KR20170121596A - Laser Device with optical isolator - Google Patents

Abstract

The present invention relates to a technique which effectively blocks light reflected from a wavelength selectable filter to prevent the light from being fed back to a laser diode chip in a semiconductor laser package which uses an optical filter to adjust a relative strength ratio of signals. According to the present invention, an optical blocking device adjusts a property of a 45-degree reflection mirror and additionally arranges one /4 wave plate in an existing TO-can-type laser device having the 45-degree reflection mirror to effectively block light feedback to a laser diode chip unlike a conventional optical isolator using an existing Faraday rotator. Therefore, the TO-can-type laser device having a small volume is allowed to effectively adjust an excess signal to improve a communication function. Also, a conventional optical isolator includes two polarizing plates, one Faraday rotator, and a permanent magnet enclosing the polarizing plates and the Faraday rotator to have a large size and an expensive price. On the other hand, a function of light feedback blockage in accordance with the present invention is carried out by adding one /4 wave plate. Therefore, space and costs can be reduced.

Description

[0001] The present invention relates to a laser device having an optical isolator function,

The present invention relates to a TO-can type laser device, and more particularly, to a TO-can type laser device having an optical isolator function for preventing light emitted from a laser diode chip from returning to a laser diode chip again inside the device .

Recently, communication services such as a video service of a smart phone and the like have been introduced with a great communication capacity. Accordingly, there is a great need to increase the communication capacity of the related art, and a DWDM (Dense Wavelength Division Multiplexing) communication method is adopted as a method of increasing the communication capacity using the optical fiber already installed in the past. Since the laser beams having different wavelengths do not interfere with each other, the DWDM can transmit light of various wavelengths at the same time through one optical fiber. However, by using a phenomenon in which there is no interference between signals, Transmission method.

The NG-PON2 specification has been globally accepted as a worldwide standard for the NG-PON2 (Next Generation-Passive Optical Network version 2), and the NG-PON2 standard adopts a laser having a frequency interval of 100 GHz as a standard of an optical communication module to be installed in a subscriber. The subscriber optical module of the NG-PON2 has a basic specification of a small form factor pluggable (SFP) transceiver module. The size of the SFP module package is small so that the size of the laser module is reduced.

Also, in digital optical communication, which distinguishes between "signal" and "signal" depending on the intensity of light emitted from the laser diode chip, the "signal" and the signal are controlled by the intensity of light emitted from the semiconductor laser diode chip. The intensity of the light emitted from the semiconductor laser diode chip depends on the intensity of the current injected into the semiconductor laser diode chip, and a chirp phenomenon occurs in which the wavelength of the chip laser light changes according to the intensity of the current injected into the semiconductor laser diode chip. . Such a chirp phenomenon occurs at a high-speed operation of 10 Gbps, a chirp phenomenon occurs in which the spectrum of the laser light emitted from the laser diode chip is widened. Such a chirp phenomenon is accompanied by dispersion characteristics of the optical fiber to shorten the transmission distance of the optical signal .

This chirp phenomenon is intertwined with the dispersion characteristic of the optical fiber, which makes it difficult to transmit a high-speed optical signal over a long distance. In order to reduce the chirp phenomenon, it is possible to reduce the modulation width of the current injected into the semiconductor laser diode chip which generates the "signal" and the signal. When this method is used, the difference of the intensity of the "signal" A difficult problem arises.

In order to solve this problem, it is necessary to optically reduce the light corresponding to the wavelength of the signal of the laser diode chip, electrically drive the modulation width of the current to be small, and then optically change the difference of the intensity of the "signal" An emphasis method was used.

FIG. 1 shows the structure of a chirp managed laser labeled US Pat. No. 8,199,785. In chirp managed lasers, an optical filter is used to selectively reduce the light corresponding to the signal to increase the modulation width of the final output signal. At this time, the wavelength of the laser light oscillated from the semiconductor laser has a wavelength change of about 0.1 nm / ° C according to the temperature, and the optical filter has to selectively reduce the signal, so that the wavelength of the light emitted from the optical filter and the semiconductor laser diode chip There is a problem that it must be very precisely matched. For this reason, a wavelength stabilizer is essential for chirp managed laser, and 308, 310, and 312 of FIG. 1 are structures for such wavelength stabilization. FIG. 2 is a graph showing the ratio of the signal intensity of the signal "1" and the signal intensity of the signal (FIG. 2-a) when the optical filter is not used, (Fig. 2-b) showing the ratio of the intensity of the signal wavelength when the difference between the intensity of the "signal" and the intensity of the signal is enlarged by using an optical filter.

1, a part of the light emitted from the DFB-LD (302 in FIG. 1) is reflected by the OSR (304 in FIG. 1) and then travels toward the DFB-LD (302 in FIG. 1) There must be light. Especially, when the optical filter has the property of etalon, the etalon optical filter improves the characteristics of the etalon filter when the incident light is disposed close to the incident surface of the etalon filter. Therefore, most of the etalon filters are incident on the etalon filter It is designed to cope with light entering the plane at a narrow angle of +/- 3 degrees vertically. Light reflected vertically from the etalon filter can be fed back to the laser diode chip, disturbing the operation of the laser diode chip. However, since the characteristic of the DFB-LD (302 in FIG. 1) changes very sensitively to the light coming from the outside, the light traveling from the OSR (304 in FIG. 1) to the DFB- 312) and blocking the DFB-LD (302 in FIG. 1) from proceeding. In the prior art of FIG. 1, an optical isolator (306 in FIG. 1) is disposed which passes light only in one direction and not in the opposite direction.

In FIG. 1, two optical isolators are shown. The optical isolator (306 in FIG. 1) has a function of blocking the light reflected from the wavelength selective filter (304 in FIG. 1) emitted from the laser diode chip from being fed back to the laser diode chip And another optical isolator (324 in FIG. 1) is an optical isolator for shielding the light entering the optical element of FIG. 1 from another optical element through the optical fiber.

The optical isolator is complex and costly because it consists of two polarizers, a Faraday rotator placed between two polarizers and a permanent magnet that applies a magnetic field to a faraday rotator.

In FIG. 1, the laser light emitted from the semiconductor laser diode chip 302 (FIG. 1) is advanced straight and is coupled to an optical fiber (318 in FIG. 1), and this type of configuration is described in the prior art US 8,199,785 called mini-flat type 3 is most preferable. However, a mini-flat type optical device package housing is disclosed in US20050200730 of Fig. 4 in which a wavelength stabilizing device is implemented using a TO-can type package having a high price and a low cost. The TO-can type is mainly used for optical communication in small-sized products whose diameter is usually within 6 mm. The size of 6mm in the TO-can type package with a diameter of 6mm or less is important because the package height of the SFP type transceiver, which is the most important specification of current optical transceiver, is about 8mm, This is because only TO-can packages can be accepted.

In US20050200730 of FIG. 4 (400 in FIG. 4) is used as an optical filter, a chirp managed laser with a wavelength stabilizer can be implemented as a TO-can type. However, in the case of FIG. 4, since there is no device for blocking the optical feedback like the optical isolator (306 in FIG. 1) shown in US Pat. No. 8,199,785 of FIG. 1, the laser diode chip 4), a part of the light reflected from the optical filter (400 in FIG. 4) and then to the 45-degree partial reflection mirror (300 in FIG. 4) is reflected by the partial reflection mirror (300 in FIG. 4) It may enter the semiconductor laser diode (100 in Fig. 4) and disturb the operation of the semiconductor laser diode (100 in Fig. 4). 4, it is desirable to reflect most of the incident light of the 45-degree partial reflection mirror 300 (FIG. 4) in order to obtain a strong light intensity. Most of the light reaching the mirror (300 in FIG. 4) is reflected by the laser diode chip (100 in FIG. 4), so that the operation of the laser diode chip (100 in FIG.

In the case of FIG. 4, it is possible to arrange the optical isolator at the position of the optical isolator (A) of FIG. 5 in such a manner that the optical isolator can be arranged. It is very difficult to apply this method to a limited size of substantially 6 mm in diameter.

6 shows a TO-can internal structure of the structure shown in Fig. 4, which is manufactured in TO-can type with a diameter of approximately 6 mm. Considering the outer lid portion of the package in a 6 mm diameter TO can type package, the space available for placing components in the TO-can type package is limited to within 4 mm. In FIG. 6, the size of the collimating lens is 0.7 mm, and when the lens size is smaller, the size of the collimated beam becomes too small, so that the characteristics of transmission / blocking due to interference in the etalon filter are not shown. In the TO-can type, it is desirable that the collimated light is emitted to the concentric axis of the TO-can type package, so that the 45 degree partial reflection mirror is preferably disposed on the central axis of the TO-can type package. As shown in FIG. 6, a TO-can type package having a diameter of 6 mm is too small to have a space for mounting an optical isolator having a size of 1 mm or more. Therefore, it is virtually impossible to dispose an optical isolator in the position (A) of Fig. In the TO-can type package, there is no limitation on the package size in the vertical direction of the 45-degree partial reflection mirror. Therefore, the optical isolator is arranged like the optical isolator (B) 5 can be prevented from being fed back to the laser diode chip 100. However, in this case, the light to be incident on the photodiode 500 (FIG. 5) is blocked by the optical isolator (B) It is impossible to implement the function of chirp manage laser.

US 8,199,785 US 20150200730

SUMMARY OF THE INVENTION The present invention has been proposed in order to solve the problems of the prior art, and it is an object of the present invention to provide a method of implementing a chirp managed laser capable of high-speed long distance communication using a miniaturized TO- The light reflected by the selectivity filter returns to the laser diode chip, thereby eliminating the optical feedback that destabilizes the operation characteristics of the laser diode chip. In the present invention, in place of an optical isolator having a large size and a high price, it is composed of two polarizers, a Faraday rotator disposed between the two polarizers, and a permanent magnet applying a magnetic field to the faraday rotator, And to provide a method for efficiently performing the function of optical isolation with a wavelength selective filter.

According to an aspect of the present invention, there is provided a laser device comprising: a laser diode chip for emitting laser light; A wavelength selective filter; A collimating lens provided on the optical path between the laser diode chip and the wavelength selective filter for collimating light emitted from the laser diode chip; A 45-degree reflection mirror installed on the optical path between the laser diode chip and the wavelength selective filter for switching the laser light traveling horizontally with respect to the bottom surface of the package to laser light proceeding perpendicularly to the bottom surface of the package; A? / 4 waveplate disposed on the optical path between said 45 degree reflective mirror and said wavelength selective filter; .

And the optical components are arranged on a thermoelectric element placed on the bottom of the TO-can type package.

Further, the 45-degree reflection mirror is characterized in that the light of the polarized light emitted from the semiconductor laser diode has a characteristic of some reflection / partial transmission, and is larger than a ratio of reflection of the light transmitting from the semiconductor laser diode. And a part of the light is partially transmitted / partially reflected / partially transmitted, and the ratio of transmission is larger than the ratio of reflection.

It is preferable that the wavelength selective filter is an FP type etalon filter. The wavelength selective filter may be fabricated by stacking a dielectric thin film having a high refractive index and a low dielectric constant.

In the present invention, the S-polarized light for the 45-degree reflection mirror emitted from the laser diode chip is mainly reflected from the 45-degree reflection mirror, transmitted through the λ / 4 waveplate and the wavelength selective filter to the outside of the TO- . The reflected light from the wavelength-selective filter passes through the λ / 4 waveplate and becomes P-polarized light, arriving at the 45-degree reflection mirror. When a 45-degree reflective mirror has the most transmissive property to P-polarized light, the light that is reflected by the wavelength selective filter and reaches the 45-degree partial reflection mirror is transmitted through the 45-degree partial reflection mirror without being reflected, The amount of light reflected from the selective filter to the laser diode chip is cut off and the disturbance generated in the laser diode chip is eliminated.

Therefore, in the present invention, a 45-degree reflection mirror having different reflectivities for P-polarized light and S-polarized light instead of a bulky optical isolator composed of two polarizers, a faraday rotator and a permanent magnet, The λ / 4 waveplate is used to effectively block reflected light from the wavelength selective filter from being fed back to the laser diode chip.

Therefore, the chirp managed laser structure of this structure can be suitably used in a compact and inexpensive T0-can laser package.

1 is an external view of a conventional chirp managed laser of the TO type.
Fig. 2 is a schematic diagram for explaining how the intensity difference of the "signal" and the "signal" emitted from the laser diode chip varies in intensity ratio of the "signal" and the signal by the wavelength selective filter.
3 is an external view of a conventional chirp managed laser having a mini-flat or butterfly type package according to the conventional invention.
4 is a layout diagram of a TO-can type laser structure in which a conventional (US20150200730) wavelength selective filter is disposed.
5 is a layout diagram showing a method of disposing an optical isolator in order to block laser light reflected by a wavelength selective filter and fed back to a laser diode chip, in addition to a TO-can type laser structure in which a conventional (US20150200730) wavelength selective filter is disposed .
FIG. 6 is a bird eye view of a practical example in which a laser diode chip, a collimating lens, and a 45-degree reflection mirror are disposed in a TO-can type package having a diameter of 6 mm or less.
7 is a cross-sectional view of a TO-can type chirp managed laser incorporating an optical isolator according to the present invention.
FIG. 8 is a schematic view for explaining a method for effectively blocking the feedback of the light reflected by the wavelength selective filter to the laser diode chip using a 45-degree partial reflection mirror and a? / 4 waveplate having different transmittances according to the polarization of the present invention to be.
9 is a graph showing the transmission / reflection ratio according to the polarization of a 45-degree reflection mirror according to an embodiment of the present invention.

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

7 shows an embodiment of the present invention.

The 45 degree reflection mirror used in the present invention has a characteristic of reflection for the polarization of light emitted from the laser diode chip and a characteristic for transmission for the polarization perpendicular to the light emitted from the laser diode chip.

Generally, light emitted from the semiconductor laser diode chip 100 has a linear polarization. In the TO-can structure of the present invention, the laser light emitted from the laser diode chip 100 is incident on the 45-degree reflection mirror 300 with S-polarized linearly polarized light. The 45-degree reflection mirror 300 reflects most of the polarized light emitted from the laser diode chip and transmits the reflected light to the wavelength selective filter 400. The light emitted directly from the laser diode chip 100 and transmitted through the 45-degree reflection mirror 300 is incident on the photodiode 600 for monitoring the intensity of the laser light, thereby monitoring the light intensity of the laser diode chip . Since the ratio of the laser beam directly emitted from the laser diode chip 100 and transmitted through the 45-degree reflection mirror 300 is an energy that can not be used for optical communication, it is preferable that the laser beam is transmitted at a rate for monitoring the intensity of the laser beam. It is preferable that at least 90% of light directly emitted from the diode chip 100 is reflected and less than 10% of light is transmitted, and furthermore, 93 to 97% of light is reflected, and light of about 3 to 7% .

The λ / 4 waveplate (450) serves to convert linear polarization into circular polarization. FIG. 8 is a diagram showing the change of the polarization in detail. The light emitted by the S-polarized light from the laser diode chip and reflected from the 45-degree reflective mirror reaches the λ / 4 waveplate while maintaining the polarization characteristic of S-polarization when it is emitted from the laser diode chip. The λ / 4 waveplate has the property of converting linearly polarized light into circularly polarized light, and the light traveling through the λ / 4 waveplate and traveling to the wavelength selective filter has right-handed circular polarization characteristics. The light reflected from the wavelet filter is mirror-reflected from the right-handed circular polarization to the left-handed circular polarization to reach the λ / 4 waveplate. The λ / 4 waveplate transforms the left-handed circular polarization into linearly polarized light of P-polarization. Therefore, the light that is reflected by the wavelength selective filter and arrives at the 45-degree reflection mirror through the λ / 4 waveplate is characterized by P-polarization. Therefore, the light emitted from the semiconductor laser diode chip and arriving directly at the 45-degree reflection mirror is characterized by S-polarization, emitted from the semiconductor laser diode chip, passed through a 45-degree reflection mirror and a λ / 4 waveplate, The light that is reflected back through the λ / 4 waveplate and arrives at the 45 ° reflection mirror is characterized by P-polarized light. Thus, the polarization characteristics of the light are changed by the S-polarized light and the P-polarized light according to the direction of the light reaching the 45-degree reflection mirror.

9 is a simulation result showing that a 45-degree reflection mirror can have different transmittance and reflectance depending on the polarization characteristics of light incident on a 45-degree reflection mirror. In FIG. 9, a 45-degree reflective mirror has a reflection ratio of 90% or more for S-polarized light at a wavelength of 1535 nm, and the same 45-degree reflective mirror can transmit most light for P-polarized light.

Therefore, in FIG. 7, most of the light emitted from the laser diode chip 100 as S-polarized light and arriving at the 45-degree reflection mirror 300 through the collimating lens 200 is emitted outside the TO- You will be able to participate. The laser light reflected by the wavelength selective filter 400 is converted into P-polarized light through the? / 4 waveplate 450 to reach the 45-degree reflection mirror 300. The 45-degree reflection mirror is converted to P- Unlike the S-polarized light, most of the light is transmitted, so that the light reflected by the wavelength selective filter 400 is effectively blocked from being fed back to the laser diode chip 100. Therefore, disturbance of the laser diode chip 100 due to light reflected by the wavelength selective filter 400 is reduced, and communication quality is improved.

In this description, the light emitted from the laser diode chip is S-polarized for a 45-degree reflective mirror, but the same effect can be achieved when the light is emitted as P-polarized light. The photodiode 500 monitors the intensity of the light reflected from the wavelength selective filter 400 so that the wavelength of the laser light is controlled by using the ratio of the photocurrent flowing through the two photodiodes 500 and 600 It can be adjusted to have a constant relationship with the transmission wavelength band of the wavelength selective filter.

Unlike the conventional optical isolator using a conventional Faraday rotator, the optical isolator in the present invention adjusts the characteristics of a 45-degree reflection mirror in a conventional TO-can type laser device having a 45-degree reflection mirror, Since it has a function to effectively block the optical feedback to the laser diode chip by arranging the waveplate, it is possible to effectively control the " and " signal in the TO-can type laser device having a small volume, Function. In addition, the conventional optical isolator is composed of two polarizers, one Faradya rotator, and a permanent magnet surrounding them, which is large in size and expensive. On the other hand, the optical feedback shield according to the present invention adds one λ / 4 waveplate It is possible to save space and economy.

The embodiments described may be constructed by selectively combining all or a part of each embodiment so that various modifications can be made.

It should also be noted that the embodiments are for explanation purposes only, and not for the purpose of limitation. In addition, it will be understood by those of ordinary skill in the art that various embodiments are possible within the scope of the technical idea of the present invention.

100: Laser diode chip
110: submount for laser diode chip
200: collimating lens
300: 45 degree partial reflection mirror
400: Wavelength selective filter
450:? / 4 waveplate
500: photodiode
510: Submount for photodiode
600: photodiode
610: Submount for photodiode
900: thermoelectric element

Claims (7)

In the semiconductor laser device,
A laser diode chip (100) for emitting laser light;
A wavelength selective filter 400;
A collimating lens 200 provided on the optical path between the laser diode chip 100 and the wavelength selective filter 400 to collimate the light emitted from the laser diode chip 100;
A laser light which is provided on the optical path between the collimating lens 200 and the wavelength selective filter 400 and moves horizontally with respect to the bottom surface of the package, A 45 degree partial reflection mirror 300;
And a λ / 4 waveplate (450) disposed between the 45 ° partial reflection mirror (300) and the wavelength selective filter (400) to convert linearly polarized light into circularly polarized light.
The method according to claim 1,
The 45 degree partial reflection mirror 400 exhibits partial reflection / partial transmission characteristics for polarized light directly emitted from the laser diode chip, and has a characteristic that the ratio of reflection is larger than transmission, and light emitted directly from the laser diode chip And the ratio of transmission is larger than the ratio of reflection. The laser device according to claim 1,
The method according to claim 1,
Wherein the wavelength selective filter is an FP type etalon filter (400).
The method according to claim 1,
Wherein the wavelength selective filter is fabricated by laminating a dielectric thin film having a high refractive index and a low dielectric constant.
3. The method of claim 2,
Wherein the wavelength selective filter has a reflection ratio of 90% or more with respect to light of polarized light directly emitted from the laser diode chip. 3. The method of claim 2,
Wherein the wavelength selective filter has a transmittance ratio of 90% or more to polarized light directly emitted from the laser diode chip and perpendicularly polarized light.
The method according to claim 1,
Wherein the photodiode monitoring photodiode (500) is attached on the thermoelectric element (900).

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