Light modulation amplitude controller circuit, light modulation amplitude control method, and optical system

Abstract

The invention provides a light modulation amplitude controller circuit, a light modulation amplitude control method and an optical system. The light modulation amplitude controller circuit comprises an input port, a processing circuit and an output port. The input port is configured to receive an average output power control setting, wherein the average output power control setting is configured to control an average output power of a laser diode. The processing circuit is configured to control an optical modulation amplitude signal according to at least the average output power control setting. The output port is used for outputting the light modulation amplitude signal to control a light modulation amplitude of the laser diode.

Description

Technical Field

[0001] The present invention relates to a control scheme for a laser diode, and more particularly to a method and apparatus for generating an optical modulation amplitude (hereinafter simply referred to as "OMA") signal according to an average output power control setting of a laser diode. Background Art

[0002] A distributed feedback (hereinafter simply referred to as "DFB") laser diode in a bi-directional optical sub-assembly (BOSA) is a semiconductor laser with high stability and good modulation characteristics. However, when the temperature changes, the characteristics of the DFB laser diode may change. Therefore, it is necessary to stabilize the average output power P AV and extinction ratio (ER) of the DFB laser diode. A conventional approach is to use a look-up table (LUT) to control the DFB laser diode in an open-loop manner. However, in most cases, the open-loop control based on the look-up table may not be practical because of its low accuracy. Therefore, an innovative laser diode control design is needed that can maintain the extinction ratio of the laser diode (e.g., the DFB laser diode in a bi-directional optical sub-assembly). Summary of the Invention

[0003] One object of the present invention is to provide a method and apparatus for generating an optical modulation amplitude signal according to an average output power control setting of a laser diode.

[0004] In one embodiment of the present invention, an optical modulation amplitude controller circuit is disclosed. The optical modulation amplitude controller circuit includes an input port, a processing circuit, and an output port. The input port is configured to receive an average output power control setting, where the average output power control setting is used to control an average output power of a laser diode. The processing circuit is configured to control an optical modulation amplitude signal based on at least the average output power control setting. The output port is configured to output the optical modulation amplitude signal to control an optical modulation amplitude of the laser diode.

[0005] In an embodiment of the present invention, an optical modulation amplitude control method is disclosed. The optical modulation amplitude control method includes: receiving an average output power control setting, where the average output power control setting is used to control an average output power of a laser diode; controlling an optical modulation amplitude signal based on at least the average output power control setting; and outputting the optical modulation amplitude signal to control an optical modulation amplitude of the laser diode.

[0006] In an embodiment of the present invention, an optical system is disclosed. The optical system includes a laser diode, a monitoring photodiode, an average output power controller circuit, an optical modulation amplitude controller circuit, a first comparator circuit, a second comparator circuit, and a laser diode driving circuit. The monitoring photodiode is used to monitor the output of the laser diode to generate a feedback output. The average output power controller circuit is used to receive an average output power control setting and generate an average output power signal based on the average output power control setting. The optical modulation amplitude controller circuit is used to receive the average output power control setting and generate an optical modulation amplitude signal based on at least the average output power control setting. The first comparator circuit is used to compare the average output power signal with a first feedback signal obtained from the feedback output and generate a first comparator output. The second comparator circuit is used to compare the optical modulation amplitude signal with a second feedback signal obtained from the feedback output and generate a second comparator output. The laser diode driving circuit is used to drive the laser diode based on the first comparator output and the second comparator output.

[0007] The optical modulation amplitude controller circuit disclosed in the present invention is designed to generate an optical modulation amplitude signal. Since the optical modulation amplitude signal will adapt to the change in the average output power caused by the adjustment of the average output power control setting, in this way, the extinction ratio of the laser diode can be maintained constant. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a schematic diagram of an optical modulation amplitude controller circuit according to an embodiment of the present invention.

[0009] Figure 2 It is a schematic diagram of an optical system using the optical modulation amplitude controller circuit proposed in the present invention according to an embodiment of the present invention.

[0010]

SYMBOL DESCRIPTION

[0011] 100: Optical modulation amplitude controller circuit

[0012] 102_1, 102_2: Input ports

[0013] 104: Processing circuit

[0014] 106: Output port

[0015] 200: Optical system

[0016] 202: Duplex optical sub-module

[0017] 204: Laser diode drive circuit

[0018] 206: Dual closed-loop functional block

[0019] 208: Laser diode

[0020] 210: Monitoring photodiode

[0021] 212: Average output power controller circuit

[0022] 214, 216: Comparator circuit

[0023] APC_DAC: Average output power control setting

[0024] ERC_DAC: Extinction ratio control setting

[0025] I OMA : Optical modulation amplitude signal

[0026] I AVG : Average output power signal

[0027] C1, C2: Comparator output

[0028] I MPD : Feedback output

[0029] I MPD_dc , I MPD_ac : Feedback signal Detailed implementation manner

[0030] In the specification and claims, certain terms are used to refer to specific elements. Those skilled in the art should understand that hardware manufacturers may use different terms to refer to the same element. The specification and claims do not use the difference in names as a way to distinguish elements, but use the difference in functions of the elements as the criterion for distinction. The terms "comprising" and "including" mentioned throughout the specification and claims are open-ended terms, and should be interpreted as "including but not limited to". In addition, the term "coupled" or "coupling" herein includes any direct and indirect electrical connection means. Therefore, if it is described in the text that a first device is coupled to a second device, it means that the first device can be directly electrically connected to the second device, or indirectly electrically connected to the second device through other devices and connection means.

[0031] Figure 1 Schematic diagram of an OMA controller circuit according to an embodiment of the present invention. The OMA controller circuit (labeled "OMACTRL") 100 includes a plurality of input ports 102_1, 102_2, a processing circuit 104, and an output port 106. The input ports 102_1, 102_2 are respectively used to receive a plurality of control settings of the laser diode. In this embodiment, the input port 102_1 is used to receive the average output power control setting (APC_DAC), and the input port 102_2 is used to receive the extinction ratio control setting (ERC_DAC). The average output power control setting APC_DAC is used to control the average output power P of the laser diode AV . The extinction ratio control setting ERC_DAC is used to control the extinction ratio ER of the laser diode. The average output power control setting APC_DAC and the extinction ratio control setting ERC_DAC can be user-defined settings. The extinction ratio control setting ERC_DAC can be a pre-defined variable set by the user and can be regarded as a constant after initialization is completed. The average output power control setting APC_DAC may be a variable that can be adjusted by the user at any time. That is, after the initialization of the average output power control setting APC_DAC, the user can update the average output power control setting APC_DAC with different values.

[0032] The processing circuit 104 is used to control the OMA signal I according to the average output power control setting APC_DAC and the extinction ratio control setting ERC_DAC (which can be regarded as a constant after initialization) OMA . In some embodiments of the present invention, the OMA signal I OMA and the average output power signal I AVG (set by the average output power control setting APC_DAC) will maintain a constant ratio. In some embodiments of the present invention, the OMA signal I generated by the processing circuit 104 OMA can be positively correlated with the average output power control setting APC_DAC. For example, the OMA signal I OMA can be exponentially proportional to the average output power control setting APC_DAC. For example, .

[0033] The output port 106 is used to output the OMA signal I OMA , so as to control the OMA of the laser diode. It should be noted that any optical system (especially, optical transmission system) adopting the OMA controller circuit 100 proposed by the present invention falls within the scope of the present invention. For example, the OMA controller circuit 100 proposed by the present invention can be used in a dual closed-loop functional block, where the dual closed-loop functional block uses the photodiode output of a monitor photodiode (MPD) to control the laser diode. Specifically, the monitor photodiode is used to detect and monitor the output power of the laser diode and provide feedback information to the dual closed-loop functional block.

[0034] Figure 2 is a schematic diagram of an optical system (such as an optical transmission system) using the OMA controller circuit proposed by the present invention according to an embodiment of the present invention. The optical system 200 includes a duplex optical sub-module (labeled "BOSA") 202, a laser diode drive circuit 204, and a dual closed-loop functional block (labeled "DCL") 206. The duplex optical sub-module 202 includes a laser diode (labeled "LD", for example, a DFB laser diode) 208 and a monitor photodiode (labeled "MPD") 210. The dual closed-loop functional block 206 supports a dual closed-loop control scheme. In this embodiment, the dual closed-loop functional block 206 includes Figure 1 the OMA controller circuit 100 proposed by the present invention as shown, and also includes an average output power controller circuit (labeled "AVGCTRL") 212 and a plurality of comparator circuits (labeled "CMP") 214, 216. The monitor photodiode 210 is used to monitor the output of the laser diode 208 to generate a feedback output I MPD . The average output power control circuit 212 is used to receive an average output power control setting APC_DAC and generate an average output power signal I according to the average output power control setting APC_DAC AVG , where the average output power control setting APC_DAC is used to control the average output power P of the laser diode 208 AV , and the average output power signal I AVG will indicate the target P of the laser diode 208 AV value (target P AV value). As described above, the OMA controller circuit 100 is used to receive the average output power control setting APC_DAC and generate the OMA signal I according to at least the average output power control setting APC_DAC OMA, where the OMA signal I OMA indicates the target OMA value of the laser diode 208. Specifically, the OMA signal I OMA is jointly controlled by the average output power control setting APC_DAC and the extinction ratio control setting ERC_DAC.

[0035] Feedback output I MPD The direct-current (DC) component of can be used as the feedback signal I provided to the comparator circuit 214 MPD_dc . The feedback output I MPD The alternating-current (AC) component of can be used as the feedback signal I provided to the comparator circuit 216 MPD_ac . The feedback signal I MPD_dc indicates the current P AV value (currentP AV value) of the laser diode 208. The feedback signal I MPD_ac indicates the current OMA value of the laser diode 208. The comparator circuit 214 is used to compare the average output power signal I AVG with the feedback signal I MPD_dc , and generate a comparator output C1 indicating the error between the average output power signal I AVG (i.e., the target P AV value) and the feedback signal I MPD_dc (i.e., the current P AV value). The comparator circuit 216 is used to compare the OMA signal I OMA with the feedback signal I MPD_ac , and generate a comparator output C2 indicating the error between the OMA signal I OMA (i.e., the target OMA value) and the feedback signal I MPD_ac (i.e., the current OMA value).

[0036] The laser diode drive circuit 204 is used to drive the laser diode 208 according to the two comparator outputs C1 and C2. For example, the laser diode drive circuit 204 can have a P AV control circuit and an OMA control circuit. Due to the inherent characteristics of closed-loop control, the laser diode drive circuit 204 adjusts the drive of the laser diode 208 to minimize the comparator output C1 (i.e., the error between I AVG and I MPD_dc ) and the comparator output C2 (i.e., the error between I OMA and I MPD_acthe error between), so when I MPD_dc = I AVG is the case, the P AV of the laser diode 208 will have the target P AV value, and when I MPD_ac = I OMA is the case, the OMA of the laser diode 208 will have the target OMA value.

[0037] The OMA, P AV and ER of the laser diode 208 can be expressed by the following formulas respectively.

[0038] (1)

[0039] (2)

[0040] (3)

[0041] In the above formulas (1), (2), and (3), P1 represents the optical output power (optical output power) when the signal is "1" (i.e., the optical transmission power of "1"), and P0 represents the optical output power when the signal is "0" (i.e., the optical transmission power of "0").

[0042] The relationship between OMA, P AV , and ER can be expressed by the following formula.

[0043] (4)

[0044] It can be seen from formula (4) that if the extinction ratio ER is a constant, the ratio will also be a constant, and vice versa. Therefore, in order to maintain a constant extinction ratio ER, it is necessary to maintain a constant ratio .

[0045] Based on the above observations, the hardware design of the OMA controller circuit 100 proposed by the present invention will adjust the OMA in response to the change of the P AV set by the user to maintain the ratio as a constant. For example, when the user adjusts the average output power control setting APC_DAC to reduce P AV by 3 dB (i.e., P AV is halved), the OMA controller circuit 100 proposed by the present invention will automatically change the OMA signal I OMA in response to the average output power control setting APC_DAC to reduce the OMA by 3 dB (i.e., the OMA is halved). By using the OMA controller circuit 100 proposed by the present invention, the user can increase or decrease P while keeping the ER unchanged.AV 。

[0046] In this embodiment, the average output power control circuit 212 adjusts the average output power signal I in response to changes in the average output power control setting APC_DAC AVG , and the OMA control circuit 100 adjusts the OMA signal I in response to the same change in the average output power control setting APC_DAC OMA . For example, both the average output power controller circuit 212 and the OMA controller circuit 100 are designed to have specific operating behaviors that can be expressed using the following formulas

[0047] (5)

[0048] (6)

[0049] In the above formulas (5) and (6), n and m are coefficients, ERC_DAC is a variable preset by the user, and can be regarded as a constant after initialization

[0050] As described above, due to the inherent characteristics of closed-loop control, the laser diode drive circuit 204 continuously operates to achieve I MPD_dc =I AVG and I MPD_ac =I OMA , therefore, the feedback signals I MPD_dc 、I MPD_ac can be expressed using the following formulas

[0051] (7)

[0052] (8)

[0053] According to formulas (4), (7) and (8), the relationship between OMA, P AV and ER can be expressed using the following formula

[0054] (9)

[0055] In the above formula (9), P AV corresponds to I MPD_dc , and OMA corresponds to I MPD_ac . When the user adjusts the average output power control setting APC_DAC, resulting in a change in I MPD_dc , I MPD_ac must be appropriately adjusted to maintain the equality in formula (9), thereby maintaining a constant ER, which is achieved by the OMA controller circuit 100, and the OMA controller circuit 100 is designed to generate the OMA signal IOMA , the OMA signal I OMA will adapt to the change in P caused by the adjustment of the average output power control setting APC_DAC. AV Change.

[0056] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the claims of the present invention shall fall within the scope of the present invention.

Claims

1. An optical modulation amplitude controller circuit, comprising: An input port for receiving an average output power control setting, wherein the average output power control setting is used to control the average output power of a laser diode; A processing circuit for controlling an optical modulation amplitude signal based on at least the average output power control setting; and An output port for outputting the optical modulation amplitude signal to control the optical modulation amplitude of the laser diode.

2. The optical modulation amplitude controller circuit according to claim 1, wherein the ratio between the optical modulation amplitude signal and the average output power signal set by the average output power control setting is maintained as a constant.

3. The optical modulation amplitude controller circuit according to claim 1, wherein the optical modulation amplitude signal is positively correlated with the average output power control setting.

4. The optical modulation amplitude controller circuit according to claim 3, wherein the optical modulation amplitude signal is exponentially proportional to the average output power control setting.

5. The optical modulation amplitude controller circuit according to claim 1, wherein the optical modulation amplitude controller circuit is used to control the optical modulation amplitude of the laser diode in a duplex optical sub-module.

6. An optical modulation amplitude control method, comprising: Receiving an average output power control setting, wherein the average output power control setting is used to control the average output power of a laser diode; Controlling an optical modulation amplitude signal based on at least the average output power control setting; and Outputting the optical modulation amplitude signal to control the optical modulation amplitude of the laser diode.

7. The optical modulation amplitude control method according to claim 6, wherein the ratio between the optical modulation amplitude signal and the average output power signal set by the average output power control setting is maintained as a constant.

8. The optical modulation amplitude control method according to claim 6, wherein the optical modulation amplitude signal is positively correlated with the average output power control setting.

9. The optical modulation amplitude control method according to claim 8, wherein the optical modulation amplitude signal is exponentially proportional to the average output power control setting.

10. The optical modulation amplitude control method according to claim 6, wherein the optical modulation amplitude signal is used to control the optical modulation amplitude of the laser diode in a duplex optical sub-module.

11. An optical system, comprising: A laser diode; A monitoring photodiode for monitoring the output of the laser diode to generate a feedback output; An average output power controller circuit for receiving an average output power control setting and generating an average output power signal based on the average output power control setting; An optical modulation amplitude controller circuit for receiving the average output power control setting and generating an optical modulation amplitude signal based on at least the average output power control setting; A first comparator circuit for comparing the average output power signal with a first feedback signal obtained from the feedback output and generating a first comparator output; A second comparator circuit for comparing the optical modulation amplitude signal with a second feedback signal obtained from the feedback output and generating a second comparator output; And A laser diode driving circuit for driving the laser diode according to the outputs of the first comparator and the second comparator.

12. The optical system according to claim 11, wherein a ratio between the optical modulation amplitude signal and the average output power signal is maintained as a constant.

13. The optical system according to claim 11, wherein the optical modulation amplitude signal is positively correlated with the average output power control setting.

14. The optical system according to claim 13, wherein the optical modulation amplitude signal is exponentially proportional to the average output power control setting.

15. The optical system according to claim 11, wherein the laser diode and the monitoring photodiode are both located in a duplex optical sub-module.

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