KR20010019755A - Wavelength Stabilized Laser Diode Module - Google Patents

Abstract

PURPOSE: An optical source module including a wavelength stabilizer is provided to maintain the center wavelength of an optical source accurately and uniformly. CONSTITUTION: An optical source module used for an optical communication system includes a wavelength stabilizer(209) that generates optical current from an interference pattern signal varying with time and compares optical current values to uniformly maintain wavelengths. The wavelength stabilizer consists of twin photo diodes for generating optical current based on the interference pattern signal and a diffracting grating for providing the interference pattern signal varying with wavelengths to the twin photo diodes. The photo diodes and the diffracting grating are configured of one semiconductor.

Description

Light source module with built-in wavelength stabilizer {Wavelength Stabilized Laser Diode Module}

The present invention relates to a light source module used in an optical communication system, and more particularly, to a light source module in which a wavelength stabilizer is built so that the center wavelength of the light source can be maintained accurately and consistently.

Optical communication technology has developed from the gigabit (Gbps) era to the terabit (Tbps) era, and thus, one of the large-capacity, high-speed optical communication technologies, wavelength division multiplexing (hereinafter, simply referred to as "WDM") method. The transmission device used is being studied.

One of the factors that determine the capacity in the WDM method is to reduce the wavelength grid of the optical signal. Currently, the wavelength division interval for the WDM adopts 1.6 nm (200 GHz Grid), but in the future, 0.8 nm is used for ultra large capacity. (100GHz Grid), 0.4nm (50GHz Grid) is expected to shrink. As the wavelength division interval becomes narrower, wavelength stabilization, in which the wavelength of the optical transmission module is kept constant, becomes the most essential requirement.

In the related art, a signal from a light source is branched from an optical fiber to monitor a change of wavelength in an external wavelength locker for wavelength selection and stabilization of a WDM system, and then the temperature of the light source is adjusted using a monitoring signal. To keep the wavelength constant. In this case, since the configuration of the system is not only complicated and expensive, but also the entire module is large, research on the development of a light source module having a wavelength stabilizer is required.

The structure of a conventional external wavelength stabilizer and a conceptual diagram of maintaining a constant wavelength of a light source using the same are illustrated in FIG. 1, and the conventional technology will be described below with reference to FIG. 1.

1 is a configuration diagram of an embodiment of a conventional wavelength stabilizer.

As shown in the figure, the light of a single wavelength emitted from the laser diode 101 is branched using the first optical coupler 102 and then the second optical coupler 103 rebranches, thereby branching. Two signals with different wavelengths ( One, 2) The photocurrent values are measured by the photodetectors 106 and 107, such as photodiodes, respectively, through the two filters 104 and 105 having the transmission characteristics, and are measured by the second photodetector 107. After the photocurrent values are amplified by the amplifier 108, these photocurrent values are compared through the comparison circuit 111. If the comparison value deviates from the comparison value of these photocurrent values with respect to the initial desired wavelength, it means to deviate from the initial wavelength. Thus, the temperature of the light source 101 is adjusted through the driving circuit 112 to maintain the initial photocurrent comparison value. Maintain a constant wavelength.

However, the conventional technique as described above, by branching the signal from the light source to the optical fiber for the wavelength selection and stabilization of the WDM system to monitor the change of wavelength in an external wavelength locker, and again using the monitoring signal Since the temperature is kept constant by controlling the temperature of the light source, the configuration of the system is complicated, expensive, and a separate filter is used. Therefore, the size of the wavelength stabilizer cannot be miniaturized. There is a problem that it is difficult to manufacture a low-cost light source module because it is very difficult to manufacture.

In addition, the wavelength of a conventional light source is very small. In the case of a continuous wave (CW) laser, since it is 0.01 nm or less, there is a limitation in manufacturing a high resolution filter capable of separating such narrow wavelengths. In the case of a laser diode that is modulated with a wavelength of about 0.3 nm, the conventional technique as described above is difficult to apply.

The present invention devised to solve the above problems is to provide a light source module incorporating a simple and compact wavelength stabilizer.

1 is a configuration diagram of an embodiment of a conventional wavelength stabilizer.

Figure 2a is a plan view of a light source module with a built-in wavelength stabilizer according to the present invention.

Figure 2b is a side view of a light source module with a built-in wavelength stabilizer according to the present invention.

3A is an enlarged plan view of a portion of a wavelength stabilizer according to the present invention;

3b is an enlarged side view of a portion of a wavelength stabilizer in accordance with the present invention;

4A is a plan view of a wavelength stabilizing device according to the present invention;

4b is a sectional view of a wavelength stabilizing device according to the present invention;

4c is a perspective view of a wavelength stabilizing device according to the present invention;

5A is a plan view of a pair of photodetecting devices fabricated without a diffraction grating in accordance with the present invention.

5B is a cross-sectional view of a wavelength stabilizing device fabricated by bonding a photodetector pair Twin PD and another diffraction grating.

5C is a block diagram of a wavelength stabilizer in which a separate diffraction grating is inserted between a photodetector pair (Twin PD) and a laser diode.

Explanation of symbols on the main parts of the drawings

101: laser diode 102, 103: optical coupler

104,105 wavelength filter 106,107 photodiode

108: amplifier 112: drive circuit

109,110: pull-down resistor

111: comparator

201: photoisolator 202: optical fiber ferrule

203: optical fiber holder 204: optical fiber protector

205: optical connector 206: package case

207: thermoelectric cooling element (TEC) 208: thermoelectric cooling element (TEC)

209 wavelength stabilizer

301: wavelength stabilizer element 302: wavelength stabilizer element mount

303: thermistor 304: electric wire

305: wavelength stabilized substrate 306: ball lens

307: laser diode 308: thermistor

309: submodule substrate 310: heat sink

311: L-shaped welding substrate 312: welding ring

313: lens holder 314: lens

315: Ball Lens Mount

401: PD-A 402: PD-B

403: incident light 404: metal layer for electrodes

405 p-type semiconductor layer 406 semi-insulating semiconductor layer

407 insulating layer 408 diffraction grating and electrode metal layer

409: n-type semiconductor

501: photodetector pair without diffraction grating

502: light receiving area 503: electrode metal layer

504: metal layer for electrode 505: bump for connection

506 transparent glass 507 diffraction grating

508: antireflective thin film 509: diffraction grating

The present invention for achieving the above object, in the light source module used in the optical communication system, wavelength stabilizing means for forming a photo current from the interference fringe signal that changes with the wavelength, and comparing the photo current value to maintain the wavelength constant It includes.

That is, the present invention as described above, the wavelength stabilization consisting of a pair of photo-detecting device pair (twin PD) and a diffraction grating for providing to the twin PD the interference fringe signal that changes depending on the wavelength The present invention relates to a light source module having a built-in wavelength stabilizer.

In the case of applying the present invention, one kind of wavelength stabilizer can be manufactured and stabilized for all wavelengths, so it is very economical and its size can be reduced, so that a small sized light source module with a wavelength stabilizer can be manufactured. It is convenient to use.

Hereinafter, the present invention will be described in detail with reference to FIGS. 2 to 4.

2a and 2b is a configuration diagram of an embodiment of a light source module with a built-in wavelength stabilizer according to the present invention, Figures 3a and 3b is an embodiment configuration of a portion of the wavelength stabilizer according to the present invention, Figures 4a to Figure 4b is a configuration diagram of an embodiment of a wavelength stabilizing device according to the present invention. That is, FIGS. 2A and 2B show a structure of a light source module having a wavelength stabilizer built therein, and FIGS. 3A and 3B show a detailed structure of the wavelength stabilizer mounted inside the light source module. 4A to 4C show in detail a wavelength stabilizing element which is a component of the wavelength stabilizer.

First, FIG. 2A is a plan view of an embodiment of a light source module having a wavelength stabilizer according to the present invention, and FIG. 2B is a side view of an embodiment of a light source module having a wavelength stabilizer according to the present invention.

As shown in the drawings, the light source module according to the present invention includes an optical isolator 201, an optical fiber ferrule 202, an optical fiber holder 203, an optical fiber protector 204, an optical connector 205, and a package case 206. ), Thermoelectric cooling elements (TEC) 207 and 208 and wavelength stabilizer 209.

3A is an enlarged plan view of an embodiment of a wavelength stabilizer portion according to the present invention, and FIG. 3B is an enlarged side view of an embodiment of a wavelength stabilizer portion according to the present invention. In addition, Figure 4a is a plan view of an embodiment of a wavelength stabilizing device according to the present invention, Figure 4b is a cross-sectional view of an embodiment of the wavelength stabilizing device according to the present invention, Figure 4c is an embodiment of a wavelength stabilizing device according to the present invention Perspective view.

When the radial light signal emitted from the back of the laser diode light source 307 is converted into parallel light through the ball lens 306 and then incident on the surface of the wavelength stabilizing element 301, the incident light 403 is formed as shown in FIG. 4. Diffraction grating (408) formed on the back of the diffraction grating (408) is a random angle as shown in [Equation 1] below _d ) to form an interference fringe.

However, since the wavelength of the incident light has a finite width, it has a lattice dispersion D as shown in [Equation 2] below, thus forming a finite angle intensity distribution on the surface 406 where the detection element is located. Therefore, a photo current due to an interference fringe is formed in the twin PD PD _A 401 and PD _B 402, which can be sensed from the outside through a wire or a circuit.

( _d : angle of interference pattern generation, _ig : angle of incidence of light in the medium, D: dispersion (d _d / d ), m: diffraction pattern order, n: refractive index of the medium, L: lattice period)

Equation 1 shows that the diffraction angle of diffracted incident light to form a pattern changes as the wavelength changes. In order to use this, the light receiving area of the twin PD is changed as the diffraction angle changes due to the wavelength change.

Initial wavelength in this case Center angle at ₀ (solid line) _If the photocurrent of the detection elements PD _A 401 is P _A0 and the photocurrent of the detection elements PD _B 402 is P _B0 , the difference between the photo currents of the two detection elements will have a constant value P _{(A 0 -B 0)} . will be.

At this time, the wavelength of the light source changes If it is lengthened to ₁ (dotted line), the diffraction angle ₁ (dotted _{To 1} ). In this case, the area in which the detection element PD _A receives light increases by ΔS in FIG. 4A, so that the photocurrent P _A1 also increases than P _A0 . While detecting element PD _B is, because it is the area subjected to light is decreased by (S in Figure 4a photocurrent P _B1 is reduced than P _B0 difference P _(A1-B1 of the detection elements photoelectric _current) is more than P _(A0-B0) If the external circuit senses this and adjusts the regulating current to the thermoelectric cooling element (TEC) 207 to lower the temperature of the light source 307, the difference between the photocurrents of the two detection elements is reduced to the original P _{(A0-B0). )} you may have a value. by doing this the wavelength of the light source _It can be returned to _zero to stabilize the wavelength.

On the contrary, the wavelength of the light source changes If shortened to ₂ , the diffraction angle Decreasing to ₂

It becomes. In this case, the area in which the detection element PD _A receives light decreases and the photocurrent P _A1 also decreases than P _A0 . On the other hand, the area in which the detection element PD _B receives light increases and the photocurrent P _B2 also increases than P _B0 . The difference P _(A2-B2 ) of the photocurrent of the twin PD will have a smaller value than P _(A0-B0) , which is also sensed by an external circuit to detect the regulated current to the thermoelectric cooling element (TEC) 207. Adjust the temperature of light source 307 to increase the wavelength _{By setting it to 0} , the photocurrent difference between the two detection elements can be made to have the original P _(A0-B0) value. In particular, the use of the blazing technique to asymmetrically shape the diffraction grating can make most of the diffracted light in the desired order, and as the diffraction order increases, dispersion as shown in [Equation 2] ) Increases to detect even finer wavelength changes. However, as the diffraction orders become larger, the diffraction angle becomes larger and the detection element for receiving the signal is farther from the incident point, so that the wavelength stabilization element needs to be larger.

For example, a semiconductor element with a refractive index of 3.5um with a lattice period of 0.93um and 1000um

Ruler, 0 (for brazing to the second diffraction pattern) _i = 0) road

The diffraction angle for light having an incident wavelength of 1550 nm _d ) is about 72 degrees, so the position where the detection element should be placed should be 3,123um away from the incident point. At this time, when the light source of 1550nm wavelength is changed to 1550.02nm, the dispersion of 0.02nm (0.2A) causes about 0.5um of displacement at the position of detection element, and the change of photocurrent between detection elements is

Approximately 1% of the photoelectric current of the ruler can be sufficiently detected and can be used as a wavelength stabilization signal. In addition, when using a lens, it is possible to adjust the change of the photocurrent.

In addition, even if the same wavelength stabilization element is used for light source modules having different wavelengths, the initial interference fringes can be positioned at the center of the twin PD by adjusting the angle of incidence, so it is necessary to make the wavelength stabilization element for a specific wavelength. It is very economical because there is no.

For example, when the light having a wavelength of 1560 nm is incident at the same angle (0 degree) using the wavelength stabilizer of the above example, the diffraction angle is increased, so that the second diffraction pattern maximum is formed at 3,363 um from the incidence point. The detection element can not detect the signal. But by rotating the wavelength stabilizer, _{If i} ) is changed from 0 degree to 1.23 degree, the diffraction pattern maximum position is also moved from 3,363um to 3,124um, so it is economical because one kind of wavelength stabilizer can stabilize several wavelengths.

The structure and fabrication process of the wavelength stabilizing element 301 including the photodetector pairs (twin PD) 401 and 402 and the diffraction grating 408 will be described in detail with reference to FIGS. 3 and 4.

As shown in FIG. 4B, the semiconductor film 409 is doped with n-type and the band gap is large so that the absorption layer 406 of the semi-insulator is grown on the wafer 409 with a large bandgap, and then a thin p-type of about 1 μm is formed thereon. A doped contact layer 405 is grown.

The grown wafer surface is sufficiently etched so that the semi-insulator layer can be separated and then covered with an insulator 407 such as SiNx except for the region where the electrode is to be formed. By depositing an ohmic electrode metal 404, a pair of photodetector elements (twin PD) 401 and 402 as shown in FIG. 4C are fabricated. At this time, the SiNx insulating layer 407 is used as an antireflection film for incident light by adjusting the thickness.

The back surface 408 of the detection element determines the lattice period L so that an interference fringe can be formed at a desired angle with respect to the wavelength of the light source, and after brazing the interference fringe of a desired order through asymmetric etching, the ohmic electrode After the deposition, the wavelength stabilization device can be used as another electrode of a pair of photodetector devices (twin PD), and the reflection efficiency of the diffraction grating can be improved. The completed wavelength stabilization element is cut into appropriate size and used as unit device.

The method of fabricating the light source module having the wavelength stabilizer 209 embedded therein using the wavelength stabilizer 301 operating on the principle described above will now be described in detail.

By attaching a ball lens 306 to the rear of the optical element (LD) 307 in the existing light source module manufactured as shown in Figure 2 to make the light emitted from the rear of the optical element into parallel light. A wavelength stabilizing element mount which can be attached to an additional thermoelectric cooling element (TEC) 208 and a wavelength stabilizing substrate 305 thereon and a wavelength stabilizing element 301 attached thereto so that the height is the same as that of the optical element LD. 302).

At this time, the additional thermoelectric cooling element 208 is to prevent the wavelength dispersion characteristic of the wavelength stabilization element from being changed by the temperature change, so that the temperature is sensed by the thermistor 303 to maintain a constant temperature at all times.

Now, the optical fiber connector 205, optically coupled to the front of the optical element 307, to the wavelength detector to drive the optical element (LD) 307 and the thermoelectric cooling element (TEC) 207 to the desired wavelength. Connect it.

While observing the wavelength detector, the thermoelectric cooling element 207 to which the optical element 307 is attached is driven to drive the desired wavelength ( _And keep getting ₀ ). While measuring the photocurrent of each photodetector PD _A 401 and PD _B 402, the direction of the wavelength stabilizing element mount 302 is adjusted so that the photocurrent of each element has a similar value as an initial value, and then fixed with solder or epoxy. .

FIG. 5A is a plan view of an embodiment of a pair of photodetector devices fabricated without a diffraction grating according to the present invention, and FIG. 5B is a view of a wavelength stabilization device fabricated by bonding a pair of photodetector devices (Twin PD) of FIG. 5A and a separate diffraction grating. 5 is a cross-sectional view of an embodiment of a wavelength stabilizer in which a separate diffraction grating is inserted between the photodetector pair Twin PD and the laser diode of FIG. 5A.

That is, as described above, a wavelength stabilizing element having one body of the diffraction grating 408 and the photodetecting device pairs 401 and 402 may be manufactured using a semiconductor, but as another alternative, a figure manufactured separately on a separate diffraction grating as shown in FIG. 5B. A wavelength stabilizing element can also be fabricated by joining a pair of photodetecting elements 501 such as 5a.

5C also illustrates a pair of photodetector pairs (twin PD) 501 and a separate diffraction grating 509.

In addition, it is another example of the block diagram which manufactures the light source module which has wavelength stabilization function. The operation principle is the same as the wavelength stabilization element described above, but the diffraction grating 509 and the photodetector pair (twin PD) 501 are separated, and the photodetector pair (twin PD) 501 without the diffraction grating is a conventional PD. The advantage is that it can be produced simply in the same way as production.

To fabricate the module, first fix the diffraction grating 509 behind the light source 307, operate the light source to emit the desired wavelength of light, and then place a pair of photodetector elements in the position where the interference fringe is formed by the diffraction grating. By aligning and fixing the wavelength stabilizing device mount 302 to which the 501 is attached, a light source module having a wavelength stabilizer can be manufactured.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the spirit of the present invention for those skilled in the art to which the present invention pertains, and the above-described embodiments and accompanying It is not limited to the drawing.

As described above, the present invention is a simple type consisting of a pair of photodetector pairs (twin PD) fabricated as a pair and a diffraction grating for providing a pair of interference fringe signals depending on the wavelength to the photodetector pairs (twin PD). By manufacturing and using the wavelength stabilizer, by adjusting the angle of incidence, stabilization of all wavelengths is possible, and it is very economical as well as the size of the device can be made small. There is an excellent effect to manufacture a built-in light source module.

Claims (7)

In the light source module used in the optical communication system, Wavelength stabilization means for forming a photocurrent from the interference fringe signal that changes with the wavelength, and compares the photocurrent value to maintain a constant wavelength Light source module comprising a. The method of claim 1, The wavelength stabilization means, Photodetecting means for forming a photocurrent in accordance with the interference fringe signal; And Diffraction grating for sending said interference fringe signal varying in wavelength to said photodetecting means Light source module comprising a. The method of claim 2, The light source module, characterized in that the light detecting means and the diffraction grating is composed of one semiconductor. The method of claim 2, The light source module, characterized in that the additional optical detection means is bonded to the diffraction grating. The method of claim 2, The light source module, characterized in that for inserting the diffraction grating between the light detecting means and the light source manufactured so that no diffraction grating. The method of claim 2, The light detecting means, As the wavelength is changed by the dispersion of the diffraction grating, the light source module is configured to have a symmetrical structure so that one device increases the photo current, and the other device reduces the photo current. The method according to any one of claims 2 to 6, Light source module using a separate thermoelectric cooling element, and to stabilize the wavelength for any wavelength by adjusting the incident angle of the light detecting means or the diffraction grating.