fine current signal output by the photo detector 212. Amplify. The analog-digital converter 214 converts the analog signal of the DC voltage input from the amplifier 213 into a digital signal. In an embodiment of the present invention, an analog-to-digital converter capable of 12-bit microprocessor control is implemented. The level of the input analog signal is compared with a predetermined reference level, the quantized level is identified, and the value is output as digital data. The microcontroller (CPU) 215 carries out a pre-built program that processes the procedure as shown in FIG. 4 and transmits the digital data (measurement value) received from the analog-to-digital converter 214 and the PC 201. The motor drive signal is output by comparing the signals. The microcontroller 215 has a built-in EEPROM circuit to protect important internal data even in case of power failure. The motor driver 216 receives the driving pulse signal received from the microcontroller 215 and provides a driving signal for driving the stepping motor 224 to the motor 224. Stepping motor used in the embodiment of the present invention is a digital motor, the rotation angle, the rotational speed is proportional to the number of pulses sent or the pulse repetition rate, and the current difference between start-up and operation of the dedicated driver for stable operation It is preferable to use an IC.

The personal computer PC 201 is for communication with a voltage regulating variable attenuator and is used for setting and changing attenuation values and for displaying attenuation values. Since the PC 201 can easily control the attenuation value, the variable attenuator can be easily used. If the user inputs a desired setting attenuation value by performing a procedure as shown in FIG. The set value is transmitted to the microcontroller 215 of the attenuation control module, and the microcontroller 215 receives and displays the level of the light output signal detected by the photodetector. In the embodiment of the present invention, the setting unit 201 is implemented as a separate personal computer (PC), but when the present invention is actually applied to an optical system or an optical path, it is implemented by other setting means such as a dip switch, a variable resistor, a key input means, and the like. And, it is preferable to include in the attenuation control module 210.

4 is a flowchart illustrating a procedure performed by a CPU of the attenuation control module according to the present invention, and FIG. 5 is a flowchart illustrating a procedure performed by a PC according to the present invention.

Referring to FIG. 4, in step 401, a setting value (unit dBm) is input from a PC, and in step 402, an optical signal measured by the photodetector 212 is converted into a digital value by the analog-digital converter 214. Receive a value in dBm. In step 403, the set value and the measured value are compared and matched, and the process is repeated from step 401. If not, the motor control procedure is performed in step 404 to adjust the attenuation level. In the motor control procedure, if the measured value is smaller than the set value, the stepping motor 224 is controlled to reduce the attenuation amount so that the damping filter 106 is moved downward. If the measured value is larger than the set value, the stepping motor is increased to increase the attenuation amount. Control 224 to cause the attenuation filter 106 to move upward.

Referring to FIG. 5, a screen for monitoring an output level is displayed on a PC screen in step 501. In step 502, a user inputs a setting value on an input screen. Then, when the transmission button on the screen is clicked, the set value is transmitted to the microcontroller 215 of the attenuation control module (503, 504).

6 is a flowchart illustrating a procedure of manufacturing the optical attenuation module according to the present invention.

As shown in FIG. 2, the optical attenuation module 220 according to the present invention has a fixed sleeve for fixing the two optical collimators 104a and 104b and the optical collimators 104a and 104b and an attenuation inserted between the optical collimators. A filter 106, a filter fixing block for fixing the damping filter 106, a conveying mechanism 223 for conveying the filter fixing block up and down, a motor 224 for rotating the conveying mechanism 223, a housing box 222, a housing enclosure 221, and the like. The process of manufacturing and assembling each component of the optical attenuation module 220 configured as described above is as follows.

In order to configure an optical link using two optical collimators, the optical collimators 104a and 104b are aligned in step 601.

In general, in the case of optical fiber alignment, the diameter of the optical fiber core is very small, such as several tens or several micrometers, and the loss of several dB occurs even with the mismatch of several micrometers, so that very accurate alignment is required to increase the coupling efficiency. In order to increase the coupling efficiency by accurately aligning two optical fibers, parallel collimation is made by using an optical collimator using a spherical lens, an aspherical lens or a GRIN (GRadient INdex) lens, which facilitates alignment between the optical fibers and reduces losses. In particular, the optical collimator using a GRIN lens having a parabolic refractive index distribution with the center of the lens as its vertex is most commonly used because of its great advantages in working distance (D) and numerical aperture (NA). . In the case of GRIN lenses, the NA varies from 0.4 to 0.7, the divergence angle is 20 mrad, and when the working distance is 0 to 60 mm, the diameter is 0.6 to 1.3 mm. Can be.

The ideal coupling condition for the alignment of optical fiber or optical collimator is when the phase distribution and beam size match between two optical fiber or optical collimator lenses. Unaligned losses that can occur when the ideal coupling condition is not included include lateral losses, axial losses, and losses due to angular losses and mismatches.

When the alignment is made like this, the light emitted from the optical fiber passes through the GRIN lens and becomes parallel light having a beam diameter of about 0.5 mm, and the light incident on the GRIN lens in parallel is transmitted to the core of the optical fiber located at the focal length. Connected. However, since it is very difficult to stably maintain a precisely aligned optical link composed of two optical collimators, in order to maintain the characteristics and environmental characteristics of the optical link composed of two optical collimators, a fixing sleeve is used to solder it. You need to configure the optical collimator link.

In order to configure the optical collimator link by soldering in step 601, first, the optical collimator fixed on one side on the optical table and the optical collimator placed on the 5-axis positioner with adjustable x, y, z and tilt are placed. Use the light source and photodetector to align the optical link with the lowest initial loss. The alignment of the optical collimator link using the positioner has the advantage of correcting even if the axis of the GRIN lens and the optical fiber are slightly misaligned.

Subsequently, in step 602, the optical collimator is attached to the fixing sleeve by soldering using a fixing sleeve for fixing the optical collimator as shown in FIG. 7 in order to stably maintain the aligned optical collimator link. That is, the optical collimator fixedly aligned to the positioner is combined with the fixed sleeve and soldering. At this time, in order to solder the optical collimator and the fixing sleeve, it is preferable to go through the preliminary process for soldering by plating the surface of all components. And the optical collimator link is fixed by the positioner to the position where the light loss is minimal, but it is very sensitive by the external force, so care should be taken when heating for soldering. An example of the optical link thus constructed is as shown in FIG. 8, and the insertion loss change in this optical link is about 0.1 dB.

Referring to FIG. 7, the fixing sleeve has a shape in which a cylinder is connected to both ends of the flat plate, and has a shape in which a portion of the cylinder is drawn to date to facilitate soldering. By developing and using a fixing sleeve for fixing the optical collimator as described above, there is an advantage in that soldering is easier and reliability is improved as compared with the conventional method of soldering directly to the enclosure.

Meanwhile, in step 603 of manufacturing the damping filter 106, the glass (for example, 0.5 mm Corning Co., Ltd.) to be used as a substrate is cut into a predetermined length (for example, about 12 mm), washed with a cleaning solution such as alcohol, and then washed at 100 ° C. for about 20 minutes. Annealing (603). Nickel (Ni), which is used as a material for the damping thin film, has a purity of 99.99% or more and is preheated for about 10 minutes to remove impurities.

In general, in the case of an optical component used for optical communication, the wavelength dependent characteristic is important in the 1200 ~ 1600nm band. Therefore, the ND (Netural Density) filter whose attenuation amount is determined according to the thickness of the metal deposited on the substrate is mainly used for the damping filter 106 used as an element to attenuate the amount of light, and the metal used here is rhodium (Rh). , Palladium (Pd), tungsten (W), nickel (Ni), chromium (Cr), Ni-Cr and the like, but the embodiment of the present invention uses nickel (Ni).

In step 604, a Ni thin film is deposited on the glass substrate using an E-beam evaporator. At this time, the vacuum degree of the electron beam evaporator chamber is maintained at about 1.8 × 10 ^-5 torr, to have an optimum deposition rate for uniform deposition of the thin film, and to improve adhesion by heating the glass substrate to about 70 ° C. using a halogen lamp. Let's do it. In addition, the shutter is moved at a constant speed (for example, 0.01 mm / sec) by using a step motor to gradually change the thickness of the attenuated thin film deposited on the substrate. Allow it to be ~ 35 dB. Attenuation in which the thickness of the thin film is gradually increased as shown in FIG. 9 by maintaining the intensity of the electron beam (E-beam) to keep the deposition rate of nickel (Ni) constant, and moving the shutter finely. A thin film can be deposited on the glass substrate. Considering the length and attenuation of the glass substrate to be deposited, the operation speed of the step motor for adjusting the movement of the shutter and the intensity of the electron beam can be determined.

The damping filter 106 manufactured as described above has a wavelength-dependent periodicity with respect to the wavelength. This property is due to Fabry-Perot interference caused by reflections at the interface between glass and air, so it is necessary to treat the antireflective coating on the opposite side where Ni is deposited.

In step 605, an antireflective thin film is deposited on the glass substrate using a high frequency magnetron sputter. The antireflective thin film not only removes the periodic wavelength dependency caused by the Fabry-Perot phenomenon, but also reduces the loss of the attenuation filter itself by forming the antireflective thin film when very low attenuation is required, thereby lowering the initial attenuation value of the attenuation filter. . As shown in FIG. 9, the antireflective thin film 903 is formed of a thin film of dielectric material (eg, TiO ₂ , SiO ₂ ) having almost no extinction coefficient on the glass substrate 902, but is formed in multiple layers. Referring to FIG. 9, in the exemplary embodiment of the present invention, an attenuated thin film 901 is formed on one surface of the glass substrate 902, and an antireflective thin film 903 is formed on the other surface of the glass substrate 902 by five layers. . The antireflective thin film 903 is made of a TiO ₂ 904 layer, a SiO ₂ 905 layer, a TiO ₂ 904 layer, a SiO ₂ 905 layer, and a TiO ₂ 904 layer from the substrate 902 to contact the air layer. and, the thickness of each layer of anti-reflective films are TiO ₂ (904) from a substrate layer 307nm, SiO ₂ (905) layer is 104nm, TiO ₂ (904) layer is 39nm, SiO ₂ (905) layer is 266nm, TiO ₂ The 904 layer is 151 nm. Unlike metal thin films, dielectric multilayer thin films use a high frequency magnetron sputter because the energy required for deposition is very large and the uniformity of thin films and precise thin film thickness control are required. The reason why TiO ₂ and SiO ₂ were selected as the deposition material is that the change of reflectance can be optimized with a small number of thin film layers because the contamination in the chamber is low and the refractive index ratio of the two materials is about 0.66. The damping filter fabricated as described above has a low reflectance of about 0.5% or less.

After the optical link and the attenuation filter are manufactured, the optical attenuation module can be completed by inserting and packaging the variable attenuation filter between the two optical collimators. The packaging of the variable optical attenuation module can be manufactured in various sizes according to the intended use, and it is easy to mount when the product is miniaturized. In an embodiment of the present invention, the optical collimator optical link is constructed by metal soldering, and the housing inner box in which the motor and the damping filter are positioned, and the housing outer box in which the motor driving terminal and the optical collimator link structure are located are manufactured to manufacture a compact housing. After the classification, the inner box and the outer box are soldered together. At this time, both the enclosure and the enclosure of the housing are made of aluminum, and gold-plated thereon so as not to be affected by the external environment.

In step 606, the damping filter 106 fabricated before the filter fixing block as shown in FIG. 10 is fixed. A hole for engaging the shaft is formed in the inside of the filter fixing block, and the hole has a worm gear used to adjust the micro displacement of the damping filter. The shaft is coupled to the motor on the plate as shown in FIG. The worm gear consists of a screw of fine pitch and a nut supporting the reciprocating motion along the screw. The worm gear transfers the damping filter fixed to the filter fixing block by changing the rotational motion to the vertical motion to adjust the amount of damping.

Referring to FIG. 11, when the shaft 227 connected to the motor 224 and the worm gear is formed to rotate, the filter fixing block 225 inserted into the shaft 227 is moved axially by the worm gear 226. . In the embodiment of the present invention, the length of the shaft 227 is about 28 mm, and the length of the damping filter 106 is about 12 mm, so that all parts of the damping filter are between the optical collimator links because the length of the shaft is more than twice the length of the damping filter. The light attenuates through the entire range from about 0 to 35 dB.

The filter fixing block 225 and the variable attenuation filter 106 are fixed by using glass bonds. The filter fixing block 225 and the variable attenuation filter 106 are fixed so that the filter and the optical collimator link can be placed in a direction close to an angle of about 8 °. To this end, as shown in FIG. 10, one side of the groove for inserting the damping filter is inclined by about 8 °. If the attenuation filter fails to tilt about 8 ° with the optical collimator link, ripple may occur.

In step 607, the previously prepared damping filter part is assembled with the housing box as shown in FIG. 12 and then soldered in step 608. In step 609, the housing enclosure and the housing inner box as shown in FIG. 13 are assembled, and then coupled in a soldering manner in step 610. When joining the enclosure and the housing of the housing, the previously fabricated optical collimator link structures are assembled together and soldered together.

In step 611, a sealing material such as an epoxy adhesive is used to seal the housing by combining the housing's enclosure and the upper lid. At this time, a groove is formed in the edge of the enclosure so that the adhesive flows out of the edge when the upper lid is joined to prevent the aesthetic view. That is, as shown in Figure 13, because the groove is formed in the edge of the enclosure filled with the epoxy adhesive in the groove and the upper lid, it is possible to prevent the epoxy adhesive flows to the outside. In addition, since the upper lid can be filled only with epoxy adhesive without using fixing bolts, there is also an advantage that the appearance is clean as compared with the related art.

The light attenuation module 220 completed in this way is connected to the attenuation control module 210 to adjust the light output through the optical fiber to the user set through the setting unit 201. That is, when the user inputs the setting value on the PC 201 and presses the transmit button, the setting value is transmitted to the microcontroller 215 of the attenuation control module. The tap coupler 211 of the attenuation control module 210 branches a portion of the optical signal output from the optical attenuation module 220 to the photodetector 212, and the photodetector 212 transmits the optical signal to an electrical signal. Convert to The amplifier 213 amplifies the minute current signal output from the photodetector 212 and outputs it as a voltage signal. The analog-to-digital converter 214 converts the analog output of the amplifier 213 into digital and converts the measured value into a microcontroller ( 215).

The microcontroller 215 compares the measured value transmitted from the analog-digital converter 214 with the set value input from the setting unit 201, and repeats the above process while maintaining the current state. If the measured value is lower than the set value, in order to reduce the amount of attenuation, a motor control signal is generated and transmitted to the motor 224 through the motor driving unit 216. Accordingly, the motor 224 rotates the appropriate amount shaft to reduce the damping filter ( The filter fixing block 225 to which 106 is attached is transferred in a direction in which the attenuation amount is reduced. As a result, the amount of attenuation in the optical link is reduced to increase the light output. This process is repeated until the set value and the measured value coincide. On the contrary, if the measured value is higher than the set value, a process for increasing the attenuation is performed. The operation of increasing the attenuation amount is performed in the reverse of the operation of decreasing the amount of attenuation.

As described above, the voltage-adjustable variable optical attenuator according to the present invention maintains the light output at the set value by automatically transferring the attenuation filter located between two optical collimators using a motor when the set value and the measured value are different. You can. In particular, the variable optical attenuator according to the present invention can adjust the attenuation linearly over a wide range ranging from a minimum reduction of about 0.4 dB to a maximum attenuation of about 35 dB, and a polarization dependent loss of about 0.05 dB or less and about ripple. Less than 0.1dB can be realized, and the anti-reflection coating has a good anti-reflection loss.

Claims (12)

Optical link forming means attached to one end of each of the two optical cables to form a parallel optical link; An attenuation filter inserted between the parallel optical links to attenuate light passing between the optical cables; Conveying means for conveying said damping filter; And And attenuation amount control means for controlling the transfer means according to a setting value to adjust an attenuation amount of light passing between the optical cables. 2. The voltage regulating variable optical attenuator according to claim 1, wherein the optical link forming means comprises a pair of optical collimators and a fixing sleeve for fixing the optical collimators. The damping filter of claim 1, wherein the damping thin film is deposited on the glass substrate, and the thickness of the damping thin film is linearly increased or decreased according to the position on the glass substrate. Voltage adjustable variable light attenuator, characterized in that any one or more of rhodium, palladium, tungsten. The method of claim 1, wherein the conveying means is a stepping motor, a gear is formed and the shaft is rotated by a motor, and the screw is coupled to the shaft is transferred in the axial direction in accordance with the rotation of the shaft to fix the damping filter Voltage adjustable variable optical attenuator, characterized in that consisting of a filter fixing block for. 5. The voltage regulating variable optical attenuator of claim 4, wherein the filter fixing block is provided with a groove for fixing the attenuation filter, and one surface of the groove is inclined at a predetermined angle. The method of claim 1, wherein the voltage adjustable variable optical attenuator The optical link forming means, the damping filter and the conveying means are formed in a housing made of an inner box and an enclosure, and are formed as a single module, and a groove for forming an adhesive is formed at the edge of the housing enclosure to cover the housing enclosure. Voltage-adjustable variable light attenuator, characterized in that to prevent the adhesive from leaking to the outside when combined. The method of claim 1, wherein the attenuation amount control means includes a setting unit for inputting a set value, a tap coupler for branching an optical signal to monitor the light output from the optical link forming means, and a monitoring output from the tap coupler. A photodetector for converting an optical signal into an electrical signal, an amplifier for amplifying the output of the photodetector, an analog-to-digital converter for digitally converting the analog output of the amplifier, and a setting input through the setting unit And a control unit for generating a motor control signal by comparing the value with a measured value output by the analog-digital converter, and a motor driving unit for outputting a motor driving signal according to the output of the control unit. 8. The voltage regulating variable optical attenuator of claim 7, wherein the setting unit is a PC. 8. The voltage regulating variable optical attenuator of claim 7, wherein the controller is a microcontroller having a built-in EEPROM to hold data during a power failure. Aligning a pair of photocollimators; Soldering the aligned optical collimator to an integrated fixed sleeve to create an optical link; Depositing the damping thin film on the other surface of the glass substrate coated with the antireflective thin film so that the thickness of the damping thin film increases or decreases linearly with the position on the glass substrate; Fixing the glass substrate to a filter fixing block and assembling and soldering the housing to the housing inner box; And And assembling and soldering the housing inner box, the optical link and the housing outer box to each other. The method of claim 10, wherein the depositing of the attenuated thin film comprises depositing nickel while moving the shutter using an electron beam evaporator. The method of claim 10, wherein when fixing the glass substrate to the filter fixing block, the glass substrate is fixed by being inclined about 8 ° from the vertical with respect to the parallel light of the optical link.