KR20110095097A - Wavelength stabilization device - Google Patents

Abstract

PURPOSE: An apparatus for stabilizing wavelength is provided to monitor the wavelength change of laser light, which flowing into a package, with a cheap TO(Transistor Outlines) package. CONSTITUTION: Laser light with a component, which perpendicularly passes through a beam splitter(130) with 45 degrees, flows into a first photo diode(120) which is arranged in the lower part of the beam splitter with 45 degrees. Laser light, which flows into the first photo diode, forms a photo current which has a proportional size to the intensity of the laser light flowing into a TO(Transistor Outlines) package. The light reflected at the beam splitter with 45 degrees flows into a wavelength selectivity filter(140). The laser light flowing into the wavelength selectivity filter is advanced into a second photo diode(150). A beam splitter has the tilt angle of 45 degrees to the floor side of a stem(230).

Description

Wavelength Stabilization Device {Wavelength Stabilization Device}

The present invention relates to a wavelength change monitoring module having a TO (transistor outline) type appearance and a wavelength stabilizing device.

Background Art In recent years, optical communication using light as a medium for information transmission has become common for large-capacity information transmission and high-speed information communication. In recent years, a semiconductor laser diode chip having a length of 0.3 mm and a length of about 0.3 mm can be used to easily convert an electric signal of 10 Gbps (giga bit per sec) into laser light, and an optical fiber using a semiconductor light receiving element. It is easy to convert the optical signal transmitted through the electrical signal.

Light is an energy wave with very peculiar characteristics. In order for several lights simultaneously in one region to interact with each other, the light to be interacted with must have the same wavelength or have the same phase. In addition, the direction of travel must match. Therefore, light has very low coherence with each other, and wavelength division multiplexing (WDM) is widely adopted to transmit laser light of various wavelengths to one optical fiber using such characteristics of light. In order to apply the wavelength multiplexing method, a laser light source capable of emitting a laser light having a fixed wavelength appropriately spaced between adjacent wavelengths is required.

In the current high density wavelength multiplexing scheme, the interval between wavelengths is gradually narrowing to about 1.6 nm (nano meter) or 0.8 nm or 0.4 nm. Therefore, for the wavelength multiplexing, the wavelength line width of the light source must be very narrow, and the wavelength of the laser light source must be fixed very tightly with respect to the change of the driving environment of various laser light sources such as temperature and laser driving current. Wavelength precision within 1/4 is required. Therefore, when the wavelength spacing of wavelength multiplexing is 1.6 nm or 0.8 nm or 0.4 nm, the degree of stabilization of the wavelength should be precisely controlled within ± 0.2 nm, ± 0.1 nm and ± 0.05 nm.

Distributed feedback laser diode chip (DFB-LD) is a laser diode chip that can be used for high density wavelength multiplexing at 1.6 nm or 0.8 nm or 0.4 nm wavelength intervals, where the wavelength line width of the laser is 0.1 nm or less. The laser diode chip is very small in size and can be mounted in a package such as a TO type, a mini-dil type, a mini-flat type, a butterfly type, or the like.

However, the oscillation wavelength of conventional DFB-LD is changed to 0.1nm / ℃ by external driving temperature, so that the temperature of laser diode chip is ± 2 when wavelength wavelength of wavelength multiplexing is 1.6nm, 0.8nm or 0.4nm, respectively. It should be adjusted very precisely about ℃, ± 1 ℃, ± 0.5 ℃. Temperature control of the laser diode chip is mounted on the thermoelectric element, and equipped with a thermistor capable of monitoring the temperature on the thermoelectric element to measure the temperature of the thermoelectric top plate and drive the thermoelectric element to operate the laser diode chip. Temperature control can be used.

However, in this method, the thermistor is to measure the temperature of the thermistor, not directly to the temperature of the laser diode chip. Therefore, it is very difficult to directly verify the temperature of the laser diode chip, and also to accurately measure the temperature of the laser diode chip. It was difficult to control. In addition, the oscillation wavelength of the semiconductor laser diode typically varies depending on the driving current as well as the temperature, and in the case of the conventional semiconductor laser diode, a wavelength change is caused by a driving current of about 10 pm / mA. Therefore, it is very important to strictly control the oscillation wavelength of the laser diode chip.

On the other hand, the wavelength stabilization apparatus is used as a method of strictly controlling the oscillation wavelength of a semiconductor laser. The wavelength stabilization device may be mounted in one package at the same time with the laser diode chip. However, since the wavelength stabilization device is mounted in one package at the same time as the laser diode chip, there is a problem in yield. Wavelength stabilization device is implemented in another package, and then the wavelength stabilization is achieved by introducing a portion of the laser light emitted from the package mounting the laser diode chip into an external wavelength stabilization device composed of a package independent of the laser diode chip. There is a way to perform the function. The device for stabilizing the oscillation wavelength of a laser diode used in this method is called an external wavelength locker.

1 is an internal view of a conventional external wavelength stabilization device. The operation principle of the wavelength stabilization device is as follows. First, laser light oscillated from a laser diode chip not shown in the drawing is introduced into one side of the external wavelength stabilization device through an optical fiber not shown in the drawing. Laser light emitted from the optical fiber into the package housing 16 is collimated by the lens 11 of FIG. 1 and then emitted into the package 16.

The laser light collimated by the lens 11 of FIG. 1 is directed to the first photodiode 12 by a beam splitter 13 of FIG. 1 irrespective of the wavelength of the laser light. The remaining laser light passing through) travels toward the second photodiode 15. The beam splitter 13 refers to a filter having a characteristic of transmitting laser light incident on the beam splitter 13 by a predetermined ratio and reflecting by a predetermined ratio. The photodiodes 12 and 15 are typically manufactured using materials of InGaAs, which have characteristics in which the photoelectric conversion efficiency is almost constant for wavelength changes of about tens of nm.

Since there is no device blocking the laser light between the first photodiode 12 and the beam splitter 13, the photoelectric conversion current is proportional to the intensity of light emitted from the optical fiber regardless of the wavelength of the laser light emitted from the optical fiber. Flows in the first photodiode 12. At this time, the laser light passing through the beam splitter 13 passes through the wavelength selective filter 14 that selects and transmits a specific wavelength before entering the second photodiode 15. Typically, the wavelength selective filter may use an etalon filter. In the present description, the wavelength selective filter is mainly an etalon filter. However, another type of wavelength selective filter, for example, a diffraction grating type wavelength selective filter, may be used. Therefore, in the present description, for ease of explanation, the etalon filter is described as a wavelength selective filter.

2 is a transmission characteristic according to the frequency (wavelength) of a typical etalon filter, which is a representative example of the wavelength selective filter. As shown in FIG. 2, the etalon filter exhibits a transmission characteristic in which the transmittance rapidly changes according to the frequency (wavelength). Therefore, in FIG. 1, only the wavelength of the component through which the laser light transmitted through the beam splitter 13 is transmitted by the wavelength selective filter 14 is introduced into the second photodiode 15 to be photoelectrically converted. Therefore, while the first photodiode 12 measures the intensity of the laser light irrespective of the wavelength of the laser light introduced into the external wavelength stabilization device, the second photodiode 15 has a wavelength selective filter 14 having a photoelectric conversion efficiency. Very sensitive to wavelength selectivity at Therefore, by appropriately adjusting the transmission wavelength of the wavelength selective filter 14, it is possible to accurately measure the intensity and the wavelength characteristics of the laser light introduced into the external wavelength stabilization device.

External wavelength stabilization device having such a characteristic has been implemented to be mounted in a package having a butterfly package or a mini-flat type typically having a rectangular parallelepiped. But the butterfly and mini flat packages are very large and expensive.

Currently, a low cost communication light source package type is a package called a TO (transistor outline) type or a TO can type of FIG. 3. The TO-type package is provided with a through hole in a metal substrate, a metal electrode pin 24 is inserted through the through hole, and is sealed by bonding a glass between the metal electrode pin 24 and the metal substrate. It refers to a package of a structure consisting of a stem (23) of the structure and a cap 20 through which a through hole through which laser light can enter and exit.

The through hole of the cap 20 has a structure in which a glass-like window or the lens 11 is inserted into the through hole of the cap 20 so that laser light may enter or exit, but moisture or dust does not enter. Such a TO-type package housing is very common, and is commonly used in the description of the present invention, so that the electrode pins 24 of the stem and the lens 11 of the cap are omitted in the drawings after FIG. 1 to facilitate the display of the drawings. Will be shown. The TO type package is easier to process than other types of packages used in the optical module, such as mini-flat type, mini-Dil type, butterfly type, etc., and thus the manufacturing cost of the package housing is low. It is widely used as a package of.

In the case of the wavelength stabilization device, a plurality of optical components such as a first photodiode, a second photodiode, a beam splitter, and a wavelength selective filter are required. Therefore, laser light is typically introduced into the package in a direction parallel to the bottom of the wavelength stabilizing device package. This characteristic is difficult to realize in the TO-type package in which the bottom surface of the package in which the various optical components are to be placed is perpendicular to the direction of the laser light introduced through the through hole formed in the upper portion of the package.

In addition, in FIG. 1, the incident angle of the laser light introduced into the beam splitter 13 and the package 16 is disposed to be close to the vertical. This characteristic is that the beam splitter made of a conventional dielectric thin film has a very large change in the transmission reflection ratio according to the polarization of the laser light incident on the beam splitter. When the beam splitter 13 has a small angle of incidence with respect to the laser light entering the package, the difference in the transmission reflection ratio due to the polarization becomes small, and the larger the angle of incidence of the laser light incident on the beam splitter 13, the higher the polarization angle. The difference in the transmission reflection ratio accordingly becomes large.

Typically, the polarization of laser light entering the wavelength stabilization device through an optical fiber not shown in the figure of FIG. 1 may vary randomly. Therefore, in the conventional wavelength stabilization device, the beam splitter 13 is disposed so that the laser light incident to the beam splitter 13 is close to the vertical incidence, thereby minimizing the difference in the transmission reflection ratio due to the polarization. However, since the optical path of the laser light incident to the beam splitter 13 and the laser light reflected from the beam splitter 13 are close in FIG. 1, the first photodiode for detecting the laser light reflected from the beam splitter 13 is provided. The distance between the beam splitter 13 and the first photodiode 12 is increased in order to secure a space for disposing the 12, and thus the size of the package housing 16 is large.

The present invention is to solve the above-mentioned problems, the beam splitter for dividing the laser light flowing into the wavelength stabilization device into two optical paths are irrelevant to polarization so that the path of the laser light reflected from the beam splitter is incident on the beam splitter. By making the laser light path orthogonal to the path of the laser light, it realizes the wavelength stabilization device which is independent of polarization even with the very small package housing. An object of the present invention is to provide a TO type wavelength stabilization device.

The wavelength stabilization device configuration for solving the above-described conventional problems and to achieve the technical problem according to the present invention is a wavelength stabilization device for monitoring a change in the wavelength of the incident laser light, to the bottom of the package inside the TO-type package And a 45 degree beamsplitter or a 45 degree reflecting mirror for horizontally redirecting some or all of the vertically incident laser light.

In addition, a first photodiode is disposed below the 45 degree beamsplitter, and a wavelength selective filter and a second photodiode are disposed on one side of the 45 degree beamsplitter.

In addition, a first photodiode is disposed below one side of the 45 degree beamsplitter, a wavelength selective filter and a second photodiode are disposed on one side of the 45 degree beamsplitter, and the laser enters the first photodiode. Light passes through the side of the 45 degree beamsplitter directly into the first photodiode and laser light reflected from the 45 degree beamsplitter enters the wavelength selective filter.

In addition, a first photodiode is disposed below the 45 degree beamsplitter, a wavelength selective filter and a second photodiode are disposed on one side of the 45 degree beamsplitter, and the laser light entering the first photodiode is Laser light entering the first photodiode directly through the anti-reflective coated region of the 45 degree beamsplitter and directed towards the second photodiode enters the site where the dielectric thin film having the metal or total reflection properties is deposited. It is characterized by being light.

In addition, the laser light introduced into the wavelength stabilizing device is characterized in that the light intensity of a predetermined ratio is reflected by the 45-degree beam splitter, and the light intensity of the predetermined ratio is not introduced into the 45-degree beam splitter.

In addition, the wavelength stabilization device is further provided with a beam splitter for dividing the laser light on one side of the 45 degree reflective mirror, a first photodiode for receiving the laser light reflected from the beam splitter, and a laser beam transmitted through the beam splitter A wavelength selective filter and a second photodiode are disposed on a path of light.

In addition, the 45-degree beam splitter is characterized in that the metal layer and the dielectric thin film layer is laminated on a transparent substrate to the laser light considered.

In addition, the metal layer is characterized in that any one or two or more selected from gold, silver, alluminium, titanium, platinum, chrome having a thickness of 2nm to 15nm range.

In addition, the dielectric thin film layer is characterized by consisting of a thin film having a refractive index of 1.2 to 2.2 range.

In addition, it characterized in that it further comprises a temperature sensor for measuring the temperature.

In addition, it characterized in that it further comprises a thermoelectric element for adjusting the temperature of the wavelength selective filter.

In addition, the cap of the TO-type package is characterized in that coupled to the laser housing and the metal housing including a collimation lens made integrally with the optical fiber.

In addition, it is characterized in that the inner surface of the stem and the inner surface of the cap of the TO-type package is coated with a light absorbing agent having an absorbance of 100 cm -1 or more.

In the wavelength stabilization device according to the present invention, in dividing the path of the laser light traveling in the direction to the beam splitter into two, even if the incident angle of the laser light entering the beam splitter and the beam splitter has a very large angle of 45 degrees, the polarization is polarized. Irrespective of the ratio, there is an effect of dividing the laser light into two at a constant ratio. Therefore, since the laser light reflected from the beam splitter is orthogonal to the laser light entering the beam splitter, it is possible to arrange a photodiode for detecting the laser light reflected from the beam splitter even at a very small volume. In addition, when the package is implemented as a TO-type package, a part of the laser light incident perpendicularly to the bottom surface of the package is converted into light having a direction component horizontal to the bottom surface of the package, thereby proceeding horizontally with respect to the bottom surface of the package. The wavelength characteristics of the incoming light can be easily checked by using laser light. Since the wavelength stabilization device is small in volume, it can be implemented by using a TO can type package, which has the effect of lowering the wavelength stabilization device. .

1 is a butterfly wavelength stabilization device according to the prior art
2 is a transmission characteristic according to the wavelength of the wavelength selective filter according to the prior art
3 is a view of the TO-type package according to the prior art
4 is a schematic diagram of a wavelength stabilization apparatus according to an embodiment of the present invention.
Figure 5 is an embodiment of the manufacturing method of 45 degree tap filter according to the present invention
Figure 6 is another embodiment of the manufacturing method of 45 degree tap filter according to the present invention
7 is a transmittance according to polarization and wavelength for laser light incident at 45 degrees in a tap filter fabricated using a dielectric film having high refractive index and low 20 layers.
FIG. 8 is a transmittance according to incident angle and polarization for 1520 nm laser light in a tap filter fabricated using a dielectric film having high refractive index and low 20 layers.
FIG. 9 is a transmittance according to incident angle and polarization for 1570 nm laser light in a tap filter fabricated using a dielectric film having high refractive index and low 20 layers.
10 is a transmittance according to polarization and wavelength for laser light incident at 45 degrees in a tap filter made of a metal thin film and a single dielectric thin film laminated on the metal thin film.
FIG. 11 is a transmittance according to incident angle and polarization for a 1520 nm laser light in a tap filter made of a metal thin film and a single dielectric thin film laminated on the metal thin film.
12 is a transmittance according to incident angle and polarization for 1570 nm laser light in a tap filter made of a metal thin film and a single dielectric thin film laminated on the metal thin film.
13 is a schematic diagram of a wavelength stabilization device fabricated so that the direction of the laser light is switched using a 45 degree beamsplitter having the characteristics of full reflection according to the present invention, and the laser light which is not incident on the beamsplitter combs the beamsplitter and goes straight.
FIG. 14 is a side view of a laser light traveling in the wavelength stabilization device of FIG. 13;
15 is a schematic diagram of a beamsplitter fabricated such that all of the beamsplitter has reflection characteristics and all of the beamsplitter has transmission characteristics;
16 is a view of the optical coupling of the module made of the collimation lens and the optical fiber integrally to the TO-type wavelength stabilization device according to the present invention,
17 is a schematic diagram of a wavelength stabilization apparatus equipped with a thermoelectric device according to the present invention;
FIG. 18 is a diagram illustrating laser light entering in a direction perpendicular to a package in a TO type wavelength stabilization device using a reflection mirror to convert a laser traveling direction in a direction horizontal to the package, and then split a laser beam through a beam splitter and stabilize the wavelength. Schematic diagram of the structure that implements the function

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, terms used in the present invention will be described. The beam splitter functions to transmit and reflect laser light traveling in a beam splitter direction at a predetermined ratio. The 45 degree beam splitter is a beam splitter having a 45 degree inclination angle with respect to the incoming laser light, and has a function of transmitting and reflecting a predetermined ratio of the laser light entering the beam splitter. The reflecting mirror refers to a mirror having a function of reflecting all the laser light entering the mirror, and the 45-degree reflecting mirror has a 45 degree inclination to the incoming laser light and has a characteristic of reflecting all incoming laser light. Refers to. The wavelength selective filter refers to a filter whose transmission and reflection are determined according to the wavelength of laser light introduced into the filter. 4 is a schematic diagram of a wavelength stabilization apparatus according to an embodiment of the present invention, FIG. 5 is an embodiment of a manufacturing method of a 45 degree beamsplitter according to the present invention, and FIG. 6 is a manufacturing method of a 45 degree beamsplitter according to the present invention. In another embodiment, FIG. 7 is a graph showing transmittance according to polarization and wavelength for a laser beam incident at 45 degrees in a beam splitter fabricated using a dielectric film having 20 layers having a high refractive index and a low refractive index. Transmittance graph of incident angle and polarization with respect to 1520 nm laser light in a beam splitter fabricated using a layered dielectric thin film. FIG. 9 is a 1570 nm laser in a beam splitter fabricated using a dielectric film having 20 layers with high refractive index. Transmittance graph according to incident angle and polarization for light, FIG. 10 is a beam splitter made of a metal thin film and a single dielectric thin film laminated on the metal thin film Fig. 11 is a graph of transmittance according to polarization and wavelength for laser light incident at 45 degrees in Fig. 11 and Fig. 11 shows the angle of incidence and polarization for a 1520 nm laser light in a beam splitter made of a metal thin film and a single dielectric thin film laminated on the metal thin film. 12 is a graph showing transmittance according to incident angle and polarization of a 1570 nm laser light in a beam splitter made of a metal thin film and a single dielectric thin film laminated on the metal thin film, and FIG. 13 is a 45 degree beam according to the present invention. Of the laser light traveling vertically with respect to the bottom of the package using the splitter, the laser light of the component incident on the beam splitter is horizontally redirected, and the laser light which is directed away from the 45 degree beam splitter is a photodiode at the bottom of the 45 degree beam splitter. Wavelength stabilization device fabricated to have a characteristic of being incident to Fig. 15 is a side view of the traveling direction of the laser light in the purification apparatus, FIG. 15 is a schematic diagram of a beam splitter manufactured so that all of the beam splitters have reflection characteristics and all of the beam splitters have transmission characteristics. FIG. 17 is a view illustrating a light coupling of a module having a collimation lens and an optical fiber integrated with a TO type wavelength stabilizing device according to the present invention. FIG. 17 is a schematic view of a wavelength stabilizing device with a thermoelectric device according to the present invention. In the wavelength stabilization device, a laser beam is introduced in a direction perpendicular to the package, and a laser beam is converted in a direction horizontal to the package by using a reflection mirror to split the laser beam through a beam splitter and implement wavelength stabilization. It is a schematic diagram of the structure.

4 is a diagram of a mechanism corresponding to the core mechanism of the wavelength stabilization device electrode pin and TO cap of the TO package in the TO can type wavelength stabilization device. As shown in FIG. 4, the laser light introduced in the vertical direction through the upper through hole of the TO package, which is not shown in the drawing, is vertically and horizontally through the 45 degree beam splitter 130 which is inclined at 45 degrees with respect to the package bottom surface. Laser light having a traveling direction of.

The laser light of the component passing vertically through the 45 degree beam splitter 130 is directly proportional to the intensity of the laser light incident on the first photodiode 120 disposed under the 45 degree beam splitter 130 and introduced into the TO package. To form a photocurrent having a size that is, and the laser light reflected by the 45-degree beam splitter 130 to have a horizontal component with respect to the bottom surface of the package is introduced into the wavelength selective filter 140 having the characteristic of wavelength selectivity. . The laser light flowing into the wavelength selective filter 140 has a transmission characteristic according to the wavelength of the wavelength selective filter 140 and enters the second photodiode 150. Therefore, by dividing the photocurrent of the second photodiode 150 by the photocurrent of the first photodiode 120, the wavelength characteristic of the laser light may be extracted regardless of the light intensity of the laser light flowing into the TO-type package.

In this case, the beam splitter 130 should have an inclination angle of 45 degrees with respect to the bottom surface of the stem 230, and this inclination angle has one side of the beam splitter 130 transmitted by the beam splitter 130 as shown in FIG. 4. It may have a self-standing shape that is processed to have an angle of 45 degrees with respect to the reflecting surface, and as shown in FIGS. 5 and 6, the beam splitter 130, which is manufactured in a flat form, may be removed from the bottom surface of the package. It can be manufactured by attaching to a mechanism manufactured to have an angle of view.

In the beam splitter 130 according to the present invention, the transmission characteristics of the beam splitter 130 should not be changed according to the polarization of the incoming laser light. The polarized light of the laser light flowing into the TO package may be changed at random. If the transmission / reflection characteristics of the beam splitter 130 vary according to the polarized light, the first photodiode 120 may also depend on the polarized light for the laser light having the same wavelength. And the intensity of the laser light flowing into the second photodiode 150 is changed, which may be misunderstood by a change in wavelength. Therefore, the polarization dependence of the transmission / reflection ratio of the beam splitter 130 depends on the precision of the wavelength to be controlled by the wavelength stabilization device. However, it is preferable that the transmission / reflection ratio change due to polarization is usually 5% or less. Do.

Currently, optical communication has been assigned a communication wavelength for each band according to the wavelength band. One of the most commonly used communication wavelengths is a wavelength band called C-band and has a wavelength band of 1530-1560 nm. Therefore, it is preferable that the wavelength stabilization device is manufactured to be applied to all wavelengths of at least one band. Therefore, the beam splitter which is not sensitive to polarization is preferably applied to at least one band of the communication wavelength band. A beam splitter having a property of partially transmitting / reflecting laser light incident to the beam splitter may be obtained by stacking a plurality of dielectric thin films having a high refractive index and a low refractive index on a transparent substrate with respect to the wavelength of the laser light to be considered.

FIG. 7 illustrates the polarization dependence of the transmission reflection characteristic according to the wavelength of the laser light incident at 45 degrees with respect to the beam splitter made of 20 dielectric thin films so that the difference in transmission reflection ratio according to the polarization is minimized.

FIG. 8 illustrates polarization dependence of transmission reflection characteristics according to an angle at which a laser light having a wavelength of 1520 nm is incident on the beam splitter with respect to the beam splitter manufactured to have the characteristics of FIG. 7.

FIG. 9 illustrates polarization dependence of a transmission reflection characteristic according to an angle at which a laser light having a wavelength of 1570 nm is incident on the beam splitter with respect to the beam splitter manufactured to have the characteristics of FIG. 7.

As in the case of FIGS. 7 to 9, even when using 20 dielectric thin films, it is difficult to obtain a beam splitter having a stable transmission reflection ratio due to polarization with respect to a sufficiently wide wavelength range and a wide incidence angle change. That is, in order to fabricate the beam splitter with the dielectric thin film having the characteristics of FIGS. 7 to 9, the thickness of one layer of the dielectric thin film of up to 20 layers must be controlled very precisely, which causes a drop in yield.

The polarization independent beam splitter may be implemented by stacking a thin metal layer and a dielectric thin film on a substrate transparent to laser light. 10 is MgF _{2 having a} refractive index of about 1.38 on a 6 nm thick Au thin film. The polarization dependence of the transmission reflection characteristic according to the wavelength of the laser light incident on the beam splitter manufactured in the form of a 250 nm single layer laminated film is shown.

In the case of FIG. 7, the transmission / reflection ratio due to polarization is rapidly changed at a wavelength shorter than 1520 nm and a wavelength larger than 1570 nm. However, in the beam splitter including the metal thin film and the single-layer dielectric thin film of FIG. 10, the transmission / reflection ratio according to polarization is shown. It can be seen that the change in is very gentle.

11 and 12 illustrate the angle at which laser light is incident on the beam splitter and the transmission / reflectance according to polarization when the wavelengths of the laser light incident on the filter having the characteristics of FIG. 10 are 1520 nm and 1570 nm. 11 and 12, unlike the case of FIGS. 8 and 9, there is no sudden change in the transmission / reflection ratio according to the change in the incident angle.

In the beam splitter structure in which a metal thin film and a monolayer dielectric thin film are sequentially stacked on a substrate, the light intensity splitting is very easily controlled compared to a beam splitter consisting of dielectric thin films only because the transmission / reflection ratio is changed very slowly according to the incident wavelength or the incident angle. It has the advantage of being easy to manufacture. At this time, a thin film of gold (Au), Al (aluminium), Ag (silver), Ti (titanium), Pt (platinium), Chrom (Cr), etc. is suitable as the metal thin film layer, and a dielectric thin film laminated on the metal thin film. The dielectric thin film having a refractive index of about 1.2 to 2.2 is suitable. In particular, the dielectric thin film having a refractive index of about 1.3 to 1.6 suppresses the difference in the transmission / reflection ratio due to the polarization best in a wide wavelength range.

In the present invention, the laser light directed to the first photodiode is always absorbed at the first photodiode, but the light directed at the second photodiode is between the beamsplitter and the second photodiode in order to change from the second photodiode to the photocurrent. It must pass through the wavelength selective filter. In addition, the laser light incident on the second photodiode is preferably composed of only the laser light of the wavelength selected by the wavelength selective filter.

However, when the laser light directed to the second photodiode does not pass through the wavelength selective filter and reflects, the laser light reflected by the wavelength selective filter rotates inside the package and enters the first photodiode or the second photodiode. This acts as noise in measuring the precise wavelength shift. Therefore, it is desirable that a small proportion of the laser light split by the beam splitter be directed to the second photodiode, but if the intensity of the laser light directed to the second photodiode is too small, the photocurrent changed by the wavelength selective filter is reduced. As it becomes so small, the transmission / reflection ratio of the beam splitter should be an appropriate ratio. As a result of the experiment, the beam splitter's transmission ratio is about 20 to 80%. In the polarization-independent beam splitter produced by combining the metal thin film and the dielectric thin film, the thickness of the Au thin film which determines the above-mentioned transmission ratio is about 2 nm to 15 nm.

As described in the present invention, after splitting laser light at a constant ratio irrespective of polarization using a beam splitter having polarization independence, one laser beam is directly incident on the photodiode and the other laser light is wavelength selective. The change in the wavelength of the laser light incident on the wavelength stabilization device can be monitored by comparing the photocurrent flowing through the photodiode after entering the photodiode through the filter.

7 to 12 show that a beam splitter composed of only a dielectric thin film is difficult to produce a beam splitter independent of polarization in a wide wavelength range, and a beam splitter independent of polarization by depositing a dielectric thin film and a metal layer laminated on a substrate. It was possible to make of.

When the laser light is divided into the first photodiode and the second photodiode, there is another method of dividing the laser light at a constant ratio without depending on polarization. Fig. 13 is a plan view from above of the device according to the invention in which the transmission reflection ratio does not change with polarization, and Fig. 14 is a side view of the device from the side. In this configuration, the state in which the laser light entering the device is projected onto the 45 degree beam splitter portion is indicated by the circle 350 of FIG. 13.

In FIG. 13, the laser light introduced into the TO-type wavelength stabilization device according to the present invention is led to a part of the 45-degree beam splitter 135 but not to some of the light. The light reflected from the 45-degree beam splitter 135 The traveling direction is switched 90 degrees to proceed to the wavelength selective filter 140. The laser light traveling to the wavelength selective filter 140 has a transmittance determined by the wavelength selective filter 140 according to the wavelength, and the laser light passing through the wavelength selective filter 140 is directed to the second photodiode 150. On the contrary, the laser light that is not drawn over the 45 degree beam splitter 135 passes straight along the side of the 45 degree beam splitter 135 and is led to the first photodiode 120. Therefore, since the laser light entering the first photodiode 120 enters the first photodiode 120 directly without passing through any device, the laser light is irrelevant to the polarization of the laser light.

When the 45-degree beamsplitter 135 has a reflection characteristic close to 100%, the beamsplitter is a method of depositing a dielectric thin film on a substrate such as glass or silicon. Mirrors can be easily manufactured, or all reflective mirrors that are independent of polarization can be easily manufactured by depositing a metal material having good reflectance at a desired wavelength such as Au (gold) on a substrate. Therefore, in this configuration, since the 45 degree beam splitter 135 is independent of polarization, the reflectance of the laser light reflected by the 45 degree beam splitter 135 and directed to the wavelength selective filter 140 does not depend on the polarization.

In addition, since the laser light entering the first photodiode 120 enters the first photodiode 150 directly without passing through the 45 degree beam splitter 135, the laser light does not depend on polarization. Therefore, as shown in FIGS. 13 and 14, the polarization dependence of the beam splitter can be eliminated by applying only a portion of the laser light to the 45 degree beam splitter 135 having all reflection characteristics.

13 and 14, the laser light entering the first photodiode passes through the side of the 45 degree beam splitter 135, but when the 45 degree beam splitter 135 is manufactured as shown in FIG. The laser light entering the diode may be manufactured to pass through the beam splitter 135. That is, in FIG. 15, a part of the beam splitter 135 is manufactured to have a property of totally reflecting irrespective of polarization to a metal or dielectric thin film, and the other part of the beam splitter 135 is treated to be antireflective coating so as to have all transmission characteristics regardless of polarization. do.

In FIG. 15, all of the laser light projected on the beam splitter 135 is projected onto the reflective dielectric thin film or the metal thin film area to be reflected and proceed to the second photodiode 150, and enters the antireflective coated area. Light passes through the 45 degree beamsplitter 135 and proceeds to the first photodiode 120.

On the other hand, the laser beam proceeds to the wavelength selective filter 140, the laser light having a characteristic of the wavelength that is not transmitted through the wavelength selective filter 140 and reflected from the wavelength selective filter 140 is floating around the package. As such, lights that randomly travel in an unwanted path are called stray lights. A part of the lost light may enter the first photodiode 120 or the second photodiode 150.

Since such light causes noise to operate in the device, it is preferable to apply the absorber to absorb the laser light considered inside the wavelength stabilization device. A preferred absorbency of such a sorbent is 100 cm ^- to have a value of ^1, and accordingly it is desirable to have an even more preferably at least 1000 cm ^-1 value. In addition, when attaching various components such as the reflecting mirror, wavelength selective filter and photodiode of the device to the package housing, it is preferable to attach them using an adhesive having a light absorption function, and the light absorption of the adhesive for attaching the component is also 1000 cm ^-1. It is preferable to have the above. In particular, it is important to apply some or all of the inner surface of the cap 20 through which the through hole of the present invention and the inner surface of the stem 23 are applied with a light absorbing agent.

Typically, laser light can determine the direction of travel using the optical fiber. Therefore, one of the important means for optically connecting the laser light source and the wavelength stabilization device by the device is an optical fiber. The laser light emitted from the optical fiber ends is spread and diverged at a wide angle, which is not the collimated laser light required by the device. Therefore, between the optical fiber and the apparatus, a collimation lens for collimating laser light emitted from the optical fiber is needed.

In FIG. 2, the lens 20 is integrally attached to the cap 20, but as shown in FIG. 16, the cap 200 is finished with a flat glass surface, and the collimation lens 110 is manufactured integrally with the optical fiber 500, and then the optical fiber. The optical fiber may be attached to the wavelength stabilization apparatus in the form of welding the adhesive parts and the cap 200 to which the 500 and the lens 110 are coupled to each other, and then attaching the cap 200 to each other.

Since the lens 110 is typically made of glass, it is difficult to attach directly to the optical fiber 500, so that the lens 110 is inserted into the housing 600 of a metallic material having a through hole at one side thereof so that the optical fiber can enter the lens 110. The optical fiber 500 may be integrally manufactured, and the metal housing 600 and the cap 200 may be attached by metal-to-metal welding. This method is different from a method in which a typical TO type laser diode package is connected to an optical fiber by using a lens attached to the TO side, and the optical fiber is independently moved to perform optical coupling.

When optically combining a conventional TO can type laser diode package and an optical fiber, both the focal length and the laser propagation direction are changed by the relative position of the optical fiber, but the optical fiber 500 and the lens 110 are changed as in the present invention. ), The fiber optic lens lens and the wavelength stabilization device do not change when the optical fiber 500-lens 110 block is displaced with respect to the cap 200 of the TO can. Light alignment becomes easy.

In addition, although not shown in the drawings in the present invention, the wavelength selective filter has a characteristic of a transmission wavelength of 0 to 15 pm / depending on the structure of the filter. Therefore, a device for measuring and adjusting the temperature change of such a package may be further added. FIG. 17 shows a wavelength stabilization device incorporating a thermoelectric element for controlling the temperature of the package. In addition, Figure 17 is an embodiment of the TO-type wavelength stabilization device having a thermoelectric element 290 according to the present invention, the structure thereof is overlapped with the structure shown in Figures 1 and 4, detailed description thereof has been omitted.

In the description of the present invention, the 45 degree beam splitters 130 and 135 have been described as having an inclination angle of 45 degrees with respect to the incident laser light, but the most important function of the 45 degree inclination angle is to implement the wavelength stabilization device in the TO type package. This is to convert the laser light incident perpendicularly to the bottom of the package into a laser light in a direction horizontal to the bottom of the package, which can be easily utilized for the wavelength stabilization device.

Therefore, in the case of FIG. 4 or FIGS. 13 to 17, the structure of FIG. 1 as shown in FIG. 18 is mounted when the 45 degree reflecting mirror 137 that horizontally converts the laser light incident perpendicularly to the package bottom surface is mounted. The wavelength stabilization apparatus borrowing as it is can be implemented. That is, as shown in FIG. 18, after all of the light incident perpendicularly to the package bottom surface by the 45 degree reflective mirror 137 is horizontally switched, the path of the light is the same as that described in FIG. 1. That is, by using the 45 degree reflective mirror 137 according to the present invention to provide a wavelength stabilization device manufactured so that the entire laser light incident perpendicularly to the package bottom surface is redirected horizontally with respect to the package bottom surface. It becomes possible.

As described above, in the present invention, in dividing the laser light flowing into the package into two orthogonal optical paths, a method using a beam splitter in which a dielectric thin film and a metal thin film are stacked in a stack, and entering the package The laser beam is arranged so that a part of the laser beam is partially reflected to the beam splitter having the characteristic of reflection, and the light beam is split into two optical paths, the laser light reflected by the beam splitter and the laser light not reflected by the beam splitter.

The method of dividing the laser light flowing into the package by a method of reflecting only a part of the laser splitter, the beam splitter comprising a laminate of the dielectric thin film and the metal thin film, and a laser beam introduced into the package to the beam splitter having the characteristics of a close screw. Since it is not affected by the polarization of the laser light that is introduced into the polarization independent wavelength monitoring device or polarization independent wavelength stabilization device can be manufactured.

As described above, although the present invention has been described with reference to limited embodiments and drawings, the terms or words used in the present specification and claims are not to be construed as being limited to ordinary or dictionary meanings, and are consistent with the technical spirit of the present invention. It must be interpreted as meaning and concept. Therefore, the embodiments described in the specification and the configuration shown in the drawings are only the most preferred embodiments of the present invention and do not represent all of the technical idea of the present invention, various equivalents that may be substituted for them at the time of the present application It should be understood that there are water and variations.

11: collimating lens 12: first photodiode
13 beam splitter 14 wavelength selective filter
15 second photodiode 16 butterfly type package housing
20: Cap of TO can 11: Lens attached to TO can
23 stem 24 electrode pin
110: lens 120: first photodiode
130: 45 degree beamsplitter 135: 45 degree beamsplitter using space
137: 45 degree reflective mirror 139: beam splitter
140: wavelength selective filter
150: second photodiode 210, 220: through hole
230: stem 290: thermoelectric element
500: optical fiber 600: metal housing

Claims (13)

In the wavelength stabilization device for monitoring the change in the wavelength of the incident laser light,
A wavelength stabilizing device having a 45 degree beamsplitter or a 45 degree reflecting mirror which horizontally redirects some or all of the laser light incident perpendicularly to the bottom of the package inside the TO type package. The method of claim 1,
A first photodiode is disposed below the 45 degree beamsplitter, and a wavelength selective filter and a second photodiode are disposed on one side of the 45 degree beamsplitter. The method of claim 1,
A first photodiode is disposed below one side of the 45 degree beamsplitter, a wavelength selective filter and a second photodiode are disposed on one side of the 45 degree beamsplitter, and the laser light entering the first photodiode is A wavelength stabilizing device that enters the first photodiode directly through the side of the 45 degree beamsplitter and reflects the laser light reflected from the 45 degree beamsplitter into a wavelength selective filter The method of claim 1,
A first photodiode is disposed below the 45 degree beamsplitter, a wavelength selective filter and a second photodiode are disposed on one side of the 45 degree beamsplitter, and the laser light entering the first photodiode is 45 The laser light entering the first photodiode directly through the antireflective coated region of the beam splitter and towards the second photodiode is the laser light entering the site where the dielectric thin film having the metal or total reflection characteristics is deposited. Featured wavelength stabilization device The method of claim 3, wherein
Laser light entering the wavelength stabilizing device is a wavelength stabilization device characterized in that the light intensity of a predetermined ratio is reflected by the 45 degree beam splitter, the light intensity of a predetermined ratio is not introduced into the 45 degree beam splitter The method of claim 1,
The wavelength stabilizing device further includes a beam splitter for splitting laser light on one side of a 45 degree reflective mirror, a first photodiode for receiving laser light reflected from the beam splitter, and a laser beam transmitted through the beam splitter. Wavelength stabilization device, characterized in that the wavelength selective filter and the second photodiode disposed on the path The method of claim 1,
The 45-degree beamsplitter is a wavelength stabilizing device comprising a structure in which a metal layer and a dielectric thin film layer are laminated on a transparent substrate to be considered laser light. The method of claim 7, wherein
The metal layer is a wavelength stabilizer, characterized in that any one or two or more selected from gold, silver, alluminium, titanium, platinum, chrome in the range of 2nm to 15nm thickness The method of claim 7, wherein
The dielectric thin film layer is a wavelength stabilization device, characterized in that consisting of a thin film having a refractive index range of 1.2 to 2.2 The method of claim 1,
Wavelength stabilizing device further comprises a temperature sensor for measuring the temperature The method of claim 1,
Wavelength stabilizing device further comprises a thermoelectric element for adjusting the temperature of the wavelength selective filter 12. The method according to any one of claims 1 to 11,
The cap of the TO-type package is a wavelength stabilization device, characterized in that coupled to the laser housing with a metal housing including a collimation lens made integrally with the optical fiber The method of claim 12,
A wavelength stabilizing device, characterized in that the inner surface of the stem and the inner surface of the cap of the TO-type package is coated with a light absorber having an absorption of at least 100 cm −1.

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